JP2008010684A - Solid electrolytic capacitor, and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a niobium solid electrolytic capacitor in which a leakage current and an ESR are small. <P>SOLUTION: In this solid electrolytic capacitor, a capacitor element 10 is embedded inside an exterior body 1 of a rectangular parallelepiped shape consisting of a resin composition containing epoxy resin or the like. The capacitor element 10 is equipped with: an anode 11, a niobium oxide layer 12 formed on the anode 11, and a cathode 13 formed on the niobium oxide layer 12. On an anode lead 11a, one end of an anode terminal 14 is connected. On the cathode 13, one end of a cathode terminal 16 is connected through a tertiary conductive layer 15. Near an interface of the anode 11 and the niobium oxide layer 12, there is formed a primary interface region A containing sulfur. Furthermore, near an interface at the cathode 13 side of the niobium oxide layer 12, there is formed a secondary interface region B containing the sulfur. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a solid electrolytic capacitor and a method for manufacturing the same.

  Conventionally, niobium solid electrolytic capacitors using niobium oxide as a dielectric layer are known. This niobium solid electrolytic capacitor is generally formed by anodizing a niobium anode to form a niobium oxide layer on the anode surface and further forming a cathode on the niobium oxide layer with an epoxy resin or the like. It is formed by doing. The solid electrolytic capacitor is surface-mounted on printed circuit boards of various electronic devices by reflow soldering or the like.

  However, niobium oxides are more susceptible to heat than tantalum oxides and aluminum oxides used in other solid electrolytic capacitors. Therefore, niobium solid electrolytic capacitors have a capacitance due to a reflow process or the like. There was a problem of being easy to change.

On the other hand, a niobium solid electrolytic capacitor using a niobium oxide containing nitrogen as a dielectric layer has been recently proposed (see, for example, Patent Document 1).
JP 11-329902 A

  However, in the solid electrolytic capacitor using the niobium oxide containing nitrogen as the dielectric layer, the leakage current increases after heat treatment such as a reflow process and the equivalent series resistance (ESR) in the high frequency region near 100 kHz increases. There was a problem.

The present invention has been made to solve the above problems,
One object of the present invention is to provide a niobium solid electrolytic capacitor with low leakage current and low ESR.

  Another object of the present invention is to provide a method of manufacturing a solid electrolytic capacitor with low leakage current and ESR.

  A solid electrolytic capacitor according to a first aspect of the present invention includes an anode containing niobium, a niobium oxide layer formed on the anode, a cathode formed on the niobium oxide layer, and an exterior formed on the cathode. A first interface region containing sulfur is formed in the vicinity of the interface between the niobium oxide layer and the anode.

  In the solid electrolytic capacitor according to the first aspect, a second interface region containing sulfur is preferably formed in the vicinity of the interface between the niobium oxide layer and the cathode.

  In the solid electrolytic capacitor according to the first aspect, preferably, the concentration of sulfur in at least one of the first interface region and the second interface region is in the range of 2 at% to 25 at%.

  A method of manufacturing a solid electrolytic capacitor according to a second aspect of the present invention includes a step of forming a surface layer containing sulfur on an anode containing niobium, and an anode formed by anodizing the anode having the surface layer in an aqueous solution. A step of forming a niobium oxide layer thereon, a step of forming a cathode on the niobium oxide layer, and a step of forming an outer package on the cathode.

  In the method for producing a solid electrolytic capacitor according to the second aspect, preferably, the step of forming the surface layer includes a step of electrolytically treating the anode in a molten salt containing sulfur.

  In the solid electrolytic capacitor element according to the first aspect, as described above, since the first interface region containing sulfur is formed in the vicinity of the interface between the anode and the niobium oxide layer, heat treatment such as a reflow process is performed. Even when thermal stress acts between the anode and the niobium oxide layer, the stress can be relaxed. As a result, cracks are less likely to occur in the niobium oxide layer, and the anode and the niobium oxide layer are less likely to peel off. As a result, a niobium solid electrolytic capacitor capable of reducing leakage current and ESR can be easily obtained.

