JPH02305405A - thin film thermistor - Google Patents

Abstract

PURPOSE:To make it possible to conduct temperature measurement in a precise manner for a long period even under adverse surroundings by a method wherein a thermistor element, inner lead wires and outer lead wires housed in a protective tube in a state wherein they are airtightly closed at one end each, and they are shut off from external environment. CONSTITUTION:A thermistor element 4, inner lead wires 7 and 7'. and outer lead wires 5 and 5' are housed in a one closed type metal protective tube 11, and the thermistor element 4 is fixed using an element supporting member 6, the outer lead wires 5 and 5', a cover 9 and the protective tube 11. Besides, the protective tube 11 and the cover 9 are fixed by caulking the narrow parts 12a to 12b formed by partially cutting the outer circumferential surface of the cover 9 and the protective tube 11. Consequently, as the thermistor element, the inner and outer lead wires are shut off from external environment, temperature can be measured precisely under adverse surrounding, and the high reliability of the title thin film thermistor can be maintained for a long period.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application 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 stoves, combustion appliances such as kerosene fan heaters, and the like.

Background Art Various mounting structures have been considered for thin film thermistors in order to protect a thermistor element, which includes a pair of thick film electrode films and a temperature sensitive resistor formed on an alumina substrate, from the environment in which it is used.

For example, electronics ceramics, °85.5
According to the Monthly Issue, Special Feature on Thin Film Electronic Materials, page 16, thin film thermistors are made by hermetically sealing the thermistor element inside a glass tube, and welding the PT internal lead wire from the thermistor element to a Kovar wire (external lead wire). It's being taken out of the tube. Then, a protective cover was installed to complete the process.

Problems to be Solved by the Invention The above-mentioned conventional thin film thermistor has a usable temperature of 3.
The temperature is up to 50°C, and if the temperature is higher than that, the characteristics will be greatly affected by the external environment due to the following problems, and it cannot be used.

The first problem is that water scum generated in large quantities inside the cooking cabinet or in the combustor tends to adhere to external lead wires, thermistor elements, holding bases, etc. that are exposed to the outside environment. Electrical conduction occurs due to the adhesion of water vapor, and electrical insulation tends to deteriorate. To counter this, conventional thin film thermistors are coated with polytetrafluoroethylene resin to make them water repellent and prevent condensation.
The heat resistance of this resin is 350°C, and when the temperature exceeds that temperature, the resin deteriorates and the water repellency effect decreases, and the electrical insulation properties decrease accordingly, making it impossible to accurately measure the temperature.

The second? i. The problem is that the glass tube that protects the thin film thermistor element from the external environment is sealed to the Kovar external reed wire through a chemical bonding layer at the interface.
'C or higher, due to the difference in thermal expansion characteristics of the two materials,
When a large temperature difference occurs, a large strain occurs, causing damage and deterioration of the glass tube. This means that for conventional thin film thermistors, after examining materials with various chemical compositions, we selected silicic acid-based glass as a glass material with a glass thermal expansion coefficient close to that of the Kovar external lead wire. This is because it has been confirmed that there is no practical problem at operating temperatures up to 350°C. Therefore, there was a problem that it could not be used at temperatures above 350° C. where large temperature differences tend to occur.

Means for Solving the Problem In order to solve this problem, the thin film thermistor of the present invention has the following features:
a thermistor element, an element support to which the thermistor element is fixed, a pair of external lead wires that hold the element support and are electrically connected to the thermistor element through an internal lead wire; It consists of a cylindrical ceramic lid that holds and fixes the pair of external lead wires in the through holes, and a metal protective tube with one end sealed that houses the thermistor element and the lid. A narrow portion formed by partially cutting is held and fixed by caulking with the protection tube.

