Microstructure, creep deformation behavior and reliability of Sn-6.5wt%Zn-0.3wt%Cu lead free solder after Bi additions

Creep characteristics of Sn-6.5Zn-0.3Cu plain solder was studied and compared with Sn-6.5Zn-0.3Cu-1Bi and Sn-6.5Zn-0.3Cu-3Bi solder alloys. The results show that 3Bi-containing alloy solder has the higher creep resistance (~80 times) than the other two solders at the same stress level and testing temperatures. The higher creep resistance was attributed to the solid solution and precipitations strengthen effects of Bi atoms. The precipitation of Bi atoms or particles can significantly refine the microstructure, blocks the movement of dislocations and increases the creep resistance of Bi-containing solders. Moreover, the creep life time of plain SZC plain solder alloy was extremely enlarged ~23.7 times with the addition of 3 wt. % Bi, which could result in improving the reliability of Bi-containing solders. Additionally, the minimum creep strain rate in the steady state flow is developed during secondary creep and Garofalo model was created from the experimental data to predict the creep deformation mechanism. According to the obtained stress exponents and activation energies, it is proposed that the dominant deformation mechanism is dislocation climb over the whole temperature range investigated.