Philips Leadfree solder ball adhesion
improvement in BGA-packages

Philips Applied Technologies
March 2006
Jo Caers, Zhao ...
Problem Description



       • Missing SAC405 solder balls are observed on some BGA
         packages after shipment to t...
Cross sections of products showing missing
       SAC405 solder balls on NiAu pad



                              Ni
    ...
Root Cause Description of Missing Ball Issue

     • Present used Pb-free solder (SAC405) is very sensitive for
       imp...
Solution to the problem
     1. Controlling growth and structure of the IMC
        layer
     2. Reducing the strength, w...
New Solderball
     • Composition of
     • SAC101                                                           SAC405
      ...
Effects of Ag and Cu concentration
                                            Effect of Cu in SAC alloys on brittle failu...
Effect of Ag on liquidus temperature




Jo Caers c.s. – Elfnet workshop, March 2006   8
Evaluation methods for new solder ball

             –       Component level high speed shear testing : BGA 23 x 23
      ...
High Speed Shear testing
                       Alloy                  Composition       Supplier
                       S...
High speed shear test
      • Test equipment : Instron micro tester
      • Test location  : Instron Singapore

      •   ...
High speed shear test-Failure modes
      Three typical failure modes were found:

             • Fracture in IMC
        ...
High speed shear test - Failure modes on Supplier A finish

         Failure m odes of SAC 0535 on                 Failure...
High speed shear test - Failure modes on Supplier B finish

          Failure m odes of SAC 0535 on            Failure m o...
Summary of high speed shear test
       • 6 solder alloys selected
       • Evaluation method selected and made available
...
BLR tests: JEDEC Drop testing
       • Test board                           : standard JEDEC test board
                  ...
BLR tests: JEDEC Drop testing
      • Test packages:

                    Component                 UBM finish   Solder ba...
BLR tests: JEDEC Drop testing. Method.

       • Board assembly
              – SAC 305 solder paste
              – Stand...
BLR tests: JEDEC Drop testing. Method.
       • Drop test set-up




                                              To even...
BLR tests: JEDEC Drop testing. Method.
      • Test conditions
         – Acceleration: 1500g, 0.5ms half-sine pulse
     ...
BLR tests: JEDEC Drop testing results.
                                                             SAC 101 versus SAC405
...
BLR tests: JEDEC Drop testing results.
                                              PbSn versus SAC 101
                 ...
Failure analysis – NiAu-SAC 405


                                    3rd       2nd 1st
             (a) U5 right corner 2...
Failure analysis (1) – NiAu-SAC 101




        (a) U3 up corner, fail @ 16 drops.      (b) Details of (a). Fracture throu...
Failure analysis – summary
     • SAC 101 solder ball, supplier A and B
             – From the cross sectioning analysis,...
Reliability Test Results of new solder ball
             – HTSL
                    •      No missing balls after 1500 hrs...
BLR TMCL data
     • BGA256, NiAu finish (SAC101 vs SnPb)
             – Test condition             : -55     125 °C (20/2...
BLR TMCL data
       • Conclusion:
              – BLR TMCL behavior of SAC 101 is much better than that of
              ...
Summary
    • Pro’s of SAC101
           – Excellent solution to missing ball issue, for all substrate suppliers!!
       ...
Acknowledgements


       • Dr. J. de Vries (Apptech E’hven)
       • Wong Ee Hua, Ranjan Ranjoo (IME, Sgp)
       • Dr. T...
Philips ELFNET 2006 SAC101
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Philips ELFNET 2006 SAC101

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This presentation was given to a meeting of the ELFNET project (European Lead-Free Soldering Network) in Zurich in March 2006.
http://tinyurl.com/ybcumh3

