Improvement of the heat resistance of a liquid mold compound by bismaleimide resin

For next-generation power semiconductors, a highly heat-resistant liquid mold compound was developed based on an epoxy resin having a functional group that can react with bismaleimide (BMI) resin. A liquid resin with a maleimide skeleton was created by prereacting BMI, which has a low melting point of 70-150 degrees C, with an epoxy resin having allyl and epoxide groups. The maleimide-skeleton epoxy resin was able to precure at <= 150 degrees C using peroxide and imidazole curing agents. The liquid maleimide-modified epoxy mold compound (EMC) containing silica filler had not a clear glass transition temperature, so the change in physical properties to temperature is very small. This study compared the heat resistance of the developed maleimide-modified liquid mold compound with a general-purpose EMC and silicone gel. The weight loss at 200 degrees C was less than that of the EMC, and changes in physical properties, which are important for mold compounds, were also small, indicating excellent heat resistance. Therefore, a liquid mold compound containing maleimide resin is likely to be suitable as a mold compound for power semiconductor devices operating at 200 degrees C.