Control Panel Cooling units Technical Information
3-2. Precision air conditioners (TCU/ECU) and clean rooms
This section describes the temperature and humidity control in precision air conditioning and cleanliness level of a clean room.
(1) Industrial air conditioning and conditions by process
As its name suggests, industrial air conditioning is air conditioning used for industrial applications. In the manufacturing processes of a factory, the purpose of industrial air conditioning is to maintain and improve the working environment of workers and the quality control of products. In the research and development field, its purpose is to stabilize product evaluation and analytical accuracy. Therefore, air conditioning conditions required in industrial air conditioning differ depending on the application. Recently, quality control of products is an important issue in the manufacturing industry. High-quality air conditioning control has attracted attention as one of the most effective measures for this purpose, and the scope of industrial air conditioning is expanding even further. Industrial air conditioning has become indispensable in the manufacturing processes of factories nowadays.
(2) Cleanliness level and clean room
Table 1 Temperature and humidity conditions by the industrial air-conditioning process
| Industry | Process | Temperature condition | Humidity condition |
|---|---|---|---|
| Semiconductor | Photolithography | 22～24℃±0.2℃ or less | 45～50％±2～5％ |
| Dry etching | 22～24℃±2℃ or less | 45～50％±5％ or less | |
| Sputtering | 22～24℃±2℃ or less | 45～50％±5％ or less | |
| Pharmaceutical | Powdered chemical storage | 24℃±3℃ or less | 30～50% |
| Tableting | 24℃±2℃ or less | 20～40% | |
| Micro-analysis/blood serum | 24℃±2℃ or less | 50% | |
| Optical lens | Grinding | 25℃±2℃ or less | 50±5% |
| Printing | Printing | 24～27℃±5℃ or less | 50±2% |
| Cutting, drying, pasting etc. | 21～27℃ | 45～50％ | |
| Foodstuffs | Fresh bread | 24～26.5℃ | 40～50％ |
| Raw material storage | 26.5～29.5℃ | 80～85％ |
*The list above serves simply as a general guide. Temperature and humidity conditions vary depending on the environment.
Cleanliness level
One effective measure to improve product yield and quality is to improve the environmental control accuracy. One of the important factors in environmental control is the management of the cleanliness level. The cleanliness level refers to the extent of air pollution inside a space based on certain criteria. The standard was originally established to quantify the level of the air cleanliness in a clean room, but together with the advancement in environmental separation technology, its use has expanded to spaces other than clean rooms where cleanliness needs to be controlled.
Clean room
A clean room is a special room to achieve and maintain the cleanliness of a space. Clean rooms can be divided into two types depending on the purpose of use. One type is the Industrial Clean Room ICR, which aims to control floating particles in the air used in industrial applications. The other type is the Biological Clean Room (BCR) used in the biotechnology, medical and food sectors to mainly control floating microorganisms in the air. Clean rooms are also classified by the air flow methods such as the “downflow method”, “turbulent flow method” and so on. Clean rooms achieve a high level of cleanliness by discharging or diluting floating particles in the air, which is an environmental factor of cleanliness, using clean air. In addition, where necessary, control of environmental factors such as temperature, humidity, and pressure etc. may be required.
Table 3 Type of clean room
| Industrial Clean Room (ICR) | Liquid crystals, semiconductors, LSIs, electronic components, precision instruments, printing, etching, deposition, printed circuit boards, lenses, optical disks, powder manufacturing, raw material manufacturing, etc. |
|---|---|
| Biological Clean Room (BCR) | Chemicals, operating rooms, neonatal rooms, meat processing, mushroom cultivation, plant cultivation, brewing and cooking rooms, biotechnology, genetic testing facilities, etc. |
(3) Cleanliness standards and class
The class (cleanliness level) prescribes the amount of particulate matter in a space according to the standards.
Although standards have now been unified to international ISO standards, US federal standard “FED-STD-209D”, which was often used in the past, is still widely used today.
ISO14644-1
The number of particles of size 0.1 μm or more per m3 of air is used to classify the cleanliness level into 9 classes from 1 to 9. The number of digits determine the class i.e. Class 1 if the number of particles per m3 of air is 10, and Class 2 if it is 100 or less, and so on.
