EMI gaskets rarely fail because the material itself is flawed. In most field failures, the gasket is performing exactly as specified. What fails instead are the assumptions made about how that gasket would behave once the product left the lab.
In industrial electronics, the same sequence plays out again and again. A system passes EMC testing. It ships. Early deployments look clean. Then intermittent issues begin to appear. Noise emerges under load. Communication becomes unstable near other equipment. The behavior cannot be reproduced reliably on the bench.
When those failures are traced back far enough, they almost always lead to the same place. The interface changed, but the design assumed it would not.
Treating EMI Gaskets as Static Shields
A foundational mistake is treating EMI gaskets as static shielding components. In practice, EMI gaskets manage an inherently dynamic boundary.
They sit between surfaces that move, relax, oxidize, vibrate, and age. Compression changes over time. Surface conditions evolve. Fasteners lose preload. Environmental exposure alters material behavior. None of this shows up in a shielding effectiveness number taken during initial testing.
When EMI gaskets are selected as if shielding performance exists independently of these factors, performance appears stable only until real conditions intervene. At that point, the gasket has not failed. The interface it depends on has drifted outside the conditions for which it was designed.
This distinction matters because shielding problems caused by interface drift do not announce themselves cleanly. They appear intermittently, under specific operating states, and often disappear during troubleshooting.
Designing for the Test Instead of the Service Life
Many EMI gasket failures are locked in during enclosure design, long before procurement or assembly.
During validation, enclosures are closed once, torqued evenly, and left undisturbed. The gasket is compressed uniformly. Surfaces are clean. Temperature is controlled. Under those conditions, shielding performance looks excellent.
In service, the enclosure behaves differently. Panels are opened and closed. Vibration introduces micro movement. Thermal cycling changes contact pressure. Over time, compression becomes uneven, particularly at corners, long spans, and areas with limited fastener support.
At higher frequencies, it takes little. Small discontinuities at seams can behave like slot antennas. A gasket that looked robust in testing can lose effectiveness when parts of the interface fall below minimum compression.
This is not a manufacturing error. It is the predictable result of designing for a moment in time rather than a service life.
Assuming Electrical Continuity Without Verifying It
Another common failure path begins with a reasonable assumption that turns out to be false. Designers assume electrical continuity exists at a seam because the parts are metal.
In reality, surface treatments often break that continuity. Paint, powder coating, anodizing, and oxidation all introduce insulating layers. The gasket may be installed correctly, compressed to spec, and still pressed against a surface that cannot carry current.
This assumption tends to fail in the same ways across industries:
- Coated or anodized surfaces block current flow at gasket interfaces.
- Oxidation increases contact resistance even on initially bare metal.
- Fasteners provide point contact, not continuous electrical bonding.
- Gaskets are expected to bridge gaps they were never meant to overcome.
From a systems perspective, what appears grounded is not always bonded. Without deliberate surface preparation and defined contact zones, the shielding path is broken exactly where continuity matters most.
Selecting by Shielding Numbers Alone
Published shielding effectiveness values are useful, but they are not sufficient. Those numbers are generated under controlled conditions that do not reflect real assemblies. They do not account for compression variation, recovery behavior, tolerance stack-up, or long-term material aging. Two EMI gaskets can show similar attenuation during testing and behave very differently once installed.
The compression range defines whether the gasket operates within its functional window. Recovery determines whether it maintains contact after cycling. Resistance to compression set determines whether performance degrades gradually or holds over time.
When tolerance variation pushes the gasket outside its intended operating range, shielding performance drops regardless of what the datasheet promised. Engineers who investigate these failures often find that the material was appropriate, but the interface conditions were not.
Separating Environmental Sealing From EMI Performance
Environmental exposure does not act independently of EMI performance. It attacks the same physical contact that shielding depends on.
As moisture, dust, and contaminants reach the interface, contact resistance increases. Corrosion forms at mating surfaces. Elastomer behavior changes with temperature and humidity cycling. Compression slowly relaxes as materials age. In industrial environments, these effects are not edge cases. They are routine.
EMI gaskets that also provide environmental sealing preserve the physical conditions required for electrical continuity. Without sealing, shielding performance erodes gradually, often without a clear failure point. By the time symptoms appear, the interface has already changed.
Treating sealing as optional or secondary ignores how EMI performance is actually maintained over time.
Allowing Substitutions Without Redefining the Interface
Many field failures originate not in design, but in purchasing decisions made under time or cost pressure.
Substitutions are approved based on perceived equivalence, often defined by a single shielding value. What gets overlooked is how differences in base elastomer, conductive filler, hardness, compression behavior, and environmental resistance affect long-term performance.
The substitution does not fail because it is inferior. It fails because the specification described a test outcome rather than the interface requirements. Without redefining those requirements, substitutions introduce uncontrolled variation into a boundary that was already sensitive.
Experienced teams learn this lesson the hard way. Once interface behavior is lost, failures follow slowly and unpredictably.
Where EMI Gasket Decisions Actually Matter
Most EMI gasket failures are not sudden. They develop quietly as interface conditions drift away from the assumptions made during design and procurement.
Avoiding those failures requires treating EMI gaskets as boundary components with lifecycle behavior. Compression behavior, surface conditions, environmental exposure, and service history all shape performance. When those factors are addressed intentionally, EMI gaskets stabilize systems and preserve predictable operation.
When they are ignored, the gasket becomes a convenient scapegoat for failures built into the system from the start.