Influence of Sn crystal preferred orientation on the reflective and environmental stability of electroplated Sn/Ag films

Highlights: • The influence of Sn preferred orientation on the performance of Sn/Ag films is revealed. • Sn crystal preferred orientations can be controlled by cooling rate. • Sulfidizing resistance of Sn/Ag couples is evaluated using potentiodynamic polarization technology. • Annealing twin Ag is prepared by cyanide-free electroplated fine-grain Ag films. The effect of Sn crystal orientation on the solid-solid interfacial reactions of the Sn–Ag system at 150 °C were systematically investigated. XRD, EBSD and SEM were employed to reveal the microstructure evolution behavior of Ag/Sn films. The experimental data indicated that lattice matching degree between Ag and Sn film was quite different due to the various preferred orientations. The results confirmed that crystal orientation of Sn had a substantial influence on the electroplating speed, surface morphology as well as the resulting reflectivity of Ag films. After annealing treatment, the reflectivity of as-prepared Sn/Ag films decreased, attributing to the grain size changing from nano-scale to submicron and/or micron scale and the as-formed Ag₃Sn phase. At the research field of Ag-based reflective coatings, it was firstly proposed and implemented the evaluation on sulfidization resistance of Sn/Ag films by analyzing the potentiodynamic polarization information. Based on the thermodynamics calculation, the types of intermetallic compounds(IMCs) formation were discussed. This paper provides a guiding principle for improving the optical properties and chemical stability of multilayer Sn/Ag reflective materials from the optimized selection view of Sn bottom materials.