JPH10214673A - Ceramic heater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ceramic heater having a structure with an exothermic body layer which generates heat by energization and with a conducting layer for energizing said exothermic body layer arranged on an insulative ceramic base board, and provide a heater structure for preventing a fire accident and for shutting off energization when said heater is overheated and overdriven. SOLUTION: In a ceramic heater having a basic structure, a through hole 4 charged with a material having a thermal expansion coefficient larger than that of a ceramic base board 1 is arranged at a location excluding an exothermic body layer 2 and a conducting layer 3 on the ceramic base board 1. This structure is shaped such that a cross-section of the through hole 4 have a corner forming at least one acute angle. Alternatively, a plurality of through holes 4 are arranged on the base board 1, and a heater structure bridges the plurality of through holes 4 by using the material having a thermal expansion coefficient larger than that of the base board 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a heater in which a heating element layer is provided on an electrically insulating ceramic substrate.
More specifically, the present invention relates to a method for interrupting energization when the heater overruns.

[0002]

2. Description of the Related Art Conventionally, an insulating ceramic is used as a substrate,
In the case of a resistance heating type heater provided with a layered heating element layer on its surface and a conductive layer which is an electrode for supplying electricity to the layer, when an overcurrent flows in the heating element circuit, the temperature usually provided in the heater The control circuit operates to cut off the power supply. However, if the power supply is not interrupted for some reason, the power supply is continued, and there is a possibility that the circuit may ignite or a fire may occur.

For this reason, a method for forcibly interrupting energization without relying on a temperature control circuit is disclosed in JP-A-5-205851 and JP-A-8-186340. In the former case, a through hole or a groove is provided in a place other than the heating element layer and the conductive layer on the substrate, or a substance having a larger thermal expansion coefficient than the substrate is filled in the through hole. When the heating element layer overruns, the substrate is broken by using the through hole or the groove itself as a fracture starting point or by local stress due to expansion of a filling material in the through hole. In the latter case, a layer of a substance that sublimates by heating is formed between the substrate surface and the heating element layer. When the heating element layer runs out of heat, the sublimable substance layer sublimates and disappears, and a cavity is generated. The heat generated in the circuit is not transferred to the substrate, and the circuit is abnormally heated, oxidation of the surface thereof and increase in resistance proceed in synergy, and the circuit is melted and the current is cut off.

[0004]

However, even in such a method, the temperature may not be broken depending on the ceramic material of the substrate in the early stage of the overheating runaway. For example, it may break in alumina, but may not break in a material having high thermal shock such as aluminum nitride and silicon nitride. The present invention provides a heater structure capable of reliably breaking the substrate even when this type of ceramic is used for the substrate.

[0005]

Means for Solving the Problems To solve the above problems, the present invention takes the following means. That is, according to the present invention, in a ceramic heater having the above structure, a through-hole filled with a substance having a larger thermal expansion coefficient than that of the substrate is disposed in a place other than the heating element layer and the conductive layer on the substrate of the heater, A through hole is formed in a cross-sectional shape having at least one acute angle corner.

According to a further preferred aspect of the present invention,
In the heater having the above-described configuration, a plurality of through holes are formed, and at least one set of a combination arrangement in which acute-angled corners face each other is formed.

According to another preferred embodiment of the present invention, there is provided a structure in which a plurality of the above-mentioned through holes are formed, and the plurality of the through holes are connected by a substance having a larger thermal expansion coefficient than that of the substrate. And

Further, the structure is such that a groove is formed on the substrate surface between the plurality of through holes.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS By using the above-described means, even when ceramics having high thermal shock resistance and not easily broken by rapid heating are used for a substrate, the ceramics can be used in the early stage of overheat runaway. The ceramic substrate can be reliably broken. In addition, as ceramics having thermal shock resistance, for example, a thermal shock fracture resistance coefficient is 20 ca.
1 / cm · sec or more. Incidentally, alumina is usually about 4 in the same unit, and 20 or more include silicon nitride, aluminum nitride, silicon carbide, beryllia, boron nitride and the like.

According to the present invention, first, the cross-sectional shape of the through-hole penetrating the substrate has at least one acute-angled corner and is filled with a substance having a larger thermal expansion coefficient than the substrate. . By filling such a substance in the through hole, it is possible to break at a certain temperature depending on the substance. Furthermore, by making the cross-sectional shape of the through hole as described above, the stress generated by the thermal expansion of the above-mentioned substance filled in the through hole is concentrated at the corner thereof, and it is easy to break the ceramic. Become.

