The Aerosol-on-Demand (AoD) jet-printing principle:
a novel concept for 3D-printed electronics

Additive manufacturing of electronics is experiencing increasing demand. Since neither molds nor printing forms are required, the integration of functional electronic components onto 3D objects by means of digital printing technologies such as inkjet, extrusion, aerosol and electrohydrodynamic printing facilitate mass customization. Due to a constant jet width over a large range, aerosol jet printing has the advantage to allow printing onto 3D surfaces without adaptation of the distance between the printhead and the object. However, existing aerosol jet printing systems require the printheads to be orientated in the direction of gravity, operate only continuously and thus need a shutter system to realize discontinuous structures. We develop a novel Aerosol-on-Demand (AoD) jet-printing system that solves the major challenges of digital printing technologies. The core of the patented AoD technology is a new method for aerosol generation from a point-like source within the printhead directly in a sheath gas flow, which hydrodynamically focuses the generated aerosol by means of the inner contour of the attached nozzle. Based on the results obtained by first experiments we implement a CFD model of the printhead. CFD simulations show the feasibility of the hydrodynamic focusing of the locally generated aerosol as well as the existence of stable operating points. Furthermore, the simulations lead to the design of a test setup. Experiments with the test setup verify that aerosol generation can be controlled on demand and thus printing of discontinuous microstructures is possible without ink loss and need for a shutter. There are no aerosol-conducting parts other than the nozzle, i.e. there is no dead volume and no material waste. The minimum ink volume and the cleaning effort are extremely reduced; ink degradation occuring in common atomizers is eliminated. In addition,after a short initial run-in period for the sheath gas no further run-in period is required for the aerosol jet. The aerosol mass flow can be controlled inline to provide a constant ink transfer rate over a wide range of printing speeds. Finally, the printhead can be freely rotated in space during the printing process. Thus, it is also possible to print on stationary components of complex 3D-shape. In conclusion, the novel AoD jet-printing principle shows great potential for applications in functional printing of 2D & 3D electronics