Board mount EMI enclosures are typically metallic shielding enclosures that are designed to fit over sensitive electronic components to prevent EMI from getting into the circuit and affecting performance. They are also used to prevent spurious emissions radiating from the circuitry and interfering with other devices. This can include equipment that may have subsystems that may interfere with each other and thus require shielding.

High-speed digital circuitry generates harmonics associated with the clocks and many sub-multiples of clocks along with considerable broadband noise. This noise can radiate from the printed circuit board, every track being a potential radiating antenna. Board Mounted EMI Enclosures help solve this problem by sitting over the electronics circuit, and connecting with a ground plane layer of the electronics or another shield on the other side of the PCB. This connection to the PCB makes them board mounted. EMI Enclosures create Faraday Cage style enclosures so named after the effect discovered by Faraday pertaining to metallic enclosures having their volume at equipotential. The reality is that localized eddy currents can be set up by impedance differences and inductive pickup and that this can lower the effectiveness of the enclosure to reduce EMI. Materials can be selected to reduce these effects. Absorbers can be added to the Enclosure to improve their capability. Improvements can be made by taking care in the earthing of the enclosure (which is usually in a star connection) to suppress currents or force any currents to flow in understood ways.

Customized EMI Enclosures can be obtained from manufacturers in return for a one-off engineering charge (NRE) and in many cases, the material has holes as this does not adversely affect performance. Some enclosures come in two parts. For example, one part could be the walls of the enclosure and a second part the roof, being a sprung, soldered or attached by twisting tabs. There are various forms of this kind of enclosure, some even being press fit into the PCB.