A Study Of Tantalum Capacitor Manganizing Technology

The solid electrolyte tantalum capacitor with manganese dioxide cathode features many advantages such as high capacitance within small size, good performance in filtering circuit, good temperature performance, high reliability, long-life and so on, thus it is widely used in various types of circuit. With the evolution of electronic devices to smaller in size and higher in frequency, tantalum capacitors also develop into smaller size, higher capacitance, lower ESR (Equivalent Series Resistance) products to meet market demand.Manganizing is the very important step in tantalum capacitor producing. The purpose of this step is the formation of manganese dioxide as capacitor’s cathode in the porous anode which covered with Ta2O5 (tantalum pentoxide dielectric film). The characteristic of the formatted manganese dioxide in this step will greatly affect the parameters such as capacitance, dissipation factor, ESR and so on.This thesis introduces the basic category of electrolyte capacitors and the characteristic of different types, especially solid electrolyte tantalum capacitor with manganese dioxide cathode and gives a explanation of the common used parameters of a tantalum capacitor. Then this thesis illustrates the basic theory of the manganizing process and dissects the reasons why manganizing process affects those electrical parameters. Introduce the modified processes to improve electrical parameters such as capacitance achieve rate, dissipation factor and ESR. These processes are:1. The specific gravity, temperature, different additives and catalysts of manganese nitrate solution.2. The dipping speed and method of tantalum pellet.3. Whether dewatering after dipping.4. The temperature, airflow speed, steam content when pyrolysing.Some contrast experiments between modified processes and original processes were taken and the result data was contrasted. The reasons for these results are analyzed theoretically.After each individual improvement experiments are completed the author combines some good solution of the modified processes and proposing a set of improved manganizing process with experimental verification. Comparisons are made between the capacitors which used the improved process and the original standard process in parameters, surface topography and internal micro-structure. The differences are:1. The improved process takes advantages in capacitance, dissipation factor and ESR, the leakage current is a bit larger but is still acceptable and under the control limit.2. The surface of improved-processed anode pellet distributes much micro-granule, which enlarges the surface area of anode pellet.3. Internal micro-pore filling.To test the capacitor with improved process in the actual filtering circuit, the author designed a particular filtering circuit which uses white noise and simple R.C filter. To simulate the power driving in practical application a specialized amplifier is designed. This amplifier is made up of discrete components, features specialties such as high bandwidth, high power driving capacity, high stability when driving RC load. The amplifier completes the test perfectly.Take the capacitor with improved manganizing process to the filtering test, the result shows the capacitor with improved process possesses better performance at the mid and high frequency. Analysis of this result shows it coincides to the electrical parameter of lower ESR.