| 摘要 |
In order to realize through hole conduction of an internal layer wiring pattern 4 and respective external layer conduction layers 2 and 5 on both sides, a through hole partially blocked is formed to the internal layer wiring pattern 4 from one external layer conduction layer 2 by laser means. Similarly, another through hole which is partially blocked and displaced from the former hole within an allowable range is formed to the internal layer wiring pattern 4 from the other external layer conduction layer 5 by the laser means, thereby forming a stepped through hole 6. At last, a through hole coating layer 7 is formed.
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