In a Cleanroom environment, high-efficiency air filters (HEPA) and ultra-high-efficiency air filters (ULPA) are core equipment for controlling particulate contamination and maintaining cleanliness levels. Their requirements are significantly higher than those of ordinary industrial or civil filters, and they must meet special requirements in four core dimensions: cleanliness compatibility, operational stability, low pollution characteristics, and compliance. The following is the specific requirement breakdown:
I. “Precise Filtration Requirements” Strongly Compatible with Cleanliness Grades
Cleanrooms are classified into ISO 1 to ISO 9 grades according to the ISO 14644-1 standard (the smaller the number, the higher the cleanliness). The concentration limits for key particle sizes, such as 0.1 μm and 0.5 μm, vary significantly among different grades. Filters need to precisely match the target cleanliness grade, which is mainly reflected in the following two points:
Strict matching of filtration efficiency
Select HEPA filters for low cleanliness levels (such as ISO 7-8 grades, commonly used in electronic assembly and food processing), ensuring a filtration efficiency of ≥99.97% for 0.3μm particles (EN 1822 standard H13 grade) to meet basic particle interception requirements.
For high cleanliness levels (such as ISO 4-5, used in semiconductor wafer manufacturing and aseptic filling of biopharmaceuticals), choose ULPA filters, which achieve a filtration efficiency of ≥99.999% for 0.12μm particles (EN 1822 standard U15 grade and above), and even require U17 grade filters to control ultrafine particles (<0.1μm).
Provide an extreme clean level (such as ISO 1-3, photolithography workshop) by equipping the room with a combined system of high-efficiency filters, chemical filters, and membrane filters, using filters that meet silicon-free and volatile standards to avoid superposition of particles and chemical contamination.
Targeted interception of key particle sizes
The size of “core contaminant particles” varies across different industries: The semiconductor industry focuses on “killer particles” of 0.1μm and below (lethal particles that may cause short circuits in chips). Biopharmaceuticals focus on microbial carriers larger than 0.5μm (such as bacteria attached to dust particles). Filters should achieve the optimal filtration efficiency at the corresponding particle size based on industry demands, rather than merely meeting general standards.
Ii. Low Pollution and Low Emission “Self-cleanliness Requirements”
The core of a cleanroom is “controlling external contamination”, and if the filter itself contains particles or volatile substances, it will directly damage the clean environment. Therefore, it must meet the special requirement of “self-cleanliness”
Select HEPA filters for low cleanliness levels (such as ISO 7-8 grades, commonly used in electronic assembly and food processing), ensuring a filtration efficiency of ≥99.97% for 0.3μm particles (EN 1822 standard H13 grade) to meet basic particle interception requirements.
For high cleanliness levels (such as ISO 4-5, used in semiconductor wafer manufacturing and aseptic filling of biopharmaceuticals), choose ULPA filters, which achieve a filtration efficiency of ≥99.999% for 0.12μm particles (EN 1822 standard U15 grade and above), and even require U17 grade filters to control ultrafine particles (<0.1μm).
Provide an extreme clean level (such as ISO 1-3, photolithography workshop) by equipping the room with a combined system of high-efficiency filters, chemical filters, and membrane filters, using filters that meet silicon-free and volatile standards to avoid superposition of particles and chemical contamination.
Targeted interception of key particle sizes
The size of “core contaminant particles” varies across different industries: The semiconductor industry focuses on “killer particles” of 0.1μm and below (lethal particles that may cause short circuits in chips). Biopharmaceuticals focus on microbial carriers larger than 0.5μm (such as bacteria attached to dust particles). Filters should achieve the optimal filtration efficiency at the corresponding particle size based on industry demands, rather than merely meeting general standards.
Ii. Low Pollution and Low Emission “Self-cleanliness Requirements”
The core of a cleanroom is “controlling external contamination”, and if the filter itself contains particles or volatile substances, it will directly damage the clean environment. Therefore, it must meet the special requirement of “self-cleanliness”
No particle shedding (low dusting property)
Filter material selection: Glass fiber (HEPA/ULPA mainstream) or PTFE (polytetrafluoroethylene) membrane filter materials should be adopted. Synthetic fiber or paper filter materials that are prone to shedding fibers should be avoided. Hot melt adhesive (rather than solvent-based adhesive) should be used for the splicing of filter materials to reduce the risk of adhesive layer aging and peeling.
