Resin composition for circuit board, and metal-base circuit board using same

Provided are: a metal-base circuit board having exceptional solder crack resistance, thermal conductivity, adhesiveness, and insulating properties; and a resin composition for a circuit board used for the metal-base circuit board. The resin composition for a circuit board containing: a vinylsilyl-group-containing polysiloxane (vinylsilyl group equivalent: 0.005-0.045 mol/kg) including (A) a double-terminal vinylsilyl-group-containing polysiloxane having a weight-average molecular weight of 30000-80000, and (B) a side-chain double-terminal vinylsilyl-group-containing polysiloxane having a weight-average molecular weight of 100,000 or greater; a hydrosilyl-group-containing polysiloxane (hydrosilyl group equivalent: 6 mol/kg or greater); and 60-80 vol% of an inorganic filler. The mass ratio of (A) to (B) ((A)/(B)) is 80/20 to 30/70, and the molar ratio of (C) hydrosilyl groups to (D) vinylsilyl groups ((C)/(D)) is 2.5-5.0. 本发明提供耐焊料裂纹性、导热性、粘接性及绝缘性优异的金属基底电路基板及该金属基底电路基板中使用的电路基板用树脂组合物。电路基板用树脂组合物，其含有含乙烯基甲硅烷基的聚硅氧烷(乙烯基