Is QQ-S-365 still valid?

No: it was cancelled on 2 February 2001 and its named replacement is ASTM B700. If the drawing still cites it, the current reference is ASTM B700, but the codes must be reread: in QQ-S-365 Type is the appearance and Grade says whether there is a chromate treatment, in B700 Type is the purity and Grade the finish.

What is the difference between Type, Grade and Class in ASTM B700?

Type is the minimum silver purity: 1 ≥ 99.9 %, 2 ≥ 99.0 %, 3 ≥ 98.0 %. Grade is the finish: A matte, B bright from brighteners, C bright from mechanical or chemical polishing, D semi-bright. Class says whether there is a chromate anti-tarnish treatment: N without, S with. Thickness has no classes: it is written on the drawing.

How much silver does a sliding contact need?

The drawing decides: the standards do not set a thickness. As a guide, the ASTM B700 appendix gives 2.5 µm for connectors with limited wear and at least 40 µm for severe wear; QQ-S-365 suggested 13 to 250 µm for contacts, depending on pressure and friction. For sliding contacts, hard silver, up to about 200 HV, resists wear better. We plate from 1 to 250 µm.

Copper or nickel under the silver?

Both, depending on the part. Nickel is the barrier against copper-silver diffusion and is needed at high temperatures (AMS 2410 and 2411; QQ-S-365 requires it above 149 °C) and on steel, zinc and aluminium. If required, we carry out the 502–518 °C bake of AMS 2410 ourselves. Copper is the strike and levelling layer, with the copper strike and low bake of AMS 2412. On copper and brass, silver can also go on directly.

Pure silver or hard silver?

Pure silver, about 80–110 HV, has the highest conductivity, is soft and solderable. Hard silver, up to about 200 HV, resists wear: it is for sliding contacts, such as high mating-cycle connectors, slip rings and brushes.

Do you perform ASTM B809 or the thioacetamide test?

They are tests, not silver plating specifications. ISO 4538 is the thioacetamide corrosion test, to assess anti-tarnish protection. ASTM B809 is sulphur vapour porosity testing for non-tarnishing coatings, such as gold, nickel and tin, applied over silver or copper: it is not used on silver as the top layer. If the drawing cites them, let's discuss it before the order.

What does the certificate contain?

Conformance of the lot to the required standard, the result of the adhesion test and the thickness measurements for the lot, taken by X-ray.

How do I request a quote?

Through the contact page, with the drawing, the standard and the callout as it appears on the drawing, and the quantity. We plate on racks up to 2 m and in barrels for small parts, in Cormano (Milan).

Silver plating to specification

We silver plate connectors, contacts, slip rings and brushes, busbars and fasteners to the specifications called out on drawings: UNI EN ISO 4521, ASTM B700 and SAE AMS 2410, 2411 and 2412. Pure or hard silver, over copper or nickel, from 1 to 250 µm, with a certificate for every lot.

ISO 4521
ASTM B700
AMS 2410
AMS 2411
AMS 2412

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01Standards
02Callout
03Thickness
04Pure or hard
05Underplate
06Tarnish
07Testing
08Quote

thicknesses to spec: 1–250 µm
silver in the AMS specs: ≥ 99.9 %
from pure to hard: ≈ 80–200 HV

01Genealogy

The standards, and where they come from

Five standards in force and one cancelled specification that still turns up on older drawings. The arrows show what superseded what; the AMS family splits by strike and bake.

