Patent ID: 7737368

Claim:
A circuit board comprising: a plurality of wiring layers; an insulating layer which insulates the plurality of wiring layers, the insulating layer containing a fibrous filler and a resin; and a conductor film on a sidewall of a via hole extending through the insulating layer, and wherein the fibrous filler protrudes from the sidewall along the sidewall of the via hole, and the protruding portion of the fibrous filler is covered with the conductor film; and the length of the protruding portion of the fibrous filler protruding from the sidewall is greater than the thickness of the conductor film; the conductor film has a surface roughness in a region where the conductor film covers the fibrous filler protruding from the sidewall that is greater than a surface roughness in a region where the conductor film covers the sidewall from which the fibrous filler does not protrude; the thickness of the conductor film covering the fibrous filler protruding from the sidewall is greater than the thickness of the conductor film covering the side wall from which the fibrous filler does not protrude; and the circuit board including a step at a border between the conductor film covering the fibrous filler protruding from the side wall and the conductor film covering the side wall from which the fibrous filler does not protrude.