The thin metal coatings on a data centre’s power bars

Some of the metal supplying an AI data centre is measured in micrometres. Surface-finishing supplier Technic describes silver coatings around 2.5–5 micrometres thick on busbars: the rigid conductors that distribute electricity through power equipment. The coating serves a particularly important part of the journey—where current crosses from one component to another.[1][2]

Two flat bars pressed together do not make electrical contact across their entire overlap. The Copper Development Association’s engineering guide describes small conducting patches occupying roughly 1% of that area. Pressure brings those patches into contact. Their condition helps determine how readily current crosses the joint.[2]

A small resistance can make a concentrated heat source

Electrical resistance converts some of the passing power into heat. The relationship is P = I²R: heating power equals current squared multiplied by resistance. For a fixed resistance, doubling current produces four times as much heat.[2]

The last two rows show what a change at the interface can mean while the current stays the same. The extra ten watts are generated at the joint. Its temperature then depends on how effectively the surrounding metal and cooling conditions remove that heat. The calculation explains the incentive to preserve a good contact; it does not assign either resistance to a particular finish.

Each finish has a different job

Tin’s softness can be useful. Storm Power Components explains that it deforms under bolt pressure, increasing the real contact area. Its June design guide describes tin as a practical finish for mild to moderate environments, with good solderability. That same softness makes it easier to scratch and less suitable for sliding or abrasive contacts.[3]

Nickel provides a harder, more durable surface and can also form an underlayer beneath silver. Silver is selected when very low contact resistance and good performance at higher temperatures matter. Choosing a finish therefore involves the way parts are assembled, the environment around them and the movement they must tolerate.[3]

Silver has its own chemistry to manage. Sulfur-containing contamination can form a poorly conducting sulfide film. Technic uses an anti-tarnish treatment to protect the contact surface during exposure and ageing.[1]

The surface after ageing

Technic’s published test gives a concrete example. After eight hours of accelerated steam ageing, its table reports contact resistance of 7.827 milliohms for a cyanide-process silver sample, 7.388 milliohms for its cyanide-free silver sample, and 5.016 milliohms for the cyanide-free sample with electrolytic anti-tarnish treatment.[1]

Our calculation puts the treated sample about 32% below the otherwise untreated cyanide-free sample after that exposure. The supplier’s test supports a benefit from protecting the surface as it ages. It is a laboratory contact measurement; the page does not provide enough test detail to turn those values into the resistance or expected lifetime of an installed power joint.[1]

Plating also has to earn its place. The copper industry’s guide says sound copper-to-copper joints can work without it, and warns that a soft coating can flow at elevated temperature, reducing contact pressure. That is a reason to design the coating and joint together.[2]

The finish specification consequently belongs alongside decisions about bolts, soldering, welding and maintenance. Storm’s guide explicitly links those choices: a coating suitable for one assembly process may complicate another. The result has to remain a working electrical contact through the equipment’s service.[3]

The large copper bar and its microscopic surface are parts of the same power path. As designers fit more current into compact equipment, every additional ampere still has to cross those small patches of contact.

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