PURPOSE: To contrive large cost down by applying copper paste to copper bumps, mounting the copper bumps on copper patterns, and bonding the copper bumps to the copper patterns by heat treatment in an unoxidizing gas atmosphere.

CONSTITUTION: Copper paste 4 is applied to the lower faces of copper bumps 3 with a dipper. Copper patterns 6 are formed on the upper face of a substrate 5. Because the copper paste 4 and the copper patterns 6 are made of the same material and bonded well, the patterns 6 are not plated with gold. A flip chip P is held by a nozzle 7 and the copper bumps 3 are mounted on the copper patterns 6. The substrate 5 is sent to a reflow apparatus and heat-treated to thermally harden the copper paste 4 and bond the copper bumps 3 to the copper patterns 6. This treatment is performed in a reducing or unoxidizing gas atmosphere because copper is oxidized and liable to deteriorate when heated.