Effect of trace rare earth Er on the properties of Sn-0.3Ag-0.7Cu-0.05Mn lead-free solder material

The effect of adding trace rare earth Er on the properties of Sn-0.3Ag-0.7Cu-0.05Mn lead-free solder material is investigated. The experimental results show that the addition of Er elements can improve the Vickers hardness of lead-free Sn-0.3Ag-0.7Cu-0.05Mn solder. The wettability of lead-free Sn-0.3Ag-0.7Cu-0.05Mn-xEr solder exhibits an initial increase followed by a decrease with increasing Er content. Microscopic analysis of the solder's structure reveals that when the Er content is 0.1wt.%, the β-Sn matrix becomes significantly refined, and intermetallic compound (IMC) grain size is minimized and uniformly dispersed in the matrix, playing a role in grain refinement. However, when the Er content exceeds 0.1wt.%, the IMC grain size increases, and the presence of brittle large-sized IMCs adversely affects the reliability of the solder joints. The addition of rare earth Er noticeably suppresses the growth of the interface IMC layer. Furthermore, when the Er content at 0.1 wt.%, the surface smoothness of the solder joint interface reaches its optimal state, with virtually no observable Kirkendall voids.