The plating and surface finishing of printed circuit boards face new demands with the use of new assembly and interconnection technologies and the miniaturization of structures. Gold layers gain increasing importance as a versatile surface finish for soldering, wire and adhesive bonding. Certain structural units of the conductive pattern such as bond pads or connectors must be plated selectively. To achieve suitable surface properties and selective plating, autocatalytic electroless deposition must be used. The key components of an autocatalytic plating bath are a complexing agent and a reducer. While the complexer keeps the cations of the plating metal in solution, they are reduced only at a catalytically active surface by the reducing agent and deposited there. If the deposited metal itself acts as a catalyst for further deposition, the reaction is autocatalytic. With autocatalytic plating, high-grade layers of any thickness can be deposited that meet the requirements of gold wire bonding applications.
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