Effects of rare earth element Nd on the solderability and microstructure of Sn-Zn lead-free solder

Effects of trace amount addition of rare earth Nd on the properties of eutectic Sn-Zn solder were studied in this paper. Results indicate that adding trace rare earth element Nd could remarkably improve the solderability and mechanical properties of Sn-9Zn solder joints. Especially when the content of Nd was 0.06 wt%, the wettability of the solder was improved significantly, and the shear force of Sn-9Zn-0.06Nd solder joint was enhanced by 19.6% as well as pull force increased by 26.6% compared to that of Sn-9Zn solder joint,respectively. It is also found that addition of rare earth Nd could refine the microstructure of the solder and some NdSn3 phase appeared in the solder matrix. Moreover, the IMCs thickness at the solder/Cu interface was reduced. NdSn3 phase appeared at the interface with excessive addition of Nd, which is the key reason that deteriorates the mechanical properties of soldered joint.