JP5898998B2 - Solid electrolytic capacitor - Google Patents

Description

  The present invention relates to a solid electrolytic capacitor, and more particularly to a solid electrolytic capacitor having a solid electrolyte containing a conductive polymer.

  In recent years, with the development of portable electronic devices, there is a need for a solid electrolytic capacitor that is small, has a large capacitance, and is excellent in frequency characteristics. In particular, with the digitization of electronic devices, excellent high frequency characteristics are required for solid electrolytic capacitors. Therefore, in order to reduce the equivalent series resistance (hereinafter referred to as ESR (Equivalent Series Resistance)) of the solid electrolytic capacitor, a conductive polymer having high conductivity is used as the cathode material of the solid electrolytic capacitor.

  Patent Document 1 discloses a technique relating to a solid electrolytic capacitor that is low in cost and can suppress deterioration of ESR characteristics.

JP 2008-135460 A

  As described in the background art, ESR of the solid electrolytic capacitor can be reduced by using a conductive polymer having high conductivity as the cathode material of the solid electrolytic capacitor. Generally, in a solid electrolytic capacitor, a capacitor element containing a conductive polymer is sealed with an exterior resin. Therefore, the conductive polymer can be isolated from the external environment, and the oxidative deterioration of the conductive polymer can be suppressed.

  However, even if the capacitor element is sealed with the exterior resin, the conductive polymer is oxidized and deteriorated when oxygen enters the solid electrolytic capacitor from the outside. When the conductive polymer is oxidized and deteriorated, there is a problem that the conductivity of the conductive polymer is lowered (that is, the resistance is increased), and the ESR of the solid electrolytic capacitor is increased.

  In view of the above problems, an object of the present invention is to provide a solid electrolytic capacitor capable of suppressing oxidative deterioration of a conductive polymer contained in a capacitor element and suppressing an increase in ESR.

  A solid electrolytic capacitor according to the present invention includes an anode body in which an anode wire is embedded, a dielectric film provided on the surface of the anode body, and a solid containing a conductive polymer provided on the surface of the dielectric film. A capacitor element comprising an electrolyte, an exterior resin that covers the capacitor element, an anode lead frame that is electrically connected to the anode wire, extends from the interior of the exterior resin to the outside, and functions as an anode terminal; A cathode lead frame that is electrically connected to the solid electrolyte layer, extends from the inside of the exterior resin to the outside, and functions as a cathode terminal. A surface of the cathode lead frame is provided with a solder plating layer, and the solder plating layer is divided in a region including a first boundary portion that is an inner and outer boundary of the exterior resin on the cathode lead frame side. Have

  According to the present invention, it is possible to provide a solid electrolytic capacitor that can suppress oxidative deterioration of a conductive polymer contained in a capacitor element and suppress an increase in ESR.

1 is a cross-sectional view of a solid electrolytic capacitor according to a first embodiment. FIG. 3 is a side view of the solid electrolytic capacitor according to the first exemplary embodiment as viewed from the cathode lead frame side. 2 is an enlarged cross-sectional view of the solid electrolytic capacitor according to Embodiment 1 on the cathode lead frame side. FIG. 2 is an enlarged cross-sectional view of the solid electrolytic capacitor according to Embodiment 1 on the cathode lead frame side. FIG. 2 is an enlarged cross-sectional view of the solid electrolytic capacitor according to Embodiment 1 on the cathode lead frame side. FIG. 2 is an enlarged cross-sectional view of the solid electrolytic capacitor according to Embodiment 1 on the cathode lead frame side. FIG. FIG. 3 is a cross-sectional view of a solid electrolytic capacitor according to a second embodiment. It is an expanded sectional view by the side of the cathode lead frame of the conventional solid electrolytic capacitor. It is an expanded sectional view by the side of the cathode lead frame of the conventional solid electrolytic capacitor.

<Embodiment 1>
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a cross-sectional view of a solid electrolytic capacitor 1 according to the present embodiment. As shown in FIG. 1, the solid electrolytic capacitor 1 includes a capacitor element 11, an exterior resin 12 that covers the capacitor element 11, an anode lead frame 13, and a cathode lead frame 14.

  Capacitor element 11 includes an anode body in which anode wire 15 is embedded, a dielectric film provided on the surface of the anode body, a solid electrolyte provided on the surface of the dielectric film and containing a conductive polymer, Is provided. As the anode body, for example, a porous body formed by sintering a valve action metal such as tantalum can be used.

