Investigation on wetting behavior of Cu/Sn systems by molecular dynamics simulation

In lead-free soldering, the wettability of the solder or substrate is of great significance in improving the quality of solder joints. In this study, the molecular dynamics simulation is used to analyze the wettability of Sn droplets on the Cu surface, rough surface, and Sn surface. The simulation results showed that higher temperatures could promote the wettability of Cu/Sn systems but led to the formation of more intermetallic compounds. According to the change in the contact angle on different rough surfaces, it was found that the roughness had a positive effect on the wettability of Cu/Sn systems and the contact between the Sn droplet and substrate. Further, the existence of Sn layer on the substrate was conducive to enhancing the wettability of Cu/Sn systems and the phenomenon was more noticeable when the Sn layer was thicker. Additionally, the contact angle of high-purity Sn solder on various substrate surfaces was experimentally analyzed, implying that the Sn surface played an important role in improving the wettability of Cu/Sn systems. In this work, it explores the wetting behavior of Cu/Sn systems from a microscopic perspective and provides theoretical guidance for improving the wettability of flexible printed circuit board substrates.