Clean room static control
(1) Basic principles of static control
1 Determine the level of static control
2 Minimize the generation of static charge
3 Venting and neutralization methods accelerate the dissipation of static charge and prevent static electricity accumulation
4 Protect the product from ESD damage
(2) Determine the level of static control
1 Components, components and equipment electrostatic sensitivity rating
Level 1: susceptible to damage from 0-1999V electrostatic voltage
Level 2: susceptible to damage from 2000-3999V electrostatic voltage
Level 3: susceptible to damage from 4000-5999V electrostatic voltage
If the sensitive static voltage is greater than 16000V, it is not necessary to take anti-static measures.
2 Classification of electrostatic protection work area
Class A: Allow electrostatic potential to ground not to exceed ±100V
Class B: Allow electrostatic potential to ground not to exceed ±1000V
In actual engineering, the electrostatic potential is not more than 100V, 500V, 1000V and other components, components and equipment static sensitive voltage level 3.
(3) Minimize the generation of static charge
This is the first step in controlling the three-step static electricity. In this clean working environment, the best measures are:
1 Try to use similar equipment to reduce the electrostatic charge generated during the contact friction separation process;
2 Try to use equipment that conducts static electricity or static dissipative materials to reduce the accumulated static charge generated by the contact friction separation process;
3 Try to reduce the production process by reducing the contact friction and generating static charge.
(4) Release and neutralization
This is the second step in controlling the triode of static electricity. The most common measure in the clean room of microelectronics production is grounding, the discharge of static charge by conductive or dissipative materials, and the static charge in ionized consumers.
1 ground
The clean room shall be provided with an independent electrostatic grounding system, including ground grounded metal mesh support system and production line workstation (stage) ground support system. So that the metal casing of all equipment in the room, the metal bracket of the mobile equipment, the anti-static equipment, etc. safely and effectively discharge the static charge to the earth, and the worker's electrification is grounded through the wrist strap, and the anti-static shoes or the heel strap are anti-static. The ground is vented to the earth. The ground, wall, ceiling, partition, etc. are hard grounded, and the equipment casing, mobile equipment (car, chair, shelf, etc.), workbench, etc. are soft grounded.
2 ionization Xiao electrical
It is inevitable that there will be some insulated conductors that cannot be grounded in the components, PCBs, production lines and workstations in the clean room. Insulating dielectric materials (such as most common plastics), in some environments, ionization consumers are often used. Locally dissipating the static charge on these objects, and more often by means of air ionization to neutralize the electrostatic charge carried on the insulating medium and on the isolated conductor.
3 conductive static and static dissipative materials
Conductive materials and static dissipative materials are also good static charge bleed materials due to their electrostatic conductivity, and are safer than metal conductor bleed. They are commonly used as floors, walls, work benches, and turnover containers. Anti-static equipment such as tweezers and brushes.
(5) Protection against ESD, protection of products
This is the last step in the three-step control of static electricity. In the clean room of microelectronics production, in order to prevent ESD from happening on electrostatically sensitive components or components, PCBs, one method is to provide proper grounding for components and components. The shunt is to "dissipate" the static charge present on the product; the second method is to handle the packaging and transport of the electrostatically sensitive device with appropriate packaging methods and materials. These materials effectively shield the charge from intruding into the product and reduce the product's movement in the package to create an electrostatic charge.
Internationally, semiconductors, flat-panel liquid crystal displays, optoelectronics are developing rapidly, and integration is getting higher and higher. 8"12" chips appear, chip diameters are getting thinner and thinner, and anti-static requirements are getting higher and higher, see Table 4.
The ESD Association of the United States has begun to revise the ANS ESD S20.20-1999 electrostatic discharge control steel, and has made some modifications to the SSD electrostatic sensitivity classification, see Tables 5, 6, and 7.
This gives the component user a warning that the environmental control requirements can be required, whether the person or equipment is being manufactured. If the allowable voltage in the EPA area reaches 25V, I am afraid that our existing anti-static equipment, equipment, tools and engineering will have to work hard.