  For example, the capacitor element 11 is formed by embedding an anode wire 15 in tantalum powder, press-molding it into a predetermined shape, and sintering it to form a porous body of tantalum metal. Then, a dielectric oxide film is formed on the surface of the porous body using an electrochemical method. Thereafter, a solid electrolyte layer of a conductive polymer is formed on the surface of the dielectric oxide film, and further a graphite layer and a silver paste layer are formed, whereby the capacitor element 11 can be manufactured. As the conductive polymer, for example, polythiophene, polypyrrole, polyaniline, or derivatives thereof can be used.

  The anode lead frame 13 is electrically connected to the anode wire 15, extends from the inside of the exterior resin 12 to the outside, and functions as an anode terminal. The anode lead frame 13 includes a base material containing copper, a nickel plating layer formed on the surface of the base material, and a solder plating layer formed on the surface of the nickel plating layer. As a plating layer formed between the base material and the solder plating layer, for example, gold plating having a resistance lower than that of nickel plating may be used. As the plating layer formed between the base material and the solder plating layer, any material may be used as long as the melting point is 300 ° C. or higher.

  The cathode lead frame 14 is electrically connected to the capacitor element 11 via the conductive resin 16. The cathode lead frame 14 extends from the inside of the exterior resin 12 to the outside and functions as a cathode terminal. FIG. 2 is a side view of the solid electrolytic capacitor 1 as viewed from the cathode lead frame side 20. As shown in FIGS. 1 and 2, the cathode lead frame 14 is formed from the side surface to the bottom surface of the solid electrolytic capacitor 1. The same applies to the anode lead frame 13.

  The cathode lead frame 14 includes, for example, a base material containing copper, a nickel plating layer formed on the surface of the base material, and a solder plating layer formed on the surface of the nickel plating layer. As a plating layer formed between the base material and the solder plating layer, for example, gold plating having a resistance lower than that of nickel plating may be used. As the plating layer formed between the base material and the solder plating layer, any material may be used as long as the melting point is 300 ° C. or higher.

  FIG. 3 is an enlarged sectional view of the cathode lead frame side 20 of the solid electrolytic capacitor 1 shown in FIG. As shown in FIG. 3, the cathode lead frame 14 includes a base material 21, a nickel plating layer (not shown) formed on the surface of the base material 21, and a solder plating layer formed on the surface of the nickel plating layer. 22. In the solid electrolytic capacitor 1 according to the present embodiment, the solder plating layer 22 is divided in the region including the inner and outer boundary portions (first boundary portions) 23 of the exterior resin 12 on the cathode lead frame side. It is comprised so that it may have. In other words, the exterior resin 12 is formed so as to straddle the base material 21 whose surface is plated with nickel or the like at the boundary portion 23 (divided portion 25) between the inside and the exterior of the exterior resin 12.

  FIG. 9 is an enlarged cross-sectional view of the conventional solid electrolytic capacitor on the cathode lead frame side, and corresponds to the enlarged cross-sectional view of FIG. In FIG. 9, reference numerals indicating the respective components are shown in the 100s. That is, the solid electrolytic capacitor includes a capacitor element 111, an exterior resin 112, an anode wire 115, a conductive resin 116, a base material 121 having a nickel plating layer, and a cathode lead frame 114 including a solder plating layer 122. Have.

  As shown in FIG. 9, when the solder plating layer 122 is formed in the region including the boundary portion 123 of the exterior resin 112, the solder plating layer 122 is melted when the solid electrolytic capacitor is mounted on the circuit board. A gap is formed at the boundary portion 123 of the exterior resin 112. Then, oxygen enters the exterior resin 112 through the formed gap, and there is a problem that the characteristics of the capacitor element 111 deteriorate due to the oxidative deterioration of the conductive polymer formed in the capacitor element 111. That is, when the conductive polymer is oxidized and deteriorated, the conductivity of the conductive polymer is reduced (that is, the resistance is increased), and the ESR of the solid electrolytic capacitor is increased.

  On the other hand, in the solid electrolytic capacitor 1 according to the present embodiment, as shown in FIG. 3, in the region including the boundary portion 23 of the exterior resin 12, a divided portion 25 where the solder plating layer 22 is not formed is provided. Yes. Therefore, when the solid electrolytic capacitor 1 is mounted on the circuit board, it is possible to suppress the formation of a gap in the boundary portion 23 of the exterior resin 12 by melting the solder plating layer 22. Oxygen can be prevented from entering the glass.

  Therefore, the invention according to the present embodiment can provide a solid electrolytic capacitor that can suppress the oxidative deterioration of the conductive polymer contained in the capacitor element 11 and suppress the increase in ESR.

