Design principles and screening projects for electronic component screening solutions

The inherent reliability of electronic components depends on the reliability design of the product. Therefore, it is necessary to try to eliminate the components with early failure as much as possible before installing the complete components and equipment on the electronic components. Filter the components. So what are the options for component screening? What is the principle? What are the common screening items?

Arrange two options for testing the screening order:

a) Option 1: Put the failure mode screening that does not produce a chain-initiating effect in front, and put the failure mode screening that can produce a chain-initiating effect with other failure modes.

b) Option 2: Put the failure mode screening that can produce a chain-initiating effect with other failure modes first, and put the failure mode screening that does not produce a chain-initiating effect behind.

If option 1 is selected, it will be found that when the failure mode filter that can generate a chain-initiating effect with other failure modes is placed behind, if the failure mode is not triggered and the other associated failure modes are triggered, Defective components cannot be accurately located and rejected because the detection of this type of failure mode has been done before. Option 2 can be very effective in avoiding the above problems, making the screening process quality, economical and efficient.

Design principles and screening projects for electronic component screening solutions

Design principles for screening programs

The definition is as follows:

Screening efficiency W = number of rejects / actual number of defectives

Screening loss rate L=good product damage/actual good number

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

The ideal reliability screening should be such that W = 1, L = 0, in order 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 Q value, the worse the reliability of the batch before screening, that is, the greater the problem in the production process, and the lower the yield of the product.

The more choices of screening items, the stricter the stress conditions, the more thorough the inferior products are eliminated, the higher the screening efficiency, and the closer the reliability level of the selected components is to the inherent reliability level of the products. However, it requires a high cost and a long period of time, and at the same time, the reliability of a product having no defects and good performance is lowered.

Therefore, if the screening conditions are too high, it will cause unnecessary waste. If the condition is too low, the inferior products will not be completely eliminated, and the reliability of the product cannot be guaranteed. It can be seen that insufficient screening strength or too strict screening conditions are unfavorable for the reliability of the entire batch of products.

In order to effectively and correctly perform reliability screening, screening items and screening stress must be reasonably determined. To this end, it is necessary to understand the failure mechanism of the product. When the types of products are different, the production units are different, and the raw materials and process flow are different, the failure mechanism is not necessarily the same, and the conditions for reliability screening should also be different.

Therefore, a large number of reliability tests and screening tests must be carried out for various specific products to grasp the relationship between the product failure mechanism and the screening project.

The following principles should be mastered in the development of component screening programs:

Screening should be able to effectively eliminate early failure products, but should not improve the failure rate of normal products;

In order to improve the screening efficiency, strong stress screening can be performed, but the product should not generate new failure modes;

Reasonably choose the best stress sequence that can expose failures;

The possible failure modes of the selected objects should be mastered;

In order to develop a reasonable and effective screening program, it is necessary to understand the characteristics, materials, packaging and manufacturing techniques of the relevant components.

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

Several commonly used screening items

High temperature storage

Most of the failure of electronic components is caused by various physical and chemical changes in the body and the surface, and they are closely related to temperature. After the temperature rises, the chemical reaction speed is greatly accelerated and the failure process is accelerated. The defective components can be exposed in time and removed.

High-temperature screening is widely used in semiconductor devices, and it can effectively remove devices with surface failure, poor bonding, and oxide layer defects. It is usually stored for 24 to 168 hours at the highest junction temperature.

High-temperature screening is simple and easy, and the cost is small, and it can be implemented on many components. After high temperature storage, the parameter performance of the components can be stabilized and the parameter drift in use can be reduced. The thermal stress and screening time of various components should be properly selected to avoid new failure mechanisms.

Power electric refining

In the screening, under the joint action of thermoelectric stress, it can well expose various potential defects in the body and surface of the component. It is an important item of reliability screening.

Various electronic components are usually aged for several hours to 168 hours under rated power conditions. Some products, such as integrated circuits, cannot change conditions arbitrarily, but high-temperature working methods can be used to increase the operating junction temperature and achieve high stress conditions. The electrical stress of the component should be properly selected and can be equal to or slightly higher than the rated condition, but it cannot introduce a new failure mechanism.

Power aging requires special test equipment, and its cost is high, so the screening time should not be too long. Civilian products are usually for several hours, military high-reliability products can be selected for 100, 168 hours, and aerospace-class components can be selected for 240 hours or longer.

Temperature cycle

Electronic products encounter different ambient temperature conditions during use. Under the stress of thermal expansion and contraction, components with poor thermal matching performance are prone to failure. The temperature cycle screening utilizes the thermal expansion and contraction stress between extreme high temperature and extreme low temperature, and can effectively eliminate products with thermal defects. Commonly used screening conditions for components are -55 ~ +125 ° C, cycle 5 ~ 10 times.

Centrifugal acceleration

Centrifugal acceleration test is also called constant stress acceleration test. This screening is usually performed on a semiconductor device, and the centrifugal force generated by high-speed rotation is applied to the device, and the device with weak bonding strength, poor internal lead matching, and poor mounting can be removed. Usually, the centrifugal acceleration of 20,000 g is used for one minute. .

Monitor vibration and shock

Monitoring the electrical performance while vibrating or impacting the product is often referred to as monitoring vibration or monitoring shock testing. This test can simulate the vibration and impact environment during the use of the product, and can effectively eliminate the short-circuit, short-circuit and other mechanical structural defects and the virtual welding in the whole machine. Monitoring vibration and shock is an important screening program in highly reliable relays, connectors and military electronics.

Typical vibration conditions are: frequency 20 ~ 2000 Hz, acceleration 2 ~ 20 g, scanning 1 ~ 2 cycles, staying for a while near the resonance point. Typical impact screening conditions are 1500^-3000g and impact 3~5 times. This test is only applicable to components.

Monitoring of vibration and shock requires specialized test equipment, which is expensive and generally not used in consumer electronics.

In addition to the above screening items, there are also commonly used thickness leak detection, microscopic examination, linear discrimination screening, precision screening and so on.

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