Jan, From a power integrity perspective, you'll get the best performance if the power planes are adjacent to ground planes. In Stackup 1, there is one PWR-GND pair, but the other power plane is referenced to a different power plane, which makes decoupling less effective due to increased effective inductance. Stackup 2 has the power and ground planes separated even further, which is worse. From a manufacturing perspective, I believe Symon is somewhat correct in that the layers do not necessarily need to be balanced/symmetric. However, balanced boards are easier to fabricate and assemble to, which will save costs in production quantities. If you're dealing with low quantities, you probably won't see much difference. If you're in the 1000's to millions of boards, balancing/symmetry is important. As for SI issues, true LVDS can reference ground or power planes without much difficulty as long as the planes are properly decoupled. That said, many parts stated to be "LVDS" do not fully comply with LVDS spec, so you should look closely at the output buffer design to determine which plane (power or ground) is most appopriate. To get around these three issues, I'll offer an alternative stackup that migth be worth considering. =20 > stackup 1 stackup 2 Stackup 3 > ----------------------------------------------------------------- > L1 routing routing Routing/Attach > Substrate > L2 power plane GND PWR > Substrate > L3 power plane routing GND > Substrate > L4 GND power plane Routing > Substrate > L5 routing power plane Routing > Substrate > L6 routing routing GND > Substrate > L7 GND GND PWR > Substrate > L8 routing routing Routing/Attach Highlights from this third stackup: * Each power plane is directly adjacent to a ground plane, which will improve/ease decoupling * the stackup is balanced for ease of manufacture * the routing layers are directly adjacent to ground planes Good luck, Pat ------------------------------------------------------------------ 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