Scott, You need to specify which layers are planes and traces, Example: L1 s L2 p L3 s etc... Regards, Doug >>> Scott Decker <[log in to unmask]@yusa.com> 02/05 9:26 AM >>> Hi All I have a question / problem.... I recently used the Impedance calculator on IPC WEB site and found a very interesting problem. On one occasion a few weeks ago, I used the calculator to do a quick stackup for a board I'm working on. The results were fine and were used as a baseline for the FAB shop to find me the values they use. I was just showing another designer here this neat calculator and changed the values I used to the values that the FAB shop gave me. Guess What.... The calculator came back with an un-balanced impedance value! This is a very strange problem. I put in a balanced stackup and the values for impedance were different from the top to the bottom by 5 ohms. Sure you say, that's the 10% but, why are the numbers different? Maybe some of you out their can try these numbers. 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....(:-} -- Scott Decker Senior PCB Designer AKA: PadMasterson E-Mail: [log in to unmask] ----------------------------------------------------------------- ^ ^^^ Praegitzer Design - A Division of Praegitzer Industries ^^^^^ 7245 N.W. Evergreen Pkwy, Suite 100, Hillsboro, OR 97124 ^^^^^^^ Phone #: (503) 531-2050 Ext. 1820 Fax #: (503) 531-2051 Check out our WEB site at http://www.pii.com ----------------------------------------------------------------- ################################################################ 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 ################################################################ ################################################################ 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 ################################################################