JP2006108132A - Solid-state electrolytic capacitor and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the resistance of a solid-state electrolytic capacitor and to prevent a decline in electrostatic capacitance in a high-frequency region by reducing the potential occurring in a cathode during a manufacturing process. <P>SOLUTION: The solid-state electrolytic capacitor comprises a cathode-side electrode foil (4) which has been etched, a chemical conversion film (6) formed on the etched surface of the cathode-side electrode foil, a conductor film (coating layer 8) which is formed on the front surface of the chemical conversion film with part of it extended through the chemical conversion film to establish the conductivity path to the cathode-side electrode foil, and an anode-side electrode foil (14) which is formed with a solid-state electrolyte layer (10) interposed between the conductor layer and the anode-side electrode foil (14). The resistance value of the conductor layer including a contact resistance with respect to the solid-state electrolyte layer (10) is set to 0.01 Ω or less. The manufacture of the solid-state electrolytic capacitor includes a process of forming the conductor layer of titanium carbide, and then applying a potential of ≤2 V to the conductor layer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a solid electrolytic capacitor using a cathode formed with a chemical conversion film formed on an etching foil, and a method for manufacturing the same.

  In a capacitor for switching power supply, a large current exceeding several amperes flows due to applications such as smoothing and decoupling. For example, in a VRM (Voltage Regulate Module) power supply, the current change is steep with a few hundred A / μs or more. Presents a value. An electrolytic capacitor suitable for such an application requires a large current discharge in a short time of several μs immediately after the discharge.

  Solid electrolytic capacitors suitable for such applications are required to have low resistance, and the manufacturing method is to form a cathode film by forming a chemical conversion film on the etching foil, and a conductor layer made of titanium nitride, titanium carbide, etc. is provided on the surface. (For example, refer to Patent Document 1).

Further, if the conductor layer and the cathode portion are made conductive by removing a part of the chemical conversion film, the capacitance of the cathode portion becomes infinite, the capacitance as a solid electrolytic capacitor increases, and the solid electrolyte ESR (equivalent series resistance) is reduced when the adhesion between the film and the chemical conversion film is increased (see Patent Document 1).
JP2000-114109A

  However, a solid electrolytic capacitor having a capacitance of 1000 [μF] or less is often used for the switching power supply described above, but when used in such a high frequency region of several tens to several hundreds [kHz], the high frequency region is used. It was found that the capacitance decreased.

  By the way, such a solid electrolytic capacitor is formed by immersing a capacitor element in a chemical conversion solution as a process for repairing a damaged portion generated in the anode foil in a process such as element winding or lamination (repair formation, Re-forming). At this time, a potential is generated at the cathode. It has been experimentally confirmed by the present inventor that when this potential is high, the decrease in capacitance in the high frequency region becomes large.

Accordingly, the present invention relates to a solid electrolytic capacitor with a first object of reducing its resistance and reducing the potential generated at the cathode in the manufacturing process to prevent a decrease in capacitance in the high frequency region. Second purpose.

  In order to achieve the first object, a solid electrolytic capacitor of the present invention includes an etched cathode side electrode foil, a conversion film formed on the etched surface of the cathode side electrode foil, and a surface of the conversion film. A conductive layer that penetrates the chemical conversion film and is conducted to the cathode-side electrode foil, and an anode-side electrode foil that is disposed with a solid electrolyte layer interposed between the conductive layer and the conductive layer. The resistance value including the contact resistance of the conductor layer with the solid electrolyte layer is set to 0.01 [Ω] or less, preferably 0.005 [Ω] or less.

In order to achieve the second object, a method for producing a solid electrolytic capacitor of the present invention comprises an etched cathode side electrode foil, a chemical conversion film formed on the etched surface of the cathode side electrode foil, and the chemical conversion film. A conductor layer formed on the surface of the film and passing through the chemical conversion film and conducted to the cathode side electrode foil, and an anode side electrode foil disposed with a solid electrolyte layer interposed between the conductor layer The conductor layer is made of titanium carbide, and includes a step of applying a potential of 2 [V] or less, preferably 1 [V] or less.

  According to the present invention, the following effects can be obtained from the present invention.

  (1) According to the solid electrolytic capacitor of the present invention, ESR can be reduced.

(2) According to the method for manufacturing a solid electrolytic capacitor of the present invention, since the potential generated in the cathode portion is suppressed, it is possible to prevent a decrease in capacitance caused by the manufacturing.

