JP2000340350A - Silicon nitride ceramic heater and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ceramic heater capable of heating from room temperature to a high temperature of 1000 deg.C or higher, preventing stress concentration within the heater even when severe heat cycles are applied, and enhancing durability, and provide the manufacturing method thereof. SOLUTION: This silicon nitride ceramic heater is formed by burying a resistance heating element 2 and a lead wire 3 within a rod insulating base 1 made of silicon nitride base ceramic and installing a connecting terminal part 4 electrically connected to the lead wire 3 in the outer peripheral part of the insulating base 1, and wherein the rod insulating base 1 is constituted with a core part 1a and a shell part 1b formed in the surrounding of the core part 1a, the resistance heating element 2 and the lead wire 3 are formed with a conductor material having practically the same composition in a concentric circle region from the center of the rod insulating base 1 and in almost the symmetrical position, and the shell part 1b is made seamless.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly durable silicon nitride ceramic heater which can be widely used for electronic parts, industrial machines, automobiles and the like, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, a ceramic heater is known in which, for example, a ceramic sheet formed by sticking a resistance heating element pattern and a lead wiring pattern on a surface of a ceramic core formed of a rod-shaped body with a conductive paste is fired. In particular, it is used in a wide range of fields such as a heater for heating a sensor section of an oxygen sensor for detecting an oxygen concentration in exhaust gas.

[0003] Conventionally, ceramic heaters, for example,
A ceramic sheet on which a resistance heating element pattern or a lead wiring pattern is printed is wound around a surface of a rod-shaped core formed by extrusion-molding a ceramic composition containing alumina as a main component, integrated, fired, and then baked. Are known in which a conductive material is plated to form a connection terminal portion.

Further, in a conventional heater using an alumina ceramic as an insulating substrate, the heating temperature is at most 200.
C., which is unsuitable for a heater capable of rapidly heating to a temperature of 1000 ° C. or more, such as an oxygen sensor and a glow plug. Therefore, recently, in order to improve the rapid temperature rising performance, it has been proposed to use a silicon nitride ceramic having excellent heat resistance, thermal shock resistance and the like as an insulating base material.

As shown in FIG. 3, such a ceramic heater made of silicon nitride has a method of burying a tungsten metal wire 11 in a rod-shaped silicon nitride molded body 10 and performing hot press firing. A conductor paste prepared by mixing a metal powder such as W and an insulating powder on a surface of the fired ceramic molded body substrate is printed on a predetermined resistance heating element pattern and a lead wiring pattern, and then the insulating sheets are overlaid and hot-press fired. Flat heaters and the like are known.

[0006] Further, according to the ceramic heater, it is desired that only the tip of the heater be heated to prevent the temperature of the entire heater from rising. Therefore, it is necessary to improve the resistance ratio between the resistance heating element and the lead wiring in the ceramic heater, in other words, to extremely reduce the resistance of the lead wiring.

To cope with such a demand, it has been proposed in JP-A-3-149791 or the like to form the resistance heating element, the lead wiring, and the conductor material having different resistance values from each other.

[0008]

However, in a conventional ceramic heater, a method of burying a metal wire as a rod-shaped ceramic heater and performing hot press firing is as follows.
There is a problem that only a single shape can be manufactured, and since the surface of the sintered body is roughened, grinding and polishing are ultimately required, resulting in high costs. In the method of wrapping around the surface of the core formed body and firing, a seam is inevitably formed by winding the sheet-shaped formed body. There is a problem that durability is deteriorated due to occurrence of cracks.

A flat ceramic heater can be easily manufactured as compared with a rod-shaped ceramic heater. However, the final flat plate has anisotropic mechanical properties, so that severe conditions are required. There was a problem that the reliability when used below was inferior.

Although the method of forming the resistance heating element and the lead wiring using different types of conductor materials is effective in increasing the resistance ratio, it is difficult to co-fire with the insulating base because of the different physical properties of the conductor materials. In addition, since stress is easily generated inside the heater, there has been a problem that the wire is disconnected or the insulating substrate is broken when used under severe conditions.

The present invention provides a silicon nitride ceramic heater which can be heated from room temperature to a high temperature of 1000 ° C. or more, prevents stress concentration inside the heater even when a severe thermal cycle is applied, and has excellent durability. It is intended to provide a manufacturing method.

[0012]

The inventor of the present invention has conducted various studies on the above-mentioned problems, and as a result, the heater has a rod-like structure, and the resistance heating element and the lead wiring are substantially the same conductor. It has been found that the above object can be achieved by forming a concentric circular region from the center of the rod-shaped insulating substrate with the material and eliminating the seam in the shell portion covering the resistance heating element and the lead wiring.

