Electrical Tree Failure at DBC Substrate-Silicone Gel Interface in High-Voltage Power Module Under Positive Square Wave Voltage

The development of high-voltage high power density electronic devices has brought forward new requirements for the insulation reliability of encapsulation. The growth of electrical trees at the triple junction of the silicone gel-copper-substrate is one of the most important causes of material degradation and even insulation failure. In this paper, the growth characteristics and degradation mechanism of electrical trees at the triple junction of power modules under high-frequency positive square wave voltage are studied. The results show that a higher frequency is conducive to the generation of bush trees. As the square wave rise time increases, the number of branches, length, and width of the electrical tree decreases. The denseness of the electrical tree decreases with an increase in the duty cycle of the square wave. In addition, electrical tree growth is modeled on the cavity initiation and propagation characteristics at the triple junction, where the injection and transport of the space charge play an important role. Electrical tree failure causes the deposition of disordered graphitic carbon in the vicinity of the copper electrode as well as the chemical degradation of the silicone gel, and it precipitates elemental Al from the Al2O3 substrate, which accelerates the insulation degradation.