Richard I totally agree with your statement but let me make the point, in physics, that is easily missed.
If I apply a potential to two parallel plates then I produce an electric field between those plates. We refer to that effect as capacitance. When I introduce another plate between the existing plates I increase the capacitance by the ratio of the thickness of the plate to the distance between plates. Thieving is the equivalent to an added plate so it increases capacitance. One can argue the effect is so small that it may be neglected and that will be true in 99% of cases. That 1% might be your high frequency oscillator circuit. However any time you give design control over to vendors, even in small parameters, it can come back to bite you. If thieving is applied by the vendor, what happens when you change vendors? Undocumented ECO? It's poor design practice to let the vendor define thieving. Apply thieving in the form of a company logo or even a happy face (yes I have seen them). Just apply it to your CAD design, artwork, etc. That will allow your people to at spot those 1% situations. Otherwise your engineer will never see the problem it until the problem hits the production line. It's just good engineering practice to control as many parameters as possible. Fred Townsend Stone, Richard wrote: Fred, isnt thieving usually concentrated on the top external layer of the board? I think the fab house does a weight balance check once the copper is filled in on all the layers and then the theiving is added in to compensate for weight irregularities where the board lacks copper to even the distribution as Fred noted below. good luck, Richard, From: [email protected] [ mailto:[email protected]]On Behalf Of Fred Townsend Sent: Thursday, November 17, 2005 1:45 AM To: Sylvia Toma Cc: [email protected] Subject: Re: Thieving on PCB My guess is that unless you specify it as grounded it will be floating. Thieving can effect circuit performance so it's always better to incorporate it the design rather than let the PCB manufacturer do it where you may get uncontrolled results. Check out www.ipc.org for more info. Fred Townsend Sylvia Toma wrote: Hello group, I have a question regarding thieving on printed circuit board and hoping that you could help me: If the PCB manufacturer wants to add copper thieving to the PCB layers to help balance the copper distribution since there is a potential for thickness variation as well as possible warp without it, is the copper thieving considered to be at '0' volt or treated as 'floating' as far as safety spacing is concern? Looking forward to your reply. Regards, Sylvia __________________________________ Yahoo! FareChase: Search multiple travel sites in one click. http://farechase.yahoo.com - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/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] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc Text inserted by Panda Platinum 2006 Internet Security: This message has NOT been classified as spam. If it is unsolicited mail (spam), click on the following link to reclassify it: http://127.0.0.1:6083/Panda?ID=pav_862 http://127.0.0.1:6083/Panda?ID=pav_862&SPAM=true> &SPAM=true - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/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] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc Text inserted by Panda Platinum 2006 Internet Security: This message has NOT been classified as spam. If it is unsolicited mail (spam), click on the following link to reclassify it: http://127.0.0.1:6083/Panda?ID=pav_963 http://127.0.0.1:6083/Panda?ID=pav_963&SPAM=true> &SPAM=true - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/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] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
