Does anyone know the formula(s) for calculating the impedance of differential pairs when the lines are on adjacent layers to one another and NOT side by side on the same layer, or perhaps software that handles this type of configuration? This does not appear to be covered in IPC-D-275. Thanks in advance for any enlightenment. Brock +-----------------------------------+ | Brock Hunter [log in to unmask] | | Engineering Mgr. | | Dynamic & Proto Circuits | | TEL (905) 643-9900 | | FAX (905) 643-9437 | | http://www.dapc.com | +-----------------------------------+ ############################################################## TechNet Mail List 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://www.ipc.org/html/forum.htm) for additional information. For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311 ##############################################################