The role and measures of temperature and humidity control in Guangdong purification engineering
The temperature and humidity of the clean room in purification engineering are mainly determined according to the requirements of the processing technology. On the premise of satisfying the processing technology, human comfort should be considered. With the advancement of air cleanliness requirements, the demand for temperature and humidity in processes is also increasing, and it is necessary to achieve a certain level of temperature and humidity. For example, in the photolithography exposure process of large-scale integrated circuit production, the difference in thermal expansion coefficient between glass and silicon wafer, which are used as mask materials, is increasingly required to be smaller. A silicon wafer with a diameter of 100 μ m, when the temperature rises by 1 degree, causes a linear expansion of 0.24 μ m, so it is necessary to have a constant temperature of ± 0.1 degrees. At the same time, the humidity value is generally low, as sweating can contaminate the product, especially in semiconductor workshops that are sensitive to sodium, which should not exceed 25 degrees.
Excessive humidity can cause more problems. When the relative humidity exceeds 55%, condensation will form on the wall of the cooling water pipe. If it occurs in precision devices or circuits, it can cause various accidents. Rust is prone to occur at a relative humidity of 50%.
However, for most clean spaces, in order to prevent external pollution from entering, it is necessary to maintain the internal pressure (static pressure) higher than the external pressure (static pressure). The maintenance of pressure difference should generally comply with the following principles:
The pressure in a space with a high cleanliness level should be higher than the pressure in the adjacent space with a low cleanliness level.
2. The doors between clean rooms should open towards rooms with higher cleanliness levels.
3. The pressure in clean spaces should be higher than that in non clean spaces.
The maintenance of pressure difference depends on the fresh air volume, which should be able to compensate for the air leakage from the gap under this pressure difference. So the physical meaning of pressure difference is the resistance of air leakage (or seepage) through various gaps in the clean room.
For turbulent flow cleanrooms, the concept of air exchange rate is mainly used to reduce indoor pollution through the dilution effect of air, rather than directly using the concept of velocity. However, there are also the following requirements for indoor airflow velocity:
1. The flow velocity at the outlet of the air supply outlet should not be too high. Compared with a simple air-conditioned room, it is required that the velocity decay be faster and the diffusion angle be larger.
2. The airflow velocity blowing through the horizontal plane (such as the backflow velocity during side feeding) should not be too high to avoid blowing surface particles back into the airflow and causing re pollution. Generally, this velocity should not be too high at 0.2m/s.
The article originates from Guangdong Purification Engineering: http://www.0571pet.cn/
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