In recent years many electric equipments have come to be used for cars. Solder joints in electric device utilizing car are exposed to harder environment and required higher reliability than that in electric household appliances. Because of this reason, thermal fatigue reliability of solder joints has become one of the most important issues in car electronics. Generally thermal fatigue reliability is estimated by thermal cycle examination, but it needs long time. Estimation by FEM enables it to improve reliability and to reduce time. Analysis of solder life generally can predict only initial crack. But it is important to predict crack propagation and solder joints break down, considering that a function of solder joints is electric connection. In this study, the authors proposed a method to predict break down life by analytical approach.
