JP2009252389A - Ceramic heater and gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a plated part formed in a ceramic heater from being peeled off. <P>SOLUTION: A ceramic heater includes a ceramic base substrate having an exothermic resistor inside, electrode pads arranged on a surface of the ceramic base substrate to send electricity to the exothermic resistor, a joint part formed of a brazing material to joint the electrode pads with a terminal member which is electrically connected to outside, and a plating part covering the joint part. The joint part, equipped with side faces for the electrode pad to be erected from the ceramic base substrate and opposed faces coupled with the side faces and opposed to faces in contact with the ceramic base substrate, covers all the opposed faces so as to reach a boundary between the opposed faces and the side faces of the electrode pads. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a ceramic heater and a gas sensor using the ceramic heater.

  Conventionally, as a ceramic heater used in a gas sensor for detecting a specific gas component contained in an exhaust gas in an internal combustion engine or the like and measuring a concentration, a ceramic base provided with a heating resistor, and an electrode pad on the surface of the ceramic base It is known to have a joint formed by a brazing material and joining a terminal member and an electrode pad that are electrically connected to the outside, and a plating part that is coated by plating in order to prevent corrosion of the joint. (Patent Documents 1 to 4). In such a ceramic heater, the joint portion is provided on the facing surface of the electrode pad facing the ceramic base. At this time, the boundary and the gap between the facing surface of the electrode pad and the side surface (the surface standing on the ceramic base) are formed. Further, there is known a shape in which a plating portion is brought into contact with an opposing surface provided with a joint portion and is not provided with a joint portion so as to cover the joint portion.

JP 2005-216718 A JP 2006-294479 A JP 2003-347010 A JP 11-292649 A

By the way, in recent years, a brazing material having a high melting point (900 ° C. or higher) such as Cu is used in order to improve the thermal durability of the joint. Using such a brazing material, when the terminal member is brazed to the electrode pad, an insulating ceramic (for example, alumina or the like) added to the electrode pad for bonding to the ceramic base is deposited to the surface of the bonded portion, In some cases, the adhesion between the bonded portion and the plated portion may be hindered. Therefore, the amount of insulating ceramic added to the electrode pad is reduced.
However, if the amount of the insulating ceramic added to the electrode pad is reduced, sintering of the noble metal (for example, tungsten) constituting the electrode pad becomes rough during firing. Then, when the plated portion is brought into contact with the rough surface of the electrode pad, a part of the component of the plated portion enters the electrode pad, and then the component of the plated portion that has entered the electrode pad due to heat is aired. There is a risk that the film will be peeled off at the interface between the plated portion and the opposing surface of the electrode pad.

  The present invention has been made to solve at least a part of the above-described conventional problems, and an object thereof is to prevent the plating portion formed on the ceramic heater from peeling off.

  According to a first aspect of the present invention, a ceramic base including a heating resistor therein, an electrode pad disposed on the surface of the ceramic base for energizing the heating resistor, a brazing material, and an external In a ceramic heater comprising: a joint portion that joins a terminal member electrically connected to the electrode pad; and a plating portion that covers the joint portion, the electrode pad is a side surface provided upright from the ceramic substrate And an opposing surface that is coupled to the side surface and that opposes the surface that contacts the ceramic substrate, and the joint portion reaches the boundary between the opposing surface and the side surface of the electrode pad. Cover the entire surface.

According to the ceramic heater according to the first aspect of the present invention, in order to cover the entire facing surface so that the joining portion reaches the boundary between the facing surface and the side surface of the electrode pad, the plating portion covering the joining portion is provided. It is not formed on the opposing surface of the electrode pad. Therefore, it can suppress that a plating part touches an electrode pad directly, As a result, it can prevent peeling at the interface of a plating part and the opposing surface of an electrode pad.
In addition, the amount of insulating ceramic added to the electrode pad can be reduced, the insulating ceramic can be prevented from depositing to the surface of the joint, and the adhesion between the joint and the plated portion can be improved. it can.

