I agree with Bob K.   I would look at drill (+ wicking) to copper before layer to layer.  What is the drill budget against an internal conductor.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert Kondner
Sent: Friday, April 08, 2016 10:30 AM
To: [log in to unmask]
Subject: EXT :Re: [TN] Recommendations for Failure Analysis / Root Cause of PCBA Failure...

I would be curious what the drill to copper clearance was. 

Bob K.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Friday, April 08, 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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