Paul,
 Just to make sure we are talking about the same process here, these
boards have not been processed thought the screen printer, correct? If
so I have seen where improper cleaning practices from mis prints cause
trapped solder spheres and result in solder balls. Most of the trapped
paste is located around the vias and PTH barrels. Some can become
trapped in corners of SMDP (Solder masked defined pads). Just a question
to make sure nothing from the process was inducing the solder balls.

>>> [log in to unmask] 9/24/2003 6:57:24 AM >>>
Hi TechNet Gurus,

Has anyone experienced solder balls resulting from the board
fabrication
process? We have been getting them from our offshore supplier for a
few
months now and have had to add a wash step to our no-clean process. We
know
that it's fro the board because we have run bare boards through the
reflow
oven using the normal reflow recipe from that board and we are seeing
25-60
random solder balls on our 9" x 7", 8 layer, .062", HASL FR4  board.
We
believe the problem is caused by uncured solder mask that erupts when
exposed to reflow temperatures but have been unsuccessful trying to
eliminate the problem. We have tried baking the board @ 320 F for
anywhere
from 1.5 - 6 hours. This has reduced the number of solder balls to
maybe a
dozen or less. Anyone have a suggestion?

Thank you,
Paul Black
Manufacturing Engineer
Kronos



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