Solid electrolytic capacitor

Details Solid electrolytic capacitor Solid electrolytic capacitor

1999-12-21

2001-04-17

Reichard, Dean A (Department: 2831)

Electricity: electrical systems and devices

Electrolytic systems or devices

Solid electrolytic capacitor

C361S536000, C361S518000, C361S519000

Reexamination Certificate

active

06219224

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to solid electrolytic capacitors, and more particularly to hermetic seal structures for use in solid electrolytic capacitors comprising a capacitor element impregnated with a solid electrolyte, and a case having the capacitor element enclosed therein and hermetically sealed off.
BACKGROUND OF THE INVENTION
JP-B No. 51489/1987, JP-B No. 51491/1987, JP-B No. 66373/1992, U.S. Pat. No. 4,580,855, etc. disclose solid electrolytic capacitors which comprise a capacitor element including a metal member and impregnated with a TCNQ complex salt as an electrolyte, the metal member acting as a valve and being formed with a chemical conversion coating. “TCNQ” stands for 7,7,8,8-tetracyanoquinodimethane.
FIG. 5
shows one type of solid electrolytic capacitor which is already known and has a bottomed tubular aluminum case
40
accommodating a capacitor element
1
therein, filled with an epoxy resin
9
and having its opening sealed off. The capacitor element
1
comprises an anode foil which is an etched aluminum foil formed with a chemical conversion coating, and a cathode foil opposed to and superposed on the anode foil with a separator interposed therebetween. The capacitor element
1
is prepared by winding up the assembly of the foils and separator into a roll, and impregnating the roll with a solid electrolyte such as a TCNQ complex salt. A pair of lead terminals
12
,
12
extend from the anode foil and the cathode foil, and lead pins
13
,
13
extend from the respective terminals.
The solid electrolytic capacitor described is fabricated by filling a suitable amount of powder of TCNQ complex salt into a case
40
first, heating the case at 250 to 350° C. to melt the salt into a liquid, immersing the roll into the molten salt to impregnate the roll with the salt, thereafter rapidly cooling the roll as placed in the case to solidify the salt and finally filling an epoxy resin
9
into the case
40
.
The prior-art solid electrolytic capacitor described has the problem of impaired reliability involving variations in capacitance and increases in equivalent series resistance (ESR) due to the degradation of the sealing epoxy resin in a high-temperature environment or the penetration of moisture through the portion of contact between the sealing epoxy resin and the case or through the portion of contact between the sealing epoxy resin and the lead pin.
Accordingly, the present applicant has proposed in JP-A No. 3840/1999 a solid electrolytic capacitor having a hermetic seal structure and shown in FIG.
6
. The proposed capacitor comprises a capacitor element
1
impregnated with a solid electrolyte and a bottomed tubular metal case
4
enclosing the capacitor element
1
therein, the capacitor element
1
comprising an anode foil formed with a chemical conversion coating, a cathode foil opposed to the anode foil and a separator interposed between the foils, and prepared by winding up the assembly of these components into a roll. The case
4
has an opening which is closed with the hermetic seal structure
6
to be described below.
The opening of the case
4
is closed with a disklike seal plate
61
made of metal and having a pair of through holes. A pair of metal pipe pieces
63
,
63
each having a center bore are inserted through the respective holes of the seal plate
61
without contacting the inner peripheries of the plate
61
defining the holes. A glass material
62
is filled in a clearance in each through hole around the pipe piece
63
to provide electrical insulation and to seal off the clearance. The pipe pieces
63
are made of Cu, CuZn alloy or the like.
A pair of lead pins
13
,
13
extending from the capacitor element
1
extend through the respective center bores of the pipe pieces
63
,
63
without contacting the inner peripheries of the pipe pieces defining the bores. Solder or like brazing metal material
33
is filled in a clearance in each pipe piece
63
around the lead pin
13
to seal off the clearance. The edge portion of the case
4
defining its opening is joined to the outer peripheral edge portion of the seal plate
61
by resistance welding.
The hermetic seal structure
6
described gives high airtightness to the case
4
, therefore renders the capacitor element
1
free of the influence of moisture and assures the capacitor of high reliability over a prolonged period of time.
However, the pipe piece
63
which is made of Cu, CuZn alloy or the like differs greatly from the glass material
62
provided around the pipe piece
63
in coefficient of thermal expansion, so that when the pipe piece
63
is heated to seal off the clearance therein with the brazing metal material
33
, the glass material
62
is likely to separate from the pipe piece
63
at the joint therebetween or to develop cracks in the vicinity of the outer periphery of the pipe piece, consequently impairing the sealing effect.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a solid electrolytic capacitor having a hermetic seal structure which is unlikely to become impaired in its sealing properties even if exposed to heat in the assembling process thereof.
The present invention provides a solid electrolytic capacitor comprising a tubular metal case having an opening at at least one end thereof, and a capacitor element enclosed in the case and having an anode member formed with a chemical conversion coating, the capacitor element being impregnated with a solid electrolyte and having at least one lead pin extending therefrom, the opening of the case being closed with a hermetic seal structure.
The hermetic seal structure comprises:
a metal seal plate
71
having at least one through hole
76
and provided on the case
4
to close the opening thereof, the seal plate
71
having an outer peripheral edge portion joined to an edge portion of the case
4
defining the opening,
a pipe member
73
attached to the seal plate
71
and inserted through the hole
76
thereof, the pipe member
73
having a center bore with the lead pin
13
extending therethrough,
a glass material
72
filling a clearance in the through hole
76
of the seal plate
71
around the pipe member
73
, and
a brazing metal material
33
filling a clearance in the pipe member
73
around the lead pin
13
,
the pipe member
73
comprising a ceramic pipe piece
74
, and a metal thin film
75
formed on the pipe piece
74
at least at a portion thereof joined to the brazing metal material
33
.
Even if the pipe member
73
is heated to seal off the clearance therein with the brazing metal material
33
, the glass material
72
is unlikely to separate from the pipe member
73
at the joint therebetween or to develop cracks in the vicinity of the outer periphery of the pipe member
73
because of a small difference in coefficient of thermal expansion between the ceramic pipe piece
74
which is a major portion of the pipe member
73
in volume and the glass material
72
provided externally thereof. Consequently, the hermetic seal structure assures the capacitor of high sealing properties.
Preferably, the pipe piece
74
and the metal thin film
75
of the pipe member
73
are each made from a nonmagnetic material.
Further preferably, the glass material
72
is a glass containing PbO and B
2
O
3
, or a glass containing Zn and B
2
O
3
, and the pipe piece
74
of the pipe member
73
is made from a ceramic containing alumina.


REFERENCES:
patent: 3255387 (1966-06-01), Giacomello
patent: 3439231 (1969-04-01), Booe
patent: 4538212 (1985-08-01), Montgomery
patent: 5798906 (1998-08-01), Ando et al.
patent: 6052273 (2000-04-01), Inoue et al.
patent: 0 704 871 A1 (1996-04-01), None
patent: 0 872 859 A2 (1998-10-01), None

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