  Note that the side surface of the electrode pad may be erected from the ceramic substrate, may be erected perpendicularly to the ceramic substrate, or may be erected with inclination to the ceramic substrate. . Further, the facing surface of the electrode pad only needs to face the surface in contact with the ceramic base, and may be substantially parallel to the ceramic base or may not be substantially parallel. Furthermore, “covering the entire facing surface” means that the facing surface of the electrode pad cannot be visually recognized by the joint portion.

  In the ceramic heater according to the first aspect of the present invention, the joining portion may cover at least a part of the side surface beyond the boundary between the facing surface and the side surface of the electrode pad. Thereby, since it becomes difficult for a plating part to go around to the side surface of an electrode pad, it can further suppress that a plating part touches an electrode pad directly, and can further prevent peeling at the interface of a plating part and an electrode pad.

  In the ceramic heater according to the first aspect of the present invention, the electrode pad may be a porous layer. In this case, the joint portion enters the electrode pad, and the adhesion between the electrode pad and the joint portion is improved. In addition, since the bonding portion covers the entire facing surface of the electrode pad, the plating portion is prevented from coming into direct contact with the porous electrode pad, and a decrease in adhesion between the plating portion and the electrode pad can be suppressed.

  In the ceramic heater according to the first aspect of the present invention, the plated portion may have a thickness of 3 μm or more. In this case, corrosion of the joint portion can be suppressed by the plated portion.

  In the ceramic heater according to the first aspect of the present invention, the electrode pad includes a first layer formed on the surface side of the ceramic base and a second layer formed on the bonding portion side, and the second The layer may have a lower content of the insulating ceramic than the first layer. In this case, the first layer having a relatively high content of the insulating ceramic improves the adhesion with the ceramic substrate, while the insulating ceramic in the first layer has a relatively high content of the insulating ceramic. It can suppress depositing on the surface of a junction part with few 2nd layers, and can improve the adhesiveness of a plating part.

  In the ceramic heater according to the first aspect of the present invention, it is preferable that at least half of the facing surface is opposed to the terminal member in the extending direction of the ceramic base and the direction orthogonal to the extending direction. In this case, since it can suppress that the insulating ceramic in an electrode pad precipitates on the surface of a junction part by a terminal member, the adhesiveness of a plating part can be improved.

  Hereinafter, a ceramic heater and a gas sensor using the ceramic heater according to the present invention will be described based on examples with reference to the drawings.

A. First Example A1. Gas sensor configuration:
FIG. 1 is an explanatory diagram showing the configuration of a gas sensor as one embodiment of the present invention. The gas sensor 10 includes an oxygen detection element 20, a metal shell 11, an inner terminal member 30, an outer terminal member 40, and a ceramic heater 100.

  The oxygen detection element 20 has a substantially U-shaped cross section extending in the axial direction (vertical direction in FIG. 1) along the axis AX, with the front end 20s (lower side in FIG. 1) closed and the rear end 20k (upper side in FIG. 1) opened. It has a bottomed cylindrical shape. The oxygen detection element 20 includes a solid electrolyte body 21 having oxygen ion conductivity, an outer electrode layer (not shown) formed by plating or the like on a part of the outer peripheral surface of the solid electrolyte body 21, and an inner circumference of the solid electrolyte body 21. An inner electrode layer (not shown) formed by plating or the like is provided on a part of the surface. Further, on the outer peripheral surface of the oxygen detection element 20, an engagement flange portion 20f protruding outward in the radial direction is provided at an intermediate portion in the axis AX direction, and is engaged with a metal shell 11 described later.

  The metal shell 11 is formed in a cylindrical shape surrounding a part of the outer periphery of the oxygen detection element 20, and is engaged by interposing metal packings 81, 82, 83, insulators 13, 13b, and ceramic powder 14 inside. The oxygen detecting element 20 is held by engaging with the flange portion 20f. Thereby, the oxygen detection element 20 is kept airtight inside the metal shell 11. Moreover, the protector 15 is attached to the metallic shell 11 so as to cover the distal end portion of the oxygen detection element 20 protruding from the distal end side opening of the metallic shell 11. The protector 15 has a double structure of an outer protector 15a and an inner protector 15b, and the outer protector 15a and the inner protector 15b are formed with a plurality of gas permeation ports through which exhaust gas permeates. An outer electrode layer (not shown) of the oxygen detection element 20 can come into contact with the exhaust gas through the gas permeation port of the protector 15.