That is, the silicon nitride ceramic heater of the present invention has a resistance heating element and lead wires embedded inside a rod-shaped insulating substrate made of silicon nitride ceramics, and the lead wires are provided on the outer periphery of the insulating substrate. Wherein the resistance heating element and the lead wiring are made of a conductive material having the same composition substantially containing a metal component and an inorganic component. Are formed in a concentric circle region from the center of the shell, and there is no seam in the shell portion.

In this configuration, the resistance heating element and the lead wiring may have different line widths and / or film thicknesses, and a plurality of the resistance heating elements or the lead wiring may be provided in a cross section of the heater. It is desirable to form them in concentric regions with an interval.

Further, as a method of manufacturing a ceramic heater made of silicon nitride, a step a of forming a rod-shaped core molded body from a ceramic composition containing silicon nitride as a main component; B step of depositing and forming a resistance heating element pattern and a lead wiring pattern with a conductor material having substantially the same composition containing a component and an inorganic component; and forming the rod-shaped core molded body in a slurry containing the ceramic composition. C) forming an insulating shell on the surfaces of the resistance heating element pattern and the lead wiring pattern of the rod-shaped core molded body; and drying the composite molded body obtained by the c step. B) firing in a non-oxidizing atmosphere.

According to this manufacturing method, the step (b) includes the steps of forming a resistive heating element pattern and a lead wiring pattern on a predetermined transfer sheet, and then transferring the pattern to the surface of the rod-shaped core molded body. Preferably, the firing is performed in a pressurized nitrogen gas atmosphere.

[0017]

According to the silicon nitride ceramic heater of the present invention, a resistance heating element and a lead wiring are provided inside a rod-shaped insulating base composed of a core made of silicon nitride ceramics and a shell formed around the core. Is formed in a concentric region from the center of the rod-shaped insulating substrate by a conductor material having substantially the same composition, and the shell portion has a seamless structure. It is possible to reduce the occurrence of stress due to differences in physical properties between the constituent members, that is, the insulating base, the resistance heating element, and the lead wiring, thereby preventing cracks in the insulating base and disconnection of the resistance heating element and the lead wiring. In addition, the durability of the ceramic heater can be improved.

In particular, since the resistance heating element and the lead wiring are formed of a conductor material having substantially the same composition containing a metal component and an insulation component, a resistance ratio is changed by changing a line width and / or a film thickness. Can be adjusted, and in the cross section of the heater, by forming a plurality of the resistance heating elements or the lead wires in concentric regions at equal intervals, it is possible to further prevent the concentration of stress, Further, the durability can be improved.

Further, as a manufacturing method, a resistance heating element pattern and a lead wiring pattern are formed by applying a conductor material having substantially the same composition to the surface of a rod-shaped core molded body made of a silicon nitride ceramic composition. After dipping in the slurry containing the composition, and drying, by forming an insulating shell on the surface of the resistance heating element pattern and the lead wiring pattern of the rod-shaped core molded body, the shell is seamless and uniform. As a result, even when the composite molded body is fired, generation of cracks and disconnections during firing can be suppressed by uniform firing shrinkage behavior of the entire heater.

In particular, by forming the resistive heating element pattern and the lead wiring pattern on the surface of the core molded body by transferring from a predetermined transfer sheet, the pattern on the core molded body having a curved surface can be easily formed at a high yield. Can be well formed. In addition, since this method does not require the production of a sheet-shaped molded body, the sheet molding technique is not required, and complicated steps such as a winding process thereof are not required. Manufacturing costs can be reduced. Further, the firing is performed in a pressurized nitrogen gas atmosphere.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. FIG. 1A is a schematic perspective view of the ceramic heater of the present invention, and FIG. 1B is a cross-sectional view in the longitudinal direction thereof. As shown in FIG. 1, the ceramic heater made of silicon nitride of the present invention comprises:
A resistance heating element 2 and a pair of lead wires 3 are buried inside a rod-shaped insulating base 1 made of silicon nitride ceramics, and the outer periphery of the insulating base 1 is electrically connected to the lead wiring 3. A pair of connection terminal portions 4 are formed.

FIG. 2 is a cross-sectional view of (a) the resistance heating element 2 forming portion (Y ₁ -Y ₁ ) of the ceramic heater of FIG.
(B) a cross-sectional view of the lead wiring 3 forming portion (Y ₂ −Y ₂ );
(C) Cross-sectional views of the connection terminals (Y ₃ -Y ₃ ) are shown.

