Reactive systems like Ni/Al, Co/Al, Ru/Al, Ti/Al and Ni/Ti show strong exothermic behavior upon ignition, creating a self-propagating reaction. The latter allows these systems to be efficiently used for thermally sensitive packaging and bonding applications, since despite the high temperature required to sustain the reaction, this dissipates rapidly outside the localized bonding interface. Thus, the components to be joined do not suffer damage from high-temperature exposure. In the field of MEMS (Micro-Electro-Mechanical-Systems) packaging, Al/Ni systems are specially investigated due to the fast reaction that these two metals exhibit upon ignition. In the most common approach, Al/Ni systems come in the form of multilayer foils (40-150 µm) and are commercially fabricated by vacuum deposition technologies and magnetron sputtering. These techniques can be costly and relatively slow. In that sense, electrochemical deposition lends itself as a cost-effective and scalable option for the fabrication of such systems.

In this study, a novel method for preparing Al/Ni reactive coatings by electrochemical deposition is being investigated. The process involves the electrodeposition of Al from an AlCl3:[EMIm]Cl 1.5:1 ionic liquid and the co-deposition of Ni in form of nanoparticles (NPs) into the Al metallic matrix. These NPs are initially well dispersed in the Ionic liquid bath. Initial attempts of electrochemical deposition of Al in the presence of Ni NPs have been carried out applying current by pulses and fixed potentials at different substrates like Pt, Ti and glassy carbon. A magnetic stirrer was used at 400 rpm to maintain the NPs suspended in the electrolyte and to transport them towards the working electrode. With this setup, free-standing Al/Ni reactive dispersion coatings were obtained from a stirred ionic liquid bath containing 20 g/L of Ni NPs. With this setup a maximum amount of 22 at% of Ni NPs could be incorporated into the Al layer, as confirmed by atomic absorption spectroscopy. For the targeted application (reactive layers) amounts of 50 at% Ni are required. But even for the lower amounts reactive behavior of the coatings was verified via differential scanning calorimetry (DSC). A higher incorporation of Ni NPs (~50 at%) could be achieved using a stationary solution basic electrochemical cell with a magnet behind the substrate. Using this setup, Al/Ni layers were obtained by applying pulses of potentials over a bottom-placed Ti substrate. Scanning electron microscopy (SEM) and energy-dispersive X-Ray spectroscopy (EDS) reveal a good Ni particle dispersion in some deposition areas of the coatings. Our next steps will target the improvement of the homogeneity and the deposition rates.