JP2543174B2 - Thin film thermistor - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-resistant thin film thermistor used as a temperature sensor for cooking appliances such as electric ovens and gas ovens, and combustion appliances such as oil fan heaters.

2. Description of the Related Art As a thin film thermistor, various mounting structures have been devised in order to protect a thermistor element in which a pair of thick film electrode films and a temperature sensitive resistor are formed on an alumina substrate from a use environment.

For example, according to Long, et al., Electronics and Ceramics, '85, May issue, Special Issue on Thin Film Electronic Materials, page 16,
In the thin film thermistor, the thermistor element is hermetically sealed inside the glass tube, and the Pt internal lead wire from the thermistor element is welded to the Kovar wire (external lead wire) and taken out of the glass tube. Then, the holding base and the protective cover are attached to complete the process.

Problems to be Solved by the Invention Conventional thin film thermistors such as the above can be used at temperatures up to 350 ° C, and at higher temperatures the characteristics are greatly affected by the external environment due to the following problems and cannot be used. .

The first problem is that a large amount of water vapor generated in the cooking chamber or in the combustor easily adheres to the external lead wire, thermistor element, holding base, etc. exposed to the external environment. This is because the adhesion causes electrical conduction, and the electrical insulation is likely to be deteriorated. To prevent this, for example, a conventional thin film thermistor has been coated with a tetrafluoroethylene resin to prevent condensation by utilizing water repellency.
The heat resistance of this resin is 350 ° C., and at temperatures higher than 350 ° C., the resin deteriorates and the water repellency effect decreases, and along with that, the electrical insulation decreases and the temperature cannot be measured correctly.

The second problem is that the glass tube that protects the thin film thermistor element from the external environment is sealed through the chemical bond layer at the interface with the Kovar external lead wire. Due to the difference in the thermal expansion characteristics, a large strain is generated and the glass tube is damaged and deteriorated. This is because the conventional thin film thermistor, as a glass material having a glass thermal expansion coefficient close to the Kovar external lead wire, as a result of examining materials of various chemical compositions,
This is due to the fact that we have selected borosilicate glass and confirmed that it does not hinder practical use up to the operating temperature of 350 ° C. Therefore, there is a problem that it cannot be used at 350 ° C or higher where a large temperature difference is likely to occur.

Means for Solving the Problems In order to solve the above problems, a thin film thermistor of the present invention is a thin film thermistor element having a pair of thick film electrode films and a temperature sensitive resistor formed on a substrate, and fixing a pair of external lead wires. Fixed on the element support, electrically connecting each of the pair of thick film electrode films and the pair of external lead wires with an internal lead wire, and a protective container containing the element support,
The lid fixing the pair of external lead wires was fitted, and the fixing portion between the pair of external lead wires and the lid was covered with an insulating material to increase the creeping distance between the pair of external lead wires. It is as a configuration.

In the above structure, the insulating material is at least one selected from the group consisting of heat resistant adhesive, heat resistant paint, glass, enamel and heat resistant rubber.

The thin-film thermistor of the present invention has the thin-film thermistor element housed in the protective container, so that it is shielded from the external environment and prevents chemical deterioration of the thin-film thermistor element due to harmful environmental factors such as organic matter, moisture and corrosive gas. it can. Therefore, high reliability can be maintained for a long period of time. Also, not only the thin film thermistor element but also the internal and external lead wires are housed in a protective container, so they are shielded from the external environment.
The deterioration of the electrical insulation due to the adhesion of water vapor to these parts does not occur. Therefore, the temperature can be accurately measured even in an atmosphere in which a large amount of water vapor easily causes dew condensation.

On the other hand, the protective container that shields the thin film thermistor element from the external environment is not sealed with materials having different thermal expansion coefficients, and is made of only the same material, so that distortion due to thermal shock does not occur. Therefore, even if the temperature is rapidly lowered from high temperature to room temperature, the protective container is not damaged and deteriorated, the thin film thermistor element is shielded from the external environment for a long period of time, and the temperature is accurately measured at a high temperature for a long period of time.

Further, the thin film thermistor element is fixed on the element support, and this element support is fixed to a pair of external lead wires, and the pair of external lead wires is a lid part fitted with the protective container. Due to the fixed construction, the thin film thermistor element is firmly fixed in the protective container. Therefore, it is possible to prevent the thin film thermistor element from coming into contact with the protective container due to mechanical vibration or the like, and there is no occurrence of mechanical damage or electrical short.

Furthermore, since the creeping distance along the lid between the pair of external lead wires is increased by using a means of covering the pair of external lead wires with an insulating material in the vicinity of the fixed portion with the lid, this thin film thermistor is It is possible to prevent a decrease in electrical insulation due to dew condensation in a high temperature atmosphere, and to correctly measure the temperature in the high humidity atmosphere.

Examples Hereinafter, examples of the present invention will be described in detail.

FIG. 1 is an external view of the thin film thermistor element of the present invention. A pair of thick film electrode films 2 and a temperature sensitive resistor 3 are formed on a ceramic substrate 1. As the ceramic substrate 1, an alumina substrate is used in consideration of practicality, and its surface roughness is 2 to 3 μm.
m.

