Disclosed is a structure of a flexible circuit board combined with a carrier board. The carrier board includes a thick copper layer, a thin copper layer, and a release layer formed between the thick copper layer and the thin copper layer. The flexible circuit substrate and the carrier board are bonded together by an adhesive layer. In a subsequent process, the release layer, together with the thick copper layer, is peeled from a top surface of the thin copper layer and the thin copper layer is preserved by being bonded by the adhesive layer to the flexible circuit substrate.