On the Microstructure of Off-Eutectic Au-Ge Joints: A High-Temperature Joint
Peer reviewed, Journal article
Accepted version
Permanent lenke
https://hdl.handle.net/11250/2711702Utgivelsesdato
2019Metadata
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Originalversjon
Larsson, A. & Aamundtveit, K. E. (2020). On the Microstructure of Off-Eutectic Au-Ge Joints: A High-Temperature Joint. Metallurgical and Materials Transactions A, 51(2), 740-749. https://doi.org/10.1007/s11661-019-05530-4Sammendrag
Joining delicate electronic components for high-temperature applications is challenging. Regular soldering with lead-free or lead-based materials is typically not suitable for high-temperature applications due to their low melting points. Using off-eutectic compounds for joints offer an easy and gentle process creating joints that can be formed at a lower process temperature than the final operation temperature. Microstructural evolution near the eutectic melting point is key to be able to form reliable joints. A layered Au/eutectic Au-Ge/Au structure was used to form Au-rich off-eutectic Au-Ge joints. Columnar-like structures of primary α-phase (Au) protruded through a Ge-rich off-eutectic Au-Ge mixture at the center of the joint. These structures connect the joined pieces with a single solid phase with a melting point of ca. 1064 °C. The microstructure coarsened when exposed to temperatures between 300 °C and 380 °C, i.e., near the eutectic melting point at 361 °C. Ge diffused and accumulated along grain boundaries between Au grains. Annealing above the eutectic melting point, Ge rapidly diffused and formed larger colonies of pure Ge surrounded by a Au matrix. This accords well with our previously published results demonstrating shear strength capacity of similar joints at temperatures well above the eutectic temperature.