Exploring material chemistry for direct ink writing of reactively formed conductors†
In recent years, there has been a precipitous rise of additive manufacturing (3D printing) as a means of rapid prototyping as well as quickly and cost-effectively fabricating parts or entire systems in small quantities. One limiting factor has been the ability to seamlessly incorporate electrical components into 3D printed systems. While implementation of pick-and-place methods to insert components has readily been achieved, the connections between these components as they are embedded in systems during a build has been limited by the number of suitable inks. Silver inks have been most widely used, but are unsuitable for applications with moderate to high current density as they are susceptible to electromigration induced failure. Here we present a new material concept for 3D printing of electrical conductors: particles with stored chemical energy which, when provided some input energy, undergo a self-propagating high-temperature synthesis (SHS) reaction to form a mechanically and thermally stable, electrically conductive product. Inks incorporating these particles are non-conductive as-printed, but can be converted on demand into a conductive state. In this work, we explore and characterize model chemistries for this approach using physical vapor deposition of multilayer foils and particles and demonstrate a proof of concept of on demand conductor formation.