A signal transmission board includes a substrate, a conductive via, a cavity and a connecting hole. The substrate has a first external surface and a second external surface. The conductive via penetrating through the substrate has a first end and a second end. The first end is disposed on the first external surface, and the second end is disposed on the second external surface. The cavity is disposed in the substrate and penetrated by the conductive via. The connecting hole disposed on the substrate has a third end and a fourth end. The third end is disposed on the first external surface, and the fourth end communicates with the cavity.