JPS6142406B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a solid electrolytic capacitor with excellent moisture resistance and almost no migration of Ag. At present, solid electrolytic capacitors are Ta, Al, etc. equipped with an anode lead wire or an anode lead part 2 as shown in Figure 2.
A dielectric oxide film 3 is formed on the surface of an electrode body 1 made of a valve metal such as, an electrolyte layer 4 such as manganese dioxide is formed thereon, and a colloidal carbon layer 5 and a silver paint layer 7 are further formed. An external lead wire 10 is connected to the anode lead wire by welding, and an external lead wire 9 is connected to the silver paint layer of the cathode by soldering 8, and these are sheathed with resin 11 to produce a solid electrolytic capacitor. The silver paint used as the cathode layer of this capacitor is widely used because it has excellent conductivity, excellent solderability, and can be easily made into a paint. However, such silver is easily oxidized and reduced, and easily turns into ions, so it is particularly susceptible to so-called silver migration in high humidity environments, which causes deterioration of solid electrolytic capacitors. There is. In the conventional solid electrolytic capacitor shown in FIG. 2, a colloidal carbon layer 5 is also formed on the electrolyte 4.
Colloidal carbon has the role of penetrating into the inside of manganese dioxide, which is a porous electrolyte with fine irregularities, and drawing out the capacitance from inside. Colloidal carbon has excellent adhesion to various substances, and using this property, manganese dioxide can be In fact, it acts to reduce the contact resistance between the silver paint layer 7 of the cathode and the cathode silver paint layer 7 laminated thereon. On the contrary, a colloidal carbon solution works in this way, and this colloidal carbon layer 5 is required to reduce the tan δ of the capacitor. However, this colloidal carbon is a water-soluble or organic solvent-based colloidal solution, and although it has excellent adhesion to various substances, it is not a so-called paint, so it is difficult to form a thick film or layer, and the adhesive strength is poor. is so weak that it easily peels off even if it is applied thickly. If it is deposited too thick, stress such as heat or physical stress will cause cracks, resulting in an increase in contact resistance.
Therefore, it is necessary to form a thin film of approximately 50 μm or less. The present invention eliminates the drawbacks of the prior art, uses very little or no conductive silver paint, and
Tanδ increases slightly, but by making Ag migration difficult or eliminating, it improves failures at high temperatures and high humidity, significantly improves moisture resistance, and is a reliable and inexpensive solid electrolyte. The purpose is to obtain a capacitor. The present invention uses fine carbon black with high electrical conductivity as the main component, uses acrylic resin as a binder, and carbon is mixed with methyl isobutyl ketone (MIBK) dissolved in acrylic resin. The purpose of this method is to use a conductive paint of the same type as the cathode layer. However, instead of carbon black, graphite powder, graphite powder, acetylene black or a mixture of these powders is used. As a binder, a thermoplastic resin such as a vinyl resin or an alcohol resin may be used instead of an acrylic resin, and an organic solvent such as methyl ethyl ketone, xylene, or toluene may be used instead of methyl isobutyl ketone (MIBK). Further, thermosetting resins such as phenolic resins and epoxy resins can be used as binders, and butyl carbitol, butyl carbitol acetate, alcohol, etc. can also be used as organic solvents. Hereinafter, carbon black will be abbreviated as carbon. The electrical conductivity of the conductive paint of the present invention is 3 to 50 times worse than that of a conductive paint whose main component is Ag, but this disadvantage can be considerably covered by making the paint film thicker. . In addition, since this paint uses acrylic resin as a binder, the paint film can be made as thick as desired, and the binding strength between various substances and especially the electrolyte, manganese dioxide, is strong, and the strength of the paint film itself is also strong. The paint film itself will not crack due to severe physical stress such as heat stress. (Like a colloidal carbon solution.) However, since the paint has a relatively high viscosity, it is difficult to fully penetrate the fine uneven pores of MnO ₂ , which is a porous electrolyte. However, the electrical conductivity of the coating film itself can be improved by increasing the coating thickness to 250μ or more.
It turned out that it was possible to obtain something quite close to that of Ag paint. Of course, there are various kinds of paints whose main components are fine carbon and acrylic resin, and they have various electrical conductivities. However, there is a limit to how thick a coating film can be made with the conductive paint that is mainly composed of carbon and acrylic resin used for this purpose, so it must have an electrical resistance value of 25Ω/pq/mil or less. Can be used as the cathode layer of solid electrolytic capacitors
The tan δ increases greatly, making it impossible to use. As mentioned above, even when the paint of the present invention is applied, it does not penetrate into the fine pores of the porous MnO ₂ that has irregularities, so the contact resistance with the manganese dioxide layer becomes large, and the tan δ of the capacitor is also relatively large. value. In order to further improve this, in order to improve the penetration of MnO ₂ into the micropores and adhesion to the MnO ₂ surface, thin colloidal After the carbon layer is formed, a solid electrolytic capacitor that can be put to practical use can be manufactured by forming the carbon-based paint layer of the present invention to a thickness of 250 μm or more. There are various electrical resistances of commonly used silver conductive paints, but the electrical resistance values range from 4Ω/sq/mil to 0.05Ω/sq.
/mil is common. Therefore, for example, when using a silver conductive paint of 4Ω/sq/mil and when using a carbon-based conductive paint, it is important to know what electrical resistance value and how thick the coating film should be formed. A theoretical estimate of the equivalent electrical resistance is, for example, 20Ω/sq.
/mil carbon-based conductive paint,
It can be seen that almost the same electrical resistance value can be obtained by forming a coating film five times as thick as the silver conductive paint. In other words, if the silver conductive paint is applied to a thickness of 50μ, the carbon-based conductive paint will need to be applied to a thickness of 250μ. Table 1 shows examples of actual experiments conducted using solid electrolytic capacitors.

