Supergalvanica provides electrolytic gold plating as a subcontractor to the four specifications most often called out on drawings of connectors, electrical contacts and electronic components. We cover every thickness class the standards define, and every lot ships with a certificate of conformance.
Standards covered
MIL and ASTM classes covered
Class minimum thicknesses
01 / The standards
The US Department of Defense specification for electrodeposited gold. MIL‑DTL‑45204 superseded MIL‑G‑45204, which many drawings and purchase specifications still cite: we plate to either one. Thickness is defined by eight classes, from 00 to 6.
Open the standardThe American specification for engineering gold plating, from electrical contacts to electronic components. Thickness is selected by class, each one named after its minimum thickness in micrometres, and the standard prescribes thickness and adhesion testing of the coating.
Open the standardThe international standard for electrodeposited gold and gold alloy coatings, adopted in Europe and Italy as UNI EN ISO 27874. It sets out how the coating is specified on the drawing, the minimum thickness on significant surfaces and the methods used to verify thickness and adhesion.
Open the standardThe SAE International aerospace material specification for electrodeposited gold on contacts and electrical parts. It defines the requirements for the coating and the inspections used to accept each lot.
Open the standard02 / How to read a callout
On the drawing, gold plating is called out with a few codes: the standard and, in MIL‑DTL‑45204 and ASTM B488, the Type for gold purity, the Grade (Code in ASTM) for hardness and the Class for thickness. The three sections that follow explain how the standards classify each of the three.
Example callout
ASTM B488Type IICode CClass 1.25
A callout built for illustration in the form used with ASTM B488: it is not a quotation from the standard. MIL-DTL-45204 follows the same logic, with Type, Grade and Class.
03 / Thickness classes
The standards do not set a single thickness: the designer chooses it for the application. Two standards express it as a class, two write it on the drawing or the order. Below, how each one does it.
Thicknesses are minimums, measured on the significant surfaces, as defined by the standard or shown on the drawing.
The standard gives minimum thicknesses in inches: micrometres are the conversion. MIL‑G‑45204 uses the same classes.
Shared axis in micrometres, logarithmic scale
04 / Purity and hardness
Besides thickness, MIL‑DTL‑45204 and ASTM B488 classify the deposit by gold purity and by hardness, and both use the same scale: three types and four grades. Not every combination is allowed.
As with thickness, this is how the standards classify the deposit: the type and grade are chosen by whoever designs the part, and they belong in the callout.
04.1
The Type states the minimum gold content of the deposit, as a percentage.
Three purity types. The order of the designations does not follow purity: Type III is the purest, Type II the least. MIL‑G‑45204 has the same types.
Shared axis: gold content in percent, from the type's minimum upwards
04.2
The Grade, which ASTM B488 calls Code, states the Knoop hardness of the deposit in four bands: from A, the softest, to D, the hardest.
Four Knoop hardness grades. If the order does not state the Grade, the standard assigns Grade A to Type I and Grade C to Type II.
Shared axis: Knoop hardness; band D is open-ended
04.3
Purity and hardness do not combine freely: each Type allows only some grades. MIL‑DTL‑45204 and ASTM B488 allow the same combinations.
| Type (gold, minimum) | Grade / Code (Knoop hardness) | |||
|---|---|---|---|---|
| A≤ 90 | B91–129 | C130–200 | D> 200 | |
| Type I≥ 99.7 % | Allowed combination. Grade that MIL‑DTL‑45204 assigns if the order does not state one | Allowed combination | Allowed combination | Not allowed |
| Type II≥ 99.0 % | Not allowed | Allowed combination | Allowed combination. Grade that MIL‑DTL‑45204 assigns if the order does not state one | Allowed combination |
| Type III≥ 99.9 % | Allowed combination | Not allowed | Not allowed | Not allowed |
05 / The process
Coating cross-section
class or drawing value
We gold plate over a nickel underplate. On copper, brass and copper alloys there is always nickel under the gold: it acts as a barrier between the base metal and the gold.
Rack
Parts hung one by one
Barrel
Small parts in bulk
We gold plate on racks and in barrels, the latter for small parts. Typical applications are connectors, electrical contacts, slip rings and electronic components.
06 / Testing the coating
We verify the coating with the methods the standards call for.
Measured by X-ray fluorescence (XRF), a non-destructive measurement.
XRF
With the methods the standards provide, including:
Bend
Scribe
Heat test
the part is heated and then checked for any lifting of the coating
07 / The certificate
Each shipment comes with a certificate of conformance stating:
Conformance of the lot to the required standard
The result of the adhesion test
The thickness measurements for the lot
08 / How to request a quote
To prepare a quote we need three things:
With the significant surfaces, if it shows them.
As it appears on the drawing, with the class or the required thickness.
An estimate is fine.
FAQ
Yes. MIL‑DTL‑45204 superseded MIL‑G‑45204, but many drawings still carry the old designation: we plate to either one. Just copy the specification callout from the drawing onto the purchase order.
In MIL‑DTL‑45204 and ASTM B488 the Type is the minimum gold purity (I ≥ 99.7%, II ≥ 99.0%, III ≥ 99.9%), the Grade, Code in ASTM, is the Knoop hardness (A ≤ 90, B 91–129, C 130–200, D above 200) and the Class is the minimum thickness. Not every combination is allowed: Type I goes with A, B or C, Type II with B, C or D, Type III only with A.
Every class in the standards: for MIL‑DTL‑45204 from class 00 (0.51 µm) to class 6 (38.1 µm), for ASTM B488 every class, from 0.25 to 5 µm. The thickness of each lot is measured by X-ray fluorescence and reported on the certificate.
We gold plate over a nickel underplate. On copper, brass and copper alloys there is always nickel: it acts as a barrier between the base metal and the gold.
Those the standards provide, including bend, scribe and heat (bake) testing. The result is reported on the lot certificate.
Conformance of the lot to the required standard, the result of the adhesion test and the thickness measurements for the lot.
The part drawing, the specification callout with the class or the required thickness, and the quantity. You can send everything through the contact page.
