Aerosol Jet® Direct-Write for Microscale Additive Manufacturing

The unique capabilities of Aerosol Jet® technology for noncontact material deposition with in-flight adjustment of ink rheology in microdroplets are explained based on first principles of physics. The suitable range of ink droplet size is determined from the effectiveness for inertial impaction when depositing onto substrate and convenience for pneumatic manipulation, in-flight solvent evaporation, etc. The existence of a jet Reynolds number window is shown by a fluid dynamics analysis of impinging jets for Aerosol Jet® printing with long standoff between nozzle and substrate, which defines the operation range of gas flow rate according to the nozzle orifice diameter. The time scale for ink droplets to remove volatile solvent is shown to just coincide that for them to travel in the nozzle channel toward substrate after meeting the coflowing sheath gas, enabling the in-flight manipulation of ink properties for high aspect-ratio feature printing. With inks being able to solidify rapidly, 3D structures, such as tall micropillars and thin-wall boxes, can be fabricated with Aerosol Jet® printing. Having mist droplets in the range of 1–5 μm also makes it possible to print lines of width about 10 μm.