In a build-up step, a plurality of resin insulation layers and a plurality of conductive layers are alternately laminated in multilayer arrangement on a metal foil separably laminated on a side of a base material, thereby forming a wiring laminate portion. In a drilling step, a plurality of openings are formed in an outermost resin insulation layer through laser drilling so as to expose connection terminals. Subsequently, in a desmear step, smears from inside the openings are removed. In a base-material removing step performed after the build-up step, the base material is removed and the metal foil is exposed.