lNDUSTRIAL + Specialty Printing - July/August 2011

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Printed BatteriesE-Book TechnologyHigh-Performance

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Methods and Materials for Organic Solar CellsP. 32

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When you need fine line conductive traces, or the highest quality graphics to be printed with the utmost precision and consistency, MacDermid Autotype is in the forefront of developing screen printing stencil materials, substrates and scientifically proven software tools to achieve your ultimate goals. Improve consistency of your printed images with our unique capillary films, Capillex CP or CX and validate your prints using the "Acuity Index" from our QA software.

Specialty substrates are manufactured and converted in clean room environments to the most exacting standards to meet your highest quality needs for precision printing. Gain control of your web process by using Autostat heat stabilized polyesters for critical flexible circuitry. Hard coated, specialty finish film coatings are provided on polycarbonate and polyester for film insert molding, membrane touch switches, displays and touch screens.

For more information on our capabilities to support your printed electronic needs , visit: www.macdermidautotype.com or callToll free: 800-323-0632

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CONTENTSINDUSTRIAL + SPECIALTY PRINTING July/August 2011 • Volum

e 02/Issue 04

24

FEATURES

12 Polymer Solar Cells Move Closer to Industry Integration Tom Aernouts, Claudio Girotto, Els Parton, and Jef Poortmans, imecDiscover the ways in which advancements in printing techniques and materials are bringing organic solar cells closer to mass production.

16 Printed Electronics and � in Batteries: Powering a World of Product Innovation Matt Ream, Blue Spark Technologies� in, printed batteries can have a profound eff ect on the development of new products, including speed, quantity, cost, and speed to market.

20 Flexibility on Display Brendan Florez, Polyera Corp.Production of e-readers and other fl exible displays requires precision. Learn about printing’s role in the manufacturing process and how all of the parts fi t together.

24 Challenges and Opportunities in Solar Screen Printing Lars Wende, Ph.D., ASYS Group� is article describes the inner workings of screen printing as it’s used for the production of solar technologies and demonstrates why the process continues to grow in this segment.

28 Driven to Succeed: � e Life of High-Performance Labels Ken Koldan, FLEXcon Few environments are as harsh or unpredictable as what you’ll fi nd under the hood of an automobile. Find out how labels can perform under the extreme conditions there.

32 A Look at Lasers for Industrial Finishing Steve Aranoff , Vytek Laser Solutions Choosing a laser-based cutting systems requires a deep understanding of the materials, processes, and applications with which you’re involved.

COLUMNS8 Business Management

William E. Coleman, Ph.D., Photo Stencil� is column explores the ways in which stencils must adapt to today’s printed-electronics app-lications.

40 Shop TourCubbison CompanyTake a look inside Youngstown, OH-based Cubbison Co., a provider of product-identifi cation solutions to diverse industries.

DEPARTMENTS4 Editorial Response6 Product Focus36 Industry News39 Advertising Index

ON THE COVEROrganic solar cells are making inroads in large-scale manufacture. Turn to page 12 for an explantion of the major factors that are contrib-uting to this important develop-ment. Photo Courtesy of imec.Cover design by Keri Harper.

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facebook.com/iSPmagINDUSTRIAL + SPECIALTY PRINTING, (ISSN 2125-9469) is published bi-monthly by ST Media Group International Inc., 11262 Cornell Park Dr., Cincinnati, OH 45242-1812. Telephone: (513) 421-2050, Fax: (513) 362-0317. No charge for subscriptions to qualifi ed individuals. Annual rate for subscriptions to non-quali-fi ed individuals in the U.S.A.: $42 USD. Annual rate for subscriptions in Canada: $70 USD (includes GST & postage); all other countries: $92 (Int’l mail) payable in U.S. funds. Printed in the U.S.A. Copyright 2011, by ST Media Group International Inc. All rights reserved. � e contents of this publication may not be reproduced in whole or in part without the consent of the publisher. � e publisher is not responsible for product claims and representations. POSTMASTER: Send address changes to: Industrial + Specialty Printing, P.O. Box 1060, Skokie, IL 60076. Change of address: Send old address label along with new address to Industrial + Specialty Printing, P.O. Box 1060, Skokie, IL 60076. For single copies or back issues: contact Debbie Reed at (513) 421-9356 or [email protected]. Subscription Services: [email protected], Fax: (847) 763-9030, Phone: (847) 763-4938, New Subscriptions: www.industrial-printing.net/subscribe.

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they’ve created on the computer will look, feel, and handle in a way that consumers will love,” says John Reed, master proto-type specialist for SB&D. “SB&D can print a model overnight and have a nice looking, multicolored concept prototype the next morning.”

The 3D printers use a 3D computer � le and convert design information into cross-sectional slices. Each slice is then printed one on top of the other in an ad-ditive process to create the 3D printed object, usually out of resin powder, though some use other consumables. This is a faster, less costly alternative to subtractive machining.

Though it sounds space-agey, this tech-nology has been around at least since 2003 with many differences between printers found in the way the material is melted or softened and fused. Some use laser sinter-ing and fused-material deposition; others print using inkjets and cure with a variety of systems. Others deposit liquid materials that are then cured. Any way you look at it, it’s cheaper than modeling done using molding or die casting—and faster in most instances.

Anticipation is at least half the fun, and printing in 3D is rapidly gaining strength. Speaking of anticipation and fun, have you requested a battery in response to the Visionary Innovator contest published in this issue? I’m sure there are some multidi-mensional ideas out there that are ready to take shape.

Have you ever wanted to just play out some creative idea to see the end result before the true product came about? I did that when building a dream house once. With carpenters in the family, I knew a bit about the house-building process, but I wanted to see and touch a doll-house-size model before the foundations were even laid.

I visited a similar house in a builders’ tour, then added features to the blueprints. I added in an attached glass-and-wood greenhouse, walkways, and patios around a back porch and pool, a � replace in the living room using the same chimney as a � replace in the upstairs master bedroom, a large master bath—well, you get the pic-ture. It was whatever I wanted—just once within reason.

The blueprints didn’t even resemble the actual house. Blueprints are � at. After all of that excitement of designing on paper and crunching numbers, we had to watch it emerge piece by piece over most of a year for a de� nitive 3D view. It was a painstak-ingly long year.

In our industry, 3D printers play on that same need to produce physical models using computer-aided designs and to give the user a quick, affordable, full-color (de-pending on the printer) model of an object in prototype. For instance, in the hand-tool area, Stanley Black & Decker uses 3D printing technology to help make its tool prototypes.

“ZPrinters [the particular 3D printers used] help us make concept models that let our designers verify that the product

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3D Printing: � e End Product Isn’t Flat

GAIL FLOWEREditor

EDITORIAL RESPONSE

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Viscosity- Management solutionsNorcross Corp. (www.viscosity.com) introduces viscosity-man-agement tools designed to con-trol quality and boost efficiency. Norcross’s VISC6000 Viscosity Control System is a PLC-based pro-cess-control system that operates viscosity sensors and can moni-tor and control up to ten stations through a touchscreen interface. It features trend-plot software and displays trend data for each sta-tion in real time, provides data log-ging for one hour up to seven days, and permits set-point and other viscosity-parameter adjustments on the fly. VISC6000 is capable of displaying set-point, actual vis-

cosity, and automatic/manual mode for each trend plot and can be equipped with pH- and temperature-control options. Norcross’s M50 Viscosity Sensor installs directly in the main feed line and operates on the piston time-of-fall principle to detect changes in the viscos-ity of liquids such as adhesives, coatings, and inks. It is designed to eliminate bypass installation and to hold viscosity within 0.1 cps. Norcross says the sensor is not affected by flow rate or pressure and needs no special piping or cleaning cycles and notes that it op-erates from 0.1-2,000 cps at 5 gal/min (20 l/min) flow and pressure to 20 psi (1.4 bar). All wetted parts are stainless steel, Delrin, and Teflon, and a variety of NPT and BSPP connections are available.

product focusTh

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Wide-Format UV Inkjet PrinterRoland DG Corp. (www.rolanddg.com) announces the arrival of its 64-in. (1625-mm) LEJ-640 UV-LED inkjet printer, the newest addition the company’s VersaUV line. It prints ECO-UV inks (CMYK+White+Clear Gloss) on roll media and rigid substrates up to 0.51 in. (13 mm) thick and supports imaging resolutions up to 1440 dpi. The printer features a UV-LED curing system, designed to operate efficiently and at low tempera-tures. The system comes standard with an automated white-ink circulation system to prevent pigment from settling, and it’s compatible with Roland OnSupport for remote production tracking online.

july/august 2011 | �

Film-Coat ApplicatorNordson ASYMTEK (www.nordson.com) recently introduced a film coater designed for automated, selective, and precision application of conformal coating materials. According to Nordson ASYMTEK, Select Coat SC-280 provides greater than 99% fluid-transfer ef-ficiency, improving material utilization by 30-50%, and selectively coats complex circuit boards in seconds. The company also notes that, because coating material is not atomized and is precisely ap-plied to the selected areas, overspray, masking, and rework associ-ated with conventional conformal coating processes are minimized or eliminated.

The SC-280 has a single-valve design and comes in two versions, circulating (SC-280C) and non-circulating (SC-280N). It handles viscosities of less than 100 cps. Coating thicknesses range from 0.5-8 mils for solvent-based materials. A variety of cross-cut nozzles are available to dispense film pattern widths from ~0.25-0.75 in. (6-19 mm). Each nozzle is engineered to deliver edge definition with a tolerance of ± ~0.030 in. (0.75 mm). The film coater has a 0-90° rotating axis. An optional five-axis accessory allows tilting of the nozzle to coat all four sides and under the components.

Blade-Holding SystemOvation Products (www.ovation-products.com) says it has designed an enhancement to its Magna-Print universal blade-holding system that makes paste deposition even more robust. According to Ovation, the new Magna-Print DeFlex technology takes the guesswork out of manual paste deflector modifications, delivering an auto-adjusting system that improves the unifor-mity of solder-paste deposition and prevents problems common to improper paste-deflector-height position, including material waste and stencil damage. Magna-Print DeFlex is available as part of the Magna-Print universal squeegee-blade system, which comes equipped with a proprietary blade-locking system, a variety of squeegee blades and types, angle converters, and a choice of deflectors.

Registration ShearSpartanics (www.spar-tanics.com) bills its new M250 Registration Shear as a system for faceplate and nameplate printers/manufacturers who require extremely accurate reg-istration shearing at high speeds. It supports registra-tion tolerance of ±0.002 in. (0.0508 mm), touchscreen controls for job setup and

changeover, software to optimize scrap reduction, production speeds up to 1200 cuts/hr, and automatic stacking of cut parts. PLC electronics and color cameras are standard and designed to maximize consistency in registration accuracy. M250 can be used with stainless steel, aluminum, PVC, polycarbonates, and more.

Upgraded Wide-Format Inkjet PrintersPolytype (www.polytype.com) has upgraded its Virtu Quantum series of wide-format inkjet printers with 10-pl printheads. As Polytype puts it, the unprecedented quality promised by the Virtu Quantum series will deliver excep-tionally fine output for a wealth of industrial and display products, including closely viewed applications such as back-lit displays, décor, and industrial glass. The printhead is designed to use variable droplet sizes to extend grayscale technology, improve resolution, and optimize ink coverage.

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busIness m

anagement

step stencilsprinting solder paste and Flux for tomorrow’s electronicspart I

In the early days of surface mount technol-ogy (SMT), step stencils were used to reduce the stencil thickness for 25-mil-pitch leaded device apertures. However, as SMT requirements became more complex and, consequently, more demanding, so did the requirements for complex step stencils. Mixed technology applications of solder-paste printing for through-hole/SMT, as well as solder-paste/flux printing for flip-chip/SMT, require special step-stencil designs. Keeping up with changes in technology is always a challenge for doing business in a fast-paced high-tech field.

