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Gold
plating is intended for electrical applications, and where good corrosion
resistance, excellent solderability, or high tarnish resistance is need.
It also has uses in many other applications. The color is yellow to orange
depending on the proprietary process used, and will range from a matte
to bright finish depending on the base metal and purity of deposit. It
has low contact resistance, and is a good conductor.
 Specification:
MIL-G-45204 Gold Plating, Electrodeposited (This spec has been cancelled,
but is still in wide use.)
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Type-I |
99.7%
gold minimum; hardness grade A, B, or C |
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For general-purpose, high-reliability electrical contacts, solderability,
and wire wrap connections. |
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Type-II |
99.0%
gold minimum; hardness grade B, C, or D |
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A
general-purpose, wear-resistant gold. It will not withstand high-temperature
applications because the hardening agents in the gold coating will
oxidize. |
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Type-III |
99.9
% gold minimum; hardness grade A only |
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For
semiconductor components, nuclear engineering, thermocompression
bonding, and high-temperature application. |
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Hardness
Grades: |
A |
90
knoop, maximum |
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B |
91-129
knoop, inclusive |
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C |
130-200
knoop, inclusive |
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D |
201
knoop, minimum |
Specification:
ASTM B 488 Standard Specification for Electrodeposited Coatings of Gold
for Engineering Uses
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Type-I |
99.7%
gold minimum; hardness grade A, B, or C * |
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Type-II |
99.0%
gold minimum; hardness grade B, C, or D * |
|
Type-III |
99.9
% gold minimum; hardness grade A only * |
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Hardness
Grades: |
A |
90
knoop, maximum |
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B |
90-200
knoop |
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C |
130-200
knoop |
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D |
201
knoop, minimum |
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* New purity types as of 2001 -- makes them identical to the original MIL-G standard. |
Specification:
AMS 2422 Gold Plating for Electronic and Electrical Applications
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An
underplate of copper (from a copper cyanide solution) is required
unless the base material is copper or a copper alloy containing less
that 15% zinc. |
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Copper Thickness: Not less than 0.0001" |
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A
layer of nickel (from a Watt's or chloride solution) is required over
the copper underplate or copper base material. |
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Nickel
Thickness: Not less than 0.0001" |
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The
gold (from a cyanide solution) is to be deposited directly on the
nickel layer. |
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Gold
Thickness: Not less than 0.00005" on all functional surfaces. |
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Gold
Purity: Not less than 99.0% pure. |
About
solderability: MIL-G-45204 extract: Codeposited impurities can
make soldering more difficult, and for this reason high purity gold coatings
should be used for those applications. Excellent solderability is best
achieved when the gold thickness is between 0.00005 and 0.0001 inch.
About
Undercoating: MIL-G-45204 extract: a) Unless otherwise specified,
gold over silver underplate combinations should be excluded from electronics
hardware (3.4). b) When gold is applied to a copper rich surface such
as brass, bronze, or beryllium copper, an antidiffusion underplate such
as nickel should also be applied (3.4).
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