Conductive paste containing tin particles and silver particles is packed in a substantially cylindrical via hole formed in a thermoplastic resin film that interposes between conductor patterns and is hot-pressed from both sides. When the metal particles contained in the conductive paste are sintered to form a unified conductive compound, the volume of the conductive paste shrinks. Synchronously, the resin film around the via-hole protrudes into the via-hole. Therefore, the shape of the side wall on the cross-section of the conductive compound provides an arch shape, and a side wall adjacent to a junction part of the conductive compound, which contacts the conductor pattern, is formed with an inclination. Therefore, it is possible to prevent the stress concentration due to deformation of the board.