This phenomenon is called "Pad Crater"!

>>> [log in to unmask] 11/24/08 2:45 PM >>>
Dear TGA colleagues:
After microsection inspection, I can not find out suitable reference 
and/or judgement for this phenomenon.
In my opinion, that should be a suspected crack or delamination and is

critical for BGA connection.
Is there any solid and clear judgement for these phenomena, especially
for 
post reliability test?
Basic information: New pilot, Non-rework, after TCT 700cycles(-40C,
+90C, 
dwell 30mins)
Thanks for your reply in advance.
Yenchi