knowledge of anti-static electrostatic discharge and basic knowledge of protection

1. Terms and definitions

1. Static electricity: excess or insufficient static charge on the surface of an object

2. Electrostatic field: the electric field formed by static electricity around it

3. Electrostatic discharge: two objects with different electrostatic potentials, due to direct contact or electrostatic field induction, transfer of electrostatic charge between the two objects. The energy of electrostatic field reaches a certain level. The phenomenon of discharging through the dielectric is electrostatic discharge.

4. Electrostatic sensitivity: electrostatic discharge voltage that components can withstand

5. Electrostatic sensitive devices: devices sensitive to electrostatic discharge

6. Grounding: electrically connected to objects that can supply or receive a large amount of charges, such as the earth, Ships, etc.

7. Neutralization: using opposite charges to make static electricity disappear

8. Anti-static work area: it is equipped with various anti-static equipment and equipment, which can limit electrostatic potential, and has clear regional boundaries and special marks, which are suitable for engaging in electrostatic protection operations

2. Generation of static electricity:

1. Friction: In daily life, any two objects with different materials contact with each other. The most common way to generate static electricity is triboelectricity. The better the insulation of the material, the easier it is to use triboelectricity. In addition, any two objects with different substances can also generate static electricity after they are separated. .

2. Induction: for conductive materials, because electrons can flow freely on its surface, if placed in an electric field, positive and negative electrons will transfer because like charges repel and opposite charges attract.

3. Conduction: for conductive materials, because electrons can flow freely on its surface, if they contact with charged objects, charge transfer will occur.

3. The breakdown voltage is reduced, and the circuit area is reduced, which makes the device's ability to withstand electrostatic shock weakened. Static ElectricField and ESDcurrent become the fatal killers of these high-density components. At the same time, the widespread application of a large number of high-insulation materials such as plastic products leads to a great increase in the chance of static electricity. In daily life, such as walking, air flow, Handling can generate static electricity. It is generally believed that only CMOS chips are sensitive to static electricity. In fact, components and circuits with high integration are very sensitive.

A. Influence of static electricity on electronic components

A) Electrostatic adsorption of dust changes the impedance between lines, affecting the function and life of products.

B) Damage to the insulation or conductor of components due to electric field or current, Make the component unable to work (completely destroyed).

C) Due to the heat generated by instantaneous electric field or current, the component can still work and its service life is damaged.

B. Features of electrostatic damage:

1. Hidden human body cannot directly perceive static electricity unless electrostatic discharge occurs, but electrostatic discharge occurs. The human body may not feel it. This is because the electrostatic discharge voltage perceived by the human body is 2-3KV.

2. Latency Some electronic components have no obvious decline in performance after being damaged by static electricity, but multiple cumulative discharges will cause internal injuries to the devices and increase the sensitivity of the devices to static electricity. There is no way to cure the problems that have arisen.

3. Under what circumstances will random electronic components suffer from static electricity damage? It can be said that all the processes from the production of a component to its damage are threatened by static electricity, and the generation of static electricity is also random. Because the generation and discharge of static electricity are instantaneous, it is difficult to predict and protect.

4. Complex electrostatic discharge damages the work of dividing boards, which is time-consuming, troublesome and expensive because of the fine and tiny structural characteristics of electronic products, and requires more complicated technology, often requiring the use of precision instruments such as scanning electron microscope. Even so, some electrostatic damage phenomena are difficult to distinguish from those caused by other reasons, which makes people mistake electrostatic damage failure for other failures. This is often attributed to early failure or failure with unknown conditions before electrostatic discharge damage is fully understood, thus unconsciously covering up the real cause of failure.

5. The serious ESD problem seems to only affect the users of finished products, but in fact it also affects manufacturers at all levels. Such as: warranty fee, maintenance and company reputation, etc.

4. Three types of ESD

1. Human body type refers to the friction between body and clothes when human body is active. When people hold ESD-sensitive devices without dragging the charges to the ground first, the friction charges will move to the ESD-sensitive devices and cause damage.

2. The charged types of microelectronic devices refer to these ESD-sensitive devices, especially. In the process of automatic production, friction charges will be generated, and these friction charges will be discharged to the highly conductive solid grounding surface very quickly through low-resistance lines, thus causing damage; Or the metal part of ESD-sensitive device is charged by induction, resulting in damage.

3. The type of field induction is that there is a strong electric field around it, which may come from plastic materials or people's clothes, and electrons will be converted across the oxide layer. If the potential difference exceeds the dielectric constant of the oxide layer, an arc will be generated at the side to destroy the oxide layer, resulting in a short circuit.

