Microstructural and Micromechanical Characteristics of Tin-Based Solders Under Self-Propagating Exothermic Reaction Heat
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https://doi.org/10.1007/s11664-020-08363-9 Ó 2020 The Minerals, Metals & Materials Society
Microstructural and Micromechanical Characteristics of Tin-Based Solders Under Self-Propagating Exothermic Reaction Heating ZHENG ZHOU ,1 ANNA ZHANG,1 XU GUAN,1 HUI LIU,1 CHANGQING LIU,2 and FENGSHUN WU1,3 1.—School of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan, China. 2.—Wolfson School of Mechanical, Electrical and Manufacturing Engineering, Loughborough University, Loughborough, UK. 3.—e-mail: [email protected]
In this study, a rapid solder melting process has been examined through a selfpropagating exothermic reaction using Al/Ni nanofoil as a localized heat source. Four kinds of tin-based solder preforms were partly melted under this process, and the thicknesses of the fusion zone in solder preforms around the Al/Ni nanofoil were experimentally analyzed. The microstructure and morphology of the fusion zone in different kinds of solder preforms were studied by metallographic analysis. In Sn42Bi58 solder, the mean grain size of Bi-rich phases in the fusion zone was finer than the original structure, and decreased from 2.7 lm to 0.8 lm away from the Al/Ni nanofoil. Similar trends of mean size of grains in the fusion zone were also found in the Sn, Sn-3 wt.%Ag0.5 wt.%Cu(SAC), and SnPb solder preforms. The widths of the fusion zone in the Sn, SAC, SnPb, and SnBi solder preforms were 150 lm, 173 lm, 188 lm, and 233 lm, respectively. In addition, the nano-hardness and distribution in the fusion zones were evaluated. The results show that the value of nanohardness increased along with the decrease of distance from Al/Ni nanofoil. The average hardness and the lower and upper bounds of Sn, SnPb, SAC, and SnBi solder in the fusion zone are 0.260 (0.045, +0.039) GPa, 0.246 (0.059, +0.114) GPa, 0.260 (0.014, +0.070) GPa, and 0.404 (0.072, +0.134) GPa, respectively. The statistical significance of solder hardness is related to its alloy component, element content, and microstructure. Key words: Self-propagating reaction, Al/Ni nanofoil, Sn-based solder, nanohardness
INTRODUCTION In general, most of the micro- and nano-sized functional devices, such as integrated circuits (IC), microelectromechanical systems (MEMS), and so on, are fabricated by traditional interconnect technologies including wire bonding, reflow soldering, thermo-compression bonding, and eutectic bonding, etc. During these bonding processes, it is common to have an entire bonding structure exposed to a high
(Received September 26, 2019; accepted July 28, 2020)
temperature to ensure strong and reliable bonding.1,2 Because of the difference between the coefficients of thermal expansion (CTE) of different materials of substrates and components, the induced thermal stress in the bonding process will reduce the interconnect reliability and shorten the lifetime of the device. Also, the elevated temperature will potentially cause damages to the temperature-sensitive components inside integrated devices. One possibl
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