  The solid electrolytic capacitor and the manufacturing method thereof according to the present invention will be described with reference to FIG. FIG. 1 is a cross-sectional view showing an outline of a solid electrolytic capacitor.

  The solid electrolytic capacitor includes a capacitor element 2. The capacitor element 2 has a cathode side electrode foil 4 as a cathode side electrode portion, a first chemical conversion film 6, a coating layer 8 as a conductor layer, a solid electrolyte layer 10, a first electrode. 2 and the anode side electrode foil 14 etc. are provided as the anode side electrode part. The cathode-side electrode foil 4 is formed of a metal material such as aluminum, which is a valve metal or a film-forming metal, and the form thereof is made of a foil. The surface of the cathode-side electrode foil 4 is enlarged by an etching process or the like on its surface, and a pit portion 18 is formed on the etching surface 16.

  The above-described chemical conversion film 6 is formed on the etching surface 16 of the cathode side electrode foil 4 by immersing the cathode side electrode foil 4 in a chemical conversion solution or the like. This chemical conversion film 6 is also penetrated into the inner wall portion of the pit portion 18 of the etching surface 16.

  A coating layer 8 is formed on the cathode-side electrode foil 4 on which such a chemical conversion film 6 is formed by a conductor vapor deposition process. For example, titanium carbide (TiC) is used as the conductive material for forming the coating layer 8.

  Further, through the vapor deposition process of the conductor, a through-hole portion 20 is formed in the chemical conversion film 6 by partially removing the chemical conversion film 6, and the coating layer 8 enters the through-hole portion 20, so Continuity is achieved.

  And between the surface part of the coating layer 8 and the chemical conversion film 12 by the side of the anode side electrode foil 14, for example, a conductive polymer (PEDT) is installed as the solid electrolyte layer 10, and this solid electrolyte layer 10 has a pit part. The chemical conversion film 6 formed along the inner wall 18 is also in contact. That is, the cathode portion 22 is configured by the cathode side electrode foil 4, the chemical conversion film 6, the coating layer 8, and the solid electrolyte layer 10.

  Further, the anode side electrode foil 14 is formed of a metal material such as aluminum, which is a valve metal and a film forming metal like the cathode side electrode foil 4, and the form thereof is made of foil. On the surface of the anode side electrode foil 14, the above-described chemical conversion film 12 is formed by immersing the anode side electrode foil 14 in a chemical conversion solution or the like. That is, the anode portion 24 is constituted by the chemical conversion film 12 and the anode-side electrode foil 14.

  The capacitor element 2 constituting the solid electrolytic capacitor can be configured as a wound element by winding the cathode portion 22 and the anode portion 24, for example.

  An equivalent circuit of the capacitor element 2 will be described with reference to FIG. FIG. 2 shows an equivalent circuit displayed so as to overlap the capacitor element 2 described above.

  Between the cathode terminal 26 and the anode terminal 28 of the capacitor element 2, the chemical conversion film 6 has a capacitance Cc, a resistance Rc including contact resistance with the coating layer 8 and the solid electrolyte layer 10, and a resistance with the solid electrolyte layer 10. The capacitance Ca and the inductance L are formed by Rp and the chemical conversion film 12. The inductance L is generated when a current flows through the cathode side electrode foil 4, the anode side electrode foil 14, the cathode terminal 26, the anode terminal 28, and the like.

  Therefore, in the low frequency region, 1 / ωCc >> Rc, and the current route 30 is formed through the series circuit of the resistors Rc, Rp, capacitance Ca and inductance L, whereas in the high frequency region, 1 / ωCc << Rc. Thus, the current route 32 is formed through a series circuit of the capacitance Cc, the resistance Rp, the capacitance Ca, and the inductance L. As a result, in the high frequency region, the capacitances Cc and Ca of the chemical conversion films 6 and 12 are generated, and the capacitance C of the capacitor element 2 is reduced. That is, this capacitance C is

C = Ca · Cc / (Ca + Cc) (1)
Given in. For example, if it is assumed that Ca = Cc, the capacitance C in the formula (1) becomes C = Ca / 2 or Cc / 2, and therefore it can be understood that the capacitance C decreases.

As described above, the decrease in the capacitance in the high frequency region is caused by the high potential generated during the repair formation in the manufacturing process, and the potential forms the chemical conversion film 6 on the cathode-side electrode foil 4. It is presumed that the resistance of the coating layer 8 increases due to this, the contact resistance between the coating layer 8 and the solid electrolyte layer 10 increases, and the like. The resistance of this portion, that is, the resistance Rc described above increases, and the capacitance decreases in the high frequency region due to the formation of the current route 32. Therefore, if the resistance Rc is suppressed to a certain value or less, a decrease in capacitance can be suppressed by the current route 30 even in a high frequency region.

