Cleanroom Principles , Classification and Engineering Guide

A cleanroom is a controlled environment where the concentration of airborne particles is maintained within specified limits. It is designed to support human activity while ensuring strict contamination control for precision manufacturing and scientific research.

However, a cleanroom is far more than just a “dust-free" space. It is a highly integrated engineering system that combines architectural sealing, HVAC purification, electrical systems, process piping, and environmental monitoring. In addition to particle control, modern cleanrooms must also regulate temperature, humidity, pressure, lighting, noise, vibration, and electrostatic discharge.

These multi-disciplinary requirements make cleanrooms essential infrastructure in industries such as semiconductors, electronics, pharmaceuticals, aerospace, and high-purity chemical processing.

Industrial cleanrooms are primarily designed to control non-living particles such as dust. These environments are typically maintained under positive pressure to prevent external contamination.

They are widely used in:

• Semiconductor and integrated circuit manufacturing
• Precision machinery and aerospace industries
• Optical and magnetic product production
• LCD panels, hard drives, and advanced electronics

Biological cleanrooms control both viable (microorganisms) and non-viable particles.

They can be further divided into:

• General bio-cleanrooms: Focus on preventing microbial contamination of products. Materials used must withstand sterilization processes, and the environment is typically maintained under positive pressure.
• Biosafety cleanrooms: Designed to prevent harmful biological agents from escaping into the environment. These rooms operate under negative pressure to protect personnel and surroundings.

Cleanrooms are also categorized based on airflow design:

• Unidirectional flow cleanroom
• Non-unidirectional (turbulent) flow cleanroom
• Radial (or directional) flow cleanroom
• Mixed flow cleanroom

Among these, unidirectional and non-unidirectional systems are the most widely used in industrial applications.

Unidirectional flow cleanrooms are designed so that air moves in parallel streams at a uniform velocity across the entire working area. The airflow direction can be vertical (ceiling to floor) or horizontal (wall to wall).

The core working principle is a “piston effect," where clean air continuously pushes contaminated air out of the room.

Key engineering features include:

• High-efficiency filters covering a large portion of the ceiling
• Uniform airflow velocity, typically 0.3–0.5 m/s
• Minimal turbulence and rapid contamination removal

To achieve effective airflow coverage, industry standards recommend that HEPA or ULPA filters cover at least:

• 60% of the ceiling area for vertical flow systems
• 40% for horizontal flow systems

It is important to note that full ceiling coverage is not always feasible due to structural and economic constraints. Therefore, modern designs focus on ensuring that unidirectional airflow dominates critical working zones rather than the entire room.

Non-unidirectional cleanrooms operate on a dilution principle rather than displacement.

Air enters the room at varying velocities and directions, creating mixed airflow patterns with recirculation and vortices. This prevents the formation of a uniform airflow field.

Clean air supplied through diffusers mixes with contaminated air, reducing particle concentration through dilution. The mixed air is then removed through return air systems.

• Airflow is non-uniform and multi-directional
• Cleanliness is achieved through repeated air changes
• Higher air change rates result in better cleanliness levels
• Typically used for ISO Class 1000 to Class 300,000 environments

Compared to unidirectional systems, turbulent cleanrooms are more cost-effective and easier to maintain, making them suitable for general manufacturing and pharmaceutical applications.

Proper fresh air supply is critical for maintaining indoor air quality and pressure balance.

According to cleanroom design standards:

• Non-unidirectional cleanrooms require 10%–30% fresh air
• Unidirectional cleanrooms typically require 2%–4% fresh air

Actual values may vary depending on process requirements and occupancy levels.

Air cleanliness is defined by the number of airborne particles within a given volume of air. The lower the particle concentration, the higher the cleanliness level.

Cleanroom classification is based on:

• Particle size (e.g., ≥0.3 μm, ≥0.5 μm)
• Particle concentration per cubic meter

Cleanroom design and operation must minimize the introduction, generation, and retention of particles while maintaining stable environmental parameters such as temperature, humidity, and pressure.

A complete cleanroom facility typically includes:

The main controlled environment where manufacturing or research takes place.

Including personnel airlocks, material transfer rooms, and auxiliary spaces.

Housing HVAC systems, electrical systems, ultra-pure water systems, and gas supply systems.

• Cleanroom panels and aluminum framing
• Airtight doors and windows
• Epoxy or PVC flooring systems

• Air handling units and ductwork
• HEPA/ULPA filters
• FFU (Fan Filter Units)
• Air volume control valves and diffusers

• Lighting and power supply
• Environmental monitoring sensors
• Automation and control systems

When planning or sourcing a cleanroom project, key considerations include:

• Required ISO cleanliness level
• Airflow design (unidirectional vs turbulent)
• Process-specific environmental controls
• Energy efficiency and operating costs
• Supplier experience and integration capability

Selecting the right cleanroom solution is essential to ensure product quality, regulatory compliance, and long-term operational efficiency.

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1. What is the difference between industrial and biological cleanrooms?
Industrial cleanrooms control dust particles, while biological cleanrooms control both particles and microorganisms.

2. What airflow is used in high-end semiconductor cleanrooms?
Unidirectional airflow is typically used due to its ability to rapidly remove contaminants.

3. Why are HEPA filters important in cleanrooms?
They remove ultra-fine particles from incoming air, ensuring high cleanliness levels.

4. How is cleanroom cleanliness measured?
By counting the number of particles of specific sizes per cubic meter of air.

5. Which cleanroom type is more cost-effective?
Non-unidirectional (turbulent) cleanrooms are generally more cost-effective than unidirectional systems.