  Here, sulfur contained in the vicinity of the interface between the anode and the niobium oxide layer may be contained at least in the niobium oxide layer, but is preferably contained in both the niobium oxide layer and the anode. This further improves the adhesion between the anode and the niobium oxide layer.

  In addition, when sulfur is contained near the interface of the niobium oxide layer with the cathode, thermal stress acts between the cathode formed on the niobium oxide layer and the niobium oxide layer. Even if it exists, the stress can be relieved. As a result, cracks are less likely to occur in the niobium oxide layer, and the cathode and niobium oxide layer are less likely to peel off. As a result, leakage current and ESR can be further reduced.

  When the concentration of sulfur contained in the first interface region or the second interface region is small, the stress relaxation effect is reduced in each region. Further, when the concentration of sulfur is high, cracks are likely to occur in the niobium oxide layer, so that the leakage current tends to increase in each region. Accordingly, in either one of the first interface region and the second interface region, the sulfur concentration is preferably in the range of 2 at% to 25 at%, and both the sulfur concentrations in the first interface region and the second interface region are in the above range. It is more preferable that The sulfur concentration is defined by the maximum concentration of sulfur in the first interface region and the second interface region, and can be measured by an energy dispersive X-ray analysis (EDX) method or the like.

  In the method for manufacturing a solid electrolytic capacitor according to the second aspect of the present invention, as described above, a niobium oxide layer is formed by performing anodization after forming a surface layer containing sulfur on the surface of the anode. Therefore, sulfur can be easily included near the interface between the anode and the niobium oxide layer. Thereby, even if a thermal stress is applied between the anode and the niobium oxide layer during a heat treatment such as a reflow process, the stress can be relaxed. As a result, cracks are less likely to occur in the niobium oxide layer, and the anode and the niobium oxide layer are less likely to peel off. As a result, a niobium solid electrolytic capacitor capable of reducing leakage current and ESR can be easily manufactured.

  Furthermore, by the above anodic oxidation, a second interface region containing sulfur can be formed near the surface of the niobium oxide layer (on the side of the interface with the cathode). As a result, even if a thermal stress is applied between the cathode formed on the niobium oxide layer and the niobium oxide layer, the stress can be relaxed, so that a crack is formed in the niobium oxide layer. And the cathode and the niobium oxide layer are difficult to peel off. As a result, leakage current and ESR can be further reduced.

  The surface layer containing sulfur can be easily formed by subjecting an anode containing niobium to electrolytic treatment in a molten salt containing sulfur. Thereby, since the surface layer containing sulfur can be formed on the anode with good adhesion, the adhesion between the anode and the niobium oxide layer can be further improved.

  Hereinafter, the present invention will be described based on embodiments, but the present invention is not limited to the following embodiments, and can be appropriately modified and implemented without departing from the scope of the present invention. is there.

  FIG. 1 is a cross-sectional view for explaining the structure of a solid electrolytic capacitor according to an embodiment of the present invention.

  In the solid electrolytic capacitor according to one embodiment of the present invention, as shown in FIG. 1, a capacitor element 10 is embedded in a rectangular parallelepiped exterior body 1 made of a resin composition containing an epoxy resin or the like.

  The capacitor element 10 includes an anode 11, a niobium oxide layer 12 formed on the anode 11, and a cathode 13 formed on the niobium oxide layer 12. The niobium oxide layer 12 is a so-called dielectric. Functions as a body layer.

  The anode 11 includes an anode lead 11a made of niobium or the like, and a base body 11b made of a porous sintered body formed by sintering niobium powder or niobium alloy powder. It is embedded in the base 11b. One end of the anode terminal 14 is connected to the anode lead 11 a exposed from the base body 11 b, and the other end of the anode terminal 14 is exposed from the exterior body 1.

  The cathode 13 includes a conductive polymer layer 13a made of polypyrrole, polythiophene, polyaniline, or the like formed on the niobium oxide layer 12, and a first conductive layer 13b including carbon particles formed on the conductive polymer layer 13a. And a second conductive layer 13c containing silver particles formed on the first conductive layer 13b. The conductive polymer layer 13a functions as a so-called electrolyte layer.

