Fabrizio, There is much work done by the makers of the connectors in modelling the connectors. However my experience is that due to many dependencies you will probably have to make a test board with optional clearances and configurations as we have done for our backplanes and connector types regarding 2.5G and above. If you are interested and can send you a ppt with some indications of how to determine impedance match. My experience is also that the "screened" connectors are not very well matched and will require the adation of clearance etc. for compensation. I cannot see any good reason for "oval" clearance other than you have some special crosstalk problem. Much success -- Regards, __________ James G Roberts /___ ____ | jrobert@xxxxxxxxxxxxxxxxxxxxx Jim __ / /___/ / jgroberts@xxxxxxxxxx / /_/ /---| | Room: BE436, Hilversum \____/ /_/ Tel: +31 35 687 4308 Fax: 5976 Fabrizio Zanella wrote: > I have a question regarding ground clearances for signal vias in a > backplane connector, like the Molex/Teradyne HSD. Connector and > semiconductor manufacturers recommend using an oval ground clearance > around the differential pairs, to minimize reflections. > Do you agree with this recommendation, especially at signal speeds of > 2.5Gbs and above? Can anyone share their experiences? How large should > the clearance be on the backplane? > > Thanks and regards, > > Fabrizio Zanella > Principal Hardware Design Engineer > Broadbus Technologies > fzanella@xxxxxxxxxxxx > =20 > -------------------------------------------------------- > > =20 > This email message and any files transmitted with it contain = > confidential information intended only for the person(s) to whom this = > email message is addressed. If you have received this email message in = > error, please notify the sender immediately by telephone or email and = > destroy the original message without making a copy. Thank you.=20 > =20 > ------------------------------------------------------------------ > 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