Hi Jack,

You must be using the Cadence tools for your analysis (hee hee). It
defaults to the same values. I have been using 4.3-4.5 for my
controlled impedance measurements and have been quite accurate
with deteremining trace widths and layer separation that our fab
house could confirm.

I have used an impedance calculator from IUD in the past that uses
ranges that you have talked about, but for standard FR4 material I
still revert back to 4.3-4.5

BTW, which INTEL do you work at, if you don't mind me asking? I've done
some work for INTEL, Hillsboro and they always seemed to knowthese
values.

Good luck,

Mitch Morey
Sr. PCB Designer
ComStream Corp

>>> "Olson, Jack C" <[log in to unmask]> 03/03/98 09:21am >>>
WARNING: this is a very unexciting question...

My software does some basic signal integrity analysis,
and I just noticed it defaults the dielectric constant for
regular FR4 to 4.7

I was under the impression that most FR4 is at 4.2-4.3
these days (more resin? thinner cores? can't remember...)

Even a brief response will be appreciated!
                                                                Jack

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