The Effect of Droplet Sizes on Overspray in Aerosol‐Jet Printing

Abstract

One of the most important concerns of aerosol-jet based printing (AJP) is the substantial amount of overspray (OS) that can accompany printed traces. In this study, the authors develop a full, three-dimensional (3-D) computational fluid dynamics (CFD) model of the aerosol carrier gas flow (CGF), that is, confined by an annular sheath gas flow (ShGF) during the AJP process. The authors then use this model to pinpoint the fundamental fluid mechanics principles that control the OS in a standard AJP process as a function of the droplet size distribution and the ShGF rate. In their model, the authors consider the trajectories of various sized, monodisperse droplets in an inkstream in order to unravel the manner in which the OS is dictated by the intricate interplay between drop size and both gas flow (CGF and ShGF) rates. Their results explain several experimental results, namely 1) that there is an abundance of smaller sized drops in the OS region at low ShGF rates; 2) that the OS first reduces and then increases as the ShGF rate increases; and 3) that there is no longer a prevalence of smaller particles in the OS region at larger ShGF rates. The authors also discuss the hitherto unaddressed issues related to how 1) the large impact velocity of the ink droplets at the substrate surface (and the resultant Weber number) and 2) the misalignment between the CGF and the cylindrical axis of the ShGF annulus appear to affect OS. The authors anticipate that their analysis will provide an important understanding in the optimization of operating parameters for AJP with respect to OS that can result in an overall improvement in printing resolution.

A review of aerosol jet printing—a non-traditional hybrid process for micro-manufacturing

“…Improving edge definition and overall line quality by minimising overspray is currently achieved through empirical optimisation. Analytical models aiming to increase understanding of the deposition mechanism are starting to be developed, which will lead to a greater appreciation of the interdependence of process parameters and accelerate the development of robust print recipes [24,26].…”

Fabrication Techniques for Curved Electronics on Arbitrary Surfaces

“…[ 208 ] This method first aerosolizes a functional liquid into aerosol cloud with a diameter of 2–5 µm. [ 209 ] The carrier gas then transfers the aerosol to a printhead, where a coflowing sheath gas focuses the droplets onto the jet with a diameter of 10–100 µm. The droplets are focused into a collimated beam as small as 10 µm in diameter, and the aerosol beam is emitted with a velocity of ≈80 m s −1 .…”

Aerosol jet printed capacitive strain gauge for soft structural materials

“…2a-e where the electrode structure with trailing ends associated with overspray is observed in addition to a porous structure. Overspray is caused by the smallest droplets within the aerosol, and can be minimized to some extent by varying the sheath, exhaust, or atomizer flow rates 35,36 . However, overspray, like void formation, is an inherent feature of aerosol jet printed devices and was found to contribute between 5 and 25 µm of additional width to the digits.…”