You might consider 'taping off' the aperture that is losing the solder
paste and instead apply solder paste using a dispenser (if you have one
in your line).  The dot of dispensed solder paste could be at any
location and in any volume that works for you.  You could do some quick
trial and error evaluation to see what works best for this particular
location.  Putting the paste further from the ground plane sounds like
the correct thing.

Wade Oberle
[log in to unmask]


        -----Original Message-----
        From:   Dallas R. Obenland [SMTP:[log in to unmask]]
        Sent:   Wednesday, March 03, 1999 2:51 PM
        To:     [log in to unmask]
        Subject:        [TN] Solder Robbing During Reflow.

        Looking for help with solder moving from pad-to-pad during
reflow.

        I have an low noise amp. (LNA) in what looks like an SOIC-8 with
a
        continuous ground pad on the bottom of the package.  For RF
reasons this
        bottom plad must be soldered to a ground pad which has several
vias to an
        internal ground plane.  My problem is that after reflow, I end
up with one
        of the eight leads with excessive solder and one with
insufficient solder.
        I suspect that this solder movement is partially due to the
thermal effect
        of the ground pad along with the .015" spacing between the
ground pad and
        lead pads causing solder to be robbed to and from the ground
pad.  I've
        tried playing with the oven profile but can see no difference.

        The RF designers will not give me more than this .015" spacing
between the
        heel end of the lead pad and the dreaded ground pad, so I plan
on widening
        the separation of the solder deposits on my stencil to prevent
slumping and
        bridging of the solder mounds prior to reflow.

         Any other ideas on what may be causing this solder swap or what
I might do
        to minimize the problem?

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