Electrospray Deposited Silver Films for Electromagnetic Interference (EMI) Protection on Insulating Targets

There is a growing drive to miniaturize electronic devices while maximizing their available internal space. Electromagnetic interference (EMI) protection is a critical concern as the proximity of components increases and their housing volume decreases. Thin films manufactured by electrospray deposition (ESD) can offer an effective, costconscious alternative to current board-level shielding, which is not optimized for space constrained environments. Electrospray is a low-cost additive manufacturing technology that uses an electric field to deposit conformal films onto complex surface geometries. Electrospray deposition has many advantages over traditional thin film manufacturing processes such as chemical vapor deposition (CVD), sputtering, and inkjet printing. In electrospray, a high electric potential atomizes a liquid precursor solution into a spray of electrically charged solvent droplets which contain the solute (print) material. In flight, the carrier solvent partially evaporates, and the solute material is continuously deposited onto a target substrate. Over time, the solute particles aggregate to form thin, continuous, conformal films with highly controlled microstructure. The film microstructure is governed by the processing conditions of the spray, thus directly influencing the film's functional characteristics. While ESD is best suited for deploying material onto (grounded) conductive surfaces due to the charge-driven nature of the spray, we report on a new, low-cost approach to improve deposition efficiency to dielectric (insulating) targets through a material 'mismatch.' Using this method, we manufacture thin, silver films on two dielectric samples: epoxy molding compound (EMC) test structures and model flip chips. Films are evaluated from 1 GHz-5GHz, with a minimum target of 5 0 d B of isolation.