Solid electrolytic capacitor

A solid electrolytic capacitor of the present invention includes a capacitor element with an anode element and a cathode layer, having an anode lead member planted on one end surface of the anode element, an anode terminal connected to the anode lead member, a platy cathode terminal placed on a reverse surface of the capacitor element and connected to the cathode layer, and an enclosure resin part enclosing the capacitor element, a part of the cathode terminal and a part of the anode terminal being exposed from a bottom surface of the enclosure resin part. At least the cathode terminal has formed thereon a plurality of projections projecting in a position apart from a reverse surface of the enclosure resin part in a direction along the reverse surface.

The priority application Number 2004-295881 upon which this patent application is based is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a solid electrolytic capacitor, and particularly, to an improvement in a terminal structure of a solid electrolytic capacitor capable of being surface-mounted on a circuit board.

2. Description of Related Art

A solid electrolytic capacitor having a structure shown inFIG. 11has been conventionally known. A capacitor element6included in the solid electrolytic capacitor includes an anode element3made of a sintered body of a valve-action metal (tantalum, niobium, titanium, aluminum, etc.), a dielectric coating4made by oxidizing a surface layer of the anode element, and a cathode layer5having sequentially formed therein a solid electrolyte layer5amade of a conductive inorganic material such as manganese dioxide or a conductive organic material such as TCNQ complex salt, a conductive polymer, etc. and a cathode lead layer5bmade of carbon, silver, etc. An anode lead frame11is connected to an anode lead member7planted on one end surface of the anode element3, while a cathode lead frame12is connected to the cathode layer5. A periphery of the capacitor element6is coated and sealed by an enclosure resin part80made of epoxy resin or the like. The anode lead frame11and the cathode lead frame12are bent along a surface of the enclosure resin part80(see JP 10-64761 A).

However, there has been a problem that the capacitor element6cannot be sufficiently large in overall size relative to a solid electrolytic capacitor finished product because the solid electrolytic capacitor of the above-described structure needs to have an entire periphery of the capacitor element6coated with an enclosure resin.

Accordingly, the present inventors have proposed a technique of incorporating a capacitor element6with a larger occupying volume relative to an overall size of a solid electrolytic capacitor finished product by mounting the capacitor element6on a platy anode terminal10and cathode terminal20as shown inFIG. 12to make a gap as small as possible between an outer peripheral surface of the capacitor element6and an outer peripheral surface of an enclosure resin part80(JP 2001-244145 A).

In the solid electrolytic capacitor, an ESR (Equivalent Series Resistance) and an ESL (Equivalent Series Inductance) in the solid electrolytic capacitor finished product can be reduced because it is unnecessary to provide a lead frame bent along a surface of the enclosure resin part as conventionally, so that a current path from the capacitor element6to a circuit board can be shortened. Furthermore, a distance between current paths of an anode and a cathode to the circuit board can be shortened by extending the cathode terminal20of the solid electrolytic capacitor to the vicinity of the anode terminal10as shown inFIG. 13. An ESL in a high-frequency area can be thereby further reduced.

However, there has been a problem in the solid electrolytic capacitor shown inFIG. 12andFIG. 13that if a great external force acts on the anode terminal10and the cathode terminal20during manufacture or after completion, the anode terminal10and the cathode terminal20are likely to peel off from the enclosure resin part80, and especially the cathode terminal20peels off easily.

There has been also a problem in the solid electrolytic capacitor shown inFIG. 12andFIG. 13that if moisture infiltrates from a bottom surface side of the enclosure resin part80into an interface between both the terminals10,20and the enclosure resin part80, because a distance from the bottom surface of the enclosure resin part80to the capacitor element6is short, the moisture easily reaches to the capacitor element6through a short path to thereby degrade characteristics of the capacitor element6.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a solid electrolytic capacitor of a structure that prevents an anode terminal and a cathode terminal from easily peeling off due to action of an external force and prevents moisture from infiltrating, as well as obtains a reduction effect for an ESR and an ESL.

A solid electrolytic capacitor of the present invention comprises a capacitor element6with an anode part and a cathode part, an anode terminal1connected to the anode part of the capacitor element6, a platy cathode terminal2placed on a reverse surface of the capacitor element6and connected to the cathode part, and an enclosure resin part8enclosing the capacitor element6, the anode terminal1and the cathode terminal2, a part of the cathode terminal2and a part of the anode terminal1being exposed from a bottom surface of the enclosure resin part8. At least the cathode terminal2has formed thereon at least one projection projecting in a position apart from a reverse surface of the enclosure resin part8in a direction along the reverse surface, the projection being embedded in the enclosure resin part. The projection may be parallel to or inclined against the reverse surface.

