Electrospray Printed Silver Films on Insulating Targets for EMI Protection*

Electrospray printing is a low cost additive manufacturing technique that uses a high potential to generate a spray of charged droplets containing the solute (print) material. The solvent evaporates in-flight, depositing the print material onto a target surface; over time, thin films are formed. Traditional thin film processes like CVD and sputtering are expensive and offer poor uniformity on complex topographies. Alternatively, electrospray printing is an electrophoretic process, allowing the formation of uniform, conformal films with targeted, non-line-of-sight coverage on 3D surfaces. Here, we deploy silver in triethylene glycol monomethyl ether to form thin films that provide electromagnetic interference protection to system-in-package architectures. We seek to replace board-level shielding, which is not optimized for space-constrained environments. We evaluate the relationship between the print parameters, the film microstructure, and the resulting functional properties. We present a method to use electrospray printing to preferentially target insulative surfaces through manipulation of the electrical properties of the substrate and an optimized "stencil" that repels charge and facilitates delivery to the target. We test the films from 100 MHz - 6 GHz of applied frequency.