Effect of Magnetic Particles on the Microstructure and Wettability of Sn-Zn Lead-free Solders

Sn-Zn solder has gained much attention because of its low soldering temperature, excellent mechanical properties and low-cost. However, there are two main problems that restrict its applications, poor wettability and poor oxidation resistance. To improve the wettability of the Sn-Zn solders, magnetic particles (Fe and Ni) were added into the alloys. The microstructure and interfacial reaction were examined by backscatter electron microscopy (BSE) and the phases were identified by energy-dispersive spectroscopy (EDS). The results indicated that the Fe particles were mainly distributed in the surface of solder and intermetallic (IMC) was not observed at the interface between Fe particles and solder matrix. However, the Ni particles were distributed in the solder matrix uniformly and the Ni-Zn IMC was formed at the interface between Ni and solder. The wettability of these composites were also investigated in this paper. The results of wettability tests showed that the wettability noticeably improved after adding the magnetic particles. With vertically down and move magnetic field, the wetting angle decreased from 64.9 to 8.7 and 15.2 for Fe and Ni, respectively, when the mass fraction of magnetic particles increased from 0 to 6%.