U.S. patent application number 11/657695 was filed with the patent office on 2007-07-26 for solid electrolytic capacitor and method for manufacturing the same.
This patent application is currently assigned to SANYO ELECTRIC CO., LTD.. Invention is credited to Yoshiyuki Fushimi, Kazuhiro Kato, Keiko Matsuoka, Kunio Shibata.
Application Number | 20070171599 11/657695 |
Document ID | / |
Family ID | 38285303 |
Filed Date | 2007-07-26 |
United States Patent
Application |
20070171599 |
Kind Code |
A1 |
Matsuoka; Keiko ; et
al. |
July 26, 2007 |
Solid electrolytic capacitor and method for manufacturing the
same
Abstract
A portion of an anode lead frame 3 of a solid electrolytic
capacitor 1 is bent to form a protruding portion 4 that protrudes
toward an anode lead 20. The protruding portion 4 includes a first
horizontal portion 41 positioned higher than and substantially
parallel to the anode lead 20, a second horizontal portion 40
contacting the anode lead 20, a sloping portion 42 linking the
inner end of the first horizontal portion 41 with the outer end of
the second horizontal portion 40, and an auxiliary bent portion 43
bent upward from the inner end of the second horizontal portion 40
and substantially symmetrical with the sloping portion 42. A
contact surface 46 of the second horizontal portion 40 with the
anode lead 20 is formed flat, and a surface 47 of the second
horizontal portion 40 on the opposite side to the contact surface
46 is formed with a rounded curvature.
Inventors: |
Matsuoka; Keiko; (Osaka,
JP) ; Kato; Kazuhiro; (Osaka, JP) ; Shibata;
Kunio; (Nikko-shi, JP) ; Fushimi; Yoshiyuki;
(Nikko-shi, JP) |
Correspondence
Address: |
ARMSTRONG, KRATZ, QUINTOS, HANSON & BROOKS, LLP
1725 K STREET, NW, SUITE 1000
WASHINGTON
DC
20006
US
|
Assignee: |
SANYO ELECTRIC CO., LTD.
Moriguchi-shi
JP
FURUKAWA PRECISION ENGINEERING CO., LTD.
Nikko-shi
JP
|
Family ID: |
38285303 |
Appl. No.: |
11/657695 |
Filed: |
January 25, 2007 |
Current U.S.
Class: |
361/540 |
Current CPC
Class: |
H01G 9/012 20130101;
H01G 9/10 20130101; H01G 9/042 20130101 |
Class at
Publication: |
361/540 |
International
Class: |
H01G 9/00 20060101
H01G009/00; H01G 4/228 20060101 H01G004/228 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 26, 2006 |
JP |
2006-17210 |
Claims
1. A solid electrolytic capacitor comprising: a capacitor element
with a protruding anode lead; an anode lead frame connected to the
anode lead; and a cathode lead frame attached to a peripheral
surface of the capacitor element, wherein the capacitor element, a
portion of the anode lead frame, and a portion of the cathode lead
frame are covered by a housing, wherein the anode lead frame has a
protruding portion that protrudes within the housing toward the
anode lead, the protruding portion includes a first horizontal
portion positioned higher than and substantially parallel to the
anode lead, a second horizontal portion contacting the anode lead,
a linking portion linking the first and second horizontal portions,
and an auxiliary bent portion bent upward from an inner end of the
second horizontal portion and substantially symmetrical with the
linking portion, and a contact surface of the second horizontal
portion with the anode lead is flat, and a surface of the second
horizontal portion on an opposite side to the contact surface has a
rounded curvature.
2. The solid electrolytic capacitor according to claim 1, wherein
the contact surface of the second horizontal portion with the anode
lead is formed by a pressing process for flattening the protruding
portion.
3. The solid electrolytic capacitor according to claim 1, wherein
the first horizontal portion is positioned at substantially the
same height from the anode lead as the cathode lead frame
contacting the peripheral surface of the capacitor element.
