[MIL-T-10727C]
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.
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.
Specification:
MIL-T-10727 Tin Plating: Electrodeposited or Hot-Dipped
- Type I
Electrodeposited. Reference ASTM B-545 Standard Specification for
Electro-deposited Coatings of Tin
- Type II Hot-Dipped
About
Composition: Tin should be not less than 99.5% except where
deliberately alloyed for special purposes. The codeposition of lead,
bismuth, antimony, copper, or nickel with the tin reduces the risk of
whisker growth (Metal filaments, or whiskers, sometimes grow
spontaneously from the surface of electrodeposited metals such as tin,
cadmium, and zinc within a period that may vary from weeks or months to
years. These whiskers are about 0.0001 inch (2.5 µm) in diameter,
can grow up to 3/8 inch (10 mm) 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 % (with allowed variations of ±5 %) by mass, the balance being
tin.
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 proprietary brightening agents
to the plating bath. Flow-brightened coatings are obtained by heating
the matte coating above the melting point of tin for a few seconds
followed by quenching.
Thickness:
As specified on drawing. Color is gray-white in a plated condition. Has
very high luster in fused condition. Soft and very ductile. Corrosion
resistance good. (When specified, coated items should meet 24-hour 5%
salt-spray requirement.) Solderability is excellent. Tin is not good
for low temperature applications (changes structure and loses adhesion
when exposed to temperatures below -40°C). If bright finish is
desired specify Bright Tin plate to be used in lieu of fused tin.
Thickness can exceed that of fused tin and thicker deposits show
excellent corrosion resistance and solderability.
Guide:
(.0001-.00023"
thickness) Flash for soldering.
(.0002-.0004"
thickness) To prevent galling and seizing.
(.0003" minimum
thickness) Where corrosion resistance is important.
(.0002-.0006"
thickness) To prevent formation of case during nitriding.
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