IGBT module technology with high partial discharge resistance

The high operating voltages of 6.5 kV IGBT modules place additional demands on the insulation and partial-discharge resistance. The most important component affected here is the metallized aluminum nitride ceramic which is embedded in a silicone gel. A high electric field strength can cause a local electric discharge in the silicone gel known as partial discharge, leading ultimately to electric insulation failure and reducing the reliability of the IGBT module. For a 6.5 kV IGBT module, the insulation test must be performed up to a voltage of 10.5 kV rms. Technological steps have been carried out to reduce the maximum electric field strength along the edge of the copper metallization. The edge of the ceramic was coated with a high-impedance layer of doped amorphous silicon. The electric current along the edge of the ceramic homogenizes the electric field strength. The partial discharge was determined up to 11 kV and a considerable reduction was observed compared to standard modules. Without an a-Si:H coating, the partial discharge already increases strongly at low voltages of 3-4 kV. At high voltages, the interface between the silicone gel and the substrate is a major source of partial discharge. The a-Si:H coating reduces electric field peaks and the partial discharge does not exceed 10 pC up to a voltage of 10 kV.