4. A manufacturing method for the solid electrolytic capacitor as
claimed in claim 1, comprising the steps of: forming a protruding
portion by performing a bending process or a deep drawing process
on a portion of an anode lead frame; and applying a pressing force
to and flattening a contact surface with an anode lead by further
performing a pressing process on a second horizontal portion of the
protruding portion, and forming a rounded curvature on a surface of
the second horizontal portion on an opposite side to the contact
surface.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a solid electrolytic
capacitor that includes a lead frame, and a method for
manufacturing the same.
[0003] 2. Description of the Related Art
[0004] Conventionally, a solid electrolytic capacitor (1) having
the configuration shown in FIG. 8 is known (see Japanese Patent No.
3157722). The solid electrolytic capacitor (1) includes a capacitor
element (2) with a thin wire-like anode lead (20) protruding
therefrom. An anode lead frame (3) is resistance welded to the
anode lead (20), and a cathode lead frame (30) is attached to the
peripheral surface of the capacitor element (2) by a conductive
adhesive (26). The capacitor element (2) and base ends of both lead
frames (3) and (30) are covered with a synthetic resin housing (5),
while portions of the lead frames (3) and (30) that protrude
outside the housing (5) are bent downward along the peripheral
surface of the housing (5), and then horizontally along the base of
the housing (5).
[0005] When forming the solid electrolytic capacitor (1), the
capacitor element (2) with the lead frames (3) and (30) attached is
deployed in a space (91) between removable upper and lower dies (9)
and (90), as shown in FIG. 9. After injecting resin into the space
(91), the dies (9) and (90) are removed to form the housing (5)
covering the capacitor element (2). Tapered surfaces (5a) (see FIG.
8) are formed on lower side portions of the housing (5) due to the
removal of the dies. The lead frames (3) and (30) are then bent
downward along the peripheral surface of the housing (5).
[0006] The capacitor element (2) is obtained by sequentially
forming a dielectric oxide film (21), a solid electrolytic layer
(22) made of a conductive polymer, and carbon and silver paste
layers (23) on the surface of an anode body (24) composed of a
sintered valve metal such as tantalum to cover the anode body (24),
as shown in FIG. 10. The anode lead (20) is made of a valve metal,
and protrudes from the center of the anode body (24).
[0007] As shown in FIG. 8, the anode lead frame (3) forms a step
portion (7) within the housing (5). The step portion (7) includes a
first horizontal portion (41) positioned higher than and
substantially parallel to the anode lead (20), and a second
horizontal portion (40) contacting the anode lead (20). The anode
lead frame (3) is bent from the end of the first horizontal portion
(41) along the outside of the housing (5) to form a vertical
portion (35).
[0008] Due to variation in length of the anode lead (20), the
leading end (20a) of the anode lead (20) sometimes comes in close
proximity to an intersection X between an extended surface of the
anode lead (20) and the housing (5).
[0009] By positioning the upper end of the vertical portion (35)
above the second horizontal portion (40) by the height of the step
portion (7), room is provided between the intersection X and the
vertical portion (35) by an amount equal to the horizontal distance
of the tapered portion (5a) corresponding to the height of the step
portion (7). Damage to the leading end of the anode lead (20) due
to the vertical portion (35) contacting the leading end of the
anode lead (20) when bending the anode lead frame (3) along the
housing (5) to form the vertical portion (35) is thereby
prevented.
[0010] The applicant was aware of the following problems with the
above configuration in need of resolution.
[0011] Springback sometimes occurs because of the step portion (7)
being formed by bending the metal anode lead frame (3). Here,
springback indicates the deformation of the step portion (7) in
such a way that the angle of bend widens after the metal has been
bent, as shown by the angles Y and Z magnified in FIG. 11.
Consequently, the anode lead (20) of the capacitor element (2) is
attached to the second horizontal portion (40) of the anode lead
frame (3) at an angle, as shown in FIG. 12, possibly causing
variation in the size of the contact area between the anode lead
(20) of the capacitor element (2) and the anode lead frame (3).
[0012] Also, if the anode lead (20) is welded to the second
horizontal portion (40), as shown in FIG. 13, the capacitor element
(2) welded at an angle pushes the cathode lead frame (30) upward,
possibly resulting in the cathode lead frame (30) jutting out from
the housing (5) and affecting the appearance of the solid
electrolytic capacitor (1). Variation in the bonding strength of
the capacitor element (2) occurs as a result, and reliability is
brought into question.
