I'm confused by this, probably because I'm not knowledgeable on plasma
cleaning. But so far as I understand this area, the principal uses of plasma
are
- ash off surface contamination to get a clean surface,
Or
- it can be used to impregnate or burn surfaces to make them 'active' (eg
to make PTFE bondable with adhesive)
It depends (!) on the type of plasma and energies used.
This seems to be a confusion of these two functions. Oxidising epoxy would
make a carbon rich layer, oxidizing silver would make silver oxide, both AgO
and C are conductive so we have weakly conductive substrate.
This is a powered device so we have some volts,. The only missing item for
Ag migration is a little damp.
Altogether: not a recipe for high reliability. Or did I miss something?
Regards
Mike
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Hernefjord Ingemar
Sent: Friday, August 31, 2007 9:53 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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