This technical information has been contributed by
Tech-Etch Inc.

Click here to find suppliers

EMI/RFI Shielding Types - Mesh Gaskets

Mesh Gaskets

Knitted wire mesh can be used as economical gaskets for EMI shielding. Knitted mesh configurations are supplied on spools, coils or cut to length as individual gaskets with or without end seals. Standard profiles for a wide variety of applications are round, round with tail, double round with tail, half round (D) and rectangular.

Most profiles are available as all mesh and all are available with an elastomer core to enhance compression characteristics and increase the deflection range. Standard wire materials are monel, TCS (tin plated copper clad steel) stainless steel and aluminum. Consult the factory for other materials. Wire selection should take into account attenuation potential, mechanical characteristics, and corrosion resistance.

Materials

Monel
The most commonly used for good conductivity, corrosion resistance and good mechanical characteristics. Not recommended for applications contacting aluminum.
Monel Wire: Per QQ-N-281 - Class A - 0.0045 in. dia.

TCS
Tin plated copper clad steel has similar characteristics to Monel, with improved shielding at lower frequencies but slightly lower corrosion resistance.
TCS Wire: ASTM-B-520 - 0.0045 in. dia.

Aluminum
Aluminum wire is normally used only when galvanic compatibility with aluminum housing is required.
Aluminum Wire: AMS 4182 - Alloy 5056, 0.005 in. dia.

Silver/Monel
Silver/Monel is silver plated nylon filament with a fine strand of Monel wire knitted over a soft elastomer core to provide a very low compression force while achieving excellent attenuation values.


Core Materials

Standard core materials are available in neoprene (sponge and solid), silicone (sponge and solid), and polyurethane foam. Core materials should be selected for temperature, chemical resistance and mechanical characteristics.

Neoprene
Neoprene rubber is an economical, general-purpose elastomer with good compression characteristics. It is available in solid and sponge and in hollow core cross sections.

Sponge: ASTM D6576 Type II Grade A (Formerly MIL-R 6130)
Temperature Range: -31 to 100 C
Solid: MIL-R-6855, Class II, Grade 40
Temperature Range: -40 to 100 C

Silicone
Silicone rubber is noted for its retention of flexibility, resilience and tensile strength over a wide temperature range. Silicone is more resistant to cleaning solvents than neoprene.

Sponge: AMS-3195
Temperature Range: -75 to 205 C
Solid: A-A-59588 Class II, Grade 40 (Formerly ZZ-R-765)
Temperature Range: -60 to 260 C

Polyurethane Foam
Polyurethane Foam should be specified for light compression force applications. This material has good compression set characteristics and is available in rectangular and square solid cross sections.

Temperature Range: -40 to 121 C

End Seal
Cut to length gaskets are available with sealed ends to capture lose particles produced when the gaskets are cut.

End Seal: 3M 1357 Adhesive
Dow Corning 3145RTV

Shielding Performance

Maximum attenuation for all gaskets is achieved as compression force increases. Care must be taken with mesh gaskets to avoid compression set, which will occur when the gasket is compressed beyond 25% of the free height. The use of elastomer cores will extend the operating range. In applications where the gasket is permanently installed between two surfaces, compression set can be tolerated.

EMI Shielding Performance
Material
H-Field
100kHz
E-Field
10MHz
P-Field
1GHz
BeCu
>110 dB
>110 dB
<110 dB
Monel
60 dB
>115 dB
95 dB
TCS
80 dB
125 dB
100 dB
Aluminum
38 dB
100 dB
80 dB
Silver Monel
60 dB
75 dB
70 dB


Mounting Methods

Groove Mounting
Die-castings can be designed for groove mounting to provide good retention and to control the amount of compression.

Stick-On Mounting

All profiles except round can be mounted with double-sided pressure sensitive transfer tape for a fast, reliable installation. 3M F9469PC transfer tape may be used at ambient temperatures from -67F to 300F. Apply on clean, oil free surface, and allow a 24-hour cure time for maximum adhesion.

This technical information has been contributed by
Tech-Etch Inc.

Click here to find suppliers

Home |  About Us |  Back To Technical Library |  Contact Us
Copyright © 1996-2010 JobShop.com. All Rights Reserved.
General or Technical Questions? E-mail support@JobShop.com