Wiring substrate and multi-piece wiring substrate

A wiring substrate comprising:

• a substrate body formed of a plate-like ceramic, having a front surface and a back surface, and having a height between the front surface and the back surface of 0.8 mm or less;
• a cavity opening at the front surface of the substrate body;
• and
• side walls having a thickness of 0.3 mm or less between a side surface of the cavity and a side surface of the substrate body;
• the wiring substrate being characterized by further comprising:
• an electrically conductive layer having the form of a frame as viewed in plane and formed on the front surface of the substrate body in such a manner as to surround an opening of the cavity;
• a ceramic surface having the form of a frame as viewed in plane and located adjacently to the electrically conductive layer and along an outer periphery of the front surface of the substrate body;
• and
• a via conductor formed in the substrate body along the side surface of the cavity between a bottom surface of the cavity and the front surface such that a portion thereof is exposed at the side surface of the cavity and such that one end thereof is connected to the electrically conductive layer.