Thanks everyone.

I'd like to summarize everything said, and answer all the questions in ways
that don't reveal confidential info.

I'm looking at moisture ingress opportunities and moisture control prior to
assembly since it's non-destructive and could provide a smoking (water)gun.

Wayne Thayer:

Drop a wire in the via and solder on ring or nearby pad. Not sure about
reliability unless it’s a 2 layer board.


Scott Decker:

Drop a wire if it’s the same via. And wire up connections to internal
planes.


Steven Kelly:

Whether or not PCBAs were pre-baked before SMT could have a factor.


jkoo@:

Need to find root cause.


Jose Rios:

isolated thin areas of plating that didn't hold up to thermal stress
(requires DPA to diagnose)

plated copper properties (low elongation, less likely IMO)

it could mean there is partial plating voids (as plated)

Note sometimes ICT covers nets that aren't part of the bare board
electrical test (IPC bare board net listing)


Questions:

Pre-bake? – investigating pre-assembly as well as shipping and storage
conditions

TH or microvias?: TH

Two layer? multi layer (more than 2) rigid flex.

Thanks Again,

Stephen Golemme
Manufacturing Engineer, Makani
650-214-5647
solveforx.com/makani

On Fri, Nov 11, 2016 at 12:17 PM, Jose A Rios <[log in to unmask]> wrote:

> Possible root causes (seen 2 of the 3 in actuality); It could be isolated
> thin areas of plating that didn't hold up to thermal stress (requires DPA
> to diagnose), or plated copper properties (low elongation, less likely
> IMO). I've also seen where ICT covers nets that aren't part of the bare
> board electrical test (IPC bare board net listing). In the case of the
> latter, it could mean there is partial plating voids (as plated), not
> induced by thermal stress. I've seen this (rare), on 30:1 aspect ratio
> boards with 10-12 mil drilled holes with a 60K or so hole count so 1 hole
> out of hundreds of thousands in a lot, can have a single partial void thats
> hard to detect.
>
> Sent from my iPhone
>
> > On Nov 11, 2016, at 2:14 PM, Steve Golemme <[log in to unmask]>
> wrote:
> >
> > We have a couple of expensive first time build boards that failed ICT in
> > assembly due to what appears to be cracked vias. Adding solder to the via
> > hole seems to fix the issue.
> >
> > What are folks thoughts on plugging vias with solder to fix them? What
> > risks are we taking by adding solder vs another technique? Could folks
> > recommend alternate repair techniques that may provide better
> > thermal/vibration?
> >
> > Also, I'd love to hear up alternate possible root causes? This problem
> > screams insufficient plating during fab or thermal shock during assembly,
> > but I'd like to investigate all possible failure modes. This is a
> > multi-layer double sided SMT + wave rigid-flex PCB and the cracking is on
> > the rigid portion.
> >
> > Thanks,
> > Stephen Golemme
> > Manufacturing Engineer, Makani
> > 650-214-5647
> > solveforx.com/makani
>