PURPOSE: To increase the reliability of calking and to prevent poor calking and to improve workability by a method wherein the dimension of the recessed section of the rear side at a calking projected section formed at a heat sink is formed larger than the projected section and the height dimension of the projected section is simultaneously heightened.

CONSTITUTION: A projected section 5 and a recessed section 7A are formed at the surface and rear of the calking level of a heat sink 1 respectively. The recessed section 7A is of tapered form making the diameter dimension d3 of the inlet larger than the diameter dimension d4 of the bottom section and furthermore, d4 is made bigger than the diameter dimension d2 of the projected section 5. In this way, the height dimension of the projected section can be formed smaller than the dimension of the recessed section 7A without changing heat sink thickness. And the projected section sufficiently projects from a hole 6 perforated at a lead 3 and covers as far as the circumference of the hole 6 when the projected section is calked and deformed with a punch 11. In this way, strong and positive calking is achieved.