PURPOSE: To greatly improve adhesive properties, moisture resistance of a mold while obtaining flatness of a heat sink by providing protrusions on the sink by shearing and compressing.

CONSTITUTION: A shape-punched heat sink 2 is sheared partly at the periphery to its intermediate in a thickness direction by using a shearing punch l and a die 3 to form a protrusion 2a. Then, the sink 2 having the protrusion 2a is applied by a compression force to the protrusion 2a by a collapsing punch 4 and a collapsing die 5 to collapse the end 2b. The protrusion 2a collapsed at the end 2b is easily formed to hold flatness of the sink 2. Thus, die bondability is improved, flow of the mold to the rear surface of the sink 2 at the time of resin molding can be prevented. Since the shape of the protrusion to be formed at the sink 2 is complicated, the adhesive properties, moisture resistance of the mold can be improved.