Thick metal stencils that have both re-lief etch pockets and reservoir step pockets are very useful for glue and paste reservoir printing. Electroform and laser-cut step-up stencils for ceramic BGAs and RF shields are a good solution to achieve additional solder-paste height on the pads of these components. Special 3-D electroform sten-cils are a workable solution for odd PCBs that have some raised areas on the board (up to 0.120 in. high). These applications, and the stencil design to achieve a solution, will be discussed in detail along with some other unique applications.

step-stencIl applIcatIons and solutIonsCeramic BGAs present a challenge to the SMT-assembly process. Since the high melting temperature prevents solder balls from melting at normal reflow tempera-tures, any slight coplanarity problem can

William E. Coleman, Ph.D.Photo Stencil

result in an open contact to the CBGA balls. It is desirable to print higher solder bricks on the CBGA pads to prevent this problem. Normally, a solder-paste brick height of 7-8 mils is desirable.

On the other hand, SMT components like 0.5-mm-pitch QFPs, 0402 chip com-ponents, and R-Packs will not tolerate an 8-mil-thick stencil. Their aperture sizes are too small to achieve good paste release with a stencil this thick. Therefore, a step-up stencil is required for this application. An example of this stencil is shown in Figure 1. This stencil starts out as an 8-mil-thick foil, and the foil is etched back to 5 mils in all areas except in the CBGA area. The foil then has all the apertures, including the CBGA apertures, laser-cut into the foil. Electropolish and nickel plating are recom-mended for this stencil to achieve good paste release for the small apertures.

In cases where 0201 chip components and 0.5-mm pitch µBGAs are present, a stepped AMTX electroform stencil is recommended to achieve good paste release for these small apertures. A picture of a step-up AMTX stencil is shown in Figure 2. The stencil is made by plating up to 5 mils in all areas and then continuing to plate up to 8 mils in the CBGA areas. Customers usually prefer the step on the squeegee side of the stencil, and this is the case for the prior two examples.

A general rule for spacing between the step ledge and first aperture in the lower thickness area (keep-out design) is 0.035-

0.050 in. per 0.001 in. of step. User feed-back indicates that metal squeegee blades work fine with step-up stencils as long as these keep-out designs are followed.

Figure 1 (Top) An example of a step stencilFigure 2 (Bottom) A step-up AMTX stencil

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Top Stories • Printing Photovoltaics Screen printing photovoltaic cells

is the most reliable method and fastest growing application in industrial printing.

• Automating Your Pad-Printing Operation

Automation is an important part of effi cient, consistent pad printing. Find out about some of the options designed to enhance speed and precision for industrial applications.

• Membrane Switch: Screen Printing 101

The membrane-switch market has experienced dramatic growth and soared to an unprecedented level.

• Industry InsiderThe Importance of Printed Electronics to P&G

Textured Polyester Film >> Autotex S (Steel) is a textured

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step-up stencIl for through IntrusIve reflowThere has been an increasing trend to reflow through-hole components along with the SMT components rather than wave sol-dering them. To achieve this, solder paste is printed on, in, and around the through-hole hole and pad (annular ring).There are three stencil alternatives to achieve sufficient solder paste for this application: overprint the hole/annular ring with an oversized stencil aperture, step-up and overprint the hole/annular ring with an oversized stencil aperture, or use a two-print stencil where the second print stencil is very thick and provides more solder paste for the require-ment (described in the section below).

For an example, a step-up stencil with the step on the squeegee side for a through-hole edge connector would be 10 mils thick in the through-hole area and 5 mils thick elsewhere. The squeegee stroke is parallel to the stepdown ledge so the entire length of the blade drops down to 5 mils during the squeegee stroke.

relIef step stencIl wIth relIef etch pockets on the contact sIde raised via pads on the pcB If a board has raised via pads, they will prevent the stencil from gasketing to the PCB. To achieve good stencil/board contact, a relief pocket is etched on the contact side of the stencil wherever there is a raised via. Typically, the relief pocket depth is one half of the stencil thickness, which is usually enough to clear the raised via. A picture of this stencil is shown in Figure 3.

Bar code on the pcB Many PCBs have bar-code identifiers attached to the board surface. If it gets too close to board pads, it can prevent the stencil from gasketing to these pads during printing. A simple solution is to use a stencil that has a relief pocket etched in the area of the bar code. This allows the stencil to sit flat on the PCB during printing.

Board-holddown clips Some stencil printers have edge clips that hold the PCB down during the print operation. If there are component pads close to the edge of the board, the stencil may not be able to gasket to the board on the edge. Again, a solution is to provide a relief etch pocket in the area of the holddown clips.

pcB with additive traces Additive traces are added to the surface of the PCB to correct a design problem by altering the lead wiring. Unfortunately, this trace adds height to the board surface. A solution is to provide a relief pocket around the additive trace. An example of this stencil is shown in Figure 4.

step stencIl for two-prInt operatIon for mIxed technologySMT/through-hole mixed technologies When overprint (oversized apertures for the through-hole) with a normal step-up stencil does not provide enough solder-paste volume for proper intrusive reflow, a thicker stencil must be used. However, the normal SMT components will not tolerate a thick stencil (15-20 mils thick) and a step-down (20 mils down to 5 mils) is impractical. The two-print stencil operation is a viable solution. Consider a PCB that has a fully populated pin-grid array (PGA). Overprint is limited because of the fully populated geometry. The only alternative to provid-ing more solder paste is to make the stencil thicker. In this case, a stencil 15 mils thick was required. In the two-print operation,

all of the surface-mount solder paste is printed with a normal SMT stencil 5 or 6 mils thick. The second print stencil is 15 mils thick with relief etch pockets etched on the contact side of the stencil any place that SMT solder paste was printed during the first print. As a rule of thumb, the relief pocket depth should be 4 mils deeper than the SMT first-print stencil.

Flip-chip/SMT mixed technologies There are applications where it is desirable to print flux or solder paste for a flip-chip component and solder paste for normal SMT devices. Both are then placed and run through the reflow cycle. Normally, the stencil thickness for the flip-chip print-ing is 1-2 mils thick—much too thin for normal SMT printing. Two print stencils are ideal for this application. A thin (1-2 mil) thick AMTX electroform is used to print either flux or solder paste on the flip-chip pad sites on the PCB. Then a SMT stencil (5 mils thick) is used to print solder paste on all the SMT pads. This stencil has relief pockets formed on the contact side anywhere flip-chip flux or paste was previ-ously printed. An example is a 3-D AMTX electroform stencil that is 5 mils thick with 3-mil relief pockets formed on the contact side, which is ideal for this application. This stencil has a formed step-up relief pocket. The height of the stencil in the flip-chip area is 8 mils (5-mil stencil thick-ness and 3-mil relief pocket). If you were to look at the stencil from the squeegee side, you could see the raised area over the flip chip area.

Visit www.industrial-printing.net to read the remainder and conclusion of this article in Part 2.

Figure 3 (Top) Relief pockets etched on the contact side of a stencilFigure 4 (Bottom) A stencil with a relief pocket around the additive trace

Bill Coleman earned his Ph.D. in physics from West Virginia University. His early career was spent with NCR developing memory and visual display devices. He has spent the past 23 years at Photo Stencil as VP of technology, working closely with customers to understand their SMT-printing requirements. Coleman has published more than 20 papers in this field and is pres-ently co-chair of IPC 5-21e committee, which produced IPC 7525 Stencil Design Guidelines. Bill is on the Advisory Board for West Virginia University.

wIllIam e. colemanPhoto Stencil

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cover story

Polymer Solar Cells Move Closer to Industry Integration

polymer solar cells promise a variety of new applications for PV, such as integration in clothing, product packages (Figure 1), curtains, or wall paper. For this to happen, the flexible, light-weight solar cells should be printed using low-cost, large-scale pro-cesses. Current industrial silicon solar cells achieve efficiencies of 15-18%, whereas organic solar cells (OSC) have to cope with 4-8% power-conversion efficiencies. Yet, industry is very interested in organic solar cells because of their mechanical flexibility and large-scale, low-cost production poten-tial. Moreover, they operate well under low illumination conditions and non-perpendic-ular light angles. These are enough reasons to start dreaming about PV-integrated prod-uct packages, windows, backpacks, etc.

low cost and large scaleOrganic solar cells come in many flavors. The two largest groups are the small-mol-ecule OSC and the polymer-based OSC. The small-molecule OSCs are typically evaporated with a planar structure, similar to the junctions in silicon solar cells. Polymer–based OSCs, on the other hand, are processed from a solution in a different structure—a bulk heterojunction structure in which the donor and acceptor material

Tom Aernouts, Claudio Girotto, Els Parton, and Jef Poortmansimec

are fully intermixed. This article deals with the polymer-based OSC.

The low-cost potential of polymer solar cells is partly based on the amount of mate-rial used for the active layer. Although the polymers are rather expensive, the active layer is very thin. It is 0.1-0.3 µm as com-pared to the 100- to 200-µm active layer in silicon solar cells. This explains the ex-tensive difference in cost per square meter between silicon and polymer solar cells.

Large-scale production potential con-tributes to the cost-efficiency of polymer solar cells. Today, researchers are study-ing the usability of different deposition techniques. In general, the polymers are dissolved in a solvent and deposited onto a low-cost substrate (glass or plastic). When the solvent evaporates, a very thin active layer remains with the bulk heterojunction structure.

deposItIon technIques for polymer solar cellsSpin coating uses a solution on a substrate rotating at high speed to spread the fluid uniformly. It is the most commonly used technique because it produces very flat films with reproducible thickness. It is a valuable technique for the R&D on polymer

solar cells to characterize and optimize polymer mixtures, solvents, and deposi-tion parameters. The disadvantage of spin coating is that it’s limited to small areas and is not scalable to roll-to-roll produc-tion, which is a vital step towards industrial mass production of polymer solar cells.

Screen printing is a valuable deposition technique for polymer solar cells because it is well established in the PV world. How-ever, screen printing uses a viscous paste, while polymers for OSC are more fluid. One option is to find ways to make the polymer solutions more viscous. This would require additives, which can negatively in-fluence the electronic behavior when they remain in the final film.

Inkjet printing is established in the decorative-graphics industry. With today’s advanced equipment, the deposition speed is high enough to produce OSC on an industrial scale. It has the advantage to be able to deal with all sorts of substrates with different morphologies. The disadvantage is that the droplets inkjet prints on the substrate take a considerable time to dry by solvent evaporation. Coffee-ring structures appear during drying and are detrimental to proper bulk heterojunction structures.

Spray coating is a technique that seems

This article describes the processes and consumables necessary to achieve low-cost, high-speed production of solar cells.

july/august 2011 | 13

Al (100 nm)

Yb (40 nm)

P3HT:PCBM (220 nm)

PEDOT:PSS (30 nm)

ITO (100 nm)

Glass Substrate

+ -

to tackle all obstacles mentioned in the processes above. The polymer solution is sprayed onto the substrate. It is a low-cost, high-speed technique and one that can be used on large areas and different sorts of substrates. It also can deposit a broad spec-trum of fluids with different rheologies. The fluidity of the polymer solution is no drawback, and the droplets are very small, which is beneficial for the drying time. A short drying time implies a rapid evapora-tion of the solvent. In this case, the latter will not be able to dissolve the underlying layer and harm the heterojunction layer.

But there are some issues with spray coating too, such as control of the film thickness and roughness. In this article, we demonstrate that these issues can be tackled by the use of a two-solvent system with some specific design rules.

spraying solar cellsResearchers at the Belgian research institute imec are optimizing the spray coating technique in all its facets (type of solvents, solute concentration, deposition rate, substrate temperature, etc.). The goal is to achieve a fully spray-coated solar cell with good efficiency and fill factor (ratio of actual maximum obtainable power to the theoretical power), comparable to the cur-rently used spin-coating technique.

Earlier results showed that the active layer and metal electrodes can be spray coated successfully. Nevertheless, these results showed that spray coating leads to rough depositions with peak-to-valley values of up to a few tenths of a microm-eter. This roughness has a negative impact on the fill factor of the resulting solar cells, often limited to values below 55%, which is a rather low value with respect to standard organic solar cells. It is clear that spray-coating (Figure 2), although it shows many benefits for industry, cannot replace spin coating if the thickness variation of the deposited films is not reduced and finely controlled.