As is apparent from FIG. 2, the insulating base 1 in the ceramic heater according to the present invention comprises a ceramic core 1
a and its shell portion 1b, and each of the resistance heating elements 2 and the lead wires 3 has a structure buried around the ceramic core portion 1a as at least one pair of wires. In the cross section, the resistance heating element 2 or the lead wiring 3 is formed in concentric regions of r ₁ , r ₂ , and r ₃ from the center C of the rod. As described above, by forming the resistance heating element 2 and the lead wiring 3 in the concentric region, it is possible to prevent the occurrence of local stress, to suppress the generation of distortion even under severe heat cycle application, and to increase the durability. Can be. In addition, the difference in distance from the center in each cross section is ± 0.
It means that it is acceptable up to about 2 mm.

Preferably, as shown in FIG. 2, an even number (four in FIG. 2) of resistance heating elements 2 and lead wires 3 are formed in each cross section, and these are equally spaced in a concentric region. The formation can further suppress the occurrence of distortion.

It is desirable that the shell portion 1b has a thickness of 0.3 to 1.5 mm. This is because if the thickness is larger than 1.5 mm, the rate of temperature rise on the heater surface becomes slow, and if the thickness is smaller than 0.3 mm, porcelain destruction occurs due to thermal shock.

In the ceramic heater having the above configuration,
The resistance heating element 2 and the lead wiring 3 are both formed of a conductive material. However, in order to increase the heating efficiency of the resistance heating element 2 alone, the resistance ratio between the resistance heating element 2 and the lead wiring 3 (resistance heating). Larger body / lead wiring) is desired.

In such resistance adjustment, when the resistance heating element 2 and the lead wiring 3 are formed of, for example, different conductor materials in which the content ratio of the conductive component and the insulating component is changed, that is, the resistance heating element 2 has a high resistance. When the lead wire 3 is formed of a low-resistance conductor by the conductor and the conductor material itself has different thermal expansion characteristics, firing shrinkage behavior, and other physical properties such as different particle diameters of the conductive component, the conductor material differs from the insulating base. At the same time, or when a thermal cycle is applied, distortion or the like is likely to occur in the entire heater, and the durability is reduced.

According to the ceramic heater of the present invention, since the resistance heating element 2 and the lead wiring 3 are both made of the same conductive material, the resistance ratio between the resistance heating element 2 and the lead wiring 3 is increased. For this purpose, adjustment is made by the film thickness and line width of each conductor. At this time, if the thickness difference between the resistance heating element 2 and the lead wiring 3 becomes large, stress concentration occurs at the step portion due to abnormal heating, which may cause disconnection or breakage of the insulating base. It is desirable to arrange a connection wiring 5 having an intermediate thickness larger than the thickness of the resistance heating element 2 and smaller than the thickness of the lead wiring 3 between the resistance heating element 2 and the lead wiring 3. .

The identity of the conductor material is determined by the content ratio of the metal component in the conductor, and the content is acceptable up to ± 5% by volume, and if the difference exceeds 5% by volume, the characteristics between the conductors are reduced. Instead, and the durability is reduced.

In the ceramic heater of the present invention, as shown in FIGS. 1B and 2C, the lead wiring 3 and the connection terminal 4 formed on the outer peripheral portion of the insulating base 1 are insulated. A metal terminal 7 made of a low thermal expansion metal such as a Kovar alloy or an Invar alloy is connected to the connection terminal portion 4 by spot welding or a brazing material. ing.

As shown in the cross-sectional view of FIG. 2B, the through hole conductor 6 has a taper near the connection portion of the through hole conductor 6 with the connection terminal portion 4 in which the hole diameter increases toward the connection terminal portion. It is desirable to have the part 8. this is,
This is for relaxing the stress generated in the through-hole conductor 6 due to the difference in thermal expansion and improving the durability.

The through-hole conductor 6 is formed as shown in FIG.
As shown in the cross-sectional view of (b), it is desirable to form the rod-shaped insulating substrate 1 at a position symmetrical to the center of the rod-shaped insulating substrate 1. This is for simplifying the terminal bonding step and suppressing the occurrence of distortion due to the formation of the through-hole conductor.

A current is supplied from a power source (not shown) to the resistance heating element 2 through the two metal terminals 7 to the ceramic heater configured as described above. Energy is converted to heat energy,
The temperature at the tip of the heater rises.

