Electricity: electrical systems and devices – Electrolytic systems or devices – Solid electrolytic capacitor
Reexamination Certificate
2000-07-13
2002-12-10
Dinkins, Anthony (Department: 2831)
Electricity: electrical systems and devices
Electrolytic systems or devices
Solid electrolytic capacitor
C361S532000, C361S538000
Reexamination Certificate
active
06493214
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a solid electrolytic capacitor including a sintered body composed of powder of valve acting metal such as tantalum. More particularly, the present invention relates to a solid electrolytic capacitor having the structure in which it is possible to enhance the reliability of welding between an anode lead embedded in a sintered body and a tip end of an outside lead.
BACKGROUND OF THE INVENTION
As shown in
FIG. 3
, a solid electrolytic capacitor in the prior art is configured such that an anode lead
11
of a capacitor element
1
is electrically connected to one outside lead
3
, and further, a cathode
12
formed at the outer periphery of the capacitor element
1
is electrically connected to another outside lead
3
via a fuse
4
, wherein the entirety is molded with a resin to be covered with a resin package
5
. Reference numeral
13
designates a water-repellent insulation ring. The anode lead
11
of the capacitor element
1
is formed by embedding a wire made of tantalum in a sintered body composed of powder of valve acting metal such as tantalum, aluminum or niobium. The tip end of the anode lead
11
of the capacitor element
1
is resistance-welded to the tip end of the first outside lead
2
, as described above, to be electrically connected to the first outside lead
2
formed of a lead frame. After the formation of the resin package
5
by molding, the outside leads
2
and
3
are cut and separated from the lead frame, followed by forming, to be thus formed into the above-described structure.
In the solid electrolytic capacitor in the prior art, the sintered body in the capacitor element is as remarkably small as about 1 mm cubic, the anode lead embedded in the sintered body is formed of a wire having a diameter as fine as about 0.2 mm, and a length of the anode lead projecting from the sintered body is as short as about 1 mm as requested for miniaturization of a part. Consequently, the contact area between the anode lead and the outside lead becomes remarkably small. Moreover, the anode lead is made of a material having a high melting point such as tantalum, as described above, so that the anode lead is hardly melted by welding: namely, it is poor in weldability. Additionally, even if a current in welding is increased or a welding time is prolonged for the purpose of sufficient welding, only the outside lead is melted and sunk in since the outside lead, in contrast, is made of a soft material such as Alloy 42, Ni or Cu, thereby making complete welding impossible. Therefore, the anode lead may be inclined in welding to the outside lead, as shown in
FIG. 3
, and therefore, the welding reliability may be degraded to induce a break of the wire caused by separation of a welded portion during use.
In the meantime, in the case where the area of the welded portion between the leads is enlarged by extending the anode lead, and further, the outside lead, the package per se is increased in size. This is contradictory to the reduction in the size and weight of electronic parts. Moreover, if the profile of the package is suppressed, the volume of the sintered body in the capacitor element is decreased, thereby making it impossible to achieve the desired characteristics of the capacitor.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a solid electrolytic capacitor having the structure in which it is possible to enhance the welding reliability of an anode lead and to prevent any inclination of a welded portion of the anode lead without reducing the volume of a sintered body in a capacitor element or enlarging a package.
A solid electrolytic capacitor according to the present invention comprises: a capacitor element having an anode formed by embedding one end of an anode lead in a sintered body composed of valve acting metal from one side face of the sintered body and a cathode formed on a side wall of the sintered body; a first outside lead, to which the other end of the anode lead is welded; a second outside lead, to which the cathode is electrically connected; and a resin package covering the capacitor element; wherein the tip end of the first outside lead, to which the other end of the anode lead is welded, is configured in such a manner as to have a capacity greater than those of other portions of the first outside lead.
Here, “the tip end of the first outside lead is configured in such a manner as to have a capacity greater than those of the other portions” means that the volume of the lead per unit length in a direction in which the outside lead extends becomes larger at the tip end of the first outside lead than those of the other portions, for example the tip end of the first outside lead is widely formed more than the other portions, or the widely formed portion is folded over to form a thick portion, or only the tip end is thickly formed.
With this configuration, since there is originally a space corresponding to the width of the capacitor element in a direction perpendicular to the direction in which the outside lead extends, the tip end of the first outside lead can be enlarged without exerting any adverse influence on the size of the package or capacitor element, and further, the anode lead can be increased in length by bending in a lateral direction, thereby enlarging the welded area. Moreover, since a thermal capacity can be increased by folding the wide portion so as to thicken the tip end or thickly forming the tip end from the beginning, the fine anode lead can be increased in temperature to be securely welded to the first outside lead before the first outside lead may be sunk in even if the welding condition is reinforced by increasing a current in welding. Therefore, it is possible to prevent any bending or inclination and enhance the reliability of welding strength.
Specifically, a portion of the first outside lead, to which the anode lead is welded, is widely formed so that the capacity can be increased, and the other end of the anode lead bent in a lateral direction is welded to the first outside lead at the wide portion; a portion of the first outside lead, to which the anode lead is welded, is widely formed toward both ends from the center or is widely formed toward mainly either end from the center, and further, the wide portion is folded over toward the center, and then, the other end of the anode lead is welded to the folded portion; or a portion of the first outside lead, to which the anode lead is welded, is thickly formed, and the other end of the anode lead is welded to the thick portion.
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Aoyama Makoto
Kanetake Yasuo
Dinkins Anthony
Rohm & Co., Ltd.
Thomas Eric W.
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