JP4780726B2 - Multilayer solid electrolytic capacitor - Google Patents

Description

  The present invention relates to an electrolytic capacitor having a solid electrolyte as a cathode, and more particularly to a multilayer solid electrolytic capacitor.

  Conventionally, as a solid electrolytic capacitor, a valve metal such as aluminum or tantalum is used as an anode, an anodic oxide film is formed on the surface thereof as a dielectric layer, and a solid electrolyte layer and a cathode lead layer are sequentially formed thereon. Later, a resin-sealed structure with a resin package is often used. (For example, refer to Patent Document 1).

The capacitor is used as a bypass capacitor, for example, connected between an electronic device such as a CPU and a power supply circuit. Recently, along with the speeding up and digitization of electronic devices, there is a need for a power supply system that is stable and capable of high-speed response.
For this reason, solid electrolytic capacitors used for noise removal and power supply system stability are also required to have excellent noise removal characteristics in a wide frequency range and high-speed response when supplying power. In addition, there is a strong demand for a large electrostatic capacity and high reliability for preventing ignition in response to power supply with a large current. (For example, refer to Patent Document 2).

  In order to meet these demands, a technique for laminating flat elements and thin sintered elements has been put into practical use as a method for increasing the capacity and reducing the ESR while keeping the occupied area during mounting as small as possible. (For example, refer to Patent Document 3).

  The multilayer solid electrolytic capacitor has a structure in which a plurality of flat capacitor element substrates having an anode part and a cathode part are laminated such that the anode part overlaps the anode part and the cathode part overlaps the cathode part. 2. Description of the Related Art A two-terminal configuration in which a capacitor element unit is manufactured and a plurality of these units are connected in parallel on one lead frame is known (for example, see Patent Document 4).

  There is also a three-terminal structure in which a plurality of flat capacitor element substrates having an anode part and a cathode part are laminated so that the anode parts are alternately staggered so that the cathode part is the center (for example, patents) Reference 5).

In the solid electrolytic capacitor having such a laminated structure, since it is necessary to connect a plurality of capacitor element anode portions and the anode lead frame, welding that is stable in strength is performed. Known welding methods include resistance welding, arc welding, laser welding, and ultrasonic welding. (For example, refer to Patent Document 6).
Japanese Patent No. 2996992 JP 2005-223113 A JP 2005-158769 A JP 2000-138138 A Japanese Patent Application No. 2005-308846 JP 2003-257788 A

  Among the above welding, laser welding can uniformly melt the anode part and anode frame of the capacitor element, so the welding point is stronger than other welding (resistance welding, arc welding, ultrasonic welding). Yes, excellent connection strength.

  However, in the case of laser welding, if there is a minute space between the capacitor element anode part or between the anode part and the anode lead frame, the anode part and the anode lead frame cannot be uniformly melted, resulting in poor connection. There was a problem that it was.

  In order to solve the above problem, the multilayer solid electrolytic capacitor according to the present invention has a valve metal having an oxide film serving as a dielectric on the surface thereof, and a cathode portion comprising a solid electrolyte layer and a cathode lead layer on one side. In a multilayer solid electrolytic capacitor in which a capacitor element substrate having an anode portion that is an exposed portion of a valve action metal is laminated on the other side, a resistance welding portion in which the anode portion and the lead frame are welded by resistance welding. The resistance welded portion has a laser welded portion by laser welding with a spot diameter (so-called non-extruding size) that is 50 to 100% of the joint width of resistance welding.

  Preferably, a plurality of capacitor element substrates are stacked so that the anode exposed portions are alternately staggered left and right with the cathode portion as the center.

  More preferably, a plurality of resistance welds are provided.

In the multilayer solid electrolytic capacitor provided by the present invention, after welding the capacitor element anode portions and the anode lead frame by resistance welding, the center portion of the welded portion having a substantially rectangular shape is a spot smaller than the width of the joining portion. Conductive joining is performed by laser welding of diameter.
As a result, it is possible to electrically and physically join the aluminum foil and the copper-based lead frame that are difficult to join, to stabilize the coupling between the anode part of the capacitor element and the anode frame, and to make a connection with low electrical resistance. Moreover, since the coupling portion is strong, the performance against heat stress is also improved.

  As a result, a multilayer solid electrolytic capacitor having a lower ESR can be obtained, and performance deterioration due to poor contact due to anode dislocation can be prevented.

  Hereinafter, embodiments of the multilayer solid electrolytic capacitor according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 and FIG. 2 are diagrams for explaining the basic configuration of a capacitor element substrate before being laminated in the multilayer solid electrolytic capacitor of the present invention. FIG. 1 is an external perspective view of one capacitor element substrate C. FIG. FIG. 2 is a cross-sectional view showing a detailed configuration of FIG. In FIG. 2, the thickness is enlarged and displayed for convenience of explanation. FIG. 4 is a perspective view showing a stacked solid electrolytic capacitor in which four capacitor element substrates are stacked.