  The dividing portion 25 where the solder plating layer 22 is not formed is only required to be formed in a region including the boundary portion 23. For example, as shown in FIG. 4, the dividing portion 25 is the dividing portion shown in FIG. It may be formed to be shorter than 25.

  Further, the divided portion 25 where the solder plating layer 22 is not formed may be formed on at least one of the upper surface (first surface) and the lower surface (second surface) of the cathode lead frame 14. That is, as shown in FIG. 5, the dividing portion 25 may be formed only on the upper surface of the cathode lead frame 14. Further, the dividing portion 25 may be formed only on the lower surface of the cathode lead frame 14. Moreover, the parting part 25 should just be formed in the area | region containing the boundary part 23, and should just be formed in at least one of the inside of the exterior resin 12, and the exterior.

  Further, the divided portion 25 where the solder plating layer 22 is not formed is a surface of the cathode lead frame 14 and extends horizontally by a predetermined length in a direction away from the boundary resin 23 from the exterior resin 12 (region of FIG. 4). 24).

  On the other hand, as shown in FIG. 6, after the cathode lead frame 14 is bent outside the exterior resin 12, a divided portion 25 may be formed in a region including a portion extending downward. That is, the divided portion 25 can be formed without providing the region 24 extending horizontally for a predetermined length shown in FIG.

<Embodiment 2>
Next, a second embodiment of the present invention will be described. FIG. 7 is a cross-sectional view of the solid electrolytic capacitor 2 according to the second embodiment. The present embodiment is different from the first embodiment in that the capacitor element 31 is arranged at a predetermined distance from the cathode lead frame side. Other than this, since it is the same as the solid electrolytic capacitor 1 described in the first embodiment, the same components are denoted by the same reference numerals, and redundant description is omitted.

  As shown in FIG. 7, in the solid electrolytic capacitor 2 according to the present embodiment, the capacitor element 31 is arranged at a distance d2 from the cathode lead frame side. Here, the distance d2 is a distance (a distance along the cathode lead frame 14) from the boundary portion 23 of the exterior resin 12 to the end portion 32 of the capacitor element 31.

  For example, the capacitor element 31 can be arranged such that the distance d2 is ¼ or more of the distance d1 that is the outer dimension of the exterior resin 12. Here, the distance d1 which is the external dimension of the exterior resin 12 is the inside and exterior boundary portion (first boundary portion) of the exterior resin 12 on the cathode lead frame side and the interior of the exterior resin 12 on the anode lead frame side. This corresponds to the distance from the external boundary portion (second boundary portion).

  Furthermore, the capacitor element 31 may be arranged such that the distance d2 is equal to or greater than ½ of the distance d1 that is the outer dimension of the exterior resin 12. Here, when the distance d2 is excessively increased, the capacitor element 31 is reduced and the capacitance of the capacitor element 31 is reduced. Therefore, more preferably, the capacitor element 31 can be arranged such that the distance d2 is ½ or more and 3/4 or less of the distance d1 that is the outer dimension of the exterior resin 12.

  In this way, by disposing the capacitor element 31 at a predetermined distance from the boundary portion 23, the time for external oxygen to reach the conductive polymer of the capacitor element 31 from the boundary portion 23 can be delayed. Therefore, the oxidative deterioration of the conductive polymer can be further suppressed, and the ESR of the solid electrolytic capacitor can be further reduced.

  As shown in FIG. 7, when the size of the capacitor element 31 is reduced, the capacitance of the capacitor element is reduced. However, in the solid electrolytic capacitor 2 according to the present embodiment, the size of the capacitor element 31 is deliberately reduced, and the capacitor element 31 is arranged at a predetermined distance from the boundary portion 23, thereby oxidizing the conductive polymer. Deterioration is suppressed.

<Example 1>
Next, examples of the present invention will be described.
Anode wire 15 was embedded in tantalum powder, which is a valve metal, press-formed into a predetermined shape, and then sintered at 1250 ° C. to form a tantalum metal anode body. Then, the formed anode body was immersed in a phosphoric acid aqueous solution, and a DC voltage of 15 V was applied to form a dielectric oxide film (anodized film) on the surface of the anode body. Thereafter, a solid electrolyte layer of a conductive polymer was formed on the surface of the dielectric oxide film. The solid electrolyte layer was formed by repeating polythiophene chemical polymerization, suspension impregnation and drying. Then, the capacitor | condenser element 11 was produced by forming the graphite layer and the silver paste layer, respectively on the surface of the solid electrolyte layer.

