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EMI shielding gaskets
EMI shielding gasket -- Conductive Fabric Over Foam
Conductive fabric over foam makes sense where no environmental seal, complex profile, or demanding mechanical durability is needed. It can be the lowest-cost option.The covering can consist of nylon thread coated with conductive metals woven into a fabric and wrapped over a soft urethane foam. Alternatively,a woven fabric may be metallized with nickel-copper or other metal coating, then wrapped around the foam core.
Flexible, conformable fabric over foam maintains close contact with surfaces with minimal compression for low-closure-force applications. It provides snug contact over irregular surfaces and around bends and corners, making it good for electronic enclosures such as doors and access panels.
Less demanding EMI applications include grounding contact pads in cell phones and laptop computers. Fabric-over-foam gaskets also can shield the input/output backplane of laptops and PCs.
The manufacturing process limits it to relatively simple cross-sectional profiles such as squares, rectangles, and D-shapes. When a more complex profile is necessary, fabric over foam may not be the best solution.
Flexible, conformable fabric over foam maintains close contact with surfaces with minimal compression for low-closure-force applications. It provides snug contact over irregular surfaces and around bends and corners, making it good for electronic enclosures such as doors and access panels.
Less demanding EMI applications include grounding contact pads in cell phones and laptop computers. Fabric-over-foam gaskets also can shield the input/output backplane of laptops and PCs.
The manufacturing process limits it to relatively simple cross-sectional profiles such as squares, rectangles, and D-shapes. When a more complex profile is necessary, fabric over foam may not be the best solution.
EMI shielding gasket --Conductive Elastomers
For more demanding shielding applications, conductive silicone elastomers provide a wide range of attenuation capabilities plus environmental and moisture sealing. The metal-filled elastomers can be extruded or molded into a wide range of form-fitting shapes and cross sections.For very small cross sections, a formed-in-place silicone-based silver-copper-filled or nickel-graphite-filled conductive
elastomer is dispensed robotically.The robot can deposit the elastomer on a surface as narrow as 0.025 to 0.030 in.
Conductive elastomers are filled with a range of materials, from silver (highest conductivity) to carbon. Carbon-filled elastomers, having the lowest conductivity and cost, serve applications requiring low shielding levels. Other filler materials include nickel-coated graphite, silver-plated glass, silver-plated copper, and silver-plated aluminum. Nickel-graphite is the most popular for commercial applications because of good cost/performance attributes.
Conductive elastomers are filled with a range of materials, from silver (highest conductivity) to carbon. Carbon-filled elastomers, having the lowest conductivity and cost, serve applications requiring low shielding levels. Other filler materials include nickel-coated graphite, silver-plated glass, silver-plated copper, and silver-plated aluminum. Nickel-graphite is the most popular for commercial applications because of good cost/performance attributes.
EMI shielding gasket -- BeCu Strips also called fingerstock
When you need mechanical durability, such as frequent direct compression actuations or shearing forces, BeCu strips make the best choice. BeCu fingerstock withstands lateral shearing forces as well as perpendicular forces, where other shielding materials are best suited for perpendicular, direct-compression applications.Thin BeCu strips, available in many profiles, provide shielding
or grounding but do not supply an environmental seal. BeCu fingerstock can be plated with many different metal types, offering broad galvanic compatibility with substrate metals.
The use of stainless steel is progressing slowly because of the expense of developing new tooling. Presently, only a relatively small number of profiles are offered in stainless steel. In some cases, customers are sharing the expense of developing tooling for specific applications with the EMI gasket manufacturer.
The use of stainless steel is progressing slowly because of the expense of developing new tooling. Presently, only a relatively small number of profiles are offered in stainless steel. In some cases, customers are sharing the expense of developing tooling for specific applications with the EMI gasket manufacturer.
Applications
A prolific application for EMI shielding materials is wireless telecommunications in base stations and cellular phones. Here are two examples:- An aluminum casting for a wireless base station component posed both an EMI and an environmental shielding challenge because the electronics were isolated with a pattern of thin walls which formed separate compartments. The walls were too thin to accommodate fabric-over-foam or BeCu gaskets.
The solution was to mold a conductive elastomer with a rigid insert in the pattern that fit over the compartments. The resulting rigid gasket simplified assembly in the casting. - The circuit boards of a small cellular phone handset are isolated by erecting thin ledges around them and covering the ledges with EMI and environmental shielding. To lay down the ultrathin gasket, a robot dispenses a form-in-place conductive elastomer on top of the ledges.