JP2010040960A - Solid-state electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid-state electrolytic capacitor having a low impedance in a high frequency range. <P>SOLUTION: An anodic oxidation coating is formed on the back and front surfaces of a plate-shape valve-action metal having porosity on the front surface and smoothness on the back surface. An anode area and a cathode area are separated by insulating body layers 4 formed on the anodic oxidation coating. A solid-state electrolytic layer 5, a graphite layer 6, and a conductive pasted layer 7 are formed in order on the anode oxidation coating of the cathode area, to be used as a cathode. A conductive member is connected to a part where the anode oxidation coating of the back surface in the anode area is removed, and the part is used as an anode. The anode and the cathode on the back surface are connected to an anode external terminal and a cathode external terminal respectively. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a solid electrolytic capacitor using a valve metal, and more particularly to a solid electrolytic capacitor having low impedance characteristics in a high frequency region.

  In recent years, digital devices have become smaller and more functional, and solid electrolytic capacitors have been used in electronic circuits, such as around and directly under CPUs for the purpose of eliminating noise and stabilizing power supply voltage. It is becoming important.

  As an example of a conventional solid electrolytic capacitor using a conductive polymer as a solid electrolyte, the production of an aluminum solid electrolytic capacitor having a flat element structure will be described with reference to the drawings. FIG. 2 is a view showing a conventional solid electrolytic capacitor, FIG. 2 (a) is a perspective view, and FIG. 2 (b) is a cross-sectional view taken along line AA of FIG. 2 (a). First, an anodic oxide film, which is an insulating film, is formed by anodic oxidation on the surface of an aluminum substrate 1 made of flat plate-like aluminum having a porous portion 2 whose both surfaces are made porous. Next, an insulating layer 4 is formed of epoxy resin or the like at a predetermined position of the anodized film to divide the aluminum base into two regions, that is, an anode region and a cathode region, and one cathode portion of the regions The solid electrolyte layer 5 made of a conductive polymer is formed only in the region. Further, a graphite layer 6 is formed on the solid electrolyte layer 5 by screen printing or the like, and a conductive paste layer 7 is further formed on the graphite layer 6 to form a cathode portion. On the other hand, in the anode region, which is another region divided by the insulator layer 4, the aluminum substrate 1 is exposed by peeling the anodized film or the like, and the metal lead frame is welded to form the anode portion. The anode part and the cathode part of the solid electrolytic capacitor element are electrically connected to the external anode terminal 9 and the external cathode terminal 11 of the electrode substrate 10, respectively, to serve as mounting terminals for the solid electrolytic capacitor. Next, the solid electrolytic capacitor is formed by molding the exposed portion of the capacitor element not connected to the electrode substrate with an epoxy resin (see, for example, Patent Document 1).

  A solid electrolytic capacitor using a conductive polymer as an electrolyte has a low equivalent series resistance (hereinafter referred to as ESR). Therefore, the impedance in a low frequency region is sufficiently low. However, in order to apply this capacitor to a high frequency driving circuit, It is also necessary to reduce the impedance in the high frequency region at the same time. However, in the solid electrolytic capacitor, the wiring length of the electrode wiring circuit inside the capacitor is increased due to the internal configuration of the element, which causes an increase in equivalent series inductance (hereinafter referred to as ESL), There has been a problem that the impedance in the high frequency region is relatively increased.

  As a solution, firstly, there is a method of reducing the length of the wiring circuit of the electrode by reducing the size of the capacitor itself. However, since the volume efficiency of the cathode part is inferior to the multilayer ceramic capacitor in conventional solid electrolytic capacitor manufacturing technology, realizing a solid electrolytic capacitor with a smaller shape than the multilayer ceramic capacitor is a characteristic aspect such as capacity and ESR. In addition, a solid electrolytic capacitor having a conventional shape has a higher impedance in a high frequency region than a multilayer ceramic capacitor.

