I. Terms and definitions
1. Static electricity: a static charge that is excessive or insufficient on the surface of the object.
2. Electrostatic field: The electric field formed by static electricity around it.
3, electrostatic discharge: two objects with different electrostatic potential, due to direct contact or electrostatic field induction caused by the transfer of electrostatic charge between the two objects. After the energy of the electrostatic electric field reaches a certain level, the phenomenon of discharging through the medium and discharging it is electrostatic discharge.
4, electrostatic sensitivity: the electrostatic discharge voltage that components can withstand.
5, static sensitive devices: devices sensitive to electrostatic discharge.
6. Grounding: Electrically connected to objects that can supply or accept a large amount of electric charge, such as land, ships, etc.
7. Neutralization: The use of heterosexual charges causes static electricity to disappear.
8, anti-static work area: equipped with a variety of anti-static equipment and equipment, can limit the electrostatic potential, with clear regional boundaries and specially marked work space suitable for electrostatic protection operations.
Second, the generation of static electricity
1. Friction: In daily life, any two objects of different materials can be separated after contact, and static electricity can be generated. The most common method of generating static electricity is to generate electricity by friction. The better the insulation of the material, the easier it is to rub the electricity. In addition, the separation of any two different substances can also generate static electricity after contact.
2. Induction: For conductive materials, because electrons can flow freely on its surface, such as placing it in an electric field, due to the same-sex repellent, the opposite sex attracts, and the positive and negative ions will shift.
3. Conduction: For conductive materials, electron transfer can flow freely on its surface. If it is in contact with a charged object, charge transfer will occur.
Third, the impact of static electricity on the electronics industry
The circuit of integrated circuit components is reduced, the circuit area is reduced, and the withstand voltage is reduced, which makes the electrostatic shock resistance of the device weakened. The electrostatic electric field and electrostatic current (ESDcurrent) become the deadly 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 has led to an increase in the chance of generating static electricity. Static electricity can be generated in daily life such as walking, air flow, and handling. It is generally believed that only CMOS-type wafers are sensitive to static electricity. In fact, highly integrated component circuits are sensitive.
A. The effect of static electricity on electronic components:
1) Electrostatic adsorption of dust, changing the impedance between the lines, affecting the function and life of the product.
2) The element is inoperable (completely destroyed) due to electric field or current destroying the insulation or conductor of the component.
3) The heat generated by the instantaneous electric field or current causes the component to be injured. Although it can work, its life is impaired.
B, the characteristics of electrostatic damage:
1, concealment - the human body can not directly sense static electricity, unless electrostatic discharge occurs; but the occurrence of electrostatic discharge, the human body may not have the feeling of electric shock, this is because the human body's perceived electrostatic discharge voltage is 2-3KV.
2, latent - some electronic components are not significantly reduced in performance after electrostatic damage, but multiple accumulation of discharge will cause internal damage to the device and create a hidden danger, and increase the sensitivity of the device to static electricity, the problem has not been generated Any method can be cured.
3, randomness - under what circumstances will electronic components suffer from electrostatic damage? It can be said that all processes from the time of production of a component until it is damaged are threatened by static electricity, and the generation of these static electricity is also random. Since the generation and discharge of static electricity are instantaneous, it is extremely difficult to predict and protect.
4, complexity - electrostatic discharge damage components work, due to the fine, small structural features of electronic products, time-consuming, expensive, costly, requires more sophisticated technology often requires the use of scanning electron microscopes and other precision instruments, even so some electrostatic damage It is also difficult to distinguish it from damage caused by other causes, causing people to mistake the electrostatic damage as other failures. This is often caused by early failure or unclear failure before the electrostatic discharge damage is not fully understood, thus unconsciously concealing The real reason for the failure.
5. Severity - ESD problems seem to affect only the users of finished products, but actually affect manufacturers at all levels, such as: warranty, maintenance and company reputation.
6. The harm caused by static electricity in industrial production The generation of static electricity is inevitable in industrial production, and the damage caused mainly can be attributed to the following two mechanisms:
One: the harm caused by electrostatic discharge (ESD):
(1) Causes malfunction or malfunction of electronic equipment, causing electromagnetic interference.
(2) Breaking through integrated circuits and precision electronic components, or aging components to reduce production yield.
(3) High voltage electrostatic discharge causes electric shock, endangering personal safety.
(4) It is easy to cause explosion and fire in the production places of many inflammable and explosive materials or dust and oil mist.
