GB2432093A

GB2432093A - Ceramic heater and heating iron using it

Info

Publication number: GB2432093A
Application number: GB0703837A
Authority: GB
Inventors: Takafumi Tsurumaru; Takahiro Maruyama
Original assignee: Kyocera Corp
Current assignee: Kyocera Corp
Priority date: 2004-07-28
Filing date: 2005-07-27
Publication date: 2007-05-09
Anticipated expiration: 2025-07-27
Also published as: GB0703837D0; GB2432093B; WO2006011520A1; KR101201388B1; KR20070048710A; JPWO2006011520A1

Abstract

A high-durability ceramic heater excellent in durability even under rigorous conditions such as high temperature, vibration and exhaust gas atmosphere, and high in reliability about quick heating/cooling, comprising a ceramic body having a built-in conductor and a metallized layer conducting to the conductor, and a lead member joined to the metallized layer with a brazing filler material, wherein the coating area, covering the lead member, of the brazing filler material is set to within the 40-99% range of the distance from the proximal end, closest to the metallized layer, of the lead member to the upper end remotest from the metallized layer.

Description

DESCRIPTION

CERAMIC HEATER AND HEATING IRON USING THE SAME

TECHNICAL FIELD

10001] The present invention relates to a ceramic heater and a heating iron constituted from the same.

BACKGROUND

[0002] Ceramic heaters have been widely used as a semiconductor heater, soldering iron, hair iron, kerosene evaporating heater for kerosene burning fan heater, heat source for glow system, etc. In recent years, applications of the ceramic heater are expanding further including, in particular, onboard use in automobiles such as air-to-fuel ratio sensor (oxygen sensor) [0003] The ceramic heaters are manufactured in various configurations such as flat plate, cylinder and tube, all having such a constitution, for example, that an electrical conductor formed from a metal having a high melting point such as W, Re or Mo is embedded in a ceramic substrate made of alumina as the main component. Fig. 11 shows a ceramic heater having cylindrical shape, as an example thereof. This ceramic heater comprises a ceramic substrate in which an electrical conductor is embedded, a terminal lead-out electrode section 106 provided on the surface thereof, and a lead member 110 joined onto the surface thereof by means of a brazing material 111. The terminal lead-out electrode section 106 is constituted from a metallizing layer and an Ni plating layer, while the embedded electrical conductor and the metallizing layer are connected with each other in order to supply electric power to the embedded electrical conductor (Japanese Unexamined Patent Publication (Kokai) No. 8-109063).

[0004] In recent years, there has been proposed a ceramic heater wherein the angle between tangent on the end portion of the brazing material of the periphery of the brazing material and tangent making contact with the end point of the brazing material of the periphery of the electrode is set within a specific range, for the purpose of improving the reliability (Japanese Unexamined Patent Publication (Kokai) No. 2000-286047) [0005] However, in the case of onboard ceramic heaters of automobile which are in high demand in recent years, high reliability is required particularly in the junction where the lead member is fastened, because they are used in harsh environment involving high temperature, vibration and r exposure to exhaust gas.

[0006] Meanwhile apparatuses which use ceramic heaters have come to be required to have quick startup capability in recent years. Such ceramic heaters which are required to have quick startup capability undergo rapid temperature changes in the junction, and are therefore required to have high reliability in the junction. Specifically, there is such a problem that stress is concentrated in the brazed portion due to the difference in thermal expansion between the brazing material which fixes the lead member onto the terminal lead-out electrode section and the ceramic substrate, thus resulting in lower durability of the ceramic heater.

[0007] Particularly in a ceramic heater which has a large area of heat generation region and is held between holding members as a whole, the electrode lead-out section is heated quickly as soon as the power supply is turned on, and therefore it is important to improve the durability.

[0008]

DISCLOSURE OF THE INVENTION

Accordingly, an object of the present invention is to provide a ceramic heater of high durability which can endure harsh environment such as high temperature, vibration and exposure to exhaust gas, and has high reliability in quick r heating and cooling operations.

Another object of the present invention is to provide a heating iron which has high durability.

[0009] In order to achieve the object described above, a first ceramic heater of the present invention comprises a ceramic substrate, which has an electrical conductor embedded therein and a metallizing layer electrically connected with the electrical conductor, and a lead member which is joined with the metallizing layer by means of a brazing material, wherein a region of the brazing material covering the lead member is controlled within a range from 40 to 99 of the distance between a proximate end of the lead member that is nearest to the metallizing layer and a top end that is farthest from the metallizing layer.

10010] A second ceramic heater of the present invention comprises a ceramic substrate, which has an electrical conductor embedded therein and a metallizing layer electrically connected with the electrical conductor, and a lead member which is joined with the metallizing layer by means of a brazing material, wherein the brazing material includes at least two kinds of metal and said at least two kinds of metal exist in the brazing material in such a form that they can be distinguished from each other.

Also, in the present invention, the phrase that at least two kinds of metal can be distinguished from each other means that the metals are mixed without forming a solid solution, and the phases of different metals can be identified by observing a reflected electron image (BEI) of a cross section of the brazed portion under a scanning electron microscope (SEM), with a magnifying power of 50 times or higher.

10011] The heating iron of the present invention uses the first or second ceramic heater of the present invention as heating means.

[0012] In the first ceramic heater of the present invention having the constitution described above, a sufficient area of junction between the lead wire and the brazing material can be secured by controlling the region of the brazing material which covers the lead member in the junction, thereby decreasing the stress generated in thermal cycles.

As a result, the first ceramic heater of the present invention makes it possible to form the junction of high durability and high reliability, so as to provide a ceramic heater having high durability.

[0013] In the second ceramic heater of the present invention, the process of manufacturing the ceramic heater of the first embodiment.

Fig. 3C is a perspective view showing a third step in the process of manufacturing the ceramic heater of the first embodiment.

Fig. 3D is a perspective view showing a fourth step in the process of manufacturing the ceramic heater of the first embodiment.

Fig. 4 is a perspective view of a ceramic heater 100 according to a second embodiment of the present invention.

Fig. 5 is a sectional view schematically showing a brazed portion of the ceramic heater 100 shown in Fig. 4.

Fig. 6 is a photograph showing an example of cross section of the brazed portion of the ceramic heater 100 according to the second embodiment.

Fig. 7 is an enlarged photograph of a region E shown in Fig. 6.

Fig. 8 is an enlarged photograph of a region D shown in Fig. 6.

