BACKGROUND:
On one assembly, we
use semi-automatic air displacement paste dot dispensing and a semi-automatic
placement system. The computer says where to put the paste and parts, the
operator places them by eye in the correct location. With normal accuracy, we
get a few solder balls that squeeze out from under the chips at the
side which are easy to pick off. Recently, we got a batch that have lots of
solder balls trapped under the middle of the parts. It was a newly trained
operator that built these assemblies.
QUESTION:
What is the most
likely cause?
What is the best way to rework
a chip part with a solder ball under the
middle?