“Product problems are sometimes not a R&D problem. There have been cases where equipment in developed areas above the middle and above levels in China was exported to Colombia because it was used well in the country, but there were frequent failures. The cause of the failure was the middle level in mainland China. The altitudes of the above developed areas are relatively low, so in high altitude areas, the air tightness of the equipment is challenged, and the pressure difference between the inside and outside of the equipment increases and the leakage rate increases.
There are not only many skills in circuit design, but also many misunderstandings. This article will introduce ten misunderstandings in circuit stability design.
Misunderstanding 1: Product failure = product is unreliable
Product problems are sometimes not a R&D problem. There have been cases where equipment in developed areas above the middle and above levels in China was exported to Colombia because it was used well in the country, but there were frequent failures. The cause of the failure was the middle level in mainland China. The altitudes of the above developed areas are relatively low, so in high altitude areas, the air tightness of the equipment is challenged, and the pressure difference between the inside and outside of the equipment increases and the leakage rate increases.
When the project was established, only low altitude was considered, so the design of others is okay. Your boss just asked for it. Whoever decides to export this model to Colombia is the culprit. He is simply the biggest culprit when he raises objections. After all, the sales executives’ decision-making ignorance of technology can be forgiven, and the mistake of the vice president of technology is incompetent.
Product reliability is “the ability to complete a specified function in a specified time and under a specified condition”. Readers must savour this definition carefully, study things for knowledge, and see who can achieve more knowledge when this definition is qualified. The conditions of the use site often exceed the prescribed conditions, and this exceeding is likely to be implicit.
Misunderstanding 2: Transition process = steady state process
The introduction of “A Curve Affecting Product Reliability and Social Harmony” can explain the content of this graph.
Misunderstanding 3: Derating is easy to do, no problem
Anyone who derates can be good at painting, but not everyone can survive by painting. For details, please refer to the article “Derating Design of Electronic Products”. Here is just a brief summary:
1. Devices with the same function but different processes have different derating factors;
2. Adjustable devices and fixed-value devices have different derating factors;
3. The derating factor is different for different loads;
4. The derating factor is different when the wires of the same specification are used in multi-turn and single-turn applications;
5. Some parameters cannot be derated;
6. The junction temperature derating should not be omitted.
Misunderstanding 4: Ta, the device can be used with confidence
Why is device damage often referred to as “burning”?
Because device failures are mostly thermal failures, there are two specific precautions. First, the device environment temperature ≠ the overall environment temperature. The device environment is affected by the heat dissipation of other components in the chassis. Generally, the device environment temperature is higher than the overall environment temperature. .
Myth 5: Electronic reliability has nothing to do with mechanical and software majors
Installation, wiring, layout, and spraying treatments will affect electrical performance; electromagnetic compatibility, false welding, heat dissipation, vibration and noise, corrosion, and grounding are all related to the structure; software error prevention, error judgment, error correction, and fault tolerance processing measures can avoid mechanical And electronic defects.
Misunderstanding 6: The device is very simple, it doesn’t matter whether there is a Datasheet or not
When designing, you must get the Datasheet of all the devices, and then read all the graphs and parameters on it, and finally establish a connection with these curves in the design. The following figure is the VI characteristic curve of the diode. It is necessary to carefully confirm the static operating point of the device in our circuit when designing.
Myth 7: Maintainability has nothing to do with me
What is the purpose of electronic product reliability work? It is to make money. What do you rely on to make money? Increase income and throttling. It is difficult to increase income and easy to reduce expenditure. Don’t always think about saving on material costs. Material costs are saved, and maintenance costs are high. ? It’s better to die early and give birth early. The best way is to pay attention to maintainability and save this part of the cost. This is a genuine profit.
Misunderstanding 8: Poor process control means that there are no good craftsmen
Poor process control is not just a problem for craftsmen, it is the construction of a value chain. The requirements of the design engineer for the device, the selection of the manufacturer of the purchasing engineer, the control content of the inspection link should be designed in the part of the key indicators of the device, the detection method should not introduce the failure mechanism and damage of the component, and the assembly link should not introduce damage (peak Welding furnace temperature control, anti-static treatment of manual welding table tops, etc.), the factory inspection link should check the part of the device parameter drift that may cause product failure, and the maintenance link should not introduce failure. It can be seen from the above that the problem is the difference. A process engineer can guarantee it. Therefore, it is concluded that the specific method is to establish consistency. The premise of consistency is that the designer provides sufficient, primary and secondary technical information. The process is only based on the design drawings and design documents to ensure that the manufacturing reliability is infinitely close to the design reliability.
Misunderstanding 9: The relationship between the MTBF value and the failure rate of a single specific machine
MTBF is a macro and statistical concept, and a single machine failure is a micro and specific concept. Customers like to ask the question “The MTBF value of your product is 10,000 hours, so if I buy your one, there will be no problems within 10,000 hours?” This is a concept of Guan Gong vs. Qin Qiong who is more powerful. Let me Speaking of their conversion relationship, first tell me whether it is 1km or 1kg?
Myth 10: Strengthening testing can solve reliability problems
Since this problem can be listed as one of the top ten misunderstandings, its definition is naturally wrong. There are three conclusions:
1. Some problems cannot be detected at all through simulation test experiments;
2. Test method = engineering calculation specification review simulation test electronic simulation;
3. The corresponding low temperature working time cannot be calculated from the results of the temperature enhancement test.