  Next, examples of the solid electrolytic capacitor and the manufacturing method thereof according to the present invention will be described.

  For the cathode side electrode foil 4 and the anode side electrode foil 14, for example, a foil made of aluminum or tantalum is used as a valve metal, and the surface of the cathode side electrode foil 4 is subjected to an etching process to increase the surface area. ing. For the anode side electrode foil 14, for example, an etching foil is used.

  The etching surface 16 of the cathode side electrode foil 4 is subjected to a chemical conversion treatment to form a chemical conversion film 6, and the chemical conversion treatment is also applied to the opposing surface portion of the anode side electrode foil 14 that faces the chemical conversion coating 6 side. A chemical conversion film 12 is formed. Further, titanium carbide or titanium nitride is vapor-deposited on the surface of the chemical conversion film 6 of the cathode side electrode foil 4 to form a coating layer 8. A plurality of through holes 20 are formed in the chemical conversion film 6, and the coating layer 8 formed on the surface is processed so as to penetrate the through holes 20 and reach the cathode side electrode foil 4. And the cathode side electrode foil 4 and the anode side electrode foil 14 which passed through these processes are comprised as the capacitor | condenser element 2 by winding through a separator.

  The capacitor element 2 is impregnated with EDT (ethylene dioxythiophene) and an oxidizing agent. For example, a butanol solution of ferric p-toluenesulfonate is used as the oxidizing agent, the processing temperature is set to 150 ° C., for example, and heat polymerization is performed for 1 hour, and PEDT (polyethylenedioxythiophene) which is a conductive polymer. And the solid electrolyte layer 10 is formed. The capacitor element 2 is accommodated in a case, and the case is sealed to obtain a solid electrolytic capacitor as a product. The rating of this solid electrolytic capacitor is 2.5 [WV] -680 [μF].

  In this solid electrolytic capacitor, titanium carbide or titanium nitride is used for the coating layer 8 of the capacitor element 2. In Example 1, titanium carbide is used for the coating layer 8, and the potential applied during the manufacturing process is 0.8. [V] In Example 2, titanium carbide is used for the coating layer 8, and the potential applied during the manufacturing process is 2 [V]. In Example 3, titanium nitride is used for the coating layer 8, and during the manufacturing process, This potential is set to 0.8 [V], the capacitance is measured at frequencies of 30 [kHz], 50 [kHz] and 100 [kHz], and the capacitance is based on the frequency of 120 [kHz]. The rate of change [%] of The results are shown in Table 1.

  As is clear from these Examples 1 to 3, by setting the potential applied to the coating layer 8 during the manufacturing process to 2 [V] or less, preferably 1 [V] or less, the rate of change in capacitance can be increased. Can be lowered.

  As is apparent from Table 1, it can be seen that the decrease rate of the capacitance C can be suppressed to 15% or less, and that Rc <0.01Ω, and that 20% or less can be suppressed is Rc <0.005Ω. .

  And about this solid electrolytic capacitor, the coating layer 8 is formed with titanium carbide, and in the product A, the potential is set to 0.8 [V] during the manufacturing process, and in the product B, the potential is set to 2.0 [V during the manufacturing process. V], the change in the capacitance C was measured. The result is shown in FIG.

  As is clear from these examples, the decrease in the capacitance C in the high frequency region can be suppressed, and titanium carbide is used for the coating layer 8 to suppress the potential applied during the manufacturing process to 1 [V] or less. It has been found that the decrease in the capacitance C can be suppressed.

  More specifically, the larger the current flowing through the anode side electrode foil 14 during the formation of the capacitor element 2 in the solution, and the higher the resistance of the formation solution, the more the cathode side electrode with respect to the formation bus due to the influence of indirect power feeding. It has been found that the potential of the foil 4 is increased. Thus, after the formation of the normal element, the cathode side electrode foil 4 was formed and the influence of the characteristics was examined. As a result, as the formation time of the cathode side electrode foil 4 was extended, the change capacity of the capacitance C in the high frequency region was increased. The amount of drop in ΔCap increased, and an increase in tan δ and an increase in ESR in the low frequency region were observed.

