| Callout | Requirement |
| Type I | 99.7% pure |
| Type II | 99.0% pure |
| Type III | 99.9% pure |
| Grade A | less than 90 HK25 |
| Grade B | 91-129 HK25 |
| Grade C | 130-200 HK25 |
| Grade D | greater than 200 HK25 |
| Class 00 | 20 µin |
| Class 0 | 30 µin |
| Class 1 | 50 µin |
| Class 2 | 100 µin |
| Class 3 | 200 µin |
| Class 4 | 300 µin |
| Class 5 | 500 µin |
| Class 6 | 1500 µin |
| Include Class and/or thickness on print | |
MIL-G-45204C was reinstated as of June 2007 after being temporarily superseded by AMS2422 and/or ASTM B488. MIL-DTL-45204 then superseded MIL-G-45204. MIL-DTL-45204D is the active revision. If you are familiar with MIL-G-45204, and you are considering plating to MIL-DTL-45204, note that ¶ 4.4.3.1.1.2 requires hardness specimens to be plated and tests to be done monthly for a stable process and weekly to prove stability. Note that MIL-STD-105 sampling has been replaced with MIL-STD-1916. Also read ¶ 3.4 for newer restrictions on strikes and underplating. The appendices of the ASTM B488 specification have more background information on the function of the various types of underplating.
For the normal specification of "Gold Plate per MIL-DTL-45204" or "Gold Plate per MIL-G-45204" for all types and grades, nickel underplate is used as a diffusion barrier when plating copper or copper alloys, since gold will readily diffuse into copper. If your application will be negatively impacted by the reduced electrical conductivity of nickel or the magnetic properties of nickel, you should specify, on print or purchase order, that nickel underplating should not be used, and you should ensure that the gold thickness will be sufficient for your application. A typical print note would read "Gold Plate per MIL-G-45204 Type III, Grade A - NO nickel underplate". If your basis material is copper or a copper alloy, it does not hurt to specifically request the nickel underplate (e.g. "Gold Plate per MIL-G-45204 Type I, Grade C - WITH nickel underplate". These are not decisions that should be left to a plating shop.
It is quite difficult to achieve some combinations of Type and Grade. Normally cobalt and/or nickel is used to harden the plating to achieve the Grade C or D hardness, and it is very difficult to simultaneously achieve the 99.9% purity with the Grade C or D hardness; although, there are some sulfite-based commercial chemistries able to achieve Type III, Grade C using arsenous acid to brighten and harden the deposit. Normally the Type III (Grade A) gold is plated from a cyanide bath. The common callouts are "Gold Plate per MIL-DTL-45204 Type I, Grade C" for alloyed, hard gold and "Gold Plate per MIL-DTL-45204 Type III, Grade A" for pure, soft gold.
Neither the ASTM B488 nor the MIL-DTL-45204 specifications list bath impurities; however, we have listed them because they are crucial to successful plating results. If bath impurities are not tested and controlled, the shop will eventually fail the periodic purity tests and will then be in a recall situation.
Bath Testing
none specified
Coupon Testing - monthly
¶ 4.4.3: plate purity
¶ 4.4.3.1.1: plate hardness
Coupon/Part Testing - per lot
¶ 4.4.3: coating thickness
¶ 4.4.3: adhesion
¶ 4.4.3: heat resistance
¶ 4.4.3: solderability
¶ 4.4.3: embrittlement - if specified by contract
Impurities - recommended bi-weekly
to maintain soft gold purity
Note: Co or Ni may be hardener
< 10 ppm Pb
< 20 ppm Cr
< 20 ppm Co
< 30 ppm Cu
< 50 ppm Fe
< 100 ppm Ni
Electroplated Gold
AMS2422
| Specification | Requirement |
| Purity | Plate purity > 99.0% |
| Thickness | Specified on print but not less than 50 µin |
| Hardness | No requirement |
AMS2422E as revised in 2007 is the current revision available from SAE International. AMS2422 specifies a minimum plate purity of 99.0%, and therefore allows plating of any Mil-Spec type from Type I, Grade D to Type III, Grade A. So, if you don’t care whether the gold is hard or soft, pure or alloyed, this spec should cover your needs. The solderability test requires a solder pot dip and, unlike the Mil spec, a periodic corrosion test is required.
