Signal traces will use any copper areas they see nearby. Return switching currents will flow through all adjacent planes, even if you didn't mean for them to flow there. It makes little difference to the signal what else that plane is or is not used for, although it matters when you start looking at how return path currents get on and off the plane in question around the ends of the signal traces, or if traces fall off the ends of a finite plane or cross splits. If both driver and receiver are within the area of the copper plane, and the whole trace stays adjacent to the plane, then it may be a good reference plane. But you'd want to see how the switching currents get from the driver to this plane. Regards, Andy > If we have a copper plane that is used for thermal relief and is not tied > directly to digital ground, can it be used as a reference plane? Note : This > thermal plane is tied to the chassis which has a single point connection to > digital ground (located on the backplane). > > Will an adjacent signal layer see this as a reference plane? ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu