JP2000223247A - Ceramic heater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of a crack in a ceramic heater and the increase of the resistance of a heating part which are attributable to heat stress due to a temperature difference caused by the generation of a large temperature gradient in the vicinity of the heating part when the ceramic heater is rapidly heated. SOLUTION: In this heater 1, a heat generating resistor 11 has a heating part 4 and a braking part 5 having a resistance-temperature coefficient larger than the thereof. In this case, both of them are wired in series with each other, the ratio of the resistance of the heating part 4 to that of the braking part 5 is set in the range of 10:1-3:1, and a distance (a) between the heat generation part 4 and the braking part 5 is set within 20 mm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic heater used for a heater for an air-fuel ratio detection sensor, a heater for a carburetor, a heater for hot water, and the like for an automobile.

[0002]

2. Description of the Related Art Conventionally, an alumina ceramic heater made of a high melting point metal such as W or Mo has been generally used in ceramics containing aluminum oxide as a main component (JP-A-63-9860, 63). -58479).

For example, when manufacturing a cylindrical ceramic heater, ceramic ceramic rods 2 and ceramic green sheets 3 are prepared as shown in FIGS. 6 and 7, and W, M
After forming a heat generating portion 4 and a lead lead portion 6 by printing a paste of a high melting point metal such as o, the ceramic green sheet 3 is wound around the circular ceramic rod 2 so that the surface on which these portions are formed is inside. The ceramic heater 1 can be obtained by attaching and integrating the whole by firing.

FIG. 5 shows a pattern diagram of the heating resistor 11 built in the ceramic heater.
On the ceramic green sheet 3, a lead lead-out portion 6 is directly connected to the heat generating portion 4, and a through hole 7 is formed at the end of the lead lead-out portion 6, and the electrode pad 8 on the back surface and the lead lead-out portion 6 are connected by the through hole 7. It is connected. Conductive paste is injected into the through holes 7 as needed.

The heating resistor 11 formed on the ceramic green sheet 3 has a narrower line width at the front end side to form a meandering heat generating portion 4, and a rear end portion has a larger line width to form a lead extraction portion 6. The thickness of the heat generating portion 4 is set to about 10 μm to facilitate screen printing. Further, an electrode pad 8 is formed on the back side of the ceramic green sheet 3, and a through hole is formed between the lead extraction portion 6 and the electrode pad 8 to provide conduction. In the final ceramic heater 1, the lead wire 10 is joined to the electrode pad 8 exposed on the side surface by brazing or press-contacting, and power is supplied from the lead wire 10.

A silicon nitride ceramic heater is also used as a heater for high temperatures of 1000 ° C. or higher. The structure of this heater is such that a heating element made of a refractory metal wire or the like is embedded in a silicon nitride ceramic, and both ends of the heating element are exposed on the surface to form a lead extraction section. The lead extraction section is made of a brazing material such as silver. (JP-B-62-19034, JP-B-63-5135).
No. 6).

[0007] These ceramic heaters are excellent in corrosion resistance and durability, and are capable of rapid temperature rise. Therefore, they heat heaters for ignition of various combustion equipment such as oil fan heaters, heaters for fuel vaporizers, and fluids such as water. For various types of sensors such as a fluid heating heater, an oxygen sensor, and a measuring device.

In an oxygen sensor for an automobile, a system for heating the oxygen sensor with a ceramic heater is used to rapidly heat the oxygen sensor to an operating temperature at the time of a cold start. In recent years, it has been necessary to improve the rising characteristics at the time of cold start with the tightening of exhaust gas regulations, and a ceramic heater with high durability that can be used even at a high temperature of 800 ° C. or more has been demanded. However, if the heating value of the ceramic heater is increased and the heating time is shortened, an overshift of the temperature at the time of cold start occurs, and the electrode of the sensor is damaged, the durability of the ceramic heater is reduced, and There has been a problem that the temperature of the pad rises and the resistance of this portion increases to cause disconnection.

