A circuit board includes a pad, a transmitting trace and a plating bar. The plating bar is used for forming an electroplating metallic layer on the pad, the pad and the transmitting trace are used for the signal transmission. Due to the plating bar causes a noise during the signal transmission, a dielectric layer having at least one opening is adjacent to at least one side of the plating bar to reduce the equivalent dielectric permittivity thereof and to maintain signal transmitting quality.