  One end of a cathode terminal 16 is connected to the cathode 13 via a third conductive layer 15 containing silver particles, and the other end of the cathode terminal 16 is exposed from the exterior body 1.

  FIG. 2 is an enlarged cross-sectional view for explaining the structure near the niobium oxide layer of the solid electrolytic capacitor according to one embodiment of the present invention.

  In the solid electrolytic capacitor according to one embodiment of the present invention, as shown in FIG. 2, a first interface region A containing sulfur is formed in the vicinity of the interface between the anode 11 and the niobium oxide layer 12. A second interface region B containing sulfur is formed near the interface on the cathode 13 side of the niobium oxide layer 12. Thus, the solid electrolytic capacitor by one Embodiment of this invention is comprised.

  3-6 is sectional drawing for demonstrating the formation process of the solid electrolytic capacitor by one Embodiment of this invention. Next, a method for manufacturing a solid electrolytic capacitor according to the above embodiment of the present invention having the above structure will be described with reference to FIGS.

  First, as shown in FIG. 3, a sintered body of niobium powder or niobium alloy powder in which one end of the anode lead 11a is embedded is sintered in a vacuum, whereby the anode lead 11a and a base body 11b made of a porous sintered body are formed. Is formed.

  Next, as shown in FIG. 4, a surface layer 11c containing sulfur covering the periphery of the anode 11 is formed by electrolytic treatment (sulfurization treatment) so that the anode 11 becomes an anode in a molten salt containing sulfur. The

  Thereafter, as shown in FIG. 5, the niobium oxide layer 12 covering the periphery of the anode 11 is formed by anodizing the anode 11 on which the surface layer 11c is formed in an aqueous solution. At this time, referring to FIG. 2, a first interface region A containing sulfur is formed in the vicinity of the interface between anode 11 and niobium oxide layer 12, and the vicinity of the surface of niobium oxide layer 12 (cathode 13). The second interface region B containing sulfur is formed on the side on which is formed.

  Next, as shown in FIG. 6, a conductive polymer layer 13a is formed on the niobium oxide layer 12 by polymerization or the like. At this time, the conductive polymer layer 13a is formed so as to cover the niobium oxide layer 13 and to fill the surface of the substrate 11b and the concave portion inside. Moreover, the 1st conductive layer 13b containing a carbon particle is formed on the conductive polymer layer 13a by apply | coating and drying the carbon paste containing a carbon particle so that the circumference | surroundings of the conductive polymer layer 13a may be covered. Furthermore, the 2nd conductive layer 13c containing a silver particle is formed on the 1st conductive layer 13b by apply | coating and drying the silver paste containing a silver particle so that the circumference | surroundings of the 1st conductive layer 13b may be covered. Thus, the cathode 13 composed of the conductive polymer layer 13a, the first conductive layer 13b, and the second conductive layer 13c is formed on the niobium oxide layer 12, and the capacitor element 10 is manufactured.

  Next, as shown in FIG. 1, the anode terminal 14 is connected to the anode lead 11a exposed from the base body 11b by welding. Moreover, the 3rd conductive layer 15 containing a silver particle is formed between the cathode 13 and the cathode terminal 16 by drying in the state which contact | adhered the cathode 13 and the cathode terminal 16 through the silver paste containing silver particles. In addition, the cathode 13 and the cathode terminal 16 are connected via the third conductive layer 15. Finally, the capacitor element 10 to which the anode terminal 14 and the cathode terminal 16 are connected is embedded with a resin composition containing epoxy resin or the like, and the resin composition is thermally cured, whereby the exterior body 1 in which the capacitor element 10 is embedded is obtained. It is formed. The molding process of covering the capacitor element 10 with the exterior body 1 can be performed by transfer molding or the like. With the above method, a solid electrolytic capacitor according to an embodiment of the present invention is manufactured.

