May I ask a dumb question ????

If the 8 square inch area is unbroken, then what is it used for? It is
obvious form your statement that there are no isolation clearances, or
isotherms for holes, so this precludes the use of either leaded or SMD
components on the surface of the board. Could it be that your designers have
designed a feature that may be very costly that serves no obvious function??

I'm curious...

Dave Rooke
Circo Craft - Pointe Claire

======================
>Hi all,
>
>Recently I have had some discusions regarding breaking up large (greater than
>1" circle) conductive areas.  Both Mil-Std-275 and IPC-D-275 recommend doing
>this to prevent blistering.  During prototyping of several military, RF PWAs we
>found that the 'breaking up' of the ground planes adversely affected perfor-
>mance.  In discussing this with one of our fab suppliers to determine what
>compromises we could make to improve electrical performance, I learned that
>'breaking up' the ground plane was no longer necessary due to improvements in
>processes and materials.  I was told that there were problems in the late 70s 
>and early 80s but not any more.  
>
>Are the specs cited out of date with respect to this issue and current
processes?  Should I be concerned about not breaking up large conductive
areas?  If yes,
>how large is too large?  That is, is a 1" circle still a valid threshold?  
>
>This is more of a general question but the design specifics are - 6 layer MLB,
>11"x 9"x .063", SMOBC, layers 1, 4 and 6 are ground planes with layer 5 a 
>controlled impedence layer.  Largest area not broken up by holes is approx. 8 
>square inches.
>
>Thanks to all for your comments and opinions.
>
>Jeff  
>
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