Are you already using Type 4 paste?

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Guy Ramsey
Sent: Wednesday, October 23, 2013 7:04 AM
To: [log in to unmask]
Subject: [TN] requirement for thin solder joint.

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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