Hi KC Chan
I believe 'effective dielectric constant' is also a function of where a
trace is in a PWB layer. The closer to the surface the trace is the more
the dieletric of air (1.0) is effective in the propagation of signals.
Traces burried between two ground planes "see" the dieletric of the FR-4
material only. IPC-2141 has a nice discussion of this as well as dieletric
constants of various PWB materials (including FR-4) as a function of
frequency and the formulas to compute effective dieletric constant for
various PWB configurations.
Ray Klein
################################################################
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 technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312
################################################################