US Patent 7759583 Circuit board

A circuit board, having improved adhesion between its via conductor and insulating layer, is provided. The circuit board includes a first wiring layer, a second wiring layer, the insulating layer, a filler, and the via conductor. The first wiring layer and the second wiring layer are electrically insulated from each other by the insulating layer. The filler which has a favorable thermal conductivity is added into the insulating layer. The via conductor establishing electrical connection between the first wiring layer and the second wiring layer is formed in a predetermined position of the insulating layer. The via conductor is in direct contact with part of the filler added into the insulating layer.