Could you mechanically attach a couple of 'dummy' metal leads (or pads) into
the selective soldering pallet that are in-line with the shorting
location(s) and therefore force the short to move from the board to the
dummy leads or pads of the pallet?


Wade Oberle
Sanmina

        -----Original Message-----
        From:   Ryan Jennens [SMTP:[log in to unmask]]
        Sent:   Monday, July 26, 1999 9:36 PM
        To:     [log in to unmask]
        Subject:        [TN] Selective Wave Solder Pallet Problems

        Hey all-
         
            We use selective wave solder pallets extensively to solder
through-hole leads, as almost all our boards are mixed tech.  A couple types
boards consistently show a single short on the trailing edge of large
through-hole connectors.  One board always shorts on the trailing pins of a
PGA socket, while the other always shorts on the trailing edge of a
40-pin dual-row female header.  No amount of tweaking the wave machine
settings affects the short.  My theory is this:  When the solder leaves the
larger pallet openings, it has nothing to "snap" to.  Therefore, it "snaps"
to the last couple of pins it leaves.  I have made sure that the solder
flows off the back of the wave at the same speed as the conveyer.  Has
anybody else seen, or heard, of this problem with selective solder pallets? 
The advantages of reflowing bottom-side components make wave soldering the
whole bottom-side unfeasible.  Speaking with the pallet house has left us
with grooved pallet bottoms and chamfered openings; but the problem
remains.  Is there a way to alter the selective wave solder pallet openings
to avoid these "snap-back" shorts?

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