Kevin,
Q1 - Although a bit off the wall, would you consider a standard legend
marking ink which was black. There are black inks out there that are UV
curable. Keep the coating thin and of little volume, abide by the NASA
outgassing list, and you should not affect the reliability of the joint.
Q2 - Consider using a standard underfill such as Hysol/Henkel makes. Likely
to be just as easy to dispense for a total under-fill as it will for a
perimeter only. If you use a post-applied underfill, you may pick up some
thermal conductivity as they are still reasonably heavily silica loaded -
but you will have to deal with cure times and temps that the board my not
like too well.
Alternatively, you could use what used to be called a flux-underfill. Now
called No-flow underfills, etc. Stencil your solder paste, dispense the
flux underfill, place device, reflow. Generally, these are clear to
straw-colored.
Steve Creswick
http://www.linkedin.com/in/stevencreswick
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Glidden, Kevin
Sent: Monday, March 29, 2010 8:25 AM
To: [log in to unmask]
Subject: [TN] Low Outgassing, Black Sealant / Underfill
Good Morning, and Happy Monday.
A couple of questions for anyone:
We have a lighting application where we are getting light reflection off two
specific solder joints (we're so lucky to still use Sn63Pb37 they are just
TOO shiny!), so I am looking for a method to cover those joints with a black
(or dark gray) sealant. This would need to be a low out-gassing material.
Does anyone know of any such material? Is there such a thing as black
pigmented conformal coating?
The second question would be for this same product. I also have a need to
seal around the base of some LEDs to prevent moisture ingress to the bottom
only terminations. Would perimeter sealing be sufficient? How does one
determine when they need to underfill vs perimeter seal?
Thanks!
Kevin Glidden
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