  As described above, in the equivalent circuit of the TiC specification (FIG. 2) in which titanium carbide (TiC) is used for the coating layer 8 formed on the cathode side electrode foil 4 side, the surface of the cathode side electrode foil 4 in the low frequency region. Since the impedance (1 / ωCc) of the cathode-side electrode foil 4 is larger than the resistance Rc consisting of the resistance of the side coating layer (TiC layer) 8 and the contact resistance between the surface and the polymer (PEDT), the current is applied to the coating layer ( The product capacity is substantially the same as the capacitance formed by the anode side electrode foil 14 without being affected by the capacity of the cathode side electrode foil 4. In the high frequency region, the impedance (1 / ωCc) becomes smaller than the resistance Rc, and conversely, it becomes difficult to flow to the coating layer (TiC layer) 8, so that the capacity of the cathode electrode foil 4 is affected. Therefore, the characteristic value of the mass production product of the solid electrolytic capacitor is applied to the equivalent circuit, and the frequency characteristic is simulated. As the resistance Rc increases, the change capacitance ΔCap of the capacitance C increases. found. When the coating layer 8 is made of TiN or TiC, the product using TiC has a smaller resistance Rc including the contact resistance with the polymer constituting the solid electrolyte layer 10 than the product using TiN, and the high frequency The change capacity ΔCap in the region is reduced.

  As a result of such verification, there is a TiC specification mass-produced product that has a large drop in the change capacity ΔCap in the high-frequency region. The cause is that the cathode-side electrode foil 4 is in contact with the formation bus when the capacitor element 2 is formed. It was estimated that electrochemical oxidation occurred due to the potential, and as a result of the verification, the characteristics were reproduced. When the capacitor element 2 is a wound element, there is a pseudo short-circuited state due to the variation, and therefore the cathode side electrode foil 4 may be affected when the capacitor element 2 is formed. An equivalent circuit of the capacitor element 2 in such a state was created, and a simulation was performed when the resistance between the surface of the Ti-based vapor-deposited foil and the polymer constituting the solid electrolyte layer 10 was increased. A value was obtained.

  Next, modifications of the above embodiment will be listed.

  (1) For the electrode foils 4 and 14, an example in which aluminum is used has been described in the above embodiment, but a valve metal other than aluminum may be used for the electrode foil.

  (2) Regarding the capacitor element 2, the winding type element is exemplified in the above embodiment, but an element configuration other than the winding type element may be employed.

As described above, the most preferred embodiment of the present invention has been described. However, the present invention is not limited to the above description, and is described in the claims or the best for carrying out the invention. Various modifications and changes can be made by those skilled in the art based on the gist of the invention disclosed in the embodiments, and it goes without saying that such modifications and changes are included in the scope of the present invention.

ADVANTAGE OF THE INVENTION According to this invention, the solid electrolytic capacitor can provide the solid electrolytic capacitor which can suppress the fall of an electrostatic capacitance with the reduction of ESR, and improved the quality regarding a solid electrolytic capacitor.

It is sectional drawing which shows the outline | summary of the solid electrolytic capacitor which concerns on embodiment of this invention. It is a figure which shows the equivalent circuit of a solid electrolytic capacitor. It is a figure which shows the change of the electrostatic capacitance which formed the coating layer with titanium carbide and made the electric potential which concerns on a coating layer a parameter in a manufacturing process.

Explanation of symbols

2 Capacitor element 4 Cathode side electrode foil 6, 12 Chemical conversion film 8 Coating layer (conductor layer)
DESCRIPTION OF SYMBOLS 10 Solid electrolyte layer 14 Anode side electrode foil 16 Etching surface

Claims (2)

Etched cathode side electrode foil,
A chemical conversion film formed on the etched surface of the cathode-side electrode foil;
A conductor layer formed on the surface of the chemical film and conducted through the chemical film and conducted to the cathode-side electrode foil;
An anode-side electrode foil installed with a solid electrolyte layer interposed between the conductor layer,
A solid electrolytic capacitor in which a resistance value including a contact resistance of the conductor layer with the solid electrolyte layer is set to 0.01 [Ω] or less.
Etched cathode side electrode foil, chemical conversion film formed on the etched surface of the cathode side electrode foil, and formed on the surface of the chemical conversion film and penetrates the chemical conversion film to form the cathode side electrode foil A method for producing a solid electrolytic capacitor comprising: a conductive layer conducted to a conductive layer; and an anode-side electrode foil placed with a solid electrolyte layer interposed between the conductive layer,
A method for producing a solid electrolytic capacitor, comprising the step of forming the conductor layer of titanium carbide and applying a potential of 2 [V] or less.

Images