yes, I agree. In fact many have pointed out that other factors are far more
significant.

Not wanting to let this subject go without some postive result (at least a
step in the right direction),
I've re-read all of the responses with one simple note in mind:

NON-FUNCTIONAL PADS SHALL NOT BE REMOVED FROM LAYERS 1, 2, 3, N-2, N-1 AND
N.

I don't think anything I have read conflicts in any significant way with
that note, and I'm not even sure there needs to be a differentation between
large and small holes. This is also assuming that people developing
high-volume CLASS 1 throw-away products will want to remove them from all
layers anyway, and won't use the note.

Does anyone disagree?

Jack


.
On Wed, Aug 4, 2010 at 9:43 AM, Chris Mahanna <[log in to unmask]> wrote:

> Hey Jack,
> The problem is that it depends.  There are several other (maybe fabricator
> specific) factors that may be well understood, but you need to de-correlate
> them before you could make a decision.
> that's why many times design activities simply "allow NFP removal".  And
> "engineering punt" to the fabricator.
>
> A relatively simple way that some OEMs handle it is to include an empirical
> study during fabricator qualification.  Delphi is probably the best known
> example.  It works.
>
> Chris
>
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Jack Olson
> Sent: Wednesday, August 04, 2010 10:15 AM
> To: [log in to unmask]
> Subject: Re: [TN] non-functional pad removal
>
>  Well, maybe I should have known better than to try and summarize all the
> previous responses, both public and private.
>
> The goal I was pushing towards is related to the fact that the committee
> that
> just finished balloting on IPC-2614 (Board Fabrication Documentation)
> included
> an appendix with "sample notes".
> On the subject of non-functional pads, here are the three sample notes
> provided by IPC-2614:
> 1)  Non-functional pads may be removed from inner layers at vendor's
> discretion
> 2)Manufacturers shall not remove non-functional pads
> 3)Removal of non-functional pads from internal layers is permissible
>
> Yes, those are notes. and maybe they are representative samples in
> someone's opinion, but in my opinion they don't provide any guidance to the
> reader and they gloss over what could be a significant reliability issue.
>
> It seems like there is enough technical knowledge on this forum, and enough
> people have already replied with interesting related points about the
> subject,
> that we could write at least one other note that might be more useful.
>
> Can't we come up with a note that fits MOST applications, and leave it to
> the
> user to modify it for his specific circumstances?
>
> onward thru the fog,
> Jack
>
>
> .
> On Tue, 3 Aug 2010 20:06:01 -0400, Werner Engelmaier
> <[log in to unmask]> wrote:
>
> > Hi Jack,
> >Here are my comments
> >
> >
> >So here is what I have been told about the subject of non-functional pads
> (NFPs):
> >
> >- Drill bits last longer if NFPs are removed - "YES
> >
> >- In some cases NFPs create anchor points for stress, and barrel cracks
> occur - "I THINK YOU MISUNDERSTOOD THIS.
> >
> >- Reliability is more relevant to hole diameters less than .020", remove
> NFPs
> from larger hole diameters - "RELIABILITY IS
> >OF COURSE EQUALLY RELEVANT, YOU JUST GET DIFFERENT FAILURE MODES
> DEPENDING ON DRILLED DIAMETERS:
> >BARREL CRACKING FOR SMALLER DIAMETERS, INNERLAYER
> SEPARATION/SHOULDER CRACKS FOR LARGER DIAMETERS.
> >REMOVING NFPs FROM SMALLER DIAMETER HOLES HAS LESS RELIABILITY
> CONSEQUENCES.
> >
> >- Yield may increase by reducing possibility of inner layer shorts by
> removing
> NFPs - "???
> >
> >- NFPs only play a role with higher aspect ratios - "NO
> >
> >- Divide the hole length into three zones, and remove NFPs from the middle
> zone - "YES
> >
> >- High layer count with thin dielectric creates resin-starved pancake
> stack,
> remove some NFPs - "???
> >
> >- Keep the stack symmetrical, if a connection is made on layer 8 of a 16
> layer, leave NFP on layer 9 to balance the stress - "
> >A SYMMETRICAL STACK IS A GOOD IDEA TO REDUCE WARPAGE DURING
> SOLDERING; YOU CANNOT "BALANCE" [WHATEVER THAT MEANS] STRESSES
> THIS WAY
> >
> >- NFPs reduce voids in thin low-flow prepregs - "POSSIBLY
> >
> >- Don't remove NFPs from layers 1,2,3,n-2,n-1,n - "FOR LARGER DIAMETER
> HOLES
> >
> >
> >I assume that those working on high-tech high-reliability designs know
> what
> >they want to do and have customized their fabrication drawing to get what
> >they want. On the other hand, I'm concerned about the average designer
> who
> >wants to know best practices, but isn't sure how to form the note.
> >
>
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