Microstructural, Mechanical, Electrical, and Thermal Properties of the Bi-Sn-Ag Ternary Eutectic Alloy

Abstract

The development of lead-free solders has emerged as one of the key issues in the electronics packaging industries. Bi-Sn-Ag 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. We investigated the effects of temperature gradient and growth rate on the mechanical, electrical and thermal properties of the Bi-Sn-Ag ternary eutectic alloy. Bi-47 wt% Sn-0.68 wt% Ag alloy was directionally solidified upward with different temperature gradients ( G=2.33-5.66 K/mm) at a constant growth rate ( V=13.25 mu m/s) and with different growth rates ( V=6.55-132.83 mu m/s) at a constant temperature gradient ( G=2.33 K/mm) in the growth apparatus. The microstructures (lambda), microhardness ( HV), tensile stress ( sigma), electrical resistivity (rho), and thermal properties (Delta H, C-p, T-m) were measured on directionally solidified samples. The dependency of the lambda, HV, sigma, and rho on G and V was investigated. According to the experimental results, lambda values decrease with increasing G and V, but HV, lambda, and rho values increase with increasing G and V. Variations of electrical resistivity (rho) for cast samples with the temperature in the range of 300-400 K were also measured by using a standard dc four-point probe technique. The enthalpy of fusion (Delta H) and specific heat ( C-p) for the same alloy was also determined by means of differential scanning calorimeter ( DSC) from heating trace during the transformation from eutectic liquid to eutectic solid.