JPH10253568A - Assembly of ceramic element and electrode, and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the number of components of an assembly of ceramic element and electrode that is used for an oxygen sensor or the like, and to simplify the assembling process, by coating a holding metal fitting or an electrode metal fitting integrally with an insulating layer, instead of a usual insulating sheet. SOLUTION: A sensor element 2 being a ceramic element is fixed by a glass seal 4 or the like in fixing metal fittings 3 and 5, and exhaust gas is led thereto through an opening 6a covered with a cover 6 of the tip part of the fixing metal fitting 3. Electrode terminal parts are formed in the base part of the sensor element 2 by metallize and a lead wire as an electrode metal fitting is laid on each electrode terminal part and put in a state of electrical connection by a holding metal fitting 10. An insulating layer 13 is applied on the inner surface of the holding metal fitting 10 or the outer surface 15 of the lead wire 8 and made integral therewith. The thickness of the insulating layer 13 is in the range of 20-150μm (e.g. about 100μm) and it is much thinner than a usual insulating sheet member (about 0.7-17mm thick), thus contributing to miniaturization of an electrode connecting part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an assembly of a ceramic element and an electrode used for, for example, an oxygen sensor and a method of manufacturing the same, and more particularly to an improved technique of a joint between the ceramic element and an electrode.

[0002]

2. Description of the Related Art For example, a ceramic element (sensor element) 100 of an oxygen sensor for a vehicle shown in FIG. 12 has a conductive path inside and an electrode terminal portion formed of a conductive film 101. A strip-shaped electrode fitting 102 (lead wire) is superposed on the conductive film 101, and an annular holding fitting 104 is press-fitted through an insulating plate 103, so that the electrode fitting 10 is formed.
2 is electrically connected to the conductive film 101 of the ceramic element 100 while being electrically insulated from the holding fitting 104. Then, the housing 10 as illustrated in FIG.
6. The lead wire 107 and the like are assembled to form an oxygen sensor.

[0003]

However, FIG.
In order to construct an assembly 105 such as
0, electrode fitting 102, insulating plate 103, and holding fitting 104
There is a disadvantage that the number of parts is large. In addition, the number of assembling steps is accordingly large, and the holding bracket 104 is assembled in a state where the insulating plate 103 is positioned and assembled in addition to the ceramic element 100 and the electrode fitting 102, and the process is complicated. .

An object of the present invention is to reduce the number of parts of an assembly of a ceramic element and an electrode used for an oxygen sensor or the like,
Another object is to simplify the assembly process.

[0005]

According to the present invention, the conventional insulating plate is abolished, and instead, an insulating layer is integrally coated on the holding fitting or the electrode fitting. That is, one surface of the electrode fitting is superimposed on the electrode terminal portion of the ceramic element, is restrained in a press-contact state by the holding fitting fitted from the outside, and is insulated on the inner surface of the holding fitting or the other surface of the electrode fitting. A layer is coated, and the coated insulating layer is interposed between the inner surface of the holding metal and the other surface of the electrode metal to maintain an electrical insulation therebetween.

[0006] In the process of manufacturing such an assembly, an inner surface of the annular holding metal is coated with an electrical insulating layer. Alternatively, one side of the electrode fitting to be pressed against the electrode terminal portion of the ceramic element is coated with an electrically insulating layer on the other side. Then, with one surface of the electrode fitting overlaid on the electrode terminal of the ceramic element,
The holding fitting is press-fitted from outside so as to restrain the ceramic element and the electrode fitting inside. Thus, one surface of the electrode fitting is pressed against the electrode terminal portion of the ceramic element, and the other surface is pressed against the inner surface of the holding fitting via the insulating layer.

By adopting such an assembly structure and manufacturing process, a conventional insulating plate becomes unnecessary, and the number of parts is reduced accordingly. In addition, since there is no need for a step of positioning and assembling the insulating plate, the number of assembling steps is reduced, and efficient assembling with good productivity becomes possible. In addition, by using a thinner coating layer than the conventional insulating layer, the size of the assembly can be reduced.

