(A) the definition of clean room
Clean room, also known as clean room or clean room.
"Clean room" refers to a specially designed room that removes particulate matter, harmful air, bacteria and other pollutants in the air within a certain space range, and controls indoor temperature, cleanliness, indoor pressure, airflow speed and distribution, noise and vibration, lighting and static electricity within a certain demand range. In other words, no matter how the outside air conditions change, the room can maintain the original requirements of cleanliness, temperature, humidity, pressure and so on.
The main function of clean room is to control the cleanliness, temperature and humidity of the atmosphere where products (such as silicon wafers) come into contact, so that products can be manufactured in a good environmental space. This space is called "clean room".
All countries in the world have their own norms, but generally use American federal standard 209. The following is only an introduction and comparison between 209D and 209E and the standards formulated by other countries in the world.
The biggest difference between 209E and 209D is that metric units are added to the units represented by 209E, and the clean room grade is represented by the prefix' m', such as M 1, M 1.5, M2.5, M3 ... and so on, which conforms to the international standardization of metric units, and the Arabic numerals after the letter m are >: number of dust particles per cubic meter. If the number of dust particles is between the complete powers of the former and the latter, it is expressed by 1.5, 2.5 and 3.5. ....
The American federal standard FS 209D takes the English system as the unit per cubic foot, and Japan adopts the metric system, that is, the counting standard is 0. 1μm particles. The Japanese standard is represented by 1 grade, grade 2 and grade 3 ... Grade 8, the best grade is 1 grade, and the worst grade is grade 8. The total number of dust particles per cubic meter is converted into the power of 10, and its index is obtained.
(3) Clean room control project
1. It can remove dust particles floating in the air.
2. It can prevent the generation of dust particles.
3. Control of temperature and humidity.
4. Adjustment of pressure.
5. Eliminate harmful gases.
6. Airtightness of structures and compartments.
7. Prevention and control of static electricity.
8. Prevent electromagnetic interference.
9. Consideration of safety factors.
10. Energy saving considerations.
(4) Classification of clean rooms
1. Turbulence:
Air enters the clean room from the air conditioning box through the air duct and air filter (HEPA) of the clean room, and returns from the partition wall panels or raised floors on both sides of the clean room. The airflow moves in a nonlinear way and is in an irregular turbulent or eddy state. This type is suitable for clean room grade 1 0,000-100,000.
Advantages: simple structure, low system construction cost and easy expansion of clean room. In some special-purpose places, the dust-free workbench can be used together to improve the level of clean room.
Disadvantages: The dust particles floating in the indoor space caused by turbulence are not easy to be discharged, and it is easy to pollute the process products. In addition, if the system stops running and restarts, it often takes a long time to reach the required cleanliness.
2. Laminar flow (laminar flow):
The laminar airflow moves into a uniform straight line, and the air enters the room through the filter with the coverage of 100%, and returns from the raised floor or the partition boards on both sides. This type is suitable for use in the environment where the clean room level is high. Generally, the clean room level is 1~ 100. Its types can be divided into two types:
(1) Horizontal laminar flow: horizontal air is blown out from the filter in one direction and sent back by the return air system on the opposite wall, and dust is discharged outdoors with the wind, which generally causes serious pollution to the downstream side.
Advantages: simple structure and stability in a short time after operation.
Disadvantages: the construction cost is higher than turbulence, and the indoor space is not easy to expand.
(2) Vertical laminar flow: The ceiling of the room is completely covered with ULPA filter, and the air is blown from top to bottom, so that a high degree of cleanliness can be obtained, and the dust generated during the process or by workers can be quickly discharged outside without affecting other working areas.
Advantages: easy to manage, it can reach a stable state in a short time after the start of operation, and it is not easily influenced by the running state or operators.
Disadvantages: high cost, difficult flexible use of space, large space occupied by hangers on the ceiling, and troublesome maintenance and replacement of filter screens.
3. Hybrid:
Compound type is the combination or use of turbulence and laminar flow, which can provide local ultra-clean air.
(1) clean tunnel: the process area or work area is covered with 100% HEPA or ULPA filter, which can improve the cleanliness level to above 10, thus saving installation and operation costs.
This type needs to isolate the operator's work area from product and machine maintenance to avoid affecting work and quality during machine maintenance. This type is mostly used in ULSI process.
Clean tunnel has two other advantages: a. It is easy to expand flexibly; B. Equipment maintenance can be easily carried out in the maintenance area.