(Insulating Substrate) The insulating substrate 1 in the silicon nitride ceramic heater of the present invention has a thermal shock resistance and a high strength, and is made of a ceramic containing silicon nitride as a main component in order to enhance durability. Things.

This silicon nitride ceramic has β-type silicon nitride as a main crystal phase. The grain boundary phase includes a crystal phase containing at least a rare earth element, oxygen and silicon as a sintering aid component. It is composed of a glass phase. Desirably, a crystal phase exists at the grain boundary, and in particular, disilicate (RE ₂ Si
₂ O ₇ ) It is preferable to precipitate the crystal phase as a main phase. By precipitating the disilite phase as the main phase as the grain boundary crystal phase, the insulator has high oxidation resistance even when it comes into contact with the oxygen of the outside air at the time of heat generation. Can increase the long-term stability.

In connection with the precipitation of a disilicate phase at the grain boundaries of the sintered body of the insulator, the conversion of the total rare earth element oxide in the sintered body into oxide and the amount of impurity oxygen in terms of SiO _{2 are} calculated. It is desirable that the molar ratio represented by SiO ₂ / RE ₂ O ₃ is 2 or more.

The amount of impurity oxygen is obtained by subtracting the oxygen bonded to the rare earth element oxide or other oxides (excluding SiO ₂ ) at a stoichiometric ratio from the total oxygen amount. The remaining amount of impurity oxygen, specifically, impurity oxygen contained in silicon nitride powder or SiO 2
₂ Consists of oxygen added as a powder. Further, by completely crystallizing the grain boundaries of the sintered body, the durability can be further improved.

When the SiO ₂ / RE ₂ O ₃ ratio is smaller than 2, a nitrogen-containing crystal phase such as a YAM phase or an apatite phase containing a large amount of a nitrogen component is mainly formed in the grain boundary phase, thereby reducing the oxidation resistance. Will deteriorate. However, SiO ₂ /
If the RE ₂ O ₃ ratio is excessively high, the densification is hindered. Therefore, it is desirable to control the molar ratio to 5 or less.

As the rare earth element contained in the silicon nitride ceramics, Y, Er, Yb, Lu, Sm and the like are desirable. Although the room temperature characteristics between these elements do not differ significantly, the high temperature characteristics depend on the melting point of the formed grain boundary phase. Therefore, judging from the fact that the melting point of the generated disilicate is higher, Lu, Yb, and Er are preferable. This rare earth element is contained in the sintered body in an amount of 1 to 10 mol% in terms of oxide,
In particular, it is desirable to be present at a ratio of 2 to 5 mol%.

In the above-mentioned silicon nitride ceramics, the total amount of Al and Mg contained in the sintered body is 1.0% by weight or less, especially 0.5% by weight or less, more preferably 0.5% by weight or less in terms of oxide. It is desirably 1% by weight or less.
This is because, if these components are present in amounts larger than those described above, grain boundary crystallization is likely to be inhibited, and the desired oxidation resistance may not be obtained. Fe content of 10,000 pp as a cation impurity element of the above metal element
m or less, other metals such as Cr and Ni
pm or less.

It is to be noted that the silicon nitride-based ceramic contains an appropriate amount of dispersed particles or whiskers such as element metals of Groups 4a, 5a and 6a of the periodic table, and carbides, nitrides, silicides or SiC thereof. Of course, it is also possible to add and disperse the composition to improve the properties.

(Conductive Material) It is desirable that the resistance heating element 2, the lead wiring 3, and the connection wiring 5 are formed by simultaneous firing with the insulating base 1. When silicon nitride ceramics is used as the insulating substrate 1, W, Ta,
And at least one selected from the group consisting of Mo and its carbides and nitrides, and further containing at least one of silicon nitride, boron nitride and silicon carbide as a dispersing substance. It is desirable to include a seed.

This dispersion material is used to adjust the resistance of the resistance heating element 2, to make the thermal expansion characteristics close to that of the insulating substrate 1, to simultaneously sinter the insulating substrate 1,
Auxiliary agent for increasing the adhesion to the substrate, and also for controlling the grain growth of the resistance heating element.
It is desirable that boron nitride is dispersed at a ratio of 1 to 10 parts by weight, silicon nitride is dispersed at a ratio of 5 to 30 parts by weight, and silicon carbide is dispersed at a ratio of 2 to 15 parts by weight.

