the improved plastic - metal unitary composite of the invention formed by the present method , includes a thin copper foil , for example , weighing about 1 or 2 ounces per square foot , one side of which has a rough irregular surface with improved bondability to plastic but increased propensity for staining , a thin layer of metal selected from cr , al , cd or a cd alloy of sn , zn or cu , or a mixture thereof , encapsulating the rough surface so as to decrease its staining characteristic without substantially descreasing its bondability , and a plastic substrate bonded to the encapsulating layer . the rough irregular surface of the foil includes a plurality of discrete particles of copper and / or copper oxide adherent to the copper foil but detachable therefrom and embeddable in the plastic . however , the encapsulating metal layer , substantially reduces such detachment and embedding and thus substantially reduces , as noted above , undesirable staining which commonly occurs during utilization of such composites in the manufacture of such items as printed circuit boards and the like . these advantages are achieved while reducing the tendency of fine lines of copper conductor made therefrom on the circuit boards to lift from the substrate . processing of the boards is facilitated , since standard etching solutions can be employed .