Reliable evaluation method for solder joints in vehicle electronics devices considering the actual use conditions

This paper presents the result of verifying Miner´s law of the solder joint part by mechanical fatigue tests and FEM analysis. The author´s group have studied the Manson-Coffin´s law for lead free solder joint by using the isothermal fatigue test and FEM analytical approaches to establish the practicable evaluation of thermal fatigue life of solder joints, for example, for the Sn-Cu solder, because this solder is attracted from the aspect of the decrease of solder leach in the flow process and material cost. To studying the Manson-Coffin´s law, mechanical shear fatigue tests and FEM analysis are used. The mechanical shear fatigue test use the relative displacement corresponding to the thermal strain. However, life of the solder joints has been evaluated at the thermal cycle range by the repetition of a constant temperature between the lowest temperature and the maximum temperature of the expected usage conditions. It is thought that this is over spec compared with actual use conditions. However, there are enormous difficulties in the consideration of actual use conditions. The first, the actual use conditions are different according to the users. The second, the extraction method of the thermal data in actual use conditions is not established. In this study, Miner´s law of the BGA solder joint part was verified by the mechanical shear fatigue tests. It is for adapting to classifying the actual use conditions to some patterns.