The role of Ni minor additions on the mechanical characteristics of Sn-1.5Ag-0.5 wt.% Cu (SAC155) Pb-free solder alloy

Abstract

Microstructure analysis, thermal behavior, and tensile creep characteristics of the Sn-1.5Ag-0.5Cu-x wt.% Ni (SAC155-xNi, x = 0, 0.05, 0.1, 0.2, and 0.5 wt.%) solder alloys have been examined. The Ni additions have greatly modified the microstructure of Ni-free alloy into bulky fibrous eutectic regions and included the contemporary (Cu, Ni)6Sn5, and (Ni, Cu)3Sn4 IMCs. Ni additions slightly increased solidus temperature and melting temperature of them. The results of tensile creep resistance have shown dependence on Ni content and testing temperatures due to bulky fibrous eutectic regions and finer IMCs. Creep rates vary with Ni content across all temperatures and stresses. The SAC155-0.05Ni alloy has the lowest and the SAC-0.0Ni alloy has the highest creep rates at all tested conditions. The delicate dispersed IMCs of Ag3Sn and Cu–Ni–Sn resulted in a significant increase in stress exponent (n$$\approx $$ ≈ 5–8), enhancing its deformation resistance. The $$n$$ n values of alloys decrease as the testing temperature rises due to a change in the dominant creep mechanism. The average values of activation energy (Q) of SAC155-xNi alloy ranged from 60.20 to 68.02 kJ/mol. These Q values are coherent to the process of pipe self-diffusion through dislocation cores.