Jim

Assuming your geometries are correct (line width/thickness and dielectrics)
and you have good estimates of what the resin content of the dielectrics
are, then I'll give you two hints:

What is the rise time of the pulse coming out of the signal generator?

What is the effective dielectric constant of the laminate core and cured
pre-preg at the knee frequency of this rise time given the resin contents?

Feed this back into your calculator and see what happens.

Gerry


From: Jim Henderson <[log in to unmask]>
Reply-To: TechNet E-Mail Forum <[log in to unmask]>,              Jim Henderson
<[log in to unmask]>
To: [log in to unmask]
Subject: [TN] impedance testing
Date: Tue, 15 Nov 2005 09:28:08 -0500

Hello,

If there are any impedance testing gurus out there I have a question for
you.  We are testing an edge coupled offset strip line coupon.  We modeled
the stack up to give us 100 ohms differential.  When we test the coupon we
get around 130 ohms.  We have done a microsection of the coupon and modeled
the coupon data and Polar says we should have 105 ohms, within tolerance.
We had a 4 panel lot and it is consistent across the board.  The coupon is
constructed correctly.  My question is, other than what I am seeing on the
microsection should I look for to find the culprit of the high reading?  Any
help would be great.

Jim Henderson
Colonial Circuits

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