Comparison investigation of thermal fatigue and mechanical fatigue behavior of board level solder joint

The thermal fatigue and mechanical fatigue are the two main failure modes for board level solder joint in SMT. The comparison investigation of thermal fatigue and mechanical fatigue behavior of solder joint are carried out by experimental method in this study. The surface mounted test PCB is used and two kinds of solder materials, including SAC305 and Sn37Pb, are considered. It is shown that lead-free solder joint (SAC305) has a longer thermal fatigue lifetime, but a shorter mechanical fatigue lifetime than traditional eutectic lead-tin solder. Moreover, the inelastic strain (including creep and plastic strain) evolutions of solder joint during thermal and mechanical fatigue procedure are analyzed by FEM individually. It shows that the creep and plastic strain in mechanical fatigue procedure is different from those in thermal fatigue.