R: [SI-LIST] Impedance Mismatch due to neck downThanks guys for the responses. One reason for which we do not want to have 4-5 mil traces all the way is the resistive loss. 5 mils within the DUT and then gradual increase to 8 mils looks like a pretty good solution. Rgds, Qazi Iqbal -----Original Message----- From: Guasti Giovanni [mailto:Giovanni.Guasti@xxxxxxxxxx] Sent: Friday, June 24, 2005 12:41 AM To: 'qazi@xxxxxxxxxx'; si-list@xxxxxxxxxxxxx Subject: R: [SI-LIST] Impedance Mismatch due to neck down I agree with Paul, a slow signal would not notice the 1-2 cm long trace impedance mismatch. But you could think to make 5 mils traces ewerywere too. 65 Ohm is not so high but there are some simple ways to reduce it further. If you choose a dieletric thickness around 0.150mm you'll obtain an impedance of 50 ohm. Isn't er=4 too low? with an er=4.3-4.4 the impedance reduces from 65 to 60ohm. With a 8 mil trace and er=4.4 -> Zo=47ohm. Is it what you would like to obtain? By Giovanni -----Messaggio originale----- Da: Qazi Arif Iqbal [mailto:qazi@xxxxxxxxxx] Inviato: giovedì 23 giugno 2005 19.59 A: si-list@xxxxxxxxxxxxx Oggetto: [SI-LIST] Impedance Mismatch due to neck down Hi Experts, The board that I am using is of a stripline setup with 8mil traces (1 oz Cu), FR-4 (4.0) and 10 mil dielectric thickness which gives 50ohm (relatively low speed). The BGA is tightly pitched and I have to neckdown traces around 4-5 mils which gives impedance mismatch (65.4 ohm). Neckdown is a must but I also want to avoid impedance mismatch, is there any way of doing it? Does doubling help? (looks like this would give a parallel of 2 65.4ohms = 32.7, worse than what I have). Thanks in advance, Qazi ------------------------------------------------------------------ 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 FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org 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 -- PRIVACY WARNING: For auditing purposes, a copy of this message has been saved in a permanent database. -- PRIVACY WARNING: For auditing purposes, a copy of this message has been saved in a permanent database. ------------------------------------------------------------------ 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 FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org 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 -- PRIVACY WARNING: For auditing purposes, a copy of this message has been saved in a permanent database. -- PRIVACY WARNING: For auditing purposes, a copy of this message has been saved in a permanent database. ------------------------------------------------------------------ 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 FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org 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