An insulating layer (3) having an opening portion (3a) at a position conformable to an electrode pad (2) is formed. Next, a resin projection portion (4) is formed on the insulating layer (3). Thereafter, a resist film is formed which has opening portions made in regions conformable to the opening portion (3a), the resin projection portion (4) and the region sandwiched therebetween. A Cu plating layer (6) is formed by electrolytic copper plating, using the resist film as a mask.