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. ï»żan Alent plc Company Reducing Head in Pillow Defects September 2009
- 2. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION ï»żan Alent plc Company Introduction âą Potential sources of Head in Pillow Defects âą What is the mechanism of failure âą Evaluation of Package Warpage â Measurement â Industry Standards âą How Can Solder Paste Reduce HIP Defects? â Print Volume â Wetting Force/Speed â Paste Activation Level âą Future Experiments
- 3. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION ï»żan Alent plc Company What is Head in Pillow? Board Side Component Side
- 4. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION ï»żan Alent plc Company Difficult Problem ïŒ In circuit testing may not detect the HIP defect ïŒ Z Direction X-Ray may not detect the HIP defect ïŒ 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. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION ï»żan Alent plc Company Head in Pillow Defect C&E Overview ï·Warpage of substrate ï·Inconsistent bump size ï·Insufficient solder paste volume ï·Printing misalignment ï·Inaccurate XY placement ï·Insufficient placement force ï·inadequate reflow profile that results in component & PCB warpage ï·Lifting of BGA bumps due to wetting force ï·Excessive Peak Temperature ï·Too much TAL Opportunities of defects from the different stages of a SMT process
- 6. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION ï»żan Alent plc Company Head in Pillow Defect Mechanism âąBGA Oxidizes âąFlux Activity Being consumed âąFlux Becomes Liquid âąBGA Oxidizes âąFlux Activity Being Used âąOxidized Sphere rejoins the Paste deposit with Limited Activity
- 7. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION ï»żan Alent plc Company Jeita Maximum Warpage Standards
- 8. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION ï»żan Alent plc Company Measuring BGA Warpage Schematic of Shadow MoirĂ© Method
- 9. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION ï»żan Alent plc Company Shadow MoirĂ© Test Unit
- 10. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION ï»żan Alent plc Company MoirĂ© Computer Generated Image
- 11. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION ï»żan Alent plc Company How Can Solder Paste be Engineered to Reduce HIP? I
- 12. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION ï»żan Alent plc Company Alpha Response Solder Paste that⊠ïproduces higher and more consistent volume deposition ïhas a greater resistance to longer soak profiles ïhas faster wetting speed âą Gage R&R testing for determining in-house Head on Pillow defects to confirm solder paste effectiveness
- 13. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION ï»żan 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. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION ï»żan Alent plc Company Preventing Defect with Paste Print Height Probable Defect Defect Prevented 70” Deposit 100” Deposit
- 15. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION ï»żan Alent plc Company Wetting Force âą Test Method â Malcom Wetting Balance Test âą Equipment â Malcom SWB-2 âą Test Procedure â See Malcom SWB-2 Operating Manual
- 16. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION ï»żan 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. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION ï»żan Alent plc Company Head in Pillow Test Method
- 18. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION ï»żan 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. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION ï»żan Alent plc Company Manage Reflow and Warpage Time, Temperature, Z-Axis Location
- 20. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION ï»żan Alent plc Company HIP Test Equipment âą Test Vehicle (TV) âą BGA338 Dummy component âą BGA rework station âą Fabricated TV holder and fixture for holding the dummy BGA with vacuum. âą Thermocouple data acquisition âą Solenoid Valve
- 21. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION ï»żan Alent plc Company HIP Experimental Set-Up
- 22. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION ï»żan 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. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION ï»żan Alent plc Company Reflow Profile Indicator
- 24. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION ï»żan Alent plc Company Drop Component at Precise Time During Reflow
- 25. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION ï»żan Alent plc Company Experimental Results âą Test Highly Activated Paste vs. Very Low Activity Paste and Measure HIP DPMO.
- 26. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION ï»żan 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. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION ï»żan Alent plc Company Less Activated Paste After prying BGA from TV Obvious HIP joint in the center of the BGA block!
