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The Effect of Mixing BGA and Solder Paste Alloys on the Formation of Voids

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This presentation examines the drivers for mixed alloy systems, typical voiding requirements, common ways of reducing voids and the effects of mixed alloys on voiding.

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The Effect of Mixing BGA and Solder Paste Alloys on the Formation of Voids

  1. 1. an Alent plc Company The effect of mixing BGA and solder paste alloys on the formation of voids September 2010 Alan Plant Regional Applications Manager
  2. 2. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Introduction • Reflow Profile is a known method of managing voiding in BGA’s. – Alpha has recently uncovered the mechanism behind this and is actively formulating lower voiding pastes. • Since 2006 there has been a trend for BGA and CSP package makers to supply components with lower silver alloys • SAC 305 is still a primary lead free solder paste alloy – Along with SAC 405 and SAC 387 • Low silver SAC alloys are known to have better drop shock resistance • This study also looks at voiding as a function of alloy composition
  3. 3. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Introduction • Reflow Profile is a known method of managing voiding in BGA’s. – Alpha has recently uncovered the mechanism behind this and is actively formulating lower voiding pastes. • This study also looks at voiding as a function of alloy composition • Total volume of the BGA/CSP Sphere and Paste Deposit has a significant effect on Voiding • Stencil Aperture design also can reduce voiding
  4. 4. an Alent plc Company BGA Voiding – Peak Temperature Effect
  5. 5. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Introduction It is empirically observed that: – For the same reflow profile • Different flux formulations have different voiding performance – For the same flux formulation • Different profiles will yield different voiding performance – A lower peak temperature profile will yield better voiding results than a higher peak temperature profile
  6. 6. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Differential Scanning Calorimetry Differential scanning calorimetry was used to assess the relative reaction rates of different activators with copper. Note that there is a sharp exothermal reaction between activator 1 and copper at 241.7º C. Blue = Flux Weight% Green = Sample Temp vs. Control Red = Sample Temp Exothermal reaction = Creates vapor which contribute to voiding
  7. 7. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Voiding Performance Void Size Distribution BGA256 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0-4% 4-9% 9-12% 12-16% 16-20% >20% % of Joint area %ofJoints OM350 (Activator 2) HS 175C / 60 sec soak 240C peak CVP-380 (Activator 1) HS 175C / 60 sec soak 240C peak The expected trend is observed, as with a peak reflow temperature of 240ºC, the paste containing activator 2 has better voiding performance than the paste containing activator 1
  8. 8. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Voiding Performance Also, as predicted, voiding performance improves measurably for the same paste formulation reflowed with a lower peak temperature. Void Size Distribution BGA256 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0-4% 4-9% 9-12% 12-16% 16-20% >20% % of Joint area %ofJoints CVP-380 240C peak temperature CVP-380 230C peak temperature Activator #1 Same Flux & alloy Red = Peak 240ºC Green = Peak 230ºC Voiding Red = Class II Green = Class III
  9. 9. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Another Example Void Size Distribution BGA256 90% 0.00% 10.00% 20.00% 30.00% 40.00% 50.00% 60.00% 70.00% 80.00% 90.00% 100.00% ZERO 0-4% 4-8% 8-12% 12-16% 16-20% >20% %of Joint area %ofJoints Cerf St ramp 229Cp Cerf 175-60 soak 245Cp Cerf St ramp 1.5Cs 240Cp Activator 2 Ramp vs. Soak profile NOTE Peak temperature has a greater impact vs. soak profiles
  10. 10. an Alent plc Company BGA Voiding – Alloy Composition Effect
  11. 11. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company What effect do the package ball alloy and the solder paste alloy have on solder joint voids?
  12. 12. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company DOE Test Matrix Reflow Profile Short Soak Long Soak Short Soak Long Soak Short Soak Long Soak SACX 0307 SAC 105 SAC 305 Sphere Alloy PasteAlloy SACX 0307 SAC 105 SAC 305 Voiding Measured for all 18 Combinations Paste Alloy / Profile / Sphere alloy
  13. 13. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Voiding Test Procedure • Test Method – ALPHA PUT Procedure JC-PUT-0016 • Equipment- Phoenix Micromex-HLN • Measure and report voiding area on 256 IO BGA Package
  14. 14. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Cookson Electronics Test Vehicle 2 x BGA-256
  15. 15. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Low Soak Profile 175C/60S Soak 240C Peak 60S TAL