  In the solid electrolytic capacitor according to this embodiment, since the first interface region A containing sulfur is formed in the vicinity of the interface between the anode 11 and the niobium oxide layer 12, the anode 11 and niobium are subjected to heat treatment such as a reflow process. Even if a thermal stress is applied between the oxide layer 12 and the oxide layer 12, the stress can be relaxed. As a result, cracks are less likely to occur in the niobium oxide layer 12, and the anode 11 and the niobium oxide layer 12 are less likely to peel off. As a result, leakage current and ESR can be reduced.

  In this solid electrolytic capacitor, the first interface region A containing sulfur is formed across both the anode 11 and the niobium oxide layer 12. That is, since sulfur is contained in both the niobium oxide layer 12 and the anode 11, the adhesion between the anode and the niobium oxide layer is further improved.

  In this solid electrolytic capacitor, since the second interface region B containing sulfur is formed in the vicinity of the interface between the niobium oxide layer 12 and the cathode 13, thermal stress is generated between the cathode 13 and the niobium oxide layer 12. Even when is applied, the stress can be relaxed. As a result, cracks are less likely to occur in the niobium oxide layer 12, and the cathode 13 and the niobium oxide layer 12 are less likely to peel off. As a result, leakage current and ESR can be further reduced.

  In the method of manufacturing the solid electrolytic capacitor according to this embodiment, as described above, the niobium oxide layer 12 is formed by performing anodic oxidation after forming the surface layer 11c containing sulfur on the surface of the anode 11. Therefore, sulfur can be easily included in the first interface region A in the vicinity of the interface between the anode 11 and the niobium oxide layer 12. Thereby, even if a thermal stress acts between the anode 11 and the niobium oxide layer 12 during a heat treatment such as a reflow process, the stress can be relaxed. As a result, cracks are less likely to occur in the niobium oxide layer 12, and the anode 11 and the niobium oxide layer 12 are less likely to peel off. As a result, leakage current and ESR can be reduced.

  Furthermore, the second interface region containing sulfur can be formed in the vicinity of the surface of the niobium oxide layer 12 (on the interface side with the cathode 13) by the above anodic oxidation. Thereby, even when a thermal stress is applied between the cathode 13 formed on the niobium oxide layer 12 and the niobium oxide layer 12, the stress can be relaxed. 12 is difficult to crack, and the cathode 13 and the niobium oxide layer 12 are difficult to peel off. As a result, leakage current and ESR can be further reduced.

  Further, the surface layer 11c containing sulfur can be easily formed by electrolytic treatment so that the anode 11 containing niobium becomes an anode in a molten salt containing sulfur. Thereby, since the surface layer containing sulfur can be formed on the anode with good adhesion, the adhesion between the anode and the niobium oxide layer can be further improved.

  Next, a solid electrolytic capacitor was produced based on the above embodiment and evaluated.

(Experiment 1)
In the solid electrolytic capacitor of Experiment 1, the substrate 11b was formed by sintering niobium particles having an average particle diameter of about 2 μm.

The niobium oxide layer 12 including the first interface region A and the second interface region B was formed as follows. First, the anode 11 and the carbon electrode were immersed in molten lithium sulfide-sodium sulfide-potassium sulfide (molten Li ₂ S—Na ₂ S—K ₂ S) at about 700 ° C. Then, an electrolytic treatment (sulfurization treatment) was performed between the anode 11 and the carbon electrode at a constant voltage of about 3.5 V for about 30 minutes so that the anode 11 became an anode. Here, the molten _{Li 2 S-Na 2 S-} K 2 S is an example of the "molten salt containing sulfur" in the present invention. As a result, a surface layer 11 c containing sulfur was formed on the anode 11. Next, after the electrolytic treatment, anodic oxidation was performed at a constant voltage of about 16 V for about 10 hours in an about 0.1 wt% nitric acid aqueous solution in which the anode 11 was maintained at about 60 ° C. Thereby, the niobium oxide layer 12 was formed on the anode 11. At this time, the first interface region A is formed in the vicinity of the interface between the anode 11 and the niobium oxide layer 12, and the first interface region A is formed in the vicinity of the surface of the niobium oxide layer 12 (the side on which the cathode 13 is formed). Two interface regions B are formed.

