Bubble Degassing Characteristics in Silicone Gel and Improved Degassing Process to Enhance Its Insulation Capacity

Silicone gel is widely used in the packaging of high-voltage power devices because of its sealing, high temperature resistance and good insulation performance. However, the residual bubbles of silicone gel in the process of encapsulation are very easy to produce partial discharge or even breakdown phenomenon, which seriously restricts insulation reliability of high voltage power devices. To this end, the bubble motion in silicone gel during degassing is investigated to guide process optimization and enhance insulation performance in this paper. Firstly, by simulation and experiment, the influence of viscosity of silicone gel and different degassing pressure conditions on rising velocity of the bubble with initial bubble diameter are obtained. Then, the influence of thickness of silicone gel on the bubble rising velocity rate is also investigated. Furthermore, an optimized repeated degassing curve and stratified degassing method are proposed. The experimental results show that the breakdown voltage of the silicone gel treated by the repeated pressure buck process method increased by 16.84% compared with original process. Moreover, the insulation capability of silicone gel made by stratified degassing method is at least increased by 5.8%. Overall, methods proposed in this paper provide guidance for the advanced preparation process of silicone gel to promote insulation capability of IGBT device encapsulation.