In this case, the cross-sectional shape of the through hole is, for example, as shown in FIGS. Note that the angle between the corners (however, when the corners intersect a curved surface as in b and c, the angle between the tangents as shown in the figure) is 20.
It is desirable that the temperature be not less than 80 degrees and not more than 80 degrees. If the angle is less than 20 degrees, it becomes difficult to form a corner of the through hole. If it exceeds 80 degrees, the effect of stress concentration at a corner for breaking the substrate may be reduced as described later.

In this case, when a plurality of through holes are further formed and the vertices, that is, the corners forming an acute angle are arranged in the directions facing each other, stress is concentrated between the vertices of the facing through holes, so that the fracture is more likely to occur. It will be easier. At least one such combination arrangement portion is provided. In this case, the rupture effect is increased by combining and arranging the substrates in a direction parallel to the short length direction of the substrate (for example, the width direction of a rectangular substrate surface).

The object of the present invention can also be achieved by interposing a substance having a larger thermal expansion coefficient than that of the substrate between the through holes and connecting the through holes. In this case, it is not always necessary to provide sharp corners in the cross-sectional shape of the through hole. The substance to be interposed between the through holes may be the same substance as the substance filling the through holes, or may be a completely different substance. The same substance can be provided as a single body. FIG. 2 shows an example. In the figure, the uppermost figure is a top view of the heater, the center is a bottom view showing the back side of the substrate, and the bottom is a cross-sectional view taken along the line AA 'of the bottom view. In FIG. 1, reference numeral 1 denotes a ceramic substrate, 2 denotes a heating element layer disposed thereon, 3 denotes a conductive layer that conducts electricity, 4 denotes through holes, and 5 denotes a substance having a larger thermal expansion coefficient than the substrate. Considering the thermal efficiency of the heating element layer, the surface on which the main body of the substance 5 to be interposed is preferably a rear surface opposite to the heating element layer arrangement side of the substrate as shown in the figure. However, if it can be arranged practically or functionally, it may be arranged on the same surface as the heating element layer. By arranging a substance having a larger thermal expansion coefficient than the substrate as described above, stress acts between the through holes in the direction of compressive bending of the substrate. Therefore, the breaking of the substrate becomes easier. However, in consideration of the thermal efficiency of the heater, it is desirable that the area of the portion on which the intervening substance is mounted is as small as possible and the thickness is as small as possible.

Further, in addition to the above structure, by forming a groove on the substrate between the through holes, the substrate can be more easily broken. In this case, it is desirable that the direction in which the grooves are formed be perpendicular to the direction in which the through holes are arranged.
This is because compressive bending stress is applied to the substrate in the direction in which the through holes are arranged, so that the notch effect of the groove is synergistic and breakage is facilitated. However, when the groove is formed at right angles to the arrangement direction of the through holes, the groove crosses the heating element layer. Therefore, it is preferable to form the groove on the back side of the substrate in consideration of the thermal efficiency of the heating element layer.

The formation of the through holes may be performed after sintering the ceramics or at the time of the formed body before sintering, and various methods such as cutting and laser processing can be used.

A method of filling a substance having a larger thermal expansion coefficient than the substrate into the through-hole may be to fix the substance to a required shape and then fix it with a resin. However, when the hole is overheated, Since the resin may emit smoke or fire, it is desirable to sufficiently cool the substance to be charged with a refrigerant such as liquid nitrogen and insert and fix the substance to a size slightly smaller than room temperature. Since the lower limit of the coefficient of thermal expansion at a desired breaking temperature can be designed, an appropriate filler material satisfying the lower limit may be determined. Depending on the desired breaking temperature, an appropriate substance may not always be available, but in such a case, it is sufficient to adjust the breaking temperature conversely by the dimensional difference between the through hole and the filling material. It is possible. Hereinafter, the present invention will be described by way of examples.

[0017]

【Example】

(Example 1) A thermal shock resistance coefficient of 80 cal processed to a length of 50 mm, a width of 5 mm, and a thickness of 0.635 mm.
/N·sec./AlN sintered body and thermal shock resistance coefficient 2
A ceramic substrate made of a Si ₃ N ₄ sintered body of 0 cal / cm · sec was prepared, and a heating element layer 2, a conductive layer 3 and a through hole 4 were formed on each substrate 1 as shown in FIG. The total length in the longitudinal direction of the heating element layer was 35 mm, and the through hole was 0.4 m on one side near one end of the heating element layer.
m was formed in the shape of an equilateral triangle. First, a through hole was formed with a laser, and then a conductive layer pattern was printed with an Ag paste, and a heating element layer pattern was printed with an Ag-Pd paste, and this was fired at 830 ° C. in air to obtain a heater sample.

