Electrospray Deposited Silver Films for Electromagnetic Interference (EMI) Shielding of Flip Chips

Electrospray deposition (ESD) is a novel additive manufacturing process that uses a high electric potential to generate a spray of charged, solvent-encapsulated particles. The solvent evaporates in-flight to deposit solute material onto a target, which aggregates to create a continuous film. ESD is an electrophoretic process, allowing the formation of conformal films with targeted, non-line-of-sight coverage on 3D surfaces. Material emitted by electrospray is highly charged and will follow the electric field lines established between the emitter and a grounded target; thus, this process is best suited for deploying material onto (grounded) conductive surfaces. In contrast, delivering material to insulating surfaces is more difficult due to charge accumulation on the target. We report on a new approach to improve deposition on insulating targets by manipulating the local electric field and distribution of charge near the target through a dielectric “stencil.” Using this method, we manufacture thin silver films that can provide electromagnetic interference protection to SiP architectures and replace board-level shielding, which is not optimized for space-constrained environments. We evaluate film shielding performance from 1 - 10 GHz, with a minimum target of 50 dB of isolation.