4 Things to Consider When Choosing a Conductive Elastomer

Thermal Stability

Elastomers used in gaskets must withstand expected operating temperatures without degrading, and this is only marginally affected by the added conductor phase. Silicone rubber elastomers maintain stability over a broad temperature range, typically from -55°C to 200°C, making them suitable for very demanding applications. Even minor changes in conductivity or elasticity/shape-memory impact shielding performance dramatically.

Selecting an elastomer whose thermal profile suits the operating conditions will help sustain the reliability of shielding.

Mechanical Properties

The elasticity, compression, tear resistance, and shape memory of a gasket can all be important, depending on the application. Indeed, each of these properties can be a decisive factor in selection since they influence how the material withstands stress and repeated use.

For example, a material with high flexibility and resilience will maintain its conductive path by resisting compression set, ensuring sustained connection pressure at contact points for good connectivity.

Relevant test standards for mechanical properties include:

• ASTM D412 Tensile strength test
• ASTM D624 Tear strength test
• ASTM D395 Compression set test

Assessing the property-suitability of a gasket where mechanical requirements for high vibration or physical stress endurance ensures that the elastomer will provide long-term reliability.

2. Environmental Factors

Operational environments can have significant impacts on gasket performance in a variety of ways.

Exposure to Aggressive Chemicals

Depending on the application, the elastomer may come into contact with various aggressive chemicals – solvents, acids, alkalis, oils, or fuels. Some conductive elastomers are better able to resist certain types of chemical attack/degradation. Therefore, carefully selecting materials according to known exposure risks ensures stable application performance. In other words, assessing the material’s compatibility with all the chemicals it may encounter helps prevent premature deterioration and loss of EMI shielding and sealing.

Temperature Range

Rapid temperature changes can stress elastomers, causing expansion or contraction that affects conductivity and shielding effectiveness. Conductive elastomers that perform well in a broad temperature range or have been tested for thermal cycling are ideal for applications where thermal stability is critical.

Weather and UV Resistance

For outdoor or exposed applications, UV resistance is a key factor. UV exposure can lead to cracking or material breakdown in some elastomers. Materials such as fluorosilicone are more resistant to UV and weathering effects, making them suitable for outdoor or aerospace use.

3. Application-Specific Requirements

No two applications are identical, so a careful selection of material and design for optimization of the unique problems and opportunities a context presents is critical.

Closure Force

The force required to compress a conductive elastomer is critical in gasket applications, where localized loss of closure force can result in ineffective EMI shielding.

• The elastomer’s intrinsic hardness, typically measured on the Shore A scale, determines the required closure force and influences how it interfaces with other components.
• The addition of some conductive phases can negatively influence the resilience of elastomers, hardening them. More additives can greatly increase this effect.
• Low-closure-force elastomers are ideal for applications with delicate or lightweight components.
• Softness is a result of design as well as material property, so flexibility can be increased by the design of the section profile to compensate for the raised stiffness that typically results from high conductive-additive proportion.

Percentage Gland Fill

For gaskets, the gland fill—literally how much of the groove or channel that retains the gasket is occupied by the elastomer in the uncompressed state—influences both mechanical sealing effectiveness and potential contact pressure. Optimizing gland fill helps balance mechanical performance with electrical connectivity for shielding. Moderating compression is essential to avoid compression damage to the elastomer or bending loads on adjoining parts.

Compression/Deflection

Most applications require careful management of how elastomeric conductive shielding gaskets compress or deflect, keeping within specific tolerances to maintain performance. To illustrate, a low compression set is essential for elastomers that will experience frequent compression cycles or long-duration compression. This property summarizes the material’s ability to return to its original shape after compression/distortion. The criticality of this lies in the need to maintain contact pressure at a sufficient level to make good electrical contact. A material that distorts under load will relax away from compression, reducing contact load. Sufficient compression set resilience ensures long-term reliability in both sealing and shielding.

Galvanic Compatibility

Conductive elastomers can cause galvanic corrosion when making electrical contact between dissimilar potential-level metals. Selecting materials that are galvanically compatible with surrounding components helps prevent this corrosion process, preserving both the elastomer and the metal parts.

Industry and Compliance Standards

Conductive elastomers must generally meet specific performance standards, especially in regulated industries like aerospace and defense.

MIL-STD-83528, for example, outlines requirements for EMI gaskets in military applications, ensuring a baseline for shielding effectiveness and the durability of that protection. Compliance with RoHS (Restriction of Hazardous Substances) may also be necessary, particularly in European markets, reducing the use of lead and other toxic chemicals.

4. Durability and Longevity

Long-term function and durability are basic requirements. Conductive elastomers must maintain shield and/or seal performance throughout equipment lifespans. This implies resistance to wear, environmental degradation, and mechanical stress that triggers tearing or permanent shape changes. Conductive elastomers with low compression set, high tear resilience, and strong adhesion properties offer longer-lasting performance.

For high-stress applications, validating elastomer gasket performance and endurance under simulated field conditions will expose challenges to their longevity, helping to ensure reliable performance. Highly accelerated life testing (HALT) can help measure long-term performance by compounding thermal, vibration, chemical stress, and other factors to simulate an extended timeline.

Conclusion

Choosing the most effective conductive elastomer and profile for EMI shielding requires careful evaluation of all performance requirements, environmental resilience demands, EMI-specific performance factors, and durability.

By understanding the material’s electrical, mechanical, and environmental attributes, you can select an elastomer that provides reliable EMI shielding tailored to your unique operational needs. Whether for telecommunications, aerospace, defense, or commercial applications, a well-chosen conductive elastomer ensures robust protection against EMI while meeting industry standards and longevity expectations.

Many factors must be considered when selecting a conductive elastomer, and in some cases, it can be difficult to make the right choice for a specific application. Our experts have years of experience helping manufacturers, product designers, and engineers choose effective EMI RFI shielding products and materials. Do not hesitate to contact us to discuss your project and requirements.