JPH10189225A - Ceramic heater - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a ceramic heater in which a heater and a current-carrying electrode are arranged on a ceramic substrate.
When it overheats and runs away, it surely shuts off the power to the heater. A ceramic heater having a ceramic substrate, a heater circuit formed on the substrate and generating heat by energization, and an electrode for energizing the heater circuit, wherein the conductor portion mainly composed of aluminum is formed by the heater Ceramic heater connected in series with part of the circuit. In this heater, when the heater is overheated and runaway, the main component aluminum of the conductor is oxidized and changed to electrically insulating alumina, so that the power supply to the heater is cut off.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called ceramic heater of an energization type having a heater circuit portion in the form of a film on a ceramic substrate, and a heater provided with a heating and energization cut-off mechanism for preventing overheat runaway in the heater itself.

[0002]

2. Description of the Related Art Heaters using a substrate made of electrically insulating ceramics and having a film-shaped energizing heat-generating portion on the surface thereof have been used in a wide range of applications, mainly home appliances and office equipment. These heaters are usually provided with a control section for adjusting the temperature of the heating section. If the part causes some trouble and the temperature control becomes ineffective, the temperature fuse is activated and the power supply to the heater is cut off within a certain period of time. However, if the heater becomes energized in any way before the fuse is activated and runs out of control, smoke and fire may occur around the heater, resulting in a fire.

Therefore, even in such a situation, various safety measures have been devised to surely and promptly shut off the power supply to the heater. JP-A-5-205851 discloses that
A method in which through holes or grooves are provided on a substrate and the substrate itself is broken starting from these holes is introduced.
Japanese Patent Application Laid-Open No. Hei 8-186340 discloses that a layer of a sublimable substance is provided between a substrate and a layered heater. A method is introduced in which the upper heater layer is overheated to cut off the current. However, JP-A-5-20
In the method disclosed in Japanese Patent No. 5851, when a ceramic having high thermal shock resistance is used for a substrate, the substrate may not be damaged and may not be effective. Also, JP-A-8-18634
In the method disclosed in Japanese Patent Publication No. 0, when the sublimable substance remains on the substrate surface in the sublimated hollow portion, the heater layer itself does not exhibit an excessively high temperature state, and it may not be possible to cut off the power supply by fusing. In the former case, the substrate is damaged, and in the latter case, the heater is damaged. Therefore, in any case, the heater cannot be regenerated or reused after the power is cut off.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a ceramic heater using a ceramic substrate.
An object of the present invention is to provide a means for surely shutting off the power supply to the heater in case of overheating runaway.

[0005]

According to the present invention, a conductor portion mainly composed of aluminum is provided in series with a part of a heater circuit on a substrate. That is, according to the present invention, there is provided a ceramic heater having a ceramic substrate, a heater circuit formed on the substrate, and generating heat by energization, and an electrode for energizing the heater circuit, wherein the conductor is mainly composed of aluminum. A portion provides a ceramic heater connected in series with a portion of the heater circuit. Thereby, the above-mentioned problems are solved.

Further, the present invention provides the above basic structure, in particular, one in which the cross-sectional area of a part of the circuit pattern of the conductor portion is smaller than the cross-sectional area of a heater pattern directly connected to the pattern. Further, the present invention also provides a ceramic heater whose ceramic substrate is a ceramic containing aluminum nitride as a main component and a ceramic heater using aluminum nitride as a substrate whose conductor is formed by irradiating a laser.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, the ceramic heater of the present invention is provided with a conductor mainly composed of aluminum in series with a part of a heater circuit on a ceramic substrate. Aluminum, the main component, is a substance that is very easily oxidized in the atmosphere, but from room temperature to around 300 ° C, only a very small part of its surface is oxidized. No alteration of the conductor occurs. Therefore, at the time of normal use, the conductor part only exists in a part of the heater and performs only an energizing function. However, when the temperature exceeds 400 ° C., the reaction with oxygen in the air rapidly proceeds, and alumina becomes an insulator. For this reason, if an excessive current flows through the heater and the temperature rises abnormally, the resistance of this conductor will rise rapidly and the amount of heat generated will increase. Can be reliably shut off.

