JPS6134250B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of manufacturing a solid electrolytic capacitor. Conventionally, in the field of solid electrolytic capacitors, valve metal powder, particularly tantalum powder, has been pressure-formed into a cylindrical or square shape, and vacuum sintered at a temperature of around 2000°C, and used as an anode body. This type of solid electrolytic capacitor has a porous anode body and a large specific surface area.
Furthermore, since tantalum oxide has a high dielectric constant, a large capacity per unit volume can be obtained, and the capacitance range extends from 0.1 μF to 1000 μF. In addition, because a solid electrolyte is used and the tantalum oxide film is extremely stable chemically, thermally, and electrically, various characteristics such as capacity, temperature characteristics, frequency characteristics, tanδ, leakage current, etc. , much better than other aluminum electrolytic capacitors and porcelain capacitors. On the other hand, as electronic circuits have become smaller in recent years, there has been a demand for smaller passive components. Particularly in the case of capacitive elements, there is a desire for small-sized components with large capacitance. Currently, there are multilayer ceramic capacitors, planar printed thick film capacitors, vapor deposited or sputtered thin film capacitors, etc. that meet these demands. However, these capacitors, especially multilayer ceramic capacitors, require printing and sintering dielectric paste and electrode paste many times, resulting in a very complicated manufacturing process. Further, due to the structure of such electrodes, there is a limit to the maximum capacitance value, and furthermore, since noble metal paste such as Pt or Pd is used for the electrodes, the price becomes high. In addition, there are problems in terms of performance, such as temperature characteristics, and they do not satisfy the requirement that small circuit elements must be resistant to heat during soldering. Further, similar problems exist with thick film capacitors, and there are still points to be improved. Various tantalum thin film capacitors have also been developed and commercialized by sputtering, electron beam evaporation, etc., but because thin film tantalum is used, the capacitance per unit area is small, usually 100 μm.
Only F grade can be obtained. Although this capacitance is suitable for thin film electronic circuits, it is somewhat low when used for external electronic circuits of ICs. Moreover,
This thin film capacitor still belongs to the field of special electronic circuits, and there are still various problems with its characteristics. In addition, in solid electrolytic capacitors used in small circuits, electrodes can be bonded directly to the circuit board.
It is important to use a so-called leadless face bonding type in terms of volumetric efficiency. Moreover, this reduces the contact resistance, which is also required from the viewpoint of the frequency characteristics and impedance characteristics of the capacitor. In order to meet these requirements, several ultra-small solid electrolytic capacitors using tantalum sintered bodies as anode bodies have been developed and are commercially available. For example, as shown in Fig. 1, the anode terminal 3 is connected to the anode lead wire 2 of a conventional sintered capacitor 1 to form a face bonding type capacitor, or as shown in Fig. 2 a and b. There is also a face bonding type using metal caps 4 and 5 for the positive and negative terminals. However, the solid electrolytic capacitor shown in Figure 1 is simply a modification of the conventional sintered capacitor, not only is it disadvantageous in terms of volumetric efficiency and frequency characteristics, but also in terms of electrode configuration, and is ultra-small. It has only a temporary meaning of transition to capacitors. In addition, the solid electrolytic capacitor shown in Figure 2 is
Since it is composed of the metal caps 4 and 5 of both electrodes, it has very good volumetric efficiency of capacitance, and the electrode shape is close to the ideal state of the face bonding type mentioned above, and has excellent capacitance, tanδ frequency characteristics, and impedance characteristics. However, it is extremely difficult to cover both ends of the small sintered capacitor 1 with the metal caps 4 and 5 and to weld the metal cap 4 and the anode lead wire 2 together. , the price will be higher. Next, we will discuss the costs involved in manufacturing a solid electrolytic capacitor using a tantalum sintered body as an anode. As mentioned above, solid electrolytic capacitors that use tantalum sintered bodies as anodes have a very wide capacity range.
