The role of nano and micro particles on dielectric strengths in epoxy composites

Epoxy composite is expected to become the substrate insulation of gate bipolar transistors (IGBTs) that can replace ceramics if it has high thermal conductivity. Fillers with high thermal conductivity were added to the epoxy resin, while this composite often suffers from lowering in breakdown (BD) strength. In order to reveal the above phenomena and to clarify the breakdown (BD) mechanism, we carried out experiments using two electrode structures, i.e. an MB-PWB (metal-base printed wiring board) insulation simulated structure and a sphere-to-sphere electrode for BD strength. As a result, it was clarified that the IGBT insulation breaks down after successive partial discharges (PDs), and the BD strength of microcomposite decreases with increasing the content of micro-fillers. A trial was made to raise the once-lowered BD strength by adding nano-Al₂O₃ fillers. Above experiments were carried out for nanocomposites and nano-micro-composites. It was clarified that nano-fillers improve the BD strength of composite. Such a phenomenon was found that the BD strength of composites was increased with the dispersion state of nano-fillers.