• Foreign language name: Clean Room

• Also known as: clean workshop, clean room

• Main function: control air pollution

• Application: precision machinery industry, semiconductor industry and other industries

• Introduction to the

• Classification (a. by flow state of airflow; B. Classification by properties of controlled particles)

• Implement the ventilation measures required for cleanliness

• Air distribution considerations in clean rooms

• Clean room load characteristics and energy saving

• Requirements of clean room design for production process

1. Introduction

The development of clean room is closely connected with modern industry and advanced technology. Due to the environmental requirements of precision machinery industry (such as gyroscope and miniature bearing processing) and semiconductor industry (such as large-scale integrated circuit production), the development of clean room technology has been promoted. Domestic statistics have shown that the qualified rate of MOS circuit core produced in the environment without the requirement of clean level is only 10%~15%, and 64 is only 2% of the storage. At present, clean room is widely used in precision machinery, semiconductor, aerospace, atomic energy and other industries.

Classification of 2.

A. according to the flow state of airflow

According to the flow state of airflow, there are mainly three types of airflow distribution in the clean room:

(1) non-unidirectional flow clean room: it is often called turbulence type clean room before, and indoor airflow does not flow in a single direction. Non-unidirectional flow clean room has several common characteristics: terminal filter (high efficiency or sub-high efficiency) as close as possible to the clean room, it can be the air supply port or directly connected to the air supply port, or it can be connected to the air supply static pressure box of the room; The return air outlets are located at the lower part of the clean room to avoid "ash raising". Non-unidirectional flow vortex exists in clean room, not suitable for high cleanliness clean room, should be used in 6~9 class clean room;

(2) unidirectional flow clean room: unidirectional flow clean room is characterized by parallel streamline, flow in a single direction, and uniform wind speed on the section. There are vertical unidirectional clean room, quasi-vertical unidirectional flow, horizontal unidirectional flow clean room, etc.

(3) vector clean room: fan type hepa filter is used for air supply at the upper corner of the room, or ordinary hepa filter can be used for fan type air supply. Return air outlet is set at the lower part of the other side. The height and length of the room are usually between 0.5 and 1. The clean room is also rated 5 (100) clean;

The flow patterns of clean rooms are basically the three types mentioned above, but they can evolve in many forms in practical application. A clean room can be a mixture of unidirectional and non-unidirectional flows to achieve a high level of clean room in a local area (unidirectional flow section). For example, a horizontal one-way flow "tunnel" (one side is open) is set in the clean room, and the rest of the clean room is a vortex one-way flow pattern, so that the "tunnel" part can reach the cleanliness level above 5, and the work table is located in the "tunnel".

B. Classification by properties of controlled particles

(1) industrial clean room: the controlled particles are clean rooms for non-biological particles such as dust;

(2) biological clean room: controlled particles are clean rooms for biological particles

3. Ventilation measures required for cleanliness

To achieve the cleanliness level, the clean room must have comprehensive measures, including process layout, building plan, building structure, building decoration, personnel and material purification, air cleaning measures, maintenance and management, etc. Among them, air cleaning measures are the fundamental guarantee to achieve the clean level. In terms of air cleanliness, there are the following specific measures:

(1) the air supply to the clean room must be of high cleanliness. Therefore, high efficiency or sub-high efficiency filter (low cleanliness level) must be used as terminal filter to carry out the final level filtration of the air entering the clean room. In order to protect the terminal filter and extend its life, the air must be filtered through the intermediate filter first.

(2) according to the grade of clean room, reasonably select the flow pattern of airflow distribution in the clean room, and avoid eddy current zone in the working area; Try to make the clean air into the room directly to the work area; The flow of airflow is conducive to the removal of particles from the return air outlet in the clean room.

(3) sufficient air volume, not only to dilute the dust concentration of the air, but also to ensure a stable flow pattern;

(4) different levels of clean room, clean room and non-clean room or clean room and outdoor should maintain a certain positive pressure value;

4. Air distribution in clean room should be considered

(1) when the product is required to be clean at level 100, the laminar flow type shall be selected; When the product requirements of cleanliness is 1000~100000 level, choose turbulence flow type;

(2) reduce eddies and avoid bringing pollutants outside the work area into the work area;

(3) in order to prevent secondary dust flying, the airflow speed should not be too high. Return air vents for turbulence cleanrooms should not be located above the work area. Appropriate is on the floor or side wall bottom is decorated equably return wind mouth;

(4) the airflow in the working area should be uniform, and the flow rate must meet the requirements of technology and sanitation; Clean air flow should be as far as possible to cover the working area, so that pollutants will flow to the return air outlet before diffusion;

(5) the layout of working equipment should be kept at a certain interval to create conditions for the layout of air inlet and air return and the patency of air flow.

(6) the clean table should not be arranged in the laminar flow cleaning room. When it is arranged in the turbulence clean room, it should be placed on the upwind side of the airflow in the work area to improve the indoor air cleanliness;

(7) when there is a fume hood in a clean room, it is advisable to place it downwind of the airflow in the working area to reduce indoor pollution

5. Load characteristics and energy saving of clean room

In general, the energy consumption of purification air-conditioning system is much larger than that of general air-conditioning system. The reason is the different load characteristics between the two. As for the clean room, especially the semiconductor industry clean room, its load characteristics are as follows: large amount of fresh air is caused by large amount of exhaust air, so large amount of cooling consumption is required for fresh air treatment; Large air supply, large power consumption, high temperature rise fan pipeline; The production equipment has high calorific value and large amount of cooling consumption. The sum of these three loads generally accounts for 70%~95% of the total load. Therefore, the energy saving measures of purifying air conditioning system should reduce the fresh air volume (reduce the exhaust air volume). Control the air supply (reasonably determine the number of air changes); Make full use of return air volume; Choose low resistance and high efficiency air conditioning and purification equipment and variable air volume fan, etc.

6. Requirements of clean room design on production process

(1) the clean environment serves the production process, and it is natural that the design of clean room must meet the environmental requirements of the production process. Therefore, in the design of the clean room, the production process should be practical and realistic requirements for environmental parameters, such as the area, floor height, temperature, humidity, cleanliness should be high, low, not the higher the better. On the premise of not affecting the normal operation of the production process, the parameter requirements should be reduced as much as possible, the purification area should be controlled, the scope of high-purification clean area should be narrowed, and the one-way flow clean area of level 100 and higher level should be strictly controlled.

(2) in the production process when the plane division as much as possible to the same level of clean room together, put the process of high cleanliness requirements set in the upper hand side, the blues, toxic, hazardous, flammable and explosive gas, process equipment, containers, as far as possible in a clean area, if must be placed in clean areas should be airtight measures to reduce dust and exhaust emissions.