It ranges from 0.1μF to 1000μF. For capacitors from 1 μF to 1000 μF within this capacitance range, the size of anodization is large, and molding press processing, sintering, chemical conversion, manganese dioxide (MnO ₂ ) adhesion, cutting of lead wires, spot welding, housing, etc. It is also relatively easy to work with. However, when the capacitance becomes less than 1 μF, the size of the anode body also decreases to 1 mm.
It is very difficult to mold such a small anode body into various shapes, pass lead wires through it, spot weld it at the time of housing, and cover it with metal caps 4 and 5 to form the anode. involves complicated work and increases the price. Here, the relationship between the capacitance of a capacitor and manufacturing costs such as material costs and labor costs is illustrated in FIG. 3. As is clear from Figure 3, for capacitors with a capacitance of 1 μF or more, the manufacturing cost increases by the increase in material costs, but for capacitances of 1 μF or less, although the material costs are minimal, the manufacturing cost increases as mentioned above. For this reason, work costs have increased, and as a result, manufacturing costs have increased. That is, the manufacturing cost is minimal when the capacitance is around 1 μF. The present invention is a method for manufacturing a small, large-capacity face-bonded solid electrolytic capacitor that can reduce manufacturing costs for solid electrolytic capacitors with a capacitance of 1 μF or less, has high capacitance/volume efficiency, and has easy terminal removal. It provides: Hereinafter, conventional examples related to the present invention will be described, and then the content of the present invention will be specifically explained. This is a completely new solid electrolytic capacitor that replaces the solid electrolytic capacitor that uses a tantalum sintered body as an anode as described above. There has been interest in various fields regarding the use of an anode body constructed by forming a film. However, all of these methods lacked specificity and were still in an immature state as technology. The present invention embodies a technology for forming an anode body by welding tantalum powder to an aluminum substrate by thermal spraying to form a tantalum layer. is used. First, the manufacturing process of the solid electrolytic capacitor according to the present invention will be explained step by step. (1) The surface of the aluminum substrate is roughened using a suitable abrasive such as silicon carbide or aluminum oxide. Aluminum oxide, silicon carbide, etc. are suitable as the abrasive material for surface roughening, but in the case of an aluminum substrate, which will be described later, aluminum oxide is preferable from the standpoint of preventing contamination with impurities. (2) After roughening the surface of the valve metal substrate, wash it.
Thereafter, tantalum powder is sprayed onto the surface of the aluminum substrate by plasma spraying, flame spraying, etc. to form a tantalum layer. At this time, the tantalum powder used for thermal spraying has a particle size of 325 mesh to 30 mesh.
Use items within the mesh range. Furthermore, if tantalum powder having a particle size within the range of 100 mesh to 30 mesh is used, a good tantalum layer can be formed on the aluminum substrate.
More preferably, thermally sprayed tantalum powder having a substantially uniform particle size within ±30 mesh may be used. (3) The tantalum layer formed on the aluminum substrate is anodized using a suitable chemical solution, and the anodic oxide film is heat treated. This anodic oxidation and heat treatment operation is repeated several times. (4) Thereafter, a semiconductor oxide layer such as manganese dioxide is formed on the tantalum oxide film by thermal decomposition of a thermally decomposable metal salt such as manganese nitrate. (5) After that, a cathode layer made of colloidal carbon, silver paint, etc. and a solder layer are sequentially laminated on the semiconductor oxide layer. The solid electrolytic capacitor of the present invention is constructed through such a manufacturing process. Next, the particle size of tantalum powder will be explained in detail. FIG. 4 is a characteristic diagram showing the relationship between the particle size and wet capacity of thermally sprayed tantalum powder. Note that the number of times of thermal spraying is the same regardless of the particle size. Figure 5 is a characteristic diagram showing the relationship between the film thickness and wet capacity of a tantalum layer sprayed onto an aluminum substrate.
In the case of thermal spraying using SGVR-4 (trade name) manufactured by Norton, B shows the case of thermal spraying using tantalum powder with a particle size within the range of 100 mesh to 40 mesh. In addition, SGVR- manufactured by Norton in the United States
4 (trade name) is a mixed product with a particle size of 500 mesh to 40 mesh. As is clear from Figure 4, the capacity value becomes minimum when the particle size is between 200 mesh and 300 mesh.