In the conductor pattern in the above configuration, the cross-sectional area of a part of the pattern (that is, substantially the product of the width and thickness of the film) is reduced by the same cross-sectional area of the heater pattern at the connection with the heater. By making it smaller, the effect of the present invention is promoted. By partially reducing the cross-sectional area of the conductor pattern, the oxidation of aluminum due to overheating progresses rapidly in the small cross-sectional area, so that insulation interruption occurs at a lower heater surface temperature. This is because the smaller the cross-sectional area of the conductor portion, the less energy required for oxidation is required, and the higher the energy density for promoting oxidation per unit cross-sectional area.

For example, even when the circuit pattern 2 of the conductor is formed with the same width as the heater circuit pattern 1 over the entire length as viewed from the top as shown by the hatched portion in FIG. . However, as shown in some examples of the hatched portions in FIGS. 4A to 4C in the same pattern as FIG. 3, a portion having a small width is added to a part of the conductor portion pattern while maintaining the same film thickness. Due to the provision, the interruption of the energization takes place in that part at a lower superheating temperature stage. Similarly, if the thickness of the film is smaller than that of the heater even with the same pattern width, the same effect can be obtained.

The ceramic substrate material to be used in the present invention is basically required to be insulative. However, considering the heat transfer efficiency and thermal shock resistance of the heater, aluminum nitride, boron nitride, and silicon carbide are excellent. , Silicon nitride, alumina or a composite material of these components, or a composite material containing these as a main component is desirable. Among them, aluminum nitride is desirable.

The method for forming the heater layer includes a thin film method such as vapor deposition and sputtering, and a thick film method such as thermal spraying, spraying and printing. It is desirable to use a stable material whose specific resistance hardly increases at a temperature up to the melting point of aluminum in the atmosphere. For example, Ni-Cr, Ta, Cr and composite materials and alloys based on them, conductive ceramics such as TaN, or precious metals such as Ag, Pt, Pt-Pd and composite materials and alloys based on them The following can be used.

Examples of the method of forming the aluminum conductor portion include a thin film method such as vapor deposition and sputtering, and a thick film method such as thermal spraying, spraying and printing. Any existing film forming method may be used. In this case, the thickness of the film depends on the normal operating temperature of the heater, but is desirably changed depending on the magnitude of the current flowing through the circuit. The conductor may be located anywhere in the heater circuit. In addition, although only one location is sufficient, a plurality of locations may be provided. In view of the heat conduction efficiency of the heater, it is desirable that the area ratio in the heater circuit pattern is small. When the heater is formed by baking in an oxidizing atmosphere at a temperature of 400 ° C. or higher at which aluminum oxidation starts rapidly, it is necessary to perform baking of the heater circuit pattern before forming the conductor. is there.

As described above, in order to reduce the temperature at which the heater circuit is cut off, it is desirable to reduce the cross-sectional area ratio of the conductor portion to the heater portion as much as possible. In this case, the pattern width of the film and the thickness of the film may be controlled, but the effect of controlling the film thickness is particularly large. In any of the above-described methods for forming a film, the temperature at which current can be cut off can be adjusted by the thickness of the film of the aluminum conductor. If it is desired to cut off at a relatively high temperature close to the melting point of aluminum, the thickness is preferably in the range of 5 to 30 μm by the thick film method. However, if it is desired to cut off at a lower temperature, the thickness is desirably less than 5 μm by the thin film method. A more desirable film thickness is 0.5 to 3 μm.
As the thickness of the film becomes thinner, the ratio of the surface area to the aluminum volume of the conductor portion becomes larger, and the rate of increase of the electric resistance value due to the oxidation becomes accelerated. Therefore, the required time for interruption is also shortened in an acceleration manner. Therefore, it is necessary to select the position of the conductor portion and the thickness of the film in consideration of the ignition point or the heat-resistant temperature of the component adjacent to the heater and the safety.