In order to cope with such a problem, as disclosed in Japanese Patent Application Laid-Open No. Hei 8-2738813, "an arbitrary heating element which is integrally formed with an electrode extraction portion on a ceramic sheet containing aluminum nitride as a main component. A ceramic heater in which a heat pattern having a shape and thickness is printed and a conductive material having a larger temperature resistance coefficient than the heating element is connected in series with the heating element in the heating pattern serving as the heating element has been proposed. I have. Also, Japanese Patent Application Laid-Open No. 5-343
No. 13 also discloses an example of "a ceramic heater made of aluminum oxide using a nickel chromium alloy for the first heating element and tungsten for the second heating element".

FIG. 8 is a development view of the ceramic heater 1 having such a built-in braking section 5. A heating portion 4, a breaking portion 5, and a lead lead portion 6 forming a heating resistor 11 on a ceramic green sheet 3 are formed so as to be connected in series, and are closely adhered to the periphery of the ceramic rod 2 so that these are inside. After that, 1500 ~ 1600 ℃
And the ceramic heater 1 is obtained. To raise the temperature of the ceramic heater 1 to 900 ° C. in about 5 seconds,
It is necessary to reduce the length of the heating section 4 to about 5 mm. Then, the breaking portion 5 is extended from the vicinity of the heating portion 4 to the vicinity of the electrode pad portion 8 so that the braking portion 5 is in series with the heating portion 4.

[0011]

However, in a conventional ceramic heater having no built-in braking portion as shown in FIGS. 6 and 7, the length of the heating portion 4 is reduced to about 5 mm for rapid temperature rise, and the ceramic heater 1 Is rapidly heated to 900 ° C. for about 5 seconds, a large temperature gradient is generated in the vicinity of the heat generating portion 4. This temperature gradient is 80 to 4 seconds after heating due to the temperature difference between the highest heat generating portion and the portion 10 mm away from the highest heat generating portion.
It reaches as large as 0 ° C. The thermal stress due to this temperature difference,
Cracks may occur in the ceramic heater 1 or the heating section 4
However, there is a problem that the resistance increases. 900 ° C
If the temperature rises rapidly in 5 seconds, the maximum temperature of the heating section 4 rises to about 1200 ° C. due to the overshift of heat generation, so that the resistance of the heating section 4 further increases.

FIG. 9 shows the temperature rise characteristics of the ceramic heater. As can be seen from the figure, the highest temperature part is 900 for 5 seconds.
When the temperature is raised to 100 ° C., the temperature at the point B 10 mm from the highest heat generating part A is about 100 ° C.
It can be seen that a temperature difference of 0 ° C. has occurred.

On the other hand, in the ceramic heater 1 shown in FIG. 8, the temperature rise of the heat generating portion 4 is restricted by the braking portion, and the problem of the overshift can be solved, but the braking portion 5 is moved from the vicinity of the heat generating portion 4. The heating center of the braking part 5 is separated from the heating part 4 because it is formed long to the vicinity of the electrode pad part 8.
Since no consideration is given to the ratio between the resistance value of the heating portion 4 and the resistance value of the braking portion 5, there is a problem that it cannot contribute to the mitigation of the temperature gradient generated near the highest temperature portion of the heat generating portion 4. Also,
In the conventional ceramic heater having a built-in braking portion, the braking portion 5 is attached to the vicinity of the electrode pad portion 8. Is 4
Since the electrode pad 8 is heated to a temperature of 00 ° C. or more, the metallization of the electrode pad 8 is oxidized, resulting in a problem of disconnection. This tendency increases as the resistance ratio of the braking section 5 to the heating section 4 increases.

[0014]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that a ceramic heater in which a heating resistor mainly composed of a high melting point metal such as W, Mo, and Re is embedded in a ceramic substrate. The heat generating resistor includes a heat generating portion and a braking portion having a larger temperature coefficient of resistance than the heat generating portion, and both are wired in series, and the resistance ratio between the heat generating portion and the braking portion is 10: 1 to 1. The ratio is 5: 1, and the distance between the heat-generating portion and the breaking portion is formed to be within 20 mm, so that the temperature distribution of the heat-generating portion is relaxed and a ceramic heater excellent in thermal shock and durability is supplied. I found that it became possible.

