Phil;

We have been using a MacDermid Matte Tin Bath as both an etch resist
before SMOBC and as a final solderable finish with a Nickel diffusion
barrier. After about a year in opeation, the Tin is not as white and
does not always pass a solder float solderability test. The bath
itself has turned to a muddy brown appearance which MacDermid says
is normal. 

Do you have any comments on Tin baths for a final finish?


George Anderson
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>Paul.
>
>If I understand your process, you are only going to use tin as an etch 
resist
>and strip it and go SMOBC
>
>A supplier down in Conn., MacDermid, sells a tin electroplate formulation
>used mainly for your type of process and is one of the cheapest based on a
>tin sulphate bath.  You will find the tin stripping easier and faster than
>the tin/lead.  Obviously, after etching don't fuse it and don't use
>solderbright.  The plating is pretty normal and you can convert your 
tin/lead
>process and pre-tin/lead pickle using the same process line and change the
>acid predip accordingly.   
>The tin thickness minimum is about 0.0003 inch, but to be safe a 0.0005 is
>often used.
>
>Your process removes all of the tin plating and you  are not concerned 
with
>whiskers, slivers and gray tin.  If you are going to use the tin as a 
final
>finish, put another note on technet and I can furnish additional 
information.
>
>Phil Hinton 
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