[0008] The insulating layer can be formed by a coating layer of an insulating material mainly composed of a glass component. For example, S
comprises iO _2, B ₂ O _3, and _{Al 2 O 3, BaO, K} 2 O, Li
_A binder is mixed with glass powder having an average particle diameter of 15 to 50 μm containing one or more components selected from ₂ O, Na ₂ O, ZnO, and MgO to form a paste. The inner surface of the holding member or the other surface of the electrode member is coated by coating, spraying or other methods.
Thereafter, the binder is removed by heating, and the coating layer is heated to a glass baking temperature to be baked on the inner surface of the holding fitting or the other face of the electrode fitting. In addition, in order to improve the wettability between the glass and the metal (holding fitting or electrode fitting), the metal surface of the holding fitting or the electrode fitting coated with glass can be oxidized (for example, heat-treated) in advance. .

The baking thickness of the glass layer is, for example, 150 μm.
If it exceeds, cracks and partial peeling are likely to occur at the time of press-fitting of the holding fixture. Therefore, it is desirable to determine within a range not exceeding this. Further, the minimum thickness of the baking thickness is a lower limit value at which electrical insulation can be maintained, but is determined based on the average particle size when the average particle size of the glass is more than this.

[0010] If a taper that opens outward is formed on the press fitting inlet side of the holding fitting, it becomes easier to press the holding fitting into the electrode fitting and the ceramic element.

In order to reduce frictional resistance when the holding fitting is pressed in, a predetermined lubricating material (for example, a resin emulsion or the like) is used.
The inner surface of the holding fitting (the surface of the insulating layer if coated) and / or the other surface of the electrode fitting (the surface if the insulating layer is coated)
In addition, it can be applied before the press-fitting.

[0012] application of the present invention, for example an oxygen sensor, a so-called NO _x sensor, the junction of the ceramic sensor element and the electrode fitting such as a temperature sensor, joined like the ceramic heater element and the electrode fitting further use in the heater, wide ceramic It extends to the field of joining elements and electrode fittings.

[0013]

Next, embodiments of the present invention will be described with reference to the drawings. First, FIG. 1 shows an example of an oxygen sensor 1, which includes a sensor element 2 which is a ceramic element such as alumina or zirconia. The sensor element 2 is attached to an exhaust pipe (not shown) of the vehicle, and measures the oxygen concentration in the exhaust gas. The sensor element 2 has a rectangular column shape obtained by stacking and firing an oxygen concentration sensor section and an electric heater section. Take the form. The sensor element 2 is fixed via a glass seal 4 or the like in fixing metal fittings 3 and 5 which are connected to each other in a cylindrical shape.
A portion protruding from the front end of the fixture 3 is covered with a cover 6, and exhaust gas is guided to one end of the sensor element 2 through an opening 6 a there.

On one surface of the other end side (base) of the sensor element 2, two electrode terminals 7 for extracting an output signal of the oxygen concentration sensor are formed by metallization, and on the surface on the opposite side of the base. Two electrode terminals (hidden and invisible) for energizing the electric heater are also formed by metallization. As shown in FIG. 2, a strip-shaped lead wire 8 as an electrode fitting is superimposed on each of the electrode terminal portions 7 on both sides of the base, and has a substantially rectangular annular holding shape as shown in FIGS. Each lead wire 8
Are pressed against the electrode terminal portions 7, respectively, and become electrically connected.

As shown in FIG. 4, electrical insulation between the lead wire 8 and the holding fitting 10 is maintained by the insulating layer 13. The insulating layer 13 is thinly coated on the inner surface 14 of the holding member 10 or on the surface opposite to the surface of the lead wire 8 pressed against the electrode terminal portion 7 (hereinafter, also referred to as the lead wire outer surface 15). Alternatively, it is integral with the lead wire 8.

FIGS. 5 and 6 show an example in which the inner surface 14 of the holding fitting 10 is coated with the insulating layer 13. The insulating layer 13 is formed of a baking coating layer of glass, for example, silica-based crystallized glass (Al, K, Ca, etc., and SiO _2).
(Silicate glass containing). Alternatively, a single substance or a composite substance such as zirconia (ZrO ₂ ), chromium oxide (chromia: Cr ₂ O ₃ ), alumina magnesia (spinel: Al ₂ MgO ₄ ) is coated by thermal spraying, coating or other methods, and then baked to insulate. Layer 13 can be used. For example, when baking glass, the inner surface of the holding fixture 10 can be pre-oxidized (for example, heat-treated for a predetermined time) in order to improve the wetting of the holding fixture 10 with the metal surface.

