JP2007235101A - Solid electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid electrolytic capacitor for improved ESR characteristics. <P>SOLUTION: The solid electrolytic capacitor 1 has a plurality of capacitor elements 2 stacked together. The capacitor element 2 comprises a positive electrode part 4, a negative electrode part 5, and a resist part 6 which electrically insulates the positive electrode part 4 from the negative electrode part 5. A conductive adhesive 13 and a conductive paste part 14 which electrically connect the negative electrode parts 5 of the capacitor element 2 together are interposed between the negative electrode parts 5 of the capacitor elements 2. The conductive adhesive 13 is so formed as to avoid the region corresponding to the ends on the negative electrode parts 5 side of the capacitor elements 2. The conductive paste part 14 is so adjoined to the conductive adhesive 13 as to cover the ends of the negative electrode parts 5 side of the capacitor elements 2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a multilayer solid electrolytic capacitor in which a plurality of capacitor elements each having an anode part and a cathode part are laminated.

As a conventional multilayer solid electrolytic capacitor, for example, as described in Patent Document 1, a plurality of substantially flat capacitor elements having an anode part and a cathode part are aligned in the direction of the anode part and the cathode part. In addition, there is known a structure in which the cathode portions of the capacitor elements are connected to each other with a conductive adhesive.
JP 2004-289142 A

  However, in the above prior art, it is difficult to bond the cathode portions of the capacitor elements to the end region sufficiently and evenly with the conductive adhesive. Therefore, there has been a problem that variation in equivalent series resistance (ESR) characteristics of the capacitor becomes large.

  An object of the present invention is to provide a solid electrolytic capacitor capable of improving ESR characteristics and reducing characteristic variations.

  The present invention is a solid electrolytic capacitor formed by laminating a plurality of capacitor elements each having an anode part and a cathode part, and is provided between the cathode parts of each capacitor element and has a conductive property for bonding the cathode parts of each capacitor element together An adhesive and a conductive paste portion provided adjacent to the conductive adhesive between the cathode portions of the capacitor elements and electrically connecting the cathode portions of the capacitor elements in cooperation with the conductive adhesive. And the conductive adhesive is formed so as to avoid a region corresponding to the cathode portion side end of each capacitor element, and the conductive paste portion covers the cathode portion side end surface of each capacitor element. It is formed as follows.

  In such a solid electrolytic capacitor formed by laminating a plurality of capacitor elements, the gaps between the cathode portions of the capacitor elements are reduced if the end portions on the cathode portion side of the capacitor elements are sufficiently bonded with a conductive adhesive. Therefore, it is considered that the equivalent series resistance (ESR) characteristic of the capacitor is improved. However, if the amount of the conductive adhesive is increased so that the conductive adhesive sufficiently wraps to the end of each capacitor element on the cathode side, the conductive adhesive may protrude beyond the end face of the capacitor element more than necessary. In this case, for example, it becomes difficult to set the capacitor on the jig in a later manufacturing process. As described above, it is difficult to appropriately bond the ends of the capacitor elements on the cathode side only by adjusting the amount of the conductive adhesive, and thus it is not suitable for mass production of capacitors. It is not.

  Therefore, in the present invention, a conductive paste portion is provided in addition to the conductive adhesive between the cathode portions of the capacitor elements. Specifically, a conductive adhesive is provided so as to avoid a region corresponding to an end portion on the cathode portion side of each capacitor element, and a conductive paste portion is provided so as to cover an end surface on the cathode portion side of each capacitor element. Form. As a result, a current easily flows between the cathode portions of the capacitor elements, and a current path between the cathode portions of the capacitor elements is shortened. Therefore, the ESR characteristic of the solid electrolytic capacitor is improved, and the characteristic variation of the capacitor can be reduced.

  Preferably, the conductive paste portion is provided between the cathode portions of the capacitor elements on the side of the end face from a position 200 μm inside from the end face on the cathode portion side of each capacitor element. When the end face on the cathode portion side of each capacitor element is uneven (has irregularities), the position entering 200 μm inside from the end face on the cathode portion side of each capacitor element is from the bottom of the recess on the end face. The position inside 200 μm.

