Benefits of SPI Use

Powder Particle Size

Effects of Changes in Particle Size Distribution

Type III is most commonly used Paste. Finer pitch devices generally require finer metal particle sizes

Disadvantages of Finer Powders: Disadvantages of Finer Powders:

• Cost (Lower Metal Powder Yield)

• Decreased Reflow Performance

Advantages of Finer Powders:

• Increased Print Performance

• Reduced Print Defects Performance

Most customer choose Type III for finer pitch printing applications.

The cost of larger particle sizes means higher levels of random defects.

Koh Young delivers the solution for 100% performance during the printing process.

Powder Particle Size (Variance)

Manufacturing Techniques:

• IPC or JIS standards Supply Different Standards.

Who Supplies the Powder:

• Paste can be Manufactured from Various Suppliers

Powder Manufacturing has Natural Variance (from Batch to Batch):

• Where is your Powder in the Particle Size Distribution Range?

Koh Young enables the customer to reassign priorities, bringing continuous measurable improved performance, whilst reducing engineering workload.

Even though the range can be specified to be the same the distribution from batch to batch can be very different, creating completely different printing performance.

It is understood and Expected that Suppliers send Products within Specification, but what happens When Something goes Wrong in their Process

• Flux Materials are Naturally Occurring Substances (Rosin is from Trees)

• Rosin Changes from Year to Year with Changes in the Environment.

• Age of Flux when the Paste is Manufactured.

• Age of Paste when Added to the Printer

• Storage Conditions of the Paste

• Transportation Conditions of the Paste to your Facility

• Powder Variance

Paste: How Many Variables

• Powder Variance

• Powder Batch to Batch Variance

• Flux Constituent Parts

• Powder Shape and Size

Solder paste alters performance throughout the shelf life of the product. Where is your paste in this cycle when manufacturing your production boards?

Koh Young automatically gives the customer the ability to easily control the process without interfering in the production cycle.

Are You Aware and in Control of all these Conditions ?

Solder Paste Changes State During Production in a Number of Ways

• Solder Paste additions: Are the Operators aware of

• How Much Paste to Add

• When to Add Paste

• Number of Prints Before New Paste is Added

• Flux to metal Ratio Changes

• Dependent on Board Design

• Dependent on the Number of Prints

Printer: Process

• Pressure and Speed of the Squeegee Blades

• Temperature and Humidity of the Environment

• Does the solder Paste have suitable rheological

Values for Efficient Rolling and Recovery ?(See Graph)

• How Long has the Paste Been on the Stencil?

Koh Young can work to develop your engineering capability for fault finding in process applications.

Do you Know Your Process to Identify the Main Effects and Where the Process Safe Limits Are?

From Careful Setup in New Product Introduction, How is the Production Process Performing?

• Personnel with Access to Changes

• Who is Allowed to Make Changes and How are these Reported?

• Valid Changes

• Decisions Based Upon Data Analysis.

• Invalid Changes

• Changes Without Fully Validating the Change

Using SPC Rules

Printer: Set Up

Using SPC Rules

• Are the Personnel Trained in Evaluation and

Reason for Changes Made?

• What Qualification of the Printer Takes Place on a Regular

Basis to Ensure Good Repeatable Performance?

Through statistical methods, Koh Young can deliver the optimal settings for any product. Deviations from these optimal settings can quickly be established and normal production can resume.

Printer Performance Varies when Regular Maintenance Does not Occur

Under Stencil Wiper Performance

• Out of Sight: How do you Know the Wiper is Performing Well ?

• Is the Solvent Dispense Consistent?

• Is the Wiper Paper Moving Correctly?

Tooling

• Has the tooling been Added Correctly?

• Is the tooling Clean?

Printer: Maintenance

• Is the tooling Clean?

Calibrations

• Have the regular calibrations been performed ?

Print Head

• Has the Print Head Squeegee Force Calibration been Performed?

• Are the Squeegee Blades Replaced at Regular intervals?

Koh Young has invested in printing equipment and developing strategic relationships with printer suppliers to continually develop to your requirements with integrated solutions to improve your printer performance.

Examples

The Best Way to Utilize 3D SPI

Process

The 3D Solder Paste Inspection System is not just a defect finder.

It should be used for optimizing and controlling the process.

Process Optimization

with statistical data

Random Defect Removal

Optimising the Printing Process: Case Studies

1. Using Histogram Analysis for Optimisation

2. Squeegee Direction

3. Squeegee Blade Problem

6 Case Studies: Optimising the Printing Process

3. Squeegee Blade Problem

4. Printer Level Settings

5. Solder Paste Batch Issue

6. Stencil Design Review

What’s the Best Tolerance Setting for your Application?

