Resin composition for circuit board, and metal-base circuit board in which same is used

A resin composition for a circuit board, the resin composition comprising:

• component (i), a vinylsilyl group-containing polysiloxane;
• component (ii), a hydrosilyl group-containing polysiloxane;
• and
• component (iii), an inorganic filler, wherein
• the vinylsilyl group-containing polysiloxane as the component (i) comprises (A) a dual-end type vinylsilyl group-containing polysiloxane having a weight average molecular weight of 30,000 to 80,000 and (B) a side-chain dual-end type vinylsilyl group-containing polysiloxane having a weight average molecular weight of 100,000 or more,
• a mass ratio of (A) to (B), (A)/(B), is 80/20 to 30/70,
• the vinylsilyl group-containing polysiloxane as the component (i) has a vinylsilyl group equivalent of 0.005 to 0.045 mol/kg,
• the hydrosilyl group-containing polysiloxane as the component (ii) has a hydrosilyl group equivalent of 6 mol/kg or more,
• a molar ratio of (C) a hydrosilyl group in the component (ii) to (D) a vinylsilyl group in the component (i), (C)/(D), is 2.5 to 5.0, and
• the inorganic filler as the component (iii) is contained at 60 to 80% by volume.