Patent ID: 8766106

Claim:
A double-sided circuit board comprising: a substrate layer having a first surface and a second surface on an opposite side of the first surface and having a penetrating hole extending between the first surface and the second surface; a first conductive circuit formed on the first surface of the substrate layer; a second conductive circuit formed on the second surface of the substrate layer; and a through-hole conductor formed in the penetrating hole of the substrate layer and electrically connecting the first conductive circuit and the second conductive circuit, wherein the penetrating hole comprises a first hole having a first opening with a diameter R 1 on the first surface of the substrate layer such that a portion of the through-hole conductor in the first hole is connected to the first conductive circuit, a second hole having a second opening with a diameter R 2 on the second surface of the substrate layer such that a portion of the through-hole conductor formed in the second hole is connected to the second conductive circuit, and a third hole connecting the first hole and the second hole, having a diameter smaller than at least one of R 1 and R 2 and tapering from the first surface of the substrate layer toward the second surface.