Two principal factors that can lead to the failure of tantalum capacitors

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There are two principal factors that can lead to the failure of tantalum capacitors, one factor is tantalum powder and tantalum wire that can be used as the material of capacitor, the other factor is the manufacturing process of capacitor.

Influence of tantalum powder and tantalum wire

The chemical properties, physical properties and impurities content of tantalum powder and tantalum wire as well as the particle shape, size and breakdown voltage of tantalum powder all can have direct influence on the quality of tantalum capacitor. The impurities content of tantalum powder and tantalum wire will have great influence on the quality of oxide film. The anode core of tantalum capacitor needs to be sintered under high temperature of 1500 degrees Celsius to 2050 degrees Celsius before molding so as to remove the impurities in tantalum powder and tantalum wire, however, those refractory impurities, such as tungsten, molybdenum, silicon, iron, copper and so on are difficult to remove in the sintering process, which will become the “crystal nucleus” of defect in forming the oxide film and will become the electric channel. Therefore, the content of impurities is controlled very strict, which should be less than 10-50PPM. Tantalum powder has various specifications, which can be divided into high voltage powder, medium voltage powder and low voltage powder according to the working voltage of tantalum capacitor. As these kinds of powders have different specific volume, physical properties and breakdown voltage, we should choose the tantalum powder reasonably and appropriately when producing the tantalum capacitor so as to ensure the quality of tantalum capacitor.

Influence of capacitor manufacturing process

The manufacturing process of tantalum capacitor can directly influence the performance of tantalum capacitor, especially some of its critical processes will directly influence the leak current of tantalum capacitor.

Firstly, the anode manufacturing process, in which the tantalum metal powder is molded and sintered under high temperature and vacuum so as to mold and purify the tantalum powder. This sintering process should be done under high vacuum and high temperature of 1500 degrees Celsius to 2050 degrees Celsius so as to remove the impurities and achieve the purpose of purification. If the purification effect is not very good, the impurities will residue in the tantalum anode core and become the “crystal nucleus” in the dielectric film, which will become the hidden danger that can cause leak current.

Secondly, empowerment process, in which the tantalum anode is put into the electrolyte before the direct voltage is applied, afterwards, the oxygen ion in the electrolyte and tantalum in the anode of tantalum will form Ta2O5 film. In this process, the formula, temperature, voltage, boost current density and the constant voltage time all should be strictly controlled according to the process requirements. After the empowerment process is finished, the empowerment effect should be inspected, especially the capacitance and leak current, which should both meet the process requirements (the smaller the leak current, the better the empowerment effect). In the empowerment process, the “crystallization” phenomenon will be easy to occur if one of its processes is poorly controlled, therefore, in which the complete dielectric film is required as well as the crystallization is prohibited.

Thirdly, film covering process, which is a critical process in producing the cathode of tantalum (MnO2) and influencing the leak current. Currently, “steam film process” is applied, which can improve the quality of MnO2 and reduce its resistance value, thus the loss value of capacitor will become small. The performance of leak current depends on the process control of film covering and the effect of empowerment process.

Fourthly, the quality of assemble process and ageing process effect both can influence the leak current performance of capacitor.

Fifthly, screening process, which is a kind of process that further inspect the finished products of tantalum capacitor and often uses high and low temperature screening, long time high temperature burn-in screening, X-ray transmission inspection and so on.

Tantalum electrolytic capacitor has storage capacity as well as charge and discharge properties, which is mainly used in smoothing, energy storage and conversion, marking bypass, coupling and decoupling as well as used as the time constant element, etc. Its performance feature should be paid attention to when using, for example, the products operating environment and the heating temperature should be considered. It will play its effect only when it is correctly used, otherwise, the inappropriate use will have influence on its service life.