Tactile Switch Overview
A tactile switch, also known as a push-button switch, is referred to in English as a Tact Switch or touch Switch. It is typically identified by its external dimensions (e.g., 6 x 6 x 5 mm, representing length, width, and height).
As a type of electronic switch, it differs from common household wall switches in both application areas and structural function, hence its classification as an electronic component.
Classification and Structure
These switches are divided into two main types based on actuation method and mounting: press-actuated type (primarily through-hole components with larger volume) and surface-mount touch type (characterized by a low-profile, slim design).
The fundamental operation involves the actuator pressing down on a metal spring/dome, which makes contact with a stationary contact to establish an electrical connection.
Based on their electrical function, they can be categorized as Normally Open (NO), Normally Closed (NC), or Double-Action types. The terminal (pin) configurations commonly include 2-pin, 3-pin, 4-pin, and 5-pin versions.
Structurally, a tactile switch consists of a plastic base, metal terminals, a metal spring/dome, a metal cover, a plastic actuator, the spring plate, and in some cases, a PI film for sealing.
Working Principle
As a passive component, a tactile switch cannot function alone and must be used in conjunction with active components within a control system to realize its purpose.
- Normally Open (NO) Switch Principle: Pressing the button connects the circuit (switch turns ON); releasing the button disconnects it (switch turns OFF). This action relies on the deformation of an internal metal spring/dome.
- Normally Closed (NC) Switch Principle: Pressing the button disconnects the circuit (switch turns OFF); releasing it reconnects the circuit (switch turns ON).
An inherent limitation of this operating principle is the finite fatigue life of the metal spring/dome. Once it loses its elasticity, the switch becomes inoperable, thus defining the switch’s operational lifespan.
Applications and Variants
Given their operating principle, these switches are widely used for volume control in audio equipment, as power keys and function selectors in various electronics, buttons on remote controls, and keys on computer keyboards.
Their extensive use in diverse environments has driven the development of specialized variants to meet market demands. Common types now include low-profile, waterproof, dustproof, bracket-mounted, recessed-mounted, LED-lit, long-life, miniature, light-force, and heavy-force switches.
Procurement Considerations
Switch quality critically impacts end-product performance. Key factors to evaluate before purchase include:
- Solderability, Protection Level (e.g., IP rating), and Electrical Performance (e.g., stable conduction).
- Lifespan ratings and the tolerance of actuation force (should be within a reasonable range for consistent.
- Pin Plating: To reduce contact resistance, pins are typically silver-plated. High-quality switches employ superior plating processes with sufficient thickness (e.g., >0.3µm) and often a protective coating to prevent oxidation from exposure to atmospheric gases like SO₂.
Usage Precautions
- Process Confirmation: Confirm production conditions beforehand. Different soldering methods (e.g., wave soldering, hand soldering) require switches with appropriate terminal types and temperature resistance. Terminals are mainly categorized as Through-Hole (DIP) or Surface-Mount (SMD/SMT).
- Post-Assembly Testing: After production, test switches for proper ON/OFF operation, consistent tactile feel, correct contact resistance, physical integrity, and correct pin alignment. Appropriate Standard Operating Procedures (SOPs) should be established for different processes.
The Metal Spring/Dome’s Role
The modern tactile switch evolved from the simpler metal dome (or “snap dome”) used in membrane switches. While metal domes are quick to produce, their limited lifespan and functionality led to the development of the more robust and versatile tactile switch. The metal spring/dome remains the core component responsible for the actuation and tactile feedback.
Switch Body Construction
The switch body is primarily a plastic base. Common base materials include Nylon, PBT, and LCP, which offer good precision and contribute to a positive tactile feel.
The lifespan of these materials varies but typically reaches up to 10 years or more under normal conditions before risk of aging occurs. The cover plate can be metal (e.g., iron or stainless steel, offering long life but requiring proper care) or treated for corrosion resistance (e.g., salt-spray resistant plates, which may have a shorter service life of around five years).
Sealed variants like waterproof and dustproof switches can have longer lifespans as the internal mechanism is isolated from air, slowing oxidation. Preventing internal oxidation is key to maximizing service life. Techniques like ensuring a complete solder seal at the base can effectively isolate the internal components from air and extend longevity.