In this article we also discuss this issue for the realization of a hole transport layer (HTL) and the active heterojunction layer of polymer solar cells (see structure and function of layers in polymer solar cells in Figure 3). More specifically, we want to achieve a 40-nm layer of PEDOT:PSS for the HTL and 200- to 250-nm layers of P3HT:PCBM (Figure 4) for the active

Hot Plate

Ultrasonic nozzle

Substrate

Bottom

Righ

t sid

e

Left

sid

e

Top

Effective deposition

Spray pattern

Nozzle trajectory

Figure 1 A possible application for low-

cost organic solar cells is a smart

medicine box. The solar cells generate power for an active RFID that contains

for example the instructions for use

or an authenticity check. Copyright

Philippe Brems & imec.

Figure 2 In single-pass spray coating the nozzle atomizes the solution into a spray of micrometer-sized droplets that land on the substrate and form a full wet layer. The solvent evaporates, leaving behind a smooth solid film. The spray pattern is slightly larger than the substrate width, allowing full coverage. As a consequence, the sample is surrounded by solution on the hot-plate at the right and left side while the top and bottom side are clear and reproduce the edge effect of the deposition.

Figure 3 Structure of a polymer solar cell: ITO and Yb/Al are the

two contacts of the cell, the anode and cathode, respectively; P3HT:PCBM is the heterojunction layer

where light is absorbed and con-verted into charges that contribute to the current produced by the de-vice under illumination; PEDOT:PSS

is the hole transport layer which provides a smoother interface (ITO

is quite rough) with the active layer, and a work function which is

better aligned to the energy levels of the

P3HT donor material.


layer, all with low surface roughness. A computer-controlled ultrasonic spray coater was used in the experiments.

gettIng smooth layers wIth controlled thIcknessTo achieve smooth layers with controlled thickness, we started with engineering the inks (PEDOT:PSS and P3HT:PCBM) according to some design rules known from literature. To achieve a thin, wet layer during spray coating, it is essential to start with a liquid with a low surface tension. This guarantees that less volume of liquid is required to fully cover the substrate, al-lowing a more uniform evaporation over the whole surface.

If the original ink has a high surface tension, it can be reduced by adding a surfactant. The drawback is that often the surfactant remains in the solid film and may negatively impact the electrical behav-ior of the solid film. To solve this problem, one can add a secondary solvent (the main solvent of the ink being termed the primary solvent) with a lower surface tension than that of the primary solvent. The secondary solvent has to be miscible and soluble in the primary solvent. Also, the secondary solvent has to have a higher vapor pres-sure than the primary solvent. In this case, it evaporates faster, reducing its impact on the solid film. Moreover, this kind of two-solvent system leads to the Marangoni

effect. This effect enhances the spreading of the deposited liquid into areas of the substrate not directly covered by the spray. Also, it has been proven that the Maran-goni effect makes the film surface smooth.

The formulations of both inks (PEDOT:PSS and P3HT:PCBM) were based on this two-solvent system concept whereby the addition of a secondary, low-boiling-point solvent with lower surface tension than the primary solvent enhances the spreading of the liquid on the substrate due to outward Marangoni flows.

spray coatIng the hole-transport layer of polymer solar cellsDeionized water (DIW) is the primary sol-vent for the PEDOT:PSS ink and isopropa-nol (IPA) is used as secondary solvent.

The experiments showed that the IPA concentration should be in the range of 55-81 vol.%. Below 55% the ink solution showed good spreading but bad film unifor-mity. Above 81% we observed instabilities in the ink during deposition. A volume frac-tion of 73 vol.% IPA was chosen because this produced the most uniform deposi-tions. Further, 18 vol.% of PEDOT:PSS and 9 vol.% of DIW was used, resulting in film thicknesses between 20-40 nm.

A range of substrate temperatures between 30-75°C (close to the boiling point of IPA) was tested to study the effect of the evaporation. At 75°C, the liquid dries

upon impact with the substrate and is not able to cover the entire substrate surface. The ink does not spread but instead forms visible coffee-ring shapes. The situation is better at 55°C, but still the edges of the substrate are not covered, and coffee ring structures are still formed. Best results were obtained at 30°C substrate tempera-ture. We observed complete wetting of the whole surface at this temperature. A highly uniform film remains after a drying time ≥20 seconds.

We studied the effect of the PEDOT:PSS concentration with fixed IPA volume fraction of 73% and a substrate temperature of 30°C. We observed that the thickness of the deposited layer varied in an almost linear fashion from 15 nm (9 vol.%) to 40 nm (18 vol.%) to 55 nm (27 vol.%). We fixed the PEDOT:PSS concentration to 18 vol.% because the favorable layer thickness for the hole transport layer is 40 nm.

Next, the deposition rate was tested. Interestingly, the film thickness was not in-fluenced by the deposition rate. The spray-coated HTL with the variables mentioned above were integrated with a spin-coated P3HT:PCBM active layer. The photovoltaic response of the resulting solar cells was measured (Figure 5).

The optimal deposition was obtained with a 18:9:73 vol.% (PEDOT:PSS):DIW:IPA ratio, with the substrate at 30°C and a solution flow rate that can be chosen arbitrarily between 1.5 mL min-1 and 3.5 mL min-1 to ensure a uniform coverage—although a lower rate is preferred when considering the material utilization.

spray coatIng the actIve layer of polymer solar cellsOrthodichlorobenzene (oDCB) was used as primary solvent for the P3HT:PCBM ink, while mesitylene was used as secondary solvent. Mesitylene volume concentrations varied from 20-40 vol.%. This had no effect on the uniformity or the absorption spectra of the layer, although 30 vol.% seemed to be the optimal concentration for the PV response of the solar cells.

Absorption spectra were measured for spray-coated P3HT:PCBM layers deposited

Figure 4 Organic solar cells with spray coated active layer (P3HT:PCBM), on glass substrate.


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Figure 5 Comparison of organic solar cells produced with spray-coated PEDOT:PSS layers: (a) with different solute concentrations (with Tsub= 30°C and 2.5 mL min-1 flow rate); (b) at different substrate temperatures (with a (PEDOT:PSS):DIW:IPA ratio of 18:9:73 vol.% and 2.5 mL min-1 flow rate); (c) with different flow rates (with 18:9:73 vol.% ratio and Tsub = 30 °C).

sample (PEDOt:Pss-P3Ht:PCBM) PCE [%] jsc [ma cm -2] FF [%] Voc [mV]

spin-spin 3.62 9.37 65 595

spray-spin 3.65 9.08 68 587

spin-spray 3.53 8.84 69 575

spray-spray 3.52 8.79 70 573

Figure 6 Average values of 8 organic solar cells produced with spin coated and spray coated PEDOT:PSS (with a (PEDOT:PSS):DIW:IPA ratio of 18:9:73 vol.%, Tsub= 30°C and 2.5 mL min-1 flow rate) and P3HT:PCBM (8 mg ml-1 in oDCB:mesitylene at 70:30 vol.%, Tsub = 55 °C and 2.5 mL min-1 flow rate) layers annealed for 15 min at 110°C.

at different substrate temperatures, with slow and fast drying, and with or without a post-drying annealing step. The deposition at 55°C with slow drying produced films with a good compromise between unifor-mity and morphology.

The additional post-deposition thermal treatment showed promise for yielding favorable bulk heterojunction morphol-ogy, so we produced several solar cells at 55°C and investigated the effect of thermal annealing on their performance before the top-contact evaporation. A spin-coated reference cell was produced with the same thickness using the slow drying method followed by thermal annealing (80-130°C). Surprisingly, the as-produced spray-coated cells show a peak fill factor of 67%, which is progressively increased to values of approxi-mately 70% with annealing temperatures up to 110°C and then decreases when the temperature is further raised.

We applied the process to different commercially available P3HT materi-als successfully with slightly different regioregularity and molecular weight to

demonstrate the universality of the ink-design rules we developed. Solar cells with four different P3HTs show good perfor-mance with each of the materials, in line with spin-coated devices. The most striking result concerns the fill factor, above 70% for each of the materials used, which dem-onstrates that spray coating can be used to create films with thickness in the range of 200-300 nm with excellent properties.

sPray-COatED HOlE-transPOrt layEr anD aCtiVE layErWith the ink-design rules defined for PEDOT:PSS and P3HT:PCBM we could compare the performance of devices where both layers were replaced selectively from a reference fully spin-coated device. The re-sults in Figure 6 clearly demonstrate that there is a close similarity between devices produced by spin coating and spray coating. This is very important for the industrial production of polymer solar cells. Moreover, it was observed that the thickness of the active layer could be varied in the range 200–500 nm by changing the concentra-

tion of the P3HT:PCBM solution. This finding is particularly relevant for industrial applications, where the possibility to deposit thicker films without decreasing the power-conversion efficiency of the device simplifies the process and increases the yield of production, as thick films reduce the prob-ability of having pin holes in the layers or the likelihood of generating short circuits during subsequent production steps.

In conclusion, these experiments show for the first time a close similarity between polymer solar cells produced by spin coat-ing and spray coating. It proves that spray coating is a valuable alternative to other de-position techniques, which is an important evolution to get cost-effective polymer solar cells to the market.

Please consult the authors directly for a complete list of references.

Els Parton received her engineering degree and Ph.D. in biological sciences at the Katholieke Universit-eit Leuven, Belgium. She joined IMEC in 2001 as a scientific editor.

Els PartOn, PH.D.

Claudio Girotto joined imec in 2006 for a research on printable organic solar cells. He obtained his Ph.D. in electrical engineering at the Katholieke Universiteit Leuven, Belgium.

ClauDiO girOttO, PH.D

Tom Aernouts has served as R&D team leader of the Organic Photovoltaics team at imec since 2006. He earned his master’s and Ph.D. degrees in physics at the Katholieke Universiteit Leuven, Belgium.

tOM aErnOuts, PH.D.

Jef Poortmans joined imec in 1985. He received his Ph.D. in June 1993. He is program director of the strategic program SOLAR+ at imec.

jEF POOrtMans, PH.D

FEATURESTORY

POWERING A WORLD OF PRODUCT INNOVATION

Matt ReamBlue Spark Technologies

Learn how the integration of thin, printed batteries can

help reduce costs in numerous applications, from R&D activities

to full-scale production.

Printed Electronics and

� in Batteries:



Powering a world of Product innovation

supporting product development and innovation can be a tough challenge in a tight economy when manufacturing com-panies need to focus on reducing costs and retaining customers. Fortunately, there are technologies that can help manufacturers continue to bring new products to market quickly and with lower development and production expenses. Among these recent-ly commercialized technologies are printed electronics and thin, printed batteries.

innovative thin-battery design and ProductionPrinted electronics is generally defined as the printing of electronic devices on common media such as paper, plastic, or textiles using standard printing processes. Low-cost, thin, flexible batteries are print-ed on a recyclable plastic PET base using carbon, zinc, and manganese dioxide. The anode material is a laminate of zinc foil or printed zinc, and the cathode material is a manganese dioxide paste mixed with carbon. After a piece of separator paper is placed atop the printed design, a couple of drops of electrolyte are added to start the battery’s reaction, and a top layer of PET is used to seal the battery cell. Power genera-tion in the battery results from a chemical reaction between the electrolyte liquid and other materials.

While this process may sound com-plex, in actuality it can be done relatively quickly and cost-effectively. The batteries are manufactured using conventional, high-speed, roll-to-roll printing processes, which means they can be prototyped economically and mass produced quickly. This scalability factor makes it possible to achieve significant economies of scale as product development advances from pilot-test quantities to high-speed, high-volume production.

Thin, printed carbon-zinc batteries function as primary battery cells, which means they are not rechargeable. However, they are relatively low in cost, offer a broad range of capabilities, and may be safely stored in cold storage to slow the chemical reaction in the battery.

Awareness of the capabilities of low-voltage, printed batteries continues to expand around the globe, which has increased acceptance levels. Standard

and customized batteries are currently being tested and deployed across diverse industry sectors. Users include designers and developers of battery-assisted RFID and sensor systems, powered cards, smart packaging and merchandising displays, consumer healthcare and cosmetic aids, and novelty products.

Following is a representative sampling of applications in which thin, printed, low-voltage carbon-zinc batteries can work.

battery-assisted Passive rfid Since its emergence many years ago, RFID technology has matured, global standards have been established, and benefits have become clear. Despite the fact that return on investment (ROI) has been slower than anticipated in open consumer product goods, distribution applications such as Wal-Mart, the majority of industry analysts agree that RFID adoption is growing steadily. Closed-loop RFID systems have proven useful in asset management, inven-tory control, product and people tracking, and disaster and event management, with many showing relatively quick ROI.

