As a ROT I have used 500V/mil for the dielectric breakdown of FR4. Derate
this value liberally (25-50% as thickness goes up. As to calculating the
capacitance of planes, I ask the same question (in a previous lifetime) and
received this answer:
>
> At 10:10 15/08/97 -0400, you wrote:
> >Does anyone have a formula for calculating the distributed
> >capacitance of copper planes? I Know I have seen this before
> >in PCD magazine but I seem to have *lost* the issue.
> >
> >Thanks in advance for your assistance.
> >
> >Jeffrey McGlaughlin
> >BFGoodrich Avionics Systems Inc.
> >1105 Schrock Road
> >Suite 800
> >Columbus Ohio 43229
> >(614)825-2232 (voice)
> >(614)825-2037 (fax)
> >[log in to unmask]
> >
>
> Jeff,
>
> Not sure if this is what you're after:
>
> Capacitance of a parallel plate capacitor (or parallel copper planes)
> is given as:
>
>       C = Eo x Er x A
>           -----------
>                D
>
> Where:
>        C  = capacitance in Farads      (F)
>        Eo = permittivity of free space (8.854 x 10exp-12) (F/m)
>        Er = relative permittivity  (typically FR-4 is 4.6 at 1 MHz) (no
units)
>        A  = area of the plates (or planes) (m x m)
>        D  = distance between plates (or planes) (m)
>
> This equation neglects fringing effects.
>
> Best regards
>
> Andy Burkhardt <[log in to unmask]>
> Tel: + 44 1481 53081
> Fax: + 44 1481 52476
> http://www.polar.co.uk


Hope this helps,

Jeffrey McGlaughlin CID
Battelle Memorial Institute
Columbus Ohio
[log in to unmask]

-----Original Message-----
From: Darnell, Barry (IndSys, GEFanuc, CDI)
[mailto:[log in to unmask]]
Sent: Thursday, September 27, 2001 9:56 AM
To: [log in to unmask]
Subject: [TN] Dielectric Strength


Can someone tell me the dielectric strength (how many dc volts per mil,
layer to layer) can FR-4 handle?  Also, I need to create a capacitor between
two pieces of copper
on opposite sides of the board.  How do I calculate the size of the copper
to achieve a given capacitance.

Thanks,

> Barry Darnell
> (864)627-8800 Ext. 217
> mailto:[log in to unmask]
> Computer Dynamics, Inc.
> Printed Circuit Board Designer
>

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