Hi Stuart, Your stackup #2 is the correct choice to prevent warpage especially if this is a substrate for a device package with buildup outer layers. In stackup #1 with build up technology, layers #4 and 5 are the core layers. With routing on 1 layer, it stress relieves that layer cousing possible warpage. In Stackup #2 layers 4 and 5 are balanced and cancel one another. The outer layers with buildup technology are of less concern. Ed. L. Symon wrote: >Hi Stuart, >To the best of my knowledge, and IME, I think you're mistaken. As long as >the cores and prepregs etc. are symetrical there won't be a warpage problem. >The copper planes per se don't matter. The designer can even use copper >balancing if they're paranoid! >HTH, Syms. > >----- Original Message ----- >From: "Stuart Brorson" <sdb@xxxxxxxxxx> > > > > >>Forgetting about any minor SI advantages/disadvantages, stackup 1 has >>the major disadvantage that the plane layers are unbalanced, which can >>lead to board warpage. That is, the planes will strain the top >>layers of stackup 1 more than the non-plane bottom layers, which can >>lead to bent, warped boards. The problem would become acute over wide >>temperature ranges. I'd stick with stackup 2. >> >>Stuart >> >> >> >>>I need to specify a 8layer board. Fastest edges on the board are on the >>>600Mbit LVDS channels : about 500ps. I have two stackups in mind : >>> >>> stackup 1 stackup 2 >>>--------------------------------------------------------- >>>L1 routing routing >>>Substrate >>>L2 power plane GND >>>Substrate >>>L3 power plane routing >>>Substrate >>>L4 GND power plane >>>Substrate >>>L5 routing power plane >>>Substrate >>>L6 routing routing >>>Substrate >>>L7 GND GND >>>Substrate >>>L8 routing routing >>> >>> > >------------------------------------------------------------------ >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 > > > > ------------------------------------------------------------------ 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