| 摘要 |
<p>PROBLEM TO BE SOLVED: To greatly decrease the occurrence rate of a mounting defect since a ball can be prevented from falling. SOLUTION: Denoting the diameter of the solder ball 20 as A and the diameter of a through hole 18 as B, A/B<1.25 holds, so the force of the solder ball 20 to become spherical never becomes larger than the bonding force between the solder ball 20 and a wiring pattern 16. The relation A/B<1.25 is found by an experiment by the inventor as a condition that the ball never falls.</p> |
