PURPOSE: To improve reliability such as heat resistance and shock resistance by using prepreg, which contains epoxy resin, inorganic filler and titanate coupling agent as essential ingredients and is impregnated with epoxy resin composite material formed by mixing a prescribed quantity of inorganic filler with a prescribed quantity of epoxy resin.

CONSTITUTION: Epoxy resin, inorganic filler and titanate coupling agent are used as essential ingredients. Then, prepreg impregnated with epoxy resin composite material which is formed by mixing 35-90wt.% inorganic filler with 100wt. epoxy resin is used. When the mixing quantity is less than 35wt.%, heat resistance, shock resistance and through hole reliability are deteriorated, and when it is over 90wt.%, it causes impregnation defects with glass nonwoven fabric, coating nonuniformity and board thickness defects. As for the inorganic filler, aluminum hydroxide and magnesium hydroxide, etc., are used. As for the titanate coupling agent, isopropyltridecil benzenesulfoniltitanate can be used.