Electrochemical Nucleation and Growth of Copper–Tin Alloys from Ammonia-Free Citrate-Based Electrolyte

The cyclic voltammetry and chronoamperometry methods are used in the present work for the purpose of investigating the electrodeposition mechanism of Cu–Sn alloys onto Pt and Mo substrates from a slightly acidic aqueous electrolyte (pH ≈ 4.2) containing CuCl2 and SnCl2 as metal sources, and tri-sodium citrate as a complexing agent. The structural properties of the deposits were characterized by means of the X-ray diffraction (XRD) technique, whereas the surface morphology and composition were examined using the field-emission scanning electron microscopy (FESEM) and energy-dispersive spectroscopy (EDS). The resulting crystalline films were mainly composed of Cu, Sn, and intermetallic Cu6Sn5 phases with spherical grains, at the early stages of nucleation, and a mixture of spherical grains and dendrites with hierarchical secondary branches after long electrolysis duration. The analysis of potentiostatic current transients, using the Scharifker–Hills model, showed that the electroplating of Cu–Sn alloy followed the instantaneous nucleation mode on platinum substrate and the progressive nucleation mode on the molybdenum substrate.