  Thereafter, the conductive resin 16 was applied to the cathode lead frame 14 to mount the capacitor element 11, and then dried at 150 ° C. for 30 minutes to make the capacitor element 11 and the cathode lead frame 14 conductive. At this time, the distance d2 (distance along the cathode lead frame 14: see FIG. 7) from the boundary portion 23 (see FIG. 3) of the exterior resin 12 to the end of the capacitor element was 0.3 mm. The anode wire 15 and the anode lead frame 13 were connected by resistance welding.

  The cathode lead frame 14 is produced by forming a nickel plating layer having a thickness of 0.5 μm on the copper material as the base material 21 and then forming a solder plating layer 22 having a thickness of 4 μm on the nickel plating layer. did. In addition, in order to form the divided portion 25 in the region including the boundary portion 23 of the cathode lead frame 14, before sealing with the exterior resin 12, the portion other than the portion where the divided portion 25 is formed is masked and then divided by the sandblast method. The solder plating layer 22 of the portion 25 was scraped off. As a method for scraping off the solder plating layer 22, for example, a mechanical grinding method or a laser grinding method may be used in addition to the sandblast method.

  The divided portion 25 was formed by scraping the solder plating layers on both the inside and outside of the exterior resin 12 straddling the boundary portion 23 and on both sides of the cathode lead frame 14 to expose the underlying nickel plating. The length of the divided portion 25 was 0.1 mm. Then, it sealed with the exterior resin 12, and produced the fixed electrolytic capacitor which has external dimensions of 7.3 mm long, 4.3 mm wide, and 1.9 mm in height.

<Comparative Example 1>
As Comparative Example 1, a solid electrolytic capacitor in which a divided portion 125 exists in the exterior resin 112 and the divided portion 125 does not straddle the boundary portion 123 as shown in FIG. Example 1 is the same as Example 1 except that the position of the divided portion 125 is different.

<Comparative Example 2>
Further, as Comparative Example 2, a solid electrolytic capacitor in which a part as shown in FIG. 9 was not formed was produced. Example 1 is the same as Example 1 except that no part is formed.

<Test result 1>
Twenty solid electrolytic capacitors according to Example 1, Comparative Example 1, and Comparative Example 2 were each produced and left in an environment of 105 ° C. Then, ESR (equivalent series resistance) after standing for 250 hours and after standing for 500 hours was measured. ESR measurement conditions were a frequency of 100 kHz, DC = 1.5 V, and AC = 500 mV. HP 4263A of HP company was used for the measuring device. After measuring each ESR, the rate of change of ESR relative to the initial value was calculated, and the average value of 20 samples was obtained. Table 1 shows the initial value when left in an environment of 105 ° C., the rate of change of ESR after 250 hours with respect to the initial value, and the rate of change of ESR after 500 hours with respect to the initial value.

  As shown in Table 1, in Example 1, the change rate after 250 hours was 1.03, and the change rate after 500 hours was 1.05. On the other hand, in Comparative Example 1, the rate of change after 250 hours was 1.06, the rate of change after 500 hours was 1.09, and the rate of change of ESR was larger than that in Example 1. . In Comparative Example 2, the rate of change after 250 hours was 1.10, the rate of change after 500 hours was 1.20, and the rate of change of ESR was larger than that in Example 1.

  Therefore, by providing a part where the solder plating layer is not formed at the boundary part of the exterior resin, it is possible to suppress the oxygen from entering the interior of the exterior resin and the conductive polymer from being oxidized and deteriorated. An increase in ESR could be suppressed.

  Note that when the divided portions 25 are formed on both surfaces or one surface of the cathode lead frame 14 inside the exterior resin 12 across the boundary portion 23, or when the divided portions 25 are formed on both surfaces or one surface of the cathode lead frame 14 outside the exterior resin 12. The effects of the present invention were also obtained when formed. In particular, when the divided portions 25 are formed both on the inside and outside of the exterior resin 12 and on both surfaces of the cathode lead frame 14 across the boundary portion 23, the effect of the present invention is most remarkable.

<Example 2>
Using the same method as in Example 1, a capacitor element including a tantalum metal anode body, a dielectric oxide film, a solid electrolyte layer of a conductive polymer, a graphite layer, and a silver paste layer was produced. The capacitor element had a length of 1.8 mm, a width of 2.4 mm, a height of 1.2 mm, a rated voltage of 2.5 V, and a capacitance of 220 μF.

  After the capacitor element is manufactured, the conductive resin 16 is applied to the cathode lead frame 14 manufactured in the same manner as in Example 1, and after mounting the capacitor element, the capacitor element and the cathode lead frame are dried at 150 ° C. for 30 minutes. 14 was conducted. Further, as in Example 1, a divided portion 25 was formed in a region including the boundary portion 23 of the cathode lead frame 14. The anode wire 15 and the anode lead frame 13 were connected by resistance welding.