Structural design: The frame should be made of anodized aluminum alloy (with a smooth surface and no rust) or stainless steel (grade 304/316, suitable for biological/pharmaceutical clean rooms), and avoid materials prone to slag shedding, such as galvanized steel plates. The sealant should be a “low-dust-generating sealant” of silicone or polyurethane type, and the sealant layer should be uniform without bubbles.
Factory inspection: It must pass the “dust emission test” (such as using a laser particle counter to detect the downstream particle increment during the operation of the filter) to ensure that the dust emission of each filter itself is ≤0.1 particles/(min · L) (for ISO Class 5 and above clean rooms).
No release of chemical pollutants (low VOCs/silicon-free)
The semiconductor, photolithography and other industries are extremely sensitive to “silicon contamination” (silicon can adhere to the surface of wafers and affect etching accuracy). Filters must meet the “silicon-free certification” – from filter materials, frames, sealants to adhesives, none of them must contain silicone substances.
The biopharmaceutical and food industries need to avoid the release of “volatile organic compounds (VOCs)”. Filters must pass the “VOCs release detection” (such as using a gas chromatography-mass spectrometry GC-MS detection) to ensure that the release is less than 0.1μg/ (m³ · h).
Iii. “Reliability and Safety Requirements for Long-term Stable Operation
Cleanrooms mostly operate continuously for 24 hours (for instance, the annual operation time of semiconductor factories exceeds 8,000 hours). The stability of filters directly determines the continuity of production and must meet the requirements of “low resistance, long service life, and risk resistance”.
Low initial resistance and slow resistance growth
The “initial resistance” of the filter directly affects the energy consumption of the air conditioning system: The initial resistance of HEPA filters is usually controlled at 120-180Pa, and that of ULPA filters at 180-250Pa. If the resistance is too high, it will lead to a sharp increase in the energy consumption of the fan and frequent replacement of the filter (increasing the cost of shutdown).
The “dust-holding capacity” of the filter material must be large enough (HEPA dust-holding capacity ≥500g/m², ULPA≥800g/m²) to ensure that the rate of resistance increase with dust accumulation is slow – under ideal conditions, the service life of the filter can reach 1-3 years (the service life of ordinary civil filters is only 3-6 months).
Impact resistance and environmental resistance performance
Anti-airflow impact: When the cleanroom air conditioning system starts or stops, “airflow fluctuations” may occur. The filter must be able to withstand a short-term impact of 1.2 times the rated air volume. The filter material must not be damaged, and the frame must not be deformed.
Temperature and humidity resistance: In hot and humid environments (such as biological fermentation clean rooms, humidity ≥60%), “anti-mold filter materials + stainless steel frames” should be selected to prevent mold growth on the filter materials and rusting of the frames. High-temperature environments (such as electronic packaging clean rooms, with a temperature of ≥40℃) should select high-temperature resistant glass fiber filter materials (with a temperature resistance of ≥120℃).
Fire resistance: It must pass the fire protection certification of UL 900 or GB 8624 standards, reaching “Class 1” (non-combustible grade), to prevent the filter from becoming an oxidizer in case of fire.
Strict leakage control
The “leakage” of filters is a major risk of contamination in cleanrooms – even if the filter material efficiency meets the standards, if there are gaps between the frame and the filter material or between the filter and the installation frame, unfiltered air will directly seep into the clean area.
Requirement: Before leaving the factory, each unit shall undergo an “integrity test” (using PAO aerosol scanning method), and the leakage rate shall be ≤0.01% (EN 1822 standard). After installation, the sealing surfaces of the “filter and static pressure box” need to be scanned again to ensure there are no leakage points.
Iv. “Industry Certification Requirements” for Compliance and Traceability
Cleanrooms in different industries have mandatory regulations or standard requirements. Filters must pass the corresponding authoritative certification to ensure compliance with industry-specific norms
Filter material selection: Glass fiber (HEPA/ULPA mainstream) or PTFE (polytetrafluoroethylene) membrane filter materials should be adopted. Synthetic fiber or paper filter materials that are prone to shedding fibers should be avoided. Hot melt adhesive (rather than solvent-based adhesive) should be used for the splicing of filter materials to reduce the risk of adhesive layer aging and peeling.