Fig. 9 is an enlarged photograph of a region C shown in Fig. 6.

Fig. 10 is a perspective view of a heating iron according to one embodiment of the present invention.

Fig. 11 is a perspective view of a ceramic heater of

the prior art.

since at least two kinds of metal are included in the brazing material and said at least two kinds of metal exist in the brazing material in such a form that they can be distinguished from each other, one of said at least two kinds of metal constituting the brazing material which has a lower electrical resistance contributes to the electrical continuity, thus decreasing the electrical resistance. As a result, heat generated by the brazing material is decreased, thus making it possible to improve the reliability of the junction between the brazing material and the metallizing layer and between the brazing material and the lead member, and provide a ceramic heater of high durability.

BRIEF DESCRIPTION OF THE DRAWINGS

[00141 Fig. 1A is a perspective view of a ceramic heater according to a first embodiment of the present invention.

Fig. lB is a sectional view of the ceramic heater of the first embodiment.

Fig. 2 is a sectional view showing a junction of a lead member 10 of the ceramic heater of the first embodiment.

Fig. 3A is a perspective view showing a first step in a process of manufacturing the ceramic heater of the first embodiment.

Fig. 3B is a perspective view showing a second step in Fig. 12 is a photograph showing a cross section of the brazed portion of the ceramic heater of the prior art.

[Description of Reference Numerals]

[0015] 1: 100: Ceramic heater 2: Ceramic core member 3: Ceramic sheet 4: Electrical conductor 5: Lead-out section 6: Terminal lead-out electrode section Ga: Metallizing layer 6b: Plating layer 7: Via hole 8: Bonding layer 9: Ceramic substrate 10: Lead member 11: Brazing material 12: Electrode lead-out section 13: Void 14: Diffusion layer of lead member component into brazing material 16: Proximate end 17: Distal end 18: Height of covering region 22: Ceramic core member 23: Ceramic green sheet 24: Electrical conductor 25: Lead-out section 26: Metallizing layer 27: Through hole for via hole 28: Electrode lead-out section

DETAILED DESCRIPTION OF THE PREFFERED EMBODIMENT

[00161 Embodiments of the present invention will now be described by making reference to the accompanying drawings.

First Embodiment Fig. 1A is a perspective view schematically showing a ceramic heater according to a first embodiment of the present invention, Fig. lB is a sectional view taken along lines A-A in Fig. 1A, and Fig. 2 is a sectional view showing the structure of a junction in detail.

[0017] As shown in Fig. 1A and Fig. 1B, the ceramic heater).

of the first embodiment comprises a ceramic core member 2 having cylindrical shape and a ceramic sheet 3 which is rolled around the ceramic core member 2 via a bonding layer 8.

An electrical conductor 4, a lead member 5 and an electrode lead-out section 12 are embedded between the ceramic core member 2 and the ceramic sheet 3. The electrode lead-out section 12 is connected to a metallizing layer 6a which is provided on the outside of the ceramic sheet 3. A plating layer 6b formed from Ni is placed on the surface of the metallizing layer 6a, so that a terminal lead-out electrode section 6 is constituted from the metallizing layer 6a and the plating layer 6b, and the terminal lead-out electrode section 6 and the lead member 10 are connected and fixed with each other by the brazing material 11. The electrode lead-out section 12 and the metallizing layer 6a are connected with each other through via hole 7 provided below the metallizing layer 6a and in the ceramic sheet 3 as shown in Fig. lB. The ceramic heater 1 having such a constitution functions as a heater when the electric power is supplied through the lead member 10 to the metallizing layer 6a and the electrical conductor 4 generates heat accordingly.

[0018] In the ceramic heater of the first embodiment, the height of the cover region 18 which is a region of the brazing material 1]. covering the lead member 10 is controlled within a range from 40 to 99 of the distance between a proximate end of the lead member 10 nearest to the terminal lead-out electrode section 6 and a top end farthest from the terminal lead-out electrode section 6.

When the height of coverage 18 in a cross section of the lead member 10 is less than 40% of the distance between -10 -the proximate end 16 nearest to the terminal lead-out electrode section 6 and the top end 17 farthest from the terminal lead-out electrode section 6 (this distance will hereinafter be called the lead height in this specification) in the junction between the terminal lead-out electrode section 6 and the lead member 10, initial bonding strength of the lead becomes lower due to a small area of the bonding interface between the lead member 10 and the brazing material 11, and results in large variation. When the height of coverage of the brazing material 11 is in a range from 40 to 99% of the lead height as in the first embodiment, sufficient area of junction can be secured so as to ensure high initial bonding strength of the lead and the variability can be made small.

In case the lead member 10 has a round cross section as shown in Fig. 2, the lead height is equal to the diameter of the cross section.

[0019J In case the height of coverage 18 of the brazing material 11 covering the lead member 10 is larger than 99% of the lead height, cracks are likely to occur in the interface between the lead member 10 and the brazing material 11, thus resulting in a decrease in the lead bonding strength.

Specifically, in case the lead member 10 is covered by the brazing material over such en extent as the lead height -11 -exceeds 99% of the height of coverage 18, stress is generated in the interface between the lead member 10 and the brazing material 11 due to the difference in linear thermal expansion between the lead member 10 and the brazing material 11, thus causing cracks in the interface because the stress cannot be relieved. The brazing material 11 has a higher thermal expansion coefficient than the lead member 10. Specifically, cracks occur in the interface between the lead member 10 and the brazing material 11 when thermal cycle test is conducted on such a constitution as the lead member is covered by the brazing material over the entire circumference thereof.

[0020) When the height of coverage 18 is controlled in a range from 40 to 99% of the lead height, in contrast, since a part of the lead member 10 is not covered by the brazing material 11, stress generated in the interface between the lead member and the brazing material 11 due to the difference in thermal expansion between the lead member 10 and the brazing material 11 can be mitigated so that cracks is suppressed occur in the interface between the lead member 10 and the brazing material 11 during thermal cycle test.

[0021] In the ceramic heater, the height of coverage 18 is controlled preferably within a range from 60 to 99% of the lead height, in order to prevent the occurrence of cracks in -12 -the interface between the lead member and the brazing material during thermal cycle test more effectively.

