Circuit substrate and method for manufacturing the same

A circuit substrate, comprising:

• a core substrate having a cavity formed such that the cavity is penetrating through the core substrate;
• a metal block accommodated in the cavity of the core substrate;
• a first build-up layer laminated on a first side of the core substrate and comprising a plurality of insulating resin layers such that the first build-up layer is covering a first surface of the metal block in the cavity of the core substrate from the first side;
• and
• a second build-up layer laminated on a second side of the core substrate on an opposite side with respect to the first side and comprising a plurality of insulating resin layers such that the second build-up layer is covering a second surface of the metal block in the cavity of the core substrate from the second side,
• wherein the first build-up layer comprises an electronic component mounting structure formed on an outermost portion of the first build-up layer such that the electronic component mounting structure mounts an electronic component on the first build-up layer, and the metal block is formed such that the first and second surfaces of the metal block comprise roughened surfaces, respectively, and that the roughened surface of the first surface has a surface roughness which is different from a surface roughness of the roughened surface of the second surface.