- 28. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION ï»żan Alent plc Company Initial results suggests that flux chemistry does affect HIP More Active Paste Less Active Paste
- 29. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION ï»żan 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. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION ï»żan Alent plc Company Summary ïŒ Component Size/Warpage Can Affect HIP Defect Rate ïŒ Key attributes for Solder Paste to reduce HIP DPMOâs ïTaller, More Consistent Paste Deposits ïFaster, Stronger Wetting Force ïEnhanced paste flux Activity and Activity Duration ïHigh Gage R&R HIP Test to Confirm Paste Properties
- 31. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION ï»żan Alent plc Company For more information click the link below: Alpha Products
Hinweis der Redaktion
- The goal of this discussion is to look at the effects of alloy, reflow peak temperature and flux chemistry and itâs affect on voiding
- Baseline facts: Reflow profile is known to have a affect on voiding Now we have a better understanding of why More and more packages are now being made with low Ag alloy spheres SAC305 is still the predominant alloy in paste Lower silver alloys exhibit better drop shock resistance vs. higher silver alloys This study is looking at voiding as a function of alloy composition and what affect peak temperature can have on the chemistry
- Baseline facts: Reflow profile is known to have a affect on voiding Now we have a better understanding of why More and more packages are now being made with low Ag alloy spheres SAC305 is still the predominant alloy in paste Lower silver alloys exhibit better drop shock resistance vs. higher silver alloys This study is looking at voiding as a function of alloy composition and what affect peak temperature can have on the chemistry
- Lets start off with looking at the affect the profile can have on voiding by focusing in on peak temperature
- We know from experience thatâŠ. With the same profile and different solder paste materials, IE different flux formulations with the same alloy show different voiding performance Also With the same flux and alloy formulation we can see variations in voiding based on profile Typically lower peak temperatures show better yields with regards to voiding when compared to higher peak temperature profiles
- This is the key. Looking at a very common activator used in many of the Alpha OM series pastes, you can see that at 241.7C there is a spike where activator reacts with the copper and creates an exothermic reaction which creates a vapor which may become entrapped in the alloy causing voiding Green line = the activator Blue line = weight of available flux at different temperatures still available Red Line = slope of the green line Thus keeping the peak profile under this exothermic reaction temperature will avoid any voids that would be created due to it. CVP-380
- Here we see that using the same alloy and a paste using activator #1 and one using activator #2 with all other conditions being the same, you can see that the material with activator #2 had fewer voids when the reflow peak temperature is held at 240C This shows that given the same process conditions and boards, that this exothermic phenomenon does have an influence on the voiding.
- Here we are using the same flux and alloy with only changing the peak temperature from 230C to 240C and the voids with the profile with the 230C peak profile had fewer voids and was Class III vs. the higher peak temperature of 240C created Class II voids
- In this example we see that a straight ramp at 229C vs. a soak profile at 245C vs. a straight ramp at 240C The results are that the profile with the straight ramp at the lower peak temperature had the best overall results. Longer soak can reduce voiding, but this shows that peak temperature has a bigger effect on voiding than soak versus straight ramp profiles.
- Now lets look at the affect of mixing alloys between the sphere and the paste and see what affect this has???
- BGA spheres are usually attached to packages using flux only. BGA/CSP packages are attached to PCBâ using solder paste.
- This represents the design of experiment used. Three different paste alloys were used to solder 3 different sphere alloys. Two reflow profiles were used for each of the 9 alloy combinations?
- The test vehicle is a 256 IO BGA PUT Procedure Specifies board, component and x-ray machine
- Each test vehicle contains 2 BGA-256
- Here is the low soak profile used
- Here is the high soak profile used
- SACX Paste Red Solid Shot soak SACX Sphere Blue SolidShort soak SAC105 Sphere Green SolidShort soak SAC305 Sphere Red Dotted Long soak SACX Sphere Blue DottedLong soak SAC105 Sphere Green Dotted Long soak SAC305 Sphere Notice how the Red or SACX sphere with the SACX paste in both the long and short profile had the best overall results That the number of defects is also lower compared to the other alloys The Green or SAC305 showed the highest instance of voiding and that the low soak profile did worse then the high soak profile We believe that this is likely due to the largest difference in liquidus is the SACX 0307 and SAC 305
- SAC105 paste Red Solid Shot soak SACX Sphere Blue SolidShort soak SAC105 Sphere Green SolidShort soak SAC305 Sphere Red Dotted Long soak SACX Sphere Blue DottedLong soak SAC105 Sphere Green Dotted Long soak SAC305 Sphere Again here we see that the SAC 105 and SACX paste which are closer in alloy composition to the SAC 105 paste then with the SAC 305 sphere. However we also see a shift to the left or a higher number of larger voids compared to the SACX
- SAC 305 paste Red Solid Shot soak SACX Sphere Blue SolidShort soak SAC105 Sphere Green SolidShort soak SAC305 Sphere Red Dotted Long soak SACX Sphere Blue DottedLong soak SAC105 Sphere Green Dotted Long soak SAC305 Sphere Using the SAC305 paste, the number of voids comes together amongst the three alloys however the size overall is a little bigger. Also that the SACX sphere with the SAC305 paste did worse vs. the other combinations, as expected
- So looking at scoring this, the best results are to the left side of the grid. IE if the majority of the voids are Scoring: <3% voids10 3-5% voids 5 5-7% voids 1 >7% voids 0 Red Solid Shot soak SACX Sphere Blue SolidShort soak SAC105 Sphere Green SolidShort soak SAC305 Sphere Red Dotted Long soak SACX Sphere Blue DottedLong soak SAC105 Sphere Green Dotted Long soak SAC305 Sphere So with the SAC105 paste, the SAC 305 spheres showed the worst voiding
- That the closer the alloys match between the sphere and the paste, the fewer large voids tend to be produced That peak reflow temperature can have an affect on voiding. We believe this is dependant on the temperature at which material in the flux has an exothermic reaction with copper. That solder paste formulation can have a strong influence on voiding.