Robert,

The effectiveness of a shield varies according to the frequencies from
which you are attempting to shield. We are using cofired alumina substrates
for microwave multichip modules and the cofired suppliers request the use of 
gridded planes primarily to mitigate substrate camber. In RF circuits, shieldingand grounding are of utmost importance, Our microwave engineers prefer void 
sizes on the order of 1/10 to 1/20 the smallest wavelength of interest with 
smaller void sizes providing a better shield.  

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Mike McNulty
Lockheed Martin Government Electronic Systems
Moorestown NJ
Phone:(609)722-7323
Fax:(609)722-2207
[log in to unmask]
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After reading the mail by Jamie Baumgart on Solid vs. Crosshatch fill areas 
I realized there is another area to consider.

I occasionally have customers who wish to have large areas on the SURFACE
of boards to serve as ground shields. 
Those large areas tend to have the same problems as internal areas AND
they also have the problem of poor reflow quality.
The solution is to convert the areas to crosshatch patterns which yields
much better quality boards. 
If the customer fears the crosshatch, then we try to pursude to go SMOBC to 
prevent the reflow problem, but are back to the problems of solid fill.

My concern however....
Does the crosshatch area actually achieve the ground shielding or does it
just act as a "screen door". 
What is the curve of grid width / line width vs shielding ?

If anyone can shed some light I would be grateful. 
--
Robert Blomstrom            Advanced Interconnection Technology, Inc. - Atlanta
Phone: 404-938-9387 x226    3289 Montreal Industrial Way, Tucker, Ga. 30084
fax:   404-934-9885         e-mail address: [log in to unmask]                 



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