Why should electronic products be tested for reliability? Specific contents of reliability test

Date：2021-08-23 13:32:00 Views：2650

catalogue

Electronic product development is a complex process. Generally speaking, the test conducted to evaluate and analyze the reliability of electronic products is called reliability test. It is to predict the quality from the delivery of products to the end of their service life. After selecting the environmental stress with high similarity to the market environment, set the degree and application time of environmental stress, The main purpose is to correctly evaluate the product reliability in the shortest possible time. There are many factors affecting the reliability of electronic products, including natural environment, mechanical environment and electromagnetic environment. Reliability design is to take corresponding measures in design and manufacturing around these environmental factors to improve the protection ability and applicability of products, so as to ensure the quality of electronic products and enhance the core competitiveness of electronic products.

1、 Characteristics of modern electronic products

Electronic products refer to relevant products based on electric energy manufactured by electronic technology, including power / electrical equipment and microelectronic instruments, equipment and systems. Electronic products are widely used in national defense, various departments of the national economy and various fields of people's life.

Early electronic products were mainly manufactured based on electronic tubes, with simple functions, uncomplicated circuits and structures, and little difficulty in manufacturing. With the development of production, science and technology, the application of new processes and materials, and the development and promotion of ultra miniaturized components and medium and large-scale integrated circuits, great changes have taken place in the circuit and structure of electronic products. The emergence of miniaturization, ultra miniaturization and miniaturization structure has gradually combined some traditional design methods with electromechanical Replaced by new technologies such as photoelectric combination.

With the continuous enhancement of product performance, the continuous improvement of complexity and the continuous expansion of application fields, the reliability requirements of electronic products are increasing, especially in military, communication, life medical and aerospace fields. The reliability of electronic products has become an important index to measure the service performance of electronic products.

Compared with early electronic products, modern electronic products have the following characteristics.

(1) The product composition is more complex and the assembly density is greater

Early electronic products were usually made of a small number of electronic tubes and discrete components through simple connection, with single function. Modern electronic products usually have multiple functions. The product composition is more complex, the number of components and parts is more, and the volume and quality of products are smaller, so the assembly density is higher. In particular, the emergence of VLSI and its derived functional modules has greatly improved the assembly density of electronic products compared with the past.

(2) The equipment has a wide range of applications and complex working environment

With the continuous expansion of applications, the scope of working environment that electronic products need to adapt to is expanding. Modern electronic products often work in harsh and harsh environments, such as geological drilling, offshore operations, Antarctic scientific research, deep space exploration and so on. At this time, the product needs to withstand the changes of high temperature, low temperature and huge temperature difference, high humidity and low pressure, strong impact and vibration, external electromagnetic interference and cosmic ray radiation. These will have an impact on the normal operation of electronic products.

(3) The equipment requires high reliability and long service life

Early electronic products are not easy to use because of their simple structure, single function and small number of components. Moreover, even if there are occasional faults, it is relatively easy to maintain. Modern electronic products have higher complexity and precision, and more components. In case of failure, the difficulty and cost of maintenance will be greatly increased. Therefore, it is required to have higher reliability and long enough service life, and electronic products with low reliability will lose their use value. In order to obtain high reliability electronic products, not only the quality level of components used is required to be higher, but also greater efforts should be made in circuit design and structure design.

(4) Products require high precision, multifunction and automation

Modern electronic products often require high precision, multi-function and automation. Some have also introduced intelligent control units, so their control systems are more complex. Precision machinery is widely used in electronic products, which is another feature of modern electronic equipment. With the close combination of automatic control technology, remote control and telemetry technology, computer data processing technology and precision machinery, and intelligent human-computer interaction, the accuracy and automation of electronic products have reached a very high level.

The characteristics of the above electronic products are only for the whole, and each product has its own characteristics. Contemporary electronic products have the above characteristics and have higher requirements for circuit design and structural design. Only when designers and producers fully understand these characteristics can they develop modern electronic products that meet the use requirements.

2、 Reliability requirements for electronic products

Reliability is an important aspect of product quality. Generally speaking, good product quality includes two meanings: one is to achieve the expected technical indicators, and the other is to be very reliable in use. Reliability is directly related to the use performance of products and affects customer experience and satisfaction. In the fields of military industry, navigation, communication and aviation / aerospace, reliability is one of the core indicators that users pay most attention to.