Further, the resistance heating element 2 made of the above-mentioned conductor,
At the contact interface between the lead wiring 3 and the connection wiring 5 with the insulating base 1, a silicide phase of a main metal in the conductor, for example, WS
There may be a silicide phase such as i ₂ , TaSi, MoSi ₂ , in which case the silicide phase has a thickness of 10 μm.
The thickness is preferably 5 μm or less.

(Production Method) An example for producing the silicon nitride ceramic heater of the present invention will be specifically described. (A) First, as a main raw material for forming a rod-shaped insulating substrate,
An α-type or β-type silicon nitride powder having a cation impurity amount of 10,000 ppm or less is used. Then, a rare earth element oxide is added as a sintering aid to the silicon nitride powder at a ratio of 1 to 10 mol%, particularly 2 to 5 mol%.
Further, SiO ₂ may be added as an additional component to adjust the amount of oxygen. Further, Al ₂ O ₃ , MgO and the like are desirably suppressed to a total of 1.0% by weight or less, particularly 0.5% by weight or less, and further preferably 0.1% by weight or less in order to increase the strength at high temperatures. .

As described above, the amount of impurity oxygen equivalent to SiO ₂ in the compact after the compaction and the oxide of the Group 3a element of the Periodic Table in forming the disilicate crystal phase at the grain boundary of the sintered compact were determined. The molar ratio of SiO ₂ / RE ₂ O ₃ to the reduced amount is adjusted to be 2 or more.

These are mixed and pulverized by a ball mill or the like. A rod-shaped compact is produced from the mixed powder thus obtained by a known molding method, for example, an extrusion molding method, and after drying, is cut into a required length to produce a core compact. This core molded body can be produced by an injection molding method or a casting method other than the extrusion molding method.

It is desirable that the core formed body thus prepared is subjected to a degreasing and calcining step before forming a conductor pattern described later. This is because stacking faults accompanying degassing are likely to occur in the pattern portion when the binder is removed from the core portion.

The degreasing step is performed in a non-oxidizing atmosphere at 300 to
The calcining treatment may be performed at 1000 ° C., and the calcining treatment is desirably performed at 1200 to 1500 ° C. in a non-oxidizing atmosphere to densify the particles to a relative density of about 1.4 to 1.6 g / cm ³ .

(B) Next, on the surface of the obtained rod-shaped molded body, an insulating material such as silicon nitride is insulated from a conductive component such as tungsten or molybdenum having an average particle size of 0.1 to 10 μm as described above. The components are added to adjust the resistance to prepare a conductor paste. Then, a resistive heating element and a lead wiring pattern are formed by using the conductive paste.

It is desirable to use a transfer method for forming the resistance heating element and the lead wiring pattern. According to this transfer method, first, a resin film is prepared as a transfer sheet. For this film, PET (polyethylene terephthalate), PP (polypropylene), PTFE (polytetrafluoroethylene) or the like is suitably used. A release agent such as a silicone resin may be applied to the pattern forming surface of the transfer film in advance.

By driving the squeegee with the release surface of the resin film facing upward, the conductive paste whose resistance has been adjusted with a conductive material such as tungsten and an insulating material such as silicon nitride can be used as a resistive heating element pattern and a lead wiring pattern. Screen thick film printing. When the thickness of the resistance heating element pattern and the thickness of the lead wiring pattern are different, it is preferable to print the thick film on the transfer sheet in several times.

Next, since the printed surface has an uneven surface due to the thickness of the resistive heating element pattern and the lead wiring pattern and the difference in film thickness thereof, silicon nitride is used to make the uneven surface uniform. Paste made of ceramic composition between resistance heating element and lead wiring pattern,
Screen thick film printing is performed by the same method as above, and the total thickness difference between the lead wiring pattern portion and the resistance heating element pattern portion is 2
It is desirable that the thickness be 0 μm or less.

Further, on the surfaces of the resistance heating element pattern and the lead wiring pattern, a thick film of a silicon nitride-based overcoat layer of 5 to 30 μm made of the same silicon nitride ceramic composition as the core molded body is printed. desirable.

Then, after drying sufficiently, the transfer sheet, the respective conductor patterns and the overcoat layer are pressed by a uniaxial press or the like. This makes the thickness of the transfer layer composed of each conductor pattern and the overcoat layer uniform, and further,
There is an advantage that the thickness control when printing the resistance heating element 4 is facilitated. In other words, the pores in the resistance heating element 4 can be eliminated, and the generation of a neck during firing can be made constant. As a result, the resistance value of the resistance heating element 4 can be stabilized. Further, by forming the overcoat layer, the adhesion between the core molded body and the resistance heating element pattern or the lead wiring can be improved, and the occurrence of stacking faults after sintering can be suppressed.

