Fabrizio, I've had some experience with this from a design measurement and simulation perspective. Yes, an oval anti-pad will have a large positive impact on differential via performance. In general, larger is better. If you want a good "rough" number, 30 mils over the pad diameter (15 mil clearance) works quite well. The idea is to give the signal unrestricted passage as it travels through the board. If you want something more exact for your board stackup, then it needs to be modeled with a full-wave simulator like CST Microwave, Flomerics Microstripes, or Ansoft HFSS. scott p.s. - I assume you mean an oval via that surrounds both differential pair vias. 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: >http://www.freelists.org/webpage/si-list > >For help: >si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > >List archives are viewable at: > http://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 > > > > -- Scott McMorrow Teraspeed Consulting Group LLC 2926 SE Yamhill St. Portland, OR 97214 (503) 239-5536 http://www.teraspeed.com -- Scott McMorrow Teraspeed Consulting Group LLC 2926 SE Yamhill St. Portland, OR 97214 (503) 239-5536 http://www.teraspeed.com ------------------------------------------------------------------ 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: http://www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: http://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