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Philips ELFNET 2006 SAC101

  1. 1. Philips Leadfree solder ball adhesion improvement in BGA-packages Philips Applied Technologies March 2006 Jo Caers, Zhao Xiujuan, Jan Kloosterman
  2. 2. Problem Description • Missing SAC405 solder balls are observed on some BGA packages after shipment to the customer • Drop test performance for on board / mobile applications of Pb-free (L)FBGA packages shows decreased performance compared to Pb-containing packages Jo Caers c.s. – Elfnet workshop, March 2006 2
  3. 3. Cross sections of products showing missing SAC405 solder balls on NiAu pad Ni Ni Ni Ni SEM/BSE images of PSK sample (missing bump), showing almost no intermetallic residues Jo Caers c.s. – Elfnet workshop, March 2006 3
  4. 4. Root Cause Description of Missing Ball Issue • Present used Pb-free solder (SAC405) is very sensitive for impact loading because of: – Very high strength of the bulk solder – Formation of brittle intermetallic layer between solder ball and package substrate. – Formation of large Ag3Sn needles (CuNi)6Sn5 (CuNi)3Sn4 Ni Image of 0hr SAC-ball overview Jo Caers c.s. – Elfnet workshop, March 2006 4
  5. 5. Solution to the problem 1. Controlling growth and structure of the IMC layer 2. Reducing the strength, while improving the ductility of the Pb-free solder used Above items resulted in proposal to modify the composition of the SAC solder ball (SAC101). Jo Caers c.s. – Elfnet workshop, March 2006 5
  6. 6. New Solderball • Composition of • SAC101 SAC405 – Ag : 1% 4% – Cu : 0.1% 0.5% – Ni : dopant no – X : dopant no – Sn : balance balance – Remarks: • Ag : lowering the melting point; improving the wet-ability; increasing the stiffness of the bulk solder • Cu : lowering the melting point; suppressing the diffusion of Ni into the solder; reduces the elongation. However, lowering the Cu-content results in improved drop test performance. • Ni : suppressing mutual diffusion between Sn of the solder bulk and Cu or Ni of the land; reduces the elongation. Improves TMCL behavior, and IMC composition • X : restores wet-ability decrease due to lowering the Ag-content, restores elongation Jo Caers c.s. – Elfnet workshop, March 2006 6
  7. 7. Effects of Ag and Cu concentration Effect of Cu in SAC alloys on brittle failure 60 50 Brittle failures (%) 40 30 20 10 0 0 0.2 0.4 0.6 0.8 1 1.2 Cu level (%) Effect of Cu-content (Supplier Presentation) Effect of Ag-content (Supplier presentation) Jo Caers c.s. – Elfnet workshop, March 2006 7
  8. 8. Effect of Ag on liquidus temperature Jo Caers c.s. – Elfnet workshop, March 2006 8
  9. 9. Evaluation methods for new solder ball – Component level high speed shear testing : BGA 23 x 23 – Board level JEDEC drop test : LFBGA240 – Board level TMCL : BGA256, TFBGA228 – HTSL : 1500 hours @150 °C – Wetting test of solder balls Jo Caers c.s. – Elfnet workshop, March 2006 9
  10. 10. High Speed Shear testing Alloy Composition Supplier SnPb (ref1) eutectic A SAC405 (ref2) Sn-4Ag-0.5Cu A SAC305 + NiGe Sn-3Ag-0.5Cu- B xNiGe Castin 258 Sn-2.5Ag-0.8Cu- C 0.5Sb (SAC101 + doping) Sn-1Ag-0.1Cu- A 0.02Ni-x SACX Sn-0.3Ag-0.7Cu- D 0.1Bi – X Jo Caers c.s. – Elfnet workshop, March 2006 10
  11. 11. High speed shear test • Test equipment : Instron micro tester • Test location : Instron Singapore • Instruction and test set up by IME-Instron-Apptech Singapore • Test speed : 0.45m/s • Shear height : 50μm • Ball diameter : 600μm High speed ball shear tester Jo Caers c.s. – Elfnet workshop, March 2006 11
  12. 12. High speed shear test-Failure modes Three typical failure modes were found: • Fracture in IMC • Fracture in Bulk solder • Pad peel Fracture in IMC Fracture in Bulk solder Fracture of Pad peel Jo Caers c.s. – Elfnet workshop, March 2006 12
