I just say: wow! Real Sci-Fi!//Ingemar//EMW




> 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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