In particular, the capacity value rises significantly in the case of 100 mesh, which has a large particle size. Regarding appearance, particle size
The surfaces of those sprayed with tantalum powder of 100 mesh or more were the most uneven, while those of 325 mesh to 400 mesh were very flat, similar to those obtained by thermal spraying. In addition, the adhesion strength of large particles to the underlying substrate is very strong, while those of fine particles (325 mesh to 400 mesh) have a tantalum layer that peels off during chemical formation and do not adhere very strongly. Ta. Furthermore, small particles with a particle size of 400 mesh or less were too fine and fluffy, so thermal spraying was almost impossible. Furthermore, as is clear from Figure 5, when using tantalum powder with a uniform particle size within the range of 100 mesh to 40 mesh, compared to using tantalum powder with a mixture of various particle sizes, , the humidity capacity has increased by about 30-40%. Regarding the ease of thermal spraying, when tantalum powder with different particle sizes in the range of 500 mesh to 40 mesh is mixed,
The tantalum powder often flies out from the spray gun muzzle in the form of lumps of non-uniform size, and as a result, the sprayed film obtained also has non-uniform irregularities, making it very difficult to operate. In solid electrolytic capacitors using conventional sintered anodes, the finer the tantalum powder particle size, the larger the capacity per unit volume. In the case of structuring, the tendency is slightly different as mentioned above. This will be explained. First, regarding the difference in capacity due to the difference in particle size, in the case of a sintered anode, the sintering operation is
The process is carried out at a temperature of around 2000℃ and in a high vacuum of 10 ^-6 Torr. The melting point of tantalum is 2996°C, and at this temperature tantalum is still a solid, and only a solid-solid reaction occurs in which tantalum atoms move between particles. In other words, the area ratio predicted from the powder state can be directly applied to the sintered body, and as a result, the capacity per unit volume is higher when tantalum powder with fine particle size is used, which has more particles per unit volume. becomes larger. On the other hand, in the case of thermal spray coatings, tantalum powder is melted at a high temperature, reaches the substrate in that state, cools, and gradually accumulates. As a result, unlike in the case of conventional sintering molds, once the fine-grained powder is melted, the surface of the fine powder is not necessarily fully utilized when it is cooled and deposited on the substrate. There is no guarantee that the film will be formed. In this respect, tantalum powder with a large particle size of 325 mesh or more allows the surface area of the powder to be utilized even after melting and cooling, resulting in a large capacity per unit area. This is supported by the fact that powders smaller than 400 mesh cannot be thermally sprayed. This tendency is considered to be particularly strong when the powder used is a primary fine particle agglomeration type powder such as SGVR-4 (trade name) manufactured by Norton, Inc. in the United States. In addition, SGVR-4 manufactured by Norton in the United States
(Product name) Primary fine particle agglomerated powder is one in which 4μ primary particles are aggregated to various particle sizes.
