Some time ago, in a company far away (well, not THAT far away -- grin) I had to evaluate problems with a nickel painted plastic chassis, and later, its copper-painted follow-on. I found I could get good correlation with performance on the OATS by measuring attenuation between a pair of shielded loops about an inch or so across, separated far enough to let pass a painted chassis or test sample. By comparing air (zero), galvanized iron (essentially infinite) and the test sample, I could develop a good idea how much it would attenuate fields from currents on the PWB close to it, inside, and the rest of the world.
In every case, when a deficiency was noted using this method, close inspection of the subject chassis revealed problems in the paint application, too thin, too many interruptions (crack) die to chassis detail, or failure to make sufficient contact with ground bosses pressed into the chassis. Resistance measurements did not always catch the problem, as cracks and detail problems were paralleled at DC by a sufficient number of other paths. Thickness problems WERE always caught by resistance measurements, however. Cortland ====================== Original Message Follows ==================== >> Date: 14-Apr-99 10:00:21 MsgID: 1067-92308 ToID: 72146,373 From: "Richard Haynes" >INTERNET:[email protected] Subj: Re: Conductive Paint Chrg: $0.00 Imp: Norm Sens: Std Receipt: No Parts: 1 Hey, I am just now writing a paper on measurements of several metals and coatings so I will just summarize some of the results: System frequency range Ohm/sq Zn 50 Hz to 3GHz ~0.1 to ~8 AgCu 50Hz to 3GHz 1 to 7 (plated Ag onto Copper particles as fillers) Ni 50 Hz to 3GHz 3 to 27 (particle fillers) Cu 50 Hz to 3GHz 1 to 10 (Metal) There are several other systems that I have measured. May get to a publication this year? Richard Haynes 609-497-4584 P.S. This is a better technique than the Z technique for absolute measurement that are reproducable. -----Original Message----- From: Douglas McKean <[email protected]> To: [email protected] <[email protected]> List-Post: [email protected] Date: Tuesday, April 13, 1999 9:26 PM Subject: Re: Conductive Paint --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