  1 and 2, reference numeral 1 denotes a thin plate (foil) obtained by roughening a valve metal such as aluminum or tantalum, which is a portion constituting an anode. Reference numeral 2 denotes an oxide film layer formed on the surface of the valve metal thin plate 1 whose surface is roughened, and is a layer constituting a dielectric. Reference numeral 3 denotes a solid electrolyte layer formed on the surface of the right side portion of the oxide film layer (dielectric layer) 2, which is a layer constituting the cathode portion, for example, a conductive polymer such as polyethylenedioxythiophene (PEDT). Is a layer formed by chemical polymerization. 4 and 5 are cathode extraction layers, 4 is a carbon layer, and 5 is a silver layer.

  Functionally, the valve metal thin plate 1 as a whole is the anode, but in this embodiment, the portion of the valve metal thin plate 1 where the cathode portion (solid electrolyte layer) 3 is not formed, that is, the left side of FIG. The protruding portion is an anode portion (anode exposed portion) P, and the portion composed of the solid electrolyte layer 3, the carbon layer 4 and the silver layer 5 is a cathode portion N.

  As shown in FIGS. 1 and 2, the capacitor element substrate C includes an anode part P and a cathode part N. The anode part P and the cathode part N are completely insulated and isolated by the insulating masking member 6.

  As shown in FIG. 4, the multilayer solid electrolytic capacitor of this example is configured by laminating a plurality of four capacitor element substrates C1 to C4. In each of the capacitor element substrates C1 to C4, the anode portions P1 to P4 are alternately arranged on the left and right with the cathode portions N1 to N4 as the center.

  In the solid electrolytic capacitor, the cathode elements N1 to N4 of the capacitor element substrates C1 to C4 and the cathode part N1 of the capacitor element substrate C1 and the cathode lead frame 8 are electrically conductively connected by a conductive adhesive. ing.

  Further, as shown in FIG. 3, the solid electrolytic capacitor includes the anode portions P1 to P4 of the capacitor element substrates C1 to C4 and the anode portions P1 and P2 of the capacitor element substrates C1 and C2 and the anode lead frames 7, 7 ′. Are temporarily fixed to each other by resistance welding (three resistance welds 10), and the resistance weld 10 becomes 50 to 100% of the joint width of resistance welding (so-called protrusion). Conductive joining is performed by laser welding with a spot diameter (not so large) (three laser welds 11). Thereafter, the solid electrolytic capacitor connected to the lead frames 7, 7 ′ is sealed with the exterior resin 9.

  Next, in order to explain the effect of the multilayer solid electrolytic capacitor according to the present invention, examples, conventional examples and comparative examples are shown below.

Example 1
An aluminum foil having a thickness of 0.1 mm whose surface is electrochemically roughened is used as a valve metal thin plate 1, and a voltage of 10 V is applied to the aluminum foil 1 in an aqueous solution of ammonium adipate for about 60 minutes. Anodization is performed to form a dielectric layer (oxide film layer) 2 on the surface.

  As shown in FIG. 1, the aluminum foil (valve metal) 1 having the dielectric layer (oxide film layer) 2 thus formed has a width (w) of 11 mm and a length (l) of 11 mm. As shown in FIG. 2, a masking member 6 such as an insulating resin is applied in a circumferential direction at an appropriate position to divide the left and right regions (anode portion P and cathode portion N).

  After that, the end surface portion where the aluminum foil (valve action metal) 1 is exposed by cutting is again subjected to an oxidation treatment for about 30 minutes by applying a voltage of 10 V in an aqueous solution of ammonium adipate. Film layer) 2 is formed. Thereafter, the cathode portion N is formed by providing the solid electrolyte layer 3, the carbon layer 4, and the silver layer 5 made of polyethylenedioxythiophene (PEDT) on the right side of the masking portion 6.

  As shown in FIG. 4, the cathode portions N1 to N4 of the four capacitor element substrates C1 to C4 are sequentially laminated, and the gap between the laminated surfaces is tightly sandwiched with a conductive adhesive (not shown). Join. On the other hand, the capacitor elements substrates C1 to C4 are laminated so that the anode portions P1 and P3 are on the left side and the anode portions P2 and P4 are on the right side, that is, alternately in opposite directions.

