JPH11121207A - Temperature sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a temperature sensor which can be used at a high temperatures in a range of 800 to 1,000 deg.C. SOLUTION: A resistor pattern 3 made of a platinum group element and having a thickness of 2.5 to 5 μm and an average crystal grain size of 10 μm or greater is formed on an insulating board 2 by electroless plating. Terminal mounting electrodes 4 and 4 are formed on both ends of the resistor pattern 3. Lead terminals 5 and 5 are connected and fixed to the terminal mounting electrodes 4 and 4 by a method such as welding. Connection parts between the terminal mounting electrodes 4 and 4 and the lead terminals 5 and 5 are coated with fixing materials 6 and 6. Moreover, a protective coating film 7 made of resin or glass is formed on the resistor pattern 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high temperature sensor used for measuring the temperature of a catalyst, an exhaust pipe or the like of an automobile at a high temperature.

[0002]

2. Description of the Related Art FIG. 2 shows a conventional general temperature sensor 11. A resistance pattern 13 made of a temperature-sensitive film is formed on an insulating substrate 12 made of ceramic, and terminal mounting electrodes 14 and 14 are formed at both ends of the resistance pattern 13. Lead terminals 15, 15 are connected and fixed to the terminal mounting electrodes 14, 14 by means such as welding. Terminal mounting electrode 14, 1
The fixed portions of the connection between the lead 4 and the lead terminals 15, 15 are coated with fixing materials 16, 16, and a protective coat film 17 such as resin or glass is formed on the resistance pattern 13.

The temperature-sensitive film constituting the resistance pattern 12 is usually made of a noble metal such as platinum or an alloy containing platinum, or a base metal such as nickel, iron, copper or an alloy thereof. Among them, a temperature-sensitive film using a base metal such as nickel, iron, copper or an alloy thereof has a problem that the temperature-sensitive film is oxidized at a high temperature, so that a characteristic change such as a change in resistance occurs. I was The temperature-sensitive film made of these base metals has a practical temperature of about 300 ° C., and when used at a higher temperature, the characteristics change as described above, so that the exhaust temperature reaches an average temperature of 800 to 1000 ° C. It could not be used for high temperature measurements of tube temperature.

[0004] On the other hand, platinum is chemically extremely stable, so that temperature sensors such as a resistance temperature detector using platinum as a temperature-sensitive film are often used for high-temperature applications.

As a method for forming such a temperature-sensitive film using platinum, there are methods such as a sputtering method as disclosed in JP-A-63-269502 and an electroless plating method as disclosed in JP-A-57-207835. . The thickness of these platinum thermosensitive films is set to about 1 μm in the sputtering method of JP-A-63-269502.
In the electroless plating method of No. 207835, the thickness is set to about 1.5 μm. That is, 0.5 to 1.5 μm
Was used as an average thickness.

Japanese Patent Application Laid-Open No. 6-96904 discloses an electroless plating method having a film thickness of 3 μm and a crystal grain size of 450 ° to 50 °.
A platinum temperature sensor having a 0 ° platinum sensitive film is described.

[0007]

By the way, even in the case of such a temperature sensor having a platinum temperature-sensitive film, 600 to 7
00 ° C. is the maximum usable temperature, and if it exceeds this, there is a problem that characteristic fluctuations such as a change in resistance value occur. That is, a temperature sensor having a platinum temperature-sensitive film having a conventional structure cannot be used as a general-purpose temperature sensor for an automobile or the like used at a high temperature of 800 to 1000 ° C.

As a temperature sensor used at a high temperature such as 800 to 1000 ° C., a temperature sensor in which a platinum wire is wound around a high-purity alumina tube is known, but the resistance value is as low as 3 to 5 Ω and at least 50 Ω. It could not be used as a general-purpose temperature sensor for an automobile or the like that requires a certain resistance value.

