Propagation of Cavities caused by Surface Discharges in Gel-filling for Semiconductors

Silicone gel is widely used to encapsulate power electronic circuits. It is known that the weakness of this insulation system is the triple point which is composed of metallization, gel and substrate. Partial discharges (PDs) occurs at this triple point and propagates between gel and the substrate. The propagation of PDs gives rise to electrical degradation, which may lead to eventual failure of the insulation. Despite the fact, surface discharges in gel has not yet been studied enough. Therefore we have obtained images synchronized with the applied voltage. It showed that the degradation occurs when the applied voltage is positive.