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November 2002

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Fri, 15 Nov 2002 08:33:59 +0800
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The heat of a HASL coating can bring epoxy filling out in bumps if you
don't have a fab house that's expert in this process, though I have had
some very smooth finishes so that you cannot detect the filled holes at
all.

The plated surfaces wind up being smoother (ENIG and immersion tin being
the other two that I've tried), but I've been disappointed with the
over-plating coverage, even when the copper plating has completely capped
the epoxy fill. As an overall reaction, I would say that epoxy filling is
not the best process I've met in terms of consistency or cost/time
effectiveness - certainly as a thermally conductive filler.

Peter



"Dan R. Johnson" <[log in to unmask]> 15/11/2002 07:30 AM
Sent by: TechNet <[log in to unmask]>

Please respond to "TechNet E-Mail Forum."; Please respond to "Dan R.
Johnson"

              To:  [log in to unmask]
              cc:  (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
              Subject: [TN] another conductive epoxy question.









I've used silver fill epoxy with thick film substrates but never with
PCB's. Any hints on what finishes are compatible? I did a quick and dirty
test with HASL and wasn't impressed with the adhesion. Is Gold better? None
of the typical finishes I see look like they would have the "tooth" that
thick film does. How do the COB folks do it?
Dan
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