PURPOSE: To prevent generation of voids, blow-holes which occur in the case of soldering by forming a groove extended radially from a through hole or a blind viahole on a circuit board at a land provided around the hole.

CONSTITUTION: A circuit board 11 has a through hole 4 or a blind viahole formed thereat. At least one or more grooves extended radially from the hole 4 is provided at a land 16 formed at a periphery of the hole 4 or the viahole of the board 11 so that a surface of the board 11 is exposed in a bottom of the groove 17. Since the board surface exposed in the bottom of the groove 17 provided at the land 16 is not moistened with melted solder, the groove 17 is not blocked. Thus, the groove 17 forms a venting route of gas. As a result, gas generated in the solder melted in the hole is vented out of the hole not only from above the hole but also via the groove 17. Accordingly, generation of voids, blow-holes in the melted solder can be prevented.