Analysis on reliability control and management of electronic components in low pressure environment

1. Low pressure environment

Under the influence of the earth's gravity, air clings to the earth to form the atmosphere, which extends from the ground to hundreds of kilometers high. The earth's gravity makes the air have a certain weight to form atmospheric pressure. The atmospheric pressure at a certain height is the weight of the entire air column per unit area above that point perpendicular to the ground. Atmospheric pressure is isotropic, that is, at a certain point, the atmospheric pressure is equal no matter in which direction it is measured. The size of atmospheric pressure mainly depends on the altitude. As the altitude increases, the atmospheric pressure gradually decreases and the atmosphere gradually becomes thinner. At an altitude of nearly 5.5km, the atmospheric pressure decreases to about half of the standard atmospheric pressure at sea level; the atmospheric pressure at nearly 16km is 1/10 of the standard sea level value; the atmospheric pressure at nearly 31km is 1/100 of the standard atmospheric pressure at sea level. The reduction in atmospheric pressure will inevitably affect the electrical and electronic products used in high-altitude areas. About 50% of the earth's surface area in my country is above 1000m above sea level, and about 25% of the area is above 2000m above sea level. The greater the pressure gradient, the faster the pressure changes, and the greater the chance of component damage.

2. Impact of low pressure environment on electronic components

1. Impact on heat dissipation products

A considerable number of electrical and electronic products are heat dissipation products, such as motors and transformers. These products consume a portion of electrical energy during use, which is converted into heat energy, causing the product temperature to rise. The temperature rise of heat dissipation products increases as the atmospheric pressure decreases. Table 1 lists the temperature rise of small three-phase asynchronous motors as a function of altitude.

It can be seen from Table 1 that the temperature rise of heat dissipation products increases with the increase of altitude (the decrease of atmospheric pressure).

The temperature rise is roughly linearly related to the altitude, as shown in Figure 1. Its slope depends on factors such as its own structure, heat dissipation, and ambient temperature.

The heat dissipation of heat dissipation products can be divided into three forms:

Conduction, convection and radiation. The heat dissipation of a large number of heat dissipation products mainly relies on convection, that is, it relies on the air flow around the product to dissipate heat. Convection heat dissipation can generally be divided into forced ventilation heat dissipation and natural convection heat dissipation. Natural convection heat dissipation relies on the temperature field generated by the heat of the product to create a temperature gradient in the air around the product, so that the air flows to dissipate heat. Forced ventilation heat dissipation is to force air to flow through the product through compulsory measures to take away the heat generated by the product. For forced convection heat dissipation, when the volume flow remains unchanged, the atmospheric pressure will decrease with the increase of altitude. The decrease in air density will directly affect the effect of forced convection heat dissipation. This is because forced convection heat dissipation relies on the flow of gas to take away heat. The cooling fan used for general motors is to ensure that the volume flow rate flowing through the motor remains unchanged. When the altitude increases, due to the decrease in air density, even if the volume flow rate remains unchanged, the mass flow rate of the airflow will decrease accordingly.

2. Impact on the performance of electronic components

As the altitude increases, the air pressure decreases, which will also affect the performance of electronic components. Especially for equipment that uses air as an insulating medium, the impact of low air pressure is more significant. Under normal atmospheric conditions, air is an excellent insulating medium, and many electrical products use air as an insulating medium. When these products are used as mechanical equipment in high-altitude areas, due to the decrease in atmospheric pressure, local discharge often occurs near electrodes with strong electric field strength. Even more serious is that air gap breakdown sometimes occurs, which means that the normal operation of the equipment is disrupted. 3. Reliability control of electronic components in low-pressure environments

1. Reasonable selection of components

Design analysis and reasonable selection of components based on the usage characteristics of components in the circuit are the basis of component reliability. The reliability control point of electronic components should be moved forward and start from the source, that is, from design selection, optimal manufacturer selection, compression of varieties, reliability testing, and improvement of quality level, so that those preventive measures that are paid for can play a role at the source, and cannot always be in a remedial measure state. In addition, from the perspective of physical analysis of component reliability, systematic collection and analysis of failure information, failure analysis, destructive physical analysis, analysis of the internal atmosphere of sealed devices, analysis of the correlation between failure modes and mechanisms and processes, failure mode and effect analysis, and other component quality and reliability analysis technologies should be carried out, and component quality and reliability analysis technologies should be integrated into the component product design and manufacturing process to achieve component reliability growth.

