Larry

It may be old hat, but I vaguely remember in the days of MIL specs that
it says somewhere words to the effect of thou shalt cross-hatch all
areas greater than 1" diameter. There was a good reason for it, and
probably still is. I remember about 30 years ago, a designer produced a
board, about 200 x 300 mm, where about 1/3 of it was solid copper at one
end on the solder side and 1/3 of it was the same at the other end on
the other side. After wave soldering, it took on a beautiful S shape,
even when restrained with temporary stiffeners. I told the guy to
cross-hatch the solid zones. The unbalance still caused an S-shape but
to about only an acceptable 1/3 of what it was before. The "bimetal
effect" is largely broken with cross hatching and this can only improve
reliability.

FWIW

Brian

Larry Jindra wrote:
>
> We are having some discussion of the pros/cons of crosshatch vs. solid fill for copper ground planes on surface layers of multilayer boards.  Perhaps someone can help me with some answers.
>
> Is there a discernable difference in soldermask adhesion?
> Does the extra copper detract from reflow or rework operations?
> Is there a difference in board warp susceptibility?
> Why would an electrical guy want one vs. the other?
>
> > Larry Jindra
> > TRW/Avionics Systems Division
> > mailto:[log in to unmask]   ph (858) 592-3424   fax (858) 592-3606
> >
>
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