Hello Itzhak, as long as the traces are truly perpendicular crosstalk will be minimal. The issue then is mostly the restricted routing flexibility - e.g. you can't just have the traces make turns at arbitrary locations, lest they do run parallel to some trace on the adjacent layer. With fast rise times, even short sections of parallel traces will result in full-blown near-end crosstalk (NEXT). To get an initial idea how strong the coupling is for a given length of trace, there are a few free(!) tools that at least allow first-order estimates, good to build some confidence in your design decisions: TNT/MMTL field solver (available from Sourceforge) - a 2D solver that you can use to get coupling (crosstalk) parameters between parallel traces. It even gives you total NEXT and FEXT directly, for given coupling length and signal rise time. Sonnet Lite - the free version supports 2 signal layers, plus you can use top and bottom box cover as your ground planes, which allows simulation of your 4-layer stack (G-S-S-G). Since it is a planar (2.5D) field solver you can use it to simulate more advanced situations, e.g. estimate residual coupling of traces running at e.g. 45 degree angles. (I'm not connected with Sonnet in any way, other than that I am using their free software version). Hope that helps Wolfgang Hirshtal Itzhak <ihirshtal@xxxxxxxxxx> Sent by: si-list-bounce@xxxxxxxxxxxxx 06/02/2010 04:37 AM To si-list@xxxxxxxxxxxxx cc Subject [SI-LIST] MGB/s pair crossing on adajent layers Hi Experts! I use double-stripline layers for MGb (PCI-Ex, sRIO) pair routing. I ordered the PCB Designer not to route such pairs on adjacent layers, close to each other, not even PERPENDICULAR to each other. Now it seems I can't avoid it any more. My PCB Designer seems to run out of real-estate. I have 4-mil separation between the 2 layers and 4-mil from each one to a GND layer on each side. The pairs are running at 2.5 to 3.125 Gb/s What risks, if any, I run into, if I do permit routing the pairs perpendicular to each other? Are there any precautions I should take while doing it? Thanks Itzhak Hirshtal Elta The information contained in this communication is proprietary to Israel Aerospace Industries Ltd., ELTA Systems Ltd. and/or third parties, may contain classified or privileged information, and is intended only for the use of the intended addressee thereof. If you are not the intended addressee, please be aware that any use, disclosure, distribution and/or copying of this communication is strictly prohibited. If you receive this communication in error, please notify the sender immediately and delete it from your computer. Thank you. This message is processed by the PrivaWall Email Security Server. ------------------------------------------------------------------ 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 technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list 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 technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu