Characteristics of Constructing High - level Cleanrooms in Electronic Factories
1. Requirements of the Production Process in Electronic Factories for a Controlled Environment
Electronic factories, such as microelectronics (IC) factories for large - scale integrated circuits (LSI), very - large - scale integrated circuits (VLSI), and optoelectronics factories for liquid - crystal displays (LCD), thin - film transistor - liquid - crystal displays (TFT - LCD), plasma display panels (PDP), light - emitting diodes (LED), organic light - emitting diodes (OLED), and polymer organic light - emitting diodes (PLED), all rely on a clean production environment. The required environment encompasses not only building enclosures, structures, air, water, gases, solvents, and other raw materials, but also various environmental factors such as sound, light, electricity, magnetism, and vibration. For example: the form and storey height of the building, the load - bearing capacity of the structure, the finishing materials of the enclosure structure; the cleanliness, temperature, humidity, and static pressure of the ambient air; the purity and particle and heavy - metal content of water and gases; as well as the environmental noise, illumination, static electricity, electromagnetic shielding, and micro - vibration. Generally speaking, the requirements of the production process in electronic factories for the environment can be summarized by the five characters: large, clean, precise, pure, and strict.
·Large: The production process demands that the area of cleanrooms is getting larger and larger. Take the cleanroom area for TFT - LCD production as an example. The area of a cleanroom for 5th - generation TFT production is about 28,000 m²; that for 6th - generation TFT is about 40,000 m²; and for 8th - generation TFT production, the area of a single cleanroom exceeds 80,000 m², large enough to park more than 20 Boeing 747 aircrafts.
·Clean: Cleanrooms in the front - end processes of microelectronics (IC) and optoelectronics (TFT - LCD) in electronic factories have increasingly strict requirements for environmental cleanliness. For example, the cleanliness requirement for the photolithography room in the front - end process of 12 - inch wafer VLSI is as high as Class 1 (0.1μm), meaning that the number of particles ≥ 0.1μm in each cubic foot of air should not exceed 1, which is equivalent to ISO Class 1.
·Precise: The production process in electronic factories has increasingly precise requirements for the control accuracy of ambient air temperature and humidity. Take the photolithography room of microelectronics mentioned above as an example: its temperature accuracy is ± 0.1°C, and the relative humidity accuracy is ± 3%.
·Pure: The front - end process of large - scale integrated circuits has increasingly strict requirements for the purity of high - purity water, high - purity gases, and high - purity solvents used in production. For high - purity water, for example, not only is there a requirement for its resistivity, but also strict requirements for the particles, bacteria, heavy metals, and ionic components of other elements contained in it. With the development of the production process, the requirements for its purity are getting higher and higher, truly "pure and purer".
·Strict: The production in the electronics industry has strict requirements not only for environmental cleanliness, temperature, and humidity, but also for environmental factors such as sound (noise), light (illumination), electricity (static electricity), magnetism (electromagnetic field shielding), and vibration (micro - vibration). Especially in microelectronics production, new and strict requirements have been put forward for molecular - level pollution in the environment. Molecular pollution refers to the strict control of elements harmful to semiconductor processes in ambient air, such as sodium (Na), carbon (COx), sulfur (SOx), and nitrogen (NOx). Therefore, when treating air, water spraying (using tap water or pure water) is used to absorb harmful molecular components in outdoor air, and chemical filters are used to adsorb harmful molecular components in fresh air.
2. High - level Cleanrooms in Electronic Factories Mostly Adopt Mixed - flow Cleanrooms
In order to reduce the initial construction investment and operating energy consumption of cleanrooms, in high - level cleanrooms of electronic factories, vertical unidirectional flow with high purification levels from ISO Class 1 to ISO Class 5 is generally used in the most important and critical parts of the process production. Large - area non - unidirectional flow (ISO Class 6 - ISO Class 8) is used instead of large - area unidirectional flow. That is, vertical unidirectional flow and non - unidirectional flow are combined in one cleanroom to form a mixed - flow cleanroom. The purification air - conditioning system of a mixed - flow cleanroom generally adopts the air - supply scheme of a makeup air unit (MAU) + fan filter unit (FFU) + dry cooling coil (DC). The mixed cleanrooms widely adopted in large - area production plants of microelectronics and optoelectronics at home and abroad have the advantages of convenient adjustment, remarkable energy - saving, strong flexibility, adaptability to the upgrading of the electronic industry process, and the ability to save non - production area and non - production space. It is the best air - handling scheme and the most excellent air - supply system.
The makeup air unit (MAU) in the scheme has five major tasks:
(1) The MAU should maintain the positive pressure in the cleanroom and supply enough fresh air to compensate for the exhaust air of process equipment, so as to prevent the infiltration of polluted outside air. Generally, the fresh air volume should be equal to the sum of the exhaust air volume of the cleanroom and the leakage air volume for maintaining the indoor positive pressure.
(2) The MAU should ensure the strictly required relative humidity in the cleanroom. Therefore, in summer, the MAU should have sufficient cooling and dehumidification capacity, and in winter, certain humidification measures are also required.
(3) Multiple - stage filters (coarse - effect, medium - effect, and high - efficiency filters) should be installed in the MAU to protect the ultra - high - efficiency filter at the terminal of the FFU.
(4) The MAU should be able to absorb and adsorb harmful gas components in the outdoor atmosphere to eliminate molecular pollution in the fresh air. For this purpose, a water - spraying chamber should also be installed in the MAU to absorb harmful elements such as nitrogen and sulfur. The water - spraying chamber has single - stage and two - stage water spraying (spraying tap water in the first stage and pure water in the second stage). At the same time, a chemical filter (activated carbon filter) should be installed to adsorb harmful molecular components in the fresh air.
(5) North of the Yellow River, especially in the northeastern region of China, the outdoor air temperature in winter is dozens of degrees below zero. Therefore, anti - freezing pre - heating measures need to be considered for the MAU in the north.
The fan filter unit (FFU) in the scheme is to ensure the high - level cleanliness in the cleanroom. According to the cleanliness requirements, the filter in the FFU can be a high - efficiency filter (H14) or an ultra - high - efficiency filter (U15, U16, U17).
Performance requirements for the FFU:
(1) The cross - sectional air velocity v of the FFU outlet should be ≥ 0.45 m/s; the uniformity of the cross - sectional air velocity should be ± 15%.
(2) The external static pressure of the FFU should be ≥ 120 Pa.
(3) The external noise of the FFU should be ≤ 50 dB(A).
(4) The service life of the FFU fan should be 5,000 - 8,000 hours.
Suzhou Pharma Machinery Co.,Ltd.
2025/11/20
Gino
