Abstract
Sn-58Bi eutectic solder is the most recommended low temperature Pb-free solder but is also limited from the interfacial embrittlement of Bi segregation. Since the quaternary Sn-38Bi-1.5Sb-0.7Ag solder provides a similar melting point as Sn-58Bi eutectic, this paper systematically investigated the properties of this solder from wettability, bulk tensile properties, interfacial microstructure in solder joints with a Cu substrate, interfacial evolution in joints during isothermal aging and the shear strength on ball solder joints with effect of aging conditions. The results were also compared with Sn-58Bi solder. The wettability of solder alloys was evaluated with wetting balance testing, and the quaternary Sn-38Bi-1.5Sb-0.7Ag solder had a better wettability than Sn-58Bi solder on the wetting time. Tensile tests on bulk solder alloys indicated that the quaternary Sn-38Bi-1.5Sb-0.7Ag solder had a higher tensile strength and similar elongation compared with Sn-58Bi solder due to the finely distributed SnSb and Ag3Sn intermetallics in the solder matrix. The tensile strength of solder decreased with a decrease in the strain rate and with an increase in temperature, while the elongation of solder was independent of the temperature and strain rate. When soldering with a Cu substrate, a thin Cu6Sn5 intermetallic compound (IMC) is produced at the interface in the solder joint. Measurement on IMC thickness showed that the quaternary Sn-38Bi-1.5Sb-0.7Ag had a lower IMC growth rate during the following isothermal aging. Ball shear test on solder joints illustrated that the quaternary Sn-38Bi-1.5Sb-0.7Ag solder joints had higher shear strength than Sn-58Bi solder joints. Compared with the serious deterioration on shear strength of Sn-58Bi joints from isothermal aging, the quaternary Sn-38Bi-1.5Sb-0.7Ag solder joints presented a superior high temperature stability. Therefore, the quaternary Sn-38Bi-1.5Sb-0.7Ag solder provides better performances and the possibility to replace Sn-58Bi solder to realize low temperature soldering.
Highlights
The increasing functionality and trend towards miniaturization of personal electronic devices has driven the need for smaller and thinner components, which inversely exerts a considerable challenge to the electronic assembly industry
We systematically investigated the properties of this quaternary solder from the wetting, bulk solder strength, growth behavior of intermetallic compounds (IMCs) in solder joints and shear strength of ball solder joints
Wettability is very important for a solder alloy because it will influence the solderability Wettability veryPCB
Summary
The increasing functionality and trend towards miniaturization of personal electronic devices has driven the need for smaller and thinner components, which inversely exerts a considerable challenge to the electronic assembly industry. To realize the assembling between components and the printed circuit board (PCB), Sn-based solder is the most used interconnected material. Among all the developed Pb-free solders, Sn-Ag-Cu series have the most application because they provide superior mechanical performances, wettability and reliability [1,2]. Metals 2019, 9, 791 usually above 245 ◦ C, promotes thermal warpage on a PCB and thinner components [3]. The development of low temperature solder provides a lower processing temperature, and reduces the thermal damage caused from using high-temperature solders. The developed low-temperature solders are mainly selected from the Sn-Bi, Sn-In or Sn-Zn series [4]; but Sn-Bi solder provides the most potential due to its low cost and better comprehensive properties [5]
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