Effect of Bath Composition on the Composition and Morphology of Electrodeposited Ag-Cu Alloys

One of the common brazing alloys, Cusil^TM, has eutectic composition of 72 % silver and 28 % copper. The electrochemical codeposition of Ag and Cu is difficult due to the large difference between the standard reduction potentials of silver (0.799 V) and copper (0.337 V). A complex ion bath containing KAg(CN)₂, CuCN, KCN and K₄P₂O₇ was used to overcome this difficulty and bring the reduction potentials closer to each other.

The effects of KAg(CN)₂, KCN and K₄P₂O₇ concentrations on the composition and microstructure of electrodeposited Ag-Cu films was investigated in this study. The effect of K₄P₂O₇ addition to the electrolyte was examined in a set of experiments by employing a three-level full-factorial statistical design. The concentrations of bath ingredients: KCN, KAg(CN)₂ and K₄P₂O₇ were the factors that were investigated. The levels of the design were chosen at the minimum, mean and maximum amounts of the three factors. Therefore, (3³) 27 experiments were designed to investigate the effects of changes in bath concentration on composition and morphology of deposits. All the other plating parameters were fixed during the experiments.

The increase in K₄P₂O₇ concentration caused a minor decrease in Ag content of the film where the increase in KCN and KAg(CN)₂ concentrations caused major increases in Ag contents. The microstructures of deposits were found to be globular clusters when high KAg(CN)₂ concentrations were used. K₄P₂O₇ addition to the electrolyte suppressed cluster formation and produced more compact microstructures. Increasing the KCN concentration resulted in deposits having finer microstructures and higher Ag contents.