Influences of Ag and In Alloying on Microstructure and Mechanical Properties of Sn-58Bi Solder
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https://doi.org/10.1007/s11664-020-08595-9 Ó 2020 The Minerals, Metals & Materials Society
ORIGINAL RESEARCH ARTICLE
Influences of Ag and In Alloying on Microstructure and Mechanical Properties of Sn-58Bi Solder JIE YANG,1,2 QINGKE ZHANG
,1,3 and ZHENLUN SONG1
1.—Key Laboratory of Marine Materials and Related Technologies, Zhejiang Key Laboratory of Marine Materials and Protective Technologies, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, People’s Republic of China. 2.—Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, People’s Republic of China. 3.—e-mail: [email protected]
Ag (2.0 wt.%) and In (1.5 wt.%) were alloyed into Sn-58Bi eutectic solder, and the individual and combined influences of Ag and In on the microstructure, microhardness, and impact toughness of the SnBi solder were investigated. The results reveal that the microstructures of the SnBiAg, SnBiIn, and SnBiAgIn alloyed solders are coarser than that of the SnBi eutectic solder. Fine Ag3Sn particles are formed in the SnBiAg and SnBiAgIn solders, while small regions of In-rich phases appear in the SnBiIn and SnBiAgIn solders. The microhardness of the three alloyed solders are higher than the SnBi solder, and the Sn-rich phases in the alloyed solders show higher nanohardness, while the nanohardness of the Bi-rich phases with Ag and In addition changes little. The impact toughness of the SnBiAg, SnBiIn, and SnBiAgIn solders are observed to be higher than the SnBi solder, especially in the case of the SnBiAgIn solder. The improvement in ductility of the Sn-rich phase induced by the In solution, and the strengthening effect from the Ag3Sn particles are predicated to be the reason for the increase in impact toughness. The fracture surfaces demonstrate that plastic deformation of the SnBiAgIn solder during the impact process is more obvious. Overall, the combined addition of Ag and In can increase the microhardness and impact toughness of SnBi eutectic solder. Key words: SnBi solder, Ag and In addition, microhardness, nano-indentation, impact toughness, fracture mechanism
INTRODUCTION The low melting point of Sn-58Bi eutectic solder (138.9°C) can avoid thermal damage during the soldering process, making it more suitable for soldering of temperature-sensitive devices or components.1–3 Moreover, the application of lowtemperature solder can significantly reduce energy consumption during the reflow soldering process.4,5 Additionally, Bi metal is relatively cheap. Therefore, Sn-58Bi solder is considered to be promising in mass applications of low-temperature soldering,
(Received August 12, 2020; accepted October 28, 2020)
such as in the electronic and photovoltaic industries.6,7 Usually, SnBi solder shows superior ductility at a low strain rate.8 However, because of the inherent brittlement of Bi metal, there exists a high risk of brittle fracture for Sn-58Bi eutectic solder and its impact toughness is quite pool, so that even a common shock or drop can result in fractu
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