In order to solve such a problem, Japanese Patent Laid-Open Publication No.
Japanese Patent No. 503511 proposes a configuration in which a glass film and a ceramic film are laminated on a platinum temperature-sensitive film. That is, in Japanese Patent Application Laid-Open No. 4-503511, as in the case of the base metal, oxygen enters the platinum temperature-sensitive film and oxidizes the platinum temperature-sensitive film when used at a high temperature. As a cause, a characteristic change is prevented by laminating a glass film and a ceramic film on the platinum temperature-sensitive film.

However, since platinum is a substance that is very resistant to oxidation, there is almost no change in the characteristics of the thermosensitive film due to oxidation even at high temperatures. Actually pursuing the cause of the characteristic fluctuation of the temperature-sensitive film, the characteristic fluctuation of the temperature-sensitive film is caused by a trace amount of impurities such as sulfur and carbon entering the crystal grain boundary of platinum at a high temperature. It has been found.

The present invention has been made in view of the above problems, and has as its object to provide a temperature sensor that can be used at a high temperature of 800 ° C. to 1000 ° C.

[0012]

According to the present invention, there is provided a temperature sensor in which a temperature-sensitive film containing a platinum group element as a main component is formed on an insulating substrate. At the same time, the temperature-sensitive film is formed to have a thickness of 2.5 to 5.0 μm, and the average particle size in the surface spreading direction of the temperature-sensitive film is 10 μm or more.

As a result, the density of grain boundaries in the temperature-sensitive film decreases.

Further, in the invention according to claim 2, the insulating substrate is an alumina substrate, and the temperature-sensitive film is a platinum temperature-sensitive film having a purity of 99.9% or more.

[0015] Thus, the possibility of impurities being mixed in is lower than that of a platinum thermosensitive film having a purity of platinum lower than 99.9%.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment of the present invention will be described. As shown in FIG. 1, the temperature sensor 1 is formed by forming a resistance pattern 3 made of a temperature-sensitive film on an insulating substrate 2. The insulating substrate 2 is an alumina substrate, and the resistance pattern 3 is a 99.9% pure platinum film.

On both ends of the resistance pattern 3, terminal mounting electrodes 4, 4 are formed. Lead terminals 5, 5 are connected and fixed to the terminal mounting electrodes 4, 4 by a method such as welding. The connecting portions between the terminal mounting electrodes 4 and 4 and the lead terminals 5 and 5 are coated with fixing materials 6 and 6, and a protective coating film 7 such as resin or glass is formed on the resistance pattern 3.

The resistance pattern 3 is formed to have a thickness of 3 μm, and the average crystal grain size in the film spreading direction is set to 10 μm.

With this configuration, the average crystal grain size of the resistor pattern is set to 10 μm, which is larger than the average crystal grain size of the conventional temperature sensor. Therefore, the problem that impurities are mixed in the grain boundaries to change the resistance value can be reduced.

Next, a method of manufacturing the temperature sensor 1 will be described. First, a 96% alumina mother substrate is prepared, and the alumina mother substrate is subjected to ultrasonic cleaning and degreasing, and then subjected to surface roughening with hydrofluoric acid. After that, the surface on which the resistance pattern has been roughened is not chlorinated, but is activated and sensitized with a palladium chloride solution to facilitate plating. Further, the alumina mother substrate is sufficiently washed with water to remove the deposits, and is immersed in a platinum electroless plating bath to form a platinum thermosensitive film on the surface of the alumina mother substrate. After the formation of the temperature-sensitive film, the film is baked at 1000 ° C. for 2 hours to stabilize characteristics and grow platinum crystals. At this time, the average crystal grain size can be adjusted by the thickness of the temperature-sensitive film formed by the electroless plating, the firing temperature after the formation, and the firing time. For example, if the film thickness is set to 2.5 μm and 135
When calcined at 0 ° C. for 2 hours, the average crystal grain size can be 20 μm. Further, the film thickness is set to 5 μm and 1350
When calcined at 2 ° C. for 2 hours, the average crystal grain size can be greater than 25 μm. With such an average crystal grain size, the density of grain boundaries can be further reduced, so that the problem that impurities are mixed into the grain boundaries and the resistance value changes can be further reduced.