The particle size referred to in this text refers to the particle size of secondary particles. Figure 6 shows a cross section of the sprayed film when mixed powder 6 containing particles of various particle sizes is sprayed onto a substrate 7, and Figure 7 shows a cross-section of a sprayed film obtained by spraying mixed powder 6 containing particles of various particle sizes onto a substrate 7. 3 shows a cross section of a thermally sprayed film when a material) is thermally sprayed onto a substrate 7. In the case where the mixed powder 6 shown in FIG. 6 is used, the resulting thermal spray film, that is, the tantalum layer, is also a mixture of large and small particles, with the small particles acting as a link between the large particles. On the other hand, in the case of using the classified powder 8 shown in FIG. 7, particles of the same particle size are arranged in an orderly manner on the substrate 7, and the packing density per unit volume is extremely high. Regarding the appearance, the sprayed surface of the one shown in FIG. 6 is very non-uniform, whereas the one shown in FIG. 7 has a uniform sprayed surface although it has irregularities. The difference in capacity per unit volume and appearance due to the difference in particle size of thermally sprayed tantalum powder is further magnified when it is solidified into a finished product. This will be discussed below. Regarding the solidification method, a tantalum oxide film is formed on the surface of the tantalum layer by anodic oxidation, manganese dioxide is formed on this by thermal decomposition of manganese nitrate, and then colloidal carbon, silver paint, etc. The solder was layered one after another and solidified. FIGS. 8 and 9 respectively show the relationship between the capacity and tan δ with respect to the particle size of tantalum powder when it is solidified. As is clear from FIGS. 8 and 9, both the capacity and tan δ become minimum when the particle size is between 200 mesh and 300 mesh, similar to the wet characteristics. Table 1 also shows the tan δ of various tantalum powders upon solidification. Rating is 10V, 12μF
It is. The powders used are the aforementioned SGVR-4 (trade name) manufactured by Norton in the United States and Metco in the United States.
These are powders with a particle size of 100 mesh or more, which are obtained by classifying Metco62 (trade name) and SGVR-4 (trade name).

[Example 1]

A 10 mm x 25 mm surface of a capacitor-grade 0.3 mm thick aluminum plate (99.99% purity) is roughened with silicon carbide or aluminum oxide, and then ultrasonically cleaned with trichlene, acetone, and distilled water. Then 10%
The aluminum plate was degreased and cleaned in NaOH solution. Then wash away the alkali with pure water. Next, 100 to 40 meshes of tantalum powder obtained by classifying tantalum powder SGVR-4 (trade name) manufactured by Norton Co., Ltd. in the United States are used in a plasma spraying device (e.g., Plasmatron (trade name) manufactured by Plasmadyne Corporation in the United States). Plasma spraying onto aluminum plate using After 50 times of thermal spraying, the surface of the tantalum sprayed film is again ultrasonically cleaned using trichloride, acetone, and distilled water to remove all unmelted and unattached tantalum powder and other impurities. In this way, an aluminum plate with a thermally sprayed tantalum layer on the surface is formed, and a 0.1M/1L film at a temperature of 90°C is placed on top of this.
A 50V tantalum oxide anodic oxide film is generated by applying a DC current of 10mA in a sodium borate chemical solution. Next, this aluminum plate was kept at 300° C. for 30 minutes, washed with water, and then anodized again under the above conditions. This operation (chemical formation→heat treatment) is repeated 3 to 5 times. Next, manganese dioxide is produced on the tantalum oxide film by thermal decomposition of manganese nitrate having a specific gravity of 1.3. Finally, colloidal carbon, silver paint, and solder are sequentially laminated to form a finished product, and the solidification performance is measured. Table 2 shows the characteristics of the capacitor constructed in this manner (rated at 10V, 12μF). Additionally, the results obtained when operations such as thermal spraying in an inert gas atmosphere and purification of the thermally sprayed tantalum layer by chemical etching are also included.

[Example 2]

A 10 mm x 25 mm surface of a capacitor-grade 0.3 mm thick aluminum plate (99.99% purity) is roughened with silicon carbide or aluminum oxide, and then ultrasonically cleaned with trichlene, acetone, and distilled water. Then 10%
The aluminum plate was degreased and cleaned in NaOH solution. Then wash away the alkali with pure water. Next, 100 meshes to 40 meshes of tantalum powder obtained by classifying SGVR-4 (trade name) tantalum powder manufactured by Norton Co., Ltd. in the United States are used to use a plasma spraying device (e.g., Plasmatron (trade name) manufactured by Plasmadyne Corporation in the United States). Plasma spraying onto aluminum plate using The number of thermal spraying was 50 times. After that,
The surface of the tantalum sprayed film is again ultrasonically cleaned using trichlene, acetone, and distilled water to remove all unmelted and unattached tantalum powder and other impurities.
In this way, an aluminum plate with a sprayed tantalum layer on the surface is formed, and on top of this an aluminum plate is heated at a temperature of 90°C.