In this embodiment, the anode portions P1 and P3 projecting to the left and the anode potential extracting lead frame 7 on the lower surface, the anode portions P2 and P4 projecting to the right and the anode potential extracting lead frame 7 ′ having a diameter of 50 mm and a width, respectively. Using a 0.8 mm disk electrode, a part of the circumference of the disk electrode is pressed against the capacitor element substrate, and temporarily fixed at three locations under the conditions of 1500 mV and 2.5 ms by resistance welding, and then resistance welding. The central portion of the spot was conductively joined by YAG laser welding with a laser spot diameter of φ = 0.8 mm (100% of the resistance welding joint width 0.8 mm).
At this time, the joint portion 10 formed by resistance welding has a substantially rectangular shape, and the size thereof is 0.8 mm wide × 3.7 mm long. Reference numeral 8 denotes a lead frame for taking out the cathode potential, which is connected to the cathode portion N1 through a conductive adhesive. The output waveform of laser welding was a two-step waveform in which irradiation was performed at 2.5 J for 2.5 ms after irradiation at 4.0 J for 2.5 ms.
The lead frame material used here was a copper alloy.

In addition, since the oxide film 2 formed on the surfaces of the anode portions P1 to P4 is resistance-welded, the coating film 2 on the joint surface is dissolved by the welding temperature, so that it is electrically conductively joined.
After that, as shown in FIG. 4, the whole is covered with a resin 9 (broken line) in a state where only the connection portions of the lead frames (terminal plates) 7, 7 ′, 8 to the external circuit are exposed, and the laminated solid An electrolytic capacitor was produced.

(Example 2)
Since the second embodiment is substantially the same as the first embodiment, only different points will be described. In this embodiment, the anode portions P1 to P4 and the anode lead frames 7 and 7 ′ are pushed using a disc electrode similar to that of the embodiment 1 and a part of the circumferential portion of the disc electrode is pushed onto the capacitor element substrate. After applying resistance welding and temporarily fixing each of the three locations, the laser spot diameter is set to φ = 0.4 mm (50% of the resistance welding joint width of 0.8 mm), and the central portion is conductively joined by YAG laser welding. Thus, a multilayer solid electrolytic capacitor was produced.

(Comparative Example 1)
Since the comparative example 1 is substantially the same as the said Example 1, only a different point is demonstrated. In this comparative example, the anode portions P1 to P4 and the anode lead frames 7 and 7 ′ are pushed using a disc electrode similar to that of the first embodiment, and a part of the circumferential portion of the disc electrode is pushed onto the capacitor element substrate. After applying resistance welding and temporarily fixing each of the three locations, the laser spot diameter is φ = 1.2 mm (the width of the resistance welding joint is larger than 0.8 mm), and the central portion is conductively joined by YAG laser welding. Thus, a multilayer solid electrolytic capacitor was produced.

(Comparative Example 2)
Since the comparative example 2 is substantially the same as the said Example 1, only a different point is demonstrated. In this comparative example, the anode portions P1 to P4 and the anode lead frames 7 and 7 ′ are pushed using a disc electrode similar to that of the first embodiment, and a part of the circumferential portion of the disc electrode is pushed onto the capacitor element substrate. After applying resistance welding and temporarily fixing each of the three locations, the laser spot diameter was set to φ = 0.3 mm (40% of the resistance welding width of 0.8 mm), and the central portion was conductively joined by YAG laser welding. Thus, a multilayer solid electrolytic capacitor was produced.

(Conventional example 1)
Since Conventional Example 1 is substantially the same as Example 1, only different points will be described. In this conventional example 1, the anode parts P1 to P4 and the anode lead frames 7 and 7 ′ are made of disk electrodes similar to those of the example 1, and a part of the circumferential part of the disk electrode is used as the capacitor element substrate. The laminated solid electrolytic capacitor was manufactured by pressing and resistance welding, temporarily fixing each of the three locations, and without performing subsequent laser welding.

(Conventional example 2)
Since Conventional Example 2 is substantially the same as Example 1, only different points will be described. In this conventional example 2, the anode parts P1 and P3 projecting to the left and the potential extracting lead frame 7 projecting to the left side, the anode parts P2 and P4 projecting to the right side, and the potential extracting lead frame 7 ′ are configured without resistance welding. Conductive bonding was conducted at three locations by YAG laser welding to produce a multilayer solid electrolytic capacitor.

  FIG. 5 is a graph showing the results of actual measurement of ESR (mΩ) when the temperature cycle test was performed on the multilayer capacitors of Examples, Comparative Examples, and Conventional Examples. ESR was measured at 100 kHz. The temperature cycle condition was 1000 times under the temperature condition of −55 ° C. to + 125 ° C.

  As can be seen from FIG. 5, the ESR value of the multilayer solid electrolytic capacitor of the example shows the same value as the initial value even after 1000 temperature cycles, whereas the multilayer solid electrolytic capacitors of the conventional example and the comparative example have the same value. The ESR value has already deteriorated after 500 temperature cycles.

