JP2001043962A - Silicon nitride ceramic heater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve durability by preventing the occurrence of a crack caused by thermal expansion in the vicinity of a connection terminal part 4 formed on the circumferential surface of a rod-like base body formed of a silicon nitride-based ceramics. SOLUTION: A metalized layer 12 comprising a first layer 15 and a second layer 16 on the first layer 15 is formed on the circumferential surface of a base body 1 formed of a silicon nitride-based ceramics. The first layer 15 contains at least one of V, Ti, Mo and Mn as a main constituent, and is improved in wettability, and the second layer 16 is formed of a wax material containing Au and Ni. An interlaid layer 13 of Pt or the like is formed on the second layer 16, a connection terminal 14 formed of an Fe-Ni-Co alloy is mounted on it, and a lead terminal 7 of, for instance, Ni is fixed to the connection terminal 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic heater which can be widely used for households, electronic parts, industrial machines, automobiles, etc., and more particularly to a structure of a connecting terminal portion thereof.

[0002]

2. Description of the Related Art Conventionally, a ceramic heater used for an oxygen sensor or the like has a heating element made of a high melting point metal such as W or Mo embedded in a base material mainly composed of alumina ceramics, and a connection terminal portion thereof. In this example, a metallized layer is provided on the lead-leading conductive portion, and a connection terminal for external connection is provided thereon. Silicon nitride ceramics are also used as heaters for higher temperatures. In this structure, a heating element and a lead wire made of a high melting point metal wire or the like are buried, and this is exposed from the end of the lead wire to the outer surface, metallized as a conductive portion, and a connection terminal is formed thereon. Provide. Further, the connection terminal for external connection is a metal pad or the like having the same curvature on the ceramic substrate, and has a shape in which a metal lead terminal is connected thereon, and a current flows from the lead terminal. In this structure, the resistance heating element generates heat. In particular, silicon nitride ceramic heaters have high room temperature strength, high temperature strength, low coefficient of thermal expansion, and high utility value as heaters for high temperature applications.
It is used as a glow plug for starting a diesel engine, an ignition heater for a combustor, a heater for an oxygen sensor, and the like (for example, Japanese Patent Publication Nos. 62-19034 and 63-5).
No. 1356).

[0003] In a ceramic heater represented by an oxygen sensor, a glow plug, or the like, a silicon nitride material is excellent in heat resistance, thermal shock resistance, etc. in order to improve its rapid temperature rising performance. It is promising as a possible and durable ceramic heater support. In this connection terminal, similarly to a ceramic heater made of alumina ceramics, the exposed lead-out conducting portion is metallized, and an external connection terminal is provided thereon.

For the metallized layer and the connection terminals, a material having high conductivity is used in order to supply a current to the heater which is a heating element. However, the metal material and the metallized layer composition have a higher thermal expansion coefficient than silicon nitride. Is big. For this reason, a thermal stress due to a difference in thermal expansion is generated at the time of the required repeated energization. In such a heater, cracks are likely to occur in the porcelain and the metallized layer due to thermal stress due to the difference in thermal expansion between these materials. The silicon nitride material has a characteristic of a lower coefficient of thermal expansion than other ceramics represented by alumina ceramics and the like. Specifically, the thermal expansion coefficient of the silicon nitride substrate is 3 * E-6 / ° C. (* E-6 represents × 10 ⁻⁶ , the same ^applies hereinafter) which is half or less of that of alumina ceramics. Therefore, as compared with alumina ceramics or the like, thermal expansion with a metal terminal such as Invar alloy KV-6 (trade name) used as a connection terminal for external connection to be used (the coefficient of thermal expansion is E-5 level) There is a problem that the difference is large and high stress is generated during a thermal cycle during use, cracks are generated in the ceramic base and the metallized layer, and durability is deteriorated.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a silicon nitride ceramic having improved durability by suppressing the occurrence of cracks due to thermal expansion in the vicinity of a connection terminal attached to the outer peripheral portion of the silicon nitride ceramic. It is to provide a heater.

