JPS6157682B2 - - 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 a 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. For example, Almeru Cromel thermocouples are heat resistant (500-1000℃ in air)
Although it is excellent in performance and inexpensive, it only generates an electromotive force of ~40 μV/°C. copper-constantan thermocouple,
Platinum-platinum-rhodium thermocouples not only provide a thermoelectromotive force of only (30 to 60) μV/℃;
Low heat resistance (copper-constantan thermocouple),
It had drawbacks such as being expensive (platinum-platinum-rhodium thermocouple). Various other thermocouples exist, but all of them have the drawbacks mentioned above. As mentioned above, when controlling the amount of heat generated by a heat source by electrically detecting a small thermoelectromotive force, a large electrical amplification is required, which increases the cost and requires a complicated electrical circuit. Shortcomings also emerged.

On the other hand, when temperature is detected using a thermistor instead of the thermocouple, the rate of change of resistance value with respect to temperature can be as large as (1 to 7%/°C). Therefore, it does not require a complicated electric circuit and has the advantage of 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, bead-type thermistor elements usually have a shape similar to a sphere or a spheroid, so even if the thermistor element is fixed to the support container 3, it has a drawback of increasing thermal resistance. 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 element can be connected to the support container 3 by brazing as shown in FIG. 2, it has the advantage of providing high-speed response. However, in this case, the following drawbacks also occurred. That is,
A general thin film thermistor element usually has an electrode film 5 and the aforementioned thin film temperature sensitive resistor film 6 formed on one surface of a flat insulating substrate 4 made of aluminum or the like, and further connects a lead wire 7 to the electrode film 5. It is composed of
If this continues, the thin film thermistor element will be placed in the support container 3.
(Usually made of heat-resistant metal such as stainless steel) cannot be brazed, so a metallized film 8 of W, Mo, etc. is formed on the other surface of the insulating substrate 4.
The support container 3 and the brazing material layer 9 were connected to each other by brazing. However, since metals such as W and Mo have high melting points and are easily oxidized, the metallized film 8
Usually at 1400℃ in a reducing atmosphere containing _H2 etc.
Formed at higher temperatures. For this reason, the manufacturing process is complicated and requires special equipment, as well as being expensive. Further, as the electrode film 5, a thick film electrode film with excellent heat resistance is often used.
Thick film electrode films easily deteriorate in reducing atmospheres, and their heat resistance is below 1000°C in air, so thick film electrode films are not suitable for the process of forming metallized films, and conversely, metallized films are also It is not compatible with the thick electrode film formation process (usually fired in air at a high temperature of 600 to 1000°C). Therefore, in the configuration shown in FIG. 2, a metallized film must also be used for the electrode film 5. For this reason, not only is the price high,
Since the metallized film has a high melting point when connecting the lead wire 7 to the electrode film 5, there is also the drawback that it is difficult to perform the commonly used welding connection.

The present invention provides a thermistor which eliminates these conventional drawbacks, and its configuration is shown in FIG.
The gist of the present invention is a thermistor constructed by connecting a thin film thermistor chip formed by forming an electrode film 5 and a temperature-sensitive resistor film 6 on one surface of a flat ceramic insulating substrate 4 to a support container 3. At least, a Ti foil 10 or a Zr foil 10 is interposed between the other surface of the ceramic insulating substrate 4 and the support container, and the two are connected by brazing.

The present invention will be described in detail below using an example using Ti foil 10.

The ceramic insulating substrate 4 and the protective container 3 are connected by brazing through the brazing metal layers 9 and 11 with a Ti foil 10 interposed therebetween. The brazing connection between the Ti foil 10 and the support container 3 is performed by metal bonding through the brazing material layer 9. Alumina, mullite, steatite, etc. are used for the ceramic insulating substrate 4. This ceramic insulating substrate 4 and Ti foil 10 are connected by brazing through a brazing material layer 11. usually,
The ceramic insulating substrate 4 made of alumina or the like and the brazing material layer 11 do not wet each other, that is, there is almost no chemical bonding force between them, so it is difficult to connect the ceramic insulating substrate 4 with brazing. .
However, when the brazing material layer 11 is formed between the Ti foil 10 or Zi foil 10) and the ceramic insulating substrate 4, the brazing material layer 11 and the ceramic substrate 4 wet each other well, and the Ti foil 10 and the ceramic substrate 4 are connected to each other by brazing through the brazing material layer 11. The details of this reason are unknown, but when the brazing filler metal is heated to a temperature higher than its liquidus temperature, a small amount of Ti atoms (or Zr atoms) diffuse through the molten brazing filler metal layer 11 and touch the brazing filler metal on the surface of the ceramic insulating substrate 4. layer 1
It is thought that 1 and ceramic are chemically bonded.