The above-mentioned coating thickness, in other words, the thickness of the insulating layer 13 is desirably in the range of, for example, 20 to 150 μm (for example, about 100 μm) so as to obtain a desired insulating property. If the thickness is too small, the reliability of the insulation cannot be ensured. If the thickness is too large, cracks and partial peeling are liable to occur, the benefit of miniaturization is reduced, and the economy of the insulating material is impaired. The coating thickness of the insulating layer 13 is much thinner than a conventional insulating plate member (about 0.7 to 1 mm), and contributes to downsizing of the electrode connection portion.

The coefficient of linear expansion of the insulating layer 13 is, for example, 5 to 12 × 10 ⁻⁶ / ° C. (0 to 500 ° C.), preferably 8 to 10 × 10 ⁻⁶ / ° C.
It is recommended to secure １２12 × 10 ⁻⁶ / ° C. Regarding the heat resistance of the insulating layer 13, in the case of an oxygen sensor, since the exhaust gas is at a considerably high temperature, the softening point is 600 ° C. or more,
Above all, it is desirable to set the temperature to 800 ° C. or higher from the viewpoint of reliability against high temperatures.

The holding bracket 10 is preferably made of an iron-based low expansion metal, for example, a FeNiCo alloy (Kovar), if necessary.
It is formed of an iron-based alloy to which l, Nb, Ti, etc. are added, and is subjected to a heat treatment for solution treatment (homogenization) (for example, 850 to 950).
C.), and heat treatment for age hardening (aging) (for example, about 720 ° C. for 8 hours, and further about 620 ° C. for 8 hours).
Time) can be adopted. In addition, a heat-resistant alloy, for example, SUS, SUH, or the like can be suitably used. The baking temperature of the above-mentioned coating such as glass is, for example, 90
It is set at about 0-1000 ° C, but after baking,
It is desirable to perform the above-mentioned age hardening heat treatment. In addition, it is a matter of course that an appropriate cooling form other than the above can be adopted as the age hardening. In addition, even if the holding bracket has a form in which a part of an annular shape is missing (for example, a U-shape), it is acceptable as long as a predetermined restraining force is obtained.

As shown in FIG. 5, it is desirable to form rounded portions R (arc-shaped surfaces) at four corners on the inner periphery of the holding fitting 10 to prevent stress concentration. This radius portion is also effective in improving the coating property of the insulating layer 13. The insulating layer 13 can be continuously coated in a ring shape on the inner periphery of the holding fitting 10 as shown in FIG. 6 (a). However, as shown in FIG. May be coated with the insulating layer 13 only or partially.

Furthermore, it is desirable to form a tapered surface 16 that opens outward at one opening of the holding fitting 10 (an end which is an inlet side of press-fitting in a press-fitting step described later). This facilitates the press-fitting process. Since the tapered surface 16 does not contact the outer surface of the lead wire, it is not necessary to form the insulating layer 13 on the tapered surface 16 for the purpose of insulation. However, in order to increase the strength of the insulating layer 13 against cracking and peeling during press-fitting. It may be advantageous to coat the insulating layer 16 over a portion of the tapered surface 16 or over the entire tapered surface 16.
In that case, the entrance portion of the insulating layer 13 on the press-fit side has a tapered surface that opens outward.

FIG. 7 shows a press-fitting step of the holding fitting 10 having the inner surface coated with the insulating layer 13. On the electrode terminal portion 7 (metallized portion) of the sensor element 2 described above, a total of four lead wires 8 are set, for example, two on each side, and set by a jig 18 for positioning and holding. Held in state. The holding fitting 10 is press-fitted with the tapered surface 16 as an inlet side so as to restrain the pre-assembly of the sensor element 2 and the lead wire 8 inside. In other words, the holding fitting 10 is fitted to the pre-assembly by an interference fit.

