Necessity of electronic component screening

We should know that the screening of electronic components is very necessary, so we will analyze the selection principle of the screening items and stress conditions of electronic components today, and introduce several commonly used screening items and typical semiconductor screening scheme design. Take a look

1. The necessity of component screening

The inherent reliability of electronic components depends on the reliability design of the product. In the manufacturing process of the product, due to human factors or fluctuations of raw materials, technological conditions and equipment conditions, the final product can not all achieve the expected inherent reliability. In every batch of finished products, there is always a part of the product has some potential defects and weaknesses, these potential defects and weaknesses, under certain stress conditions, manifested as early failure. Components with early failures have a much shorter average life than normal products.

Whether electronic equipment can work reliably depends on whether electronic components can work reliably. If the early failure of the components installed on the machine, equipment, will make the early failure of the machine, equipment failure rate will greatly increase, its reliability can not meet the requirements, but also pay a great price to repair.

Therefore, before the electronic components are installed on the whole machine and equipment, it is necessary to try to exclude the components with early failure as much as possible, so as to screen the components. According to the screening experience at home and abroad, the total use failure rate of components can be reduced by 1-2 orders of magnitude through effective screening. Therefore, whether for military products or civilian products, screening is an important means to ensure reliability.

Necessity of electronic component screening2. Design principle of screening scheme

The definition is as follows:

Screening efficiency W = number of rejected items/actual number of items

Screening attrition rate L = number of good products damaged/number of actual good products

Screening elimination rate Q = number of products removed/total number of products screened

The ideal reliability screening should be W=1, L=0, so as to achieve the purpose of reliability screening. Q values reflect the size of problems in the production process of these products. The higher the value of 0, the worse the reliability of this batch of products before screening, that is, the greater the problems in the production process, the lower the yield of products.

The more screening items are selected, the stricter stress conditions are, and the more thoroughly inferior products are eliminated, the higher the screening efficiency is, and the reliability level of selected components is closer to the inherent reliability level of products. But to pay higher costs, longer cycle, but also make the absence of defects, good performance of the product reliability. Therefore, if the screening conditions are too high, unnecessary waste will be caused; if the selection conditions are too low, inferior products will not be eliminated completely and the reliability of products can not be guaranteed.

Thus, insufficient screening intensity or strict screening conditions are detrimental to the reliability of the whole batch of products. In order to carry out the reliability screening effectively and correctly, it is necessary to determine the screening items and the screening stress reasonably, for which the failure mechanism of the product must be understood. The failure mechanism may not be the same when the product type is different, the production unit is different, and the raw materials and process flow are different, so the conditions of reliability screening should also be different.

Therefore, it is necessary to carry out a large number of reliability tests and screening tests for various specific products, so as to grasp the relationship between product failure mechanism and screening items. The formulation of component screening scheme should grasp the following principles:

① Screening should be able to effectively eliminate the early failure of the product, but should not make the normal product to improve the failure rate.

② In order to improve the screening efficiency, strong stress screening can be carried out, but the product should not produce a new failure mode.

③ Choose the best stress sequence that can expose failure reasonably.

④ The possible failure modes of the screened objects should be mastered.

⑤ In order to formulate a reasonable and effective screening scheme, it is necessary to understand the characteristics, materials, packaging and manufacturing technology of the relevant components.

In addition, in accordance with the above five principles, should be combined with the production cycle, reasonable formulation of screening time.

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