Board Level Shielding Cans: Design, Attachment and Removal

A shielding can is a metal cover soldered or clipped over a circuit that radiates or is susceptible. It is effective, it is expensive, and it is frequently specified where a layout change would have been cheaper and more reliable.

What the Can Actually Does

A metal enclosure attenuates the electric field that would otherwise escape, and the attenuation depends on the conductivity and thickness of the metal, and on the frequency. At the frequencies used in most digital products the metal is not the limiting factor.

The limiting factor is the openings. A can with a large aperture behaves as an antenna at the wavelength corresponding to the aperture dimension, and the shielding effectiveness collapses at that frequency.

This is why the design of the can is mostly the design of its openings and its ground connection, and why a can that appears solid can still fail to contain an emission that the layout produces.

Apertures, Slots and Seams

The rule that matters is that the largest dimension of any opening should be small compared with the wavelength of the highest frequency of concern. A long narrow slot radiates along its length, so a single long seam is worse than several small holes whose total area is the same.

Where a can needs openings for ventilation or for a cable, the opening should be split into a group of small apertures rather than left as one large one. A honeycomb pattern is the classical solution and it is effective because every dimension is small.

Cable penetrations are the hardest case, because the cable itself carries the current that radiates. Filtering or ferrite suppression on the cable is usually required in addition to the can, and our ferrite bead notes describe how the suppression is chosen.

Grounding the Can to the Board

The can must be connected to the ground reference with a low impedance at the frequencies of interest. A connection at one point only leaves the rest of the perimeter as an aperture, and the can then behaves as a resonant cavity coupled to the board.

Continuous grounding along the perimeter is achieved with a fence of vias connected to the ground plane, and the spacing between the vias sets the highest frequency at which the fence behaves as a continuous wall. Sparse stitching turns the fence into a series of slots.

The connection between the can and the board must also be reliable over temperature and over the life of the product. A mechanical clip relies on contact pressure, while a soldered attachment is permanent, and the choice affects the rework strategy.

Mounting Methods and Their Consequences

A soldered can is attached with a paste deposit around its perimeter and reflowed with the rest of the assembly. It gives the best electrical connection and it is the most difficult to remove.

A clip or frame system allows the cover to be removed for inspection and rework, at the cost of a less certain contact. The frame is soldered and the cover clips onto it, so the electrical connection depends on the clip.

A conductive gasket between the can and the board improves the contact and compensates for surface roughness, and it requires the can to be pressed against the gasket with some force.

Thermal Consequences

A can traps heat as well as radiation. Components inside it run hotter than the same components on an open board, and the temperature rise depends on the can size, the airflow and the amount of power dissipated inside.

Where the circuit inside the can dissipates significant power, the can may need a thermal path to a heatsink or to the chassis, and the can itself may become the heatsink.

Our thermal design notes describe how the internal copper is used to spread heat, which becomes more important once the can reduces the convective path.

<img src="https://www.gopcba.com/wp-content/uploads/2026/06/Point-to-Point-Wireless-Bridge-PCBA.jpg" alt="Ground fence vias around a shielding can footprint” />

Interaction With the Layout Beneath

The can occupies the area on both sides of the board if it is a full enclosure, and it changes the impedance of any trace that runs close to it. A trace that runs near the can wall sees a different environment from one that runs in open air.

The cavity formed by the can and the ground plane below has a resonant frequency of its own. Where a circuit radiates at that frequency the emission is enhanced rather than suppressed, and the remedy is to change the cavity dimensions by moving the can boundary or adding a partition.

Components placed at the edge of the can footprint must respect the can wall and the ground fence, which reduces the usable area inside. The footprint should be drawn in the layout with its keep-out, not added afterwards.

Cost and the Alternatives

A can adds the part, the attachment process, the ground fence, the keep-out area and a rework complication. It is worth comparing against the cost of fixing the source.

A layout change that shortens a return path, a slower edge rate on a clock, or a better decoupling arrangement often satisfies the emission requirement at lower cost. Our EMI immunity notes describe the layout measures that reduce the need for shielding.

Our cost reduction notes cover the assembly cost implications of a shielding step, which are often larger than the part cost.

Susceptibility in the Other Direction

A can also protects a sensitive circuit from external fields, and in that role the requirements are the same. A well grounded enclosure with small apertures attenuates an incoming field, and a poorly grounded one may make the situation worse by concentrating the field at its edges.

Where a circuit is sensitive to a narrow band, a ferrite absorber or a resistive material on the inside of the cover can damp the cavity resonance, which is a common fix for a product that passes marginally.

Our solder defects notes describe the attachment defects that produce a can whose ground path is intermittent, which appears as a product that passes in one unit and fails in the next.

Process Control and Verification

On a design of this kind, aperture is the item that decides how the rest of the board is arranged. The measurements that matter are the repeatable ones: conductor width and spacing, annular ring, finished hole size, plating thickness and surface finish are all verifiable on a coupon that travels with the panel. Running a first article through the same checks as the production panel confirms that the two agree, and that comparison is the cheapest form of process control available at prototype stage.

FAQ

Is a shielding can always necessary? No. Many products meet their limits with layout alone, and the decision should follow from a measurement rather than from the assumption that a shield is required.

Does a metal lid need to be soldered all round? It needs a continuous low impedance connection around the perimeter, which can be provided by a soldered seam or by a dense via fence with a clip or gasket contact.

What does gopcb provide where shielding is required? We provide the can footprint and ground fence in the layout, stencil and attachment support for soldered or clip-mounted parts, cavity resonance guidance, and inspection of the ground connection. Where the requirement can be met by layout, we say so and save the cost.