Surface Potential Measurement of Power Module Packaging Insulation based on Electrostatic Observation

With the increasing blocking voltage of the power module, the insulation issue has garnered widespread attention, with localized electric field concentration emerging as a key concern. The accumulation of interfacial charges is responsible for the electric field distortion. However, there are few experimental studies on interfacial charge distributions within the power module packaging insulation. This paper employed the active electrostatic probe method to investigate the surface potential of the power module packaging insulation under different operating voltage conditions. Based on the experimental results, the interfacial charge distribution inside the packaging insulation was further investigated using the charge inversion algorithm. It was found that compared to conditions where the lower electrode of the directly bonded copper substrate is not grounded, grounding the lower electrode significantly increases the surface potential and the accumulation of charges. Moreover, the average surface charge density generally increases linearly with the applied voltage. After a short circuit, the rate of charge dissipation is faster when the lower electrode is grounded. The surface potential and interfacial charge testing method proposed in this paper provides theoretical support for the optimal design of package insulation.