Hi Genny - yes, these structures have been reported in the industry before 
so you are in luck. If these were tin/lead solderballs, you most likely 
are looking at copper/tin intermetallic needles structures and if these 
are SAC305 solderballs, you are most likely looking at silver/nickel 
intermetallic needles. These structures are an indication that the 
original reflow solder profile or the rework profile was temperature/time 
excessive. Once the intermetallic phases form, they have melting points 
much higher than the surrounding solder so  when you removed the BGA 
component, they become more visible as the solder joint volume is removed. 
A second root cause would be incorrect metallurgical composition issues. 
Nice photo - the first one is going into my photo gallery. Do you have any 
higher magnification shots?

Dave Hillman
Rockwell Collins
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Genny Gibbard <[log in to unmask]> 
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[TN] Crystalline solder balls






http://ipc-technet.groupsite.com/gallery/13595
May not get many responses on a Friday before a long weekend, but your
ideas on what I am seeing is appreciated. 
Sorry the camera on our microscope is not great.
This is some of what remains on a board after a BGA is removed with a
Summit hot air rework station.

> Genny 

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