Bath Testing
¶ 4.4.3: processor to specify
frequency and analysis methods
and establish periodic test plan
Coupon Testing - periodic
¶ 3.4.4: plate purity
¶ 3.4.5: corrosion resistance
Coupon/Part Testing - per lot
¶ 3.4.1: coating thickness
¶ 3.4.2: adhesion bend test
¶ 3.4.3: solderability test
Electroplated Gold
ASTM B488
| Callout | Requirement |
| Type I | 99.7% pure |
| Type II | 99.0% pure |
| Type III | 99.9% pure |
| Code A | less than 90 HK25 |
| Code B | 91-129 HK25 |
| Code C | 130-200 HK25 |
| Code D | greater than 200 HK25 |
| Class 0.25 | 0.25 µm (9.84 µin) |
| Class 0.5 | 0.5 µm (19.67 µin) |
| Class 0.75 | 0.75 µm (29.53 µin) |
| Class 1.0 | 1.0 µm (39.37 µin) |
| Class 1.25 | 1.25 µm (49.21 µin) |
| Class 2.5 | 2.5 µm (98.43 µin) |
| Class 5.0 | 5.0 µm (196.85 µin) |
| Include Class and/or thickness on print | |
ASTM B488-11(2011) is available from ASTM. There was a time when the ASTM B488 Type and Code call outs did not align with the MIL-G-45204 call outs, and plating shops should be very careful to ensure that a print calling for Gold Plate per ASTM B488 Type III Code A is really asking for 99.9% gold, since Type 1 Code A was the 99.9% gold call out for quite some time before ASTM decided to change back to the old specifications. The other common callout is Gold Plate per ASTM B488 Type I Code C for alloyed, hard gold, and this call out was Type 3 Code C in the ASTM B488-95 specification. Similar confusion exists in the hardness callouts: the B488-95 specification used a wider range for Code B (90-200 HK25), while the B488-11 specification has Code B for 130-200 HK25, which aligns with MIL-G-45204 Grade B. Note also that the adhesion bake specification is 325 ± 25 °F for 30 min which is not the same as the MIL-DTL-45204. Check the notes on MIL-G-45204 for more general information on gold plating.
Bath Testing
¶ 8.1: processor to use SPC
¶ X5.3.3: bath must be kept
in spec by regular additions
and/or analysis and additions
Coupon Testing - periodic
¶ X5.3.4: plate purity
¶ X5.3.4: plate hardness
Coupon/Part Testing - per lot
¶ X5.3.4: coating thickness
¶ X5.3.4: porosity
Impurities - bi-weekly
to maintain soft gold purity
Note: Co or Ni may be hardener
< 10 ppm Pb
< 20 ppm Cr
< 20 ppm Co
< 30 ppm Cu
< 50 ppm Fe
< 100 ppm Ni
MIL-R-46085
| Callout | Requirement |
| Class 1 | minimum 2 µin |
| Class 2 | minimum 10 µin |
| Class 3 | minimum 100 µin |
| Class 4 | minimum 20 µin |
| Class 5 | minimum 250 µin |
MIL-R-46085B is the current revision.
Bath Testing
no bath parameters or tests
mentioned in specification
Coupon Testing - periodic
no periodic coupon tests
mentioned in specification
Coupon/Part Testing - per lot
¶ 4.5.1: coating thickness
¶ 4.5.2: adhesion
¶ 4.4.3: reflectivity
¶ 4.4.4: embrittlement
FED QQ-S-365
| Callout | Requirement |
| Type I | Matte finish |
| Type II | Semi-bright finish |
| Type III | Bright finish |
| Grade A | Chromate (anti-tarnish) |
| Grade B | As-Plated |
| Note: newer specifications switch meanings of Type and Grade call outs. | |
The QQ-S-365 specification was cancelled at QQ-S-365D revision, but any silver shop should know the spec, and machine shops should pay attention to the Intended Use section when machining threaded fasteners. Unfortunately, the superseding ASTM B700 spec did not follow the same reference call outs. Silver Plate per QQ-S-365 Type I Grade A/B is a matte finish, Silver Plate per QQ-S-365 Type II Grade A/B is a semi-bright finish, and Silver Plate per QQ-S-365 Type III Grade A/B is a bright finish. The Grade is used to specify chromate anti-tarnish post-plating. The ASTM B700 uses the Type reference to specify plate purity, the Grade reference to specify the finish, and the anti-tarnish treatment is specified by the Class reference. "Type I" or "Type II" silver needs to be qualified by the referenced specification.
