Sean: As stated by others you are oxidizing the Sn causing the turbid coffee
cream color. This is being caused by the solution turnover thru the eductors
and filter system. My advice would be to get rid of the eductors and
minimize the use of the filter system. The more turbulence the more
oxidation. You don't need to be constantly filtering the bath.
We used a LeaRonal Tinglo-Culmo bright acid Sn bath for years. As the
stannic Sn built up we would treat it with a proprietary material from the
supplier that acted more or less as a floc and precipitated out the stannic.

Also we used bagged slab anodes and filtered only 2-4 hrs per day with a
graduated density filter 20-5 microns. The graduated density filter is not
as prone to blinding out or clogging as a standard rated filter.
Just some thoughts that may help.


Regards


Michael Barmuta

Staff Engineer

Fluke Corp.

Everett Wa.

425-446-6076

-----Original Message-----
From: Sean Clinton [mailto:]
Sent: Monday, August 27, 2001 12:48 PM
To: [log in to unmask]
Subject: [TN] Tin Plating bath (not clear anymore)


Techneters,

I am bringing up a tin plating bath to replace our tin/lead plating system
for etch resist and have noticed something about our new bath.  Upon
makeup, the bath was clear, albeit a slight butterscotch color.  It has
since become somewhat murky, and looks like its on its way to becoming a
murky coffee and cream color.  I was told this is normal, but I seem to
recall that stannic tin is not soluble in acid tin baths.  Am I converting
the stannous to stannic tin?  If so, will this adversely affect my plating
efficiency?  Basically, is it ok to have a murky looking acid tin bath?  My
plating results using test panels seem to indicate that performance has not
changed.  My plating calculations indicate the efficiency is on the order
of 98-99%.  My vendor says it's ok, but I'd like some other opinions on
this.

Also, the system uses eductors for solution turnover and the pump runs
solution continuously through a polypropylene filter.  I am not using bags
over my anodes (slabs), and I don't have a flow meter on the pump yet, so I
cannot judge the solution turnover rate.  The eductors do move a large
amount of solution  in the tank though.


Thanks,

Sean Clinton
Process Engineer
Proto Engineering Corporation
(408) 737-4136

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