Kathy, Earl,
SEM/EDX will not tell you whether you have tin(II) or tin(IV) oxide.  In
fact, unless you have a very $ expensive EDX it won't tell you if there is
any oxygen there at all!  Most EDX don't go any lower than sodium in the
periodic table.  To determine the type of tin oxide present you have several
options, all of them but one not easy:
1) top-of the-line geology grade mass spec with quantitative capability
2) Auger (will detect oxygen and I presume from the amount you might be able
to infer type of oxide?)
3) ESCA (determines oxidation state of all elements)
4) Mossbauer Spectroscopy (determines oxidation state of tin and some other
elements)
5) Raman Spectroscopy (like infra-red spectroscopy, measures molecular
vibrations.  There are definite differences between stretching vibrations of
tin(II) and tin(IV).  May not give good spectra if a lot of organic crude
around that will cause the sample to fluoresce.)
6) And then there are really fancy things like EELS and PAS, which I know
very less about!  :)
and finally
7) If there is an accessible, flat surface with this stuff on it you and
just use SERA (Sequential Electrochemical Reduction Analysis), a form of
chronopotentiometry, which will tell you which oxide and how thick.

regards,
Bev Christian
Nortel


> -----Original Message-----
> From: [log in to unmask] [SMTP:[log in to unmask]]
> Sent: Thursday, November 26, 1998 5:56 AM
> To:   [log in to unmask]
> Subject:      [TN] Tin Oxide
>
> Kathy,
>
> The answer is not to eliminate tin oxide. It is to prevent it. Once the
> oxide is formed, in
> excessive amounts, it is difficult if not impossible to perform soldering
> operations, of any type,
> to effect acceptable solder joints. When the oxide is present, no type
> atmosphere removes it. Your
> flux didn't. Nitrogen won't as it only prevents.
>
> Your oxide analysis should include SEM/EDX. Objectively, this will show
> type and amount present.
> When excessive, cause is found and eliminated to prevent further
> occurrences.
>
> To prevent it is not always easy either. This especially is true when the
> tin coating process is not
> effectively managed (sometimes difficult) or post coating handling and
> storage requirements are not
> met (less difficult). Most tin coatings oxidize readily and rapidly. A
> newer type (white) is said
> not to do so, though I've not had the opportunity to see evidence.
>
> Enjoy,
>
> Earl Moon
>
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