Direct current in chemical solution of 0.1M/l boric acid leader
First, a chemical conversion film is formed in 2 hours by applying a current of 10mA. Next, the aluminum plate was kept at 300° C. for 30 minutes, washed with water, and then anodized again under the above conditions. This operation (chemical formation → heat treatment)
This is repeated 3 to 5 times, and then manganese dioxide is produced on the tantalum oxide film by thermal decomposition of manganese nitrate having a specific gravity of 1.3. Finally, colloidal carbon, silver paint, and solder are sequentially laminated to form a finished product, and the solidification performance is measured. Table 3 shows the capacitor configured in this way (rated 10V 12μF)
shows the characteristics of

[Table] As is clear from Table 3, when heat treatment is applied during chemical formation, the frequency characteristics of tanδ, LC, and capacity decrease.
This is greatly improved compared to the case without heat treatment. Finally, we will summarize the important conditions and their effects mentioned in the above explanation. (1) The particle size of tantalum powder for thermal spraying should be from 325 mesh in terms of thermal spraying workability and tantalum layer formation.
A range of 30 meshes is appropriate, and from the viewpoint of capacitor capacity, a range of 100 meshes to 30 meshes is appropriate. (2) The particle size of tantalum powder should be uniform;
It is best to have a uniformity within ±30 meters. (3) After spraying tantalum on the substrate, it is possible to improve the adhesion between the substrate and the tantalum layer by sintering it for 20 minutes in a vacuum of 10 ^-5 Torr at a temperature of 1600°C or higher. , purification of the sprayed tantalum layer can also be achieved. (4) By etching the surface of the sprayed tantalum layer in an etching solution such as HF or NH ₄ F,
Impurities and oxides on the surface of the sprayed tantalum layer and in the tantalum layer can be removed, and a clean tantalum layer can be exposed. (5) When thermal spraying of tantalum powder is carried out in an inert gas, the surface of the generated tantalum sprayed layer is not oxidized by atmospheric oxygen, which prevents the generation of tantalum oxide generated by thermal oxidation. Various characteristics improve. (6) Aluminum or its alloys are suitable as a substrate for thermal spraying from various viewpoints. (7) When using an aluminum substrate, a chemical solution capable of producing barrier-type aluminum oxide, such as sodium borate, ammonium borate, boric acid, or ammonium phosphate, is desirable. (8) In the case of (7), the leakage current LC is drastically reduced by including an appropriate heat treatment step for the oxide film during chemical formation. Further, the optimum heat treatment temperature is 200 to 300°C. (9) When aluminum or its alloys are used for the substrate, aluminum oxide abrasives are the most suitable material for roughening the substrate, and are less likely to be contaminated with impurities. As described above, according to the present invention, it is possible to make an ultra-small leadless capacitor without using a conventional sintered anode body, and the conventional complicated high-temperature vacuum sintering operation and molding press process can be made. etc. become unnecessary.
In addition, since the substrate is flat and the capacitor itself is also flat, it is easy to attach positive and negative electrodes without leads, making it suitable for face bonding, and is extremely efficient in terms of volumetric efficiency. It is a structure. This naturally suggests that manufacturing costs are low. Furthermore, regarding the various features mentioned in the description of the present invention, such as powder particle size and aluminum substrate,
It has the following advantages when compared with conventional sprayed film capacitors. (1) Because the particle size is uniform, thermal spraying operations are easy;
The sprayed layer is uniform. (2) A clean coating surface can be obtained by thermal spraying in an inert gas. (3) When an aluminum substrate is used, the material cost is extremely low and the price can be reduced. (4) When an aluminum substrate is used, the adhesive strength with the tantalum layer is strong. (5) Due to the effect of (4), a chemical conversion film can be formed smoothly. (6) Since aluminum is easy to process, workability can be improved. (7) Since the material is lightweight, the capacitor itself should also be lightweight. In this way, it is possible to provide an extremely excellent method for manufacturing solid electrolytic capacitors.

