Magnetron sputtering preparation of Cu6Sn5 preferred-orientation coating and its influence on wettability of Sn-based lead-free solder

Cu6Sn5 preferred-orientation coatings with high surface energies were prepared on Cu substrates using magnetron sputtering to improve the wettability of Sn-based lead-free solder without introducing elements other than the composition of solder. The influence behavior and mechanism of the preferred-orientation of Cu6Sn5 coating on the wettability and wetting kinetic of Sn-based lead-free solder were investigated using both exper-imental methods and molecular dynamics simulations. Based on the results, Cu6Sn5 coatings were prepared successfully on Cu substrates with the substrate temperatures of 25-200 degrees C and sputtering powers of 60-140 W, and their preferred-orientations are affected by sputtering power and substrate temperature simultaneously. Sn-based lead-free solder has a greater wettability on (40-2)-preferred and (132)-preferred Cu6Sn5 coatings than that on Cu substrate, but has a poorer wettability on (351)-preferred Cu6Sn5 coating, because the interaction intensities between Sn with Cu6Sn5(40-2) and Cu6Sn5(132) are greater than that with Cu6Sn5(351). Meanwhile, Sn-based lead-free solder demonstrates the shortest time to reach wetting stabilized state on (351)-preferred Cu6Sn5 coating due to the largest diffusion coefficient of Sn element on Cu6Sn5(351), followed by (132)-preferred coating, Cu substrate and (40-2)-preferred Cu6Sn5 coating.