Melting Temperature and Physical Properties of Sn-Ag-Cu-Mg Lead-Free Solders Based on Uniform Design

In this paper, Sn-Ag-Cu-Mg lead-free solders based on an eutectic Sn-Ag-Cu alloy were prepared by means of uniform design. Further investigations were carried out in aspects of melting, wettability, thermal stability and other physical properties employing differential thermal analysis (DTA), X-ray diffraction (XRD), etc. It is showed that the melting temperatures decrease when the element of Mg was added in the ternary Sn-Ag-Cu solder alloy systems, and the ranges of melting temperature are wider for those solders with lower melting points. For Sn-Ag-Cu-Mg solders, the melting range with less Mg addition is wider, while its melting point is lower. The wettability of the solders is associated with the Mg concentration. With the Mg content ranged from 0.1% to 0.7% , the spreading areas of Sn-Ag-Cu-Mg solders are only 50-70% of that of the near-eutectic Sn-4.0Ag-0.5Cu. With the added Mg, the thermal stability of solders is depressed, while the density and electrical conductivity are as same as those of Sn-4.0Ag-0.5Cu.