4. Others include: ⒊ ⒊∮⒆⒆⒆⒆⒆⒊ (4) ⒆⒉⒏⒌⒌⒏⒌⒏⒌⒌⑼⑼⑿? ∑ Skull? P ting? br> V. electrostatic protection

1. grounding

grounding is to directly discharge static electricity to the ground through a line connection, which is the most direct and effective anti-static measure. For conductors, grounding method is usually used. For example, the anti-static wrist strap is manually worn and the workbench is grounded.

The grounding is implemented by the following methods:

1) The human body is grounded through the wrist strap.

2) The human body is grounded through the anti-static shoes (or shoelaces) and the anti-static floor.

3) The workbench is grounded.

4) The testing instrument, tool holder and soldering iron are grounded.

5. The frame should be grounded as much as possible.

7) The anti-static chair should be grounded.

2. Electrostatic shielding

Electrostatic sensitive components will be exposed to areas with static electricity during storage or transportation, and the influence of external static electricity on electronic components can be weakened by electrostatic shielding. The most common method is to use electrostatic shielding bags and anti-static turnover boxes as protection. In addition, anti-static clothing has a certain shielding effect on human clothes.

3. Ionization neutralization < P > Insulators are often prone to generate static electricity, and grounding method is ineffective to eliminate the static electricity of insulators. The commonly used method is ion neutralization (partially shielded), that is, ion fans are used in the working environment. Provide a working area with equal potential.

Therefore, antistatic materials and antistatic facilities are all products derived from these three ways, which can be divided into antistatic instruments, grounding system antistatic products, shielding antistatic packaging, transportation and storage antistatic materials, and neutral electrostatic elimination equipment. And other anti-static products.

a. Anti-static instrument

1. Wrist strap/foot strap/anti-static shoes comprehensive detector-use: used to test whether wrist strap, foot strap and anti-static shoes meet the requirements.

2. When testing foot strap and anti-static shoes, It is necessary to add a wire connecting the metal plate and the instrument.

3. Detector for removing electrostatic ion fan-Use: regularly detect and check the balance and decay time of the ion fan to ensure that the ion fan works in a safe index range.

4. Electrostatic field detector-Use: measure the electrostatic field to reflect the existence of static electricity, and read it in the form of voltage to test the electrostatic intensity of the environment. Generally, it is affected by the environment and the instantaneous characteristics of static electricity. It is difficult to truly reflect the actual situation.

5. Electrostatic shielding bag tester-use: used to test the shielding effect of electrostatic shielding bags.

6. Surface resistance tester-use: used to measure the surface resistance and volume resistance of materials.

B. Grounding antistatic products

1. Anti-static wrist strap: widely used in various operating stations, there are many kinds of wrist straps, which are recommended to be generally used. There should be a certain margin for the length of the wire.

2. Anti-static watches: other anti-static measures are needed (such as adding ion fans and wearing anti-static heel straps, etc.) to achieve better anti-static effect. It is recommended not to wear anti-static watches in large quantities.

3. Anti-static foot straps/shoes: After the anti-static floor is used in the factory building, anti-static shoelaces or shoes should be worn. It is recommended. It can reduce the introduction of dust. The effect will be better if the operator and staff are combined with anti-static wrist bands.

4. Anti-static table mats: used for laying the surfaces of various tables. Each mat is connected to the anti-static ground reliably after being connected with 1 megohm resistor.

5. Anti-static floor:

Anti-static floor is divided into PVC floor, polyurethane floor and movable floor.

Anti-static wax and anti-static paint: Anti-static wax can be used on various floor surfaces to increase anti-static function and make the floor brighter and cleaner

Anti-static paint can be used on various floor surfaces and can also be applied on various shelves. On containers such as turnover boxes.

C. Shielding anti-static packaging, transportation and storage materials

1. Anti-static turnover boxes and anti-static component boxes: used for turnover, transportation and storage of workshop veneers and components.

2. Anti-static shielding bags: used for packaging, transportation and storage of veneers and components, with certain moisture-proof effect.

3. Anti-static tapes: used for all kinds of products. Or unpack and transport.

5. Anti-static shelves, trolleys and worktables: Anti-static shelves and trolleys are widely used for the turnover and handling of single boards and components in electronic assembly workshops. Anti-static shelves and worktables should be connected in an anti-static way, and the anti-static pads on trolleys should be contacted with anti-static ground by metal chains

6. Anti-static work clothes work shoes: In the processing workshops with electrostatic sensitive components and certain cleanliness requirements, Generally, employees should be strictly required to wear anti-static work clothes. work shoes

7. Anti-static finger covers: If employees at the operating station often need to hold workpieces or electrostatic sensitive components, It is necessary to wear anti-static finger gloves.

