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Grade classification and application standard of clean room
2023/9/8
1. Grade description of clean room
According to the standard issued by the Federal government of the United States [Federal Atandard (FS) 209E, 1992], clean rooms can be divided into six levels. They are 1 level, 10 level, 100 level, 1000 level, 10000 level, 100000 level, if the grade of the clean room is described only by the number of dust particles, it can be assumed that the size of the dust particles is 0.5um, and the clean room grade should be expressed by the level of a specific dust particle size. For example: Grade 10 at 0.2um (dust particle size of 0.2um or greater, density of no more than 75 pieces/cubic foot), Grade 1 at 0.1um (dust particle size of 0.1um or greater, density of no more than 35 pieces/cubic foot).
2. Clean room grade standard
According to the number of versions of clean room grade standards, this paper sorted out two more commonly used division standards, namely the international standard IOS14644-1 and the Chinese standard GB/T16292-1996, please see the following table for details:
Air cleanliness classification standard: IOS14644-1 (International standard)
Air cleanliness classification standard: GB/T16292-1996 (China standard)
3. Standard classification of clean room
Turbulent Flow
The air enters the clean room from the air conditioning box through the air duct and the air filter (HEPA) in the clean room, and is returned by the wall panels or elevated floors of the compartmented walls on both sides of the clean room. The air flow is not linear and is in an irregular turbulent or eddy state. This type is suitable for clean room class 1,000-100,000.
Advantages: simple structure, low system construction cost, clean room expansion is relatively easy, in some special places can use clean table, improve the level of clean workshop.
Disadvantages: Dust particles caused by turbulence floating in the indoor space is not easy to discharge, easy to pollute the product. In addition, if the system stops running and then activates, it will take quite a long time to achieve the required cleanliness.
Laminar flow
Layer flow air flow into a uniform linear shape, the air by the coverage of 100% filter into the room, and by the elevated floor or two sides of the wall panel return air, this type is suitable for clean room grade demand higher environment use, generally its clean room grade is Class 1~100.
Its type can be divided into two types:
Horizontal layer flow in the dust-free workshop: the horizontal air is blown out from the filter in a single direction, and the air is returned by the return air system on the opposite wall. The dust is discharged to the outside with the wind, and the pollution on the downstream side is generally serious.
Advantages: simple structure, can become stable in a short time after operation.
Disadvantages: The construction cost is higher than the turbulence, and the interior space is not easy to expand.
Vertical layer flow in dust-free workshop: The ceiling of the room is completely covered with ULPA filter, and the air is blown from top to bottom, which can obtain a high degree of cleanliness, and the dust generated by the production or staff can be quickly discharged outside without affecting other work areas.
Advantages: Easy management, the operation can reach a stable state within a short time, and is not easily affected by the operating state or the operator.
Disadvantages: The construction cost is high, the elastic use of space is difficult, the ceiling hanger takes up considerable space, and the maintenance and replacement of the filter is more troublesome.
Mixed Type
The compound type is the combination of turbulent flow and layer flow, which can provide local ultra-clean air.
Clean Tunnel: 100% coverage of the production area or work area with HEPA or ULPA filters to raise the cleanliness level to more than 10, which can save installation and operation costs. This type needs to isolate the working area of the operator from the product and machine maintenance to avoid affecting the work and quality of the machine maintenance, and the production of very large scale integrated circuits mostly uses this type. Clean tunnels have two other advantages: easy flexible expansion and easy maintenance of equipment in the maintenance area.
Clean Tube: The automatic production line of the product process is surrounded and purified, and the cleanliness level is raised to more than 100. Because the product and the operator and the dust environment are isolated from each other, a small amount of air supply can be obtained with good cleanliness, which can save energy, and automated production lines without manual labor are most suitable for use. Drugs, food and semiconductors are applicable.
Clean workshop and local clean room (Clean Spot) : the cleanliness level of the product production area of the turbulence clean room is raised to more than 10~1000 for production.
Fourth, the application standard of clean room
If you want to test whether the clean room meets the application standards, you can first consider the four aspects of shelter rate, wind speed & temperature and humidity, pressure difference, and composition requirements:
Obscuration ratio
Air Change: Surface area of FFU * Wind speed * Number of FFU/volume of clean room
HEPA shielding rate: Surface area of FFU * Number of FFU/clean room area
Wind speed, temperature and humidity
Air flow speed: 0.3-0.5m/s (60-100ft/min)
General temperature control range: T= (21±2) ℃
General humidity control range: (45±5) %RH
Differential pressure
A reasonable design pressure difference between the two clean rooms should be 10Pa, while a pressure difference of 15Pa should be maintained in the clean room and in the area where the cleanliness level is not confirmed. When there are practical difficulties in generating these pressure differences, maintaining a minimum pressure difference of 5Pa is acceptable.
Constitutive requirement
A. Cracks will not occur due to temperature changes and vibration
B, it is not easy to produce dust particles, and it is difficult to attach particles
C, low hygroscopicity
D, in order to maintain indoor humidity conditions, thermal insulation should be high
