Thanks Rudy,
We are using your stripper (RDZ-1568) in our O/L stripping line right now,
although I see us needing a stripper with a higher solvent, (RDZ-1399?) to
get our resist out of air gaps of less than 2 mil. I haven't seen any
reimmersion plating, save one time when I over juiced the bath and raised
the pH to astronomical levels (13+ pH), and then it was only tin attack, no
replating. I should have listend to my own better judgement on that. A
new bath makeup solved that issue. Otherwise, I have not seen any tin
attack on our boards. The other good news is that we don't see overetching
or pitting. Thanks for clarifying though.
Thanks Gary,
We run our tin bath matte-semibright. It saves us on maintenance adds, yet
provides the benefits of a bright finish. Plus it looks cooler than the
dull gray Sn/Pb we were using. I have not heard of using a coagulent to
clear up a tin plating bath. The makeup is relatively cheap, so I can't
say we would find any real benefit from treating the bath as opposed to
making up a new one as efficiency drops off.
Again thanks,
Sean
At 05:26 PM 8/27/01 -0400, you wrote:
>Sean:
>
>The murky solution is due to Stannic Tin, and since Stannic is converted from
>Stannous, by oxidation, there really is only two ways it can happen.
>
>The first obvious one is by reaction with Oxygen in the air. This is
>certainly a factor always, but if you are entraining a lot of air with the
>eductors, you could raise the rate of this occurring many times.
>
>The other way it can occur is by excessive (anode) current density..so if you
>are using bar anodes ask if they are being replenished as often as they
>should be.
>
>The next question to ask is, what is the effect of STannic Tin in the plating
>bath, and the answer, as in all of PCB's is "That depends"...
>The oxide dissolves a helluva lot faster in alkaline solutions than the
>metal, and this COULD cause/allow (apparent) etching of the Tin at a much
>faster rate, and thus could cause apparent overetching, or perhaps pitting of
>the Copper.
>
>And the other thing that can happen is that this Stannic Oxide in the deposit
>can dissolve into the photoresist stripper. Some resist strippers lack the
>key ingredient in them to prevent immersion plating back on to the Copper,
>and thus you can wind up with copper partly unetched due to the presence of
>immersion Tin. This is especially the case if you are attempting to strip in
>a tank, although, in this day of insane tight dimension specs, I have seen it
>cause problems in spray stripping as well.
>
>Filtration of Stannic is EXTREMELY difficult due to the extreme fine particle
>size (the brightener/leveler in the Tin plating is a surfactant that causes
>extreme small particles to form).
>
>Rudy Sedlak
>RD Chemical
>
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