Hi Ryan! If the QFPs do have a palladium finish then what may be happening is
the flux activators from your solder paste are not effective in promoting
wetting (you may not have a temperature issue at all). I have experienced some
problems with Pd finishes - some flux formulations do not seem to be compatible
in promoting wetting as well as other flux formulations. You may need to alter
the flux formulation in your solder paste to achieve successful results. Good
Luck.

Dave Hillman
Rockwell Collins
[log in to unmask]




Ryan Jennens <[log in to unmask]> on 02/17/2000 01:41:09 PM

Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond to
      Ryan Jennens <[log in to unmask]>

To:   [log in to unmask]
cc:

Subject:  [TN] Tin/Silver Paste and Palladium



Hey Everybody-

    We are using 96.5/3.5 tin/silver solder paste on our top side and I have
been noticing that on some QFPs the paste forms a heel fillet, a negligible
toe fillet, and does not wick over the top of the lead "foot".  I am
checking to see of the components have a palladium finish (I am pretty sure
they do).  If it turns out they do, is there an issue with tin/silver paste
and palladium coated leads?  We are peaking at 230-235 C (ten zone
convection Conceptronics) so the boards are getting plenty hot.  Why does
the paste seem to bulge up at the toe fillet, but not wick onto the lead
surface?

-Ryan Jennens
TelGen Corporation