[00221 The proportion of the height of coverage 18 to the lead height can be controlled by the wettability of the lead member 10 to the brazing material, more specifically by the kind of material and surface roughness of the lead member 10, the kind of material of the brazing material, joining temperature and atmosphere. According to the first embodiment, it is preferable to control by the surface roughness of the lead member 10, which makes it possible to control the proportion of the height of coverage in a predetermined range relatively easily and reliably.

[0023) Also, according to the first embodiment, it is preferable that there are voids 13 in the interface between the lead member 10 and the brazing material 11. When there are no voids in the interface between the lead member 10 and the brazing material 11, heat is transferred from the ceramic substrate 9 to the lead member 10 at a high rate during heating operation of the ceramic heater 1, thus making the surface temperature of the lead member too high. When there are voids 13 in the interface, heat transfer from the ceramic substrate 9 to the lead member 10 is impeded, thus making the surface temperature of the lead member lower than in the case -13 -where there are no voids. As a result, the existence of the voids 13 in the interface between the lead member 10 and the brazing material 11 decreases the thermal stress in the lunction and mitigates the deterioration of bonding strength of lead after thermal cycle test.

[0024] Measurements of the size of the void 13 and initial bonding strength of the lead showed that initial bonding strength of the lead and bonding strength of lead after thermal cycle test were high with no significant difference therebetween in case the size of the voids 13 was in a range from 0.1 to 200 pm, while the initial bonding strength of the lead and bonding strength of the lead after thermal cycle test were low in case the size of the voids 13 was larger than 200 pm and the initial bonding strength of the lead was high due to high surface temperature of the lead member 11 but bonding strength of lead after thermal cycle test becomes lower in case the size of the voids 13 was less than 0.1 pm.

[0025] In case the voids 13 were formed over a region larger than 40% of the interface, initial bonding strength of the lead was low. Accordingly, it is more preferable that voids 13 of sizes ranging from 0. 1 to 200 pm exist in a region of to 40% of the interface, in order to achieve lower surface temperature of the lead member, high initial bonding strength -14 -of the lead and high bonding strength of the lead after thermal cycle test.

In case there is not the diffusion layer 14 of the component of the lead member 10 into brazing material 11 in the first embodiment, initial bonding strength of the lead and bonding strength of lead after thermal cycle test become lower. When there is the diffusion layer 14 in the interface, the initial bonding strength of the lead becomes high. This is supposedly because diffusion of the component of the lead member 10 into brazing material 11 changed the state of a part of the interface from physical bonding into chemical bonding, thereby increasing the lead bonding strength.

Therefore, according to the present invention, it is preferable that the component of the lead member 10 is diffused into the brazing material 11.

[0026] In order to effectively increase the lead bonding strength, distance (thickness) of the diffusion layer 14 in the interface is preferably in a range from 0.1 to 30 pm, more preferably from 3 to 30 pm. When the diffusion layer 14 is less than 0.1 pm, the effect of increasing the lead bonding strength becomes smaller. When the diffusion layer is larger than 30 pm, significant portion of the component of the lead member 10 diffuses into the brazing material 11 leading to an increase in the hardness of the brazing -15 -material 11, and the lead bonding strength may become lower since cracks are likely to occur in the brazing material 11 after the thermal cycle test.

10027] In order to form the diffusion layer 14 stably and achieve sufficient anchoring effect so as to increase the lead bonding strength, arithmetic mean surface roughness Ra of the lead member 10 is preferably in a range from 0.05 to 5 pm. When arithmetic mean surface roughness Ra of the lead member 10 is less than 0.05 pm, thickness of the diffusion layer 14 may be limited to 0.05 pm, thus resulting in insufficient effect of increasing the bonding strength of lead after thermal cycle test. When arithmetic mean surface roughness Ra of the lead member 10 is larger than 5 pm, crack may grow from the lead surface due to thermal cycles of thermal cycle test thus resulting in breakage of the lead wire.

[00281 A method of manufacturing the ceramic heater 1 of the first embodiment will now be described.

[0029] The ceramic heater 1 is manufactured by a method including the steps shown in Fig. 3A to Fig. 3D.

[0030] First, a ceramic green sheet 23 is prepared and a -16 -through hole 27 for the via hole is formed in the ceramic green sheet 23 (refer to Fig. 3A) [0031] After filling the through hole 27 with an electrically conductive paste, an electrically conductive paste layer which constitutes the electrical conductor 24 and the lead-out section 25 is formed and dried (refer to Fig. 3B) (0032] Then the ceramic green sheet 23 is turned over and an electrically conductive paste layer which constitutes the metallizing layer 26 is formed on the back surface (refer to Fig. 3C) [0033] Then the ceramic green sheet 23 is turned over again, and is rolled around the ceramic core member 22 so as to prepare a green compact yet to be sintered (refer to Fig. 3D).

[0034] The green compact thus formed is fired at a temperature from 1500 to 1650 C in reducing atmosphere so as to obtain the ceramic substrate 9. Then after forming the plating layer 6b from Ni on the surface of the metallizirig layer 6a, as shown in Fig. 1, the lead member 10 is fixed by the brazing material 11, so as to obtain the ceramic heater 1.

[0035] The ceramic heater 1 may be formed from alumina, -17 -silicon nitride, aluminum nitride, silicon carbide, mullite or the like.

[00361 In the case of alumina, for example, such a composition S may be used that includes 88 to 951 by weight of A1203, 2 to 7% by weight of Si02, 0.5 to 3% by weight of CaO, 0.5 to 31 by weight of MgO and 0 to 31 by weight of Zr02. When the concentration of A1203 is less than that described above, higher content of glass component may cause significant migration when electric power is supplied. When the concentration of A1203 is higher than that described above, on the other hand, durability of the ceramic heater 1 may become lower due to insufficient content of glass component which diffuses into the metal layer of the heat generating resistive member 4 which is incorporated in the ceramic heater 1.

[00371 In the case of silicon nitride, such a composition may be used that includes 85 to 95% by weight of Si3N4, oxide of rare earth element such as Y203, Yb203 or Er203 in a proportion of 2 to 12% by weight, 0.3 to 2.0% by weight of A1203 and oxygen in such a quantity as the concentration of Si02 becomes 0.5 to 3% by weight. In the case of aluminum nitride, such a composition may be used that includes 85 to 97% by weight of A1N, oxide of rare earth element such as Y203, Yb203 -18 -or Er203 in a proportion of 2 to 8% by weight, 0 to 5% by weight of CaO and oxygen as an impurity in such a quantity as the concentration of A1203 becomes 0 to 1% by weight. In the case of mullite, such a composition may be used that includes 58 to 75% by weight of A1203, 25 to 42% by weight of Si02 and 1% by weight or less inevitable impurity.

