Damage Path Simulation of Solder Joints

Abstract

Fatigue life prediction of solder joints is one of the most important areas of research in the development of reliable electronic packages. In the present study, a new method of estimating the crack propagation, which is based on finite element analysis without geometrical crack model, was examined. On the basis of a damage model assumed for solder, the new method called 'damage path simulation' was verified for solder joints in QFP (Quad Flat Package). It was clear that the extension of the damage path showed good agreement with the behavior of crack propagation observed in the actual thermal cycle tests. Damage path extension from a pointed end of outer lead was also simulated simultaneously with that from the upper surface of the solder fillet, and both damage paths were finally combined. The advantage of the proposed method was especially evident when the fatigue cracks were initiated from two or more regions. The effects of the frequency of thermal cycle were also discussed. It was shown that the frequency of thermal cycle has a noticeable effect on the crack propagation rate. It was concluded that the estimation of the crack propagation in solder joints based on the proposed method is satisfactory for engineering purposes.