The LED display has the advantages of high brightness, flexible installation, low energy consumption, etc., which makes it widely used in places with flexible display area requirements and long viewing distances. At present, there are nearly a thousand LED display manufacturers in China, but less than a hundred have a certain production scale (Estec is one of them).
For the LED display, its life can be divided into economic life, technical life, service life and average life. The economic life of a product (also known as the value life) is determined based on the maintenance cost and depreciation cost of the product. It usually refers to the life of the product on the basis of the lowest average annual use cost; the economic life is used to determine the minimum of the product. The best depreciation period and the best time for renewal; technical life is the period of technical value of the product, that is, the entire experience period from the beginning of use of the product to the replacement of more technologically advanced new equipment. The length of the technical life determines Due to the speed of invisible wear and tear of equipment, in fact, the current technical life of LED displays is generally only 3 years; the life span refers to the time from when the product is put into use to complete failure. As an integrated system that integrates LED display technology, visual principles, computer technology, video technology, and electronic technology, LED display screens can be divided into independent parts, and each part is replaceable, so in actual use , The service life of LED displays is quite long, some even up to decades. The average life span (also known as the mean time between failures or MTBF) refers to the time elapsed between two failures. It is a statistical average value. The determination of the MTBF value usually uses theoretical statistical methods, empirical statistical methods, and theoretical statistical methods. It is the data obtained by accumulating and averaging according to the actual conditions of devices, components and constraints. The empirical statistics method is based on the destructive records of factories or laboratories and accumulates average data. No matter what method is used, the reliability of the product changes regularly. Taking the failure rate as an example, its curve with time is like a bathtub, which is commonly referred to as the "bathtub curve", as shown in Figure 1. It can be seen from the bathtub curve that the life of the product can be divided into three stages: early life; service life; and depletion life.
The above figure shows the famous "bathtub" curve. The oblique line on the left is the early failure rate. The failure rate is generally high and decreases quickly over time. The middle part of the curve is the service life, and its failure rate is generally very low and basically fixed. The rightmost part is the period of wear and tear, and the failure rate rises rapidly. Electronic product manufacturers generally eliminate early failures as much as possible through testing, aging, screening and other means, and then provide them to customers for use. When the service life is about to expire, the product is about to enter a period of high failures and needs to be scrapped or replaced.
The impact of environmental factors on product life
1. The influence of temperature on product life
The failure rate of any product during its service life and only under suitable working conditions is very low. As an integrated electronic product, the LED display is mainly composed of a control board with electronic components, switching power supplies, light-emitting devices, etc. The composition, and the life of all these are closely related to the operating temperature. If the actual working temperature exceeds the specified use range of the product, not only the life span will be shortened, but the product itself will also be severely damaged.
2. The impact of dust on product life
In order to maximize the average life of LED displays, the threat of dust cannot be ignored. Working in a dusty environment, because the printed board absorbs dust, and the deposition of dust will affect the heat dissipation of the electronic components, which will cause the temperature of the components to rise, and then the thermal stability will decrease or even cause electric leakage, which will lead to burns in severe cases. . In addition, dust can also absorb moisture, corrode electronic circuits, and cause short-circuit failure. Although the volume of dust is small, the harm to the product cannot be underestimated. Therefore, it is necessary to clean up regularly to reduce the probability of failure. When cleaning the dust inside the display, remember to disconnect the power supply and operate with care.
3. The influence of humidity on product life
Although almost all LED displays can work normally in an environment with a humidity of 95%, humidity is still an important factor affecting product life. The moist gas will enter the IC device through the packaging material and the joint surface of the components, causing the internal circuit to oxidize and corrode the circuit, and the high temperature during the assembly welding process will cause the moist gas entering the IC to heat and expand and generate pressure, which will make the plastic from Internal separation (delamination) on the chip or lead frame, wire bonding damage, chip damage, internal cracks and cracks extending to the surface of the component, and even component swelling and bursting, also known as "popcorn", which will lead to assembly Parts are repaired or even scrapped. More importantly, those invisible and potential defects will be incorporated into the product, causing problems in the reliability of the product. Reliability improvement methods in humid environments include the use of moisture-proof materials, dehumidifiers, and protective coating covers.
4. The influence of corrosive gas on product life
Humidity and salty air environment can cause the degradation of system performance, because they will aggravate the corrosion effect of metal parts, but also beneficial to the production of primary batteries, especially when different types of metals are in contact. Another harmful effect of moisture and salty air is the formation of a film on the surface of non-metallic parts that causes the insulation and dielectric properties of these materials to deteriorate, thereby forming a leakage path. Moisture absorption by insulating materials can also increase the volume conductivity and dissipation factor of the material. Reliability improvement methods for humid and salty air environments include the use of air-tight seals, moisture-proof materials, dehumidifiers, protective coatings/covers, and reduction of the use of different types of metals.
5. The influence of electromagnetic radiation on product life
The interference of radio frequency radiation on electronic systems generally comes from two sources. One way is that the electrical noise interference of the radiated field enters the system directly. Experiments show that when the field strength reaches 5V/m, the system will definitely make mistakes. Electromagnetic interference is enough to change the value of the CPU program counter PC, causing the microcomputer to "jump out" of the executing program by mistake, especially for small signal circuits. The memory cannot work normally when the field strength is 15V/m. Another way of radio frequency interference is introduced through the power supply. The transmission line on the outer frame is equivalent to the receiving antenna, which introduces radiation interference into the system, which can burn the power supply of the system itself when the interference is severe.
6. The impact of vibration on product life
Electronic equipment is often subjected to environmental shocks and vibrations during normal use and testing. When the mechanical stress caused by the generated deflection exceeds the allowable working stress of the component parts, this environment can cause physical damage to the components and structural parts.
7. The influence of load on product life
Regardless of whether it is an integrated chip, an LED tube or a switching power supply, whether it is working under a rated load, the load is also an important factor affecting the life. Because any component has a fatigue damage period, take the power supply as an example. The brand power supply can output 105%~135% of the power. However, if the power supply is operated under such a high load for a long time, it will inevitably accelerate the aging of the switching power supply. Of course, the switching power supply does not necessarily fail immediately, but it will quickly reduce its life.
Summary
It can be seen from the influence of the above-mentioned various environmental factors on product reliability indicators that each environmental factor experienced by a product during its life cycle requires consideration in the design process. Only in this way can it be ensured that sufficient environmental strength is incorporated into the reliability design. Of course, improving the use environment of the product and regular maintenance of the product can not only eliminate hidden troubles in time, but also improve the reliability of the product and extend the average life of the product.