When the substrate is made of aluminum nitride, a laser may be applied to a portion where the conductor is to be formed, so that aluminum is deposited at that portion. According to this method, the conductor portion can be formed efficiently at very low cost and with high positional accuracy and high dimensional accuracy. In addition, the film formation of the heater is performed at 400 ° C. where oxidation of aluminum starts rapidly.
In the case where firing is performed in the above temperature and oxidizing atmosphere, it is necessary to fire the heater before forming the conductor.

The ceramic heater according to the present invention can be regenerated after the current is cut off by oxidation of the conductor portion, as long as the heating function of the heater circuit itself is not impaired by the temperature rise at the time of cut-off, so that the ceramic heater can be reused. It is. In the regeneration treatment, the heater is first heat-treated at 700 to 800 ° C. in the air, and then rinsed with water. This is because alumina in the conductor does not usually react with the ceramic substrate and the heater layer and does not adhere to them. Thereafter, a conductor portion is formed again on the substrate.

[0016]

【Example】

(Example 1) An aluminum nitride substrate having a square shape of 25 mm and a thickness of 1.0 mm was prepared. Next, after the Ag-Pd paste was screen-printed with the heater circuit pattern 1 in the shaded area shown in FIG. 1, it was baked at 800 ° C. in air to form the circuit pattern on the substrate. The thickness of the circuit film was 10 μm. After that, a part of the surface of the circuit (hatched part in FIG. 1) is irradiated with a laser to deposit aluminum on the part,
A conductor circuit pattern 2 having a length of 5 mm and a width of 1 mm, which is the same as the heater circuit pattern portion directly connected, was formed. The thickness of the film of the conductor was 1.0 μm. Ag-P
In order to connect to the d heater circuit, a laser was irradiated over a length of 7 mm so that the circuit took 1 mm at a time.

When electricity was supplied to the completed heater circuit and heat generation was performed, when the temperature of the substrate surface reached 420 ° C., a part of the aluminum conductor became white and the electricity supply was interrupted. After shutting off, the heater was heat-treated at 750 ° C. in the air, immersed in water and subjected to ultrasonic cleaning. There was no residue in the conductor portion, and neither Al nor alumina was confirmed by X-ray diffraction. Thereafter, laser irradiation was performed in the same manner as in the beginning and electricity was supplied again as a heater, and the electricity was cut off at the same substrate temperature as above. The surface temperature of the substrate was measured by an infrared radiation thermometer.

Using the same aluminum nitride substrate, and using Ni-Cr, TaN, and Ta as heater materials, a heater was prepared and evaluated in the same manner as above. It was confirmed that the heater could be regenerated and reused as described above.

(Embodiment 2) As a substrate material, each sintered body of silicon nitride, alumina and boron nitride having the same shape as that of Embodiment 1;
A silicon carbide sintered body whose surface was covered with aluminum nitride and a substrate of the same aluminum nitride sintered body as in Example 1 were prepared. With the same heater circuit pattern and film thickness as in Example 1,
First, an Ag-Pd paste was printed and baked in the same manner as in Example 1, and an Al paste was printed and applied to the same portions as in Example 1 in the same conductor pattern shape. Thereafter, the circuit was fired at 450 ° C. in the air to burn all the circuits. The film thickness of this conductor was 15 μm.

When power was applied to the completed heater circuit to increase the heat generation, all heaters
At a substrate surface temperature of 620 ° C., a part of the conductor portion turned white, and the current was cut off. After blocking, heat treatment was performed in the air in the same manner as in Example 1, and ultrasonic cleaning was performed. In any of the heaters, no residue of the conductor was observed, and neither Al nor alumina was confirmed by X-ray diffraction. Then, the aluminum conductor portion of the heater circuit was regenerated in the same manner as in the beginning, and the heaters were heated. When the heaters reached almost the same substrate temperature as in the beginning, energization was cut off.

