Abstract: End-face through holes each comprising a concave-curved end-face opening groove and an end-face electrode covering the inner wall of the groove are formed in the end-faces of a substrate. Furthermore, a solder having a semi-circular shape is attached to the end-face electrode. The solder comprises an electrode facing portion facing the end-face electrode in the end-face groove, and a protuberant portion elongated from the electrode facing portion to protrude on the back-surface side of the substrate. Thereby, even if the substrate or the like is warped, a gap between the end-face electrode and the electrode pad of a mother board can be filled with the protuberant portion of the solder to connect the end-face electrode and the electrode pad to each other.