As described above, in the thermistor of the present invention, the ceramic insulating substrate 4 of the thin film thermistor chip and the support container 3 are directly brazed and connected through the brazing material layers 9 and 11 with the Ti foil 10 interposed.
For this reason, 90% thermal response time, i.e. first T1℃
_The temperature at the bottom of the pot in Figure ₁ , which had been maintained at
The time required for the temperature of the thin film thermistor chip to reach T ₁ + 0.9 ₍ T ₂ − _{T 1} )°C when the temperature changes to
~5 seconds, showing almost the same high-speed response as the configuration shown in Figure 2. Furthermore, the adhesive strength of the ceramic insulating substrate 4 to the support container 3 is 100 to 500 g/ ^mm2 ,
It showed sufficient strength for practical use. Further, in the configuration shown in FIG. 2, a metallized film 8 is formed on the other surface of the ceramic insulating substrate 4, but this is not necessary in the thermistor of the present invention. Therefore, the manufacturing process is simple and no special equipment is required. On the other hand, as the electrode film 5, Au-pt,
It also makes it possible to use thick electrode films such as Au, Ag, and Ag-Pd. That is, since it is not necessary to form the metallized film 8, the electrode film 5 is not exposed to a high-temperature reducing atmosphere. Therefore, a thick electrode film can be used as the electrode film 5 in FIG. Therefore, not only is the cost low, but also welding can be easily performed when connecting the lead wire 7 to the electrode film 5. It is clear that these things are the same even if Zr foil is used instead of Ti foil.

Note that since the thermal expansion coefficient of the ceramic insulating substrate 4 is (50 to 90) x 10 ^-7 /°C, it is desirable that the support container 3 has a similar value. Therefore, the support container 3 is made of Kovar alloy. , Ti, Ta, Zr, Mo,
It is preferable to use a material selected from W, Pt, stainless steel, Fe--Ni alloy, etc. actual,
The alumina ceramic insulating substrate 4 and the stainless steel (SUS-430) support container 3 were connected with brazing as shown in Fig. 3, and a thermal shock test was conducted in air at 350℃←→room temperature water.
Even after 1000 cycles, no mechanical deterioration of the brazed joint was observed, and the thermal response remained almost unchanged.

Also, Ag-Cu eutectic silver solder is excellent. This is because this silver brazing material is easy to process into a foil shape and is also used industrially in foil shape, so when forming the thermistor of the present invention, the support container 3 and the ceramic insulating substrate 4 are Ti foil between 10
Alternatively, by interposing the Zr foil 10, placing a foil brazing material at the position of the brazing material layers 9 and 11 in FIG. 3 and heating it, brazing connection can be easily achieved.

As described above, the thermistor of the present invention eliminates the conventional drawbacks and is industrially useful.

[Brief explanation of the drawing]

1 and 2 are cross-sectional views showing the structure of a conventional thermistor, and FIG. 3 is a cross-sectional view showing the structure of a thermistor according to an embodiment of the present invention. 3... Support container, 4... Ceramic insulating substrate,
5... Electrode film, 6... Temperature sensitive resistor film, 7... Lead wire, 9, 11... Brazing material layer, 10... Ti foil or Zr foil.

Claims (1)

[Scope of Claims] 1. A thermistor constructed by connecting a thin film thermistor chip, which is formed by forming an electrode film and a temperature-sensitive resistor film on one surface of a flat ceramic insulating substrate, to a support container, at least: A thermistor characterized in that a Ti foil or a Zr foil is interposed between the other surface of the ceramic insulating substrate and the support container, and the two are connected by brazing. 2 The support container is made of Kovar alloy, Ti, Ta, Zr,
The thermistor according to claim 1, characterized in that it is made of a material selected from Mo, W, Pt, stainless steel, Fe--Ni alloy, etc. 3. The thermistor according to claim 1, wherein the brazing material is Ag--Cu eutectic silver brazing material.