We have done our multilayer boards both ways, suppressing the internal pads 
and including the pads.  The end result, to us, it made no difference in the 
attachment of the thru-hole component.  The main difference is how the 
vendorvenbor generates his board and if it makes a difference, real or 
imagined, to them.  We've heard that the internal pad helps to hold the 
plating inside the hole since we're giving it an extra anchor, but you can 
also increase other problems with desmear too.  It may be only a function of 
the thickness of your board.  Generally, for us, .062.  If you have a thicker 
board, .093-.125, this may come in effect where an extra anchor or two will 
help, but there has been no documentation that I have seen.  One vendor 
doesn't like to have them because he believes of the possibility of spinning 
the internal pad since there is no track to hold it in place.  This may or 
may not be a valid point.  He may be trying to extend the use of a marginal 
drill bit too.  What about it Pete?  Don't you guys do this kind of testing 
to right about in your magazine?  I for one would like to know some 
documented facts and get the matter settled.  Until that time, as long as my 
boards continue to work, I'll let the vendor do whichever way he considers 
viable for his operation.  I won't force him into possibly making a bad board 
if I can't show him otherwise.

One other item.  Plated and unplated drilled holes.  We separate the two 
files even though the finished hole size is the same.  Our vendors tell us 
that if we don't separate them then they have to manually find them to 
oversize the plated holes somewhat.  I don't like manual operations, to easy 
for errors.  Besides, it is very easy to set up your cad system to have 
different drill types with the same drill size.  The electronic drill 
information file sent to the vendor has them broken down into drill sizes and 
we specify plated or unplated.

Larry Campbell
BFGoodrich, Avionics Systems
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