S6 Design Guide 05
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Custom Membrane Switch Design GuideUpdated 12/05- All Rights Reserved
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This design guide is intended as an outline for communicating the requirements of our
customers to Sigma 6 Electronics, a mutual understanding of technology is critical.
A membrane switch is a momentary switch device in which at least one contact is on, or
made of, a flexible substrate. The top layer of the switch is the graphic interface between
the user and the machine. While other layers make the switch work, it is a well designedattractive graphic layer that impresses your customers first. The other layers of the
membrane switch need to support the graphic layer by providing the qualities and
functionality you need. The user of a machine judges the product based on both the
appearance and functionality of your switch. As such, the membrane switch can be themost important part of a product. Sigma 6 Electronics works with customers to design the
optimal switch that meets their needs. We can maximize a switch for appearance,
functionality, and price. Sigma 6 Electronics prides itself on quality testing each switch toyour specifications so that there are no surprises in the field.
Our in-house production capabilities were designed for flexible manufacturing allowingus to provide customers rapid prototyping, production ramp-up as product demand grows,
and even efficient production of long product runs. For larger runs Sigma 6 Electronics
has developed close ties with offshore partners.
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Membrane Switch Design Guide
Table of Contents
▫ Standard Membrane Switch Construction
1. Materials
2. Artwork
3. Embossing
4. EMI/ESD/RFI Shielding
5. Tactile Feel (Domes)
6. Embedded LEDs
7. Rear Adhesive
8. Sub-panels
9. Backlighting
10. Connectors
11. Prototyping
12. Membrane
Appendix “A” Electrical and Mechanical Specifications Standard
Appendix “B” Membrane Switch Checklist
Appendix “C” Glossary
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Membrane Switch- Standard Construction
Membrane Keypad
▫ The Graphic presentation layer of the membrane switch is a graphic overlay.The configuration is dependant on the function of the device. The graphic presentation layer is typically a printed material, such as polyester or
polycarbonate.
▫ Graphic adhesive layer facilitates the assembly of the graphic presentation layer to
the circuit layer, which receives the mechanical pressure applied to the membrane
switch domes.
This layer is typically made from polyester type material with adhesive on both
sides, and is normally designed a few thousands of an inch smaller than the domeheight. This is done to allow a small preload on the dome to facilitate a tactile feel
on the selection pads. Sometimes, as dictated by the membrane switchapplication, this layer will include venting of the domes to allow the trapped airwithin the dome to escape during actuation/pressing of the pad-dome.
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▫ The Circuit or PCB layer includes the membrane switch electronics, as well as the
dome feature.The circuit layer includes the integrated switch pole pairs for each button-dome
combination of the membrane switch.
▫ Adhesive separator layer is an optional layer to facilitate an additional circui try
required for some Membrane switch applications.
This layer will accommodate the interconnection to the dome circuit layer. This
layer will have adhesive on both sides for assembly.
▫ Optional second circuit or PCB layer incorporates additional circuitry required by
the membrane switch application.This layer typically includes the necessary flex cable or interface pins to integrate
the membrane switch.
▫ Adhesive layer on the mounting surface of the membrane switch is provided as a
design option to mount the membrane switch to the target installation
▫ Metal domes used on membrane switches can be designed with a wide range of
stainless steel shapes and degree of tactile responsiveness.Typical applications may have 4 legs and me 12 mm square with trip or snap
forces between 200 to 500 grams.
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1. Materials
A variety of overlay materials are used in membrane switch applications. A commonlyused material is polycarbonate. It is easy to print on, die cut and emboss. For these
reasons it is very cost effective. The disadvantage of polycarbonate is that it begins to
show signs of wear and tear sooner than some of the alternate materials. In most
applications polycarbonate overlays will last a minimum of 100,000 cycles during lifecycle testing. Uncoated polycarbonate is also susceptible to damage from a variety of
chemicals. If a polycarbonate overlay is going to be in an environment that will subject it
to chemicals, a Neltex hard coat should be used to protect the overlay.
Polyester is a more robust material that has superior life cycle and chemical resistance
properties. In life cycle testing, polyester shows no signs of wear at 1,000,000 cycles. It
often needs to be hydro formed instead of embossed because of its memory.
Hydro forming is more expensive for both tooling and unit costs than is embossing.
Polyester is also more difficult to die cut. Dies will require more frequent reblading. Both polyester and polycarbonate are available with a variety textures and hard coats. In their
uncoated glossy form both materials are very susceptible to scratching. For this reason
gloss materials should always be hard coated, Contact your Sigma 6 Electronics engineer
for additional technical data on any of these materials.
Generally, for excellent tactile feel in a switch with stainless steel domes we recommend
an overlay thickness between .006’ and .008.” Thicker overlays will decrease the tactilefeedback and thinner material with decrease the life.
