A material of each of the insulating layers 211a, 211b, and 211c is not particularly limited. For example, an insulating material may be used as the material of each of the insulating layers 211a, 211b, and 211c. In this case, the insulating material may be a thermosetting resin such as an epoxy resin, a thermoplastic resin such as a polyimide resin, a resin in which the thermosetting resin or the thermoplastic resin is mixed with an inorganic filler or is impregnated together with an inorganic filler in a core material such as a glass fiber (or a glass cloth or a glass fabric), for example, prepreg, ABF, FR-4, BT, or the like. Alternatively, a PID resin may also be used as the insulating material.