Electrical Properties of Silicone Gel for WBG-Based Power Module Packaging at High Temperatures

Abstract

Trends toward high power density designs and emerging wide bandgap (WBG)-based semiconductors will lead to a severe temperature rise in power electronic modules. In this regard, the insulation performance of silicone gel used for power module packaging deteriorates at high temperatures and frequencies is a concern and has not been well studied. This study focuses on the electrical properties of silicone gel at high temperatures, including its dielectric properties, volume resistivity, and breakdown strength. A Cole-Cole model was used to describe the dielectric response process. In particular, the dielectric loss density under PWM voltage was calculated, and the temperature rise of the encapsulation structure caused by the dielectric loss was observed. It was found that the high-frequency dielectric constant at 200°C decreases by 24% compared to room temperature; when the temperature is raised to 180°C, the volume resistivity drops by three orders of magnitude, and the 50 Hz AC and 10 kHz unipolar square wave breakdown strength of silicone gel is reduced by 50% and 42% compared with those at room temperature. The dielectric loss under PWM voltage increases by four orders of magnitude as the temperature increases up to 200°C but does not lead to a significant temperature rise in the encapsulation structure.