Solid electrolytic capacitor

Details Solid electrolytic capacitor Solid electrolytic capacitor

2002-08-13

2003-12-16

Dinkins, Anthony (Department: 2831)

Electricity: electrical systems and devices

Electrolytic systems or devices

Solid electrolytic capacitor

C361S528000, C361S532000

Reexamination Certificate

active

06665172

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates, in general, to a solid electrolytic capacitor and, in particular, to an improved solid electrolytic capacitor including a capacitor element with a capacitance that is increased by enlarging the space occupied by the capacitor element within a limited space of the epoxy case, and an anode lead frame which can minimize the heat transfer to the capacitor element during an assembly of a capacitor element and a lead frame, simplifying the production of the solid electrolytic capacitor.
2. Description of the Prior Art
A solid electrolytic capacitor is an electronic device for storing an electric charge, preventing the passage of a direct current, and passing an alternating current. Among various solid electrolytic capacitors, a tantalum capacitor is most widely applied to general industrial machinery, and to an application circuit used in a low rated voltage range. In particular, the tantalum capacitor is used to reduce a noise of a circuit or a portable communication apparatus in which a frequency characteristic is important.
The tantalum capacitor
100
, as shown in
FIGS. 1
to
4
, comprises a capacitor element
110
consisting of dielectric powder which determines the capacitance and characteristic of a capacitor, an anode lead frame
130
and a cathode lead frame
140
connected to the capacitor element
110
so as to easily mount the capacitor on a printed circuit board (hereinafter referred to simply as a ‘PCB’), and an epoxy case
150
for protecting the capacitor element
110
.
A process of manufacturing the tantalum capacitor
100
, comprises the steps of pressing tantalum powder into rectangular parallelepiped-shaped pellet, sintering and degassing the rectangular parallelepiped-shaped pellet, anodizing the pellet to form tantalum oxide (Ta
2
O
5
) layer on the exposed tantalum surfaces, infiltrating a manganese nitrate solution into the pellet, and thermally decomposing the infiltrated pellet to form a manganese dioxide layer, that is, a solid electrolyte on a surface of the resulting pellet.
A process of connecting the anode lead frame
130
and the cathode lead frame
140
to the capacitor element
110
thus manufactured comprises the steps of welding a rod-shaped anode wire
120
protruding by a predetermined length from a lateral side of the capacitor element
110
to a plate-shaped anode lead frame
130
by an electrical spot welding process to form an anode terminal, and soldering the cathode lead frame
140
to an external surface of the capacitor element
110
using a conductive adhesive such as carbon or silver powder coated on the external surface of the capacitor element
110
to form a cathode terminal (See Japanese Laid-Open Patent Publication No. 5-335189 of Honda Hisafumi et al.). Thereafter, the capacitor element
110
, electrically connected to the anode lead frame
130
and cathode lead frame
140
is molded with epoxy powder in an encapsulating step so as to form an epoxy case
150
for protecting the capacitor element
110
, and subjected to a marking step which ends the manufacturing process of the capacitor
100
.
However, the conventional process of welding the anode wire
120
to the anode lead frame
130
while they are in contact with an upper and a lower electrodes
161
and
162
, indispensably comprises a bending step of forming a flat pressed surface
122
on an external side of the anode wire
120
before welding of the anode wire to the anode lead frame in order to prevent shaking occurring in welding, and to increase a contact efficiency between them. The conventional process is thus disadvantageous in that an external mechanical impact readily occurring in the bending step is transferred through the anode wire
120
to the capacitor element
110
destroying the dielectric layer. As a result, the electrical property of the capacitor, for example, an LC value is degraded. In addition, the production cost of the capacitor is increased owing to the bending step.
In addition, in case that the anode wire
120
is welded to the anode lead frame
130
with a metal such as lead or tin, said metal can be melted due to the high temperature generated when mounting the capacitor. Thus, a broken electrical connection can occur.
Furthermore, a conventional process of soldering an external lower side of the capacitor element
110
to an upper side of the cathode lead frame
140
with a conductive adhesive is disadvantageous in that the space occupied by the capacitor element
110
within a limited space of an epoxy case
150
is relatively small, and a volume of the capacitor element
110
is small, thereby limiting capacitance of the capacitor
100
and the increasing impedance.
Meanwhile, the anode wire
120
of the capacitor element
110
may be welded to the anode lead frame
130
by a laser welding process instead of the electrical spot welding process as disclosed in Japanese Laid-Open Patent Publication No. 8-195330 by Mitsui Koichi et al. More specifically, a V-shaped notch part
132
is formed on the anode lead frame
130
, the anode wire
120
of the capacitor element
110
is mounted on the notch part
132
, and portions of the frame
130
located at both sides of the anode wire
120
are melted by a laser beam to weld the anode wire
120
to the anode lead frame
130
, as shown in
FIGS. 5
a
to
5
c.
However, when the anode wire
120
is welded to the anode lead frame
130
by the laser beam, the welding process is very complicated because the laser beam is simultaneously irradiating two portions of the frame
130
located on both sides of the anode wire
120
.
In addition, because the portions irradiated by the laser beam are restricted to a cut section of the notch part
132
corresponding to the thickness of the anode lead frame
130
, an area for welding the anode wire
120
to the anode lead frame
130
is small, and so the laser output of the laser welding machine must be increased in order to increase welding efficiency. At this time, a spark occurring during the laser welding may reach the capacitor element
110
, damaging the capacitor element
110
.
Moreover, the external surface of the anode lead frame
130
has a high absorbability of the laser beam because the external surface usually has a dark gray color, and so the welding characteristic thereof is excellent, but the notch part formed in a shape of ‘V’, having a color of an inner metal of the anode lead frame
130
has a poor absorbability of the laser beam and a high reflectivity against the laser beam, and so the welding characteristic thereof becomes poor. Accordingly, the laser output of the laser welding machine must be increased in order to improve the welding efficiency, and thus consumption of electricity is increased, and heat impact and sparks transferred to the capacitor element
110
are increased, thereby increasing the damage to the element.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to avoid the above disadvantages, and to provide a solid electrolytic capacitor, which can avoid a bending process, minimize the heat transfer to its capacitor element in order to obtain a stable electrical characteristic, increase its operational reliability, and reduce its production cost owing to a simplified production process of the solid electrolytic capacitor.
It is another object of the present invention to provide a solid electrolytic capacitor, which can sufficiently enlarge the capacitance of its capacitor element by increasing the space occupied by the capacitor element within a limited space of an epoxy case.
It is still another object of the present invention to provide a solid electrolytic capacitor, which can improve welding efficiency between a lead frame and an anode wire by preventing a shaking of the anode wire.
Based on the present invention, the above objects can be accomplished by a provision of a solid electrolytic capacitor, comprising a capacitor element; an anode wire extending from a first side of the capacitor element by a predetermi

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