June 13, 2023 @ 9:00 am – 10:00 am

XSD/MIC Special Presentation

Speaker: Amey Luktuke, Purdue University

Title: Understanding the microstructural evolution of Sn-Bi solder alloys during solidification using Synchrotron X-ray Tomography and Diffraction

Date: June 13, 2023

Time: 9:00 a.m.

Location: Microsoft Teams meeting
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Meeting ID: 266 581 214 831
Passcode: m2DBrd


With a constant emphasis on the miniaturization of electronic devices, there has been significant attention given to new electronic packaging strategies in recent years. One such strategy is Heterogeneous Integration Packaging (HIP), which favors the use of low-melting solder alloys. Among these alloys, Sn-Bi alloys have been investigated as potential replacements for traditional Sn-Pb and SAC solder alloys due to their considerably lower melting temperatures. The presence of the Bi phase in the microstructure plays a vital role in determining the mechanical behavior and reliability of Sn-Bi solder joints. However, the underlying mechanisms governing the evolution of the Bi phase during solidification are still not fully understood. Additionally, the morphology of the faceted Bi phase remains poorly characterized. Experimental characterization of the phase formation is crucial to develop appropriate processing conditions for enhanced solder performance. In this presentation, I will discuss a systematic approach to characterizing the microstructure of alloys during solidification, utilizing non-destructive X-ray tomography and diffraction techniques, starting from lab-scale experiments, and progressing to the use of Synchrotron sources. The influence of critical experimental parameters, such as the cooling rate during solidification, was evaluated to better understand their impact on the microstructure. To gain a comprehensive understanding of the solidification dynamics, a 4D study was conducted, involving the analysis of 3D microstructures along with time evolution, using Synchrotron White beam tomography. To successfully image high-density materials, a specialized experimental setup was developed at the 7-BM beamline at Argonne National Lab. This involved optimizing various imaging parameters, including X-ray spectrum filtering, the number of X-ray projections etc. The 4D analysis of microstructural evolution provided crucial insights into facet formation, growth kinetics, and the atomistic mechanisms governing the formation of the Bi phase. Moreover, simultaneous X-ray tomography and Energy Dispersive Diffraction (EDD) were employed to understand the morphological and compositional changes during the solidification process. The presentation will discuss the detailed quantitative and qualitative correlation between the growth of the Bi phase and the evolution of diffraction peaks. The experimental methodology developed in this work has the potential to be extended to investigate a wide range of alloy solidification mechanisms, enabling a deeper understanding of the field.