Ramakrishnan,

If you are willing to spend some extra money, there is one extremly good
way to study crossections with no smear problems and that is FIB SEM
(Focused Ion Beam Scanning Electron Microscopy). I've used it many a times.
I'll send a photo offline to you, that tells more than words. In this
crossection you will see absolutely no smear and cracks and voids are
undisputable. Contact your university and they will adress you to nearest
lab with FIB SEM. Yes, the time cost is high, on the other side polishing
whole days is expensive as well.

Inge




On 22 December 2012 16:03, Ramakrishnan Saravanan <[log in to unmask]>wrote:

> Dear Mr ,
>
> We have a in house facility for making hi reliability PCBs.
>
> We use Park Nelco N4000-6 material (Tg=175 C ).
>
> We use hot mounting techniques for PWB coupon micro section.
>
> We polish up to 5 microns normally bur if a problem is found we go up to
> 0.05 micron polish.
>
> We don't do micro etch. A Hi reliability PCB has failed in the field
> trials.
>
> We analyzed  the coupon again  no problem found. We polished up to 1
> microns  still no problem found.
>
> But when we micro etched  the specimen we found a barrel separation.
>
> Do the micro etch is essential in finding a fault?.
>
> What are the false alarms possible and how to exclude ?
>
> Kindly advise . regards.
>
> Ramakrishnan Saravanan
>


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