Solid electrolytic capacitor and method of making the same

Details Solid electrolytic capacitor and method of making the same Solid electrolytic capacitor and method of making the same

2003-06-27

2004-10-26

Nguyen, Ha Tran (Department: 2812)

Metal working

Barrier layer or semiconductor device making

Barrier layer device making

C361S523000, C361S540000

Reexamination Certificate

active

06808541

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a solid electrolytic capacitor for mounting on a printed wiring board and a method of making the same.
2. Description of the Related Art
FIGS. 34 and 35
illustrate an example of prior art tantalum solid electrolytic capacitor (hereinafter simply referred to as “solid electrolytic capacitor”). The solid electrolytic capacitor
61
includes a cathode lead
62
, an anode lead
63
, a capacitor element C
1
and a resin package
65
for partially sealing these elements. The capacitor element C
1
includes an element body
64
and an anode wire
66
extending from an end surface
64
a
of the element body. The element body
64
is formed with a metal layer
67
for covering the outer surfaces thereof. The metal layer
67
is electrically connected to the cathode lead
62
. The anode wire
66
is electrically connected to the anode lead
63
. A method for making the solid electrolytic capacitor
61
will be described. First, an element body
64
is connected, with a conductive adhesive
68
, to a cathode lead
62
formed on a manufacture lead frame (not shown). Further, an anode wire
66
extending from the element body
64
is connected, by e.g. spot welding, to an anode lead
63
similarly formed on the manufacture lead frame. Thereafter, these parts are sealed by a resin package
65
formed of an epoxy resin for example. Subsequently, the leads
62
,
63
extending outward from the resin package
65
are separated from the manufacture lead frame. Then, each lead
62
,
63
is bent to have a desired configuration.
In bending each lead
62
,
63
into a desired configuration, a considerable bending stress is exerted on the resin package
65
. Therefore, the solid electrolytic capacitor
61
need be strong enough to withstand the bending stress. Generally, damages due to the bending stress are prevented by making the resin package
65
relatively thick. However, an increase in the thickness of the resin package
65
provides a large thickness at a portion other than the element body
64
, which leads to an increase in the product size.
Recently, there is an increasing need for a solid electrolytic capacitor
61
of a high capacitance. Generally, to provide a solid electrolytic capacitor of a high capacitance, the size of the capacitor element itself need be increased. For this purpose, the size of the solid electrolytic capacitor accommodating the element need be increased.
However, the mounting density of a printed wiring board for mounting a solid electrolytic capacitor
61
becomes higher in accordance with the size reduction of electronic components. Therefore, a solid electrolytic capacitor
61
also need be reduced in size. Thus, it is not desirable to increase the size of the solid electrolytic capacitor to provide a higher capacitance.
Further, in the capacitor element C
1
, the anode wire
66
extending from the element body
64
is made of tantalum for example. Therefore, good conduction cannot be established between the anode wire
66
and the anode Lead
63
made of e.g. copper because of the affinity between the materials.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a solid electrolytic capacitor which is capable eliminating or at least reducing the problems described above.
According to a first aspect of the present invention, there is provided a solid electrolytic capacitor comprising a capacitor element including an element body and a conductive wire extending therefrom, a first electrode electrically connected to the element body, a second electrode electrically connected to the conductive wire, and a resin package integrally sealing said parts. Each of the first electrode and the second electrode comprises a conductive plate and has a lower surface exposed at a lower surface of the resin package for serving as a terminal surface. The first electrode has an upper surface to which the element body is connected, and the second electrode has an upper surface to which the conductive wire is connected via a conductive bolster.
Preferably, the lower surface of the first electrode is stepped, and the upper surface is larger in area than the terminal surface.
Preferably, the lower surface of the first electrode is partially etched to be stepped.
Preferably, the upper surface of the second electrode has an edge formed with a stepped portion.
Preferably, the stepped portion is formed by partially etching the upper surface of the second electrode.
Preferably, the conductive bolster is in the form of a rectangular parallelepiped, and at least one end surface of the conductive bolster is exposed at a side surface of the resin package.
Preferably, the conductive wire is formed of tantalum, whereas the conductive bolster is formed of nickel or an alloy containing nickel. The two members are connected to each other by resistance welding.
Preferably, the element body is connected to the upper surface of the first electrode with a conductive adhesive, and the conductive bolster is connected to the upper surface of the second electrode with a conductive adhesive.
According to a second aspect of the present invention, there is provided a method of making a solid electrolytic capacitor which comprises a capacitor element including an element body and a conductive wire extending therefrom, and a resin package for sealing the capacitor element. The method comprises preparing a plate-like fabrication frame including a plurality of unit regions arranged in a matrix. Each of the unit regions includes a first electrode and a second electrode having respective inner ends spaced from each other by a predetermined distance. An element body of a capacitor element is connected to an upper surface of each of the first electrodes, whereas a conductive wire extending from the element body is connected to an upper surface of a corresponding one of the second electrodes via a conductive bolster. An intermediate article is provided by resin-sealing the fabrication frame to enclose the capacitor elements while exposing the lower surfaces of the first electrodes and the second electrodes. The intermediate article is divided into each of the unit regions.
Preferably, the conductive bolster is connected to the conductive wire by resistance welding. The element body is connected to the upper surface of the first electrode with a conductive adhesive, whereas the conductive bolster is connected to the upper surface of the second electrode with a conductive adhesive.
According to a third aspect of the present invention, there is provided a solid electrolytic capacitor comprising a substrate having an upper surface formed with a first and a second electrodes and a lower surface formed with terminal surfaces electrically connected to the first and the second electrodes, respectively, a capacitor element including an element body and a conductive wire extending therefrom, and a resin package for sealing the capacitor element. The element body is connected to the first electrode of the substrate, and the conductive wire is connected to the second electrode of the substrate via a conductive bolster.
Preferably, the conductive bolster is in the form of a rectangular parallelepiped, and at least one end surface of the conductive bolster is exposed at a side surface of the resin package.
Preferably, the conductive wire is formed of tantalum, and the conductive bolster is formed of nickel or an alloy containing nickel. The two members may be connected to each other by resistance welding.
Preferably, the element body is connected to the upper surface of the first electrode with a conductive adhesive, whereas the conductive bolster is connected to the upper surface of the second electrode with a conductive adhesive.
According to a fourth aspect of the present invention, there is provided a method of making a solid electrolytic capacitor which comprises a capacitor element including an element body and a conductive wire extending therefrom, and a resin package for sealing the capacitor elemen

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