Jack, What about using your bottom layer as a voltage plane for at least 2 of your powers ? and the layer next to the bottom as a GND plane (solid). That way you have a external plane carrying your voltage (higher current capacity), and shielded by your next inner layer, eliminating the traces running over a split. Probably be a good idea to put your bypass caps as near as possible under that part also.. It definitely becomes a problem when everything needs to be @ the BGA device. I would split the minor voltages on the bottom, and put a solid 5v on a internal layer. Good luck, yer gonna need it :-) Karl >From: "Jack C. Olson" <[log in to unmask]> >To: "(Designers Council Forum)" <[log in to unmask]>, Karl >Bates <[log in to unmask]> >CC: [log in to unmask] >Subject: Re: [DC] Reference Planes for Impedance Controlled Signals >Date: Mon, 14 Jul 2003 15:26:11 -0500 > > >8MHz > >Here's more info. We have a PowerPC processor BGA >that has many +5V and +2.6V pins. Instead of trying >to do a split plane, and having the impedance controlled >stuff possibly traveling over a split, I thought it was >better to have both a solid +5v plane and solid +2.6v >planes on different layers. But as soon as you do that, >you have some signals closer to one plane that the other, >and the question is will there be signal integrity issues >by using the +5v plane as a reference. > >On the other hand, how do you guys create complicated >split planes and keep signals from crossing the split? >(Veribest/Mentor Expedition/Mentor BoardStationRE >router) > >thanks, >Jack > > > > > > Karl Bates > <[log in to unmask] > > > Sent by: > DesignerCouncil To: >[log in to unmask] > <DesignerCouncil@listse cc: > rv.ipc.org> > > > 07/14/2003 02:10 PM Subject: Re: [DC] >Reference Planes for Impedance Controlled Signals > Please respond to > "(Designers Council > Forum)"; Please respond > to Karl Bates > > > > > >Caterpillar: Confidential Green Retain Until: 08/13/2003 > Retention Category: G90 - > General > Matters/Administration > > > > >And...What frequency is the circuit operating at ? Khz or Mhz or Ghz ? > > > > > > > _________________________________________________________________ MSN 8 helps eliminate e-mail viruses. Get 2 months FREE*. http://join.msn.com/?page=features/virus --------------------------------------------------------------------------------- DesignerCouncil Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF DesignerCouncil. To set a vacation stop for delivery of DesignerCouncil send: SET DesignerCouncil NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site http://www.ipc.org/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------