| 摘要 |
A through hole is formed in a printed board. Conductor patterns are formed on an upper face and a lower face of the printed board in such a manner that the conductor patterns are electrically connected to each other, by means of a through hole solder. A lead terminal of an electronic component is inserted into the through hole and soldered with a lead free solder. According to this invention, an area of an opening of the through hole is set to be four times or more as large as a cross sectional area of the lead terminal. In this manner, heat conduction on occasion of soldering can be enhanced, and the soldering can be favorably performed, even when the lead free solder having a high melting point is used.
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