Multishield, Weaveshield and Embedded Wire Gaskets

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General description

There are three main types of EMI shielding gaskets based on oriented wire, or embedded wire elastomer materials. The basic principle in each case is based on moulding (encapsulating), either, individual wires, woven wire mesh or expanded mesh into an elastomer sheet. The resultant gasket material in each case has the combined properties of excellent low contact resistance and a high level of environmental sealing afforded by the elastomer carrier.

Product types:

Multishield orientated wires in silicone / fluorosilicone

In Multishield (formerly Duroseal), individual wires are moulded into a silicone sheet so that they are orientated at right angles to the sealing faces of the gasket. When compressed each wire acts as a point contact electrically connecting the two sealing faces whilst the silicone provides a very effective hermetic seal. One advantage of this gasket type is that there is no conductivity possible across the width of the gasket which can be useful in some applications.

Multishield Datasheets

	OWG-SSM001 are EMI gasket materials comprising of orientated Monel wires bonded into a silicone sponge elastomer sheet.
	OWG-SM001 and OWG-SA001 are EMI gasket materials comprising of orientated wires bonded into a silicone elastomer sheet.
	OWG-FSM001 and OWG-FSA001 are EMI gasket materials comprising of orientated wires bonded into a fluorosilicone elastomer sheet.

The three main elastomer types are:

Silicone ZZ-R-765 2B 40 – a 40 shore A hard silicone elastomer with excellent high temperature performance

Silicone sponge AMS 3195 – a sponge elastomer carrier where lower compression force is required

Fluorosilicone Mil-R-25988 50 – a fuel and oil resistant elastomer with a wide temperature operating range and excellent ageing characteristics

In combination with the above the two main wire types normally used are

Monel (copper/nickel) alloy - a corrosion resistant alloy that provides reliable long term shielding performance

Aluminium – where improved galvanic compatibility with aluminium enclosures is required

This material is available in strips, fabricated sheets or lengths. Small gaskets can be supplied die cut as a single piece whilst larger gaskets must be assembled from strips (frame style). We would normally recommend that we supply gaskets pre-fabricated to your drawing.

Multishield sheets come in either 100mm or 152mm widths with a length of 900mm and can have self adhesive backing if required.

Each material is available in thicknesses up to 10mm and is available with self adhesive backing if required.

Design considerations

It is recommended that where possible these gaskets are designed in with some form of compression limitation. To this end compression stops in the form of collars or studs may be incorporated into the gasket itself. Ideally compression should be controlled within 5 – 25% depending on gasket cross-section and enclosure construction.

This material type can require relatively high closure forces, therefore it is important to ensure that covers/flanges are sufficiently rigid and that fastener spacing is not so large as to cause poor sealing due to ‘quilting’ or distortion of the sealing faces.

Elastomer filled woven aluminium mesh

Commonly known as 'Weaveshield', this is an effective thin (typically 0.5mm) EMI gasket material comprising of a woven aluminium cloth infilled or ‘over’ moulded with elastomer. The elastomers used are silicone, fluorosilicone or synthetic type (similar to neoprene). It can provide a watertight or pressure seal where sealing faces have a flatness tolerance of >0.05mm.

A high level of EMI shielding performance is reliably achieved by virtue of the array of aluminium mesh contact points exposed at the surface. This material also has the advantage that the woven mesh layer acts as an internal compression limit allowing small cross-sectional area gaskets to be designed in without the requirement for additional mechanical compression stops

Weaveshield Datasheets

	IWG SA001 is a woven aluminium cloth infilled or ‘over’ moulded with a Silicone elastomer.
	IWG FSA001 is a woven aluminium cloth infilled or ‘over’ moulded with a Fluorosilicone elastomer. The elastomer used is resistant to solvents, fuels and oils.
	IWG AN001 is a woven aluminium cloth infilled or ‘over’ moulded with a synthetic elastomer. The elastomer used is resistant to hot lubricating oils and exceeds the requirements of AMS 3222c.

The main elastomer types available are:

Silicone ZZ-R-765 2B 50 – a high specification silicone

Silicone AMS 3302D – a more general purpose silicone

Low out-gassing silicone ASTM 595-84 – a silicone elastomer with very low levels of condensable and non condensable volatiles

Fluorosilicone Mil-R-25988 – a fuel and oil resistant version of silicone

Synthetic elastomer AMS3222C - a high performance synthetic elastomer resistant to fuels and hot oil

This material is available 15 meter rolls up to approximately 600mm in width (usually 300mm)

Design considerations

This material is ideally suited to connector gaskets because of the way in which it ‘self limits’ compression negating the need for additional compression control features. In order to achieve reliable environmental sealing gasket mating surfaces should be machined (flat)

This material cannot be joined, therefore gaskets are die cut as a single piece

Elastomer filled expanded metal foil

This is similar to the above material with the same elastomer options but instead of incorporating a woven aluminium mesh expanded metal foils are used instead. These expanded metal foils can provide improved contact, and therefore improved shielding performance, along with slightly more compliance than woven aluminium in some applications.