Despite investing time and money in electromagnetic compatibility testing, engineering teams still see their designs run into unexpected interference. When a prototype fails, people often blame luck or manufacturing rather than asking whether the data were ever used. From a JEMIC perspective, those compression curves, corrosion charts, and attenuation graphs should be a road map, not a paperweight. What if you could translate test results into clear, simple rules that everyone from CAD designers to procurement can follow?

Why Shielding Test Data Often Sits Unused

Many companies invest in thorough lab testing only to stash the results in a folder and rely on intuition. It is common to hear, “We tested it once and moved on,” while different teams make decisions in isolation. Reports full of compression curves, surface roughness limits, and corrosion results never reach the drawing board or the purchasing desk. An article in Medical Device and Diagnostic Industry explains that each gasket profile has a unique compression curve and that underdeflection undermines conductivity while overdeflection causes permanent set.

A study in Interference Technology notes that aluminum is an active metal and corrodes rapidly when paired with more noble fillers. When these findings remain separate from design and procurement workflows, small missteps add up to costly failures. Integrating lab data into specifications is not optional; it is the only way to ensure that tested evidence guides the next build.

Core Parameters in EMI Gasket Testing That Must Feed Your Spec

1. Compression range

A gasket is more than a piece of rubber; it is a spring that needs to be squeezed just enough. Publications aimed at hardware designers stress that proper deflection is non-negotiable. If you do not compress a conductive elastomer within its working range, it will not make continuous electrical contact. Squeeze it too much and the cell walls collapse, making the gasket brittle and less conductive. Long-standing sources say that most profiles are designed for about thirty percent deflection and that designs should include compression stops. In our experience, conductive elastomer gaskets hold contact reliably when compressed roughly ten to thirty percent. Specifications should therefore call out:

• A numeric compression range for each gasket material and profile.
• A requirement that enclosure hardware and flange design preserve that range across manufacturing tolerances and environmental conditions.

2. Galvanic compatibility and operating frequency

When two different metals touch, electrons flow from the less noble to the more noble, setting up a battery and accelerating corrosion. An Interference Technology paper describes how silver-coated particles are highly conductive but can drive aluminum to corrode quickly, and how nickel-graphite fillers behave more like graphite and cause even greater aluminum weight loss during salt-spray tests. The same paper introduces a composite filler with an aluminum core and tungsten carbide coating that virtually eliminates galvanic coupling.

From a JEMIC perspective, the lesson is clear: pair gasket fillers with enclosure materials explicitly. Our specifications pair aluminum enclosures with fillers that minimize galvanic potential, such as aluminum-based or tungsten carbide-coated particles, while steel or stainless enclosures may use nickel-graphite fillers with protective surface treatments. For high-frequency applications, higher-conductivity fillers are preferred; lower-frequency devices can accept lower-cost materials.

3. Surface finish and flange flatness

The smoothness of the mating surfaces is just as important as the gasket itself. Design notes emphasize that flange surfaces must allow for compression set and that surface roughness and flatness strongly influence gasket performance. Our tests confirm that surfaces rougher than about 63 microinches (1.6 µm) reduce electrical contact, and that flange flatness should be held within roughly ±0.002 inches per linear inch. Any paint, anodisation, or debris left on the interface acts like an insulator.

Specifications should state these limits, require cleaning of oils and oxide layers before installation, and call for conductive surface treatments on the enclosure where needed.

4. Termination and cross-section geometry

A gasket’s shape affects how it compresses and seals. Industry publications caution that different profiles have distinct compression and deflection characteristics. D-shaped profiles provide predictable deformation and low closure force, making them ideal for wide, thin flange gaps. Hollow or round profiles require careful selection of wall thickness to avoid over-collapsing. Our experience shows that terminating gaskets near fasteners improves compression uniformity and reduces leakage. The specification should therefore include:

• A rule for termination placement relative to fasteners.
• Allowed profile families and wall thickness ranges for each enclosure style.

Make Data-Driven Shielding Decisions

Data is only valuable when it guides action. Effective shielding depends on four parameters that come directly from testing: compression range, galvanic compatibility, surface quality, and profile geometry. Each one is measurable, repeatable, and tied to clear failure modes when ignored. The goal is not to interpret test results by feel, but to turn them into numeric requirements that engineering, procurement, and QA can follow reliably.

A practical next step is to gather all existing gasket and RF bag test data, identify which values correlate with pass or fail outcomes, and formalize those values in the specification. Share these ranges with suppliers and request their supporting evidence, such as data showing reduced galvanic coupling when using aluminum tungsten carbide fillers with aluminum frames. When every build decision follows the same verified parameters, teams avoid preventable interference issues and ensure that each revision performs the way the test data predicted.

Related Reading

• Why Conductive Foam is the Best Choice for EMI Gaskets in Flexible Electronics
• Why Every Gasketed Joint Needs to Consider Wave Impedance
• Material Selection for EMI Gaskets: Comparing Conductive Elastomers and Metal Alloys for Shielding Efficiency
• Four Proven EMI Gasket Junction Design Principles to Maximize Shielding Performance