[0013] Also, the following problems occur if the positional
relation between the anode lead (20) and the anode lead frame (3)
is out of alignment when the capacitor element (2) is attached to
the cathode lead frame (30). The substantial contact area between
the anode lead (20) and the anode lead frame (3) is narrowed
because of the anode lead (20) and the anode lead frame (3) not
being parallel. This results in problems such as weak bonding
strength and increased ESR (Equivalent Series Resistance).
[0014] Further, if the second horizontal portion (40) is formed on
a large scale with a die when mass producing the anode lead frame
(3), the second horizontal portion (40) becomes rounded due to
wearing of the die, possibly reducing the contact area with the
anode lead (20).
[0015] There are also calls for further reductions in the size and
increases in the capacity of capacitors of this type.
SUMMARY OF THE INVENTION
[0016] An object of the present invention, which was made in
consideration of the above problems, is to provide a highly
reliable solid electrolytic capacitor with improved bonding
strength between the anode lead and the anode lead frame, and
reduced ESR, etc. A further object of the present invention is to
provide a solid electrolytic capacitor of reduced size and
increased capacity in which the anode lead frame is made longer
than an initial length by performing a pressing process to flatten
out the anode lead frame.
[0017] A solid electrolytic capacitor comprises a capacitor element
with a protruding anode lead, an anode lead frame connected to the
anode lead, and a cathode lead frame attached to a peripheral
surface of the capacitor element. The capacitor element, a portion
of the anode lead frame, and a portion of the cathode lead frame
are covered by a housing, and the anode lead frame has a protruding
portion that is bent into a V-shape and protrudes toward the anode
lead within the housing.
[0018] The protruding portion includes a first horizontal portion
positioned higher than and substantially parallel to the anode
lead, a second horizontal portion contacting the anode lead, a
linking portion linking the first and second horizontal portions,
and an auxiliary bent portion bent upward from the inner end of the
second horizontal portion and substantially symmetrical with the
linking portion.
[0019] An outer surface of the second horizontal portion where
contact is made with the anode lead is formed into a flat contact
surface, and an inner surface of the second horizontal portion on
an opposite side to the contact surface is formed with a rounded
curvature.
[0020] The contact surface of the second horizontal portion with
the anode lead is formed by flattening the surface using a pressing
process.
[0021] Further, a manufacturing method for the solid electrolytic
capacitor comprises the steps of forming a protruding portion
having a second horizontal portion at an end portion of an anode
lead frame by performing a bending process or a deep drawing
process on the anode lead frame; and flattening a contact surface
of the second horizontal portion with an anode lead by performing a
pressing process on the second horizontal portion, and forming a
rounded curvature on a surface of the second horizontal portion on
an opposite side to the contact surface.
EFFECT OF THE INVENTION
[0022] 1. A protruding portion (4) of an anode lead frame (3) is
formed by bending a portion of the anode lead frame (3) into a
first horizontal portion (41), a linking portion (specifically,
sloping portion (42) in FIG. 2), a second horizontal portion (40),
and an auxiliary bent portion (43). When forming the protruding
portion (4) of the anode lead frame (3), the bending load acting on
both sides of the protruding portion (4) is symmetrical and
balanced, because processing is preformed using a center impeller
structure for pressing symmetrically with both ends of the
protruding portion (4) held down. Any displacement due to
springback of the anode lead frame (3) is thereby symmetrical,
allowing the protruding portion (4) to be kept horizontal. Also,
since the pressing load of the welding electrode is supported on
both sides of the protruding portion (4) when welding the anode
lead (20) to the second horizontal portion (40), the parallelism of
the anode lead (20) and the second horizontal portion (40) is not
disturbed during welding.
