Thanks Dave,

I appreciate your kind words.  I do my own stunts.

I think the left-side of the capacitor and the top and bottom areas of the right-side show the Cu plating was good (once-upon-a-time) so I’m leaning towards #2.

I am leaning towards believing that the Cu dissolved into the Sn (at high temperature) and then precipitated on the existing nucleation sites on the pad-side intermetallic (slow cool-down).

The part that baffles me most is: how could the giant crater in the solder have formed?







From: David Hillman [mailto:[log in to unmask]]

Sent: Wednesday, September 06, 2017 1:00 PM

To: TechNet E-Mail Forum <[log in to unmask]>; Giamis, Andy <[log in to unmask]>

Subject: Re: [TN] Crazy Solder



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]<mailto:[log in to unmask]>



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