Abstract: There is disclosed a fabrication method comprising: stacking and forming an Ni bond layer 3 and oxidation preventive layer 4 on a Cu interconnection layer 2 formed on the surface of a BGA package 1 in an electroless plating process; and applying a flux 5 to coat the oxidation preventive layer 4. Moreover, the method comprises: laying a Cu-added solder ball bump 6 onto the oxidation preventive layer 4; and performing a heat treatment in a temperature range of 190° C. to 220° C. to melt/bond the bump into the Ni bond layer 3. Sn and Cu in the Cu-added solder ball bump 6 rapidly react with Ni in the Ni bond layer 3 to form a diffusion inhibitive alloy layer 7. Subsequently, an electrode pad 10 on a mother board 9 which is a interconnection substrate is molten/bonded into the Cu-added solder ball bump 6, and a semiconductor device 8 is mounted on a mother board 9.