Conductive polymer composite materials and their utility in electromagnetic shielding applications

Commercial electronic devices require shielding solutions that ensure electromagnetic compatibility (EMC) while accounting for effects of specific enclosure structural features such as seams, vents, and port dimensions. In practice, suitable EMC materials combine with the device operating characteristics to determine an overall shielding response. To optimally couple plastic design practices with EMC requirements, both polymer materials science and electrical engineering concepts, must be considered. Use of extrinsically conductive polymer (ECP) formulations for electronic applications has advantages in that they can be directly molded to a desired shape and serve to provide the necessary shielding while also meeting mechanical integrity requirements. Shielding and mechanical performance can be varied via filler loading or altered through wall thickness changes to satisfy demands associated with a particular device. Injection-moldable ECP polycarbonate-based formulations can attain average shielding effectiveness (SE) levels of similar to 50-60 dB through 2 GHz at 2-mm thickness as measured using ASTM D 4935 procedures. These values vary with thickness, and SE improvements of similar to 10-20 dB are observed when increasing from I to 2 mm. Additionally, resultant mechanical properties of shielding composites are strong functions of overall fiber content. These interrelated material and shielding characteristics, which form the basis for filled conductive polymer use within practical enclosure shielding designs, are described. (c) 2007 Wiley Periodicals, Inc.