JPS6052570B2 - solid electrolytic capacitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solid electrolytic capacitor using an anode body formed by molding and sintering valve metal powder, and in which the pores between the aggregated powder of the anode body are enlarged to form a semiconductor layer. The aim is to provide reliable products with excellent characteristics.

Generally, as an anode body of a solid electrolytic capacitor, high-purity powder of a valve metal such as tantalum, niobium, or aluminum is press-molded as shown in Figure 1.
It is manufactured by sintering at high temperature in a high vacuum of -0 Torr.

In the figure, the anode body is shown, and 2 is the anode internal lead. In order to reduce the size and cost of a solid electrolytic capacitor using such an anode body, it is necessary to increase the surface area per unit volume and unit weight of the anode body 1.

For this reason, it is necessary to increase the surface area of the valve metal powder particles, and there are various methods for increasing the particle surface area. To give a few examples, one is a method to make the single particle size as small as possible, and the other is a method to make a fine powder of about 0.1 to 50μ made by various methods such as sodium reduction method. In order to increase the surface area of each fine individual powder, the particle shape and its surface are made complex by chemical and physical methods.

However, these methods have reached their limits in terms of workability, such as the fluidity of filling the mold when press-molding the powder, and recently, extremely fine single particles have been processed under high vacuum. A plurality of single particles are bonded and aggregated by heat treatment at high temperature in a vacuum chamber to form an agglomerated powder of approximately 10 to 300μ, which has good fluidity and a high CV value (μF-ri/gr).
) powder is now used.

However, since this agglomerated powder uses relatively fine diameter single particles as its base, the pores between each single particle are extremely small, and even in an agglomerated powder, the pores are 10 to 300μ. 3 Even if this agglomerated powder is used to form the anode body 1 as described above, the pores between the agglomerated powders are small and it is difficult to form a semiconductor layer such as manganese dioxide to the inside of the anode body 1. In addition, the capacitor had color defects such as a large tan δ.

The reasons for this increase in tan δ are that the pores in the anode body 1 are small, so the path through the semiconductor layer through which the current flows is narrow, increasing the resistance value. This is due to the fact that the In order to improve this Tan δ, efforts have been made to increase the porosity by lowering the compacting density when press-molding the valve metal powder. This resulted in decomposition, and there was a limit to the reduction in molding density.

For these reasons, in the past, the characteristics were unstable and the capacitance was limited to a maximum of about 500 μF.

The present invention eliminates the drawbacks of the prior art as described above. Hereinafter, the present invention will be explained with reference to FIGS. 2 to 4 of the drawings of one embodiment.

That is, as shown in FIGS. 2 and 3, the present invention makes the pores 4 between the agglomerated powders 3 very large to widen the passages in the semiconductor layer and reduce the electrical resistance, while at the same time A semiconductor layer is easily formed in the pores 6 between each particle 5, and the agglomerated powder 3 with a very large diameter and the very fine 0.
The feature is that the anode body 8 is made of a mixed powder of single particles 7 of about 1 to 50 microns.

Of course, an anode internal lead 9 is embedded in this anode body 8, and this anode body 8 is anodized to form an anodic oxide film 10 that becomes a dielectric, and a manganese nitrate solution is impregnated on the anode oxide film 10. A semiconductor layer 11 of manganese dioxide or the like is formed by thermal decomposition, a cathode layer 12 of carbon or the like is formed on the semiconductor layer 11, a conductive layer 13 of silver paint or the like is formed on the cathode layer 12, and a solder layer 14 is formed on the cathode layer 12. A cathode lead wire 15 is connected to this solder layer 14 with solder 16, a semi-transformable anode lead wire 17 is connected to the anode inner lead 9, and the whole is molded with resin or the like to form an outer device 8. is formed to form a solid electrolytic capacitor as shown in FIG.

That is, by enlarging the pores of the anode body 8, the interior is sufficiently impregnated with the above-mentioned manganese nitrate solution, and by thermally decomposing this, the semiconductor layer 11 is formed up to the interior. Generally, Tan δ of a solid electrolytic capacitor is expressed by the following formula.

Tanδ=ω●CIR Note that ω=2πF, C=electrostatic capacity (μF), and R=equivalent series resistance (Ω).

As can be seen from the above equation, ω and C are determined when the frequency is kept constant, and Tan δ can be improved by reducing the equivalent series resistance R.

