Reliability research and thermal fatigue life prediction of backwards compatible mixed solder joint based on simulation

This paper analyzes strains of backwards compatible mixed solder under different mixed degrees, and makes the prediction of its thermal fatigue life. The research is based on a finite element simulation tool called COMSOL Multiphysics. The finite element models of mixed solder joint which are respectively consist of leaded, lead-free and hybrid materials are set up. The mixed degrees of mixed solder joint are 30%, 70% and 100%. Anand constitutive model is used to describe the property of solder joint and to be the analyzing basic of strains under thermal cycle. In the meanwhile, Darveaux energy model based on damage accumulation is applied to predict thermal fatigue life of mixed solder joint. From the results of simulation, it can be seen that the maximum strain of solder joint with homogeneous material appeared at the edge region far from the center of the chip. It is concluded that the smaller plastic strain, the longer thermal fatigue life and the higher reliability. On the other hand, long fatigue life and high reliability is corresponding to high mixed degree of backwards compatible mixed solder joint. Another discovery is that reliability of completely mixed solder joint is between leaded and lead-free solder joints reliability.