How Does a Metal Dome Work?
A metal dome (also called a snap dome or shrapnel) is a precision-stamped stainless steel disc that buckles under a specific force to create an audible click and electrical contact. It is the core component behind the tactile feel of almost every keypad, remote control, membrane switch and industrial panel. This article explains the working principle, force curve and material science behind metal domes.
1. Snap-Action Mechanism
When you press a key, force is applied to the top of the convex dome. Initially, the dome resists with increasing force while maintaining its curved shape. When the force reaches the rated actuation point (typically 100–500g for consumer electronics), the dome suddenly inverts - this is the "snap." The center touches the PCB contact below, closing the circuit. The inverted state produces the audible click and confirms the keystroke to the user. Releasing the pressure allows the dome to spring back to its original convex shape.
2. The Force-Displacement Curve
A metal dome's performance is defined by its force-displacement curve. The key parameters are:
- Actuation force (F1): The peak force at which the dome snaps over, typically 180g–3000g depending on size.
- Contact force (F2): The force needed to fully bottom out after the snap.
- Tactile ratio: (F1–F2) / F1 × 100%. A higher ratio means a crisper click. Standard domes offer 40–60%; high-tactile types reach 60–70%.
- Travel distance: Usually 0.2–0.6mm, determining how deep the key feels.
3. Why SUS301 Stainless Steel?
Most metal domes are stamped from SUS301 stainless steel, selected for its high yield strength, fatigue resistance and spring memory. Beryllium copper (BeCu) domes are also available for higher conductivity and lower resistance, but they cost more. The material gauge (typically 0.05–0.15mm) and dome geometry directly determine the force rating and cycle life.
Shanyo manufactures a wide range of snap domes in round, cross, triangle and square shapes. Our RCG series 4-leg tactile domes are popular for medical and industrial keypads requiring high tactile feedback.
4. Dome Life Cycle and Durability
| Dome Type | Typical Life Cycles | Application |
|---|---|---|
| Standard round dome | 100,000 – 1,000,000 | Remote controls, keypads |
| High-life (gold-plated) | 1,000,000 – 5,000,000 | Medical, industrial equipment |
| Cross / 4-leg dome | 500,000 – 2,000,000 | Walkie talkies, rugged devices |
5. Dome Arrays vs. Individual Domes
Individual domes can be manually placed on a PCB, but for volume production they are supplied as dome sheet arrays - multiple domes pre-attached to a PET film with adhesive on the bottom. This allows fast peel-and-place assembly by automation. Our mobile phone dome arrays and medical button dome arrays are manufactured on high-speed die bonders with 100% electrical testing.
Need a custom metal dome or dome array? Contact Shanyo for a free sample and technical consultation.