[Table] Electrical resistance is 1Ω/sq/mil for silver conductive paint.
Prepare graphite-based conductive paint with an electrical resistance of 10Ω/sq/mil, and use 16V10
After forming a colloidal carbon layer using μF tantalum solid electrolytic capacitor elements, A (conventional type) was coated with the above-mentioned Ag paint to a thickness of approximately 50μ, and B (invention) was coated with the above-mentioned Ag paint. The carbon-based conductive paint layer was applied with various thicknesses, the leads were connected, and the tan δ value at 120 Hz was measured. However, in the case of the present invention, Ag paint was applied spot-on only to the parts to be soldered, and the lead wires were connected with solder. As can be seen in Table 1, although it does not follow the theoretical value, it shows a tendency that corresponds to the theoretical thickness, and by ensuring a certain thickness or more, it is sufficient to use it as the cathode layer of a solid electrolytic capacitor. I can do it. A configuration diagram of the present invention is shown in a sectional view in FIG. In the figure, the same reference numerals as in FIG. 1 indicate the same parts. In the figure, numeral 17 indicates a carbon coating layer of 250 μm or more, and numeral 18 indicates an Ag coating layer. Ag
In this case, the paint is used for the purpose of imparting solderability.
This is an example in which the Ag paint is applied to the area, and as the amount of Ag paint used is reduced, costs can be reduced. Furthermore, since the Ag paint layer 18 is formed on the thick layer of the carbon paint layer 17, the distance to the dielectric surface is longer, and since it is a paint, the coating film is dense, so migration is reduced. Since it has the effect of hindering the progress, it is possible to improve the moisture resistance of the capacitor. In order to completely eliminate silver migration, a slight increase in δ is required. But the third
It is also possible to avoid using Ag paint at all by adhering the cathode lead with a layer 17 of carbon paint as shown. in this case
The properties of tan δ are sufficiently commercially valuable for applications requiring reliability (particularly moisture resistance) even if some sacrifice is made. So far, we have talked about conductive substances that have carbon as their main component, but on the other hand, in response to the desire to reduce costs without sacrificing tan δ too much, it is possible to mix silver powder into carbon. As the amount of silver powder increases, the electrical conductivity is improved;
As a result, the cost of the paint increases, so the price limit for mixing Ag powder with respect to the weight of carbon is approximately 20 Wt%. The term carbon is used in various ways depending on its manufacturing method or crystal structure. For example, graphite, carbon black,
Acetylene black, graphite powder, etc. However, their element symbols are exactly the same, C (carbon), and both have electrical conductivity. This time, we mainly investigated carbon paint, but we have confirmed that almost the same characteristics can be obtained using graphite powder. It is also within the scope of the present invention to mix these powders in order to improve various properties. Next, Table 2 shows the moisture resistance test results of the solid electrolytic capacitor constructed according to the present invention.

