JPH09251931A - Solid electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the tangent δ and improve the withstand voltage. SOLUTION: A dielectric film 4 is formed on the surface of an anode base 2 made of a valve-acting metal and manganese oxide or oxide of manganese layer 5 to be a solid electrolyte is formed on the film 4. The crystal of an adjacent part of this layer 5 to the film 4 is a plate-like laminate granule like a thick plate, short column or barnacle, this reducing the tangent δ of the capacitor. A polyhedral granular manganese oxide exists at a part of the oxide layer 5 not directly contacted with the film 4 and hence the withstand voltage can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid electrolytic capacitor, and more particularly to a solid electrolytic capacitor having an improved fine structure of a solid electrolyte to improve dielectric loss tangent and withstand voltage.

[0002]

2. Description of the Related Art Generally, a solid electrolytic capacitor is provided with an anode substrate 2 made of a valve metal in which an anode lead wire (tantalum wire) 3 is embedded as shown in FIG. 3, and a dielectric film 4 is formed on the entire surface thereof. Further, a manganese oxide (or manganese oxide) layer 5 serving as a solid electrolyte is further formed thereon. Further, a conductor layer 6 is formed on the surface of the manganese oxide layer 5, a lead frame (anode terminal) 7 is welded to the anode lead wire 3, and a lead frame 8 is joined to the conductor layer 6 with a conductive paste 9. The epoxy resin 10 covers the entire lead frames 7 and 8 except a part thereof. Reference numeral 11 is a water repellent plate made of fluororesin.

As a metal having a valve action, tantalum,
Metals such as aluminum and niobium can be used.
Tantalum is used in the form of pellets obtained by sintering fine powder and attaching a tantalum wire serving as an anode to a porous tantalum sintered body. In the case of aluminum, the surface is electrochemically etched using aluminum foil as an anode to form pores on the surface. The dielectric film 4 formed on the surface of the anode substrate 2 made of a tantalum sintered body or an aluminum foil is usually formed by electrochemical anodization. This anodization uses nitric acid, phosphoric acid, and lead wire attached to a tantalum sintered body or aluminum foil as an anode.
The solution is used as a cathode in an acid solution such as acetic acid or oxalic acid, and a voltage of several V to several tens of V is applied. The manganese oxide layer 5 which is a solid electrolyte layer is obtained by impregnating and adhering a manganese nitrate solution on the anode substrate 2 on which the dielectric film 4 is formed.
It can be formed by heating and precipitating manganese oxide on the dielectric film 4, and repeating the impregnation, adhesion, and thermal decomposition operations of the manganese nitrate solution several times. Then, for example, a carbon layer and a conductive silver paste layer are formed to form the conductor layer 6. Then, after connecting the lead frames 7 and 8, the whole is covered with a synthetic resin 10 to manufacture a solid electrolytic capacitor.

[0004]

However, the above-mentioned conventional solid electrolytic capacitor has a problem that its dielectric loss tangent (hereinafter referred to as tan δ) is large and its withstand voltage (surge voltage) is low due to its application. Since these properties are determined by the material of the solid electrolyte, organic conductors (tetracyan, quinodimethane, polypyrrole, polyaniline) and lead dioxide have been studied as alternatives to manganese oxide. However, all of these are heat resistant,
There is a problem that the moisture resistance and productivity are inferior to those of manganese oxide.

Therefore, as a result of various studies on the tan δ and the withstand voltage property of the capacitor, it was found that the crystal habit of manganese oxide is related to the tan δ and the withstand voltage property. That is, the crystal habit of manganese oxide is slightly different depending on the starting material to be thermally decomposed and the thermal decomposition conditions. In the conventional capacitor, polyhedral granular manganese oxide is precipitated at the portion in contact with the dielectric film as shown in FIG. Therefore, tan δ was large. On the other hand, if the plate-like crystals of manganese oxide are laminated lumps and the form is a short column shape, a thick plate shape, or a barnacle shape (a truncated cone shape), tan δ is small, and the plate-like crystals are If manganese oxide, which is a polyhedral granular material, is deposited on the surface, the withstand voltage becomes high. The mixing ratio is not clear, but 8
It is preferably about 0% or less. Note that FIG. 4 is a scanning micrograph of the crystal habit of manganese oxide, where 20 is tantalum, 21 is a dielectric film, and 22 is polyhedral granular manganese oxide.

The present invention has been made on the basis of the above-mentioned conventional problems and examination results. An object of the present invention is to provide a capacitor having a manganese oxide layer or a manganese oxide layer as a solid electrolyte and having a small tan δ. , To provide a solid electrolytic capacitor having excellent withstand voltage.

