Improving the shielding effectiveness of a board-level shield by bonding it with the waveguide-below-cutoff principle

This paper discusses the shielding performance or shielding effectiveness of a board-level shield in function of its bonding method. Improved shielding performance at board-level in order to harden integrated circuits against unintentional and intentional electromagnetic interference, and this under harsh environmental conditions, is getting more and more important to achieve the desired levels of functional performance and operational reliability despite an ever more aggressive electromagnetic environment. High levels of operational reliability are increasingly being required to help control functional safety or other risks. As a board-level shield on its own only provides 5 of the 6 required walls to form a complete Faraday Cage, its overall shielding performance depends heavily on the way it is bonded to the printed circuit board´s ground plane. It is shown by full-wave simulations that the shielding effectiveness can improve by more than 40 dB when bonded with the waveguide-below-cutoff principle compared to a classic perimeter bond of a single row of vias. And this even if the waveguides-below-cutoff are formed by rows of vias. Finally, the paper stresses the influence that internal resonances of the board-level shield have on its shielding effectiveness.