Structural design: The frame should be made of anodized aluminum alloy (with a smooth surface and no rust) or stainless steel (grade 304/316, suitable for biological/pharmaceutical clean rooms), and avoid materials prone to slag shedding, such as galvanized steel plates. The sealant should be a “low-dust-generating sealant” of silicone or polyurethane type, and the sealant layer should be uniform without bubbles.
Factory inspection: It must pass the “dust emission test” (such as using a laser particle counter to detect the downstream particle increment during the operation of the filter) to ensure that the dust emission of each filter itself is ≤0.1 particles/(min · L) (for ISO Class 5 and above clean rooms).
No release of chemical pollutants (low VOCs/silicon-free)
The semiconductor, photolithography and other industries are extremely sensitive to “silicon contamination” (silicon can adhere to the surface of wafers and affect etching accuracy). Filters must meet the “silicon-free certification” – from filter materials, frames, sealants to adhesives, none of them must contain silicone substances.
The biopharmaceutical and food industries need to avoid the release of “volatile organic compounds (VOCs)”. Filters must pass the “VOCs release detection” (such as using a gas chromatography-mass spectrometry GC-MS detection) to ensure that the release is less than 0.1μg/ (m³ · h).
Iii. “Reliability and Safety Requirements for Long-term Stable Operation
Cleanrooms mostly operate continuously for 24 hours (for instance, the annual operation time of semiconductor factories exceeds 8,000 hours). The stability of filters directly determines the continuity of production and must meet the requirements of “low resistance, long service life, and risk resistance”.
Low initial resistance and slow resistance growth
The “initial resistance” of the filter directly affects the energy consumption of the air conditioning system: The initial resistance of HEPA filters is usually controlled at 120-180Pa, and that of ULPA filters at 180-250Pa. If the resistance is too high, it will lead to a sharp increase in the energy consumption of the fan and frequent replacement of the filter (increasing the cost of shutdown).
The “dust-holding capacity” of the filter material must be large enough (HEPA dust-holding capacity ≥500g/m², ULPA≥800g/m²) to ensure that the rate of resistance increase with dust accumulation is slow – under ideal conditions, the service life of the filter can reach 1-3 years (the service life of ordinary civil filters is only 3-6 months).
Impact resistance and environmental resistance performance
Anti-airflow impact: When the cleanroom air conditioning system starts or stops, “airflow fluctuations” may occur. The filter must be able to withstand a short-term impact of 1.2 times the rated air volume. The filter material must not be damaged, and the frame must not be deformed.
Temperature and humidity resistance: In hot and humid environments (such as biological fermentation clean rooms, humidity ≥60%), “anti-mold filter materials + stainless steel frames” should be selected to prevent mold growth on the filter materials and rusting of the frames. High-temperature environments (such as electronic packaging clean rooms, with a temperature of ≥40℃) should select high-temperature resistant glass fiber filter materials (with a temperature resistance of ≥120℃).
Fire resistance: It must pass the fire protection certification of UL 900 or GB 8624 standards, reaching “Class 1” (non-combustible grade), to prevent the filter from becoming an oxidizer in case of fire.
Strict leakage control
The “leakage” of filters is a major risk of contamination in cleanrooms – even if the filter material efficiency meets the standards, if there are gaps between the frame and the filter material or between the filter and the installation frame, unfiltered air will directly seep into the clean area.
Requirement: Before leaving the factory, each unit shall undergo an “integrity test” (using PAO aerosol scanning method), and the leakage rate shall be ≤0.01% (EN 1822 standard). After installation, the sealing surfaces of the “filter and static pressure box” need to be scanned again to ensure there are no leakage points.
