JPS622685B2 - - Google Patents

Description

Detailed Description of the Invention The present invention relates to a thermistor that detects temperature by mechanically contacting an object whose temperature is to be detected, such as a thermistor that detects the temperature of food inside a pot through the bottom of the pot when cooking food in a pot. It is related to.

Conventionally, this type of temperature detection has been carried out by mechanically bringing a thermocouple 2 into contact with the pot bottom 1 and detecting the thermoelectromotive force of the thermocouple 2, as shown in FIG. At this time, the thermocouple 2 was fixed to the support container 3 in order to bring the thermocouple 2 into strong mechanical contact with the pot bottom 1. However, the drawback is that thermoelectromotive force usually only has a small value. The parable is Armel.
Chromel thermocouples have excellent heat resistance (500 to 100°C in air) and are inexpensive, but they only generate an electromotive force of ~40 μV/°C. The thermoelectromotive forces of copper-constantan thermocouples and platinum-platinum/rhodium thermocouples are (30~
60) In addition to being able to obtain only μV/°C, it also had drawbacks such as low heat resistance (copper-constantan thermocouple) and high price (platinum-platinum-rhodium thermocouple). Various other thermocouples exist, but all of them have the drawbacks mentioned above. When controlling the amount of heat generated by a heat source by electrically detecting a small thermoelectromotive force as described above, a large electrical amplification is required, which increases the price. There were also disadvantages such as the need for complex electrical circuits.

On the other hand, when temperature is detected using a thermistor instead of the thermocouple, the rate of change in resistance value with respect to temperature can be as large as (1 to 7%/°C). Therefore, it has advantages such as not requiring a complicated electric circuit and being inexpensive. In this case, the thermistor element is selected to be as small as possible and to have a low heat capacity. This is because miniaturization allows for faster thermal response. Such small thermistor elements include bead-type thermistor elements that use composite oxide sintered bodies such as Fe, Ni, Co, and Mn as the temperature-sensitive resistor, or composite oxides such as those mentioned above, Ge, Si, SiC, etc. There is a thin film thermistor element that uses a thin film of However, since the beat-type thermistor element usually has a shape similar to a sphere or a spheroid, it has the disadvantage that even if the thermistor element is fixed to the support container 3, the thermal resistance becomes large. That is, even though the heat capacity of the thermistor element itself is small, it is difficult to reduce the thermal resistance at the connection part with the support container 3 due to its complicated shape, and as a result, the thermal response becomes slow. It was hot.

On the other hand, since the thin film thermistor chip can be connected to the support container 3 by brazing as shown in FIG. 2, it has the advantage of providing high-speed response. A thin film thermistor chip is usually constructed by forming an electrode film 5 and a temperature sensitive resistor film 6 on one surface of a flat ceramic insulating substrate 4 made of alumina or the like, and further, a lead wire 7 is connected to the electrode film 5. . The soldered connection between the thin film thermistor chip and the support container 3 is made of titanium.
This is done by using a brazing material layer 9 via a Ti foil or a zirconium Zr foil 8. However, in this case, the electrode film 5
Since the temperature-sensitive resistor film 6 is exposed to the external atmosphere, there is a drawback that characteristics change due to conductive dirt such as water droplets.

The present invention aims to protect the entire surface of the insulating substrate including the electrode film 5 and the temperature sensitive resistor film 6.

The gist of the present invention is to fabricate a thin film thermistor chip comprising an electrode film and a temperature sensitive resistance film formed on one surface of a flat ceramic insulating substrate and a support container made of titanium.
The entire surface of the flat ceramic insulating substrate, on which the electrode film of the thin-film thermistor chip and the temperature-sensitive resistor film are formed, is connected by brazing via Ti foil or zirconium Zr foil, and has a coefficient of thermal expansion of (40 to 60). ) ×
This is because it is coated with glass at a temperature of 10 ^-7 /℃.

In this way, in the fast-response thin-film thermistor of the present invention, the entire surface of the flat ceramic insulating substrate on which the electrode film and temperature-sensitive resistor film are formed is coated with electrically insulating glass, so water droplets etc. can protect thin film thermistor chips from conductive dirt. At this time, it is desirable that the coefficient of thermal expansion of the glass is in the range of (40 to 60) x 10 ^-7 /°C. This is because by selecting the coefficient of thermal expansion within this range, the glass coating film can form a dense film without cracks or pinholes.
This is because cracks and pinholes are likely to occur outside this range.

