I had a case where they tried to add metal in the insulation spacing region between primary and secondary. You must make sure any changes to the board need regulatory review, especially since these often do not appear on the CAD outputs and may be added following initial production runs.
Fred Townsend wrote: 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 - ---------------------------------------------------------------- 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
