Thermal fatigue life of Sn-3.0Ag-0.5Cu solder joint under temperature cycling coupled with electric current

In this paper, the physical and mechanical properties of Sn-3.0Ag-0.5Cu (SAC305) solder and the thermal fatigue properties of solder joints under different electric current densities and heat sink temperatures are investigated. The thermal and electrical conductivities of the SAC305 specimens are measured for the electric current density between 6.37 x 102 A/cm² and 2.55 x 10³ A/cm². Through comparisons against the experimental results, it is found that the prediction results of finite element simulations can reasonably characterize the mechanical properties of SAC305 solder materials. In order to evaluate the effect on mechanical behaviour of solder alloys, a typical solder joint of mechanical properties for the upper and lower bounds under thermo-electric coupling conditions are analyzed by finite element simulations. The original Coffin-Manson model is improved to predict the fatigue life of SAC305 solder joints under temperature cycling coupled with electric current. Comparisons show that the different mechanical behaviour of SAC305 solder materials results in different performances at varying electric current densities and heat sink temperatures. For low current densities and heat sink temperatures, the solder material with lower yielding and ultimate strengths has a higher fatigue life. On the contrary, at high current densities and heat sink temperatures, the solder material with higher yielding and ultimate strengths will exhibit advantages in terms of fatigue life. From the numerical simulation point of view, this study reveals the performance advantages of lead-free solders with higher yielding and ultimate strengths in terms of thermal fatigue and current density for high temperature and power applications.