What are the reasons for the sudden failure of components? How to find and replace?

Date：2021-10-19 15:35:06Views：1441

Why do components sometimes fail for no reason? The integrated circuit structure follows Moore's law and becomes smaller and smaller. The migration of materials at normal operating temperature increases the risk of device failure in decades. In addition, fatigue caused by magnetostriction can lead to inductive mechanical fatigue, which is a well-known effect. Some types of resistance materials will oxidize slowly in the air, and the oxidation rate will accelerate when the air becomes more humid.

Therefore, when selecting equipment, it is necessary to understand its structure and possible aging related failure mechanism. Even if the equipment is used under ideal conditions, these mechanisms may be affected. However, under appropriate working conditions, the life expectancy of most electronic equipment can reach decades or even longer, but some still fail prematurely. The reason is often the pressure of not being noticed. Anyone who designs electronics in a marine environment will consider salt fog and humidity. In fact, many electronic devices may encounter less terrible chemical challenges, but they may still cause harm. The designer must consider the environmental challenges encountered by the circuit. Where economically feasible, any potential hazards should be minimized through design.

Electrostatic damage (ESD) is a stress mechanism, and related warnings are the most common, but we often ignore them. During PCB production, the factory will take sufficient measures to eliminate ESD in the manufacturing process, but after delivery, many systems with insufficient ESD protection measures caused by PCB like operation. Adequate protection is not difficult, but it will increase the cost, so it is often ignored. Evaluating what kind of ESD protection is required for system electronic devices under the most extreme conditions of normal use and considering how to realize it should be a part of all designs.

Another factor is overpressure. Few people require that semiconductors or capacitors are healthy even under significant overvoltage, but it is common for large resistance to encounter a voltage far greater than the absolute maximum value in the data book. The problem is: Although the resistance value is high enough not to get hot, a small arc may be generated inside, resulting in its slow drift, deviation from the specification and final short circuit. Large winding resistors usually have hundreds of volts of breakdown voltage, so this problem was not common in the past, but now small surface mount resistors are widely used. The breakdown voltage may be lower than 30 volts, which is quite vulnerable to overvoltage.

High current can also cause problems. Everyone is familiar with a common fuse - it's a wire. If the current is too large, it will become hot and fuse to prevent similar problems such as short circuit of power supply. However, if a very small conductor has a high current density, the conductor may not become very hot, but may eventually fail. The reason is the so-called electromigration. In other words, the momentum transfer between conductive electrons and diffused metal atoms leads to the gradual movement of ions in the body, resulting in the effect of material transport. This means that with the passage of time, the thin conductor carrying large DC current becomes thinner and thinner, and finally fails.

But some parts will fail like fuses, that is, fusing, such as wires or conductive wiring on semiconductor chips. A common reason for this phenomenon is that the capacitor charging current is too large. Considering that ESR is 1 ω If the 1hf capacitor is connected to 110V and 60Hz AC power supply, about 41ma AC current flows through it. However, when the voltage is at the maximum value (110 √ 2 = 155.6v), only ESR will limit the flow, and the peak current will reach 155.6a, although its duration is less than 1 μ s. But it is also enough to damage many small signal semiconductor devices.

Repeated surges may damage the capacitor itself, especially the electrolytic capacitor. This is a particularly common failure mechanism for charging small electronic devices. If the wrong time of an AC cycle is inserted, the rectifier and capacitor will carry very large surge current. If it occurs many times, it may eventually damage the equipment. Using a small resistor in series with the rectifier can limit the surge current and minimize the problem.

With luck, ESD or overvoltage / overcurrent events will immediately damage the equipment, so it is easy to know the problem. But more often, damage caused by pressure leads to equipment failure, and the pressure that initially led to the failure has disappeared. It is very difficult or even impossible to diagnose the cause of this failure. No matter what circuit is designed, it is necessary to consider the working life and failure mechanism of the equipment used, whether there are potential problems or pressure sources under the allowable extreme service conditions, and whether the equipment will be damaged. Any such problem should be considered and minimized in the final design.

So how to effectively find invalid electronic components and replace or repair problems?

During debugging, when the circuit cannot work or works abnormally. Firstly, through the dynamic observation method, when the line equipment is powered on, judge the fault of electronic components by listening, looking, touching and smelling. For example, listen to the equipment for abnormal sound, and carefully check whether there are smoke, sparks, etc. in the circuit; Touch the components and check whether the circuit is hot; Smell whether there is burnt smell. It can also be judged by measuring the on-off in the circuit with a multimeter and by measuring various values in normal and abnormal circuits.

The above is the relevant content of "failure analysis of electrical components" brought by the core creation test. I hope it can be helpful to you. We will bring more wonderful content in the later stage. The company's testing services cover: electronic component testing and verification, IC authenticity identification, product design and material selection, failure analysis, function testing, factory incoming material inspection, tape braiding and other testing items. Welcome to call Chuangxin testing, we will serve you wholeheartedly.