First thing to do is run a profile. I would test cross belt temperature
uniformity and rise rates. MOST IMPORTANT - get a copy of the recommended
reflow profile for the solder paste manufacturer. Ensure you are meeting all
specs like rise rate, soak time, time above reflow, etc.

Brian Stumm
a reflow manufacturer



>Hi,
>
>        Need some advice on how to eliminate or reduce the solder on finger
>that
>we are having right now. So far what we understand is that 90% of the
>problem is
>due to the reflow process where solder traps in vias causing explosion when
>subjected to high temp during reflow. Not sure whether this is the right
>assumption but from what we have seen on the reject there are solder balls
>all
>over the 'exploded' vias.  The signature of solder on finger defects is
>10-40
>mils of 'dot' which could be caused by solder balls.  SO this is my
>questions:
>
>1.  Is it possible that the vias can 'explode' during reflow?
>
>2.  Does the ramp from room temp to soaking time(145-160 deg C) and from
>soaking
>time (160-183 deg C) play an important role in determining the amount of
>'explosion'.  So far our data shows that it does.
>
>3.  Is there any other possible causes of solder explosion...Solder paste?
>
>
>Thank you and really appreciate the help.
>
>Masdi Muhammad,
>Process Engineer.
>
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ETS, LLC - West                      ETS, Inc. - East
3939 N. Freya St.                    PO Box 47887
Spokane, WA 99207                    Plymouth, MN 55447
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