Discussion on the secondary screening method of electronic components

Component screening Apply different stresses to components through tests to stimulate potential defects of components, observe whether the operating status and performance parameters of components under different stress conditions are consistent with production standards, and ensure that the quality and batch pass rate of components meet Requirements.

One-time screening is performed by electronic component manufacturers before the components leave the factory in accordance with the detailed specifications of components or the requirements of the national military standard to screen the reliability of components; users in some fields have higher requirements on the reliability of components, such as aerospace and other military scientific research user units In order to meet the high reliability and high performance requirements of the whole equipment, this type of user unit will conduct a second quality and stability review based on the first screening, combined with the characteristics of the components and the actual application requirements, referring to the acceptance process and standards Screening, a process known as secondary screening (also known as secondary screening). For users in military scientific research fields such as aerospace, secondary screening is an important link in the quality and reliability control of military electronic components, and an important way to ensure the quality and stability of high-reliability components in the aerospace field.

1. Importance of secondary screening

The bathtub curve of the failure rate of electronic components is shown in Figure 1.

Fig 1 Bathtub curve of component failure rate

The bathtub curve of component failure rate reflects the ups and downs of failure probability during the life cycle of components, and is divided into three stages: early failure period, accidental failure period and wear-and-tear failure period:

1) Early failure occurs at the initial stage of service and is caused by defects in the components themselves;

2) Accidental failure occurs in the mid-service period and is caused by various stress effects;

3) Attrition failure occurs in the later period of service and is caused by long-term wear and tear. To improve the reliability of components, it is necessary to reduce early failure, reduce accidental failure, and delay loss failure.

The early failure period is a period of high incidence of component failure. The failure in this period comes from the unreasonable structural design of components or the influence of uncertain factors such as fluctuations in raw materials, process conditions and equipment conditions or human factors during the manufacturing process. The secondary screening of components induces potential defects of unqualified components through various performance tests, and accelerates the occurrence of failure. In the screening stage, products that are prone to early failure are eliminated in the batch of products, so that components can safely pass through the early failure period. Smoothly transition to the accidental failure period, maintain stable operation of equipment for a long time, improve the reliability of batch products, and ensure the stability of equipment system operation. And the secondary screening is a 100% non-destructive test for devices with no defects and good performance, and will not affect the reliability of components. Therefore, secondary screening of components is important and necessary for aerospace and other users who have high requirements on the reliability of components.

2. The scientific nature of the secondary screening

The secondary screening of components is very important to ensure the reliability of components and complete equipment, but attention should be paid to the scope of application and scheme design of the secondary screening. Inappropriate selection of secondary screening objects and scheme design will not only affect the screening effect, but also It will have an irreversible impact on the life and performance of components. Therefore, it is also crucial to clarify the scope of application of the second sieve and the design principles of the scheme. Scientific and reasonable selection of second sieve objects, screening items, and stress value settings can ensure While the effectiveness and adequacy of the second screening are achieved, the cost-effectiveness ratio of the screening is optimized.

2.1 Determination of the applicable scope of secondary screening

Improper secondary screening will not only increase the cost of the enterprise, but also affect the reliability of components and reduce the service life of components. Therefore, the secondary screening of components should not be abused or used in general. The scope of application of the secondary screening should be clarified as follows:

1) The manufacturer of electronic components did not conduct a screening of the components before leaving the factory, or the implementation process of the screening did not meet the relevant quality control requirements;

2) One-time screening does not meet the user's quality requirements due to process or level limitations;

3) When the user has doubts about the results of a screening and needs to further ensure the quality;

4) When the scheme design of one screening cannot meet the user's quality requirements for components.

2.2 Selection of secondary screening test items

The selection of secondary screening test items for components should be based on the type of components, manufacturing process, application environment and reliability requirements, and corresponding screening test items should be formulated to ensure the pertinence and effectiveness of the screening test items.

The selection of secondary screening test items is affected to a certain extent by the user's subjective factors. Therefore, clarifying the screening mechanism of each screening test and the targeted functional test direction is an important part of scientifically and rationally realizing the selection of secondary screening items. Secondary screening can be roughly divided into inspection screening, sealing screening, environmental stress screening and life screening according to the different screening properties. Detection, the detection focus of different inspection methods is also slightly different, for example, ultrasound focuses on the identification of cracks, voids, delamination and other defects inside the organic epoxy packaging material, while X-ray focuses on foreign objects in the shell, or internal chips, keys, etc. Screening of quality defects such as bonding and packaging; airtightness screening Place components in liquids or trace gases with different boiling points, observe the escape of gas that invades the package of components, and analyze and judge whether the external structure of components can achieve high performance Sealing, which can effectively detect the shell and sealing defects of components, and eliminate components with quality defects such as cracks and leaks; environmental stress screening uses environmental factors such as impact force, acceleration force, vibration force, temperature, centrifugal force and thermal shock, etc. Test the structural strength of components under different external environmental conditions, observe whether the components are deformed or cracked under the stress of external conditions, and eliminate components with reduced structural strength and poor environmental stress resistance; life screening passes in components Apply electrical stress and thermal stress in the early stage to accelerate the exposure of defects such as device breakdown, corrosion, fracture, electromigration, oxidation, and diffusion, and remove components that have defects or whose performance does not meet the standards during the manufacturing process.