It is desirable that the printed surface of the transfer sheet be protected by a release protection sheet or the like until the transfer step is performed. In addition, mass productivity can be improved by forming a plurality of sets of resistance heating element patterns and lead wiring patterns on the transfer sheet.

Then, the resistance heating element pattern and the lead wiring pattern formed on the surface of the transfer sheet as described above are transferred to the surface of the core molded body produced in the step (a) together with the overcoat layer.

In the transfer step, first, a set of patterns is prepared by appropriately cutting a transfer sheet on which a resistance heating element pattern and a lead wiring pattern are printed, and an adhesive layer is screen-printed on the surface thereof. The resistive heating element pattern and the lead wiring pattern are adhered to the surface of the core molded body together with the overcoat layer via the adhesive layer on the surface, and the transfer can be performed by peeling off only the transfer sheet.

(C) Thereafter, an insulating layer serving as a shell is formed on the surface of the core molded body to which the pattern of the resistance heating element and the lead wiring has been transferred, to produce a molded heater. In forming the insulating layer, the core molded body is prepared by preparing a slurry containing the silicon nitride ceramic composition, immersing the slurry in the slurry, and then drying the slurry. An insulating shell can be formed on the surface of the pattern and the lead wiring pattern. The thickness of the coating layer can be easily adjusted by the viscosity of the slurry, the pulling speed after immersion, and the like.

(D) Then, the formed heater is fired in a nitrogen-containing atmosphere at 1700 to 1900 ° C. At this time, since silicon nitride may be decomposed depending on the firing temperature, it is preferable to perform firing in a pressurized nitrogen atmosphere at a nitrogen pressure of 1.5 atm or more. In particular, in nitrogen gas pressure firing, 1700-1800 degreeC, 1.5-
After firing in a nitrogen pressure of 30 atm, 1800 to 190
By baking at 0 ° C. and a nitrogen pressure of 30 atm or more, formation of a silicide phase of a conductor such as a resistance heating element can be suppressed together with densification.

Further, after the above firing method, 100
By performing hot isostatic firing at 1600 to 1900 ° C. in an inert atmosphere of 0 atm or more, a sintered body having more excellent durability can be produced.

(E) The through-hole conductor for connecting to the connection terminal portion and the lead wiring is formed by forming a through-hole in a predetermined portion of the rod-shaped sintered body by laser or micro drill after firing. A in the hall
After filling a conductor paste containing at least one of u, Pd, and Pt as a main component, the conductor paste having the above composition is further printed and applied on the surface of the rod-shaped sintered body in a pattern of a connection terminal portion, and then subjected to 1100 to 1200. It can be formed by performing a baking process at a temperature of ℃.

Another method is to form a through-hole in the heater molded body after the step (c), fill it with a paste in which a resistance heating element and the like are formed, and form a connection terminal part. After printing this pattern, baking may be performed under the baking conditions described above.

When the through-hole conductor is formed, it is desirable to form a tapered shape such that the hole diameter on the connection terminal portion side is increased. This tapered shape is formed by irradiating laser light from the connection terminal portion side. It can be formed by forming holes.

(F) Thereafter, a Kovar alloy pad is resistance-welded to the Ni lead in advance with respect to the connection terminal, and the pad is joined to the connection terminal by brazing or ultrasonic welding. By doing so, the ceramic heater is completed.

Hereinafter, the characteristic operation and effect of the method of manufacturing the ceramic heater according to the present embodiment will be listed. (1) Since a conventional ceramic sheet material is not used, an expensive doctor blade device is not required, and equipment costs can be reduced. Also, the production of technically difficult thick film sheets is unnecessary, and the lamination of multiple sheets is unnecessary,
Cost reduction becomes possible.

(2) The inconvenience of performing printing on a curved surface of a rod-shaped core molded body as in the related art in order to print and apply the conductor paste once to the transfer sheet plane is eliminated. . That is, since the resistance heating element can be formed with high accuracy, the resistance value can be controlled (stabilized), the resistance yield can be improved, and the cost can be reduced.

(3) Since it can be formed by nitrogen pressure sintering without using conventional hot press sintering, the number of grinding steps can be reduced, large-scale sintering can be performed, and a significant cost reduction can be achieved.

(4) By flattening the pattern and the like formed on the transfer sheet by a uniaxial press before transfer, unevenness on the printed surface is eliminated, stacking faults after transfer and coating of the insulating layer are eliminated, and durability performance is improved. it can.

