Pat, If you are required to split your ground plane, as you might in a mixed signal design, then be very careful to keep a return current path with minimum inductance. You can do this by placing ground vias at the ground plane ovelaps as close as possible to the traces that are changing layers. Be advised that you will pay a crosstalk penalty for this, as some conductors on your bus may have to share return current vias. If your layer 6 routing is coupled to your power plane (thin dielectric material relative to ground plane dielectric thickness), you will have to provide a return current path by placing caps to ground near the layer trasistion. Here you will suffer crosstalk penalties, and your return current path will have an increase in inductance associated with the ESL of the cap. If there is no way around it, I have seen high speed digital busses work using these tricks. But my best advice is to avoid the described layer transitions when possible. James J. -----Original Message----- From: Pat Sharkey [mailto:psharkey@xxxxxxxxxxx] Sent: Friday, February 01, 2002 8:10 AM To: Si-List@Freelists. Org Subject: [SI-LIST] Split Plane Routing Hello all, Given the following stackup with planes split in different areas - 1 - S1 2 - GND (SPLIT 1) 3 - S2 4 - GND(SPLIT 2) 5 - POWER(SPLIT 3) 6 - S3 7 - GND (SPLIT 4) 8 - S4. For a signal which originates on layer 8, should the signal only be routed on layers 6 & 8? Or, can layers 1 and 3 also be used to cross a plane split on layer 7, assuming layers 2 and 4 are not split in the same place (z axis)? Thanks in advance, Pat ------------------------------------------------------------------ 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 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 ------------------------------------------------------------------ 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 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