Using Histogram Analysis for OptimisationOptimising Print Pressure and Print Speed

Optimising Print Pressure and Print Speed

Speed(mm/s)

Pre

ssu

re(K

g)

OBSERVATION: Random defects occur and many personnel have adapted parameters without success

SOLUTION: By varying the speed and pressure of the stencil printer a Cpk histogram matrix(Volume) was created. The table gives the optimal statistical performance of

•Pressure = 6.6Kg•Speed = 80mm/sec

PROBLEM DEFINITION:No statistical analysis of the printing process has been performed

Squeegee DirectionAn Example of Print Direction Issues

and How to Resolve

• Volume Histogram by Pad

Removal Offsets Caused by Print Direction

PROBLEM DEFINITION

PCB

Stencil Mask

Squeegee

Blade

PROBLEM DEFINITIONOffset problem between metal mask and PCB. Possible reasons for this are• Excessive Printing Force• Incorrect Print Offsets• Table or machine instability

OBSERVATION: Offset between Front to Rear squeegees observed

SOLUTION:Removal of the offset can be performed by dialing in the values output from the Koh Young directly into the stencil printer.

Squeegee Blade ProblemSqueegee Blade Damage

Squeegee Blade Damage

OBSERVATION: Many excessive defects occurred within a straight line on a single print stroke.

Squeegee Direction

Squeegee Blade Damage

PROBLEM DEFINITIONOne line of solder paste can be seen on the stencil mask after the Rear->Front Squeegee Stroke. This is not visible in the printer as the print head remains down and the stencil cannot normally be viewed. The rear blade is damaged.damaged.

SOLUTION:Replace the blade after the first defect has occurred. Without SPI, this defect could have gone unidentified.

Printer Level SettingPrinter Level Condition

Printer Level Condition

Volume Trend Analysis

OBSERVATION: A large variance in the sigma value is occurring and the volume histogram is giving low Cpk values.

Analysis using the SPC PlusTM volume trend analysis has shown that there is a variance in the level of the board to the stencil.

After Leveling of the PrinterPROBLEM DEFINITIONThe cause of the variance of the board to stencil is due to the table level that supports the board. The table is incorrectly adjusted and requires immediate adjustment to correct the issue.

SOLUTION:Make the PCB surface Level to the Height Guide of the Printer

Printer Level Condition

NOTE: For Effective Adjustments of the Printer Parameters, Leveling should Always be Done in Advance.

Height Guide of the PrinterMake the PCB Rail Parallel to the Base by Using a Dial Indicator

The printer volume Sigma performance is much improved and the volume Cpk performance has also improved.

Solder Paste Batch IssueDelivering Short and Long Term Solutions

Solder Paste Batch Issue

OBSERVATION:

Problems observed with random open circuits on BGA parts prior to installation of the Koh Young system.

Many changes were made to the production process without success including

• Stencil design changes• Stencil design changes

• Automatic paste dispenser addition

• Changes to under stencil wiping

• Increased manual checks

• Increased stencil washing

• Changes to the reflow profile

• Component review

• X / Y centering improvement

PROBLEM DEFINITIONBecause no data could be produced for the solder printing, assumptions were made and pieces of work were started with limited success.The issue was resolved by introduction of the Koh YoungAfter starting, the production ran well for a number of hours, then an event occurred that created SOLUTION:

Solder Paste Batch Issue

Koh Young can deliver effective short term and long term solutions with no loss to production.

an event occurred that created random defects.The Koh Young found all the random defects and the boards were removed which solved the issue, but reviewing the SPCPlus files allowed analysis of the root cause for a permanent fix.

SOLUTION:A performance change in the paste happens after a delay in production of one hour. Good manufacturing practices were followed, but the issue still occurred (for example; cleaning the stencil, kneading the paste, cleaning and setting blade height)A new batch of paste was used and the problem was solved.Further review had shown that the paste did not recover after a delay. An issue with paste manufacturing was established and resolved.

Stencil DesignEffects of Design on Printing

Stencil Design

OBSERVATION:

The centre of the BGA has more insufficient deposits than the rest of the component.

80 90 100 110

PROBLEM DEFINITION: The design of the component causes the stencil “supporting” metal to be less. When the paste metal to be less. When the paste releases from the stencil, the “weaker” areas of the stencil (centre) are pulled down due to the surface tension of the paste in the apertures. When the stencil finally releases, this causes the paste to peak and release inconsistently.

SOLUTION:A different stencil material was selected for the combined strength properties and the problem was removed.

Error Removal

Recurrent errors can be removed by optimisation.

However, random errors can still occur after optimisation

Various types of defects

1. Excessive error

2. Insufficient error

3. Missing paste

4. Offset

5. Bridging error

6. Shape error

• KohYoung systems are capable of detecting

• Insufficient

• Excessive solder pastes

• Bridging

• Position errors,

• Shape deformities

• Tailing

• Paste Scooping errors

Defect Detection Capability

Insufficient Error Excessive Error

• Paste Scooping errors

occurring in normal volume.

Shape (Scooping)Shape Error (Tailing) Offset Error

Volume of solder paste deposit is bigger than the desired one.

Desired amountof paste

Excessive Error

Chip

Chip

Volume: 205%(Excessive Error)

Excessive Error (Example)

� Excessive paste may result in shorts between pads, after reflow.

CSP or BGA

After Reflow

CSP or BGA

Short Error: Electrical test failure. Can only be

found if 100% test is performed, otherwise

failure can be passed to the customer

Excessive errors can lead to long term reliability problems and

latent failures after manufacture

Cause of Excessive Error• Excessive Wet Wiping causes the solder paste to lose its elastic properties

� Set the Stencil wiper up correctly

• Lack of correct board supports or incorrect height settings for the stencil printer

�Correct the height of the tooling supports

�Adjust the stencil printer table or stencil level

• Dust and dirt from board manufacture and storage cause poor gasketing from stencil to PCBs

�Clean the bottom of stencil

� Remove foreign material on PCB

• Poor solder gasket between board and stencil

Excessive Error

• Poor solder gasket between board and stencil

� Change wiping frequency

Desired amountof paste

Insufficient Error

Volume of solder paste deposit is smaller than specification.

Insufficient paste may lead to parts separation or cracking of the fillet

during accelerated life testing.

Volume: 35%(Insufficient Paste)Clogged stencil hole

�Change the stencil wiping cycle

� Regular cleaning of the stencil in a wash tank

�Check solder paste maintenance procedures are suitable for the design of board and the

solder paste being used

Solder paste not filling the aperture properly

� Reduce the squeegee speed and check the PCB snap off position

Insufficient Error

CSP or BGA

After Reflow

� Insufficient paste may lead to parts separation or cracking after soldering.

After Reflow

CSP or BGA

Insufficient errors can lead to long term

reliability problems and latent failures after

manufacture

Open Circuit Error: Electrical test failure. Can only be found if

100% test is performed, otherwise failure can be passed to the customer

Cross-Sectional Analysis

Insufficient Defect

from 3D SPI

Escaped by AOI and X-Ray

If the insufficient solder paste defect is not stopped at the SPI

machine, the defect could occur at the customer.

The crack of the solder joint occurred due to the insufficient volume.

Paste printed off the pad land

Paste Offsets

PCB not firmly fixed on Screen Printer tooling block . When the blade hits the front edge of the board during

the print cycle the board moves.

�Improve the tooling / hold down method of the board

PCB is firmly fixed on Screen Printer conveyors but still gives offset errors

� Adjust Printer X,Y offset parameters using Koh Young’s Offset Histogram

Bridging can lead to short circuits

Bridging Error

Caused by Foreign Material

Too many prints without wiping the stencil

�Change the quantity of prints before wiping

Foreign substances are on the PCB’s

�Clean the bottom of stencil.

� Remove foreign material on PCB before printing

Cold slump in the solder paste due to solder paste properties

� Remove old paste more frequently

Why the Shape deformity is important? Mounting errors or bridge defect may occur on normal volume of deformed solder paste.(The importance of deformity control is raised when dealing with fine pitch parts.)

Tailing occurs when PCB and mask get separated.→ Shows adequate amount of paste but may

cause bridging

C H I P

C H I P

Shape Error

• Shape diagnostic data is provided to allow customersto detect defects from shape deformity even with theadequate volume.

• User can choose one from ‘Line Stop’ mode and ‘JustWarning’ mode to react to the shape deformity detected

Using a true 3D profilometry method, KohYoung can measure the authenticvolume of solder pastes on PCB’s, differently from rough approximationor simplification.

Highly Reliable and Accurate 3D Measurement

In-Line 3D SPI Adds Value

Only One Supplier Can Deliver the Inspection Solution

• Process Knowledge

• Statistical Knowledge Solutions

• Commitment to Customer Issues

• Continual Learning Packages for Internal Staff, Customers and Distribution Partners

• Investment into the Customer, Products and People by an Integrated • Investment into the Customer, Products and People by an Integrated Working Solution

• Partnership with Customers for Creative Thinking

• Research and Development into New Technologies

• Cost Effective Solutions to the User

Koh Young Repeatedly Delivers on All of Your Requirements.