Elasto-viscoplastic nonlocal damage modelling of thermal fatigue in anisotropic lead-free solder

A finite element analysis has been performed of the thermal cycling of Sn–Ag–Cu solder. Experimental observations revealed damage to occur at grain boundaries even in the absence of external mechanical loading. The effect of the anisotropy of the material has been investigated through a three-dimensional simulation of the experiment. Anisotropy was included in the model in the elastic and thermal expansion properties. Stress concentrations arise at grain boundaries, dependent on the orientation of the connected grains and their interface. Qualitative comparison of the numerical results with the experimental observations indicated a reasonable agreement. A more accurate prediction requires three-dimensional experimental data on the grain structure of the sample.