[0038] The shape of the ceramic heater 1 may also be flat plate, as well as cylindrical or tubular shape.

[0039] The ceramic heater of the present invention is not limited to that described above, and various modifications can be made without departing from the substance of the present invention.

[0040] Second Embodiment A ceramic heater 100 according to the second embodiment of the present invention will now be described with reference to the accompanying drawings.

The ceramic heater 100 according to the second embodiment shown in Fig. 4 and Fig. 5 has such a constitution as the electrical conductor 4 is incorporated in the ceramic substrate 9 similarly to the first embodiment, and the metallizing layer 6a. connected to the electrode lead-out section 12 is formed on the electrode lead-out section 12 -19 -

V

which extends to the surface of the ceramic substrate 9, so that the lead member 10 is connected by the brazing material 11 onto the terminal lead-out electrode section 6 which is constituted from the metallizing layer 6a. A plating layer is formed on the metallizing layer 6a as required so as to constitute the terminal lead-out electrode section 6 from the metallizing layer 6a and the plating layer.

[0041] The ceramic substrate 9 may be made by forming a green sheet (which makes the sheet 3 when fired) by, for example, doctor blade process, forming the compact having cylindrical shape which would make the ceramic core member 2 by extrusion molding, and integrating these members. The ceramic substrate 9 may be formed from oxide ceramics such as alumina, mullite or forsterite, non-oxide ceramics such as silicon nitride or aluminum nitride, or the like. Among these, oxide ceramics is preferably used. In case the ceramic substrate 9 is made of alumina, for example, such a composition may be used that includes 88 to 95% by weight of A1203, 2 to 7% by weight of Si02, 0.5 to 3% by weight of CaO, 0.5 to 3% by weight of MgO and 1 to 3% by weight of Zr02. The material is not limited to alumina ceramics, and such materials as silicon nitride ceramics, aluminum nitride ceramics or silicon carbide ceramics may also be used.

[0042] -20 -The green sheet is provided with the electrical conductor 4 printed thereon by screen printing process, and the electrode lead-out section 12 is formed in the through hole which is formed in advance by punching through or other process at a predetermined position in the green sheet. The electrical conductor 4 and the electrode lead-out section 12 are formed from an element such as W, Mo or Re as the main component with an alloy or silicate or carbide of these metals such as TiN, WC, etc. added thereto. It is preferable that the electrical conductor 4 and the electrode lead-out section 12 are formed by controlling the proportions of these materials so that the electrical conductor 4 has a high resistance and the electrode lead-out section 12 has a low resistance, and are formed by separately screen printing.

[0043] In this stage, in order to eliminate the step between the green sheet and the electrical conductor 4 and put the green sheet in close contact with the cylindrical compact, it is preferable to apply a paste prepared from A1203 as the main component with Si02, MgO or the like, a binder and an organic solvent, by screen printing on the electrical conductor 4.

[00441 The compact which has been integrated is fired at a temperature from 1500 to 1650 C in reducing atmosphere so as -21 -to obtain the desired sintered member.

[0045) A paste including W as the main component is applied to the electrode lead-out section 12 of the sintered member and is baked in vacuum, so as to form the metallizing layer 6a.

The metallizing layer Ga is formed preferably from a metal having high melting point such as W, Mo or Re, and an alloy thereof as the electrically conductive material. The thickness of the metallizing layer 6a is preferably 10 pm or more. When the thickness is less than 10 pm, bonding strength between the electrode lead-out section 4 and the ceramic substrate 9 becomes lower, thus resulting tensile strength and durability of the lead member 10 become lower due to thermal cycles during operation. The thickness of the metallizing layer 6a is more preferably 15 pm or more, and further more preferably 20 pm or more. The thickness of the metallizing layer 6a has an influence on the tensile strength of the lead member 10 because the metallizing layer 6a is a porous sintered member formed from a metal having high melting point such as W, Mo or Re, where glass component included in the grain boundary of the ceramic substrate 9 diffuses into the pores and achieves anchoring effect to increase the strength. Therefore, the larger the thickness of the metallizing layer Ga, the higher the tensile strength of the lead member 10 which is bonded.

-22 -[0046] After forming the nietallizing layer 6a, the metallizing layer 6a may be plated, preferably with a plating material including Ni as the main component.

[0047] Then the lead member 10 is attached to the metallizing layer 6a by brazing in vacuum.

[00481 The lead member 10 is preferably made of an alloy based on Ni or Fe-Ni which has high heat resistance, because the lead member 10 is heated and may be deteriorate by the heat transferred from the electrical conductor 4 during operation.

When the lead member 10 is made of an alloy based on Ni or Fe-Ni, in particular, mean crystal grain size of the material is preferably not larger than 400 pm. When the mean grain size is larger than 400 kim, the lead member may be fatigued in the vicinity of the brazed portion due to the vibration and thermal cycles during operation, thus resulting in theoccurrence of cracks. In case other material is used, too, grain size of the lead member 10 larger than the thickness of the lead member 10 is not desirable since it causes the stress to be concentrated in the grains located near the interface between the brazing material 11 and the lead member thus resulting in cracks. Mean crystal grain size of the lead member 10 can be controlled to 400 im or smaller by -23 -keeping the temperature of brazing as low as possible and the processing time shorter.

[0049] The present invention is characterized by the structure of the brazing material 11. Specifically, as shown in Figs. 6 to 9, the brazing material includes at least two kinds of metal, preferably two kinds of metal which are included in speckled configuration or scattered distribution. In this specification, the phrase "speckled configuration or scattered distribution" means that said at least two kinds of metal exist in such a form that they can be distinguished from each other under a microscope or the like. Fig. 6 shows an example where a lead member lOa having a rectangular cross section is used. The metals included in speckled configuration or in scattered distribution are preferably two kinds selected from the group 10 elements (Ni, Pd, Pt, etc.) or group 11 elements (Cu, Ag, Au, etc.). This is because the elements of group 10 and group 11 have relatively low diffusion coefficient which suppresses the metals from diffusing, and therefore uniform phase is not readily formed and low specific electrical resistance and high electrical conductivity can be obtained.

[0050] The brazing material 11 may be Ag-Cu brazing material, Au-Cu brazing material or the like, while Ag-Cu brazing -24 -material is preferably used.