  With this configuration, the conductive paste portion forming region is sufficiently close to the end surface of each capacitor element on the cathode portion side, so that the end surface of each capacitor element on the cathode portion side is easily and reliably covered with the conductive paste portion. be able to. In this case, since the conductive paste portion is easily buried between the cathode portions of the capacitor elements, the current path between the cathode portions of the capacitor elements can be further shortened. As a result, the ESR characteristics of the solid electrolytic capacitor can be further improved.

  At this time, the conductive paste portion is preferably formed so that the protruding length from the end surface on the cathode portion side of each capacitor element is 150 μm or less. When the end face of each capacitor element on the cathode part side is uneven (has unevenness), the protrusion length from the end face on the cathode part side of each capacitor element is the protrusion from the tip of the protrusion on the end face. Say long.

  In this case, the conductive paste portion is formed so as to protrude somewhat from the end face on the cathode portion side of each capacitor element, so that the conductive paste portion is sufficiently buried between the cathode portions of each capacitor element. The current path is further shortened. In addition, since a sufficient thickness of the conductive paste portion covering the surface of the end portion of each capacitor element on the cathode portion side is ensured, it becomes easier for current to flow between the cathode portions of each capacitor element. Thereby, the ESR characteristic of the solid electrolytic capacitor can be further improved. At this time, since the protruding length of the conductive paste portion is 150 μm or less, for example, in manufacturing a solid electrolytic capacitor, it is difficult to set the capacitor in the jig because of the excessive amount of the protruding portion of the conductive paste portion. Can be reliably prevented.

  Preferably, the thickness of the conductive paste portion that covers the surface of the end portion of each capacitor element on the cathode portion side is 10 μm to 150 μm.

  In this case, since it becomes easier for the current to flow between the cathode portions of the capacitor elements, the ESR characteristics of the solid electrolytic capacitor can be further improved. Further, since the protruding length of the conductive paste portion from the end surface on the cathode portion side of each capacitor element is shortened, for example, in manufacturing a solid electrolytic capacitor, it is possible to prevent adverse effects due to the excessive protruding amount of the conductive paste portion. it can.

  According to the present invention, since the conductive paste portion is formed adjacent to the conductive adhesive so as to cover the end surface on the cathode portion side of each capacitor element, the high quality solid with good ESR characteristics and little variation An electrolytic capacitor can be obtained.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of a solid electrolytic capacitor according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a cross-sectional view showing an embodiment of a solid electrolytic capacitor according to the present invention. In the figure, a solid electrolytic capacitor 1 of the present embodiment includes a capacitor element laminate 3 in which a plurality (here, five) of capacitor elements 2 are laminated. The capacitor element 2 includes an anode part 4, a cathode part 5, and a resist part 6 that electrically insulates the anode part 4 and the cathode part 5. A partial detailed cross section of the capacitor element 2 is shown in FIG.

  1 and 2, the capacitor element 2 has a foil-like or plate-like aluminum substrate 7. The surface of the aluminum base 7 is roughened (expanded) to increase the surface area and has a porous shape.

  An insulating aluminum oxide film (dielectric layer) 8 is formed on the porous surface of the aluminum base 7 by chemical conversion treatment (anodic oxidation). As the chemical conversion treatment, for example, in the state where the aluminum substrate 7 is immersed in an aqueous solution of ammonium adipate, a voltage of 6 V, for example, is applied to cause anodic oxidation. The one end side region of the aluminum base 7 subjected to the chemical conversion treatment is in a state in which the roughened structure of the surface is broken, and constitutes the anode portion 4 described above.

  The resist portion 6 is formed on the surface of the boundary portion between the region constituting the anode portion 4 and the other region in the aluminum substrate 7. The resist portion 6 is formed by applying an epoxy resin or the like by a screen printing method or the like, for example.

  A solid polymer electrolyte layer 9 containing a conductive polymer compound is formed on the surface of the aluminum substrate 7 excluding the anode portion 4 and the resist portion 6. This solid polymer electrolyte layer 9 is in a state of entering into the fine holes 7 a formed by roughening the aluminum substrate 7. Formation of the solid polymer electrolyte layer 9 is, for example, 0.94 g of 3,4-ethylenedioxythiophene (BAYTRON M manufactured by Bayel) and 10.81 g of iron paratoluenesulfonate (BAYTRON C-B50 manufactured by Bayel) Then, a mixed solution (polymerization solution) with 2.63 g of butanol is impregnated with the aluminum substrate 7 and subjected to chemical oxidative polymerization. The maximum thickness of the solid polymer electrolyte layer 9 is, for example, about 10 μm.

