By the way, solder balling material/process got a lot to do with the  
final structure integrity: the best is laser on melt of solder sphere  
- pricy (large volume production on the high end), 2nd best is solder  
sphere attach with either paste or flux - less pricy - you may need  
to clean the flux or use vapor phase reflow etc - medium volume  
parts, the cheapest is solder paste screen on and reflow... look like  
you might got the cheaper side with slow cooling rate --- double  
guess ;-).  don't quote me on it... (you pay what you get is my guess).
           jk
On Aug 6, 2014, at 5:56 PM, Yuan-chia Joyce Koo wrote:

> (1) 45 degree inclined crack with grain boundary sliding - some  
> kindly of cyclic stress due to possibly thermal expansion  
> difference between the module and board.  (either a large chip, or  
> multi-chip stack on module side... compare to the board of cte of  
> 17ppm or so for example).  The module must be very rigid or very  
> flexable... - look like rigid would be apply... just a guess.
> (2) significant ppt of high melting phase prior to eutectic  
> formation, the solder ball material look  like is off eutectic Pb/ 
> Sn with reballing cooling at low rate. - weak structually speaking.
> (3) the operating temperature and environment may got something to  
> do with it.  - no info provided based on the email below.
> just a guess.
>        jk
> On Aug 6, 2014, at 2:48 PM, Chris Mahanna wrote:
>
>> We see hundreds of cracked solder joints every year, but I can't  
>> say that I've ever seen one quite like this.  I have some  
>> suspicions, but I'll keep them to myself, as to not prejudice the  
>> crowd.
>> EDS maps are forthcoming.
>>
>> This is a caught in-the-wild field failure of a 48-pin BGA
>> Reballed to SnPb
>> ENIG on board side
>> Ni barrier on component side
>>
>> http://stevezeva.homestead.com/45268-1.JPG
>>
>> http://stevezeva.homestead.com/45268-2.JPG
>>
>> http://stevezeva.homestead.com/45268-8.JPG
>>
>> Thoughts?  And Thanks to Steve!
>>
>>
>> Chris Mahanna
>> President, Technical Manager
>> Robisan Laboratory Inc.
>>
>>
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