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Tin
plating intended for engineering purposes is used for corrosion protection,
to facilitate soldering, to improve antigalling characteristics, and as
a stop-off barrier in the nitriding of high-strength steels. Color is
gray-white, matte to bright in appearance depending on the process used.
Soft and very ductile, not good for low temperature applications.
 Specification:
MIL-T-10727 Tin Plating: Electrodeposited or Hot-Dipped (This spec has
been cancelled, but is still in wide use.)
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Type-I |
Electrodeposited.
Reference ASTM B 545 - Standard Specification for Electro-deposited
Coatings of Tin |
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Type-II |
Hot-Dipped |
Specification:
ASTM B 545 Standard Specification for Electrodeposited Coatings of Tin
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Thickness
Classes: |
A |
0.0001" |
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B |
0.0002" |
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C |
0.00032"
(0.0004" for steel) |
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D |
0.0006"
(0.0008" for steel) |
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E |
0.0012" |
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F |
0.00006" |
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Tin should
be not less than 99.5% pure except when alloyed for special purposes |
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An
underplate of nickel at least 50µ" thick is required for
tin coatings of 100µ" or less that will not be exposed
to solder temperatures (especially ones that will function as a conductive
surface). |
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To
prevent zinc migration and poor solderability during service or storage,
brass or other copper alloys containing more that 5% zinc must have
a copper layer of at least 100µ", or a nickel layer of
at least 50µ", added prior to tin plating. |
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Whiskers:
Metal whiskers sometimes grow spontaneously from the surface of
electrodeposited metals such as tin, cadmium, and zinc during a
period that can vary from weeks to years. These whiskers are about
100µ" in diameter, can grow up to 3/8 inch long and can
have a current carrying capacity of as much as 10 mA.
A tin-lead
plating that is extensively used for the prevention of whiskering
has a nominal lead composition of 7.0±5 % by mass, the balance
being tin. |
Specification:
AMS 2408 Tin Plating
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Specification
Suffix: |
-1 |
0.0001" |
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-2 |
0.0002" |
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-3 |
0.0003",
etc. |
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Tolerance:
+0.0002" unless otherwise specified |
About
Corrosion Protection: Some corrosion may be expected from tin coatings
exposed outdoors. In normal indoor exposure, tin is protective on iron,
steel, copper, and copper alloys.
About
Surface Finish: Coatings may be matte, bright, or flow brightened.
Matte coatings are obtained without the use of brightening agents. Bright
coatings are obtained by adding brightening agents to the plating solution.
Flow-brightened coatings are obtained by heating the matte coating above
the melting point of tin for a few seconds followed by quenching.
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