Dielectric Properties and Microstructure of Silicone Gel at Different Thermal Aging Stages

The chip junction temperature of high-power insulated gate bipolar transistor (IGBT) devices leads to the thermal aging of silicone gel inside the module, which directly affects the service life of IGBT. The microstructure and dielectric properties of silicone gel at different aging stages are the key to reveal the insulation degradation mechanism of IGBT packaging. In this article, the crosslinking density, chemical structure, and dielectric properties of silicone gel under different aging stages were tested. Combined with molecular dynamics theory calculation, the variation characteristics of dielectric properties were studied from the microstructure of silicone gel. The results show that with the increasing aging, the side chain groups with nonpolarity of silicone gel will be gradually consumed, and the Si–O–Si with higher bond energy will gradually increase and be exposed to the electric field; thus, the polarization will become more significant. The crosslinking density and free volume ratio of the silicone gel increase with aging, which has the effects on charge transport and group polarization. The research results provide a data basis for the packaging design of IGBT under long-term service conditions and also provide theoretical support for further optimizing the thermal aging resistance of packaging materials.