Static electricity is a static state of charge. In dry and windy autumn, people often encounter this phenomenon in their daily lives: when they undress and sleep at night, they often hear buzzing noises in the dark, accompanied by blue light; when they shake hands, their fingers just touch The other person will suddenly feel acupuncture stinging at the fingertips, which is quite shocking; in the morning, when the hair is combed, the hair will often “fly away” and become more and more chaotic. When the door handle is opened and the faucet is turned on, “electricity” will be issued. The sound of "squeak, bang, bang" is the static electricity that occurs in the human body.

The principle of static electricity generation
Friction, collision, peeling, flow electrification, jet charging, stirring and charging, such as roller movement, personnel walking, when the tanker drains, the solvent sprayed by the nozzle, the static electricity of the mixer is due to the contact separation between objects in different electrification sequence positions. Causes the phenomenon of positive and negative charges on the object to be out of balance.
When two substances with different dielectric coefficients are rubbed, the positive and negative polarity charges are accumulated on two objects, respectively: when two objects come in contact, one tends to attract electrons from the other, so the two will form different The charging potential.
Frictional electrification is a mechanical process that relies on the relative surface to move electricity. The amount of electricity delivered depends on the number of contacts, surface roughness, humidity, contact pressure, friction properties of the friction material, and relative movement speed.
Two charged objects also become static power. As far as the human body is concerned, the static electricity generated by the friction between the clothes and the skin is one of the main reasons for the body's electrification.
When the static power source is in contact with other objects, there is a flow of charge based on the principle of charge neutralization, and enough electric power is delivered to offset the voltage. During the transmission of this high-speed electricity, potential damage voltages, currents and electromagnetic fields will be generated, and objects will be destroyed in serious cases. This is the electrostatic discharge.

Electrostatic induction charging: CRT display capacitance changes the piezoelectric effect Electromagnetic radiation induction Electrostatic charges only exist on the surface of the object, not inside the object, and the charge in the insulator remains only in those regions where static electricity is generated, but not on the entire surface. Therefore, the insulator does not lose these charges after it is grounded. In contrast to insulators, the charge conductor loses its own charge when it is grounded.
If the conductor is momentarily grounded (for example, the object is touched by a person standing on the ground), then the charge that is away from the surface of the charged body is released and the conductor will be positively charged.

Definition of ESD
Electrostatic discharge: charge transfer due to the proximity or direct contact of objects with different electrostatic potentials (GB/T4365-1995)”
ESD can cause serious damage or misoperation of electronic devices. Are semiconductor experts and users of equipment thinking about ways to suppress ESD? Static electricity is a static charge. The generation of static electricity is due to the electrons under the action of external forces, from one object to another object or the polarization phenomenon caused by the influence of the external magnetic field? A kind of electric energy, is the positive charge and negative charge in the local range lose balance result.
Excess or insufficient static charge on the surface of the object.
Stay on the surface of the object.
Formed by the transfer of electrons or ions.


The harm of static electricity
environment safety
Explosive fire, etc. in dangerous situations
Work requirements for precision equipment
Product performance and reliability
Anti-interference ability, affect product sales
Potential damage to the product
With the development of high technology, the consequences of static electricity have broken the boundaries of security issues.
The harm caused by electrostatic discharge is one of the direct causes of equipment malfunction, signal loss, and error codes in the fields of electronics, communications, aviation, and all applications of modern electronic equipment and instruments.
Electrostatic discharge currents may be coupled directly to the data lines, signal lines, control lines, etc. of the electronic devices. In this case, integrated circuits and special-purpose integrated circuits are affected by electrostatic discharge.
Before 1970, many static electricity problems were caused by people's lack of awareness of ESD. Even now, many people suspect that ESD will cause damage to electronic products. This is because most ESD damages occur below people's feelings, because the body's perceived voltage for electrostatic discharge is 3 KV, and many electronic components are damaged in hundreds of volts or even tens of volts. Usually, electronic devices are not damaged by ESD. Obviously, the components were mounted on the PCB and then tested. As a result, many problems occurred and the analysis was quite difficult.
Especially the potential damage, even if the use of precision instruments is difficult to measure its performance has changed significantly, so many electronic engineers and designers are skeptical of ESD, but in recent years the test proved that this potential damage after a definite time, the electronic product The reliability has dropped significantly.

