Influence of embedding materials on heat transfer and ignition transfer time in heterogeneous reactive material system
Reactive materials comprise particulate systems or multilayer materials consisting of two or more materials reacting with each other after they are ignited. The reaction initiation is possible using different sources of energy transfer, for example, an electric spark, laser pulse, mechanical forces or heating the whole system to a certain temperature. The propagation velocity in multilayer foils is in the order or greater than 10 m/s in dependence of the materials used in the bilayer stack. Typical application fields of this bilayer systems are soldering, welding, brazing or heating, especially important in microelectronic and microelectromechanical systems processing technology. For this applications different materials are used and in particular cases they are micro-heterogeneous. Due to the high propagation velocity and the accompanying large temperature gradients stress issues may arise. For this reason, it is necessary to design the heat and reaction propagation velocity in the heterogeneous reactive material system. In the current presentation the heat propagation in a heterogeneous reactive material system is studied using the COMSOL simulation tool. For the study of the heat transfer and ignition transfer time a model system was designed. It consists of a silicon substrate, 525 µm thick and 1 cm long, covered with a 100 nm thick silicon dioxide layer. On top of the layer a multilayer reactive material stripe was placed having a width and a height of 1 µm, respectively. The space between this material stripes was filled with different materials (SiO2, Si3N4, AlN, Si, diamond). On top of this heterogeneous layer a 1 µm thick sealing layer, consisting of an identical or another material was placed. The carried out two dimensional simulations demonstrated that the embedding material allows to scale the ignition transfer time and the heat propagation velocity to values in a wide range. For example, for a transfer length of 1 µm the ignition time can be designed from nanoseconds to several microseconds. This means, that a proper material selection in the heterogeneous reactive material system can accelerate the ignition velocity. On the other hand, a reduction of the heat propagation velocity and the ignition transfer velocity is possible if low thermal conductive materials are used as filling material, as shown for particulate systems. A detailed analysis and comparison of the obtained results to available experiment will be given.