Ryan,

What you have described is a problem for anyone who is using selective
solder pallets.  The openings should always be chamfered and as large as
possible to allow the solder to flow into and out of the opening.  The
copper tape may also work for you and I have seen others attach stainless
steel strips to the pallet as a permanent fix.  If you have already tweaked
the process and can't eliminate the problem there is one other thing you
can try.  Reduce the lead length of the connectors that are bridging so
there is only about .020 protruding through the bottomside of the board.
If your board is .062 then the lead length should be .085.  You can find
connectors from some vendors cut at this length.  You can also get a lead
prep machine that will cut the leads to the required length.  The type and
amount of flux you are using may be a factor here also.
Good luck.

Ken Kirby
Process Specialist
Speedline Technologies





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cc:    (bcc: Kenneth Kirby/ElectrovertUS/Cookson)
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?