Ed,
    Depending on your board shop's process, if you delete the pads on one 
side, they may not be able to provide 100% barrel plating, particularly on 
the component (padless) end of the holes.  While this might not seem to be a 
concern depending on you application, you could potentially be enhancing 
your original problem of shorting.
    One of the sources of solder shorting under connectors is outgassing as 
they go over the wave.  This can occur when there is moisture inside the 
laminate and voids in the plating inside the hole.  As the solder begins to 
fill the hole the moisture turns to steam and blows some of the solder out 
of the hole.  Since there are only two ways out, the path of least 
resistance is often up under the component.  The expelled solder can easily 
attach itself to nearby metallic surfaces producing hidden shorts that can't 
be found by normal visual inspection.
     One other thought, before you delete your pads you may want to verify 
your wave soldering settings.  Your wave could be promoting wicking of 
excess solder if the wave is too high, speed too slow or solder temperature 
too high.  The shape and placement of the solder shorts should provide you 
some clues as to the source.

            Norm Dill
 ----------
From: [log in to unmask]
To: [log in to unmask]; [log in to unmask]
Subject: ASSY - Padless Plated Thru Holes
Date: Wednesday, November 13, 1996 8:04AM


  To extend clearance and eliminate potential shorts to the bottom
of a connector, the component side pad must be reduced to zero.
In other words,a top side padless PTH. The shorts are occuring during
wave solder.

   What reliability down sides can we expect? Im advised that PCB
fabrication will not be a problem. Im mostly concerned with assembly
and repair operations.

  Parameters: .093", 14 layer board
               Finished hole .033" with solder side pad at .060"
               No external layer traces or connections.
               All connections are internal planes.

 Thanks in advance: Ed Cassinelli
                    Stratus Computer Inc
                    508-490-6821

<<File Attachment: ASSY.rtf>>

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