Reduced Electrical Resistivity of Ternary Solder Alloy of Tin–Copper–Sulfur: An Anti-Oxidative Role of Sulfur in Binary Solder Alloy of Tin–Copper

Abstract

Each electrical resistivity of the ternary solder alloy of tin–copper–sulfur was compared to that of the binary solder alloy of tin–copper. A mixture of various tin, copper, and sulfur powder compositions was prepared by adding different amounts of sulfur into a eutectic composition of tin and copper. After each specimen axially compressed with 10 MPa was sintered at 250°C, tin sulfide was induced in the solder alloy because sulfur reacted with tin. Simultaneously, the oxide layers of the solder alloy were removed through a complicated combustion reaction between tin sulfide and tin oxide. As a result, the electrical resistivity of the ternary solder alloy (Sn-0.70Cu-0.32S) having 0.32 mass% of sulfur was reduced to at most 10.56 µΩ·cm, compared to 12.47 µΩ·cm of the binary solder alloy (Sn-0.70Cu) without sulfur.