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Gold Plating

Electroplating & electroless plating · Electrolytic bath

Gold plating supplies tarnish-free, low-resistance contact surfaces and decorative color.

CNC machiningSheet metalHigh cost $$$$Conductive
Quote a part with Gold plateCompare electroplating & electroless plating
Gold Plating on a machined part

What is Gold plate?

ASTM B488 defines purity, hardness, and thickness classes for engineering gold.

How it works

Parts are cleaned, activated, and usually nickel underplated to block copper diffusion. Direct current deposits pure or alloy-hardened gold from a controlled electrolyte. Selective rack, brush, or reel-to-reel methods confine precious metal to functional areas. Current density still drives edge buildup and recess thinning, so contact-zone thickness must be measured locally. Cobalt or nickel additions harden connector gold, while high-purity soft gold is reserved for wire bonding and similarly sensitive interfaces.

Why specify it

  • Does not form insulating oxide in service
  • 0.5–5 µm covers decorative through durable contact classes
  • Very low contact resistance
  • Nickel underplate limits copper diffusion

Where it falls short

  • High material cost
  • Thin soft gold wears rapidly under sliding contact
  • Porous deposits can expose reactive underlayers
  • Nickel underplate may be prohibited in wire-bonding systems

Gold plate at a glance

Gold plate is strongest on cosmetic quality (92 of 100), at a high cost.

Corrosion protectionGood68 / 100
Surface hardnessFair39 / 100
Cosmetic qualityExcellent92 / 100
LubricityFair40 / 100
Relative costHigh96 / 100
CorrosionHardnessCosmeticLubricityEconomy

Each score is 0–100 against every finish in this catalog. Corrosion comes from salt-spray life (ASTM B117, log scale) and hardness from the finish layer's Vickers or pencil hardness; cosmetic, lubricity and cost are FabDigit's engineering assessment. Economy on the radar is the inverse of cost.

Gold plate key numbers

Typical values from the governing specifications and shop practice; bars are this finish against the highest value among electroplating & electroless plating finishes.

Thickness0.5–5 µm0.02–0.2 mil
Hardness60–200 HV
Thickness
0.5–1.25 µm for light-duty contacts; 1.25–2.5 µm or more for durable separable contacts
Hardness
60–200 HV — Soft high-purity gold is at the low end; cobalt- or nickel-hardened contact gold is higher.
Corrosion (salt spray)
— — Gold itself does not corrode, but 0.1–2.5 µm deposits are porous; protection of the base metal comes from the nickel underplate and the pore count (ASTM B735), not from the gold. Specified for contact resistance and solderability, not as a barrier coating.
Electrical
Conductive
Colours
  • gold
Appearance
Bright yellow gold; shade varies with purity and hardening alloy.

Where Gold plate sits among all finishes

Surface hardness (Vickers, log scale) against corrosion protection (salt-spray hours, log scale) for every coating FabDigit offers, one cloud per finish group. Gold plate is highlighted; hover a dot for its name or open the full map.

