Sounds like you need to either find a flux aggressive enough to do the
job, or to place the boards in a reducing environment for an
"appropriate" period of time.
Creating a reducing environment may not be that difficult.
I have used a retort (sealed chamber in an oven) at 100C with
industrial nitrogen flood until an O2 meter tells me its below 10ppm O2.
Apparently there are enough trace contaminant reducing agents in the
industrial nitrogen to create the reducing environment. I suppose you
could also dope the environment with a tiny bit of H2. I'd try a 4 hour
100C bake in such an environment to start with.
Of course, if you don't have a retort, you will need to find an
alternate reducing technique. Chemicals can do it, but then we have to
worry about the parts on the other side.
We've been nailed by counterfeit parts too, so I feel your pain!
Wayne Thayer
>>> [log in to unmask] 10/18/2006 9:47 am >>>
Mornin' Rich,
Just curious, what kind of flux are you using in your paste?
-Steve Gregory-
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Rich Wolbert
Sent: Wednesday, October 18, 2006 8:32 AM
To: [log in to unmask]
Subject: [TN] Oxidized PCBs
OK, I know you guys are probably going to shake your head on this one,
but I have to ask. We have a double sided fine pitch SMT assembly and
we
decided to go to white tin for the pad material. Here's where the
problem comes in, we ran one side and when we started process the
other
side we found counterfeit chips. We stopped production for two weeks
until the correct parts came in. When we tried to run the boards
again,
the PCB's oxidized so badly over the two weeks that we can not get the
solder to wet. Any suggestions, other than scrapping the 170
assemblies
at $600 a piece?
---------------------------------------------------
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
847-615-7100 ext.2815
-----------------------------------------------------
---------------------------------------------------
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 847-615-7100
ext.2815
-----------------------------------------------------
---------------------------------------------------
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 847-615-7100 ext.2815
-----------------------------------------------------
|
