An electronic device includes an insulating layer, a metal layer and at least one electrical connecting element. The insulating layer has a top surface and a bottom surface opposite to the top surface, and defines an opening extending between the top surface and the bottom surface. The metal layer is disposed in the opening of the insulating layer and has a top surface and a bottom surface opposite to the top surface. The bottom surface of the metal layer is substantially coplanar with the bottom surface of the insulating layer. The electrical connecting element is attached to the bottom surface of the metal layer through a seed layer.