In addition, the equivalent series resistance R can be considered by breaking it down into various resistances: (a) resistance of the valve metal, {b) resistance of the anodic oxide film serving as the dielectric, (C) specific resistance of the semiconductor layer, {
d) Contact resistance between the semiconductor layer and the anodic oxide film, (e) resistance depending on the thickness of the pores and the length of the pores due to differences in the pores and shape of the anode body, and several other resistances. can.

The present invention focuses on the contact resistance between the semiconductor layer and the anodic oxide film, the size of the holes 4 in the anode body 8, and the shape and distance of the semiconductor layer passage.

That is, in a capacitor, the impregnating property and Tan δ of the semiconductor layer stock solution depend on the porosity and the size of the pores in the anode body 8, so it is desirable that the porosity is high and the pores are large. Further, even if the porosity is high, if the pores are very small, the impregnating property of the semiconductor layer stock solution will be poor, making it impossible to obtain a large capacity, and the resistance value will also increase.

Therefore, the present invention uses 32 meshes (particle size 0.4951I).
The above extremely large porous agglomerated powder 3 with a particle size of 0
．． Single particles 5 with a size of about 1 to 50μ are made by high-temperature vacuum heat treatment, agglomeration, etc., and the agglomerated powder 3 has a particle size of 0.
A mixed powder of the porous agglomerated powder 3 and the single particles 7 is prepared by mixing fine single particles 7 of about 1 to 50μ as a binder, and this is used to manufacture the anode body 8, thereby forming the agglomerated powder. A very large hole 4 is formed between the holes 3 and 3, and the semiconductor layer 11 can be formed up to the inside of the anode body 8.

Further, the mixing ratio of the fine single particles 7 added to the agglomerated powder 3 is preferably 1 to 30% (ωt), otherwise good results will not be obtained.

That is, if only the agglomerated powder 3 is press-molded into a pellet shape and sintered in a high-temperature vacuum, a porous anode body 8 can be obtained, but the contact area between the agglomerated powder 3 is reduced, and Since the agglomerated powder 3 has already been subjected to high-temperature vacuum heat treatment similar to high-temperature vacuum sintering, the surface energy of the agglomerated powder 3 is small, and sufficient diffusion does not occur at normal sintering temperatures, causing the anode It is assumed that the mechanical strength of the body 8 is weak.

Also, if the sintering temperature is too high, shrinkage will occur,
This results in a decrease in surface area, which is not preferred in practice.

Therefore, by mixing fine single particles 7 with a large surface energy as a binder into the agglomerated powder 3, the single particles 7 are diffused at a relatively low temperature, making it possible to sinter at a low temperature. The body 8 can have a high mechanical strength. If the amount of the single particles 7 exceeds 30% (ωt), the large voids 4 between the aggregated powders 3 will be filled, making it impossible to achieve the initial purpose.

Since the solid electrolytic capacitor of the present invention is constructed as described above, it is possible to form a semiconductor layer up to the center of the anode body, and it is possible to greatly improve Tan δ, increase and stabilize the capacitance, and further improve leakage current. It is possible to stabilize and improve various characteristics such as, and even if the capacitance is increased, it can be manufactured up to 5000 pF and close to the conventional one, and is of great industrial value.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing an anode body of a conventional solid electrolytic capacitor, Fig. 2 is a perspective view of an anode body showing an embodiment of the solid electrolytic capacitor of the present invention, and Fig. 3 is an enlarged sectional view of the same essential parts. , FIG. 4 is a sectional view of the same capacitor. 3...Agglomerated powder, 4...Vacancies, 5
...Single particle, 6...Pore, 1...
...Single particle, 8...Anode body, 9...
・Anode internal lead, 10...Anodic oxide film, 1
1... Semiconductor layer, 12... Cathode layer, 1
5...Cathode lead wire, 18...Exterior.

Claims (1)

[Claims] 1 A large powder made by molding and sintering a porous agglomerated powder of 32 mesh or more (particle size 0.495 mm) made of valve metal such as tantalum, niobium, aluminum, etc., mixed with single particles with a particle size of 0.1 to 50 μm. An anodic oxide film, a semiconductor layer, and a cathode layer are formed on an anode body having holes, and the anode body,
A solid electrolytic capacitor with leads drawn out from the cathode layer and an exterior covering applied to the entire body.