Electrodeposition of ternary Sn-Cu-Ni alloys as lead-free solders using deep eutectic solvents

Abstract

The paper presents several experimental results regarding the electrodeposition of Sn-Cu-Ni ternary alloys as an attractive lead-free solder candidate, involving deep eutectic solvents (DESs), namely using choline chloride-ethylene glycol and choline chloride-malonic acid eutectic mixtures. The influence of the metallic ions concentration in the electrolyte and of the applied current density on the Sn-Cu-Ni alloy composition and morphology has been investigated, in order to achieve the corresponding alloy composition (Sn99.4Cu0.6 alloy + Ni) able to possess the eutectic or near eutectic melting temperature of about 227 °C. Adherent, bright and uniform Sn-Cu-Ni alloy deposits have been obtained onto Cu substrate from choline chloride-ethylene glycol-based electrolytes for applied current densities between 5–8 mA.cm−2 at 60 °C. According to the TGA measurements, values of melting point of 229 °C have been obtained, corresponding to an alloy stoichiometry of Sn99.29-Cu0.65-Ni0.06 as indicated by EDX elemental analysis. In addition, analysis of the current-time curves using the Scharifker-Hills’ model suggested that the alloy deposition process corresponds to a nucleation and tridimensional growth controlled by diffusion mostly under instantaneous nucleation. Preliminary results related to the solder joints behavior showed adequate solderability characteristics and adhesion to the substrate with no fractures. Moreover, the electrodeposited Sn-Cu-Ni (Sn99.29-Cu0.65-Ni0.06) alloy coatings exhibited a slightly better corrosion performance as compared to Sn-Ni alloys electrodeposited from DESs and to the metallurgically prepared lead-free solders possessing a relatively similar composition.