PURPOSE: To reduce the damage of the titled device due to an external strain and to increase the strength thereof against thermal fatigue, by using undercoat resin having little stress, and by increasing the thermal conductivity and expansion coefficient thereof to the same degree as those of sealing mold resin.
CONSTITUTION: A power transistor element 2 is connected to a header substrate 1, and the electrode of the element 2 is bonded to a lead 3 through the intermediary of a gold wire 4. An epoxy resin monomer having excellent curing property is dropped down on the element 2 and polymerized by heat to be formed into a cured undercoat resin body 9. Then, sealing resin 10 is cured by molding in a metal mold. Epoxy resin or silicone resin is used as the resin for this purpose. When an external force is applied, slippage A occurs on an interface between the sealing resin 10 and the undercoat resin 9, a strain is relaxed thereby, and thus no stress is applied directly on the element 2. Since the resin coat thus prepared is hard, the effect of pressing-in B resulting therefrom makes it possible to attain a thermal fatigue strength unvaried from that obtained by direct molding.
SUDA MINORU
YAMAGUCHI MASAO
AKEYAMA KENJI
ARAKI ISAO