Here, the interference δ is δ = (b + 2)
c) -a2 (where b: thickness of the sensor element 2 (including the thickness of the metallized portion), c: thickness of the lead wire, and a2: inner dimensions including the insulating layer before press-fitting the holding fitting 10). This interference δ is, for example, about 10 to 130 μm,
１００ / a 2 = 0.3-4.4%, preferably 0.66
% To 3.3%. If this is too small, the reliability of the connection between the lead wire 8 and the sensor element 2 (electrode terminal portion 7), and eventually, the integrity of the three members of the holding metal fitting 10, the lead wire 8 and the sensor element 2 will be weakened. Conversely, if the interference δ is too large, press-fitting becomes difficult, and cracking or peeling is likely to occur in the insulating layer 13 during press-fitting, so that the elastic deformation of the holding fitting 10, the sensor element 2, the lead wire 8, and the like. Therefore, it is preferable to set the pressure in the above range in order to generate an appropriate pressing force due to the pressure. Prior to the press-fitting of the holding fitting 10, for example, if a sliding material (for example, an emulsion of stearic acid or the like) is applied to the entrance end or the inner surface (the surface of the insulating layer 13) of the press-fitting of the holding fitting 10, the press-fitting is facilitated. It is effective in performing.

FIGS. 8 and 9 show an example in which an insulating layer 20 is coated on the outer surface of one end of a lead wire 8 as an electrode fitting. This insulating layer 20 is also substantially the same as that of the above-mentioned holding fitting 10, and can be formed by a baking coating of glass or a baking coating of ceramic such as zirconia. Lead wire 8
For example, the surface (the inner surface 21) opposite to the lead 8 made of a heat-resistant metal such as Inconel X-750, Ni, SUS303 or the like and having the outer surface 15 of the lead coated with the insulating layer 20.
Is superimposed on the electrode terminal portion 7 of the sensor element 2 and the jig 18
In this state, the holding fitting 30 (the inner surface 31 of which is a metal surface) is press-fitted so as to restrain the sensor element 2 and the lead wire 8 inside. The conditions for the press-fitting are substantially the same as those in the above-described example. As a result, the inner surface 31 of the holding member 30 is pressed against the insulating layer 20 of the lead wire 8 so that the two are electrically insulated, and the inner surface 21 of the lead wire is pressed against the electrode terminal portion 7 of the sensor element 2. Thus, the two become electrically conductive.

[0025]

Embodiment 1 Next, a more specific embodiment will be described. In the first embodiment and a second embodiment to be described later, as shown in FIG.
The electrode terminal portions 7 at the locations were formed by metallization, and a pair of lead wires 8 were overlapped on these. A holding metal fitting 10 having an insulating layer as shown in FIGS. 5 to 6 was used.

SiO ₂ : 65% by weight, B ₂ O ₃ : 18
%, Al ₂ O ₃ : 8.4%, BaO: 3.1%, K ₂ O:
3.1%, Li ₂ O: 0.5%, Na ₂ O: l. A suitable amount of butylcarbidol, ethylcellulose and acetone are added to glass powder adjusted to a composition of 9% and an average particle diameter of 30 μm, and mixed in an alumina mortar to form a paste. FIG.
Incoloy 909 holding bracket (wall thickness t: 1 mm,
Holding dimension a1: about 3 mm, holding outer dimension D: 5 mm, width W: 6 m
m, height H: 3 mm) was heated in air at 450 ° C. for 5 hours to perform a surface pre-oxidation treatment.

Next, the above-mentioned pastes were individually applied to the inner surfaces of the plurality of holding fittings obtained in this manner so as to have different thicknesses of the baked glass. Next, this was heated in the air at 350 ° C. for 30 minutes to volatilize the resin added for the purpose of cost reduction.
Further, the glass was heated in a nitrogen atmosphere at 1000 ° C. for 10 minutes, and the glass was baked on the holding fitting (FIG. 6). Thereafter, the holding dimension a2 (FIG. 6) was measured at room temperature, and the baked state of the glass was observed with a magnifying glass.

In this case, the ceramic element 2 (FIG. 10) is a heater element made of alumina, in which a heater containing tungsten as a main component is formed. This is a pair of electrode terminals whose outermost surface is Ni. A part 7 is provided. The dimensions of the ceramic element 2 are as follows: width W: 3.5 mm, length L: 30
mm, thickness b: about 2.5 mm. The element thickness b is N
Including the thickness of the i-electrode terminal portion. The lead wire 8 has a width w: 2.0
mm, thickness c: Ni of 0.15 to 0.25 mm was used. The reason why the thickness of the lead wire is variously changed is that the interference (δ) according to the following equation is set to about 50 to 60 μm. .delta. = (b + 2c) -a2 The electrodes were assembled by press fitting as shown in FIG.

