Field characteristics and dielectric tests on an IGBT module plate

This paper presents results from dielectric tests along the surface of the base plate of an IGBT module as well as on printed circuit boards (PCBs). The PCBs have simplified geometries representative for base plates used in IGBT modules. The module will be applied in subsea converters, submerged in a liquid dielectric and exposed to subsea hydrostatic pressure. One base plate was cut to examine geometric details of the cross section with a microscope. These results were used for accurate modeling of the geometry used in FEM analysis of the electric field distribution. Pd-measurements with ac voltage were performed in both air and MIDEL 7131 oil on the base plate and the PCB test objects. The discharges were detected optically by using both a photomultiplier and a light-sensitive and high-speed CMOS video camera to respectively measure the pd inception voltage and the location of the discharges. It was found that at some critical voltage the pd activity increases rapidly before leading to an electric breakdown. The inception voltage of the measurements in oil showed up to be independent from the shape of the electrode geometry.