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In electronics manufacturing facilities, air cleanliness is one of the most critical factors affecting product quality. Acting as the “lungs” of a cleanroom, air filters establish a multi-layered contamination control system through precise classification and well-structured configuration.

This article provides an in-depth analysis of cleanroom air filters from three key dimensions — filtration purpose, filter material, and filtration efficiency — outlining the core categories, definitions, and application characteristics of air filters in electronic cleanroom environments. The goal is to offer professional insights and guidance for the design, implementation, and maintenance of high-performance cleanroom systems.

 

 

1. Purpose-Based Classification of Air Filters in Electronics Cleanrooms

 

In electronics manufacturing facilities, cleanroom air filters can be classified into six major types based on their functional roles. Each category serves a specific purpose within the air handling system, forming a multi-tiered defense against contamination.

 

 

1.1 Fresh Air Intake Filters – The First Line of Defense Against Outdoor Pollutants

 

Definition: Designed specifically to purify outdoor air before it enters the cleanroom. These filters remove atmospheric dust, microorganisms, and chemical contaminants, providing an initial level of air cleanliness.

Key Features:

• Multi-Stage Filtration: Typically configured as a combination of coarse filters, medium filters, fine filters, and sub-HEPA or HEPA filters. In some scenarios, chemical filters (e.g., for SO₂, NOx removal) are added.
• High Dust-Holding Capacity: Filter media such as durable nonwoven fabrics or fiberglass are selected to withstand particulate shock and allow for longer replacement intervals.
• Core of Pre-Treatment: Serves as the heart of the fresh air system. In heavily polluted regions (e.g., smog-prone areas), enhanced coarse filtration is critical.

Applications: Used at the fresh air inlets of electronics cleanrooms, often integrated into AHU (Air Handling Unit) systems. Common in semiconductor fabs and LED chip workshops.

 

1.2 Supply Air Filters – The Final Barrier Ensuring Cleanroom Standards

 

Definition: End-stage filters in purification HVAC systems that ensure the air delivered into cleanrooms meets required cleanliness levels.

Key Features:

• High Filtration Precision: Commonly employs sub-HEPA (≥95%@0.5μm), HEPA (≥99.95%@0.3μm), or ULPA (≥99.999%@0.1μm) filters. In some cases, molecular filters are used for controlling airborne molecular contamination (AMC).
• Low Pressure Drop: Optimized pleated filter designs (e.g., separatorless) minimize fan energy consumption. Frequently used in FFU (Fan Filter Unit) systems.
• High Sealing Integrity: Installed in ceiling plenums. Leak tests (scanning method) are required to prevent bypass leakage and secondary contamination.

Applications: End-stage cleanroom supply, such as photolithography areas in integrated circuit fabs, or TFT-LCD panel clean zones.

 

1.3 Exhaust Filters – Environmental Safety for Pollutant Discharge

 

Definition: Capture harmful substances generated during cleanroom production processes to ensure emission compliance.

Key Features:

• Targeted Media Selection: Filter materials are chosen based on the contaminant type. HEPA filters for microorganisms; activated carbon or chemical filters for VOCs.
• Corrosion Resistance: For corrosive gases, frames are typically made of stainless steel with acid/alkali-resistant media. Common in pharmaceutical cleanroom exhaust systems.
• Redundant Safety Design: Often configured in multiple stages (e.g., HEPA + chemical filters) to guarantee compliance and reduce environmental risk.

Applications: Used for exhaust from semiconductor etching processes or biosafety exhaust treatment systems.

 

1.4 Built-In Equipment Filters – Guardians of Local Microenvironments

 

Definition: Installed inside cleanroom process equipment (e.g., lithography machines, coating systems) to maintain high cleanliness via internal recirculation.

Key Features:

• Compact and Customizable: Designed to fit limited spaces; often non-standard. ULPA filters are commonly used to achieve cleanliness levels down to 0.1μm.
• High Reliability: Integrated with equipment controls for real-time monitoring of pressure drop, ensuring uninterrupted operation.
• Low Vibration Design: Equipped with silent fans and anti-vibration structures to protect sensitive instruments.

Applications: Used in advanced process tools and semiconductor wafer inspection systems.

 

1.5 Integrated Equipment Filters – Clean Air Modules for Manufacturing Tools

 

Definition: Integrated with manufacturing equipment to provide clean air or process gases required for equipment operation.

Key Features:

• Custom Engineered: Tailored to equipment requirements such as temperature, pressure, and gas compatibility. For instance, high-temp HEPA filters for thermal processes.
• Compatible with Process Conditions: Filters particles ≤0.1μm while resisting corrosion from process gases (e.g., used in epitaxial growth with high-purity gases).
• Quick-Replace Design: Supports on-site replacement without full shutdown, minimizing equipment downtime.

Applications: Ion implanters, thin-film deposition systems, and other semiconductor processing tools.

 

1.6 High-Pressure Pipeline Filters – Precision Filtration for Pressurized Gases

 

Definition: Used in pipelines with pressures >0.1 MPa to remove particles from compressed air or high-purity gas lines.

Key Features:

• Pressure-Resistant Design: Uses sintered metal or high-strength media to withstand operating pressures of 1–10 MPa.
• Minimal Particle Shedding: Strict fiber shedding control to ensure gas purity (e.g., electronic-grade nitrogen or argon).
• Precision Levels: Filters available for 0.01μm to 5μm based on process specifications.

Applications: Gas supply systems in semiconductor fabs and LCD production lines using high-purity or high-pressure gases.

