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Specification for High-Efficiency Filter Evaluation and Application in High-Tech Cleanrooms
1. Objective
To standardize the selection, evaluation, testing, installation, monitoring, and replacement processes for High-Efficiency Particulate Air (HEPA) and Ultra-Low Penetration Air (ULPA) filters. This ensures their performance continuously meets the stringent air cleanliness requirements of high-tech cleanrooms, guaranteeing the stability and reliability of the production process environment. This specification is established for this purpose.
2. Scope
This specification applies to all high-efficiency and ultra-high-efficiency air filters used at the terminal ends of ventilation and air conditioning systems within cleanrooms of semiconductor and other high-tech manufacturing facilities. It covers the entire lifecycle management of filters, from initial selection and evaluation to decommissioning and replacement. All departments and personnel related to facility operation and maintenance, quality control, and engineering management must comply.
3. Basic Understanding and Selection Evaluation of High-Efficiency Filters
3.1 Filter Types and Definitions
HEPA Filter: High-Efficiency Particulate Air filter, with a capture efficiency of no less than 99.97% for particles of 0.3 micrometers in size.
ULPA Filter: Ultra-Low Penetration Air filter, typically with a capture efficiency of no less than 99.999% for particles of 0.12 micrometers or other specified smaller sizes.
3.2 Key Performance Parameters and Selection Basis
Selection evaluation must be based on the following core parameters, ensuring they meet the cleanroom design classification (e.g., ISO 14644 class) and process requirements:
Filtration Efficiency: Select the filter class that meets the minimum efficiency requirement based on the target particle size to be controlled (e.g., 0.3μm, 0.1μm) and the target cleanliness level.
Initial Pressure Drop: The airflow resistance of a new filter at its rated airflow. This value impacts system energy consumption and should be the basis for fan selection and energy assessment.
Rated Airflow: The optimal airflow range the filter is designed to handle. Selection must match the system's actual operating airflow.
Dust Holding Capacity: The total amount of dust a filter can hold before reaching its final resistance. High dust holding capacity can extend service life.
Material and Structure: Filter media material (e.g., glass fiber), separator structure, sealant, and frame material (e.g., aluminum alloy, stainless steel) must be evaluated for corrosion resistance, strength, and compatibility with the facility environment (temperature, humidity, potential chemical exposure).
4. Filter Performance Testing and Verification
To ensure filter performance meets standards, the following tests must be performed:
4.1 Factory Testing
The supplier must provide a test report for each filter compliant with relevant standards (e.g., EN 1822, IEST-RP-CC001), including at minimum:
Efficiency Test: Determination of the filter's minimum efficiency at the Most Penetrating Particle Size (MPPS) via particle counting method.
Resistance Test: Initial pressure drop at rated airflow.
Integrity Test: Scan testing to ensure no leaks in the filter media or seals.
4.2 Post-Installation Field Testing
After filter installation in the cleanroom, field verification testing must be conducted. This is a core part of system acceptance:
Leak Test: Using an upstream aerosol challenge (e.g., PAO, DOP, DOS) and downstream scanning with a photometer or particle counter across the filter media, frame, and seals between the filter and its housing. Any leak point exceeding the limit (e.g., local reading >0.01% of upstream concentration) must be documented and addressed until re-test passes after repair.
Air Velocity Uniformity Test: For unidirectional flow cleanrooms (e.g., tunnels, FFU systems), measure the air velocity across the filter face. Uniformity must meet design requirements (typically within ±20% of the average).
Airflow Test: Verify that the total installed filter supply airflow meets the system design value.
5. Application and Management in Cleanrooms
5.1 Installation Management
Installation must occur after all civil and finishing work is complete and following thorough cleaning.
Installation personnel must receive professional training and strictly follow installation procedures to ensure no damage during transportation and handling.
The seal between the filter and its housing frame must be reliable, using appropriate sealing materials (e.g., liquid gasket, closed-cell foam rubber gasket, gel seal) and methods to prevent bypass leakage.
5.2 Operation Monitoring and Maintenance
Pressure Differential Monitoring: Install differential pressure gauges upstream and downstream of filters for continuous or periodic monitoring. Initial and operating pressure drops should be recorded as baselines.
Replacement Criteria: Filter replacement must be planned and executed when any of the following occurs:
a) Operating pressure drop reaches 1.5 to 2 times the initial drop, or reaches the fan's capacity limit, affecting system airflow.
b) Periodic leak test fails and cannot be rectified to meet requirements.
c) Although final resistance is not reached, service time exceeds the manufacturer's recommended lifecycle (requires assessment considering ambient air quality).
d) Filter failure due to irreversible physical damage, contamination (e.g., chemical corrosion, heavy oil mist), or system modification.
Periodic Testing: Establish and execute a regular filter integrity leak test schedule based on cleanroom class and regulatory requirements (typically every 12 months, shortened to 6 months for critical areas).
5.3 Records and Traceability
Establish an individual file for each critical area high-efficiency filter, recording the following information:
Filter model, serial number, manufacturing date.
Key performance parameters (efficiency, initial pressure drop, rated airflow).
Supplier information and factory test report.
Installation location, installation date, and post-installation test report.
Historical pressure differential records, leak test reports.
Replacement date, reason for replacement, and decommissioning/disposal record.
6. Responsibilities
The Facility Operations and Maintenance team is responsible for the daily monitoring, periodic testing, replacement execution, and record keeping for high-efficiency filters. The Engineering Project department is responsible for filter selection and installation quality in new facilities or renovation projects. The Quality Assurance department is responsible for supervising the compliance of test methods and the validity of data.
7. Review and Update
This specification will be reviewed periodically or revised following updates in filter technology, testing standards, or process requirements to continuously ensure its technical advancement and management effectiveness.
