A circuit board includes a flexible board, a composite film, and a copper layer. The composite film is formed on the flexible board and defines at least one through hole. The composite film includes a base layer having an active surface, and a conductive layer formed by coated a conductive polymer on the active surface. The conductive polymer is made by a mixture comprising liquid crystal monomers, a silver complex, an initiator, and a catalytic agent, and a solvent, the mixture is heated to undergo atom transfer radical polymerization. The copper layer covers the conductive layer and an inner wall of each of the at least one through hole. The copper layer is electrically connected to the flexible substrate by the through hole.