Effects of Ni Addition to Sn–5Sb High-Temperature Lead-Free Solder on Its Microstructure and Mechanical Properties

Abstract

The purpose of the present study is to investigate the melting properties, microstructures, tensile properties and fatigue properties of Sn 5Sb(0.050.50)Ni (mass%) high-temperature lead-free solders. The solidus temperature and liquidus temperature of the Sn5SbNi solders are approximately equal to those of the Sn5Sb alloy. From the result of EPMA mapping analysis and the SnSbNi ternary phase diagram, the Sn 5SbNi solders are found to consist of -Sn, SbSn and NiSb phases. As the amount of Ni in the Sn5SbNi solder increases, the number of NiSb phases increases and the phases are coarsened so that the 0.1% proof stress and tensile strength increase, and the elongation decreases at 25C. In contrast, the effects of the Ni content on the tensile properties are negligible at 150C and 200C. The fatigue ductility exponent of the Sn 5SbNi solders is smaller than that of the Sn5Sb solder at 25C. At 150C and 200C, the values of Sn5Sb0.05Ni and Sn5Sb0.10Ni remain small, whereas those of Sn5Sb0.25Ni and Sn5Sb0.50Ni increase. This means that the Sn5SbNi solders with 0.050.10 mass% Ni have superior fatigue properties to the Sn5Sb solder in the temperature range from 25C to 200C.