Effects of Ni, CO and In on microstructures, electrical properties and mechanical properties of Sn-Cu solder alloy

Abstract

Pb-containing solder alloys were widely used in electronic industries for decades but due to toxicity of Pb, worldwide restrictions were emerged to ban Pb usage in all electronic parts. Subsequently, several lead-free solder alloy compositions were developed. Sn-Ag-Cu alloy systems have been proposed to be amongst the first candidates. However, due to price fluctuation of Ag, many manufacturers are moving toward Sn-Cu solder alloys. Despite of lower cost, Sn-Cu solder alloys have inferior properties. In this research, we study the effects of Ni, Co and In additions to Sn-Cu solder alloy in order to improve its key properties for electronic applications. The result shows that addition of In lowers the melting point of Sn-Cu alloys to comparable value of that of Sn-3.0Ag-0.5Cu. The optimal amounts of Ni, Co and In additions result in improved hardness and shear strength by formation of intermetallic compounds that strengthen the soldered interface. The additions result in increased electrical resistivity. The Sn-Cu-Ni-Co-In solder alloys can maintain their shear strength after aging at 150oC for 1,000 hours. Sn-3.0Ag-0.5Cu shows 25.33% drop in its shear strength while Sn-Cu-Ni-Co-In alloys show only 3.82% drop. This is due to the uniformly distributed intermetallic compound which serves as dislocation obstacles and multiple sites for local stress concentration.