Helping this growth is battery-assisted passive (BAP) RFID, sometimes termed semi-passive RFID. BAP RFID is proving valuable for quite a number of applications because its simple architecture and the power boost provided by low-voltage batter-ies can extend the capabilities of passive RFID significantly without having to incur the complexity and expense required to implement active RFID systems.

For example, BAP RFID can extend read ranges and improve RFID tag read-ability–especially in applications involving RFID-unfriendly materials, such as liquids and metals, or applications in which individual tagged items are densely packed or stacked. Properly designed BAP RFID systems can also provide extended memory capabilities, as well as increased security.

Additional battery-assisted passive RFID applications and benefits include asset tracking of goods, materials or work-in-process in manufacturing plants, warehouses and distribution centers to im-prove accuracy, streamline workflow, and reduce costs by increasing visibility and minimizing waste. It can work with stock and inventory management in retail stores

through the use of smart-shelf or smart-case systems to provide instant visibility of stock on hand and minimize overstocks and out-of-stocks.

Gen 2 BAP RFID is one of the highest value applications for thin, flexible, printed batteries because BAP, or semi-active, tags effectively fill both the performance and price gap between pure passive RFID and high-end active RFID and real-time loca-tion systems (RTLS). In fact, BAP RFID systems can be implemented at a fraction of the cost of active RFID while delivering many of the same benefits.

rf-linked sensors and data-logging systems Radio-frequency-enabled time-and-tem-perature sensors are becoming increasingly popular, especially in the food industry, as a solution for ensuring consumer safety, maintaining quality control, and reducing waste. Meat, poultry, seafood, produce, dairy, and frozen-food processors can derive measurable value from RF-enabled systems for time and temperature monitor-ing and data logging.

RF-enabled sensor systems are also useful for shippers and distributors of temperature-sensitive pharmaceuticals, biologicals, and chemical products. The pharmaceuticals industry is taking a hard look at temperature-data loggers as an increasing number of new drugs being developed require strict temperature con-trol during their distribution to maintain their efficacy. Other types of sensor and data-logging systems could be designed to monitor and track such factors as ambi-ent humidity, shock, or vibration from the point of origin to the point of delivery.

In all of these sensor applications, stan-dard low-voltage, thin, printed, carbon-zinc batteries can be embedded within a smart card or smart label form factor to provide the power boost required for time-phased monitoring and autonomous data-logging systems. The value proposition of real-time sensor systems is high because they offer a more accurate alternative to static-sensor/data-logging systems and a more cost-ef-fective choice than sophisticated PC-based systems. A radio-frequency-based inter-face, such as those compatible with most RFID readers, has proven invaluable in


speeding the data-collection process from the sensors/loggers and enabling hands-free operation.

smart cards The worldwide plastic-card market has exploded in recent years, with an estimat-ed four billion or so smart cards—cards containing ICs or chips—being shipped annually. Several major trends are driving this growth: the urgent need for increased security and authentication to counter-act fraud and identity theft; the growing popularity of contactless payments; and consumer preference for wallet-size cards integrating visual, interactive and tactile innovations. Battery-powered cards can incorporate lighted or color-changing displays, stored-value and account-status information, authentication codes, and other interactive functions. Powered card applications include:

• One-time-password (OTP) cards for secure Internet credit transactions, access to brokerage accounts, mon-etary wires, IT, and other high-value security assets

• Contactless credit and debit cards• Stored-value gift or transit cards• Membership and loyalty cards• Secure identification cards and

badges for access control in buildings or at events

smart packagIng, retaIl dIsplay Thin, printed, carbon-zinc batteries are extremely well suited to a wide range of smart packaging products and point-of-purchase merchandising displays because they are manufactured in a conventional printing process. According to NanoMar-kets, a Virginia-based industry analyst, some niche applications for battery-pow-ered smart packaging might eventually encompass: pharmaceutical-compliance packaging, monitoring devices for case and pallet freshness, and tamper-proof courier packages.

The medical-device, healthcare, and cosmetics markets are already deep into research and development efforts using thin, printed batteries in the design and manufacture of iontophoretic (i.e., trans-dermal) patches for direct application onto the skin. Printed batteries can be custom-ized relative to size and shape, making them particularly attractive for this market

segment. The primary role of the battery in typical patch applications is to actively drive the patch’s ingredients through the dermal layer of the skin. Batteries may also be used to regulate the dosage of the patch’s active ingredient(s).

greetIng cards, consumer noveltIes, and toys According to the Greeting Card Associa-tion, Americans purchase more than seven billion greeting cards each year, generat-ing estimated retail sales upwards of $7.5 billion. This segment of the consumer market is typically driven by a “What’s new, different and fun?” mentality. So it’s not surprising that there has been extraor-dinary growth of electronically powered cards, stationery, and toys featuring lighted and changing displays, LCDs, singing, music, self-recorded messages, and other sound effects. The cost of manufacturing is a significant factor for producers of these impulse-driven consumer items.

real-world ImplIcatIons for prod-uct desIgn and manufacturIngManufacturers and electronic-system designers and integrators seeking a low-voltage primary power source for integra-tion into new or existing products would be considered primary markets for thin printed carbon-zinc batteries. The 1.5-volt batteries offer advantages over traditional coin and button batteries in certain ap-plications for a variety of reasons.

Unlike traditional batteries containing lithium, mercury, and other battery chem-istries, thin, printed, carbon-zinc batteries are completely green. They are lead-free and contain no toxic substances, fully meeting the European Union’s Restric-tions on Hazardous Substances (RoHS) Directive. Therefore, they are safely dis-posable without harm to the environment. The green factor is increasingly important as the sheer quantity of electronic devices on our planet continues to grow and global environmental regulations become more stringent.

Small, thin, printed batteries can be used in many applications where conven-tional batteries just won’t fit or where inte-gration of a battery would be too complex or expensive. Additionally, the batteries can be custom designed to fit specific ap-plication requirements. Users can typically

specify size and shape (linear and non-linear), overall voltage, storage capacity, and thickness. Within certain limits, each of these can be adjusted according to the application, usually within several weeks.

Printed carbon-zinc batteries feature a chemistry that produces 1.5 v, have a thickness of about 700 µm or 0.027 in., and are typically capable of delivering peak drain currents of at least 1 mA. Voltages above 1.5 v can be supplied by integrating multiple 1.5-v cells in series into a single package. Depending on the application, customizable versions can also be de-signed, including form factors as thin as 500 µm or 0.020 in. or high-drain batteries offering peak current delivery of more than 8 mA for applications requiring an extra boost of power.

Because of their flexibility, thin profile, and light weight, printed batteries can share real estate on a thin, flexible sub-strate with other small-form-factor elec-tronic devices, such as printed integrated circuits (ICs), printed displays, and radio-frequency-identification (RFID) inlays and antennas. This capability helps to simplify and drive costs out of the assembly and integration of smart electronics into any number of imaginative, new products.

On the production side, thin, printed, carbon-zinc batteries offer a definite advantage over other types of low-voltage batteries. Because they are produced in a conventional printing process, production is typically faster and less costly. There are also advantages on the integration side. If the battery can be printed or mounted on the same substrate as other printed elec-tronics (IC chip, RFID inlay/antenna), the assembly and integration of the electronic elements with products becomes faster, easier, and less costly.

the rIght technology for the applIcatIonA common subject that comes up among designers and integrators is the question of how printed carbon-zinc batteries compare to other types of existing battery technolo-gies, the most common being coin or but-ton-cell batteries. This is true from a cost, price, and performance basis.

The driving force behind most compa-nies considering printed-battery technol-ogy is the thin, flexible form factor. These two features are just not available in any


other type of battery technology currently on the market. Thin and flexible are para-mount in the markets previously discussed. Designers are starting from the ground up in these applications. They are not typically looking to replace another type of battery used in a previous incarnation of their product.

Cost is certainly a factor in most applications. Coin and button cells, for example, are very mature in their product lifecycle. As such, a variety of low-price options are available from a variety of manufacturers. However, when looking at battery technologies, a designer should consider the total cost of integration in a product. In the case of a coin cell, the cost of a retaining clip/holder, cost of sol-dering it to a rigid circuit board, and the cost of insertion of the battery must also be considered.

Integration of component printed bat-teries in the short term lends itself to high levels of automation and production. In most cases, printed component batteries are attached using automated pick-and-place machinery and conductive adhe-sives. Longer term, printed batteries will reduce the total cost of integration even lower by being printed together with other components on a shared substrate, such as printed displays, integrated circuits, and antennas.

thin, battery-powered electronicsThe maturation of printed electronics is projected to revolutionize major segments of the industry, and low-cost, disposable batteries are recognized as essential to this transformation. This depends on alliances formed by leading developers of printed electronic devices, including thin, printed batteries. Together, these key players can help drive global market adoption by building awareness of the capabilities, potential applications, and business value of printed electronics.

Tight economic times need not signal the end of product innovation. In fact, there may be no better time to focus on ex-panding product choices and gaining new customers by harnessing innovative tech-nologies that can help bring products to market faster and with lower development and production costs. Printed electronics and thin, printed batteries are among these transformational technologies.

With more than 20 years in the high-tech engi-neering industry, 15 of them specifically in RFID, Matt Ream is currently responsible for worldwide marketing for Blue Spark Technologies, founded as Thin Battery Technologies in 2002 with pat-ented technology and technical leadership from Energizer (Eveready Battery Co.). For more infor-mation, visit www.bluesparktechnologies.com.

Matt reaMBlue Spark Technologies add your ideas.

To enter the VISIONARY INNOVATOR: Find a Use for This Battery Contest, turn to p. 37 of this issue or go to www.industrial-printing.net and submit your best ideas.

www.stmediagroup.com/digital/?m=07&y=2011&b=ISP&p=19&l=www.dynamesh.com/vscreen


� is article

explores the

infl uence of

components,

materials,

and deposition

techniques on

the manufacture

of cutting-edge

displays.

FEATURE STORY

FLEXIBILITY on DISPLAY

Brendan FlorezPolyera Corp.

JULY/AUGUST 2011 | 21

Printed, � exible electronics is an emerging area that has the potential to rede� ne manufacturing and the electron-ics industry itself. Fueled by the develop-ment of advanced materials with unique physical and electrical properties, it holds forth the promise of creating electronics that are robust, lightweight, and—in some cases—optically transparent, all using low-cost, high-throughput printing techniques. While the performance of most such ma-terials are nowhere near that of traditional crystalline silicon—high-performance microprocessors would still be made the traditional way—they do hold the potential to open up entirely new areas for electron-ics where novel form factors, � exibility, robustness, large area, long term, and low cost are required.

One major application for this technol-ogy is � exible displays. The bene� ts of such a technology are obvious. Besides the aesthetic appeal for end consumers, the technology also offers substantial bene� ts for convenience, robustness, and weight. Think of an e-reader that folds up to � t in your pocket or a display with an unbreak-able screen for high-impact environments. The potential for � exible displays is well recognized, and the largest display manu-facturers in the world have identi� ed three upcoming technologies they believe will de� ne the next major advances in displays: organic light-emitting diodes (OLED), 3D, and � exibility.

COMPONENTSWhen talking about displays and display technologies, it is important to distinguish between the two major components of a display: the frontplane and the backplane. The frontplane displays the image; the backplane controls which image is dis-played (which pixels are on or off). When most people talk about different types of displays, they are typically referring to the frontplane technology. E-paper, OLED, and LCD are all different types of front-plane technologies, and each produces the images that we see in a fundamentally different way. The backplane, however, is a separate construct. Provided the perfor-mance requirements of the back and front-plane technologies match, you could swap out frontplane and backplane technologies independently. What’s important to note here is that e-paper and OLED frontplane

technologies are already � exible—only the backplane keeps these displays rigid.

