The reliability of electronic products refers to the ability of products to complete the specified functions under the specified conditions and within the specified time. It is an important part of the quality of electronic products. Although an electronic product has a high technical performance index, if its reliability is not high, its quality cannot be considered good. The low reliability of the product will bring great losses to the production. With the enlargement of the control system, more and more electronic components are used in a system. As long as one of the components fails, it will generally cause the entire system to fail. The resulting economic loss will far exceed the value of a component itself, so the reliability of the component is increasingly important. Whether the electronic product adapts to the predetermined environment and meets the reliability index must be identified or evaluated through reliability testing; sometimes it is necessary to expose the problems in the design and process of the product through testing, and determine the main failure mode and occurrence through failure analysis The reasons for further improvement measures. Therefore, reliability testing is not only an important part of reliability activities, but also an effective measure to further improve product reliability.
Reliability changes of electronic products generally have certain rules. The characteristic curve is shown in Figure 1. Because of its shape like a bathtub, it is usually called "bath curve". As can be seen from Figure 1, in the early stages of product testing and design, due to errors in design and manufacturing, imperfect software, and insufficient component screening, the early failure rate was high. The whole machine test makes the product enter a stable accidental failure period; after a period of use, the product enters the consumption loss period due to device wear, aging of the whole machine and maintenance. This is why the reliability characteristic curve is of the "bathtub curve" type.
Usually we define that in many experiments, the number of occurrences of a random event is called the frequency of the event. If in the M trials, the frequency of event A is M, then the relative frequency of event A is M / N. Under the condition that the state is unchanged, in many practices, the relative frequency of occurrence of event A reflects the possibility of the occurrence of event A. It is an approximate percentage of the occurrence of event A, which is called the probability of event A and is denoted as P (A).
P (A) = M / N (N is very large)
Therefore, the "ability to complete the specified function" in the definition of reliability of electronic products is exactly the probability of completing the specified task. For example, suppose a batch of electronic products leaves the factory at t = 0, and there are N faults left at time t. Obviously, N is a function of t, denoted as N (t). Among the N (t) working at t, the percentage of failures per unit time is called the instantaneous failure rate of this batch of electronic products, which is recorded as λ (t).
When t + â–³ t, there are N (t + â–³ t) working, that is from t to (t + â–³ t) / â–³ t, so
λ (t) = [N （t） -N (t + △ t)] / N （t） △ t
≈-N '(t) △ t ​​/ N （t） △ t
=-N '(t) / N (t)
The reciprocal of the product failure rate is called the product's mean time between failures (also known as average life), and it is used to indicate the level of reliability. For example, the failure rate is equal to 2% / month, that is, the average life is equal to 50 months, which means that 2% of the products that are working will fail in 1 month. At this time (50 months), 36.4% are still working. By the time the average life span has doubled, roughly 13.2% are still working normally.
The failure laws of electronic products have their own characteristics. A large number of reliability test data at home and abroad indicate that the failure rate of electronic products during normal operation is approximately equal to a constant. Its physical meaning is: at any time, the products that are still working, generally have a fixed percentage of products that will fail in a unit time. For example, the failure rate of a certain high-power tube is 2% per month. If 10,000 tubes are shipped from the factory, then 2%, that is, 200 tubes will fail in the first month, and 9,800 will be left. In the second month, roughly 2%, or 196, failed.... And so on. At the end of the 50th month, there were roughly 3,641 remaining. It is characterized by continuous failures during normal operation. The quality of electronic products is based on the level of failure rate. Unlike mechanical products, there is a normal working period where there is basically no failure.
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