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Home > Materials > Electrically Conductive Silicones, EMI Shielding Materials

Electrically Conductive Silicones for EMI Shielding Gaskets

EMI / RFI gasket materials are used to attenuate electronic emissions from electronics and electro-mechanical devices. Electrically conductive gaskets/EMI shielding gaskets are most commonly applied to enclosure covers, doors and penetrations to prevent or restrict electromagnetic emission that can interfere with other electronic components. Critical devices are also tested for EMI susceptibility, ensuring external EMI and RFI emissions do not interfere with the function of the device.

EMI Gaskets

In addition to managing EMI emissions and susceptibility, Stockwell Elastomerics' conductive gaskets are used for environmental sealing. With proper compression, these gaskets can seal out rain (NEMA 3), withstand pressure washing (IP65, IP66, NEMA 4X) and prohibit water ingress during submersion (IP67, NEMA 6).

EMI shielding materials are an extension of Stockwell Elastomerics' silicone rubber capabilities - EMI gaskets can be die cut, water jet cut or compression molded from electrically conductive silicone rubber compounds with age and weather resistance or conductive fluorosilicone rubber for additional chemical resistance.







Nickel-Graphite Filled Silicone - EMI Shielding Gasket Material

Nickel-graphite filled compounds have been developed with high shielding effectiveness values (over 100dB from 100MHz to 1GHz) at a cost far less than silver filled compounds. Further, nickel-graphite filled silicones withstand harsh environmental conditions including salt fog/spray, UV and ozone.

Commercial Applications

Nickel-Graphite Filled Silicone EMI Shielding Gaskets

Nickel-graphite filled silicone gaskets are widely used for commercial applications where the higher cost of silver or copper filled materials is prohibitive. Industries such as lighting, signage, and instrumentation that historically haven't required EMI attenuation, now do as a result of integrated electronics for "smart" features and tighter regulations. With more innovation and mobile devices, EMI emissions will need to be addressed by designers of OEM equipment – and often at the end of the design cycle. Stockwell Elastomerics offers nickel-graphite filled silicones, readily available from inventory, in sheet form with thicknesses: .020", .032", .045", .062", .093", and .125" to support prototyping and fast-turn gasket production. Customers can send a CAD file, .stp or .dxf of the gasket design so Stockwell Elastomerics can determine the best choice of material and provide a waterjet cut gasket for testing.

Aerospace and Defense Applications

Designers in defense and aerospace related applications are now specifying nickel-graphite filled silicone gaskets for custom molded gaskets, O-rings and fabricated gaskets, thereby reducing costs of applications where silver filled or silver plated particle filled compounds were previously specified. These compounds have been specified for applications ranging from seals for power supply gaskets to enclosure gaskets. The SNE-540, 40 durometer and SNE-556, 65 durometer nickel-graphite filled silicone compounds in particular have been subjected to extensive testing by several independent testing facilities. Along with shielding effectiveness values (see chart below), independent testing determined the thermal conductivity of SNE-556 to be 0.8 W/m-K and Low Temperature Flex, TR10 to pass at -40°C.


Nickel-Graphite Filled Silicone – Die Cut and Water Jet Cut EMI Gaskets

Stockwell Elastomerics inventories uncured nickel-graphite filled silicone compound as well as cured sheets from .020" to 0.125" thicknesses. If sheets are not immediately available, Stockwell Elastomerics' on-site Molding operations can quickly produce sheets to support requirements for die cut and fabricated gaskets. The standard sheet size is 15" x 20".

Continuous Roll EMI Gasket Material

Continuous Roll EMI Gasket Material

If 15" x 20" standard sheets are not suitable due to large gasket dimensions, continuous roll material SNE-540-C is available in .010", .020" thick and .032" thick rolls up to 15" wide, custom thicknesses are available upon request. Continuous format offers designers the ability to design EMI shielding gaskets for larger enclosures with fewer splices. Stockwell Elastomerics has on-site water jet cutting for precise corner jointed gaskets and tightly fitting splices for environmental and shielding integrity.

