A compliant and creep resistant sac al(ni) alloy - presentation


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A compliant and creep resistant sac al(ni) alloy - presentation

  1. 1. A Compliant and CreepResistant SAC-Al(Ni) Alloy Dr. Benlih Huang, Dr. Hong-Sik Hwang, and Dr. Ning-Cheng Lee Indium Corporation of America 1
  2. 2. Background• SAC solder with high Ag content needed for thermal fatigue performance & for narrow pasty range. IMC particles of Ag-Sn and Cu-Sn responsible for the fatigue resistance.• However, for high Ag SAC alloys, a greater ductility is also desired for non-fragility.• Addition of element which can reduce IMC particles may improve the ductility. 2
  3. 3. Approaches• Al reacts with both Ag and Cu, which promises a reduction in the quantity of Ag3Sn and Cu6Sn5, is a very capable candidate.• Adding Ni is reported to be beneficial, due to its effect in suppressing the growth of IMC scallop size and thickness on Cu. 3
  4. 4. Tests• Tensile test – The diameter and length of the cylinder central testing region is 0.125 inch and 2 inch, respectively. – Crosshead speed - 0.2 inch/min. – Yield strength, ultimate tensile strength, elongation at break, and modulus determined. – 5-15 specimen used for each alloy.• SEM & EDX for microstructure• DSC – 10°C/min heating & cooling, between -40 & 260 °C – 2nd heating run used for comparison• Creep test – Two specimen used for each combination of alloy and stress condition. 4
  5. 5. Effect of alloy composition on yield strength SAC(n)05-XY vs Yield Strength SA C YS Ni0.88 A l0.96 A l0.6Ni0.04 A l0.48Ni0.04 A l0.05Ni2 A l0.19 A l2Ni0.02 A l0.15Ni0.01 A l0.2Ni0.012 A l0.3Ni0.018 A l0.15Ni0.05 A l0.073Ni0.05 7000 y = -63.742x 2 + 1059.8x + 2774.9 R2 = 0.9328 6000 5000 Yield strength increases Yield Strength (psi) with increasing Ag content 4000 3000 Addition of Al and Ni can 2000 result in a significantly At Ag > 2%, Al 0.1-0.6% most reduced yield strength 1000 effective in reducing YS High Ni also reduce YS 0 0 1 2 3 4 5 Ag % 5
  6. 6. Effect of Al addition on yield strength of SAC(n)05-XY Al % vs Yield Strength (for SAC(n)05-XY, where n = 3.8-4) 7000 6000 YS of SAC405 & SAC305Yield Strength (psi) 5000 4000 YS of SAC105 & 1505 3000 Note: 2000 All Ni ≤ 0.05%,- has no Ni At Ag 3.8-4.0%, Ni ≤ 0.05%, Al reduces Al dominant in effect on 1000 YS most effectively at 0.1-0.6%. YS (w & w/o Ni, trends comparable) 0 0 0.5 1 1.5 2 2.5 Al % 6
  7. 7. Effect of Ni addition on yield strength of SAC(n)05-XY Ni % vs Yield Strength ( for SAC(n)05-XY, where n = 3.8-4 ) 6000 Addition of Ni results in a slight decrease in yield strength.Yield Strength (psi) 4000 Note: All Al ≤ 0.05% The extent of yield Ni addition slightly reduces YS strength drop is about 2000 1/3 of Al addition (6000 →4000) 0 0 0.5 1 1.5 2 2.5 Ni % 7
  8. 8. Effect of alloy composition on tensile strength SAC(n)05-XY vs Tensile Strength SAC TS Ni0.88 Al0.96 Al0.6Ni0.04 Al0.48Ni0.04 Al0.05Ni2 Al0.19 Al2Ni0.02 Al0.15Ni0.01 Al0.2Ni0.012 Al0.3Ni0.018 Al0.15Ni0.05 Al0.073Ni0.05 10000 Tensile strength increases with increasing Ag content Tensile Strength (psi) 8000 The effect of Al and Ni 6000 addition not significant 4000 y = -45.527x2 + 988.47x + 4727.1 R2 = 0.8212 2000 Al & Ni not significant on TS 0 0 1 2 3 4 5 Ag % 8