[0006]

According to the present invention, there is provided a connection terminal in which a resistance heating element and a lead wire are buried in a rod-shaped base made of silicon nitride ceramics, and the lead is electrically connected to the outer periphery of the base. In the silicon nitride ceramic heater in which the portion is formed, the connection terminal portion is (a) a metallized layer formed on the outer peripheral surface of the base, is connected to the lead wire, and has at least one of V, Ti, Mo, and Mn. A metallized layer having a first layer mainly containing Au, a second layer formed on the first layer and mainly containing Au and Ni and containing 5 to 20 vol% of Ni silicide; and (b) the metallized layer. A connection terminal made of an alloy containing at least Fe and Ni formed on the second layer, and (c) a lead terminal fixed to the connection terminal. A.

Further, according to the present invention, the connection terminal is made of Fe-Ni-
Co alloy, whose coefficient of thermal expansion (room temperature to 500 ° C.)
It is characterized by being at most 6.0 × 10 ⁻⁶ / ° C.

According to the present invention, the concentration of stress generated by increasing the adhesion of the connection terminal portion to the substrate while suppressing the generation of brittle compounds in the connection terminal portion of the ceramic heater used from room temperature to high temperature. Deterioration of durability performance due to cracks caused by cracks is prevented, and the characteristics of silicon nitride ceramics excellent in durability performance are sufficiently exhibited.

Therefore, in the present invention, the metallized layer 1
2 on the silicon nitride substrate interface side, a first layer 15 containing V, Ti, Mo, and Mn as main components, and Au and Ni on the connection terminal side.
And a second layer 16 containing Ni as a main component, and the deposition amount of Ni silicide in the second layer is 5 vol%.
As described above, the content is set to 20 vol% or less. Preferably, an intervening layer 13 such as platinum is formed on the metallized layer interface side of the external connection terminal 14. The material of the connection terminal 14 is an alloy containing Fe-Ni, preferably Fe-N
An i-Co alloy having a coefficient of thermal expansion (room temperature RT to 500
° C, the same applies hereinafter) to 6.0 * E-6 / ° C or lower, and preferably 3 * E-6 / ° C to 5 * E-6 / ° C.

[0010] Since the metallized layer, the silicon nitride substrate and the connection terminals have different coefficients of thermal expansion, they exhibit different expansion and contraction behavior during the temperature rise and fall during use. As a result, thermal stress is generated, which causes deterioration of durability. Here, since silicon nitride itself exhibits difficulty in sintering, a dense body is obtained by adding a sintering aid such as rare earth oxide, alumina, and magnesia. Although the amount of this auxiliary varies depending on the material, it is contained in a ratio of 5 to 25% by weight in total, and its thermal expansion slightly varies depending on the amount ratio of the grain boundary phase, but is approximately 3 * E-6 / ° C. ~ 4
* E-6 / ° C. The connection terminal for external connection is F
-Ni-Co alloy has 6 * E-6 / ° C, but the metallized layer has a high thermal expansion of 10 * E-6 / ° C or more, and is sandwiched between the connection terminal and the porcelain base. It has a structure in which stress concentrates.

In order to alleviate the thermal stress, the Young's modulus of the metallized layer is reduced to absorb the thermal stress. Specifically, the composition in the metallized layer is controlled. The Au / Ni second layer of the metallized layer has a Young's modulus that varies depending on the Ni content, and is composed of a structure in which a Ni compound is precipitated in an Au matrix. This Ni compound is silicided by decomposition of silicon nitride or diffusion of Si during the metallization forming process. This Ni silicide is a brittle compound,
Cracks are selectively developed at the time of stress concentration, which causes deterioration of durability of the electrode portion. As a result of the study by the present inventor, it has been found that crack control can be suppressed by controlling the amount ratio of the Ni compound. The precipitation amount of the Ni compound in the Au matrix, that is, the content of Ni silicide was set to 20 vol.
It is necessary to make it 1% or less. If it is larger than 20 vol%, the Young's modulus of the second layer becomes large, and the crack suppressing effect is insufficient. It is desirable that the content of Ni silicide be 15 vol% or less.

However, when the Au / Ni alloy brazing material has a Au-rich composition, the Young's modulus is reduced, but when the Ni content is small, the wettability with silicon nitride is poor, and the quality is altered due to scale. The Ni-Si alloy needs to be present in an amount of 5 vol% or more, since the Ni-Si alloy is easily peeled off. In addition, Au, N of the metallized layer
By providing the first layer which becomes the interface wetting improvement layer between the second layer containing i as the main component and the porcelain, the wettability can be further improved. Specifically, a first layer mainly containing an active metal such as V, Ti, Mo, and Mn is formed. This first layer may be formed by sputtering, thermal spraying, or the like.

