Nonlinear Finite Element Analysis of An Automotive High-Power Module under Impact Loading

In this paper, the dynamic responses of an automotive high-power module under impact loading are studied at the board level. The effects of different bonding between the pins and the PCB, the geometry of the pin, and the effects of slots in PCB are studied to build robust power module solutions. The module is mounted to the printed circuit board (PCB) with metal pins. Each pin has a base that is soldered to the DBC substrate. The pin is mounted onto the PCB by the press-fit process followed by soldering to form good mechanical and electrical connections. However, the pins are ductile materials and may undergo very large plastic deformation with extreme impact loading, causing reliability issues of the power modules in the field use. Therefore, nonlinear finite element analysis is conducted to understand the dynamic behaviors of the pins. For the finite element analysis, a quarter three-dimensional model is used. The contact pairs are defined between the pin and PCB. For the pins are soldered to PCB, bonded contacts are defined; for the pins that are press-fit only, frictional contacts are used. The plastic behaviors of the pins are modeled by a bilinear plastic model. The impact loading adopted is a standard half-sine shock impulse, with a magnitude of 201G and a frequency of 1000 Hz. The input-G method is employed to conduct the impact analysis in ANSYS Mechanical. Three impact directions (x, y, and z, respectively, with z normal to the PCB) are computed. The results show that the impact in the z- direction leads to much higher von Mises stress of the pins than in X and Y directions, and thus z-direction impact is more critical. With z-direction impact applied, the max plastic strains are found at the pin base. In addition, the metal pins that are soldered to PCB are found to experience greater stress and plastic strains than the pins without soldering, indicating that there is a trade-off when using solder to enhance the bonding between the pins and the PCB. To improve the performance of press-fit pins, the geometry of the pin is modified by reducing the pin waviness and increasing the pin cross-section area. The modified pins are then examined by finite element analysis. The results show that much smaller accumulated plastic strains are achieved in the modified pins than the original ones. Furthermore, the effects of the slots in PCB are also investigated. The PCB slots could slightly reduce the pin plastic strains based on the numerical results. Through the simulation, a better understanding of the dynamic response of the pins of the power module is obtained, which is useful to build a reliable and robust power module product.