This product is a result of the developing of more and more complicated circuits. It can be made by pressing solder coating to both sides of a double-sided copper-clad panel. Circuits in both sides are connected through the holes in the panel. However, in actual processing, there are various technologies, such as the technology of multiple levels in double sides -- in areas which would bend frequently; we treat it level by level, so that the double-sided circuits in this area become two separate single-sided circuits. In this way, the flexible nature is strengthened. These technologies are mostly applied in products like mobiles phoness, digital cameras, etc.