Karen,
Many of the mold release compounds that I have seen or analyzed with ion
chromatography had significant amounts of sulfur in them, as sulfur is
apparently a slippery material. As such, I would expect it to be
incompatible with silver and an expected reaction agent would be
silver/sulfur complex. I do not know if the organic barrier that is part
of the present immersion silver finishes would be proof against such
materials. On the other hand, if the mold release is Teflon, then there
is probably not an issue.
Doug Pauls
"David D. Hillman"
<ddhillma@rockwellc To: [log in to unmask]
ollins.com> cc:
Sent by: TechNet Subject: Re: [TN] Corrosion in lead frames
<[log in to unmask]>
08/27/2004 03:05 PM
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Hi Karen! I don't have the background to definitively comment on whether
mold compound adhesion and silver finishes would be an issue. My guess
would be that the component fabrication community problem can/could make
the combination work. However, electrolytic silver has long been restricted
on military applications and very much non-recommended for commercial
applications as a component finish due to its poor solderability
performance and problems with electrochemical migration/corrosion. The new
immersion silver chemistries, if adapted to component finish applications,
may eliminate those issue if successful application is achievable.
Dave
Karen Walters
<karen.walters@SKYWO To: [log in to unmask]
RKSINC.COM> cc:
Sent by: TechNet Subject: Re: [TN]
Corrosion in lead frames
<[log in to unmask]>
08/27/2004 10:14 AM
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karen.walters
Hi David Hillman
I have a question for you. Do you see Ag lead finishes as a problem with
mold compound adhesion because of the surface finish. I was told that this
could impact the adhesion property and cause moisture ingress problems.
Please advise.
Hi Jose! The photo shows what appears to be silver sulfide (based on
observations we have made on silver issues at Collins). Depending on the
severity of the surface species attack you may or may not be able to
chemically restore the silver surface. Having the discoloration may not be
an indication that you will have problems - at least in terms of soldering,
some discoloration does not impede a flux's ability to create a
metallurgical joint. The same assumption may not hold true for wirebonding.
Good Luck.
Dave Hillman
Rockwell Collins
Hello together!
hier is the link with the image of my problem. Sure is easier to see it
than
my explanations!
http://www.geocities.com/karlsruhero/Silver_corrosion_image.ppt
Thank you for your help!
Best regards
Jose
Hi Jose! It has been my observation/experience that silver oxides are clear
in appearance, silver chlorides are yellowish in appearance and silver
sulfides can be black-to-purpleish in appearance. We have used SERA testing
to confirm the surface species identification. I have not observed a red
color appearance in conjunction with silver. Good luck on solving the
problem.
Dave Hillman
Rockwell Collins
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Steve,
You are right, I am speaking of an alumina substrate with a Ag/Pt
metallization, but I have just realized that I was wrong in my first
message: the lead frame is really Ag/Pt and the coating is pure Ag. There
is
not more metalls involved.
I think the red spots are oxides of Ag or Pt or maybe both. But the oxides
of silver are not red coloured, aren't they? So, the red spots have to be
oxides of Pt... Maybe the tempeature helps the reaction of oxidation of Pt.
Anyway I am not sure.
What do you think?
Thank you very much!
Regards
Jose
Jose,
Could the red-orange color be from exposed, oxidized copper?
You did not say whether the lead frame was copper, phosphor bronze, or
maybe
a Kovar (Fe, Ni, Co) composition.
.... although, I am confused by a lead frame having Ag/Pt plating. Hmmm.
Possibly, are you speaking of an alumina substrate having Ag/Pt
metallization (traces) on it?
Steve Creswick - Gentex
Hello together!
I have an hybrid circuit with lead frames for bonding encapsulated with
gel.
These lead frames are used for bonding the wires of aluminium only with
heat
(without using solders, flux, etc.). We have made some durations test,
after
them appears some red-orange spots on the lead frames preferably in the
borders, and, in some cases, comes into view blue parts too. We have seen
with Infra-Red photographs that this part (wire+lead frame) is by far the
warmest of the PCB when it is working, because through it comes high
electric flow.
The lead frames have a coating of Ag/Pt and the gel's major components are:
silicone, Pt (polymerization's activator) and alumina (for the thermal
conductivity). The lead frames have not solder nor flux residues.
So, anybody could tell me what is happening in the lead frame? I suppose
that a chemical reaction involves the Ag and/or the Pt but I have no idea
which could be!
Thank you all for your help!
Best regards
--
José Antonio García Ontalba
Quality department
NAGARES, S.A.
Ctra. Madrid-Valencia, Km. 196
16200 Motilla del Palancar (Spain)
Tel: 00 34 969 18 00 21
Fax: 00 34 969 33 11 31
E-mail: [log in to unmask]
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