A backplane generally consists of two major components: an array that con-trols the behavior of the frontplane, and driving circuitry—usually at the edge of the display—that controls the behavior of the array. What actually constitutes the array depends on whether the display is considered passive or active matrix. In a passive matrix, the array comprises simple rows and columns of a transparent conductive material, usually indium-tin oxide (ITO); voltage is applied to both a row and column, and the pixel at the point of intersection turns on. The problem with this is two-fold. First, control of the voltage is very imprecise, causing not only lack of control of the intensity with which a pixel turns on, but also of which pixels turn on (sometimes nearby pixels turn on slightly, creating fuzzy images). Second, the refresh times are slow. In an active matrix, by contest, the array comprises thin-� lm transistors controlling the pixels (one transistor controls one pixel). This allows for much � ner voltage control and faster refresh times.

It is important to note that while all components of the backplane need to be � exible for a display to be truly � exible in every direction, only the array needs to be � exible for one to start getting bene� ts such as robustness—even if the display can’t yet be truly bent, folded, or rolled. Then, depending on where you place the driving ICs for the source and gate lines, you can create displays that are � exible along one or more axes.

It is also important to note that dif-ferent frontplane technologies have very different requirements in terms of the controlling thin-� lm transistor (TFT) performance. Electrophoretic displays—EPDs, the most common e-paper display technology—are considered the easiest to control. They are bi-stable, require power only when switching, can be refreshed slowly, and require very little current. OLED displays, by contrast, are current driven. They only display when the TFT is operating, and the more current that is driven into the OLED pixel, the more intensely that pixel shines. However, the human eye is very adept at detecting variations in intensity, so this requires that the transistors in an OLED backplane be

highly uniform—that is, the I-V charac-teristics are highly similar across transis-tors—and highly stable—the I-V curve doesn’t change or shift over time.

Semiconductor

Dielectric

DrainSource

Gate

Figure 1A Bottom-gate, bottom-contact TFT architecture

Semiconductor

Dielectric

DrainSource

Gate

Figure 1B Bottom-gate, top-contact TFT architecture

Semiconductor

Dielectric

DrainSource

Gate

Figure 1C Top-gate, bottom-contact TFT architecture

Semiconductor

DielectricDrainSource

Gate

Figure 1D Top-gate, top-contact TFT architecture

FLEXIBILITY on DISPLAY


structureThe TFT structure and materials stack is important to understand, as this stack pro-vides display flexibility. Though additional layers can be added to improve perfor-mance, the basic materials stack starts with the substrate and includes the source and drain contacts, the semiconductor, a gate dielectric, and a gate contact. The TFT architecture is definite in the location of the contacts relative to the semiconduc-tor within the materials stack; the most common (Figures 1A-1D) are known as top-gate, bottom-contact (TGBC); bottom-gate, bottom-contact (BGBC); bottom-gate, top-contact (BGTC); and top-gate, top-contact (TGTC).

There are advantages and disadvantages to each architecture. Bottom-gate, top contact structure is used more commonly in traditional LCD manufacturing because of the photosensitive nature of a-Si. An extra photo-blocking layer must be created in a top-gate structure because the a-Si must be shielded from the backlight. In a bottom-gate structure, by contrast, the gate electrode serves this function, requiring one less step in processing. Furthermore, top-contact structures make it easier to provide an ohmic contact between n-doped a-Si and S/D metal. For fully printed struc-

tures, however, many believe that top-gate devices will be easier to create because you can print a high-resolution S/D line by using gravure and microcontact methods without damage to the bottom layer.

Top-gate devices may demonstrate better device performance because this architecture orients the largest surface of the S/D contacts with the semiconductor-dielectric interface along which the charge actually travels. Many other factors come into play, but the net takeaway is that un-derstanding that the TFT architecture can have a significant impact on device perfor-mance, as the architecture, materials, and deposition and patterning techniques used are all interrelated.

MaterIalsThe substrate in traditional displays has typically been glass, but in flexible displays it is either polyethylene terephthalate (PET), polyethylene naphthalate (PEN), or polyimide. PET is the cheapest but has the lowest processing temperature (~100°C). PEN and polyimide work at higher tem-peratures but are more expensive—though some companies have developed less costly polyimide substrates. However, a few companies are exploring the manufacture of very thin, flexible, glass substrates.

The key drivers when choosing a source and drain contact material are cost and charge injection—ensuring that the work function of your contacts matches the HOMO or LUMO level of your n- or p-type semiconductor, respectively, which depends on your semiconductor type. For organic semiconductors, the noble metals are best and can be treated with a surface-modification layer to maximize charge injection but are the most expensive. ITO is currently cheaper than copper due to significant reserves found in China, but the conductivity is not high and the price has increased over time. A molybdenum/aluminum/molybdenum (Mo/Al/Mo) tri-layer structure is often used for a-Si.

Printing patterned contacts may be feasible for some applications, but photo-lithography remains the primary pattern-ing method for displays. The reasons? Screen resolution and refresh rate. High screen resolution requires high pixel (TFT) density, meaning small transistors. But high refresh rates require high on currents, which are proportional to the transistor W/L ratio (channel width/channel length). Small transistors require small W, meaning you need an even-smaller L to keep the ratio—and thus the on currents—high enough. Displays require L = ~5 μm; print-ing technologies can currently get to about 20 μm ± 5 μm. Some people say printing can get down to less than 100 μm, but this has been difficult in practice at manufac-turing scales.

The semiconductor material is at the heart of the TFT. Currently, the mate-rial most often used for existing advanced displays is amorphous silicon (a-Si), usually deposited through plasma enhanced chem-ical vapor deposition (PECVD), which can deposit the silicon nitride (SiNx), semiconductor, and an n-doped a-Si used to prepare the ohmic contact all in one continuous process—without a vacuum break. It is then patterned by photolithog-raphy. From a flexible-display perspective, this layer of a-Si is usually fairly thin—ap-proximately 200 μm—so at least some degree of flex does not damage this layer. However, the SiNx usually used as the gate dielectric is very easy to crack and is not the best candidate for flexible displays (more on dielectrics later). Furthermore, a-Si’s mobility is not quite high enough for high-end display applications.

Figure 2 Flexible OTFT array on PET


Metal-oxide semiconductors (MOS) de-posited by sputtering have also been used to create flexible displays. The relatively high performance of these materials makes them potentially interesting for flexible OLED displays, but there are still sig-nificant stability issues to work out. They require relatively high processing tempera-tures (300°C or higher for many metal oxides), which require more energy and more robust substrates such as polyimides or metal foils. None takes advantage of the benefits of deposition by printing. Recent developments in solution-processed metal oxides might have potential, but they are still in the early stages of development.

Finally, there are organic semicon-ductors. These have the benefit of low processing temperatures (~150°C), flex-ibility and true rollability, and lower cost. There are some in the industry who think the performance of organics may never be high enough to power anything beyond monochromatic e-paper displays, though recent results have demonstrated organic TFTs (Figure 2) with high mobility and very strong bias-stress stability, suggesting they may be suitable for flexible OLED or other display types as well. One other benefit of organics is their true printabil-ity—first through inkjet or other sheet-to-sheet processes and then moving to gravure or other roll-to-roll processes. But even here, some in the industry are at least starting out by depositing the materials via spin-coating and patterning organics with photolithography—the same way as other semiconductors.

The choice of a gate dielectric is driven primarily by the overall TFT architecture and the type of semiconductor material used. First, because the majority of the charge in the semiconductor travels along the semiconductor-dielectric interface, the nature of that interface—electrically and morphologically—has a significant effect on device performance. Second, any solvents used in creating the dielectric formulation must be orthogonal to not re-act with the semiconductor and to ensure the surface of the semiconductor remains pristine to form a good interface with the dielectric.

Here again, we can see the influence that device architecture plays on materi-als selection. In an organic TFT bottom-gate device, for example, the dielectric

Brendan Florez is assistant general manager for Skokie, IL-based Polyera Corp. He holds a B.S.E. in electrical engineering from Princeton University and has an extensive background in marketing, project and change management, software design, and more.

Brendan FlorezPolyera Corp.

is deposited on the substrate prior to the semiconductor. Crosslinkable (usually UV-crosslinkable) dielectrics are necessary to ensure the dielectric interface is not damaged. In a top-gate device, where the dielectric is deposited after the semicon-ductor, it’s more important that whatever dielectric solvent is used does not damage the semiconductor film. SiOx and SiNx can be used for metal-oxide semiconduc-tors, but these materials—though flex-ible—are not as flexible as organics.

Finally, the gate contact is again made out of materials similar to the source/drain contacts—gold, silver, copper, or ITO—or replacements thereof. The requirements for the gate electrode are less stringent—they can be less precise because they’re not dictating the channel length and don’t affect charge injection. Therefore, some have tried printing them.

It’s important to note that what mat-ters here is not just the property of each individual material, but how the entire material stack interacts. You could have wonderful semiconductor material, but with an incompatible dielectric or a con-tact material whose work function doesn’t match, the device becomes completely inoperative. Material interactions also affect basic deposition. One of the most common problems is material dewetting caused by surfaces being too hydrophobic. For example, CYTOP, one of the most common gate dielectrics for organic TFTs, suffers from this issue.

dePositionWe’ve talked a bit about the various mate-rials within a TFT stack, but you’ll notice that, especially in displays, many of these materials are often deposited by means other than printing. While the resolution and uniformity with which you can print is not yet at levels where all layers in flexible displays can be printed, work is progressing on improving processes every day. Because these TFT arrays—and any other circuitry to be printed— consist of a relatively high density of multilayer devices, two of the most important parameters for any printing method are the registration and alignment resolution.

Registration, in this context, is how narrow a line you can print versus how nar-row a space between lines you can leave, and alignment resolution refers to how well

you can align the features of one layer with the features of other layers. These factors can have a significant effect on device performance. For example, if the gate and S/D contacts were to overlap, the outcome would create parasitic capacitances that hinder device switching. These reasons currently prevent more manufacturers of flexible displays from using flexo, screen, offset, and gravure printing; however, a few companies are trying to roll-to-roll printing in other types of electronics where the resolution demands are not quite as stringent.

For displays, however, inkjet printing is the first imaging technique with which most companies start. It supports high-res-olution deposition—crucially important for consistent transistor performance— but, of course, roll-to-roll processes ultimately promise the highest throughputs and low-est costs.

trendsThe amount of time people spend interact-ing with printed electronics grows as the world becomes more digitally enabled. Display technologies will be the most prominent way for people to participate in the digital world.

On the electronics-manufacturing front, we’re seeing a broad shift away from high-cost, low-throughput production methods such as vacuum processing and vapor deposition in favor of sheet-to-sheet methods such as slot die and spin coat-ing—and, in some cases, inkjet—and ulti-mately moving to low-cost, high-through-put, roll-to-roll processes. Flexible displays have the potential to be a highly disrup-tive technology over the coming decade, combining the novel physical and electrical properties of new materials with the manu-facturing techniques that improve yields, reduce costs, and bring the power of print-ing to high-tech manufacturing.


Over the past decade, three screen-printing steps have been used repeatedly in the metallization process of solar cells. The most commonly used manufacturing line con� guration is Back-Back-Front (BBF), where the � rst print step is the silver-bus-bar print on the wafer’s backside, followed by the Al-BSF (Aluminium Back Surface Field), then after � ipping the cell, the front-side silver print is applied to form the Ag bus bar and Ag � nger grid of the solar cell.

The main advantage of this print order is that the front side of the cell is sunny side up following the last print step; thus, after the subsequent fast-� ring step, the cell can be tested in a solar-cell tester directly inline without an additional � ip step required.

Lars Wende, Ph.D.ASYS GroupASYS Group

However, there is an inherent risk that dirt and other contami-nants, such as silicon debris, can collect on the cell’s sensitive front side during the preceding print steps on the backside, at which time the cell is top down. In such a line con� guration, and as long as standard, low-cost screens are being used for all the screen print steps, no higher cost of consumables can be expected.

While a single print step on the front side will always result in similar heights of the Ag bus bar and the Ag � nger grid, newer processes now allow the cell manufacturers to print the � nger grid higher than the bus bars. Typically, a bus bar height of 10 μm or less is suf� cient for the subsequent soldering process in module manufacturing. Solar-cell manufacturers now have the challenge

Keeping up with technology changes and controlling the cost along the way is strategically important in the world of PV manufacturing.

Challenges and Opportunities in Solar Screen Printing

FEATURESTORY


to reduce the � nger width while increasing the height of the � nger to 25 μm or more to ensure a suf� cient conductive path.

