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 μm/s) and with different growth rates (V=6.55-132.83 μm/s) at a constant temperature gradient (G=2.33 K/mm) in the growth apparatus. The microstructures (λ), microhardness (HV), tensile stress (σ), electrical resistivity (ρ), and thermal properties (ΔH, C _p, T _m) were measured on directionally solidified samples. The dependency of the λ, HV, σ, and ρ on G and V was investigated. According to the experimental results, λ values decrease with increasing G and V, but HV, λ, and ρ values increase with increasing G and V. Variations of electrical resistivity (ρ) 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 (ΔH) 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.

Keywords

solidification / microhardness / tensile stress / electrical resistivity / enthalpy

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