Method of manufacturing composite circuit board

A method of manufacturing a composite circuit board, the method comprising:

• providing a composite circuit board unit comprising a first adhesive material layer, a first circuit layer located on one side of the first adhesive material layer, and a second circuit layer located on another side of the first adhesive material layer, the first circuit layer comprising a first inner conductive circuit and a first outer conductive circuit located at both ends of the first inner conductive circuit, and the second circuit layer comprising a second inner conductive circuit and a second outer conductive circuit located at both ends of the second inner conductive circuit;
• forming a first metal protection layer on a surface of the first inner conductive circuit, and forming a second metal protection layer on a surface of the second inner conductive circuit;
• forming a first solder mask and a second solder mask respectively on a portion of a surface of the first metal protection layer and a portion of a surface of the second metal protection layer, the first solder mask defining a first opening revealing a portion of the first metal protective layer, the second solder mask defining a second opening revealing a portion of the second metal protective layer;
• providing two second adhesive material layers, each of the two second adhesive material layers defining a third opening, a size of the third opening being smaller than a size of the first solder mask layer or the second solder mask layer, the two second adhesive material layers respectively provided on a surface of the first inner conductive circuit and a surface of the second inner conductive circuit;
• folding back the first outer conductive circuit at two ends so that the first outer conductive circuit at the two ends faces the first inner conductive circuit and is laminated on the second adhesive material layer, the two ends spaced a predetermined distance apart to form a first window, wherein the first window, the third opening in one of the second adhesive material layers, and the first opening of the first solder mask communicate with each other;
• folding back the second outer conductive circuit at two ends so that the second outer conductive circuit at the two ends faces the second inner conductive circuit and is laminated on the second adhesive material layer, the two ends spaced a predetermined distance apart to form a second window, wherein the second window, the third opening in the other one of the second adhesive material layers, and the second opening of the second solder mask communicate with each other.