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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