Hi again Dave,

So the PCB is a .090" thick, 8-layer board, the stack-up is this:

Soldermask
Layer 1
----------
Ground
----------Pre-preg
Layer 3
----------
+12V
----------Pre-preg
-12V
----------
Layer 6
----------Pre-preg
Ground
----------
Layer 8
Soldermask

Steve


On Fri, Apr 8, 2016 at 10:18 AM, David Hillman <
[log in to unmask]> wrote:

> Hi Steve - yes, you have enough physical details that a lab that routinely
> conducts FA work on electronic assemblies (there are several who are part
> of Technet) would have a reasonable chance of finding the root cause. At a
> very minimum with the details you have on this issue, the laboratory should
> be able to rule out possible root causes even if they can't find a specific
> root cause. I didn't see any dendritic shorting - is the belief that the
> shorting is internal to the pwb?
>
> Dave Hillman
> Rockwell Collins
> [log in to unmask]
>
>
> On Fri, Apr 8, 2016 at 11:00 AM, Steve Gregory <[log in to unmask]> wrote:
>
>> 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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