In the first picture there is only a small amount of copper remaining from the end cap, on the top and bottom of the component. The solder is full of burnt particulate matter along the side of the part where the copper completely dissolved into the molten solder and released the gases and materials of the capacitor itself into the solder. It is apparent that an overheating/overtemp incident happened due to excessive heat applied by a solder iron tip. Reflow ovens typically never produce something like this.
In the picture 25 there is severe outgassing, I suspect again from an overtemp condition. I note that there is also damage to the PWB surface and it goes up the side of the center of the cap. This appears to be from placing a solder iron alongside the part, as if attempting to heat both terminations at the same time, for a long enough time to really cook out the gases into the SJ. That is what all of the black particulate matter is in the SJs that display this; burnt material, or actually a form of dross from leaving the solder molten for too long a time.
The picture CS and pocket Left displays a normal Reflow solder joint including a small void, which is perfectly normal.
The pocket right picture shows total dewetting or dissolution of the copper, similar to 25.
The pocket left picture shows an enlarged view of a normal solder joint (enlarged view of same SJ in CS picture)
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Giamis, Andy
Sent: Wednesday, September 06, 2017 1:13 PM
To: [log in to unmask]
Subject: Re: [TN] Crazy Solder
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
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