Further, the present invention is characterized in that an intervening layer made of platinum Pt or palladium Pd is provided between the second layer of the metallization layer and the connection terminal.

According to the present invention, an intervening layer such as platinum is formed on the metallized layer interface side of the external connection terminal. Since the connection terminal is made of an alloy containing Fe and Ni, when the connection terminal is brazed to the second layer, the Ni in the connection terminal is reduced.
The components diffuse into the second layer, and a large amount of the Ni—Si alloy precipitates in the second layer, thereby deteriorating the durability. According to the present invention, at the interface between the second layer and the connection terminal for external connection,
By providing an intervening layer 13 of platinum or the like to prevent generation of Ni silicide due to diffusion of Ni into the second layer, the amount of the Ni—Si alloy in the second layer is stably controlled to the above ratio, and the durability is improved. Maintenance becomes possible. Specifically, a platinum film is formed by plating or the like. The thickness of the intervening layer is preferably 3 μm or more, particularly preferably 20 μm or more. If the thickness is less than 3 μm, the intercalation layer of platinum or the like is eluted due to the reaction of platinum or the like with gold during brazing, and the diffusion of Ni cannot be effectively prevented.

[0015]

FIG. 1 is an enlarged cross-sectional view of a connecting terminal portion 4 of a silicon nitride ceramic heater according to one embodiment of the present invention, which is perpendicular to an axis. On a rod-shaped electrically insulating substrate 1 made of silicon nitride ceramics, a through-hole conductor 6 described later is formed extending in the radial direction. The connection terminal portion 4 according to the present invention is connected to the conductor 6, where the metallization layer 12 and the connection terminal 14 are arranged and connected in this order from bottom to top. This connection terminal 1
4, the lead terminal 7 is fixed by welding. The metallized layer 12 has a first layer 1 formed on the outer peripheral surface of the base 1.
5 and a second layer 16 formed on the first layer 15.

FIG. 2 is a perspective view showing the entire structure of the silicon nitride ceramic heater provided with the connection terminal portion 4 shown in FIG. 1, and FIG. 3 is a cross-sectional view showing a part of the ceramic heater cut away. With reference to these drawings, the base 1
, A resistance heating element 2 and a pair of lead wires 3 are embedded therein, and a pair of connection terminal portions 4 electrically connected to the lead wires 3 are formed on the outer peripheral portion of the base 1.

FIG. 4 is a cross-sectional view of a portion (Y ₁ -Y ₁ ) of the resistance heater 2 of the ceramic heater shown in FIG. 2, and FIG.
FIG. 6 is a cross-sectional view of the formation portion (Y ₂ −Y ₂ ).
FIG. _{3 is} a transverse sectional view taken along line ₃ -Y ₃ ). The base 1 of the ceramic heater includes a ceramic score portion 1a and its shell portion 1b.
Resistance heating element 2, lead wire 3
Since each of them has a structure buried around the ceramic score portion 1a as at least a pair of wires,
In each cross section of the ceramic heater, the resistance heating element 2 or the lead wire 3 is r ₁ ,
It is formed in a concentric region of r ₂ and r ₃ . in this way,
By forming the resistance heating element 2 and the lead wire 3 in the concentric region, it is possible to prevent the occurrence of local stress, suppress the occurrence of distortion even when a severe heat cycle is applied, and improve the durability. The concentric area means that a difference in distance from the center in each cross section can be allowed up to about ± 0.2 mm.

The resistance heating element 2 and the lead wire 3 are shown in FIGS.
By forming an even number (four in FIG. 5) in each of the cross sections and forming them at equal intervals in the concentric regions, the occurrence of distortion can be further suppressed.

The shell 1b has a thickness of 0.3-1.
Preferably, it is 5 mm. This is because the thickness is 1.
If the thickness is more than 5 mm, the rate of temperature rise on the heater surface becomes slow. If the thickness is less than 0.3 mm, porcelain destruction occurs due to thermal shock.