  Further, polypyrrole formed by polymerization or the like was used for the conductive polymer layer 13a. Moreover, the exterior body 1 was formed by embedding the capacitor element 10 with an epoxy resin and curing it.

(Experiment 2)
The solid electrolytic capacitor of Experiment 2 was fabricated in the same manner as in Experiment 1 except that the anode was directly anodized in an aqueous nitric acid solution without performing the above sulfiding treatment on the anode. That is, in the solid electrolytic capacitor of Experiment 2, the anode and the niobium oxide layer do not contain sulfur, and the niobium oxide layer is formed directly on the anode.

(Experiment 3)
The solid electrolytic capacitor of Experiment 3 was the same as that of Experiment 1 except that the anode was subjected to heat treatment (nitriding treatment) in nitrogen gas at about 300 ° C. for about 5 minutes instead of performing the above sulfidation treatment. A capacitor was produced. That is, in the solid electrolytic capacitor of Experiment 3, the anode and the niobium oxide layer contain nitrogen instead of sulfur.

(Evaluation)
First, composition analysis in the thickness direction was performed on the niobium oxide layer 12 of the solid electrolytic capacitor produced in Experiment 1 above. FIG. 7 is a diagram showing a measurement result of the niobium oxide layer 23 produced in Experiment 1 by an energy dispersive X-ray analysis (EDX) method. The measurement was performed before forming the conductive polymer layer 14. In FIG. 7, the vertical axis represents the abundance ratio (at%) of the element, and the horizontal axis represents the depth from the surface of the niobium oxide layer.

  From FIG. 7, it is considered that almost no oxygen is present in the region (i) having a depth of about 40 nm or more from the surface of the niobium oxide layer 12, and the region (i) functions as the anode 11. A region (ii) from the surface where oxygen is present to a depth of about 40 nm is the niobium oxide layer 12 and is considered to function as a dielectric layer.

  Further, the region (ii) and the vicinity of the interface on the region (ii) side of the region (i) contain sulfur, and in particular, the region (iii) near the interface over the regions (i) and (ii). And the region (iv) near the surface of the region (ii) contained sulfur at a higher concentration (up to about 10 at%) than the other regions. The average sulfur concentration in region (ii) was about 2.5 at%. These regions (iii) and (iv) are considered to correspond to the first interface region A and the second interface region B of the above embodiment, respectively.

  Next, the solid electrolytic capacitor produced in each of the above experiments was heat-treated at about 240 ° C. for about 5 minutes, and then a constant voltage of about 5 V was applied between the anode terminal and the cathode terminal, and after about 20 seconds. The leakage current was measured. Furthermore, ESR at a frequency of about 100 kHz was measured using an LCR meter. The results are shown in Table 1.

  As shown in Table 1, the solid electrolytic capacitor of Experiment 1 was found to have sufficiently reduced leakage current and ESR compared to other solid electrolytic capacitors.

  As described above, in the solid electrolytic capacitor of Experiment 1, approximately 2.5 at% sulfur is also present in the region between the first interface region A and the second interface region B of the niobium oxide layer 12. It was. Thereby, it is considered that cracks are hardly generated not only in the interface regions between the anode 11 and the cathode 13 but also in the niobium oxide layer 12, and the leakage current is effectively reduced. It is done.

(Experiments 4-11)
Next, the relationship between the maximum sulfur concentration in the first interface region A and the second interface region B, the leakage current, and the ESR was examined.

