In the wiring board (package) 20, reference numeral 21 denotes an insulating base material (e.g., a glass cloth immersed in thermosetting resin, such as epoxy resin or polyimide resin) as a core substrate of this package; reference numeral 22 denotes a copper foil attached to each surface of the core substrate 21; reference numeral 23 denotes a plated layer of metal (e.g. copper (Cu)) formed on th