Splitting the print step on the front side of the cell into two separate steps can save more than 260 kg of silver paste per 40-MW cell production line per year, which at a silver cost of €800/kg, compares to an annual cost savings of more than €250,000/ production line. At the same time, the smaller � nger widths and the taller � nger heights of the grid result in increased cell ef� ciency due to reduced shading of the cell area covered by the � nger grid. An associated ef� ciency increase of 0.25% (absolute) compares to an annual revenue increase of more than €470,000/40-MW line at an average selling price of €0.77 /Watt for 156-mm2-sized cells.

A comparison of paste consumption and achievable ef� ciency, as well as related paste costs and cell revenues of multicrystalline solar cells is found in Table 1. The downside of the above cost-savings analysis is the requirement for additional screen-printing equipment in each metallization line, as well as the explicit use of a new generation of high-quality and high-precision screens for the frontside prints. The associated equipment costs are in the range of additional €450,000-500,000—increasing capital expenditures by 30% for the whole metallization line. The increased cost of consumables associated with the new screen technology screens must also be factored in. The main challenge is the intrinsic need to print one � nger grid exactly on top of an existing one, requiring advanced alignment technologies and low-distortion screens. Thus two major uncertainties contribute to the total error budget of this process: the machine capability of the screen printer, including the position repeatability of the wafer alignment, and the ma-chine-to-machine correlation and screen accuracy and distortion.

Figure 1 shows a possible design of the new layouts with 80-μm � nger width in the � rst print and 60-μm � nger width in the second print on top of the � rst one. In this example, the allowed

print tolerance is ±10 μm, which necessitates screen-to-screen ac-curacy of ±5 μm or less. The maximum screen distortion allowed over the total lifetime of the screen must be less than 10 μm. A simple method to measure and monitor the real screen distortion over screen lifetime is to measure the distance between the two outmost � ngers of the grid after each print (Figure 2).

Unfortunately, most common screen technologies that use metal or polyester mesh show more signi� cant screen distortion over the lifetime of the screen. Therefore, new screen technologies or materials are needed to allow cell manufacturers to implement new approaches in mass production of solar cells. At the same time, cost and lifetime of such new screens must satisfy the asso-ciated � nancial cost-of-consumables analysis and may not increase the price per watt of the solar cells.

Two possible solutions exist for this new approach to screen printing solar cells: special mesh material made of theromotropic liquid-crystal-polyacrylate (LCP) threads or screen-like stencils (or stencil-like screens?) using a perforated metal foil instead of a mesh.

Figure 3 shows a comparison of screen distortion of a low-cost metal screen and a thermotropic LCP screen, measured over the

Figure 1 A simple method to measure and monitor the real screen distortion over screen lifetime is to measure the distance between the two outmost fi ngers of the grid after each print.

Figure 2 A brand new screen can be compared to a worn-out old one by measuring the distance between the two outer most fi ngers of the grid after each print.

Figure 3 � is shows a comparison of screen distortion on a low-cost metal screen and thermotropic LCP screen measured over the number of prints.

Low-Cost ScreenVecry Y bottomVecry Y top

Vecry X bottomVecry X top

Number of Prints

153,600

153,800

153,400

153,200

153,000

152,800

152,6001 3069 4600 10000 15000 20000

Dist

ance

out

mos

t Fin

gers

(mm

)

154

153.

5

60-μm screen

80-μm screen

Tolerance for second print


in the print process itself, which could be caused by mishandling or contamination of the screens in the metallization line. The risk of screen contamination can be reduced in a line con� guration using an FFBB print sequence, where the critical print steps with the high-tech screens are � rst after the wafers come from a previ-ous cleaning step. However, care must be taken of the thermal budget of the various pastes in the drying processes after each print step, especially when the print sequence is changed.

The annual screen costs for frontside metallization more than double from €70,000 to €160,000 or even €240,000 per line as screens for two front-side printers are needed now, although the lifetime of the new screen materials is at least twice as long at the same time. However, taking all added capital investments and consumables costs into account, the investment for new printing methods will achieve the break-even point in fewer than ten months due to higher revenues of high-ef� ciency cells and reduced paste consumption. A break-even period of less than one year for investments that increase cell ef� ciency is well accepted in the solar industry, while longer amortization periods bear too much risk of investment due to the high price pressure in this industry.

Challenges of availability and cost ef� ciency remain for high-precision screens with lowest distortion. However, using the techniques introduced here splits the front-side metallization into one print step for the creation of thin bus bars and a separate print step for printing higher � nger grids. The screens for the bus-bar print and the � nger grid can be optimized independently. The same advantage counts for the pastes, which can be selected independently for both process steps.

In this fashion the mesh density as well as the thickness of the emulsion layer on the screen can be optimized for printing thin and highly conductive bus bars. No glass frit is needed in the paste of the bus-bar print to electrically contact the conductive � nger grid through the insulating, anti-re� ective, silicon-nitride coating to the silicon emitter of the cell. Quite the contrary, print-ing the bus bars without glass frit in the paste avoids the genera-tion of additional recombination centers underneath the bus bars, which are mainly generated by the metal ions of the glass frit introducing defect levels in the energy band gap of the bulk semi-conductor. Minimizing the concentration of such recombination

number of prints. A screen distortion of 0.5 mm or greater, which is measured over the lifetime of many low-cost screens, is not ac-ceptable. Moreover, most other print processes used in the manu-facturing of high-ef� ciency solar cells, such as selective-emitter (SE) technology or Metal-Wrap-Through (MWT) cells, do not allow any screen distortion larger than 50 µm. Therefore, common metal or polyester screens cannot be used to print dopant pastes or for frontside metallization on existing SE patterns. Additionally, these types of common screens cannot be used for the front and backside prints on MWT cells, where all prints must be aligned precisely to the MWT pattern.

As can be seen in Figure 3, the maximum screen distortion on thermotropic LCP screens is less than 25µm, making this material suitable for screen printing on SE or MWT cells but still critical for the new methods described here. However, vision systems for short-loop process control can ensure precise alignment in both print steps.

The costs of available screen technologies are compared to low-distortion solutions in Table 1. It is important to emphasize that the cost-saving bene� ts of new technology can be achieved with new, more costly screen materials only when the longer lifetime of such screens can compensate for their higher price. Therefore, it is critical to minimize the risk of accidental breakage of the screen

Figure 4 A grid structure with a 50 µm-wide opening of the grid’s fi nger shown on a Vecry mesh with 23 µm-wire diameter, 330 wires/inch, and a mesh opening of 54-µm on NBT’s stencil-like screen with approximately 56-µm hole diameter in the perforated metal foil.

Conventional screen technologies

Low-distortion solutions

Cells/year 9,996,359 9,996,359

Cell Effi ciency 16.44% 16.69%

Watts per Cell 4.00 4.06

MW per year per lane 40.0MW 40.6MW

Revenue per year per lane /EUR 30.8M 31.2M

Weight of Ag paste per front side print 0.16g 0.12g

Consumption of Ag paste per year 1563.56kg 1240.43kg

COC of Ag paste per year 1,250,852 EUR 992,345 EUR

Table 1 A comparison of paste consumption, achievable effi ciency, related paste costs, and cell revenues of multicrystalline solar cells.


centers additionally increases the ef� ciency of the cells by more than 0.05% absolute at no costs added, as expensive, high-viscos-ity silver paste is no longer needed for the print of the bus bars.

On the other hand, the screens and silver pastes for the print of the � nger grid can be optimized for this process step as well without affecting the cost of consumables of the bus-bar print. By selecting new screen materials and the latest generation of high-viscosity pastes for printing the � nger grid, aspect ratios of up to 0.5 can be achieved with the latest generation of screen- or stencil-printing technology. ASYS is working closely together with technology leaders in screen, stencil, and paste business to go beyond this frontier.

Keep an eye on the associated risks when moving to � ne-grid-printing technology with high aspect ratios. Only the right combination of screen (or stencil) material design and paste choice can result in good print quality of � ne grids with high aspect ratios and can be also be achieved in mass production. This is especially important when the feature size to be printed is of same size or even smaller then the open area in the screen mesh or in the stencils.

In Figure 4, a grid structure with a 50-µm-wide opening of the grid’s � nger is shown on a theromotropic LCP mesh with 23-µm wire diameter, 330 wires/in., and a mesh opening of 54 µm, and on a stencil-like screen with an approximate 56-µm-hole diameter in the perforated metal foil. At � rst glance, both screen materials look very similar. Although the perforated metal foil has a larger open area of more than 51% compared to the open area of the theromotropic LCP mesh of 49%, the � nger grids printed with the stencil-like screens show more interruptions in the printed � ngers, using same high-viscosity paste on both screen materials and same emulsion thicknesses on the screens.

The red circles in Figure 4 highlight the root cause of the interruptions in the printed grid. It seems more dif� cult to get a suf� cient amount of the high-viscosity paste through those holes in the foil, which are more than half covered by the emulsion layer while the round form of the theromotropic LCP wires allow the paste to � oat around the wires during the � ood step, bringing a suf� cient amount of paste to even those areas that are virtually blocked by the crossings of the wires. This effect can be used to achieve an even better print quality when the speed of the print stroke increases. However, the heavy, thixotropic behavior of this new generation of high-viscosity paste may be an alternative

explanation of this phenomenon. A non-disclosed modi� cation of the squeegee’s geometry can improve the print quality of the narrow � ngers even further. It has also been demonstrated that the theromotropic LCP screens allow higher emulsion thicknesses than the current stencil-like screens while maintaining the higher print quality.

Using the right combination of paste, screen, and print tech-nology, grid � ngers with less than 70-µm printed � nger widths and 35-µm � nger heights when measured after the paste lost more than 20% of its weight in a drying step can be realized. Upcom-ing screen and stencil technologies will move this frontier another step beyond the current limitations of solar screen-printing technologies experienced today. The main advantage is the com-bination of stencil technologies with screen-type emulsion layers, offering an increased open area in the stencil-like screen for � ne-line print. First tests have proven printed � nger widths of 70 µm in combination with more than 35-µm height. As can be seen in Figure 5, the � nger shows a uniform height distribution over the length of the � nger, resulting in an unmatched grid performance.

As already mentioned in a previous paragraph, depend-ing on the parameters of the required paste the new state-of-the-art screen and stencil technologies, such as the theromotropic LCP screens or the stencil-like screens, open the door for new print applications in the solar-cell manufacturing or extend cur-rent screen-printing technology to the next level. Low screen distortion is the key to technologies like selective emitter or metal-wrap-through, and metallization prints must be well aligned to other processes in the front-end of the cell manufacturing line. Thus, the race for new screen technologies has just begun—and will keep screen-printing technology in growth mode as the most cost-ef� cient solution for solar-cell metallization.

Figure 5 Uniform height distribution over the length of the fi nger yields unmatched grid performance.

Table 1 A comparison of paste consumption, achievable effi ciency, related paste costs, and cell revenues of multicrystalline solar cells.

Lars Wende is VP of solar and new technologies at ASYS Group. Before joining the company in 2007, he held various management positions in product marketing and development of semiconductor process machines at ADE, Axcelis Technologies, and Hitachi Kokusai. In 1995 he received a Ph.D. in semiconductor physics from the University of Berlin on his research work about intrinsic defects in semiconductor materials at Hahn-Meitner Institute Berlin.

LARS WENDE, PH.D.ASYS Group

FEATURESTORY

There are few labeling environments more challenging that those that fall within the automotive industry. Here, labels are subjected to some of the harshest conditions imaginable. Labels must be able to withstand high heat, subfreezing temperatures, and exposure to solvents, chemicals, and UV light. In many cases, they must adhere perma-nently for the life of the vehicle, which can run into decades.

This labeling can take myriad forms. Some labeling, as in the case of vehicle identi� cation and under-the-hood warning labels, must be permanently adhered for the life of the vehicle. Oth-ers, such as tracking and sales labeling, may need to feature an aggressive repo-sitionable adhesive that can be removed cleanly from fabric, glass, painted metal, or plastic.

Fortunately, pressure-sensitive � lms offer a versatile and enduring solution for automobile labeling needs. These � lms, which comprise a substrate, adhesive, liner, and topcoat, can be custom tailored to meet the grueling environment of under-the-hood or under-the-chassis applications. The key to creating a successful label lies in understanding the rigorous demands associated with this � eld.