On the other hand, the temperature-sensitive resistor 3 includes metal oxide, silicon carbide (hereinafter referred to as SiC), etc., but because of its high sensitivity and the ability to measure over a wide temperature range, SiC is used and the comb-shaped sputtering method is used. On the thick electrode film 2 of
m) was formed.

The thick film electrode film 2 is an Au-Pt film, a Pt film, an Au film, or the like, and it is obtained by using a highly reliable Au-Pt film and printing, drying, and baking a paste on an alumina substrate.

FIG. 2 is a sectional view of a thin film thermistor which is an embodiment of the present invention.

The thin film thermistor element 4 is fixed on an element support 6 to which a pair of external lead wires 5 are fixed, and the pair of thick film electrode films 2 and the pair of external lead wires 5 are electrically connected by an internal lead wire 7. A protective container 9 accommodating the element support 6 and a lid 8 to which the pair of external lead wires 5 are fixed, and further fitted to each other, and further to the pair of external lead wires 5 and the lid 8. The fixed portion is covered with an insulating material 11 to increase the creepage distance between the pair of external lead wires 5.

As the insulating material 11, heat-resistant adhesive or heat-resistant paint, glass, enamel, porcelain, heat-resistant rubber, etc. are used, and the components are silica, alumina, silica-alumina, polyimide, fluorine, silicon, polyimide amide, polyarylate, polysulfone. , Polyphenylene sulfide, polyether ether ketone, polyether sulfone, polyphenylene ether, polyether imide, alkali metal silicate, acidic metal phosphate, borosiloxy acid and the like.

When the pair of external lead wires 5 are fixed to the lid 8, these insulating materials 11 cover the fixed portions thereof. In this fixing method, a heat-resistant adhesive, a heat-resistant paint, glass, enamel, etc. were obtained by a step of applying a slurry viscous fluid and drying and firing. On the other hand, the insulator and the heat resistant rubber were fixed by applying a pair of external lead wires 5 through the inside and further applying a heat resistant adhesive, a heat resistant paint, glass, enamel or the like. By covering the vicinity of the fixed portion between the pair of external lead wires 5 and the lid 8 with this adhesive insulating material 11, not only the creepage distance between the pair of external lead wires 5 increases, but also the external lead wires. There is also an advantage that the fixation between the lid 5 and the lid 5 becomes firm. Further, since it is not necessary to cover the entire surface of the external lead wire 5 with the insulating material 11, the insulating material 11 can be saved.

The thin film thermistor element 4 and the element support 6 are fixed to each other via the glass coating layer 10.
Also serves to cover and fix the connection portion of the internal lead wire 7 electrically connected to the thick film electrode film 2.

The material of the external lead wire 5 and the protective container 9 is SUS306, S
It is a heat resistant metal such as US430, nickel and copper.

The material of the element support 6 and the lid 8 is ceramic, and is one or more selected from the group consisting of alumina, calcium oxide, magnesium oxide, zirconium oxide, titanium oxide, and silicon oxide.

The internal lead wire 7 is a platinum wire, a nickel wire, a Kovar wire, or the like.

FIG. 3 is a sectional view taken along the line AA ′ of FIG. The thin film thermistor element formed of the temperature sensitive resistor 3 formed on the ceramic substrate 1 is covered with the glass coating layer 10 and the element support 6 is provided.
You can see that it is fixed to. The glass coating layer 10 further strongly protects the temperature sensitive resistor 3 from the external environment.

The protective container 9 has a structure in which one end of the pipe is closed to reduce the cost.

The glass coating layer 10 is made of a material having a coefficient of thermal expansion substantially equal to that of the element support 6, and is made resistant to thermal shock.

The effect of the present invention was determined based on the examples of FIGS.

Example 1 A thick electrode film of Au: Pt = 3: 7 (thickness: about 12 μm) was formed in a comb shape on an alumina substrate (1.8 mm × 6.5 mm × 0.5 mm), and then high frequency sputtering deposition method was used. Thus, a SiC resistor film was formed to a thickness of about 6 μm to obtain a thin film thermistor element.

In this thin film thermistor element, an internal lead wire made of platinum is electrically connected to a pair of thick film electrode films by a welding method, and then fixed on an alumina element support using glass.

Next, the external lead wire of SUS304 and the lid of alumina were fixed to each other by using a means for covering the insulating material as shown in FIG. 2 to increase the creepage distance (specifically, 6 mm or more) to form a component, The moisture resistance of the thin film thermistor housed in a SUS430 protective container was evaluated. To evaluate the moisture resistance, fill the beaker with water and boil it to generate a large amount of water vapor, while preparing a thin film thermistor held at room temperature.
Quickly expose this thin film thermistor to the water vapor,
The electrical insulation is measured at DC 15V between the external lead wire and the ground terminal when condensed water is generated on the surface.

As insulating material, silicone resin, fluororesin, glass,
The structure coated with enamel showed an insulation resistance of 100 MΩ or more and had excellent moisture resistance. On the other hand, the other structural products coated with the above-mentioned heat-resistant material also had an electric resistance of about 100 MΩ and had no practical problem. In addition, the method of applying the coating material after coating the adhesive provides a structure that is firmly fixed and resistant to vibration.