(2) Clean pipe: the automatic production line through which the product flows is surrounded and purified, and the cleanliness level is increased to above 100. Because the product is isolated from the operator and the dust-producing environment, good cleanliness can be obtained by a small amount of air supply, which can save energy and is most suitable for automatic production lines without manual operation. Suitable for pharmaceutical, food and semiconductor industries.
(3) assembling local cleaning points: improving the cleanliness of the product process area in the turbulent clean room with the clean room level of10,000 ~100,000 to above1000 for production; Clean workbench, clean shed and clean air cabinet all belong to this category.
Clean workbench: grade 1~ 100.
Clean shed: In order to enclose a small space in the turbulent clean room space with antistatic transparent plastic plates, independent HEPA or ULPA and air conditioning fan units are adopted to become a relatively advanced clean space, with the grade of 10~ 1000, the height of about 2.5 meters and the coverage area of about1000 m2. The four columns are equipped with movable wheels for flexible use.
(5) Air flow in clean room
The cleanliness of clean room is often influenced by airflow, in other words, the movement and diffusion of dust produced by people, machine rooms and building structures are dominated by airflow.
HEPA and ULPA are used to filter the air in the clean room, and the dust collection rate is as high as 99.97~99.99995%, so the air filtered by this filter can be said to be very clean. However, in addition to people, there are dust sources such as machines in the clean room. Once the dust diffuses, it can't maintain a clean space, so it is necessary to use airflow to quickly discharge the dust outside.
The airflow in the clean room is an important factor affecting the performance of the clean room. Generally, the airflow speed of clean room is 0.25~0.5m/s, which belongs to the breezy area and is easily confused by the actions of people and machines. Although increasing the wind speed can restrain the influence of this disturbance and maintain cleanliness, it will affect the increase of operating expenses, so it is necessary to supply it with the most suitable wind speed to achieve the appropriate wind speed and meet the required cleanliness level.
On the other hand, in order to achieve the stable effect of clean room cleanliness, maintaining uniform airflow is also an important factor. If you can't maintain a uniform airflow, it means that the wind speed is different, especially on the wall, and the airflow will swirl along the wall. At this time, it is actually difficult to achieve high cleanliness.
To maintain a uniform airflow in the vertical direction of laminar flow, it is necessary to: (a) there should be no difference in the speed of the blowing surface; (b) There should be no difference in wind speed on the suction surface of the floor return air plate. When the speed is too low or too high (0.2m/s, 0.7m/s), eddy current will be generated, while when the speed is 0.5m/s, the airflow is uniform. At present, the wind speed of general clean rooms is between 0.25 and 0.5m/s.. ..
There are many factors that affect the airflow in the clean room, such as process equipment, personnel, clean room assembly materials, lighting appliances and so on. At the same time, the distribution point of airflow above the production equipment should also be considered.
The gas distribution point on the surface of the operation console or production equipment should generally be located at the distance of 2/3 between the clean room space and the partition, so that when workers work, air can flow from the inside of the process area to the operation area and take away dust; If the shunt point is arranged in front of the process area, it will become an inappropriate airflow shunt. At this time, most of the airflow will flow to the process area, and the dust generated by the operator's operation will be carried behind the equipment, so that the workbench will be polluted and the yield will be reduced.
Eddy current will be generated at the junction of obstacles such as clean room workbench, and the cleanliness nearby will be relatively poor. Drilling back air holes on the workbench will minimize eddy current phenomenon. Whether the selection of assembly materials is appropriate and whether the equipment layout is perfect is also an important factor for whether the airflow becomes a vortex phenomenon.
(6) Composition of clean room
The composition of the clean room consists of the following systems (these systems are indispensable in the system molecules), otherwise a complete and good-quality clean room cannot be formed:
(1) suspended ceiling system: including suspended ceiling poles, rigid beams (I-beams or U-beams) and suspended ceiling grid beams (suspended ceiling grids or suspended ceiling frames).
(2) Air conditioning system: including air cabin, filtration system, windmill, etc.
(3) Partition wall: including doors and windows.
(4) Floor: including elevated floor or anti-static Shu Mei floor.
(5) Lighting equipment: including fluorescent lamps and yellow tubes.
The main building structure of clean room generally adopts steel bars or bone cement, but no matter which structure, the following conditions must be met:
A cracks will not occur due to temperature change 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, heat preservation should be high;
Cleanrooms are classified by purpose (can be divided into two categories)
(1), industrial clean room-for controlling inanimate particles. It mainly controls the pollution of air dust particles to the working object, and generally maintains positive pressure inside. Suitable for precision machinery industry, electronic industry (semiconductor, integrated circuit, etc. ), aerospace industry, high-purity chemical industry, atomic energy industry, magneto-optical products industry (optical disc, film and tape production), LCD (liquid crystal glass), computer hard disk, computer magnetic head production and many other industries.
