Electricity: electrical systems and devices – Electrostatic capacitors – Fixed capacitor
Reexamination Certificate
1999-03-19
2001-01-30
Dinkins, Anthony (Department: 2831)
Electricity: electrical systems and devices
Electrostatic capacitors
Fixed capacitor
C361S308100, C361S309000, C361S321200
Reexamination Certificate
active
06181543
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a high voltage ceramic capacitor, and in particular, a high voltage ceramic capacitor which is suitable for use in environments requiring halogen resistance. Such capacitors are useful, for example, in an atmosphere containing halogen gas, such as a high voltage ceramic capacitor for an excimer laser apparatus.
2. Description of the Related Art
A high voltage ceramic capacitor is conventionally used for discharge excitation in an excimer laser apparatus. Because it is used in an atmosphere containing halogen gas, it must be resistant to halogen.
A high voltage ceramic capacitor
51
which is designed to be halogen resistant is shown in FIG.
5
and disclosed in Japanese Unexamined Patent Publication No. 8-130158. The high voltage ceramic capacitor
51
includes a capacitor device
52
made of a dielectric ceramic having electrodes
52
b
,
52
c
on the top and bottom surfaces
52
a
thereof. Metal terminals
53
,
54
are connected to the electrodes
52
b
,
52
c
of the capacitor device
52
, respectively.
The capacitor device
52
is arranged in a housing
55
. The housing
55
includes a housing body
55
a
which is open at the top and a lid member
55
b
which covers the opening. The housing body
55
a
and the lid member
55
b
are made of aluminum oxide, which is superior in halogen resistance. One of the metal terminals
53
passes through the lid member
55
b
, and the other of the metal terminals
54
passes through the bottom of the housing body
55
a.
A series of seals are formed to increase the halogen resistance of the capacitor device
57
. Seal members
56
,
57
, made of elastic rings or the like, are arranged between each of the two metal terminals
53
,
54
and the housing
55
, respectively, to form airtight seals. Another seal member
58
, made of an elastic ring, is arranged at the contact surface between the housing body
55
a
and the lid member
55
b
to form an airtight seal. Finally, the housing
55
is filled with an epoxy resin
59
to increase halogen resistance.
Because housing
55
made of aluminum oxide and having the above-described airtight sealing construction is used and because an epoxy resin
59
having superior halogen resistance is used to encase the capacitor device
52
and the metal terminals
53
,
54
(other than protruding portions of the metal terminals
53
,
54
), the high voltage ceramic capacitor
51
exhibits an increased halogen resistance.
Another high voltage ceramic capacitor is disclosed in Japanese Unexamined Patent Publication No. 7-230933. This high voltage ceramic capacitor has a configuration in which a capacitor device has electrodes on two main surfaces, the electrodes being connected to metal terminals, and is arranged in an airtight sealed housing made of a ceramic material. In this construction, the tips of the metal terminals protrude outwardly from the airtight sealed housing. A hole is provided with the metal terminals so that the hole passes through from the outside of the housing to the inside thereof. Gases are removed from the inside of the airtight sealed housing through the hole, so that the pressure in the airtight sealed housing is reduced. Then, the airtight sealed housing is filled with an insulating protective material such as an epoxy resin, a silicone resin, a urethane resin, or the like.
In the conventional high voltage ceramic capacitors disclosed in Japanese Unexamined Patent Publication Nos. 8-130158 and 7-230933, when the assembled device, in which a pair of metal terminals are connected to the capacitor device, is arranged in the housing, the resin (epoxy, silicone, urethane, or the like) is filled in as an insulating protective material. However, when epoxy resin is used, the coefficient of linear expansion of the cured epoxy resin is significantly greater than that of the ceramic which makes up the housing. Therefore, cracking may occur in the epoxy resin during curing and shrinking.
When cracks occur in the epoxy resin, the insulation performance of the capacitor deteriorates and lowers the voltage which the capacitor can tolerate. In addition, each component of the high voltage ceramic capacitor reacts with the halogen gas generating secondary gas and dust and polluting the gas atmosphere.
When silicone resin or urethane resin is used instead of epoxy resin, the above-described cracking can be avoided by virtue of its superior elasticity. However, silicone resin and urethane resin are significantly affected by halogen gas, in particular by fluorine gas. When the fluorine gas content increases slightly, the resin becomes fluid.
In the above-described high voltage ceramic capacitor
51
, the housing
55
is sealed airtight with seal members
56
to
58
in the form of elastic rings. However, the seal members do not function satisfactorily. Therefore, penetration by halogen gas such as fluorine gas cannot be completely prevented. When silicone resin or urethane resin is used instead of epoxy resin
59
, the resin is fluidized leading to separation of the lid member
55
b
. As a result, the fluidized resin material leaks into the excimer laser apparatus causing deterioration of the gas atmosphere.
Therefore, silicone resin and urethane resin cannot be used in place of epoxy resin
59
in the high voltage ceramic capacitor
51
. Thus, as disclosed in Japanese Unexamined Patent Publication No. 7-230933, an airtight sealed housing must be used. However, the airtight sealed housing does not have perfect sealing ability, and therefore halogen gas may enter the housing. When halogen gas enters the housing, the resin is fluidized, causing the same problems described above.
In addition, in the conventional high voltage ceramic capacitor, an insulating protective resin which fills the housing may expand, causing, for example, the lid member of the housing to open during use.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a high voltage ceramic capacitor in which a capacitor device connected to a metal terminal is arranged in a housing, and resin is filled therein, the filled resin is not susceptible to cracking, and the halogen resistance thereof is excellent.
In accordance with the present invention, a high voltage ceramic capacitor includes:
a capacitor device comprising a dielectric ceramic capacitor body having first and second opposed surfaces and first and second electrodes located on said first and second surfaces, respectively;
first and second metal terminals connected to said first and second electrodes, respectively;
a ceramic housing having a housing cavity which houses said capacitor device and at least a portion of said first and second metal terminals; and
first and second resin layers provided in said housing cavity and surrounding at least a portion of said first and second metal terminals, respectively, said first and second resin layers being separated by an empty space therebetween.
With this arrangement, the space which is formed between the first resin layer and the second resin layer can absorb stress during curing and shrinking of the resin in the resin layer. Therefore, occurrence of cracking in the first resin layer and the second resin layer can be prevented. That is, in the conventional high voltage ceramic capacitor in which only epoxy resin is filled, cracking tends to occur in the epoxy resin due not only to significant shrinkage stress during curing and shrinking but also to stress during cooling due to the difference between the coefficients of linear expansions of the resin and the ceramic. On the other hand, with respect to the high voltage ceramic capacitor in accordance with the present invention, the above-described stresses are relieved by the presence of the empty space between the two resin layers, so that occurrence of cracking in the resin can be prevented. In addition, a ceramic housing component such as a lid member is not lifted by expansion of the resin layers.
Thus, since the capacitor device and the contact portions bet
Esumi Toshiya
Kobayashi Shin-ichi
Murata Makoto
Ubata Akemi
Dinkins Anthony
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
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