I think your question is 'why have the G layer nearest the top of the board rather than the P layer?' Probably because the chips are generally on the top side of the board and having the the G layer nearest means your hi-speed racks can reference G rather than P without needing vias. Of course with a good decoupling referencing P rather than G might not be a problem, see previous threads on this list re referencing G or P. However, the G layer is generally one complete area over the board while the P layer must often be split into sections for different voltages; giving rise to problems where signal traces have to cross the splits Regards Dave Instone +44 (0)1235 824963 OXFORD SEMICONDUCTOR LIMITED 25 MILTON PARK ABINGDON OXFORDSHIRE OX14 4SH Registered in England no 2733820 Registered Address: As above Saoer Sinaga wrote: > Dear all, > May I know the reason why people would generally use S1 S2 G P S3 S4 > configuration for six-layer stackup? Why not S1 S2 P G S3 S4? > Thanks. > > regards, > Saoer > > On Wed, Feb 20, 2008 at 11:17 PM, Fernando Yuitiro Mori <mori@xxxxxxxxxxxxx> > wrote: > > >> Hi, >> I normally use S1 S2 G P S3 S4 for the 6 layers stackup. I need the 4 >> layer with 60 ohms, so there are some problem if I use S1 G S2 S3 P S4? >> >> Regards, >> >> Fernando Mori >> ------------------------------------------------------------------ >> 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 technical documents are available at: >> http://www.si-list.net >> >> 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 technical documents are available at: > http://www.si-list.net > > 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 technical documents are available at: http://www.si-list.net 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