In addition, the first insulating layer 110 may be a flexible board having flexible characteristics.

In addition, the first insulating layer 110 may be a curved or bent board. At this time, in the first insulating layer 110, electrical wiring connecting circuit components are represented by a wiring figure based on circuit design and an electrical conductor may be formed on an insulating material. In addition, electrical components may be mounted, wiring for connecting the electrical components may be formed, and components other than the components having electrical connection functions may be mechanically fixed.

The first metal layer 115 may not be formed on the surface of the first insulating layer 110 by electroless plating but may be formed using general copper clad laminate (CCL).

At this time, when the first metal layer 115 is formed by electroless plating, plating may be smoothly performed by providing illumination to the upper surface of the first insulating layer 110.

The electroless plating method can be performed in the following order: a degreasing process, a soft corrosion process, a pre-catalyst treatment process, a catalyst treatment process, an activation process, an electroless plating process and an oxidation prevention process. In addition, the first metal layer 115 may be formed by sputtering metal particles using plasma instead of plating.

At this time, before plating the first metal layer 115, a desmear process of removing smear from the surface of the first insulating layer 110 may be further performed. The desmear process is performed to increase plating power for forming the first metal layer 115 by providing illumination to the surface of the first insulating layer 110.