What are the failure modes of aluminum electrolytic capacitors? Professional testing center

Date：2022-07-14 18:27:45Views：633

Aluminum electrolytic capacitor is made of aluminum cylinder as negative pole, which is filled with liquid electrolyte and inserted with a curved aluminum strip as positive pole. It also needs to be treated with DC voltage to form a layer of oxide film on the positive plate as the medium. In order to help you understand in depth, this paper will summarize the relevant knowledge of aluminum electrolytic capacitor failure mode. If you are interested in what this article will cover, then read on.

1、 Common failure modes of aluminum electrolytic capacitors

When capacitors fail, the materials, structures, manufacturing processes, performance and operating environment of all kinds of capacitors are different, and the failure mechanism is also different. We will reveal the common failure modes of aluminum electrolytic capacitors: liquid leakage, explosion, open circuit, breakdown, deterioration of electrical parameters, etc.

2、 Failure mode and cause analysis

1. Leakage

Liquid leakage is one of the reasons for the failure of capacitors, and aluminum electrolytic capacitors are no exception. The working electrolyte of aluminum electrolytic capacitor is acidic. If it overflows, it will seriously pollute and corrode other components and printed circuit boards around the capacitor. At the same time, the working electrolyte gradually dries up due to liquid leakage inside the electrolytic capacitor, losing the ability to repair the anodic oxide film medium, resulting in capacitor breakdown or deterioration of electrical parameters and failure. There are many reasons for liquid leakage, such as:

① Poor sealing of aluminum electrolytic capacitor;

② If the rubber plug is used to seal the aluminum electrolytic capacitor, the rubber may be aged and cracked due to long use, resulting in liquid leakage;

③ Problems in mechanical seal process;

④ Generally, manufacturers will consider the problem of liquid leakage. They will clearly stipulate that vertical installation is required in the enterprise standard, while some enterprises adopt horizontal installation, etc.

2. Explosion

The AC component of aluminum electrolytic capacitor in the working voltage is too large, or the oxide film medium has more defects, or there are harmful anions such as chloride and sulfate, so that when the leakage current is large, the rate of gas produced by electrolysis is faster, the longer the working time is, the greater the leakage current is, the more gas in the shell is, and the higher the temperature is. The air pressure difference inside and outside the metal shell of the capacitor will increase with the increase of working voltage and working time. If the seal is good and there are no explosion-proof measures, the capacitor will explode if the air pressure increases to a certain extent.

At present, the explosion-proof shell structure has been widely used. A crease is added to the upper part of the metal shell. When the air pressure is high, the crease is pushed open to increase the volume in the shell, so as to reduce the air pressure and reduce the explosion risk. In use, such as adding overload voltage, rapidly charging and discharging the capacitor, applying reverse voltage, etc., may cause the capacitor to explode.

3. Breakdown

The breakdown of aluminum electrolytic capacitor is caused by the direct contact between electrolyte and anode due to the rupture of anodic aluminum oxide dielectric film. Alumina membrane may be locally damaged due to various materials, processes or environmental conditions. Under the action of an external electric field, the oxygen ions provided by the working electrolyte can re form an oxide film at the damaged part, so that the anodic oxide film can be filled and repaired. However, if there are impurity ions or other defects at the damaged part, which makes the filling and repair work unable to be completed, micropores will be left on the anodic oxide film, and may even become through holes, causing the breakdown of aluminum electrolytic capacitors.

In addition, with the increase of use and storage time, the solvent in the electrolyte is gradually consumed and volatilized, which increases the acid value of the solution and corrodes the oxide film during storage. At the same time, due to the aging and drying of electrolyte, it is impossible to provide oxygen ions to repair the oxide film under the action of electric field, thus losing the self-healing effect. Once the oxide film is damaged, it will lead to capacitor breakdown.

Process defects are also a major cause of breakdown of aluminum electrolytic capacitors. If the riveting process is poor, the burrs on the lead out chaff will seriously puncture the oxide film, and the leakage current at the puncture part is very large. Local overheating will cause thermal breakdown of the capacitor. In use, over temperature, over ripple current or over mechanical stress may cause capacitor breakdown failure.

4. Burn down

The burning of aluminum electrolytic capacitors is generally caused by the following reasons:

① Reverse connection of positive and negative electrodes: aluminum electrolytic capacitor is a capacitor with positive and negative electrodes. If the positive and negative electrodes are connected incorrectly when installing aluminum electrolytic capacitor, the capacitor will be burned out;

② Insufficient withstand voltage: when the voltage exceeds the withstand voltage value of the aluminum electrolytic capacitor itself, the capacitor will also burn out;

③ Unqualified quality: aluminum electrolytic capacitors produced by some manufacturers are unqualified, which may also cause the burning of capacitors, etc.

5. Open circuit

The open circuit failure of aluminum electrolytic capacitor may occur when it works in high temperature or hot humid environment for a long time. The reason is that the anode foil is broken due to electrochemical corrosion. For high voltage and large capacity capacitors, there are many such failure modes.

In addition, if the anode foil is not fully leveled after riveting with the anode foil, poor contact will cause intermittent open circuit of the capacitor. In use, excessive mechanical stress may open the capacitor.

6. Deterioration of electrical parameters

① Capacitance decrease and loss increase: the capacitance of aluminum electrolytic capacitor decreases slowly in the early stage of operation, which is caused by the continuous repair of working electrolyte and thickening of anodic oxide film during the load process. At the later stage of use, due to the large loss of electrolyte, the thickening of solution, and the increase of resistivity due to the increase of viscosity, the equivalent series resistance of working electrolyte increases, resulting in the obvious increase of capacitor loss.

At the same time, the electrolyte with increased viscosity is difficult to fully contact the oxide film on the uneven aluminum foil surface after corrosion treatment, which reduces the effective area of the electrode plate of the aluminum electrolytic capacitor and causes a sharp decline in capacitance. This is also the performance that the service life of the capacitor is approaching the end.

In addition, if the viscosity of working electrolyte increases too much at low temperature, it will also cause the loss to increase and the capacitance to drop sharply. In use, over temperature and over ripple current may reduce capacitance and increase loss.

② Increase of leakage current: the increase of leakage current often leads to the failure of aluminum electrolytic capacitor. Low process level, serious oxide film damage and contamination, poor working electrolyte formula, low purity of raw materials, difficult long-term stability of chemical and electrochemical properties of electrolyte, low purity of aluminum foil, high impurity content and other factors may cause leakage current out of tolerance failure.

The chloride ion in the aluminum electrolytic capacitor is seriously contaminated, and the leakage current leads to the decomposition of the oxide film at the contaminated part, causing perforation and further increasing the current. In a word, the existence of metal impurities in aluminum foil will increase the leakage current of aluminum electrolytic capacitor and shorten the service life of capacitor In use, overvoltage may increase the leakage current of the capacitor.

The above is the content related to the failure mode of aluminum electrolytic capacitors compiled by the core detection team. I hope it will be helpful to you. Shenzhen Chuangxin Online Testing Technology Co., Ltd. is a well-known professional testing institution for electronic components in China, with 3 standardized laboratories covering an area of more than 1000 square meters. The scope of testing services covers: electronic component testing and verification, IC authenticity identification, product design and material selection, failure analysis, function testing, factory incoming material inspection, component X-ray testing, taping and other test items.