Microstructure and creep properties of Sn-Ag-Cu lead-free solders bearing minor amounts of the rare earth cerium
Abstract
Purpose
The purpose of this paper is to investigate the effects of minor addition of the rare earth (RE) element cerium, Ce, on the microstructures and creep properties of Sn-Ag-Cu solder alloys.
Design/methodology/approach
The pure Sn, Sn-Cu alloy, Sn-Ag alloy and Cu-Ce alloy were used as raw materials. Sn-Ag-Cu alloys with different contents of RE Ce were chosen to compare with Sn-Ag-Cu. The raw materials of Sn, Sn-Cu alloy, Sn-Ag alloy, Cu-Ce alloy were melted in a ceramic crucible, and were melted at 550°C ± 1°C for 40 minutes. To homogenize the solder alloy, mechanical stirring was performed every ten minutes using a glass rod. During the melting, KC1 + LiCI (1.3:1), were used over the surface of liquid solder to prevent oxidation. The melted solder was chill cast into a rod.
Findings
It is found that the microstructure exhibits smaller grains and the Ag3Sn/Cu6Sn5 intermetallic compound (IMC) phases are modified in matrix with the addition of Ce. In particular, the addition of 0.03 wt.% Ce to the Sn-Ag-Cu solder can refine the microstructures and decrease the thickness of the IMC layers of Sn-Ag-Cu solder alloys. Meanwhile, thermodynamic analysis showed that these phenomena could be attributed to the reduction of the driving force for Cu-Sn IMC formation due to the addition of Ce. Results calculated using the thermodynamic method are close to the above experimental data. Thus, the optimum content of Ce in Sn-Ag-Cu solder alloys should be about 0.030 percent. Additionally, the effect of Ce on the creep rupture life of Sn-Ag-Cu soldered joints was studied. It was found that the creep rupture life may be increased up to 7.5 times more than that of the original Sn-Ag-Cu alloy, when Ce accounts for 0.030 percent.
Originality/value
This paper usefully investigates the effects of the RE cerium (Ce), on the microstructures and creep properties of Sn-Ag-Cu solder alloys, optimizing the quantity of Ce in the Sn-Ag-Cu solder alloy through a thermodynamic method and by creep-rupture life testing.
Keywords
Acknowledgements
The present work was carried out with the support of Nanjing University of Aeronautics and Astronautics Doctoral Dissertation Innovation and Excellence Producing foundation (Project No. BCXJ09-07); supported by the Six Kind Skilled Personnel Project of Jiangsu Province (Project No. 06-E-020); supported by the Jiangsu General Colleges and Universities Postgraduate Scientific Research Innovative Plan (Project No. CX09B_074z).
Citation
Zhang, L., Xue, S.-b., Gao, L.-l., Chen, Y., Yu, S.-l., Sheng, Z. and Zeng, G. (2010), "Microstructure and creep properties of Sn-Ag-Cu lead-free solders bearing minor amounts of the rare earth cerium", Soldering & Surface Mount Technology, Vol. 22 No. 2, pp. 30-36. https://doi.org/10.1108/09540911011036262
Publisher
:Emerald Publishing Limited
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