▪ Polyester - .005 to .010 gloss or Matte▪ Polycarbonate- .005 to .020 Gloss or Matte
2. Artwork
Sigma 6 Electronics offers complete artwork layout services. The customer should
specify type styles, colors, and sizes of all copy. Artwork should be provided to us for all
logos or special symbols. We use the latest version of AutoCAD with Autoscript togenerate our drawings and artwork. It is helpful for customers to supply us with an
AutoCAD DWG file, or as an alternate, a DXF or IGES file.
We can convert other files for our use as well. Always provide Sigma 6 Electronics with
a hard copy drawing as well. The artwork will be plotted at Sigma 6 Electronics on our photoplotter that is capable of holding plus or minus .0005” tolerances over a 20” x 26”area. Proofs of artwork will be sent to our customer prior to production.
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Color Matching
Color samples provide the best method of color matching. If you have a sample, please provide it. If a perfect match is necessary, please let your sales professional know so that
a sample can be provided to you for approval.
Textured BackgroundThe surface can be printed by us or supplied on the material by our supplier. Extended
use keypads should not have a printed texture since it will show wear.
If you do not have artwork, our graphic artists and engineering team also design thegraphic overlay and circuitry for your project. Common file types accepted by Sigma 6
Electronics are:
A.
Adobe Illustrator- AI or EPS
B. CorelDraw- CDR Adobe
C. AutoCAD-DWG or DXF
3. Embossing
Embossing is capable of greatly enhancing the look of an overlay and improving the
users’ experience. There are two ways to emboss. First, you can use a male or female die.This allows for a clean finish but has height limitations. The second method is hydro-
forming; it allows for greater embossing heights but is more expensive. Typically, a
material is embossed 1 to 1.5 times the thickness of the base material. It is possible toemboss more than this but the durability of the keypad is sacrificed.
The phrase “Plateau Embossing” is used to describe keys that are raised and flat on the
top. The term “Rim Embossing” is used to describe raising only the border of a key.Embossing is ty pically .010” high and two-dimensional. Hydro-forming can be used to
attain higher embossments, up to 2-3 times material thickness. Three-dimensional dies
can also be built. Overlays can be hydro-formed with domes in them to provide tactile
feedback. Hydro-forming tools are significantly more expensive that embossing tools.We have samples of both hydro-forming and embossing on polyester and polycarbonate
that will help illustrate the different results that can be attained. Contact a Sigma 6
Electronics sales engineer to request hydro-forming and embossing samples.
4.
EMI/ESD/RFI ShieldingPrinted conductive inks, aluminum foil, copper foil or Indium Tin Oxide (ITO) isemployed in membrane switch designs to minimize the impact of electromagnetic
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interference (EMI), electric static discharge (ESD), or radio frequency interference (RFI).
Several options are available for shielding membrane switches. The most common are printed carbon, printed silver, and aluminum foil. From a functional standpoint, the main
difference among these materials is their conductivity. Either carbon or silver can be
printed on top of the top circuit to act as a shield. These shields have the advantage of not
adding any additional layers to the switch construction. Carbon shields are less expensivethan silver shields. Silver is usually printed in a grid pattern to reduce cost. A layer of
aluminum foil can also be added above the top circuit. This material is the most
conductive shield available. However, it does add two layers to the switch construction.
The shield is usually connected to the ground through the connector, or by means of a tab
with a slot for a fastener.
The customer should express their shielding requirements in Ohms per square inch. The
entire product packaging must be considered when specifying these requirements.
5. Tactile Feel (Domes)
The dome type, the material, part thickness, and embossing are all important in
determining the actuation force needed to activate the switch. For instance, in a
machinery application where panels might be bumped, you might want the actuationforce to be high. However, in a health care setting you might want the safety switch to
require a low actuation force.
There are two types of domes: Stainless steel and Mylar.
▪ Stainless steel domes are the most common. They offer the longestactuation life and a more tactile feel. Sigma 6 Electronics maintains an
inventory of domes ranging from 3mm to 12mm in size.▪ Mylar domes can be formed into the upper switch or a dome layer can be
added on top of the upper switch.
Actuation ForceThe customer may specify the switch actuation force. Typical actuation forces range from
6 to 24 ounces. Mylar domes usually have greater actuation force than do stainless steel
domes. Mylar domes have typical actuation forces of 14 to 24 ounces. Stainless steeldomes are in the 12 to 18 ounce range. The tolerance on actuation force is +/- 3 ounces.
Our engineering staff will proved expert advice on the type of dome best suited for yourapplication.
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6. Embedded LEDsIT is relatively common to include small surface mounted LEDs into membrane switches.
This is a very simple way to add annunciations to switch. A standard membrane switch isnot thick enough to accommodate the package size of most surface mount LEDs. For this
reason, the overlay may be embossed in the window area, or extra fillers may be added to
the switch construction. Silver conductive epoxies are used to mount the LEDs to the
circuit. These epoxies are not very flexible, and consequently switched with embeddedLEDs should not be bent in the LED areas prior to being installed. Stiffeners can be
added to the switch construction to add rigidity when needed.
