What the designations mean, and what to write on the print.
QQ-S-365 classifies by appearance only: Type I matte, Type II semi-bright, Type III bright. Grade covers the tarnish-resistant treatment — A carries it, B is as-plated. It sets no purity requirement. Revision D asked for 0.0005 in minimum on functionally necessary surfaces, 0.0010 in total on ferrous parts over an underplate.
ASTM B700 separates those ideas. Type is purity: 1 is 99.9 % minimum, 2 is 99.0 %, 3 is 98.0 %. Grade is appearance: A matte, B bright from brighteners, C bright by polishing, D semi-bright. Class is the chromate: N none, S treated. Thickness is stated separately, so a callout without it is incomplete.
QQ-S-365D was canceled on 2 February 2001. Notice 1 recommends ASTM B700 in its place, with a caution to evaluate it first. An old print can still be run as printed; new prints should cite B700.
Translation is mechanical: Type I to Grade A, Type II to Grade D, Type III to Grade B or C; Grade A to Class S, Grade B to Class N. Only purity is missing — for conductive or high-temperature service, choose Type 1.
No brighteners: the purest and most reliably solderable of the three, and common on aerospace hardware. See matte silver plating.
Denser and smoother than matte, with less brightener. Surface finish without a full brightener load. See semi-bright silver plating.
Hardest, lowest roughness — what RF designers want where current crowds into the skin depth, and best under wear. Costs solderability. See bright silver plating.
Tarnish. Silver reacts with airborne sulfur to form silver sulphide. The film is semiconducting, not insulating, so wiping and high-force contacts usually still conduct; it hurts solderability after storage and low-force static contacts.
Electrochemical migration. Under DC bias with moisture present, silver ionises at the anode and re-deposits as dendrites at the cathode until they bridge. On fine-pitch electronic hardware, silver belongs on shells and power conductors, not between closely spaced biased traces.
Diffusion. On copper and brass, copper diffuses through silver and oxidises at the surface, degrading contact resistance and solderability. The fix is a nickel underplate; copper is only ever an undercoat here, never the finish.
Embrittlement. Plating high-strength steel introduces hydrogen. Above roughly 180 ksi a post-plate relief bake is required; its temperature and duration belong on the print.
The SAE silver specs are scoped by process, not appearance — AMS 2410 nickel strike and high bake, AMS 2412 copper strike and low bake, AMS 2411 high temperature service. Strike and bake come with the callout.
| Designation | Sets | Values |
|---|---|---|
| Type | Minimum purity | I ≥ 99.70 %; II ≥ 99.00 %; III ≥ 99.90 % |
| Code | Knoop hardness, HK25 | A ≤ 90; B 91–129; C 130–200; D > 200 |
| Class | Minimum thickness, µm | 0.25, 0.50, 0.75, 1.0, 1.25, 2.5, 5.0 (about 10–200 µin) |
Gold Type III is the purest — the opposite of the silver convention in B700. Confirm the class list against your print’s revision.
Hard gold is gold co-deposited with cobalt, nickel or iron: roughly 99.0 % gold at 130–200 HK25, Code C, for separable contacts — pins, sockets, card edges, switch contacts. Soft gold is essentially pure, 99.9 % or better at 20–90 HK25, Code A, for wire bond pads, thermocompression and thermosonic joints, die attach and hermetic seals: the hardening elements in hard gold oxidise at bonding temperature and spoil the joint.
SAE AMS 2422 sets a minimum purity and requires a strike or flash underlayer rather than a hardness code. Confirm hardness separately when the surface wears.
ASTM B488 requires a nickel underplate before gold on copper and copper-alloy parts for every class except the heaviest, on the order of 1.2 µm minimum; 50 µin is the common target. Without it, copper diffuses through the gold at service temperature and surfaces as oxide. Thin gold is porous, and pores are where corrosion starts and creeps onto the contact face. A dense nickel layer plugs that path, levels the surface and carries contact load; sulfamate nickel where low stress matters.