Function The thin film thermistor of the present invention has a thermistor element housed in a protective tube with one end sealed, so it is isolated from the external environment and prevents chemical deterioration of the element due to harmful environmental factors such as organic matter, moisture, and corrosive gases. can. Therefore, high credibility can be maintained for a long period of time. In addition, not only the thermistor element but also the internal and external lead wires are housed in a protective tube with one end sealed, so they are isolated from the external environment, and there is no risk of deterioration of electrical insulation due to water vapor adhering to these parts. does not occur. Therefore, temperature can be measured accurately even in an atmosphere with a lot of water vapor and easy to condense.

On the other hand, the protective tube that isolates the thermistor element from the external environment does not require sealing of materials with different coefficients of thermal expansion and is made of only a single material, so there is no distortion caused by thermal shock. To prevent damage or deterioration of a protective container even if the temperature drops rapidly to room temperature, to isolate a thermistor element from the external environment for a long period of time, and to accurately measure temperature at high temperatures for a long period of time.

On the other hand, the thermistor element is fixed on the element support,
Furthermore, this element support is held by a pair of external lead wires, and these external lead wires are held and fixed to the lid, and the lid and protection tube are ultimately held and fixed by caulking, so they are strongly fixed and have mechanical strength. Excellent. In particular, the ceramic cylindrical lid and the metal protective tube are held and fixed by partially cutting the outer circumferential surface of the lid and crimping the protective tube into a narrow part, which prevents mechanical vibration. etc., and will not cause mechanical breakage or electrical shorts. In addition, a sufficient insulation distance between the pair of external lead wires and the protection tube is ensured because the narrow part formed by partially cutting the outer circumferential surface of the lid is crimped and fitted to the protection tube. No electrical short circuit occurs under iA environment.

Example Examples of the present invention will be described in detail below.

FIG. 1 is an external view of the thermistor element of the present invention. A pair of thick film electrode films 2.2° and a temperature sensitive resistor 3 are formed on a ceramic substrate 1. For the ceramic substrate 1, an alumina substrate is used in consideration of practicality, and its surface roughness is 2 to 3 μm.
It was set as m.

On the other hand, the temperature-sensitive resistor 3 is made of metal oxides, silicon carbide (hereinafter referred to as SiC), etc., but SiC is used because it has high sensitivity and can measure over a wide temperature range, and is made in a comb shape using a spunter method. The thin film (approximately 6μ thick) is placed on top of the thick film electrode film.
m) was formed.

The thick film electrode films 2 and 2' are Au-Pt film, PT film, Au film, etc., but a paste is printed, dried, and fired on the alumina substrate 1 using an Au-Pt film with high chain reliability. I got it by doing that.

FIG. 2 is a sectional view of a thermistor which is an embodiment of the present invention, and FIG. 3 is a sectional view taken along line AA'' in FIG.

A thermistor element 4 is placed on an element support 6 to which a pair of external lead wires 5 and 5' are fixed, and the pair of thick film electrodes IIi! 2.2° and the pair of external lead wires 5.5'' were electrically connected to each other at internal lead wires 7.7°.

Thereafter, the thermistor element 4 was covered with a glass coating layer 8 having a coefficient of thermal expansion approximately equal to that of the salamic substrate 1 and the element support 6 to further protect it from the external environment.

Note that when the glass covering layer 8 covers the thermistor element 4, it also fixes the thermistor element 4 and the element support 6 at the same time. On the other hand, the pair of external lead wires 5.5'' and the element support 6 are fixed by inserting the external lead wires 5.5° into the through hole provided in the element support 6, and bending or twisting the ends. A step was created so that the dimension was larger than that of the through hole.Electrical continuity between the pair of external lead wires 5 and 5' and the thick film electrode films 2 and 2° through the internal lead wires 7 and 7'' was as follows. It was obtained by connecting internal lead wires 7.7° to each other using a welding method.

