SMTA Printing Workshop The Art of Stencil Printing Steve Arneson - ASC International April 7, 2015 Due to the need for smaller components such as 01005, CSP and Micro BGAs, proper printer setup has become critical to the overall quality aspect of the production process.
According to estimates, 50 to 70 percent of total defects in surface mount assembly lines are related to the stencil printing process, and approximately 30 to 50 percent of the total manufacturing cost is due to test and rework Circuits Assembly, On-line Enhancements of the Stencil Printing Process Pan, J., . Critical variables of solder paste stencil printing for Micro-BGA and fine
pitch QFP. IEEEI/CPMT International Electronics Manufacturing Technology Symposium Feldmann, K. and Sturm, J. ) Closed loop quality control in printed circuit assembly. IEEE Transactions on Components, Hybrids and Manufacturing technology, Part A, Vol. 17,No.2 There are more than 60 Variables found within the screen printing process. By implementing a proactive quality initiative to better understand each variables impact will guarantee reliable TE. Analyzing the Key Variables ?
Printing Process - Setup Solder Paste Material Tooling and Equipment Design Environment Human Interaction Printing Process - 101
Printing Process Speed of Print - Setup Under 1 to 12 Inches/Sec Shear Thinning High Speed 4-8 Squeegee Pressure - Setup 1 to 1.5 lbs per/linear inch of blade Too high Scooping / Excessive wear
Too low poor fill /left over paste on stencil Paste Application - Setup Roll diameter of 3/8 to 1/2 inch 1/2 inch beyond end of blade Allow Paste to Flow Properly Reprint first 5 boards*
Cleaning Frequency Under wipe/Vacuum 1 to 20 prints Printing Process Stencil to PCB Proper Gasketing
Poor Alignment PWB Shrink
Aperture Size Paste Under Stencil Solder Mask on Pad HASL Dome Silk Screen Layer Solder Paste Material Paste Properties Metal % / Alloy
Powder Size Type 1 6 Lead Free No Clean Water Soluble Solder Paste Material
Storage and Handling Time out of Storage Time on Stencil Expiration of Paste Flux Reduction
Viscosity Increase Poor Roll Poor Aperture Fill Reflow Issues Tooling and Equipment Stencil
Wear/Damage Enhancements Nano-Coatings* Material Metal / Plastic Squeegee Wear / Damage
Blade Type* Rubber /Polyurethane Metal Finer Pitch Tooling and Equipment PCB Planarity Supplier Issue Board Support*
Design Elements Pads SMD or NSMD Spacing Complexity Low, Mid, High*
Board Layout Single Panelized Design Elements Stencil Technology Aperture Density
Shape Round Square Radius corners Reduction Design Elements
Stencil Technology Area Ratio* >0.66 <0.66 Type 6 paste* Step Stencil Nano-Coating Pitch Dimension
Environment Controlled Environment
Temperature Relative Humidity Seasonal Air Flow* Inside Printer Air Movement Dries Out Paste Human Factors
Time of Day
Good day / Bad day* Shift Changeover Operator Skill / Error* Diligence Access Level to Printer Typical Solder Paste Defects
The print process on many days How to be the star of your process . .. Create a Cookbook of best setups
Recipe #1 - The Taste of Sweet Success How to achieve a reliable process? Accept the fact that 1 size does not fit all 5 mil stencil rarely yields 5 mils of paste Determine what % of defects are print related
Most likely very high percentage corrective actions Understanding First-Pass Yield Be honest Improved print process = reduced rework Implement proactive 3D Solder Paste Inspection
Fast ROI - Pay dirt all the way! Your Solution: 3D Solder Paste Inspection SPI / SPM Technology Laser
Single Stripe Scanning Laser Structured White Light Single FOV
On the fly Technology Laser SWL Simple Comparison of Technologies
Single Strip Laser Structured White Light ** No Live Ducks Injured in this Slide ** Technology Key Features Laser
SWL Accurate / Repeatable Highly Accurate / Repeatable .10 Mil / GR&R under 25% Multiple Application Use
Adhesives Thick Films Grease Lowest Cost of Ownership Starting at under $15,000.
.07 Mil / GR&R under 10% 2 Levels of Analysis Quantitative and Qualitative True 3D Height / Volume Higher Resolution Pixel by Pixel Data Points FOV / Camera Resolution
Sample Based Inspection Focus on Critical Components Strong Price / Performance Starting at under $25,000.
Excessive Solder = 2 Mils Percentage Over-Print = 40% Annual Paste Expense Per Year = $50,000 Estimated Yearly Cost Savings Due to SPI Control = $20,000 ** Typical Offline SPI System Cost = Less than $25,000 ** Summary:
The Art of the stencil printing process is made up many variables. Controlling those variables through dedicated DOE and SPI monitoring will guarantee a yield improvement strategy you can take to the bank! Questions? Thank You CyberOptics and SMTA
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