The Role of Electrically Conductive Elastomers in EMI Shielding

What Are Electrically Conductive Elastomers?

Electrically conductive elastomers are materials that blend elastomeric polymers with conductive fillers to create flexible, electrically conductive substances. The elastomer component of these materials is characterized by rubber-like properties, allowing for significant deformation while retaining their shape. This allows the gaskets to compress and act with high compliance in closing/EMI sealing gaps and service apertures in enclosures that house sensitive (or transmitting) electronics.

By incorporating conductive fillers, such as metal powders made from copper or silver or carbon in the form of carbon black, graphene, or carbon nanotubes, moderate to high conductivity can be added to elastomers to effectively block or dissipate electromagnetic radiation.

This combination of properties – compliant and conductive – makes these materials invaluable in applications requiring both fluids sealing and EMI shielding. It should be noted that the conductive fillers can influence the elasticity of the rubbers, so the highest conductivity and best EMI shielding can often be accompanied by some stiffening in the elastomer.

Despite this, the versatility and adaptability of elastomer EMI shielding solutions make them suitable for a wide range of industries, all of which we service.

What Role Do Conductive Elastomers Play in EMI Shielding?

Conductive elastomers serve two primary roles in EMI RFI shielding: shielding and sealing.

Shielding

Shielding creates a continuous, electrically conductive path between mating surfaces such as electronic enclosure components, inspection covers, and PCB-level EMI shields made of pressed metal.

This continuity path allows for the dissipation of electromagnetic energy in the enclosure walls, as radio and electromagnetic spectrum interference cannot penetrate an earthed metal part. This effectively prevents EMI from penetrating into sensitive electronic components. By ensuring that there are no gaps or high impedance electrical contacts in the conductive surface, electrically conductive elastomers help maintain the grounded integrity of the enclosure.

Sealing

Sealing is the conductive elastomers acting as a seal at gaps and irregularities between surfaces. These irregularities can create openings that act as leakage points for electromagnetic radiation, leading to potential interference. Note that the scale of the ‘gap’ required for leakage is the wavelength of the radiation interference.

By filling these gaps, ECEs not only ensure the continuity of EMI shielding but also increase protection against moisture, dust, and environmental factors, benefitting the overall durability of electronic devices used under harsh conditions. The EMI shielding benefits of conductive elastomers are thus dual-purpose, serving both electromagnetic and environmental protection functions.

Electrically Conductive Elastomer Properties

Electrically conductive elastomers possess various valuable properties that make them effective for EMI shielding/sealing applications.

Electrical Properties

• EMI/RFI Shielding: Conductive elastomers are designed to attenuate electromagnetic and radio-frequency interference. This provides a protective barrier around sensitive components by carrying the signal influence to electrical ground.
• Conductivity: The level of conductivity varies depending on the material and proportion of conductive filler used, facilitating tailored solutions for specific applications depending on expected EMI frequencies and energy levels.
• Pressure-sensitive connectivity: Many ECEs exhibit high elastic resilience/recovery properties, allowing them to conform and maintain pressurized electrical contact with mating surfaces, enhancing their EMI sealing effectiveness by preventing relaxation of contact pressure and increasing resistance over time.
• Volume resistivity: This property indicates how strongly the material can resist electrical flow – from open circuit (pure elastomer) to very low resistivity (pure silver or carbon/graphene). Low volume resistivity is essential for effective EMI shielding, carrying the interference signals to electrical ground.

Physical & Mechanical Properties

• Elasticity and flexibility: Electrically conductive elastomers are designed to retain their elasticity despite the more rigid filler materials. This allows them to stretch and compress without losing their original shape memory, making them suitable for dynamic applications.
• Compressibility: These materials can distort and displace to conform to and fill gaps between surfaces, providing effective EMI (and physical) sealing and cushioning while maintaining continuity between shield parts.
• Environmental resistance: Conductive elastomers are typically resistant to temperature fluctuations and moisture and selectively to a wide spectrum of chemicals, oils, solvents, and fuels. This ensures reliability in most challenging environments.
• Customizability: The composition and forms of conductive elastomers can be highly tailored to suit specific application requirements, allowing for wide utility in this class of solutions.

Conductive Elastomer Composition

The composition of electrically conductive elastomers is directly influential in their performance in EMI shielding applications.