  The metal shell 11 includes a connecting portion 11d on the rear end side of the hexagonal portion 11c formed on the outer peripheral surface. In the connecting portion 11d, the distal end side of the cylindrical metal outer cylinder 16 is fixed from the outside by all-around laser welding. The rear end side opening of the metal outer cylinder 16 is swaged and sealed by fitting a grommet 17 made of fluororubber. A separator 18 made of an insulating alumina ceramic is disposed on the front end side of the grommet 17. Sensor output lead wires 19 and 19b and heater lead wires 12b and 12c are disposed through the grommet 17 and the separator 18. A through-hole is formed in the center of the grommet 17 along the axis AX, and a metal pipe 86 in a state where a sheet-like filter 85 having both water repellency and air permeability is covered is fitted into the through-hole. Yes. As a result, the atmosphere outside the gas sensor 10 is introduced into the metal outer cylinder 16 through the filter 85, and then into the internal space G of the oxygen detection element 20.

  The outer terminal member 40 is made of a stainless steel plate, and an outer fitting portion 41 having a substantially C-shaped cross section in the direction perpendicular to the axis AX, and a separator insertion portion 42 extending from the vicinity of the rear end side center of the outer fitting portion 41 to the rear end side. Further, a connector portion 43 is provided on the rear end side, grips the core wire of the sensor output lead wire 19b by caulking, and electrically connects the outer terminal member 40 and the sensor output lead wire 19b. The separator insertion portion 42 is inserted into the separator 18, and the separator contact portion 42 d that branches and protrudes from the separator insertion portion 42 elastically contacts the holding hole 18 d, thereby causing the outer terminal member 40 itself to move. It is held in the separator 18. Further, the outer fitting portion 41 is formed such that the diameter of the inscribed circle in the radial cross section is smaller than the diameter of the outer peripheral surface on the rear end side of the oxygen detection element 20. For this reason, in a state where the outer terminal member 40 is assembled to the oxygen detection element 20, the outer fitting portion 41 is accompanied by a pressing force on the outer electrode layer formed on the outer peripheral surface of the oxygen detection element 20 by its own elastic force. In order to make contact, electrical conduction with the outer electrode layer is maintained. Therefore, the electromotive force generated in the outer electrode layer is extracted to the outside through the outer fitting portion 41 and the sensor output lead wire 19b.

  The inner terminal member 30 is made of a stainless steel plate, the insertion section 33 having a horseshoe-shaped cross section in the direction perpendicular to the axis AX, the separator insertion section 32 extending from the vicinity of the center of the rear end side of the insertion section 33 to the rear end side, and The connector portion 31 is provided on the end side, holds the core wire of the sensor output lead wire 19 by caulking, and electrically connects the inner terminal member 30 and the sensor output lead wire 19. The separator insertion portion 32 is inserted into the separator 18, and a separator abutting portion 32 d that branches and protrudes from the separator insertion portion 32 elastically abuts the holding hole 18 d so that the inner terminal member 30 itself is It is held in the separator 18. Moreover, the insertion part 33 is provided with the heater press part 36 which protrudes in the front end side. When viewed from the direction of the axis AX, the heater pressing portion 36 is formed in a substantially ¼ arc shape, and when the insertion portion 33 is assembled in the oxygen detection element 20, the side surface of the ceramic heater 100 is the oxygen detection element. The ceramic heater 100 is pressed so as to come into contact with the inner peripheral surface of 20.

