A method of forming a circuit board includes forming a conductive pattern on a substrate; forming a first negative resist on the substrate after formation of the conductive pattern; partially exposing the first negative resist on the surface of the conductive pattern to form a first via exposure portion; forming a second negative resist on the substrate after formation of the first via exposure portion; partially exposing the second negative resist on the first via exposure portion to form a second via exposure portion larger than the first via exposure portion; developing the first negative resist and the second negative resist after formation of the second via exposure portion to form a via opening reaching the conductive pattern; and filling the via opening with a conductive material.