How to do a good selection of components

 News     |      2018-07-24 08:40:28
Failure rate of components with time change process can be described by a similar "bathtub curve" failure rate curve, early failure rate increases with time and the rapid decline in life (or random failure period) in failure rate basically unchanged. The good and bad of things must be measured by the standard. To determine whether the failure of the components is determined by the failure criteria. Failure criterion is the index of quality and reliability, and sometimes it has the connotation of cost, so the failure of components is not only the loss of function, but also the electrical characteristics or physical parameters can be reduced to meet the requirements. In short, the function of the product is called failure.
Failure is generally divided into field failure and test failure. The failure of the site is generally in the failure of the machine, so we only consider the test failure in the process of testing the components. The failure of the test is mainly the failure of the package and the failure of the electric performance. Packaging failure mainly depends on environmental stress screening to detect. The so-called environmental stress screening, that is, select a number of typical environmental factors, applied to the product''s hardware, so that all kinds of potential defects for early failure, and then to be excluded, so that the reliability of the product is close to the inherent reliability of the design, and not to make the product subject to fatigue damage. In normal circumstances, the inspection of the appearance of the system is performed by applying a period of environmental stress, which is based on the quality of the components, and can be used to detect the appearance of the components. It can also be arranged according to the need of DPA and X ray inspection. Therefore, the general failure of the filter in the front, the failure of the electrical performance of the filter in the back.   
The failure of electrical properties can be divided into the failure of the linkage, the functional failure and the failure of the electric parameters. The failure of the link is the change of the size of the open circuit, the short circuit and the resistance value. The failure of this kind of failure is a large proportion in the failure of the components. Because of the failure of the electric stress caused by the electrical stress, the failure of the functional and electrical parameters can be caused by the failure of the functional and electrical parameters. The main reason is that when the link failure mode is triggered by specific screening conditions, it is often found that the coating has the characteristics of mechanical and thermal stress damage. However, it is not only related to the failure of metal fatigue and bonding strength, but it can be found. However, the function of the circuit and the electrical parameters of the failure are triggered by a specific selection of conditions, the phenomenon is certain function failure, electric parameters, such as ultra poor. The main reasons for these failures are: manufacturing, design defects and control of production process is not strict, so that the production process of various factors such as air cleanliness level, ultra pure water quality monitoring, ultra pure gas and chemical reagents can not reach the requirements; in the transport process due to anti-static measures are not in place will also occur. These factors will be affected by a variety of surface contamination of the semiconductor crystal, will make the product can not meet the requirements of the quality level. Under the condition of the specific external conditions, it will produce functional failure and electrical parameters failure, but the effect of these functional failure and electrical parameters can only result in the loss of function of the components, but also can not make the chip''s packaging and all parts of the link appear burned, short circuit, open circuit and so on. 
There are two schemes in the sequence of the test selection:
Scheme 1: will not produce a series of effects of the failure mode selection in front, will be with other failure mode to produce a series of effects of the failure mode selection of.
Program 2: will be able to produce a series of failure mode with other failure mode of the failure mode selection in front, will not produce a series of effects of the failure mode selection of the.
If the selection scheme 1 will be found to be able to produce a series of failure mode with other failure mode selection of the failure mode, the failure mode is not triggered, other related failure mode is triggered, the defective components can not be accurately positioned and removed, because the detection of the failure mode has been done in front of. The selection scheme 2 can effectively avoid the occurrence of the above problems, so that the screening process is high quality, economy and efficiency.
- screening method for maximum failure probability.
When a failure mode can be associated with other failure modes, the screening of the failure mode is put in the front.
Using different methods to screen the same kind of failure mode, the distribution of the failure probability is considered, and the method of selecting the failure is easy to use.
- consider the economy, the first to do cheap.
- consider the time, the long time to do.
The arrangement of the test sequence is the following parameters that can be used to check the changes that may occur after the components are tested. The voltage and insulation resistance testing requirements of the components, the voltage in the first, the insulation in the final test, the breakdown voltage and leakage current testing requirements of the components, the breakdown voltage in the first, the leakage current in the functional parameters of the final test.
The main method of screening is as follows:
A) appearance inspection: 10 times the magnifying glass to check the appearance, lead and materials are defective.
B) temperature cycle: the components are exposed to the specified limit at high temperature and low temperature, and it is not less than 1 min when the temperature is transferred from cold to hot to cold.
C) high temperature service life (non work: the life test requirements in accordance with the national standards, so that the components in the provision of environmental conditions (usually the highest temperature) storage provisions of the time.
D) the power of the electric power is the best, the condition of the maximum junction temperature is reached, and the power is selected according to the requirements of the components.
E): a cavity sealing test components, the first fine leak, after gross leak.
F) electrical parameters testing (including pressure or leakage current, etc.): according to the provisions of the technical specifications of the product.
G) function test: according to the technical specification of the product.
Based on the above principle, the optimization of the components testing and screening sequence, according to the classification of the failure mode, the detection and selection method based on the principle of the testing and selection of components to sort, first of all in accordance with the failure probability of sorting: sort results as shown in table 1.
Table 1: failure probability level is based on a variety of detection methods may trigger the probability of defects, due to the use of components to reach the use of various transport, storage process, so the appearance of rupture, corrosion, etc., generally accounted for 40% of the total number of failure, so the appearance of the failure probability level placed in first, and the high temperature (non working) failure probability level, so the temperature cycle is placed in second place; high temperature life (non working) placed in third place.
According to the principle of sorting, but also add a look, mainly in order to prevent the testing and screening process due to the occurrence of the phenomenon of the appearance of the appearance of the transfer between different laboratories, to ensure the completion of the test after the appearance of components.