A first board includes a first insulating substrate including a first main surface, a first electrode pad, and a first resist film. The first electrode pad is a conductor pattern provided on the first main surface. The first resist film is provided on the first main surface and is located closer to the first electrode pad than any conductor provided on the first main surface. The first resist film is spaced away from the first electrode pad with a gap provided between the first resist film and the first electrode pad. The first resist film is thicker than the first electrode pad.