| 摘要 |
PROBLEM TO BE SOLVED: To make it possible to reduce the total number of built-up layers by forming through holes with high density in a core board. SOLUTION: A main built-up layer 90A on the main face and a rear built-up layer 90B on the rear face are connected through a through hole 16 formed in a core board 30. The through hole 16 is filled with a filler 22, and a conductive layer 26a is formed in a way that the exposed face of the filler 22 from the though hole 16 is covered by the conductive layer 26a. An upper via hole 60 is connected to the conductive layer 26a. The conductive layer 26a is formed in a circular shape, and thereby the shape of a land of the through hole 16 is made circular. As a result, the through hole in the core board is formed with high density, and the number of built-up layers can be reduced. |
