PURPOSE: To improve adhesive properties of a conductor film with the inner surface of a drilling hole by adhering silane coupling agent to the plasma-etched surface of the hole.

CONSTITUTION: Silane coupling agent is adhered to the plasma-etched surface of a circuit board formed by removing smear-resin in a drilling hole by plasma etching after a hole is drilled. As the agent those having high heat resistance and water resistance of epoxy silane, amino silane, cationic silane, styrene silane, phenyl silane, acryl silane are selected to match the resin of the board. Accordingly, catalyst for plating or plating precipitate is uniformly and sufficiently adhered via the agent. Thus, the adhesive properties of the conductor film formed on the inner surface of the drilled hole is improved in this manner.