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Subject: Re: ASSY:  Short leads in a PWA
Author:  Jim Goss at Vicor-Automation/TestEng
Date:    3/27/96 3:23 PM
  
  
We have a similar situation, on the secondary side of our boards the protrusions
must be <25 mils. The criteria we use for leaded components are the same as 
IPC-A-610 on the board component side. Our leads are trimmed so there is a 
maximum protrusion of 5 mils before soldering.  We have no problem with filling 
PTH's but accept solder recessed into the hole 25%. 
Look at  Fig. 4-12 in IPC-A-610A. 
  
We selectively dip solder locations of our boards over a fountain. The problem 
we have is, we have random protrusions >25 mils that is caused by the meniscus 
bump formed when vertically removing the board from the solder surface. This is 
a fully automated process capable of soldering 6 board's per. min.
  
HELP!
  
Does any one have any suggestions how we could shrink protrusions?  We don't 
want to do touchup an in process solution is required. We have tested several 
process modifications with mixed results. Any recommendations or thoughts are 
appreciated.
  
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______________________________ Forward Header __________________________________
Subject: Re: ASSY:  Short leads in a PWA
Author:  [log in to unmask] at Internet 
Date:    3/27/96 7:16 AM
  
  
[log in to unmask] wrote:
>      Due to a "non-existent" clearance between a PWA and a shielded case, 
>      we would like to have certain components with lead lengths that are 
>      not long enough to protrude through to the secondary side of the
>      board.  Thus, there would be no fillet for a solder joint.
  
We had a similar situation, but in our case we specified that the leads be 
clipped (after soldering), and the fillet ground down to .030 mils. These 
boards were for airplanes and had to undergo shock, vibration, environmental 
testing etc. NO PROBLEMS. Of course, you said your clearance was 
"non-existent", can you spare 30 mils? And by "shielded case" do you mean 
conductive? You might have to apply some adhesive KAPTON over the pads after 
you grind them, but at least by grinding you have the most lead length, and 
strongest solderjoint possible, still much stronger than a SMT connection, 
right?  
					           Jack
p.s. I would like to hear what others recommend, though... anybody else?