Effect of surface oxide on the melting behavior of lead-free solder nanowires and nanorods

► Surface oxide of nanosolders plays a critical role in the melting of solder nanowires and nanorods. ► Flux can effectively remove the surface oxide layer and ensure complete nanosolder reflow. ► An interesting Ostwald ripening phenomenon was observed during the melting of solder nanowires and nanorods, which led to the formation of nano- and micro-sized solder balls. ► The smallest solder balls that we have observed are in the range of tens of nanometer. ► A significant shape change (quasi-melting) was observed for these nano-solders at a temperature well below the apparent melting point temperature, which underlines the importance of the solder reflow conditions.