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The purpose of controlling the air parameters of the Dust-free workshop is to check whether the dust-free workshop meets the given cleanliness level. Whether it is the Dust-free workshop inspection stage after the commissioning work is completed, or the dust-free workshop use stage, the air parameters control work must be completed. The test and control methods of the dust-free workshop air parameters are formulated and proposed in detail in various standards and recommendations.
In the dust-free workshop, the following parameters should be controlled according to their different uses:
Determination of test status
Concentration of particles in the air
Wind speed and unidirectionality of air flow (for unidirectional air flow)
Air volume and ventilation times
The integrity of the final filter
Air temperature and humidity
The airtightness of the dust-free workshop
The cleanliness of the surface of the dust-free workshop
Determination of test status: According to the design requirements, dust-free workshops generally perform static detection of the air in the dust-free workshop, and generally do not perform dynamic detection. If dynamic detection is required, other standards need to be formulated or referred to.
Cleanliness level
Both dust-free workshops and clean areas are divided into levels according to one indicator: the maximum allowable concentration of particles of a certain particle size (the number of particles in every 1m3 of air). The air cleanliness level and the air cleanliness determination method are determined according to the provisions in the following table.
According to the provisions of this standard, the cleanliness level of the dust-free workshop is determined by the maximum allowable concentration of particles with a particle size ≥ a given threshold value D.
| ISONlevel | Maximum allowable particle concentration Cn m3, particle size ≥ the following value, micrometer | |||||
| 0.1 | 0.2 | 0.3 | 0.5 | 1.0 | 5.0 | |
| ISO1level | 10 | 2 | _ | _ | _ | _ |
| ISO2level | 100 | 24 | 10 | 4 | _ | _ |
| ISO3level | 1000 | 237 | 102 | 35 | _ | _ |
| ISO4level | 10000 | 2370 | 1020 | 352 | 83 | _ |
| ISO5level | 100000 | 23700 | 10200 | 3520 | 832 | 29 |
| ISO6level | 1000000 | 237000 | 102000 | 35200 | 8320 | 293 |
| ISO7level | _ | _ | _ | 352000 | 83200 | 2930 |
| ISO8level | _ | _ | _ | 3520000 | 832000 | 29300 |
| ISO9level | _ | _ | _ | 35200000 | 8320000 | 293000 |
| Note: The concentration value Cn should be rounded off to three decimal places. In actual situations, there is an actual error in particle concentration, and it is impossible to calculate a concentration with high accuracy. | ||||||
When determining the cleanliness level of the actual dust-free workshop, the particles with a particle size > the threshold value should be counted. The given particle sizes of the particles below refer to the threshold particle size. The maximum allowable concentration of particles with integer level ordinal numbers N and the most common value D are listed.
Example of cleanliness level representation
ISO4 level; static: given particle size 0.5 microns (352 particles/m3).
ISO5 level: static; given particle size 0.5 microns (3520 particles/m3): 5.0 microns (29 particles/m3).
Therefore, when testing the corresponding cleanliness level of a specific dust-free workshop, it is not necessary to detect all particle sizes of the level as shown in the above table. Instead, it is only necessary to detect the particle size given for this type of dust-free workshop.
Method for determining cleanliness level
When testing the cleanliness level of a dust-free room, the concentration of suspended particles at one or several points in the dust-free room (i.e. the particle concentration at the sampling point) should be measured. Therefore, the following requirements must be met.
Confirm that the state of the dust-free workshop is consistent with the given.
Determine the number and location of sampling points in the dust-free workshop for a given particle size.
Determine the number of samples at each sampling point.
Determine the sampling volume and sampling time for each given particle size at each sampling point.
After sampling, the particles of each given particle size should be statistically recorded.
Enter the sampling data into the particle statistics record table for various given particle sizes (suitable for the occasion of using particle counters without computer software).
Organize the obtained data.
Analyze the results.
The level of the sorting plan should meet the requirements of the above table.
Airflow detection
Airflow in the dust-free workshop.
Airflow speed (usually the speed of controlling unidirectional airflow).
Airflow uniformity (unidirectional airflow speed stability) and visually check the airflow.
Wind speed in unidirectional airflow is measured 150-500 mm from the source, with at least three evenly distributed test points. Wind speed at the filter outlet is tested 150 mm from the surface. Uniformity is evaluated over 300 mm.
The measurement time for each point should not be less than 10 seconds. And the average, maximum and minimum values should be determined.
Uniformity of airflow
According to the Wind speed test data at each point on the plane perpendicular to the direction of air movement, the uniformity of the unidirectional airflow is evaluated. It is recommended that the plane should be more than 300 meters away from the filter surface (air outlet).
The wind speed difference at each point on the plane should not exceed 20%6-30%.
Check the integrity of the filter
The final filter (HEPA, ULPA filter) is an important part of the dust-free workshop. These filters are installed on the ceiling and walls of the clean room, installed in equipment and air ducts. Leakage checks should be carried out to control the integrity of the filter. The manufacturer should conduct a maximum transport particle size test on the filter in the factory, attach a filter test report, and no leak detection is performed on site.
Temperature detection In the clean room, two methods are used to control the temperature: General control Special control (General control) General temperature control should be carried out during the commissioning of the ventilation and Air conditioning system, as well as at all stages of clean room testing and use.
The temperature at the height of the work area of the specified workbench and, if necessary, the temperature of other working points should be controlled. Periodic continuous testing for 6 minutes should be carried out within 1 hour or more.
| Serial number | Room Name | aera | Cleanliness | External pressure difference | Temperature | Humidity | Illumination | Fresh air | Exhaust | |
| M2 | level | +20 | 20-26 | 40-70 | 300 | 30 | ||||
| 1 | Ten thousand level identification room1 | 23 | 70000 | +20 | 20-26 | 40-70 | 300 | 30 | none | |
| 2 | Ten thousand level identification room2 | 16 | 70000 | +20 | 20-26 | 40-70 | 300 | 30 | none | |
| 3 | Ten thousand level identification room3 | 10.3 | 70000 | +20 | 20-26 | 40-70 | 300 | 30 | none | |
| 4 | Buffer room | 6 | 70000 | +15 | 20-26 | 40-70 | 200 | 30 | none | |
| 5 | Preparation Room | 2.6 | none | 0 | 20-26 | 40-70 | 200 | 30 | none | |
Control of relative humidity
Relative humidity control After the ventilation and air conditioning system is stable, the relative humidity control can be carried out simultaneously with the temperature measurement. At least one point is set in each area where relative humidity is required to measure the relative humidity. In order to keep the sensor stable, the measurement duration shall not be less than 6 minutes.
Sampling point location diagram
