Patent ID: 8008767

Claim:
A semiconductor device comprising: a circuit board comprising a core and a buildup layer; a semiconductor element connected to said circuit board via metal bumps; a gap between said semiconductor element and said circuit board; and an encapsulating resin composition filling the gap between said semiconductor element and said circuit board; wherein the thickness of said core is at most 500 μm; said core is formed by impregnating a fiber substrate with a resin composition comprising a cyanate resin, a phenol resin, an epoxy resin and an inorganic filler, and curing; the coefficient of thermal expansion of said encapsulating resin composition from room temperature to the glass transition temperature is at least 15 ppm/° C. and at most 30 ppm/° C.; and the glass transition temperature Tg (° C.) by TMA analysis of said encapsulating resin composition satisfies the equation 75<Tg<112.5T+95, where T (mm) is the thickness of said core.