  The insertion portion 33 is formed such that the diameter of the circumscribed circle in the radial cross section is larger than the diameter of the inner peripheral surface on the rear end side of the oxygen detection element 20. For this reason, in a state in which the inner terminal member 30 is assembled to the oxygen detection element 20, the insertion portion 33 is accompanied by a pressing force on the inner electrode layer formed on the inner peripheral surface of the oxygen detection element 20 by its own elastic force. Because of the contact, electrical continuity with the inner electrode layer is maintained. Therefore, the electromotive force generated in the inner electrode layer is extracted to the outside through the insertion portion 33 and the sensor output lead wire 19.

  The ceramic heater 100 is disposed in the internal space G and is maintained by the inner terminal member 30 to maintain the posture. In the ceramic heater 100, a terminal member 130 to be described later is connected to the heater lead wires 12b and 12c, and the inner peripheral surface of the solid electrolyte body 21 is heated by supplying power from the heater lead wires 12b and 12c. The configuration of the ceramic heater 100 will be described in detail later.

A2. Configuration of ceramic heater:
FIG. 2 is an explanatory view showing the configuration of the ceramic heater. FIG. 3 is an exploded perspective view showing the internal structure of the ceramic heater. As shown in FIG. 2, the ceramic heater 100 is formed in a round bar shape (substantially cylindrical shape). Then, as shown in FIG. 1, the oxygen detection element 20 is heated by being inserted into the oxygen detection element 20. Of the both ends in the longitudinal direction of the ceramic heater 100, the side (left side in FIG. 2) provided with the heat generating portion will be referred to as “front end side”, and the opposite end will be described as “rear end side”.

  The ceramic heater 100 includes a ceramic base 102, an electrode pad 121, and a terminal member 130. As shown in FIG. 3, the ceramic base 102 is manufactured by winding green sheets 140 and 146 made of alumina ceramic having high insulating properties around the outer periphery of a round rod-like alumina ceramic tube 101 and firing them. .

  On the green sheet 140, a heating resistor 141 mainly composed of a tungsten material as a heater pattern is formed. The heat generating resistor 141 further includes a heat generating portion 142 and a pair of lead portions 143 connected to both ends of the heat generating portion 142. The rear end side of the green sheet 140 is electrically connected to an electrode pad 121 formed on the outer surface of the ceramic heater 100 through two through holes 144.

  The green sheet 146 is pressure-bonded to the surface of the green sheet 140 on the side where the heating resistor 141 is formed. Alumina paste is applied to the surface of the green sheet 146 opposite to the pressure-bonding surface, and the green sheets 140 and 146 are wound around the tub tube 101 and pressed inward from the outer periphery with the coating surface facing inward. Thus, a ceramic heater molded body is formed. Thereafter, the ceramic base 102 is formed by firing the ceramic heater molded body.

  The electrode pad 121 shown in FIG. 2 is formed on the ceramic substrate 102 and includes two of an anode side and a cathode side. The electrode pads 121 are provided at two positions on the outer surface of the green sheet 140 corresponding to the above-described through holes 144. The conduction between the heat generating resistor 141 and the lead portion 143 is performed through a conductive paste filled in the through hole 144.

  The electrode pad 121 is a pad-like metal layer containing 97 wt% or more of a main material composed of at least one element selected from tungsten and molybdenum and having an alumina powder content of 3 wt% or less. Tungsten or molybdenum is suitable for the composition of the electrode pad 121 because it has good bonding properties with the copper brazing material 124 and has a high melting point and excellent heat resistance. Moreover, since the content of the alumina powder is 3% by weight or less, the surface is formed in a porous shape. Note that examples of the insulating ceramic included in the electrode pad 121 include mullite, spinel, and the like in addition to alumina.

  The terminal member 130 is joined from a joining end portion 133 to be brazed to the electrode pad 121 using a brazing material 124 described later, a crimping portion 135 made of nickel formed in a flat plate shape, and a tip of the crimping portion 135. And a connection portion 134 extending to the end portion 133. The terminal member 130 is made of a nickel member containing 90% by weight or more of nickel.

