A printed wiring board includes an interlayer resin insulation layer, a pad structure formed on the interlayer resin insulation layer and positioned to mount a semiconductor device, and a solder-resist layer formed on the interlayer resin insulation layer and having an opening portion exposing a portion of the pad structure from the solder-resist layer. The opening portion of the solder-resist layer has a bottom surface such that the bottom surface of the opening portion is exposing an upper surface and a portion of a side surface of the pad structure.