| 摘要 |
A lower sub-board of a circuit board includes a first base layer having an upper surface, and a first wiring pattern provided on the upper surface of the first base layer. An upper sub-board of a circuit board includes a second base layer having a lower surface, and a second wiring pattern provided on the lower surface of the second base layer. A connection layer between lower and upper sub-boards includes an insulating layer having a lower surface and an upper surface, the lower surface of connection layer being situated on the upper surface of the first base layer, the upper surface of connection layer being situated on the lower surface of the second base layer, and a via-conductor passing through the insulating layer and connected to the first and second wiring patterns. This circuit board connects the sub-boards to each other via a via-conductor densely.
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