DOC KB-EMI-018REV 2026-09-21CLASS: PUBLIC
EMI and RFI Shielding Cases: When Plastic Is Not Enough
Direct answer
A standard plastic protective case provides no meaningful EMI/RFI shielding. When electronics must be shielded in transit or in use, the three established paths are: aluminum case construction (excellent inherent conductivity), plastic shells with conductive coatings (vacuum-metallized or conductive-paint interiors), and EMI gasketing — conductive elastomer seals that close the lid gap electrically. Shielding performance is set by the weakest path: an unsealed plastic lid gap defeats an aluminum body.
§01The three approaches
| Approach | Typical attenuation | Strengths | Watch out for |
|---|---|---|---|
| Aluminum case | very high, broadband | also fire/heat tolerant; durable threads | weight, denting, cost |
| Metallized / conductive-coated plastic | moderate, frequency-dependent | keeps weight and corrosion resistance of plastic | coating wear at latch/hinge points |
| EMI gaskets on any shell | — (completes the enclosure) | closes seams and lid lines | must be inspected; takes compression set like any elastomer |
§02Engineering notes
- Apertures dominate: a cable pass-through or valve hole acts as an antenna slot. Every penetration needs a filtered connector or a waveguide-below-cutoff design.
- Galvanic compatibility: pair conductive gaskets with the shell metal plating to avoid corrosion couples (aluminum body needs stainless or aluminized gasket fillers).
- Testing: shielding effectiveness is measured per IEEE 299 on the assembled enclosure — ask for the test frequency range, not just "shielded".
- Combine with ESD foam: shielding the enclosure and using dissipative foam inside are complementary, not redundant.
Reality check: many buyers specify "EMI case" when they actually need ESD-safe packaging. Shielding blocks external RF in/out; ESD protection prevents static discharge to components. If the threat is a charged operator touching a PCB, anti-static foam and packaging discipline solve it at a fraction of the cost.