  A capacitor having a multi-terminal structure has been proposed as a method of using a solid electrolytic capacitor having a conventional size and making the ESL smaller than that of a multilayer ceramic capacitor. A capacitor having a multi-terminal structure is effective in reducing the ESL regardless of the type of capacitor. As an electrical contact between the anode part and cathode part of the capacitor and the outside, an electrode substrate in which a plurality of external anode terminals and external cathode terminals are embedded is provided, and the cathode part and anode part in the capacitor are connected to this electrode. Electrically connected to external electrode terminals on the substrate to be externally connected terminals. As a result, the current loop generated between the external anode terminal and the external cathode terminal can be increased, and the ESL can be reduced in the high frequency region.

  Further, Patent Document 2 discloses a solid electrolytic capacitor excellent in high-frequency response that allows semiconductors to be directly connected by bumps.

JP 2008-91806 A JP 2001-307955 A

  If the technology relating to each solid electrolytic capacitor disclosed in Patent Document 2 and the like described above can be used, it is considered that further reduction in ESL of the solid electrolytic capacitor can be realized. However, this technique involves a complicated method for forming an electrode portion, and is difficult to apply to a conventional solid electrolytic capacitor element. That is, the subject of this invention is providing the solid electrolytic capacitor which implement | achieves low impedance in a high frequency area | region.

  In order to achieve low impedance in the high frequency region of the solid electrolytic capacitor, the present invention uses a solid electrolytic capacitor element having a conventional shape and has a thickness on the external electrode terminal (external anode terminal and external cathode terminal) side of the solid electrolytic capacitor element. It has been found that by reducing the thickness of the wiring circuit, the routing length of the wiring circuit between the capacitor element and the external electrode terminal is reduced, thereby reducing the ESL.

  The solid electrolytic capacitor of the present invention is formed by forming an anodic oxide film on the front and back surfaces of a flat valve-acting metal having a porous portion on the front surface and a smooth portion on the back surface, and an anode portion by an insulator layer formed on the anodic oxide film. Divided into an area and a cathode part area, a solid electrolyte layer, a graphite layer, and a conductive paste layer are formed in order on the anodized film in the cathode part area to form a cathode part, and the anodized film on the back surface of the anode part area is removed. Then, a conductive member is connected to form an anode portion, and the anode portion and the anode external terminal, and the cathode portion on the back surface and the cathode external terminal are connected to each other.

  According to the present invention, by adopting a configuration in which the porous portion is not formed between the solid electrolytic capacitor element and the electrode substrate, the length of the wiring circuit between the aluminum base and the electrode substrate is set to the thickness of the porous portion. It can be shortened, thereby reducing the routing length of the wiring circuit, thereby reducing ESL. Therefore, by implementing the present invention, a solid electrolytic capacitor having a low impedance in a high frequency region is realized.

  A configuration of a solid electrolytic capacitor according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a view showing a solid electrolytic capacitor of the present invention, FIG. 1 (a) is a perspective view, and FIG. 1 (b) is a sectional view taken along line AA of FIG. 1 (a).

  In FIG. 1, an aluminum substrate 1 is made of a rectangular flat aluminum foil, and one surface (front surface) is formed with a porous portion 2 by etching, and the other surface (back surface) is made porous. It is not the smooth part 3. Anodized films (not shown) are formed on both surfaces of the aluminum substrate 1 by anodic oxidation. Next, an insulating layer 4 having a narrow width is formed at a predetermined position on the anodized film by using an epoxy resin or the like to divide the aluminum substrate 1 into two regions, ie, an anode region and a cathode region. A cathode part is formed by forming a solid electrolyte layer 5, a graphite layer 6, and a conductive paste layer 7 made of a conductive polymer only in the partial region. A conductive member 8 composed of a rectangular parallelepiped metal lead frame is provided by welding to an aluminum base in a position where the cathode portion is not formed, that is, the anode portion region, through the insulating layer 4 on the smooth portion 3 side, that is, the back surface. The part is formed. The conductive member 8 is made of a metal member such as a copper foil, and has a role of electrically connecting the anode between the external anode terminal 9 provided on the bottom surface of the solid electrolytic capacitor and the aluminum substrate 1. The anodized film is peeled off at the connection portion between the aluminum substrate 1 and the conductive member 8, and both can be connected by ultrasonic welding. Next, the conductive member 8 of the solid electrolytic capacitor element and the external anode terminal 9 of the electrode substrate 10, the conductive paste layer 7 on the back surface and the external cathode terminal 11 are electrically connected with the conductive adhesive 12, respectively. The mounting surface in the electronic circuit was formed.