To evaluate an electronic product, one is to see whether the function is advanced and whether the appearance is beautiful, which belongs to the circuit and structure design of the product; The second is to see whether it can be manufactured in an efficient and low-cost way, which belongs to the manufacturability of products; Third, it depends on whether the quality is stable and whether the product is reliable, which belongs to the usability of the product. Among them, the circuit and structure determine the function, appearance and performance index of electronic products, which is the core issue concerned by designers; The manufacturability of products determines whether the design scheme can be transformed into actual products in a high-efficiency and low-cost way, which is the focus of manufacturers; The reliability of the product determines whether the product can be durable under various conditions, which is the concern of users, represents the product design level, and is also an important embodiment of the core competitiveness of the enterprise.

With the continuous development of material technology, component technology and electronic design technology, the functions of electronic products are becoming more and more complex and integrated, which also puts forward higher requirements for the reliability of electronic products. Improving the reliability of products and making them give full play to their best performance is not only the key factor to improve the quality of an electronic product, but also directly affects the evaluation of end users. Improving the reliability of electronic products is an extremely important and challenging work. In a sense, improving the reliability of products also improves the core competitiveness of products. The embodiment of scientific and technological progress is the upgrading of product quality and the improvement of reliability.

3、 Introduction to reliability of electronic products

1. Concept of reliability

Gjb450 defines reliability as the ability of systems, mechanical equipment or parts to complete specified functions under specified working conditions and within specified time. Reliability also has relevant definitions in military standards, that is, the probability of completing the specified function within the specified conditions and time. It is an important index to measure the reliability level.

The concept of reliability includes the following three meanings.

(1) Product reliability is based on "specified working conditions":

The so-called "specified working conditions" refer to the stress conditions, environmental conditions and storage conditions when the product is used within the specified time. The reliability of products varies with different specified conditions. For example, the smaller the output power of general semiconductor components, the higher the reliability. For another example, the reliability of the same electronic equipment may vary greatly in different use environments. The worse the environmental conditions, the lower the reliability of the equipment.

(2) The reliability of products is closely related to the "specified time"

Generally speaking, after aging, the product has a long stable service life. Later, with the passage of time, the stability and reliability decrease gradually. The longer the service time, the lower the reliability.

(3) The reliability of the product is measured by completing the "specified function"

The "function" here refers to all the functions of the product, not some of them. The product is considered reliable only when it has completed all specified functions.

2. Classification of reliability

The formation and evaluation of reliability are related to many factors, which not only depends on the product design and manufacturing process, but also affected by the environment and service conditions.

Reliability can be divided into the following three types:

(1) Inherent reliability

Inherent reliability refers to the inherent reliability of products during design and manufacturing. For component products, raw material quality, manufacturing process and working parameters will affect their inherent reliability. For electronic products, the inherent attributes are affected by the complexity of products, the selection and use of circuits and components, the working parameters and reliability of components, mechanical structure and manufacturing process. In general, the more complex the circuit and structure, the more components and manufacturing processes are used, the lower the inherent reliability of the product.

(2) Use reliability

Service reliability refers to the influence of users and maintenance personnel on product reliability. It includes whether the use and maintenance procedures are correct, whether the selection of equipment is reasonable, whether the operation methods are appropriate and other factors. The reliability of use depends largely on the person using the equipment. Skilled and correct operation and timely maintenance can significantly improve the reliability of products. The reliability of use is directly related to the design of ergonomics.

(3) Environmental adaptability

Environmental adaptability refers to the impact of the environmental conditions of the product on reliability, including natural environment, mechanical environment and electromagnetic environment. Improving the environmental adaptability of the equipment is mainly to take various effective protective measures for the equipment.

4、 Main factors affecting the reliability of electronic products

Generally speaking, the reliability of electronic products is related to their service life. The longer the average life of electronic components, the higher the reliability of electronic products. However, reliability and service life are not the same concept. The high reliability of electronic products does not necessarily mean long service life, and the long service life does not necessarily mean high reliability, which is related to the use requirements.

The factors affecting the reliability of electronic products mainly include the following:

(1) Natural environment

Electronic components are greatly affected by environmental factors, such as temperature, humidity, salt fog, air pressure, altitude, air pollution particles, etc., which will affect the normal operation of electronic components, reduce their electrical performance, and even damage components, resulting in failure.

(2) Mechanical structure

The mechanical structure design of electronic products should meet the requirements of service conditions. Strong mechanical vibration or collision will damage and deform the mechanical structure of the equipment, and even lead to physical damage or failure of electronic components, so that the electronic products can not operate normally.

(3) Electromagnetic environment

Electromagnetic waves are everywhere in the environment. Electronic products are in contact with electromagnetic signals in space all the time. Under the influence of electromagnetic signal, the noise of electronic circuit will become larger and the stability will become worse. If the interference is serious, it will even lead to equipment operation failure or endanger personal safety.

