| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for forming a fine through hole at a circuit board where a fine through hole of high quality, with no bur and the like, is formed to allow a fine circuit wiring. SOLUTION: A material comprising a conductive layer is prepared on both surfaces of an insulating base layer 1. One conductive layer is worked to form a prescribed circuit pattern 2 which is to be a conformal mask, and an exposed part of the insulating base layer 1 is removed to form a fine via hole 4. Both the circuit pattern 2 and the conductive layer 3 are etched so that a through hole 5 is formed at the fine via hole 4, and then a through hole plating is processed.
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