Static generation, hazard, esd protection, complete process plan
In the daily production process, the situation of encountering static damage products is more common, especially in some innovative enterprises. When the high-end products developed by the company are commissioned, the production environment of the foundry and industry is often unable to meet the requirements, mainly in the aspect of electrostatic discharge. Forcing many foundries to make positive improvements to the production site. In the process of improvement, they encountered many problems. The main problem is that they did not go deep into the improved program without deep understanding of the anti-static industry standards, thinking that they should do some surface work. It can solve the problem of electrostatic discharge.
The first thing to understand is how static electricity comes from?
First, the generation of static electricity:
1. Friction: In daily life, any two objects of different materials are separated and contacted to generate static electricity, and the common method of generating static electricity is to generate electricity by friction. The better the insulation of the material, the easier it is to use triboelectricity. In addition, static electricity can also be generated by the separation of any two different substances 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 electrons will shift.
3. Conduction: For conductive materials, charge transfer occurs due to the free flow of electrons on its surface, such as contact with charged objects.
Second, the impact of static electricity on the electronics industry
The circuit of the integrated circuit component is reduced, the withstand voltage is reduced, and the circuit area is reduced, so that the electrostatic shock resistance of the device is weakened, and the electrostatic electric field and the electrostatic current become the deadly killers of these high-density components. At the same time, the widespread use 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 damage to the insulation or conductor of the component.
3. Due to the heat generated by the instantaneous electric field or current, the component is injured and still works, and the life is damaged.
B, the characteristics of electrostatic damage:
1. Concealed human body can not directly sense static electricity, unless electrostatic discharge occurs, but electrostatic discharge occurs, the human body may not have the feeling of electric shock. This is because the human body perceives an electrostatic discharge voltage of 2-3 kV.
2. Latentity Some electronic components are not significantly degraded by electrostatic damage, but multiple accumulations of discharges can cause internal damage to the device, which increases the sensitivity of the device to static electricity. There are no cures for the problems that have arisen.
3. Under what circumstances will random electronic components suffer 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 such static electricity is also random. Since the generation and discharge of static electricity are instantaneous, it is difficult to predict and protect.
4. Complex electrostatic discharge damage sub-board work, due to the fine and small structural features of electronic products, it is time-consuming, labor-intensive, and costly. The more complicated technology requires the use of precision instruments such as scanning electron microscopy, even if there is some electrostatic damage. It is difficult to distinguish from the 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 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.
Third, ESD three types
1. The human body type means that the friction between the body and the clothes generates a triboelectric charge when the human body moves. When people hold ESD-sensitive devices without first placing charge on the ground, the triboelectric charge will move to the ESD-sensitive device and cause damage.
2. The charged type of microelectronics refers to both ESD-sensitive devices, especially for plastic parts. When automated production, triboelectric charges are generated, and these triboelectric charges are quickly discharged through a low-resistance line to a highly conductive, solid ground. The surface, thus causing damage; or causing damage to the metal portion of the ESD-sensitive device by induction.
3. The field type is surrounded by a strong electric field, which may come from plastic materials or human clothes, where electron conversion occurs across the oxide layer. If the potential difference exceeds the dielectric constant of the oxide layer, an arc is generated on the side to destroy the oxide layer, and as a result, it is short-circuited.
Electrostatic protection must be done in a loop. If any of the links are not in place, it will be like a car with a tire, and the missile cannot be moved, so that the static electricity cannot be effectively controlled.
Fourth, static protection
Ground
Grounding is to directly discharge the connection of static electricity to a ground. This is effective in anti-static measures. For conductors, grounding is usually used, such as artificially wearing an anti-static wrist strap and grounding the work surface.
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 an anti-static floor.
3) The work surface is grounded.
4) Test instrument, tool holder, soldering iron grounding.
5) Anti-static floor, grounding pad.
6) Anti-static transfer vehicles, boxes and racks should be grounded as much as possible.
7) Ground the anti-static chair.
2. Electrostatic shielding
Electrostatic sensitive components are exposed to static electricity during storage or transportation. The electrostatic shielding method can weaken the influence of external static electricity on electronic components. The usual method is to use electrostatic shielding bags and anti-static turnover boxes as protection. In addition, the anti-static clothing has a certain shielding effect on the clothes of the human body.