D. Neutralizing equipment

Ion blower and air gun

VI. General anti-static process specification requirements

A. General anti-static process specification requirements:

1. Operators must wear wired anti-static wrists

2. Anti-static table mats must be used on the table tops involved in operating electrostatic sensitive devices

. ESD-sensitive devices must be transported by electrostatic shielding and anti-static devices.

4. When preparing to open and test electrostatic sensitive devices, they must be carried out on an anti-static workbench. If possible, an ion air generator can be used to remove the charges in the air.

5. Welding equipment and forming tooling used for assembly must be grounded. Welding tools use internal heating soldering iron, and the grounding should be good. The grounding resistance should be small

6. The power supply system should be refitted and isolated with a transformer, and the grounding wire should be reliable to prevent the grounding wire from floating, and the grounding resistance should be less than 11 ohms

7. During product testing, devices should not be plugged and unplugged at will when the power supply is turned on, but must be plugged and unplugged when the power supply is turned off.

8. All ESD-sensitive devices should not be taken out of the original package prematurely, and should be operated correctly. Try not to touch the legs of ESD-sensitive devices.

9. When wave soldering is used, the solder and the transmission system must be grounded.

B. The following anti-static process requirements are often needed in situations where anti-static requirements are strict.

1. When conducting high and low temperature tests or aging tests on ESD-sensitive devices, the electrostatic potential of the workplace and high and low temperature boxes must be tested first, and the potential cannot exceed the safe value, otherwise. It is necessary to eliminate static electricity.

2. When the soldered printed circuit board is subject to three-proof treatment, anti-static measures should also be taken. Do not use general brushing, ultrasonic cleaning or

spray cleaning.

3. Low-resistance instruments and equipment (such as signals and bridges) used for debugging, measuring and inspection should be connected to the power supply of ESD-sensitive devices.

it can only be connected to the input end of ESD-sensitive devices.

4. In the production line of ESD-sensitive test instruments, electrostatic potential test should be strictly used to monitor the change of electrostatic potential, so as to

take measures to eliminate static electricity.

How to choose anti-static equipment (-)

There are many kinds of anti-static equipment, and reasonable selection can not only save money but also play a good anti-static effect?

1. Control of human static electricity

1. What is the most common static power supply?

2. What is the most effective measure to control human static electricity?

3. when people wear anti-static shoes and have anti-static mats, anti-static composite rubber sheets or anti-static raised floors, they will certainly have a good anti-static effect?

4. why do people wear anti-static work clothes besides anti-static shoes?

5. can people play an anti-static role by wearing anti-static work clothes?

6. what measures should be taken to better control human static electricity?

7. Can people wear wireless bracelets (also called wireless wristbands) to prevent static electricity?

1. What is the most common static power supply?

people will generate static electricity in activities such as walking, standing up and so on. Human body is the most common static electricity source, so the electrostatic protection of human body is the most important.

2. What is the most effective measure to control human body static electricity?

To control human static electricity, the most effective measure is to "connect" the human body with the earth, that is, to "ground". Therefore, people should wear anti-static shoes. To keep the human body connected with the earth, it is required that the ground is also anti-static before introducing human static electricity into the earth. Therefore, the ground can be connected with anti-static mats, anti-static composite rubber sheets and anti-static grounding wires. If the funds are sufficient, you can choose anti-static raised floors. Especially, anti-static raised floor can be considered when planning and designing the computer room and workshop. If the computer room and workshop have been fixed and the equipment has been installed, and you don't want to stop the production of these equipment due to the installation of anti-static equipment, you should choose anti-static floor mats and anti-static composite rubber sheets with low price and simple construction.

3. When people wear anti-static shoes and have anti-static floor mats, anti-static composite rubber sheets or anti-static raised floors, they will certainly play a good anti-static effect?

When people wear anti-static shoes and have anti-static floor mats, anti-static composite rubber sheets or anti-static raised floors, they may not have a good anti-static effect. Usually, people have to wear socks and insoles, and young people's feet are prone to sweat. These socks and insoles can also conduct static electricity, but they can't conduct static electricity in middle-aged and elderly people because their shoes are dry in dry seasons. Moreover, many manufacturers only require their workers to wear anti-static clothes and shoes, ignoring socks and insoles.