  That is, when the anode part is welded only by resistance welding as in Conventional Example 1, the joining of the anode part and the anode lead frame becomes unstable. Further, when the anode part is welded only by laser welding as in Conventional Example 2, it is considered that the bonding becomes unstable because a space is formed between the anode part and the anode lead frame.

  Further, when the spot diameter of laser welding is larger than the joint portion of resistance welding as in Comparative Example 1, the foil is broken and the capacitor element is damaged, so that the anode portion is deteriorated and is not resistant to thermal stress. It will be stable.

  In the above embodiments, the case where PEDT is used as the solid electrolyte has been described. However, it has been confirmed that known conductive polymers such as polyaniline and polypyrrole are also effective.

In each of the above-described embodiments, the case of using a YAG laser as the light source for laser welding has been described. However, it has been confirmed that it is effective even when using a YVO ₄ laser, a carbon dioxide gas laser, or an argon laser.

  In each of the above embodiments, the case where the output waveform of laser welding is a two-stage waveform has been described. However, the output waveform may be one stage or three or more stages, and a plurality of capacitor elements and lead frames are substantially electrically connected. It only needs to be mechanically connectable.

  In each of the above embodiments, the case of a copper alloy system has been described as the material of the lead frame, but it has been confirmed that the lead frame material is effective even in the case of a copper system.

  In each of the above-described embodiments, the three resistance weldings have been described. However, the resistance welding may be performed at one point or three or more, as long as a plurality of capacitor elements and lead frames can be electrically and mechanically connected.

  Furthermore, laser welding to the resistance welded portion is not limited to one location in each resistance welded portion, and may be performed at a plurality of locations so as not to protrude from the resistance welded portion.

  Further, from the above examples, the laser spot diameter is 50 to 100% of the length in the longitudinal direction (width of the joined portion) of the joined portion of resistance welding. As described above, if it is less than 50% (Comparative Example 2), there is a problem that the conductive connection is not sufficient, and if it exceeds 100% (Comparative Example 1), there is a problem that the foil is broken and the capacitor element is damaged.

  Further, in the example, the anode part of the capacitor element and the lead frame were directly connected, but between the anode part of the capacitor element and the lead frame, between the anode part of the capacitor element, nickel, iron, You may interpose the copper material of either copper, aluminum, or those alloys.

  In each of the above embodiments, the case of a disk electrode has been described. However, the shape may be a cylindrical electrode or a rectangular electrode as long as a plurality of capacitor elements and a lead frame can be electrically and mechanically connected.

  Further, the cathode potential extraction terminal plate and the anode potential extraction terminal plate have been described in the examples as being attached to the lower surface of the multilayer body, but from the side surface or intermediate portion of the multilayer body depending on the usage mode and application of the capacitor. You may make it take out.

It is an external appearance perspective view of one capacitor | condenser element board | substrate. It is sectional drawing which shows the detailed structure of FIG. It is a top view which shows the resistance welding location and laser welding location of a capacitor | condenser element. It is a perspective view which shows the solid electrolytic capacitor which laminated | stacked four capacitor | condenser element substrates. It is a graph which shows the result of having actually measured ESR (m (ohm)) when the temperature cycle test was done about the multilayer type solid electrolytic capacitor of an Example, the prior art example, and the comparative example.

Explanation of symbols

P, P1-P4 Anode part (anode exposed part)
N, N1 to N4 Cathode C, C1 to C4 Capacitor element substrate 1 Valve metal thin plate 2 Dielectric layer (oxide film layer)
DESCRIPTION OF SYMBOLS 3 Solid electrolyte layer 4 Carbon layer 5 Silver layer 6 Masking member 7, 7 'Lead frame for taking out anode potential 8 Lead frame for taking out cathode potential 9 Resin mold 10 Location of resistance welding 11 Location of laser welding

Claims (3)

A valve action metal having an oxide film serving as a dielectric on the surface, a cathode portion comprising a solid electrolyte layer and a cathode lead layer on one side, and an anode portion which is an exposed portion of the valve action metal on the other side In a multilayer solid electrolytic capacitor in which a plurality of capacitor element substrates are laminated,
A resistance welded portion in which the anode portion and the lead frame are welded by resistance welding, and a laser welded portion by laser welding with a spot diameter of 50 to 100% of the joint width of the resistance welding is provided in the resistance welded portion. A multilayer solid electrolytic capacitor.   A multilayer solid electrolytic capacitor, wherein a plurality of capacitor element substrates according to claim 1 are laminated so that the direction of the anode exposed portion is alternately left and right with the cathode portion as the center.   A multilayer solid electrolytic capacitor comprising a plurality of resistance welds according to claim 1.

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