Bath Testing
¶ 4.3.1: maintain permanent
record of bath analysis/additions
and job processing records
Coupon Testing - periodic
¶ 4.5.6: embrittlement
Coupon/Part Testing - per lot
¶ 3.4.1: coating thickness
¶ 3.4.2: adhesion
¶ 3.4.3: surface finish
¶ 3.4.4: solderability
ASTM B700
| Callout | Requirement |
| Type I | 99.9% pure |
| Type II | 99.0% pure |
| Type III | 98.0% pure |
| Grade A | Matte finish |
| Grade B | Bright (brighteners) |
| Grade C | Bright (polished) |
| Grade D | Semi-bright (brighteners) |
| Class N | As-plated (no chromate) |
| Class S | Chromate (anti-tarnish) |
ASTM B700-08 is the current revision. Beware: the older QQ-S-365 specification used the Type reference to specify the finish (matte, semi-bright, bright) and the Grade was used to specify chromate anti-tarnish post-plating. ASTM B700 uses the Type reference to specify plate purity, the Grade reference to specify the finish, and the anti-tarnish treatment is specified by the Class reference. When you mention "Type 1" silver to a plating shop, you have a 50/50 chance of communicating. The correct print note for 99.9% pure silver with no brighteners is "Silver Plate per ASTM B700 Type 1, Grade A" while the 98% pure silver without brighteners would be specified by "Silver Plate per ASTM B700 Type 3, Grade A.
no bath parameters or tests
mentioned in specification
Coupon Testing - periodic
¶ 8.6: plate purity
¶ 8.7: plate hardness
¶ 8.8: reflectance
¶ 8.9: resistivity
Coupon/Part Testing - per lot
¶ 8.2: coating thickness
¶ 8.3: adhesion
¶ 8.5: solderability
AMS2410
| Specification | Requirement |
| Purity | Plate purity > 99.9% |
| Thickness | Specified on print but not less than 50 µin |
| Chromate | None allowed |
AMS2410K is available from SAE International. The correct print note would read "Silver Plate per AMS2410".
¶ 4.2.2: periodic testing of
cleaning and plating solutions to
ensure specification conformance
Coupon Testing - periodic
¶ 3.4.2: plate purity
Coupon/Part Testing - per lot
¶ 3.4.1: coating thickness
¶ 3.4.3: adhesion bend test
¶ 3.5: general quality
AMS2411
| Specification | Requirement |
| Purity | Plate purity > 99.9% |
| Thickness | Specified on print |
| Chromate | None allowed |
AMS2411G is the latest revision available from SAE International. A nickel underplate and post-plate heat treatment is specified. The correct print note would read "Silver Plate per AMS2411".
¶ 4.2.2: periodic testing of
cleaning and plating solutions to
ensure specification conformance
Coupon Testing - periodic
¶ 3.4.2: plate purity
¶ 3.4.4: embrittlement
Coupon/Part Testing - per lot
¶ 3.4.1: coating thickness
¶ 3.4.3:adhesion test
after bake per ¶ 3.4.3
inspection for blisters
shear or chisel test
¶ 3.5: general quality
AMS2412
| Specification | Requirement |
| Purity | Plate purity > 99.9% |
| Thickness | Specified on print |
| Chromate | None allowed |
AMS2412H is the current revision available from SAE International. The copper underplate protects the base material when the silver plating is heated after plating. The correct print note would read "Silver Plate per AMS2412".
¶ 4.2.2: periodic testing of
cleaning and plating solutions to
ensure specification conformance
Coupon Testing - periodic
¶ 3.4.2: plate purity
¶ 3.4.4: embrittlement
Coupon/Part Testing - per lot
¶ 3.4.1: coating thickness
¶ 3.4.3:adhesion test
¶ 3.5: general quality