(2) The biological clean room mainly controls the pollution of living particles (bacteria) and inanimate particles (dust) to the working object. Can be divided into; First, the general biological clean room is mainly to control the pollution of microorganisms (bacteria). At the same time, its internal materials should be able to withstand the erosion of various disinfectants, and the internal pressure is generally guaranteed. In essence, the internal material should be an industrial clean room that can withstand various sterilization treatments. Examples: pharmaceutical industry, hospital (operating room, sterile ward) food, cosmetics, beverage products production, animal laboratory, physical and chemical laboratory, blood station, etc.
B. Biosafety clean room: it mainly controls the pollution of living particles of the working object to the outside world and people. The interior should keep negative pressure with the atmosphere. For example: bacteriology, biology, clean laboratory, physical engineering (recombinant gene, vaccine preparation)
Principle and characteristics of eight-story turbulent clean room
1. Definition: A turbulent clean room is defined as a clean room with uneven airflow speed and non-parallel airflow accompanied by backflow or vortex.
2. Principle: Turbulent clean room continuously dilutes indoor air by air supply, and gradually dilutes polluted air to achieve cleanliness (generally, the design purification level of turbulent clean room is above1000 ~ 300,000).
3. Features: Turbulent flow clean room relies on multiple ventilation to achieve cleanliness and cleanliness level. The number of air changes determines the purification level in the definition (the more air changes, the higher the purification level).
(1). Self-purification time: refers to the time when the clean room starts to supply air according to the designed air exchange times and the indoor dust concentration reaches the designed purification level. 1000 is expected to be less than 20min (calculated by 15min), 10000 is expected to be less than 30min (calculated by 25min) and 100000 is expected to be less than 40min (calculated by 30min).
(2) The air change frequency (designed according to the above self-purification time requirement) is 1 43.5-55.3 times/hour for class 000 (specification: 50 times/hour) 1 23.8-28.6 times/hour for class 000 (specification: 25 times/hour) 5644.
Six, clean room (clean air conditioning) structure
(1), combined purification air conditioning unit
(2), clean the air supply pipeline
(3), clean the return air pipe
(4) Air supply plenum
(5), high efficiency filter
(6), porous diffusion plate
(7), clean room ceiling
(8), clean room partition
(9), louver air return port
(10), new tuyere
Pollution source knowledge
1, dust amount
The amount of dust produced in the clean room, which comes from equipment and can be removed by local exhaust without flowing into the room; Compared with the amount of human hair dust, the dust generated by products and materials during transportation is generally very small and can be ignored; Due to the application of metal half wall (color steel sandwich panel), the dust from the building surface is very small, generally accounting for less than 10%, and the dust mainly comes from people, accounting for about 90%. On the amount of human hair dust, due to the improvement of clothing materials and styles, the absolute amount of hair dust is also decreasing.
A material: cotton has the largest dust content, followed by cotton, polyester, antistatic pure polyester and nylon.
B, style: the dust emission of the large hanging type is the largest, followed by the upper and lower packing type, and the full cover type is the least;
C. Activity: The amount of dust generated during the action is generally 3-7 times that of the static time;
D, cleaning: the amount of dust generated by solvent cleaning is reduced to one fifth of that generated by general water cleaning.
The amount of dust produced on the surface of indoor maintenance structure is based on the ground, and the amount of dust produced on the ground surface of about 8 square meters is equivalent to that of a stationary person.
2. Bacterial quantity
The analysis of external test data can be considered as follows:
(1) When workers wear sterile clothes in the clean room:
The amount of bacteria at rest is generally 10-300/min.
The amount of bacteria produced during general physical activity is 150- 1000/min.
When walking fast, the number of bacteria is 900-2500/min. People.
(2) Cough is usually 70~700 times/minute.
A sneeze is usually 4000~62000 per minute.
(3) When wearing ordinary clothes, the number of bacteria is 3300~62000/min.
(4) The number of bacteria without masks: the number of bacteria with masks is 1:7~ 1: 14.
(5) Bacterial quantity: the dust quantity is1:500 ~1:1000. According to domestic examples:
(6) The number of bacteria during the operation was 878/min.
It can be seen that the static bacterial growth of people wearing clean indoor sterile clothes generally does not exceed 300 /min. People, and the dynamic bacterial growth is generally not more than 65438+/-0000/min. People, as the calculation basis is feasible.