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Jul 13,2021| LED Knowledge
1. Product stereotyped design
There are many types of LED display screens. For different working environments and display content, as well as the special requirements of customers, it is necessary to finalize the product and determine the various indicators of the product to better meet the needs of customers. The finalization mainly involves the following points.
1. Determine product specifications
1) According to the installation environment of the LED display, determine whether to use indoor or outdoor products;
2) Determine the primary color of the display screen according to the content that the customer needs to display. Such as: to play text, select single and double color display; play video, select three primary colors, namely full-color LED display.
3) Comprehensively determine the pixel pitch of the display screen according to the viewing distance and the size of the LED display screen;
2. Determine the brightness of the product
Since the brightness of the product can be adjusted before the LED display leaves the factory, it is necessary to determine the brightness of the display according to the customer's site installation environment before production. On the premise of meeting the display requirements, the life of the display screen is increased.
3. Determine the installation method and structure of the product
According to the site to determine the installation method, the following points need to be considered.
1) Cabinet selection:
Outdoor LED displays generally have simple and sealed cabinets. For fixed installation and edging environments, simple cabinets are generally selected. For displays that often need to be moved (mostly leased), fully sealed cabinets are required.
There are generally simple box and bracket installation methods indoors. For indoor screens less than 10 square meters, you can choose the bracket installation method; for LED displays larger than 10 square meters, considering the weight and structural stability of the screen, generally choose a simple cabinet that is thinner than the outdoor;
2) Structural design
The structure design of LED display screen needs to consider the following points.
The structure is based on the premise of stability, combined with the actual situation of the site, balance the force fulcrums, and the structural bearing capacity should be greater than 20% of the weight of the display body;
The flatness of the structure surface directly affects the flatness of the screen body after the LED display is installed, and has an important impact on the display effect of the display. To ensure the flatness, the structural surface frame and the installation box of the LED display must be completely combined; when welding, the flatness of the welding must be ensured.
In addition to the installation of the screen itself, the LED display structure also includes other accessory equipment. Such as the placement of audio, exhaust fans, air conditioners, etc., the edging area of the outer structure, and the placement of outdoor lightning protection facilities. These must be considered in the initial stage of the design of the structure, and the appearance of the display must be beautiful and comfortable under the premise of ensuring quality and practicality.
Easy to install and maintain:
The design of the structure needs to consider the convenience of installation and maintenance. Such as maintenance channel, cable channel, etc.
Second, confirm the list of materials
After the product is finalized, it is necessary to make a detailed list of materials or BOM;
The raw materials needed for the entire project need to be listed on the list, including:
1. The material list of the module;
2. The material list of the box;
3. List of materials for the structure;
4. List of ancillary equipment;
Making a complete list of materials can achieve twice the result with half the effort. Material integrity can avoid prolonging the production cycle due to lack of materials in the production process. At the same time, centralized purchase of materials has a price advantage over scattered purchases of materials, which can reduce the cost of raw materials. So it is extremely important to make a detailed list of materials.
Three, module production process
1. Equipment needed for placement:
Stencil; printing machine; placement machine; reflow soldering machine.
It is made according to the driving surface of the product to be produced, and its purpose is to fix the driving element to the PCB. There are two types of stencils: red glue and solder paste. The red rubber steel mesh is to fix the components on the board, and solder the components on the PCB through wave soldering. The solder paste stencil is to solder the components attached to the board on the PCB through a reflow soldering machine. The PCB printed by the red glue stencil must be wave soldered, while the PCB printed by the solder paste stencil does not need to be wave soldered. The thickness of the steel mesh is generally: red glue 0.18MM, solder paste 0.15MM
Spread the red glue or solder paste evenly on the PCB.
When printing, pay attention: the stencil and PCB must be in good contact and compression; the printed surface must be uniform in thickness.
