Hi Jack, You must be using the Cadence tools for your analysis (hee hee). It defaults to the same values. I have been using 4.3-4.5 for my controlled impedance measurements and have been quite accurate with deteremining trace widths and layer separation that our fab house could confirm. I have used an impedance calculator from IUD in the past that uses ranges that you have talked about, but for standard FR4 material I still revert back to 4.3-4.5 BTW, which INTEL do you work at, if you don't mind me asking? I've done some work for INTEL, Hillsboro and they always seemed to knowthese values. Good luck, Mitch Morey Sr. PCB Designer ComStream Corp >>> "Olson, Jack C" <[log in to unmask]> 03/03/98 09:21am >>> WARNING: this is a very unexciting question... My software does some basic signal integrity analysis, and I just noticed it defaults the dielectric constant for regular FR4 to 4.7 I was under the impression that most FR4 is at 4.2-4.3 these days (more resin? thinner cores? can't remember...) Even a brief response will be appreciated! Jack ################################################################ DesignerCouncil E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c ################################################################ To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE DesignerCouncil <your full name> To unsubscribe: SIGNOFF DesignerCouncil ################################################################ Please visit IPC web site (http://jefry.ipc.org/forum.htm) for additional information. For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311 ################################################################ ################################################################ TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c ################################################################ To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TechNet <your full name> To unsubscribe: SIGNOFF TechNet ################################################################ Please visit IPC web site (http://jefry.ipc.org/forum.htm) for additional information. For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311 ################################################################