 

2. Classification by Filter Materials: How Media Defines Performance Boundaries

 

Filter media are the “heart” of any air filter. Different materials define a filter’s efficiency, pressure drop, and suitability for specific environments. Understanding filter media selection is crucial to ensuring optimal performance in electronics cleanrooms.

 

2.1 Paper-Based Filters – The All-Purpose Mainstream Choice

 

Definition: Filters made from glass fiber, synthetic fiber, or ultra-fine fiberglass, typically pleated to maximize surface area.

Key Features:

• High Efficiency: Suitable for manufacturing both HEPA (≥99.95%@0.3μm) and ULPA (≥99.999995%@0.1μm) filters.
• Versatile Applications: From coarse to ultra-high-efficiency stages, commonly used in fresh air pre-filtration and cleanroom terminal stages.
• Excellent Thermal Resistance: Fiberglass media withstands up to 250°C, ideal for exhaust of sterilization/drying equipment.

Typical Products: Separator/separatorless HEPA/ULPA filters.

 

2.2 Fiber Layer Filters – The Cost-Effective Solution for Medium Efficiency

 

Definition: Filters made from natural (wool/cotton), synthetic (polypropylene), or blended fibers in low packing density.

Key Features:

• Low Pressure Drop: 20–150 Pa resistance, suitable for 20%–70%@0.5μm efficiency.
• Washable Options: Some nonwoven types support reuse.
• Precision Limitation: Effective for 1–10μm particles, must be paired with HEPA for finer filtration.

Typical Products: Bag-type or panel-type medium-efficiency filters.

 

2.3 Foam Material Filters – An Outdated Early-Stage Option

 

Definition: Made of porous plastic foam relying on pore structure for filtration.

Key Features:

• Pore Variability: Efficiency inconsistent due to uncontrolled pore size.
• Low Dust Capacity: Prone to clogging and short service life.
• Current Use: Rare; replaced by fiber-based filters in most scenarios.

 

3. Classification by Filtration Efficiency: Building a Multi-Stage Defense System

 

Air filters are categorized into six levels based on their ability to remove particles of specific sizes. These levels form a progressive filtration hierarchy.

 

3.1 Coarse Air Filters – The First Line of Defense Against Large Particles

Definition: Filters particles ≥2μm to protect downstream stages.

Efficiency: Gravimetric ≥50%; Counting: 10%–50%@2μm.

Key Features:

• High dust-holding capacity with coarse-pore nonwoven media.
• Easy replacement or cleaning.

Applications: First-stage outdoor air filtration.

 

3.2 Medium Efficiency Filters – The Transitional Barrier

 

Definition: Removes particles 0.5–10μm, protects HEPA filters.

Efficiency: 20%–70%@0.5μm.

Key Features:

• Sub-classed into 20–40%, 40–60%, 60–70% categories.
• Moderate resistance (50–150 Pa).

 

3.3 Fine and High-Medium Filters – Enhanced Precision

 

Definition: For 0.5–5μm particles.

Efficiency: 70%–95%@0.5μm.

Features: Ultra-fine nonwoven media with large surface area, long service life.

 

3.4 Sub-HEPA Filters – The Bridge to HEPA

 

Definition: Removes particles ≥0.5μm before HEPA stage.

Efficiency: 95%–99.9%@0.5μm. Lower resistance (≤120 Pa).

 

3.5 HEPA Filters – The Core Barrier of Cleanrooms

 

Definition: Terminal filters for 0.3μm particle removal.

Efficiency: ≥99.95% MPPS.

Key Features:

• Ultra-fine glass fiber media, pore size ≤0.1μm.
• Separatorless design, factory scan-tested for leaks.

 

3.6 ULPA Filters – The Ultimate Nanometer-Level Defense

 

Definition: For ISO Class 1–4 ultra-clean zones.

Efficiency: ≥99.999% MPPS (some ≥99.999995%).

Features: Uses boron-free glass fiber/ePTFE, suitable for EUV zones.

 

4. Configuration Principles: Matching Filter Strategies to Cleanroom Requirements

 

 

4.1 Three-Level Configurations by ISO Class

• ISO 8–9: Coarse + Medium + HEPA
• ISO 5–7: Coarse + Medium + Sub-HEPA + HEPA
• ISO 1–4: Coarse + Medium + High-Medium + Sub-HEPA + ULPA + Chemical

4.2 Engineering Design Considerations

• Air Volume Margin: Rated airflow ≥10–20% above actual.
• Pressure Zones: Medium filters in positive zones; HEPA close to cleanroom.
• Smart Monitoring: Differential pressure sensors with alerts.

 

 

5. Conclusion: Filters – The Invisible Guardians of Cleanrooms

 

From intake to terminal filtration, every filter plays a critical role in electronics cleanrooms. Strategic classification and configuration ensure cleanliness while reducing energy and maintenance costs.

 

 

As air filtration technology continues to evolve alongside the demands of high-precision manufacturing, selecting the right cleanroom filters is more critical than ever. E-FILT, a trusted air filter manufacturer, we specialize in providing advanced, custom-engineered filtration solutions for electronics manufacturing cleanrooms, covering every layer from pre-filtration to ULPA-grade final protection.

 

With deep expertise in cleanroom HVAC systems, premium filter materials, and ISO-compliant designs, E-FILT empowers factories to achieve optimal air quality, reduce energy consumption, and maintain world-class production standards. Whether you’re building a new facility or upgrading an existing system, our filtration experts are here to support your cleanroom goals.