The Degradation Behaviors from Triple Junctions in IGBT Power Modules

The high voltage insulated gate bipolar transistors modules are widely used in different industrial fields, and the weakness of their electrical insulation usually starts at the gel-copper-ceramic triple junction. Partial discharges and electrical trees usually initiate from triple junctions, and develop at the ceramic-gel interface, eventually leading to insulation failure. The insulation performance at the triple junction directly affects the reliability of insulation in IGBT power device. Therefore, in this paper, the partial discharge characteristics and the development of electrical trees at the triple junction are investigated for the encapsulation structure composed of the direct bonded copper ceramic substrate and silicone gel under AC voltage. The results show that the phase-resolved partial discharge at the triple junction is symmetrically distributed between the pre-zero voltage and the peak voltage. As the electrical tree grows, the partial discharge pulse becomes more intense and concentrated. The electrical trees at the triple junction are mainly composed of filamentary channels and bubble-like cavities. The development of electrical trees shows two stages of growth and stagnation. This paper illustrates the insulation failure process of the triple junction in the power module insulation structure.