3M Conductive Adhesive for EMI Gaskets

Stockwell Elastomerics offers 3M 9713 conductive acrylic adhesive or 3M 9719 conductive silicone adhesives. Electrically conductive adhesives are laminated to EMI / RFI materials for ease of installation. Request a sample swatch of SNE-5XX series EMI gasket materials via the contact form.



Nickel-Graphite Filled Silicone – Molded EMI Shielding Gaskets

More complex designs, extending beyond flat cut shapes, are custom molded by Stockwell Elastomerics on-site in the United States. Compression molds are used to produce custom EMI gaskets and custom conductive parts. Three dimensional designs allow for tighter tolerances and the use of shape factors to reduce the closure force on the filled conductive polymers.

Custom EMI Gasket Tooling Cost vs. Die Cut Yield

EMI Gasket Molding

In the right quantities, molding custom EMI gaskets offers engineers significant unit cost savings over die cutting. EMI / RFI gasket materials tend to be higher in cost compared to unfilled silicone compounds; this is especially true for silver filled EMI compounds. The material savings associated with molding very often offsets the higher tooling cost of a custom mold. Generally, if the production quantities are expected to exceed 1000 pieces, the initial tooling investment in a compression mold will pay off with a reduced unit cost.

Waterjet Prototype to Custom Molding

Stockwell Elastomerics inventories nickel-graphite EMI sheet material made from the same compounds used to mold custom EMI components. Stockwell Elastomerics can waterjet cut low volume EMI / RFI gaskets to prove out engineering designs, then these designs can be easily tooled up for molding when parts move into pre-production and production phases.

Made in the USA by Stockwell Elastomerics, a USA-Based EMI Gasket Manufacturer

Stockwell Elastomerics is based in Philadelphia, PA and all gaskets and components are manufactured at this single location. Stockwell Elastomerics is an ITAR registered manufacturer, Cage Code 87585. Additionally, all electrically conductive molding compounds and molds used by Stockwell Elastomerics are manufactured in the United States and certified with supporting test data. Stockwell Elastomerics is committed to supporting medical, defense and other sensitive industries that require the highest quality and material lot traceability.


Nickel-Graphite Filled Silicone Materials for EMI Gaskets

Stockwell Elastomerics has partnered with Specialty Silicone Products (SSP) to develop product offerings in nickel-graphite filled silicone and fluorosilicone compounds, supplied with physical test reports to ensure properties are consistently met.

Nickel Graphite Filled Materials Available Molded and Fabricated for EMI Shielding Gaskets
Material       Duro "A" Tensile Strength (PSI) Elongation
at Break (%)
Tear Strength
PPI of Width
Volume Res.
(Ohm‑cm)
Comments,
Additional Info
 SNE‑553 30 100 300 25 0.75 - Soft EMI gasket material, available with conductive adhesive backing
 SNE‑540 40 150 200 25 0.05 - Widely used for commercial EMI gasket applications
- Replaces Rogers EC-2040
- Tested Shielding Effectiveness*
 SNE‑555 55 250 300 30 0.05 - Used for commercial EMI gasket applications
 SNE‑556 65 250 300 45 0.03 - Used for commercial and defense applications
- Tested Shielding Effectiveness*
 SNEF‑60 65 200 200 45 0.03 - Fluorosilicone Base for Fluid Resistance
Options for each material: Sheets, Cut Parts, Molded Parts
* SNE-540 and SNE-556 tested for Shielding Effectiveness by DLS Testing Laboratories.