In the ceramic heater having the above structure,
The resistance heating element 2 and the lead wire 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 wire 3 (resistance heating). Larger body / lead wire is desired.

In such resistance adjustment, when the resistance heating element 2 and the lead wire 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 is formed of a high resistance. When the lead wire 3 is made of a low-resistance conductor, 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. During simultaneous firing or when a heat cycle is applied, distortion or the like is likely to occur as a whole of the heater, and durability is reduced.

Therefore, in the present embodiment, the resistance heating element 2
Each of the lead wires 3 is formed of a conductor material having the same composition. In order to increase the resistance ratio between the resistance heating element 2 and the lead wire 3, adjustment is made by the film thickness and line width of each conductor. If the film thickness difference between the resistance heating element 2 and the lead wire 3 becomes large, stress concentration may occur at the step portion due to abnormal heating, which may cause disconnection, breakage of the base, and the like. For this purpose, 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 wire 3 is provided between the resistance heating element 2 and the lead wire 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 vol%, and the difference is 5 vol%.
%, The properties between conductors change, and the durability decreases.

As shown in FIG. 1, the lead wire 3 and the connection terminal 4 formed on the outer periphery of the base 1 are electrically connected by a through-hole conductor 6 formed on the base 1. The connection terminal portion 4 includes the first layer 1 of the metallized layer 12.
5 are electrically connected.

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

(Substrate 1) The 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. It is.

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₎
The O ₇ ) crystal phase is preferably precipitated as the main phase. By precipitating the disilicate phase as the main phase as the grain boundary crystal phase, the insulator has high oxidation resistance even when it comes in contact with outside air during heat generation, preventing corrosion due to oxidation of the base material. The long-term stability of the base material can be improved.

In connection with the precipitation of the 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 is} 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 that binds to the rare earth element oxide added as a sintering aid 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 the silicon nitride powder or SiO ₂
It consists of oxygen added as a powder. Also,
The durability can be further improved by completely crystallizing the grain boundaries of the sintered body.

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

The rare earth element contained in the silicon nitride ceramics is preferably Y, Er, Yb, Lu, Sm, or the like. 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 in terms of oxide.
Desirably, it is present in a proportion of 2 mol%, especially 2 to 5 mol%.

An appropriate amount of dispersed particles or whiskers such as elemental metals of Groups IVa, Va, and VIa of the Periodic Table and their carbides, nitrides, silicides, or SiC are added and dispersed in the silicon nitride ceramics. Of course, it is also possible to improve the characteristics by compounding.

(Conductive Material) Further, it is desirable that the resistance heating element 2, the lead wire 3, and the connection wiring 5 are formed by simultaneous firing with the base 1. When a silicon nitride ceramic is used as the substrate 1, the main component is at least one selected from the group consisting of W, Ta, Mo, and carbides and nitrides thereof. It is desirable that at least one of silicon nitride, boron nitride, and silicon carbide be contained as the dispersion material.

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 substrate 1, to simultaneously sinter the substrate 1, and to adhere to the substrate 1. Aid for enhancing the property, and further for controlling the grain growth of the resistance heating element, 1 to 10 parts by weight of boron nitride, 5 to 30 parts by weight of silicon nitride based on 100 parts by weight of the main component.
It is desirable that the parts by weight and silicon carbide be dispersed at a ratio of 2 to 15 parts by weight, respectively.

Further, the resistance heating element 2 composed of the above-described conductor,
At the contact interface between the lead wire 3 and the connection wiring 5 with the base 1,
The silicide phase of the main metal in the conductor, for example WS
In some cases, a silicide phase such as i ₂ , TaSi, or MoSi ₂ is present. In such a case, the thickness of the silicide phase is preferably 10 μm or less, particularly 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-like substrate, α having a cation impurity amount of 10,000 ppm or less is used.
Or β-type silicon nitride powder 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.

As described above, the amount of impurity oxygen in the compact after compaction in forming the disilicate crystal phase in the sintered body grain boundary in terms of SiO _2, and the amount in terms of oxide of Group IIIa element of the periodic table Is adjusted so that the molar ratio of SiO ₂ / RE ₂ O ₃ is 2 or more.

