Patent ID: 8446736

Claim:
A circuit board comprising: an upper board having an opening bounded by side surfaces of the upper board and forming a circuit and an insulation coat film layer on a surface layer of the upper board, a lower board forming a circuit and an insulation coat film layer on a surface layer, a connection sheet being a separate sheet from the upper board and the lower board, the both upper board and the lower board being stacked up by way of the connection sheet inserted between the boards having an opening, and a cavity formed by the opening of the upper board and the opening of the connection sheet between layers, wherein the upper board and the lower board are made of cured resin impregnated in a base material, and the connection sheet between boards further includes an adhesion layer and a conductive hole for interlayer connection, the adhesion layer containing an inorganic filler and thermosetting resin, being cured in the thermosetting resin, the conductive hole being filled with a conductive paste, the insulation coat film layer of the upper board covers both a substantially entire region of an upper surface of the surface layer excluding an entire surface of the circuit, and the side surfaces of the upper board which bound the opening of the upper board.