EMI Shielding Can Design Guide: Materials, Seams, Grounding and Apertures
An EMI shielding can is a stamped metal cover that reduces electromagnetic interference between a circuit and its surroundings. The design must balance shielding performance, assembly, cost and manufacturability.
This guide covers the main design decisions: material, wall thickness, seams, grounding, apertures and retention features.
Shielding effectiveness basics
Shielding effectiveness (SE) is measured in decibels. Higher dB means more attenuation: 20 dB is about 90% attenuation, 40 dB about 99%, and 60 dB about 99.9%. The required level depends on the product, the frequency range and the applicable standard.
Material choice
| Material | Characteristics | Typical use |
|---|---|---|
| Nickel silver | Good conductivity, corrosion resistance, formability | RF modules, sensitive circuits |
| Stainless steel | Corrosion resistance, lower conductivity | General shielding, structural covers |
| Tin-plated steel | Low cost, solderable | High-volume consumer boards |
| BeCu fingers | Spring contact, high conductivity | Grounding and removable lids |
Seams and grounding
Most leakage occurs at seams, apertures and grounding points, not through the metal itself. A can should contact the PCB ground plane at multiple points. Solder tabs, conductive gaskets or spring fingers can be used. The distance between grounding points should be short relative to the highest frequency of concern.
Apertures
Holes and slots act as antennas. As a rule of thumb, the longest dimension of an aperture should be less than about one-twentieth of the wavelength at the highest frequency of concern. Many small holes are usually better than one large slot. If ventilation is required, use a perforated pattern rather than a large opening.
Wall thickness and draft
Thin walls are easier to form but may be less rigid. A drawn can often uses 0.1-0.3 mm material, depending on size and strength. Draft helps ejection and reduces scratching; for shallow stamped covers, draft may be minimal.
Retention and assembly
- Lead-in chamfers help the can seat without damaging pins.
- Snap features or dimples can retain a removable lid.
- Solder tabs should be accessible and flat.
- Avoid features that trap the can during automated placement.
FAQ
Does thicker metal always improve shielding?
Not necessarily. At many frequencies, seams, apertures and grounding dominate. Thickness helps, but design details matter more.
Can a shielding can be removable?
Yes. Removable lids often use spring fingers, dimples or a snap fit. The trade-off is shielding performance and cost.
Is nickel silver always better than stainless?
Nickel silver usually has better conductivity and formability, but it costs more. Stainless may be sufficient depending on the frequency and the required SE.
Related: EMI shielding cans and discuss a shielding design.
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