Au–Sn solders applied in transient liquid phase bonding: Microstructure and mechanical behavior

Du, C. and Soeler, R. and Völker, B. and Matoy, K. and Zechner, J. and Langer, G. and Reisinger, M. and Todt, J. and Kirchlechner, C. and Dehm, G.

Volume: 8 Pages:
DOI: 10.1016/j.mtla.2019.100503
Published: 2019

Transient liquid phase bonding offers one option to generate a robust lead-free die attach with sound thermal and electrical conductivity in microelectronic packages. However, it is a challenge to characterize the microstructure and mechanical behavior of the bonding layer because of its ultra-thin thickness and its nano-sized constituents. We show that microstructures and local mechanical properties of such a modern solder systems are accessible with state-of-the-art methods including transmission electron microscope, synchrotron X-ray nano-beam diffraction as well as micro-scale mechanical testing. Three sub-regions with different morphologies have been identified within the bonding area, and their contained phases have been mapped. Two of the sub-regions contain nano-sized intermetallic compounds (IMC) while the third one is mostly composed of an FCC Au–Cu solid solution with a Cu concentration gradient. On top of that, micro-cantilever bending testing has been conducted to investigate the mechanical behavior of the bonding region. The two IMC sub-regions show brittle behavior while the Au–Cu sub-region is ductile. © 2019 Acta Materialia Inc.

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