Handling of particulate matter (coronavirus size)
Clean room grating |
Dust-free clothes |
Mask |
These photos are often seen on TV these days, but they are dust-free clothes, masks, and goggles used in clean rooms that manufacture semiconductors. The purpose of these clothing are to isolate semiconductor devices from worker’s particles (garbage).
The antibacterial clothing on TV is clothing intended to protect the human body. The purpose of these clothes are different, but the purpose of sealing small objects is the same. For the size of 100nm (nanometer: 10-9m) class, please refer to the length unit table below.
| Unit of length | Metric standard | Examples of applicable objects |
| Pico meter pm | 1×10-12 m | |
| Nanometer nm | 1×10-9 m | Class1 for CR, 100nm virus, 100～300 PM2.5 |
| Micrometer μm | 1×10-6 m | ８０μm hair、 ７～8μm red blood、 4μｍ Yellow dust, 20～40μm Cedar pollen、 100μm pollen |
| Milimeter mm | 1×10-3 m | |
| Meter m | １ |
The size of Covid19 has been announced as 100nm. Equivalent to the cleanliness class 1 in the semiconductor industry. The current development department is working on even finer 40nm to 5nm sizes. In semiconductor manufacturing, particle sealing is an eternal theme. Particles of fine particle size are not visible to the naked eye, but the blueness when looking far away from the horizon is due to the fine-grained object, as if it were filtered, compared to the blue when looking up directly at the sky. The smaller the particle size, the stronger the adhesion force, and it cannot be removed without special release treatment. Even in the air, it does not fall by its own weight and floats.
However, if there is an airflow of 0.11m / s to 0.16m / s or more, it will be possible to control fine particles. In a clean room, the down flow is controlled at 0.16m / s or more, and in consideration of the safety factor, the down flow is controlled by 0.21m / s or more in the semiconductor equipment. Considering this Covid19 countermeasure from the technology of semiconductor particle sealing, it does not create a state where the virus of fine particles floats. Basically, keep away from floating places. On top of that, you will be protected yourself by washing unprotected parts such as hands, face, etc. Virus attaches to the hand when you touches the surrounding objects on which the virus is attached things by physical force. Contact infection. Of course, if we received virus due to contact infection or droplet infection, or if it is contact infection, the contacted part should be washed. There is no way to prevent direct infection from droplet infection. Although not perfect, masks and goggles are one means. Then you need to take action to avoid being an assailant. Do not go to an enclosed space where the virus is floating due to droplet infection, especially a space where there is no air flow such as down flow. Scientific judgment can be made from such knowledge. However, considering the difficulty of living with these measures, it is essential to develop and provide a therapeutic vaccine as soon as possible.
1. Areas where fine objects do not float, floating areas
Fine objects are floating in the area where there is no air flow. In nature, such as outdoors where air is flowing, fine objects are thought to have attached to something. If as long as it does not receive physical force after adhesion, re-floating does not happen. In the artificial building, the return port of the air conditioner ‥ etc. Is on the ceiling, and I think that there are overwhelmingly many rooms with air circulation. I think that an air conditioning system that does not cause up flow is necessary. In winter, air conditioning air flows from under the train seats. At the time of heating, there is a dangerous situation where the virus is floating by the up flow.
2. Filtration with a filter
A) HEPA filter （High Efficiency Particulate Air Filter） is not enough
Particle collection rate of 99.97% or more for particles with a rated air flow and a particle size of 300 nm
B) ULPA filter （Ultra Low Penetration Air Filter） can be used.
Particle collection rate of 99.9995% or more for particles with a rated air volume and a particle size of 150 nm
** (Air filter with initial pressure loss of 245 Pa or less)
3. Clean room velocity
A) A semiconductor equipment that does not generate particles keeps down flow without upper flow. Particles on wafer was occurred by upper flow that means in order to prevent upper flow equipment has to keep overall area.
B) How do you think velocity of down flow?
| Down flow Velocity | <0.11m/s | 0.11～0.16m/s |
| Behavior of particles | Floating or upper flow | It occurs issue by waving utility |
| Equipment design | Redesign | Not enough |
| 0.16～0.21m/s | 0.21~0.26m/s | >0.3m/s |
| Particles come down | Particles come down | Difficult to control upper flow |
| Good design | Good design | Redesign |
The end of document
