Reactive nanometer mulitlayers as tailored heat sources for joining techniques
Established joining techniques like welding, soldering or brazing typically are characterized by a large amount of heat input into the components. Especially in the case of heat sensitive structures like MEMS this often results in stress induced deformation and degradation or even in damaging the parts. Therefore, there is an urgent need for a more reliable and reproducible method for joining, which is characterized by a well defined and small heat input for only a short time period. So-called reactive nanometer multilayers offer a promising approach to meet these needs. Reactive nanometer multilayers consist of several hundreds or thousands of alternating nanoscale layers, which can exothermicly react with each other. Placing a reactive nanometer multilayer coated with a solder or brazing layer between two surfaces, it can be used as a controllable local heat source for joining. After activating the chemical reaction by an electrical spark, laser pulse or mechanical impact, a self-sustaining intermixing reaction starts, which propagates through the whole film resulting in a stable intermetallic compound, such as NiAl. The peak temperature of the reaction can be well above 1400 °C, but this temperature is only reached for milliseconds, so that the heat is localized to the solder layers. The components itself remain at room temperature during the entire process.