We develop reactive joining processes for firm bonding of micro-system components. Nanometer multilayers, for example, can achieve extremely local energy coupling with very short process times compared to conventional joining methods. This enables low-stress, well heat-insulated, high strength, and tight connections.
Systems made of nanometer-thin multi layers give off heat over an extremely short period during exothermic alloy formation. These reactive multilayers (RML), embedded between two layers of the lot, can therefore develop enough heat to enable solder joints between two join partners (Figure 1). RML's are either a separate foil between the join partners or are deposited and structured directly on one of the join partners. Alloy formation is started by a deliberate ignition impulse. During the reaction, the join partners are pressed together.
Due to the extremely short duration (a few milliseconds) of the reaction time, only the joining zone is heated, not the component to be joined. This makes it possible to solder temperature-sensitive components. It also reduces the thermo-mechanical stress between joining partners with different coefficients of thermal expansion. Compared to adhesive connections, the connection layer has greater mechanical strength and thermal conductivity.
Typical applications of reactive joining technology are in the field of heat management, mounting of stress-sensitive sensors, or housing. Figure 2 shows an example of a micro-Peltier cooler that was soldered using reactive joining on a copper heat sink. In this case, the RML used here is a layer system made of Ni/Al, applied directly to the heat sink.