Thus, at the time of a cold start, a large applied voltage is applied to the heat generating portion having a small temperature coefficient of resistance (hereinafter abbreviated as TCR) to contribute to the temperature rise of the heat generating portion. Since the voltage applied to the tip portion gradually decreases as the temperature increases, it is possible to reduce the time required to raise the temperature at the time of a cold start and at the same time to prevent excessive temperature rise.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. FIG. 1 is a development view of a ceramic heater 1 according to the present invention. Ceramic green sheet 3
The heating part 4 is formed on the upper part, and the braking part 5 is formed so as to be connected in series via the connection part 9. The heat generating section 4 has a temperature coefficient of resistance of 1000 to 2000 p.
pm / ° C. paste is formed by printing, and the braking part 5 has a temperature coefficient of resistance of 3000 to 4500 pp.
An m / ° C. paste is printed.

In the present invention, by setting the distance a between the heat generating portion 4 and the breaking portion to 20 mm or less, the temperature difference is reduced by the heat generated by the braking portion 5 and can be reduced to 600 ° C. or less. As a result, it is possible to prevent cracks occurring in the ceramic heater 1 and an increase in resistance of the heat generating portion 4. If the distance is 20 mm or more, the temperature gradient near the heat-generating portion 4 becomes large when the heat-generating portion 4 generates heat. Therefore, cracks are generated in the ceramic due to repeated heat generation, and the heat-generating body deteriorates to increase resistance. . If the distance is kept within 20 mm, the temperature gradient near the heating resistor is alleviated due to the heat generated by the braking portion 5, so that cracks and an increase in the resistance of the heating portion 4 can be prevented.

A conventional ceramic heater 1 shown in FIGS.
Does not have the braking portion 5 and the heating portion 4
And the lead lead-out portion 6 are made of a material having the same temperature coefficient of resistance such as W or Mo. As described above, when such a ceramic heater 1 is to be rapidly heated,
There is a problem that the temperature of the ceramic heater 1 rises excessively. In addition, there is a problem that a temperature difference of 800 ° C. or more occurs between the highest temperature portion and a point 10 mm away from the highest temperature portion near the heat generating portion at the time of rapid temperature rise, and the thermal stress deteriorates the ceramic heater 1.

On the other hand, by adjusting the temperature coefficient of resistance of the heat generating portion 4 and the braking portion 5 as described above, it is possible to obtain the ceramic heater 1 which can be rapidly heated and does not overheat. . This operation is specifically described as follows. First, the heating part 4 adjusted to low resistance
The ceramic heater 1 is rapidly heated. Then
Due to this heat generation, the resistance of the braking part 5 having a large temperature coefficient of resistance becomes larger faster than the resistance of the heat generating part 4.
The voltage applied to the heating section 4 decreases. By this effect, the temperature of the ceramic heater 1 can be rapidly increased, and an excellent ceramic heater 1 which does not overheat can be obtained.

However, as shown in FIG. 8, even in the ceramic heater 1 incorporating the braking unit 5, the resistance of the heating unit 4 and the braking unit 5 is not taken into account, so that the resistance value of the braking unit 5 is low. If the heating part 4 is too small, the braking effect becomes insufficient, or if the resistance value of the braking part 5 becomes too large with respect to the heating part 4, the braking part 5 has a higher temperature than the heating part. Therefore, there is a problem that the service life is shortened due to the deterioration of the braking portion 5. Further, as for the position of the braking portion 5, if the braking portion 5 is formed from the vicinity of the heat generating portion 4 to the vicinity of the electrode pad 8, the heat generation center thereof is far away from the heat generating portion 4, so that the braking effect is reduced. There was a problem that it could not be fully demonstrated. Furthermore, when the breaking portion 5 is formed close to the electrode pad 8 and generates heat at a high temperature, the temperature of the electrode pad 8 rises to 400 ° C. or more, and the metallization of the electrode pad 8 is oxidized, causing a problem of disconnection.

