A power module substrate or the like including an insulating substrate with an upper surface and a lower surface, a metal plate with an upper surface and a lower surface, the lower surface facing and being bonded to the upper surface of the insulating substrate, and a first electroplating layer that partly covers the central portion of the upper surface of the metal plate. The first electroplating layer includes at least a silver layer, and the grain size of silver in the silver layer is more than or equal to the grain size of a metal in an upper surface portion of the metal plate.