Effect of Heat Treatment on Space Charge Accumulation in Epoxy Resin under High DC Stress

Space charge accumulation characteristics in Epoxy resin with various heat treatments were investigated under DC high stress using as pulsed-electro acoustic (PEA) method. Epoxy resin has been used as sealing material for semiconductor devices. Recently, a new semiconductor like silicon carbide (SiC) has been developed to use it at high temperature environment. However, the conventional epoxy resin is unable to be used at such high temperature. Therefore, a thermal property of the epoxy resin must be improved to use it for the device. To improve it, at first, it is necessary to understand the insulating property of the conventional epoxy resin in high temperature environment. On the other hand, it is said that a space charge accumulation in some insulating materials under high DC electric field sometimes causes a dielectric breakdown. Therefore, we tried to investigate the relationship between the space charge accumulation and the breakdown in the conventional epoxy resin under high DC stress at high temperature. A time dependent space charge distribution was observed using the PEA method. Furthermore, since the devices are used in a severe condition at high temperature with high humidity, we also tried to study the effects of a heat treatment, a humidification and drying treatment on the space charge formation in the epoxy resin. Judging from the results, it was found that a moisture content in the bulk of the epoxy resin strongly affected the space charge accumulation under dc high stress. Furthermore, it was found that the moisture content also affected the breakdown property.