Conformity Magazine - March 2008 - (Page 44)

Foam-Based Gaskets A more recent development in the EMI shielding market has been the emergence of wrapped foam gaskets. These materials have been developed to provide economical shielding in high volume applications. Typical uses include door, faceplate and backplane shielding/sealing. Some foam based gaskets consist of a conductive nickel-plated nylon material wrapped around and bonded to a soft urethane foam core. This type of material achieves a shielding effectiveness averaging 95dB between 20MHz and 10GHz and requires a closure force of typically less than 1 lb/in (0.175 N/mm). These ultra-low closure forces make foam-based shielding materials suitable for applications such as thin-walled plastic enclosures. Although foam core gaskets don’t offer the same design flexibility as molded elastomer parts in terms of the shapes that can be achieved, they are available in a significant number of popular profiles such as rectangles, P, C and D-shapes plus kiss-cut parts from a sheet. Light duty PSA affixed to one side can help simplify and improve the accuracy and repeatability of assembly. Multi-planar conductive Z-axis foam EMI gaskets represent the latest innovation in soft foam based EMI shielding technology. A unique integration of electrically conductive fibers into low density foam provides the basis for a performance driven, cost effective EMI shielding solution. This material is manufactured in rolls and is easily converted into product forms applicable for I/O panels, backplanes, connectors, and access panels along with rectangular/ square strip gasket seals, providing high Z-axis conductivity with extremely short ground paths. For many indoor consumer electronic devices that require shielding, the choice of EMI gaskets will often come down to either fingerstock or fabric-over-foam. Historically, fingerstock has been the gasket of choice, especially in highend electronics. It is reliable, proven and widely available. However, fabric-over foam gasketing is quickly becoming the preferred choice, due to improvements in the plating adhesion, advances in foam formulations, and the introduction of UL94V-0 rated versions. These gaskets are also easier to handle and less prone to damage during assembly and use. Mixed Media Gaskets Other types of EMI gaskets are available that use a mix of the above forms. These include gaskets utilizing non-conductive foams or elastomers combined with a mesh or metal gasket and are aptly named combo gaskets. They can provide both effective environmental sealing and EMI shielding. These mixed media gaskets are usually custom made. Other gaskets in this category include silicone sheets with oriented wires and mesh impregnated with neoprene or silicone elastomer. Although these can provide excellent environmental as well as EMI shielding significant pressure must be exerted to achieve this. [3] Conductive Plastics Injection molded plastics that incorporate EMI shielding Conformity marCh 2008 Figure 4: EMI shielding plastic faceplate http://www.captorcorp.com http://www.captorcorp.com

Table of Contents Feed for the Digital Edition of Conformity Magazine - March 2008

Conformity Magazine - March 2008 NewsBreaks Editor's Note Adelstein Renominated to the FCC Industry Canada Publishes FAQs On RF Fields FDA Gives Its Scientific Capabilities Poor Marks FDA Offers Guidance On its Product Review Process FDA Publishes Updates to List of Recognized Standards FDA Warns of Patient Risk From Electric Dental Handpieces Complying with the EMC Directive, Second Edition ESD Open Forum Emerging Issues in Standards - Korean "RoHS": Not Like RoHS at All The iNARTE Informer Challenges in Testing - Field-Induced Charged Device Model: What Really Happens Design Fundamentals - EMI Shielding Technologies for Consumer Electronics Equipment Focus On...Compliance Software Buyer's Guide Additional Standards Published for the EU's ATEX Directive Additional Standards for the EU's Medical Devices Directive Also Published China to Require Bar Codes to Enhance Product Safety CPSC Releases 2007 Self-Assessment CPSC Actions in News IEC Standards Update UL Standards Update Product Reviews Telcordia Standards Update From Our "You Can't Make This Stuff Up" Department Looking Back: Items from Past Issues of Conformity Advertisers

Conformity Magazine - March 2008

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