Second: the harm caused by electrostatic attraction (ESA):
(1) Electronics industry: adsorption of dust, causing contamination of integrated circuits and semiconductor components, greatly reducing the yield.
(2) Film and plastics industry: film or film is not wound up; film, CD plastic disk is contaminated with dust, affecting quality.
(3) Paper-making printing industry: paper winding is not uniform, overprinting is not allowed, serious suction, even paper bonding, affecting production.
(4) Textile industry: causing damage to the roots, broken flowers, broken yarns, etc. The harm of static electricity is obvious to all. Now more and more manufacturers have begun to implement various levels of anti-static measures and engineering. However, it should be recognized that perfect and effective anti-static engineering should be based on the actual situation of different enterprises and different work objects, and develop corresponding countermeasures. Anti-static measures should be systematic and comprehensive. Otherwise, it may be half the effort and even cause destructive reaction.
Fourth, the meaning of ESD and the meaning of three types of ESD: ESD stands for English ElectroStatic Discharge meaning "electrostatic discharge". ESD was formed in the middle of this century to study the generation and attenuation of static electricity, electrostatic discharge models, electrostatic discharge effects such as current heat (spark) effects (such as ignition and explosion caused by static electricity), and electromagnetic effects (such as electromagnetic interference). Subject. In recent years, with the rapid development of science and technology, the wide application of microelectronic technology and the increasingly complex electromagnetic environment, more and more attention has been paid to the electromagnetic field effects of electrostatic discharge such as electromagnetic interference (EMI) and electromagnetic compatibility (EMC).
1, the human body type - that is, when the human body is active, the friction between the body and the clothes produces a frictional charge. When people hold ESD-sensitive devices without first discharging the charge to the ground, the triboelectric charge will move to the ESD-sensitive device and cause damage.
2, microelectronics charged type - that is, these ESD sensitive devices, especially plastic parts, when in the automated production process, will generate frictional charge, and these frictional charges are very quickly discharged to the height through the low resistance line Conductive, strong grounded surface, causing damage; or induction of metal parts of ESD-sensitive devices to cause damage.
3, the field type - that is, there is a strong electric field around, which may come from plastic materials or human clothes, electronic conversion will occur across the oxide layer. If the potential difference exceeds the dielectric constant of the oxide layer, an arc is generated to destroy the oxide layer, and the result is a short circuit. #p#分页头#e#
4, other: machine type, field enhanced type, human body metal type, capacitive coupling type, suspension device type.
Five, static protection
1. Grounding - Grounding is to directly discharge the connection of static electricity to a ground. This is the most direct and effective way of anti-static measures. For conductors, the grounding method is usually used, such as artificial anti-static wrist strap and workbench. Grounding, etc. Grounding is implemented by the following methods:
1) The human body is grounded through the wrist strap.
2) The human body is grounded through anti-static shoes (or shoelaces) and anti-static floor.
3) The work surface is grounded.
4) Test instrument, tool holder, soldering iron grounding.
5) Anti-static floor and floor mat grounding.
6) Anti-static transfer vehicles, boxes and racks should be grounded as much as possible.
7) Anti-static chair grounding.
2, electrostatic shielding - electrostatic sensitive components will be exposed to static electricity during storage or transportation, the use of electrostatic shielding can weaken the impact of external static electricity on electronic components, the most common method is to use electrostatic shielding bags and anti-static Electrostatic turnover box as a protection. In addition, the anti-static clothing has a certain shielding effect on the human body clothes.
3, ion neutralization - insulators are often prone to static electricity, the elimination of static electricity, the grounding method is ineffective, the commonly used method is ion neutralization (partially using shielding), that is, using an ion fan in the working environment, etc. Provide an equipotential working area. Therefore, in anti-static materials and anti-static facilities, they are derived from these three methods, which can be divided into anti-static meters, grounding system anti-static products, shielding anti-static packaging, transportation and storage of anti-static materials, Neutralized static elimination equipment, as well as other anti-static products.
A, anti-static meter
1, wrist strap / foot strap / anti-static shoes comprehensive detector - use: for testing wrist straps, foot straps, anti-static shoes meet the requirements. When testing the foot strap and anti-static shoes, it is necessary to add a metal plate and the wires connected to the instrument.
2, in addition to electrostatic ion fan detector - use: Regularly check and verify the ion fan balance and decay time to ensure that the ion fan works in a safe range of indicators.