Similarly, pressure-sensitive adhe-sives can perform a variety of functions within the automotive environment. Such adhesives can replace other costly and less effective bonding mechanisms, such as rivets. What’s more, these adhesives can create a water-tight or gas-tight seal, helping to keep the pas-senger compartment of the vehicle safe. In addition, due to their viscous nature, adhesives can offer vibration and noise damping, enhancing the overall comfort of the vehicle.

THE PRESSURE-SENSITIVE SANDWICHTo fully understand how label options can be tailored to particular automotive needs, one � rst needs to understand the components of the pressure-sensi-tive � lm sandwich. The sandwich gives design engineers virtually limitless possibilities in meeting the speci� c re-quirements of the automobile industry.

� e Life of High-Performance Labels

DRIVEN to SUCCEED


Labels are among the most overlooked, but most important, components in the manufacturing process. � is article describes how they perform in extreme environments.

Ken KoldanFLEXcon


The sandwich comprises four layers—film, adhesive, topcoat, and liner—of widely varying material components. The success with which product engineers can use pressure-sensitive film to match, say, the gloss level of a dashboard, or the texture of brushed stainless steel, is a function of the film’s face stock—or film layer. There is an almost endless array of colors, gloss intensities, and finishes available for the film layer to match or enhance the look of virtually any applica-tion. Yet the face stock options go beyond aesthetics. Its material composition, for example, is vital to providing necessary durability characteristics. Film gauges and thicknesses can play an important role as well, and can range anywhere from 0.5-10 mil.

The adhesive layer of the pressure-sensitive film is a functional component of the label. It is a viscous substance when pressure is applied and enables the label to adhere permanently to the ap-plication surface. The product surface, in addition to the environmental conditions the adhesive is likely to encounter, largely dictates what the adhesive properties should be. These properties are charac-terized in terms of tack, peel, and shear, as well as attributes such as resistance to chemicals, UV radiation, heat, humidity, and other environmental conditions.

The ability of a label to stay adhered to a battery during manufacturing, given that it is in contact with highly concen-trated acid, is one example of where this adhesive layer is a key parameter in the automobile industry.

The primary job of the topcoat layer is to ensure proper ink adhesion to the surface of the film. Therefore, depending on the application, topcoats need to be compatible with a range of conventional, UV, and water-based inks, as well as printing methods such as digital imaging, screen printing, flexography, letterpress, and offset.

Liners serve a functional process, although they are sometimes viewed as the throw-away portion of the sandwich. However, pressure-sensitive film-release liners, whether in sheet or roll form, need to withstand the printing, diecutting, lamination, and application steps inher-

ent in the converting process, as well as in the various product testing and manufacturing processes.

Meeting the needs of a deManding environMentThe automobile industry requires ac-countability. Virtually every component of every vehicle needs to be verified, tracked, and accounted for throughout the manufacturing process, often through the use of a bar-code label (Figure 1). In the event of product failure, these labels may provide the only source of informa-tion to help OEMs, repair shops, and consumers understand how, when, and why failure occurred.

At the same time, automobile manu-facturers must comply with a host of regulatory and safety requirements that involve extensive labeling throughout the vehicle. Everything must function for the life of vehicle to protect the consumer and OEM.

Labels must endure a wide range of conditions (Figure 2). Tracking labels may be exposed to gasoline, motor oil, battery acid, or radiator fluid, as well as the cleaning fluids used to wipe away these solvents. They need to stand up to temperatures that can range from subfreezing to several hundred degrees, and, in the case of an engine block, all within a matter of min-utes (Figure 3). Throughout it all, they must remain adhered to their respective surfaces and remain legible.

Fortunately, pressure-sensitive-label technology has advanced to meet the needs of this industry. Experienced manufacturers have created labels that are engineered to offer excellent solvent and chemical resistance. The printed sub-strate is often protected using a durable

overlaminate, helping to seal the informa-tion from the harsh conditions. These overlaminates can be custom tailored to meet specific demands. For example, a label for an engine block would likely in-clude an overlaminate that would provide solvent resistance. In contrast, a label that may be adhered to the exterior of the car may feature an overlaminate that would protect it from the effects of UV light and moisture, helping the graphic to remain visible even after long-term weather exposure, including the hottest sunny days and the heaviest downpours.

Labels must also be coated with the right adhesive to help retain integrity for the life of the product. A weather- and

solvent-resistant label is only as good as its adhesive; it does neither the consumer nor the OEM any good if a legible label falls off before it can be read. Similarly, the label cannot interfere with the opera-tions of the vehicle. Take for example the label on the windshield-wiper motor. The part is a critical component when the vehicle is operating during a rainstorm on a highway. The label in the subsystem must not interfere with the operation of that device. A more drastic example is that of the label in the air-bag canister. Here, an interfering label could prevent proper functionality, possibly resulting in injury or death.

securing coMponent integrityIn addition to tracking a part through the manufacturing process, automobile labels can also serve as verification tools, ensur-ing product authenticity and providing ev-idence of tampering, a quality of primary importance to retailers and manufactur-ers. These security labels can be adhered to a variety of at-risk components.

This is particularly critical in the auto-

pressure-sensitive adhesives can perform a variety of functions within the automotive environment. such adhesives

can replace other costly and less effective bonding mechanisms, such as rivets.

motive market, where OEM parts are a crucial element of a vehicle’s integ-rity. OEMs have a legal and financial interest in making sure that only their authorized parts are used in the repair and maintenance of their vehicles. For the consumer, the use of authentic parts can literally be a life or death is-sue, as in the case of brake pads.

Security, as it pertains to products, generally centers around the protec-tion of company profits and ensuring customer safety. Security requirements can be classified as overt, covert, and forensic (traceability). Product-security strategy in the overt sense might take the form of a label that is holographic

in nature. For instance, the popu-lar Intel Inside label found on some computers is very visible confirmation of the product’s authenticity, and it is designed so the consumer can clearly see it. The absence of this security label may raise questions.

This same approach can easily be applied to automotive labeling. Today, many OEMs desire that the automo-tive parts be authentic to survive the operating environment and not cause problems with the integrity of any subsystems. For example, putting inferior brake fluid in the car’s braking subsystem could damage the master cylinder—or worse.

Figure 1 (Above) The automobile engine is one of the most demanding environments for labeling. Pressure-sensitive-film labels provide a solution to temperature extremes and caustic chemicals.

Figure 2 (Right) Adhering to the surface for the life of the vehicle and legibility is crucial when it comes to tracking information in the form of a bar code.

Figure 3 (Below) The under-the-hood environment can be challenging. Pres-sure-sensitive film labels offer topcoats or overlaminates to further improve resistance to specific fluids, such as motor oil.


S C R E E N P R I N T P R O D U C T S

From the labs at www.chromaline.com

INTERRUPTING INERTIA

Ultimate resolution is required for micro and nano technology. Chromaline emul-sions and capillary films redefine screen resolution possibilities.

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An example of a covert security is the ability to have a label turn a certain color or otherwise change its appearance when it encounters a set of conditions that would compromise the label or its message. The actual label change is undetect-able to the human eye, but with the appropriate detection equipment, it would become clear that the product was a counterfeit or had been damaged. This gives the warranty provider and manufacturer legal grounds to void the warranty and reduce product-lifecycle costs.

Authenticity labels may feature encoded messages that al-low for authenticators to verify the integrity of the part easily. Holographic films, for example, may incorporate overt and covert security devices to help the consumer and parts manu-facturer determine the validity of the part’s origin.

The third example of product security is product trace-ability, which is part of the product manufacturer’s forensic strategy. For example, an authenticated, unique label identify-ing each contract manufacturer can help a forensics team in the event of a compromise in security. This allows the product manager or owner to understand what has happened and then evaluate or otherwise limit liability.

Other labels provide tamper-evident elements so that OEMs can determine whether someone has tampered with a part, perhaps voiding its warranty. Some films are custom engineered to destruct upon removal, making them impossible to re-adhere. Some films employ a combination of permanent and removable adhesives. These can leave behind a pattern if someone attempts to remove a label, rendering the label ruined and, therefore, unsuitable to be re-adhered.

Rely on expeRienceOEMs, vehicle designers, and label manufacturers can take advantage of the new and exciting opportunities awaiting them in the adhesive and labeling market for automotive ap-plications by partnering with an experienced polymeric-coat-ing supplier. By working together, OEMs and converters can truly drive their own success.

Ken Koldan is FLEXcon’s manager of new business development for the company’s product-identification-business team. He holds a bachelor’s degree in electrical engineering and an MBA. In addition, he holds a Proj-ect Management Professional certification from the Project Management Institute and served as the chairman of the AIM North America UID Sup-plier Alliance for the 2010 term.

Ken KoldanFLEXcon

www.stmediagroup.com/digital/?m=07&y=2011&b=ISP&p=31&l=www.chromaline.com/labs


FEATURESTORY

A Look at Lasers for Industrial Finishing

Industrial printing has many applications in store for laser-based cutting equipment. These systems are engineered to supply � ne, high-speed � nishing for many types of rigid materials. This article presents an update on the capabilities of modern laser technology as it relates to processing functional graphics and media used in specialty printing.

WHAT LASER SYSTEMS CAN DOLasers are an alternative to mechanical cutters that use blades or bits. They can cut a variety of materials in a single pass, leave highly polished edges at the end of the cutting cycle, and enable more graphics to be ganged up—thereby providing up to 40% more saleable product from each piece of substrate (Figure 1). A 150-w laser system can acrylic up to 0.625 in. thick, and a 400-w laser can produce perpendicular, polished edges on 1-in.-thick acrylic. Major plastics companies use such systems to provide custom etched-and-cut acrylic wall decorations to their customers.

Lasers can also kiss-cut pressure-sensitive vinyl, static-cling polypropylene, and a host of other common materials without skipping. Although many screen and digital printers routinely use high-end knife cutters for kiss-cutting and through-cutting, ease of pulling out the kiss-cut part is critical in several applications. The quality of cut is paramount, particularly when dealing with

Steve Aranoff Vytek Laser Solutions

Read on to fi nd out how lasers can serve eff ectively as primary and complemetary fi nishing systems and which

confi guration to select for the materials you use.

performance decals and other adhesive-backed graphics. Figure 2illustrates a typical kiss-cut job done on a large-format laser system with a vision capability to handle print-to-cut accuracy.

Lasers can cut corrugated plastics with precise edges, and they support etching and 3D engraving with � ne detail. They can etch glass and acrylic panels/dividers (Figure 3), and typical etch times for a 3 x 5-ft panel of glass is two hours. Chemical etching or sand-blasting can be messy and time consuming, and these methods also may fail to reproduce extremely � ne details in the � nished product.

Lasers can provide full compatibility with camera-based vision systems for cut-to-print accuracy, even with lamination. Through integration with vision technology—even on smaller, fully en-closed, gantry-based laser systems—operators can achieve quiet operation with superb cutting of both laminated prints and digi-tally printed graphics applied to acrylic and other rigid materials.

By selecting from different frequencies, users can now cut thicker materials, such as the 1-in.-thick acrylic noted above, as well as aluminum—with or without backing—for name tags, equipment labels, and panels. The ability cut contours accurately on aluminum gives lasers the opportunity to complement the diecutting process typically used in the � nishing stage of the production work� ow by taking on smaller and smaller runs being

A Look at Lasers for Industrial Finishing

Figure 1 A laser cutter outfi tted with an optional stackerFigure 2 An example of a kiss-cut vinyl decalFigure 3 A modern wall panel (A) and fl oral glass panel (B)

Photo cour tesy Republic-ar t of Montreal

manufactured in just-in-time manufactur-ing processes.

More precise imaging and cutting are possible by incorporating precision motion technology beyond rack-and-pinion or lead-screw drives, with positioning feedback. This allows lasers to be used ef� ciently for high-end industrial uses, such as solar-panel manufacturing.

TYPES OF LASER SYSTEMS Galvo laser systems, as their name implies, incorporate galvanometers—precise and fast motors that focus laser beams at a particular area—in their operation. These devices are designed to deliver speeds more than ten times faster than knife cutters—even with media widths of 40 in. or wider. Galvo lasers can be used for inline � nishing with even the fastest narrow-format roll-fed printers and for branding and adding serial numbers and part numbers in applications ranging from etching eyeglass lenses to marking machined parts. Systems are avail-able with front entries and rear exits for use in conveyorized production lines. Others are con� gured with roll feeds for stencil application—similar to working with print-ed rolls of complex specialty graphics.

