Influencing Factors Of Cleanliness In Cleanroom

The main function of the cleanroom is to continuously provide a clean environment that meets expectations, and the cleanliness is the core technical indicator for evaluating the clean room level. From the perspective of clean room engineering construction, the factors affecting cleanliness include architectural design and construction quality; from the perspective of clean room management and maintenance, it includes personnel, materials and dynamic process control. When the cleanliness is evaluated statically, the categories of each element appear to be independent, but when the dynamic cleanliness performance is abnormal, the butterfly effect can appear among the influencing factors. This study puts forward a control idea based on the influence factors of the defect on the cleanliness of the example.

The clean room is also called the clean room. Its function is to ensure that the exogenous pollution particles in the outdoor environment will not affect the cleanliness of the clean room environment, and to ensure that the endogenous pollution particles generated in the clean room environment can be diluted and filtered, and continuously maintained Dust-free status in a controlled environment. With the innovation and development of aseptic sanitary product research and development, the demand for clean environment is becoming more and more extensive; at the same time, with the innovation and development of precision electronic technology, the application requirements for clean environment are becoming more and more lean. For example, the particle load in the production process of medicines, medical devices and other products will cause adverse reactions or infection of the affected people, and the dust contamination of precision instruments, electronic chips and other products in the production process will lead to abnormal wear or product scrapping.

Part 1 Cleanliness Level

The evaluation of the cleanliness of the clean room is based on the control level of suspended particles in the indoor environment. The higher the cleanliness level, the smaller the particle size of the controlled suspended particles and the lower the controlled particle concentration threshold. Cleanrooms for aseptic and hygienic products focus on the control of microorganisms in the environment, also known as biological cleanrooms. The control of suspended particles ≥ 5.0 μm can indirectly control the level of microorganisms in the cleanroom, so biological cleanrooms The cleanliness of the cleanliness is usually controlled at level 5 or below. The clean room used for precision machining and integrated electronic products is mainly to control the suspended particles in the environment, also known as the industrial clean room. With the technological innovation of nano-manufacturing process, the demand for cleanliness in industrial clean rooms has reached level 1 and above.

Part 2 Element Analysis

2.1 Interior Decoration Design

The construction and decoration principle of the clean room is to use materials that do not produce dust, the surface is smooth and easy to clean, and the gaps are closed and dust-free. The door of the clean room should not have a threshold. Unnecessary concave and convex surfaces will make the cleaning work of the clean room less effective.

2.2 Filter Integrity

The core technology to ensure that the clean room is not affected by dust particles is the air purification and filtration function in the ventilation system. The air filter is the core equipment for creating a clean environment. The coarse-effect filter can filter out particles above 10 μm, the medium-effect filter can filter out particles between 1 and 10 μm, and the high-efficiency filter can filter out particles ≥ 0.3 μm. As the last barrier in the clean room, the high-efficiency filter installed at the end of the ventilation duct can be regarded as the core technology. The integrity of its installation determines the cleanliness of the clean room. According to the aerosol photometer test, not only the air supply of the filter is required The surface transmittance is ≤ 0.01%, and the evaluation standard for the airtightness of the installation frame should also be ≤ 0.01%. This requirement shows that the airflow in the air supply duct should not have unfiltered parts entering the clean room, and the airflow entering the clean room must be effectively filtered. At multiple ends in the non-unidirectional flow clean room, the integrity of the high-efficiency filter should be 100% confirmed, and the leakage of any filter may affect the cleanliness of the clean room.

2.3 Airtightness Of Building Structure

The clean room is a closed space formed by splicing panels, and the splicing gap between material units will have an important impact on the cleanliness of the clean room. Good airtightness can protect the clean room from the infiltration and pollution of suspended particles in the outdoor atmosphere during shutdown. The suspended particles of 0.1 ~ 1.0 μm in the environment have a typical Brownian motion, and the Brownian motion will cause the suspended particles to move from a dense environment to a low density environment. Macroscopic diffusion occurs in the environment.

