How to screen electronic components? Reliability screening test method

Date：2022-04-22 14:41:21 Views：1442

With the increasing requirements of industrial, military and civil departments for the quality of electronic products, the reliability of electronic equipment has attracted more and more attention. 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. The ideal screening hopes to eliminate all the inferior products without damaging the superior products, but the actual screening cannot be perfect, because limited by the screening items and conditions, some inferior products are likely to be missed, while some items are destructive and may damage the superior products. However, various methods can be used to achieve the ideal state as much as possible. How to screen electronic components? The reliability screening test method is introduced as follows:

1. Necessity of component screening

The inherent reliability of electronic components depends on the reliability design of products. In the manufacturing process of products, due to human factors or fluctuations in raw materials, process conditions and equipment conditions, the final finished products 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 show early failure under certain stress conditions. The average life of components with early failure is much shorter than that of normal products.

Whether electronic equipment can work reliably is based on whether electronic components can work reliably. If the early failure components are installed on the whole machine and equipment, the early failure rate of the whole machine and equipment will be greatly increased, its reliability can not meet the requirements, and it will have to pay a great price to repair.

Therefore, before the electronic components are installed on the whole machine and equipment, we should try to eliminate the components with early failure as much as possible. Therefore, we should screen the components. According to the screening experience at home and abroad, the total use failure rate of components can be reduced by 1-v2 orders of magnitude through effective screening. Therefore, screening is an important means to ensure the reliability of both military and civil products.

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 greater 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 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, it needs to pay higher cost and longer cycle, and at the same time, it will reduce the reliability of products without defects and good performance. Therefore, if the screening conditions are too high, it will cause unnecessary waste. If the conditions are too low, the inferior products will not be eliminated completely, and the reliability of the 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, we must reasonably determine the screening items and screening stress. Therefore, we must understand the failure mechanism of products. 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 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 new failure modes.

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

④ The possible failure modes of the screened object 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 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

3.1 high temperature storage

The failure of electronic components is mostly caused by various physical and chemical changes in the 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 in time and removed.

High temperature screening is widely used in semiconductor devices. It can effectively eliminate devices with failure mechanisms such as surface fouling, poor bonding and defective oxide layer. It is usually 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.

3.2 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 a few hours to 168 hours under the rated power conditions. Some products, such as integrated circuits, cannot change the conditions arbitrarily, but can adopt the high-temperature working mode to improve the working junction temperature and reach the 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 can not lead to a 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 a few hours, military highly reliable products can choose 100.168 hours, and aerospace components can choose 240 hours or even longer.

3.3 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 ~ + 125 ℃, and the cycle is 5 ~ 10 times.

3.4 centrifugal acceleration

Centrifugal acceleration test is also called constant stress acceleration test. This screening is usually carried out on semiconductor devices. By applying the centrifugal force generated by high-speed rotation on the devices, the devices with too weak bonding strength, poor internal lead matching and poor mounting can be eliminated. Usually, 20000 g centrifugal acceleration is selected for continuous test for one minute.

3.5 monitoring vibration and shock

It is often called monitoring vibration or 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, and can effectively eliminate the components with poor mechanical structure such as instantaneous short circuit and open circuit, as well as the faulty welding in the whole machine. Monitoring vibration and shock is an important screening item in highly reliable relays, connectors and military electronic equipment.

The typical vibration conditions are: the frequency is 20 ~ 200Hz, the acceleration is 2 ~ 20g, the scanning period is 1 ~ 2, and it needs to stay near the resonance point for a long time. The typical impact screening condition is 1500 ^ - 3000g, impact 3 ~ 5 times, and 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.

4. Screening scheme design of semiconductor devices

Semiconductor devices can be divided into discrete devices and integrated circuits. Discrete devices include various diodes, triodes, field effect tubes, thyristors, optoelectronic devices and special devices; Integrated circuits include bipolar circuits, MOS circuits, thick film circuits, thin film circuits and other devices.

The failure modes and failure mechanisms of various devices are different. Different screening items shall be adopted for different failure mechanisms, such as finding defects such as poor welding and loose installation, and vibration acceleration can be adopted; Find out the defects such as weak bonding of components, poor chip loading and improper configuration of internal leads, and adopt centrifugal acceleration; Find defects such as intermittent short circuit and intermittent open circuit, and use mechanical impact.