ESD harm to products
The basic physical properties of static electricity are: attraction or repulsion, and there is a potential difference with the earth, and a discharge current will be generated.
Electrostatic adsorption of dust, reducing the insulation resistance of components (shortening the life).
Electrostatic discharge destroys and damages the component and does not work (complete destruction).
Electrostatic discharge Electric fields or currents generate heat, causing component damage (potential damage).
The electromagnetic field generated by electrostatic discharge has a large amplitude (up to several hundred volts/meter). The frequency spectrum is extremely wide (from several tens of megabytes to several thousand megabytes), causing interference or even damage to electronic products (electromagnetic interference). Device breakdown caused by ESD is electronic The most common and most serious electrostatic hazard in industry.
Characteristics of Electrostatic Damage to Electronic Products Concealment: The human body cannot directly sense static electricity unless electrostatic discharge occurs. The human body does not necessarily have the feeling of electric shock. This is because the electrostatic discharge voltage perceived by the human body is 2~3KV, so the static electricity is concealed.
Potentiality: The performance of some electronic components after electrostatic damage has not dropped significantly, but multiple accumulated discharges will cause internal damage to the device and cause hidden troubles. Therefore, electrostatic damage to the device is potential.
Randomness: Under what circumstances will electronic components suffer from electrostatic damage? It can be said that after a component is produced and until it is damaged, all processes are threatened by static electricity, and the generation of these static electricity is also random and the damage is also random.
Complexity: The analysis of the effectiveness of electrostatic discharge damage is time-consuming, time-consuming, and requires high technology because of the fine, fine, and tiny structural features of electronic products, and often requires the use of high-precision instruments such as scanning electron microscopes.

• ESD experiment introduction
  Damage to the semiconductor device is caused directly by energy exchange.
  The electric field and magnetic field caused by the discharge change, causing the device to malfunction.
  Different test results can be classified according to the working conditions and functional specifications of the product as follows:
  A: Normal performance within the scope of technical requirements;
  B: The function is temporarily reduced or lost, but it can resume performance on its own;
  C: The function is temporarily reduced or lost, requiring operator intervention or system reset;
  D: Unrecoverable functionality is lost or lost due to damage to equipment (components) or software or loss of data.
  A product conforms to A, and the test result is qualified. This means that the product functions normally during the entire test and the performance specifications meet the technical requirements.
  For products conforming to B, the test results shall be regarded as the product standards, product instructions, or test program requirements. If it is considered that some of the effects are not important, they can be qualified.
  In accordance with C's products, the majority of the test results were unqualified except for special circumstances and no harm.
  Products that meet D are judged as unqualified.
  The test report of products conforming to B and C shall state the criteria for class B or C evaluation. Compliance with category B should record the time when it was lost.
  

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The main purpose of ESD protection
First, increase production (IncreasedYields)
Second, Cost Saving (Cost Saving)
Third, better product reliability (Better Product Reliability)
Fourth, product life is longer (ExtendedUsageLife)

ESD method introduction
Four principles
1 Environmental Control
2 Personnel control
3 Packaging Material Control
4 Staff training

basic method
1. Grounding Grounding is to put static electricity into the earth through a line connection, which is the most direct and effective anti-static measure.
Commonly used grounding methods for conductors are: with anti-static wrist and work surface ground.

2. Electrostatic shielding Electrostatic sensitive elements may be exposed to static electricity during storage or transportation. Electrostatic shielding may weaken the influence of external static electricity on electronic components. The most common method is to use electrostatic shielding bags as protection.

3. Ion Neutralization Insulators are often prone to static electricity. Eliminating static electricity from insulators is not effective with grounding methods. The commonly used method is ion neutralization, which uses ion blowers and ion air guns in the working environment.