Further, the cross-sectional shape of the through hole is set at 0.1 mm on each side.
Another heater sample was prepared in the same procedure as above, except that it was a 3 mm square and a 0.3 mm diameter circle.
However, in the case of a square cross section, as shown in FIG. 3B, two pairs of vertices were formed so as to be arranged in parallel in the length direction and width direction of the substrate. Thereafter, triangular prisms, prisms, and cylinders having the same shape as the outer shape of the through hole of each sample were sufficiently cooled with liquid nitrogen and filled in the through holes. Each of these heaters was heated by applying a voltage of 100 V, and the condition until the substrate was broken and the heater surface temperature at the time of breaking were observed. The surface temperature was confirmed by thermography.

As a result, in the case of the AlN substrate sample, the through-hole having a regular triangular shape has a heating element layer surface temperature of 4.
When the temperature reached 20 ° C., the sample broke at a temperature of 650 ° C. for a square one, but did not break at 900 ° C. for a circular one. In the sample of the Si ₃ N ₄ substrate, the same rupture temperature was 550 ° C. and 700 ° C. for the equilateral triangle and the square, respectively, and the circular one did not rupture even when heated to 900 ° C. like the AlN substrate. .
All the fractures were caused by cracks in the width direction of the substrate.

In the case of a square cross section, the corners are 90
As a result, the effect of stress concentration was insufficient, and the surface temperature of the ruptured heater exceeded 600 ° C. It has been found that such a high temperature fracture does not solve the problem of the present invention, and that practical use is difficult. Incidentally, on the AlN substrate in the same procedure as above, a sample in which a through-hole of a rhombic cross section having substantially the same size and one corner angle of 88 °, 85 °, 80 °, and 75 ° was formed (however, a corner having the same angle) In the direction parallel to the width direction of the substrate)
And the same evaluation as above, the surface temperature of the heating element layer at the time of fracture was 520 ° C., 50
It was 0 ° C, 480 ° C, and 450 ° C. Temperature at break is 6
At such a temperature of less than 00 ° C., the object of the present invention can be achieved.

(Embodiment 2) Length 60 mm, width 6.0 m
First, a through hole having a cross section of an isosceles triangle is formed in an AlN green sheet having the same material as that of Example 1 having a thickness of 0.8 mm and a thickness of 0.8 mm, and then a heating element layer and a conductive layer are formed in the same manner as in Example 1. , And a heater. The size of the substrate after firing was 50 mm in length, 5.0 mm in width and 0.6 mm in thickness.
5 degrees, the equilateral length is 0.4 mm, and one vertex of 45 degrees is oriented in the width direction of the substrate as shown in FIG. 4, and the entire arrangement position is closer to the heating element layer. . This was filled with Ni having the same shape as the through hole as in Example 1. When a voltage of 100 V was applied to the heater and the substrate was heated, the substrate was fractured in the width direction when the surface temperature of the heating element layer reached 420 ° C. starting from the top of the through hole near the heating element layer at 45 degrees. did.

(Embodiment 3) The through-hole shape shown in FIG.
An AlN substrate heater was manufactured in the same procedure as in Example 2 except that the heater was arranged. The cross-sectional shape of the through-hole was the same as in Example 1, and was arranged such that the vertices faced each other as shown in FIG. The filling material and the filling method in the through hole were the same as in Example 1. Then Example 1
When the heater was energized and heated in the same manner as described above, when the surface temperature of the heating element layer reached 367 ° C., cracks entered between the opposing vertices of the through holes, and the substrate was broken.

