Hi Andy - first of all, awesome metallography! Tell your metallographer
"super job" for me as that's quality work. The key to this puzzle is your
Pockets-right picture. The copper barrier layer is gone which means one of
two possible causes: (1) you had thin copper plating and the soldering
process compromised its integrity which resulted in a poor solder joint;
(2) somebody was really really really really hot! There was an over
temperature situation. Run a SEM EDAX on the copper content of the right
solder fillet - you should have more copper than was in the SAC alloy. And
if the joint microstructure phases at the bottom are IMCs, then you have
another clue that it was an over temp case.  Very cool case for a material
engineer, not so much for the program manager!

Dave Hillman
Rockwell Collins
[log in to unmask]

On Wed, Sep 6, 2017 at 11:25 AM, Giamis, Andy <[log in to unmask]>
wrote:

> Hi TechNetters,
>
> Here’s something I have not seen before.
> I have seven different ‘theories’ for what’s happening here.
> Three of which do not involve mythical creatures, illegal substances or
> the alignment of celestial bodies.
>
> This capacitor is on a path that sees a lot of RF power.
> The unit went through 20 cycles of -70C to +115C while at nominal power.
> Temperature sensing suggests this device could be hitting 170C.
> No, we normally don’t test to these extremes.
> The PCB has ENiG finish and the solder is SAC.   This is normal SMT, no
> rework.
>
> I think I know in general what happened, but I am surprised.
> I don’t have an explanation for the formation of the big pocket on the
> right.
> Has anyone ever come across any solder joints like this?
>
> Thanks Steve for uploading the pictures (links below).
>
> http://stevezeva.homestead.com/pockets_25.jpg
>
> http://stevezeva.homestead.com/Pockets_CS.jpg
>
> http://stevezeva.homestead.com/Pocket-left.jpg
>
> http://stevezeva.homestead.com/Pockets-right.jpg
>
>
> Best Regards,
> Andy
> Andrew C. Giamis
> Senior Failure Analysis Engineer
> CommScope
> 2601 Telecom Pkwy
> Richardson, TX, 75082, USA
>
>
>