Stephen,
Could you kindly comment on the type of assemblies used White Tin? for
example, the common process required 5 reflow/solder process (SMT adhesive
cure, top/bottom reflow, wave, rework) for mixed technology. Does white tin
have any problems to solder after 4 reflow? Any particular flux (hopefully,
not use water soluble or any aggressive flux)? Does nitrogen a neccessary
requirement? Any resistance measurement after solder join made after
multiple reflowed board?
I am appreciate if you can point to me any published data or
reliability/shelf life studies (including storage
conditions)...particularly, any comparative studies regarding various type
of White tin existing on market. Many thanks.
Best regards,
jk
At 07:52 PM 10/23/99 EDT, you wrote:
>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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