Sean,
Yes, it is normal for the bath to become more turbid and have some change
in color.
I believe that it is stannates being produced that are insoluble.
Are you using bright, satin, or matte finish?
Yes, stannate and organic buildup will eventually reduce your plating
effeciency. Some shops change the bath around 6 months or a year.
It is not usually cost efficient to carbon treat. Too much of the tin
adsorbs. Or maybe absorbs. Anyway, you loose it.
Without bags, I have had problems with something hitting the slabs and
knocking a lot of particulate loose in the bath. Then it plates to the part
and sometimes falls off before etching.
Obviously you want to eliminate as much air entrainment as possible.
gary mccauley
PC Boards, Inc.
-----Original Message-----
From: Sean Clinton [mailto:[log in to unmask]]
Sent: Monday, August 27, 2001 2:48 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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