[0070]

EXAMPLE 1 (a) First, 12% by weight of Yb ₂ O ₃ and silicon oxide were added as sintering aids to 84% by weight of silicon nitride powder having an α ratio of 90% with a cation impurity content of 1000 ppm or less. A composition comprising a total of 3% by weight of the amount of oxygen in the silicon nitride powder in terms of SiO ₂ and 1% by weight of tungsten oxide was mixed and stirred in a barrel mill for 72 hours.

The mixture was taken out, dried, and added with methylcellulose, polyvinyl alcohol resin as an organic component, glycerin and water as a solvent, and stirred to prepare a potting clay, which was extruded into a rod-shaped 3.2 mm diameter. A core molded body was produced.

(B) Next, 90% by weight of tungsten and 10% by weight of the above silicon nitride composition are added with an acrylic resin, terpineol, a dispersant, and acetone as a solvent, mixed and stirred by a rotary mill, and then acetone is removed. Care was taken to prepare a conductor paste.

A resistance heating element and a lead wire were sequentially formed on a PET film to a predetermined thickness by a screen printing method using the conductor paste by screen printing. The connection between the resistance heating element and the connection wiring and the connection between the connection wiring and the lead wiring were processed to have a taper T as shown in FIG. 1B. Thereafter, a slurry containing the silicon nitride composition was applied to the surfaces of the resistance heating element and the lead wiring to form an overcoat layer. Embed and dry.

Then, an acrylic resin, terpineol, a dispersant, and acetone as a solvent were added to the silicon nitride-based ceramic composition on the transfer surface of the transfer sheet, and the mixture was mixed and stirred by a rotary mill. After screen printing the adjusted adhesion layer, it was brought into close contact with the surface of the core molded body, only the PET film was peeled off, and the resistance heating element, lead wiring and overcoat layer were transferred to the surface of the core molded body.

(C) Then, butyral resin, glycerin, a defoaming agent, and water as a solvent are added to the silicon nitride composition, mixed and stirred with a rotary mill, and then deaerated to prepare a slurry for filling. Then, the above-described transferred core molded body was immersed in the slurry, pulled up, and dried repeatedly to prepare a heater molded body.

After decomposing organic components at 900 ° C., this heater molded body was fired at 1850 ° C. for 11 hours under a nitrogen gas pressure atmosphere of 70 atm.

After that, the diameter of the hole reaching the lead wiring by laser light from the side surface at the end of the rod-shaped sintered body is set to 0.
After forming a through-hole of 4 mm, a metallizing paste containing gold as a main component was filled, and a pattern serving as a connection terminal portion was printed and applied to the through-hole conductor forming portion on the side surface of the rod-shaped sintered body. Then, it was baked in vacuum at 1100 ° C. Furthermore, a Kovar pad made by resistance welding a lead wire made of Ni with a diameter of 0.2 mm and 1000 ° C
And heat-bonded to produce a ceramic heater.

The manufactured ceramic heater had a diameter of 3.
It is made of a rod-shaped body having a length of 2 mm and a length of 55 mm. The core diameter of the insulating substrate was 2.4 mm, and the average thickness of the shell portion was 0.4 mm. The thickness of the resistance heating element is 2
0 μm, the thickness of the lead wiring was 250 μm, and a connection wiring having a thickness of 80 μm was interposed between the resistance heating element and the lead wiring.

Further, the resistance heating element and the lead wiring were all arranged in four cross sections, and formed so as to be symmetrical to each other. Further, as a result of observation of the cross section, both the resistance heating element and the lead wiring were formed in concentric regions of 1.6 mm ± 0.2 mm from the center of the heater.

For the produced ceramic heater, 130
After generating heat by applying a current at 0 ° C. for 2 minutes, the current is stopped for 1 minute, and this is performed as one cycle up to a maximum of 30,000 cycles, and the resistance between the anode lead and the cathode lead is changed every 1000 cycles. It was measured. Then, the number of cycles until the resistance value increased by 5% or more of the initial resistance was measured. As a result, there was no change in resistance even after 30,000 cycles, and no cracks or disconnections were observed in the heater.

Comparative Example 1 Using the silicon nitride ceramic composition prepared in Example 1, a thickness of 300 μm was prepared by a doctor blade method.
m, a resistance heating element pattern and a lead wiring pattern were printed on the surface of this sheet in the same manner as in Example 1, and the same adhesion layer as that in Example 1 was formed on the surface.

Then, a ceramic heater was manufactured in the same manner as in Example 1 except that the green sheet was wound around the surface of the core molded body manufactured in Example 1, and the outer shape was ground to a cylindrical body.

