A warpage preventing substrate is provided. A plurality of first and second conductive traces are respectively formed on a first surface and a second surface of a core layer of the substrate, each conductive trace having a terminal, and a plurality of first and second non-functional traces are respectively formed on the first and second surfaces of the core layer at area free of the conductive traces. The first non-functional traces are arranged in different density from the second non-functional traces in a manner that, stress generated from the first conductive traces and first non-functional traces counteracts stress generated from the second conductive traces and second non-functional traces, to thereby prevent warpage of the substrate and maintain flatness of the substrate.