Metal dome is responsible for two critical functions: providing the crisp, tactile feedback users expect and, just as importantly, bridging an electrical circuit. The material of a metal dome is best understood as two parts: the base alloy that forms the dome's body and the plating that coats its surface.

Stainless Steel

The primary job of the dome's body is mechanical. It must be able to deform (snap) under pressure and then instantly return to its original shape, millions of times, without cracking, warping, or losing its spring force.

By an overwhelming margin, the industry standard base material for metal domes is stainless steel.

The most common alloy used is SUS 301. This is a "spring-temper" austenitic stainless steel.

Pros

Excellent Spring Properties: SUS 301 is prized for its high yield strength and elasticity. It can be work-hardened to a specific temper, allowing manufacturers to precisely define the "snap" force (actuation force) and ensure it remains consistent over a long life.

· high cycle life

Because of its durability, a well-made 301 stainless steel dome can typically endure one million to ten million actuations before failure, making it exceptionally robust.

· good corrosion resistance

As a stainless steel, it has an inherent resistance to rust and general environmental corrosion, which is vital for component longevity.

Cons

· high electrical resistance

While conductive, raw stainless steel is not a superior conductor like copper or gold. More importantly, it forms a passive, non-conductive chromium oxide layer on its surface. This oxide layer can create inconsistent or high contact resistance, making raw stainless steel domes unsuitable for low-voltage or low-current "dry circuit" applications.

While other alloys like SUS 304 exist, SUS 301's superior spring characteristics make it the definitive choice for the mechanical demands of a tactile dome.

Surface Treatment

To overcome the electrical limitations of raw stainless steel, metal domes are almost always plated with another material. This plating serves to lower contact resistance, protect against specific environmental factors, and ensure a reliable electrical connection every time the user presses the button.

Here is a comparison of the most common plating options.

1. Nickel (Ni) Plating

Nickel is the most common and cost-effective plating solution.

Pros

· durable & hard

Nickel plating provides a hard, wear-resistant surface, which helps maintain the dome's integrity over millions of cycles.

· good corrosion protection

It enhances the base steel's natural corrosion resistance.

· stable resistance

It provides a more stable and lower contact resistance than raw stainless steel, making it a reliable workhorse for a vast range of general-purpose applications.

· cost-effective

It adds minimal cost to the dome, keeping overall switch prices low.

Cons

· moderate contact resistance

While better than steel, nickel's contact resistance is still higher than that of silver or gold. It is generally not recommended for sensitive, low-voltage applications (typically below 5V).

2. Silver (Ag) Plating

Silver is used when low electrical resistance is a primary design concern.

Pros

· excellent conductivity

Silver has a much lower electrical resistance than nickel, making it a great choice for applications that demand a stronger, more reliable signal path.

Cons

· tarnishing (sulfidation)

Silver's primary drawback is its reactivity with sulfur compounds in the air (even in trace amounts). This reaction forms silver sulfide (tarnish), which is non-conductive and can dramatically increase contact resistance over time, leading to switch failure.

· environmental sensitivity

Because of this, silver-plated domes are a poor choice for switches used in industrial environments, near vehicle exhaust, or in any high-sulfur atmosphere unless the switch assembly is hermetically sealed.

3. Gold (Au) Plating

Gold is the premium, high-performance option for metal domes.

Pros

· extremely low contact resistance

Gold is an excellent conductor and, more importantly, it does not tarnish or oxidize. This means its contact resistance remains exceptionally low and stable over the entire life of the switch.

· corrosion-proof

It is virtually immune to all forms of environmental corrosion and chemical attack.

· ideal for "dry circuits"

Gold is the go-to material for low-voltage, low-current (micro-amp) applications, such as in medical devices or sensitive test equipment, where even a small amount of resistance from oxidation could prevent the signal from being detected.

Cons

· high cost

The only significant drawback of gold plating is its high material cost. This makes it prohibitive for many cost-sensitive consumer electronics, reserving it for high-reliability, mission-critical, or medical-grade applications where failure is not an option.