• 4. Circuit design

 The I/O port circuit design is also influenced by the PCB layout and grounding design. As shown in the first figure, the grounding of the port protection device and the ground of the back-end protected IC are co-designed. Once the transient pulse is clamped to the ground, this design is also a reference to the IC. It is easy to cause abnormalities in IC ground potential elevation.
There are two main improvements: If the system is a two-wire device (without ground), the system enclosure is also non-metallic, and this ground design must also separate the reference ground of the IC from the ground of the protection device and cannot be shared together, but This system is a non-ground system. You can use these two parts to lay different grounding areas, and then use Y capacitors to connect the ground wires of the two areas together. The other is that the system has a design ground wire or the shell is a metal shell. In this case, the ground of the protection device can be directly connected to the shell ground or connected to the shell ground through a Y capacitor, but it must be separated from the reference ground of the IC.

The design of the PCB trace mentioned above leads to the failure of the protection circuit. Through the figure, you can see that the port is designed to protect the ESD of the TVS tube. However, if the wiring is routed as shown in the first picture, it can easily lead to IC damage, but the TVS The main reason is that the existing ESD or EFT is high-frequency interference and the impedance of the trace is large. Therefore, the design of the protective circuit for the port must follow the principle of proximity to the port to design the PCB.
 

ESD protection method
From the five aspects of human, machine, law, material and ring, talk about ESD protection.
Talk about people. The human body can be said to be a high static power supply, the protection of the body's static electricity, and the use of shielding and release of static electricity. Strictly speaking, it is required to be "fully armed", that is, wear anti-static helmets, anti-static masks, anti-static gloves, finger covers, etc., wear anti-static clothing and anti-static shoes, wear wrist bands, etc. To shield and guide static electricity. In short, try not to expose the skin.
Second talk about machines. The machine is also a high static power supply, because the mechanical parts of the machine, especially the motor, are prone to EMI (electromagnetic induction), so it is also very necessary to protect the static electricity of the machine. For the electrostatic protection of the machine, it is generally achieved through the elimination of the electromagnetic field, the shielding of the high electrostatic part, the grounding of the machine, and the like. Demagnetization is generally used for demagnetization, and ion blowers are used for charge elimination.
The degausser is very simple and will not be introduced. Let's take a look at the ion fan. Ion blowers produce rich positive ions and negative ions. Blowing these ions to a highly static object, the object's static electricity will be neutralized. These ions are generated by the ion generating element inside the ion fan and ionize the air. The ion-generating element stimulates air ionization by a low-current, high-voltage transformer. The transformer also contains a current limiting resistor, which enhances the stability and safety of ionization. The high-voltage alternating current that acts on the circular circuit of the ion emission point of stainless steel forms a strong alternating electric field at the top of the emission point. This electric field ionizes the air to produce a variable pole ion. When the electromagnetic field can not be eliminated or difficult to eliminate, we use static shielding equipment to shield the high electrostatic devices or high electrostatic parts of the equipment, such as motors, we all know that the motor is easy to produce EMI, but the machine must run without motors Therefore, it is not necessary to shield it. There are also worktables, power cords, and computer keyboards that can be used for electrostatic shielding to perform ESD protection. Available shielding products include anti-static mats, anti-static films, anti-static curtains, and anti-static shielding bags. Anti-static tape and so on. Finally, regardless of the machine shielding or degaussing effect, it is necessary to connect the machine to ESD ground.
Three talk about materials, that is, materials. In an absolute sense, if your product is sensitive to static electricity, then your production line must not have high electrostatic material, especially in areas close to the product. Use anti-static materials as much as possible, such as Component boxes, shelves, worktables, transportation equipment, cleaning equipment, chemical reagents, etc. Finally, even your pen and notebook should use anti-static pens and notebooks, because when you use the pen, it may contact the product. Of course, if your product is not very sensitive to static electricity, you can handle it at your discretion, but it is best to use ESD experiments to prove it and see if you can really rest assured.
Four talk about the ring, that is, the working area environment. A good anti-static working environment is very important for production. Such an environment is generally established as follows:
First, establish an ESD protection area (ESD), which is preferably an ESD protection area.