[0051] In order to have at least two kinds of metals (for example, Ag and Cu) included in speckled configuration or in scattered distribution in the brazing material 11 after brazing the lead member 10 onto the metallizing layer 6a, it is necessary to control the holding time during brazing of the brazing material 11. For example, when BAg-8 (JIS Z3261) among the brazing materials based on Ag-Cu is used, it is preferable to hold the brazing temperature from 780 to 800 C for a period of 5 to 40 minutes, since the melting point of the BAg-8 is about 780 C. By setting the duration in this range, Ag and Cu can be included in speckled configuration or scattered distribution in the brazing material 11.

[0052] When the brazing material 11 constituted from Ag and Cu is held at the brazing temperature for 60 minutes or more, it is likely that Ag and Cu diffuse into each other so as to form an alloy in which Ag and Cu are dissolved uniformly.

When Ag and Cu are dissolved uniformly, resistance of the brazing material becomes higher than that of the speckled structure in which electric current flows selectively through Ag of lower resistance, thus generating heat in the brazing material and there remains a problem in the bonding strength after enduring an operation. Therefore, in order to form the -25 -speckled structure of Ag and Cu, it is preferable to hold the brazing temperature for a period of less than 60 minutes.

The period of holding the brazing temperature must be at least 5 minutes in order to sufficiently melt the brazing material.

[0053] In the prior art, duration of holding the temperature has not been controlled and deviated from the range described above, thus resulting in uniform melting. Fig. 12 is a photograph showing the cross section of the brazed portion by means of the brazing material 111 in the ceramic heater shown in Fig. 11. The brazing material 111 is based on Ag-Cu or Au-Cu constituted from two or more kinds of metal. In the cross section of the brazed portion after brazing operation, constituent metals are not segregated and distributed uniformly as shown in Fig. 12. According to the present invention, in contrast, speckled structure can be obtained by controlling the holding time within the range described above so as to decrease the temperature below the brazing temperature before the metals are melted uniformly.

[0054] Further, in order to form the speckled structure of Ag and Cu in the brazing material, it is preferable to control the Ag content within a range from 60 to 90% by weight, more preferably from 70 to 75% by weight, while keeping the -26 -brazing temperature holding time to less than 60 minutes.

This brings the melting point of the Ag-Cu brazing material near to the eutectic point (the temperture at which Ag and Cu melt and neither Ag nor Cu form solid), so that the temperature at which the Ag and Cu is in liquid phase becomes lower, thus making it possible to lower the brazing temperature and decrease the residual stress after brazing operation.

[0055] As the speckled structure is formed in the brazing material 11, when electric power is supplied through the lead member 10 to the ceramic heater 100, electric current flows selectively through Ag of lower resistance, so that resistance of the brazing material 11 decreases and temperature of the brazing material 1]. is suppressed from rising, thus improving the reliability of the junction.

[0056] As shown in Fig. 7 which is an enlarged photograph of region E (a region in the vicinity of the interface between the brazing material and the metallizing layer) of Fig. 6, in Fig. 8 which is an enlarged photograph of region D (a region in the vicinity of the interface between the brazing material and the metallizing layer, and the interface between the brazing material and the lead member) of Fig. 6, and in Fig. 9 which is an enlarged photograph of region C (a region in -27 -the vicinity of the interface between the brazing material and the lead member) of Fig. 6, it is preferable that a metal layer having Young's modulus of lBOGpa or less is formed not in speckled structure in a portion which adjoins at least one of interface between the brazing material 11 and the metallizing layer 6a and interface between the brazing material 11 and the lead member 10. For example, Cu layer 6c is formed as the metal layer when the brazing material 11 consists of Ag and Cu. Since the Cu layer 6c which adjoins the interface between the brazing material 11 and the inetallizing layer 6a functions as a layer that relieves the residual stress after brazing, residual stress in this portion is reduced, so that lead bonding strength by brazing is improved and the bonding strength after enduring an operation is improved.

[0057] In order to form the Cu layer 6c, it is effective to apply Cu plating to a portion where the metallizing layer 6a and the lead member 10 make contact with the brazing material 11 by brazing. Since Cu has lower surface tension than Ag, Cu is likely to be wetted selectively at a portion where the brazing material 11 is melted and makes contact during brazing operation. This makes it possible to form the Cu layer 6c in the portion which adjoins the interface which contacts the brazing material between the metallizing layer -28 - 6a and the lead member.

[0058] The Cu layer 6c has surface irregularity on the side opposite to the interface with the metallizing layer 6a. The thickness of the protruding portion is preferably 10 pm or less, and the total thickness of the Cu layer 6c including the protrusion is preferably 20 pm or less. The Cu layer 6c forms irregularity in the interface with a different material which makes contact therewith and the irregularity functions as the stress relieving layer, so as to improve the bonding strength after enduring an operation.

While surface irregularity of the Cu layer 6c has been described as a preferable example, the present invention is not limited to Cu. The present invention can be applied to a case in which a metal layer other than Cu exists in the interface where thickness of the entire layer including protrusion of which height is 10 pm or less is 20 pm or less, in which case the bonding strength in the interface can be improved, too, so that reliability and durability can be improved.

[0059] However, the thickness of the protruding portion of the Cu layer of 10 pm or more and total thickness including the protrusion of 20 pm or more are not preferable since such sizes leads to lower bonding strength of the brazing material.

-29 -In this case, it is preferable to hold the brazing material melting temperature for a period of 5 to 20 minutes.

[00601 While the metallizing layer 6a is baked onto the ceramic substrate 9 in vacuum, it is preferable to use an electrically conductive material having low thermal expansion coefficient in order to reduce the residual stress due to the difference in thermal expansion coefficient with the ceramic substrate 9. Thermal expansion coefficient of the main component of the metallizing layer 6a is more preferably 5.5 x 106/ C or less. Specifically, W or Mo having the property described above is preferably used as the main component.

This relieves the residual stress generated in the interf ace between the ceramic substrate 9 and the metallizing layer Ga during heating of the metallizing layer Ga. Since such a metal is diffused in the brazing material, thermal expansion coefficient of the brazing material decreases and the residual stress generated in the interface between the brazing material and the metallizing layer after brazing can be decreased, so that reliability of bonding between the electrode lead-out section and the brazing material and between the electrode lead-out section and the lead member can be improved, thus improving the reliability and durability of the ceramic heater.

