Small knowledge of aging screening of electronic components (how to check and screen electronic components)

1. How to check and screen electronic components?

Before preparing the components, it is best to list the required components according to the circuit schematic diagram.

In order to ensure that no time is wasted in the trial production process, reduce errors, and ensure that the finished equipment can work stably for a long time, all components must be screened and tested after they are ready. In formal industrial production, there is a special component screening and testing workshop equipped with many general and special screening and testing equipment and instruments, but it is impossible for amateurs to meet these conditions. Even so, we must never give up the screening and testing of components, because many electronic components used by electronic enthusiasts come by mail order, including genuine and defective products, and more are amateurs or users. If they are not screened and tested before installation, once they are soldered on the printed circuit board, it will not only waste a lot of time and energy, but also damage the components and printed circuit board if they are removed.

(1) Appearance quality inspection After you get an electronic component, you should check its appearance for obvious damage. For example, transformer, see if all leads are broken, whether the appearance is rusty, and whether the wire package and skeleton are damaged.

Such as triode, to see whether its appearance is damaged, whether the pin is broken or corroded, and also to check whether the model on the device is clear and identifiable. For adjustable components such as potentiometers and variable capacitors, it is also necessary to check whether their activities within the adjustment range are smooth and flexible, whether the tightness is appropriate, there should be no mechanical noise, and they feel good, and ensure that all contacts are in good contact.

All kinds of electronic components have their own characteristics and requirements, so you should know more about the performance, parameters and characteristics of each component and accumulate experience. ⑵ Electrical performance screening is an essential process to ensure that the trial-produced electronic devices can work stably with electricity for a long time and stand the test of application environment and other possible factors.

The so-called screening is to carry out one or more stress tests on electronic components to expose their inherent defects without destroying their integrity. The theory of screening is: if the test and pressure level are properly selected, inferior products will fail and excellent products will pass.

In the long-term production practice, it is found that the failure rate of newly manufactured electronic components is generally high when they are just put into use, which is called early failure. After the early failure, the electronic components entered the normal use stage. Generally speaking, the failure rate of electronic components will be greatly reduced at this stage. After the normal use stage, electronic components will enter the stage of wear and aging, which will mean the end of life.

This law, like the bathtub curve, is called the efficiency curve of electronic components, as shown in figure 1. The failure of electronic components is caused by improper raw materials or technological measures used in design and production.

The early failure of components is very harmful, but it is also inevitable. Therefore, people can only artificially create early working conditions, so as to eliminate inferior products before manufacturing products, make the components used in product manufacturing enter the normal use stage from the beginning, reduce failures and increase their reliability.

In a formal electronics factory, aging screening projects generally include: high-temperature storage aging; High and low temperature cyclic aging; High and low temperature impact aging and high temperature power aging. Among them, the aging of high-temperature power supply is to electrify the tested electronic components to simulate the actual working conditions, and add high temperature of +80℃-+ 180℃ for several hours. It is an effective measure to test various potential faults of components, and it is also the most widely used method at present.

For amateurs, it is impossible to use these methods for aging detection in the production process of a single electronic product. In most cases, natural aging is adopted. For example, the components are stored for a period of time before use, so that the electronic components can naturally withstand the test of high temperature in summer and low temperature in winter, and then their electrical performance can be tested to see if it meets the use requirements, and the superior can be preserved and the inferior can be eliminated.

For some urgent electronic components, simple electrical aging method can also be adopted. Pulsating DC power supply with adjustable output voltage can be used to make the voltage at both ends of electronic components slightly higher than the rated working voltage of the components, and the current intensity flowing through the components can be adjusted to make the power 1.5-2 times of the rated power, and the simple aging process can be completed after being electrified for several minutes or even longer. (3) After appearance inspection and aging treatment, the electrical performance and technical parameters of electronic components must be measured to determine their advantages and disadvantages and eliminate those failed components.

Of course, different electronic components should have different measuring instruments, but for amateurs, there is generally no need for special electronic measuring instruments, but at least there should be a general instrument that can be used to roughly detect some commonly used electronic components. There are many electrical performance parameters involved in various electronic components, so we need to test them according to the relevant parameters that must be made clear in amateur production, instead of testing all the parameters of components.

The following are some examples of detecting basic components. ① resistor.

It is the most widely used component in all electronic devices and one of the cheapest electronic components. It is a linear element, and its main uses in the circuit are: current limiting, voltage reduction, voltage division, shunt, matching, load, damping, sampling and so on.

When testing this component, it mainly depends on the deviation between its nominal resistance and the actual measured resistance. In mass production, the actual value of the resistor can not be completely consistent with its nominal value due to the action of each process in the processing process, so its resistance value is discrete. In order to facilitate management and organize production, allowable deviation values are given according to the needs of engineering use, such as 5%, 10% and 20%.

In addition, when the multimeter detects resistance, it is generally required that the error does not exceed 10% of the allowable deviation. At the same time, it can also be comprehensively judged by appearance inspection.

② Capacitor. Capacitor is also one of the most widely used electronic components in electronic equipment.

Its quality directly affects the performance of the whole machine, and it is also a component that is prone to failure. When checking the capacitor, if the electrolytic capacitor is stored.

