Preparation and characterization of Zn-Sb based high temperature solder alloys

Abstract

In this study, three different compositions of the newly developed solder alloys were selected as of Zn-1.2wt% Sb, Zn-1.7wt% Sb (Eutectic alloy) and Zn-2.2wt% Sb. The pure Zinc (Zn: purity 99.99%) ingot and pure Antimony (Sb: purity 99.98%) were procured commercially and the new Zn-based Pb-free solders were developed by doping different amounts of Sb into Zn. The samples from each composition were prepared accordingly to investigate the microstructure and mechanical properties. Then ageing was carried out of the eutectic alloy at 200 C for 250 hours and 500 hours.

X-ray Fluorescence (XRF) was done as compositional analysis. The microstructures were investigated under optical microscope (OM) and scanning electron microscope (SEM) for both as cast and aged samples. Energy Dispersive X-ray (EDX) and X-ray Diffraction (XRD) analysis were also conducted to analyze the composition and to identify the phase in the alloy respectively. The tensile strength, microhardness, electrical conductivity as well as the creep properties were observed systematically. Creep behavior was analyzed as the function of Vickers hardness at different time duration to observe the creep strain variation.

Before ageing, the eutectic Zn-1.7wt% Sb alloy exhibited the most desired characteristics among the three alloys. Later, two samples with eutectic composition were aged for 250 hours and 500 hours at same temperature 200 C and investigated to observe the ageing effect on properties. Investigation on those three samples (as cast and aged) was narrowed down to find out Zn-1.7wt% Sb aged for 250 hours as the most appropriate high temperature solder alloy with better properties than other alloys.

Creep behavior drives the most important role in longevity and reliability of performance of any solid material. The nature of application of solder alloys demands for being in high temperature as well as high stress and both of which mostly facilitate the creep deformation in structure over the time. So, an ideal high temperature solder alloy must have well enough of creep properties to sustain and perform properly for long term. In this study, eutectic Zn-1.7wt% Sb exhibited optimum creep strain over the other two alloys. Hence, eutectic Zn-1.7wt% Sb with ageing for 250 hours was found with the required optimum properties to be the appropriate Pb-free high temperature solder alloy.