Factor Research About Electrical Properties Of Wet Tantalum Capacitors’ Cylinder Anodes

The development and research of wet tantalum capacitors is still undergoing. To keep advancing, on the one side, the improvement of assembly is needed, but on the other hand, the design of inner anode should keep pace with time. A systematic research of factors related to the electrical properties of wet tantalum cylinder anode is conducted in this work, and the the conclusion is applied to the theory discussion of design of wet tantalum cylinder anode. The main content are as follow:1. A research of anodes with different volumes is conducted. The results show that the greater the volume, the faster decrease of capacitance with increasing frequency. Based on the fact that RC (resistance and capacitance) Ladder exists in the structure of tantalum capacitors, this thesis assumes that the remaining capacitance under high frequency can be equivalently taken as only comes from a coat like surface with equal thickness (the thickness is defined as the equivalent penetration depth of cathode charge). On the basis of this assumption, a mathematical model is carried out about the relation of the equivalent penetration depth of cathode charge and the capacitance conservation rate. Taking into the data acquired by experiment, the equivalent penetration depths of cathode charge are calculated. It shows that these depths are mainly determined by the signal frequency, not by the volume of anode pellets, which corroborates the assumption above.2. A research of anodes with different aspect ratio is conducted. The results show that the greater the volume, the slimmer the anode, the slower decrease of capacitance with increasing frequency and the smaller ESR. This thesis calculates the equivalent penetration depth of cathode charge according to the assumption and mathematical model given in 1. It shows that these depths are on the one hand mainly determined by the signal frequency, on the other hand, given a certain volume, the bigger of the out surface area, the deeper cathode charge penetrates. This research suggests that the more out surface area of a certain volume the better design of an anode pellet.3. A analysis about the anode CV (production of capacitance and dielectric forming voltage) is done which suggests that the decrease of anode CV with increasing forming voltages comes from the anode metal surface area’s lose. And a analysis about the DCL (direct current leakage) K value (DCL/CV) is finished too, which suggests that when average thickness of every unit of forming voltage is equal, only keep the ratio of test voltage to forming voltage as constant, one can guarantee the same electric field strength for the test for K value of leakage current.4. A research of anodes made by different tantalum powder is conducted.The results show that flake powder has advantage on sinter-resistant, form-resistant and electric resistance. Nodular powder has advantage on the CV of a unit volume when both the sintering temperature and forming voltage aren’t very high. This thesis proposes a round flat cake model and a sphere model for flake powder and nodular powder respectively, to explain the difference between these two kinds of powder.5. A research of anodes with different pressing density is conducted. The results show that:1) CV of one unit volume increase with increase of pressing density when forming voltage is low. But when forming voltage keep going up, this trend becomes weak, and at last, backwards, that is, CV of one unit volume decreases with increasing forming voltage.2) The greater the pressing density, the smaller CV of one unit of mass, the bigger ESR. This thesis argues that the reason for above regular pattern is the inner space of anode pellet is consumed badly by big pressing density, thus some part of the inner space is more easily isolated when forming the dielectric. Tantalum powder particles stay more closely by big pressing density, thus these particles join to each other more easily when sintered with more surface area loss.6. A research of anodes with different tantalum wire penetration depth is conducted. The results show that anode’s electric properties don’t vary with different tantalum wire penetration depth. And this thesis proposes the reason is the resistance of anode charge transportation is much less than that of cathode charge.7. This thesis proposes that the design and optimization for cylinder anode of wet tantalum capacitor should meet three requirements, they are acquire and reservation of overall anode surface, excellent dielectric separator, good flowability of electrolyte and cathode charge。This thesis has discussed them respectively according to the conclusions from 1 to 6, and together with specific constrains.