1. Electronic reliability design principles The design principles of electronic reliability include: RAMS definition and evaluation indicators, electronic equipment reliability model, system failure rate impact factors, electronic product reliability indicators, work environment conditions, system design and micro design, process review and testing, Design specifications and technical standards. Some people have said that the design principle is absolutely correct nonsense. Anyone will say that no one will use it. The popular translation is that design principles are difficult to establish direct influence and connection with actual design. This section is mainly a methodology. Regarding the methodology of technology, the greatness of Qian Xuesen’s old man is well known. But what is his level and advantage? Electronics, machinery, software, testing, management? No, it is a system approach. And engineering calculations. When we want to decide on the device selection of a circuit, if there is a basic formula that directly tells us which indicator we should pay attention to, is device selection and circuit design still difficult? For example, a socket cable, which has to pass 10A of current, is connected by two 8A wires in parallel? Still using a 14A cable? The reliability model makes it easy to get answers. Is it better to use a triode to drive an LED? Or use an op amp? Visiting the beer museum of Tsingtao Beer, I saw a century ago, the German motor and the Japanese fan, still functioning today after the century, it is enviable. The influential factors of system failure rate can tell you the answer to this result. Today, Germany and Japan, like us, can't make a century-old motor and fan. If you want to improve your electronic reliability, what specific problems should you start with? These are system methods. On the issue that engineering calculation can help solve, Qian Xuesen's wisdom and thinking need someone to continue to inherit, and hope that more people will participate and understand and apply it more widely. 2, circuit reliability design specifications Circuit reliability design specifications include derating design (derating parameters and derating factors), thermal design (thermal design calculations, thermal design testing, thermal device selection), circuit safety design specifications, EMC design, PCB design (placement and routing) , grounding, impedance matching, machining process), usability design (availability factor, user operation analysis, design criteria), maintainability design (serviceability level, evaluation content, design method) One of the core ideas of circuit reliability design specifications is the monitoring process, not the monitoring results. The most common analogy is that the design specification is the maintenance of the pregnancy process to ensure eugenics. These are summaries of the experience of many previous generations. According to these specific design methods, the reliability risks of the products will be eliminated. For example, in thermal design, according to the heat dissipation method determined by the calculation of thermal power density and heat flux density, you don't have to worry about insufficient heat dissipation. According to the calculation method of thermal resistance and junction temperature, the fan and heat sink are selected, as long as there is enough Quantity, don't worry about yourself being "a blind man riding a horse, and a night at the deep pool". PCB grounding, this seems to be the simplest and most complicated problem, is there a universal grounding idea, so that we only have to be happy and no longer worry, the answer is "yes". Usability does not seem to have much impact on us. It is as if we are going to an interview. It seems that the success or failure of our interview seems to be academic credentials, work experience, etc., but the leek leaves on the front teeth will lead to failure? What is the difference between the color and size of the button, the feel and strength of the button, the shape of the button, the layout of the button, the content displayed, the method of display, the angle of the display, the size of the display, and the cleanliness of the incisors? For the user, there is one of the most popular sayings: "The interface is the system." The user does not know the profound theory and internal structure. The internal things are guaranteed to be easy to use, and the rest is the appearance. Especially for new users, the appearance is the first factor to decide whether to buy or not. Chasing girls in college is the best choice for you? The maintainability can directly determine the cost of money, and the maintainability is divided into three. Level, field level, office level, headquarters level, different levels, the value of maintenance tools, the number of supporting tools, the level of maintenance personnel, the number of maintenance personnel, the abundance of accessories are not the same, Imagine, define For the "field level" maintenance level, there is a cover that requires 3 people to move down. How many people in the maintenance team travel together? Defined as "office level", but need to be equipped with high-end instruments such as spectrum analyzer, logic analyzer, oscilloscope, etc., can be repaired, the cost of maintenance tools will be geometric? Not to mention the many facilities that need to be equipped, such as water, electricity, gas, and other equipment. 3. Reliability test Reliability testing includes standard compliance testing, edge extreme condition testing, fault tolerance testing, HALT testing, destructive testing, implicit condition testing, and interface condition testing. Communicating with many technical personnel, I want to do a good job of reliability design, but generally reflect two problems: one is the lack of experience, the other is that there is no problem at home, and there is a problem at the scene. Inexperienced problems can be solved by the second part of the method, the test problem is solved through this section. The core point of the test is the design of the test case, which is concentrated in two parts. One part is to simulate the worst application conditions of the user site as much as possible, and the other part is to target the possible failure mechanism, artificially increase the damage factor, stimulate the problem, find the weak point and improve. It. However, it should be noted that many tests are somewhat destructive and need to be analyzed. Machines that have undergone destructive testing must not be used in the factory. 