Bill, I bet your PCB has SMA connectors. What's more, measure the trace width from that connector, and I'll bet it's very close to 70 mils wide. That's 50 ohms for a FR4 material, stripline. This may not be the best way to construct the PCB, but if it was just designed to be a prototype, it was probably good enough. If this is the case, the only way to reduce the thickness of the RF layer pair, and better balance the construction, is to reduce the trace width, with the limiting factors maybe being max current, but probably is based on component size. David Ricketts Pertek Engineering Voice: 949-475-4485 Fax: 949-475-4493 -----Original Message----- From: DesignerCouncil [mailto:[log in to unmask]]On Behalf Of Brooks,Bill Sent: Monday, June 24, 2002 3:32 PM To: [log in to unmask] Subject: [DC] Board Layer Stack up Guidelines Hi folks, I have a older proto board (an IF Demodulator) that was defined with an asymmetrical stack up and I am concerned about the cost issues with leaving it alone... Since we are changing the board at this time, I thought to check for any issues with the design package and found this anomaly... It looks like this: .063 overall thick FR4 material 0.070 max ________________________ Top Layer Signal .032 separation--->________________________ GND Plane ________________________ Internal Signal 0.00 ________________________ Bottom layer Signal The odd part being, the forced separation between the ground plane and the top signal layer where the RF components reside, primarily. Have you had any experience with this sort of thing? Is there a good reference I can refer to that deals with Board stack up issues? Do you think the board is at risk for flatness problems? The EE assures me that he knows of no known issues with the electrical properties of the circuit that would require a stack up of that sort. He says the only reason he can think of was parasitics and/or shielding. Like to hear your thoughts.... - Bill Brooks ---------------------------------------------------------------------------- ----- 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 ---------------------------------------------------------------------------- ----- --------------------------------------------------------------------------------- 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 ---------------------------------------------------------------------------------