Greetings Fabrizio: Ansoft is a contributor to the XFP MSA (www.xfpmsa.org). We contributed differential via analysis and optimization for 62mil and 100mil PCBs. Our results indicate that for 10Gb/s transmission, differential vias with a 0.8mm via pitch, 0.3mm drill size, and 0.56mm pads, had best performance (lowest return loss) using a gap of 0.52mm. The "gap" is the distance from the pad to the oval-shaped ground (or power) clearance keepout. Interestingly, the optimized dimensions for both 62mil and 100mil board thicknesses are identical. This can be explained by considering the via structure as a transmission line with propagation along the dimension perpendicular to the PCB plane. It is intuitive that this transmission line should have a uniform cross-section that is independent of the length of the line (board thickness). We also performed analyses of ground-signal-signal-ground (GSSG) differential via structures. You can examine all of the results in Appendix D of the XFP specification available at http://www.xfpmsa.org/XFP_Rev_2.pdf Hope this helps. Best regards, Larry ___________________________________ Lawrence I. Williams, Ph.D. Director of Business Development Ansoft Corporation 1-714-528-9358 1-714-747-5894 cell ___________________________________ williams@xxxxxxxxxx www.ansoft.com -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Fabrizio Zanella Sent: Thursday, March 27, 2003 4:50 AM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Ground clearance at connector vias 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 -- Binary/unsupported file stripped by Ecartis -- -- Type: text/x-vcard -- File: Lawrence I Williams.vcf ------------------------------------------------------------------ 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