According to the above-described solid electrolytic capacitor of the present invention, even if a great external force acts on the cathode terminal2, because the projection formed on the cathode terminal2is embedded in the enclosure resin part8, the external force is reliably received by the projection. Therefore, the cathode terminal2is unlikely to peel off from the enclosure resin part8. If the same projection is formed not only on the cathode terminal2but also on the anode terminal1, the same peeling-off prevention effect as in the cathode terminal2is obtained also in the anode terminal1. The peeling-off prevention effect can of course be increased by increasing the number of projections.

Furthermore, moisture infiltrated from the bottom surface of the enclosure resin part8into an interface between the both terminals1,2and the enclosure resin part8needs to change a traveling direction a plurality of times in the projection-forming part when passing through the projection. This increases a distance before reaching to the capacitor element6, and therefore the infiltration can be prevented on the way thereto.

In a specific construction, the cathode terminal2has on a reverse surface thereof at least two exposed surfaces exposed from the reverse surface of the enclosure resin part8. According to the solid electrolytic capacitor having the specific construction, a difference between an area of each exposed surface and an area of the exposed surfaces of the cathode terminal2can be smaller by forming at least two exposed surfaces on the reverse surface of the cathode terminal2, which is larger in planar shape than the anode terminal1. In a process of surface-mounting the solid electrolytic capacitor on a circuit board, molten solder on the circuit board is thereby to be dispersed in each of the exposed surfaces without great deviation, so that the solid electrolytic capacitor on the solder is unlikely to move with shrinkage due to surface tension of the solder.

Furthermore, in a specific construction, one exposed surface of the two exposed surfaces of the cathode terminal2is formed in a closer position to an exposed surface of the anode terminal1than the other exposed surface is. An ESL in a high-frequency area can be thereby further reduced.

As described above, according to the solid electrolytic capacitor of the present invention, the anode terminal and the cathode terminal are prevented from easily peeling off due to action of an external force, and infiltration of moisture is suppressed, while a reduction effect for an ESR and an ESL is obtained.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention will be specifically described below with reference to the drawings. A solid electrolytic capacitor of the present invention includes, as shown inFIG. 6, a capacitor element6having an anode lead member7planted thereon, an anode terminal1connected to the anode lead member7, a platy cathode terminal2placed on a reverse surface of the capacitor element6, and an enclosure resin part8enclosing the capacitor element6, the anode terminal1and the cathode terminal2. Like the conventional solid electrolytic capacitor shown inFIG. 11, the capacitor element6has a dielectric coating4and a cathode layer5formed on a surface of an anode element3. The anode lead member7is planted on one end surface of the anode element3. In the present embodiment, the anode lead member acts as an anode part, and a cathode layer forming part of the capacitor element acts as a cathode part.

A periphery of the capacitor element6, the anode terminal1and the cathode terminal2is coated and sealed by the enclosure resin part8made of epoxy resin or the like. An exposed surface1aof the anode terminal1and two exposed surfaces2a,2bof the cathode terminal2are exposed on a reverse surface of the enclosure resin part8. The anode terminal1and the cathode terminal2are fabricated by pressing a board material made of an alloy mainly containing copper. In a description of a positional relationship given below, a projecting direction of the anode lead member7is defined as a front, and a direction orthogonal thereto is defined as a side.

As shown inFIG. 7, the exposed surface1aof the anode terminal1and the rear exposed surface2bof the cathode terminal2each have the same outline shape. The front exposed surface2aof the cathode terminal2is positioned approximately in the middle of both the exposed surfaces1a,2b.The cathode terminal2also has, in both sides thereof as shown inFIG. 8, exposed surfaces2c,2cexposed from side surfaces of the enclosure resin part8.

Furthermore, as shown inFIG. 7andFIG. 9, the anode terminal1has two exposed surfaces1b,1bexposed on a front end surface of the enclosure resin part8. Similarly, the cathode terminal2has also two exposed surfaces2d,2dexposed on a rear end surface of the enclosure resin part8.

As shown inFIG. 1andFIG. 3toFIG. 5, the anode terminal1has a prismatic protruding line portion19formed on a platy base portion18. A recessed portion13is formed in the middle of a front end surface of the base portion18. Furthermore, the protruding line portion19has formed on both ends thereof a pair of projections15,15slightly projecting from either side surface of the base portion18.

The cathode terminal2includes a platy base portion21having a smaller width than a width of the enclosure resin part8. The base portion21has formed on an end thereof on the anode terminal1side a pair of right and left arm portions22,22projecting from either side surface thereof toward either side surface of the enclosure resin part8. An end surface of each of the arm portions22forms an exposed surface2cshown inFIG. 8. A recessed portion27is formed in the middle of a rear end surface of the cathode terminal2.

Furthermore, the cathode terminal2has formed on a reverse surface thereof a recessed portion23extending across both side surfaces of the cathode terminal2, which forms the above-described two exposed surfaces2a,2bshown inFIG. 7on the reverse surface of the cathode terminal2. As shown inFIG. 6, the recessed portion23of the cathode terminal2is provided with a resin charged portion81made by charging a part of the resin of the enclosure resin part8. The resin charged portion81connects to the other part of the enclosure resin part8.