  The resist portion 6 prevents the polymerization solution from rising toward the anode portion 4 due to capillary action on the surface of the porous aluminum substrate 7 when the aluminum substrate 7 is immersed in the polymerization solution. It has a function to do.

  A graphite paste layer 10 and a silver paste layer (conductor layer) 11 are sequentially formed on the solid polymer electrolyte layer 9. These graphite paste layer 10 and silver paste layer 11 are formed by, for example, a dipping method (dip method). The thickness of the graphite paste layer 10 is, for example, about 3 μm, and the thickness of the silver paste layer 11 is, for example, about 1 to 3 μm. The solid polymer electrolyte layer 9, the graphite paste layer 10 and the silver paste layer 11 described above constitute the cathode part 5.

  The anode portions 4 of the capacitor elements 2 are electrically connected to each other through a metal fitting 12 having conductivity. The metal fitting 12 is made of, for example, iron, nickel, copper, and alloys thereof. Further, the metal fitting 12 is joined to an anode terminal (not shown) on the substrate or the lead frame. The metal fitting 12 and each anode part 4 and anode terminal are joined by laser welding or the like.

  Further, a conductive adhesive 13 and a conductive paste portion 14 that electrically connect the cathode portions 5 of the capacitor elements 2 are interposed between the cathode portions 5 of the capacitor elements 2. The distance between the cathode parts 5 of each capacitor element 2 is, for example, about 50 to 100 μm. The conductive adhesive 13 adheres the cathode portions 5 of the capacitor elements 2 to each other. For example, a silver-epoxy adhesive is used. The cathode portion 5 of the lowermost capacitor element 2 is bonded to a cathode terminal (not shown) on the substrate or the lead frame by the conductive adhesive 13. The conductive paste portion 14 is made of, for example, silver paste.

  Specifically, the electrical connection between the cathode portions 5 by the conductive adhesive 13 and the conductive paste portion 14 is performed as follows. That is, as shown in FIGS. 1 and 3, the conductive adhesive 13 avoids the region P corresponding to the end portion on the cathode portion 5 side of each capacitor element 2, that is, the upper surface 2a of each capacitor element 2 and It is formed so as not to contact the end portion of the lower surface 2b on the cathode portion 5 side. The conductive paste portion 14 covers the end portions of the capacitor elements 2 on the cathode portion 5 side, that is, the end portions and end surfaces (including corner portions) 2c of the upper surface 2a and the lower surface 2b of the capacitor elements 2 on the cathode portion 5 side. Further, it is formed adjacent to the conductive adhesive 13.

  At this time, the conductive paste portion 14 is interposed between the cathode portions 5 of the respective capacitor elements 2 in a region outside (end surface 2c side) from the position Q entering 200 μm inside from the end surface 2c of each capacitor element 2. It is preferable. As a result, the conductive adhesive 13 extends between the cathode portions 5 of the capacitor elements 2 to a position near the end face 2c of the capacitor elements 2. Accordingly, the cathode portions 5 can be effectively bonded to each other by the conductive adhesive 13.

  Moreover, it is preferable that the electrically conductive paste part 14 is formed so that the protrusion length from the end surface 2c of each capacitor | condenser element 2 may be 150 micrometers or less. As a result, even when the conductive paste portion 14 is embedded with almost no gap between the cathode portions 5 of the capacitor elements 2, the conductive paste portion 14 does not protrude beyond the end face 2c of the capacitor elements 2 more than necessary.

  Furthermore, the thickness M of the conductive paste portion 14 that covers the surface of the end portion of each capacitor element 2 on the cathode portion 5 side is preferably 10 μm to 150 μm. Thereby, the end surface on the cathode part 5 side of each capacitor element 2 is sufficiently covered with the conductive paste part 14, and the conductive paste part 14 does not protrude beyond the end face 2 c of each capacitor element 2 more than necessary. At this time, as the thickness of the conductive paste portion 14 increases, a current easily flows between the cathode portions 5 of the capacitor elements 2.

