Thanks, Mike,
another intelligent add to the discussion. The guys who 'invented' the
method of 'plasma oxidize' are both PhDs, one in Solid State Technology,
the other in Laser Physics. They performed tests with some substrates in
that they exposed these to damp environment plus voltage after the
oxidizing. As there was no silver migration, they had proven the idea.
With all respect, I'm not at all convinced. Migration and dendrite
formations are often hard to create in the lab. The reality life in the
field is different, as we all know. Testing a couple of samples is not
comparable with thousands of substrates in all kinds of situations.
Furthermore, oxidizing a few nanometers of silver on the silver epoxy
dot's surface does not inhibit possible migration paths from the
underlying millions of silver flakes. I think the whole idea is
preposterous, or I'm not learned enough to get it.
Thanks all for the contributions
/Inge
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Mike Fenner
Sent: den 3 september 2007 17:32
To: [log in to unmask]
Subject: Re: [TN] Plasma "oxidation"
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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