Cu–Sn coatings obtained from pyrophosphate-based electrolytes

The mechanism of Cu–Sn nucleation and electrodeposition was studied by cyclic voltammetry, chronoamperometry, scanning electron microscopy and energy dispersive X-rays. Cu–Sn alloys were deposited and dissolved in the solution containing metallic ions and in a 0.3 mol dm− 3 Na4P2O7 + 2.3 mol dm− 3 HCl solution. Voltammetric results displayed two anodic peaks for copper, only one oxidation peak for tin and, for Cu–Sn alloys, the results were similar to those obtained for copper, with two peaks. The sweep rate dependence found from the voltammograms for the three systems reduction processes was diffusion controlled. ALSV profiles showed different oxidation peaks for dissolution of the deposits, depending on the conditions of electrodeposition. For alloys, the oxidation of peaks obtained at different final potentials of potentiodynamic deposition showed two clear peaks. The peaks do not coincide with peak potential for the dissolutions of pure copper and tin: their maxima moved significantly towards negative potentials. The non-dimensional analyses of the potentiostatic transients for the copper, tin and Cu–Sn alloys suggest an instantaneous nucleation. The chemical and physical characterization of the electrodeposits showed dependence between the surface morphology and the composition of the electrolytic bath. Besides, EDX analyses showed that the composition of the electrodeposits always corresponds to the chemical composition of the electrolytic bath. In this way, it was possible to classify these processes as regular deposition. In addition, islands of only copper or tin were not detected, which suggests that the alloy was a solid solution.