With the increasing of voltage, the electric field has been distorted severely in insulated gate bipolar transistor (IGBT) modules. When the distorted electric field is last for a long time, it will cause the modules to insulation failure. The failure is origin from the defects, such as the growth of electrical trees. The defects locate at the junctions of the copper layer, ceramic substrate, and silicone gel. These junctions are defined as designing defects. And at the edge of the designing defects, there are a series of processing defects, such as hollows and protrusions. These processing defects lead the modules to insulation failure. However, not all of processing defects are the origin of the electrical trees. The relationship between the behaviours of discharges and those processing defects is still unclear. In this regard, this paper presents an experimental study of the origin of insulation failure in power modules. The ceramic, copper and silicone gel are considered in this study. Insulation failure is equivalent to the growth of electrical trees. And the electrical trees are observed by using a stereo-microscope. The influence of the processing defects on the origin of the electrical trees is analysed. The results show that nearly all of the protrusions defects become the root of the electrical trees. For the hollow defect, this is not the case. This means that protrusions defects are more likely to lead to failure than hollow defects. The protrusions defects must be avoided to generate during the processing.
 

packaging,DBC,insulation,fault