Direct simulation of fatigue failure in solder joints during cyclic shear

A numerical finite element analysis is undertaken to directly simulate failure of solder joint caused by cyclic shear deformation. In the model the tin (Sn)-silver (Ag)-copper (Cu) solder and two copper substrates constitute a lap-shear testing configuration. A progressive damage model is incorporated into the rate-dependent elastic-viscoplastic response of the solder alloy, resulting in the capability of simulating damage evolution and eventual failure through crack formation. The study concerns three different applied shear strain rates, 1, 10 and 100 s−1, under both the monotonic and cyclic loading conditions. It is found that, in the reference case of monotonic loading, the strain at failure can be influenced significantly by the fracture path in the solder. There is a tendency for cracking to occur closer to the interface during cyclic loading. The initiation of fatigue cracks is generally insensitive to the applied strain rate. However, the total fatigue life, in terms of the number of cycles to final failure, is seen to decrease significantly in the case of highest strain rate.