Untersuchung der Eigenschaften sowie der Anwendung von reaktiven Mehrschichtsystemen in der Aufbau- und Verbindungstechnik
Diese Dissertation befasst sich mit den Eigenschaften sowie mit der Untersuchung der Anwendbarkeit exotherm reagierender Mehrschichtsysteme in der Aufbau- und Verbindungstechnik. Die untersuchten Mehrschichtsysteme bestehen dabei aus zumeist aus Metallen, die nach überwinden der Aktivierungsenergie intermetallische Phasen bilden und dabei thermische Energie freisetzen. Dabei können Temperaturen von über 1600°C erreicht werden. In dieser Dissertation wurden vier Materialsysteme näher untersucht. Neben dem Aluminium-Nickel System, das bereits eingehender in der Literatur dargestellt wurde, waren das Titan-Silizium, Aluminium-Titan und das Aluminium-Kupfer System Gegenstand der Untersuchungen dieser Arbeit. Dazu wurde neben der Geschwindigkeit der Reaktionsfront und der Reaktionstemperatur auch die Aktivierungsenergie der Systeme ermittelt. Zudem wurde untersucht, inwieweit diese Systeme als Energiequelle für das Bonden von Bauteilen in der Aufbau-und Verbindungstechnik geeignet sind.
This work is focusing on the thermal properties of reactive multilayer systems. Reactive multilayer systems are layered materials or foils which commonly have a single layer thickness between one and 100 nm and a total thickness of one to 500 µm. In most cases, these multilayer systems comprise metallic or oxide materials and components that react after reaching an activation temperature exothermically. The reaction of oxide layers with metallic layers are known as thermite reaction where the change of the oxidation state of the reaction partners leads to a heat release. The most common example of this kind of reactions is the reduction of iron-(III)-oxide to iron and the oxidation of aluminum at the same time. In pure metallic multilayers, the heat release is attributed to the formation of intermetallic phases. The advantage of sole metallic thin films and foils is that there is no oxygen or other gases needed to keep the reaction going. The temperatures reached in these reactions can be higher than 1600°C. Therefore, this materials and foils are very suitable as heat source for soldering and welding. The reaction times are in the range of milli- and microseconds. This leads to a very low thermal stress for the soldered parts. The aim of the following research is the analysis of different material combinations that exhibit the mentioned exothermal behavior during the formation of intermetallic phases. As possible material systems aluminum-nickel, aluminum-titanium, titanium-silicon and aluminum-copper were identified. For these material systems, the analyses are focusing on the amount of heat released during the reaction as well as on the velocity of the reaction front. It could be shown, that all the different thermal properties are based on the diffusion between these materials. Therefore, the diffusion coefficients of the different material systems were determined for different temperatures using optical glow discharge emission spectroscopy for bi-layer systems of an overall thickness of 5 µm. As a result the activation energy and the diffusion constant for these systems was determined leading to the assumption that in this magnetron sputtered thin film systems the main diffusion mechanism is the grain boundary diffusion. The velocity of the reaction front was between 0.5 m/s for the slowest reaction in the material system aluminum-copper and 22 m/s for the fastest system (titanium-silicon). The reaction kinetic was determined using differential thermal analyses. Besides, the reaction enthalpy also the activation energies depending on the total film thickness could be determined. It could be shown, that two different mechanisms are important for the reaction of the multilayers. For the systems aluminum-nickel, titanium-silicon and aluminum-copper a diffusion determined mechanism is the driving force for the reaction whereas for titanium-aluminum an interface-determined mechanism is the most important. In the first case, the activation energies of the reaction are very close to the activation energy of the diffusion. In the second case, the activation energy of the reaction is much higher than the diffusion. Another focus was put on the application of reactive multilayer for bonding purposes. Therefore, two substrates were bonded using directly sputtered multilayers as well as commercially available Nanofoils ?. It could be shown, that the application of such reactive material systems is suitable for bonding different materials. The bonds of two alumina substrates exhibit a tensile strength of 10 to 30 N/mm² using commercial Nanofoils ?. Furthermore, the influence of the roughness was studied as well as the thermal conductivity of the bond after the joining process of heat producing microchips with a heat sink. The achieved results can be used as a contribution to a computational model to simulate the reaction as well as the influence of the reaction on the surrounding material. The implementation of such a model for the application of reactive multilayer systems should be the next step to give users of these materials the chance finding the most suitable multilayer system and thickness for the respective bonding system.
Nutzung und Vervielfältigung:
Alle Rechte vorbehalten