[SI-LIST] : High performance materials on PCB

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From: Chris Mesibov (Chris.Mesibov@fnc.fujitsu.com)
Date: Wed May 23 2001 - 07:48:47 PDT


Has anyone been able to justify using high performance materials such as
Nelco N6000SI, or Rogers RO4350 on digital boards? I am concerned
that FR4 has a variation of DK verses temp and frequency that would
degrade
the reliability of the card. It would be an easier task explaining the
need for a back plane design.
However, in this situation the board will have high speed digital
signals over shorter line lengths that are held to clock and buss
oriented timing requirements. In addition, these signals are plagued
with the effort of breaking out from ASICs with high ball counts such
that there are more digital signals packed into less layers, at higher
density, and routed in more directions.
Given rise times in the 150ps realm, I am concerned with the dispersive
effects (group delay and degraded loss tan) over the broader spectrum as
generated by this rise time. If my data rates are in the 750-800 MHz
range (and that's just the fundamental freq. component), this certainly
covers the range where I should be suspicious, even at relatively short
trace lengths.

Thanks,
Chris



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