  The conductive paste portion 14 is formed by an immersion method as shown in FIG. 4 as an end treatment on the cathode portion 5 side of the capacitor element laminate 3 (hereinafter, capacitor cathode end treatment).

  That is, first, as shown in FIG. 4A, a conductive paste bath (for example, a silver paste bath) 15 is prepared. And the capacitor | condenser element laminated body 3 (refer FIG. 5 (a)) by which the cathode parts 5 of each capacitor | condenser element 2 are fixed with the conductive adhesive 13 is electrically conductive paste bath 15 so that the cathode part 5 may face down. The capacitor element laminate 3 is pulled up from the conductive paste bath 15 after being lowered and immersed in the conductive paste bath 15. As a result, a conductive paste portion 14 is formed at the end portion of each capacitor element 2 on the cathode portion 5 side.

  At this time, a drop of the conductive paste is generated by pulling up the capacitor element laminate 3, and the conductive paste portion 14 attached to the end surface 2c (see FIG. 3) on the cathode portion 5 side of each capacitor element 2 may swell greatly. For this reason, as shown in FIG.4 (b), the surplus of the electrically conductive paste part 14 is carried out by pressing the end surface 2c by the side of the cathode part 5 of the capacitor | condenser element laminated body 3 against flat plates 16, such as a glass plate and a metal plate, for example. Try to get rid of minutes.

  As a result, the conductive paste portion 14 is sufficiently wrapped around the end of the capacitor element laminate 3 on the cathode portion 5 side without protruding more than necessary. At this time, if the capacitor cathode end portion treatment described above is performed only once, the conductive paste portion 14 is concave between the capacitor elements 2 with respect to the end face 2c side as shown in FIG. May become embedded. In this case, by performing the capacitor cathode end processing again, as shown in FIG. 5C, the conductive paste portion 14 is almost entirely disposed between the end portions on the cathode portion 5 side of each capacitor element 2. It may be embedded.

  Note that the method of forming the conductive paste portion 14 is not particularly limited to the above immersion method, and for example, as shown in FIG. 6, a coating spatula 17 may be used. Specifically, first, a conductive paste bath 15 similar to the above immersion method is prepared, put in the conductive paste bath 15 with the application spatula 17 in an upright state, and the conductive paste adheres to the application spatula 17 (FIG. 6 (a)). Then, the conductive paste portion 14 is formed by applying the conductive paste attached to the coating spatula 17 to the end portion on the cathode portion 5 side of each capacitor element 2 in a state where the capacitor element laminate 3 is horizontally disposed. (FIG. 6B).

  Further, as shown in FIG. 7, a dispenser 18 for discharging a conductive paste is prepared, and the capacitor element stack 3 is vertically arranged so that the cathode portion 5 faces upward. The conductive paste portion 14 may be formed by applying a conductive paste to the end portion on the cathode portion 5 side.

  By performing the capacitor cathode end treatment using such a method, the conductive paste portion 14 can be easily formed at the end of the capacitor element laminate 3 on the cathode portion 5 side. Further, by changing the number of times of performing capacitor cathode end processing, the amount of conductive paste portion 14 embedded between the capacitor elements 2 and the amount of protrusion of the conductive paste portion 14 from the end face 2c of each capacitor element 2 can be simplified. Can be adjusted. At this time, when the conductive adhesive 13 is interposed between the capacitor elements 2 up to a position near the end face 2c of the capacitor elements 2, the gap between the capacitor elements 2 is small. It is possible to minimize the number of times of extreme part processing. It should be noted that the amount of embedding and the amount of protrusion of the conductive paste portion 14 can be adjusted by adjusting the paste viscosity of the conductive paste portion 14.