  Next, the solid electrolytic capacitor was formed by covering the exposed portion of the solid electrolytic capacitor element other than the mounting surface with the mold resin 13 and performing the exterior. Although the anode portion is provided at one end portion here, the anode portion may be provided at both end portions. Further, the conductive member and the external anode terminal, and the conductive paste layer and the external cathode terminal can be connected without using the electrode substrate.

An embodiment will be described with reference to FIG. The solid electrolytic capacitor according to the embodiment of the present invention was manufactured by the following method, and its electrical characteristics and shape were measured. First, a photoresist is applied to one surface (back surface) of the flat aluminum substrate 1 for masking, and then immersed in an etching solution to form a porous portion 2 on the surface other than the masking portion of the photoresist. The covered portion of the resist was exposed and removed, and the back surface where the porous material was not formed was defined as the smooth portion 3. Next, an anodized film was formed on the front and back surfaces of the aluminum substrate 1 by anodic oxidation. Here, the nominal formation voltage for forming the anodized film on the flat aluminum substrate 1 is 4 V, and the capacitance per unit area (cm ² ) is 150 μF. Here, the total thickness of the aluminum substrate 1 and the porous portion is 100 μm, and as a breakdown, the thickness of the aluminum substrate 1 is 40 μm and the thickness of the porous portion 2 is 60 μm. This flat aluminum substrate 1 is cut into a rectangular parallelepiped shape having a width of 2.0 mm and a length of 4.0 mm, and a rectangular region of 2.0 mm in the width direction and 3.0 mm in the length direction is formed from one end portion in the length direction. A cathode part forming the cathode part, and a rectangular area of 2.0 mm in the width direction and 0.5 mm in the length direction from the end in the length direction on the side where the cathode part is not formed. A partial area. Next, in order to electrically insulate between the anode region and the cathode region, the width of the insulator layer 4 is 0.5 mm and the thickness is 15 μm between the anode region and the cathode region. An epoxy resin was formed by screen printing. Next, on the anodized film in the cathode region on both surfaces of the aluminum substrate 1, 3,4-ethylenedioxythiophene as a monomer, ammonium peroxodisulfate as an oxidant, and paratoluenesulfonic acid as a dopant have a molar ratio of 1 respectively. A solid electrolyte layer 5 made of a conductive polymer is formed by reaction at a ratio of 1: 2, and a graphite layer 6 is further formed thereon to a thickness of 25 μm by screen printing, and further 80 wt% on the graphite layer 6. The conductive paste layer 7 having the above silver content was formed to a thickness of 40 μm.

  Next, the conductive member 8 made of copper foil that has been plated with nickel and silver on both sides is fixed on the anode portion on the back surface on the smooth portion 3 side, and the conductive member 8 and the anode portion are bonded using ultrasonic welding. The aluminum bases 1 were electrically connected to enable conduction of the anode part of the capacitor element.

  Next, the external anode terminal 9 and the external cathode terminal 11 of the electrode substrate 10 for circuit board mounting are respectively conducted to the conductive member 8 and the conductive paste layer 7 constituting the anode part and the cathode part on the smoothing part 3 side. Electrically bonded with the adhesive 12.

  Next, the entire exposed portion of the solid electrolytic capacitor element not connected to the electrode substrate 10 was covered with a mold resin 13 made of an epoxy resin, and the resin was cured by heat treatment at 200 ° C., thereby producing a solid electrolytic capacitor. The number of solid electrolytic capacitors produced by this method was 30.

