A method of forming the conductor portion 22 is not particularly limited, and the conductor portion 22 may be formed a well-known method. In that case, the vias 225 may be formed after forming the upper conductor portions 221 and the lower conductor portions 223. Alternatively, the upper conductor portions 221 and the lower conductor portions 223 may be formed after forming the vias 225. The forming of the vias 225 may be carried out independently of both of the forming of the upper conductor portions 221 and the forming of the lower conductor portions 223. Alternatively, the forming of the vias 225 may be simultaneously carried out with one of or both of the forming of the upper conductor portions 221 and the forming of the lower conductor portions 223.

Referring to FIG. 11, in the circuit board 20 after forming the conductor portion, the vias 225 are formed in an area where they can pass through the cavity 121. In detail, in the area where the vias 225 can pass through the cavity 121, the vias 225 are formed to pierce the first substrate member 12 (see FIG. 10) and the second substrate member 16.