| 摘要 |
PROBLEM TO BE SOLVED: To restrain expansion of an insulating layer on the periphery of a through hole which is to be caused by thermal stress acting on a board, by forming discontinuous slits having a specified width, on the periphery of a through hole formation part of a first circuit pattern, at a specified distance from the through hole, and making a part of an insulator coating layer permeate into the slit. SOLUTION: Conducting layers 2, 2 turning to inner layer circuit patterns are compression-bonded and formed on both surfaces of an insulating board 1. Resist films are formed on the conducting layers 2, 2, exposed and developed, and an inner layer circuit pattern 2a is formed. At that time, a plurality of discontinuous slits 10 are previously formed on the periphery of a part of the inner layer circuit pattern 2a on which a through hole 5 is to be formed. The slits 10 are uniformly isolated about 100-200μm apart from the through hole 5, and the width is preferably 100-250μm. Therefore, in a process wherein a resin based insulating layer 4 is spread and formed, a part of the insulating layer permeates into the slits 10, and walls are formed by mutual adhesion of the insulating board 1 and the insulating layers 4 in the slits 10. |
