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Thermo-Calc Used to Advance Search for Pb-free Solder Designs


A new paper published in the Journal of Phase Equilibria and Diffusion discusses recent advances in the search for Pb-free solder designs from the perspective of thermodynamics and phase diagrams.

The paper relies on the work of Jack Smith, whose more than 50 year scientific career (1953-2007) was spent working on the links between thermochemistry and the constitution and crystal structures of metals, compounds and alloy systems, and discusses the value that computational tools such as Thermo-Calc can have in the advancement of Pb-free solder designs. The paper concludes:

Alloy thermodynamics and phase diagrams, as represented by the work of Jack Smith, are foundational in our continuing efforts to design Pb-free interconnect solutions with improved performance and for high temperature interfaces.[1]

Thermo-Calc, along with our solder alloys database TCSLD, was used to calculate the ternary phase diagrams, and the results were compared to experimental data.


New electronics applications demanding enhanced performance and higher operating temperatures have led to continued research in the field of Pb-free solder designs and interconnect solutions. In this paper, recent advances in the microstructural design of Pb-free solders and interconnect systems were discussed by highlighting two topics: increasing β-Sn nucleation in Sn-based solders, and isothermally solidified interconnects using transient liquid phases. Issues in β-Sn nucleation in Sn-based solders were summarized in the context of Swenson’s 2007 review of the topic. Recent advancements in the areas of alloy composition manipulation, nucleating heterogeneities, and rapid solidification were discussed, and a proposal based on a multi-faceted solidification approach involving the promotion of constitutional undercooling and nucleating heterogeneities was outlined for future research. The second half of the paper analyzed two different approaches to liquid phase diffusion bonding as a replacement for high-Pb solders, one based on the application of the pseudo-binary Cu-Ni-Sn ternary system, and the other on a proposed thermodynamic framework for identifying potential ternary alloys for liquid phase diffusion bonding. All of the concepts reviewed relied upon the fundamentals of thermodynamics, kinetics, and solidification, to which Jack Smith substantially contributed during his scientific career.

[1] Reeve, K.N., Holaday, J.R., Choquette, S.M. et al. J. Phase Equilib. Diffus. (2016) 37: 369. doi:10.1007/s11669-016-0476-9

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