2. What are the screening and aging methods for semiconductor diodes and triodes?

The main contents of the inspection are as follows:

(2) Potentiometers, variable capacitors, adjustable inductors and other components should rotate smoothly without jumping or jamming. ④ The bakelite surface is free of cracks, bubbles and delamination. The surface of porcelain is smooth and free from defects. ⑤ For the parts with sealing structure, the sealing parts should not be damaged or cracked. ⑥ The surface of silver-plated parts is bright, without discoloration and blackening. 2. Screening and aging of components ③ Connectors should be able to be plugged and unplugged freely, and the plating of pins and sockets should be bright without obvious oxidation and pollution. (1) The appearance of components shall be intact, with clear marks, and the leads and terminals shall be free from corrosion and obvious oxidation. The purpose of screening aging is to eliminate the components that fail early due to some defects, so as to improve the service life and reliability of components. Therefore, all parts with screening and aging requirements must be strictly screened and aged according to the technical requirements and relevant technical regulations of the whole machine before assembly. However, under the amateur conditions in the classroom, there is no condition for normal screening and aging of components, so we can only use multimeter and related general instruments to carry out general tests on components, such as resistance-capacitance components, diodes, triodes, integrated circuits,

The general detection of inductance coil, potentiometer and other components has been introduced in the previous course, so I won't repeat it here. However, TV manufacturers have the conditions to screen aging components, which are operated by professionals, which is more complicated. The following is a brief introduction to the technical requirements for screening and aging of semiconductor diodes, triodes and integrated circuits for students' reference only. Screening and aging of semiconductor diodes and triodes ① Screening procedures:

Transistor B: high temperature storage → temperature shock → drop (without using high power transistor) → high temperature reverse bias (silicon PNP transistor) → power supply aging → high and low temperature test (if necessary) → normal temperature test → leak detection → appearance inspection.

Heart → aging of power supply. The screening procedure can be changed according to specific conditions, but its main items are: high temperature storage → temperature shock → falling or separation ② Conditions and requirements:

Storage time: 48 hours, Grade A is Grade B, Grade B is 96 hours ... Storage temperature: silicon diode (150 3)℃; Silicon triode (175 3)℃; Germanium diode and triode (100 2)℃. A. Store leakage current at high temperature → test at room temperature → leak detection → appearance inspection. A diode (rectifier diode here): high temperature storage → temperature shock → detonation → power supply aging → high temperature test inversion.

Germanium: (-55 3)℃ and (85 2)℃. Smoothing temperature shock

Silicon element: (-55 3)℃ (125 3)℃. First low temperature and then high temperature, the conversion time is less than 65438 0 minutes, and it is placed for 65438 0 hours in each state, and the number of cycles is 5 times.

Allow curves to jump. The number of taps is 3~5 times. C tap the special fixture, tap the equipment with a small hammer, and monitor the positive curve of the maximum working current with an indicator. no

Apply a reverse voltage between the c-b poles (the specific voltage value shall be specified by the technical department). The reverse bias time is about 4h, and the leakage current does not exceed the specified value. F. The high temperature test temperature of germanium diode is (70 2)℃, the germanium medium and small power transistor is (55 2)℃, the germanium power g is (-55 3)℃, and the constant temperature time is 30 minutes.

I。 Leak detection shall be carried out according to technical documents. (2) Screening of semiconductor integrated circuits The room temperature test shall be conducted according to the technical documents. E. Turn on the high-temperature reverse bias germanium tube at (70 2)℃, turn on the silicon tube at (125 3)℃, and turn on the diode and transistor with rated reverse voltage. D. Turn on the power supply at room temperature and according to the technical requirements. The aging time is 12h, grade A is B, grade B is 24h .. The temperature of transistor is (75 2)℃, and the temperature of silicon diode and transistor is (125 3)℃. The constant temperature time is 30 minutes. ① High-temperature storage: its function is to accelerate any possible or existing surface chemical reaction by high-temperature heating, so the storage conditions are:150 ~ (175 5)℃ and storage time is 48 hours or 96 hours. 150℃ is suitable for the cycling conditions of epoxy flat packaging: the temperature is (-55 3)℃ and (125 3)℃. First low temperature and then high temperature, each temperature is kept for 30 minutes. ② Temperature Cycle This project can test whether the thermal expansion and cold contraction of different structural materials in the circuit match. The circuit is stable and the potential fault circuit is eliminated. 175℃ is suitable for circuits packaged with other materials.

I want to ask about the service life of electronic components.

Require the suppliers and technical departments of the unit to provide the standards or technical documents of these products. The contents of type test or routine test can be found in these documents, including aging or life test methods, equipment or devices, technical requirements, qualification judgment, etc.

This work can be called reliability testing. It is necessary to find out whether the purpose of doing this work is to improve the reliability level of products or just to cope with inspections.

According to the formal practice, the workload is very heavy, which requires a team, many special equipment and devices, a long time and a lot of expenses. (For example, relays have mechanical life and electrical life, usually hundreds of thousands of times).

If the technical director of your company is really an expert, you should know that most users of these components you listed don't need to have a life test. Generally, they do factory inspection, or they can carry out precision screening according to the contract with suppliers, and high temperature precision is used more. However, it should be based on the relevant provisions of product standards or technical documents, or the technical documents issued by the technical department of this unit.