Patent ID: 7759583

Claim:
A circuit board comprising: a plurality of wiring layers; an insulating layer which establishes electrical insulation between the plurality of wiring layers; a heat-conductive particulate filler added into the insulating layer; and a via conductor which covers a via hole piercing through the insulating layer in a predetermined position and establishes electrical connection between the plurality of wiring layers, the via conductor covering the via hole along a sidewall of the via hole without filling the entirety of the via hole, wherein part of the filler is exposed in the sidewall of the via hole so as to project from the insulating layer toward the via hole and is put in contact with the via conductor, and the thickness of the part of the filler projecting from the sidewall of the hole is smaller than the thickness of the via conductor, and a contact area between the via conductor and part of the filler is greater than that between the via conductor and the insulating layer.