  In Experiments 4 to 11, solid electrolytic capacitors were formed in the same manner as in Experiment 1 except that the time for the sulfurization treatment was changed. Table 2 shows the duration of sulfuration treatment in each experiment. Further, the composition analysis in the thickness direction was performed on the obtained niobium oxide layer 12 by EDX in the same manner as in Experiment 1, and the maximum of the first interface region A and the second interface region B of the niobium oxide layer 12 was determined. The sulfur concentration was measured. Further, as in Experiments 1 to 3, the leakage current and ESR of the produced solid electrolytic capacitor were evaluated. The results are summarized in Table 2. In each of the solid electrolytic capacitors of Experiments 4 to 11, the maximum sulfur concentration in the first interface region A and the second interface region B of the niobium oxide layer 12 was the same value. The value of the maximum sulfur concentration in the second interface region B is shown.

  As shown in Table 2, the leakage current and ESR of the solid electrolytic capacitors of Experiments 4 to 11 are both smaller than the solid electrolytic capacitor of Experiment 2, and the ESR is lower than that of the solid electrolytic capacitors of Experiments 2 and 3. small. In the solid electrolytic capacitors of Experiments 4 to 10, the leakage current is smaller than that of the solid electrolytic capacitor of Experiment 3, and in particular, the maximum sulfur concentration in the first interface region A and the second interface region B in the niobium oxide layer 12 is about 2. In the solid electrolytic capacitors of Experiments 5 to 8 at ˜25 at%, it was found that both the leakage current and the ESR were sufficiently small.

In the above experiment, Li ₂ S—Na ₂ S—K ₂ S was used as the molten salt containing sulfur. However, the present invention is not limited to this, and Li ₂ S—K ₂ S and Li ₂ S—Na are used. ₂ S or the like can be used. Moreover, the surface layer 11c containing sulfur was formed by subjecting the anode 11 to an electrolytic treatment (sulfurization treatment) in a molten salt containing sulfur. However, the present invention is not limited to this, and niobium is formed by thermal decomposition of H ₂ S or the like. An interface layer containing niobium sulfide can be formed on the containing anode.

It is sectional drawing for demonstrating the structure of the solid electrolytic capacitor by one Embodiment of this invention. It is an expanded sectional view for demonstrating the structure of the niobium oxide layer vicinity of the solid electrolytic capacitor by one Embodiment of this invention. It is sectional drawing for demonstrating the 1st process of the formation process of the solid electrolytic capacitor by one Embodiment of this invention. It is sectional drawing for demonstrating the 2nd process of the formation process of the solid electrolytic capacitor by one Embodiment of this invention. It is sectional drawing for demonstrating the 3rd process of the formation process of the solid electrolytic capacitor by one Embodiment of this invention. It is sectional drawing for demonstrating the 4th process of the formation process of the solid electrolytic capacitor by one Embodiment of this invention. It is a figure which shows the measurement result by the energy dispersive X-ray analysis (EDX) method of the niobium oxide layer produced in Experiment 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exterior body 10 Capacitor element 11 Anode 11a Anode lead 11b Base | substrate 11c Surface layer 12 Niobium oxide layer 13 Cathode 13a Conductive polymer layer 13b 1st conductive layer 13c 2nd conductive layer 14 Anode terminal 15 3rd conductive layer 16 Cathode terminal

Claims (5)

An anode containing niobium,
A niobium oxide layer formed on the anode;
A cathode formed on the niobium oxide layer;
An exterior body formed on the cathode,
A solid electrolytic capacitor in which a first interface region containing sulfur is formed in the vicinity of an interface between the niobium oxide layer and the anode.   2. The solid electrolytic capacitor according to claim 1, wherein a second interface region containing sulfur is formed near an interface between the niobium oxide layer and the cathode.   3. The solid electrolytic capacitor according to claim 1, wherein the concentration of sulfur in at least one of the first interface region and the second interface region is in the range of 2 at% to 25 at%. Forming a surface layer containing sulfur on the anode containing niobium;
Forming a niobium oxide layer on the anode by anodizing the anode having the surface layer in an aqueous solution;
Forming a cathode on the niobium oxide layer;
And a step of forming an exterior body on the cathode.   The method for producing a solid electrolytic capacitor according to claim 4, wherein the step of forming the surface layer includes a step of electrolytically treating the anode in a molten salt containing sulfur.

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