Circuit substrate and method for manufacturing the same

A method for manufacturing a circuit substrate comprising an insulation substrate formed with a plurality of via holes passing through a first main surface and a second main surface, and a metal with which the plurality of via holes are filled, the first main surface and the second main surface being opposing main surfaces, the method comprising:

• forming, in the insulation substrate, a via hole having openings on the first main surface and the second main surface or a non-through hole having an opening only on the second main surface;
• filling the via hole or the non-through hole with the metal;
• polishing the metal exposed on at least one of the first main surface and the second main surface to lower a polished surface of the metal in the insulation substrate and to form a step between the polished surface of the metal and the at least one of the first main surface and the second main surface;
• coating the polished surface of the metal by plating;
• and
• polishing the first main surface and the second main surface to provide a via hole of the plurality of via holes that passes through the first main surface and the second main surface.