oa Development of new lead-free Sn-2.5Mg solder for electronic packaging industries

The increasing use of lead-free solders is driven by the direct threat of strict legislation to ban the use of lead-based solders in electronics manufacturing industries by the USA, Japan and countries under the European Union. An additional driver is the market change due to public 'green awareness'. Therefore, establishing a lead-free solder has become a critical issue. In recent years, many attempts are made to develop high-performance, lead-free solders. Among the new lead-free solders, the Sn-3.5Ag, Sn-3.0Ag-0.5Cu and Sn-0.7Cu solders are the most promising alloys. However, these commercial solder alloys are more expensive and exhibit higher melting points when compared to the conventional Sn-37Pb solder alloy. Magnesium (Mg) is much cheaper than silver (Ag) and copper (Cu) and the eutectic/near eutectic temperature of Sn-Mg alloy is much lower than the lead-free Sn-Cu or Sn-Ag solders. Accordingly, in the present study, new lead-free Sn-2.5Mg solder was developed incorporating 2.5 wt. % Mg into pure tin using disintegrated melt deposition technique. Solder samples were then subsequently extruded at room temperature and characterized. Microstructural characterization studies revealed equiaxed grain morphology, minimal porosity and relatively uniform distribution of secondary phase. Better coefficient of thermal expansion was observed for a Sn-2.5Mg sample (23.1 x10-6/K) when compared to conventional Sn-37Pb solder (25 x 10-6/K) or lead-free Sn-0.7Cu solder (30 x 10-6/K). A melting temperature of Sn-2.5Mg was found to be 219 0C which is much lower than the conventional Sn-Ag-Cu or Sn-Cu (227 0C) solders. Microhardness was increased by 271% with the addition of Mg into pure tin. Room temperature tensile test results revealed that the newly developed Sn-Mg solder exhibited enhanced strengths (0.2 % yield strength and ultimate tensile strength) with comparable (if not better) ductility when compared to other commercially available, and widely used, Sn-based solder alloys.