Next, a pair of external lead wires 5 and 5" are inserted into two through holes 10 and 10° provided perpendicularly to the bottom surfaces 9a and 9b of the cylindrical lid 9.
It was inserted into the lid 9 and held and fixed to the lid 9 by bending or twisting near the bottom surfaces 9a and 9b. After that, the thermistor element 4 is stored in the protection tube ll, and the bottom surfaces 9a and 9b of the lid are
Narrow portion 12a formed by partially cutting the nearby outer peripheral surface
- 12b-12c and 12d were caulked with the protective tube 11 to form steps 13a □ 13b -13c and 13d, thereby holding and fixing them to each other. The protective tube 11 was sealed at one end.

4 and 5 are perspective views of the cylindrical lid. In FIG. 4, the narrow portions 12a, 12b, 12c, and 12d are diagonal to the outer peripheral surface, and in FIG. 5, the narrow portions 12a, 12b, 12c, and 12d are
is formed by cutting the outer circumferential surface near both bottom surfaces parallel to the outer circumferential surface.

Metal external lead wire 5.5'' and metal protection tube 11
The material is stainless steel 114 such as 5US304.5US430.

The ceramic element support 6 and the ceramic lid 9 are made of one or more materials selected from the group of alumina, calcium oxide, silicon oxide, magnesium oxide, zirconium oxide, titanium oxide, and the like.

The internal lead wires 7 and 7' are made of platinum wire, nickel wire, Kovar wire, or the like.

The effects of the present invention were determined based on the examples shown in FIGS. 1 to 4.

A thick film electrode film (film thickness approximately 12 μm) of Au:Pt=3 near was placed on an alumina substrate (1.8 mm x 6.5 Mm x 0.5
M) was formed into a comb shape, and then a SiC resistor film with a thickness of about 6 μm was formed by high frequency sputtering vapor deposition to form a thermistor element.

This thermistor element is fixed on an alumina element support using glass after electrically connecting a platinum mold internal lead wire to a pair of thick film electrode films using a welding method. Glass is 5iOz50%, Ba025%, Ca01
It is a composition containing 0%, Boo, and Al z○3 in addition, and has a thermal expansion coefficient of 7×10 −6 /′C, which is comparable to that of alumina for the substrate and element support. On the other hand, it has a transition point of 660°C and has excellent heat resistance. This glass has a particle size distribution with an average particle size of 14.5 μm and a maximum particle size of 50 μm. It is made into a paste by adding an ethyl cellulose vehicle, and is dried and fired to coat the thermistor element and form a paste with the element support. Got fixed.

Next, connect the 5US430 external lead wire (1.2 m x 10
0 mm x 1.3' M) was inserted into the alumina element support, bent and fixed, and then the internal lead was fixed to the external lead wire using a welding method.

Next, a pair of external lead wires were inserted into two through-holes provided perpendicularly to the bottom of the cylindrical lid, twisted near both bottoms to form a step larger than the through-hole, and were held and fixed to the lid. Thereafter, the thermistor element was housed in the protective tube, and a narrow portion formed by partially cutting the outer circumferential surface near the bottom of the lid was caulked with the protective tube to provide a step, and the elements were held and fixed together.

The reliability of this thin film thermistor was evaluated.

A thin film thermistor is placed in a high temperature atmosphere (500°C) for 1000°C.
When this thermal shock is repeated 2,000 times, with one cycle of (leaving in air at room temperature for 15 minutes → leaving in air at 500°C for 15 minutes → leaving in air at room temperature for 15 minutes), the rate of change in resistance value is , all were ±3% or less.

In addition, high-temperature modified surrounding air (temperature 70°C, relative humidity 95%)
or more) for 1,000 hours, or in boiling water for 8 hours.
Even when left for a long time, the rate of change in resistance value was within ±3% in all cases. On the other hand, the following dew condensation test was conducted on the sample after the above test. Fill a beaker with water and boil it to generate a large amount of water vapor, while preparing a thin film thermistor held at room temperature, and quickly exposing this thin film thermistor to the water vapor to form condensation water on the surface. Ta.

In this state, the electrical insulation was measured by applying 15 V DC between the external lead wire and the ground terminal, and it was found that the insulation resistance was 100 MΩ or more. This test is a test for evaluating electrical insulation, and since conduction is shown in the absence of insulation, it can be said that the high resistance value of the present invention means that there is no practical problem with electrical insulation.

