Alan,

I have read your response with great interest. Although I agree with logic of more copper more stability, I am curious as to what impact has been related to increase of  shorts between the non-functional pads and adjacent circuits and planes. I have seen a tremendous reduction in spacing between the required drilled hole wall and the adjacent conductive surfaces as a result of the increase in densities. Adding a pad with sufficient annular ring would reduce this spacing even more. 

Regarding the impact on stress, have you found the improvement primarily be in the x and y axis? I would suspect that the impact of the added pads on the coefficient expansion differential in the z axis would be minimal. Were the failures you where referring to post separation?

I find your conclusions on improved drill accuracy for the smaller diameter drill really interesting. I have always understood that 
the amount of drill splay or wonder was created upon the initial impact of the surface and directly affected by the feed and speed. Which is why the entry foil is so important. Could you please provide me with any documented references as to the effect of internal features on drill accuracy. I feel I'm getting behind in some things!  Wow its tough to  keep up with all this new stuff! Any help  on this matter would be greatly appreciated. 

Thanks

Ed Cosper
Director Quality Assurance and Engineering
Graphic Electronics Inc.
Tulsa, OK

----------
From:  Alan Cochrane[SMTP:[log in to unmask]]
Sent:  Tuesday, January 20, 1998 1:24 PM
To:  [log in to unmask]
Subject:  Re: [TN] Dead Pad Removal

To All,

I think we can not overlook other aspects of having non-fuctional pads.

1. With cores getting thinner in products today, the more reatained copper
on the layer the better the dimensional stability will be.
2. For x-section analysis it is far better to have a complete pad stack to
verify registration.
3. On high aspect ratio holes(>8:1) we need to look at the interconnect
stress.  We have built a significant amount of 18 layer product around .105
thick.  Initially without non-functional pads present.  Product was
assembled and opens were detected in ICT test.  In ALL cases the opens were
traced back to components or via holes that had interconnects only on
layers 1/2 and 17/18.  The next revision product was built with non
functional pads included and no defects were detected after assembly.  This
was not an isolated occurance and was not dependant on resin system(high Tg
materials minimize but do not omitt the condition).
4. In our porducts the inclusion of non functional pads has shown to
minimize the amount of drill splay on small holes(<.012)

I am not sure of the parameters of the commisioned testing that is
currently underway.  I hope this will address the higher aspect ratio
problems that are out there.  It has taken us years to overcome the stigma
of the last round robin test where a great deal of our customers were
afraid(based on that report) to design product that violated the findings
of that testing.

The only negative that we have encountered with including non functional
pads is, the increase in capacitance on some higher speed designs.  This
needs to be modeled and accounted for prior to routing.

Regards,

Alan B. Cochrane
Corporate Director of New Technology
Multek Inc.

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