2.3 Secondary screening stress value setting

In the process of secondary screening, the setting of the stress value is also very important. Excessive screening stress not only increases the cost of screening, but also causes overstress damage to components, and even damages and eliminates components that meet reliability requirements. Devices; if the screening stress is too low, defective components cannot be eliminated comprehensively and effectively, resulting in some components that do not meet the application requirements of the product successfully passing the screening, reducing the reliability level of the product. According to the summary of engineering experience, the setting of secondary screening stress value should follow the following basic principles:

1) The stress type should be screened to select the stress that can stimulate early failure, and it should be determined according to the information and failure mechanism of different devices;

2) The purpose of screening the stress value should be to stimulate early failure, so that various hidden dangers and defects of the device can be exposed as soon as possible;

3) Screening stress values should not cause normal devices to fail;

4) After the screening stress is removed, the device should not leave residual stress or affect the service life of the device.

When the above principles are applied to different screening items of components of different complete equipment, it is necessary to determine the stress value setting of each test item according to actual conditions. This process requires mastering the failure mode, failure mechanism and failure distribution of components. On the basis of a large number of preliminary tests, it will take a lot of manpower and material resources to increase the cost of the enterprise. Therefore, under the condition of not changing the failure mechanism, the constant stress or step stress accelerated test method can be used to accelerate the exposure of defects. The test data under accelerated stress is obtained in a short period of time, and then the ideal stress value is obtained by using mathematical models and calculations.

3. Establishment of secondary screening system for components

The ideal secondary screening effect of components is inseparable from excellent system support. To establish a perfect, sound and reasonable secondary screening system, we should start with the implementation of process control and the establishment of a management mechanism.

3.1 Secondary screening of components to implement process control

Different secondary screening items have different testing directions, screening effects, and cost consumption. It is not that the higher the cost of screening items, the better the screening effect, and the testing functions and time-consuming of different screening test items are also different. In order to optimize the cost-effectiveness ratio, the basic principle of the second screening implementation process control should be clarified in the process control of the secondary screening of components, that is, on the basis of promoting the early failure, save time and cost as much as possible .

For the specific implementation sequence arrangement, you can refer to the following guiding ideology:

1) First, arrange cost tests, such as appearance inspection, high temperature storage and temperature cycle test, etc.;

2) Then, arrange stress screening, such as temperature cycle test and constant acceleration test, etc.;

3) Finally, arrange leak detection, final electrical parameter test and appearance review, etc.

3.2 Establishment of secondary screening management mechanism for components

One is to strengthen the skills training of professional testing personnel. The research and development technology and manufacturing process of components are changing with each passing day, and new screening and testing methods are emerging one after another, involving many fields such as electricity, magnetism, sound, light, etc. Enterprises should strengthen the skills training of professional testing personnel to help employees master typical and new testing methods skills, improve the screening effect, and reduce cost consumption.

The second is to establish a closed-loop control mechanism for secondary screening of components covering the process of component selection, inspection and failure analysis. Enterprises should strengthen the management of component selection, inspection, and failure analysis to form corresponding standards. Component quality issues optimize the control of the secondary screening process to form a benign, dynamic and sustainable closed-loop control mechanism for secondary screening of components.

The second is to establish a closed-loop control mechanism for secondary screening of components covering the process of component selection, inspection and failure analysis. Enterprises should strengthen the management of component selection, inspection, and failure analysis to form corresponding standards. Component quality issues optimize the control of the secondary screening process to form a benign, dynamic and sustainable closed-loop control mechanism for secondary screening of components.

4. Conclusion

In recent years, with the improvement of component R&D design and manufacturing process, higher requirements have been put forward for the secondary screening technology of components. First of all, the chaff should be discarded. The second screening technology of some components is no longer applicable in the field of components. For example, the screening effect of the high-temperature storage screening test is not good, and the high-temperature storage test itself will accelerate the oxidation of the pins and affect the soldering of the components. Therefore, it is necessary to strengthen the research on the pre-screening technology of the second screen, improve the screening effect, and reduce the impact of the screening test on the reliability of the components; secondly, the research on the screening technology of the components should be strengthened, and more Use new component screening and detection technologies, such as data-driven electronic component screening methods, to classify and evaluate electronic components based on statistical data and algorithm speculation, and improve the screening effect of components without increasing costs ;In addition, it should also be noted that the second sieve is combined with destructive physical analysis (DPA: Destructive Physical Analysis). , to check the internal structure of components, materials used and process design, etc., to remove defective components to the greatest extent. For example, defects with high water vapor content in devices can hardly be found in the second screening process, but in DPA However, it can be easily identified; finally, enterprises should also strengthen the importance of the second screening of components and the importance of control, pay attention to the screening implementation process control, the establishment of a screening management mechanism, and analyze and feed back the screening results to form a A complete component quality assurance closed-loop control system covering different levels of the whole process from component management to selection, procurement, inspection, screening, warehousing, storage, and failure analysis.

The development of the secondary screening of components is not only the development and progress of a single field, the improvement of the reliability of components is the basis for the improvement of the reliability of equipment and equipment, and the design defects or manufacturing quality problems of components are located through the advanced secondary screening technology of components. It can provide a reference basis for the improvement of components, help the development of component technology research, and then promote the development of my country's electronic technology.