7. Rear AdhesiveAdhesion qualities are affected by the substrate surface energy (high or low), types of
materials used, the required bonding requirements, environmental concerns and a number
of other factors. Your sales associate will help you decide what is best.
8. Sub-Panels
In some applications it is desirable to have Sigma 6 Electronics supply the membraneswitch mounted to a rigid subpanel. The most commonly used material for such
subpanels is aluminum. These subpanels can be supplied with a variety of hardware
installed. It is important to keep in mind that the subpanel must have different mechanical
dimensions to allow for assembly tolerances. The subpanel should be .020” smaller thanthe membrane in both height and width. All cutouts and holes should be .030’ larger.
Cutouts behind windows should be .060” larger than the window. These general
guidelines are intended to help insure that the subpanel is not visible after assembly.Other subpanel materials are:
▪ Aluminum- Anodized, sealed, unsealed, dyed, or un-dyed
▪ Cold Roll Steel-Plated with, Chrome, Zinc, or other plating▪ Stainless Steel- Brushed, Sanded, other finishes.
▪ Plastic Panel
▪ Printed Circuit Board- Single or multi-Layer
9. BacklightingWe offer several backlighting solutions for viewing legends in no light and low light
applications. The most common backlighting methods used are Fiber Optics,Electroluminescent panels, and LEDs. Our ability to manufacture a switch, which meets
our customer’s expectations, is dependent on how well we understand our customer’srequirements. The customer should be sure to supply us with as much detail about isdesign requirements as possible. Appendix “B” is a checklist of issues that should be
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addressed in communicating a customer’s complete requirements. It is helpful for the
customer to supply a copy of this checklist with notes on topics not covered elsewhere in
this documentation.
10. Connectors
Sigma 6 Electronics recommends the Nicomatic connector. We have found them to be of
high quality and long lasting. However, we can supply almost any standard connectormethod.
Nicomatic Connector Specifications:
▪ .100” pitch Male, Female, and Solder tab
▪ Plating-Tin or Gold▪ ZIF-Zero Insertion Force Connector
▪ This connector is designed for installation of ZIF Connectors
11.
PrototypingA prototype is a cost-effective method for creating and executing your design with a
minimum investment in tooling and development time. Often there are changes in size,colors, hole locations and shape after a prototype run.
To assist in prototype efforts, Sigma 6 Electronics has new equipment for laser cutting
and digitally printing that can make first runs very affordable.
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Appendix AMembrane Switch - Electrical and Mechanical Specifications
A. Electrical1. Configuration – momentary SPST normally open
2. Current Rating – 30V – 100MA to 120V – 10MA maximum
3. Breakdown – 220 V RMS4. Closed – 100 OHMS typical contact resistance
5. Open – 10 MEG OHMS contact resistance minimum
6. Capacitance – 30 Picofarads
7. Life;a. Flat Switch – approximately 5 million cycles
b. Domed (embossed) layer – approximately 5 million cycles
c. Domed circuit – approximately 1 million cyclesd. Metal Dome – approximately 5 million cycles
B. Mechanical & Environmental
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Appendix B
Membrane Switch ChecklistThe following items need to be communicated to Sigma6 before an order can be
processed. ___ Mechanical dimensions of the finished part
___ Tolerance specified (+/- .015")
Type of switch
___ Non Tactile ___ Tactile with stainless steel domes
___ Tactile with polyester domes
___ Tail exit point
___ Tail length
Tail termination ___ Berg Clincher
___ AMP ___ Solder Tabs
___ Exposed silver for ZIF
___ Other _______________
Pinout ___ Determined by Sigma6
___ Customer Specified
Shielding ___ None required
___ Printed silver grid ___ Printed carbon ___ Aluminum foil
___ Other ________________
Overlay Material
___ Velvet textured polycarbonate (8B35) ___ Gloss polycarbonate with hard coats (8010)
___ Velvet textured polyester with hard coat (Autotype)
___ Gloss polyester with hard coats (Autoflex)
___ Other _________________Logos and special graphics
___ Customer supplied ___ None required
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Windows/Lens coating
___ Velvet textured (enunciator, LED)
___ Anti Glare (LED, VF, LCD) ___ Gloss, water clear (LCD)
___ Window insert
Embossing
___ Key rims ___ Plateau
___ LED windows
Hydro forming
___ Key rims ___ Plateau
___ LED windows
Insertable legends ___ Not required
___ Specified
Support panel ___ LED windows
___ Not required
___ Drawing included with material specified
Artwork ___ Sigma6 generated
___ Customer supplied (attached to order)
___ Colors specifiedColor matching
___ Custom (samples supplied) ___ Pantone Matching System
___ Federal Standard No. 595a ___ Copy size, style, and location specified
Switch Sealing Requirements
___ Standard splash resistant
___ NEMA 4Switch Venting Requirements
___ Standard internal venting
___ Externally vented
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Appendix C
Glossary
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