The UL will look to see if the combination of coating, material and process is recognized and done by a recognized vendor. This issue came up long long ago and the problem was exactly what is noted below. The material if not prepped properly, not applied properly and not suitable as a combination was show to flake off and cause trouble in the wrong places. The trouble found was seen in the field as well. I don’t know if that was what prompted UL or if they thought of it during the first submission – either way. It has to be done properly.
Two other comments to add to the others is you have to watch any mating surfaces that are subject to vibration or to opening and closing during operation or repair. These materials work just fine, if you overcome all of the other problems, but they do where pretty easily. Sometimes one has to protect the coating at these joints with another material. On a recent medical device we had to add a metal “landing pad” between the upper and lower enclosure to insure that the material did not wear away. Retaining the ground and bond connections have to be designed in and not just a screw into the plastic – the plating is only skin deep so the screw threads themselves have no value and the now you are relying on the screw retention to provide enough contact pressure to make the ground connection. If the screw backs out of the plastic because the threads are getting slightly wider with aging or vibration you loose contact force. So it can be done, it just has to be done properly and sometimes the cost of radiusing curves etc to insure the plating wicks into the nooks and crannies etc may make it not worth the cost. The cell phone industry using shielding of this type quite effectively, but I don’t know if they would continue if they had other means or not because of the production problems. I mean this literally – I don’t know and I didn’t see a response from one of those guys – maybe I missed it I’ve been out of the office all last week. Gary ________________________________ From: Bill Owsley [mailto:[email protected]] Sent: Monday, August 16, 2010 9:11 PM To: [email protected] Subject: Re: [PSES] Polycarbonate Chassis Hmmm, your inconclusive results match my experience, some up and some down. And 2 ohms per square = don't use it. And what would that UL course be?? - Bill In the event of a national emergency, click on the following links to provide directions to your duly elected mis-representatives. http://www.usa.gov/Contact/Elected.shtml or... https://writerep.house.gov/writerep/welcome.shtml http://www.senate.gov/general/contact_information/senators_cfm.cfm if really desperate... http://www.usa.gov/Contact/Elected.shtml --- On Mon, 8/16/10, Jayasinghe, Ryan <[email protected]> wrote: From: Jayasinghe, Ryan <[email protected]> Subject: RE: [PSES] Polycarbonate Chassis To: "[email protected]" <[email protected]> List-Post: [email protected] List-Post: [email protected] List-Post: [email protected] Date: Monday, August 16, 2010, 7:15 PM Hi Group, Much thanks to Ken Wyatt, Peter Merguerian, Kevin Robinson, Brian O'Connell, Ron Pickard and Bill Owsley for your good advice. I have since learned that the material is High Impact Poly Styrene HIPS, I don’t have details on the shielding material other than it is 99.96 pure aluminium, Resistance is approx 2 ohms/square, Deposition is approx 150 angstroms. I performed some rudimentary radiated emission testing by cutting out a large square of the existing metal cover and attached the sample metalized material using copper tape. The results were inconclusive as I was using a NON-semi-anechoic, shielded room, some frequencies went up while others were about the same or slightly lower. I will re-test in an anechoic room. Peter’s point on the ensuring the metalized coating material does not peel and short out electrical circuitry is a point well taken as well as Kevin’s advice on avoiding this material like the plague. Ken’s comment on recycling issues was also very valuable as well as other comment on EMI/EMC. There is a UL class on this subject towards the end of the month in Brea CA which I will be sure to attend. Thank you all again, Ryan Jazz Jayasinghe Compliance Engineer x1198 Canoga Perkins Direct:(818) 678-3898 20600 Prairie Street Company:(818) 718-6300 Chatsworth, CA 91311-6008 e-mail: [email protected] www.canoga.com <http://www.canoga.com/> FAX:(818) 678-3798 ________________________________ From: Bill Owsley [mailto:[email protected]] Sent: Thursday, August 12, 2010 6:15 PM To: Jayasinghe, Ryan; Ken Wyatt Cc: [email protected] Subject: Re: [PSES] Polycarbonate Chassis A double amen to this! And cost saving be damned, we're going to have plastic no matter what! - Bill In the event of a national emergency, click on the following links to provide directions to your duly elected mis-representatives. http://www.usa.gov/Contact/Elected.shtml or... https://writerep.house.gov/writerep/welcome.shtml http://www.senate.gov/general/contact_information/senators_cfm.cfm if really desperate... http://www.usa.gov/Contact/Elected.shtml --- On Thu, 8/12/10, Ken Wyatt <[email protected]> wrote: From: Ken Wyatt <[email protected]> Subject: Re: [PSES] Po- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]> - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]>
