Partial discharge in silicone gel on power module substrates in high-humidity conditions

Partial discharge (PD) has been shown to affect quality of insulation in power electronics modules. This paper provides a comprehensive characterisation of PD activity in gel-encapsulated direct bonded copper (DBC) power module substrates when subjected to fast unipolar square excitations. PD characteristics in low and high humidity environments are compared. PD inception voltage (PDIV) testing and time-resolved PD (TRPD) analysis is performed to investigate discharges in each condition. Two PD groups were identified, categorised by their amplitude, and prompting further investigation of the weaker group with a statistics-based approach. The strong group did not vary with humidity and is attributed to discharges between the top and bottom copper of the DBC. The weaker group varied significantly with humidity and is attributed to discharges within the lateral trench gap of the DBC top copper.