Thickness is verified by X-ray fluorescence for routine control and cross-section microscopy as a referee method; coulometric and beta backscatter are also recognized. Porosity is checked by the ASTM methods B488 points to. Name the method and the measurement location on the print.
Plated area dominates cost, so plating the whole part when only the mating face needs gold is the most expensive decision on the print. Masking, controlled-depth immersion and defined bands put metal only where the function is. What else drives cost: a heavy thickness class where a thinner one over a proper barrier would do; blind holes that trap solution; thickness measured somewhere unreachable; geometry that will not rack without a fixture. The design guide covers racking and masking.
| Spec | Governs | Designations | Write on the print |
|---|---|---|---|
| QQ-S-365 (canceled 2001) | Silver appearance, tarnish treatment | Type I / II / III; Grade A or B | Legacy only; translate to B700 |
| ASTM B700 | Silver, engineering use | Type 1–3; Grade A–D; Class N or S | Type, Grade, Class, thickness, surfaces |
| AMS 2410 / 2411 / 2412 | Aerospace silver, by strike and bake | 2410 nickel strike/high bake; 2412 copper strike/low bake; 2411 high temperature | AMS number, thickness |
| ASTM B488 | Gold, engineering uses | Type I–III; Code A–D; class = minimum µm | Type, Code, class, surfaces, nickel min |
| AMS 2422 | Aerospace gold | Minimum purity plus required strike or flash | AMS number, thickness, hardness if it wears |
1. Legacy silver. “QQ-S-365 Type II Grade A” is semi-bright silver, tarnish-treated. Now write: Silver plate per ASTM B700, Type 1, Grade D, Class S, 0.0005 in minimum on surfaces indicated.
2. Separable contact. Gold per ASTM B488, Type II, Code C, class 1.25 on mating contact area only, over 1.25 µm minimum nickel. Balance of part nickel only.
3. Wire bond pad. Gold per ASTM B488, Type III, Code A, class 1.25 on bond pads, over 1.25 µm minimum nickel. Hard gold will not bond reliably.
Gold plating, bright silver and semi-bright silver run at the McAllen, Texas plant. Sulfamate nickel runs there too, so a precious metal over a nickel barrier is a single routing. Silver plating generally and matte silver plating have their own pages. Copper is used only as an undercoat, never a standalone finish.
Gleco has plated in Texas since 1979 and is family-owned. The quality system is AS9100D and ISO 9001:2015 certified, the AS9100D certificate covering three sites; the company is ITAR Registered, DFARS and RoHS compliant. See certifications and approvals.
Send the drawing with the callout on it. If it cites a canceled spec, or a type and grade that do not exist in the spec named, resolve that first.
Semi-bright silver with a tarnish-resistant treatment, normally a chromate. No purity is implied; QQ-S-365 does not specify it.
ASTM B700, as the cancellation notice recommends. Give a Type, Grade and Class, then state thickness and surfaces separately.
Under gold on copper alloy, yes — B488 requires it for every class except the heaviest, around 1.2 µm minimum.
It follows mating cycles, force and environment. About 1.25 µm (50 µin) of hard gold over nickel is common.
Silver sulphide from airborne sulfur — normal, not a defect. Chromate slows it without preventing it, so control storage if the part must solder later.
Hard gold, cobalt- or nickel-hardened at 130–200 HK25, for anything that mates or slides. Soft gold, 20–90 HK25, for wire bonding and hermetic seals.
Usually the largest cost lever on a contact part. Call out gold on the contact area only, dimensioned on the drawing.
Silver or gold, legacy federal spec or current ASTM. We will confirm the callout reads as you intend.
Precision metal finishing since 1979. Plating, anodizing, coatings and passivation from three Texas facilities.
Our paint, powder & Cerakote division: Gleco Paint & Powder Coating
Gleco Rowlett
2220 Grisham Drive
Rowlett, TX 75088
972-475-4300
Gleco McAllen
3800 W. Ursula Ave
McAllen, TX 78503
956-800-4069
