Inge,
I'm not a wafer guys, but here are a couple of thoughts:
1) You don't say whether there is anything else laid down on the base
surface where the substrates are laid. We tried using a similar mix at
Nortel to look at "fluxless soldering", but abandoned it because of ESD
issues.
2) Silver oxide itself is still conductive so if the epoxy is heavily
loaded there is a good chance there is some of the oxide on the crisped
surface and since it is conductive couldn't it also form dendrites in
the right conditions of humidity and potential charge?
Bev
RIM
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Hernefjord Ingemar
Sent: Friday, August 31, 2007 4:53 AM
To: [log in to unmask]
Subject: [TN] Plasma "oxidation"
Yup. Strange title. I've been asked about a strange process, which one
was introduced without my knowledge, and I'm going to throw it out. But
I thought of consulting TN before. This is the case:
LTCC substrates are silver epoxy dispensed for chip mounting. In order
to avoid risk for silver migration, a guy invented plasma "oxidation",
i.e. he use a plasma cleaner, runs Argon with 6% Oxygen for a couple of
minutes on mounted substrates. The silver epoxy dots become blackish
because of oxidation, and oxidized epoxy is meant to minimize risk for
silver migration. The oxide is of course just nanometer thick. The guy
worked at a wafer manufacturing plant and had experience of cleaning
procedures.
I mean that this process is nonsense. If humidity gets in and condense
on the substrate, and if the electric field is high enough, and if there
are salts or contaminations, there is still enough silver to start
migration. Oxidation of the silver dot's surface is meaningless. Anyone
heard of such a strange process? Plasma operation on mounted LTCC
substrates is foreign to me, I want it out.
TrikeMan?
Inge
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