Therefore, the screening procedures of different devices are not necessarily the same. For example, the main failure modes of transistors include short circuit, open circuit, intermittent operation, parameter degradation and mechanical defects. Each failure mode involves a variety of failure mechanisms, which are important basis for formulating reasonable screening procedures.

① Appearance inspection: use 10x magnifying glass to check the appearance, lead and material for defects.

② Temperature cycle: make the components alternately exposed to the specified extreme high temperature and extreme low temperature, and continuously withstand the specified conditions and cycles of specified times. The total transfer time from cold to heat or from heat to cold shall not exceed 1min, and the holding time shall not be less than 10min.

③ High temperature life (non working): according to the life test requirements specified in the national standard, make the components store for the specified time under the specified environmental conditions (usually the maximum temperature).

④ Electric power aging: the aging purpose under the maximum junction temperature is achieved according to the derating conditions, and the aging power is selected according to the conditions specified by the components.

⑤ Sealing test: for components with cavities, first fine leakage detection, and then coarse leakage detection.

⑥ Electrical parameter test (including withstand voltage or leakage current test): it shall be carried out in accordance with the provisions of the product technical specification contract.

⑦ Function test: according to the product technical specifications and contract provisions.

Based on the above principles, the test and screening sequence of components is optimized. According to the classification of failure modes, the test and screening methods are sorted according to the principle of test and screening sequence of components

4.1 diode typical screening procedure

The commonly used semiconductor diodes include rectifier, switch, voltage stabilizing, detection and double base. The typical screening procedures are as follows:

(1) High temperature storage: germanium tube 100 ℃, silicon tube 150 ℃, 96h.

(2) Temperature cycle: germanium tube - 55 ℃ - + 85 ℃, 5 times; Silicon tube - 55 ℃ ~ + 125 ℃, 5 times.

(3) Knock change: knock with a hard rubber hammer for 3 ~ 5 times, and monitor the positive characteristic curve with a grapher at the same time.

(4) Drop: at the height of 80cm, press the free fall to the glass plate for 5 ~ 15 times.

(5) Power aging:

① Switch tube: 1.5 times rated forward current, 12 hours;

② Voltage stabilizing tube: 1 ~ 1.5 times of rated power, 12 hours;

③ Detection rectifier tube: 1 ~ 1.5 times of rated current, 12 hours;

④ Double base diode: rated power aging for 12 hours.

(6) High temperature reverse bias: germanium tube 700C, silicon tube 1250C, rated reverse voltage 2 hours, leakage current does not exceed the specification value.

(7) High temperature test: germanium tube 70 ℃, silicon tube 125 ℃.

(8) Low temperature test: - 55 ℃.

(9) Appearance inspection: check the appearance quality with a microscope or magnifying glass, and eliminate defective pipes such as broken glass.

4.2 typical screening procedure of triode

High temperature storage - temperature circulation - drop (not for high-power tube) - power aging - high and low temperature test (if required) - normal temperature test - coarse and fine leakage detection - appearance inspection.

(1) High temperature storage: germanium tube 100 ℃, silicon tube 175 ℃, 96 hours.

(2) Power aging: add power to the junction temperature TJM for small power tube, and aging for 24 hours. Pay attention to eliminate harmful high-frequency oscillation for high-frequency tube to avoid tube HFE degradation.

4.3 typical screening procedures for semiconductor integrated circuits

High temperature storage - temperature circulation - (drop) - centrifugation - high temperature power aging - high temperature test - low temperature test - Leak Detection - appearance inspection - normal temperature test.

(1) High temperature storage: 85 ~ 175 ℃, 96 hours.

(2) Centrifugation: 20000g, 1 minute

(3) High temperature power aging: 85 ℃, 96 hours, dynamic aging under rated voltage and rated load.

The screening of electronic components should focus on reliability screening, and the specific screening procedure can be flexibly formulated according to the structural characteristics, failure mode and use requirements of components.

Screening and quality control are important links in the production of high reliability components. For high-quality products, the whole batch of products can achieve its inherent high reliability through screening. For inferior products, due to their inherent defects, it is impossible to screen out highly reliable products. Therefore, before screening, it is necessary to carry out sampling test evaluation on the quality and reliability level of products. Through test and failure analysis, it is helpful to formulate reasonable screening procedures.