Bill, keep in mind that propagation speed will depend on frequency, too.  Lou Hart

----------
From:   Bill Beale[SMTP:[log in to unmask]]
Sent:   Wednesday, June 21, 2000 1:14 PM
To:     [log in to unmask]
Subject:        [TN] Change in Dielectric over Temp

Hi,

I'm new to this list and not sure this is an appropriate question, but
I'll try anyway.

Does anyone know where I can get data on the change of propagation
velocity, which really means relative dielectric, over temperature for
FR4?  Specifically, I'm interested in standard FR4 material from ambient
to 70 deg C.  This is very important to our timing.

I already have one data point and another source.  Dr. Howard Johnson's
book says that the relative dielectric can change as much as 10%.  Arlon
sent me some data which showed that it only changed ~2% in my range of
interest.

If relative dielectric increases with temperature, then why?  What
physical phenomena causes the material to increase charge storage with
temperature?  Is that change really 10%, or much smaller?

Thank you in advance for all your help,
Bill

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