The evaluation was performed by first measuring the resistance between the lead wire 8 and the holding fitting 10 at room temperature using an insulation resistance tester,
After heating in the air at 0 ° C. for 100 hours, the resistance value between the lead wire 8 and the holding fitting 10 was measured in the same manner. Table 1 shows the results. In Table 1 (the same applies to Table 2), “> 10
“0 MΩ” indicates that it exceeds 100 MΩ. Also,
The pull-out strength of the lead wire 8 is as follows:
All samples weighed 1 kg or more.

[0030]

[Table 1]

It was confirmed that there was no problem in the performance of the electrode portion when the baked thickness was 19 to 89 μm. When the baking thickness was 102, 115 μm, small cracks were observed in a part of the glass after baking the glass, but it was confirmed that there was no problem with the performance of the electrode part after assembling by pressing and further after heating. . In the case of 131 μm, the resistance after heating decreased. On the other hand, when the baked thickness exceeded 156 μm, cracks and peeling were observed in the glass, and the glass peeled off during press-fitting, and no insulation was obtained. Evaluating the results in Table 1, the glass baking thickness is preferably 19 to 115 μm, more preferably 19 to 115 μm.
It is 89 μm. The minimum value of the thickness of the baked glass is determined by the particle size of the glass powder, and is generally at least about 15 μm.

[0032]

Example 2 65% by weight of ZnO and 16 by weight of B ₂ O ₃
%, SiO ₂ : 15%, MgO: 4%, average particle size 5
To a glass powder adjusted to 0 μm, butyl carbidol,
Appropriate amounts of ethyl cellulose and acetone are added and mixed in an alumina mortar to make a paste. Kovar (FeNiC)
o alloy) holding bracket 10 (thickness t: 1 mm, holding dimension a1:
Approximately 3mm, holding outer dimension D: 5mm, width W: 6mm, height H: 3m
m: FIG. 5) is subjected to an oxidizing heat treatment at 450 ° C. in the air for 3 hours, and the inner surface thereof has a thickness of 70 to 80 after glass baking.
The paste was applied so as to have a thickness of about μm. next,
The resin was heated at 350 ° C. for 30 minutes in the atmosphere to volatilize the resin added for the purpose of making the paste. Next, the glass was heated at 900 ° C. for 15 minutes in nitrogen to bake the glass on the holding fitting 10 (FIG. 6). After that, the holding dimension (a2) was measured at room temperature,
Further, the baked state of the glass was observed with a magnifying glass.

The ceramic element 2 is an oxygen sensor element made of zirconia, and has an electrode terminal portion mainly composed of platinum on the surface. In FIG. 10, the dimensions of the ceramic element are as follows: width W: 3.5 mm, length L: 40 mm, thickness b: about 2.
It was 5 mm. The element thickness b includes the thickness of the platinum electrode terminal. The lead wire 8 has a width W: 2.0 mm and a thickness c: 0.15
0.25 mm Ni was used. The reason for variously changing the thickness of the lead wire 8 is that the interference (δ) according to the following equation is set to 50 to 12
This is to reduce the thickness to about 0 μm. δ = (b + 2c) −a2
The electrodes were assembled by press-fitting as shown in FIG. After the press-fitting, the state of the glass was observed with a magnifying glass.

The evaluation was performed in the same manner as in Example 1.
Table 2 shows the results. The pull-out strength of the lead wire 8 is
At the beginning and after heating, all the samples weighed 1 kg or more.

[0035]

[Table 2]

In the interference δ: 22 to 120 μm, small cracks were observed after the press-fitting in the 117 μm product and the 120 μm product, but it was confirmed that there was no problem with the performance of the other electrode parts. When the interference was 147 or 153 μm, the glass was peeled off after press-fitting, and no insulation was initially obtained. When the interference was 12 or 17 μm, the insulating property could be secured, but rattling occurred in the lead wire after the oxidation test, and there was a case where the durability as an electrode joint was a little problematic. When the results in Table 2 are evaluated, the interference is 22 to 1
20 μm is good, and more preferably 22 to 93 μm.

[Brief description of the drawings]

FIG. 1 is a half sectional view of an oxygen sensor to which the present invention is applied.

FIG. 2 is a perspective view showing a ceramic element and lead wires of FIG. 1;

FIG. 3 is a perspective view in which a holding bracket is added to FIG. 2;

FIG. 4 is a sectional view of a main part of FIG. 3;

FIG. 5 is a perspective view showing an example of a holding bracket.

