agree.
  jk
On Apr 8, 2016, at 12:49 PM, Ed Hare wrote:

> Hi Steve,
>
> +12V & -12V is 24 volts with a little prepreg layer in between.   
> Sounds like trouble.
>
> ------------------------
> Ed Hare
> [log in to unmask]
>
>
>
>
>> On Apr 8, 2016, at 9:44 AM, Steve Gregory <[log in to unmask]> wrote:
>>
>> 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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>>
>>
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