US Patent 7851707 Circuit board and method for manufacturing the same

A circuit board for reducing a transmission loss and a method for manufacturing the circuit board. In the circuit board including a ground layer and power layer facing each other, a wiring layer disposed between the ground layer and the power layer, and an insulating section formed between the ground layer and the power layer so as to sandwich the wiring layer therebetween, a low dielectric loss layer having a dielectric tangent lower than that of the insulating section is formed at least on an upper or lower surface of the wiring layer. According to such a circuit board, the low dielectric loss layer is formed on an interface between the insulating section and the wiring layer, and therefore, a transmission loss in a high frequency region is reduced.