An embodiment of the present invention will be described below with reference to FIG. With respect to FIG. 3, the same numbers refer to the same parts as described above.

Alumina substrate 4 (1.8mmW x 6.5mmL x 0.5mmt)
Au-Pt thick film electrode 5 (10~15μ
mt) and a SiC temperature sensitive resistor film 6 (2 to 3 μmt) were formed to constitute a thin film thermistor chip. This thermistor chip and support container 3 (material SUS-430,
0.4 mm thick) were connected by brazing with a brazing material layer 9 (Ag--Cu eutectic alloy) via a Ti foil (50 μm thick) 8. Next, the lead wire 7 (Pt wire, 0.1
φ) were welded and connected. Furthermore, ZnO―B ₂ O ₃ ―SiO ₂
Separately prepare a mixed fluid of glass powder (particle size 350 mesh or less) whose main component is ethyl cellulose, diethylene glycol mono-normal butyl ether acetate, and apply this fluid over the entire surface of the thermistor chip. Coated. After this, the heating rate is approximately 15℃/min, and the maximum firing temperature is
The glass powder was fired at 660°C, with a holding time of about 5 minutes at the maximum firing temperature, and a cooling rate of about 15°C/min. The glass coating film 10 formed in this way has a thickness of 0.2 to 0.5 mm.
With a thickness of , no cracks or pinholes were generated over the entire surface of the insulating substrate 4 on which the electrode film 5 and the temperature-sensitive resistor film 6 were formed.

This thermistor was tested after 1000 hours at 350℃ in air, after 3000 heat cycles of 15 minutes at room temperature and 15 minutes at 350℃ in air, and after being left in boiling water for 8 hours. It was ±3% or less, and no cracks occurred after these tests. Furthermore, the resistance value did not change even under conditions where dew condensation is likely to occur, such as in a high humidity atmosphere.

In addition, in this example, ZnO-- was used as the glass material.
B ₂ O ₃ ---SiO ₂ was used as the main component, but this is because when the temperature-sensitive resistor film 6 is a SiC film, the short-term heat resistance of the SiC film in air is 600 to 750°C. , on the other hand, the firing temperature of the ZnO-B ₂ O ₃ -SiO ₂ -based glass material is
This is because the temperature is 650 to 740°C, which is excellent in that the thermal properties of the two are the same. Therefore, depending on the heat resistance of the temperature sensitive resistor film 6, other glass materials such as
It goes without saying that the PbO--B ₂ O ₃ ---SiO ₂ system or the Al ₂ O ₃ ---SiO ₂ system may be used.

As is clear from the above description, the thin film thermistor of the present invention provides the following effects.

1. Since a glass coating film is formed over the entire surface of the flat ceramic insulating substrate on which the electrode film and temperature-sensitive resistor film are formed, the thin film thermistor chip can be protected from conductive dirt such as water droplets.

2. As mentioned above, the glass material is applied using a fluid mixture of the glass material and an organic binder, but at this time, the amount of application is kept almost constant by controlling the viscosity of the fluid mixture. Since it can be maintained, the glass coating film can be formed almost uniformly. As a result, the heat capacity of the present thin film thermistor becomes almost uniform, so that the thermal response can be made uniform.

3. Since the glass coating film is also formed at the connection portion between the electrode film and the lead wire, the mechanical strength of the lead wire can be improved.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view showing a temperature detection configuration using a thermocouple, Fig. 2 is a cross-sectional view showing the structure of a conventional fast-response thin-film thermistor, and Fig. 3 is a cross-sectional view of the fast-response thin-film thermistor of the present invention. FIG. 3 is a cross-sectional view showing the configuration. 3... Support container, 4... Flat ceramic insulating substrate, 5... Electrode film, 6... Temperature sensitive resistor film, 7...
...Lead wire, 8...Ti foil or Zr foil, 9...
Brazing material layer, 10...Glass coating film.

Claims (1)

[Claims] 1. A thin film thermistor chip formed by forming an electrode film and a temperature-sensitive resistor film on one surface of a flat ceramic insulating substrate and a support container are connected by brazing via titanium foil or zirconium foil. Then, the entire surface of the flat ceramic insulating substrate on which the electrode film of the thin-film thermistor chip and the temperature-sensitive resistor film were formed was covered with glass having a coefficient of thermal expansion of (40 to 60) x 10 ^-7 /°C. Thin film thermistor. 2. The thin film thermistor according to claim 1, wherein the glass coating contains aene oxide, boron oxide, and silicon oxide as main components.