  9. 9. Effect of alloy composition on elongation at break SAC(n)05-XY vs Elongation at Break SAC Elongation Ni0.88 Al0.96 Al0.6Ni0.04 Al0.48Ni0.04 Al0.05Ni2 Al0.19 Al2Ni0.02 Al0.15Ni0.01 Al0.2Ni0.012 Al0.3Ni0.018 Al0.15Ni0.05 Al0.073Ni0.05 Linear (SAC Elongation) 25 Elongation at break isElongation at Break (%) 20 insensitive to Ag content 15 Adding Al or Ni does cause 10 a decrease in elongation at break 5 Al & Ni reduce elongation at break 0 0 1 2 3 4 5 Ag % 9
  10. 10. Effect of alloy composition on modulus SAC(n)05-XY vs Modulus SA C M o dulus Ni0.88 A l0.96 A l0.6Ni0.04 A l0.48Ni0.04 A l0.05Ni2 A l0.19 A l2Ni0.02 A l0.15Ni0.01 A l0.2Ni0.012 A l0.3Ni0.018 A l0.15Ni0.05 A l0.073Ni0.05 3500 3000 Modulus increases with 2500 increasing Ag content Addition of Al and Ni results Modulus (ksi) 2000 in a slight decrease in 1500 y = -17.945x 2 + 291.13x + 1760.5 modulus R2 = 0.8759 1000 500 Al slightly reduce modulus 0 0 1 2 3 4 5 Ag % 10
  11. 11. SEM micrograph ofSn94.43Ag3.97Cu0.64Al0.96 (2000X) IMC particles are primarily IMC of AlAg and AlCu partially mixed with Sn 11
  12. 12. EDX graph on gray (top) anddark (bottom) IMC particles ofSn94.43Ag3.97Cu0.64Al0.96The weight ratio of Ag to Al isabout 6:1, and the weight ratioof Cu to Al is about 3:1 here.Therefore, at Al content of0.96%, most of the Ag and Cu inthis alloySn94.43Ag3.97Cu0.64Al0.96will be drained from the soldermatrix and be associated withAl. 12
  13. 13. SEM micrograph of Sn94.49Ag3.99Cu0.64Ni0.88 200X 2000XThe gray needle was identified as Many bright Ag3Sn IMC particles in the(Ni,Cu)3Sn4 form of micron-sized round particles or short rods 13
  14. 14. Sn94.49Ag3.99Cu0.64Ni0.88The weight ratio of Ni to Cu is about 2.3:1. WithNi concentration being 0.88%, the Cuentrapped in the (Ni,Cu)3Sn4 is estimated to beabout 0.4%. In other words, Cu will be highlydepleted by Ni-Cu-Sn IMC formation. As aresult, the SAC matrix composition here isexpected to be greatly skewed toward near-eutectic Sn-Ag structure. 14
  15. 15. SEM micrograph ofSn94.78Ag4.0Cu0.58Al0.6Ni0.04 1000X 5000X The bright particles are Ag3Sn IMC. The large gray particle is Al9.4-Ag90.6, indicating the extraordinary ability of Al to drain Ag from SAC matrix. 15
  16. 16. SEM micrograph ofSn94.78Ag4.0Cu0.58Al0.6Ni0.04 (5000X) The dark small particle is Al32.2-Cu57.1-Sn10.7 16
  17. 17. DSC thermographs (second run heating) of SAC387,SAC+Al (Sn94.43Ag3.97Cu0.64Al0.96), and SAC+Ni (Sn94.49Ag3.99Cu0.64Ni0.88) Ag and Cu in this SAC+Al alloy mostly drained from the solder matrix and be associated with Al. Thus, instead of forming near-ternary-eutectic SAC composition, it very likely forms near- SnAg eutectic and near-Sn-Cu eutectic structures, as suggested by the two peaks observed in DSC. Cu is virtually depleted from SAC+Ni due to the formation of (Ni,Cu)3Sn4. Consequently the copper-striped matrix becomes near-eutectic SnAg structure. 17