As shown inFIG. 1andFIG. 3toFIG. 5, the cathode terminal2is provided with a band plate-like first projection24projecting forward from a front end surface of the base portion21in a higher position than that of the exposed surfaces2a,2bof the cathode terminal2. Both side surfaces of the base portion21are also provided with a pair of right and left second projections25,25projecting toward either side in a slightly rear position of the arm portions22,22in a higher position than that of the exposed surfaces2a,2bof the cathode terminal2. Furthermore, both side surfaces of the base portion21are provided with a pair of right and left third projections26,26projecting toward either side and upward in a position adjacent to a rear end surface thereof in a higher position than that of the exposed surfaces2a,2bof the cathode terminal2.

Therefore, all of the above-described projections15of the anode terminal1and first to third projections24,25,26of the cathode terminal2are, as shown inFIG. 6, to be embedded in the enclosure resin part8, projecting in a position apart from a reverse surface of the enclosure resin part8in a direction along the reverse surface.

In a process of surface-mounting the above-described solid electrolytic capacitor of the present invention on a circuit board, as shown inFIG. 10, cream solder50is pasted covering a land40on a circuit board30, and the solid electrolytic capacitor is mounted thereon. Then, the solid electrolytic capacitor is soldered to the circuit board30by reflow process.

In the solid electrolytic capacitor shown inFIG. 13, a difference in area between an exposed surface of the anode terminal10and an exposed surface of the cathode terminal20exposed from the enclosure resin part80is greater than a difference in area in the solid electrolytic capacitor shown inFIG. 12. Therefore, as shown inFIG. 14andFIG. 15, solder50on a land40with a larger area corresponding to the exposed surface of the cathode terminal20shrinks due to surface tension when melting. The solid electrolytic capacitor on the solder50is thereby pushed up, which can cause displacement, resulting in disconnection in the anode terminal.

In contrast, in the solid electrolytic capacitor of the present invention, as shown inFIG. 7, the two exposed surfaces2a,2bare formed on the reverse surface of the cathode terminal2with the resin charged portion81held therebetween. Therefore, a difference in area between the exposed surface la of the anode terminal1and each of the exposed surfaces2a,2bof the cathode terminal2can be smaller. In the process of surface-mounting the solid electrolytic capacitor on the circuit board, the molten solder on the circuit board is thereby to be approximately uniformly dispersed on each of the exposed surfaces. Therefore, the solid electrolytic capacitor on the solder is unlikely to move with shrinkage due to surface tension of the solder. Moreover, fixing strength to the circuit board improves because the solid electrolytic capacitor is supported at three points in good balance by the exposed surface1aof the anode terminal1and the two exposed surfaces2a,2bof the cathode terminal2.

In the solid electrolytic capacitor of the present invention, the anode terminal1has formed thereon the pair of projections15,15projecting toward either side, while the cathode terminal2has the first projection24projecting forward and the pair of arm portions22,22projecting toward either side formed on a front portion thereof corresponding to one exposed surface2a,and the pair of third projections26,26projecting toward either side formed on a rear portion thereof corresponding to the other exposed surface2b, these plurality of projections being embedded in the enclosure resin part8. Therefore, even if a great external force acts on the anode terminal1and the cathode terminal2during a manufacturing process or after completion, the external force is reliably received by the plurality of projections. Thus, the anode terminal1and the cathode terminal2are unlikely to peel off from the enclosure resin part8.

Furthermore, moisture infiltrated from the bottom surface of the enclosure resin part8into an interface between both the terminals1,2and the enclosure resin part8needs to change a traveling direction a plurality of times in the projection-forming part when passing through the projection. This increases a distance before reaching to the capacitor element6, and therefore the infiltration can be prevented on the way thereto.

Furthermore, an ESR and an ESL can be reduced in the solid electrolytic capacitor of the present invention because a current path from the capacitor element6to the circuit board is short as shown inFIG. 6. In particular, an ESL in a high-frequency area can be further reduced because the cathode terminal2extends from a rear end of the capacitor element6to a base end of the anode lead member7, and reaches to a near position of the anode terminal1.

Furthermore, the cathode terminal2has the pair of right and left arm portions22,22projected therefrom, and an end surface of each of the arm portions22is exposed on a side surface of the enclosure resin part8. Therefore, it can be checked whether the soldering is good or not at a glance after completion of soldering.

The present invention is not limited to the foregoing embodiment but can be modified variously by one skilled in the art without departing from the spirit of the invention as set forth in the appended claims. For example, as shown inFIG. 2, a front end surface of the anode terminal1and a rear end surface of the cathode terminal2may each be flat with the whole surface thereof being exposed from the enclosure resin part8. In the present embodiment, a sintered tantalum was used as a material of the anode element, but the material is not particularly limited if a valve-action metal is used. Use of a sintered body or foil of niobium, titanium, aluminum, etc. can also lead to the same effect.