Scott Decker wrote: > > snip < > > First. 6 Layer Board. > .5 oz on both outside layers and 1 oz on all inside signals and planes. > .005" traces on all layers > Dielectric thickness as follows: > 6.5 > 10 > 18 > 10 > 6.5 > Er value of 4.2 > OK now you have the numbers, the impedance should be around 72 ohms. > But Wait! The values I got were 77 72 72 72...... What Gives? > > Any Comments??? > I already herd that it's because the UV rays from the sun were hitting > the top of the board more, but I don't think that's true....(:-} > Impedance is lighter than FR4 so more of it floats to the top <g>. Playing with these values on my tool I find that describing the last trace layer as 1 oz instead of 1/2 would get you about that difference. Can't get IPC's site right now, only the archives are responding to me. Hope there's not a problem w/ the server... -- Jeff Seeger Applied CAD Knowledge Inc Chief Technical Officer Tyngsboro, MA 01879 jseeger "at" appliedcad "dot" com 978 649 9800 ################################################################ 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's web site (http://www.ipc.org) "On-Line Services" section for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################