The generation of static electricity in the clean room and the harm

2019-06-25 13:45:00   Editor: Yan Hong shares    0

The generation of static electricity in the clean room and the harm


Static electricity is the product of electrons moving inside or between materials (including polarization and conduction). Two different materials are in contact with each other, and less than a certain distance between them, such as 10-25 cm, electrons in the two materials exchange through the interface due to the tunneling effect. When the exchange reaches equilibrium, a certain potential difference will be generated between the materials, and an equal amount of positive and negative charges appear on both sides of the interface. If the two materials after the contact are separated, the two materials will be charged with the same amount of positive and negative charges, which is the basic principle of static electricity generation.


There are three main ways to generate static electricity: triboelectric charging, conduction charging, and induction charging.


Frictional electrification: Because objects of different materials are separated after contact, because different nucleus has different binding abilities to electrons, when two different materials contact or rub, the peripheral electrons will be transferred to the side with strong binding ability, resulting in a material band. Positive, another material is negatively charged.


Conductive charging: Because in the conductor, electrons can move freely on his surface. When in contact with a charged body, electrons are transferred from the charge, resulting in a charge balance between the two, thereby forming an electrostatic phenomenon.


Inductive charging: refers to the induction of the adjacent electric field. For the conductor, the electron moves freely on the surface of the conductive material. If the conductor is placed in another electrostatic field, the opposite charges will attract each other, and the positive and negative ions will occur. In the transfer, the conductor is charged due to the electrostatic field induction causing the positive and negative charges to be unbalanced.


It can be seen from the basic principles and methods of static electricity generation that in many processes of general electronic product manufacturing, static electricity may be generated in many processes. Electrostatic manufacturing processes may cause static electricity to be generated by operators, work surfaces, tools, components, and packaging. As long as static electricity is present, there must be an ESD (Electro-Static Discharge) process, mainly in the case of instantaneous discharge currents. The noise generated by the induction of the circuit and the discharge current cause the reference ground potential to fluctuate from the potential of the product ground and the signal ground, thereby causing interference to the normal operation of the circuit.


Static hazards have some different characteristics from general lightning protection or electromagnetic interference:


Concealment: The general electrostatic discharge is not perceived by the human body, but the components are damaged without knowing it.


Potential and Cumulative: Some components exhibit only a drop in performance parameters after being damaged by electrostatic discharge, but have not yet failed. In the case of continued use, failure may occur, so static electricity is potentially harmful to the device.


Randomness: Electrostatic discharge damage of electronic components may occur at any point, from any step of the process, from manufacturing to manufacturing to maintenance, in contact with any charged human body (or object), and is highly random.


Complexity: Some electrostatic damage is also difficult to distinguish from damage caused by other causes, causing people to mistake the electrostatic damage as other failures, thus making a wrong judgment.


For electronic product assembly, the danger of static electricity seriously affects the quality, yield and reliability of the product. Systematic anti-static measures must be taken for the clean room for electronic product assembly to minimize the electrostatic hazard during production. .


Static electricity is generally "hard to see, and not easy to touch", but it is almost everywhere, and there is no time, so static protection is a comprehensive system engineering. In principle, static protection should be controlled from static electricity. The generation and control of the dissipation of static electricity are carried out. The control of static electricity generation is mainly to control the selection of materials in the process and the process. The control of static dissipation is mainly to release and neutralize the static electricity quickly and safely.