02550751000255075100Corrosion protection (0–100)Surface hardness (HV, log scale, 0–100)Plating — 19 finishesHard coatings — 17 finishesAnodize & conversion — 8 finishesPaint & powder — 7 finisheshard, low corrosion protectionhard and protectiveprotective, softsoft, little protectionType II anodize — corrosion 71, hardness 54BSA anodize — corrosion 71, hardness 52Type I anodize — corrosion 71, hardness 49Hard anodize — corrosion 71, hardness 61PTFE hard anodize — corrosion 71, hardness 61Nitriding — corrosion 55, hardness 73PEO — corrosion 70, hardness 74Sherardizing — corrosion 83, hardness 56Brass plate — corrosion 35, hardness 44Bronze plate — corrosion 40, hardness 49Cadmium plate — corrosion 70, hardness 26Copper plate — corrosion 32, hardness 39Decorative chrome — corrosion 64, hardness 71Electroless copper — corrosion 20, hardness 41Electroless nickel — corrosion 70, hardness 68Nickel plate — corrosion 51, hardness 55Hard chrome — corrosion 40, hardness 73Hot-dip zinc — corrosion 90, hardness 42Nickel-PTFE — corrosion 72, hardness 57Silver plate — corrosion 55, hardness 39Solder plate — corrosion 42, hardness 9Tin plate — corrosion 34, hardness 0Zinc plate — corrosion 60, hardness 30Zinc-nickel — corrosion 86, hardness 60Cerakote — corrosion 83, hardness 27E-coat — corrosion 83, hardness 15Epoxy coat — corrosion 83, hardness 15Powder coat — corrosion 83, hardness 14Wet paint — corrosion 59, hardness 10AlCrN PVD — corrosion 58, hardness 93AlTiN PVD — corrosion 52, hardness 94CrN PVD — corrosion 62, hardness 83DLC — corrosion 55, hardness 93MoS2 PVD — corrosion 20, hardness 26TiAlN PVD — corrosion 50, hardness 93TiCN PVD — corrosion 40, hardness 92TiB2 PVD — corrosion 40, hardness 94TiN PVD — corrosion 45, hardness 87WC/C PVD — corrosion 48, hardness 77ZrN PVD — corrosion 52, hardness 90CVD alumina — corrosion 70, hardness 85CVD TiCN — corrosion 38, hardness 92CVD TiN — corrosion 45, hardness 87Multilayer CVD — corrosion 62, hardness 88HVOF coating — corrosion 78, hardness 77Plasma spray — corrosion 60, hardness 68Plastic chrome — corrosion 72, hardness 71Electroless plastic — corrosion 58, hardness 39Clear coat — corrosion 20, hardness 12Soft-touch — corrosion 20, hardness 5PLATINGHARD COATINGSANODIZE & CONVERSIONPAINT & POWDERSilver plateTin plateType II anodizePowder coatZinc plateZinc-nickelHard chromeDLCTiN PVDCadmium plateE-coatCerakoteWet paintHot-dip zincNitridingHVOF coatingGold plate — corrosion 68, hardness 39Gold plate
02550751000255075100Corrosion protection (0–100)Surface hardness (HV, log scale, 0–100)Plating — 19 finishesHard coatings — 17 finishesAnodize & conversion — 8 finishesPaint & powder — 7 finishesType II anodize — corrosion 71, hardness 54BSA anodize — corrosion 71, hardness 52Type I anodize — corrosion 71, hardness 49Hard anodize — corrosion 71, hardness 61PTFE hard anodize — corrosion 71, hardness 61Nitriding — corrosion 55, hardness 73PEO — corrosion 70, hardness 74Sherardizing — corrosion 83, hardness 56Brass plate — corrosion 35, hardness 44Bronze plate — corrosion 40, hardness 49Cadmium plate — corrosion 70, hardness 26Copper plate — corrosion 32, hardness 39Decorative chrome — corrosion 64, hardness 71Electroless copper — corrosion 20, hardness 41Electroless nickel — corrosion 70, hardness 68Nickel plate — corrosion 51, hardness 55Hard chrome — corrosion 40, hardness 73Hot-dip zinc — corrosion 90, hardness 42Nickel-PTFE — corrosion 72, hardness 57Silver plate — corrosion 55, hardness 39Solder plate — corrosion 42, hardness 9Tin plate — corrosion 34, hardness 0Zinc plate — corrosion 60, hardness 30Zinc-nickel — corrosion 86, hardness 60Cerakote — corrosion 83, hardness 27E-coat — corrosion 83, hardness 15Epoxy coat — corrosion 83, hardness 15Powder coat — corrosion 83, hardness 14Wet paint — corrosion 59, hardness 10AlCrN PVD — corrosion 58, hardness 93AlTiN PVD — corrosion 52, hardness 94CrN PVD — corrosion 62, hardness 83DLC — corrosion 55, hardness 93MoS2 PVD — corrosion 20, hardness 26TiAlN PVD — corrosion 50, hardness 93TiCN PVD — corrosion 40, hardness 92TiB2 PVD — corrosion 40, hardness 94TiN PVD — corrosion 45, hardness 87WC/C PVD — corrosion 48, hardness 77ZrN PVD — corrosion 52, hardness 90CVD alumina — corrosion 70, hardness 85CVD TiCN — corrosion 38, hardness 92CVD TiN — corrosion 45, hardness 87Multilayer CVD — corrosion 62, hardness 88HVOF coating — corrosion 78, hardness 77Plasma spray — corrosion 60, hardness 68Plastic chrome — corrosion 72, hardness 71Electroless plastic — corrosion 58, hardness 39Clear coat — corrosion 20, hardness 12Soft-touch — corrosion 20, hardness 5PLATINGHARD COATINGSANODIZE & CONVERSIONPAINT & POWDERSilver plateTin platePowder coatZinc plateGold plate — corrosion 68, hardness 39Gold plate
Anodize & conversionPlatingPaint & powderHard coatings

Specifications for Gold plate

The documents a drawing cites to define this finish, with the Type / Class rows that apply. Each links to a page explaining the standard.

StandardType / ClassThicknessRequirement / testStatus
ASTM B488
Standard Specification for Electrodeposited Coatings of Gold for Engineering Uses · ASTM
Type I—At least 99.7% gold; compatible with Codes A, B, or C. · Gold purity and Knoop hardness.Active
Type II—At least 99.0% gold; compatible with Codes B, C, or D. · Gold purity and Knoop hardness.
Type III—At least 99.9% gold; soft Code A deposit. · Gold purity and Knoop hardness.
Codes A–D—A ≤90, B 91–129, C 130–200, D >200 HK25. · Knoop hardness at 25 gf.
Thickness 0.25–5.00.3–5 µmCommon minimum thickness designations of 0.25, 0.50, 0.75, 1.0, 1.25, 2.5, and 5.0 µm. · Local coating thickness.

