There are several mistakes (or  typos) in the formulas published in IPC 317A
you may find correct formulas in the calculators by Mr Brooks
http://www.ultracad.com/calc.htm
these calculators are provided by Douglas G. Brooks
and are windows based, and very easy to used

ATI Technologies Inc.,
Patrick Jabbaz
Sr. PCB Designer
33 Commerce Valley Drive East,
Thornhill, Ontario, Canada, L3T 7N6
Phone:(905) 882-2600 ext: 8254,   Fax: (905) 882-9339
Email: [log in to unmask]

> -----Original Message-----
> From: Cole, Jeff R [SMTP:[log in to unmask]]
> Sent: Thursday, February 18, 1999 4:59 PM
> To:   [log in to unmask]
> Subject:      Re: [DC] Embedded Microstrip
>
> Try this
>
> http://indy2.automata.com/tools/imped/imped-ems.unsafe.html
>
> Jeff Cole
> Battelle PNNL
> Scientific Engineering Associate
> (509) 375 - 2758 PH
> (509) 372 - 4725 Fax
> [log in to unmask]
>
>         -----Original Message-----
>         From:   Daniel A. Doherty [SMTP:[log in to unmask]]
>         Sent:   Thursday, February 18, 1999 11:27 AM
>         To:     [log in to unmask]
>         Subject:        [DC] Embedded Microstrip
>
>         Does anyone happen to know the CORRECT formula for the capacitance
> of an
>         embedded micstrip?  The one contained in -D-317A pg. 23 cannot be
> right
>         as the natural log of a negative number is not defined...
>
>         317A states:  C=(1/(H+t))*ln(1-(.6987*(E+1.41)/sqrtE))
>
>
>         Daniel A. Doherty
>         North Coast Design
>         6341 Applewood Ln.
>         Williamsburg, MI 49690-9725
>         V 616.267.9717
>         F 616.267.9718
>
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