Everyone thank you so much for the replies to my question.
I sometimes feel guilty because I don't have enough knoweledge
to contribute too much to the thread. But I always know that I
can come here for help with questions.
Once again
Thank You very much for replying
John Foster
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Dave Hillman
Sent: Friday, October 17, 2003 1:40 PM
To: [log in to unmask]
Subject: Re: [TN] Question about wetting
Hi John! Solderability restoration can come in three flavors: chemical,
electrochemical, and mechanical (ok, Rudy may correct me in that
electrochemical is a chemical process!). Mechanical restoration requires
physical removal of the suspect oxide (either tin oxide or tin/nickel
intermetallic oxide) using an abrasive media/process - usually not very
practical or component friendly. ROSA is an electrochemical method which
works well (and Bev, my system's back up next week!) but can sometimes has
a "must be used within x hours of restoration" restriction. There are a
number of chemical restoration treatments (such as Kester's SolderNu and
others) which strip off the offending oxide - these are good products but
are sometimes not component friendly. Lastly , pretinning/retinning of the
components with very active fluxes (some folks consider this a chemical
method, some a mechanical method). Good luck on your restoration efforts.
Dave Hillman
Rockwell Collins
[log in to unmask]
John Foster
<john@BROADBANDINNOV To: [log in to unmask]
ATIONS.COM> cc:
Sent by: TechNet Subject: Re: [TN]
Question about wetting
<[log in to unmask]>
10/17/2003 01:49 PM
Please respond to
"TechNet E-Mail
Forum."; Please
respond to John
Foster
One big problem we have is that the parts are not hermetic. In fact we are
looking at a alternate part because of this. I am going to look into the
mechanism of oxidation.
Thanks for all of the ideas so far.
John
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Bev Christian
Sent: Friday, October 17, 2003 11:42 AM
To: [log in to unmask]
Subject: Re: [TN] Question about wetting
John,
Are they non-solderable because the tin has oxidized, the tin has been
consumed as tin/nickel intermetallic that has then oxidized or the tin was
so porous the nickel has oxidized? Also are the parts hermetic? If they
are hermetic and you are sure they are just surface tin oxidized, throw
them
in some dilute EDTA, wash with DI water, IPA and then retape. If it
anything else you would have to use acid to dissolve off whatever layers
are
there and then immediately re-tin.
Then there is an electrochemical way to strip off the bad layers called
ROSA. But this assumes they are either hermetic or can be fixtured to just
immerse the leads. I wouldn't want that job! And Dave Hillman's ROSA
unit is not up and running at this time. EMPF's??
regards,
Bev Christian
Research in Motion
-----Original Message-----
From: John Foster [mailto:[log in to unmask]]
Sent: October 17, 2003 2:14 PM
To: [log in to unmask]
Subject: [TN] Question about wetting
I have a large inventory of trim capacitors that have exceeded the
manufacturers shelf
life by 2 years. Solderability testing has revealed inadequate wetting. The
parts are on
tape and reel. The plating is a thin layer of tin over nickel. We believe
we
have a oxidation problem. Does anyone have any ideas AT ALL on how we can
recover these
parts. The part has gone obsolete I have 86,000 of these things that I
really really need to use.
Any help would be appreciated
Thanks
John Foster
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