Why Conductive Elastomer Gaskets for EMI Shielding?
This is a brief overview of one of the many EMI Shielding options for electronic devices.
EMI and thermal management materials and technical support have been the core of KraFAB business for three decades.
EMI (Electromagnetic Interference) Gasket Function
For the frequencies most commonly used in electronic devices, thin-walled shields constructed using metal, metal-plated plastic, conductive paint, or electrically conductive plastic can provide the needed EMI shielding attenuation. However, gaps or slots are a mode of failure.
An EMI shielding enclosure is designed to function as a Faraday Cage, but the need for communications within the device and with the device from outside the shield can create gaps. Additionally, the tolerance stack-up of the various components of the assembly such as circuit boards, traces, enclosures, compression stops, flanges and grooves, connectors, and I/O openings can lead to areas of EMI leakage. EMI gaskets fill the gaps and provide electrical continuity and shield performance integrity.
Mechanical, Electrical Construction, and Performance
Elastomer EMI gaskets are typically constructed of two key components that allow the gasket to meet the mechanical and electrical requirements of an EMI gasket in a variety of applications.
- The elastomer is soft enough to allow it to be compressed and provide good surface contact.
- The elastomers are made electrically conductive by adding particles of a specific type and size distribution.
This retains integrity over a range of environmental conditions including temperature, chemical exposure, mechanical shock/vibration and UV exposure. UL 94VO flammability-rated gasket formulations are available.
Compression of the gasket by the mating surfaces is required to provide the desired electrical continuity across the assembly.
Shield design that provides a specific compression stop is generally required. Additionally, there are design guidelines when grooves are used to capture the gasket.
Elastomer options for EMI gaskets include:
Particle filler options include:
- Silver plated copper
- Silver plated aluminum
- Silver plated nickel
- Silver plated glass
- Silver plated graphite
- Nickel plated graphite
- Nickel plated aluminum
The various material formulations and gasket design options provide the needed electrical and mechanical properties for years of design performance.
Galvanic corrosion is an electrochemical process in which a metal corrodes when in electrical contact with a different metal and both metals are exposed to an electrolyte like water.
How to prevent galvanic corrosion
An Elastomer EMI gasket that contains metal particles that are not the same metal as the mating surfaces of the shield/enclosure has the potential for galvanic corrosion.
An example of this unwanted condition is an aluminum shield/enclosure mated to a silver particle-filled Elastomer EMI Gasket exposed to saltwater. The aluminum at the mating surface can be eaten away and lose mechanical and electrical integrity.
Using silver-plated aluminum particles instead dramatically reduces the potential for galvanic corrosion when using aluminum housings. Therefore the proper selection of the specific gasket type, housing material, and surface coatings is required to avoid galvanic corrosion potential.
This is a conductive elastomer EMI gasket material qualification standard. The standard includes test methods for a number of key EMI gasket measurements including, volume resistivity, temperature, vibration, Electromagnetic Pulse (EMP), and shielding effectiveness.
Military and aerospace applications may require specifying materials that meet MIL-DTL-83528. Newer materials may not be covered by this specification. That may include nickel-plated aluminum-filled elastomers. A change in conductive elastomer seal suppliers (including MIL-DTL-83528 QPL suppliers) should include system qualification testing.
Elastomeric EMI Gasket Form, Fit and Function
Initially used to shield defense and aerospace electronic devices, conductive elastomeric gaskets are now used extensively in consumer, telecommunications, business, industrial controls, automotive, medical and other electronic device applications.
Conductive Elastomer EMI Gaskets are reliable for the life of the device when properly selected, designed and installed. They provide both an EMI and environmental seal. They resist compression set and can provide low closure force.
They are available in a variety of forms that support low to high volume production processes and meet a wide variety of design and Design for Manufacturability (DFM) requirements.
- Sheets available with or without conductive PSA (pressure sensitive adhesive)
- Custom and standard Molded Gaskets
- Extruded gaskets with standard and custom cross-sections that can be spliced
- Over molded gaskets bonded to shields or covers
- Form-In-Place gaskets applied to shield or covers
We can help with your design reviews, scaling up, or troubleshooting requirements.