[0061] -30 -However, significant amount of residual stress is generated between the inetallizing layer 6a and the brazing material 11, due to the very large difference in thermal expansion coefficient between these materials, after brazing.

Therefore, it is necessary to decrease the thermal expansion coefficient of the brazing material. In order to decrease the thermal expansion coefficient of the brazing material, main component of the metallizing layer 6a which has a low thermal expansion coefficient may be caused to diffuse into the brazing material. This can be achieved by applying heat treatment after brazing. The heat treatment is preferably carried out at a temperature lower than the melting point of the brazing material, more preferably in a range from 700 to 750 C, in a reducing atmosphere which includes hydrogen. The heat treatment causes metals or alloys having thermal expansion coefficient of 5.5 x 106/ C or less to diffuse into the brazing material, thereby reducing the thermal expansion coefficient of the brazing material and improving the strength of the brazed portion after enduring an operation.

It is preferable to form a plating layer of Ni on the surface of the brazing material 11, in order to protect the brazing material 11 from corrosion and improve durability to high temperatures. In order to achieve protective function of the Ni plating layer, grain size of the crystal that forms -31 -t the plating layer is preferably controlled to 10 pm or less, which enables it to form the plating layer of high density on the surface of the brazed portion. The plating layer on the surface can be made further denser and Ni can be caused to diffuse to the inside of the brazing material 11 when the grain size is controlled to 5 pm or less. Since Ni has high Young's modulus of 250 MPa, Ni diffused to the inside of the brazing material 11 increases the hardness of the inside of the brazing material 11 and improves the strength of the inside of the brazing material 11, thus improving the initial bonding strength and bonding strength after thermal cycle test between the electrode lead-out section and the lead member and between the electrode lead-out section and the brazing material. As a result, reliability and durability of the ceramic heater can be improved.

[00621 The plating layer is preferably formed by electroless Ni plating based on boron. While there are electroless plating processes based on phosphorus in addition to that based on boron, electroless Ni plating based on boron is typically employed in case the plating layer is expected to be subjected to high temperatures.

[0063] Fig. 10 is a perspective view showing an example of heating iron which uses the ceramic heater 1 or the ceramic -32 -heater 100 of the present invention. The heating iron is used to treat hair while heating and pressing, by holding the handle members 31 with the hair pinched by arms 32 located at the distal end. The arm 32 has the ceramic heater 1 or the ceramic heater 100 inserted therein, and a metal plate 33 such as aluminum, a metal plate coated on the surface thereof or a ceramic plate is provided on the portion which makes contact with the hair. The arm 32 is provided with a cover made of heat resistant plastics on the outside thereof, in order to prevent human body from being burned.

Example 3.

[0064] The ceramic heater of the present invention was made by the method described below.

First, a stock material was prepared from aluminum as the main component with 6% by weight of Si02, 2% by weight of MgO, 2% by weight of CaD and 1.5% by weight of Zr02 added as sintering assisting agent. The stock material thus prepared was used to form the ceramic core member 2 having outer diameter of 15mm and the ceramic green sheet 23 having thickness of 800 lim, by extrusion molding and tape casting processes, respectively.

[0065] Then the electrical conductor 24, the lead-out section 25 and the electrode lead-out section 28 made of tungsten (W) -33 -were printed on one of the principal surfaces of the ceramic green sheet 23. The metallizing layer 26 was printed on the back side of the electrode lead-out section 28 at the end thereof, and the through hole for the via hole was formed in the metallizing layer 26. The through hole was filled with a paste consisting of tungsten (W) thereby forming the via hole 7, while the electrode lead-out section 28 and the metallizing layer 26 were connected with each other.

[0066) The green compact thus prepared was fired so as to sinter at a temperature of 1600GC in reducing atmosphere, and the plating layer 6b was formed from Ni to a thickness of 5 pm by electroless plating on the surface of the metallizing layer 6a.

The sample made as described above was to be provided with the lead member 10 brazed on the terminal lead-out electrode section 6. In Example 1, the lead member 10 was bonded while changing the quantity of the brazing material 11 made of Ag, so as to make test samples having covering height 18 of the brazing material on the surface of the lead member varying in a range from 20 to 100% of the lead height.

The initial lead bonding strength, lead bonding strength after 3000 cycles of thermal cycle test (25 C for 3 minutes and 400 C for 3 minutes) and occurrence of cracks in the interface were checked on these test samples.

-34 -[0067] The lead bonding strength was measured by pulling the lead member 10 in a direction perpendicular to the terminal lead-out electrode section 6.

[0068] Results of checking the covering height 18 on the surface of the lead member 10, initial lead bonding strength and lead bonding strength after thermal cycle test (3000 cycles) are shown in Table 1.

[0069]

Table 1

Ratio bonding strength (N) (Covering Occurrence After No. height to of crack in Judgment Initial thermal lead interface cycle test ________ height) ____________ ___________ ____________ _________ 1 20 60 31 None D 2 40 109 57 None B 3 60 118 61 None A 4 80 120 63 None A 99 123 62 None A 6 100 124 29 Occurred D Samples Nos. 1 and 6 are out of the scope of the present invention. Data after thermal cycle test in Table 1 are those measured after 3000 cycles of thermal cycle test.

The value of covering height to lead height in Table 1 is the value measured at the highest portion of coverage relative to the lead height in the longitudinal direction of the lead member.

[0070] -35 -Sample having initial lead bonding strength of 85 N or higher and lead bonding strength after thermal cycle test of to below 50 N was evaluated as "C", 50 to below 60 N was evaluated as "B", and 60 N or higher was evaluated as "A".

[0071] As can be seen from Table 1, good results were obtained with high mean values of the initial lead bonding strength and lead bonding strength after thermal cycle test when the covering region 18 to the surface of the lead member 10 was in a range from 40 to 99% in Samples Nos. 2 to 5 which were within the scope of Example 1 of the present invention.

Among these, very good results were obtained when the covering region 18 to the surface of the lead member 10 was in a range from 60 to 99% in Samples Nos. 3 to 5.

[0072] The initial lead bonding strength and lead bonding strength after thermal cycle test were low when the covering region 18 to the surface of the lead member 10 was 20% in sample No. 1 which was Comparative Example. In sample No. 6 where the covering region 18 to the surface of the lead member 10 was 100%, lead bonding strength after thermal cycle test was low although the initial lead bonding strength was high.