Next, the temperature-sensitive film is partially removed by laser cutting or dry etching to form a plurality of resistance patterns. Further, heat treatment is performed at 1300 ° C. for 2 hours in order to remove mechanical strain generated at the time of forming the resistance pattern.

Thereafter, a protective coating film made of heat-resistant glass, ceramic, or the like is formed for each resistance pattern except for both ends of the resistance pattern and a portion for adjustment, for mechanical and electrical protection of the resistance pattern. At this time, a paste printing method, a sol-gel coating method, or the like is used as a coating method.

Further, on both ends of the resistance pattern exposed from the protective coat film, terminal mounting electrodes made of platinum are formed for each resistance pattern by thick film screen printing. At this time,
When alumina particles having a particle size of 0.1 to 1 μm are dispersed in the terminal mounting electrode by about 10 w%, the high-temperature adhesion of the terminal mounting electrode to the resistance pattern can be improved.

Then, in order to adjust the resistance value to the standard value for each resistance pattern formed on the alumina mother substrate, the adjustment portion exposed from the protective coat film is adjusted by trimming with a laser. Thereafter, in some cases, slight mechanical distortion is caused by the adjustment laser trimming, so that a heat treatment similar to that for forming the resistance pattern can further improve the characteristics.

Next, the alumina mother substrate is cut into strips for each resistance pattern, and a lead wire is welded to the terminal mounting electrode.
After welding, a fixing material is applied to the joint between the terminal mounting electrode and the lead wire, and is baked and adhered, thereby reinforcing the joint and providing electrical insulation.

The temperature sensor manufactured through the above-described steps has a small characteristic variation even at a high temperature of 800 to 1000 ° C., and has a large resistance value of 50 to 200 Ω. It is suitable as a temperature sensor.

In the present embodiment, platinum is used as the material of the resistance pattern. However, the present invention is not limited to this. At least one element among platinum group elements (ruthenium, rhodium, palladium, osmium, iridium, platinum) Any metal or alloy that uses as a main component may be used, but platinum is preferably used in view of cost, ease of forming a thin film, and stability of characteristics.

[0028]

As described above, in the temperature sensor of the present invention, the thickness of the temperature-sensitive film is formed to be 2.5 to 5.0 μm, and the average particle diameter in the surface spreading direction of the temperature-sensitive film is set to 10 μm or more. As a result, the density of the grain boundaries is reduced, and it is possible to reduce the entry of trace impurities such as sulfur and carbon into the crystal grain boundaries of platinum at high temperatures. As a result, it is possible to suppress the fluctuation of the resistance value due to the mixing of impurities,
A temperature sensor that can be used at a high temperature can be obtained.

In the temperature sensor according to the second aspect, since 99.9% of platinum is used for the temperature-sensitive film, contamination of impurities can be further prevented. In addition, since platinum is inexpensive compared with other platinum group elements, the cost of the temperature sensor can be reduced as compared with the case where other platinum group elements are used. In addition, since platinum is easier to form a thin film than other platinum group elements, formation of a resistance pattern is easier and manufacturing cost can be reduced as compared with the case where another platinum group element is used.

[Brief description of the drawings]

FIG. 1 is a perspective view of a temperature sensor for explaining a first embodiment.

FIG. 2 is a perspective view of a conventional temperature sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Temperature sensor 2 Insulating substrate 3 Resistance pattern 4 Terminal mounting electrode 5 Lead terminal 6 Fixing material 7 Protective coating film

Claims (2)

[Claims] 1. A temperature sensor in which a temperature-sensitive film containing a platinum group element as a main component is formed on an insulating substrate, wherein the temperature-sensitive film is formed by a thin film forming technique and the temperature-sensitive film has a thickness of 2 mm. A temperature sensor having a thickness of 0.5 to 5.0 μm and an average particle size in the surface spreading direction of the temperature-sensitive film of 10 μm or more. 2. The temperature sensor according to claim 1, wherein the insulating substrate is an alumina substrate, and the temperature-sensitive film is a platinum temperature-sensitive film having a purity of 99.9% or more.