Patent ID: 7754321

Claim:
A core board for a clad board for forming circuitry, comprising: a fiber sheet; the fiber sheet comprising a non-woven fabric and a resin material impregnated into the fiber sheet, the resin material including at least one of a thermoplastic resin and a thermoplastic resin having a semi-cured portion, the fiber sheet having a top surface and a bottom surface; and a resin layer formed on both the top surface and the bottom surface of the fiber sheet, being made of material identical to the resin material; wherein the fiber sheet comprises: an inside layer having two faces and two surface layers, one which surface layers is disposed on each face of the inside layer; and wherein the density of the non-woven fabric in the inside layer is lower than the density of the non-woven fabric in each of the surface layers; and wherein the inside layer and the surface layers are made of materials identical to each other.