Solid electrolytic capacitor and its manufacturing method

Details Solid electrolytic capacitor and its manufacturing method Solid electrolytic capacitor and its manufacturing method

2002-07-30

2004-01-20

Reichard, Dean A. (Department: 2831)

Electricity: electrical systems and devices

Electrolytic systems or devices

Solid electrolytic capacitor

C361S502000, C361S503000, C361S525000, C361S528000, C029S025030

Reexamination Certificate

active

06680841

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a solid electrolytic capacitor used in a variety of electronic equipment and a manufacturing method thereof.
BACKGROUND ART
FIG. 30
is a perspective view showing the structure of a prior art solid electrolytic capacitor and
FIG. 31
is a perspective view showing the structure of a solid electrolytic capacitor element stack unit. In FIG.
30
and
FIG. 31
, capacitor element
50
is an anode body composed of aluminum foil, the aluminum being a valve action metal, and divided into anode member
50
A and cathode member
50
B. Further, cathode member
50
B has a dielectric oxide film layer, solid electrolyte layer and cathode layer (none of these are shown in the drawings) stacked on top of each other in layers on the surface thereof in succession.
Capacitor element stack unit
51
is constructed as described below:
1A) A conductive silver paste (not shown in drawings) is applied onto cathode unit terminal
52
to join with cathode member
50
B.
2A) Cathode member
50
B of another capacitor element is joined with cathode member
50
B by applying a conductive silver paste (not shown in the drawings) thereto.
3A) By repeating the steps 1) and 2) by a plurality of times, a plurality of capacitor elements
50
are stacked on top of each other in layers.
4A) Then, respective anode members
50
A of the plurality of capacitor elements
50
are integrally connected with anode unit terminal
53
.
By using capacitor element stack unit
51
thus prepared, a solid electrolytic capacitor is constructed as follows:
5A) Cathode member
50
B of capacitor element stack unit
51
is joined onto cathode lead frame
54
via a conductive silver paste (not shown in the drawings).
6A) Another capacitor element stack unit
51
is stacked on cathode member
50
B via a conductive silver paste (not shown in the drawings).
7A) By repeating the steps 5) and 6) by a plurality of times, a plurality of capacitor element stack units
51
are stacked on top of each other in piles.
8A) Respective anode members
50
A of the plurality of capacitor element stack units
51
are integrally connected with anode lead frame
55
.
9A) The plurality of capacitor element stack units
51
are encapsulated with an insulating packaging resin (not shown in the drawings) in such a way as part of respective anode lead frame
55
and cathode lead frame
54
is exposed on the outer surfaces of the insulating packaging resin.
FIG. 32
is a cross-sectional view of another prior art solid electrolytic capacitor structured differently from the one shown in FIG.
30
.
FIG. 33
is a perspective view of a capacitor element used in the solid electrolytic capacitor of
FIG. 32
, and
FIG. 34
is a perspective view showing how a plurality of the capacitor elements are stacked on top of each other in layers on anode/cathode lead frames.
In
FIG. 32
to
FIG. 34
, capacitor element
56
is an anode body formed of aluminum foil (not shown in the drawings), the aluminum being a valve action metal, and divided into anode member
59
and cathode member
60
by providing resist part
58
after a dielectric oxide film layer (not shown in the drawings) is formed on the surface of the anode body. Further, a solid electrolyte layer and cathode layer (none of these are shown in the drawings) are stacked on top of each other in layers on the surface of cathode member
60
in succession.
A capacitor element stack body of
FIG. 34
is constructed as described below:
1B) A plurality of capacitor elements
56
are stacked on top of each other in layers in such a way as having anode member
59
disposed on both upper and bottom surfaces of anode lead frame
61
and also having cathode member
60
disposed on both upper and bottom surfaces of cathode lead frame
62
.
2B) Respective anode members
59
are joined integrally with anode lead frame
61
by resistance welding.
3B) Respective cathode members
60
are connected integrally to connecting member
62
A provided on cathode lead frame
62
on the side surfaces of capacitor element
56
extending in the thickness direction thereof via a conductive silver paste (not shown in the drawings).
Additionally, connecting member
62
A is armed by bending part of a flat member of cathode lead frame
62
into a right angle.
By using the capacitor element stack body of
FIG. 34
thus prepared, the solid electrolytic capacitor of
FIG. 32
is constructed as follows:
1C) The capacitor element stack body is encapsulated with an insulating packaging resin
63
in such a way as part of respective anode lead frame
61
and cathode lead frame
62
is exposed on the outer surfaces of packaging resin
63
.
2C) Anode lead frame
61
and cathode lead frame
62
exposed from packaging resin
63
are respectively bent along the surface of packaging resin
63
. (This is not shown in the drawings.)
The solid electrolytic capacitor shown in
FIG. 30
is prepared by first producing capacitor element stack unit
51
by stacking a plurality of capacitor elements
50
on top of each other in layers and then by further stacking a plurality of capacitor element stack units
51
on top of each other in piles. Accordingly, not only a great variety of component parts are used but also the assembly work becomes complex, thereby ending up with a high cost product.
As described in above, by applying a conductive silver paste onto respective stack surfaces of a plurality of capacitor elements
50
, capacitor elements
50
are connected with one another electrically to construct capacitor element stack unit
51
. Furthermore, a plurality of capacitor element stack units
51
are stacked on top of each other in piles with a conductive silver paste applied therebetween to connect electrically between capacitor element stack units
51
. Finally, part of cathode lead frame
54
located on the bottom of the stack of capacitor element stack units
51
forms a cathode terminal for external connection, thereby making it difficult for equivalent series resistance (referred to as ESR on occasions, hereafter) characteristics to be made closer to theoretical ones since the distance of cathode lead tends to be long.
The ESR characteristics of the setup as described in above are demonstrated by a summation of the following resistance values as shown in a schematic illustration of FIG.
35
:
A) Resistance R
1
produced between the layers of capacitor element
50
that constitute capacitor element stack unit
51
.
B) Resistance R
2
produced between the piles of capacitor element stack unit
51
.
Therefore, as the number of layers of capacitor element
50
and the number of piles of capacitor element stack unit
51
increase, an alienation between actual ESR characteristics and theoretical ones is growing.
Additionally, since there exists a conductive silver paste between respective neighboring capacitor elements
50
and also between respective neighboring capacitor element stack units
51
, the dimensions in the height direction thereof become large, thereby making it difficult for the end product of solid electrolytic capacitor to be reduced in thickness.
With the solid electrolytic capacitor of
FIG. 32
, a plurality of anode members
59
, each provided to capacitor element
56
, are integrally joined to anode lead frame
61
by resistance welding as described in above. However, as
FIG. 36
shows, dielectric oxide film layer
56
B is formed on the surface of aluminum foil
56
A in anode member
59
. When anode member
59
is joined to copper made anode lead frame
61
by resistance welding, dielectric oxide film layer
56
B having a high value in resistance makes it hard for the welding currents to flow. As a result, only part of aluminum foil
56
A is welded onto anode lead frame
61
or aluminum foil
56
A is not welded onto anode lead frame
61
at all in the bad case. Therefore, not only defective capacitors due to insufficient welding strength are produced but also an increase or a wide range of variation in equivalent series resistance may be caused.
In order to solve the foregoing problems, an increase

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