Elastomeric Bases

• Silicone rubbers: Silicone-based elastomers are renowned for their excellent temperature resilience and tough flexibility, making them suitable for high-temperature applications.
• Fluorosilicone: This elastomer offers greatly enhanced chemical resistance, which is ideal for environments where exposure to fuels or solvents is expected, but flexibility must be maintained.
• Ethylene propylene diene monomer (EPDM) rubbers: EPDM provides excellent weather resistance and durability, making it a great choice for outdoor applications and harsh environments.

Conductive Fillers

• Silver: Delivering high conductivity, Silver is often used in applications requiring superior EMI shielding performance, although it results in more costly manufacture. Silver is defined as Type E in MIL-DTL-83528.
• Silver-plated Aluminum: This combination offers similar conductivity to pure silver at a reduced cost and is suitable for most EMI applications.
• Silver-plated Copper: Combining silver plating with copper bulk enhances conductivity and reduces material costs. This is ideal for applications where budget constraints exist. Silver-plated aluminum is defined as Type A (65A) and Type K (85A) in MIL-DTL-83528.
• Silver-plated Glass: This filler combination improves dielectric properties while providing adequate shielding effectiveness.
• Nickel-plated Graphite: Nickel-plated graphite offers a cost-effective alternative with moderate conductivity suitable for general-purpose and moderate-sensitivity applications.
• Nickel-plated Aluminum: This combination provides a lightweight, cost-effective solution with good EMI shielding properties.
• Carbon: Carbon fillers are less conductive than metal options but offer lightweight and corrosion-resistant properties, making them suitable for specific applications.
• Graphene: Experimental work with graphene fillers has produced interesting results – high conductivity, low cost, and well-maintained elasticity.

Conductive Elastomers Shapes and Forms

Electrically conductive elastomers are available in a wide array of shapes and forms and are manufactured through various rubber production processes to suit diverse applications in EMI shielding and environmental sealing. The versatility of these materials allows for customization to meet specific engineering requirements.

Extruded Profiles

Extrusion is a common manufacturing method that produces continuous shapes with consistent cross-sections. Common extruded profiles include:

Round (O-Ring) Profiles

• Available in solid and hollow forms
• Provides a circular sealing surface with high localized pressure for optimal contact
• Offers varying degrees of resilience and compressibility to suit different application needs
• Commonly used as conductive elastomers gaskets and seals in various industries

Channel Profiles

• Designed to fit application-specific geometries
• Enhances sealing performance in complex assemblies
• Often used for edge sealing in electronic enclosures

D-Shaped Profiles

• Combines a flat base with a rounded top
• Provides stability and ease of installation while maintaining good sealing properties
• Available in solid and hollow forms

Rectangular Profiles

• Offers consistent compression across a flat surface
• Useful for applications requiring uniform pressure distribution

Sheets and Strips

Electrically conductive elastomers can also be produced in a virtually unlimited number of sheet and strip variants to suit various applications.

Sheets

• Available in various thicknesses and sizes
• Allows for easy cutting and customization to fit specific dimensions and shapes
• Ideal for die-cutting custom gaskets or creating large area shields

Strips

• Produced in different widths and thicknesses
• Useful for linear sealing applications or creating custom-length gaskets
• Can be easily applied to curved or straight surfaces

In addition to extruded and sheet forms, electrically conductive elastomers can be molded into complex shapes tailored to specific application requirements, allowing for the integration of multiple features in a single part. This includes custom-molded components and over-molded parts, where the elastomer is directly molded onto a substrate to provide effective EMI shielding and environmental sealing. These molded forms offer flexibility in design and are ideal for high-volume production of intricate shapes.

Conclusion

Electrically conductive elastomers are an essential solution for EMI shielding in an enormous range of technologies and market sectors. Their unique combination of flexibility, conductivity, and environmental resistance makes them practical for a wide range of applications across many sectors.

By understanding the properties, formulation, manufacture, efficacy, and available forms, designers and system-specifiers can productively integrate conductive elastomers into their developments, ensuring optimal EMI shielding performance and reliability in the face of challenging environments. As electronic devices continue to evolve, the demand for effective and adaptable EMI shielding solutions like ECEs will only increase.

The ID Group proudly offers EMI RFI shielding solutions to Canadian manufacturers. In addition to conductive elastomers, we provide a wide range of EMI RFI shielding products, such as conductive foam gaskets, metalized fabric gaskets, and fingerstock gaskets. Contact our experts for sound advice on the perfect EMI RFI shielding solution for your project.