FIG. 6 is a diagram showing an example in which the inner surface of the holding fitting is coated with glass.

FIG. 7 is a process diagram showing an example of a press fitting process of the holding fitting.

FIG. 8 is a diagram showing an example in which a lead wire as an electrode fitting is coated with an insulating layer.

FIG. 9 is a process diagram showing an example of press-fitting a holding fitting into the lead wire and the ceramic element of FIG. 8;

FIG. 10 is a view showing another example of the ceramic element.

FIG. 11 is a cross-sectional view of a step of press-fitting the holding fitting into the ceramic element and the lead wire.

FIG. 12 is a perspective view of a conventional example.

FIG. 13 is a perspective view of an oxygen sensor including the assembly of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Oxygen sensor 2 Sensor element (ceramic element) 7 Electrode terminal part (electrical connection part) 8 Lead wire (electrode fitting) 10, 30 Holding fitting 13, 20 Insulating layer 14 Inner surface of holding fixture 15 Outer surface of lead wire

Continuation of the front page (72) Inventor Kuji Nishio 14-18 Takatsuji-cho, Mizuho-ku, Nagoya-shi, Aichi Japan Special Ceramics Co., Ltd.

Claims (9)

[Claims] 1. A surface of an electrode fitting is superimposed on an electrode terminal portion of a ceramic element, is restrained in a press-contact state by a holding fitting fitted from the outside, and an inner surface of the holding fitting or the other of the electrode fitting. The surface is coated with an insulating layer, and the insulating layer is interposed between the inner surface of the holding metal member and the other surface of the electrode metal member to maintain an electrical insulation between them. And electrode assembly. 2. The insulating layer according to claim 1, wherein the insulating layer is formed by a baking coating layer of an insulating material mainly composed of a glass component.
An assembly according to claim 1. 3. An inner surface of the holding metal member is coated with the insulating layer, and the insulating layer is maintained in a state of being pressed against the other surface of the electrode member by a binding force of the holding metal member. Or the assembly according to 2. 4. The other surface of the electrode fitting is coated with the insulating layer, and the insulating layer is maintained in a state where the insulating layer is pressed against the inner surface of the holding fitting by the binding force of the holding fitting. An assembly according to claim 1 or 2. 5. A step of coating an inner surface of an annular holding metal with an electrically insulating layer, a step of superposing one surface of the electrode metal on an electrode terminal of the ceramic element, and placing the ceramic element and the electrode metal inside. Press-fitting the holding metal fitting from the outside so as to restrain it, and pressing one surface of the electrode metal fitting to the electrode terminal portion of the ceramic element and the other surface to the insulating layer on the inner surface of the holding metal fitting. A method for manufacturing an assembly of a ceramic element and an electrode, comprising: 6. A step of coating an electrode fitting whose one surface is to be pressed against the electrode terminal portion of the ceramic element with an electrical insulating layer on the other surface, and applying the one surface of the electrode fitting to the ceramic element. By press-fitting an annular holding bracket from the outside so as to restrain the ceramic element and the electrode bracket inside,
Contacting one surface of the electrode fitting with the electrode terminal portion of the ceramic element and the other surface with the inner surface of the holding fitting via the insulating layer, respectively. Manufacturing method of assembly. 7. It contains SiO ₂ and B ₂ O ₃ and contains Al ₂ O ₃ and Ba.
O, K ₂ O, Li ₂ O, Na ₂ O, ZnO, MgO, containing one or more components selected from the group, and having an average particle size of 15 to 5
A binder is mixed with 0 μm glass powder to form a paste, and this glass paste is applied to the inner surface of the holding metal or one surface of the electrode metal by thermal spraying or another method, and then heated to form the binder. 7. The manufacturing method according to claim 5, wherein the coating layer is removed, and the coating layer is heated to a glass baking temperature and baked on the inner surface of the holding bracket or the other surface of the electrode bracket, and the glass layer is used as the insulating layer. . 8. The baked thickness of the glass layer is 15-15.
The method according to claim 7, wherein the thickness is 0 μm. 9. The manufacturing method according to claim 5, wherein a taper that opens outward is formed at an inlet portion of the press fitting of the holding fitting.