PURPOSE: To make an automated soldering process easy by a method wherein narrow copper foil parts are provided in a pair of copper foil patterns and heat transmission speeds in both the copper foil patterns are made to be approximately equal to each other.

CONSTITUTION: The area (s) of a copper foil 2a-1 and the area (s') of a copper foil 2b-1 have a relation: s=0.9-1.1s'. The area (v) of a copper foil 2a-3 and the area (v') of a copper foil v' have a relation: v=0.9-1.1v'. The width (u) of a copper foil 2a-2 and the width (r) of a copper foil 2a-1 have a relation: u=0.2-0.8r. The width (u') of a copper foil 2b-2 and the width (r') of a copper foil 2b-1 have a relation: u'=0.2-0.8r'. The thickness of the copper foil patterns 2a and 2b of copper foil parts are same. If the above mentioned conditions are satisfied, a heat transmission speed from the copper foil 2a-1 to the copper foil 2a-2 and a heat transmission speed from the copper foil 2b-1 to the copper foil 2b-2 are approximately equal to each other. A heat transmission speed from a copper foil 2a-3 to the copper foil 2a-2 and a heat transmission speed from a copper foil 2b-3 to the copper foil 2b-2 are also approximately equal to each other.