  18. 18. DSC thermographs (second run heating) of SAC405 and SAC405+Al(Ni) alloys, including Sn95.2Ag4Cu0.64Al0.19,Sn94.78Ag4.0Cu0.58Al0.6Ni0.04, and Sn94.43Ag3.97Cu0.64Al0.96 increase in Al content will drain more Ag and Cu from the SAC system. This in turn causes a shift of SAC405 from near ternary eutectic composition towards combination of eutectic SnAg and eutectic SnCu. 18
  19. 19. Liquidus temperature of SAC+Al(Ni) alloys as a function of Al content Liquidus vs Al % 228Liquidus Temp (deg C) 226 At Al content greater than 0.6%, 224 the liquidus temperature increases more rapidly with 222 continued increase in Al content 220 218 0 0.3 0.6 0.9 1.2 Al w t % 19
  20. 20. DSC thermographs (second run heating) of SAC105, SAC1505, andSAC405+Al+Ni alloys, including Sn95.3Ag3.92Cu0.62Al0.15Ni0.05 and Sn94.78Ag4.0Cu0.58Al0.6Ni0.04 Compared with SAC105 and SAC1505, the SAC405+Al+Ni alloys exhibit both a lower liquidus temperature and a narrower pasty range. 20
  21. 21. Effect of alloy on steady creep rate Steady Creep Rate vs Stress SA C 105 SA C1505 The yield strength of both SnA g3.92Cu0.62A l0.15Ni0.05 SnA g4.0Cu0.58A l0.6Ni0.04 SAC405+Al+Ni alloys is much lower SA C305 SA C405 than SAC405 & 305, and is similar to that of SAC105 and SAC1505 1.E-04 SAC305 However, both SAC405+Al+Ni alloys 1.E-05 exhibit a steady creep rate lower thanSteady Creep Rate (1/sec) SAC105 that of SAC105 and SAC1505, 1.E-06 comparable with SAC305, and are SAC+Al0.6Ni0.04 higher than SAC405. SAC1505 1.E-07 SAC405 Thus, new alloy exhibit SAC305 creep rate but SAC105 softness. 1.E-08 SAC+Al0.15Ni0.05 1.E-09 10 20 30 40 Stress (MPa) 21
  22. 22. Discussion• Softening attributed to – Large no. of small hard Ag3Sn converted into small no. of large soft non-stoichiometric Ag-Al IMC particles – Reduction in Cu6Sn5 particles due to formation of non-stoichiometric Al-Cu and large (Ni,Cu)3Sn4 IMC particles• Creep rate – Non-stoichiometric IMC particle or large particle, although less effective in increasing yield strength, are considered still harder than Sn, therefore are expected to provide resistance in creep. 22
  23. 23. Conclusion• Addition of Al into SAC alloys reduces the number of hard Ag3Sn and Cu6Sn5 IMC particles, and forms larger, softer non- stoichiometric AlAg and AlCu particles. This results in a significant reduction in yield strength, and also causes some moderate increase in creep rate.• For high Ag SAC alloys, adding Al 0.1-0.6% to SAC alloys is most effective in softening, and brings the yield strength down to the level of SAC105 and SAC1505, while the creep rate is still maintained at SAC305 level.• Addition of Ni results in formation of large (Ni,Cu)3Sn4 IMC particles and loss of Cu6Sn5 particles. This also causes softening of SAC alloys, although to a less extent than that of Al addition.• For SAC+Al+Ni alloys, the pasty range and liquidus temperature ° are about 4°C less than that of SAC105 or SAC1505 if the added quantity is less than about 0.6%.• Thus, new alloys exhibit SAC305 creep rate, SAC105 softness, & lower mp than SAC105. 23