Aspects of the present disclosure relate to determining the location and/or density of vias that form part of an RF isolation structure of a packaged module and the resulting RF isolation structures. From electromagnetic interference (EMI) data, locations of where via density can be increased and/or decreased without significantly degrading the EMI performance of the RF isolation structure can be identified. In certain embodiments, one or more vias can be added and/or removed from a selected area of the packaged module based on the EMI data.