Thermo-mechanical reliability of lead- free solder joints in solar cell assembly.

The fatigue failure of lead-free SnAgCu solder joints in solar cell assembly is studied to determine the effect of thickness of intermetallic compound (IMC) layer on the reliability of the joints. Finite element modelling (FEM) is used to simulate the non-linear deformation of solder joints in crystalline silicon solar cell assembly. In this study, five geometric models of solar cell assembly with IMC thickness layer in the range of 2 to 10 μm were subjected to accelerated thermal cycling utilising IEC 61215 standard for photovoltaic panels. Creep response of each of the assembly’s solder joints to the induced thermal load were simulated using Garofalo-Arrhenius creep model. Analysis of the results indicates that the thickness of IMC in the joints significantly impacts the thermo-mechanical reliability of the assembly joints. The effect is such that the mean-time-to-failure (MTTF) of the assembly depends on the thickness of the IMC layer – such that solder joint fatigue life decreases as IMC thickness increases.