One reason for failures during the manufacturing process of electronic systems is the creation of thermo-mechanical stress caused by reflow soldering. Transferring heat only locally to the solder joints instead of heating the entire component by using a reactive multilayer system (RMS) can be an option to reduce this stress. Such a system consists of at least two metal components that are arranged in alternating nanolayers with a thickness of 10 to 300 nm and a total stack thickness of up to 300 µm. After the ignition of this system (e.g., by an electrical spark) the materials intermix on atomic level in a high-speed and high-grade exothermic reaction. The amount of heat and the propagation speed is influenced by the materials used (both the reactive system and the target substrate), the thickness of each layer, the number of bilayers and the mechanical pre-processing of the surface. The deposition of an RMS on silicon substrates is already well-established, but it is more challenging on low temperature cofired ceramic (LTCC) substrates due to their significantly higher roughness and much lower thermal conductivity.

In this work, the deposition of an RMS consisting of aluminum and nickel on LTCC substrates with different pre-treatments is presented and analyzed. A raw unmachined substrate was used as reference material, whereas the surface of other samples was modified by chemical-mechanical polishing (CMP), laser ablation with different settings or coating with an additional metallization and/or solder layer, resulting in a difference in surface roughness and thus in different behavior concerning crack formation and adhesion.

To get more information about the exothermic reaction a suitable 2-D computational fluid dynamics (CFD) model was developed to provide insightful information which is not feasible to determine experimentally. The results of the simulations will also be presented and focus especially on the distribution of the temperature within the ceramic body, which will all help to ascertain the impact that is being made by the reaction and this can similarly be compared to other processes, such as reflow soldering, such that the benefits of reductions in induced mechanical stress can be quantified.