Development of Lead Free sn-bi-cu Solder Alloy

Abstract

Until recently, lead-containing alloys were considered
to be the most suitable soldering materials widely applied in the automotive industry and in several other sectors.However,with the implementation of EU(European union) environmental directives, the use of such alloys has become prohibited for negative effect on health. In this work we have studied various eutectic system like Sn-8.8 wt.% Zn, Sn-3.5 wt. % Ag and Sn-57wt. %Bi and Sn-0.7 wt. % Cu to find best alternative of Sn-Pb solder alloy. The characterization of microstructure was done by optical as well as scanning electro nmicroscopy (SEM).The composition of the solder alloys were determined by using Energy Dispersive X-ray spectroscopy (EDX). Differential scanning calorimetry (DSC)was done to find out the melting temperature of the alloys. Phase analysis for the alloys was done using X-ray diffraction. Tensile test was performed to find out the mechanical properties of the alloys. The present work reports the effect of addition of Cu on the melting point, hardness and electrical resistivity of Sn-57 wt. % Bieutectic solder alloy. Both binary eutectic Sn-57wt. % Bi and ternary Sn-(57-x) Bi-xCu (x = 0.1, 0.3, 0.5, 0.7 and 1 wt. %) alloys containing various amounts of Cu were developed by melting casting route.The microstructure of the various solder alloys were analyzed using an optical microscope and a SEM. The variation in melting point, hardness and electrical resistivity of the Sn-Bi eutectic solder alloys with the addition of Cu was determined. The melting point of the eutectic Sn-Bi solder alloy was found to decrease upto the addition of 0.7 wt. % Cu. However, further addition of Cu led to an increase in the melting point of the alloy. Addition of Cu led to an increase in the hardness of the eutectic Sn-Bi solder alloy whereas the electrical resistivity of the eutectic Sn-Bi solder alloy was found to increase upto the addition of 0.7 wt. % of Cu beyond which a decrease in the electrical resistivity was observed.A change in the microstructure of the solder alloy was observed when it was reheated above the melting temperature.