In modern society, the aerospace industry is in full swing. Having learned lessons paid in blood and through experiences, people are increasingly focusing on research and exploration in reliability engineering. The reliability of electronic components is the foundation of reliability engineering and also the most complex task within it. From production to secondary screening, then to installation debugging and final application, ensuring the reliability of electronic components is of great importance. This article mainly summarizes the reliability assurance work in the process of component secondary screening.
Secondary screening is a crucial reliability assurance process for components before they are installed. However, improper operation and protection during secondary screening can leave hidden dangers for the application of electronic components or directly cause failures. Therefore, in secondary screening tests, it is critical to ensure the reliability of electronic components from aspects such as environmental protection, operation review and careful handling, electrostatic protection, and DPA & FA.
Electronic components have specific requirements for their operating environment, especially regarding temperature, humidity, electrical stress, and mechanical stress. For temperature-sensitive devices like temperature sensors and thermistors, they should be stored under normal temperature conditions as much as possible during storage and operation. During operation, they should be avoided in containers with high thermal resistance and poor thermal conductivity; otherwise, abrupt temperature changes may cause device failure, or prolonged high-temperature conditions may lead to thermal stress fatigue.
Electronic components should generally be handled with care (gently picked up and placed); otherwise, shape deformation or dimensional changes may occur. When inserting or removing components from test fixtures, excessive force should be avoided, as it may cause mechanical damage or mechanical stress fatigue. Under the condition of ensuring good contact, the stress applied to the component pins should be minimized.
Storage humidity should not be too high; otherwise, surface corrosion of pins or deterioration of electrical performance may occur. QJ2227-92 Requirements for Storage and Overdue Re-inspection of Electronic Components for Aerospace Use (Clause A2) specifies the effective storage period and storage environment for electronic components—the higher the storage humidity, the shorter the effective storage period.
In addition, radiation-sensitive devices such as optoelectronic devices should be kept away from radiation sources to prevent radiation damage.
Sources of Static Electricity: Static electricity comes from various sources. In daily life, common sources include triboelectrification, induced electricity, human bodies, and dust. In industrial production, static charges are easily generated due to mechanical movement, electromagnetic induction, etc., so static charges may also exist on mechanical objects.
Moreover, the radiation and absorption of energy quanta can also generate charges. In materials, especially semiconductor materials, the absorption of corresponding energy quanta causes charges in the valence band to jump to the conduction band, forming free charges. Alternatively, radiation energy quanta may cause charges in the conduction band to jump to the valence band, reducing the number of charges in the conduction band and resulting in charge imbalance. The schematic diagram is as follows:
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Introduction to Electrostatic Discharge (ESD) Models and Classification: Internationally, ESD can be roughly categorized into three main models: Human Body Model (HBM), Machine Model (MM), and Discharge Model. The HBM has a relatively large equivalent resistance, while the MM has a slightly smaller equivalent resistance. The Discharge Model refers to discharge caused by induced static charges, which can include the Charged Device Model (CDM), Electric Field Induction Model, and Charged Chip Model. With the rise of nanodevices and the advancement of semiconductor processes to the nanoscale, the impact of the Discharge Model on electronic components will become increasingly prominent.
ESD sensitivity levels are classified according to component types and electrostatic sensitivity. According to GB1649-93 Outline for Control of Electrostatic Discharge in Electronic Products, they are divided into Level 1 (0–1999V), Level 2 (2000V–3999V), and Level 3 (4000V–15999V).
- Level 1 electrostatically sensitive components generally include microwave devices, discrete MOS field-effect transistors, Surface Acoustic Wave (SAW) devices, Junction Field-Effect Transistors (JFETs), Charge-Coupled Devices (CCDs), precision Zener diodes, operational amplifiers, thin-film resistors, integrated circuits, hybrid circuits using Level 1 components, and Very High-Speed Integrated Circuits (VHSIC).
- Level 2 sensitive components include components and microcircuits identified as Level 2 through test data, precision resistor networks, hybrid circuits using Level 2 components, and low-power bipolar transistors (Ptot < 100mW, Ic < 100mA).
- Level 3 components and microcircuits include those identified as Level 3 through test data, small-signal diodes with Ptot < 1W or Io < 1A, silicon rectifiers with general requirements, optoelectronic devices, and chip resistors.