  As described above, in this embodiment, the conductive paste portion 14 is formed adjacent to the conductive adhesive 13 so as to cover the end portion of each capacitor element 2 on the cathode portion 5 side, and the conductive adhesive 13 Since the cathode portions 5 of the capacitor elements 2 are electrically connected to each other by the cooperation of the conductive paste portion 14 and the conductive paste portion 14, a current easily flows between the cathode portions 5 of the capacitor elements 2. In addition, since the conductive paste portion 14 is embedded between the cathode portions 5 of the capacitor elements 2, the current path between the cathode portions 5 is shortened. Thereby, since the equivalent series resistance (ESR) of the solid electrolytic capacitor 1 is reduced, the quality and performance of the solid electrolytic capacitor 1 are improved, and variations in ESR characteristics of the plurality of solid electrolytic capacitors 1 can be reduced. .

  Moreover, when it is going to adhere | attach the edge parts by the side of the cathode part 5 of each capacitor | condenser element 2 with the conductive adhesive 13, the protrusion amount of the conductive adhesive 13 from the end surface 2c of the capacitor | condenser element 2 will increase more than necessary, For example, there may be a problem that it is difficult to set the capacitor on the jig in the manufacturing process. In the present embodiment, since the conductive paste portion 14 is formed at the end portion on the cathode portion 5 side of each capacitor element 2 by the above-described capacitor cathode end portion processing, it is possible to prevent such troubles during manufacturing. Thereby, a yield can be improved and it is advantageous for mass production of the solid electrolytic capacitor 1.

  Actually, the ESR characteristics were evaluated by the end processing on the cathode side of the capacitor element, which will be described below.

  First, a surface-treated aluminum substrate (3.5 mm × 10.0 mm) was prepared, and a resist portion was formed on the aluminum substrate. Then, an aluminum oxide film (dielectric layer) was formed on the surface of the aluminum substrate by the above method. Subsequently, a capacitor element was obtained by sequentially forming a solid polymer electrolyte layer, a graphite paste layer, and a silver paste layer on the dielectric layer by the above method.

  Subsequently, a capacitor element laminate formed by laminating five capacitor elements was produced. At this time, the cathode portions of the capacitor elements are bonded to each other with a conductive adhesive, and the conductive paste portion is formed on the cathode portion side end of each capacitor element by the capacitor cathode end treatment using the dipping method shown in FIG. Formed. The capacitor sample was completed by performing this capacitor cathode end treatment twice. At this time, 20 samples of a plurality of types (eight types) with different thicknesses of the conductive paste portions covering the cathode portion side end surface of each capacitor element were produced. In addition, the thickness of the electrically conductive paste part in each kind of sample was 5 micrometers, 10 micrometers, 15 micrometers, 30 micrometers, 50 micrometers, 100 micrometers, 150 micrometers, and 200 micrometers (refer Table 1).

  With respect to the sample thus obtained, an equivalent series resistance (ESR) at 100 kHz was measured using an impedance analyzer 4194A manufactured by Agilent Technologies.

  Further, as a comparative example, 20 samples without a conductive paste portion at the end portion on the cathode portion side of each capacitor element were prepared (capacitor end portion treatment was not performed), and the ESR value at 100 kHz was measured in the same manner. .

The measurement results are shown in Table 1 and FIG. In addition, the numerical value in a table | surface (graph) is an average value of 20 samples about each kind.

  As can be seen from Table 1 and FIG. 8, when the capacitor cathode end treatment is not performed, that is, when the thickness of the conductive paste portion covering the end surface on the cathode portion side of each capacitor element is 0, the average of the ESR values The value was 35 mΩ. The variation of the ESR value was 10 mΩ (variation range: 29 to 39 mΩ).

  In contrast, when the capacitor cathode end treatment was performed, the average ESR value was lower than when the capacitor cathode end treatment was not performed. At this time, it was clear that the ESR value was sufficiently lowered by setting the thickness of the conductive paste portion covering the end portion surface of each capacitor element on the cathode portion side to 10 μm or more. Further, the variation of the ESR value was 3.5 mΩ at maximum (variation range: 7.2 to 10.7 mΩ), which was smaller than the case where the capacitor cathode end treatment was not performed.

  Further, a reliability (yield) test was performed on four types of samples in which the thickness of the conductive paste portion covering the end surface on the cathode side of each capacitor element was 50 μm, 100 μm, 150 μm, and 200 μm.