[0073] Supposedly lead bonding strength showed smaller -36 -

I

decrease because there was no crack in the interface when the covering region 18 to the surface of the lead member 10 was in a range from 40 to 99% in Samples Nos. 2 to 5 which were within the scope of Example 1 of the present invention.

10074] In the case of sample No. 6 which was Comparative Example where the covering region 18 was 100%, it is considered that lead bonding strength decreased because cracks occurred in the intert ace.

10075] Crack generated in the interface is considered to occur due to the difference in thermal expansion coefficient between the lead member 10 and the brazing material 11. Thus the sample in which the covering region 18 was 100% is considered likely to experience cracks in the interface as the stress generated due to the difference in thermal expansion coefficient is difficult to mitigate.

[0076] Relationship with the size of voids 13 formed in the interface, proportion of the interface occupied by the voids, initial lead bonding strength, lead bonding strength after thermal cycle test and surface temperature of lead member when the ceramic heater was heating to 800 C was studied.

Sample having initial lead bonding strength of 85 N or higher and lead bonding strength after thermal cycle test of 35 to -37 -below 50 N was evaluated as "C", 50 to below 60 N was evaluated as "B", and 60 N or higher was evaluated as "A" with the results shown in Table 2.

[0077]

Table 2

bonding strength (N) ________ Surface Ratio Size After temperature (Proportion of thermal of lead No. () of. Judgment void. . cycle member when voids in Initial (i.m) test heating to interface) (3000 800 C ______ ____________ _______ _________ cycles) ____________ _________ 7 0 0 121 48 157 C 8 1 250 110 47 151 C 9 1. 200 119 56 146 B 1 50 125 57 143 B 11 1 0.1 121 59 141 B 12 20 250 98 45 144 C 13 20 200 112 62 136 A 14 20 50 119 65 135 A 20 0.1 117 63 135 A 16 40 250 94 47 133 C 17 40 200 104 62 132 A 18 40 50 110 64 125 A 19 40 0.1 108 66 126 A 50 250 87 41 130 C 21 50 200 90 43 127 C 22 50 50 92 43 120 C 23 -50 0.1 93 47 119 C All samples had covering region of 60%.

[0078] very good results with lead bonding strength after thermal cycle test of GON or higher were obtained when the sizes of the voids 13 generated in the interface were in a range from 0.1 to 200 1.lm and proportion of the interface -38 -occupied by the voids 13 was in a range from 20 to 40% in Samples Nos. 13 to 15 and 17 to 19 which were Example 1 of the present invention.

[0079] Good results with lead bonding strength after thermal cycle test of 50 to 60N were obtained when the sizes of the voids 13 generated in the interface were in a range from 0.1 to 200 pm and proportion of the interface occupied by the voids 13 was in a range from 0.1 to below 20% in Samples Nos. 9 to 11. This is supposedly because the voids 13 formed in the interface impeded the transfer of heat from the ceramic substrate 9, thus lowering the surface temperature of the lead member.

[00801 In sample No. 7, lead bonding strength after thermal cycle test was low because surface temperature of the lead member was high. In Samples Nos. 20 to 23 where the voids 13 occupied high proportion of 50% of the interface, surface temperature of the lead member was -20 C or lower but the bonding strength was low. The lead bonding strength of Samples Nos. 12 and 16 were low supposedly because the size of the voids 13 was as large as 250 tim.

10081] Samples were made while changing the temperature of bonding and duration and changing the distance between the -39 -interface and the diffusion layer 14. The initial lead bonding strength and lead bonding strength after thermal cycle test of the samples were measured, and sample having the initial lead bonding strength of 85 N or higher and lead bonding strength after thermal cycle test of 35 to below 50 N was evaluated as "C", 50 to below 60N was evaluated as "B", and 60 N or higher was evaluated as "A" with the results

shown in Table 3.

[0082]

Table 3

Thickness bonding strength (N) of After No. . . Judgment diffusion Initial thermal ____________ layer (j.im) ____________ cycle _____________ 24 0 94 41 C 0.1 112 52 B 26 3 114 63 A 27 5 118 66 A 28 15 120 62 A 29 30 119 65 A 45 118 38 C [0083] Very good results with lead bonding strength after thermal cycle test of 60 N or higher were obtained when the distance between the interface and the diffusion layer 14 was in a range from 3 to 30 I.lm in Samples Nos. 26 to 29 which were Example 1 of the present invention. Good result with lead bonding strength after thermal cycle test from 50 to below 60 N was obtained when the distance between the -40 -

V

interface and the diffusion layer 14 was 0.1 I.lm in Samples No. 25. This is supposedly because diffusion of the component of the lead member into the brazing material changed the state of the interface from physical bonding into chemical bonding, thereby increasing the lead bonding strength.

[0084] Sample No. 24 which included no diffusion layer at all showed low initial lead bonding strength and lead bonding strength after thermal cycle test. In sample No. 30 which had diffusion layer 14 of 45 pm, since significant portion of the component of the lead member diffused into the brazing material 11, hardness of the brazing material 11 became higher and cracks occurred in the brazing material 11 after thermal cycle test, thus resulting in low lead bonding strength.

[0085] Arithmetic mean surface roughness Ra of the lead member which is used to bond, the initial lead bonding strength and the lead bonding strength after thermal cycle test were measured. Sample having initial lead bonding strength of 85 N or higher and lead bonding strength after thermal cycle test of 35 to below 50 N was evaluated as "C", 50 to below 60 N was evaluated as "B", and 60 N or higher was evaluated as "A" with the results shown in Table 4.

[0086] -41 -

Table 4

Arithmetic Thickness bonding strength (N) mean of After No. surface diffusion. . thermal Judgment Initial roughness layer cycle _________ Ra(pm) (kim) _________ test _________ 31 0.01 0.05 104 43 C 32 0.05 3 116 63 A 33 0.5 9 123 62 A 34 1.0 10 119 65 A 2.0 9 123 63 A 36 3. 0 9 115 62 A 37 5.0 12 117 61 A 36 (Lead 38 7.0 9 119 was C ___________ __________ broken) ___________ Data after thermal cycle test are those measured after 3000 cycles of thermal cycle test.

