Session: Government Agency Student Posters

Paper Number: 171730

Understanding Droplet Evaporation in Aerosol Jet Printing to Mitigate Adverse Drying Effects 

Aerosol jet printing is an additive manufacturing method that enables conformal, multimaterial printing with high precision capable of meeting complex fabrication challenges in the automotive, aerospace, and healthcare industries. This technique utilizes a fine aerosol mist containing micron-sized droplets which are transported to the printhead on a carrier gas flow. An annular sheath gas, which serves to focus and accelerate the aerosol through a converging nozzle, allows for droplet impingement on a substrate 1-5 mm away at high resolution. These characteristics enable broad materials compatibility, printing on non-planar surfaces, and rapid prototyping, thereby supporting fabrication of hybrid electronics, sensors, and RF communications. However, the conventional use of a dry sheath gas promotes uncontrolled vapor diffusion and droplet evaporation which can compromise overall print quality especially when printing under dry conditions. Excessive droplet drying can increase the prevalence of overspray, rebounding particles, and feature porosity leading to poor device performance, low material throughput, and raising health and safety concerns. These effects are exacerbated while printing in dry, undersaturated conditions such as low carrier gas flow rates and high focusing ratios. Coincidentally, these are common operator practices to achieve high resolution without much concern for their negative externalities such as curtailed deposition rates and overspray.

To address this, we present a straightforward method to reduce the extent of evaporation in undersaturated conditions by pre-saturating the sheath gas with solvent vapor. This is done by passing the dry sheath gas through a bubbler containing solvent analogous to the ink’s individual chemistry. The sheath gas saturation technique was demonstrated across a variety of inks in a water-based polymer solution (polyimide), a colloidal dispersion in nonpolar organic solvents (xylenes-based silver nanoparticles), and a colloidal dispersion in an aqueous medium with polymeric binders (water-based silver nanoparticle) to illustrate the method’s generalizability to solvent-based inks within aerosol jet printing. Printed features were quantitatively evaluated for overspray extent and deposition rate using an optical microscope and optical profilometer, respectively. Image analysis utilized a python code for baseline fitting and calculations to obtain cross sectional area and volumetric deposition rate measurements. In this work, sheath gas saturation significantly reduced the prevalence and extent of droplet evaporation in the aerosol phase, particularly at the periphery of the carrier gas flow. In turn, this improved line edge morphology, pitch capabilities, resistivity, aspect ratios, and surface finish of printed samples. Using this in-flight mechanism to tailor droplet properties reduced the overall footprint of the overspray by 47% in the polyimide ink and decreased the resistivity of the printed silver nanoparticle ink by 34%. In addition, experimental results were complemented by theoretical analysis and a supporting COMSOL numerical model to provide a more generalized understanding of the underlying process physics associated with droplet drying within the printhead. This supports our understanding of the mechanisms that cause overspray which can facilitate guided ink formulation and process development. The capability to meaningfully amend droplet properties in flight allows print outcomes to be tailored for a variety of complex challenges facing additive manufacturing such as fine pitch, high surface finish, and increasing aspect ratios, paving the way for improved functionality of printed electronics.

Presenting Author: Bella Guyll Iowa State University

Presenting Author Biography: Bella Guyll is a Ph.D. candidate in mechanical engineering at Iowa State University. She is funded by the NSF GRFP and is focused on studying the fundamentals of aerosol jet printing as it relates to droplet evaporation and high throughpiut printing capabilities.

Authors:

Bella Guyll Iowa State University
Brayden Sanford Iowa State University
Cary Pint Iowa State University
Ethan Secor Iowa State University