  16. 16. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company High Soak Profile 160-180ºC/120S Soak 250ºC Peak 60S TAL
  17. 17. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Results
  18. 18. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company SACX® 0307 Paste Solder paste SACX-BGA256-20mil 0 50 100 150 200 250 300 0-1 1-3 3-5 5-7 >7 Void size, % Numberofvoids SACX SAC105 SAC305 SACX SAC105 SAC305 Solid lines •175C @ 60s Soak •245C Peak •60s TAL Dotted lines •160-180C @ 120s Soak •250C Peak •40s to 76s TAL
  19. 19. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company SAC 105 Paste Solder paste SAC105-BGA256-20mil 0 50 100 150 200 250 300 0-1 1-3 3-5 5-7 >7 Void size, % Numberofvoids SACX SAC105 SAC305 SACX SAC105 SAC305 Solid lines •175C @ 60s Soak •245C Peak •60s TAL Dotted lines •160-180C @ 120s Soak •250C Peak •40s to 76s TAL
  20. 20. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company SAC 305 Paste Solder Paste SAC305-BGA256-20mil 0 50 100 150 200 250 300 0-1 1-3 3-5 5-7 >7 Void size, % Numberofvoids SACX SAC105 SAC305 SACX SAC105 SAC305 Solid lines •175C @ 60s Soak •245C Peak •60s TAL Dotted lines •160-180C @ 120s Soak •250C Peak •40s to 76s TAL
  21. 21. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Data Analysis-Scoring Results Solder paste SAC105-BGA256-20mil 0 50 100 150 200 250 300 0-1 1-3 3-5 5-7 >7 Void size, % Numberofvoids SACX SAC105 SAC305 SACX SAC105 SAC305 10 5 1 0
  22. 22. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Confirmation Run SACX 0807 Void Size Distribution BGA256 0.00% 10.00% 20.00% 30.00% 40.00% 50.00% 60.00% 70.00% 80.00% 90.00% 100.00% ZERO 0-4% 4-8% 8-12% 12-16% 16-20% >20% %of Joint area %ofJoints CVP-360 CERF ST.RAMP 0.7c_s 245cp 60 TAL CVP-360 CERF ST.RAMP 1.5c_s 245cp 60 TAL SAC 305 Spheres, SACX 0807 Paste- Class II Voiding
  23. 23. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company SACX 0807 Example Void Size Distribution - SACX0807 CVP-360 Paste, SAC105 BGA 256 (20 mil Sphere) 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% ZERO 0-4% 4-8% 8-12% 12-16% 16-20% >20% %of Joint area %ofJoints Ramp: 0.7 C/sec, 240 Peak, TAL - 85 s Ramp: 1.5 C/sec, 245 Peak, TAL - 45 s SAC 105 Spheres, SACX 0807 Paste- Class III+
  24. 24. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Print Deposit Effect on Voiding • Reducing aperture size reduces voiding • Smaller paste/sphere volumes = reduced voiding
  25. 25. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Reducing Aperture Size Reduces Voiding No Aperture Reduction Void Size Distribution BGA256 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% ZERO 0-4% 4-8% 8-12% 12-16% 16-20% >20% %of Joint area %ofJoints 438_167B19 CERF HS 160_60 SOAK 240CP 438_167B19 CERF HS 175_60 240CP 438_167B19 CERF ST.RAMP 1.5c_sec 245CP 60 TAL
  26. 26. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Reducing Aperture Size Reduces Voiding Void Size Distribution BGA256 90% 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% ZERO 0-4% 4-8% 8-12% 12-16% 16-20% >20% %of Joint area %ofJoints 438_167B19 CERF HS 160_60 SOAK 240CP 438_167B19 CERF HS 175_60 240CP 438_167B19 CERF ST.RAMP 1.5c_sec 245CP 60 TAL 10% Aperture Reduction
  27. 27. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Reducing Paste/Sphere Volumes Reduces VoidingVoid % Distribution For BGA256 20Mil 0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 90.00 100.00 Zero <0-4 4-9 9-12 12-16 16-20 >20 % of Void Area %ofVoidDistribution Void % Distribution For BGA256 15Mil 0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 90.00 100.00 Zero <0-4 4-9 9-12 12-16 16-20 >20 % of Void Area %ofVoidDistribution 20 Mil Circles (0.5 mm) 15 Mil Circles (0.4 mm) Same Solder Paste and Reflow Profile
  28. 28. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Reducing Paste/Sphere Volumes Reduces Voiding Void % Distribution For BGA256 15Mil 0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 90.00 100.00 Zero <0-4 4-9 9-12 12-16 16-20 >20 % of Void Area %ofVoidDistribution 15 Mil Circles (0.4 mm) Same Solder Paste and Reflow Profile Void % Distribution For BGA225 12Mil 0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 90.00 100.00 Zero <0-4 4-9 9-12 12-16 16-20 >20 % of Void Area %ofVoidDistribution 12 Mil Circles (0.3 mm)
  29. 29. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company Overall Conclusions • Like alloys tend to produce fewer large voids than mixed alloy combinations – Slight difference in melting point is one possible cause. • Peak Reflow Temperature – Has a significant effect on voiding due to the interaction of the flux with the Cu at key temperatures. • Solder Paste Formulation – Has a significant effect on voiding due to the type of chemistries used and where they become reactive with the Cu. • Solder Joint Volume – Reduced volume of paste and/or sphere reduces voiding
  30. 30. HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company For more information please visit: www.Alpha.Alent.com

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