Microanalyses for a better understanding of active soldering processes

0568409 - ÚPT 2023 CZ eng A - Abstrakt
Zobačová, Jitka - Motlová, Tereza - Vlček, Ivan - Dupák, Libor - Zobač, Martin
Microanalyses for a better understanding of active soldering processes.
16th Multinational Congress on Microscopy, 16MCM, 04-09 September 2022, Brno, Czech Republic. Book of abstracts. Brno: Czechoslovak Microscopy Society, 2022 - (Krzyžánek, V.; Hrubanová, K.; Hozák, P.; Müllerová, I.; Šlouf, M.). s. 367-368. ISBN 978-80-11-02253-2.
[Multinational Congress on Microscopy /16./. 04.09.2022-09.09.2022, Brno]
Institucionální podpora: RVO:68081731
Klíčová slova: active soldering * sapphire * titanium * indium * wetting
Obor OECD: Materials engineering
https://www.16mcm.cz/wp-content/uploads/2022/09/16MCM-abstract-book.pdf

Sapphire is a brittle, non-conductive material with excellent dielectric and thermal properties. It is used in advanced designs e.g. as part of an ion trap in extremely precise atomic clocks. For these designs would be very beneficial to join sapphire dielectrics permanently to metallic electrodes. Standard soldering techniques fail when used with non-metallic surfaces but so-called active soldering overcomes problems with the wettability of dielectrics. Different thermal expansion coefficients of the sapphire and metal can induce very high stresses if not properly controlled. One way is to use a ductile solder with a low working temperature. Active solders contain active elements such as titanium as part of a pre-prepared soldering alloy or can be added during the soldering process. Diffusion through solder can be sufficient to successfully wet the sapphire surface. The aim of this work is an investigation of titanium sapphire bonding using indium based solder activated by titanium. Different sample configurations were prepared according to Figure 1. Pure In is very ductile and has a low melting point of 156 °C which avoids the use for higher working temperatures. However, diffusion of the Ti during processing rises dramatically the melting temperature. The bonding quality of the joints was examined by electron microscopy. EDX analysis reveals the diffusion rate and distribution of the Ti during processing. For example, the scanning electron micrograph in Figure 3 shows differences between samples with and without additional Ti foil. The top row reveals the titanium foil did not melt uniformly in indium solder. The EDX microanalysis proved the presence of titanium beyond a few per cent in solder. The resulting solid-state solution may be detrimental concerning solder plasticity. The cracks on the interface of the sapphire surface may indicate the presence of plastic deformation, which, however, should be confirmed by future investigations. Future research will look for connections between process parameters, diffusion rates and resulting material properties and microstructure to find out the optimal combination of the above. The goal is a strong vacuum-tight joint with a working temperature range from cryogenic temperature up to at least 200 °C. Also, more complex alloys such as InAg20Ti2 are considered for further investigation.
Trvalý link: https://hdl.handle.net/11104/0339719