Investigation of Liquid Insulating Material for Power Module Encapsulation: Effects on Partial Discharge and Electric Field Characteristics

Next-generation power modules require rigorous evaluation of insulating substrates due to increasing voltage levels and the associated risk of partial discharge (PD). PD typically occurs in regions of high electric field intensity, particularly at encapsulant-metal interfaces, and leads to dielectric degradation. Conventional encapsulants, such as epoxy resins and silicone gels, suffer from poor thermal conductivity and lack self-healing properties. This study investigates liquid dielectric materials as alternative encapsulants, specifically Novec 7100, Vertrel XF, FC3283, and Pastel NEO. These liquids, each exhibiting distinct dielectric and thermal properties, were applied to ceramic substrates. Partial discharge inception voltage (PDIV) measurements were conducted under a 60 Hz AC voltage, in conjunction with electric field analysis. The results indicate that high-permittivity insulating liquids can effectively modulate electric field distribution, thereby influencing PDIV. These findings suggest that appropriate selection of liquid encapsulants, based on dielectric strength and field relaxation characteristics, can enhance the insulation reliability of power modules.