Richard,
     I would be very interested in any specific problems that you're hearing
about.  I'm not sure who told you that the vendors or the people selling the
tin don't know anything about it.  I sell it and know a lot about it, also
working with me are the formulators of the tin and Ph.D. chemists as well as
strong technical service in any issues that may arise in the assembly
process, we happen to sell solder pastes and assembly fluxes as well.
     I really know of only three different manufacturers of the white tin
right now, Florida CirTech's "Omikron", Dexter's "FST" (who I believe just
got purchased by Alpha), and Mcgee and Roco's equivalent I'm not sure how to
spell the companies name and I don't know what they call their tin.
     I would encourage everyone interested to use me and this forum as a
resource to help answer specific questions and help find answers to any
problems that may arise.  I think the phrase "drop in replacement" must have
taken on a life of it's own, white tin immersion is nothing like hot air
leveling although the transition can be quite easy.  In the past I've used
that phrase but more from an assembly perspective, when the boards get to
assembly they really (in most cases) don't have to be treated much
differently that Hot Air Leveled boards.
     I have personally installed over six lines in Northern California and it
is true that each line gets adjusted specifically to fit that shops current
processes.  Sometimes space is an issue so we'll utilize an existing
conveyorized persulfate micro-etch, maybe the pre-clean section of the black
oxide line, I have even shared the existing pre-clean tanks for electroless
nickel/gold lines, I'm not jealous and don't need to sell you something you
don't need.  The bottom line is clean copper.  I see big differences in the
way solder masks hold up, just as in ENIG some are better than others.  Times
and temperatures can be adjusted in most cases to achieve the proper tin
thickness in spite of the solder mask that's being used.
     I don't want a novel here, just that it seems there is no perfect
alternative final finish yet, but we're working on it.  With many new
technologies there will be "bugs" to work out, whether it's a learning curve
on how to process panels in the board shop or maybe an adjustment in
assembly.  I don't think I've seen an alternative finish that's never had any
issues of any kind.  Of course my opinion may be biased but I think that the
white tin immersion looks very promising, I have seen it gaining popularity
and momentum in my area for good reason, it works.  We'll see what the future
holds.

Stephen M. Wentz
Florida CirTech Inc.
VM# 408-233-0443

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