 

Nickel Graphite Filled Materials Test Results
Material        Test Frequency Shielding
Effectiveness
(dB)
Test Method Comments,
Additional Info
 SNE‑540

    &

 SNE‑556
100 MHz (E field) 125.2 MIL‑DTL‑83528D Third party tested ‑ DLS
400 MHz (E field) 126.3 MIL‑DTL‑83528D Third party tested ‑ DLS
600 MHz (E field) 126.1 MIL‑DTL‑83528D Third party tested ‑ DLS
2 GHz (Plane Wave) 115.7 MIL‑DTL‑83528D Third party tested ‑ DLS
10 GHz (Plane Wave) 115.5 MIL‑DTL‑83528D Third party tested ‑ DLS
40 GHz (Plane Wave) 76.3 MIL‑DTL‑83528D Third party tested ‑ DLS

 


Conformable Conductive Nickel-Graphite Filled Silicone Gasket Material

Nickel Graphite Filled Silicone EMI Gaskets

Rogers Corporation's EC-2130 nickel-graphite filled silicone rubber is a compressible 30 durometer electrically conductive gasketing material. EC-2130 is the only nickel-graphite filled gasketing material available in 36" wide continuous rolls making it ideal for large EMI gaskets. Available in .062" and .125" thickness, EC-2130 is UL 94HB flame rated. Application of 3M #9713 conductive fabric supported acrylic adhesive provides both a conductive adhesive surface for EMI shielding integrity and dimensional stability to reduce tears during handling and assembly of this very conformable material.

Note that Rogers EC-2040, 40 durometer nickel-graphite filled silicone was recently discontinued. However, SNE-540, 40 durometer nickel-graphite filled silicone is now produced in continuous rolls .020" thick x 15" wide and .032" thick x 15" wide to replace EC-2040 in Stockwell Elastomerics' product line.




Silver Plated Aluminum Filled Silicone - EMI Shielding Gasket Material for Military Electronics and MIL-DTL-83528 Gasket Material Specifications

Silver Plated Aluminum Filled Silicone EMI Shielding Gaskets

Military electronics such as communication equipment and radar equipment requiring maximum shielding effectiveness from high frequencies often require silver or silver plated particle filled compounds. Stockwell Elastomerics has teamed up with Specialty Silicone Products (SSP) to specify compounds with silver plated aluminum fillers having a tight particle size distribution. This provides consistently low volume resistivity and a smooth surface condition that contributes to Stockwell Elastomerics' ability to compression mold these compounds into custom gaskets.

Each of the silver plated aluminum filled compounds listed below are available in sheets that are .010", .020", .032", .040", .050" and .062" thick for gasket fabrication. On-shelf inventory in .020" and .032" thicknesses is frequently available to support fast-turn initial production requirements and limited material sampling for evaluation.

Compounds for Stockwell Elastomerics' silver plated aluminum filled silicones and fluorosilicones are supplied with physical test reports to ensure properties are consistently met.


Silver Plated Aluminum Filled Materials Available Molded and Fabricated for EMI Shielding Gaskets
Material         Duro "A" Tensile Strength (PSI) Elongation
at Break (%)
Tear Strength
PPI of Width
Volume Res.
(Ohm‑cm)
Comments,
Additional Info
 SCF‑444* 45 150 300 20 0.004 Soft EMI / environmental gasket with low volume resistance
 SSE‑586 65 150 100 30 0.008 MIL-DTL-83528,
Type B
 SCF‑447* 70 180 150 35 0.008 MIL-DTL-83528,
Type D
Options for each material: Sheets, Cut Parts, Molded Parts
* SCF-444 and SCF-447 are fluorosilicone base compounds for fluid, fuel and oil resistance.

Environmental EMI Gaskets

The main advantage of EMI shielding gaskets fabricated from conductive elastomers is the combined benefit of environmental sealing over a broad temperature range along with EMI shielding. This EMI gasket material is typically silicone rubber or fluorosilicone rubber with embedded silver plated aluminum particles, silver plated glass beads, silver plated copper particles, nickel-graphite particles or conductive carbon. Many of these EMI shielding materials meet the properties of MIL-G-83528. Conductive silicone rubber materials are typically molded into sheets from .010" to .125" thick and 12" x 12" to 10" x 15" in size and then die cut or water jet cut to the final gasket configuration.