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

It is desirable that the core molded body thus produced is subjected to a degreasing and calcining step before forming a conductor pattern described later. This is because stacking faults due to degassing are likely to occur in the pattern portion when the core portion is debindered.

(B) Next, on the surface of the obtained rod-shaped molded body, the conductive component of tungsten W or molybdenum Mo having an average particle diameter of 0.1 to 10 μm is added to the surface of the rod. The resistance is adjusted by adding an insulating component to prepare a conductor paste. Then, a conductor pattern of a resistance heating element and a lead wire is formed by using the conductor paste.

It is desirable to use a transfer method for forming the pattern of the resistance heating element and the lead wire. 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.

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 wire pattern. Screen thick film printing. When the thickness of the resistance heating element pattern and the thickness of the lead wire pattern are different, screen thick film printing is performed on the transfer sheet several times.

After sufficient drying, the transfer sheet and each conductor pattern are pressed by a uniaxial press or the like.

The resistive heating element pattern and the lead wire 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).

(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 wire has been transferred, to produce a heater molded body. 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 to form the rod-shaped core molded body. An insulating shell can be formed on the surface of the pattern and the lead wire pattern.

(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.

(E) After firing, the through-hole conductor 6 for connecting to the connection terminal portion and the lead wire is formed with a laser or a microdrill to form a through-hole in a predetermined portion of the rod-shaped sintered body. Au, Pd,
After filling a conductor paste containing at least one of 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 the connection terminal portion.
It can be formed by baking at 100 to 1200 ° C.

Another method is to form a through-hole in the heater molded body after the step (c), fill the paste with a resistance heating element, etc. After printing this pattern, baking may be performed under the baking conditions described above.

(F) Metallized layer 1 on outer peripheral surface of substrate 1
Form 2 First layer 15 constituting metallization layer 12
Are V, Ti, M by sputtering, thermal spraying, etc.
o. At least one of Mn is a main component, and functions to improve the wetting with the substrate 1. Thus, the first layer and the through-hole conductor 6 are electrically connected. The thickness of the first layer 15 is 0.3 to 3 μm.

On the first layer 15, a second layer 16 is formed. The second layer 16 is an Au / Ni-based brazing material containing Au and Ni as main components. The thickness of the second layer 16 is 5 to
20 μm.

(G) FIG. 7 shows lead terminals 7 and connection terminals 14.
FIG. The lead terminals 7 are fixed to the connection terminals 14 by spot welding or the like, and a plating layer 17 made of platinum Pt or palladium Pt having a thickness of 3 mm or more is formed on the entire outer peripheral surfaces of the lead terminals 7 and the connection terminals 14. . The connection terminal 14 is made of an Fe-Ni-based alloy,
The characteristics differ depending on the composition. Specifically, 29Ni
KOVAR of -16Co-55Fe composition (trade name: KV
-2, Sumitomo Special Metals Co., Ltd.), 32Ni-17Co
Low thermal expansion Fe-Ni-C, such as Super-Invar alloy having 36Ni-4Co-60Fe composition, such as THERLO (trade name: KV-4, manufactured by Sumitomo Special Metals Co., Ltd.) having -51Fe composition
o-based alloys. The thermal expansion is preferably as low as possible, the most suitable metal is KOVAR alloy,
The coefficient of thermal expansion up to 500 ° C is 6.0 * E-6 / ° C.

Here, the KOVAR alloy is punched into a predetermined shape and then subjected to a curved surface processing according to the shape of the ceramic base. The cylindrical shape of the base 1 shown in FIGS. 1 to 7 is formed by pressing with a die that matches the curvature of the base. Further, a film made of a platinum plating layer 17 is formed on the connection terminal 14 by plating, sputtering, thermal spraying or the like. This film is formed by metallizing layer 1
Only the metallized interface facing the second layer 16 of FIG.
In the figure, the portion on the metallized interface side is shown as an intervening layer 18. In order to simplify the process, plating is particularly desirable.

(H) The intervening layer 18 of the connection terminal 14 is brazed on the second layer 16. Thus, the connection terminal portion 4 is completed.

FIG. 8 is a simplified organization diagram of the metallization layer 12. The first layer 15 improves the wettability with the substrate 1 as described above. In the second layer 16, N
i-silicide 19 is precipitated in the Au matrix. In the present invention, such Ni silicide 19 is contained in the second layer 16 in an amount of 5 to 20 vol%, whereby crack propagation can be suppressed, durability can be prevented from deteriorating, and durability can be improved.

