i) step i of bringing a compound having a structure capable of coordinating to metal atoms or metal ions into contact with one or both sides of a resin base material formed from a curable resin composition containing an insulating resin and a curing agent, and removing an excess of said compound from the one or both sides of the resin base material after said contact of said compound with the one or both sides of the resin base material, wherein said compound is I) an organic compound having an amino group, a thiol group, a carboxyl group, or a cyano group, II) a heterocyclic compound having a nitrogen atom, an oxygen atom, or a sulfur atom, or III) an imidazole, a pyrazole, a triazole, or a triazine having an amino group, a thiol group, a carboxyl group, or a cyano group, wherein said compound is penetrated into the one or both sides of the resin base material, and wherein the excess of said compound is removed from the surface of said resin base material whereby no layer of said compound is formed on the one or both sides of the resin base material;

ii) step ii of curing said resin base material to form a cured resin base material, wherein the compound having a structure capable of coordinating to metal atoms or metal ions has penetrated into the cured resin base material and is held within the cured resin base material; and

iii) step iii of performing electroless plating or sputtering to form a metallic thin film on the surface of said cured resin base material.