No, the traces are not imbedded. The traces of interest are not on layer 1, they are on layer 4. But that is not even important. Sorry if I was unclear. The real question is: What if the traces are interspersed between solid planes, and although they are part of a +2.6V circuit, they happen to be closer to a +5V plane. I think they will use the +5V plane but it doesn't matter. Does it matter? Is a plane a plane? "Kowalewski, Andy" <AKowalewski@sych ip.com> To: "'(Designers Council Forum)'" <[log in to unmask]> 07/14/2003 02:04 "'Jack C. Olson'" <[log in to unmask]> PM cc: Subject: RE: [DC] Reference Planes for Impedance Controlled Signals Caterpillar: Confidential Green Retain Until: 08/13/2003 Retention Category: G90 - General Matters/Administration Need more info. Is your trace of interest on layer 1 and the planes are in sequence below that? I assume you don't mean that the trace is embedded in the +2.6V or +3.3V layers? I'm not sure why you mention the 4th signal layer. Is that significant? Is that where your trace of interest is? The power and ground planes are equal reference planes if they are tightly coupled together to AC signals. That happens if the planes are very close together or there are lots of decoupling capacitors scattered around the board that tightly couple them. Of course, changing signal layers can change a microstrip configuration to a stripline, balanced or unbalanced, as well as change reference planes. Andy K. Sychip Inc Office (972) 202 8852 -----Original Message----- From: Jack C. Olson [mailto:[log in to unmask]] Sent: Monday, July 14, 2003 12:56 PM To: [log in to unmask] Subject: [DC] Reference Planes for Impedance Controlled Signals Reference Planes for Impedance Controlled Signals I might be showing my ignorance by asking this question. I thought I knew, but now I'm being challenged on it. If I have impedance controlled signals that are part of a circuit that is being run on +2.6V or +3.3V, but there is a closer plane available, like +5V, the signal returns will snap to the closer one, right? Does it matter which TYPE of plane is being used a reference? The text I received from a colleague implies that if my 2.6V plane is too far from my 4th signal layer, which is next to the +5V plane, then they will not be impedance controlled. Doesn't sound right to me... Jack (the new guy) --------------------------------------------------------------------------------- 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 ---------------------------------------------------------------------------------