A novel electrochemical plating process for depositing gold and silver surface finishes using environmentally benign, organic-based solutions as the plating bath is being investigated. The plating bath solution consists of an extractant and a diluent of the types used in conventional organic solvent extraction. The organics are very poor electrolytic conductors and can sustain only short range electrochemical reactions. The deposition mechanism involves the dissolution of a less noble substrate metal with the simultaneous deposition of more noble metal particles on the surface of the substrate, similar to immersion plating in an aqueous solution. Feasibility of the concept was demonstrated by loading the organic extractants with gold or silver in the form of complexed ions. The metal bearing organic liquid was then placed in contact with blank or patterned copper and nickel surfaces commonly used in the printed circuit board industry. Deposition of a continuous, adherent gold and silver surface finishes from the organic liquid was achieved with the proper processing conditions. Gold and silver films were deposited only on the exposed metallic surfaces of the substrate, indicative of a selective area deposition process similar to immersion plating. Scanning electron microscopy (SEM) indicated that the films were composed of nanometer sized particles.
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