For components with different anti-static levels, attention to anti-static protection should be increased accordingly, and appropriate anti-static measures should be taken.
Electrostatic Damage and Protection: Electrostatic damage mainly affects the insulated gates of field-effect transistors, peripheral devices of circuits (such as protective diodes), thin-film resistors, and metallized strips. Severe damage can directly cause device breakdown or destruction. Some circuits damaged by static electricity may not show issues through visual inspection or electrical parameter testing, and minor damage may not be detected even through tests and electrical parameter measurements, leaving hidden dangers for device application. After electrostatic damage, failure modes such as open circuits, short circuits, deterioration of characteristic curves, increased reverse current, and degraded frequency characteristics may occur. Therefore, electrostatic protection is also crucial in secondary screening laboratories.
In addition to following the provisions and requirements of relevant standards and specifications, electrostatic protection should also consider the sources of static electricity and the conditions for electrostatic discharge.
Destructive Physical Analysis (DPA) and Failure Analysis (FA) are emerging engineering disciplines that originated in the late World War II period. Foreign countries began researching reliability technologies in the 1950s, while China started developing them in the early stage of reform and opening-up.
Failure Analysis (FA)
From the late 1960s to the early 1970s, the U.S. military adopted a component quality assurance program centered on failure analysis. Through identifying problems in manufacturing and testing, finding causes through failure analysis, improving design, processes, and management, and then repeating the cycle of manufacturing, testing, analyzing, and improving, the failure rate of integrated circuits decreased from 7×10⁻⁵/h to 3×10⁻⁹/h within 6–7 years—a reduction of four orders of magnitude. This successfully supported the Minuteman II intercontinental missile program and the Apollo moon landing program. It is evident that FA plays an indispensable role in major engineering projects.
In summary, the main roles of FA are as follows:
- Obtain theories and ideas for improving design, processes, or applications through FA.
- Derive predictive reliability model formulas by understanding the physical phenomena causing failures.
- Provide a theoretical basis and practical analysis methods for reliability test conditions (such as accelerated life tests and screening).
- Provide a decision-making basis for whether to reject an entire batch of components when dealing with component issues in engineering.
- Implementing corrective measures based on FA can improve yield and reliability, reduce failures during system testing and operation, and achieve significant economic benefits.
Destructive Physical Analysis (DPA)
DPA, as a supplementary means to failure analysis, is a test conducted by an authoritative third party or the user during product delivery acceptance tests. Its main feature is analyzing qualified components.
Roles of DPA: Reducing defects is a key part of factory reliability work. Even qualified products may have defects. Analyzing qualified products using the same technical methods as failure analysis helps investigate and evaluate defects in electronic components with good performance. In secondary screening tests, sampling qualified products for analysis can easily detect defects in electronic components at an early stage, providing feedback to manufacturers to improve their production processes. DPA helps identify abnormal batch products, ensuring the reliability of components installed in equipment.
For example, during DPA testing of a batch of imported integrated circuits by a certain aerospace institute, cracks that did not meet standard requirements were found in both the sampled and additional samples, as shown in Figure 2. In DPA sampling tests of certain domestic mica capacitors, many devices were found to have large voids between the terminal electrodes and mica sheets, as shown in Figure 3. These findings help reject components with batch defects, thereby better ensuring the reliability of aerospace products.
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In general, conducting DPA and FA in secondary screening tests plays a significant role in ensuring the quality and improving the reliability of major engineering products.
In the process of component screening and testing, the following types of failures may occur:
- Detection failures of electronic components due to improper program settings;
- Component failures caused by reverse polarity connection;
- Component failures caused by wrong signals;
- Component failures caused by electrical stress overshoot;
- Electronic component failures due to misuse of adapters;
- Mechanical stress failures caused by improper plugging/unplugging methods;
- Accidental reversal of polarity of some polar components during storage.
There have been actual cases of these phenomena. For example, a certain institute burned out a triode due to unreasonable program settings during testing; a factory found failures in tantalum electrolytic capacitors during system debugging, and the investigation showed that one of the components near the used ones had its polarity reversed accidentally during storage. 