Gantry systems, on the other hand, use an X-Y axis plotter con� guration to move

MANUFACTURERS OF LASER CUTTERS

Automation Alternatives auto-alt.com

AXYZ Automation Inc axyz.com

Coherent Inc. coherent.com Epilog Laser epiloglaser.com

GCC America Inc. gccamerica.com

Jamieson Laserjamiesonlaser.com

Kern Laser Systemskernlasers.com

LasX Industries Inc. lasx.com

MultiCam Inc. multicam.com

Preco Inc. precoinc.com

Spartanics spartanics.com

Trotec Laser Inc. troteclaser.com

TRUMPFus.trumpf.com

Universal Laser Systems Inc. ulsinc.com Vytek Inc. vy-tek.com

Zünd/Eurolaserzund.com

the laser head around a � atbed cutting table. They often consist of servomotors and belt drives. For print-manufacturing applications where prototyping requires versatility and manufacturing requires speed, putting together a gantry system for short runs and the galvo high-volume production allows the printer to ensure that the product quality shown to customers with product prototypes will be maintained throughout the production process.

Three-axis galvo systems can reach in-line � nishing speeds for offset sizes, while gantry-based laser cutters are used for near-line production and prototyping, so that a manufacturer can produce prototypes, one-of-a-kind wide-format graphics, and regular production runs ef� ciently for their customer base—and all � nished goods will have the same look and feel. If a knife system were used for wide-format � nish-ing and prototyping and a galvo laser for production, there might not be a common product feel to the end customer between prototype and � nal delivery.

APPLICATION-BASED SYSTEM SELECTIONI’d like to introduce a close, but somewhat different, industrial application to show what can be done with such galvo systems. A copy of a stencil outline that was tested,

1

3A

3B

2


Photo cour tesy Republic-ar t of Montreal

and could be considered a very complex cut pattern for a specialty graphic, is shown in Figure 4. If the stencil were designed with rounded edges and cut on a traditional, high-end cutter, the job would probably take six to eight minutes. If the same graphic were designed with edges that join at true points, the job would likely take up to 50 minutes and would require a physi-cal lift and turn on the cutting blade—a time-consuming process. However, on a three-axis, galvo-based laser, the measured cutting time is 54 seconds, not counting loading/unloading and other activities. Although this system isn’t used exactly the same way as for cutting printed material, it is close enough to be indicative of the vast difference in throughput possible with modern laser systems.

Laser compatibiLity for etching/engraving and cutting Historically, most observers in the industry consider lasers to be a sub-solution. For those specialty and industrial printers need only look at Table 1, you can readily see that lasers do much more and provide more product depth than they’ve been given credit for in the past. And in some ways they’re the best finishing solution for the following reasons: non-contact cut-ting and engraving significantly reduces consumable costs for router bits, blades, and service; higher density/ more detailed engraving is possible on more materials; set-up time is reduced; and laser cutting produces no sawdust. For acrylic, the laser allows for one step operation with polished edges. It isn’t necessary to flame-polish or otherwise handle cut pieces after cutting with a laser.

Figure 4 A complex flower stencil

Steve Aranoff is the business development manager at Vytek Laser Solutions. He also founded ARTTEX Associates and has more than 30 years of experience in the development and distribution of products for digitally printed and converted images. Steve has also provided business, marketing, and sales strategy and implementation consulting. He holds a master’s degree in systems engineering and an MBA.

steve aranoffVytek Laser Solutions

34 | industriaL + speciaLty printing www.industrial-printing.net

Photo cour tesy of Stencil Ease

Processed Material CNC Router CNC Laser (CO2) Quality/Finish/Accuracy Cut Engrave Cut Engrave Router Laser

All types of wood X X X X - +Inlay Wood X X - +3D Wood X - +Acrylic X X X X - +

Extruded Plastic/PVC* X X + -Polycarbonate* X X + -

Leather X X - +Metals X X X - +Textiles X X - +

Fiberglass X X + -Glass/Crystal X - +

Foam X X X - +Stone X - +

Coroplast X X - +Cloth with Sealed Edges X X - +

*A customized laser solution can allow for the safe handling of PVC and polycarbonate.

Table 1 Material-based system selection

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soligie awarded sensor contracts In March, Soligie announced that they have been awarded various contracts to develop printed sensors. Currently, there are prototypes being evaluated by several customers that will be considered for 2011 and 2012 production cycles.

“The sensor market continues to see significant growth and the availability of sensors in new form factors creates opportunities for our customers,” says Matt Timm, president of Soligie.

Industry neWs

July 12-14 seMIcOn West IpcSan FranciSco, ca www.ipc.org

septeMBer 22-23International conference on Flexible and printed electronicsTokyo, Japanwww.icfpe2011.org

septeMBer 27-28 rFId europe Idtechexcambridge, Ukwww.idtechex.com

upcOMIng events

Market m

ovements and association updates

report explains color gamut and resolutionA recent report from Digital Dots explains the importance of color gamut and resolu-tion and how they influence output quality and consistency across different wide-for-mat UV printers and materials.

Researched and written by Michael Walker and Paul Lindström, “UV-Curable Large-Format Printers Technology Test & Guide” provides insight into how wide-for-mat UV printers and inks have developed and the relevance and importance of color gamut and resolution.

Manufacturers EFI VUTEk, HP Scitex, Inca, Polytype, Océ, and Mimaki provided test submissions of UV-curable output on selected media. As these companies have solutions that cover different areas of the wide-format market, the test results are said to cover most of the scenarios likely to be encountered by print-service providers.

The resulting research provides infor-mation for all involved in the wide-for-mat-inkjet sector, whether printer and ink manufacturers or the end users or buyers of the machines.

pV book-to-bill Forecasted to dipThe PV book-to-Bill analysis that was featured in the Solarbuzz PV Equipment Quarterly report in Q1, 2011 posted a three-month average of 1.01, meaning that $101 of new orders were received by PV equipment suppliers for every $100 of rec-ognized product revenues. The PV book-to-bill is forecasted to dip below parity before rebounding in Q4 of 2011.

“PV equipment suppliers remain con- fronted by a highly fragmented manufacturing landscape, compromised of poten-tial customers each at varying stages of technology acceptance and product com-petitiveness,” says Finlay Colville, senior analyst for Solarbuzz. “Understanding the role of book-to-bill ratios at the process tool level, and how each of these is likely to trend moving forward, provides an external benchmarking resource for tool makers to complement their internal marketing strategies.”

An analysis of the new PV book-to-bill findings, which include bookings, backlogs, and quarterly revenues, will be featured in the forthcoming Solarbuzz PV Equipment Quarterly.

gm nameplate receives award from boeingSeattle, WA-based GM Nameplate was recognized as Supplier of the Year in the Interiors category by Boeing Co. on May 18, 2011. Boeing says the selection was based on stringent performance criteria for quality, delivery performance, cost, environmental initiatives, customer service, and technical expertise. Boeing currently has more than 17,525 active suppliers in nearly 52 countries.

Brad Root, president of GM nameplate, says that after winning Boeing’s Supplier of the Year award last year, he was dedicated to continuing to improve the company’s level of service. “Working together, we look forward to our mutual success for many years to come. On behalf of all of the employees of GM Nameplate, thank you, Boeing, for this incredible honor and recognition.”

Find a Use for � is

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CONTEST GUIDELINES:• Cost of submissions: FREE• Who can submit: An individual or a group of individual readers of

iSP may submit their best idea. No one related in any way to iSP, Blue Spark, Nortech, or ST Media Group may participate.

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who contributed to the idea must be listed in the submission.• A project review of 800 words detailing how the battery could

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All submissions will be read by a panel of independent judges.

� e winner will recieve a $200 cash prize courtesy of NorTech and a one page, full color published article in the November/December issue of iSP.

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Printechnologics Wins AwardsGerman-based technology developer Print-echnologics received the Printed Electron-ics 2011 Award at the Printed Electronics Conference in Düsseldorf, Germany, that was held on April 5-6, 2011.

Printechnologics won the best product development award for the company’s Air Touch, a product the company says makes it possible to tag every print product with a recyclable and low-cost code that has the ability to be read simply by a touch on modern devices, such as smart phones.

“These awards are a very important recognition of our work, proving once again that our uncommon approach to printed electronics is heading in the right direc-tion,” says Sascha Voigt, founder and CEO.

Flex Circuit Book-to-Bill Ratios AnnouncedFlexible-circuit shipments were up 30.3% in April, 2011, according to IPC, and bookings increased 7.2% from April, 2010. Compared to the preceding month, flexible shipments decreased 2.4% and bookings declined 0.8%. Flexible-circuit shipments increased 14.3%, and bookings were up 9.0% year-to-date.

Flexible-circuit sales generally include services, such as assembly,and bare flex circuits. The flexible-circuit manufactures in IPC’s survey sample in April indicated that bare circuits accounted for nearly 52% of shipment value reported for the month.

“Growth in North American PCB sales continues to follow normal seasonal patterns and seems to have returned to normal, and the book-to-bill ratio is holding steady at just under parity,” says Denny McGuirk, IPC’s president and CEO. “This suggests the slowdown in sales growth is likely to continue into the third quarter.”

On the Move

FUJIFILM North Amer-ica, Graphic Systems Division, Valhalla, NY, appointed Matt sisson marketing manager for the commercial printing market. THIEME GmbH & Co. KG recruited armin gerland as the new manager of technol-ogy and sales for the company’s printing-systems division. Pulse Roll Label Products Ltd. appointed craig lock to technical sales for its range of label-printing products.

Sisson

Gerland

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ADVERTISING INDEXJuly/August 2011

Advertiser page Advertiser page

ASYS Group Americas Inc. 11 MacDermid Autotype 1

AWT World Trade Inc. 38 McLoone Metal Graphics 35

Chromaline 31 Mimaki USA 5

Douthitt Corp. 3 Nazdar OBC

Dynamesh Inc. 19 RH Solutions 5

Franmar Chemical Inc. IBC Sakurai 38

Graphic Parts International 38 Specialty Graphic Imaging Assn. Insert

Industrial-Printing.net 9 Xenon Corp. 35

Inx Digital IFC

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A Review of Rotary

Screen Printing

Make an Impression

with Hot Stamping

RFID for the Masses

Industrial Printing

Gets SmartP. 24

SEPTEMBER/OCTOBER 2010

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Industrial Printing

july/august 2010www.industrial-printing.net

The Power of Organic PhotovoltaicsA Look at Diecutting TechnologiesOpportunities Abound in Medical Electronics

thin Films Push the limits in Printed ElectronicsP. 22

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shop tour

Stainless-steel membrane switches merge old and new technology to create a non-tactile switch with audible alert.

Cubbison’s digital flatbed cutter with optical registration cuts flexible materials in exact alignment with printed graphics.

Screen-printing presses are used to print conductive traces for membrane circuits and graphics for overlays.

A digital measuring device gauges thickness of printed traces to ensure consistency of ink-deposition height.

cubbison companylocatIon Youngstown, OHother Info Since 1951, Cubbison has provided product-identification solutions in a variety of materi-als and processes to diverse industries. The company’s experienced staff, up-to-date equipment, and advanced imaging and finishing processes have allowed them to meet challenging requirements in using a variety of materials from stainless steel to paper. Cubbison has merged these existing capabilities with printed conductive inks to manufacture membrane switches, supplying the current demand for touch-sensitive input devices.

1 The pick-and-place unit enables Cubbison to place metal domes, surface-mount LEDs, and resistors using optical registration for optimum accuracy.

Testing electrical resistance ensures that conductive ink is cured completely.

Cubbison does 100% testing on all membrane switches to verify that the products are manufactured to exact specifications.

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www.stmediagroup.com/digital/?m=07&y=2011&b=ISP&p=C3&l=www.franmar.com

www.stmediagroup.com/digital/?m=07&y=2011&b=ISP&p=C4&l=www.nazdar.com

lNDUSTRIAL + Specialty Printing - July/August 2011

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