  13. 13. High speed shear test - Failure modes on Supplier A finish Failure m odes of SAC 0535 on Failure m odes of SAC101 on supplier Failure m odes of SAC305 + NiGe on supplier A substrate A substrate supplier A substrate 0% 2% 3% Pad peel 38% Pad peel IMC Pad peel 48% IMC 50% Bulk IMC Bulk 62% Bulk 0% 97% Failure m odes of Castin 258 on Failure m odes of SAC 405 on supplier Failure m odes of SnPb on supplier supplier A substrate A substrate A substrate 0% 9% 0% 16% 0% 38% Pad peel Pad peel Pad peel IMC IMC IMC Bulk 62% Bulk Bulk 84% 91% • Bulk failure happens in SnPb and in SAC101 solder joints • The SAC0535 (SAC-X) alloy, SAC305 and SAC405 mainly fail in the intermetallic compounds • In general more intermetallic failure than for Supplier B finish Jo Caers c.s. – Elfnet workshop, March 2006 13
  14. 14. High speed shear test - Failure modes on Supplier B finish Failure m odes of SAC 0535 on Failure m odes of SAC101 on Supplier Failure m odes of SAC305 + NiGe on Supplier B substrate B substrate Supplier B substrate 0% 15% 29% Pad peel Pad peel Pad peel IMC IMC IMC 71% 85% 100% Failure m odes of Castin 258 on Failure m odes of SAC 405 on Supplier Failure m odes of SnPb on Supplier Supplier B substrate B substrate B substrate 14% 17% 0% Pad peel 44% Pad peel Pad peel IMC IMC IMC Bulk 56% 86% 83% • Bulk failure only happen in SnPb solder joints • SAC101 only failed with Pad peel • Assume the IMC strength > the strength in Pad interface if failure in pad peel, SAC101 is better than other solder alloys to resist the high speed impact. Jo Caers c.s. – Elfnet workshop, March 2006 14
  15. 15. Summary of high speed shear test • 6 solder alloys selected • Evaluation method selected and made available • Results from high speed shear test: – SAC101 closest to SnPb with respect to failure mode; no intermetallic failure observed for this alloy – Except from SAC101, SAC-X shows most pad peel failures and least intermetallic failures of the Pb-free alloys – No physical explanation for the differences in failure mode yet: • effect from intrinsic strength of the intermetallic layer? • effect of inhomogeneities causing a tail in the strength distribution at the lower strength values? • effect of ductility of the bulk solder? – Resolution of max. force, total deflection and total energy still being evaluated • Results from wetting: – From on-line monitoring: uniform proceeding of the wetting for all alloys – From the Pb-free alloys, SAC101 performs best, based on wetted area Jo Caers c.s. – Elfnet workshop, March 2006 15
  16. 16. BLR tests: JEDEC Drop testing • Test board : standard JEDEC test board according to JESD22-B111 Jo Caers c.s. – Elfnet workshop, March 2006 16
  17. 17. BLR tests: JEDEC Drop testing • Test packages: Component UBM finish Solder ball Supplier LFBGA240 NiAu SAC 101 (0.3mm) A LFBGA240 NiAu SAC 101 (0.3mm) B LFBGA240 OSP SAC101 (0.3mm) A LFBGA240 NiAu SAC405 (0.3 mm) A LFBGA240 NiAu PbSn A Jo Caers c.s. – Elfnet workshop, March 2006 17
  18. 18. BLR tests: JEDEC Drop testing. Method. • Board assembly – SAC 305 solder paste – Standard lead-free reflow profile with peak reflow temperature 245°C Jo Caers c.s. – Elfnet workshop, March 2006 18
  19. 19. BLR tests: JEDEC Drop testing. Method. • Drop test set-up To event detector (AnaTech: Model 128-256 STD) Jo Caers c.s. – Elfnet workshop, March 2006 19
  20. 20. BLR tests: JEDEC Drop testing. Method. • Test conditions – Acceleration: 1500g, 0.5ms half-sine pulse – Test duration: 30 drops – Failure criteria: daisy chain resistance larger than 500Ω and the first event of intermittent discontinuity followed by 3 additional such events during 5 subsequent drops • Sample size: 6 boards per type of package 1800 1600 1400 1200 1000 exp a (g) 800 calc 600 400 200 0 -200 398.0 398.5 399.0 399.5 400.0 400.5 401.0 t (ms) Acceleration measured from base plate Jo Caers c.s. – Elfnet workshop, March 2006 20
  21. 21. BLR tests: JEDEC Drop testing results. SAC 101 versus SAC405 Probability 99. 90. Supplier B-NiAu SAC101 Supplier A-NiAu SAC101 50. Cumulative failures (%) Supplier A-OSP SAC101 Supplier A-NiAu SAC405 10. Supplier A-NiAu SAC405 5. 1. 1. 10. 100. N-drops • SAC 101 clearly shows improved drop test performance compared to SAC405. • Failure distribution of supplier B is more narrow than that of supplier A • Following table shows the characteristic lifetime at 63.2% failure with 95% 2- sided confidence level, for SAC 101. A-NiAu B-NiAu Upper Limit 84 68 Drops 56 45 Lower Limit 37 30 Jo Caers c.s. – Elfnet workshop, March 2006 21