Paste the electronic components on the PCB. Pay attention to when mounting:
1. The direction and polarity of the components;
2. The component pins should be aligned with the pad package pins;
Reflow soldering machine:
Fix the components attached to the PCB on the board. Both red glue and solder paste are semi-solid during printing. Through reflow soldering, the red glue is solidified and the components are adhered to the PCB; while the solder paste can be melted by reflow soldering, thereby soldering the components on the PCB.
Attention should be paid when reflow soldering:
1. The temperature setting of each temperature zone;
2. Time setting of each temperature zone for reflow soldering;
The process of inserting the LED on the PCB according to the polarity of the PCB package is called a plug-in.
The plug-in process needs to pay attention to the following points:
The damage of static electricity to the LED is obvious, the whole production needs to be well grounded, and the plug-in personnel must wear a wired anti-static ring;
The long leg of the LED is positive before the leg is cut, and the negative is the broken leg, but after the leg is cut, the lamp pin is the same length, so the positive and negative poles cannot be judged from the lamp pin. And the lamp cup cannot be determined as the negative electrode. For some counter-electrode LEDs, the end with the lamp cup is the negative electrode. Therefore, for insurance, the technician needs to measure the polarity before plugging in the light, and then inform the staff of the polarity.
(Three), wave soldering
Equipment required for wave soldering:
Wave soldering machine:
Wave soldering is a very important process in the production of LED display screens. The following points need to be paid attention to:
Compatibility of fixture and PCB: The fixture must be made in line with the hole position of the product, and the verticality of the lamp can be ensured after the wave soldering is completed.
The uniformity and completeness of the spray flux: The flux can make the solder adhere well to the pad of the component at the wave crest. If the flux is sprayed unevenly and does not cover the entire board, this will cause false soldering and false soldering, which will bring trouble to the subsequent processes and affect the reliability and stability of the product.
Grounding: Wave soldering must be well grounded.
Ensuring the verticality of the lamp is an important problem to be solved by wave soldering, because the light of the lamp is generated by the surface chip, and the deviation of the lamp will cause the deviation of the luminous intensity and angle. As a result, the luminescence of the display screen is uneven, causing color deviations from various angles, and reducing the effect and quality of the displayed image. Therefore, wave soldering must ensure the verticality of the lamp.
(4) After welding
Some large components cannot be soldered by wave soldering, such as power sockets, input and output interface pins, electrolytic capacitors, etc., which require manual soldering. We call this process post soldering. In addition to soldering components, post-soldering also has the function of overhaul. After wave soldering, the boards are often not so satisfactory. At this time, post-soldering is required to re-paste some untinned pins and check for some vacancies on the board. Defects such as welding and false welding. Since the post-welding operator is also in direct contact with the LED, anti-static is necessary. The production pull needs to be grounded, and the operator must wear a wired anti-static ring.
The post-welded board can be lighted up through the system, where it must be tested to determine whether the board is good or bad.
The test mainly detects the following aspects:
Dead light, dark light;
Whether the electronic components are broken;
Whether the component has false welding or false welding;
Whether the signal timing is correct;
(6) Aging of semi-finished products
Focus on the tested products and make a judgment on the quality of the entire screen. The aging of semi-finished products is more important for mass production. When the semi-finished products are aging, the entire production can be evaluated, and the quality problems of the LED display in the production process can be found and solved in time. Thereby improving production quality, ensuring product reliability and reducing risks.
(7) Module kit assembly and glue filling
Assemble the tested mold to the bottom shell and mask. For outdoor products, glue is required to be waterproof, so the bottom shell of the module must be installed first, and then turn to the glue group to fill the glue. After the glue is dry, the module mask is put on. When assembling the module, it is necessary to ensure the verticality of the lamp to avoid the deviation of the lamp due to human factors. At the same time, when assembling, pay attention to the strength of the electric screwdriver, and do not damage the bottom shell and mask of the module due to excessive force.