[0023] Consequently, the capacitor element (2) is correctly
attached to the anode lead frame (3), increasing the substantial
contact area between the anode lead (20) and the anode lead frame
(3). Problems such as weak bonding strength and increased ESR
resulting from incorrect attachment of the capacitor element (2) as
in the prior art can thereby be resolved. [0024] 2. Also, because a
contact surface (46) of the second horizontal portion (40) with the
anode lead (20) is formed flat, the contact area between the
contact surface (46) and the anode lead (20) is enlarged. In this
respect also, the bonding strength between the anode lead (20) and
the anode lead frame (3) can be enhanced, and ESR reduced. Further,
because a surface (47) of the second horizontal portion (40) on the
opposite side to the contact surface (46), that is, the underside
of the second horizontal portion (40) is rounded for reinforcement,
cracking or the like when the contact surface (46) of the second
horizontal portion (40) with the anode lead (20) is pressed flat
can be prevented. [0025] 3. Also, because the contact surface (46)
of the second horizontal portion (40) with the anode lead (20)
undergoes a pressing process for flattening out the protruding
portion (4) using a die to make the protruding portion (4) thinner,
the distance from the first horizontal portion (41) to the
auxiliary bent portion (43) via the sloping portion (42) and the
second horizontal portion (40) is lengthened in comparison to when
a pressing process to flatten out the contact surface (46) is not
performed. That is, because the contact surface (46) is formed by
flattening out the protruding portion (4) to make it thinner, an
equivalent amount of the material is protruded, elongating the
sloping portion (42) and the auxiliary bent portion (43), and
increasing the overall length of the protruding portion (4).
[0026] A vertical distance H between the first horizontal portion
(41) and the second horizontal portion (40) can thereby be
lengthened without changing the initial cutoff length of the anode
lead frame (3), making it possible to also accommodate cases where
the peripheral surface height or outer diameter of the capacitor
element (2) is large. Being able to accommodate increases in the
size of the capacitor element (2) enables the capacity of the solid
electrolytic capacitor (1) to be increased.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a front sectional view of a solid electrolytic
capacitor,
[0028] FIG. 2 is an enlarged view of the leading end of an anode
lead frame,
[0029] FIGS. 3A and 3B are illustrative diagrams showing the
effects of a protruding portion in the present embodiment, while
FIG. 3C shows an alternative protruding portion,
[0030] FIG. 4 is a plan view of a metal plate that is to form lead
frames,
[0031] FIG. 5 is a perspective view showing the step of forming a
lead frame,
[0032] FIG. 6 is a cross-sectional view showing the step of forming
a lead frame,
[0033] FIG. 7 is a perspective view showing the step of forming a
solid electrolytic capacitor,
[0034] FIG. 8 is a front sectional view of a conventional solid
electrolytic capacitor,
[0035] FIG. 9 shows a manufacturing step for a conventional
electrolytic capacitor,
[0036] FIG. 10 is a cross-sectional view of a conventional
capacitor element,
[0037] FIG. 11 is a front view showing a conventional lead
frame,
[0038] FIG. 12 shows a conventional capacitor element attached at
an angle, and
[0039] FIG. 13 shows a conventional capacitor element attached at
an angle.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0040] An embodiment of the present invention will be described
below with reference to the accompanying drawings. A capacitor
element (2) used in a solid electrolytic capacitor (1) of the
present embodiment is the same as the prior art shown in FIG. 10.
Here, polypyrrole is used to form the solid electrolytic layer (22)
of the capacitor element (2), although other materials that may be
used instead include conductive polymers such as polythiophene,
polyaniline and polyfuran, and TCNQ (7, 7, 8,
8-tetracyanoquinodimethane) complex. An alloy that includes copper,
an iron-nickel alloy or the like is used to form the lead frames
(3) and (30).
[0041] Apart from tantalum, the valve metal constituting the anode
body (24) and the anode lead (20) may, for example, be niobium,
titanium, or aluminum.
[0042] FIG. 1 is a front sectional view of the solid electrolytic
capacitor (1) of the present embodiment. A thin wire-like anode
lead (20) protrudes from the capacitor element (2). An anode lead
frame (3) is resistance welded to the anode lead (20), and a
cathode lead frame (30) is attached to a peripheral surface of the
capacitor element (2) with a conductive adhesive (26). The
capacitor element (2), a portion of the anode lead frame (3) and a
portion of the cathode lead frame (30) are covered with a synthetic
resin housing (5), while portions of both lead frames (3) and (30)
that protrude outside the housing (5) are bent downward along a
peripheral surface of the housing (5) and then horizontally along
the base of the housing (5).