FED-STD-209D
Depends on the number of particulate matter with a size of 0.5 μm present in one cubic foot (1 foot = about 30 cm) of air in the target space. “Class 100” if the number of floating particles in one cubic feet of air is less than 100, and “Class 1,000” if it is less than 1,000.
Table 5 Measurement particle size and upper limit concentration according to the air cleanliness class
| Cleanliness class | Upper limit concentration (pcs/m upper limit concentration (pcs/m3)) | ||||||
|---|---|---|---|---|---|---|---|
| International uniform standards ISO 14644-1 |
US federal standards FED-STD-209D |
Measurement particle size | |||||
| 0.1μm | 0.2μm | 0.3μm | 0.5μm | 1.0μm | 5.0μm | ||
| Class 1 | 10 | 2 | |||||
| Class 2 | 100 | 24 | 10 | 4 | |||
| Class 3 | 1 | 1,000 | 237 | 102 | 35 | 8 | |
| Class 4 | 10 | 10,000 | 2,370 | 1,020 | 352 | 83 | |
| Class 5 | 100 | 100,000 | 23.700 | 10,200 | 3.520 | 832 | 29 |
| Class 6 | 1,000 | 1,000,000 | 237,000 | 102.000 | 35,200 | 8,320 | 293 |
| Class 7 | 10,000 | 352,000 | 83,200 | 2,930 | |||
| Class 8 | 100,000 | 3,520,000 | 832,000 | 29,300 | |||
| Class 9 | 35,200,000 | 8,320,000 | 293,000 | ||||
(4) Other items related to the cleanliness level
Air filter
Table 6 Type of filter
| Coarse dust filter | High-performance filter | HEPA filter | ULPA filter | Ultra-ULPA filter | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Clean in use | None in particular | Class 100,000～200,000 | Class 100～1,000 | Class 10～100 | Class 1～10 | |||||
| Example of use | General office etc. | General office etc. | Semiconductor manufacturing Post-processes etc. |
Semiconductor pre-processes Manufacturing line etc. |
Ultra LSI manufacturing process | |||||
| Capacity | Foreign contaminant, dirt capturing capacity | Higher capturing capacity than a coarse dust filter | Possesses the capacity to capture 99.97% of 0.3 μm particles | Possesses the capacity to capture 99.95% of 0.15 μm particles | Possesses the capacity to capture 99.99% of 0.15 μm particles | |||||
| Blowing method | Turbulent ventilation | Down flow ventilation | ||||||||
Table 7 Other filters
| Activated carbon filter | Chemical filter | |
|---|---|---|
| Description | Absorption of ammonia, acetic acid, aldehyde gas and other VOC | Chemical contaminants Removal of molecular contaminants |
| Application | Deodorization | Semiconductor/liquid crystal manufacturing process |
Ventilation frequency
Recommended ventilation frequency table
| Class of clean room | General value | USA209E standard | Average air flow rate |
|---|---|---|---|
| Class 100,000 | 20～ 30 times／h | 20 | .005-.041m／sec |
| Class 10,000 | 30～ 70 times／h | 75 | .051-.076m／sec |
| Class 1,000 | 100～200 times／h | 150 | .127-.203m／sec |
| Class 100 | 200～600 times／h | 250～400 | .203-.408m／sec |
Air flow system
Table 9 Typical alert system
| Down flow system | Turbulent flow system | Other typical system | |
|---|---|---|---|
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| Cleanliness level | Class 10～1,000 | Class 1,000～ | Class 10,000～ |
| Features | Easy to distribute the temperature, humidity and cleanliness level uniformly Installation is restricted because ducts are required on the ceiling and floor. | Management is simple. An non-uniform zone occurs in the four corners of the space. |
Non-uniform zones tend to occur in direct proportion to the distance from the outlet. |
| Initial cost | High | Slightly high | Low |
| Running cost | High | Slightly high | Relatively low |
| Non-control zone | Few | Generated in the 4 corners | Generated in the furthest venting areas |
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