  The electrical characteristics and shape of the produced 30 solid electrolytic capacitors were measured. The measurement items were five items of capacitance, ESR, leakage current, ESL, and product thickness. Capacitance and ESR are both measured by the AC impedance bridge method. Among these, the measurement conditions of the capacitance were that the frequency of the applied reference signal was 120 Hz, the voltage was 1 Vrms, and the DC bias was 0V. On the other hand, in ESR, the frequency of the applied reference signal is 1 MHz, the voltage is 1 Vrms, and the DC bias is 0V. As for leakage current, a signal of 2.5 V, which is the rated voltage of the solid electrolytic capacitor, was applied, and the value after 1 minute was measured. The solid electrolytic capacitor was joined to a predetermined evaluation board by soldering, and the S21 characteristic (transfer characteristic) at 100 MHz was measured using a network analyzer, and the equivalent circuit was simulated based on the result. The average value of each characteristic of the produced 30 solid electrolytic capacitors is shown in the examples of Table 1.

(Comparative example)
As a comparative example, a method for producing a conventional solid electrolytic capacitor in which porous portions are formed on both surfaces of a flat aluminum substrate of a solid electrolytic capacitor element will be described with reference to the drawing of the conventional solid electrolytic capacitor in FIG.

First, the flat aluminum substrate 1 was etched, and a solid electrolytic capacitor element was produced in the same manner as in the example using the aluminum substrate 1 provided with the porous portions 2 on both sides. The flat aluminum substrate 1 used here has a nominal chemical formation voltage of 4 V and an electrostatic capacity per unit area (cm ² ) of 150 μF for forming an anodized film on the surface. Here, the total thickness of the aluminum substrate 1 and the porous portion is 100 μm. As a breakdown, the thickness of the aluminum substrate 1 is 40 μm, the thickness of the porous portion is 30 μm on one side, and 60 μm on both sides. The anode part and the cathode part of the porous part 2 of the solid electrolytic capacitor element were connected to the external anode terminal 9 and the external cathode terminal 11 of the electrode substrate 10, respectively. Thereafter, the exposed portion of the solid electrolytic capacitor element was covered with a mold resin 13 to form a solid electrolytic capacitor. The number of solid electrolytic capacitors produced by this method was 30. In addition, the measurement of electrical characteristics and shape is the same as in the example, and the average value of each characteristic of the 30 solid electrolytic capacitors produced is shown in the comparative example of Table 1.

  From Table 1, it can be seen that the ESL is lower in the example than in the comparative example.

  The above results show that the porous part 2 is not provided on the surface of the solid electrolytic capacitor element on the external electrode terminal (external anode terminal 9 and external cathode terminal 11) side, so that the thickness of the porous part 2 is 30 μm from the comparative example. It is possible to reduce the ESL by reducing the length of the wiring circuit of the electrode by reducing the thickness of the electrode portion and the cathode portion.

  As described above, according to the solid electrolytic capacitor of the present invention, the porous portion 2 is not formed between the solid electrolytic capacitor element and the electrode substrate 10, so that the space between the aluminum substrate 1 and the electrode substrate 10 can be reduced. The routing length of the wiring circuit can be shortened by the thickness of the porous portion 2, thereby reducing the routing length of the wiring circuit and thereby reducing the ESL. Therefore, by implementing the present invention, a low impedance solid electrolytic capacitor is realized.

The figure which shows the solid electrolytic capacitor of this invention, Fig.1 (a) is a perspective view, FIG.1 (b) is sectional drawing of the AA line of Fig.1 (a). The figure which shows the conventional solid electrolytic capacitor. 2A is a perspective view, and FIG. 2B is a cross-sectional view taken along line AA in FIG. 2A.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Aluminum base body 2 Porous part 3 Smooth part 4 Insulator layer 5 Solid electrolyte layer 6 Graphite layer 7 Conductive paste layer 8 Conductive member 9 External anode terminal 10 Electrode substrate 11 External cathode terminal 12 Conductive adhesive 13 Mold resin

Claims (1)

  An anodized film is formed on the front and back surfaces of a flat valve action metal having a porous portion on the front surface and a smooth portion on the back surface, and divided into an anode region and a cathode region by an insulating layer formed on the anodized film. Then, a solid electrolyte layer, a graphite layer, and a conductive paste layer are sequentially formed on the anodic oxide film in the cathode part region to form a cathode part, and the anodic oxide film on the back surface of the anode part area is removed and a conductive member is connected to form an anode. The solid electrolytic capacitor is characterized in that the anode part and the anode external terminal, and the cathode part on the back surface and the cathode external terminal are connected to each other.

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