Hi Guy,

I'm a really old school soldering person.  There is nothing better than SnPb soldering to an electroplated copper surface.  Also I still hate the "Black Pad" name.  Black Pad isn't a failure mode it is a name given to what you see after a failure.  Black Pad failures have been evaluated for years and I still don't think they really have pinned down the cause for the failure mode.  In my 45 years in the telecommunications industry the one thing I learned is that solder joints made to electroless platings are not as strong as solder joints made to electrolypic platings.  The attached file (sorry TN will strip it but you will see it) lists some of the brittle interface failures I've experienced during my years doing failure mode analysis.  The common factor is solder joints made to electroless platings are prone to brittle interface failures.  Although I've listed the manufacturer in the attached list the failures are not due to the manufacturer but to the type of surface finish. Other than immsersion tin which and ENIG , which I really dislike, EPENIG is my other least favorite surface finish.  It has three negatives (Pd and two electroless platings EP and EN).  Pd as a top coating on a PCB does what Pd in a cars catalictic converter does (i.e., it attacks crap out of the environment it is in) and it is easily contaminated and loses it's solderability.  If you don't dissolve all of the EPd you solder to an electroless Pd surface and if you do you solder to an Eni  surface and those solder joints are not strong and subject to brittle interface failure. 

I've always been a fan of IAg.  Yes silver oxidizes and yes silver tarnishes but most of  the fluxes used in soldering can reduce the oxide and tarnish and if the tarnish is really bad you know it by sight before you do the soldering.  And the silver is so thin it dissolves into the solder and you solder to the electroplated cooper below the immersion silver so you have as strong a solder joint as possible.


So I'm not surprised that when you are using components with ENIG plating and PCBs with EPENIG plating that you have a rash of soldering problems.

Since you are using a WS Pb-free flux you really shouldn't be having solderability issues unless your supplier is going a really crappy job and your storage is terrible.  As for solder joint reliability  issues when soldering to electroless platings you need to make sure you are doing everything possible to make sure there is minimum stress on the solder joint.  If not you are going to get "Black Pad" looking brittle interface failures.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Guy Ramsey
Sent: Monday, January 22, 2018 10:03 AM
To: [log in to unmask]
Subject: [TN] soldering problems

So, is poor solderability like the flu . . .
We are having a rash of it.
We identified the EPENIG solder problem as a surface contaminate, originating at the board house in the final rinse water.
We did not get to the bottom of the ENIG problem which I am thinking we own.
Here is why.
The "black pads" may be found on either the board or the device. I have attached a photo of each, one on the board and one on the device package.

These are soldered with a WS Pb-free flux. We have carefully developed the profile with  a long soak, to minimize the void problems on LGA. Ramp, soak, and reflow are all within recommendations of the solder paste manufacturer.

Steve can you put these up for me. The problem does seem to be more common on the DDR3 memory devices than any of the other BGA types.