[0043] FIG. 2 is an enlarged view of the leading end of the anode
lead frame (3). The base end of the anode lead frame (3) is formed
into a protruding portion (4) that protrudes downward using a
pressing process. The protruding portion (4) includes a first
horizontal portion (41) positioned higher than and substantially
parallel to the anode lead (20), a second horizontal portion (40)
contacting the anode lead (20), a first sloping portion (42)
forming a linking portion that links the horizontal portions (40)
and (41), and an auxiliary bent portion (43) bent upward from the
inner end of the second horizontal portion (40) and substantially
symmetrical with the first sloping portion (42). The auxiliary bent
portion (43) includes a second sloping portion (44) that extends
upwardly at an angle from the inner end of the second horizontal
portion (40), and a third horizontal portion (45) that extends
inwardly from an upper end portion of the second sloping portion
(44). The first and third horizontal portions (41) and (45) are
substantially the same height as the cathode lead frame (30)
contacting the peripheral surface of the capacitor element (2)
within the housing (5).
[0044] A contact surface (46) of the second horizontal portion (40)
with the anode lead (20) is, as described later, flattened using an
additional pressing process. A surface (47) of the second
horizontal portion (40) on the opposite side to the contact surface
(46) is formed with a rounded curvature R.
[0045] Because the protruding portion (4) is processed using a
center impeller structure for pressing symmetrically on the first
and second sloping portions (42) and (44), the bending load acting
on both sides of the protruding portion (4) is symmetrical and
balanced. Springback of the anode lead frame (3) is thereby
cancelled out, and any displacement or tilting of the anode lead
frame (3) is suppressed.
[0046] Also, since the pressing load of the welding electrode is
supported on both sides of the protruding portion (4) when welding
the anode lead (20) to the second horizontal portion (40), the
parallelism of the anode lead (20) and the second horizontal
portion (40) is not disturbed during welding.
[0047] Consequently, the capacitor element (2) is correctly
attached to the anode lead frame (3), enabling problems such as
weak bonding strength and increased ESR resulting from incorrect
attachment of the capacitor element (2) as in the prior art to be
resolved.
[0048] Since the contact surface (46) of the second horizontal
portion (40) with the anode lead (20) is formed flat, the contact
surface (46) contacts closely with the anode lead (20). This
enables the bonding strength between the anode lead (20) and the
anode lead frame (3) to be enhanced. In particular, forming the
protruding portion (4) by bending the anode lead frame (3) made
from a metal plate means that the contact surface (46) easily
becomes rounded when there is a large vertical interval (H in FIG.
2) between the first and second horizontal portions (41) and (40).
This gives rise to reduced bonding strength between the anode lead
frame (3) and the anode lead (20), and increased ESR.
[0049] By performing the additional pressing process to flatten the
contact surface (46), the contact area between the contact surface
(46) and the anode lead (20) is increased. Consequently, the
bonding strength between the anode lead (20) and the anode lead
frame (3) can be enhanced and ESR reduced, even when there is a
large vertical interval between the first and second horizontal
portions (41) and (40).
[0050] Further, because the surface (47) of the second horizontal
portion (40) on the opposite side to the contact surface (46), that
is, the underside of the second horizontal portion (40) is formed
with a rounded curvature R for reinforcement, cracking or the like
when the contact surface (46) of the second horizontal portion (40)
with the anode lead (20) is flattened can be prevented.
Large Vertical Interval H between Horizontal Portions (41) and
(40)
[0051] With solid electrolytic capacitors of this type, there are
cases where it is desirable to enlarge the diameter of the
capacitor element (2) in order to accommodate increased capacity.
In this case, the vertical interval H between the first and second
horizontal portions (41) and (40) needs to be widened to avoid
contact between the peripheral surface of the capacitor element (2)
and the auxiliary bent portion (43). This is described below.
