|Electrostatic hazards and protective measures during LED display production|
In recent years, the production technology of P3 LED display screens has gradually matured in China, and the application fields have become widespread and popularized. However, most LED display manufacturers are not fully equipped to produce such products, which brings hidden dangers to LED display products and affects the entire market. How to standardize production, how to produce a true low-attenuation, long-life LED display products? This article only discusses the harm caused by static electricity in this process and its protection methods from the perspective of electrostatic protection in the LED display production process.
The cause of static electricity:
Microscopically, according to the theory of atomic physics, when electricity is neutral, the substance is in an electrical equilibrium state. The electrons are lost due to the contact of electrons of different substances, causing the material to lose its electrical balance and generate static electricity.
From a macroscopic point of view, the causes are: friction between objects, heat generation, excitation of electron transfer; contact and separation between objects to produce electron transfer; electromagnetic induction causes an imbalance in the surface charge of the object; the combined effect of friction and electromagnetic induction.
The electrostatic voltage is generated by the contact and separation of different kinds of substances. This effect is known as triboelectric charging, and the voltage generated depends on the nature of the material itself that rubs against each other. In the actual production process, the LED display mainly generates static electricity by direct contact and indirect contact between the human body and related components. Therefore, according to the characteristics of the industry, we can do some targeted static precautions.
The harm of static electricity in the production process of LED display
If you ignore anti-static at any point in production, it will cause the electronic device to malfunction or even damage it.
When the semiconductor device is placed alone or mounted in a circuit, even if it is not powered, permanent damage to these devices may occur due to static electricity. As we all know, LED is a semiconductor product. If the voltage between two pins or more pins of the LED exceeds the breakdown strength of the component medium, it will cause damage to the component. The thinner the oxide layer, the greater the sensitivity of the LED and the driver IC to static electricity. For example, the solder is not full, the quality of the solder itself is problematic, etc., which can cause serious leakage paths and cause devastating damage.
Another type of failure is caused by the temperature of the node exceeding the melting point of semiconductor silicon (1415 ° C). The pulse energy of static electricity can generate localized heat, so there is a direct breakdown of the lamp and the IC. This failure occurs even if the voltage is lower than the breakdown voltage of the medium. A typical example is that the LED is a diode composed of a PN junction, and the breakdown between the emitter and the base causes a sharp drop in current gain. After the LED itself or the IC in the drive circuit is affected by static electricity, functional damage may not occur immediately. These potentially damaged components are usually displayed during use, so the life of the display is affected. It is fatal.
Protective measures for static electricity in LED production
Grounding is to directly discharge static electricity to the earth through the wire connection. This is the most direct and most effective anti-static measure. For the conductor to be grounded, we require manual tool grounding, grounding anti-static wrist strap, and work. Ground the table, etc.
(1) In the production process, workers are required to wear a grounded electrostatic wristband. Especially in the process of cutting feet, inserts, commissioning and post-welding, and monitoring, quality personnel must do a static test of the bracelet at least every two hours to make a test record.
(2) When soldering, the soldering iron should use anti-static low-voltage soldering iron as much as possible, and maintain good grounding.
(3) In the assembly process, use a low-voltage DC electric screwdriver with a grounding wire (commonly known as electric batch).
(4) Ensure effective grounding of production pull-up, glue-filling station, aging frame, etc.
(5) We require the production environment to lay copper wire grounding, such as floors, walls, and ceilings used in some occasions, etc., should use anti-static materials. Usually, even ordinary plasterboard and lime paint walls are acceptable, but plastic ceilings and ordinary wallpaper or plastic wallpaper are prohibited.
The embedding of anti-static ground wire:
(1) The lightning rods of the building buildings are generally welded to the reinforced concrete of the building to be properly grounded. When lightning strikes occur, the grounding point and even the ground of the entire building will become the discharge point of high voltage and high current. It is generally believed that there will be a "step voltage" in the range of 20M of the bleed ground point, that is, it is no longer an ideal zero potential in this range. In addition, since the neutral line of the three-phase power supply cannot be absolutely balanced and there is an unbalanced current generated and flows into the grounding point of the neutral line, the buried point of the anti-static ground line should be 20 meters away from the building and equipment.
