Thermal Conductivity Variation with Temperature for Lead-Free Ternary Eutectic Solders

Abstract

The variations of the thermal conductivity with temperature for the lead-free ternary eutectic solders Bi-42.73 wt.%Sn-1.03 wt.%Ag (Bi-Sn-Ag), Sn-3.5 wt.%Ag-0.9 wt.%Cu (Sn-Ag-Cu), Sn-6 wt.%Sb-5 wt.%Ag (Sn-Sb-Ag), Sn-42.8 wt.%Bi-0.04 wt.%Cu (Sn-Bi-Cu), and In-48.4 wt.%Sn-2.31 wt.%Ag (In-Sn-Ag) were measured using a linear heat flow apparatus. It was observed that the thermal conductivities of solid phases for the Bi-Sn-Ag, Sn-Ag-Cu, Sn-Sb-Ag, Sn-Bi-Cu, and In-Sn-Ag solders decrease linearly with increasing temperature. The thermal conductivities of the Bi-Sn-Ag, Sn-Ag-Cu, Sn-Sb-Ag, Sn-Bi-Cu, and In-Sn-Ag solders at their melting temperature were obtained as 17.89 ± 1.6 W/K-m, 49.89 ± 4.5 W/K-m, 41.96 ± 3.8 W/K-m, 20.03 ± 1.8 W/K-m, and 70.21 ± 6.3 W/K-m, respectively. The thermal temperature coefficients for the Bi-Sn-Ag, Sn-Ag-Cu, Sn-Sb-Ag, Sn-Bi-Cu, and In-Sn-Ag solders were also determined to be −2.894 × 10⁻³ K⁻¹, −0.907 × 10⁻³ K⁻¹, −1.246 × 10⁻³ K⁻¹, −2.638 × 10⁻³ K⁻¹, and −1.250 × 10⁻³ K⁻¹, respectively, from plots of thermal conductivity versus temperature.