PURPOSE: To prevent peeling malfunction of a land due to heat generated in case of soldering by providing a through hole electrically connected to the land real the land.

CONSTITUTION: Through holes 5 of the same number as that of lands 4 are pattern-formed near the lands 4, and the lands 4 are electrically connected to the holes 5 near the lands through wirings 6. High heat of about 260°C is applied to the land 4 in case of soldering a lead 3 to the land 4. Part of the heat is transferred to the hole 5 through the wiring 6, and further dissipated to the rear face of a microcomputer board 1 via the hole 5. Thus, a thermal stress is not concentrated at a boundary between the land 4 and the body of the board 1. In this manner, peeling malfunction of the land due to heat generated in case of soldering is prevented.