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Aluminum capacitorThe difference between tantalum capacitors and tantalum capacitors
The capacitor we use for high-frequency bypass (decoupling) is MLCC capacitor, that is, multilayer Ceramic capacitor. Mainly due to its good high-frequency characteristics, the limiting frequency point of its capacitance can be accurately determined by using SIPCAP software.
The comparison between tantalum capacitors and aluminum capacitors is as follows:
Electrolytic capacitorThe traditional method of classification is based on the anode material, such as aluminum or tantalum. Therefore, Electrolytic capacitor are divided into the following categories according to anode:
1. Aluminum Electrolytic capacitor. Whether SMT or in-line, as long as their anode material is aluminum, they are all called aluminum Electrolytic capacitor. The packaging method of capacitors is not directly related to their quality, and the performance of capacitors only depends on the specific model.
2. Tantalum Electrolytic capacitor. The anode is composed of tantalum. At present, many tantalum Electrolytic capacitor are installed in chip mounting mode, and their shells are generally sealed with resin (aluminum Electrolytic capacitor may also be sealed with the same package). However, the cathode of tantalum capacitors is also an electrolyte.
The traditional view is that the performance of tantalum capacitor is better than that of aluminum capacitor, because the dielectric of tantalum capacitor is Tantalum pentoxide generated after anodic oxidation, and its dielectric capacity (usually ε It is higher than the aluminum oxide dielectric of aluminum capacitors. Therefore, under the same capacity, the volume of tantalum capacitors can be smaller than that of aluminum capacitors. (The capacitance of Electrolytic capacitor depends on the dielectric capacity and volume of the medium. Under a certain capacity, the higher the dielectric capacity, the smaller the volume can be. On the contrary, the larger the volume needs to be.) In addition, the nature of tantalum is relatively stable, so it is generally believed that the performance of tantalum capacitance is better than that of aluminum capacitance.
However, this method of judging capacitance performance by anode is outdated. At present, the key to determine the performance of Electrolytic capacitor is not the anode, but the electrolyte, that is, the cathode. Because different cathodes and anodes can be combined into different types of Electrolytic capacitor, their performance is also very different. Capacitors using the same anode can have significant differences in performance due to different electrolytes, and in short, the impact of the anode on capacitor performance is much smaller than that of the cathode.
The cathode material is the other electrode plate of the capacitor, and the cathode is the electrolyte of the capacitor. There are currently several types of cathodes for capacitors:
1. Electrolyte. Electrolyte is the most traditional electrolyte, which is obtained by heating GAMMA butyrolactone organic solvent and weak acid salt capacitor. The cathode of aluminum Electrolytic capacitor in the ordinary sense we see is this electrolyte. There are many benefits to using electrolyte as a cathode. Firstly, the contact area between the liquid and the medium is relatively large, which helps to increase the capacitance. The second is the Electrolytic capacitor made of electrolyte, which can withstand a high temperature of 260 degrees at most, so that it can pass wave soldering (wave soldering is an important process of SMT chip installation), and has strong pressure resistance. In addition, when the dielectric is broken down, the Electrolytic capacitor using electrolyte as cathode can self heal as long as the breakdown current does not continue. But electrolytes also have their shortcomings. Firstly, it is prone to volatilization and leakage in high-temperature environments, which greatly affects its lifespan and stability. At high temperatures and pressures, the electrolyte may also vaporize instantly, causing an explosion due to an increase in volume (commonly known as slurry explosion); Secondly, the ionic conductivity method adopted by the electrolyte has a very low conductivity, only 0.01S (conductivity, reciprocal of ohm)/CM, which causes the ESR value (Equivalent series resistance) of the capacitance to be particularly high.
2. Traditionally, it is believed that the performance of tantalum capacitor is better than that of aluminum capacitor mainly because tantalum plus Manganese dioxide cathode is significantly better than that of aluminum electrolyte capacitor. If the cathode of the aluminum electrolyte capacitor is replaced with Manganese dioxide, its performance can also be improved.
Manganese dioxide. Manganese dioxide is the cathode material for tantalum capacitors. Manganese dioxide is a solid, and its conduction mode is electronic conduction. Its conductivity is ten times (0.1S/CM) that of electrolyte ions, so ESR is lower than that of electrolyte. So, traditionally, people believe that tantalum capacitors are much better than aluminum capacitors, and there is no risk of solid electrolyte leakage. In addition, Manganese dioxide has good high-temperature resistance, and the instantaneous temperature is about 500 degrees. The disadvantage of Manganese dioxide is that it is easy to generate high temperature when the polarity is reversed, and oxygen is released under high temperature environment. At the same time, the Tantalum pentoxide medium layer has crystalline changes, becoming brittle and producing cracks. Oxygen is mixed with tantalum powder along the cracks and explodes. In addition, the price of this cathode material is also relatively expensive. Compared to aluminum electrolyte capacitors, although they are all explosive, the principle is different. How many people can notice this?