Conductive elastomers can be used as gaskets and gasket strips for EMI shielding of electronic devices. The base elastomer is silicon for normal environments and fluorosilicon for fuel and oil resistance. Both offer a temperature range of -40 to +160°C, or up to +200°C for some grades. The conductive fillers available are silver-plated aluminium, silver-plated copper, pure nickel and nickel-coated graphite. Other fillers, such as silver-plated nickel, are available to special order. The conductive elastomer will have a shore A hardness of between 60 and 75 depending on grade and still maintain good tensile strength. This will ensure that the gasket will deflect sufficiently when under compression, yielding a good EMI and environmental seal, claims the company. The volume resistivity of silver-plated aluminium in silicon will be a maximum of 0.008Ohm/cm, resulting in a shielding effectiveness of 102db at 2GHz, whereas nickel-coated graphite will have a volume resistivity more than 10 times greater but exhibits a similar shielding effectiveness. Nickel-coated graphite in silicon is the most cost-effective conductive elastomer: it has excellent shielding characteristics as the nickel-graphite particles are irregular in shape and have sharp edges. When the gasket is put under pressure, the particles dig into the surface, giving the gasket very low contact resistance; graphite is also a good microwave absorber, thereby enhancing the shielding performance. Nickel graphite in silicon costs approximately 60% less than silver-plated aluminium in silicon and 70% less than silver-plated copper in silicon. Nickel graphite also offers galvanic corrosion resistance over silver-plated particles when in contact with aluminium flanges. The company's process capability is extrusion, moulding and conductive vulcanised jointing.
