Hi Amund,
If you have the space on the board then a ground fill around the perimeter (on all layers) probably won’t do any harm. Whatever ground fill strategy you decide on for the signal layer I would make sure it is well connected with vias to both of the adjacent planes along the edge nearest to the signals and around the perimeter of the PCB. The distance between these vias probably isn’t that critical but you often see the figure of wavelength/20 or wavelength/10 used as a guideline. For a digital signal you could use 0.35/Trise as a rule of thumb for working out the frequency. Lambda = c/f takes care of the rest. Edge plating (as Ken points out) is an option but obviously adds cost to the PCB. Part of the aim will be to maintain the correct characteristic impedance of your transmission line to help ensure good signal quality. You could model the PCB stackup and trace geometry in something like Polar or Hyperlynx (this free tool <https://www.eeweb.com/tools/edge-coupled-stripline-impedance> doesn’t account for a co-planar ground) and see how far away the co-planar ground needs to be to maintain the correct impedance. Or just choose an arbitrarily large, conservative (small c) number like 10h (h being height of the smallest gap between trace and plane). If you have noise leakage, that would suggest that your “differential” lines might not be as differential as you think. Unequal rise/fall times and skew between rising and falling edges will create common mode noise on these pairs. This is usually a fundamental characteristic of the driver circuit itself and there’s not much you can do about it. May be worth trying a HF common mode choke at the source – Wurth, Murata and TDK make good ones. Local ground via where your HF signals transition between layers to ensure that the return path currents can transfer from one side of the plane to the other (skin effect). This should be balanced, that is equidistant between the traces, or use two in symmetrical layout, to avoid imbalance in parasitic capacitance. You may also want to think about via “anti pads” to improve your impedance matching. What bus technology are you using for these high speed traces? HTH James James Pawson EMC Problem Solver Unit 3 Compliance EMC Testing / Design for EMC / Problem Solving / Pre Compliance / Consultancy / Environmental & Vibration <http://www.unit3compliance.co.uk/> www.unit3compliance.co.uk -- 07811 139957 Opening Hours: Tuesday to Friday, 0830 to 1800. Closed Monday. From: Amund Westin <am...@westin-emission.no> Sent: 19 February 2020 06:51 To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: [PSES] SV: [PSES] Ground copper fill on signal layer on multilayer PCB Hi Ken No, I have not considered edge-plating. I’ll look into this now. We have some high frequency noise (400-500MHz) from differential lines leaking out from an inner layer of a multilayer pcb. Edge-plating might be a good solution. Thanks for the tip. BR Amund Fra: IBM Ken Sendt: 18. februar 2020 23:18 Til: EMC-PSTC@LISTSERV.IEEE.ORG <mailto:EMC-PSTC@LISTSERV.IEEE.ORG> Emne: Re: [PSES] Ground copper fill on signal layer on multilayer PCB Hi Amund! Have you also considered edge-plating? Are you trying to reduce radiated noise outside your product, or cross-talk within the product (or both)? On Tue, Feb 18, 2020 at 3:03 AM Amund Westin <am...@westin-emission.no <mailto:am...@westin-emission.no> > wrote: Between two solid ground planes, we have a signal layer, routing high speed differential lines. What do you recommend: I. fill the remaining area with copper in the signal layer II. fill only the border of the layer (5mm ground copper trace around the layer edge) III. no fill at all Best regards Amund - ---------------------------------------------------------------- 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 <emc-p...@ieee.org <mailto:emc-p...@ieee.org> > All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) <http://www.ieee-pses.org/list.html> List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org <mailto:sdoug...@ieee.org> > Mike Cantwell <mcantw...@ieee.org <mailto:mcantw...@ieee.org> > For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org <mailto:j.bac...@ieee.org> > David Heald <dhe...@gmail.com <mailto:dhe...@gmail.com> > - ---------------------------------------------------------------- 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 <emc-p...@ieee.org <mailto:emc-p...@ieee.org> > All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) <http://www.ieee-pses.org/list.html> List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org <mailto:sdoug...@ieee.org> > Mike Cantwell <mcantw...@ieee.org <mailto:mcantw...@ieee.org> > For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org <mailto:j.bac...@ieee.org> > David Heald <dhe...@gmail.com <mailto:dhe...@gmail.com> > - ---------------------------------------------------------------- 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 <emc-p...@ieee.org <mailto:emc-p...@ieee.org> > All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) <http://www.ieee-pses.org/list.html> List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org <mailto:sdoug...@ieee.org> > Mike Cantwell <mcantw...@ieee.org <mailto:mcantw...@ieee.org> > For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org <mailto:j.bac...@ieee.org> > David Heald <dhe...@gmail.com <mailto:dhe...@gmail.com> > - ---------------------------------------------------------------- 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 <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
