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June 2000

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Subject:
From:
"Stephen R. Gregory" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 15 Jun 2000 19:47:08 EDT
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In a message dated 06/15/2000 5:20:22 PM Central Daylight Time,
[log in to unmask] writes:

> Bev
>
>   Please follow your own suggestions and check the TechNet
>   archived.  I talked about this several months ago.  I have used the term "
> Immersion White Tin" since 1995 to describe a coating called OMIKRON.  I
took
>  the name from  an IBM research paper published back in 1984.  They used
that
>  term to describe a long term solderable immersion tin finish.  It has
> nothing to do with your definition.
>
>  Rich Edgar

Hi Rich!

The "White Tin" in the term "Immersion White Tin" is what sometimes confuses
many people. Bev described exactly what "white tin" is from the periodic
table of elements. So you are right, his description of "White Tin" has
nothing to do with OMIKRON, just as the words "White Tin" in "Immersion White
Tin" has nothing to do with the actual description of White Tin in the
periodic table of elements.

Bev is probably more knowledgable in material sciences than many people,
that's why he has his PHD. Not to speak for him, but I'd bet he was talking
about white tin as it's clearly defined from the periodic table...not from
your "trade name"...

There's some pastes below from a few web pages that talk about white tin,
organic tin, white immersion tin...whatever you want to call it. This ought
to confuse everybody :)

-Steve Gregory-

From: http://pearl1.lanl.gov/periodic/elements/50.html

Properties

Ordinary tin is composed of nine stable isotopes; 18 unstable isotopes are
also known. Ordinary tin is a silver-white metal, is malleable, somewhat
ductile, and has a highly crystalline structure. Due to the breaking of these
crystals, a "tin cry" is heard when a bar is bent.

Forms

The element has two allotropic forms at normal pressure. On warming, gray, or
alpha tin, with a cubic structure, changes at 13.2 degrees C into white, or
beta tin, the ordinary form of the metal. White tin has a tetragonal
structure. When tin is cooled below 13.2 degrees C, it changes slowly from
white to gray. This change is affected by impurities such as aluminum and
zinc, and can be prevented by small additions of antimony or bismuth. This
change from the alpha to beta form is called the tin pest. There are few if
any uses for gray tin. Tin takes a high polish and is used to coat other
metals to prevent corrosion or other chemical action. Such tin plate over
steel is used in the so-called tin can for preserving food.

Alloys of tin are very important. Soft solder, type metal, fusible metal,
pewter, bronze, bell metal, Babbitt metal, White metal, die casting alloy,
and phosphor bronze are some of the important alloys using tin.

Tin resists distilled sea and soft tap water, but is attacked by strong
acids, alkalis, and acid salts.Oxygen in solution accelerates the attack.
When heated in air, tin forms Sn2, which is feebly acid, forming stannate
salts with basic oxides. The most important salt is the chloride, which is
used as a reducing agent and as a mordant in calico printing. Tin salts
sprayed onto glass are used to produce electrically conductive coatings.
These have been used for panel lighting and for frost-free
windshields. Most window glass is now made by floating molten glass on molten
tin (float glass) to produce a flat surface (Pilkington process).

Of recent interest is a crystalline tin-niobium alloy that is superconductive
at very low temperatures. This promises to be important in the construction
of superconductive magnets that generate enormous field strengths but use
practically no power. Such magnets, made of tin-niobium wire, weigh but a few
pounds and produce magnetic fields that, when started with a small battery,
are comparable to that of a 100 ton electromagnet operated continuously with
a large power supply.


From: http://www.omnigraph.com/omnireview.html

Organic White Tin

About six months ago we sent out samples of white tin finish on printed
circuit
boards. Some people liked it and some did not. Those that did not like it had
solderability issues. It didn't wet as well as Hasl. We had difficulty in
figuering out why it did not wet as well. Was there a difference when the
assembler used
a water soluable or no-clean flux? Did the soldering temperture make a
difference?

It turns out the biggest problem was the plating thickness in our process. We
thought if it looks good then it should work. We discovered that .2 microns of
white tin look good but there will be de-wetting. And .4 microns wets fine
for a
single thermal pass, but will cause difficulty on subsequent thermal passes.
For
multiple thermal passes, .6 to .8 microns of plating is required. We have
decided
to be on the safe side and plate .8 to 1 microns on all our boards.

To refresh your memory, here are some characteristics of white tin.

THE HASL REPLACEMENT IMPROVED IMMERSION WHITE TIN
Compatible with all fluxes and solder pastes
Capable of multiple assembly cycles
Uniform flat and dense pads
Shelf life equal to hasl
No solder pot contaminaton
Can be electrically tested after coating

This coating will not add cost to your board and will guarantee your product
acceptability in the Japanese and European market in 2002 and thereafter.

We will be sending more samples out to you for testing.

Please try this process again.


From: http://www.filtranmicro.com/desgui.html

B) White Immersion Tin

    Filtran provides immersion tin processing using Omikron chemistry.
Typical
    thickness will be under 40 microinches (1 micron).  This finish is thin
and will not
    affect the circuit resolution as will 300-500 microinches of tin-lead
solder.
    Immersion tin acts as an acceptable solderable coating with a shelf life
of 6 -
    12 months if stored under ideal conditions.  Tarnishing can occur when
    exposed to moderately hostile environments.  In such cases, a mild acid
    cleaning and/or light abrasive cleaning immediately prior to soldering is
    recommended.

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