  The distal end portion of the connection portion 134 is connected to the joint end portion 133 by being bent in a step shape in the thickness direction. Further, the terminal member 130 is bent between the connection portion 134 and the crimping portion 135 so as to be twisted at a substantially right angle with the longitudinal direction of the connection portion 134 as an axis. Further, the terminal member 130 grips the core wires of the heater lead wires 12b and 12c shown in FIG. 1 to the crimping portion 135, and electrically connects the heating resistor 141 and the heater lead wires 12b and 12c.

  FIG. 4 is an explanatory view illustrating the arrangement of the joining end portion 133 and the electrode pad 121. In FIG. 4, a joining portion 124a and a plating portion 125, which will be described later, are omitted. As shown in FIG. 4, the electrode pad 121 includes a side surface 121 b erected from the ceramic substrate 102, and a substantially rectangular facing surface 121 a that is connected to the side surface 121 b and faces the ceramic substrate 102. Since the facing surface 121a has a substantially rectangular shape, four side surfaces 121b are provided. The opposed surface 121a and the four side surfaces 121b form a boundary El. Further, a boundary Bl is formed by the side surface 121b of the electrode pad 121 and the ceramic base 102. The terminal member 130 is arrange | positioned along the axial direction of the ceramic heater 100, and the joining end part 133 is arrange | positioned on the opposing surface 121a. At this time, when the length in the axial direction of the facing surface 121a is Lp, the length in the circumferential direction is Wp, the length in the axial direction of the joint end 133 is Lt, and the length in the circumferential direction is Wt, the electrode pad 121 The terminal member 130 is formed so that Lp <Lt × 2 in the axial direction and Wp <Wt × 2 in the circumferential direction.

  FIG. 5 is an explanatory view exemplifying a state in which the joining end portion 133 and the electrode pad 121 are joined by the joining portion 124a. In FIG. 5, a plated portion 125 described later is omitted. As shown in FIG. 4, the terminal member 130 and the electrode pad 121 are joined by the brazing material 124 so as to cover the joining end portion 133 and the facing surface 121 a of the electrode pad 121. At this time, the brazing material 124 covers the entire facing surface 121a and covers the side surface 121b beyond the boundary El. By this brazing, a joint portion 124a for joining the terminal member 130 and the electrode pad 121 is formed. The joint portion 124a corresponds to a “joint portion” in the claims. The brazing material 124 contains copper in an amount exceeding 50% by weight. In this embodiment, the electrode pad 121 and the terminal member 130 are brazed using a brazing material 124 of 100% by weight of copper.

  FIG. 6 is an explanatory view illustrating a part of the AA cross section of FIG. 2. The electrode pad 121 is formed on the outer surface of the green sheet 140 wound around the outer periphery of the soot tube 101, and is electrically connected to the lead portion 143 formed on the inner surface of the green sheet 140 through the through hole 144. A nickel plated portion 125 is formed on the joint 124 a and the joint end 133 formed by the brazing material 124. The plated part 125 is formed so that the thickness of the thinnest part on the joining end part 133 and the joining part 124a is 3 μm or more. Since the joining portion 124 a covers the entire facing surface 121 a of the electrode pad 121 and further wraps around a part of the side surface 121 b of the electrode pad 121, the plating portion 125 is prevented from contacting the electrode pad 121. The plated portion 125 suppresses corrosion due to oxidation of the joint portion 124a.

A3. Manufacturing method of ceramic heater:
A metal resistor ink (metalized ink) to be a heating resistor 141 and an electrode pad 121 is applied (printed) to the green sheet 140 shown in FIG. 3 in a predetermined pattern shape, and the metalized ink is formed in the through hole 144. (Or conductive paste) is filled. Next, the green sheet 146 is pressure-bonded to the green sheet 140, and the green sheet 140 and the green sheet 146 are wound around the soot tube 101 to form a ceramic heater molded body. Subsequently, the ceramic heater molded body is fired to perform a process of forming the ceramic base body 102 in which the green sheets 140 and 146 and the soot tube 101 are integrated.

