Lou,

I believe there are two mechanisms that tend to deplete tin with time. The
first and I think predominant one is that tin oxides form faster than the
lead oxides. Therefore as you dross the solder pot, a higher percentage of
tin is removed. The second factor is that intermetalics are generally Cu/Sn
compounds. Therefore the tin is preferentially removed from the solder pot
during intermetallic growth. This is not as big an issue with HASL finished
boards as the majority of intermetallic is already formed. However, with OSP
boards all the tin that forms intermetalics is coming from the solder pot. I
hope this helps.

Thanks,
Robert Furrow
SMT Process Engineer
Lucent Technologies
978-960-3224    [log in to unmask]

> -----Original Message-----
> From: Lou Hart [SMTP:[log in to unmask]]
> Sent: Monday, August 21, 2000 12:36 PM
> To:   [log in to unmask]
> Subject:      [TN] tin depletion
>
> TechNetters, is tin preferentially depleted from the solder pot in wave
> soldering?  If so, what is the mechanism?  My recollection is that I
> learned some months back that, left unadjusted, tin content of a solder
> pot will slowly drop.  Thanks for any comments.
>
> Lou Hart
>
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