(4) Assembly process

In addition to the quality and design factors of components, the manufacturing process will also directly affect the reliability of products. Different assembly processes will directly affect the connection firmness, sealing and environmental corrosion resistance, and then affect the quality and reliability of electronic products.

In fact, in addition to the use reliability, the inherent reliability and environmental adaptability of electronic products are determined by the design and manufacturing process, that is, after the electronic products are manufactured, the main reliability indicators of electronic products have been fixed, and the external environment is only a test of reliability. Therefore, The key to improve the reliability of electronic products is to improve the level of design and manufacturing.

5、 Main measures to improve the reliability of electronic products

Improving the reliability of electronic products mainly refers to improving its inherent reliability. The starting point is the source design and manufacturing process. The main measures shall be formulated according to the relevant factors affecting the reliability, including the quality selection of components, the design of structure and circuit, the selection of assembly process, etc.

1. Reliability design

The measures to improve product reliability mainly include the following aspects at the design level:

(1) Reliability prediction

Reliability prediction is a measure at the design level, which refers to the reliability requirements of products. The reliability indicators are decomposed and evaluated in advance in the overall design stage, so as to lay a foundation for the smooth development of subsequent design work.

For reliability prediction, the following requirements shall be noted.

① The reliability of electronic products shall be predicted and analyzed according to the selected circuit form, reliability structure model, components, working environment and previously accumulated data, so as to take measures in advance and scientifically deal with the possible faults of such products in future application.

② Designers shall pay enough attention to the reliability prediction of electronic products, and implement the corresponding prediction analysis to ensure the effectiveness of reliability prediction of such products.

(2) Rational selection of electronic components

For electronic products, the reliability level of components determines the reliability of the whole machine. In the development of reliability design of electronic products, we need to pay attention to the reasonable selection of electronic components related to it in practice, so as to meet its reliability design requirements.

The following requirements shall be paid attention to in the selection of electronic components.

① Electronic components that meet the use requirements and have good cost performance shall be selected by comprehensively considering circuit performance, operating environment, cost control and other factors, so as to provide support for the formation of reliability design scheme of electronic products.

② In the process of selecting electronic components, it is necessary to compare and analyze different types of components to determine the best electronic components required by electronic products.

③ The actual application effect of electronic components selected in the design process shall be scientifically evaluated to ensure that such components have good applicability in the application of electronic products.

④ Derating of components. In the process of component selection, the working stress of electronic components is usually moderately reduced below the specified rated value, so as to reduce the basic failure rate of components. "Derating design" is a common means to reduce the basic failure rate. Within the optimal derating range, level I, level II and level III derating can be adopted to realize the optimal scheme of reliability improvement and cost control.

(3) Thermal design

With the increasing density of components in modern electronic products, a large number of thermal coupling is generated between components through conduction, radiation and convection. Thermal stress has become one of the important factors affecting the reliability of electronic products. Therefore, it is necessary to carry out reasonable thermal design of electronic products to ensure that the electronic products under the action of their design scheme can be in a good application mode.

The following requirements shall be paid attention to in thermal design.

① The thermal design of electronic products shall adopt three basic technical means of heat dissipation, installation of radiator and refrigeration separately or comprehensively according to the use requirements, so as to obtain an ideal thermal design scheme and meet the reliability design requirements of electronic products to the greatest extent.

② In the thermal design process of electronic products, designers need to reasonably use convection heat dissipation, conduction heat dissipation and thermal radiation characteristics in combination with the actual situation, so that the electronic products under these modes can maintain a good heat dissipation condition. This will help to enhance the effect of reliability design of electronic products and make it more scientific in the application of the final design scheme.

(4) Redundancy design

Redundancy design of electronic products refers to the use of one or more of the same systems to form a parallel form, and make a scientific response in case of failure of one of the systems. Under the function of redundant design, when a component in the application of electronic products fails, other components can still work normally, so as to meet the reliability design requirements of electronic products.

For redundancy design, attention shall be paid to the following requirements.

① On the premise of following the redundancy theory, we should fully combine practical experience to determine the redundancy design scheme required by electronic products, so as to provide guarantee for the improvement of its reliability design level.

② Redundant design will increase the volume, mass and cost of the whole system. Therefore, it is only used in more important electronic products (such as missile guidance, atomic bomb fuse, etc.).

(5) EMC design

In the process of reliability design of electronic products, in order to make the final products meet the requirements of national EMC standards and avoid mutual interference in the operation of electronic circuits, it is necessary to consider the EMC design of electronic products.

