Hi Ernie,
The fact that the tin concentration is going down faster then the other
metals is NOT unusual, it's due to the fact that tin oxidises more rapidly
then most other metals in your bath. This is especially true when the bath
is idle and liquid. If you absolutely need tighter control, you would need
to blanket the area above the liquefied solder with an inert atmosphere. We
use nitrogen, it reduces dross production, and therefore disposal, and also
helps to stabilise the tin content.
As for Lou's question, well more information might be in order, what type of
finish are you running? What is your volume? high? low? Is the wave often
idle? Frankly I've never ran across this problem before, did you talk to
your Kester's rep about it? Remember YOU are the customer and they are
responsible for the support they are giving, if you see it as a problem,
they should be involved.
Alain Savard, B.Sc.
Chemical Process Analyst
CAE Electronics Ltd.
e-mail: [log in to unmask]
-----Original Message-----
From: Ernie Crump [mailto:[log in to unmask]]
Sent: December 6, 2000 3:58 PM
To: [log in to unmask]
Subject: Re: [TN] Copper contamination is wave solder
Lou; We don't run a large quantity of cca's through our machine, but with
pwb's
solder masked over tin/lead, we don't see much movement in the copper
reading.
Always around .075%
I find it wise every so often to do several tests at an independant lab on
the
solder from the bath, and in several cases on the bar stock received, which
is
to the QQ-P spec.
One phenon. I find strange is the need to add tin fairly regularly, we can
drop
1% in a short time, with very little soldering being processed. Less than
100
6x8 " boards.
Your case may have to do with the use of bare copper runs, even with smobc.
Ernie Crump
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