(Embodiment 4) Length 50 mm, width 5.0 m
m, thickness 0.635 mm, AlN of the same material as in Example 1.
Substrates each made of a sintered body and a Si ₃ N ₄ sintered body were prepared, and as shown in FIG.
A 3 mm through hole was formed by laser processing at a span of 40 mm. A heating element layer and a conductive layer were baked thereon in the same manner as in Example 1. Next, a Cu plate having an upper surface shape shown in a back view in the middle part and a sectional shape shown in a sectional view in the lower part was prepared. This Cu plate has a body thickness of 1.0 m.
m, the width is 1.0 mm, formed in an arrangement corresponding to the through-hole span formed in the substrate, the diameter is 0.3 mm,
The projections had a thickness of 0.635 mm. In addition, the outer diameter of the projection was processed to be smaller than the inner diameter of the through hole so as to be fitted. This plate was press-fitted from the back surface of the substrate on which the heating element layer was not arranged as shown in FIG. Thereafter, when heating was performed in the same manner as in Example 1, the temperature of the AlN substrate was 250 ° C.
In the case of the Si ₃ N ₄ substrate, the substrate was broken at 298 ° C. by a crack in the width direction at the center thereof. It should be noted that substantially the same results were obtained when the Cu plate was press-fitted from the heating element surface of the substrate.

Example 5 An AlN substrate heater as shown in FIG. 7 was prepared through substantially the same procedure as in Example 4.
However, as shown in the figure, a width of 0.2 in the width direction of the substrate is provided at the center of the rear surface of the substrate opposite to the surface on which the heating element layer is formed.
A groove 6 having a rectangular cross section of 0.2 mm in depth and 0.2 mm in depth was formed. Next, a Cu plate similar to that of Example 4 was prepared, and the Cu plate was press-fitted from the back surface side of the substrate on which the groove was formed in the same manner as in Example 4. When the substrate was heated in the same manner as in Example 4, the substrate was broken at the point where the heater surface temperature reached 247 ° C. at the groove forming portion.

[0025]

According to the present invention, a ceramic heater in which a heating element layer that generates heat by energization and a conductive layer for energizing the heating element layer is disposed on an insulating ceramic substrate, particularly a ceramic substrate material having high thermal shock resistance In this case, by adopting the structure of the present invention in the heater structure, even if the heater overheats and runs away, the ceramic substrate can be reliably broken and the power supply to the heater can be cut off, thereby preventing a fire accident. Can be.

[Brief description of the drawings]

FIG. 1 is a schematic view showing various cross-sectional shapes of a through hole formed in a substrate of a heater to which the present invention is applied.

FIG. 2 is a schematic view showing one structural example of a heater to which the present invention is applied. Note that the upper part of the figure is a top view, the middle part is a bottom view, and the lower part is a cross-sectional view taken along the line AA 'of the bottom view.

FIG. 3 is a schematic diagram illustrating a heater structure according to the first embodiment of the present invention.

FIG. 4 is a schematic diagram illustrating a heater structure according to a second embodiment of the present invention.

FIG. 5 is a schematic diagram illustrating a heater structure according to a third embodiment of the present invention.

FIG. 6 is a schematic diagram illustrating a heater structure according to a fourth embodiment of the present invention. Note that the upper part of the figure is a top view, the middle part is a bottom view, and the lower part is a cross-sectional view taken along the line AA 'of the bottom view.

FIG. 7 is a schematic diagram illustrating a heater structure according to a fifth embodiment of the present invention. Note that the upper part of the figure is a top view, the middle part is a bottom view, and the lower part is a cross-sectional view taken along the line AA 'of the bottom view.

[Explanation of symbols]

 1: Ceramic substrate 2: Heating element layer 3: Conductive layer 4: Through hole formed in substrate 5: Material having a larger coefficient of thermal expansion than substrate 6: Groove formed in substrate

Claims (4)

[Claims] 1. A ceramic heater comprising: a heating element layer that generates heat when energized; and a conductive layer for applying current to the heating element layer on an insulative ceramic substrate. In a place other than the layer, a through hole filled with a substance having a larger thermal expansion coefficient than the substrate is arranged, and the cross section of the through hole has a shape having at least one acute angled corner. Ceramic heater. 2. The ceramic according to claim 1, wherein a plurality of said through holes are formed, and at least one combination arrangement is made so that said acute-angled corners face each other. heater. 3. A ceramic heater comprising: a heating element layer for generating heat when energized; and a conductive layer for energizing the heating element layer on an insulating ceramic substrate. A plurality of through holes filled with a substance having a larger coefficient of thermal expansion than the substrate are formed in places other than the layers, and the plurality of through holes are connected by a substance having a larger coefficient of thermal expansion than the substrate. A ceramic heater characterized in that: 4. The ceramic heater according to claim 3, wherein a groove is formed on the substrate surface between the plurality of through holes.