A vertical cross section, well polished, will greatly help pinpoint the
cause.   First, it will help decide if there was ever any
electroless/direct metallization in the holes.   Techniques like
backlighting of the hole wall during manufacture help determine the
coverage, especially after the microetch step in the acid copper
electroplate line.

It is possible that there was good chemical plating coverage, but that
over-agressive microetch took away the metallization in the holes.  Perhaps
a rack of boards got stuck when a plating line shut down unexpectedly.
Finally, there is a chance there were air bubbles in the hole in various
plating steps causing incomplete coverage by some process step.  However,
this appears to be a simple 2 sided board with large holes that should not
be subject to bubble problems.

Remotely, there is a chance that the copper in the hole was removed by the
solder assembly step - called copper erosion.   That is most predominant
with lead-free solders, but most all problems with erosion were solved some
8-10 years ago.

Again, vertical cross sections of the failing holes will be very
beneficial.

Denny Fritz

On Mon, May 6, 2019 at 3:12 PM Christopher Brand <[log in to unmask]> wrote:

> Greetings,
>
> I'm having issues with open vias on a couple of runs of PCBAs and was
> hoping to get some help on finding a root cause or at least point me in
> the right direction.  I know that there is lots of knowledge and
> experience on this forum and I'm hoping someone will say they've seen
> this before, as my knowledge is rather limited on this.
>
> Here are a few photos of the vias in question.
>
>     https://ludlums.com/software/BadVias/badvia_01.jpg
>     https://ludlums.com/software/BadVias/badvia_02.jpg
>     https://ludlums.com/software/BadVias/badvia_03.jpg
>     https://ludlums.com/software/BadVias/badvia_04.jpg
>     https://ludlums.com/software/BadVias/badvia_05.jpg
>     https://ludlums.com/software/BadVias/badvia_06.jpg
>     https://ludlums.com/software/BadVias/badvia_07.jpg
>     https://ludlums.com/software/BadVias/badvia_08.jpg
>     https://ludlums.com/software/BadVias/badvia_09.jpg
>     https://ludlums.com/software/BadVias/badvia_10.jpg
>     https://ludlums.com/software/BadVias/badvia_11.jpg
>     https://ludlums.com/software/BadVias/badvia_12.jpg
>
> On some, the via barrel has a void in the center and on others the edge
> of the barrel doesn't connect with the pad, Both issues are causing an
> open via as you can see in the photos.
>
> I know that the board shop recently changed up their plating tanks (new
> chemical and power supply).  Could these bad vias be the result of
> insufficient current in the plating process or some other process?
>
> I'd be much appreciative of any insight this forum could give.
>
> --
> Thank you kindly,
>
> Christopher Brand
> Ludlum Measurements, Inc.
>  501 Oak Street
>  Sweetwater, TX 79556 USA
>  (325) 235-5494 Phone, ext:3318
>


-- 
Denny Fritz
Consultant
812 584 2687