Electroplated Gold

MIL-DTL-45204

Callout Requirement
Type I99.7% pure
Type II99.0% pure
Type III99.9% pure
Grade Aless than 90 HK25
Grade B91-129 HK25
Grade C130-200 HK25
Grade Dgreater than 200 HK25
Class 0020 µin
Class 030 µin
Class 150 µin
Class 2100 µin
Class 3200 µin
Class 4300 µin
Class 5500 µin
Class 61500 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MIL-G-45204C was reinstated as of June 2007 after being temporarily superseded by AMS2422 and/or ASTM B488. MIL-DTL-45204 then superseded MIL-G-45204.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
PurityPlate purity > 99.0%
ThicknessSpecified on print
but not less than 50 µin
HardnessNo 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 I99.7% pure
Type II99.0% pure
Type III99.9% pure
Code Aless than 90 HK25
Code B91-129 HK25
Code C130-200 HK25
Code Dgreater than 200 HK25
Class 0.250.25 µm (9.84 µin)
Class 0.50.5 µm (19.67 µin)
Class 0.750.75 µm (29.53 µin)
Class 1.01.0 µm (39.37 µin)
Class 1.251.25 µm (49.21 µin)
Class 2.52.5 µm (98.43 µin)
Class 5.05.0 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

Electroplated Rhodium

MIL-R-46085

Callout Requirement
Class 1minimum 2 µin
Class 2minimum 10 µin
Class 3minimum 100 µin
Class 4minimum 20 µin
Class 5minimum 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

Electroplated Silver

FED QQ-S-365

Callout Requirement
Type IMatte finish
Type IISemi-bright finish
Type IIIBright finish
Grade AChromate (anti-tarnish)
Grade BAs-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

Electroplated Silver

ASTM B700

Callout Requirement
Type I99.9% pure
Type II99.0% pure
Type III98.0% pure
Grade AMatte finish
Grade BBright (brighteners)
Grade CBright (polished)
Grade DSemi-bright (brighteners)
Class NAs-plated (no chromate)
Class SChromate (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.

Bath Testing
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

Electroplated Silver

AMS2410

Specification Requirement
PurityPlate purity > 99.9%
ThicknessSpecified on print
but not less than 50 µin
ChromateNone allowed

AMS2410K is available from SAE International. The correct print note would read "Silver Plate per AMS2410".

Bath Testing
¶ 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

Electroplated Silver - High Temp

AMS2411

Specification Requirement
PurityPlate purity > 99.9%
ThicknessSpecified on print
ChromateNone 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".

Bath Testing
¶ 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

Electroplated Silver - Copper Strike

AMS2412

Specification Requirement
PurityPlate purity > 99.9%
ThicknessSpecified on print
ChromateNone 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".

Bath Testing
¶ 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