To improve the wettability of a member to solder, whose wettability to the solder is comparatively inferior, to enable us to perform strong soldering, and to improve reliability on connection.

In an execution form to mount a LSI element on a printed circuit board 11, on a predetermined soldering part 9 at the tip of the lead pin 4 of the LSI element, a groove 5 is provided, which has the action of a capillary phenomenon. The soldering part 9 having this groove 5 is aligned on the land 12 of the printed circuit board 11, and in the soldering part 9 having the groove 5, a soldering process by melted solder is carried out. By this soldering process, the melted solder spreads itself into the inner wall surface of the groove 5 by the action of the capillary phenomenon, and gets wet. This wet area diffuses, a strongly soldered layer 10 is formed in a desired area by a temperature-decreasing process, and soldering is performed.