Electrostatic Control in Cleanrooms
There are three steps in controling the static.
1. Reducing the static is the first step. The best measures are:
①Using similar equipments to reduce electrostatic charges during the process of friction.
②Trying to use static conductive or static dissipative materials to reduce the accumulation of static.
③Trying to choose the production procedure that are less friction.
2. Bleeding or neutralization is the second one. The most common measures in microelectronic production are earth connection, using static conductive or static dissipative material, ion eliminator, etc.
①Earth connection cleanroom should be an independent system. So that static of the metal cases of all equipments, metal pedestals and antistatic equipments could be bleeded into the earth effectively. Staff could use wrist strap or antistatic shoes to bleed static.
②There are a few insulated conductor or insulation materials in ion eliminator, components, PCB, production lines or work stations. Under some circumstances, ion eliminator is only used to eliminate static in some parts. Aeroionization is more used to neutralize the statice on insulation materials and isolated conductors.
③Static conductive or static dissipative materials are also very good electrostatic discharge materials which are safer than metal materials. It is widely used in antistatic equipments such as floors, walls, work stations, turnover containers, tweezers and brushes.
3. Anti-ESD is the last step. In order to prevent ESD in the electrostatic sensitive components, one way is to provide suitable earth connection to eliminate the static, the other way is to use appropriate packaging and material to deal with the electrostatic sensitive components. They can prevent electric charge invading in the product and reduce the movement of product in the package.