When it comes to electromagnetic interference (EMI) shielding, every engineer knows the frustration of unexpected test failures. Hours spent ensuring proper grounding, meticulously specifying materials, and carefully designing enclosures can quickly become pointless if even a single gasket junction is compromised. These tiny interfaces, often easily overlooked, can significantly degrade the effectiveness of your shielding solution, especially under rigorous EMC testing or in harsh operating environments.

At JEMIC, we’ve supported numerous companies through the intricate nuances of gasket junction design. Here, we share four tested, science-driven design tips specifically focused on gasket junctions. These insights are drawn directly from empirical research and extensive testing conducted by JEMIC engineers, ensuring that your EMI gasket junctions reliably maintain shielding performance without guesswork or assumptions.

1. Maintain Electrical Continuity through Stable Gasket Compression

Consistent and stable electrical contact between conductive gasket material and enclosure mating surfaces is essential to maintain shielding effectiveness. This continuity depends primarily on the compression of the gasket itself.

For conductive elastomer gaskets, typical industry recommendations advise a target compression between 10% and 30%. Compression beyond 30% increases the risk of permanent deformation or gasket set, while compression below 10% often yields unreliable contact. JEMIC’s extensive testing confirms a recommended compression range for various gasket profiles and materials, validating this practice.

Real-world gasket testing conducted by JEMIC highlights these specifics:

• Silver-plated Aluminum Elastomers:Recommended compression approximately 15% to 20%. Lower compression can lead to inconsistent conductivity due to inadequate surface contact, particularly after multiple closure cycles or temperature fluctuations.
• Nickel-Graphite Filled Silicone Elastomers:Optimal compression approximately 25% due to slightly higher material stiffness and lower surface conductivity compared to silver-filled alternatives.

Maintaining these precise compression ranges ensures stable electrical continuity even after repeated gasket cycling and exposure to operational vibration.

2. Select Gasket Material by Galvanic Compatibility and Shielding Frequency

Galvanic corrosion between gasket materials and enclosure surfaces poses a direct threat to EMI shielding effectiveness, particularly in harsh environments. As documented extensively by JEMIC and other industry research, galvanic mismatch accelerates corrosion at gasket interfaces, quickly degrading conductive paths.

JEMIC specifically highlights these tested material compatibilities based on rigorous corrosion and environmental testing:

• Aluminum Enclosures:Nickel-plated aluminum gaskets or silver-plated aluminum elastomers provide excellent galvanic compatibility. These pairings maintain electrical conductivity even under salt-spray conditions (ASTM B117 tests up to 500 hours).
• Steel or Stainless-Steel Enclosures:Nickel-graphite elastomers show improved corrosion resistance compared to silver-based materials. JEMIC’s environmental exposure tests confirm stable surface resistivity and galvanic compatibility in these combinations over extended periods.

Moreover, gasket selection based on EMI frequency range is critical, as demonstrated in JEMIC testing:

• Silver-plated materialstypically offer superior shielding effectiveness at high frequencies (1 to 10 GHz), ideal for wireless or RF-heavy environments.
• Nickel-graphite or carbon-filled elastomersperform better in lower frequency ranges (less than 500 MHz), providing sufficient shielding at reduced cost without unnecessary performance tradeoffs.

Pairing gasket materials thoughtfully, based on proven galvanic and frequency-specific characteristics, reliably prevents shielding degradation.

3. Minimize Surface Irregularities and Ensure Proper Flange Flatness

Even microscopic surface irregularities at gasket junctions drastically reduce EMI shielding effectiveness. JEMIC’s empirical data clearly illustrates how minor surface anomalies, often as small as a few thousandths of an inch, can introduce gaps or intermittent electrical connections.

Detailed surface-preparation recommendations from JEMIC testing include:

• Surface Roughness:Target maximum surface roughness of 63 microinches (1.6 microns) Ra or better at gasket interface points. Tests consistently show noticeable EMI performance losses above this threshold.
• Flange Flatness:Maintain flange flatness within ±0.002 inches per linear inch. Verified flange flatness within these tolerances ensures uniform gasket compression and uninterrupted surface contact, thereby maintaining a stable seal.

Furthermore, removing surface contaminants such as oils, machining fluids, or particulate debris (verified by solvent wipe-down and surface inspection methods) has consistently shown to improve gasket junction conductivity and long-term performance.

4. Design for Effective Gasket Termination Points and Gasket Cross Section

Gasket junction effectiveness also critically depends on properly engineered gasket terminations and the geometry of the gasket cross-section itself. JEMIC’s documented research emphasizes specific design details that improve shielding continuity:

• Gasket Termination:Gasket ends should not simply abut or overlap randomly. Instead, gasket termination points should be strategically located near mechanical fasteners (e.g., bolts, screws) to maximize localized compression and electrical contact. Empirical testing confirms that these termination locations reduce leakage points.
• Recommended Gasket Cross Sections:

• “D”-Shaped Profiles:Widely validated in test scenarios for EMI performance, D-shaped elastomeric gaskets provide stable compression and consistent electrical contact due to predictable deformation characteristics.
• Hollow Gaskets:JEMIC’s testing reveals hollow gaskets compress easily but are sensitive to excessive deformation; selecting a wall thickness approximately 0.020 to 0.040 inches is critical. Thinner walls risk collapsing or improper sealing; thicker walls significantly increase required closure forces and risk uneven contact.

These detailed design considerations directly contribute to maintaining stable EMI shielding performance, even under rigorous long-term testing and harsh operational conditions.

Stop EMI Problems Before They Start: Optimize Your EMI Gasket Junctions Now

Each of these design principles reflects clear empirical validation, not hypothetical theory or guesswork. At JEMIC, we recognize how small oversights at gasket junction points lead to major EMI compliance headaches.

Related Reading

• Compression Set: The Silent Killer of EMI Gaskets
  Jemic’s EMI gaskets, for instance, maintain a compression set of 15%-19% under standard conditions, ensuring long-term reliability.
• Why Conductive Foam is the Best Choice for EMI Gaskets in Flexible Electronics
• Why Every Gasketed Joint Needs to Consider Wave Impedance