A second protective film is formed by applying high-viscosity resin by an inkjet method, in two patterns that extend parallel to and along a boundary between a first protective film and a plating film, the boundary being sandwiched between the two patterns. A low-viscosity resin is applied between these first and second patterns of the second protective film by the inkjet method. The low-viscosity resin has a viscosity that is lower than that of the high-viscosity resin for forming the second protective film, and a fluidity that is higher than that of the high-viscosity resin and thus, leaks and spreads into a gap between the first protective film and the plating film. The third protective film adheres to the first and second patterns, is formed across the boundary between the first protective film and the plating film, and is embedded in the gap whereby the gap is plugged.