I have long felt that control by titration is not sensitive enough. Someone else suggested checking pH, an excellent idea. Alkaline solutions can (and do) absorb carbon dioxide, and the pH is lowered, yet, they may titrate the same.
This is quite possibly the mechanism of your problem. I would recommend never dumping the whole bath, but dumping only 50% of it, and making up the rest fresh. This will maintain your carbonate buffer, and prevent the problem from recurring.
Rudy Sedlak
RD Chemical Company
--- On Tue, 8/18/09, Skillborg Fredrik <[log in to unmask]> wrote:
From: Skillborg Fredrik <[log in to unmask]>
Subject: Re: [TN] Cleaning a little too much...
To: [log in to unmask]
Date: Tuesday, August 18, 2009, 10:58 PM
By titration with a Zestron Easy Bath Control Indicator. It contains
hydrochloric acid and some sort of indicator I guess.
// Fredrik
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of R Sedlak
Sent: den 18 augusti 2009 16:36
To: [log in to unmask]
Subject: Re: [TN] Cleaning a little too much...
How do you check concentration to know how much Vigon to add?
Rudy Sedlak
RD Chemical Company
--- On Tue, 8/18/09, Skillborg Fredrik <[log in to unmask]>
wrote:
From: Skillborg Fredrik <[log in to unmask]>
Subject: [TN] Cleaning a little too much...
To: [log in to unmask]
Date: Tuesday, August 18, 2009, 1:22 AM
Hello,
We have a problem when cleaning populated boards before conformal
coating.
Problem: The color on our labels on the boards "dewet" during the
cleaning step, but only when we have set a new bath. Then it is getting
better and better and after a week or so the problem is gone.
During production we are constantly adding cleaning agent to keep
concentration steady.
Cleaning agent: Vigon US (Zestron), 26%
Settings: 50 deg C, 12 minutes, agitation and immersed spraying.
Has anyone else seen this problem and figure out how to overcome it
(apart from laser mark the boards instead of using labels)?
We have tried to increase the heat in the printers, changed batch of
labels, changed brand of labels, changed ribbon in the printer but the
problem persists.
We have sent labels to Zestron and to the labelmanufacturer and they
have made their own tests, repeated the problem but have no solution. We
can go down to 15% concentration to avoid the problem but then the
boards won't be clean...
To add some more trickiness to the question the problem; it appeared
last summer but we have used the same settings, cleaning agent, labels
and printers for much longer than that. Usually we change the bath every
3 -4 months but we have postpone the current change when searching for
some light in the tunnel.
All inputs are highly appreciated!
Best regards,
// Fredrik
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