Analysis of Discharge Caused by Soldering Defect in Wire-Bonding Power Module

Partial discharge (PD) assessment, widely applied in HV IGBT (insulated gate bipolar transistor) module, is not generally adopted for modules at low-to-medium voltage levels. In this article, a type of PD defect induced by the cavity in the solder layer of 1700-V IGBT modules. Using a zonal PD test method and the scanning acoustic microscope (SAM) analysis, we characterized the cavity defects in the solder layer and proposed a hypothesis for the underlying mechanism of the cavity formation. The hypothesis was then proved by adding two pretreatments during the attaching period of the substrates, which effectively suppressed the cavity defects. This suggests a method to settle the cavity defect by a half-etched dimple structure, which can improve the product pass rate during PD assessment.