New Diagnosis Method for Space Charge-Dependent Interfacial Electrical Tree in Packaging Insulation Using Current Integrated Charge Measurement

Interfacial electrical tree (IET) is easily initiated by a high electric field near the triple point (TP) in the power modules, propagating along the packaging material and ceramic substrate interface until electrical breakdown occurs. To assess the degree of IET degradation, this study fabricates the silicone elastomer (SE) packaging modules without IET and with three levels of IET degradation. Then, a novel diagnostic indicator is derived from the charge measurement results by the direct current integrated charge [DCIC- Q(t)] equipment. This indicator can effectively, nondestructively, and quantitatively distinguish different levels of IET degradation based on the charge ratio values within the voltage range of 250–2000 V at 150 °C. Notably, the charge ratio value of the IET-degraded modules exhibits significant voltage dependency at low voltages and high temperatures due to the interfacial space charge accumulation effect. The diagnostic indicator increases with the IET degradation degree, indicating a higher accumulation of interfacial space charges in the IET channels, consistent with theoretical analyses. It is expected that the proposed diagnostic indicator may help to diagnose the degradation levels in other electrical equipment as well.