2. Supervision, testing and acceptance of components

The production, testing and acceptance of components are important links to ensure the quality of components, and are also the key control points for the reliability of components of aerospace products. The quality of process control determines the inherent quality of components. Electronic components are divided into electronic components, discrete devices and microcircuits according to their functions; they are divided into imported and domestic components according to procurement channels ; they are divided into shelf products and new devices according to product maturity. Different components have different control requirements, and different processing methods and procedures should be adopted during factory supervision and acceptance and arrival inspection. Therefore, components should be classified into different categories, and the supervision methods, special test requirements and acceptance methods of various components should be specified, and the corresponding procedures and execution units or departments should be clarified.

3. Destructive physical analysis

The main purpose of component DPA (destructive physical analysis) is to prevent components with obvious or potential defects from being installed and used. In addition to being used for the quality identification of components, in aerospace products, it is also used for component acceptance, quality review of components before installation, re-inspection of expired components, and failure analysis of components. In general products, DPA is usually used for quality verification of installed components. In aerospace products, DPA must be completed before the components are installed. Therefore, it is necessary to clarify the timing of DPA for components used in aerospace products, the test items of DPA, the organization that implements DPA, the data recording requirements of DPA, and the processing methods of DPA results.

4. Failure analysis methods of components

The main task of component failure analysis is to conduct necessary electrical, physical and chemical tests on failed components, and analyze them in combination with the specific conditions before and after the failure of the components and relevant technical documents to determine the failure mode, failure mechanism and cause of failure of the components. Through failure analysis, inherent quality problems of failed components can be found, and it is also possible to find quality problems in the use of components that fail due to failure to use them according to the specified conditions. By giving feedback to relevant parties, the responsible party is prompted to take corrective measures to improve the inherent quality or use quality of the components. Relatively speaking, the determination of failure mode is relatively simple, while the determination of failure mechanism is more difficult. Analysts must master the design, process and relevant physical and chemical knowledge of components and have certain practical experience. In addition, more complex instruments and equipment are required. After clarifying the failure mechanism, the cause of failure must also be found to avoid repeated failures and improve the inherent quality or use quality of components. However, determining the cause of failure based on the failure mechanism often involves specific circumstances such as the failure site and the person responsible, which is quite difficult to determine. Therefore, first of all, it is necessary to determine the unit that conducts the failure analysis, stipulate the procedures and failure information for submitting the failure analysis, and the failure information recording requirements for failed components at each stage of product development , etc. Then, based on the conclusion of the failure analysis, the cause of the failure should be zeroed out. If it is a design defect, the problem should be found out and improved together with the manufacturer; if it is an operational error, the operating specifications must be strictly followed to avoid introducing human errors. In this way, the purpose of failure analysis is achieved and device manufacturing and production operations are taken to a higher level.

5. Management of component quality information

In the process of component selection, procurement, supervision and acceptance, screening and re-inspection, and failure analysis quality assurance, there is a large amount of component quality information, such as the specifications, models, manufacturers, quality grades of components outside the catalog, and their use in aerospace products; the manufacturers and use of domestic new components; the quality assurance of imported components; component failure analysis reports and handling, etc.

In summary, low air pressure can greatly affect the performance of electronic components and sometimes cause direct damage.

The impact of low-pressure environmental conditions on components cannot be simulated under normal atmospheric conditions and must be tested in accordance with relevant standards. To this end, it is necessary to strengthen the standardization of environmental condition testing, consider the impact of environmental changes on products from the design stage, enhance the adaptability of products to the environment, and thus improve product reliability.