Therefore, in the present invention, as shown in FIG. 1, a heating section 4 and a braking section 5 having a higher temperature coefficient of resistance are provided, both of which are wired in series. The resistance ratio of the braking unit 5 is 10: 1 to 1
1.5: 1, the heating part 4 and the braking part 5
By using a ceramic heater having an interval of 20 mm or less, it is possible to obtain an excellent ceramic heater 1 that can rapidly raise the temperature and does not overheat.

The connecting portion 9 is for effectively connecting the thin wires of the heating portion 4 and the breaking portion 5 to each other.
When wiring with different composition is printed and connected separately,
As shown in FIG. 1, when the connection portion 9 having a large area is formed, the reliability of the connection is increased, and it is possible to prevent problems such as heat generation and disconnection due to poor contact of the connection portion. Although the connection portion 9 is formed between the heating portion 4 and the braking portion 5 in FIG. 1, the connection portion 9 may be provided at the end of the heating resistor 4 and the braking portion 5. Alternatively, the two may be directly joined without using the connecting portion 9.
In that sense, the distance a between the heating part 4 and the braking part 5
The minimum value of the distance a is 0.3 mm, which is the minimum value for keeping the insulation between the wirings. The interval a is defined as the end of the comb tooth or meandering part forming the heat generating part 4 and the breaking part 5.
Is the distance from the tip of the comb tooth or meandering part.

The resistance ratio between the heating section 4 and the breaking section 5 is adjusted to 10: 1 to 1.5: 1. If the resistance value of the heat generating portion 4 is larger than this range, the effect of forming the braking portion 5 is lost, and if the resistance value of the heat generating resistor 4 is smaller than this temperature range, the braking portion at the time of temperature rise is reduced. The heat generation of No. 5 is too large, which is not preferable. In this case, since the root portion of the oxygen sensor is heated, the temperature of the electrode pad 8 of the ceramic heater increases due to the heat retention effect, and when the temperature exceeds 400 ° C., the metallized portion is oxidized.

As shown in FIG. 2, the distance between the electrode pad 8 and the rearmost end of the comb tooth or meandering part of the braking part 5 is defined as a distance b. If there is no comb portion or meandering portion in the breaking portion 5, it means the distance between the rearmost end of the portion determined to be the pattern and the electrode pad portion.
This interval b is preferably adjusted to 20 mm or more. If the thickness is set to 20 mm or less, the temperature of the electrode pad 8 rises to 400 ° C. or more, and the metallization of the electrode pad 8 is oxidized.

FIG. 3 shows another pattern diagram of the ceramic heater of the present invention. The heat generating part 4 and the breaking part 5 are formed on the ceramic green sheet 3 so as to be directly connected. The breaking part 5 is further connected to a lead lead-out part 6, and at the end thereof, is connected to an electrode pad 8 formed on the back side by a through hole 7.

As a material used for the heat generating portion 4, an alloy such as W-Re, W-Mo, Mo-Re may be used. Usually, the factor of increasing the resistance of the metal resistor by heating is due to phonon scattering. When a single metal is used for the heating resistor 4, the movement of electrons is suppressed due to phonon scattering due to heat when the temperature rises, and the resistance increases rapidly, so that the temperature resistance coefficient increases. On the other hand, when alloying, phonons are structurally scattered in the alloyed portion and the intermetallic joint portion, so that the resistance value increases from room temperature and the temperature dependence of the resistance value decreases. On the other hand, as a material of the braking part 5, W, which is a high melting point metal,
It is preferable to use a single metal of Mo. Among them, W is the most suitable because it has the largest temperature coefficient of resistance.

