1. Field of the Invention
The present invention relates to a solid electrolytic capacitor and a method of manufacturing the same.
2. Description of the Related Art
In general, solid electrolytic capacitors having a function of storing electricity are electronic components used for blocking direct currents and passing alternating currents. Among the solid electrolytic capacitors, the most representative one is a tantalum capacitor which is used in application circuits, of which the rate voltage range is low, as well as general industrial equipments. In particular, the tantalum capacitor is frequently used in circuits requiring an excellent frequency characteristic or for reducing noise of communication equipments.
FIG. 1 is a perspective view of a conventional solid electrolytic capacitor, and FIG. 2 is a cross-sectional view of the conventional solid electrolytic capacitor. As shown in FIGS. 1 and 2, the solid electrolytic capacitor 10 includes a capacitor element 11 which determines the capacity and characteristic of the capacitor and is formed of dielectric ceramic powder, anode and cathode lead frames 13 and 14 which are connected to the capacitor element 11 so as to be easily mounted on a printed circuit board (PCB), and an epoxy case 15 which is molded of epoxy so as to protect the capacitor element 11 from the external environment and to form the shape of the capacitor element.
In one side of the capacitor element 11, a rod-shaped anode wire 12 is formed to project with a predetermined length.
The anode wire 12 has a planar surface 12a provided thereon, the pressed surface 12a increasing a contact area with the anode lead frame 13 and preventing the anode lead frame 12 from rocking from side to side during welding.
The capacitor element 11 is manufactured by the following process. First, dielectric ceramic powder is molded in a rectangular parallelepiped shape in a pressing process and is then sintered. Further, a dielectric oxide film is formed on the surface of the sintered body. Then, the body is dipped into a manganese nitrate solution such that a manganese dioxide layer composed of a solid electrolyte is formed on the outer surface of the body.
A process of connecting the anode and cathode lead frames 13 and 14 to the capacitor element 11 manufactured in such a manner includes two steps. In the first step, the plate-shaped anode lead frame 13 is welded on the planar surface 12a of the rod-shaped anode wire 12, which projects from one side surface of the capacitor element 11 at a predetermined length, so as to derive an anode terminal. In the second step, a cathode terminal is derived through the surface of the capacitor element 11 or a conductive adhesive coated on the cathode lead frame 14.
Then, the capacitor element 11 is electrically connected to the anode and cathode lead frames 13 and 14, respectively, and the epoxy case 15 is molded of epoxy. Then, the solid electrolytic capacitor is completed through a subsequent assembling process.
The above-described conventional electrolytic capacitor has the following problems.
While the anode wire 12 and the anode lead frame 13 are directly welded, high-temperature heat is generated. The generated heat has an effect upon the capacitor element 11 through the anode wire 12, thereby damaging the capacitor element 11 which is vulnerable to heat.
Further, dielectrics are destroyed by the heat shock applied to the capacitor element 11 such that a product quality is degraded and defects occur. Therefore, a manufacturing cost increases.
Further, the anode lead frame 13 and the cathode lead frame 14 occupy such a large space in the epoxy case 15. Therefore, the capacitor element 11 is inevitably reduced in size within the epoxy case 15. As a result, the capacitance of the capacitor decreases.