Effect of Thermal Oxidative Aging on Cross-Linking Network and Electrical Property of Silicone Gel for IGBT Packaging

Due to power loss, the internal junction temperature of insulated gate bipolar junction transistor (IGBT) devices increases. Long-term operation in the environment of high junction temperature will lead to the aging of silicone gel, the insulating packaging material for IGBT devices. Its electrical property will decline after aging, which will directly affect its service life. However, its impact law and mechanism are still unclear. For this reason, this article focuses on the accelerated thermal-oxidative aging of silicone gel materials to carry out experimental research. Combined with Fourier transform infrared spectrometer (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and other analytical means to observe the microstructure of silicone gel in different aging stages, we explore the changes in its electrical property and analyze the mechanism of thermal aging on its insulation performance. The results show that the side chain oxidative crosslinking reaction mainly occurred after aging, and the degree of side chain crosslinking increased with the increasing degree of aging. The free volume of silicone gel increased after aging, the average free travel of electrons increased, and the breakdown voltage decreased. Due to the side chain oxidative cross-linking reaction, the molecular chain structure became neater, the polarity was weakened, and it was more difficult to polarize under the external electric field, which made its real part of relative complex relative permittivity decline, the dielectric loss increased at the same time, and the insulation performance became worse. The experimental results of this article can provide a certain theoretical basis for the evaluation of IGBT insulation status.