Further, the lead extraction portion 6 and the electrode pad 8
There are no particular restrictions on the material of
It is preferable to use the same material as that described above because it is not necessary to increase the number of steps.

As the material of the ceramic heater 1, it is possible to use alumina, mullite, silicon nitride, aluminum nitride or the like.

[0029]

EXAMPLE 1 A ceramic green sheet 3 containing aluminum oxide as a main component and containing silicon oxide, calcium oxide and magnesium oxide in a total amount of 10% by weight or less was prepared. The heating part 4 and the braking part 5 composed of W and the lead drawing part 6 were printed. Also,
An electrode pad 8 was printed on the back surface. Then, a through hole 7 was formed at the end of the lead lead portion 6 made of W, and conduction was established between the electrode pad 8 and the lead lead portion 6 by injecting a paste into the through hole 7. The ceramic green sheet 3 thus prepared was brought into close contact with the periphery of the ceramic rod 2, and was fired at 1500 to 1600 ° C. to obtain a ceramic heater 1. At this time, a sample was prepared in which the length of the heat generating portion 4 of the ceramic heater 1 was 5 mm, and the distance a between the heat generating portion 4 and the breaking portion 5 was varied from 3 to 25 mm. Separately, a sample was manufactured in which the resistance ratio between the heating section 4 and the breaking section 5 was varied from 15: 1 to 2: 1.

Ten samples were prepared for each, and the temperature rising characteristics and durability of these samples were evaluated. The temperature rise characteristics were measured for the time up to 900 ° C. at the time of cold start when a voltage at which the maximum temperature of the heat generating portion 4 was 1000 ° C. was applied. As for the evaluation of the durability, the highest temperature portion of the heat generating portion 4 was 120 °.
A cycle of applying a voltage of 0 ° C. for 2 minutes and forcibly air-cooling for 2 minutes was repeated 5000 cycles.
Was evaluated for the change in resistance and the occurrence of cracks. Investigation of the highest temperature part is performed by confirming the highest temperature part with an infrared temperature distribution measuring device (thermoviewer) and then using a wire diameter of 0.2 mm
The thermocouple of φ was fixed and the temperature rise characteristics were confirmed.

The results are shown in Table 1. No. 13 in which the resistance ratio between the heating part 4 and the braking part 5 was adjusted to 15: 1 out of the claims, with the conventional product (No. 13) having no braking part. In No. 6, cracks occurred in 2 to 4 samples out of 10 in the cycle test of 5000 cycles. In addition, in the case of No. 1 in which the above resistance ratio was 1: 1 In 12, 5 out of 10 samples were disconnected at the electrode pad 8. In addition, a sample in which the interval a was set to 25 mm outside the claims (No. 5)
In the evaluation of durability, two out of ten cracks were generated.
On the other hand, the samples within the range of the present invention showed good results without cracks and the resistance change of the ceramic heater 1 within 3%.

FIG. 4 shows the temperature rise characteristics (A) of a conventional ceramic heater having no built-in braking portion, and the N-value of the present invention.
o. 10 is a diagram showing a temperature rise characteristic (B) of a ceramic heater of No. 10 and a temperature rise characteristic (C) of a braking portion built in the ceramic heater. FIG. The temperature rising conditions in this figure show the respective saturation temperatures when the temperature is raised from room temperature to 500 ° C. in 3.4 seconds. As can be seen from the figure, the temperature rise characteristics of (A) and (B) are almost the same. On the other hand, the saturation temperature of these ceramic heaters is about 1090 ° C. on the temperature rise curve (A) of the conventional ceramic heater, whereas the saturation temperature of the ceramic heater of the present invention is about 1090 ° C. It can be seen that the saturation temperature is about 940 ° C and there is a difference of about 150 ° C. The saturation temperature of the heating curve (C) of the braking section 5 is about 820 ° C.

