Determination of mechanical, electrical and thermal properties of the Sn―Bi―Zn ternary alloy

Abstract

The development of lead-free solders has emerged as one of the key issues in the electronics packaging industries. Sn―Zn―Bi eutectic alloy has been considered as one of the lead-free solder materials that can replace the toxic Pb―Sn eutectic solder without increasing soldering temperature. This study investigates the effect of temperature gradient and growth rate on the mechanical, electrical and thermal properties of the Sn―Zn―Bi eutectic alloy. Sn-23wt.% Bi-5wt.% Zn alloy was directionally solidified upward with different growth rates (V=8.3–478.6μm/s) at a constant temperature gradient (G=3.99K/mm) and with different temperature gradients (G=1.78–3.99K/mm) at a constant growth rate (V=8.3μm/s) in the Bridgman-type growth apparatus. The microhardness (HV), tensile stress (σt) and compressive stress (σc) were measured from directionally solidified samples. The dependency of the HV, σt and σc for directionally solidified Sn-23wt.% Bi-5wt.% Zn alloy on the solidification parameters (G, V) were investigated and the relationships between them were obtained by using regression analysis. According to present results, HV, σt and σc of directionally solidified Sn-23wt.% Bi-5wt.% Zn alloy increase with increasing G and V. Variations of electrical resistivity (ρ) for cast samples with the temperature in the range of 300–420K were also measured by using a standard dc four-point probe technique. The enthalpy of fusion (ΔH) and specific heat (Cp) for same alloy was also determined by means of differential scanning calorimeter (DSC) from heating trace during the transformation from eutectic liquid to eutectic solid.