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Wed, 14 Jan 1998 12:33:43 -0500 |
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Applied CAD Knowledge Inc |
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Doug McKean wrote:
>
> Does anyone know if gridding a ground plane
> under a trace of controlled impedance increases
> or decreases by having to actually work with this?
>
> I can guess and theorize all day long...
> My guess is that since there's more distributed
> capacitance with a solid ground plane, that
> increasing the grid pattern of the ground will
> lower the distributed capacitance thus INCREASING
> the controlled impedance.
>
> big snip <
>
> Is this old stuff being hashed out again?
Well I lack definitive experience but have found that
you're not alone.
In the newsgroup sci.electronics.design this very same
topic is being debated, relative to techniques for in-
creasing the impedance of a flex circuit.
The opinions there agree with your expectation of a mesh
causing an increase in impedance, for the same reasons
you cite.
The only caveat to surface thus far is a quote from
Howard W.Johnson and Martin Graham's "High-speed Digital
Design" advising against this technique but perhaps from
the perspective of _large_ grids such as found in two
layer boards.
I believe the module community is doing more with this
type of geometry than the traditional rigid board world,
perhaps there would be more experience from the substrate
folks, "somewhere".
Good luck,
--
Jeff Seeger Applied CAD Knowledge Inc
Chief Technical Officer Tyngsboro, MA 01879
jseeger "at" appliedcad "dot" com 978 649 9800
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