  22. 22. BLR tests: JEDEC Drop testing results. PbSn versus SAC 101 PbSn SAC 101 ReliaSoft's Weibull++ 6.0 - www.Weibull.com Probability 99. Weibull 90. NiAu W2 RRX - SRM MED F=9 / S=36 50. CB[FM]@95.00% Cumulative failures (%) 2-Sided-B [T1] 10. 5. Philips Philips CFT 2005-11-02 13:17 1. 10. 1. 100. N-drops β=2.9551, η=51.6013, ρ=0.9898 • Drop test performance of SAC 101 on NiAu is comparable to that of PbSn on NiAu! Jo Caers c.s. – Elfnet workshop, March 2006 22
  23. 23. Failure analysis – NiAu-SAC 405 3rd 2nd 1st (a) U5 right corner 2nd bump, fail @ 7 (b) U5, right corner 1st bump. Crack drops. Crack through Ni/Ni3Sn interface at in PCB. the component side. (c) U13, down corner. Complete (d) Details of (c). fracture through Ni/Ni3Sn interface at the component side. Jo Caers c.s. – Elfnet workshop, March 2006 23
  24. 24. Failure analysis (1) – NiAu-SAC 101 (a) U3 up corner, fail @ 16 drops. (b) Details of (a). Fracture through first Cu6Sn5 IMC layer then metal line at the substrate side. (c) U3 down corner, fail @ 16 drops. (d) Details of (c). Jo Caers c.s. – Elfnet workshop, March 2006 24
  25. 25. Failure analysis – summary • SAC 101 solder ball, supplier A and B – From the cross sectioning analysis, it becomes clear that all failures are caused by the Cu track fracture in the daisy chain on PCB – Drop test performance of SAC 101 /NiAu is comparable to that of PbSn / NiAu. Drop test performance of SAC 101/OSP is a factor 2 better than PbSn / NiAu • SAC405 solder ball, supplier A – Complete fracture through Ni/Ni3Sn interface at the component side is observed in many cases. Fracture of the Cu traces in the PCB, and of the PCB does occur, but is not the main failure mode. Jo Caers c.s. – Elfnet workshop, March 2006 25
  26. 26. Reliability Test Results of new solder ball – HTSL • No missing balls after 1500 hrs testing • Single uniform IMC layer with decreased thickness compared to SAC 405 (see picture) Jo Caers c.s. – Elfnet workshop, March 2006 26
  27. 27. BLR TMCL data • BGA256, NiAu finish (SAC101 vs SnPb) – Test condition : -55 125 °C (20/20 minutes) – Preliminary result : 0 failures after 3000 cycles with SAC 101 – First failures : 2 after 3016 and 3053 cycles resp. – SAC101 1 % failures : ~ 3000 cycles – PbSn 1 % failures : 2464 cycles – PbSn first failures : 668, 1638, 2051, 2514 etc. On-line monitoring with event detector • TFBGA228 (SAC101 vs SAC405) – Test condition : -40 125 °C (30/30 minutes) – Preliminary result : 0 failures after 820 cycles with SAC 101 – SAC405 1 % failures : 317 cycles – SAC405 50% failures : 594 cycles Off-line evaluation Jo Caers c.s. – Elfnet workshop, March 2006 27
  28. 28. BLR TMCL data • Conclusion: – BLR TMCL behavior of SAC 101 is much better than that of SAC405 – BLR TMCL behavior of SAC 101 is comparable or better than PbSn Jo Caers c.s. – Elfnet workshop, March 2006 28
  29. 29. Summary • Pro’s of SAC101 – Excellent solution to missing ball issue, for all substrate suppliers!! – Excellent BLR drop test performance, for all suppliers!! So, excellent for mobile applications. – Excellent BLR TMCL and wetting behavior • Con’s of SAC101 – Liquidus* is higher compared to SAC405 (228 v. 220°C); however, reflowing the SAC101 30 to 60 seconds above liquidus, results in a stable and reliable joint. – Material properties? • Philips is recommending the introduction of the SAC 101 because of it’s excellent reliability, both wrt. JEDEC drop testing and BLR TMCL testing. • High speed shear tester excellent evaluation tool Jo Caers c.s. – Elfnet workshop, March 2006 29
  30. 30. Acknowledgements • Dr. J. de Vries (Apptech E’hven) • Wong Ee Hua, Ranjan Ranjoo (IME, Sgp) • Dr. Tsai (Instron, Sgp) Jo Caers c.s. – Elfnet workshop, March 2006 30

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