4, component selection Component selection includes the basic principles of selection, classification of components, characteristics, selection indicators, reliability application notes, etc., including capacitors, resistors, diode transistors, connectors, crystal oscillators, electronically controlled optics (light) Coupling, LED), AD/DA and op amp, electronically controlled mechanical action device, energy conversion device (switching power supply, power conversion chip, transformer), digital IC, protection device (fuse, magnetic ring bead, varistor, TVS Tube), power module, etc. Girls are popular with a slogan, "It’s better to marry well than to marry." Although online debates between the two sides are fierce, no one can deny the fact that the final outcome of a girl is really better than marrying. Much more. Well done is the circuit design is good, marry well is the device selection is good. The same is the difference between capacitors, tantalum electrolysis and aluminum electrolysis, the difference between electrolysis and ceramic sheets, the difference between wirewound resistors and membrane resistors, which indicators are mainly concerned with digital ICs, and the choice of protection devices is based on what, everyone knows, The deterioration of the bodyguard guard can be terrible. We are like chefs, we don’t care about growing vegetables, but the taste of the dishes we brew is influenced by vegetables, water, fertilizer, climate, etc. Otherwise, there will be no Maotai in Maotai Town, wine in Shanxi, and rainy season in Meiyu. Stinky tofu and other exclusive products. In the same way, the manufacturing process of the device and the device characteristics derived from its manufacturing process need to be understood and circumvented in the application. For example, the inductance of the wirewound resistor is large, the leakage current of the paper capacitor is large, the ESR value of the capacitor affects the circuit design, the temperature resistance and the vibration resistance of the ceramic capacitor are low, and the TVS surge current is small but the reaction The time is fast, the effect of the magnetic ring depends on the material and assembly, the vibration resistance is poor and so on. 5, component failure mechanism and analysis method Component failure mechanisms and analytical methods include common failure mechanisms, analytical methods, and tools. All of the above are how to prevent the circuit from working abnormally and prevent the device from being broken. However, the wise man will inevitably lose it. Once it is broken, don't stay away from it, but it should be a treasure. People who drive know that where is the best level of driving? The highway is not available, only when it is downtown and bad road conditions. The development of society is a process of finding problems and solving problems. It is not terrible to have problems, but it is terrible to have the same kind of problems frequently. The analysis of device failure is based on a basic improvement, "precautions based on failure mechanisms." The problem has been discovered. The elements that caused the problem have been circumvented, and the norms have been formed. Everyone will follow the design in the future, and the problem will naturally not be reproduced. For example, ESD protection, many companies are doing, the method of doing it includes humidification, but humidification may bring MSD problems. If I/V curve test is passed, it is found that some pin pairs of the device appear after wave soldering. When VCC and GND are open, then the MSD problem should be considered. The solution is to heat the air for several hours before soldering. For example, if the device burns out, it is necessary to check which pin is broken, and what is the broken phenomenon. Through the multimeter, I/V curve plotter, oscilloscope, and the advanced point of the external search to find X-ray fluoroscopy, judge The mechanism of failure, and the way to find the circuit associated with the pin, analyze the circuit and the process in the factory, find the point that causes the failure mechanism and improve it. 6, circuit reliability design micro management method The micro-management method to improve reliability is very simple, including three parts: software tools, AAR, checklist. It is reasonable to say that technical content should not be mismanaged, but in fact management can promote technology. For example, someone in the company has mastered a certain knowledge point, but others do not know that he will, management measures can know him. Inspired and guided the design practice of others, this is equivalent to solving technical problems with non-technical means. This part of the method is mainly implemented for several obstacles to the reliability work. The first obstacle is that people are prone to laziness. They feel that they are almost the same. The cost of finding instructional documents is a bit large. They feel that they are almost self-contained. The role of software tools is to reduce technical communication barriers. The second is the lack of technical level experience. Then carry out the After Action Review, and summarize the causes, phenomena, and improvement methods of each problem, and share them through software tools. We have been working hard every day, and we have no experience. Why fear, growing fast is also a means of solving technical experience; the third obstacle is that a person can think of a problem at a certain moment is limited, let a master review a design, the status of his review will make him miss the content, checklist The comparison system can be used for designers' self-examination, as well as for reviewing expert references and avoiding omissions. It is a good learning material for low-level people and a reference for high-level people.
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