2.4 Personal Protection

Personnel come in and out frequently in the clean room and have a large amount of activity. The metabolism of the human body will secrete pollutants, and the clothing will also release pollutants. Therefore, personnel are the main source of pollution in the clean room. The best measure for controlling personnel to reduce particle pollution in a clean room is to wear clean clothes, wrap the body surface and daily clothing with clean clothes, and the cloth of the clean clothes has barrier properties to the particles released by the personnel’s body, so it can realize the protection of human pollution sources purify. Since personnel have a great influence on the clean room, the role of clean clothes is particularly important. Clean clothes with good performance should ensure that the material does not produce dust, and has good dust resistance, antistatic properties and wear resistance.

2.5 Selection Of Materials

2.5.1 Selection Of Sanitary Ware

When there is no special requirement, the materials entering the clean room should at least comply with the basic principle of no dust production.

2.5.2 Selection Of Paper

Three types of paper that are common in clean rooms are selected for evaluation. Using the airflow organization characteristics of the vertical unidirectional flow environment, in a dust-free experimental condition, the sample is shaken by stretching to collect the particles emitted from the sample at a rate of 100 cm2 per minute. When materials with high dust generation cannot be avoided in the clean room, the necessary conditions for their use should be limited to reduce the impact on cleanliness.

2.6 Airflow Organization In The Cleanroom

The clean air flow conveyed in the clean room can dilute the generated suspended particles, so as to realize the control of cleanliness. The ideal airflow organization should fill all the spaces in the clean room, and the evaluation index is the self-cleaning time of the clean room. The use of the clean room will directly affect the organizational form of the indoor air supply.

2.7 Process Control

2.7.1 Dynamic Differential Pressure

The specification requires that the static pressure difference between adjacent clean rooms of different levels should be ≥ 5 Pa, and the static pressure difference between the clean room and the outside should be ≥ 10 Pa. During the production process, due to the dust or odor generated during the mixing or configuration process, local exhaust ventilation is required to limit the spread of pollutants in the clean room. The dynamic partial exhaust air intervention will change the static balance of the air supply and return air volume in the clean room, and disrupt the static pressure difference. In extreme cases, the positive pressure clean room can be turned into a negative pressure state, and the negative pressure air flow will make the outdoor air carrying suspended particles It penetrates into the clean room through structural gaps and reduces the cleanliness of the clean room.

2.7.2 Management O&M

Cleaning is a necessary maintenance behavior to maintain the cleanliness of the clean room, and immediate cleaning can avoid secondary pollution of settled particles.

Part 3 Conclusion

The dynamic cleanliness of a clean room is determined by the cross-linking of independent elements in the static state. The static cleanliness can only indicate that the controlled environment basically meets the clean conditions, while the dynamic cleanliness plays a decisive role in controlling the risks of activities in the cleanroom. Personnel The impact of the control of material and process on the dynamic cleanliness is critical and complex. The fluctuation of any element will affect the dynamic cleanliness. The regulation and optimization of elements will play a positive and beneficial role in controlling the cleanliness.

The ideal clean room design is the basis for maintaining the cleanliness of the clean room during use. It has a multiplier effect on the clean operation and maintenance of the clean room. The construction quality of the clean room is the key to ensuring the cleanliness. It complements the engineering design and determines the The success or failure of the clean room project; the closed enclosure structure is an active protection measure for the clean room. When the airtightness of the clean room is poor, passive protection can be provided by the fan on duty to prevent the clean room from being polluted by the diffusion of outdoor atmospheric dust during the standby period. ;Wearing clean clothes can effectively control the impact of personnel on the clean room. Cleaning and wear will cause the densification of the clean clothes fabric to attenuate and reduce the barrier to human pollution sources. Therefore, it is also very important to verify the timely update of clean clothes to control the cleanliness; Dust-free is the basic property of materials used in clean rooms. When the application of dust-producing materials cannot be avoided, measures should be taken to prevent the spread of particles to ensure that the dust source is controllable and the impact is acceptable; maintaining a reasonable airflow organization in the clean room can prolong The self-cleaning time of the clean room shortens the residence time of particles in the clean room and reduces the risk of particle pollution in the clean room; pressure difference control is the main measure to ensure cleanliness, and the clean room should meet the minimum static pressure under both static and dynamic conditions Poor requirements; in the clean room management work, the pollution risk caused by lack of awareness and observation should be avoided, and the adequacy and suitability of the documentation should be evaluated at the same time.