  The processing so far corresponds to an electrode pad forming step in which the electrode pad 121 is formed by applying metal resistor ink (metallized ink) to the ceramic substrate 102 on which the heating resistor 141 is formed.

  Next, as shown in FIG. 5, the brazing material 124 and the terminal member 130 are arranged on the electrode pad 121 so as to contact each other. In this state, the brazing material 124 is melted by heating to 900 ° C. or higher, and the terminal member 130 and the electrode pad 121 are joined by brazing (joining process). In this bonding step, the brazing material 124 is brazed so as to spread over the entire facing surface 121 a on the electrode pad 121, and the facing surface 121 a is covered with the brazing material 124.

  Then, as shown in FIG. 6, nickel plating is performed by an electroless plating method so as to cover the electrode pad 121 and the joint portion 124a (brazing portion) of the terminal member 130, thereby forming a plated portion 125 ( Plating layer forming step). Accordingly, the terminal member 130 and the joint portion 124a (brazed portion) are protected from corrosion due to oxidation or the like by the plating portion 125.

  As described above, according to the first embodiment, since the bonding portion 124 a covers the entire facing surface 121 a of the electrode pad 121, the plating portion 125 covering the bonding portion 124 a is not formed on the facing surface 121 a of the electrode pad 121. . Therefore, it can suppress that the plating part 125 contacts the electrode pad 121 directly, and can improve the adhesiveness of the plating part 125. FIG.

  Furthermore, since the bonding portion 124a covers a part of the side surface 121b beyond the boundary EI between the facing surface 121a and the side surface 121b of the electrode pad 121, the plating portion 125 is difficult to go around the side surface 121b of the electrode pad 121. Further, it is possible to further suppress the plating part 125 from being in direct contact with the electrode pad 121.

  According to the first embodiment, since the plated portion 125 has a thickness of 3 μm or more and covers the terminal member 130 and the joint portion 124a, the terminal member 130 and the joint portion 124a (brazed portion) are corroded. Can be suppressed.

  According to the first embodiment, when the opposing surface 121a of the electrode pad 121 is viewed in the extending direction of the ceramic heater 100 and the direction orthogonal to the extending direction, more than half of the opposing surface 121a of the electrode pad 121 is a terminal member. 130. Thereby, it is possible to prevent the insulating ceramic in the electrode pad 121 from being deposited on the surface of the joint portion 124a by the terminal member 130, and to improve the adhesion of the plated portion 125.

B. Second embodiment:
In the second embodiment, the ceramic heater 100 in which the joint portion 124a covers the boundary Bl between the side surface 121b of the electrode pad 121 and the ceramic base 102 will be described. The configuration of the gas sensor 10 using the ceramic heater 100 according to the second embodiment is the same as that of the first embodiment, and only the joining portion 124a of the ceramic heater 100 is different. In the second embodiment, components having the same reference numerals as those in the first embodiment are the same as the components in the first embodiment.

  FIG. 7 is an explanatory view illustrating the state of the joint portion 124a according to the second embodiment. In FIG. 7, the plating part 125 is omitted. FIG. 8 is an explanatory view illustrating a part of the AA cross section of the ceramic heater according to the second embodiment. In the first embodiment, the brazing material 124 joining the terminal member 130 and the electrode pad 121 covers the boundary El, but in the second embodiment, the side surface 121b of the electrode pad 121 and Cover to the boundary B1 with the ceramic substrate 102. The raw material of the brazing material 124 is the same as that of the first embodiment.

As shown in FIG. 8, a plated portion 125 is formed on the joint portion 124 a formed by the brazing material 124. Since the bonding portion 124a covers the entire opposing surface 121a and side surface 121b of the electrode pad 121, the plating portion 125 is almost completely restricted from contacting the electrode pad 121.

  According to the second embodiment, since the joining portion 124a covers the boundary Bl between the side surface 121b of the electrode pad 121 and the ceramic base 102, the plating portion 125 can be further suppressed from coming into contact with the electrode pad 121. In addition, the adhesion of the plating part 125 can be improved.

