Group, Calling that stuff a Faraday Cage is way to optimistic. At such a close distance the E-field would be attenuated substantially, but it would do nothing for the H-field (magnetic)as it's way to close to the RF-currents. It would have done nothing for earth potentials creating cable Common Mode currents either. It's just a close field E-shielding. And then one should know that the E-field component emitting from a PCB can most of the time be neglected in real life emission problems. That's probably why it did not achieve market acceptance.
For effective shielding one needs two (2) shields: - a defined potential (grounded) shield to block E-field - a thicker conductive shield that may carry induced currents to shield the H-field The more distance between the source, and the shield, the better it's efficiency , simply because less magnetic field lines have to cross the shield, and at a lower amplitude. Or in terms of field impedance (the quotient E/H): the closer to the source of a H-field, the lower the field impedance is, the lower shield impedance is required to achieve a certain amount of blocking. I mean: lower shield impedance both in terms of conductivity (material, thickness) and in terms of permeability (mu). Gert Gremmen -----Original Message----- From: [email protected] [mailto:[email protected]]On Behalf Of Charles Grasso Sent: woensdag 3 juli 2002 18:24 To: [email protected]; [email protected] Subject: RE: Conductive Conformal Coatings for reducing PCB Emissions Actually Chris there was a product that provided for a solder mask then had a conductive film ontop of that. The manufacturers could also tie this outer skin to the grounds on the printed circuit boord finally making the Faraday cage !! Papers I have read on this showed an excellent reduction in emissions (>20dB) - neglecting the effects of the ICs I know that AMP used to market this but it did not seem to achieve markey acceptance. Charles Grasso >From: Chris Chileshe <[email protected]> >Reply-To: Chris Chileshe <[email protected]> >To: "[email protected]" <[email protected]> >Subject: RE: Conductive Conformal Coatings for reducing PCB Emissions >Date: Wed, 3 Jul 2002 16:21:55 +0100 > > >Mat, > >Can we assume you mean conductive spray coatings for plastic >caseworks? Wouldn't a conductive conformal coating would short >out all the components on the PCB? Or is a two-pass technology >with the ordinary insulating coating over the components and a >conductive layer on the outside? > >Awaiting your clarification. > >- Regards > >- Chris > >-----Original Message----- >From: Aschenberg, Mat [SMTP:[email protected]] >Sent: Tuesday, July 02, 2002 3:36 PM >To: [email protected] >Subject: Conductive Conformal Coatings for reducing PCB Emissions > > >Hi All, >A while back there was a push to use conductive conformal >coatings for PCB emissions. Does anyone know if the >technology still exists and if so who makes it?? > >Thanks > > > > >------------------------------------------- >This message is from the IEEE EMC Society Product Safety >Technical Committee emc-pstc discussion list. > >Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ > >To cancel your subscription, send mail to: > [email protected] >with the single line: > unsubscribe emc-pstc > >For help, send mail to the list administrators: > Ron Pickard: [email protected] > Dave Heald: [email protected] > >For policy questions, send mail to: > Richard Nute: [email protected] > Jim Bacher: [email protected] > >All emc-pstc postings are archived and searchable on the web at: > http://ieeepstc.mindcruiser.com/ > Click on "browse" and then "emc-pstc mailing list" > >________________________________________________________________________ >This e-mail has been scanned for all viruses by Star Internet. The >service is powered by MessageLabs. 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