In my experience with these coatings the choice of material for EMI puposes doesn't matter that much. Nickel or copper work just fine. I have seen 30db attenuation based on the coating alone. The are some other problems with safety/reliability, and material selection is important.
Select compatible coatings and plastics as listed in the UL Plastics Recognized Ccomponent Directory Select an application vendor and test incoming samples with the ASTM 3359 Tape Adhesion Test. We have found compatible materials that fail this test due to improper application. The coating doesn't always adhere to the substrate well. Poorly applied or incompatible materials can cause problems by flaking over time, or with abrasion, thereby sprinkling your PCBs with conductive dust. Recyclability is becoming an issue in Europe which should give copper an advantage. Darrell Locke Advanced Input Devices ---------- From: George Tang To: Westerdahl, Eric Cc: 'EMI-PS Group' Subject: Re: Conductive Coating List-Post: [email protected] Date: Wednesday, November 03, 1999 6:24PM There are many different types of conductive coatings available. Silver paint is very conductive, less than 5 ohms per square inch. But it is not as scratch resistant as sheet metal surfaces. Electroless copper / nickel plating is very conductive and durable. You can get as low as 1 ohm per square inch. If you don't, your plating is not thick enough. This plating should pass the safety fault current test, as long as the safety ground wire makes "surface area" contact with the plating and not "point" contact. This plating has 60 dB shielding effectiveness for frequencies above 30 MHz, since it is much thicker than the skin depth. You need the thickness for the safety fault current. The best feature of the plating is that it allows you to mold your chassis into one piece of plastic with no extra metal pieces to assemble. It's kinda nice that way. :-) go to www.ccoatings.com or call (972) 851-0460 George Tang "Westerdahl, Eric" wrote: > Our company has decided to use a conductive coating to mitigate some EMI > problems on one of our units. We have not used this method before. I have > a question as to the correct resistivity of the coating. What range should > I be looking at, and does the range change if the frequency of the strong > signal are high or low? > > The equipment is IEC 950 and EMC Directive stuff with many noisy DC motor > and motor controller combinations. Most of the signals we are concerned > about are at the lower end of the CISPR 22 region. 30 to 150 MHz. > > Eric Westerdahl > Regulatory Engineer > Roll Systems, Inc. > [email protected] > > --------- > 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). --------- 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). --------- 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).
