Paul Gould wrote:
>
>Take an average panel with say 9000 holes and assume there are 6000 non
>functional pads. If it is a 4 layer with 1oz inner layers then you have
>nearly 3
>mil of copper extra for each hole with NFP's. This amounts to 18 inches of
>extra
>copper drilled during that drills life. Multiply that up for 6,8, and 10
>layers,
>and then 2oz and even 3oz inners. Ground planes are the biggest culprit, as
>tracked layers generally have thinner 0.5oz copper which is not so bad.
>
[snip]


Paul,
I do not see the point here.  Are your panels actually 3 mils thinner when
you remove the non-functional pads?  It is my experience that the non
functional pad area is filled in with pre-preg epoxy, leaving the overall
thickness the same.  So instead of drilling through 3 mil of copper with
the non-functional pads in place, you are drilling through 3 mil of epoxy
fill with them gone.

I don't claim to be a drill expert, and please correct me if I am wrong,
but I thought drilling through the copper helped clean epoxy from the drill
bit and provided some cooling in the process.  Isn't the effect similar to
metal entry and exit material?

I understand that double sided boards can be drilled with higher feeds and
chip loads than can multilayers.  Do manufacturers increase feeds and
speeds on multilayers when the non-functionals are removed?  In theory,
would this not impact the quality of the holes which have functional pads?
If so, why compromise the quality of the innerconnect which is often the
entire reason the hole exists?

Thank you for letting me further my education on Technet, and thank you,
Paul Gould, for your note which made me challenge some of my beliefs for
which I don't really understand the basis.  I hope no negitive tones were
read into my questionings, none are intended.



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