Recently, LED displays have become more and more widely used, and the good display screens are exquisite and colorful. However, in reality, after a short period of six months or a rainy season, the beautiful picture is not reproduced at the beginning, color distortion, dead lights, large flower screens, etc., professional technicians know that this must have happened. The device has failed, or rust has occurred, resulting in poor contact.
In the field of advertising, LED display is a relatively expensive electronic product, hundreds of thousands, and even hundreds, tens of millions. Then, investing in such a huge equipment, how long its lifespan guarantees, whether it can maintain a good display effect and a low failure rate during the lifetime, has become a topic of concern to both manufacturers and investors. From the technical point of view, analyze the factors that affect the life of the display, and explore measures to ensure the longevity of the LED display.
1. Factors affecting the life of LED displays
The factors affecting the life of the LED display are classified according to internal and external factors. The internal factors include the performance of the LED light-emitting device, the performance of the peripheral components, and the fatigue resistance of the product. The external environment has the working environment of the LED display.
1.1 LED lighting device performance impact
LED light-emitting devices are the most critical and long-lasting components of the display. For LEDs, we focus on the following indicators: attenuation characteristics, water vapor permeability, and UV resistance.
Brightness decay is an inherent characteristic of LEDs. For a display with a design life of 5 years, if the brightness of the LED used is reduced to 50% for 5 years, the design should consider the reserve margin. Otherwise, the display performance will not reach the standard after 5 years; the stability of the attenuation index is also It is very important that if the attenuation has exceeded 50% in 3 years, it means that the life of this screen is terminated early.
Display screens for outdoor use are often eroded by moisture in the air. LED light-emitting chips can cause stress changes or electrochemical reactions that cause device failure in the case of contact with water vapor. Under normal circumstances, the LED light-emitting chip is not eroded by the epoxy resin, and some LED devices with design defects or material process defects have poor sealing performance, and the water vapor is easily passed through the pin gap or the gap between the epoxy resin and the outer surface of the outer casing. Entering the inside of the device causes the device to fail quickly, which is called "dead light" in the industry.
Under the ultraviolet light, the properties of the colloid and the support material of the LED will change, which will cause the device to crack and affect the life of the LED. Therefore, the LED anti-ultraviolet ability for outdoor use is also an important indicator.
The performance improvement of LED devices requires a process that requires market testing. At present, Japan and some Taiwan-funded enterprises are very cautious and do not promise SMD outdoor waterproofing. However, some domestic manufacturers are eager to introduce new products to occupy the market, and blindly promise excellent outdoor performance in the case of poor evaluation. In the display application of the SMD5050 for outdoor use, there have been a large number of quality accidents caused by many manufacturers, and some losses are as high as tens of millions of dollars, which is shocking.
1.2 Impact of peripheral components
In addition to LED lighting devices, the display also uses many other peripheral components, including circuit boards, plastic housings, switching power supplies, connectors, chassis, etc., any problem with the components, may lead to reduced display life . Therefore, if the longest life of the display is determined by the life of the key component of the shortest life, it is not an exaggeration. For example, LED, switching power supply, and metal casing are all selected according to the 8-year standard, and the protective process performance of the circuit board can only support its work for 2 years. After 2 years, it will be damaged due to rust, then we can only get a piece of 2 years. Life display.
1.3 Product fatigue resistance impact
The fatigue resistance of display products depends on the production process. The anti-fatigue performance of the module made by the poor three-proof treatment process is difficult to guarantee. When the temperature and humidity change, the protective surface of the circuit board will be cracked, resulting in a decrease in the protective performance.
Therefore, the production process is also a key factor in determining the life of the display. The production processes involved in the production of display screens include: component storage and pretreatment process, over-furnace welding process, three-proof process, and waterproof sealing process. The effectiveness of the process is related to material selection and ratio, parameter control and quality of the operator. The accumulation of experience is very important, so a factory with many years of experience will be more effective in controlling the production process.
1.4 Impact of the working environment
The operating conditions of the display vary widely depending on the application. From the environmental point of view, the indoor temperature difference is small, no rain, snow and ultraviolet light; the outdoor temperature difference can reach up to 70 degrees, plus wind and sun and rain. A harsh environment can exacerbate the aging of the display, which is an important factor affecting the life of the display.
2. Life support measures
It can be seen that the life of the LED display is closely related to the use environment. For the display screen whose environmental variables can be determined, the life span can be ensured by selecting appropriate devices and appropriate manufacturing processes, including: life design, process control , reliability verification.
2.1 Life design
The general design pays attention to the function realization and performance index realization, and the life design also pays attention to the performance index after a certain time or a certain number of uses. The output of the design affects the selection of the device, the selection of the production process, and the selection of the verification method. Only when a full life design is performed, the life of the display is likely to be controllable.
2.2 Process control with a focus on life
Effective design requires an efficient process to achieve. In the process of product realization, there are many processes that need to be controlled, including the selection and verification process of the device, including the effectiveness control of the production process. It is different from the quality control program, which is focused on long-life.
2.3 High-intensity reliability verification
The use of high-intensity reliability verification to ensure predictable product life is expected, including verification of raw materials, components generated during the process, and final verification of the product, which is a very important and often overlooked point. Think about a few questions:
Can the selected LED be valid for 5 years? Is the seller promised or verified by himself? Is the verification method effective?
Can the three-proof process of the board guarantee 5 years of anti-corrosion? Verified? Is the verification method effective?
How does the shell material change after 5 spring, summer, autumn and winter? How to validate?
Finding ways to validate for five years or more is not a simple matter. Boeing's approach to spacecraft life control is worth learning. We use the method of high acceleration stress test [1] to verify the high-intensity reliability and achieved good results.
The high-acceleration stress test includes a high-acceleration life test and a high-acceleration stress screening. The former aims to make the product and the process of manufacturing the product reach maturity before being put into mass production, and it is almost impossible to use the design-induced failure. Product; the latter purpose is to eliminate potential defects in the product and obtain a product with stable performance.
3. Application effect
In practical applications, in order to meet the individual needs of customers, LED manufacturers must complete the design-production-delivery work in just a few months. We have applied effective life control methods in several sets of large-area landmark displays with an area of ​​more than 1000 square meters. Statistics show that the products are running stably.
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