Conformity Magazine - December 2008 - (Page 34)

Meeting the Shielding Challenges of Injection-Molded Plastics by Jim Skelly, Cybershield B eing non-conductive, plastic components do not shield electromagnetic interference (EMI) from being emitted from electronic equipment, or from penetrating and interfering with its operation. Many electronic systems built with plastic components require shielding to meet regulations and ensure reliable device performance. Conductive coatings essentially consume no volume inside an electronic device and, if applied properly, can assist the design engineer in meeting ever-shrinking cost budgets. Conductive coatings, first applied in electronic devices over 20 years ago, have demonstrated reliable and cost effective performance in laptop computers, cellular handsets, telecom switchgear, medical devices, military electronics, industrial equipment and a host of other electronic systems that utilize injection-molded plastic enclosures. When designing products housed in injection-molded plastic, several factors need to be taken into account for electromagnetic interference (EMI) shielding, including: 1. 2. 3. Selecting plastic resin compatible with the process; Mechanical design of the plastic components to be compatible with coating processes; Determining shielding requirements and potential conductive coating systems. This article will address the key issues facing engineers specifying EMI shielding systems, including plastic resin selection, important mechanical design issues, and shielding effectiveness of conductive coatings. Real world examples will be reviewed to provide insight into the issues that lead to successful EMI shielding design. First, we will begin with a synopsis of the EMI shielding processes. EMI Shielding Processes Electroless and Electrolytic Plating The starting point for plating on plastic is electroless plating, where an initial layer of copper is deposited directly onto the plastic part. Electroless plating is an autocatalytic, chemical plating process which deposits a pure, continuous metal layer. The part is immersed into a series of plating tanks, including a chemical etch to roughen the surface, and activation to deposit a catalyst onto the part prior to deposition of copper. The etching and activation steps impact only the outer skin of the plastic. The bulk material properties of the plastic part are not affected. Electroless plating produces uniform thickness on all surfaces of plastic part, even in recesses and holes. 3 Conformity DeCember 2008

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Conformity Magazine - December 2008 Contents Editor's Note FCC Warns Regulatory Fee Payers About Potential "Phishing" Commission Prowls the Web to Enforce Its Regulations First DTV Rollout Initiated in Wilmington, NC New Standards List Released for the EU's Directive on the Safety of Toys ESD Association Call for Papers ESDA. JEDEC Announce Standards Development Cooperation Commission Releases Data on Local Telephone Competition The Future of ESD Testing ESD Open Forum Emerging Issues in Standards: China RoHS: One Year and Counting Challenges in Testing: Revisiting 10-Meter and 3-Meter Radiated Emission Measurements Design Fundamentals: Meeting the Shielding Challenges of Injection-Molded Plastics Focus On...Microwave Absorbers Buyer's Guide FDA Recalls Automated External Defibrillators FDA Revises Guidance on Medical Device Tracking Guidance Document Safety of Passive Implants Released FDA Offers Guidance on Marketing Diagnostic Ultrasound Systems EU Commission Issues Correction on Machinery Directive Standards Other CPSC Actions in the News Product Reviews IEC Standards Update UL Standards Update Looking Back: Items from Past Issues of Conformity Advertisers

Conformity Magazine - December 2008

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