ISO
ISO 4521:1985
1985
First edition
The first edition, superseded together with ISO 4522.
UNI EN ISO 4521
2008 · confirmed in 2023
Metallic and other inorganic coatings — Electrodeposited silver and silver alloy coatings for engineering purposes — Specification and test methods
The international standard for electrical, electronic and engineering uses, adopted in Italy as UNI EN ISO 4521. Thickness is the minimum local thickness in micrometres on the significant surface; the minimum silver purity is set by the purchaser and appears in the designation on the drawing.
Open the standard
USA
QQ-S-365
rev. D, 1985
Cancelled 2 Feb 2001
US federal specification, cancelled on 2 February 2001 with ASTM B700 named as its replacement. It still turns up on older drawings: its Type and Grade codes do not mean what they mean in B700.
ASTM B700
latest edition B700-26
Standard Specification for Electrodeposited Coatings of Silver for Engineering Use
The American specification for engineering silver plating, at least 98 % silver. Type gives the purity, Grade the finish, Class whether there is a chromate anti-tarnish treatment. Thickness is written on the drawing; the non-mandatory appendix gives typical values.
Open the standard
SAE AMS
Nickel strike · high bake
SAE AMS 2410
aerospace
Plating, Silver, Nickel Strike, High Bake
Nickel strike, silver ≥ 99.9 %, post-plating bake at 502–518 °C: if the standard or the drawing calls for it, we bake the parts ourselves. For bearing and anti-galling surfaces on steels and metals that can take the high bake.
Open the standard
SAE AMS 2411
aerospace
Plating, Silver, for High Temperature Applications
Nickel strike (13 µm max), silver ≥ 99.9 % without brighteners. Anti-galling for bolts and nuts up to 760 °C.
Open the standard
Copper strike · low bake
SAE AMS 2412
aerospace
Plating, Silver, Copper Strike, Low Bake
Copper strike (13 µm max; omitted on copper and copper alloys), silver ≥ 99.9 %. For materials that a high bake would damage.
Open the standard

02On the drawing

Reading a callout

An ISO callout is a designation: base metal, underplate, silver with its purity, and thickness, in a row separated by slashes. An ASTM callout is a list: the standard, Type, Grade, Class and minimum thickness. Hover over or tap the parts to read them one by one.

ISO 4521 designation

ISO 4521 -

1
Febase metal
Fe for iron and steel, Cu for copper and its alloys, Al for aluminium.
2
Ni5nickel underplate, 5 µm
The underplate metal and its thickness: Cu5 would be copper.
3
Ag(99,8)silver, minimum purity 99.8 %
The purity is set by the purchaser and goes in brackets.
4
10minimum local thickness, 10 µm
It applies on the significant surface.

Example from the standard. A heat treatment goes on the same line, Fe/SR(200)3/Cu5/Ag(98,8)15/ER(190)12: SR is stress relief before plating, ER hydrogen embrittlement relief after, in degrees and hours. On copper the designation may have no underplate: Cu/Ag(98,8)20.

ASTM B700 callout

1
ASTM B700the standard
The specification the deposit must meet.
2
Type 1purity ≥ 99.9 %
Type 2 ≥ 99.0 %, Type 3 ≥ 98.0 %.
3
Grade Amatte finish
B bright from brighteners, C bright from mechanical or chemical polishing, D semi-bright.
4
Class Nno chromate treatment
Class S: with chromate anti-tarnish treatment.
5
10 µm minminimum thickness
The standard has no thickness classes: it is written on the drawing.

Typical usage form, not an example from the standard.

The pitfall

Type and Grade do not mean the same thing

In QQ-S-365 the same words mean something else. An old drawing that calls for “Type II, Grade A” is asking for a semi-bright finish with chromate treatment, not a matte 99.0 % silver.

Type
QQ-S-365 (cancelled)
Appearance: I matte, II semi-bright, III bright
ASTM B700
Purity: 1 ≥ 99.9 %, 2 ≥ 99.0 %, 3 ≥ 98.0 %
Grade
QQ-S-365 (cancelled)
Chromate treatment: A with, B without
ASTM B700
Finish: A matte, B bright, C bright by polishing, D semi-bright
Class
QQ-S-365 (cancelled)
Does not exist
ASTM B700
Chromate treatment: N without, S with

Code	QQ-S-365 (cancelled)	ASTM B700
Type	Appearance: I matte, II semi-bright, III bright	Purity: 1 ≥ 99.9 %, 2 ≥ 99.0 %, 3 ≥ 98.0 %
Grade	Chromate treatment: A with, B without	Finish: A matte, B bright, C bright by polishing, D semi-bright
Class	Does not exist	Chromate treatment: N without, S with

03The gauge

From 1 to 250 µm

No silver standard has thickness classes: the drawing decides. The standards do say what a thickness is for, though: the non-mandatory appendix of ASTM B700 and the guidance in QQ-S-365. Here they are, lined up on a ruler.

We cover the whole range, from 1 to 250 µm, on racks and in barrels.

logarithmic scale · 1–250 µm

Given in QQ-S-365, cancelled

Default thickness on functional surfaces

0.0005″: what QQ-S-365 assumes if the drawing says nothing else.