As described above, by incorporating the braking section 5, the ceramic heater 1 can be improved while improving the temperature rising characteristics.
, The life of the ceramic heater 1 can be extended, and at the same time, there is no need to provide a mechanism for preventing excessive temperature rise on the power supply side of the ceramic heater. Can be.

[0034]

[Table 1]

Example 2 A sample was prepared in the same manner as in Example 1. Here, the distance b between the electrode pad 8 and the meandering part of the braking part 5
Of each of the samples was changed to 15 to 40 mm, and the durability and the temperature of the electrode pad 8 when the heating resistor was held at 1200 ° C. for 10 minutes were evaluated. The location of the interval b was specifically defined using FIG. The durability was evaluated by applying a voltage for maintaining the highest temperature portion of the heat generating portion 4 at 1200 ° C. for 5 minutes and allowing the device to cool for 5 minutes.
Zero cycle was repeated, and a change in resistance and a change in appearance were confirmed.
The results are shown in Table 2.

In the case of No. 3 in which the interval b was set to 15 mm outside the scope of the present invention. In No. 1, the temperature of the electrode pad 8 reached 500 ° C., and after 1000 cycles of the durability test, 2 out of 10 wires were disconnected, and the Ni-plated portions of the other samples also turned black. On the other hand, No. 2 within the scope of the present invention. In Nos. 2 to 5, the temperature of the electrode pad 8 was 400 ° C. or less, and no disconnection was observed. Further, the discoloration of the electrode pad 8 was only to the extent that it was discolored to gray, and no black discoloration was recognized.

[0037]

[Table 2]

[0038]

According to the present invention, the heating resistor pattern comprises a heating portion and a braking portion having a higher temperature coefficient of resistance, both of which are wired in series, and the resistance of the heating portion and the braking portion is reduced. The ratio is 10: 1 to 1.
By setting the distance between the heating part and the braking part within 20 mm, the overshift of the ceramic heater temperature at the time of cold start is reduced, and the electrode of the sensor is damaged, and the durability of the ceramic heater is reduced. It is possible to prevent such a problem that the resistance is lowered and the resistance of this portion is increased due to an increase in the temperature of the lead take-out portion and the wire is disconnected.

[Brief description of the drawings]

FIG. 1 is a development view showing a ceramic heater of the present invention.

FIG. 2 is a partially cutaway side view of the ceramic heater of the present invention.

FIG. 3 is a pattern diagram of a heating resistor of the ceramic heater of the present invention.

FIG. 4 is a diagram showing a temperature rise characteristic of the ceramic heater of the present invention.

FIG. 5 is a pattern diagram of a heating resistor of a conventional ceramic heater.

FIG. 6 is a development view of a conventional ceramic heater.

FIG. 7 is a perspective view of a conventional ceramic heater.

FIG. 8 is a development view of a conventional ceramic heater.

FIG. 9 is a diagram showing a temperature rise characteristic of a conventional ceramic heater.

[Explanation of symbols]

 1: Ceramic heater 2: Ceramic rod 3: Ceramic green sheet 4: Heating section 5: Breaking section 6: Lead extraction section 7: Through hole 8: Electrode pad 9: Connection section 10: Lead wire (Ni) 11: Heat generation resistance Body a: Spacing between heating part and braking part b: Spacing between braking part and electrode pad

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3K034 AA02 AA04 AA06 AA14 AA22 AA37 BB06 BB13 BB14 BC12 BC28 CA18 CA22 CA27

Claims (2)

[Claims] 1. A ceramic heater in which a heating resistor mainly composed of a high melting point metal such as W, Mo, Re or the like is embedded in a ceramic substrate, wherein the heating resistor has a heating portion and a resistance temperature coefficient larger than the heating portion. And the resistance ratio between the heat generating part and the braking part is 1
A ceramic heater characterized by being in the range of 0: 1 to 1.5: 1, and wherein the distance between the heat generating part and the braking part is within 20 mm. 2. The ceramic heater according to claim 1, wherein a distance between an electrode pad provided at a rear end of the heating resistor and the breaking portion is 20 mm or more.