Reducing material usage is essentially important to construct sustainable society . For this purpose FPC is important  as it is useful to reduce equipment size and numbers of interconnection components. It is also important to expand lifetime of equipment  with minimal replacement of obsolete components. Even though the material utility of FPC is higher than other printed circuit, reducing material in FPC is important. But it is difficult to simply reduce the thickness because the mechanical strength is damaged. We proposed a structure for this challenging task. The key technology is Proton Beam Writer (PBW) that uses accelerated proton to modify materials. By PBW we can create extra circuit space in surface layer of FPC with no extra film. As the thickness of surface layer is unchanged, the mechanical strength is not damaged. This technology also has possibility to create extra circuit space on FPC surface in use.