Subject: | |
From: | "Jeff Seeger" <simon.ipc.org!bort.mv.net!rapidcad!jseeger> |
Date: | Thu, 26 Sep 96 16:22:58 EDT |
Content-Type: | text/plain |
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> on which is best. Here are the 2 views.
> 1. Suppressing inner layer pads will give a better drilled hole, and so
> will produce a more consistant & cleaner plated hole.
The comment I've heard more often than quality of hole involves
drilling productivity. Removal of non-functional copper allows
higher drilling speeds and/or gives longer drill bit life.
> 2. NOT suppressing inner layer pads will produce a stronger & more
> reliable PTH less prone to failiure.
Agreed, although I've heard this expressed as the PTH being more
tolerant of less than ideal materials and processes.
We've standardized on leaving non-functional copper in place on
the datasets we ship out, and using fab notes to allow or disallow
the addition/removal of non-fucntional copper. Here's some of
our reasoning:
- The pads are alot easier for the CAM dept to remove than they
are to put back in place, if that became desirable.
- Not all CAD platforms allow automatic suppression "gracefully",
but all CAM platforms do.
- Keeping the non-functional pads in place on sparsely used layers
can be desirable, in effect the descision to remove can sometimes
be layer specific.
When advising someone on to suppress or not, I'd look at the number
of thermal cycles in the manufacturing and also in the equipment's
environment. Speaking entirely empirically, for boards with two
solder cycles, stable operating environment, and non-catastrophic
failure modes, and good materials grades, we say "sure, remove the
copper and save some fabrication process money".
Good luck,
Jeff Seeger Applied CAD Knowledge Inc
Chief Technical Officer Tyngsboro, MA 01879
[log in to unmask] 508 649 9800
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