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Silver
plating intended for engineering purposes is usually employed for solderable
surfaces, electrical contact characteristics, high electrical and thermal
conductivity, thermocompression bonding, wear resistance of load-bearing
surfaces, and spectral reflectivity.
 Specification:
QQ-S-365 Silver Plating, Electrodeposited (This spec has been cancelled,
but is still in wide use.)
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Type-I |
Matte
finish |
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Type-II |
Semi-Bright
finish |
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Type-III |
Bright
finish |
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Grade |
A |
With
supplementary tarnish-resistant treatment (chromate treatment) |
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Grade |
B |
Without
supplementary tarnish-resistant treatment |
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Thickensses: |
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0.0003" |
For
articles such as terminals which are to be soldered |
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0.0005" |
For
corrosion protection of nonferrous basis metals or for increasing
the electrical conductivity of basis metals |
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0.0050"-0.0100" |
For electrical contacts, depending on pressure, friction and electrical
load |
Specification:
ASTM B 700 Electrodeposited Coatings of Silver for Engineering Use
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Type-1 |
99.9%
silver minimum |
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Type-2 |
99.0%
silver minimum |
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Type-3 |
98.0
% silver minimum |
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Grades: |
A |
Matte,
no brighteners in plating bath |
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B |
Bright,
by use of brighteners in plating bath |
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C |
Bright,
by mechanical or chemical polishing of Grade-A |
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D |
Semibright,
by use of brighteners in plating bath |
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Classes: |
N |
No
chromate treatment |
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S |
With
supplementary tarnish-resistant chromate treatment |
About
solderability & tarnish-resistance: Silver plating with chromate-type
supplementary dips have a low contact resistance in the order of 300 to
400 microhms per square inch. The items must be solderable with rosin
cored solder.
About
corrosion protection: For applications where corrosion protection
is important, the use of an electrodeposited nickel undercoat is advantageous.
About
Undercoating: a) Silver plating on steel, zinc and zinc-based alloys
should have an undercoat of nickel over copper. b) Silver plating on copper
and copper alloys should have a nickel undercoat. Copper and copper alloy
material on which a nickel undercoat is not used, and other basis metals
where a copper undercoat is employed, should not be used for continuous
service at a temperature in excess of 300 degrees F (149 degrees C). Adhesion
of the silver plating is adversely affected because of the formation of
a weak silver and copper intermetallic layer.
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