Example 3 A substrate made of the same sintered body of silicon nitride, alumina, and aluminum nitride as in Example 2 was prepared. The Ag-Pd heater circuit pattern of FIG. 1 was formed on one surface of the substrate in the same manner as in Example 1. Thereafter, an aluminum layer having a thickness of 3.5 μm and the same position and the same length and width as in Example 1 was formed on this pattern by a vacuum vapor deposition method to obtain a conductor. As a result of conducting an energization overheating test in the same manner as in Example 1, the conductors of all the substrates turned white at a substrate surface temperature of 520 to 550 ° C., and the energization was cut off.

(Example 4) Except that the Ag-Pd heater coating film was formed in the same outer shape as in FIG. 1 and in a hatched portion pattern without the hatched portion in FIG. 1, the same method as in Example 1 was used.
A ceramic heater using aluminum nitride as a substrate was prepared. Thereafter, the laser was applied to the same position and the same size range as in Example 1 (that is, the range substantially corresponding to the hatched portion in FIG. 1). This irradiation removed the Ag-Pd coating film and formed an aluminum conductor portion having a film thickness of 1.2 μm on the aluminum nitride substrate thereunder. When an energization overheating test was performed in the same manner as in Example 1, energization was interrupted when the surface temperature of the substrate was 460 ° C. It was confirmed that this heater can be recycled and reused by the same heat treatment and cleaning as in Example 1.

Example 5 A substrate made of the same sintered body of silicon nitride, alumina, and aluminum nitride as in Example 2 was prepared. On one surface of the substrate, a 10 μm-thick Ag-P
A d heater circuit pattern was formed. Thereafter, a conductor portion having a thickness of 15 μm and having a thickness of 15 μm as shown in FIG. 2 was formed on the unconnected portion of the heater circuit pattern shown in FIG. The minimum width of the aluminum conductor is Ag-P directly connected
It was 1/2 of the width of the d heater circuit. When the energization circuit cutoff temperature was confirmed in the same manner as in Example 1, all the heaters were at 510 to 530 ° C.

[0024]

As described above, according to the present invention, by providing an aluminum conductor in the heater circuit in series with the heater circuit, it is possible to reliably shut off the power supply when the heater overheats and runs away. Furthermore, if a heater material whose specific resistance is stable at a temperature up to the melting point of aluminum in the atmosphere is used, a reusable heater can be obtained by regenerating the aluminum conductor portion after the power is cut off.

[Brief description of the drawings]

FIG. 1 shows a heater circuit pattern (top view) of a ceramic heater according to an embodiment of the present invention.

FIG. 2 shows a heater circuit pattern (top view) of the ceramic heater according to the embodiment of the present invention.

FIG. 3 shows a heater circuit pattern (top view) of the ceramic heater according to the embodiment of the present invention.

FIG. 4 shows a heater circuit pattern (top view) of the ceramic heater according to the embodiment of the present invention.

[Explanation of symbols]

 1: Heater circuit pattern 2: Conductor circuit pattern

Claims (4)

[Claims] 1. A ceramic heater comprising: a ceramic substrate; a heater circuit formed on the substrate and generating heat when energized; and an electrode for energizing the heater circuit. And a ceramic heater connected in series with a part of the heater circuit. 2. The ceramic heater according to claim 1, wherein a cross-sectional area of a part of the circuit pattern of the conductor is smaller than a cross-sectional area of a heater circuit pattern directly connected to the circuit. 3. The ceramic heater according to claim 1, wherein the ceramic substrate is a ceramic containing aluminum nitride as a main component. 4. The ceramic heater according to claim 3, wherein the conductor is formed by irradiating a laser.