Corrosion resistance enhancing electroplating process, and plated article

To simplify manufacture of plated metal parts with high corrosive resistance, especially suitable for use as sealing lids or cover elements for semiconductor packages, a substrate (12) of Kovar, or Alloy 42, which are nickel-containing iron alloys, are electroplated with a base layer (14) of a metal having an electromotive potential high with respect to that of the substrate, over which an intermediate layer is electroplated. The intermediate layer (16) has an electromotive potential which is low with respect to the base layer; and over that a cover layer (18) is plated which has an electromotive potential similar to that of the base layer. A difference of about 1.2 volts of electromotive potential between the intermediate layer (16) with respect to the base layer (14) and the cover layer (18) is desirable. Suitable metals are gold-nickel-gold combinations, in which the gold layers should be over 10 microinches (0.25 micrometer) thick, preferably and in order to meet MIL-STD 883C, about 25 to 50 microinches (0.64 to 1 .27 micrometers) thick. The intermediate nickel layer (16), and preferably about 150 microinches (3.82 micrometers) thick, has an electromotive potential which is at the negative side of the electromotive series. Pin holes through the three layers may cause, under the influence of a corrosive atmosphere, migration of ions up to the base layer but, due to the arrangement of electromotive potential of the intermediate layer (16) and the cover layer (18), will not extend further so that the corroded substrate material will, effectively, form a plug for the pin hole and prevent progression of corrosion.