04Pure or hard

The indent tells the hardness

We plate pure silver and hard silver. Hardness is measured with a Vickers indenter: under the same load, the harder the metal, the smaller the indent.

Pure silver

≈ 80–110 HV

Highest conductivity, soft, solderable.

For where conductivity and solderability matter.

Hard silver

up to ≈ 200 HV

Wear-resistant: for sliding contacts.

For high mating-cycle connectors, slip rings, brushes.

Indents drawn to true proportion for 110 and 200 HV: the diagonal goes as 1/√HV. Hardness values are indicative.

Purity in the standards

Type and purity

ASTM B700 classifies it in three Types; the AMS require silver ≥ 99.9 %; in ISO 4521 the purchaser sets it and it goes in the designation.

Type
1
≥ 99.9 %
silver, minimum
Type
2
≥ 99.0 %
silver, minimum
Type
3
≥ 98.0 %
silver, minimum

Finish in ASTM B700

Grade and finish

Four finishes, from matte to bright.

GradeA
matte
GradeB
bright from brighteners
GradeC
bright from mechanical or chemical polishing
GradeD
semi-bright

05Under the silver

Copper or nickel

We choose the underplate to suit the part and the callout: we plate both.

Strike and levelling layer. It is the copper strike with the low bake of AMS 2412. Mind the temperature: without nickel underneath, silver on copper must not exceed 149 °C in continuous service, because copper and silver diffuse into each other.

Where the standards call for it

AMS 2412
ISO 4521: Cu5

On copper and brass, silver can also go on directly, with no underplate: ISO 4521 writes it Cu/Ag.

AgSilver

thickness per drawing

CuCopper

above 149 °C copper migrates into the silver

Fe · Cu · AlBase metal

steel, copper and its alloys, aluminium

06The air

Silver tarnishes, passivation stops it

Silver reacts with the sulphur in the air and forms sulphides: first it turns yellow, then dark. Our anti-tarnish passivation is chromium-free and solvent-free, and keeps the silver white.

Without passivation

tarnishes

With chromium-free passivation

stays white

Even when tarnished, silver conducts: conductivity remains excellent.

Class N and Class S

Class N: without chromate treatment
Class S: with chromate treatment
Our passivation: chromium-free and solvent-free, on request

Our passivation contains no chromium: it is not Class S. If you want it, ask for it on the order, alongside the callout.

07In the lab

Testing and the certificate

On every lot we measure thickness and test adhesion, and the certificate reports the results.

Thickness by X-ray

X-ray fluorescence (XRF) with a Fischerscope spectrometer: it measures thickness without touching the part.

Adhesion

With the methods of the referenced standard:

01Bend
02Scribe or cut
03Oven heat test

Two codes found on drawings

They are tests, not silver plating specifications.

ISO 4538 ·: Thioacetamide (TAA) corrosion test, to assess anti-tarnish protection.
ASTM B809 ·: Sulphur vapour porosity, for non-tarnishing coatings (gold, nickel, tin) applied over silver or copper. It is not used on silver as the top layer.

Certificate of conformance

The lot tag

Each shipment comes with a certificate of conformance stating three things:

08The quote

What to send us

Three things, and we reply with a quote or with the questions we need answered to prepare one.

On racks up to 2 m and in barrels for small parts, in Cormano (Milan).

The quote · Supergalvanica

01
The drawing
With the significant surfaces, if it shows them.
02
Standard and callout
As they appear on the drawing: ISO designation or Type, Grade, Class and thickness; the underplate, if specified.
03
The quantity
An estimate is fine.

info@supergalvanica.it

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FAQ

Frequently asked questions

Both, depending on the part. Nickel is the barrier against copper-silver diffusion and is needed at high temperatures (AMS 2410 and 2411; QQ-S-365 requires it above 149 °C) and on steel, zinc and aluminium. If required, we carry out the 502–518 °C bake of AMS 2410 ourselves. Copper is the strike and levelling layer, with the copper strike and low bake of AMS 2412. On copper and brass, silver can also go on directly.

For anything else, write to us: info@supergalvanica.it

Request a Quote

Silver plating to specification

ISO 4521:1985

UNI EN ISO 4521

QQ-S-365

ASTM B700

SAE AMS 2410

SAE AMS 2411

SAE AMS 2412

Pure silver

Hard silver

Class N and Class S

Thickness by X-ray

Adhesion

The drawing

Standard and callout

The quantity