Plating method of circuit substrate, production method of plated circuit substrate, and silver etching liquid

Provided is a plating method of a circuit substrate comprising a conductive pattern in which a metal layer containing at least silver and copper is exposed on an outer surface. The plating method comprises: step (A) of treating the circuit substrate with a first liquid agent containing an oxidizing agent; step (B) of treating the circuit substrate after the step (A) with a second liquid agent which dissolves copper oxide, and thereby removing copper oxide from the conductive pattern's surface; step (C) of treating the circuit substrate after the step (B) with a third liquid agent whose rate of dissolving silver oxide (I) at 25° C. is 1000 times or more faster than its rate of dissolving copper (0) at 25° C., and thereby removing silver oxide from the conductive pattern's surface; and step (D) of performing electroless plating on the conductive pattern of the circuit substrate after the step (C).