Vias can sometimes be filled with subcomposite build by filling them with the
epoxy resin (blind, not through vias).

In thin boards, with a multiple print, it is sometimes also possible to fill
them with LPI, but this is "iffy" and time consuming.

Filling them with a higher temperature solder might also be an option  (paste
and reflow or high temp wave).

if you only need to fill one or two vias, manually filling them with an epoxy
works.

Another possible option is to just "tent" both ends of the hole with a thick
dry film solder mask.

However, if you can avoid the need to fill them, it will make building the
"fab" a lot easier, and less costly.

Except for product around 23 mils thick, we do not fill vias 100%.  Your
requirement sounds very "painful" to the manufacturing folks.  Best of Luck!
Perhaps you can share your "goal" (why fill them) and maybe we can propose
another alternative also?

Jim Herard
KBL, Product Quality Engineering
IBM Microelectronics Endicott
t/l 857-7026

---------------------- Forwarded by Jim Herard/Endicott/IBM on 07-31-97 06:06 PM
 ---------------------------

        [log in to unmask]
        07-31-97 01:45 PM
Please respond to [log in to unmask] @ internet

To: [log in to unmask] @ internet
cc:
Subject: Fab/Assy:  Thermal Vias

Hello Technetters,

 Has anyone found a method to completely fill a via?  I don't think
that the standard plating process will guarantee 100 % fill.  We're also
looking at the option of screen printing conductive epoxy and trying to force
it through the hole.  But, I don't have a lot of confidence in this process
either.  The last option we're considering would be to plug the vias with LPI
soldermask.  This seems like the best guarantee of fill.  Thermal conductivity
is not so great, but it is better than air.
 I'd sure appreciate any comments.

Glenn Pelkey
Quality/Reliability Engineer
Maxtek Components Corp.

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