Thin film thermistors vibrate close to a sine wave (frequency 300 to 3
600Hz, amplitude 0.2-3.2mm, acceleration 1-3G
) was applied in the x, y, and z directions for 2 hours each, but no change in temperature-resistance characteristics was observed, and it was confirmed that the material was resistant to mechanical vibration.

As described above, the thin film thermistor of the present invention has a thermistor element, an internal lead wire, and an external lead wire housed in a metal protective tube with one end sealed, and the thermistor element is housed in an element support, an external lead wire, and an external lead wire. It is fixed using a lid and a protective tube, and the protective tube and lid are fixed by caulking the protective tube and the narrow part formed by partially cutting the outer circumferential surface of the lid. It has the following effects.

(1) Since the thermistor element is isolated from the external environment,
It can prevent chemical deterioration of the device due to harmful environmental factors such as organic matter, moisture, and corrosive gases, and can maintain high reliability for a long period of time.

(2) Not only the thermistor element but also the internal and external lead wires are isolated from the external environment, so there is no drop in electrical insulation due to water vapor adhesion.Therefore, temperature accuracy can be maintained even in an atmosphere with a lot of water vapor and prone to condensation. Can be measured well.

(3) The one-end sealed metal protective tube that isolates the thermistor element from the external environment does not seal materials with different coefficients of thermal expansion, so no distortion occurs due to thermal shock.

Therefore, even if the temperature is drastically lowered from high temperature to room temperature, there is no damage or deterioration of the protective container, the thermistor element is isolated from the external environment for a long period of time, and the temperature can be measured accurately for a long period of time at high temperatures.

(4) The protection tube and the lid are fixed by caulking the protection tube with the narrow part formed by partially cutting the outer circumferential surface of the lid, so the lid moves axially inside the protection tube. It is firmly fixed to the lid without moving or rotating in the circumferential direction. In addition, the insulation distance between the external lead wire and the protection tube is only slightly reduced due to the reduction in the inner diameter of the protection tube formed by caulking the protection tube, so there is no problem with electrical insulation in a humid environment. Furthermore, if the narrow portions are formed on the outer circumferential surface near both bottom surfaces of the lid, the lid can be easily molded using a press or the like, resulting in an advantage of low cost.

[Brief explanation of the drawing]

Fig. 1 is an external perspective view of a thermistor element according to an embodiment of the present invention, Fig. 2 is a cross-sectional view of the same thin film thermistor, Fig. 3 is a cross-sectional view taken along line AA' in Fig. 2, and Fig. 4 is a cross-sectional view of the thermistor element according to the present invention. FIG. 5 is an external perspective view of a lid according to another embodiment of the present invention. 1... Ceramic substrate, 2.2゛...
Thick film electrode film, 3... Temperature sensitive resistor, 4...
・Thermistor element, 5, 5'...External lead wire, 6...Element support, 7,7''...Internal lead wire, 8... Glass coating layer, 9...
...Lid, 9a/9b...Bottom of lid, 10-10
'...Through hole, 11...Protection tube, 1
2a, 12b-12c, 12d... Narrow area. Name of agent: Patent attorney Shigetaka Awano. Toso regret

Claims (2)

[Claims] (1) A thermistor element, an element support to which the thermistor element is fixed, a pair of external lead wires that hold the element support and are electrically connected to the thermistor element through an internal lead wire, and a pair of external lead wires that are perpendicular to the bottom surface. It is composed of a cylindrical ceramic lid that holds and fixes the pair of external lead wires in two through holes provided in the lid, and a metal protective tube with one end sealed that houses the thermistor element and the lid. A thin film thermistor in which a narrow portion formed by partially cutting the outer peripheral surface of the thermistor is held and fixed by caulking with the protective tube. (2) The thin film thermistor according to claim (1), wherein the narrow portion is partially cut off from the outer peripheral surface near both bottom portions of the lid.