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.
MIL-G-45204
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 |
