A process for fabricating process a circuit substrate having a base layer, a first patterned conductive layer, a dielectric layer, a conductive block and a second patterned conductive layer. The first patterned conductive layer is disposed on the base layer and has a first pad. The dielectric layer is disposed on the base layer and covers the first patterned conductive layer, wherein the dielectric layer has an opening and the first pad is exposed by the opening. The conductive block is disposed in the opening and covers the first pad. The second patterned conductive layer is disposed on a surface of the dielectric layer and has a second pad, wherein the second pad and the conductive block are integrally formed.