Patent ID: 7139176

Claim:
A circuit substrate comprising: a substrate having a first through-hole formed therein; a reinforcing film of an organic resin formed only on the surface of at least one side of the substrate, covering the opening of the first through-hole and exposed to the cavity inside the first through-hole, the reinforcing film having a second through-hole formed therein with a diameter wider than the first through-hole and a third through-hole formed in a part of the reinforcing film which covers the opening of the first through-hole; an element formed on the underside of the substrate; and a conducting film formed continuously on the inside wall of the first through-hole and on the surface of the substrate below the reinforcing film, and exposed in the cavity inside the first through-hole and in the bottom of the second through-hole, for electrically connecting the element from the first through-hole to the second through hole.