FIG. 9 is a sectional view of another embodiment of the present invention. This embodiment is similar to the embodiment of FIGS. 1 to 8 described above, and corresponding parts are denoted by the same reference numerals.
FIG. 9 corresponds to FIG. 6 in the above embodiment. The connection terminal portion 4 for the ceramic heater is formed on a cylindrical or prismatic sintered body containing silicon nitride as a main component. Here, the substrate 1 containing silicon nitride as a main component is:
A predetermined ratio of a sintering agent is added to a silicon nitride raw material, and after mixing and stirring, it is obtained by a hot pressing method which is a generally known technique. From the viewpoint of thermal shock and strength, the average particle size is 3 μm
In addition, it is desirable to form a dense body in order to prevent moisture and the like from entering and obtain a smooth surface roughness. The lead wires 3 in the base 1 are arranged at equal intervals or circumferentially from the center 20 of the core material as the base 1. The lead wire 3 is a high-melting point metal of the periodic table IVa, Va, VIa represented by W, or a carbide or nitride thereof,
It is formed by printing or embedding a metal wire, a molded body, or the like, and silicon nitride, boron nitride, or the like may be added to approximate the coefficient of thermal expansion of silicon nitride. Further, the first layer 1 of the metallization layer 12 of the lead wire 3 and the connection terminal portion 4 is formed.
5, a through-hole conductor 6 is formed.

In the hot pressing method, a heating element 2 and a lead wire 3 are sandwiched between two plate-like ceramic green sheets (unfired bodies), and are closely adhered to each other. Baking while applying pressure). Thereafter, the rod-shaped body is ground. Other configurations are the same as those of the above-described embodiment.

The experimental results of the present inventor will be described. Example 1 First, as shown in FIGS. 1 to 7, a cylindrical ceramic heater is manufactured. The conductor pattern is transferred to a rod, the upper part of which is formed by slurry dipping to form an outer layer, then degreased and baked under nitrogen gas pressure to form a resistance heating element 2, a lead wire 3, and a connection wiring 5. I do. Thereafter, the outer periphery is ground, and the metallized composition is filled in the through-hole-shaped conductive holes by laser processing and baked in a vacuum heating furnace. A metallized layer 12 is formed on the outer peripheral surface of the base 1 so as to cover the through-hole conductor 6. First, the first layer 15 is formed of at least one of V, Ti, Mo, and Mn, for example, Ti by sputtering, thermal spraying, or the like. Next, as a second layer 16, a paste produced by adding an acrylic binder and terpineol to Au / V is subjected to screen printing by screen printing, and then formed by baking at 1180 ° C. in a vacuum heating furnace. It was formed to a thickness of 10 μm. Further, an external connection terminal 14 is bonded thereon. This connection terminal 14 is a pad made of KOVAR alloy (6 * E-6
/ ° C), the Ni lead terminal 7 was joined by resistance welding, and the pad was placed on the metallized composition and brazed at 1000 ° C. At this time, the connection terminal 14 and the lead terminal 7 have been previously plated with platinum Pt, and the intervening layer 13 made of platinum exists at the metallized interface.

The obtained ceramic heater was subjected to a cycle test by external heating from room temperature to a predetermined temperature. Specifically, the maximum heating part of the ceramic heater is 1250 ° C.
And the temperature of the connection terminal portion 4 was set to 500 ° C. by external heating. Temperature is the connection terminal 4
The measurement was performed with a thermocouple embedded in the sample. Cycle condition is 2 minutes O
N, OFF for 1 minute. In Examples 1 to 6, the intervening layer 13 formed by plating does not exist, and the intervening layer 13 is formed in Examples 7 to 11.

Table 1 shows the experimental results of the silicon nitride ceramic heater thus obtained. Example 2 in Table 1
No. 11 was manufactured in the same manner as in Example 1, and an experiment was performed. Comparative Examples 1 to 9 were also manufactured in the same procedure as in Example 1 described above, and an experiment was performed.

