Effect of porous Cu addition on the microstructure and mechanical properties of SnBi-xAg solder joints
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Effect of porous Cu addition on the microstructure and mechanical properties of SnBi‑xAg solder joints Yang Liu1 · Boqiao Ren1,2 · Min Zhou1 · Yuxiong Xue1 · Xianghua Zeng1 · Fenglian Sun2 · Xuejun Fan3 · Guoqi Zhang4 Received: 8 June 2020 / Accepted: 18 August 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The effects of porous copper (P-Cu) on the microstructure, hardness, and shear strength of SnBi, SnBi-0.4Ag, and SnBi1Ag solder joints were investigated in this paper. The experimental results show that P-Cu frames distribute in the solder bulks and form triangular areas. The addition of P-Cu leads to the microstructural refinement in the enclosed areas by the P-Cu frames in the solder bulks. The average hardness here is increased due to the fine grain strengthening mechanism. The SnBi-1Ag@P-Cu solder bulk shows smaller Bi-rich grains but larger β-Sn dendrites than the other two P-Cu-enhanced solder bulks. Porous Cu exists as a frame structure in the solder joints, which hinders the initiation and propagation of cracks and has a positive effect on the improvement of joint strength. Compared to the SnBi and SnBiAg solder joints, the shear strength of the P-Cu-enhanced solder joints is increased by 15%. The average shear strength of the SnBi-0.4Ag@P-Cu solder joint is 79.34 MPa, which is the highest among all the solder joints investigated in this study. Keywords Porous Cu · Microstructure · SnBi · Hardness · Shear behavior
1 Introduction With the development of the electronics industry, the integration and miniaturization of electronic products have become an inevitable trend, which require higher reliability of solder joints [1–5]. This is a huge challenge for the electronic packaging technology [6–9]. At present, Sn58Bi (SnBi) alloy has a low melting point, good wettability, low cost, and high mechanical strength, and is one of the most promising low-temperature solder materials [10–13]. Although Bi-rich grain enhances the mechanical strength, it leads to the poor ductility of the solder joint. These
* Yang Liu [email protected] 1
College of Electrical, Energy and Power Engineering, Yangzhou University, Yangzhou 225127, China
2
School of Material Science and Engineering, Harbin University of Science and Technology, Harbin 150040, China
3
Department of Mechanical Engineering, Lamar University, Beaumont, TX 77710, USA
4
EEMCS Faculty, Delft University of Technology, 2628CD Delft, The Netherlands
disadvantages limit the application of Sn58Bi solder in the packaging industry [14–16]. Adding a small amount of Ag into SnBi solder can improve the microstructure and mechanical properties of the solder joint. Sun et al. [17] reported that adding 0.4 wt% Ag element or nano-Ag particles in the solder joint can improve the microstructure and performance of the solder joint. Also, the shear strength of the SnBi-nano Ag solder joint is higher than that of the SnBi-0.4Ag and SnBi eutectic solder joints. Liu et al. [18] added 1 wt% Ag into SnBi solder alloy. The experimental re
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