Drawing call-out

GOLD PLATE PER ASTM B488, TYPE II, GRADE C, CLASS 1.25, 1.25 µm MIN OVER 2.5 µm MIN NICKEL UNDERPLATE ON CONTACT AREA ONLY

Pattern: GOLD PLATE PER ASTM B488, TYPE <I|II|III>, CODE <A|B|C|D>, THICKNESS <µm>, UNDERPLATE <SYSTEM>

Which materials take Gold plate?

Verdict per material family, with the grades that behave differently. Each family links to its datasheets in the material library.

Material familyVerdictNotes
Brass
YesCommon decorative and electrical substrate after cleaning.
Copper Alloy
YesCommon over nickel underplate.
Nickel Alloy
YesCommon barrier and support substrate.
Aluminum
With careRequires zincate and multilayer underplating.
DMLS / SLM
With careMetal AM parts can be plated after density, powder, and porosity review.
Stainless Steel
With careRequires activation and strike.
Steel
With careRequires copper and/or nickel underplates.
Zinc Alloy
With careDie castings need a protective strike before acid baths.
Magnesium Alloy
LimitedHighly reactive; needs a qualified pretreatment and is rarely plated this way.
Polymer
LimitedOnly plateable resins after etch, catalyst, and electroless metallization.
SLA
LimitedOnly if the resin is qualified for metallization; most SLA parts are not.
Titanium
LimitedPossible only with specialized activation; not a routine job-shop sequence.
FDM
NoFused-filament polymers are not a standard plating substrate.
MJF
NoPorous nylon powder-bed parts are not a standard plating substrate.
SLS
NoPorous nylon powder-bed parts are not a standard plating substrate.

How Gold plate is applied, and what it does to the part

  1. 1Clean
  2. 2Activate
  3. 3Nickel underplate unless prohibited
  4. 4Gold plate selectively
  5. 5Rinse
  6. 6Porosity or thickness test
  7. 7Package against abrasion
DimensionsInclude nickel or copper underplate in total buildup; measure gold on the specified contact surface.
Build-up per side0.5–5 µm — Add underplate thickness separately; selective plating minimizes nonfunctional coverage.
MaskingUsually needed. Selective masking is normally essential to control precious-metal area and protect dimensions.
ElectricalConductive
AppearanceBright yellow gold; shade varies with purity and hardening alloy.
Added lead time4–8 working days on top of the bare part

Design rules for Gold plate

What to decide on the drawing before the part goes to the finisher.

  1. Define the selective plating boundary.Gold outside the contact zone adds cost without function.
  2. Specify gold type and hardness code.Soft and hard gold have different wear and bonding behavior.
  3. Specify underplate material and thickness.Copper diffusion can reach thin gold and degrade the surface.
  4. Avoid sharp contact edges.Current crowding wastes gold and increases mating wear.

Gold plate versus the alternatives

Finishes engineers weigh against Gold plate, and when each wins.

FinishCorrosionHardnessCosmeticCostThicknessChoose it when
Gold plate
this page
683992$$$$0.5–5 µm—
Silver Plating
Gold plate vs Silver Plating →
553972$$$$5–20 µmwhen high-current conductivity outweighs tarnish resistance
Tin Plating
Gold plate vs Tin Plating →
34045$$3–15 µmwhen a low-cost solderable termination is sufficient
CorrosionHardnessCosmeticLubricityEconomy
Gold plateSilver Plating

The radar overlays Gold plate with Silver Plating, its most common alternative — chosen when high-current conductivity outweighs tarnish resistance. Scores in the table are 0–100 across every finish in the catalog.

Cost, lead time and compliance

Relative cost

Gold Plating is a high-cost finish ($$$$): more expensive than about 98 % of the finishes FabDigit quotes.

Finishing is priced per part with a lot minimum, from FabDigit's own China-side rates cross-checked against US job-shop pricing. The exact figure appears on the instant quote once the part is uploaded.

Lead time and compliance

Added lead time4–8 working days
RoHSCompliant
NotesGold deposits are RoHS compatible; bath chemistry and nickel underlayers require occupational and wastewater controls.

What Gold plate is used for

  • High-reliability connectors
  • Sensor contacts
  • RF hardware
  • Medical contacts
  • Decorative hardware

Gold plate — frequently asked

how thick is gold plating on contacts

Light-duty contacts often use 0.5–1.25 µm, while durable separable contacts commonly use 1.25–2.5 µm or more. ASTM B488 class and local contact-zone thickness should be stated.

hard gold vs soft gold plating

Soft gold is high purity and suits wire bonding or low-force applications. Hard gold includes small cobalt or nickel additions, reaches roughly 130–200 HV, and better resists connector wear.

why nickel under gold plating

A nickel layer blocks copper diffusion and provides a harder support under 0.5–5 µm of gold. Without it, copper can migrate to the surface and oxidize.

gold plating vs silver plating

Gold remains tarnish-free and is preferred for low-level reliable signals. Silver is more conductive and less costly for high-current use, but sulfur tarnish must be managed.

can gold plate aluminum

Yes, through an aluminum-specific zincate and nickel or copper underplate sequence. The total buildup is much greater than the 0.5–5 µm gold top layer.