The general requirements for EMC design are as follows.

① Designers should make rational use of printed circuit board design, power line filtering, shielded chassis, signal line filtering, cable design, grounding and other technologies to make electronic products meet the requirements of electromagnetic compatibility in application, so as to improve its application value.

② In the process of forming the EMC design scheme of electronic products, the electromagnetic characteristics and sensitive characteristics of components shall be fully considered, and the circuit condition of electronic products shall also be paid special attention, and improvement shall be carried out when necessary.

③ In the process of EMC design, it is necessary to accurately identify the circuits susceptible to interference and those not susceptible to interference, and take targeted measures according to the principle of classified treatment, so as to maintain good EMC of electronic products.

(6) Maintainability design

In practice, considering the repairability characteristics of electronic products, we need to pay attention to the design of maintainability in its reliability design, so as to eliminate the potential safety hazards in the application of electronic products.

The following requirements shall be paid attention to in the maintainability design of electronic products.

① The maintainability design scheme required by electronic products should be determined from the aspects of maintenance convenience and cost economy, so as to provide scientific guidance for the development of product maintenance.

② Maintenance tools with reliable performance should be selected to improve the maintenance efficiency of electronic products supported by such tools and improve its maintainability design scheme.

③ The details in the maintainability design of electronic products should be handled well to ensure the effectiveness of the application of the design scheme.

(7) Structural reliability design

Electronic products will be affected by various environmental factors in use and transportation, which may accelerate or cause damage to electronic products. In the process of electronic product structure design, the impact of these adverse factors should be fully considered to improve the protection ability of electronic products, so as to improve the reliability of electronic products.

The functions and requirements of structural reliability design mainly include:

① Control the temperature rise of components by using effective heat dissipation device;

② Reduce the harm to products caused by mechanical factors such as vibration, impact and collision;

③ Eliminate internal and external noise interference;

④ Strengthen the research on anti-corrosion, moisture-proof and mildew proof to prolong the service life of structural materials;

⑤ The design process shall follow the requirements of standardization, serialization and generalization.

2. Reliability test verification

Reliability test is the general name of various tests to study failure and its influence results and to improve or evaluate the reliability of test objects. In a broad sense, any test conducted to understand, evaluate, assess, analyze and improve reliability can be called reliability test. Reliability test technology began to develop in the 1950s. It was first used in military products and has been widely used in aviation, aerospace, electronics, automation, automobile, computer and other industries. Reliability test is an important means to investigate, analyze and evaluate the reliability of products, and it is also an important link to improve and ensure the reliability of products.

When a product is manufactured, in principle, its performance index should meet the reliability requirements specified in the original design, but the actual situation is much more complex. In fact, it is difficult to fully consider all reliability problems in the design process. There are even contradictions or conflicts between different reliability indexes. Compromise design can only be adopted, which is more obvious for complex systems. Therefore, it is necessary to verify the realization degree of reliability index through a series of reliability tests, or find and identify various faults and defects.

The principle of reliability test is to simulate the on-site working conditions and other environmental conditions in the life cycle, and repeatedly apply various working modes and stress conditions to the tested products according to a certain time proportion and a certain cycle order. After analyzing and handling the failure of the tested products, the obtained information is fed back to the design, manufacturing, material and management departments for improvement, so as to improve the inherent reliability of the products. At the same time, the reliability of electronic products is evaluated according to the test results. In order to achieve the expected effect of reliability test, special attention must be paid to the selection of test conditions, the design of test cycle and the determination of failure criterion.

It is worth noting that the formulation of environmental test conditions for various electronic products must be considered according to the specific use situation. For example, for the cycle test of electronic products, different test sequences will produce different test results. Taking the cyclic test of climatic factors as an example, when the test sequence of high temperature → humidity → low temperature is adopted (that is, the electronic products are heated in the oven to dry the components. Then, they are put into the damp oven to absorb moisture under the action of capillary force. Finally, the components are placed in the freezer for cooling). If the product quality is not qualified, Under the action of thermal expansion and cold contraction, it is very easy to cause cracking. If it is carried out in the order of humidity → high temperature → low temperature, because the high-temperature baking first dehumidifies the components, the impact of humidity on the product is equivalent to being artificially shielded. At this time, the test process can only reflect the impact of alternating cold and heat on the product, and the results are obviously different.

6、 Introduction to reliability test of electronic products

1. Purpose of reliability test

According to statistics, in electronic products, the defects of components and parts, process defects and design defects account for about 1 / 3 respectively. Correct these defects to gradually improve the reliability of the product and meet the design requirements. The time spent is 5 ~ 25 times of the required MTBF. Therefore, a product from development and finalization to mass production is always inseparable from reliability test. Although the cost of reliability test is often very high, effective reliability test can double the reliability of the initial prototype, so as to obtain greater economic benefits.

