Investigation on Reliability of Power Devices by Finite Element Analysis

Power devices refer to semiconductor devices capable of handling high voltages and large currents. Compared with traditional Si-based IGBT, silicon carbide (SiC) metal-oxide-semiconductor field effect transistors (MOSFETs) have lower resistance, stable blocking ability under high temperature conditions, may withstand higher working temperature and so on. As a result, SiC-based power devices have become the current research hotspot. However, the characteristics of high-power operation also bring great challenges to device reliability. In addition to the significant differences in coefficients of thermal expansion (CTE) between different packaging materials and chips, the high temperature gradients and high heat flux density may bring additional thermal stress and strain. Especially for a planar package structure, the thermal stress is more significant, and it is much easy to cause fatigue failure of the connected solder layer.In this paper, for a typical planar SiC MOSFET, the evolutions of the solder stress during temperature cycling (TC) and power cycling (PC) are analyzed in detail through finite element analysis (FEA). In PC, the relationship between heating power and junction temperature is firstly studied by thermal-mechanical coupling method, and the influence of the internal temperature evolution of SiC device on the stress of solder layer is also analyzed. Furthermore, we discuss the accelerating effects of temperature and power on the stress of the solder layer based on Norris-Landzberg (NL) model. Our work is expected to provide support for qualitative and quantitative evaluation of the reliability lifetime of power devices.