Abstract: A metal structure (100) for a contact pad of a semiconductor device, which has interconnecting traces of a first copper layer (102). The substrate is protected by an insulating overcoat (104). In the structure, the first copper layer of first thickness and first crystallite size is selectively exposed by a window (110) in the insulating overcoat. A layer of second copper (105) of second thickness covers conformally the exposed first copper layer. The second layer is deposited by an electroless process and consists of a transition zone, adjoining the first layer and having copper crystallites of a second size, and a main zone having crystallites of the first size. The second thickness is selected so that the distance a void from the second layer can migrate during the life expectancy of the structure is smaller than the combined thicknesses of the first and second layers. A layer of nickel (106) is on the second copper layer, and a layer of noble metal (107) is on the nickel layer.