Gold Plating is a specialized electrochemical process that deposits a thin layer of gold onto a substrate, usually over a “nickel strike” or copper base. In the aerospace, medical, and telecommunications industries is specified because it is the only metal that offers total reliability in extreme environments. Because gold is a “noble” metal, it does not react with oxygen, meaning it never tarnishes or corrodes. In industrial applications, gold is usually categorized into two types:

Soft Gold (99.9% purity): Used for wire bonding and high-temperature applications.
Hard Gold: Contains a small amount of cobalt or nickel (approx. 0.1%) to increase the hardness and wear resistance of the surface.

Best Industries:

Performance Types:

Best Materials:

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Key Advantages: Contact Reliability and Reflectivity

Gold is the ultimate “insurance policy” for critical systems.

Corrosion Immunity: Gold will not form an oxide layer. This ensures that electrical contact is instantaneous and perfect, even after years of storage in humid or salty environments.
Low Contact Resistance: It provides a very low and stable electrical resistance, which is vital for low-voltage signals in sensors and microprocessors.
Infrared Reflectivity: Gold is highly efficient at reflecting infrared radiation (heat). This makes it essential for thermal shielding in spacecraft and satellites.
Solderability: It provides an excellent surface for soldering, particularly in micro-electronics.

The Role of Underplating

Gold Plating almost always requires an underplate:

Nickel Underplate: This is critical. Without a nickel barrier, the base copper or brass can “migrate” through the gold layer to the surface, where it will tarnish. The nickel acts as a fence to keep the gold pure.
Thinness (Flash vs. Heavy): “Gold Flash” is a very thin layer (approx. 3–5 micro-inches) used for basic protection. “Heavy Gold” (30–50+ micro-inches) is used for high-cycle connectors that will be plugged and unplugged hundreds of times.

Specifications

Specification	Comments
MIL-G-45204
Type I	99.7% gold min.
Type II	99.0% gold min.
Type III	99.9% gold min.
Class 00	0.00002″ min. – Grade A = 90 Knoop max
Class 0	0.00003″ min. – Grade B = 91-129 Knoop
Class 1	0.00005″ min. – Grade C = 130-200 Knoop
Class 2	0.00010″ min. – Grade D = above 200 knoop
Class 3	0.00020″ min.
Class 4	0.00030″ min.
Class 5	0.00050″ min.
Class 6	0.00150″ min.

Industry Applications

Gold is a critical material in high-stakes engineering where failure is not an option:

Aerospace: Used on the visors of astronaut helmets and the thermal blankets of satellites to reflect solar radiation.
Medical Electronics: Used for internal implants and diagnostic sensors because gold is “biocompatible” and will not react with the human body.
Telecommunications: High-speed connectors, fiber-optic components, and 5G infrastructure rely on gold for signal integrity.
Defense: Missile guidance systems and trigger mechanisms use gold to ensure they function perfectly even after decades of being “on the shelf.”

Finish Comparison

	Gold Plating	Silver Plating	Copper Plating
Primary Goal	Reliability / Tarnish-Free	Maximum Conductivity	Conductive Underplating
Corrosion Defense	Highest (Immune)	Moderate (Tarnishes)	Low (Oxidizes)
Cost	Highest	Moderate	Lowest
Wear Resistance	Moderate (Hard Gold)	Low (Soft)	Low
Main Industry	Aerospace / Semiconductors	RF / High-Power Audio	PCBs / Automotive / Industrial

Gold Plating
Primary Goal	Reliability / Tarnish-Free
Corrosion Defense	Highest (Immune)
Cost	Highest
Wear Resistance	Moderate (Hard Gold)
Main Industry	Aerospace / Semiconductors

Silver Plating
Primary Goal	Maximum Conductivity
Corrosion Defense	Moderate (Tarnishes)
Cost	Moderate
Wear Resistance	Low (Soft)
Main Industry	RF / High-Power Audio

Copper Plating
Primary Goal	Conductive Underplating
Corrosion Defense	Low (Oxidizes)
Cost	Lowest
Wear Resistance	Low
Main Industry	PCBs / Automotive / Industrial

Why Choose One Over the Other?

Gold Plating:
The “Reliability” Choice

As noted, gold is the ultimate choice for critical connections and harsh environments. Because gold is chemically inert, it does not oxidize or tarnish. This ensures that even after years of exposure to air or moisture, the electrical resistance remains stable. However, gold is expensive and relatively soft, so it is often alloyed with small amounts of cobalt or nickel (Hard Gold) to improve its durability against mechanical wear.

Best for: Semiconductor components, medical devices (non-magnetic), and “mission-critical” aerospace connectors where failure is not an option.

Silver Plating:
The “Performance” Choice

Silver is the king of conductivity—it actually conducts electricity better than gold or copper. It is the go-to for high-power applications because it generates the least amount of heat. The trade-off is that silver tarnishes (forming silver sulfide) when exposed to sulfur in the air. While silver oxide is still somewhat conductive, the tarnish can be an aesthetic issue and can slightly affect sensitive high-frequency signals.

Best for: High-power audio equipment, RF (Radio Frequency) components, and electric vehicle (EV) charging terminals.

Copper Plating:
The “Foundation” Choice

Copper is the most cost-effective of the three and offers excellent thermal and electrical conductivity. However, copper oxidizes very quickly in open air, turning green or brown and losing its ability to be easily soldered. Because of its excellent “throwing power” (the ability to coat evenly), it is most often used as an underplate to improve the adhesion and thickness of a final layer of gold or silver.

Best for: Printed circuit boards (PCBs), automotive wiring, and as a base layer for more expensive precious metal finishes.

A Note on "Porosity"

Because gold is so expensive, engineers try to make the layer as thin as possible. However, if the gold is too thin, it becomes porous. This allows moisture to seep through the gold and attack the nickel or copper underneath, causing “green spots” to appear on a gold surface. High-quality aerospace specifications require a porosity test (like a nitric acid vapor test) to ensure the gold layer is a solid, protective seal.

Gold Plating