José,
I have seen exactly this on the PWBs of and old Bang&Olufsen tape recorder (world famous HiFi kits , wish such a one, but wife don't give OK to such a big hole in family economy!). B&O were among first ones to use silver pads for the edge connectors. The red-black surface disturbed the electrical connections, but with a few strikes with a cotton pin dipped in ordinary home silver polish, the discoloration disappeared. This was probably the result of many years of exposure to the environment in our attic (humidity, paper boxes etc.) You may get same phenomenon because of heat, which use to accelerate many chemical processes. I guess it's about a sulphur impact. Not a very scientific add to your posting, but maybe the stuff is more daily a cause than expected!
http://www.bladestuff.com/conserva/silver1.html
Regards
Ingemar
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Jose Antonio Garcia
Ontalba
Sent: den 26 augusti 2004 17:06
To: [log in to unmask]
Subject: Re: [TN] Corrosion in lead frames
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
-----Mensaje original-----
De: TechNet [mailto:[log in to unmask]]En nombre de David D. Hillman
Enviado el: jueves, 26 de agosto de 2004 15:39
Para: [log in to unmask]
Asunto: Re: [TN] Corrosion in lead frames
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
[log in to unmask]
Jose Antonio
Garcia Ontalba To: [log in to unmask]
<ja.garcia@nagare cc:
s.com> Subject: Re: [TN] Corrosion
in lead frames
Sent by: TechNet
<[log in to unmask]>
08/25/2004 12:21
PM
Please respond to
ja.garcia
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
-----Mensaje original-----
De: TechNet [mailto:[log in to unmask]]En nombre de Creswick, Steven
Enviado el: miércoles, 25 de agosto de 2004 18:02
Para: [log in to unmask]
Asunto: Re: [TN] Corrosion in lead frames
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
-----Original Message-----
From: Jose Antonio Garcia Ontalba [mailto:[log in to unmask]]
Sent: Wednesday, August 25, 2004 10:59 AM
To: [log in to unmask]
Subject: [TN] Corrosion in lead frames
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]
--
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
-----------------------------------------------------
|