C. Third embodiment:
In the third embodiment, a ceramic heater 100 having a multilayered electrode pad will be described. The configuration of the gas sensor 10 using the ceramic heater 100 according to the third embodiment is the same as that of the first embodiment, and only the structure of the electrode pad is different. In the third embodiment, components having the same reference numerals as those in the first embodiment are the same as the components in the first embodiment.

  FIG. 9 is an exploded perspective view showing the internal configuration of the ceramic heater according to the third embodiment. The ceramic heater 100 includes a multilayer electrode pad 151 in place of the electrode pad 121 in the first embodiment. The multilayer electrode pad 151 has a two-layer structure in which a lower electrode pad 155 and an upper electrode pad 153 are stacked. In the multilayer electrode pad 151, the lower layer electrode pad 155 is disposed on the side facing the green sheet 140, and the upper layer electrode pad 153 is laminated so as to cover the lower layer electrode pad 155. Since the ceramic base 102 and the terminal member 130 are the same as those in the first embodiment, description thereof will be omitted. The lower electrode pad 155 corresponds to the “first layer” in the claims, and the upper electrode pad 153 corresponds to the “second layer” in the claims.

  As the electrode ink for forming the multilayer electrode pad 151, the content of alumina, which is the main component of ceramic, is different between the lower electrode ink and the upper electrode ink, and the alumina content in the upper electrode ink is different. An ink having a lower content than the alumina content in the lower electrode ink is used.

  Specifically, 6 parts by weight of a resin binder, 100 parts by weight of acetone, and 70 parts by weight of butyl carbitol with respect to 100 parts by weight of a raw material powder in which 90% by weight of tungsten powder and 10% by weight of alumina powder are blended. Are added and mixed on the slurry in a pot, then degassed under reduced pressure, and acetone is evaporated to produce an ink for a lower electrode. Also, 6 parts by weight of a resin binder, 100 parts by weight of acetone, and 70 parts by weight of butyl carbitol are added to 100 parts by weight of raw material powder in which 97% by weight of tungsten powder and 3% by weight of alumina powder are blended. Then, after mixing on the slurry in a pot, defoaming under reduced pressure and evaporating acetone produce an upper electrode ink.

  In the electrode pad forming step, after applying the lower layer electrode ink, the upper layer electrode ink is applied on the lower layer electrode ink to form a two-layer electrode ink, and then By baking, an electrode pad composed of two layers can be formed.

  Thus, by forming the multilayer electrode pad 151 having a two-layer structure using two types of electrode inks, the bonding state between the lower layer electrode pad 155 formed by the lower layer electrode ink and the ceramic substrate 102 is excellent. Can be.

  By forming the multilayer electrode pad 151 having a two-layer structure using two types of electrode inks, it is possible to suppress the precipitation of alumina on the surface of the joint portion 124a by the upper layer electrode pad 153 formed by the upper layer electrode ink. can do.

D. Modifications The present invention can be implemented in various modes without departing from the spirit of the present invention.

  In the first embodiment, the joint portion 124a is provided up to the side surface 121b beyond the boundary EI. However, the joint portion 124a is not provided up to the side surface 121b, but reaches the boundary EI, and the entire facing surface 121a is provided. It may be provided so as to cover.

D1. Modification 1:
In the first embodiment, the electrode pad 121 has an alumina powder content of 3% by weight or less and a porous surface, but the alumina powder content is 3% by weight or more. The present invention is also applicable to electrode pads 121 that are not formed in a porous shape.

D2. Modification 2:
In the first embodiment, the terminal member 130 is formed using a nickel member containing 90% by weight or more of nickel. However, the terminal member 130 may be configured as a clad material in which a nickel member and a SUS member are clad in a laminated form. In the first to third embodiments, the terminal member 130 has a substantially rectangular cross section. However, the present invention is not limited to this, and the cross section may be a substantially circular shape.

D3. Modification 3:
In the third embodiment, the upper electrode ink constituting the upper electrode pad 153 contains 3% by weight of alumina powder, but the alumina powder may be 3% by weight or less, and contains alumina powder. You don't have to.

