Hi, The proposed stackup will indeed reduce the noise on your 3.3v plane. However, instead of surrounding the plane with two gnd planes, I would suggest adding a second pwr/gnd pair to the stackup to maintain symmetry. Make sure you couple the pwr/gnd pairs as closely as possible. I usually use 4 mil cores for pwr/gnd pairs. If you need 6 routing layers, I would probably try to do the following; 1) G 2) S 3) S 4) +3.3V 5) G 6) S 7) S 8) +3.3V 9) G 10)S 11)S 12)G I wouldn't be surprised if someone else has a better idea, which is why is subscribe. Matt -----Original Message----- From: Peterson, James F (FL51) [mailto:james.f.peterson@xxxxxxxxxxxxx] Sent: Wednesday, June 18, 2003 6:56 AM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] pcb stackup a typical stackup at our company might look like this: 1) G 2) S 3) S 4) +3.3V 5) S 6) S 7) G 8) S 9) S 10)G note that we use layer 4 (+3.3V) as a reference plane. an alternate stackup is now being pushed here that doesn't allow this. the alternative approach says that this puts too much noise in the +3.3V plane. that we should surround the +3.3V plane with ground planes, as shown below : 1) G 2) S 3) S 4) G 5) +3.3 6) G 7) S 8) S 9) G 10)S 11)S 12)G Comments? thanks, Jim Peterson Honeywell ------------------------------------------------------------------ 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