You are welcome to give my calc a try (pitiful plug I know :p) but I used a
formula
from Linear Tech and I have had good results with it. I too have seen some
odd numbers in the past with measured results. I have a vender in Singapore
that swears
the dk of his FR-4 is 3.8. Well, give it a shot...
Ken
http://www.saturnpcb.com/Software.htm
----------------------------------------------------------------------------
---
Kenneth J. Wood C.I.D
Saturn PCB Design
2737 Bishop Lane
Deltona, Fl 32725
407-340-2668
www.saturnpcb.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Eddie Rocha
Sent: Friday, November 18, 2005 7:00 PM
To: [log in to unmask]
Subject: Re: [TN] impedance testing
Wrong. The dielectric constant is a separate factor.
Thank you,
Eddie Rocha
South Bay Circuits
Eddie
All Z0 calculators have a built in "fudge factor" to make modelled results
agree with emperical data. It is called "dielectric constant"
Gerry
From: Eddie Rocha <[log in to unmask]>
Reply-To: TechNet E-Mail Forum <[log in to unmask]>,
Eddie Rocha
<[log in to unmask]>
To: [log in to unmask]
Subject: Re: [TN] impedance testing
Date: Tue, 15 Nov 2005 11:53:11 -0700
I've evaluated multiple impedance calculators. I did as you are doing, used
actual x-section data with actual TDR results and compared it to the
calculators results. Some calculators worked well with some stack-ups but
not with all types of stack-ups. A good calculator should have a "fudge
factor" that allows you to determine the best "factor" that works for a
particular stack-up. Actual data is needed to make an impedance calculator
accurate.
Thank you,
Eddie Rocha
South Bay Circuits
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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