Effect of deposition potential on electrodeposition of Sn-Ag-Cu ternary alloy solderable coating in deep eutectic solvent

Ternary Sn-Ag-Cu solderable alloy coatings were electrodeposited using deep eutectic solvent-based electrolytes, at different deposition potentials. The obtained deposits have been characterized from surface morphology, composition, crystalline grain and phase via Scanning Electron Microscopy (SEM) associated with Energy Dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). To get information on the alloy melting point, Differential Scanning Calorimetry (DSC) has been involved.

The results showed that the crystalline grain became finer and the coating became denser as the deposition potential increased. In addition, the presence of Cu₆Sn₅ phase is facilitated by more cathodic deposition potentials while the Ag₃Sn phase was evidenced at lower potential values. The value of the melting point of Sn-Ag-Cu alloy (Sn90.9-Ag7.6-Cu1.5) deposited at potentials of −1.2 V was of 215.02 ℃. Based on the results obtained during the analysis of the current–time curves using the Scharifker-Hills' model, it has been found that both single metal and alloy deposition processes correspond to a nucleation and tridimensional growth controlled by diffusion. The deposition processes of Sn and Ag are conducted by an instantaneous mechanism, while in the case of Cu, a progressive one has been determined. The deposition process of Sn-Ag-Cu alloy showed a deviation from the instantaneous nucleation.