| 摘要 |
A circuit substrate includes a single-layer insulating substrate, a through-hole, and wiring conductors that are provided in both main surfaces of the single-layer insulating substrate. The through-hole includes first and second concave portions that are formed in both of the main surfaces of the single-layer insulating substrate, respectively, and a through-portion through which both of the concave portions communicate with each other. An opening area of a portion at which the first and second concave portions overlap each other is a half or less of an opening area of any large concave portion between both of the concave portions, and a metallic film is formed on the respective inner wall surfaces of the first and second concave portions, and the through-portion.
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