Gold Plating

Gold plating is considered as one of the most ancient coating techniques and processes. Gold plating is considered a noble metal, therefore resistant to corrosion and oxidation in moist air. Gold plating enriches the metal with various elements such as electrical conductivity, esthetical features, reflectivity and solderability.

Gold Plating- Usage

Gold is often used in the electronics and electrical industries. It is used mainly for the purpose of providing a corrosion-resistant electrically conductive layer, specifically in semiconductors, electric conductors and printed circuit boards.

Gold plating is also commonly used in the jewelry industry, religious articles and other decorative items.

Gold Plating Types

Gold plating is usually classified by the hardness of the material; hard gold is typically used for engineering applications and in the electronics industry. Soft hard is usually used solely for soldering.


Classification by Type- Plating composition

Type Gold Content (Minimum)
Type I 99.7%
Type II 99.0%
Type III 99.9%

Classification by Knoop- Grade

Knoop- plating hardness level, measured by a specific and designed device

Grade Knoop Hardness
Grade A 90 MAX
Grade B 91-129 (including)
Grade C 130-200 (including)
Grade D 201 and above (including)

Relation between plating composition and plating hardness (Knoop)

Type Grade – Hardness level
Type I A, B, C
Type II B, C, D
Type III A

The integration of plating composition and hardness presents a variety of hardness levels of the different gold compositions.

For example:
Type I gold content contains 99.7% gold and can be coated with A, B and C hardness level. This means that it is possible to obtain KNOOP levels that vary
between the values of 0 – 200.

Hardness values are marked as HK.

Classification by Class- plating thickness

Class Minimum Thickness (inch) Minimum Thickness (micron)
Class 00 0.00002 0.51
Class 0 0.00003 0.762
Class 1 0.00005 1.27
Class 2 0.00010 2.54
Class 3 0.00020 5.08
Class 4 0.0003 7.62
Class 5 0.0005 12.7
Class 6 0.0015 38.1

ASTM B 488

Classification by Type- Plating composition

Type % Minimum Gold
Type I 99.7
Type II 99.0
Type III 99.9

Classified by ASTM code

(Knoop hardness is marked as standard HK25)

ASTM Code Knoop Hardness
Code A 90 max
Code B 91-129 (including)
Code C 130-200 (including)
Code D Above 201 (including)

Integration between hardness and plating composition*

Grade Type
A, B, C Type I
B, C, D Type II
A Type III

* See explanation for table at standard MIL-G-45204

Micron thickness according to Class

Class Minimum micron thickness
0.25 0.25
0.5 0.5
0.75 0.75
1.0 1.0
1.25 1.25
2.5 2.5
5.0 5.0
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