Study of creep performance of Sn-0.7Ag-0.5Cu-3.5Bi-0.05Ni/Cu by nanoindentation

The creep performance of the lead-free solder joint Sn-0.7Ag-0.5Cu-3.5Bi-0.05Ni/Cu(SAC0705BiNi/Cu) was investigated and compared with that of the lead-free solder joint Sn3Ag0.5Cu/Cu(SAC305/Cu) after thermal shock by nanoindedtation. It was found that the indentation creep of SAC0705BiNi/Cu solder joint was lower than SAC305/Cu solder joint before and after thermal shock. The Creep rate sensitive index of SACBiNi/Cu solder joint was smaller than SAC305/Cu. The anti-creep property of SAC0705BiNi/Cu solder joint shows better than SAC305/Cu solder joint. The hardness of SAC0705BiNi/Cu was increased 5MPa after thermal shock, in contrast with SAC305/Cu decreased 19MPa. The results indicated that Bi and Ni additions could significantly improve hardness and elastic modulus of BGA solder joints. In addition, the elastic modulus of SAC0705BiNi/Cu solder joint decreased by 8.57%, while the elastic modulus of SAC305/Cu reduced by 28.92%, it shows Bi and Ni could block the generation of defects. Results shows that adding Bi and Ni elements into low-Ag solders have notable effort to improve the creep resistance.