3. Ion neutralization
Insulators tend to generate static electricity, and the static electricity of the insulator is eliminated. 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 to provide an equipotential operation. region.
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, Neutral-type static elimination equipment, as well as other anti-static products.
A. Anti-static meter
1. Wrist strap/foot strap/anti-static shoes comprehensive detector is also called human body comprehensive tester - use: for detecting wrist straps, foot straps, anti-static shoes meet the requirements.
2. When testing the foot strap and anti-static shoes, it is necessary to add a metal plate and the wires connected to the instrument.
3. 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.
4. Electrostatic field detector is also called electrostatic tester or electrostatic voltmeter - use: measuring the electrostatic field to reflect the presence of static electricity, reading in voltage form, used to test the electrostatic strength of the environment. Generally, it is difficult to truly reflect the actual situation due to the environmental impact and the instantaneous characteristics of static electricity.
5. Electrostatic shielding bag tester - use: used to detect the shielding effect of the electrostatic shielding bag.
6. Surface resistance measuring instrument - use: used to measure material surface resistance, volume resistance.
B. Grounding anti-static products
1. Anti-static wrist strap: 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 be left with a certain margin.
2. Anti-static watch: Remedial of other anti-static measures (such as adding an ion fan, wearing an anti-static heel strap, etc.) to achieve better anti-static effect. It is not recommended to wear a large number of anti-static watches.
3. Anti-static foot strap / anti-static shoes: After using anti-static floor, the factory should wear anti-static shoelaces or anti-static shoes. It is recommended to wear anti-static shoes in the workshop to 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: It is used for the laying of the surface of each workbench. Each mat has a 1 megaohm resistor on the string and is reliably connected with anti-static ground.
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 brighter and cleaner. Anti-static paint can be used on various floor surfaces, and can also be applied to various shelves, turnover boxes. Wait for the container.
C. Shielded anti-static packaging transportation and storage materials
1. Anti-static turnover box, anti-static component box: used for the turnover, transportation and storage of the veneer and components of the workshop.
2. Anti-static shielding bag: used for packaging, transportation and storage of veneers and parts, with a certain moisture-proof effect.
3. Anti-static tape: used in various packaging boxes, etc.
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 and trolleys are widely used in the turnover and handling of veneers and components in electronic assembly workshops. 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 an anti-static finger cot.
D. Neutralization equipment
1. Ion fan: According to the placement method, there are desktop, horizontal and hanging type. According to the number of holes, single-head ion fan, double-head ion fan, three-head ion fan, four-head ion fan, five-head ion fan, There are ion wind drums suitable for harsh environments and requiring a wide range of applications and rapid elimination of static electricity. Benchtop ion fans, horizontal ion fans and single-head ion fans can be placed on the workbench or suspended, double-headed, three-headed, The four heads and the five heads are all suspended ion fans. The ion fan only needs to be plugged into the 220V power supply to be used, and the air volume can be adjusted. In addition to the ion wind drum, the ion fan is suitable for eliminating the electrostatic residual voltage requirement. In higher places, the dust removal function will be inferior to other static elimination equipment;
2. Ion air gun: divided into ordinary ion air gun, plastic gun body ion wind gun, big head ion air gun, TOP GUN ion air gun (also called high precision ion air gun, suitable for use in high-purity purification room), ion Air guns are generally hand-held. Eliminating static electricity and dust removal at the same time requires external compressed air. The air source is required to be free of moisture and oil. (Generally, air compressors are equipped with filters for filtering oil. If not, Purchase at hardware stores, each ranging from 30-100 yuan);
3. Ion wind nozzle: there are ordinary ion wind nozzle, inductive ion wind nozzle (automatic induction object blowing), generally fixed installation on the assembly line;
4. Ion wind snake: similar to the ion wind nozzle, the difference is that there is a base, the air duct can be folded, and the blowing direction can be changed at will;
5. Ion wind bar: According to the material, there are copper rods (ion copper rods, ion wind copper rods), aluminum alloy rods (ion aluminum rods, ion wind aluminum rods, ion wind curtains), and ionization according to ion generation method. Inductive, copper rods generally have electric ions, aluminum alloy rods are generally inductive, the length is generally customized according to needs, there are wind and non-wind, and generally installed on the equipment;
6. In addition to static electricity net: generally installed in the air inlet at the top of the workshop, the clean room is installed well, can cover the entire room, the size is customized according to requirements.