EMI Gaskets | EMI Shielding, MIL-DTL-83528
EMI Gaskets play an important role in any electronic design that is attempting to shield EMI from their assembly. In our eyes, there are two different types of EMI Gaskets. There are environmental gaskets, and there are EMI Gaskets. However, some of the solutions below are able to serve both purposes simultaneously. The material below is mainly rubber based materials that are shielding EMI interference.
Electrically Conductive Silicone Rubber/Fluorosilicone Rubber/EPDM Rubber
Commercial/Military Grade Options
Frequently, gasket manufacturers are being asked to certify to the MIL-DTL-83528. This is a widely used specification. These different electrically conductive rubbers really come down to two variables for the selection. There are the particle fillers, and there is the rubber content. Many combinations of these are available. For example, nickel graphite is able to come with EPDM, fluorosilicone, and silicone.
The elastomer options really come down to a few variables which are toughness, temperature range, and fluid resistance. The elastomer essentially binds the electrically conductive particles into the molded/extruded shape to make it electrically conductive while also maintaining an elastic nature. Typically fluorosilicone is utilized for situations where fluid resistance is required. Silicone has always been the good general purpose option for EMI Gaskets. EPDM is usually utilized for outdoor applications that will not see temperature extremes nor fluid contact. Silicone Rubber for NEDC is easily the most popular through MIL-DTL-83528 Type B, however.
Fillers Available Table:
|FIller Particles Available:||Cost($, $$, $$$, $$$$):||Included In the MIL-DTL-83528|
|Pure Silver||$$$$||Yes(Type E, Type F, Type H, Type J)|
|Silver Aluminum||$$$||Yes(Type B, Type D)|
|Silver Nickel||$$||Yes(Type L)|
|Silver Glass||$$||Yes(Type M)|
|Silver Copper||$$$||Yes(Type A, Type C, Type K)|
|Passivated Silver Aluminum||$$$||Yes(Type D)|
Cost Sensitive Solutions for EMI Gaskets
It is good to note that the electrically conductive rubber also have some cost sensitive solutions that may serve the same purpose. Many design engineers will utilize nickel/graphite filler instead of costly silver based fillers. It has been shown that nickel/graphite can have similar performance in some applications for shielding effectiveness. Although, testing should be key to making sure the solution you are selecting will match the performance requirements.
These gasketing materials are able to be fabricated into finished gaskets through waterjet cutting, or die cutting. However, bonding of gaskets through vulcanizing cord stock. Cord stock is produced through extrusion machines.
Whats Popular when it comes to EMI Solutions?
One of the things we mention a lot on this website is it is important to choose materials that converters/fabricators are familiar with. The reason for this, many converters should be able to get the material quickly, and be familiar with it. In addition, many companies who manufacture electrically conductive gasket materials should have them too.
-Silicone Rubber Silver Aluminum
-Fluorosilicone Rubber Silver Aluminum
-Fluorosilicone Rubber Passivated Silver Aluminum
-Silicone Rubber Nickel Graphite
MIL-DTL-83528 Slash Sheets
The MIL-DTL-83528 specification utilizes so-called “slash” sheets to make it easier for design engineers to call out different types of normally custom configurations of these materials. For example M83528/004D001 calls out a Type D connector gasket with a custom configuration of dimensions. There are other slash sheets for flange gaskets, washers, and other configurations.
The different configurations are listed below in the table:
|M83528/001||Solid O-Strip Channel Extrusion|
|M83528/003||Solid D-Strip Channel Extrusion|
|M83528/004||Connector Gaskets(.032’’ thickness)|
|M83528/007||Hollow D-Strip Channel Extrusion|
|M83528/008||Hollow P-Strip Channel Extrusion|
|M83528/009||Solid Rectangular Strip Extrusion|
|M83528/010||U-Channel Strip Extrusion|
|M83528/011||Hollow O-Strip Channel Extrusion|
|M83528/012||Circular Washer Die-Cut|
|M83528/013||Molded Waveguide Parts|
It is good to keep in mind as well that there are many other extruded options available for EMI Gasketing, some custom ones may include “bunny ears”, or “cowboys hats”.
Modified EMI Rubber Gaskets
There are a number of different options when it comes to modifying a EMI Rubber gasket material into something slightly different than what they normally are available in.
For example, there are soft durometer gaskets. Some EMI Rubber materials are available in 45 durometer.
Lamination/Converting of EMI Gaskets:
All of the different materials above are either die-cut or waterjet-cut into custom shape gaskets. When these gaskets are fabricated there are times when an electrically conductive adhesive tape may be required on the back. NEDC is a 3M converter, so we utilize electrically conductive tape products such as 3M 9713(acrylic adhesive), and 3M 9719(silicone adhesive). These tapes are laminated to the material.
Oversized EMI Gasketing Options
One thing to keep in mind when designing an EMI Gasket is many times electrically conductive rubber options are molded sheets. For this reason, beyond 24’’ in any one direction can be difficult to fabricate out of a single piece of EMI material. In these cases, it may be a good idea to specify how the gasket can be put together. There are electrically conductive adhesives available for fabricating bigger gasket shapes by vulcanizing separate pieces together and then cutting a complete shape.
For more information on electrically conductive gasketing products, please contact our sales department.
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All of the information presented above is believed to be factual and accurate; however, NEDC is not liable for any design or application utilizing this information.
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