Mark,
     Really the only way to get rid of them is to fine tune you solder
volume.  I had the same problem about a year ago.  It took 3 iterations of
stencils to get rid of them completely.  I narrowed the homeplate on each
iteration until I found the size that still gave me a good solder fillet
and did not create a solder ball.  I am not sure what your application is
and I know it would take small trace to go between 0603 pads, but a 3/3
trace/space might allow for it.  You cannot let a trace run between those
pads or it will pull a ball to the trace, I have seen this also.  But if no
trace is present, it is a squeeze ball and you will need to reduce your
volume some more.

Brad Kendall
Hella Electronics Corp.





[log in to unmask] on 10/14/98 05:07:37 PM

Please respond to [log in to unmask]; Please respond to [log in to unmask]

To:   [log in to unmask]
cc:    (bcc: Brad Kendall/Hella North America Inc.)
Subject:  [TN] No-Clean Solder Ball.




Dear Technetter.
        We are facing Solder Ball problem for SMT No-Clean process. The
balls are always in contact with 0603 Chip capacitor and resistor and also
fixed by flux. Diameter of the balls is less than 5 mils.
        Stencil thick is 6 mils. Stencil apertures of the 0603 component
        are
home plate shapes. Solder paste thickness is about 7.4 mils.
        We had extended preheat portion of reflow profile to cure solder
paste and reduce peak temperature of reflow portion to stop splash but
solder balls are still found after reflow.
        Would anybody please suggest us how to eliminate the solder balls.
Thank you.
Mark.

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