ASTM B488
Standard Specification for Electrodeposited Coatings of Gold for Engineering Uses
Specifies electrodeposited engineering gold by purity type, Knoop-hardness code, and minimum thickness.
What ASTM B488 specifies
ASTM B488 classifies engineering gold in three independent dimensions. Type I is at least 99.7% gold, Type II at least 99.0%, and Type III at least 99.9%. Hardness Codes A, B, C, and D are at most 90, 91–129, 130–200, and over 200 HK25. Thickness is called out directly in micrometres, with common classes 0.25 through 5.0 µm. Buyers should state type, code, thickness, significant contact surfaces, underplate material and thickness, and any porosity, solderability, ductility, or embrittlement testing. Gold thickness must be measured locally in the functional zone.
ASTM B488 types and classes
Every designation the document defines, with the thickness it requires and the tests it imposes.
| Designation | Meaning | Thickness | Requirement / test |
|---|---|---|---|
Type I | At least 99.7% gold; compatible with Codes A, B, or C. | — | Gold purity and Knoop hardness. |
Type II | At least 99.0% gold; compatible with Codes B, C, or D. | — | Gold purity and Knoop hardness. |
Type III | At least 99.9% gold; soft Code A deposit. | — | Gold purity and Knoop hardness. |
Codes A–D | A ≤90, B 91–129, C 130–200, D >200 HK25. | — | Knoop hardness at 25 gf. |
Thickness 0.25–5.0 | Common minimum thickness designations of 0.25, 0.50, 0.75, 1.0, 1.25, 2.5, and 5.0 µm. | 0.3–5 µm 0.01–0.2 mil | Local coating thickness. |
Tests and the drawing call-out
Tests the document imposes
- Gold purity
- Knoop hardness
- Coating thickness or mass per area
- Adhesion
- Porosity when specified
- Solderability or ductility when specified
How to cite it
Drawing call-out
GOLD PLATE PER ASTM B488, TYPE <I|II|III>, CODE <A|B|C|D>, THICKNESS <µm>, UNDERPLATE <SYSTEM>Angle brackets mark the choices the drawing must make; every finish page shows a completed example.
Finishes specified to ASTM B488
ASTM B488 — frequently asked
What is soft gold under ASTM B488?
Type III Code A is at least 99.9% gold and no more than 90 HK25. It is commonly selected for wire bonding and similar sensitive interfaces.
What thickness should a connector use?
The standard offers common minimums from 0.25 to 5.0 µm, but contact force, cycles, porosity, and environment determine selection. State the functional contact zone.
Is a nickel underplate automatic?
No. It is often needed as a diffusion barrier, especially over copper alloys, but the purchaser should state its material and thickness.
ASTM B488 is copyrighted by ASTM International. This page explains the document so a drawing can be read; it does not reproduce the standard. Purchase the current edition from the publisher. Official source ↗