[0061]

[Table 1]

"None" in Table 1 indicates that the intervening layer 13 made of Pt was not formed. The second layer 16 of the metallization layer 12 has a weight ratio wt of the starting composition of Au / Ni.
%. The unit of thickness is μm. Judge by actual measurement from the cross-sectional photograph. Thermal expansion shows a value of 500 ° C. from room temperature. The unit of the coefficient of thermal expansion is * E-6 / ° C. The amount of precipitated Ni was determined by image processing from a micrograph of the cross section, and expressed as vol%
It is the value converted to. The durability shows the value of the number of cycles and the resistance change of 2%. This resistance change is a ratio to the overall resistance of the heater. “Meta failure” in Table 1 indicates that the metallized layer 12 was not formed. “Metallized peeling” indicates that the metallized layer 12 has been peeled from the substrate 1.

Embodiments 12 and 13 A cylindrical ceramic heater is first manufactured as shown in FIG. After firing in a hot press, resin molding was performed, and the resultant was ground into a cylindrical shape to expose through-hole-shaped conduction holes. A metallized layer 12 is formed on the outer peripheral surface of the base 1 so as to cover the through-hole conductor 6. Au / N as metallization layer 12
A paste prepared by adding an acrylic binder and terpineol to i / V is subjected to screen printing by screen printing, and then baked at 1180 ° C. in a vacuum heating furnace.

Further, the connection terminal 14 for external connection is further provided thereon.
Is fixed as shown in FIG. The connection terminal 14 is a pad made of a KOVAR alloy, to which a Ni lead wire 7 is joined by resistance welding. The pad is placed on the metallized layer 12 and brazed at 1000 ° C.
In some cases, plating made of platinum is performed to form the intervening layer 13. Examples 12 and 13 and Comparative Example 1
At 0 and 11, the Au / Ni mixture ratio was changed, and the connection terminal 14 with or without platinum plating was prepared.
The obtained heater was subjected to a cycle test by external heating from room temperature to a predetermined temperature in the same manner as in Example 1. Other configurations and the state of the experiment are the same as those in the first embodiment.

Embodiments 14 and 15 First, as shown in FIG. 9, a cylindrical ceramic heater is manufactured. After firing in a hot press, resin molding was performed, and the resultant was ground into a cylindrical shape to expose through-hole-shaped conductive holes. CVD covering the through-hole conductor 6 on the outer peripheral surface of the base 1
The first layer 15 of the metallized layer 12 is formed by sputtering a Ti film by (chemical vapor deposition). On this first layer 15, a second layer 16 is formed. The second layer 16 is made of A
After a paste produced by adding an acrylic binder and terpineol to u is screen-printed by screen printing, it is baked at 1180 ° C. in a vacuum heating furnace.

Further, the external connection terminal 14
Is fixed as shown in FIG. The connection terminal 14 is a pad made of a KOVAR alloy (6 * E-6 / ° C.), to which a Ni lead wire 7 is joined by resistance welding, and the pad is put on a metallized composition to 1000 ° C.
Brazing with. The inner surface of the pad facing the metallized layer 12 of the connection terminal 14 is subjected to platinum sputtering by the CVD method to form the intervening layer 13. In each of Examples 14 and 15 and Comparative Example 12, products having a different Au / Ni mixing ratio, and products with or without platinum plating on the connection terminals were prepared.

The obtained heater was subjected to a cycle test by external heating from room temperature to a predetermined temperature in the same manner as in Example 1.

As is evident from the results in Table 1, according to the present invention, the coefficient of thermal expansion on the connection terminals is 6 * E-6 / ° C. or less.
In each of Examples 1 to 15 using a sample in which the Ni component in the second layer 16 is 20 vol% or less in the two-layer metallized layer 12 having the first layer for improving the wetting, the resistance in the electrode durability test is all low. The number of holding cycles having a change rate of 2% or less showed an excellent value.

On the other hand, in Comparative Examples 1 and 2 in which the Ni component in the second layer 16 of the metallized layer 12 was more than 20 vol%, cracks occurred in the metallized layer 12 and at a certain number of cycles. A sharp change in resistance was observed.

In Comparative Examples 5 and 6 using samples in which the first layer 15 for improving wetting was not formed, the metallized layer 1
The wettability of No. 2 was insufficient, and the evaluation was not completed.

