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Specs for Gold
Here are the applicable specifications:
MIL-G-45204C
Yellow to orange color depending on proprietary process used. Will range from matte to bright finish. Good corrosion resistance, and has high tarnish resistance. Provides a low contact resistance, and is an excellent conductor. Has excellent solderability. If the hardness grade for the gold is not specified, Type I shall be furnished at hardness Grade A, and Type II shall be furnished at hardness Grade C. For soldering, a thin, high purity soft gold coating is preferred. A minimum thickness of .000050 inch and a maximum thickness of .00010 inch shall be plated.
Unless otherwise specified, gold over silver underplate combinations shall be excluded from electronics hardware. Silver or copper plus silver may not be used as an underplate unless required by item specification. When gold is applied to brass, bronze or beryllium copper or a copper plate or strike an antidiffusion underplate such as nickel shall be applied.
| Type Class | Thickness | Comments |
| Type 1 | 99.7% gold minimum (Grades A, B, or C) | |
| Type II | 99.0% gold minimum (Grades B, C, or D) | |
| Type III | 99.9% gold minimum (Grade A only) | |
| Grade A | Aluminum alloy, heat-treatable, processed to improve the adhesion of the nickel deposit. | |
| Grade A | 90 Knoop maximum | |
| Grade B | 91-129 Knoop | |
| Grade C | 130-200 Knoop | |
| Grade D | 201 Knoop and over | |
| Class 00 | .00002" min | |
| Class 0 | .00003" min | |
| Class 1 | .00005" min | |
| Class 2 | .00010" min | |
| Class 3 | .00020" min | |
| Class 4 | .00030" min | |
| Class 5 | .00050" min | |
| Class 6 | .00150" min |
Yellow to orange color depending on proprietary process used. Ranges from matte to bright finish depending on basis material and type, grade and class of gold used. Brightness of underplating will also affect appearance. Gold plating improves solderability, electrical conductivity, corrosion resistance, performance and appearance of electronic and electrical parts. Finished product shall be smooth, continuous, adherent to basis metal, bright of a color associated with high quality 24-carat gold. Should be free of most pinholes, porosity, blistering, nodules, pits and indicators of burning and other imperfections detrimental to usage of plating. No evidence of spotting-in or double plating is acceptable. Some staining or discoloration acceptable, provided that it does not affect solderability.
Post Treatment. To remove hydrogen embrittlement. Best in circulating air oven within 4 hours of plating the part.
33-45 HRC: Heated to 375°F ±25 for 3 hours. Carburized parts which will decrease in hardness or be negatively affected by heating to 375°F shall be heated to 275°F ±25 for 5 hours.
46 HRC: Heated to 275°F ±25 for 23 hours.
Purity: 99%
| Type Class | Thickness | Comments |
| Copper strike | not less than 0.00010" | Electrodeposited from copper cyanide, alkaline noncyanide, except omit copper strike if part is less than 15% zinc and is copper or a copper alloy. |
| Nickel strike | not less than 0.00010" | Electrodeposited from a Watt's type nickel solution or nickel chloride or nickel sulfumate solution I n all surfaces which gold plating is specified directly onto the nickel strike over the copper alloy or copper strike. |
| Gold plating | not less than 0.00005" | In all surfaces which gold plating is specified directly onto the nickel strike. |
| Gold plating (to improve solderability) |
not greater than 0.00010" | To prevent the formation of the gold/tin intermetallic which results in brittle solder joints. |
