Patent ID: 7955454

Claim:
A method for forming wiring on an insulating resin layer, the method comprising: laminating a thermosetting resin film in a semi-cured state and a metallic foil in this order on an insulating substrate on which base-layer wiring is formed, a mat surface of the metallic foil having a surface roughness and facing the thermosetting resin film, and pressing the thermosetting resin film and the metallic foil with application of heat so that the surface roughness of the metallic foil is substantially transferred to a surface of the thermosetting resin film facing the metallic foil to form an even roughened surface; forming a single-piece structure in which the insulating resin layer including the thermosetting resin film in a cured state and the metallic foil are laminated on the insulating substrate; forming openings in the metallic foil so as to expose parts of the insulating resin layer in which via holes are to be formed; forming via holes in the insulating resin layer by irradiating a laser beam onto the insulating resin layer by using the metallic foil in which the openings are formed as a mask; performing a desmear process of the via holes via the openings of the metallic foil before removing the metallic foil; removing the metallic foil by etching to expose the even roughened surface of the thermosetting resin film; forming an electroless-plated layer that continuously covers the even roughened surface, a side surface of the via holes and a top surface of the base-layer wiring corresponding to the bottom of the via holes; and forming wiring including an electroplated layer on the electroless-plated layer by a semi-additive process.