PURPOSE: To prevent the premature deterioration of a post-treatment liquid, and the discoloration and deterioration of an insulating property of a substrate by forming a recess in an area corresponding to the outer periphery of a bore, and by placing over the recess a copper-clad laminate that is filled with a thermoplastic having a release characteristic.

CONSTITUTION: Interlayer adhesive prepregs 2 having bores formed in predetermined positions are laminated on a flexible circuit plate 1 on which a circuit is formed by an etched foil method. Spacers 4 are fitted into the bores, and a recess is formed at an area corresponding to the outer periphery of the bore by the irradiation of a CO2 gas laser or a routing treatment. A copper-clad laminate 3 filled with thermoplastics is laid over this recess. This prevents an etchant from being impregnated into the interior of a substrate when a copper foil is etched. Hence, it is possible to prevent the premature deterioration of a post-treatment liquid, and the discoloration and deterioration of an insulating property of the substrate due to the exuding of the etchant into the inside of the substrate. The surface of the substrate integrated by pressurization and heating becomes smooth, whereby it is possible to reduce failures in the formation of an external layer pattern.