Hi Steve,

Before anyone cuts into this thing.......
Avoid tainting the crime scene. :)
Finding the shorts power-to-ground is like looking for a needle in a haystack.

Do you have access to a IR thermal Imager?
Some PCBA houses have them on hand for this very purpose.

If you do, or know a colleague (or lab) that does have one with a reasonable resolution, I'd suggest very "lightly" powering the shorted planes and looking at the resulting IR thermal image to see what's heating up first, which would be the shorted location.
With a sensitive IR gun you only need enough power to get the short to heat up not blow it.

Mark the hot spot location with an arrow, and take an x-ray of the area.

Good hunting.

Gerry



________________________________________
From: TechNet <[log in to unmask]> on behalf of Steve Gregory <[log in to unmask]>
Sent: Friday, April 8, 2016 12:00 PM
To: [log in to unmask]
Subject: [TN] Recommendations for Failure Analysis / Root Cause of PCBA Failure...

Good Morning All,

We have an assembly that we build here for a customer that we built for
some time, over 2,000 assemblies. There have been some failures that our
customer has had field returns with that are beginning to escalate. There
have been 12 field failures that we know of. The failures are avionic
assemblies that have been in the field ranging from 111 days to 472 days.
The actual failures are internal +12V to -12V shorts and we need to know
why. I have two failed assemblies here. Here are a couple of external
photos of a via that shows the short:

http://stevezeva.homestead.com/Internal_Short.jpg

http://stevezeva.homestead.com/Internal_Short_Close.jpg

So my question is, can a lab take these boards and examine them to
determine what the root cause actually is from the two assemblies that I
have, or does there need to be more samples? What is the range we should
expect to pay for this type of analysis?

We're trying to work with our PCB vendor on this issue, but I have also
been asked by my boss to pursue this with a third party.

Thanks!

Steve


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