Everyone should know that the screening of electronic components is very necessary, so today we will analyze the selection principles of electronic components screening items and stress conditions, and introduce several commonly used screening items and typical semiconductor screening scheme design. Let‘s have a look!

1. The necessity of component screening

The inherent reliability of electronic components depends on the reliability design of the product. During the manufacturing process of the product, due to human factors or fluctuations in raw materials, process conditions, and equipment conditions, the final product cannot all achieve the expected inherent reliability. In each batch of finished products, there are always some potential defects and weaknesses in some products. These potential defects and weaknesses manifest as early failure under certain stress conditions. The average life of components with early failure is much shorter than normal products.

Whether electronic equipment can work reliably is based on whether electronic components can work reliably. If the components that fail early are installed on the whole machine and equipment, the failure rate of early failure of the whole machine and equipment will be greatly increased, the reliability cannot meet the requirements, and a great price will be paid for maintenance.

Therefore, it is necessary to try to eliminate the components with early failure as much as possible before the electronic components are installed on the whole machine and equipment, and for this reason, the components must be screened. According to the screening work experience at home and abroad, the total failure rate of components can be reduced by 1 - v 2 orders of magnitude through effective screening. Therefore, whether it is a military product or a civilian product, screening is an important means to ensure reliability.

2. Design principles of the screening program

Defined as follows:

Screening efficiency W = number of rejected products / actual number of defective products

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

Screening elimination rate Q = number of defective products rejected / total number of products to be screened

The ideal reliability screening should make W=1, L=0, so as to achieve the purpose of reliability screening. The size of the Q value reflects the size of the problems in the production process of these products. The larger 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, and the lower the product yield.

The more selection of screening items, the stricter the stress conditions, the more thorough the elimination of inferior products, the higher the screening efficiency, and the closer the reliability level of the screened components is to the inherent reliability level of the product. However, it requires higher costs and longer cycle times, and at the same time, it also reduces the reliability of products that do not have defects and perform well. Therefore, if the selection conditions are too high, unnecessary waste will be caused. If the selection conditions are too low, the inferior products will not be eliminated completely, and the reliability of the products will not be guaranteed.

It can be seen that insufficient screening intensity or strict screening conditions are detrimental to the reliability of the entire batch of products. In order to perform reliability screening effectively and correctly, the screening items and screening stress must be reasonably determined, and for this reason, the failure mechanism of the product must be understood. Different types of products, different production units, and different raw materials and technological processes have different failure mechanisms, so the conditions for 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 the product failure mechanism and the screening items. The formulation of the component screening plan should master the following principles:

① Screening should be able to effectively eliminate products with early failure, but should not increase the failure rate of normal products.

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 Reasonably select the best stress sequence that can expose failure.

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

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

In addition, while following the above five principles, the screening time should be reasonably formulated in combination with the production cycle.

We have talked about the necessity of component screening and the design principles of the screening scheme, hoping to help everyone.