Dielectric losses and breakdown in silicone gel

Silicone gels are used for the packaging and insulation of power electronic components such as high voltage IGBT modules, mainly due to their good mechanical and thermal properties. Nevertheless, the knowledge of their dielectric properties is still uncompleted. The aim of this paper is to present the results of measurements of dielectric losses versus frequency, as well as breakdown field under a large temperature range (up to 160 degC). Losses are essentially due to conduction phenomena, while the effect of polarization is less important. The influence of temperature is rather large, and a marked effect of time (ageing) is also recorded, especially when the temperature is raised. Results are discussed with the perspective of use in high temperature power semiconductors.