In the production of outdoor waterproof products, it is necessary to fill the surface of the module with glue to play a waterproof role. Nowadays, electronic potting glue is generally used, there are AB types, mixed according to the ratio of 10:1, and the glue is automatically poured on the surface of the module by hand or machine.
Pay attention when filling glue: AB glue should be mixed evenly;
The amount of glue is moderate, not too little or too much. Too little is not good for waterproofing, and too much affects the light-emitting angle of the lamp and the assembly of the mask.
(8) Aging of finished modules
The modules of the glue-filled kit are put together to light up the test, which is called aging.
The aging of the finished module is mainly to make an overall assessment of the screen. Such as the life and attenuation of the lamp, the chromatic aberration phenomenon of the screen, the white balance effect, the display angle, the quality of the playback image and text, etc.
Fourth, the cabinet assembly is aging
Box assembly materials:
Box body (sealed box body generally has fan, power supply and signal aviation seat);
Power supply (5V switching power supply, power backplane);
Signal connection line (flat line, DB line, network cable);
Power cord (5V power cord between modules, 220V power cord between power sources);
Screws, nuts, copper posts, screwdrivers;
LED display box assembly process:
1. Install the module on the box;
2. Connect the signal cable between the modules;
3. Connect the 5V power cord of the module;
4. Install the power supply and connect the 5V power cord on the module to the power supply;
5. Connect the 220V power cord between the power supplies. If there is a fan and an aviation seat, connect them together;
6. Install the system, connect the output of the system to the module, and connect the 5V power cord to the system;
Precautions for cabinet assembly:
The flatness of the module;
Control the length of power cables and signal cables, and keep the cables as short as possible under the premise of meeting requirements (reduce the voltage drop and signal attenuation on the cables, and save materials at the same time);
The polarity of the power cord is distinguished. The power cord is divided into positive and negative poles. The positive and negative poles cannot be reversed between the module and the module, the module and the power supply, and the power supply and the power supply;
The input and sequence of the system output line and the module signal cannot be reversed;
Aging of the cabinet:
Vibration test and waterproof test are required before the cabinet is aging. The vibration test is mainly to test whether each assembly device is firmly installed, and the waterproof test is mainly to check whether the waterproof rubber ring of the module is well installed and whether the module has a screw leak.
Combining the cabinets with vibration and waterproof tests to light up and aging is called cabinet aging.
Cabinet aging steps:
Splice the cabinet;
Connect the power cord;
Connect the signal wires between the boxes;
Connect the system line;
Check before power-on (whether there is a short circuit between the power supply and the module);
Power on, system debugging;
Deal with problems;
The following work needs to be done before installing the display screen:
Determine the site frame structure;
Learn more about the power distribution system;
Understand the control platform system;
Understand the placement of various auxiliary facilities;
The personnel and tools needed to install the display screen;
Five, the installation and debugging process of the display screen:
1. LED display installation. Install the box on the outer frame structure. The boxes are usually connected by connecting pieces (connecting pieces will be made at the same time as the boxes are produced) to ensure that the gap between the boxes is minimized and the surface of the screen is flat.
2. Wiring. Including power line and signal line;
The power cord includes the power cord between the cabinets and the power cord from the power distribution system to the screen.
The signal line includes the cable connection between the boxes (the air head connection between the sealed boxes) and the network cable connection between the systems.
3. Install ancillary facilities. Such as air conditioners, exhaust fans, audio equipment, etc.
4. Detection. Test whether there is a short circuit between the power cables, whether the system signal trend is consistent, and whether there is an abnormal short circuit caused by external metal objects.
5. Power on and debug.
Through the system settings, check whether the wiring of the LED display is correct, whether the module is displayed normally, whether the signal is transmitted normally, whether the image can be transmitted and displayed normally, etc.
6. Hemming of the outer frame.
7. Training customers to use, such as the use of operating software, the playback of various files and images, and how to deal with common problems on the screen.
8. Project acceptance.