Abstract: The present invention is directed to an improved method for treating an oxidized surface of a copper film for bonding to a resinous layer such as in the formation of a single-sided, double-sided, or multi-layered circuit board and to a layered product produced by the method. In particular, the method of the present invention comprises the steps of: contacting the oxidized surface of a copper film, having cupric oxide whiskers protruding therefrom, with an acidic reducing solution having a pH of 1 to 6.5 and having an effective amount of a water soluble thiosulfate reducing agent dissolved therein to provide a reduced copper surface; and rinsing the reduced copper surface with an acidic solution to produce a rinsed and reduced copper surface having reduced whiskers protruding therefrom, said reduced whiskers each being a mix of cuprous oxide and metallic copper. Preferably, the reduced surface is treated with a passivating agent to minimize any reoxidation prior to laminate formation.