Cleanroom static control
1. Basic principles of static control
(1) Determine the level of static control (2) Minimize the generation of static charge (3) Discharge and neutralize to accelerate the dissipation of static charge and prevent static accumulation (4) Protect products from ESD damage
2. Determine the level of static control
(1) Classification of static sensitivity of components, assemblies and equipment
Level 1: susceptible to 0-1999V static voltage
Level 2: susceptible to 2000-3999V static voltage
Level 3: susceptible to 4000-5999V static voltage If the sensitive static voltage is greater than 16000V, no anti-static measures are required.
(2) Classification of electrostatic protection work areas
Class A: The electrostatic potential to the ground is allowed to be no more than ±100V
Class B: The electrostatic potential to the ground is allowed to be no more than ±1000V. In actual engineering, there are three levels of electrostatic potential no more than 100V, 500V, 1000V, etc., corresponding to the electrostatic sensitive voltages of components, assemblies and equipment.
3. Minimize the generation of static electricity
This is the first step in the three-step process of controlling static electricity. In this purified working environment, the best measures are:
(1) Try to use equipment with similar properties to reduce the generation of static electricity during the contact, friction and separation process;
(2) Try to use equipment with electrostatic conductive or electrostatic dissipative materials to reduce the accumulation of static electricity during the contact, friction and separation process;
(3) Try to use production processes that reduce the generation of static electricity due to contact, friction and separation.
4. Discharge and neutralization
This is the second step in the three-step process of controlling static electricity. The most common measures in the clean room of microelectronics production are grounding, using conductive or dissipative materials to discharge static electricity, and ionizing eliminators to neutralize static electricity.
(1) Grounding The clean room should have an independent electrostatic grounding system (including the ground grounding metal mesh system and the production line workstation grounding system) so that all metal housings of equipment in the room, metal brackets of mobile equipment, anti-static equipment, etc. can safely and effectively discharge static charges to the ground. The staff's charge is grounded through the wrist strap, and then discharged to the ground through the anti-static floor through the anti-static shoes or heel straps. The ground, walls, ceilings, partitions, etc. are hard grounding, while the equipment housing, mobile equipment (cars, chairs, shelves, etc.), workbenches, etc. are soft grounding.
(2) Ionized electrical appliances There are always some insulated conductors and insulating dielectric materials (such as most ordinary plastics) that cannot be grounded on the components, PCBs, production lines, and workstations produced and assembled in the clean room. In some environments, ionized electrical appliances are often used to locally dissipate the static charges on these objects, and more often, air ionization is used to neutralize the static charges on the insulating medium and isolated conductors.
(3) Conductive and dissipative materials
Conductive and dissipative materials are also good materials for discharging static electricity because of their conductivity. They are also safer than metal conductors. They are usually used as anti-static equipment such as floors, walls, workbenches, turnover containers, tweezers, and brushes.
5. Prevent ESD
Protecting products is the last step in the three-step process of controlling static electricity. In the clean room of microelectronics production, in order to prevent ESD from occurring on static-sensitive components or assemblies, and PCBs, one method is to provide appropriate grounding or shunts for components and assemblies to "dissipate" the static electricity on the products; another method is to use appropriate packaging methods and materials to handle the packaging and transportation of static-sensitive devices. These materials can effectively shield the charge from invading the product and reduce the static electricity generated by the product moving in the packaging box. This is a warning to component users, telling you the environmental control requirements that can be needed when manufacturing equipment, whether for personnel or equipment. If the voltage allowed in the EPA area reaches 25V, I am afraid that our existing anti-static equipment, equipment, tools, and engineering will have to go through a lot of hard work.