An electronic component is mounted on a surface layer of a multilayer substrate constituting a wiring substrate, and a signal wire of the surface layer is electrically connected to the electronic component. A conductor pad for contact with an inspection probe is composed of a via and a solder filled in an internal opening portion thereof. The via has a laser-processed taper-shaped hole with a metal-plated inner peripheral surface and connects the inter-layer connection between the signal wire of the surface layer and a signal wire of the inner layer. The solder is filled in the opening portion of the via by filling, heating and melting solder material therein. Since the peripheral edge portion is solidified first at the time of the cooling and the solidification, the middle part is recessed compared to the peripheral edge portion. This ensures a reliable contact of the inspection probe.