Influence of aging on microstructure and hardness of lead-free solder alloys
Soldering & Surface Mount Technology
ISSN: 0954-0911
Article publication date: 8 July 2020
Issue publication date: 4 January 2021
Abstract
Purpose
The purpose of this paper is to carry out a study of the evolution of the microstructure and the microhardness of Sn-Cu-Ag alloys from as-cast condition and under artificial isothermal aging at different temperatures (100ºC and 180ºC) for a treatment time up to 500 h. A comparison with Sn-37% Pb eutectic solder samples was also made.
Design/methodology/approach
Sn-3.5%Ag, Sn-0.7%Cu and Sn-3.5%Ag-0.9%Cu were poured in two different cooling rate conditions and then aged at 100ºC (373ºK) and 180 °C (453ºK) during 500 h. Microstructural changes were observed by optical microscopy, scanning electron micrograph and energy dispersive X-ray microanalysis. Differential scanning calorimetry technique (DSC) was also used to confirm the obtained results.
Findings
A decrease up to 20% in microhardness respect to the value of the as-cast alloy was observed for both aging temperatures. These changes can be explained considering the coarsening and recrystallization of Sn dendrites present in the microstructures of all the systems studied.
Originality/value
There is no evidence of dissolution or precipitation of new phases in the range of studied temperatures that could be detected by DSC calorimetry technique. The acting mechanisms must be the result of coarsening of Sn dendrites and the residual stresses relaxation during the first stages of the isothermal aging.
Keywords
Acknowledgements
Acknowledgments: This work was carried out in the Instituto de Física de Materiales Tandil – Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires, IFIMAT-CIFICEN (CICPBA, UNCPBA, CONICET) and partially funded by Consejo de Investigaciones Científicas y Técnicas, CONICET (PIP 0627/15) and Secretaría de Ciencia, Arte y Tecnología de la Universidad Nacional del Centro de la Provincia de Buenos Aires, SeCAT-UNCPBA (SeCAT 2018/19 grant).
Conflicts of interest or competing interests: The authors declare that they have no conflict of interest.
Citation
Morando, C. and Fornaro, O. (2021), "Influence of aging on microstructure and hardness of lead-free solder alloys", Soldering & Surface Mount Technology, Vol. 33 No. 1, pp. 57-64. https://doi.org/10.1108/SSMT-03-2020-0013
Publisher
:Emerald Publishing Limited
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