Common MIL-G-83528 Polymer and Filler Specifications

  • Type A = Silver Coated Copper - Silicone (65 Durometer)
  • Type B = Silver Coated Aluminum - Silicone (65 Durometer)
  • Type C = Silver coated Copper - Fluorosilicone (75 Durometer)
  • Type D = Silver Coated Aluminum - Fluorosilicone (70 Durometer)
  • Type M = Silver Coated Glass - Silicone (65 Durometer)



Combination EMI Gasket – Soft Silicone with Bonded Knitted Monel Wire Mesh

Combination EMI Gasket – Soft Silicone with Bonded Wire Mesh Cord

Enclosures requiring environmental gaskets that seal out dust and rain sometimes also require EMI / RFI shielding. Industries such as telecommunications, military and smart grid require long term sealing as well as EMI attenuation; often these larger enclosures have low closure forces due to sheet metal construction or limited latches. Stockwell Elastomerics offers combination gaskets made from closed cell silicone sponge or silicone foam with knitted wire mesh cord bonded to the edge of the gasket. The soft sponge and wire mesh construction allow for thicker gaskets that can be compressed with less closure force as compared to particle filled silicone gaskets. Large enclosures and server racks benefit from Stockwell Elastomerics' combination EMI gaskets since the thicker material (0.125" – 0.250") allows for more gap filling created by tolerance stack ups in large parts.


Soft EMI Gasket – Sponge / Mesh Cord

Compared to metal filled EMI gaskets, Stockwell Elastomerics' combination sponge / wire mesh gaskets are very soft. Softer means less compression force needed to properly compress the gasket for a seal. Filled silicone EMI gaskets may require 150 – 300psi to deflect the gasket 33% whereas the sponge/mesh takes 15 – 50psi (depending on the sponge used).


Force deflection comparison bar chart for EMI gasket materials: 50 durometer filled vs. Sponge/Monel

Custom EMI Gaskets – Sponge / Mesh Cord

Stockwell Elastomerics is a leading supplier of custom silicone gaskets and silicone components for commercial, industrial and defense applications. For this reason, a full inventory of silicone sponge products is maintained that can be combined with Monel wire mesh cord to make a combination EMI gasket. These EMI gaskets are cut to customer specifications and drawings.


Dovetail Gasket

Corner Bonded Gasket – Sponge / Mesh Cord

Server rack gaskets and large NEMA enclosure gaskets can generate significant waste if cut from a single piece of silicone sponge. To help reduce waste and associated costs, Stockwell Elastomerics offers corner bonded gaskets. Dovetail and other interlocking joints are cut into the four legs of the gasket and bonded in a secondary process. Corner bonded gaskets are available with or without the Monel wire mesh cord used for EMI gaskets.


Fluorosilicone Wire Mesh EMI Gaskets

Fluorosilicone Sponge Combination EMI Gasket

Particular applications require a higher level of chemical resistance for exposure to fuels or cleaning agents. Stockwell Elastomerics offers combination EMI gaskets made from closed cell fluorosilicone sponge and knitted monel wire mesh.



UL Silicone Sponge for EMI Combination Gaskets

EMI Gaskets - Wire Mesh

UL 50E silicone foam and silicone sponge are available to make EMI combination gaskets. While the final configuration of wire mesh and sponge has not been qualified by UL, the silicone foam and silicone sponge have been tested to UL 50E gasket standards. In addition, the silicone foam also meets UL 94V-0 flame rating.





EMI Shielding Material Conductivity Video

This video offers a simple visual demonstration of the conductivity of various EMI shielding gasket materials. The tan material in the video has silver coated aluminum particles, the dark grey material is nickel coated graphite. The last example shows a 3M conductive adhesive where the conductive path flows through the metal plate, up through the adhesive, through the conductive material into the LED.



Contact Stockwell Elastomerics for Electrically Conductive Silicones and EMI Shielding Materials

Contact Us for further assistance with EMI shielding materials and electrically conductive silicone materials to manufacture EMI gaskets.

Related Information:


EMI Shielding Materials

    ESD, EMI, and Electrically Conductive Materials Technical Data Sheets

Listing of Pressure Sensitive Adhesives

3M9713 - 3 Axis Electrically Conductive Tape