On the other hand, even in the two-layer metallization having the platinum-coated intervening layer 13 and the first layer, Comparative Examples 7, 8, and 10 using a sample in which Ni silicide in the metallization is more than 20 vol% are used. Cracks occurred during metallization, and a sharp change in resistance was observed at a certain number of cycles.

Comparative examples 3, 4, 9, and 1 in which the metallized layer 12 has a Ni-silicide content of less than 15 vol%.
In Nos. 1 and 12, the second layer was peeled off in a scale-like manner, and the durability was poor.

[0073]

According to the first aspect of the present invention, cracks in the vicinity of the connection terminal portion of the substrate made of silicon nitride ceramics can be suppressed, whereby the durability can be improved. In order to ensure wettability with silicon nitride on the outer peripheral surface of the substrate, a first layer for improving wetting containing V, Ti, Mo, and Mn as a main component is provided, so that adverse effects are caused when the second layer is brazed. A smooth metallized surface that is not given can be obtained. By forming a second layer on the first layer and suppressing the amount of Ni silicide generated in the second layer, crack progress due to stress concentration during metallization is controlled to prevent deterioration of durability performance. Can be improved.

The connection terminal is made of an alloy containing at least Fe and Ni, which has a small difference in thermal expansion from the silicon nitride-based ceramic substrate, so that thermal stress at the time of temperature rise can be relaxed.

According to the second aspect of the present invention, the connection terminal is
By using an Fe—Ni—Co alloy having a smaller difference in thermal expansion from the silicon nitride ceramic substrate, thermal stress at the time of temperature rise can be further reduced.

According to the third aspect of the present invention, the diffusion of Ni from the connection terminal to the second layer at the time of brazing is prevented by providing an intervening layer such as platinum on the inner surface of the pad of the connection terminal for external connection. However, embrittlement of metallization can be suppressed, and deterioration of durability performance can be prevented.

[Brief description of the drawings]

FIG. 1 is an enlarged cross-sectional view perpendicular to an axis showing a connection terminal portion 4 in a silicon nitride ceramic heater according to one embodiment of the present invention.

FIG. 2 is a perspective view showing an overall configuration of a silicon nitride ceramic heater including the connection terminal portion 4 shown in FIG.

1. FIG. 3 is a cross-sectional view showing a part of the ceramic heater of FIG.

4 is a cross-sectional view of the resistance heating element 2 forming part of the ceramic heater of FIG. 2 (Y ₁ -Y _1).

FIG. 5 is a cross-sectional view of a lead wire 3 forming portion (Y ₂ −Y ₂ ).

FIG. 6 is a cross-sectional view of a connection terminal (Y ₃ -Y ₃ ).

FIG. 7 is a sectional view showing a lead terminal 7 and a connection terminal 14.

FIG. 8 is a simplified organization diagram of the metallization layer 12.

FIG. 9 is a sectional view of another embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 base 2 resistance heating element 3 lead 4 connection terminal 5 connection wiring 6 through-hole conductor 7 lead terminal 12 metallization layer 13 intervening layer 14 connection terminal

Claims (3)

[Claims] 1. A silicon nitride ceramic heater in which a resistance heating element and a lead wire are embedded in a rod-shaped substrate made of silicon nitride ceramics, and a connection terminal portion electrically connected to the lead wire is formed on an outer periphery of the substrate. In the above, the connection terminal portion is: (a) a first layer which is a metallized layer formed on the outer peripheral surface of the base, is connected to a lead wire, and contains at least one of V, Ti, Mo, and Mn as a main component. A metallized layer formed on the first layer and having a main layer of Au and Ni and containing 5 to 20 vol% of Ni silicide; and (b) a metallized layer formed on the second layer of the metallized layer. A connection terminal made of an alloy containing at least Fe and Ni, and (c) a lead terminal fixed to the connection terminal. 2. The connection terminal is made of an Fe—Ni—Co alloy, and has a coefficient of thermal expansion (room temperature to 500 ° C.) of 6.0 × 10 ⁻⁶ /.
The silicon nitride ceramic heater according to claim 1, wherein the temperature is lower than or equal to ° C. 3. The silicon nitride ceramic heater according to claim 1, wherein an intervening layer made of platinum or palladium is provided between the second layer of the metallized layer and the connection terminal.