delamination will resulted moisture ingress.  If there are sufficient  
ionics, some time related to poorly cured laminate, it will form  
ionic conduction or corrosion or ACF.  If it is "wet" (trapped  
moisture), bake the board will reduce the short.  Above mentioned  
failure are difficult, if not impossible to be spotted using standard  
x-ray imaging (soft x-ray).  Delam should be detectable using  
acoustic C-scan (use reference).  As for laminate  thin or not,  it  
is  related  to electrical  and  mechanical design and stack and  
material  selection.  The designer should answer the question.
     jk (my 2 cents)
On Oct 2, 2007, at 12:22 PM, Jack Olson wrote:

> THANK YOU everyone for taking the time to respond,
>
> I really appreciate it.
>
>
>
> My problem is, we paid for a report to evaluate some board failures,
>
> and I'm having trouble evaluating the report!
>
> Most of it is related to chemistry, (I won't bore everybody with  
> that),
>
> but the failures are result of shorts and delamination,
>
>
>
> I'll only ask two more questions
>
>
>
> Does this picture indicate the following?
>
> "no visible short is present.
>
> This indicates a fiber-thin short
>
> not able to be imaged by X-ray".
>
>
>
> That seems like quite a stretch, with no evidence
>
> (and isn't delamination more often a moisture issue?)
>
>
>
> http://www.frontdoor.biz/PCBportal/bubbles1.jpg
>
>
>
> and part of the report talks about contamination.
>
>
>
> http://www.frontdoor.biz/PCBportal/bubbles2.jpg
>
> http://www.frontdoor.biz/PCBportal/bubbles3.jpg
>
>
>
> and part of the report suggests the laminate is too thin.
>
>
> Is 3.5mils too thin?
> Aren't there 2.5mil laminates out there now? Or less?
>
>
> Maybe its not appropriate to talk about other company's
> work in public,
>
> If so, don't answer and I apologize for filling mailboxes
>
> onward thru the fog,
> Jack
>
>
> On 10/1/07, Jack Olson <[log in to unmask]> wrote:
>>
>> I'm not accustomed to looking at reliability issues,
>> (my designs are usually so perfect... (grin))
>> so every time I see an X-Ray or a cross-section
>> I get nervous wondering what I'm actually seeing.
>>
>> Can anyone explain what the following picture means?
>>
>> http://www.frontdoor.biz/PCBportal/208what.jpg
>>
>> onward thru the fog,
>> Jack
>>
>
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