<Example 2> Next, a thin film thermistor element was used, and the transition point was 675 ° C and the yield point was 7
Glass with a softening point of 861 ℃ at 42 ℃ (Composition: SiO ₂ 50%, BaO 25%, C
A thin film thermistor with a structure coated with aO 10% and other Al ₂ O ₃ and B ₂ O ₃ was manufactured as shown in Fig. 2 and its reliability was evaluated. The insulating material is fluororesin.

When the thin film thermistor is left in a high temperature atmosphere (500 ° C) for 1000 hours or ((room temperature air for 15 minutes → 500 ° C
When this thermal shock was repeated 1000 times with one cycle of standing in the air for 15 minutes → standing at room temperature in the air for 15 minutes, the rate of change in resistance was ± 3% or less in all cases.

Furthermore, when left in a high-humidity atmosphere (temperature 70 ° C., relative humidity 95% or more) for 1000 hours, or when left in boiling water for 8 hours, the rate of change in resistance was within ± 3%. The same characteristics were obtained when silicon resin, glass, enamel or other heat resistant material was used as the insulating material.

This glass-coated product exhibits excellent heat resistance, thermal shock resistance, and moisture resistance as compared with the structure product without glass coating of Example 1. For example, the heat resistance is 1000 even at 500 ° C.
While the rate of change in resistance value of ± 3% was maintained, the rate of change in resistance value of ± 3% could be maintained for only 200 hours at 500 ° C. without the glass coating. It is considered that this is because the glass coating further strengthened the shielding of the thin film thermistor element from the external environment.

On the other hand, the composition of the thick film electrode film is Au: Pt = 1: 9, Au: Pt = 2: 8,
Even when changed to Au: Pt = 4: 6, Au: Pt = 5: 5, Au: Pt = 6: 4, Au: Pt = 7: 3, almost the same characteristics as those of Example 1 and Example 2 were obtained. Was given.

Effects of the Invention As described above, the thin film thermistor of the present invention has the thin film thermistor element and the internal lead wire / external lead wire housed in a protective container, and the thin film thermistor element is an element support /
Fix via external lead wire, lid, protective container, and
Since the creepage distance along the lid between the external lead wires is made large by using a means of covering the fixing portion between the external lead wires and the lid with an insulating material, the lead wire fixing method is provided. (1) Thin film thermistor Since the element is shielded from the external environment, it is possible to prevent chemical deterioration of the element due to harmful environmental factors such as organic matter, water and corrosive gas, and to maintain high reliability for a long time.

(2) Not only thin film thermistor element but also internal lead wire
Since the external lead wire is shielded from the external environment and the external lead wire that is partially exposed to the external environment also has a large creepage distance, there is no reduction in electrical insulation due to water vapor adhesion. Therefore, the temperature can be accurately measured even in an atmosphere where a large amount of water vapor is likely to be condensed.

(3) Since the protective container that shields the thin film thermistor element from the external environment is made of the same material and is not sealed with a material having a different coefficient of thermal expansion, distortion caused by thermal shock is small. Therefore, even if the temperature is rapidly decreased from high temperature to room temperature, the protective container is not destroyed and deteriorated, the thin film thermistor element is shielded from the external environment for a long time, and the temperature can be measured accurately at a high temperature for a long time.

(4) Since the thin film thermistor element is firmly fixed in the protective container, it is resistant to mechanical vibration. In particular, in the lead wire fixing method in which the fixing portion between the external lead wire and the lid is covered with an insulating material having an adhesive action, the fixing is strong and mechanical vibration is further strengthened.

[Brief description of drawings]

FIG. 1 is an external perspective view of a thin film thermistor element which is an embodiment of the present invention, FIG. 2 is a sectional view of the same thin film thermistor, and FIG.
The drawing is a sectional view taken along the line AA 'in FIG. 1 ... Substrate, 2 ... Thick film electrode film, 3 ... Temperature-sensitive resistor, 4
...... Thin film thermistor element, 5 ...... External lead wire, 6 ......
Element support, 7 ... Internal lead wire, 8 ... Lid, 8 '...
Recessed portion, 8 "... raised portion, 9 ... protective container, 10 ... glass coating layer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuo Ebisawa, 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP 6327001 (JP, A) JP 61- 23301 (JP, A)

Claims (2)

(57) [Claims] 1. A thin film thermistor element having a pair of thick film electrode films and a temperature sensitive resistor formed on a substrate is fixed on an element support having a pair of external lead wires fixed thereto, and the pair of thick film electrode films is fixed. And a pair of external lead wires are electrically connected to each other by an internal lead wire, and a protective container accommodating the element support is fitted with a lid fixing the pair of external lead wires, and further, A thin film thermistor in which a fixing portion between a pair of external lead wires and the lid is covered with an insulating material to increase a creepage distance between the pair of external lead wires. 2. The thin film thermistor according to claim 1, wherein the insulating material is at least one selected from the group consisting of heat resistant adhesives, heat resistant paints, glass, enamel, insulators and heat resistant rubbers.