D4. Modification 4:
In this embodiment, the ceramic heater 100 formed by the round rod-shaped alumina ceramic rod 101 is shown. However, the ceramic heater 100 is formed in a plate shape using a plate-shaped alumina ceramic substrate. May be.

  The present invention can be realized in various aspects other than the above. For example, a method of manufacturing a ceramic heater including a ceramic base, an electrode pad, a joint, and a plated portion, and the ceramic heater according to the present invention It can be realized in the form of a gas sensor element provided with or a gas sensor provided with a ceramic heater according to the present invention.

  As mentioned above, although this invention was demonstrated based on the Example and the modification, Embodiment mentioned above is for making an understanding of this invention easy, and does not limit this invention. The present invention can be changed and improved without departing from the spirit and scope of the claims, and equivalents thereof are included in the present invention.

It is explanatory drawing which showed the structure of the gas sensor as one Example of this invention. It is explanatory drawing which showed the structure of the ceramic heater. It is the disassembled perspective view which showed the internal structure of the ceramic heater. 6 is an explanatory view illustrating the arrangement of a bonding end portion 133 and an electrode pad 121. FIG. It is explanatory drawing which illustrated the state by which the junction edge part 133 and the electrode pad 121 were joined by the junction part 124a. It is explanatory drawing which illustrated a part of AA cross section of FIG. It is explanatory drawing which illustrated the state of the junction part 124a which concerns on a 2nd Example. It is explanatory drawing which illustrated a part of AA cross section of the ceramic heater which concerns on a 2nd Example. It is the disassembled perspective view which showed the internal structure of the ceramic heater which concerns on a 3rd Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Gas sensor 11 ... Metal fitting 20 ... Oxygen detection element 30 ... Inner terminal member 40 ... Outer terminal member 100 ... Ceramic heater 101 ... Saddle tube 102 ... Ceramic base 121 ... Electrode pad 124 ... Brazing material 124a ... Joint part 125 ... Plating part 130 ... Terminal member 133 ... Junction end part 140,146 ... Green sheet 141 ... Heat-generating resistor 151 ... Multilayer electrode pad

Claims (7)

A ceramic substrate with a heating resistor inside;
An electrode pad disposed on the surface of the ceramic substrate to energize the heating resistor;
A joining portion formed by a brazing material and joining the electrode pad and a terminal member electrically connected to the outside;
In a ceramic heater provided with a plating portion that covers the joint portion,
The electrode pad includes a side surface erected from the ceramic base, and a facing surface that is connected to the side surface and faces the surface that contacts the ceramic base.
The ceramic heater that covers the entire facing surface so that the joint reaches the boundary between the facing surface and the side surface of the electrode pad. The ceramic heater according to claim 1,
The bonding portion is a ceramic heater that covers at least a part of the side surface beyond a boundary between the facing surface and the side surface of the electrode pad. In the ceramic heater according to claim 1 or 2,
The electrode pad is a ceramic heater which is a porous layer. The ceramic heater according to any one of claims 1 to 3,
The plated portion is a ceramic heater having a thickness of 3 μm or more. The ceramic heater according to any one of claims 1 to 4,
The electrode pad includes a first layer formed on the surface side of the ceramic base and a second layer formed on the bonding portion side,
The first layer and the second layer contain a noble metal material and an insulating ceramic,
The second layer is a ceramic heater in which the content of the insulating ceramic is smaller than that of the first layer. The ceramic heater according to any one of claims 1 to 5,
A ceramic heater in which at least half of the facing surface faces the terminal member in the extending direction of the ceramic substrate and in a direction orthogonal to the extending direction. A gas sensor element comprising a bottomed cylindrical solid electrolyte body with a closed tip, an outer electrode disposed on the outer peripheral surface of the solid electrolyte body, an inner electrode disposed on the inner peripheral surface of the solid electrolyte body, and the gas sensor A gas sensor having a heater inserted and arranged in the element,
A gas sensor, wherein the heater is a ceramic heater according to any one of claims 1 to 6.

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