Meaning
Surface mounted metal enclosures placed directly over printed circuit board regions isolate sensitive circuitry from external radiation and contain internal emissions. Board level shielding consists of a thin metallic frame soldered to a ground plane fence with a removable or fixed cover covering the component area. Conductive barriers of this type attenuate both electric and magnetic fields, establishing an RF isolation zone for wireless transceivers and switching regulators.
Effectiveness drops at higher frequencies where gaps in solder joints or cover attachment teeth create parasitic radiating slots.
Attenuating Performance
Metal thickness and permeability dictate the absorption and reflection losses of the shield frame. Implementing board level shielding requires continuous ground stitching vias along the perimeter pad frame to prevent noise currents from escaping underneath the enclosure wall. Higher frequency signals demand smaller hole spacings between ground vias to maintain high isolation levels across the entire operating spectrum.
Thermal Dissipation
Enclosed integrated circuits generate localized heat that cannot easily escape through solid metallic covers. Perforated covers improve thermal airflow but allow high frequency electromagnetic energy to escape if hole diameters exceed maximum slot limits.
Mechanical Attachment
Frame spring fingers secure the top cover while allowing removal during rework or inspection steps. Mechanical deflection of the frame wall during reflow soldering can cause gaps, degrading RF isolation performance.