Anti-static work area
In the field of production, assembly and maintenance of common electronic equipment, various static electricity generating materials and electric fields generated by them are very common phenomena. These static electricity generating materials and electric fields generated by them may cause damage to electrostatic sensitive devices. Therefore, it should be protected during the entire use of electrostatic sensitive devices. Conductor containers with shielding properties provide the necessary protection during the storage and transfer of electrostatically sensitive devices. However, there are also operations outside the shielded container for electrostatically sensitive devices. In this case, electrostatic sensitive devices are very vulnerable and therefore it is necessary to provide a safe working area. The anti-static work area (EPA) is designed for this purpose. In order to ensure the safety of the workstation against static electricity, it must meet the following requirements:
(1) All electronic components in the antistatic area should be treated as electrostatically sensitive devices.
(2) The operation of any static-sensitive device outside of the protected state (outside of the Faraday cage) must be performed within the antistatic work area.
(3) Electrostatic sensitive devices that transmit in non-anti-static areas between anti-static work areas must be in a safe state of protection.
(4) The design of the antistatic work area should ensure that the electrostatic sensitive devices do not easily reach the metal grounded enclosure of the instrumentation.
(5) It is forbidden to place static electricity-producing materials that are not necessary for work in the anti-static work area, such as plastic bags, boxes, foams, tapes, notebooks, paper sheets, personal articles and other items that are not anti-statically treated. These materials must be away from the static-sensitive devices 30 More than cm.

Secondly, the installation of the ESD safe operation area, we talk about the anti-static floor system, dust removal system, grounding system and air temperature and humidity. Anti-static floor system, the most important is to lay anti-static flooring on the ordinary floor, generally this floor has anti-static PVC floor, anti-static epoxy floor, etc. For anti-static floor, the requirements must meet the international anti-static Association Standard, of course, anti-static flooring must also be connected to the ESD ground.

An ESD-free working environment, so that no dust is a key, because the dust in the air collide with each other in the process of movement, it will also produce ESD. If it does not remove dust, then it will find the cause of ESD problems. It's hard to say. Generally we use the dust removal system to solve this problem. The first requirement is air dust filtration system, such as: air shower, air shower channel, cargo shower room, dust pad, dust roller, air filter, dust-free transfer window, clean room air shower transfer window and so on. Second, as far as possible the establishment of purification lamps, clean room clean glass, clean room color steel ceiling, clean room color steel plate corner, clean room color steel package column and so on. The selection of the above equipment, companies should be based on the sensitivity of the product to the ESD, it is best to learn from the views of professionals. A complete ESD protection working environment and the establishment of an independent and perfect ESD grounding system are also very important. In addition, all equipment and work surfaces in the workplace must be connected to the ESD grounding system.

In addition, a complete ESD working environment has certain requirements for temperature and humidity. From the perspective of ESD protection, the higher the humidity is, the better, but the humidity is too high and it will corrode the equipment. So, generally speaking, 40%-60 The humidity of % is ideal. Of course, companies also have to decide according to the characteristics of their own company's products, after all, this work is more complicated. In addition, ceilings and wall outlets are also set up, and dust collectors are often used to clean the clean rooms.
In this way, with such a working environment, we would like to think about whether the human body's static electricity is dissipated through electrostatic clothes, electrostatic shoes, or through wrist straps, ESD grounding systems, and introduced into the earth. Static electricity in the environment by controlling the temperature and humidity of the air is also dissipated through the floor system and introduced into the earth.
Of course, think about it carefully. The people, machines, and materials in front should also belong to the protection of the environment. As long as the work of each link is done well, a complete ESD protection working environment is established. Coupled with a reasonable operation specification, that is, the correct method, it basically passes.

Five talk about law. In talking about the law, we must first clarify the above four points. In fact, the law is to establish reasonable methods and norms to ensure that the above four points can be effectively implemented. In addition, what needs to be supplemented is that when the cause of ESD cannot be clarified, according to the production process, the corresponding ESD experiment should be designed to carefully find the cause of the ESD problem. Ultimately, establish appropriate ESD operating procedures and disciplinary regulations to regulate production.
Of course, after the ESD protection system is established, what the staff needs to do is to constantly check this system so as to constantly discover areas of incompleteness and make corresponding improvements so as to ensure that the system can effectively maintain its ESD for a long period of time. Anti-action. In this way, the establishment of corresponding ESD functional departments, and the continuous development of their professional skills to improve their awareness of ESD protection, are also an integral part of ESD protection.
In recent years, with the rapid development of science and technology, the widespread application of microelectronics technology and the increasingly complex electromagnetic environment, ESD problems have become more and more serious, the problems have become more and more prominent, and companies are paying more and more attention to ESD protection.