PCB Plating Thickness: Copper, Nickel and Gold Explained

The Numbers That Decide Whether a Board Lasts

Plating thickness is one of the least visible specifications on a circuit board and one of the most consequential. A copper layer a few micrometres too thin raises the resistance of every via on the board and reduces the number of thermal cycles it can survive. A nickel layer outside its window lets copper diffuse into the gold above it. A gold layer specified generously where it is not needed adds cost without adding performance.

Three metals do the work, and each has a defined role: copper carries the current and connects the layers, nickel acts as a barrier and a hard surface, and gold provides corrosion resistance and reliable contact.

Two Ways to Deposit Metal

Plating happens by one of two mechanisms. Electroplating uses an electric current to deposit metal onto a conductive surface, and it is used for via copper, nickel plating and hard gold on connector contacts. Electroless plating deposits metal through a chemical reaction without current, and it is used for the thin initial copper layer in the holes and for the electroless nickel immersion gold finish on the surface.

Both processes are used on the same board in sequence, and together they determine whether the finished product meets its thickness specification and its reliability requirement. The process control behind them is part of the wider fabrication discipline described in our PCB manufacturing notes.

Why Thickness Matters

Four performance characteristics depend directly on the numbers.

• Electrical conduction. Copper thickness determines the resistance of the circuit. Too thin, and resistance rises along with the heat generated in the conductor.
• Mechanical strength. The copper on a via wall is what holds the connection together through thermal cycling. A thin wall cracks, and a cracked barrel is an intermittent fault that is difficult to find and usually appears in the field.
• Corrosion resistance. The nickel and gold layers protect the copper beneath from oxidation and environmental attack, and the protection only works if the layers are continuous and adequately thick.
• Solderability. The surface plating determines how well the pad wets, which affects the yield of every surface mount assembly operation performed on the board. Our notes on PCBA testing describe how that reliability is verified.

Copper Thickness

Copper appears in two forms on a board, and confusing them is a common source of specification error. Copper foil is the laminated conductor, and its thickness is quoted in ounces, where one ounce is roughly thirty five micrometres. Plated copper is the metal deposited on the hole walls, and its thickness is quoted directly in micrometres.

The typical ranges are as follows. Inner layer foil runs from half an ounce to two ounces. Outer layer foil runs from one to three ounces. Via plating runs from twenty to twenty five micrometres, and the industry minimum is generally twenty micrometres for reliable layer to layer connection.

The two add together. A one ounce foil, at thirty five micrometres, with twenty to twenty five micrometres of plating on top, produces the final copper structure of the board. Where the design needs more current capacity or better thermal performance, thicker plating and heavier foil are used, and both increase cost and process difficulty. Heavier constructions are described in our notes on heavy copper PCB designs.

Nickel Thickness

Nickel appears in surface finishes as a barrier layer between copper and gold. In an electroless nickel immersion gold finish, the nickel layer is typically three to six micrometres thick, and it performs four functions: it prevents the copper beneath from diffusing into the gold layer, which would degrade the surface; it provides hardness; it improves corrosion resistance; and it improves wear resistance, which matters where a surface will be contacted repeatedly. Nickel plating is used across consumer, industrial and automotive electronics, and it is the layer that gives the finish its mechanical character.

Gold Thickness

Gold is specified in two very different ways depending on what the surface has to do.

ENIG gold is an extremely thin layer, typically 0.05 to 0.1 micrometres, deposited over the nickel. Because it is so thin it does not add significant cost, and it is used on solder pads, ball grid array pads and the pads of high density packages, where its purpose is to keep the underlying nickel solderable rather than to provide a durable contact surface.

Hard gold plating is much thicker, typically 0.5 to 2 micrometres, and is used for connector contacts and edge fingers. Its advantage is wear resistance: a hard gold surface tolerates repeated insertion cycles while holding a stable contact resistance and a long connection life. The cost rises steeply with thickness, and gold plating has the largest cost impact of any plating step in the process, so it should be applied only where the contact function requires it.

Standards and Measurement

Two methods verify what has been deposited. X-ray fluorescence is non-destructive, fast and accurate enough for routine control, and it is used to measure the thickness of gold and nickel layers on the finished board. Microsectioning, where a sample is cut, mounted and examined under a microscope, gives the precise measurement of via wall copper and the complete layer structure in cross section, and it is the method used to demonstrate compliance with IPC requirements. A board specification is only meaningful if one of these methods is used to confirm it, which is why plating results belong in the qualification record of any serious quality management programme.

How Thickness Affects Performance

Three performance areas depend on the plating specification. In high current applications, from power modules to electric vehicle controllers and industrial supplies, thicker copper raises the current carrying capacity and lowers the loss in the conductor. In signal integrity, uniform plating reduces impedance variation along a trace, which is what high frequency boards, 5G equipment and radio frequency circuits need in order to hold their characteristics. In thermal behaviour, thicker copper spreads heat away from hot devices more effectively, reducing the temperature rise and the associated failure risk.

Requirements by Industry

The specification tightens as the consequences of failure rise. Consumer electronics typically use standard copper plating with an ENIG finish. Automotive electronics require greater via reliability, which means tighter control of hole plating thickness. Medical devices impose strict plating quality control because the product may be implanted or used in a critical care application. And aerospace programmes apply the strictest thickness and inspection requirements of all, because the equipment cannot be serviced. Our overview of PCB capabilities sets out how those requirements map onto process capability.

What Moves the Final Thickness

Four manufacturing variables decide the result. Current density determines the deposition rate, but a higher rate tends to reduce uniformity, particularly in the centre of a long hole. Bath chemistry affects the deposition characteristics directly. The board design itself matters, since dense via patterns and complex routing change the current distribution during plating and can produce thicker and thinner regions across the panel. And the equipment sets the achievable consistency, with automated plating lines holding tighter control than manual operations.

Cost

As a 2026 reference, standard copper plating is normally included in the base board price. Heavy copper plating adds roughly 20 to 120 dollars per batch. An electroless nickel immersion gold finish costs about 0.03 to 0.12 dollars per square inch. Hard gold plating ranges from 80 to 400 dollars, and it dominates the plating cost of any board that uses it, because it is the only step where precious metal thickness is a direct cost driver. Specifying the thickness each function actually needs, rather than the maximum available, is the most effective way to control that cost.

Frequently Asked Questions

What is the standard plating thickness on a PCB? Via copper is typically twenty to twenty five micrometres, ENIG nickel three to six micrometres, and ENIG gold 0.05 to 0.1 micrometres.

What is the minimum via copper thickness? Most fabricators treat twenty micrometres as the minimum for a reliable layer to layer connection.

Why is hard gold thicker than ENIG gold? Because hard gold is a contact surface that must resist repeated insertion, while ENIG gold only has to keep the nickel beneath it solderable.

How is plating thickness measured? X-ray fluorescence for non-destructive routine measurement, and microsectioning for precise via wall and layer measurements.

Does thicker plating always help? Thicker copper improves current capacity, thermal behaviour and via reliability, but it costs more and is harder to control. Specify what the design needs.

Conclusion

PCB plating thickness is a set of numbers that translate directly into reliability. Copper on the via wall decides whether the connection survives thermal cycling, nickel protects the copper and gives the finish its hardness, and gold provides either a solderable surface or a durable contact depending on how thick it is. Specify each layer against the function it performs, verify it with X-ray fluorescence or microsection, and resist the temptation to add gold thickness where it buys nothing. The result is a board that meets its reliability requirement at a cost that reflects actual need.