Hi Joe,

Dielectric constant doesn't vary this much, otherwise it wouldn't be much of
a constant would it? Did you request test coupons with your boards? How
about impedance coupons?

You can section either type of coupon whenever in doubt, but you have to
request them first. Otherwise you might just be out of luck.

Have a nice day,

Alain Savard, B.Sc.
Chemical Process Analyst
CAE Electronics Ltd.
e-mail: [log in to unmask]

-----Original Message-----
From: Joe Barocio
Subject: [TN] Dielectric Constant of FR4

I'm seeing variations of up to 60% in capacitance between signal traces
and ground plane on a stripline PWB; trace widths appear to be
consistent among PWB's . Can these diffferences be attributed to
variations in the dielectric constant of the FR4 material?

Is there a method to check board layer thickness without actually
sectioninng, and destroying, the PWB's?

Joe Barocio
[log in to unmask]

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