PURPOSE: To form a copper film having excellent mechanical properties by forming a silver rich layer contg. silver at the higher ratio than in the other parts in the mid-way of electroless copper plating.

CONSTITUTION: A silver compd. is intermittently added to the plating liquid under electroless copper plating to form at least one silver rich layer contg. the silver at the ratio higher than in the other parts. The preferred embodiment is to intermittently add 0.001W10g sodium iodide and 0.001W10g (initial concn.) silver chelate compd. of ethylenediaminetetraacetic acid to the plating liquid contg. 1W50g pentahydrate of copper sulfate, 5W200g tetrasodium salt of the ethylenediaminetetraacetic acid, 1W30ml formalin (aq. 37wt% soln. of HCHO), 1W100ml, α,α'-dipyridyl and 1W100g polyethyleve glycol and to execute plating under the conditions of 60W85°C liquid temp., 11.0W13.0pH value, 1W18 specific gravity (Baume), constant stirring by air blowing and 1W5μ/hr plating rate.