Iv. “Industry Certification Requirements” for Compliance and Traceability
Cleanrooms in different industries have mandatory regulations or standard requirements. Filters must pass the corresponding authoritative certification to ensure compliance with industry-specific norms
| Industry field |
Core certification/standard requirements |
Purpose |
| Semiconductor/Electronics | Silicon-free certification (such as SEMI F21 standard), ULPA U15/U17 grade certification (EN 1822) | Avoid silicon contamination, control ultrafine particles, and ensure the yield of chips |
| Biopharmaceuticals | FDA 21 CFR Part 11 Compliance (traceability), GMP certification, biosafety testing (no microbial shedding) | Comply with the Good Manufacturing Practice for Pharmaceuticals to prevent the drugs from being contaminated by microorganisms or particles |
|
Medical operating room |
Antibacterial filter material certification (such as silver ion modified filter material), EN 1822 H14 grade certification | Inhibit bacterial growth, control the concentration of particles in the surgical environment, and reduce the risk of postoperative infection |
| Food processing | FDA Food Contact grade certification (frames/sealants in contact with food), ISO 22000 food safety certification | Ensure that the filter does not release harmful substances to contaminate food and meets food safety standards |
In addition, the filters must have complete “traceability” – each filter should have a unique serial number, allowing for the traceability of production batches, filter material sources, test reports, installation dates, and other information, to meet the requirements of audits or quality traceability.
V. “Structural Design Requirements for Adapting to the Air Flow Organization in Cleanrooms”
The air flow organization in a cleanroom (such as laminar flow or turbulent flow) determines the installation form of the filter, and the structure needs to be designed specifically.
Laminar flow cleanrooms (such as photolithography workshops, aseptic filling lines) “Non-woven HEPA/ULPA filters” (with a thickness of only 60-90mm) should be adopted and densely arranged in a “filter array” (such as 1.2m×1.2m specification) to ensure uniform and vertical downward airflow (wind speed 0.3-0.5m/s), forming a “dust-free airflow barrier”.
Turbulent clean rooms (such as electronic assembly and food packaging) : “pleated HEPA filters” (with lower cost) or “bag-type HEPA filters” (increasing the filter material area and extending the service life) can be adopted, combined with the top supply and bottom return air flow organization, to achieve the dilution and discharge of particles.
Local high-cleanliness areas (such as workbenches and biosafety cabinets) : “miniaturized, low-noise filters” should be adopted and integrated into the local purification equipment to ensure that the local area achieves a cleanliness level of ISO 5 or above.
Summary
The demand for high-efficiency filters in cleanrooms is essentially “aiming for ‘zero pollution’ while taking into account reliability, economy, and compliance” – it is not only an “air filtration device”, but also the “core defense line” of the clean environment. The differences in their demands are ultimately determined by the grade standards of the cleanroom, industry characteristics, and production processes. Precise matching can only be achieved through “customized selection + strict testing + compliance certification”.
V. “Structural Design Requirements for Adapting to the Air Flow Organization in Cleanrooms”
The air flow organization in a cleanroom (such as laminar flow or turbulent flow) determines the installation form of the filter, and the structure needs to be designed specifically.
Laminar flow cleanrooms (such as photolithography workshops, aseptic filling lines) “Non-woven HEPA/ULPA filters” (with a thickness of only 60-90mm) should be adopted and densely arranged in a “filter array” (such as 1.2m×1.2m specification) to ensure uniform and vertical downward airflow (wind speed 0.3-0.5m/s), forming a “dust-free airflow barrier”.
Turbulent clean rooms (such as electronic assembly and food packaging) : “pleated HEPA filters” (with lower cost) or “bag-type HEPA filters” (increasing the filter material area and extending the service life) can be adopted, combined with the top supply and bottom return air flow organization, to achieve the dilution and discharge of particles.
Local high-cleanliness areas (such as workbenches and biosafety cabinets) : “miniaturized, low-noise filters” should be adopted and integrated into the local purification equipment to ensure that the local area achieves a cleanliness level of ISO 5 or above.
Summary
The demand for high-efficiency filters in cleanrooms is essentially “aiming for ‘zero pollution’ while taking into account reliability, economy, and compliance” – it is not only an “air filtration device”, but also the “core defense line” of the clean environment. The differences in their demands are ultimately determined by the grade standards of the cleanroom, industry characteristics, and production processes. Precise matching can only be achieved through “customized selection + strict testing + compliance certification”.