(2) Buried method: In order to ensure the reliability of the grounding, there should be more than three points of grounding, that is, digging 1.5m deep pits every 5m, and driving more than 2m iron pipes or angle iron into the pit (that is, the angle iron is inserted into the underground more than 2m) Then, the three places are welded together with a 3mm thick copper row, and the inner wire is introduced into the room by a 16m2 insulated copper core wire.
(3) Apply appropriate amount of charcoal powder and industrial salt to the pit to increase the conductivity of the soil. After landfill, measure with grounding resistance tester. The grounding resistance should be less than 4Ω and tested at least once a year.
2. Storage and handling of LED display components
Electrostatic sensitive components are exposed to static electricity during storage and transportation. Electrostatic shielding can weaken the influence of external static electricity on electronic components. The most common method is to use electrostatic shielding bags and anti-static turnover boxes for protection. . In addition, the anti-static clothing has a certain shielding effect on the static electricity of the human body.
Therefore, we require that workers must wear cordless electrostatic rings and gloves, anti-static clothing and anti-static shoes during the turnover handling process. At the same time, professional equipment such as anti-static material box, PCB anti-static material rack, stainless steel turnover car should be used. Avoid direct contact with the human body.
It should be noted that: due to the anti-static clothing, it is woven into a fabric with special synthetic fibers. Under normal circumstances, the friction does not generate static electricity. However, it is not an electrostatic shielding suit. It cannot eliminate the static electricity generated by other materials on the body. There is only one shirt or underwear inside, wearing an anti-static clothing. In the winter, wearing a lot of chemical fiber, wool clothing, etc., and then wearing anti-static clothing for no major use.
Therefore, in the process of storage and handling, it is necessary to control the ambient temperature and humidity, wear an electrostatic wristband, and properly wear an electrostatic suit. Improve the anti-static awareness of all employees. It is very necessary to "insulate" the hand and the product to prevent sweat stains from contaminating the product.
Third, the regulation of temperature and relative humidity
Electronic operation, especially SMT, has high requirements for temperature and humidity. Generally, the temperature is controlled at 18~28°C. Too high or too low will affect the normal operation and accuracy of the equipment; the relative humidity should be 50%~85%. If it is too low, it will easily generate static electricity. If the equipment is too high, it will be dew condensation, and the water content of the solder paste will increase. Therefore, monitoring and regulation should be strengthened. For anti-static, when the relative humidity is low in autumn and winter, it can be solved by humidifier or wet cloth mopping method.
Fourth, monitoring and recording
Anti-static measures must be carried out by a special person, and a system should be formed to carry out the implementation work. Otherwise, all hardware facilities investment may not be effective.
(1) Personnel: It should be jointly managed, tested and recorded by two people. In most cases, two people need to cooperate and prevent personnel from breaking.
(2) Testing and recording: To do static electricity protection work, the following tests and records should be completed every day:
a. Static test point --- static ground.
b. Soldering iron head grounding and soldering iron tip temperature measurement.
c. Small tin furnace grounding and tin furnace temperature measurement.
d. Test instrument grounding measurement.
e. Electrostatic wrist strap grounding test.
f. Measurement and regulation of indoor temperature and relative humidity.
(3) Check the implementation of the regulations on the dressing and anti-static of workers in the work area.
(4) Under certain conditions, the static voltage should be measured by static tester on the work site and on the assembly line. The electrostatic voltage should generally be less than 100V, and the special case should be less than 25V.
V. Training and literacy
Anti-static knowledge and measures should be taken as an important part of the training for all employees, so that every employee can understand and improve the anti-static awareness of all employees, and implement anti-static requirements from top to bottom to form good professional habits. Such as: enter the workshop to replace the anti-static clothing, wear anti-static shoes, must wear the electrostatic ring and gloves before you can touch the components, hold the PCB board or sensitive devices as much as possible to hold the edge, avoid contact with its leads and lugs, consciously Observe and implement anti-static systems and regulations.
In fact, anti-static should be based on the principle of preventing and suppressing the generation and accumulation of static charges and quickly, safely and effectively eliminating the static charge that has been generated. However, many measures of anti-static are actually a set of system engineering. The omission of one link may appear as "the embankment of a thousand miles collapses in the ant hole", and it must not be inadvertent.
The manufacturing process of the LED display screen is a very rigorous and subtle process, and every link must not be overlooked. The electrostatic protection work of LED display is an important part of the production of LED display. At present, the understanding of static protection in the industry is not deep enough, and it can not meet the needs of professional LED display production. It also needs more professionals to continuously research, Discuss together