> 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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