3, electrostatic field detector - use: measuring the electrostatic field to reflect the presence of static electricity, reading in the form of voltage, used to test the electrostatic strength of the environment. Generally affected by the environment and the instantaneous characteristics of static electricity, it is difficult to truly reflect the actual situation.
4, electrostatic shielding bag tester - use: for the detection of electrostatic shielding bag shielding effect.
5, surface resistance measuring instrument - use: for measuring material surface resistance, volume resistance.
B, grounding anti-static products
1. Anti-static wrist strap: It is widely used in various operating positions. There are many types of wrist straps. It is recommended to use a wrist strap with a 1 megaohm resistor. The length of the cable should have a certain margin.
2, anti-static watch: need other remedies for anti-static measures (such as: add ion fan, wear anti-static heel strap, etc.) in order to achieve better anti-static effect. It is recommended not to use a large number of anti-static watches.
3, anti-static foot belt / anti-static shoes: the factory use anti-static ground, should wear anti-static shoelaces or wear anti-static shoes, it is recommended to wear anti-static shoes in the workshop, which can reduce the introduction of dust. It is better for the operator to combine the anti-static wrist strap with the effect.
4, anti-static mat: for the laying of the surface of each workbench, each mat with a string of 1 megaohm resistance and reliable connection with anti-static.
5, anti-static floor: anti-static floor is divided into PVC floor, polyurethane floor, raised floor.
6, 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 more bright and clean; anti-static paint can be used on a variety of floor surfaces, can also be applied to a variety of shelves, turnover boxes Wait for the container.
C. Shielded anti-static packaging transportation and storage materials
1. Anti-static turnover box and anti-static component box: used for turnover, transportation and storage of workshop boards and components.
2, anti-static shielding bag: for the packaging, transportation and storage of veneers and components, with a certain moisture-proof effect.
3, anti-static tape: used in a variety of packaging boxes.
4. Anti-static IC strips and IC trays: used for storage and handling of IC components in production workshops. It is forbidden to store ICs in the open air before use; or unpack and transport.
5, anti-static shelves, trolleys and workbench: anti-static shelves, trolleys are widely used in electronic assembly workshop of the veneer, parts of the turnover, handling and so on. Anti-static shelves and workbench should be connected statically. The anti-static mat on the trolley should have metal chain and anti-static contact.
6. Anti-static overalls work shoes: In the processing workshops with static sensitive components and certain cleanliness requirements, employees should generally be required to wear anti-static overalls work shoes.
7. Anti-static finger cot: If the operator of the operation station needs to hold the workpiece or static sensitive components frequently, it is necessary to wear anti-static finger cots.
D, neutral equipment: ion fan, air gun.
Sixth, general technical requirements for anti-static
A, anti-static routine process requirements:
1. The operator must wear a wired anti-static wrist.
2. The table top involved in the operation of electrostatic sensitive devices shall be equipped with an anti-static mat.
3. ESD sensitive devices must be transported by electrostatic shielding and anti-static devices.
4. When preparing to open the seal and test the static sensitive device, it must be carried out on the anti-static workbench. Conditional ion air generator can be used to remove the charge in the air.
5. The welding equipment and forming tooling equipment used for assembly must be grounded. The welding tool uses internal heat soldering iron, the grounding should be good, and the grounding resistance should be small.
6, the power supply system should be modified with a transformer for isolation, the ground wire should be reliable, to prevent floating ground, the grounding resistance is less than 10 ohms.
7. When testing the product, the device cannot be plugged or unplugged when the power is turned on. It must be plugged and unplugged when the power is turned off.
8, ESD sensitive devices should not take out the original package prematurely, to operate correctly, try not to touch ESD sensitive device legs.
9. When soldering with wave solder, the solder and transfer system must be grounded.
B. In the case of strict anti-static requirements, the following anti-static process requirements are also often required.
1. When the ESD sensitive machine is used for high and low temperature test or aging test, the electrostatic field test of the work site and the high and low temperature box must be carried out first, and the potential cannot exceed the safe value. Otherwise, the static elimination process should be carried out.
2. When the printed circuit board is soldered for three-proof treatment, anti-static measures should also be taken. Do not use general brushing, ultrasonic cleaning or spray cleaning.
3. Low-impedance instruments and equipment (such as signals, bridges, etc.) used during commissioning, measurement, and inspection should be connected to the input of the ESD-sensitive device after the ESD-sensitive device is connected to the power supply.
4. In the production line of ESD sensitive test equipment, the electrostatic potential test should be strictly used to monitor the change of electrostatic potential, so as to take static elimination measures in time.
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