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: 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? 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. Koh Young enables the customer to reassign priorities, bringing continuous measurable improved performance, whilst reducing engineering workload.
Paste: How Many Variables 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 Powder Batch to Batch Variance Flux Constituent Parts Powder Shape and Size Are You Aware and in Control of all these Conditions? 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.
Printer: Process 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 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? Do you Know Your Process to Identify the Main Effects and Where the Process Safe Limits Are? Koh Young can work to develop your engineering capability for fault finding in process applications.
Printer: Set Up 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 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: Maintenance 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? 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 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 6 Case Studies: Optimising the Printing Process 1. Using Histogram Analysis for Optimisation 2. Squeegee Direction 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 Optimisation Optimising Print Pressure and Print Speed
Optimising Print Pressure and Print Speed Speed(mm/s) Pressure(Kg) OBSERVATION: Random defects occur and many personnel have adapted parameters without success PROBLEM DEFINITION: No statistical analysis of the printing process has been performed 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
Squeegee Direction An Example of Print Direction Issues and How to Resolve
Removal Offsets Caused by Print Direction Volume Histogram by Pad Squeegee Blade Stencil Mask PCB OBSERVATION: Offset between Front to Rear squeegees observed PROBLEM DEFINITION Offset problem between metal mask and PCB. Possible reasons for this are Excessive Printing Force Incorrect Print Offsets Table or machine instability 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 Problem Squeegee Blade Damage
Squeegee Blade Damage Squeegee Direction OBSERVATION: Many excessive defects occurred within a straight line on a single print stroke.
Squeegee Blade Damage PROBLEM DEFINITION One 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. SOLUTION: Replace the blade after the first defect has occurred. Without SPI, this defect could have gone unidentified.
Printer Level Setting Printer 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 Plus TM volume trend analysis has shown that there is a variance in the level of the board to the stencil.
Printer Level Condition PROBLEM DEFINITION The 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. After Leveling of the Printer SOLUTION: Make the PCB surface Level to the Height Guide of the Printer Make 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. NOTE: For Effective Adjustments of the Printer Parameters, Leveling should Always be Done in Advance.
Solder Paste Batch Issue Delivering 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 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
Solder Paste Batch Issue PROBLEM DEFINITION Because 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 Young After starting, the production ran well for a number of hours, then 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. Koh Young can deliver effective short term and long term solutions with no loss to production.
Stencil Design Effects of Design on Printing
Stencil Design 80 90 100 110 OBSERVATION: The centre of the BGA has more insufficient deposits than the rest of the component. PROBLEM DEFINITION: The design of the component causes the stencil supporting 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
Defect Detection Capability KohYoung systems are capable of detecting Insufficient Excessive solder pastes Bridging Position errors, Shape deformities Tailing Paste Scooping errors occurring in normal volume. Insufficient Error Excessive Error Shape (Scooping) Shape Error (Tailing) Offset Error
Excessive Error Volume of solder paste deposit is bigger than the desired one. Desired amount of paste 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 Excessive errors can lead to long term reliability problems and latent failures after manufacture Short Error: Electrical test failure. Can only be found if 100% test is performed, otherwise failure can be passed to the customer
Excessive Error 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 Change wiping frequency
Insufficient Error Volume of solder paste deposit is smaller than specification. Desired amount of paste 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 Insufficient paste may lead to parts separation or cracking after soldering. CSP or BGA 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 Offsets Paste printed off the pad land 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 Error Bridging can lead to short circuits 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
Shape Error 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.) C H I P C H I P Tailing occurs when PCB and mask get separated. Shows adequate amount of paste but may cause bridging Shape diagnostic data is provided to allow customers to detect defects from shape deformity even with the adequate volume. User can choose one from Line Stop mode and Just Warning mode to react to the shape deformity detected
Highly Reliable and Accurate 3D Measurement Using a true 3D profilometry method, KohYoung can measure the authentic volume of solder pastes on PCB s, differently from rough approximation or simplification.
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 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.