Introduction and basic structure of tantalum capacitors
Solid tantalum capacitor is tantalum powder compression molding, sintered in a high temperature furnace into the anode body, the dielectric is the anode body into the acid empowered, the formation of porous amorphous Ta2O5 dielectric film, the work of the electrolyte for the high temperature decomposition of manganese nitrate solution to form MnO2, through the graphite layer as a lead to connect with.
Tantalum capacitors have superior performance, can achieve a larger capacity at the same time can make the volume is relatively small, easy to process into small and sheet components, suitable for the current automation of electronic device assembly, miniaturization of the development of a wide range of applications, tantalum capacitors are mainly characterized by a long service life, high temperature, high accuracy, but the resistance of the voltage and current ability is relatively weak, generally used in the circuit of the high-capacity filtering part.
Production process
According to the form of electrolyte, tantalum electrolytic capacitors have liquid and solid tantalum electrolytic capacitors, liquid tantalum electrolytic dosage has been very little, this article only introduces the production process of solid tantalum electrolytic.
Solid tantalum electrolytic capacitors whose dielectric material is tantalum pentoxide; anode is sintered metal tantalum block, led by the tantalum wire, the traditional negative electrode is a solid MnO2, the latest is the use of polymers as the negative electrode material, performance is better than MnO2.
Tantalum electrolytic capacitors have leaded and chip two kinds of installation, its manufacturing process is more or less the same, now take the piece of tantalum production process as an example is introduced as follows.
Production process:
Forming → sintering → test capacity inspection → group frame → empowerment → coating tetrafluoroethylene → film → graphite silver paste → on the piece of dispensing curing → spot welding → molding curing → cutting rib → sandblasting → electroplating → marking → cutting edge → leakage prediction → aging → testing → inspection → banding → storage
The parameters and selection of tantalum capacitors leakage current and the relationship between operating temperature
The leakage current of tantalum capacitors will increase with the increase of temperature, this curve is called the leakage current temperature curve. However, the same specifications of products produced by different manufacturers, often due to the production process and the use of raw materials and equipment precision is different and high temperature leakage current change there are very big differences. High temperature leakage current changes in the high temperature state of the product will be due to their own heat generated by the accumulation of the eventual breakdown phenomenon. High temperature leakage current change is small in high temperature products work for a long time, the stability and reliability of the product will be higher. Therefore, the size of the leakage current change rate at high temperature can determine the reliability of tantalum capacitors. For chip tantalum capacitors, the high temperature performance has a decisive effect on the reliability.
Leakage Current VS Temperature：
Leakage Current VS Voltage:
Leakage current test is generally at 20 ℃ when the rated voltage is applied to the test, in the measurement circuit and capacitance in series with a 1000 OHM protection resistor, charging one to five minutes (KEMET, VISHAY, AVX for two minutes, SANYO for five minutes), and then measure the leakage current.
Dissipation factor (DF value):
Dissipation factor is a physical quantity that determines the power dissipation inside the capacitor, the smaller the better, generally DF value increases with frequency.
The size of the loss on the use of the product and the reliability of the impact of the explanation: loss (DF value) is characterized by the resistance of the tantalum capacitor itself can cause the proportion of ineffective power consumption of a parameter, the loss of smaller products ESR will also be smaller. However, the small difference in loss size will not have a significant impact on the use of the working state of the product's reliability impact and capacity deviation compared to the impact of the larger, but with the product leakage current size and ESR size of the use of the reliability of the impact of the smaller (leakage current size and ESR size impact > loss size impact > the impact of the capacity deviation), filtering, if the product's loss is larger, the effect of filtering is poorer. The filtering effect will be worse if the loss of the product is larger. At the same time, the surge resistance of products with higher losses is also poorer.
Impedance, Equivalent Series Resistance (ESR) & Inductive Resistance:
ESR is an important index to determine the capacitor filtering performance, the ESR of tantalum capacitor is mainly caused by the pin and internal electrode impedance, is a very important parameter of capacitor performance at high frequency, generally speaking, the same capacity, the same voltage value of the tantalum capacitor ESR is lower than electrolytic capacitors, but higher than the multilayer ceramic capacitors, the ESR decreases with the increase of the frequency and temperature, ESR=DF/WC. in the resonance frequency below the capacitor impedance is the capacitive impedance and ESR vector sum, after the capacitor resonates, the capacitive impedance is the inductive impedance and ESR vector sum. Below the resonant frequency, the impedance of the capacitor is the vector sum of the capacitive impedance and ESR, and after the capacitor has resonated, the impedance of the capacitor is the vector sum of the inductive impedance and ESR.
The figure below shows the equivalent composition diagram of the capacitor:
Capacitor Failure Modes, Mechanisms and Failure Characteristics
For tantalum capacitors, failure and other types of capacitors, there are also changes in electrical parameters failure, short-circuit failure and open-circuit failure. Due to the stability of the electrical properties of tantalum capacitors, and has a unique "self-healing" characteristics, tantalum capacitors rarely have parameter changes caused by the failure of tantalum capacitors, tantalum capacitors fail most of the time due to insufficient circuit derating, reverse voltage, over power consumption, the main mode of failure is a short-circuit. In addition, according to the failure statistics of tantalum capacitors, tantalum capacitors have very few cases of open-circuit failure. Therefore, tantalum capacitor failure is mainly short-circuit failure. Tantalum capacitor short-circuit failure mode mechanism is: solid tantalum capacitor medium Ta2O5 due to impurities, cracks, holes and other defects or defects in the raw material impurity or process reasons, tantalum block in the high-temperature sintering has been most of the defects or defects burned or evaporated, but there is still a small amount of existence. In the process of empowerment, old refining, these defects in the voltage, temperature under the action of field crystallization into the origin of the nucleus; in the long-term role, prompting the dielectric film at a faster rate of physical and chemical changes, resulting in the accumulation of stress, to a certain extent, it will cause localized overheating breakdown of the medium. If the defective parts of the dielectric oxide film is large and concentrated, once the thermal stress and electrical stress under the action of instantaneous breakdown, a very large short-circuit current will make the capacitor rapidly overheating and loss of thermal equilibrium, tantalum capacitors inherent "self-healing" characteristics have been unable to repair the oxide film, resulting in tantalum capacitors quickly breakdown failure.
Failure mechanism is mainly due to the oxide film defects, tantalum block and anode lead wire contact to produce relative displacement, anode lead tantalum wire and oxide film particles in contact, etc., most of the tantalum capacitor failure is catastrophic, may be burned, exploded, in the application of the process requires special attention.
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