English Translation

Micro Switch: Comprehensive Analysis of Structure, Principle, Materials, and Applications
A micro switch is a precision electronic component that triggers circuit switching through minimal mechanical displacement. Known for high sensitivity, long lifespan, and reliability, it is widely used in industrial control, household appliances, automotive electronics, and medical devices. This article provides a detailed technical analysis of micro switches across six dimensions: structural design, working principles, material selection, application fields, electrical performance parameters, and mechanical characteristics.

I. Structural Design of Micro Switches

The core structure comprises a housing, contact system, actuation mechanism, and terminals. Structural variations exist based on current capacity and protection requirements:

1. Standard Structure

   • Housing: Thermoplastics (e.g., PA66, PBT) or metals (aluminum alloy, stainless steel) for insulation and mechanical protection.
   • Contact System: Movable and stationary contacts made of silver alloys (AgCdO, AgNi) or gold plating for conductivity and arc resistance.
   • Actuation Mechanism: Includes spring plates, plungers, and snap-action mechanisms for rapid contact switching.
   • Sealing: Waterproof variants use silicone gaskets or epoxy potting (IP67/IP68 rated).

2. Low-Current vs. High-Current Designs

   • Low-Current (<5A): Small contacts, thin spring plates, short travel (0.1–0.5mm), ideal for signal detection.
   • High-Current (>10A): Thickened contacts, reinforced springs, dual-break structures to mitigate arcing.

3. Waterproof Innovations

   • Multi-Layer Seals: Bellows or O-rings between plungers and housing.
   • Gas-Filled Chambers: Inert gas (e.g., nitrogen) filling to suppress oxidation.

II. Working Principle & Actuation Mechanism

The snap-action mechanism drives operation via elastic element deformation:

1. Trigger Phase: External force compresses springs until critical threshold.
2. Switching Phase: Spring energy release causes instantaneous contact separation (<5ms).
3. Reset Phase: Spring restitution upon force removal.

Key Parameters:

• Actuation Force: 0.5N–5N (determines sensitivity).
• Travel: Total 0.5–3mm (pretravel + overtravel).

III. Material Selection & Optimization

1. Contact Materials

   • Silver Cadmium Oxide (AgCdO): High arc resistance for >10A loads.
   • Silver Nickel (AgNi): Anti-welding for frequent switching.
   • Gold-Plated: Low contact resistance (<20mΩ) for precision circuits.

2. Housing Materials

   • Plastics: PA66 (150°C resistant), PBT (chemical-proof).
   • Metals: Stainless steel (impact-resistant), aluminum (lightweight).

3. Spring Materials

   • Phosphor Bronze (C5191): High elasticity (1M+ cycles).
   • SUS304 Stainless Steel: Corrosion-resistant for humid environments.

IV. Electrical Performance Parameters

1. Current Characteristics

   • Rated Current: 0.1A–5A (low-current), 10A–25A (high-current).
   • Surge Current: High-current variants withstand 10× rated current.

2. Resistance Metrics

   • Contact Resistance: <50mΩ standard (<10mΩ gold-plated).
   • Insulation Resistance: >100MΩ (tested at 500VDC).

3. Durability

   • Mechanical Life: 100K–10M cycles (no load).
   • Electrical Life: 10K–500K cycles (under load).

V. Mechanical Performance & Protection

1. Operational Features

   • Force Curve: Matched to applications (e.g., linear feedback for automotive pedals).
   • Overtravel Design: Ensures reliable contact engagement.

2. Environmental Adaptability

   • Temperature Range: -40°C to +85°C (industrial), -20°C to +70°C (consumer).
   • Protection Ratings: IP67 (water/dustproof), UL94 V-0 (flame-retardant).

VI. Applications & Selection Guide

1. Industrial Automation

   • Limit switches (machine tool positioning), safety interlocks.

2. Automotive Electronics

   • Brake pedal switches, door locks (AEC-Q200 compliant).

3. Appliances & Medical

   • Microwave door switches, ventilator pressure monitoring (low resistance + high sealing).

4. Selection Criteria

   • Current Rating: ≥1.5× load current.
   • Waterproof Validation: 85°C/85%RH testing for long-term sealing.