| 摘要 |
PROBLEM TO BE SOLVED: To manufacture a built-up printed board having a high wiring density, by providing a coaxial via hole which connects at least three layers of circuit patterns. SOLUTION: The case of having three layers on one side is explained. First, copper toils 12 are adhered on the both planes of an insulating board and a copper laminated board 10 whereupon a first pattern is formed is prepared. From the copper laminated board 10, a laminate body 42 is obtained. Then, a second insulating layer 44 is formed on the surface of the laminate body 42, and a laminate body 48 having the three layers on one side is obtained. A small opening 52a for a via hole which penetrates the second conducting layer 46, the insulating layer 44 and a first conducting layer 38 and reaches the middle of the first insulating layer 30 is formed. Then, the small opening 52a is irradiated with laser beams. As a result, under the small opening 52a, the lower copper foil 12 appears at the bottom of a small hole 52b provided for a via hole. After conductivity is given to the surface of the small hole 52b that includes the inner plane, electrolytic plating is performed and a third conducting layer 54 is formed. The third conducting layer 54 formed on the inner plane of the small hole 52b becomes a via hole 52. |