[0087] Very good results were obtained with lead bonding strength after thermal cycle test of 60 N or higher when the arithmetic mean surface roughness Ra of the lead member 10 was in a range from 0.05 to 5 pm in Samples Nos. 32 to 37 which were within the scope of Example 1 of the present invention. The results show such a tendency that it becomes easier to form the diffusion layer 14 from the interface as the arithmetic mean surface roughness Ra of the lead member becomes larger, and such a tendency that lead bonding strength after thermal cycle test becomes higher due to the anchoring effect as the arithmetic mean surface roughness Ra of the lead member 10 becomes larger.

-42 -[0088] In sample No.' 31 where the distance between the interface and the diffusion layer 14 was small and the arithmetic mean surface roughness Ra of the lead member 10 was small, it is considered that lead bonding strength after thermal cycle test was low because sufficient anchoring effect could not be achieved. In sample No. 38, although the distance between the interface and the diffusion layer was 9 urn and the lead bonding strength showed a sufficient value, the arithmetic mean surface roughness Ra of the lead member was as large as 7 u.lm. Thus crack grew from the surface of the lead member 10 during the thermal cycle test, and the lead was broken at 36 N.

Example 2

[0089] A stock material was prepared from A1203 as the main component with 10% by weight or less in total of Si02, CaO, MgO and 2r02 added. The stock material was used to form the ceramic green sheet by doctor blade process. Then the electrical conductor 4 and the electrode lead-out section 12 were formed by printing a paste made of W on the surface of the ceramic green sheet.

[00901 A cylindrical compact was made by extrusion molding process, and the ceramic sheet with the electrical conductor -43 - 4 printed thereon was rolled around the cylindrical compact tightly and was fired at a temperature of 1600 C in reducing atmosphere, so as to prepare 20 pieces each of the ceramic heaters 100.

[0091] The electrode lead-out section 12 was coated with a electroless Ni plating having thickness of 5 pm. A paste consisting of W as the main component was applied to the electrode lead-out section 12, and was baked in vacuum.

[0092] Ni wire having diameter of 1.0mm was brazed as the lead member using Ag-Cu brazing material (BAg-B).

[0093] The brazing operation was carried out while changing the brazing temperature as 780 C, 800 C and 820 C and changing the holding time as 5 minutes, 10 minutes, 40 minutes and 60 minutes.

(0094) In order to evaluate the durability in continuous operation, tensile strength was measured before and after continuous operation at 400 C for 800 hours. In the tensile strength test, the end of the lead member 4 was pulled in a direction perpendicular to the principal surface of the ceramic heater 100 and the force at which the lead member was pulled off was measured. Two pieces sampled from each lot -44 -were observed on the cross section thereof under an electron microscope to examine the structure within the brazing material. The results are shown in Table 5.

[0095]

S Table 5

Layers in Tensile Speckles Initial strength in interface Brazing Holding tensile after brazing of No. temperature time ( C) (Minutes) strength durability material brazing material (N) test (N) No Ag/cu *39 780 5 340 178 existence alloy 780 10 345 303 Existence Cu 41 780 40 342 311 Existence Cu No Ag/Cu *42 780 60 339 188 existence alloy No Ag/Cu *43 800 5 338 191 existence alloy 44 800 10 341. 307 Existence Cu 800 40 345 305 Existence Cu No Ag/cu *46 800 60 337 183 existence alloy -No Ag/Cu *47 820 5 344 188 existence alloy 48 820 10 348 302 Existence Cu 49 820 40 339 307 Existence Cu No Ag/Cu *50 820 60 343 173 existence alloy Layers in interface of the brazing material are the layers located in the interface between the metallizing layer and the brazing material and in the interface between the lead member and the brazing material.

Samples marked with * are those out of the scope of the present invention.

[00961 -45 -As can be seen from Table 5, tensile strength after the durability test decreased to 200 N or lower in Samples Nos. 39, 42, 43, 46, 47 and 50 where the speckled structure as shown in Figs. 7 to 9 was not observed in the brazing material. In contrast, high tensile strength of 300 N or more was achieved in Samples Nos. 40, 41, 44, 45, 48 and 49 where the speckled structure as shown in Figs. 7 to 9 was observed.

-46 -

Claims

I a

CLAIMS

1. A ceramic heater comprising: a ceramic substrate having an electrical conductor embedded therein and a metallizing layer electrically S connected with the electrical conductor; and a lead member joined with the metallizing layer by means of a brazing material, wherein a region of the brazing material covering the lead member is controlled within a range from 40 to 99% of the distance between a proximate end of the lead member that is nearest to the metallizing layer and a top end that is farthest from the metallizing layer.

2. The ceramic heater according to claim 1; comprising a void having diameters ranging from 0.1 to 200 pm in the interface between the lead member and the brazing material.

3. The ceramic heater according to claim 2; wherein a contacting area is reduced to in a range from 60 to 99% of the interface by the voids.

4. The ceramic heater according to claims 2 or 3; wherein a component of the lead member is diffused into the brazing material and a depth of the diffusion is in a range from 0.lpm to 3Opm.

-47 - 5. The ceramic heater as in one of claims 1 to 4; wherein an arithmetic mean surface roughness Ra of the lead member is in a range from 0.05 to 5 urn.

6. A ceramic heater comprising: a ceramic substrate having an electrical conductor embedded therein and a metallizing layer electrically connected with the electrical conductor; and a lead member joined with the metallizing layer by means of a brazing material, wherein the brazing material includes at least two kinds of metal and said at least two kinds of metal exist in the brazing material in such a form that they can be distinguished from each other.

7. The ceramic heater according to claim 6; wherein said at least two kinds of metal are selected from a group consisting of the group 10 metals and the group 11 metals.

8. The ceramic heater according to claimS 6 or 7; wherein one of said at least two kinds of metal is a first metal having a Young's modulus of 18OGPa or less, and at least one interface of an interface between the brazing material and the metallizing layer and an interface between the brazing material and the lead member has the first metal.

-48 - 9. The ceramic heater according to claim B; wherein the first metal has a surface irregularity on the side opposite to an interface with the lead member or an interface with the metallizing layer, and wherein a height of a protruding portion is 10 pm or less and the total thickness of the layer including the protrusion is 20 pm or less.

10. The ceramic heater as in one of claims 6 to 9; wherein the metallizing layer has a metal having a thermal expansion io coefficient of 5.5 x 106/ C or less and as the main component the metal diffused into the brazing material.

11. The ceramic heater as in one of claims 6 to 10; wherein Ni is diffused into the brazing material.

12. A heating iron comprising a ceramic heater as in one of claims 1 to 11 as heating means.

-49 -