The role of minor modifying additives on soldering properties of Sn-Ag-Cu green solders

Abstract

With the very high rate of introducing new designs, the service lives of modern electronic devices have been dramatically shortened. This has created awareness on the implications of disposing electronic wastes with lots of leaded solders. As part of environmental compliance, the industry is now warming up to the use of non-leaded solders that are considered greener. Amongst the common choice is the eutectic of Sn-Ag-Cu (SAC) alloy which has shown great promise. Minor additions to the near eutectic SAC compositions have been used to improve some properties. Here, we have studied the effect of the addition of Bi and other refractory elements to near eutectic SAC. It is shown that minor Bi additions up to less than 2% improved the joint strengths peaking at 50 – 70MPa. EDS studies confirmed that the improvement in strength is attributable to solid solution strengthening. The strengthening effect of Bi diminishes vastly beyond 2% limit and are characterised by brittle failure at higher Bi concentrations. Thermal analyses suggest that compositions beyond 2% Bi had undergone hyper eutectic solidification that would have led to the existence of primary brittle Bi phase in the microstructure. XRD confirmed the existence of primary Bi phase in higher concentrations