As far as reduced shielding effectiveness of a cross-hatched plane instead
of a solid one, this is only of significance if the openings in the plane
are of the order of 10% or more of the wavelength of the highest frequency
of interest.  You can use 1% if you want to be very conservative.  This is a
crude approximation, but a very useful one.  If we use 1GHz as the highest
frequency with a propagation speed of 0.66c, the wavelength is 200mm.  Using
the more conservative limit, 1% of this is 2mm, which is much larger than
typical openings in cross-hatched planes.

Assuming a cross-hatched plane with 8mil spaces, a propagation speed of
0.66c and using the 1% of the wavelength limit, the plane is a good shield
up to 9.8GHz.  The only electrical issue with a cross-hatched plane is the
dc resistance, and you can deal with this with copper thickness.  Hope this
helps.

Seth Goodman
Goodman & Associates
7687 Leta Way
Verona, WI 53593
Tel (608)833-9933
Fax (608)833-9966

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Matthew Leary
Sent: Tuesday, December 01, 1998 1:30 PM
To: [log in to unmask]
Subject: [TN] double sided board with a twist


    I have a board that has about one quarter of the component side
covered with a copper pour.  The rest of the board just carries signal
traces.  This board has been hand assembled and soldered for over a year

without a twist.  Now we are sending it through a wave solder and
noticed a twist.   It is within spec (1.5%) but it is disturbing.  We
have received two pieces of advice on how to counteract this twist.  1.
To make the copper pour a cross hatch  2.  To make a similar copper pour

on the solder side to mirror the component side.
    I was given advice that you should strive to have less than a 20%
difference in copper in any area between any two mirrored layers.  Both
these suggestions seem to provide this solution.  However, I was told
that I might get a bend in the board if I try #2.  I was also concerned
about reducing the shielding that the copper pour provides if I try #1.
Any ideas??  Can this be minimized greatly by Fab and assembly
considerations alone?  Thanks.



--
Matthew M. Leary   (617) 338-4171 Tel
Newgrange Design   (617) 338-6748 Fax
8 Winter Street   Suite 508  email: [log in to unmask]
Boston, MA 02108   Web: http://idt.net/~ntbost19/

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