[0052] FIGS. 3A and 3B are illustrative diagrams showing the
effects of the protruding portion (4) in the present embodiment,
the protruding portion (4) having been inverted in comparison with
FIG. 2. FIG. 3A shows the protruding portion (4) having undergone
the pressing process to flatten the contact surface (46) after
forming the contact surface (46) by flattening out the protruding
portion (4) to make it thinner, while FIG. 3B shows the protruding
portion (4) before undergoing the pressing process to flatten the
contact surface (46). Consequently, the contact surface (46) in
FIG. 3B is slightly rounded.
[0053] Because the pressing process in FIG. 3A used to form the
contact surface (46) involves flattening out the protruding portion
(4) to make it thinner, an equivalent amount of material is
protruded, elongating the first sloping portion (42) and the
auxiliary bent portion (43), and increasing the overall length of
the protruding portion (4).
[0054] The vertical distance H from the first horizontal portion
(41) to the second horizontal portion (40) can thereby be
lengthened without changing the initial cutoff length of the anode
lead frame (3), making it possible to accommodate cases where the
peripheral surface height or outer diameter of the capacitor
element (2) is large. Being able to accommodate increases in the
size of the capacitor element (2) enables the capacity of the solid
electrolytic capacitor (1) to be increased.
[0055] The auxiliary bent portion (43) may be left as punched,
without providing the third horizontal portion (45), as shown in
FIG. 3C. In this case, the protruding portion (4) can be moved
toward the capacitor element (2) by an amount equal to the
horizontal length of the third horizontal portion (45), thereby
enabling the housing (5) of the solid electrolytic capacitor (1) to
be reduced in size.
Manufacturing Method for Anode Lead Frame
[0056] A manufacturing method for the anode lead frame (3) will be
shown below.
[0057] As shown in FIG. 4, a metal plate (8) forming the material
for the lead frames (3) and (30) is punched. The lead frames (3)
and (30) are cut out of the metal plate (8) to provide an anode
constituent piece (80) and a cathode constituent piece (81)
separated from one another. A recess (31) shown in FIGS. 4 and 5 is
formed where the capacitor element (2) is to be set on the cathode
constituent piece (81), thereby suppressing increases in the
overall height of the capacitor.
[0058] Next, as shown in FIG. 5, the protruding portion (4) is
formed by bending the leading end of the anode constituent piece
(80). In this case, the protruding portion (4) can also be formed
by deep drawing, although the bending process is considered
advantageous for giving height to the protruding portion (4). The
deep drawing process may, of course, be used to form the protruding
portion (4).
[0059] Next, as shown in the cross-sectional view of FIG. 6, a
receiving die (6) having a rounded top surface is placed on the
inner side of the protruding portion (4), and a pressing process is
performed on the protruding portion (4) from above using a punch
(60) having a flat working surface. The upper surface (i.e., the
contact surface (46)) of the second horizontal portion (40) is
thereby leveled, and the underside (47) of the second horizontal
portion (40) is formed with a rounded surface.
[0060] Next, as shown in FIG. 7, the anode lead (20) of the
capacitor element (2) is placed on the contact surface (46) of the
second horizontal portion (40) of the protruding portion (4), and
the capacitor element (2) is placed in the recess (31). The anode
lead (20) is resistance welded to the contact surface (46), and the
capacitor element (2) is attached to the recess (31) with a
conductive adhesive. Then, similarly to the prior art, the
capacitor element (2) is covered with the housing (5), the anode
and cathode constituent pieces (80) and (81) are cut off to form
the lead frames (3) and (30), and the lead frames (3) and (30) are
bent along the housing (5) to thereby obtain the solid electrolytic
capacitor (1). Although shown in FIG. 7 as being rectangular, the
capacitor element (2) may be cylindrical.
[0061] When attaching the capacitor element (2) to the anode lead
frame (3), the capacitor element (2) is described above as being
deployed above the anode lead frame (3), and then lowered. However,
the anode lead frame (3) may instead be turned upside down, so that
the protruding portion (4) protrudes downward, and the capacitor
element (2) deployed below the anode lead frame (3), before being
raised and attached.
* * * * *