[Brief explanation of the drawing]

Figure 1 is an external perspective view of a solid electrolytic capacitor using a conventional sintered anode body, Figure 2 a is an external perspective view of a solid electrolytic capacitor using a conventional sintered anode body, and Figure 2 b is an external perspective view of a solid electrolytic capacitor using a conventional sintered anode body. The cross-sectional view and Figure 3 are diagrams showing the relationship between the rated capacity and manufacturing cost of solid electrolytic capacitors,
Figure 4 is a characteristic diagram showing the relationship between the particle size and wet capacity of thermally sprayed tantalum powder, Figure 5 is a characteristic diagram showing the relationship between sprayed tantalum film thickness and wet capacity, and Figure 6 is a characteristic diagram showing the relationship between thermally sprayed tantalum film thickness and wet capacity. Figure 7 is a schematic cross-sectional view of a tantalum layer when a mixture of tantalum powder is sprayed, and Figure 8 is a schematic cross-sectional view of a tantalum layer when a mixture of tantalum powder with a uniform particle size is sprayed. Figure 9 is a characteristic diagram showing the relationship between the particle size of sprayed tantalum powder and the solidification capacity of the solid electrolytic capacitor. Figures range from 100 meshes to 40
Figure 11 shows the capacity reduction rate versus frequency when mesh tantalum powder is used and when a mixture of tantalum powder of various particle sizes from 500 mesh to 40 mesh is used. Figure 12 is a characteristic diagram showing the changes in voltage and leakage current with respect to the formation time for a material that has undergone chemical etching treatment after thermal spraying, and a material that has been thermally sprayed in an inert gas. An electron micrograph showing the cross section of the aluminum substrate and the tantalum powder when the tantalum powder was thermally sprayed, Fig. 13 is a characteristic diagram showing the change in voltage and leakage current with respect to the formation time of the tantalum substrate and the aluminum substrate, Fig. 1
Figure 4 is a characteristic diagram showing changes in voltage and leakage current with respect to formation time using a chemical conversion liquid during formation of a tantalum layer formed by thermal spraying on an aluminum substrate, and Figure 15 is a characteristic diagram showing changes in voltage and leakage current as a function of formation time using a chemical conversion liquid during formation of a tantalum layer formed by thermal spraying on an aluminum substrate. Figure 16 is a characteristic diagram showing changes in wet capacity; Figure 16 is a characteristic diagram showing changes in voltage and leakage current with respect to formation time when a tantalum layer formed on an aluminum substrate is subjected to heat treatment during formation;
The figure is a characteristic diagram showing the change in humid capacity and humid tan δ with respect to the heat treatment temperature of the heat treatment performed during the formation of the tantalum layer formed on the aluminum substrate. FIG. 19 is a characteristic diagram showing changes in leakage current with respect to heat treatment temperature in heat treatment; FIG. 19 is an external perspective view of a solid electrolytic capacitor according to an embodiment of the present invention;
FIG. 0 is a sectional view showing the internal structure of the capacitor, and FIG. 21 is a schematic diagram of the existing configuration of the inert gas atmosphere thermal spraying apparatus. 21...Valve metal substrate, 22...Tantalum layer, 2
3... Semiconductor oxide layer, 24... Cathode layer, 25
...Solder layer.

Claims (1)

[Claims] 1. A tantalum layer is formed by spraying tantalum powder with a particle size within the range of 100 mesh to 30 mesh on an aluminum substrate, and a tantalum oxide film is formed on the surface of this tantalum layer by a chemical conversion operation and this chemical conversion. A tantalum oxide film is formed by repeatedly performing the heat treatment operations, and then a semiconducting oxide layer is formed on the tantalum oxide film by thermally decomposing the thermally decomposable metal salt, and the semiconductor 1. A method for manufacturing a solid electrolytic capacitor, comprising: forming a semiconductor oxide layer; and sequentially laminating a cathode and a solder layer on the semiconductor oxide layer.