The number of cycles until a change in resistance of the manufactured ceramic heater was measured in the same manner as in Example 1. As a result, a change in resistance was observed at 10,000 cycles.
Cracks and disconnections occurred in the circumferential direction from near the seam of the heater.

Comparative Example 2 In Example 1, as the paste for the resistance heating element and the lead wiring, a paste was prepared in which the resistance was adjusted by changing the content of tungsten as a conductor component, and the high resistance was used for the resistance heating element. A ceramic heater was manufactured in exactly the same manner as above except that the paste was printed and applied using a low-resistance paste as lead wiring and connection wiring, and the same evaluation was performed. As a result of measuring the number of cycles until a resistance change occurs in the manufactured ceramic heater in the same manner as in Example 1, a resistance change was observed at 12000 cycles, and cracks occurred at the boundary between the resistance heating element and the lead wiring. I was

Comparative Example 3 Using the silicon nitride ceramic composition used in Example 1, a metal wire made of tungsten was buried so that the cross section of the resistance heating element forming section had a cross section as shown in FIG. Then, it was fired at 1650 ° C. for 1 hour by hot press firing.

The number of cycles until a change in resistance of the manufactured ceramic heater was measured in the same manner as in Example 1. As a result, a change in resistance was observed at 10,000 cycles.
Cracks and disconnections occurred in the heater pattern width direction.

[0087]

As described in detail above, according to the present invention,
Heating can be performed from room temperature to a high temperature of 1000 ° C. or more, and even when a severe thermal cycle is applied, stress concentration inside the heater can be prevented and durability can be increased. Further, according to the manufacturing method of the present invention, a complicated process such as a conventional ceramic sheet material or a winding process is not required, so that the process is simplified and the manufacturing cost is reduced as compared with the conventional method. Can be achieved.

[Brief description of the drawings]

1A is a schematic perspective view of a ceramic heater of the present invention, and FIG.

FIGS. 2A and 2B are cross-sectional views of a (a) resistance heating element 2 forming portion (Y ₁ -Y ₁ ) and (b) a lead wiring 3 forming portion (Y ₂ -Y ₂ ) of the ceramic heater of the present invention. , respectively a cross-sectional view of (c) connecting terminal portion (Y ₃ -Y _3).

FIG. 3 is a cross-sectional view for explaining the structure of a conventional ceramic heater.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulating base 2 Resistance heating element 3 Lead wiring 4 Connection terminal part 5 Connection wiring 6 Through-hole conductor

Claims (6)

[Claims] 1. A connecting terminal portion in which a resistance heating element and a lead wiring are buried inside a rod-shaped insulating substrate made of silicon nitride ceramics, and which is electrically connected to the lead wiring on an outer peripheral portion of the insulating substrate. Wherein the resistance heating element and the lead wiring are formed in a concentric region from the center of the rod-shaped insulating base by a conductor material having substantially the same composition containing a metal component and an inorganic component. A ceramic heater made of silicon nitride, characterized in that there is no seam in the shell portion. 2. A silicon nitride ceramic heater according to claim 1, wherein a line width and / or a film thickness of said resistance heating element and said lead wiring are different. 3. The silicon nitride ceramic according to claim 1, wherein a plurality of said resistance heating elements or said lead wirings are formed in concentric regions at equal intervals in a cross section of said heater. heater. 4. A step of preparing a rod-shaped core molded body from a ceramic composition containing silicon nitride as a main component, and substantially comprising a metal component and an inorganic component on the surface of the rod-shaped molded body. Step b of applying and forming a resistance heating element pattern and a lead wiring pattern by using a conductor material having the same composition; and dipping the rod-shaped core molded body into a slurry containing the ceramic composition, followed by drying to form the rod-shaped core-shaped body. A step of forming an insulating shell on the surface of the resistance heating element pattern and the lead wiring pattern of the core molded body; and a step of firing the composite molded body obtained in the step c in a non-oxidizing atmosphere. A method for manufacturing a silicon nitride ceramic heater, comprising: 5. The method according to claim 5, wherein the step (b) comprises forming a resistance heating element pattern and a lead wiring pattern on a predetermined transfer sheet.
5. The method for producing a silicon nitride ceramic heater according to claim 4, further comprising a step of transferring the pattern to the surface of the rod-shaped core molded body. 6. The method for manufacturing a silicon nitride ceramic heater according to claim 4, wherein said firing is performed in a pressurized nitrogen gas atmosphere.