Temperature- and Degradation-Dependent Maximum Electric Field Stress in Wire-Bonding Power Modules Under PWM Waves

Electric field stress concentration is one of the causes of partial discharge (PD) in power modules, which threatens the power modules' safe operation. Herein, this article investigates the influences of temperature (from 150 to $250~^{\circ }\text{C}$ ) and operation duration on the maximum electric field stress at the triple point (silicone elastomers, ceramic, and copper). It reveals that the maximum electric field stress rises with the increase in temperature, while the maximum electric field first increases but then decreases along the operation duration, especially under low temperature. Both the influences of temperature and the operation duration are related to the permittivity (dominated by the relaxation of Si–O bonds), low-frequency dispersion (LFD) phenomenon, and dc conductivities of silicone elastomers, which can be manipulated to suppress electric field stress concentration. This article provides a method to accurately calculate the electric field. The results are also critical to evaluation and improvement of power modules' insulation.