In addition to Dwight's comments I would like to add a warning...

If you are looking at breakout...

Look need to look at the PCB internal pads where the vias pass with x-rays..
If it is out on the visible outer layers it can be off the pad or cutting through the pad traces on the internal layers...

I have had PCBs with breakout that have missed the internal pad, just touched the internal pad and have cut through the trace to pad joint...
These gave opens, opens after processing and intermittents in flexure...

Breakout is a process indicator that tells you about the alignment quality of the PCB... and that you need to look deeper...

Paul

Paul Edwards
Surface Art Engineering

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dwight Mattix
Sent: Wednesday, June 11, 2008 9:31 AM
To: [log in to unmask]
Subject: Re: [TN] Annular Rings on Via holes

At 07:06 AM 6/11/2008, Paul Baine wrote:
>Hello all,
>
>We received some PCBs from a Vendor where the Via holes have an
>incomplete annular ring.  See attached photo.

In an of itself that may not be a problem.
2 issues in play:
1) Spec compliance/acceptability
    * What class (1, 2, 3) is specified for the pwb?
2) MRB disposition: (Reliability/technical/end use performance
requirements i.e. is it safe to use the pwb)
Breakout has little to do w/ actual PTH reliability. The mere
presence of an innerlayer pad is the 1st order contributor to reliability.
The bigger concern is whether or not the drill breakout from the pad
reduces drill to copper feature (i.e. trace or plane) spacing below
acceptable minimums required to provide adequate isolation and
prevent CAF concerns.


>We have looked at Section 2.10.3 & 2.10.4 of IPC-A-600E (we don't
>have the most recent Revision yet) and we are not sure whether these
>Sections of the Standard apply to via holes.
>
>Any comments?  Many thanks.
>
>Paul Baine
>Q.A. Manager
>C-Tech Ltd.
>
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