[Table] Upper row: Number of short circuit failures (cumulative) Lower row: tanδ (%)
Average value for non-defective products A colloidal carbon layer of a tantalum solid electrolytic capacitor manufactured using a conventional method.
A 16V10μF element coated with Ag paint to a thickness of approximately 50μ over the entire surface, and a conventional method using a conductive paint made of highly conductive carbon fine powder and acrylic resin as shown in the structure of the present invention (Figure 1). Approximately
It was painted to a thickness of 300μ, and Ag paint was applied to only one part of the bottom to enable soldering.The anode lead and cathode lead were connected to each, and the exterior was covered with a resin dip. In addition, we also made a prototype with a configuration that does not use any silver paint, as shown in Figure 3, and conducted a no-load test at 55°C and 95% RH. As a result, it can be seen that short-circuit failures are greatly improved in the structure of the present invention. As described above, the present invention provides a solid electrolytic capacitor constructed using carbon-based conductive paint that (1) improves moisture resistance, (2) reduces short-circuit failures, and (3) suppresses the Ag migration phenomenon. (4) It can be manufactured at low cost.

[Brief explanation of the drawing]

FIG. 1 shows a sectional view of a solid electrolytic capacitor according to the present invention, FIG. 2 shows a sectional view of a conventional solid electrolytic capacitor, and FIG. 3 shows a sectional view of another embodiment of the present invention. 1: Electrode body, 2: Anode lead-out portion, 3: Dielectric oxide film, 4: Electrolyte layer, 5: Colloidal carbon layer, 9, 10: External lead wire, 17: Graphite paint layer, 18: Ag paint layer.

Claims (1)

[Claims] 1. A dielectric oxide film is formed on an electrode body made of a valve metal such as Ta or Al, which has an anode lead-out portion, and an electrolyte layer such as manganese dioxide is formed on the surface of the electrode body. In a solid electrolytic capacitor in which a cathode layer or the like is laminated thereon, terminals are connected, and the cathode layer is formed on the electrolyte layer directly or via a colloidal carbon layer, the cathode layer is A solid electrolytic capacitor constructed by using an organic polymer as a binder and forming an organic solvent-based highly electrically conductive carbon paint with a resistance value of 25 Ω/sq/mil or less to a thickness of 250 μm or more. 2. Organic solvent type carbon paint with high electrical conductivity is mainly composed of graphite powder, graphite powder, carbon black, acetylene black, or a mixture of these powders, and is mixed with acrylic resin, vinyl resin, or alcohol resin. 2. A solid electrolytic capacitor according to claim 1, which comprises a thermoplastic resin such as, for example, and an appropriate amount of an organic solvent, such as methyl ethyl ketone, xylene, toluene, or methyl isobutyl ketone. 3 Organic solvent type carbon paint with high electrical conductivity has graphite powder, craftite powder, carbon black, acetylene black, or a mixture thereof as its main components, and a thermosetting resin such as phenolic resin or epoxy resin. 2. The solid electrolytic capacitor according to claim 1, further comprising an appropriate amount of an organic solvent such as butyl carbitol, butyl carbitol acetate alcohol, or methyl isobutyl ketone.