[0007]

In order to achieve the above object, the present invention is directed to forming a dielectric film by anodizing the surface of an anode base made of a metal having a valve action, and forming a solid film on the dielectric film. In a solid electrolytic capacitor in which a manganese oxide layer or a manganese oxide layer serving as an electrolyte is formed, and a conductor layer is formed thereon to adhere a cathode, in at least the dielectric film of the manganese oxide layer or the manganese oxide layer. It is characterized in that the crystal in the contact portion is a laminated granular material of a plate-like body. Further, the present invention is characterized in that the laminated granular material of the plate-like body has a thick plate shape, a short column shape, and a jar shape. Furthermore, the present invention is characterized in that polyhedral manganese oxide is present in a portion of the manganese oxide layer or manganese oxide layer that is not in direct contact with the dielectric film.

If the crystal of the portion of the manganese oxide layer or the manganese oxide layer in contact with the dielectric film is a plate-shaped laminated granular material, tan δ becomes smaller than that of the polyhedral granular material. In addition, when polyhedral manganese oxide is deposited on a portion of the manganese oxide layer or the manganese oxide layer that is not in direct contact with the dielectric film, the withstand voltage is increased.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments. The solid electrolytic capacitor according to the present invention is the same as the conventional capacitor shown in FIG. 3 in that a manganese oxide layer or a manganese oxide layer is formed as a solid electrolyte on the dielectric film. Another difference is that the laminated granular material of the plate-like body is deposited on the portion of the manganese oxide layer that is in contact with the dielectric film, and the polyhedral granular manganese oxide is deposited on the portion that is not in direct contact with the dielectric film. Other configurations are the same. As the form of the laminated granular material of the plate-like body, the laminated granular and thick plate-shaped manganese oxide of the plate-like body shown in FIG. 1 and the laminated short column shape and the manganese oxide of the plate-like body shown in FIG. There is. 1 and 2 are scanning micrographs of the crystal habit of manganese oxide,
Reference numeral 20 is tantalum, 21 is a dielectric film, 23 is a plate-like laminated granular manganese oxide, 24 is a plate-like laminated short columnar manganese oxide, 25 is a plate-like laminated thick plate-like manganese oxide, and 26 is a plate-like Figure 1 shows the laminated barnacle manganese oxide of the body.

As described above, the laminated granular material of the plate-like material is deposited on the portion of the manganese oxide layer or the manganese oxide layer that is in contact with the dielectric film, and the polyhedral granular material is deposited on the portion that is not in direct contact with the dielectric film. As a result, tan δ was smaller than that of a conventional solid electrolytic capacitor using manganese oxide as a solid electrolyte, and withstand voltage could be improved. The reason why the crystal habits of the precipitated manganese oxides are different is unknown, but it is presumed that it is due to the influence of starting materials, trace additives, impurities, thermal decomposition conditions, and the like.

Hereinafter, the present invention will be described in more detail with reference to examples.

【Example】

Example 1 A tantalum powder as a raw material is compression-molded to a size of 1.9 × 3.4 × 2.8 mm and then fired in a vacuum to produce a porous tantalum pellet. Diameter 0.3φ for pellets
The tantalum wire of mm is embedded in advance. The tantalum pellets are anodized in dilute sulfuric acid. The anodized tantalum pellets are immersed in a manganese nitrate solution, pulled up, and then heated to thermally decompose manganese nitrate to precipitate manganese oxide. Next, colloidal carbon and a conductive silver paste layer are formed on the surface of the tantalum pellet on which the manganese oxide layer has been formed by the dip method. The tantalum wire of the pellet was connected to the anode terminal of the capacitor and the silver paste layer was connected to the cathode terminal, respectively, and then packaged by the resin molding method.
A chip-type solid electrolytic capacitor as shown in is prepared.

Example 2 The anodized pellets obtained in Example 1 were immersed in a high concentration manganese nitrate solution (melting point: 35 ° C) containing 0.3% by weight of nitric acid held at 50 ° C, and then 97%. It heated at 210 degreeC in the humid atmosphere of RH for 20 minutes. After repeating this operation several times, a cathode layer was formed on the surface of the pellet with carbon and silver paste, and a chip type capacitor was prepared by a usual method.

Example 3 The anodized pellets obtained in Example 1 were dipped in a 5% by weight aqueous solution of manganese nitrate having a melting point of 23 ° C and kept at 35 ° C, and then heated to 300 ° C in the atmosphere. Further, a solid electrolyte layer was formed by sequentially repeating the operations of dipping and heating using a 20 to 100 wt% aqueous solution of manganese nitrate. After forming the solid electrolyte layer, a cathode layer was formed on the surface of the pellet with carbon and silver paste, and a chip type capacitor was formed by a usual method.

