Method and purpose of screening electronic components

Date：2022-03-17 16:55:00Views：967

Screening electronic components is one of the most effective measures to improve the reliability of electronic equipment. The purpose of reliability screening is to select highly reliable components from a batch of components and eliminate products with potential defects. Broadly speaking, in the production process of components, various process quality inspections and electrical parameter tests of semi-finished products and finished products are screening, and what we are talking about here is the reliability screening specially designed to eliminate early failure components.

1. Necessity of component screening

The inherent reliability of electronic components depends on the reliability design of products. Therefore, we should try to eliminate the problematic components as much as possible before the electronic components are installed on the whole machine or equipment. Therefore, we should screen the components. So, what are the options for component screening? What are the principles? What are the common screening items?

There are two schemes to arrange the test screening sequence:

Scheme 1: put the screening of failure modes that do not produce chain initiation effect in the front, and put the screening of failure modes that can produce chain initiation effect with other failure modes in the back.

Scheme 2: put the screening of failure modes that can produce chain initiation effect with other failure modes in the front and the screening of failure modes that do not produce chain initiation effect in the back.

If scheme 1 is selected, it will be found that the screening of failure modes that can produce chain triggering effect with other failure modes is put behind. If the failure mode itself is not triggered, but other related failure modes are triggered first, because the detection of such failure modes has been done before, Therefore, it is impossible to accurately locate and eliminate such defective components. Option 2 can effectively avoid the above problems and make the screening process more high-quality, economical and efficient.

2. Design principle of screening scheme

It is defined as follows:

Screening efficiency w = rejected defective products / actual defective products

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

Screening elimination rate q = number of defective products / total number of products screened

The ideal reliability screening should be w = 1 and L = 0, so as to achieve the purpose of reliability screening. The Q value reflects the problem of these products in the production process. The higher the Q value, 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 the stress conditions are, and the more thoroughly the inferior products are eliminated, the higher the screening efficiency is, and the reliability level of the screened components is closer to the inherent reliability level of the product. However, doing so requires higher cost and longer cycle, which ultimately reduces the screening efficiency.

Therefore, if the selection of screening conditions is too high, it will cause unnecessary waste. If the screening conditions are too low, the elimination of inferior products is not complete, and the reliability of products can not be guaranteed. It can be seen that insufficient screening strength or too strict screening conditions are unfavorable to the reliability of the whole batch of products.

In order to carry out reliability screening effectively and correctly, the screening items and screening stress must be determined reasonably. Therefore, the failure mechanism of the product must be understood. Different types of products, different production units and different raw materials and technological processes may not have the same failure mechanism, so 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, so as to master the relationship between product failure mechanism and screening items.

The following principles should be mastered in the formulation of component screening scheme:

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

2) In order to improve the screening efficiency, strong stress screening can be carried out, but the product shall not produce new failure modes.

3) Reasonably select the best stress sequence that can expose failure.

4) Master the failure modes of all products.

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

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

3. Several common screening items

1) High temperature storage

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

High temperature screening is widely used in semiconductor devices. It can effectively eliminate devices with failure mechanisms such as surface contamination, poor bonding and oxide defects. Usually, the device needs to be stored at the maximum junction temperature for 24 ~ 168 hours.

High temperature screening is simple and inexpensive, and can be implemented on many components. After high-temperature storage, the parameter performance of 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 mechanism.

2) Power aging

When screening, under the combined action of thermoelectric stress, it can well expose a variety of potential defects in the body and surface of components. It is an important item of reliability screening.

Various electronic components are usually aged for several hours to 168 hours under the condition of rated power. Some products, such as integrated circuits, can not change the conditions at will, but can adopt high-temperature working mode to improve the working junction temperature and achieve high stress state. The electrical stress of various components should be properly selected, which can be equal to or slightly higher than the rated conditions, but it can not lead to new failure mechanism.

The power aging needs special test equipment and its cost is high, so the screening time should not be too long. Civilian products usually take several hours, military highly reliable products can choose 100 or 168 hours, and aerospace components can choose 240 hours or even longer.

3) Temperature cycle

Electronic products will encounter different ambient temperature conditions in the process of use. Under the stress of thermal expansion and cold contraction, components with poor thermal matching performance are easy to fail. Temperature cycle screening utilizes the thermal expansion and contraction stress between extreme high temperature and extreme low temperature, which can effectively eliminate the products with thermal performance defects. The common screening conditions for components are - 55 ℃ to + 125 ℃, with 5-10 cycles.

4) Centrifugal acceleration

Centrifugal acceleration test is also called constant stress acceleration test. This screening is usually carried out on semiconductor devices. The centrifugal force generated by high-speed rotation is applied to the devices to eliminate the devices with too weak bonding strength, poor internal lead matching and poor mounting. The centrifugal acceleration of 20000g is usually selected and the test is continued for one minute.

5) Monitoring vibration and shock

It is often called monitoring vibration or monitoring impact test to monitor the electrical performance of products while conducting vibration or impact test. This test can simulate the vibration and impact environment during the use of the product, effectively eliminate the components with poor mechanical structure such as instantaneous short circuit and open circuit, and find the faults such as false welding in the whole machine. Monitoring vibration and shock is an important screening item in highly reliable relays, connectors and military electronic equipment.

Typical vibration conditions: the frequency is 20-2000hz, the acceleration is 2-20g, the scanning period is 1-2 cycles, and it is necessary to stay near the resonance point for an additional period of time. The typical impact screening conditions are 1500-3000g and impact for 3 ~ 5 times. This test is only applicable to components.

Monitoring vibration and shock requires special test equipment, which is expensive and generally not used in civil electronic products.

In addition to the above screening items, there are commonly used thickness leak detection, microscopic inspection, linear discrimination screening, precision screening, etc.

The above is the content related to the screening of electronic components compiled by Chuangxin testing group. I hope it will be helpful to you. Chuangxin testing is a professional testing organization for electronic components. At present, it mainly provides integrated circuit testing services such as capacitance, resistance, connector, MCU, CPLD, FPGA, DSP and so on. Specializing in functional testing of electronic components, incoming appearance testing of electronic components, anatomical testing of electronic components, acetone testing, X-ray scanning testing of electronic components and RoHS component analysis testing. Welcome to call, we will serve you wholeheartedly!