Patent ID: 7992290

Claim:
A method of making a flexible printed circuit board (FPC) which comprises a substrate comprising a first metal foil layer, a second metal foil layer, a first intervening layer interleaved the first and second metal foil layers, a second intervening layer covered on the second metal foil layer, and a third metal foil layer covered on other side of the second intervening layer, the method comprising: (a) laminating the substrate; (b) adhering a covering film to outermost surfaces of the substrate; (c) defining a hole in one side of the substrate through the covering film and the first and second metal foil layers and the first intervening layer and an additional hole in an opposite side of the substrate through the second and third metal foil layer and the second intervening layer; and (d) plating a portion of an inner wall of the hole and the additional hole with a conductive material to form a via to electrically connect the at least two metal foil layers.