Example 4 The anodized pellets obtained in Example 1 were immersed in a 30% by weight aqueous solution of manganese nitrate having a melting point of 23 ° C. and kept at 35 ° C., and then heated to 250 ° C. in the atmosphere. After repeating this operation 3 times, the operation of further immersing in a manganese nitrate solution having a melting point of 23 ° C. and heating to 250 ° C. was repeated twice. Finally, it was immersed in a high-concentration manganese nitrate solution (melting point: 35 ° C) containing 1% by weight of nitric acid and 0.7% by weight of ammonia, and then heated at 200 ° C in a humidified atmosphere to form a solid electrolyte layer. After that, a cathode layer was formed on the surface of the pellet with carbon and silver paste, and a chip type capacitor was obtained by a commonly used ordinary method.

Example 5 The anodized pellets obtained in Example 1 were dipped in a 20% by weight aqueous solution of manganese nitrate having a melting point of 23 ° C and kept at 35 ° C, and then heated to 270 ° C in the atmosphere. Further, the operation of successively immersing in a 40 to 80% by weight aqueous solution of manganese nitrate and heating was repeated 3 times, 13 times in total, to form a solid electrolyte layer. After that, a cathode layer was formed on the surface of the pellet with carbon and silver paste, and a chip type capacitor was formed by a usual method.

Example 6 The characteristics of the chip type solid electrolytic capacitors obtained in Examples 2 to 5 were evaluated under the same conditions. The withstand voltage was evaluated by a short circuit occurrence rate when 1000 V was applied with 20 V applied at 85 ° C. for 30 seconds and discharge for 5 minutes 30 seconds as one cycle. In particular, Table 1 shows a significant difference. Examples 3 and 4 are preferable because they have improved electrical characteristics. Example 2 is not practical because no improvement in characteristics is observed.

[0017]

[Table 1]

[0018]

As described above, in the solid electrolytic capacitor according to the present invention, the surface of the anode substrate made of a metal having a valve action is anodized to form a dielectric film, and the solid electrolyte is formed on the dielectric film. In a solid electrolytic capacitor in which a manganese oxide layer or a manganese oxide layer is formed, and a conductor layer is formed on the manganese oxide layer to adhere a cathode, the manganese oxide layer or the manganese oxide layer is in contact with at least the dielectric film. Since part of the crystal is a laminated granular material having a plate-like body, the dielectric loss tangent can be reduced. Further, according to the present invention, since polyhedral granular manganese oxide exists in a portion of the manganese oxide layer or the manganese oxide layer which is not in direct contact with the dielectric film, the withstand voltage property can be improved. Further, the manganese oxide layer or manganese oxide having these various crystal habits is obtained by a thermal decomposition method of a manganese nitrate solution,
It can be controlled by the additive, the thermal decomposition atmosphere condition, the heating condition and the like.

[Brief description of drawings]

FIG. 1 is a scanning micrograph showing the crystal habit of manganese oxide in the present invention.

FIG. 2 is a scanning micrograph showing the crystal habit of manganese oxide in the present invention.

FIG. 3 is a sectional view of a conventional solid electrolytic capacitor.

FIG. 4 is a scanning micrograph of the crystal habit of manganese oxide in a conventional solid electrolytic capacitor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Solid electrolytic capacitor, 2 ... Anode base, 3 ... Anode lead wire, 4 ... Dielectric film, 5 ... Manganese oxide layer, 6 ... Conductor layer, 7, 8 ... Lead frame, 9 ... Conductive paste, 1
0 ... Epoxy resin.

Claims (3)

[Claims] 1. A surface of an anode substrate made of a metal having a valve action is anodized to form a dielectric film, and a manganese oxide layer or a manganese oxide layer serving as a solid electrolyte is formed on the dielectric film. In a solid electrolytic capacitor in which a conductor layer is formed thereon and a cathode is adhered thereto, crystals of at least a portion of the manganese oxide layer or the manganese oxide layer in contact with the dielectric film become a laminated granular material of a plate-like body. The solid electrolytic capacitor characterized in that 2. The solid electrolytic capacitor according to claim 1, wherein the laminated granular material in the form of a plate has a shape of a thick plate, a shape of a short column, or a shape of a pot. 3. The solid electrolytic capacitor according to claim 1, wherein polyhedral manganese oxide is present in a portion of the manganese oxide layer or the manganese oxide layer which is not in direct contact with the dielectric film. Capacitors.