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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.)

Type-I 99.7% gold minimum; hardness grade A, B, or C
For general-purpose, high-reliability electrical contacts, solderability, and wire wrap connections.
Type-II 99.0% gold minimum; hardness grade B, C, or D
A general-purpose, wear-resistant gold. It will not withstand high-temperature applications because the hardening agents in the gold coating will oxidize.
Type-III 99.9 % gold minimum; hardness grade A only

For semiconductor components, nuclear engineering, thermocompression bonding, and high-temperature application.

Hardness Grades: A 90 knoop, maximum
B 91-129 knoop, inclusive
C 130-200 knoop, inclusive
D 201 knoop, minimum

•Specification: ASTM B 488 Standard Specification for Electrodeposited Coatings of Gold for Engineering Uses

Type-I 99.7% gold minimum; hardness grade A, B, or C *
Type-II 99.0% gold minimum; hardness grade B, C, or D *
Type-III 99.9 % gold minimum; hardness grade A only *
Hardness Grades: A 90 knoop, maximum
B 90-200 knoop
C 130-200 knoop
D 201 knoop, minimum
  * 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

  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.
    Copper Thickness: Not less than 0.0001"
  A layer of nickel (from a Watt's or chloride solution) is required over the copper underplate or copper base material.
    Nickel Thickness: Not less than 0.0001"
  The gold (from a cyanide solution) is to be deposited directly on the nickel layer.
    Gold Thickness: Not less than 0.00005" on all functional surfaces.
   

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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