Reliability test scheme for inspection and verification of electronic components

Date：2022-06-01 14:43:55 Views：1576

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 the key factor to improve the quality of an electronic product, and it also directly affects the evaluation of end users. Improving the reliability of electronic products is an extremely important and challenging task. 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.

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, first, whether the function is advanced and 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 a high-efficiency and low-cost way, which belongs to the manufacturability of products; The third is to see 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.

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. High reliability of electronic products does not necessarily mean long service life, and 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 during operation, such as temperature, humidity, salt fog, air pressure, altitude, atmospheric pollution particles, etc., which will affect the normal operation of electronic components, degrade their electrical performance, or even damage components, thus causing faults.

(2) Mechanical structure

The mechanical structure design of electronic products shall meet the requirements of service conditions. Strong mechanical vibration or collision will cause damage and deformation of the mechanical structure of the equipment, and even lead to physical damage or failure of electronic components, so that the electronic products cannot 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 of components and design factors, the manufacturing process will also directly affect the reliability of products. Different assembly processes will directly affect the connection firmness, sealing, environmental corrosion resistance, etc., 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 improving the reliability of electronic products is to improve the design and manufacturing level.

Main measures to improve the reliability of electronic products

Improving the reliability of electronic products mainly refers to improving their inherent reliability. The starting point is the source design and manufacturing process. The main measures should 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

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 at the overall design stage, so as to lay a foundation for the smooth implementation 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 applications.

② Designers should pay enough attention to the reliability prediction of electronic products, and put the corresponding prediction and analysis work in place to ensure the effectiveness of the reliability prediction of such products.

(2) Reasonable 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, it is necessary to pay attention to the reasonable selection of electronic components in practice, so as to meet the reliability design requirements.

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

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

② During the selection of electronic components, it is necessary to compare and analyze different types of components to determine the best electronic components for 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, II and III derating levels can be adopted to achieve 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 for electronic products to ensure that the electronic products under the action of their design schemes can be in a good application mode.

The thermal design shall pay attention to the following requirements.

① The thermal design of electronic products shall adopt three basic technical means of heat dissipation, radiator installation 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 process of thermal design of electronic products, designers need to reasonably use convection heat dissipation mode, conduction heat dissipation mode and thermal radiation characteristic mode 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) Redundant design

Redundancy design of electronic products refers to the use of one or more of the same systems to form a parallel form, in which a system fails to respond scientifically. Under the function of redundancy 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, the following requirements shall be paid attention to.

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 their reliability design level.

② Redundant design will increase the volume, mass and cost of the whole system. Therefore, it is only used in the 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 electromagnetic compatibility standards and avoid mutual interference in the operation of electronic circuits, it is necessary to consider the electromagnetic compatibility design of electronic products.

The general requirements for EMC design are as follows.

① Designers should make rational use of technologies such as printed circuit board design, power line filtering, shielded chassis, signal line filtering, cable design, grounding, etc., so that electronic products can meet the requirements of electromagnetic compatibility in application, and then enhance their 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 conditions of electronic products shall also be paid special attention to, and improvements shall be made if necessary.

③ In the process of EMC design, it is necessary to accurately identify the easy to be interfered circuit and the non easy to be interfered circuit, and take targeted measures according to the principle of classification, 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.

For the maintainability design of electronic products, the following requirements shall be paid attention to.

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

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

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

(7) Structural reliability design

Electronic products will be affected by various environmental factors during 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.

1. the functions and requirements of structural reliability design mainly include:

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

② Reduce the hazards 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 mould proof, and prolong the service life of structural materials;

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

2. reliability test verification

Reliability test is a general term for various tests conducted to study failure and its impact 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. 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 be able to meet the reliability requirements specified in the original design, but the actual situation is much more complex. In fact, it is difficult to take all reliability issues into consideration in the design process. There are even contradictions or conflicts between different reliability indicators, so we can only adopt compromise design, 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.

Principle of reliability testYes: 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 product according to a certain time proportion and a certain cycle order. After analyzing and handling the failure of the tested product, 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 product. At the same time, the reliability of the electronic product 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 criteria.

It is worth noting that the formulation of environmental test conditions for various electronic products must be considered according to specific use conditions. 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 first to dry the components. Then, they are put into the humidity 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 up to standard, it is very easy to cause cracking under the action of thermal expansion and cold contraction. However, if the process is conducted in the sequence of humidity → high temperature → low temperature, as 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 that the product is affected by the alternation of cold and heat, and the results are obviously different.

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. To correct these defects and gradually improve the reliability of the product to 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 achieve greater economic benefits.

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

① In the development stage, it is used to expose defects in all aspects of trial products, evaluate the reliability of electronic products to reach 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 failures.

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 for finalized products, and study the failure distribution law of electronic products.

⑥ 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 intensity, 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

According to the classification of environmental conditions, the reliability test includes:

(1) Stability test

Put the product in the artificial working environment, and assess the product's ability to resist each environmental impact factor according to the requirements of technical indicators. Such as the stability of temperature, humidity and pressure resistance, 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 the 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 propose measures to improve reliability. Reliability life test is the most important content in all kinds of 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 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 the new product to verify whether the equipment design can meet the specified performance and reliability requirements under the specified environmental conditions. This kind of test is conducted in the form of life test, which requires quantitative identification of the average life of the equipment.

(5) Complete machine reliability acceptance test

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 for use. Although the reliability acceptance test is also conducted in the way of life test, it only requires to formulate a simple acceptance scheme and acceptance criteria for the test staff to master and make judgments. The whole machine reliability acceptance scheme and its acceptance criteria are called reliability sampling inspection scheme.

3） Classification by test purpose

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 expose 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.

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.

There are many factors that affect 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.