  Thereafter, the capacitor element was sealed using a transfer mold having outer dimensions of 7.3 mm in length, 4.3 mm in width, and 1.9 mm in height. The distance d2 (distance along the cathode lead frame 14: see FIG. 7) from the boundary portion 23 of the exterior resin 12 to the end of the capacitor element in the solid electrolytic capacitor produced at this time was 3.85 mm. That is, a solid electrolytic capacitor in which the distance d2 is equal to or greater than ½ of the distance d1 that is the outer dimension of the exterior resin 12 was produced.

<Comparative Example 3>
As Comparative Example 3, a solid electrolytic capacitor in which the volume efficiency was improved by expanding the capacitor element 11 until the distance d2 from the boundary portion 23 of the exterior resin 12 to the end of the capacitor element became 0.3 mm was produced. At this time, the rated voltage of the solid electrolytic capacitor was 2.5 V, and the capacitance was 220 μF. Except for the capacitor element, the second embodiment is the same as the second embodiment.

<Test result 2>
Twenty solid electrolytic capacitors according to Example 2 and Comparative Example 3 were each produced and left in an environment of 105 ° C. Then, ESR (equivalent series resistance) after standing for 250 hours and after standing for 500 hours was measured. ESR measurement conditions were a frequency of 100 kHz, DC = 1.5 V, and AC = 500 mV. HP 4263A of HP company was used for the measuring device. After measuring each ESR, the rate of change of ESR relative to the initial value was calculated, and the average value of 20 samples was obtained. Table 2 shows the initial value when left in an environment of 105 ° C., the rate of change of ESR after 250 hours with respect to the initial value, and the rate of change of ESR after 500 hours with respect to the initial value.

  As shown in Table 2, in Example 2, the change rate after 250 hours was 1.01, and the change rate after 500 hours was 1.02. On the other hand, in Comparative Example 3, the rate of change after 250 hours was 1.06, the rate of change after 500 hours was 1.09, and the rate of change of ESR was larger than that in Example 2. .

  Therefore, the conductive polymer is oxidatively deteriorated by providing a dividing portion where the solder plating layer is not formed at the boundary portion of the exterior resin and disposing the capacitor element at a predetermined distance from the cathode lead frame side. This could be suppressed, and the increase in ESR could be suppressed.

  Note that the present invention is not limited to the above-described embodiments and examples, and can be modified as appropriate without departing from the spirit of the present invention. For example, in the above example, the case where the divided portion 25 is formed in the cathode lead frame 14 has been described. However, a solder plating layer is formed in a region including the inner and outer boundary portions of the exterior resin on the anode lead frame 13 side. There may be no parting. In this way, by providing a split portion in the anode lead frame 13 in addition to the cathode lead frame 14, the oxidative deterioration of the conductive polymer can be further suppressed.

  The present invention has been described with reference to the above-described embodiment and examples. However, the present invention is not limited only to the configuration of the above-described embodiment and examples, and the scope of the invention of the claims of the claims of this application Of course, various changes, modifications, and combinations that can be made by those skilled in the art are included.

1, 2 Fixed electrolytic capacitor 11 Capacitor element 12 Exterior resin 13 Anode lead frame 14 Cathode lead frame 15 Anode wire 15
16 Conductive resin 21 Base material 22 Solder plating layer 23 Boundary portion 25 Divided portion

Claims (4)

A capacitor element comprising: an anode body in which an anode wire is embedded; a dielectric film provided on a surface of the anode body; and a solid electrolyte provided on a surface of the dielectric film and including a conductive polymer;
An exterior resin covering the capacitor element;
An anode lead frame that is electrically connected to the anode wire, extends from the inside of the exterior resin to the outside, and functions as an anode terminal;
A cathode lead frame that is electrically connected to the solid electrolyte layer, extends from the inside of the exterior resin to the outside, and functions as a cathode terminal;
Solder plating layers are provided on both surfaces of the cathode lead frame, and the solder plating layer has a divided portion that is partially divided, and the boundary between the inside and the outside of the exterior resin in the divided portion The boundary part that is
Solid electric field capacitor. The solid electrolytic capacitor according to claim 1, wherein the anode body is a porous body formed by sintering a valve action metal. The cathode lead frame is
A base material containing copper;
A nickel plating layer formed on the surface of the base material;
The solder plating layer formed on the surface of the nickel plating layer,
The solid electrolytic capacitor according to claim 1 or 2 . The solid electrolytic capacitor according to any one of claims 1 to 3 , wherein the conductive polymer is polythiophene, polypyrrole, polyaniline, or a derivative thereof.

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