Simulation of Fatigue Crack Propagation in Solder Joints of Electronic Equipment Subjected to Combined Loading of Random Vibration and Thermal Cycling

Abstract

In various electronic equipment, it is an issue to design solder joints in consideration of vibration fatigue and thermal fatigue. It is known that the fatigue life of solder joints is sometimes much shorter than that predicted by Mines’s rule on the combined vibration and thermal cyclic loading test. In order to elucidate the mechanism of this shortening, a crack propagation simulation method considering the combined loading is proposed in this paper. In this method, critical section is incorporated in the solder part of the FEM structural analysis model, the amount of damage of elements in the critical section under random vibration and thermal cycle loading is calculated, and the elements whose amount of damage exceeds a certain value are deleted to simulate crack propagation. This simulation method is applied to a structure in which a leaded component is soldered to a wiring board. The simulation results show that, crack propagation behavior is different between vibration loading and thermal cycling, and this difference causes a shorter number of cycles to fracture than that estimated by Miner’s rule in the case where thermal cycling is first loaded and vibration is loaded later.