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November 2005

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Subject:
From:
Jim Henderson <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Jim Henderson <[log in to unmask]>
Date:
Mon, 21 Nov 2005 10:40:12 -0500
Content-Type:
text/plain
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text/plain (159 lines)
Still looking.... Is there any thoughts on reverse treated copper foil
versus standard?

Jim

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Valerie St.Cyr
Sent: Monday, November 21, 2005 10:23 AM
To: [log in to unmask]
Subject: Re: [TN] impedance testing


It is 3.8. That value "works" best and, in fact, if you were to take a Dk
reading at 1 GHz of a high layer count multilayer you would get about 3.8.
That's because the multilayer probably has a net, effective resin content
above 50%; we have a lot of boards that are probably closer to 55 to 60%
resin. When the laminators test their laminates for Dk, they use a thin
double-sided laminate which is usually 45 to 50% resin. I find about a .4
difference between published spec sheet values and measured values for
multilayers.

The impedance calculators don't have a fudge factor; they are built on
formulas, which get tweaked occasionally and get better. The "fudging" is
nothing more that knowing what values to use for the variables: Dk (3.8
for FR4), copper height (especially for outerlayers) and copper sidewall
cutback;
if you get those numbers right, you will have a pretty good first pass
that meets the targets.

As for the original problem, I don't know if it has been unraveled ...
Jim, do you have the answer yet or are you still seeking advice ?

Valerie






Ken <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
11/18/2005 07:25 PM
Please respond to TechNet E-Mail Forum; Please respond to Ken


        To:     [log in to unmask]
        cc:
        Subject:        Re: [TN] impedance testing


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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