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