I would think that up to 0.0005" (0.5 mil) is overkill.  Our process 
     uses a bright tin plate and the minimum is 0.0001".  The 0.0003" 
     sounds like the thickness needed for solder plating.
     
     Be careful when switching from solder to tin, especially if switching 
     to matte finish tin.  A high caustic (generic) stripper for the dry 
     film can easily cause pinholes in your copper.  This isn't likely when 
     using a bright tin.
     
     Also, there are multiple suppliers for this chemistry.  Ask around 
     with the suppliers who give you good service.
     
     MB
______________________________ Reply Separator _________________________________
Subject: FAB Re Tin plt. instead of Sn/Pb
Author:  [log in to unmask] at SMTPLINK-HADCO
Date:    6/18/96 03:45 PM


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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