Here are some more "outside the envelope" suggestions:

1.   Try rotating the board within the pallet 45 degrees.  It works wonders
for wavesoldering and solderpaste printing but usually is not an option for
most situations.  Who knows, you might have a 24 inch wide wavesolder.

2.   Try increasing the angle of the conveyor rails and if that isn't
possible, try to do it within your pallet.  The idea is to bring the
trouble area of the part to the lowest possible location so that there is a
minimal lip (or pallet thickness) right there.

3.  Try removing the Omega wave paddles and sealing up the holes if you
have an Electrovert machine.  The holes in the nozzle cause turbulence at
the surface and has been shown to contribute to bridging.  You can tell if
this applies to your situation if your defects occur consistently within a
certain geographical region across the nozzle in the neighborhood of the
two holes.

4.  Try slowing down the conveyor speed (after lowering the preheater
temps) to reduce the "snap back" force a little.

5.  Use press fit  for the connectors and then selectively solder the PGAs
using semi-automated solder pots system (Airvac for example)  with a
programmable conveyor so that the exiting direction of travel from the
solderpot is vertical primarily.  This is fairly common but requires design
changes.

All too often we see questions asked and suggestions made, but far to
infrequently do we see the solutions reported on the TechNet for everyone's
benefit.  If you do solve this one, please send out an email to let us know
what you did.

Hope this helped....

Phil

>        -----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 typ
>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?

Phil Bavaro

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