WTB: Aerosol shielding spray (name?) - Page 1
Forum section: electronics / general

author: SL4P
author_rank: Super Contributor
timestamp: February 09, 2017, 10:03:38 am
content: I'm looking for that metallized spray 'shield' coating that I can use to coat the inside of a PVC enclosure - to protect the internals from local RF noise.Grounding it to the local 0V rail - I suppose will be a bolt with star-washer for contact, and spade/QC terminal ?I haven't tried this approach before, but I'm using a 3G cellular antenna about 2-3 inches away from a processor board and SLA battery. It seems I'm getting some RF leakage into the circuit (occasional restarts when the cellular modem 'lights up' for transmission - I guess those old-fashioned GSM burps and farts during a session).Current testing has a sheet of heavy cooking foil (effectively a ground-plane) about 1/2 inch below the antenna between the enclosure and the processor board... seems to be significantly better - possibly fixed.Any other suggestions.

author: Ian.M
author_rank: Super Contributor
timestamp: February 09, 2017, 11:21:47 am
content: Google: EMI shielding sprayand try to find a local distributor.Connecting to it is a PITA - the only high reliability ways to do so are by applying copper tape with conductive adhesive and soldering to the tape or by mechanical pressure with a conductive elastomer or flexible metallic cloth wrapped round a non-conductive elastomer.Your proposed star washer is much harder than the paint and the underlying plastic substrate and slight movements caused by vibration or even thermal expansion and contraction will cause it to dig into and fret the coating, eventually loosing contact.

author: SMdude
author_rank: Frequent Contributor
timestamp: February 09, 2017, 11:27:49 am
content: Here are some conductive paints:http://au.element14.com/webapp/wcs/stores/servlet/Search?catalogId=15001&langId=43&storeId=10184&categoryId=800000000394&eq=N%3D203113%2B2101%26amp%3BNtk%3Ddesc_pn%26amp%3BNtt%3Dpaint%26amp%3BNtx%3Drel%2Bgensearch_store_specific%252cstatic%2528P_STORE_MARKETING_RANK_FARNELL_AU%252cascending%2529%2Bmode%2Bmatchpartialmax%26amp%3BNty%3D1%26amp%3BNtpc%3D1%26amp%3BNtpr%3D1%26amp%3BD%3Dpaint*%26amp%3BDn%3D2101%2B2101%26amp%3BDx%3Dmode%2Bmatchall&st=paint&pageSize=25&showResults=true&aa=true&pf=110029936&vw=Sorry for the extra long link!To connect to it, bury/glue/atach a wire strand in the plastic in a few spots, then paint the shielding on. You could probably run this back to a screw on the case to attach your cct. This will be rock solid

author: Ian.M
author_rank: Super Contributor
timestamp: February 09, 2017, 11:41:12 am
content: Its somewhat questionable to paint over a conductor to connect the paint. There's almost invariably a discontinuity at the edges and its quite easy for the paint to crack along that discontinuity. If I was doing it cheap without the proper conductive adhesive copper tape, I'd epoxy a piece of thin solderable foil or shim stock to a flat surface of the interior, carefully fairing all edges with a slight excess of epoxy, then sand the middle of the piece back to bare metal, leaving a thin layer of epoxy over the extreme edges. Solder the wire on, de-flux then spray paint.You'll also see some products that use a leaf or coil spring contact from the PCB to the case.If the PCB is mounted on moulded in bosses with radiused edges, simply spraying the bosses then, when dry, use Belville or wave spring washers between the mounting screw head and the PCB so that a tinned or plated annular ground ring round the mounting hole is in direct contact with the paint on the boss.

author: SL4P
author_rank: Super Contributor
timestamp: February 09, 2017, 06:10:04 pm
content: Quote from: SMdude on February 09, 2017, 11:27:49 amThat's a clever idea... thanks.

author: SL4P
author_rank: Super Contributor
timestamp: February 09, 2017, 06:11:57 pm
content: Obviously i have some learning &experimenting...Thanks to all, now to place an order.