Investigation of the Insulation Failure of Power Modules by Observation of Electrical Trees

With the increasing of voltage level, the electric field has been distorted more severely in insulated gate bipolar transistor (IGBT). When the distorted electric field lasts for a long time, it will lead to insulation failures in the modules. Triple junction is the area of copper, ceramic and silicone gel in IGBT modules. Partial discharges (PDs) usually initiate from triple junctions, spread on the interface of ceramic and gel, finally lead to insulation failure. In fact, there are processing defects at the edge of triple junctions, such as hollows and protrusions. These defects lead to insulation failure in reality. The relationship between the behaviors of discharge and defects is still unclear. This paper presents an experimental study of the origin of insulation failure in power modules. The influence of defects on the origin of the electrical trees is analyzed. The results show that protrusion defects are rare but awfully dangerous. Because electrical trees can grow from these points easily. The hollow defects are frequent but they not likely to trigger electrical trees compared with protrusion.