Conventionally, a power supply smoothing circuit is mounted on electronic equipment such as a personal computer to remove noise of a power supply voltage. Recently, as the size of electronic equipment is reduced and the operating speed thereof is increased rapidly, a tantalum capacitor the size of which is reduced and the capacitance of which is increased using a porous tantalum sintered body is widely used as a power supply smoothing circuit.
FIG. 1 is a schematic arrangement view of a tantalum capacitor 10, and FIG. 2 is a view illustrating a manufacturing method of the tantalum capacitor 10.
As illustrated in FIG. 1, the tantalum capacitor 10 is arranged such that a capacitor main body 14 is accommodated in a case 11 formed of a resin and the like, and an anode side lead frame 12 and a cathode side lead frame 13 which are connected to the capacitor main body 14 extend outside the case 11. Further, the capacitor main body 14 is composed of an internal element 14_1 having a tantalum sintered body and an anode rod 14_2, which projects from the internal element 14_1 and acts as the anode of the tantalum capacitor 10, and a conductive adhesive agent (silver and the like) applied to the internal element 14_1 forms a cathode layer 15 of the tantalum capacitor
When the tantalum capacitor 10 is manufactured, first, the anode side lead frame 12 is bonded to the anode rod 14_2 of the capacitor main body 14, and the cathode layer 15 is applied to the cathode side lead frame 13 (step S1 of FIG. 2).
Subsequently, the capacitor main body 14 is bonded to the cathode side lead frame 13 through the cathode layer 15, and they are accommodated in the case 11 (step S2 of FIG. 2).
Further, the anode side lead frame 12 and the cathode side lead frame 13 are bended (step S3 of FIG. 2) and disposed on the same surface (step S4 of FIG. 2).
Further, as illustrated in FIG. 1, the tantalum capacitor 10 is connected to a print substrate 20 in such a manner that the anode side lead frame 12 connected to the anode rod 14_2 and the cathode side lead frame 13 connected to the cathode layer 15 are fixed to an electronic component 21 by a solder 22.
FIG. 3 is a view illustrating the relation between a layer structure of the tantalum capacitor 10 and a resistance component thereof.
A tantalum sintered body 34, an oxide film 33, a functional polymer layer 32 (or manganese layer), and a carbon layer 31 are sequentially laminated on the internal element 14_1 of the tantalum capacitor 10. Further, a conductive adhesive agent, which acts as the cathode layer 15, is applied to the outside surfaces of the internal element 14_1. The cathode side lead frame 13 is connected to the cathode layer 15, and the anode rod 14_2 is inserted in the tantalum sintered body 34. The anode side lead frame 12 is connected to the anode rod 14_2. The tantalum capacitor 10 is equivalent to a circuit composed of: a resistance component 41 (R1+L1) of the cathode side lead frame 13; a resistance component 42 (R2+L2) that results from the oxide film 33, the functional polymer layer 32, the carbon layer 31, the tantalum sintered body 34, and the cathode layer 15; a capacitor component 43 (C) that results from the tantalum sintered body 34; and a resistance component 44 (R3+L3) that results from the anode rod 14_2 and the anode side lead frame 12. The resistance component 42, the resistance component 42, the capacitor component 43 (C) and the resistance component 44 are connected to each other in series. That is, the tantalum capacitor 10 is equivalent to the circuit in which an equivalent series resister 45 (ESL: L1+L2+L3), an equivalent series inductance 46 (ESR: R1+R2+R3), and a capacitor component 43 (C) are connected to each other in series.
Here, as illustrated in FIG. 1, there is a problem in that since the length of the tantalum capacitor 10 is increased by that the cathode side lead frame 13 and the anode side lead frame 12 are bent, the high frequency characteristics thereof are deteriorated by an increase of the ESL 45 and the ESR 46. In particular, recently, as the operation speed of electronic equipment is increased, a power supply frequency is increased, from which it is strongly requested to maintain a stable performance even in a high frequency region.
As to this point, Japanese Laid-open Patent Publication Nos. 2005-101279 and 2002-237431 disclose a technique for forming a cathode and an anode on the same surface of a capacitor by interposing an insulating layer between a tantalum sintered body and a cathode layer, and Japanese Laid-open Patent Publication No. 2003-332173 discloses a technique for increasing a current path by disposing anodes and a cathode across an insulation layer. It is possible to improve high frequency characteristics by reducing the ESL and the ESR making use of these techniques.
However, in the techniques disclosed in Japanese Laid-open Patent Publication Nos. 2005-101279, 2002-237431, and 2003-332173, it is necessary to surround the tantalum sintered body and the anode by the insulation layer, from which a problem arises in that the size of the overall capacitor is increased. Further, the techniques disclosed in Japanese Laid-open Patent Publication Nos. 2005-101279, 2002-237431, and 2003-332173 are disadvantageous in that since the shape and the structure of a layer are complex, a manufacturing process is complicated and a manufacturing cost is increased.