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Clean room contamination source and control test method

Industrial modular Clean Room time:2022/08/01 16:45:29 click:17

Clean room unlike room in our daily life, it does not allow you to pass in and out, it is to a certain space range of particles in the air, bacteria and other harmful air pollutants, and the indoor temperature, cleanliness, interior pressure, air velocity and air distribution, noise, vibration and lighting, static control within the scope of a certain demand, and the special design of the room.

Clean room contamination source and control test method

For the maintenance and control of clean room cleanliness, in addition to the investment of hardware equipment, it also needs good software - management system to cooperate, in order to maintain good cleanliness. The source of micro pollution in semiconductor clean room was analyzed, and the operators accounted for about 80%. Experimental data show that the dust has a significant increase when the operator enters and leaves the clean room. When someone moves, the cleanliness deteriorates immediately. It can be seen that the reason for the cleanliness deterioration is that people are the main factor.

I. Indoor air pollution sources and their transmission routes

1. Indoor staff

Human dust is the main source of clean indoor air pollution, accounting for 80%~90%. The amount of dust emitted by a person in motion is quite complex, with a difference of about 10 times between the amount of dust emitted by a person at rest and the amount emitted by a person in vigorous activity. A person in the indoor activity is not likely to be intense activities, if the average of these actions, it can be considered that a person in the indoor activity of dust is 5 times its static, that is: 5×105 particles /(min• person).

According to the nature of the process, the number and strength of the human movement, this multiple is different, can be divided into lower and higher two categories, respectively 3 and 7 times of the static dust volume, corresponding to 3×105 particles /(min• person) and 7×105 particles /(min• person).

Of course, the amount of human dust also has a great relationship with clothing, and clothing washing, drying, blowing and so on also has a great relationship. According to the actual use and experimental determination, the amount of dust generated by nylon silk clean clothes is the least, and the amount of dust generated by cotton Dacron clean clothes is greater than that of nylon silk. If you wear a cotton Dacron work clothes in nylon silk clothes, the amount of dust can be further reduced. In addition, clean work clothes should not be kneaded and washed, and should be dried in a clean environment after washing.

2, equipment and process dust

The dust generation of equipment is particularly prominent in rotating equipment. Motors, gear rotating parts, servo mechanical parts, hydraulic and pneumatic starter switches or manually operated equipment all produce particles due to friction between moving surfaces. In Japan and Western industrial countries, the typical action of mechanical equipment with different running modes, different speeds and different materials and the dust production of some electrical appliances have been studied. Some reference values OF dust emission are GIVEN FOR THE POLLUTION SOURCES OF MACHINERY AND electrical appliances IN CLEAN rooms, which PROVIDES THE calculation basis FOR THE VENTILATION design of CLEAN rooms.

3. The contaminated area adjacent to the clean room

Adjacent to or connected with the clean room, the area or the non-clean area with low cleanliness is another important source of pollution affecting the cleanliness of the room because of the polluted air carried in and out of personnel and materials, or the pollutants settled on personnel and materials are brought in. Reasonable positive pressure difference is an important measure to reduce the invasion of polluted air through cracks in the envelope and holes such as transfer Windows, doors and conveyor belt openings. The air lock room, buffer room and air shower room at the door also play a role. However, it is also difficult to completely avoid the interference and influence of surrounding polluted areas on the clean room environment, especially the area near the outer door of the clean room. Therefore, the key process area should be far away from the outer door.

4. Unfiltered air supply

Under normal circumstances, after the new or rebuilt clean room or the final filter is replaced, strict acceptance testing has been carried out according to the specification requirements, then the HEPA filter itself, the contact surface of the HEPA filter (>rfilter.com) and the support frame should be detected and treated if there are leaks. At this time, there is no unfiltered air entering the clean room in the air supply system.

Is worth to guard against and note that in the process of production not according to the operation rules and accidentally hit a weak efficient filter paper core, or high efficiency filter supporting frame due to vibration, or sealant mat aging, deterioration in the high efficiency filter and framework interface seal or strip cracks, thus unfiltered air leakage, contamination, clean room, This is also the focus of daily monitoring efforts.

5. Raw materials, packaging, etc

The place and method of pre-cleaning and unpacking of equipment, materials, containers and packages entering the clean room, as well as the procedures of entering the clean room, should be carried out in accordance with the relevant specifications of clean room operation management. But even if the relevant specifications and procedures are strictly followed, it is still difficult to completely prevent the adhesion to raw materials, containers, packaging, especially some small components of products that are difficult to thoroughly clean are brought into the clean room. They constitute another important source of pollution in the production process, which is often overlooked. When problems occur, attention is usually focused on finding defects in the air conditioning purification system.

2. Control methods for pollution sources

1. Control the dust production of process equipment and process

The process equipment in the clean room should be well-selected, smooth and wear-resistant. The rotating and sliding parts are particularly important, and wear and dust production should be reduced as much as possible. For the process of dust production, it should be closed or set up as far as possible, and supplemented by exhaust, to form a local negative pressure relative to the clean room, so as to limit the diffusion of pollutants to other areas of the clean room. It is necessary to clean and wipe the indoor machinery and equipment regularly, and it is also an effective measure to reduce the secondary flying dust.

2. Pressure difference between adjacent clean rooms of different levels

The main way to prevent the spread of contamination from adjacent areas with lower cleanliness to the cleanroom is to maintain a suitable positive pressure value in the high cleanliness area relative to the low cleanliness area, the low cleanliness area relative to the service area, and the service area relative to the outdoor. According to different circumstances, the positive pressure value of adjacent rooms at different levels is about 5PA-10Pa. The purpose of maintaining the cascade pressure difference between rooms of different cleanliness is that when the room door is closed, the flow of air through the gap is from the high-level clean room to the low-grade clean room, from the low-grade clean room to the corridor and service area, and then to the outdoor.

In this way, the transmission of suspended pollutants in the air from outdoor to the service area, the service area to the low-grade clean room, and the low-grade clean room to the high-level clean room can be reduced. Many theoretical studies and practices have proved that when people and materials pass through the door, even if the pressure difference between the two sides of the door is as high as 50Pa~60Pa, it is still difficult to absolutely avoid the pollution brought into the room by the air carried when people and materials move inward. Especially when there is a temperature difference between the two sides of the door, after the door is open, even if no one moves around, there is also reverse airflow on part of the area of the opening section, and pollutants into the air.

In addition, too high positive pressure difference will also cause the door of the clean room to be difficult to open and difficult, the air flow between the door will cause whistling noise, and the amount of air filling will increase because of excessive air overflow, waste energy and increase the burden of filters at all levels.

3. Filtration of clean room air supply

The end device of the clean room air conditioning air supply system -- high efficiency air filter or ultra-high efficiency air filter, under normal conditions can effectively filter the particulate pollutants in the fresh air and return air processed by the air conditioning unit. After the high efficiency, ultra-high efficiency air filter treatment of clean air into the room, can effectively discharge, dilute indoor pollutants, to maintain the cleanliness of the room.

However, if the final filter is damaged or the seal between the filter and the supporting frame is cracked, and the air tightness fails, then the air filtered by the HEPA filter may carry a large number of pollution particles into the room and diffuse with the air flow, causing a large range of harm. Therefore, leakage detection, plugging or replacement of the final filter before the clean room is put into use is very important. It is also very important to prevent the damage of the final filter during operation. Attention should also be paid to the timely replacement of the HEPA filter after it reaches its service life.