1. Field of the Invention
This invention relates to a solid electrolytic capacitor such as tantalum capacitor or aluminum capacitor. More particularly, the present invention relates to a package-type solid electrolytic capacitor wherein a capacitor element is enclosed in an insulating package for protection.
2. Description of the Related Art
In general, a solid electrolytic capacitor comprises a capacitor element which includes a porous chip of a sintered compacted valve metal powder which works as an anode. The chip is first treated to form a dielectric layer on the metal particles, and then treated to form a solid electrolyte layer over the dielectric layer. The solid electrolyte layer, which works as a cathode, is covered by a cathode electrode layer.
The solid electrolytic capacitor is known to provide a high capacitance per unit volume. However, such a capacitor has been found disadvantageous for its poor resistance to impacts and moisture.
To solve this problem, it is a usual practice to enclose the capacitor element in an insulating resin package which is molded with the capacitor element, as disclosed in Japanese Patent Application Laid-open No. 60-220922 for example. For establishing electrical connection of the capacitor element to an external circuit, the capacitor element has an anode wire which is attached to a plate-like anode lead, whereas the cathode electrode layer is attached to a plate-like cathode lead. The anode and cathode leads project out of the resin package and are bent toward the underside of the package for mounting to a surface of a printed circuit board.
However, the solid electrolytic capacitor described above is still disadvantageous in the following respects.
First, since the resin package is molded with the capacitor element, the latter is inevitably subjected to a molding pressure which is relatively high. Thus, the capacitor element undergoes stresses which may damage or adversely influence the capacitor element. For instance, the capacitor element may suffer from an increased leak current (LC) or electrical shorting.
Secondly, since the anode wire projects from the capacitor chip, the resin package must be large enough to enclose the anode wire. Thus, the anode wire adds to the overall size and weight of the packaged capacitor. Further, the anode and cathode leads extend laterally within the package, so that these leads are also additional to the size and weight of the package.
In the third place, since the respective leads need be attached to the capacitor element and then bent outside the package, the attaching and bending steps result in an increase of the production cost.