Understanding oblique deposition in aerosol jet printing for conformal electronics fabrication

Aerosol jet printing is a compelling additive manufacturing technology to enable direct patterning of electronic devices onto complex 3D surfaces. While aerosol jet printing can support deposition in an oblique configuration (with the nozzle misaligned from the surface normal), the altered deposition physics associated with this have not been examined. We address this gap from a fundamental perspective, coupling experiments and numerical simulation to understand the effect of asymmetry in the oblique jet, which sweeps small aerosol droplets downhill on tilted substrates. Modeling results of an oblique aerosol jet show that, although larger droplets are relatively unaffected due to their greater inertia, the altered impaction of smaller droplets results in an asymmetric cross-sectional profile and increased line width, which is sensitive to both the nozzle-surface orientation and offset distance. To complement the numerical simulations, silver traces are printed with varying gas flow rates, nozzle standoff distance, and nozzle orientation. Asymmetry, line width, and resistance increase with tilt angle, an effect reduced at higher flow rates and closer nozzle positioning, corroborating the numerical model. Finally, a printhead mounted on a 6-axis robotic arm was used to conformally print onto a complex 3D surface, showing improved flexibility in process design and highlighting the challenging geometries that can be accommodated when the fundamental mechanisms of oblique aerosol printing are considered.