The purpose of reliability test is to find the reliability problems in the product life cycle, analyze, evaluate and deal with them. Reliability test runs through all stages of product design, production, use and maintenance.

① In the development stage, it is used to expose the defects of trial products in all aspects, evaluate the reliability of electronic products reaching the predetermined indicators, and ensure the reliability of sold products.

② Evaluate new materials, new products, new processes and new designs, and study new test methods.

③ The production stage provides information for monitoring the production process, exposes the uncertain factors in the use process, and studies the measures to prevent faults.

④ Expose and analyze the failure rules, failure modes and failure mechanisms of electronic products under different environments and stress conditions.

⑤ Carry out reliability appraisal or acceptance of finalized products, and study the failure distribution law of electronic products.

⑥ In order to improve product reliability, formulate and improve reliability test scheme, provide basis for users to select electronic products and provide basis for effective reliability management.

2. Classification of reliability test

The reliability test can be divided into many types according to the environmental conditions of the test, the purpose of the test, the working stage of the product, the applied stress strength, the impact on the reliability, the damage degree of the test product, the test scale and the type of sampling scheme.

1） Classification by environmental conditions

Classified by environmental conditions, reliability test includes:

(1) Stability test

Put the product in the artificial simulated working environment, and assess the product's ability to resist each environmental impact factor according to the requirements of technical indicators. Such as temperature, humidity and pressure stability, water impermeability, and resistance to vibration, impact, acceleration and other stability tests.

(2) Comprehensive test

Test the performance index that the product can achieve under the action of comprehensive factors. This kind of test is close to the actual use, so it plays an important role in environmental test.

2） Classification by test items

According to the classification of test items, reliability test includes:

(1) Reliability life test

Destructive life test is usually used. Its task is to take a certain number of samples for life test under specified conditions, record the failure time of each component, conduct statistical analysis of all data, and calculate the reliability index of components to evaluate the reliability level of products, further analyze the causes of product failure, and put forward measures to improve reliability. Reliability life test is the most important content in various reliability tests, and it is also the content most closely related to statistical methods.

(2) Reliability environment test

Reliability environmental test studies the influence of various environmental conditions on components. Environmental stress refers to the adverse environmental conditions borne by the product during operation, such as temperature, humidity, voltage, pollution, vibration, fog, radiation, etc.

(3) Reliability screening test

Reliability screening test is to inspect all qualified products and eliminate potential early failure components, so as to improve the reliability of the whole batch of components. Reliability screening test is an effective basic work to improve product reliability.

(4) Whole machine reliability qualification test

The whole machine reliability evaluation test is arranged after the successful trial production of new products, in order to verify whether the equipment design can meet the specified performance and reliability requirements under the specified environmental conditions. This test is conducted in the form of life test, which requires quantitative identification of the average life of the equipment.

After the products are put into continuous production, a series of regular tests shall be arranged for the whole machine to determine whether the equipment can meet the corresponding performance and reliability requirements and whether each batch of products can be delivered. Although the reliability acceptance test is also carried out in the way of life test, it only requires to formulate a simple acceptance scheme and acceptance standard for the test staff to master and make judgment. The whole machine reliability acceptance scheme and its acceptance criteria are called reliability sampling inspection scheme.

Classified by test purpose, reliability test includes:

(1) Reliability engineering test

The purpose of reliability engineering test is to expose defects or faults in product design, process, components and raw materials, analyze them, take corrective measures and eliminate them, so as to improve the inherent reliability of products and meet the reliability requirements specified in the contract.

(2) Reliability statistical test

The purpose of reliability statistical test is to verify whether the product has reached the specified reliability level, rather than exposing the defects or faults of the product. Reliability statistical test is also called reliability verification test. For different products, in order to achieve different purposes, different reliability test methods can be selected.

Summary:

Electronic products are inseparable from our life. The quality of electronic products also directly affects our living standards to a certain extent. The reliability of electronic products is an important index to measure the quality and usability of electronic products. The improvement of reliability is the basic guarantee for the stable operation of electronic products.

It is very important for the durability of the product. Reliability test is to determine whether the products transferred to mass production through reliability identification test meet the specified reliability requirements under specified conditions, and to verify whether the reliability of products decreases with the changes of process, tooling, workflow, parts quality and other factors during mass production. Only through these, can the product performance be trusted and the product quality be excellent.