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Reducing Head in Pillow Defects

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Information on BGA voiding and its prevention.

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Reducing Head in Pillow Defects

  1. 1. an Alent plc Company Reducing Head in Pillow Defects September 2009
  2. 2. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Introduction • Potential sources of Head in Pillow Defects • What is the mechanism of failure • Evaluation of Package Warpage – Measurement – Industry Standards • How Can Solder Paste Reduce HIP Defects? – Print Volume – Wetting Force/Speed – Paste Activation Level • Future Experiments
  3. 3. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company What is Head in Pillow? Board Side Component Side
  4. 4. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Difficult Problem  In circuit testing may not detect the HIP defect  Z Direction X-Ray may not detect the HIP defect  Devices that are exposed to Drop Shock or Thermal Cycling in field unfortunately Will over time experience this defect Head in Pillow = Where the solder joint and the sphere are touching but no intermetallic layer is formed
  5. 5. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Head in Pillow Defect C&E Overview Warpage of substrate Inconsistent bump size Insufficient solder paste volume Printing misalignment Inaccurate XY placement Insufficient placement force inadequate reflow profile that results in component & PCB warpage Lifting of BGA bumps due to wetting force Excessive Peak Temperature Too much TAL Opportunities of defects from the different stages of a SMT process
  6. 6. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Head in Pillow Defect Mechanism •BGA Oxidizes •Flux Activity Being consumed •Flux Becomes Liquid •BGA Oxidizes •Flux Activity Being Used •Oxidized Sphere rejoins the Paste deposit with Limited Activity
  7. 7. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Jeita Maximum Warpage Standards
  8. 8. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Measuring BGA Warpage Schematic of Shadow Moiré Method
  9. 9. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Shadow Moiré Test Unit
  10. 10. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Moiré Computer Generated Image
  11. 11. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company How Can Solder Paste be Engineered to Reduce HIP? I
  12. 12. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Alpha Response Solder Paste that… produces higher and more consistent volume deposition has a greater resistance to longer soak profiles has faster wetting speed • Gage R&R testing for determining in-house Head on Pillow defects to confirm solder paste effectiveness
  13. 13. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company 0.25mm round BGAs, 0.1mm laser cut stencil OM338 T45 -20 0 20 40 60 80 100 120 140 160 1 7 13 Board # Volume(cumil) Average - Boards 1-6 (Initial) Average - Boards 7-12 (wipe) Average - Boards 13-18 (pause) Minimum vol. - Boards 1-6 Minimum vol. - Boards 7-12 Minimum vol. - Boards 13-18 450-31 -20 0 20 40 60 80 100 120 140 160 1 7 13 Board # Volume(cumil) Average - Boards 1-6 (Initial) Average - Boards 7-12 (wipe) Average - Boards 13-18 (pause) Minimum vol. - Boards 1-6 Minimum vol. - Boards 7-12 Minimum vol. - Boards 13-18 Print Volume Increased print Volume and Volume Repeatability Improved Paste Print Provides 40% More Paste Height! Standard Paste Grizzly Bear
  14. 14. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Preventing Defect with Paste Print Height Probable Defect Defect Prevented 70µ Deposit 100µ Deposit
  15. 15. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Wetting Force • Test Method – Malcom Wetting Balance Test • Equipment – Malcom SWB-2 • Test Procedure – See Malcom SWB-2 Operating Manual
  16. 16. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Wetting Force Average -12.00 -10.00 -8.00 -6.00 -4.00 -2.00 0.00 2.00 4.00 6.00 0 2 4 6 8 Wetting time , Sec WettingForce,mN Average -12.00 -10.00 -8.00 -6.00 -4.00 -2.00 0.00 2.00 4.00 0 2 4 6 8 Wetting time , Sec WettingForce,mN Grizzly BearStandard Paste Goal: Increased Wetting Force and Speed
  17. 17. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Head in Pillow Test Method
  18. 18. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Creating HIP Defects The Occurrence of the HIP defects average 200 ppm based on customer feedback Issue: How do we create a test method that creates higher DPMO (Defects per million opportunities) so we can test for it? Good Joint HIP Joint
  19. 19. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Manage Reflow and Warpage Time, Temperature, Z-Axis Location
  20. 20. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company HIP Test Equipment • Test Vehicle (TV) • BGA338 Dummy component • BGA rework station • Fabricated TV holder and fixture for holding the dummy BGA with vacuum. • Thermocouple data acquisition • Solenoid Valve
  21. 21. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company HIP Experimental Set-Up
  22. 22. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company HIP Experimental Set-Up 1. The BGA component is held a few mm above the test vehicle by applying vacuum to the cup. 2. The BGA is then dropped on to the test vehicle by releasing vacuum.
  23. 23. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Reflow Profile Indicator
  24. 24. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Drop Component at Precise Time During Reflow
  25. 25. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Experimental Results • Test Highly Activated Paste vs. Very Low Activity Paste and Measure HIP DPMO.
  26. 26. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Head in Pillow Resistant Paste Good reflow at corner pads Only one HIP Defect was Observed after prying the BGA from Test Vehicle
  27. 27. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Less Activated Paste After prying BGA from TV Obvious HIP joint in the center of the BGA block!
  28. 28. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Initial results suggests that flux chemistry does affect HIP More Active Paste Less Active Paste
  29. 29. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Future Work ZhuoMao BGA Rework -- HIP A reflow profile 0 50 100 150 200 250 0 50 100 150 200 250 300 350 Time sec Temperature°C lower left corner upper right corner lower BGA row center BGA block 217°C TC positions Under the BGA Reflow Profile vs. Head in Pillow Defect Rate
  30. 30. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Summary  Component Size/Warpage Can Affect HIP Defect Rate  Key attributes for Solder Paste to reduce HIP DPMO’s Taller, More Consistent Paste Deposits Faster, Stronger Wetting Force Enhanced paste flux Activity and Activity Duration High Gage R&R HIP Test to Confirm Paste Properties
  31. 31. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company For more information click the link below: Alpha Products

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