Hi Guy - in addition to the stencil details that have been recommend to 
review, also look at the solder joint composition. If the gold content 
gets very high, the solder alloy solidification behavior will be impacted.

Dave Hillman
Rockwell Collins
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From:   Guy Ramsey <[log in to unmask]>
To:     <[log in to unmask]>
Date:   10/23/2013 09:05 AM
Subject:        [TN] requirement for thin solder joint.
Sent by:        TechNet <[log in to unmask]>



Hi all, 

We would like to solder a thin gold foil, with some magic on top, to a 
PWB.


The foil and pad are round, about 560 um in diameter. 

We want the solder connection to end up less than 25 um thick.  So, we are
trying to print with a 50um thick stencil, and 20% reduction, the stencil
aperture is 460 um diameter.  So, area ratio, or aspect ratio look great,
printing shouldn't be a problem. 

 

Print results were inconsistent. 

 

This morning I realize that many of solder paste spheres are over half the
thickness of the stencil.  And the rule of thumb that five spheres should
fit across the aperture for good paste release.   Well, what about the
thickness of the stencil versus the diameter of the spheres? 

 

Has anyone out there wrestled with this problem?  Maybe I should be using 
a
thicker stencil, and push the aspect ratio a bit more. 

 

Thoughts? 

 



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