Pat Ground traces around clock lines are only effective on outside layers. On inside layers just leave the extra space around the clock trace, and route between ground planes. Spacing the traces more than 3 times the trace width apart doesn't reduce crosstalk by much more. An interesting book on this subject is "High Speed Digital Design - A Handbook of Black Magic" by Johnson and Graham. I do hope this is of some help on a subject were there are many different opinions. Joe Hurst Computing Devices Canada Pat wrote: ... Next question is concerning special considerations for clock signals and EMI. Some of the Engineers want a ground trace surrounding the clock lines and others say it would be better to just leave the space around the clock line that the guard band would normally take up. The clock speeds are 40 Mhz and below using 6/6 on the inners and 8/8 on the outers. One of the 2 clock routing layers is next to the ground plane and the other layer is next to the power plane. All info is greatly appreciated! Pat Paulson VTEL Corporation [log in to unmask] ################################################################ 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 technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################