Specifically, 100 samples of each type were prepared, and the number of non-defective products after being allowed to stand for 500 hours under the evaluation test conditions of a temperature of 60 ° C., 90-95% RH, and no application of voltage was examined. At this time, the capacitance is within -20 to + 40% of the initial value (120 Hz, 20 ° C.), the tangent of the loss angle is 1.5 times or less of the initial value (120 Hz, 20 ° C.), and 2 minutes have elapsed from the application of the rated voltage. Those satisfying all the conditions that the later leakage current was three times or less of the initial value were judged as non-defective products. The test results are shown in Table 2.

  As can be seen from Table 2, when the thickness of the conductive paste portion covering the cathode portion side end surface of each capacitor element is 50 μm and 100 μm, the yield rate is 100%, and the thickness of the conductive paste portion is Even in the case of 150 μm, a high yield rate was obtained.

  From the above results, it is demonstrated that the conductive paste portion 14 is formed at the end of each capacitor element 2 on the cathode portion 5 side, thereby lowering the ESR value of the capacitor and suppressing variations in the ESR characteristics of the capacitor. I was able to. At this time, by setting the thickness M of the conductive paste portion 14 covering the surface of the end portion on the cathode portion 5 side of each capacitor element 2 to 10 μm to 150 μm, the ESR characteristic of the capacitor is improved and the reliability of the capacitor is improved. It was also demonstrated that the performance is further improved.

  The present invention is not limited to the above embodiment. For example, in the above embodiment, an aluminum base is used as the valve metal base for forming the anode portion 4 of the capacitor element 2, but the metal material of the valve metal base is not only aluminum but also aluminum alloy, titanium, tantalum, niobium, and the like. Zirconium or an alloy thereof may be used.

  Moreover, in the said embodiment, although anode part 4 of each capacitor | condenser element 2 was electrically connected by the metal metal fitting, the solid electrolytic capacitor of this invention is not restricted to this type in particular, For example, each capacitor | condenser element 2 The present invention can also be applied to a structure in which the anode parts 4 are directly joined with the anode part 4 bent.

  Further, the conductive adhesive 13 and the conductive paste portion 14 may be formed of the same material.

It is sectional drawing which shows one Embodiment of the solid electrolytic capacitor concerning this invention. FIG. 2 is an enlarged cross-sectional view showing in detail a partial structure of the capacitor element shown in FIG. 1. It is sectional drawing which shows the edge part by the side of the cathode part of the solid electrolytic capacitor shown in FIG. It is the schematic which shows the method of forming the electrically conductive paste part shown in FIG. It is a conceptual diagram which shows a mode that a conductive paste part is formed with the method shown in FIG. It is the schematic which shows the other method of forming the electrically conductive paste part shown in FIG. It is the schematic which shows the further another method of forming the electrically conductive paste part shown in FIG. It is a graph which shows the measurement result of the ESR characteristic at the time of performing the edge part process by the side of the cathode part of a capacitor | condenser element.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Solid electrolytic capacitor, 2 ... Capacitor element, 4 ... Anode part, 5 ... Cathode part, 13 ... Conductive adhesive agent, 14 ... Conductive paste part.

Claims (4)

A solid electrolytic capacitor in which a plurality of capacitor elements having an anode part and a cathode part are laminated,
A conductive adhesive that is provided between the cathode parts of the capacitor elements and bonds the cathode parts of the capacitor elements;
A conductive paste portion provided adjacent to the conductive adhesive between the cathode portions of the capacitor elements and electrically connecting the cathode portions of the capacitor elements in cooperation with the conductive adhesive. And
The conductive adhesive is formed so as to avoid a region corresponding to an end portion on the cathode portion side of each capacitor element,
The solid electrolytic capacitor, wherein the conductive paste portion is formed so as to cover an end portion surface of the capacitor element on the cathode portion side.   The conductive paste portion is provided between the cathode portions of the capacitor elements on the end face side from a position entering 200 μm inside from the end face on the cathode portion side of each capacitor element. The solid electrolytic capacitor according to claim 1.   3. The solid electrolytic capacitor according to claim 2, wherein the conductive paste portion is formed so that a protruding length from the end face on the cathode portion side of each capacitor element is 150 μm or less.   3. The solid electrolytic capacitor according to claim 1, wherein a thickness of the conductive paste portion covering an end surface on the cathode portion side of each capacitor element is 10 μm to 150 μm.

Images