JP3150180B2 - Method for manufacturing a thermistor element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a glass-sealed thermistor element.

[0002]

2. Description of the Related Art A thermistor is a temperature sensor or a temperature compensating element utilizing the temperature dependence of the electric resistance of a temperature-sensitive resistor, and is widely used for temperature measurement and temperature control. Particularly for high temperature applications, they are used, for example, in automobile exhaust gas temperature detection sensors and oil / gas combustion control sensors.

As a material for a conventional temperature-sensitive resistor (thermistor chip) of a high-temperature thermistor element, that is, a thermistor material, which exhibits a stable electric resistance at high temperatures, it is possible to use silicon carbide or boron carbide as a conductive path. It is known that union is preferred. However, when a thermistor element using these materials is used at a high temperature in the atmosphere, it is particularly difficult
Above 0 ° C., surface oxidation occurs. For this reason, it is necessary to provide a protective film.

It is easy and reliable to use a method of sealing a chip with glass for forming a protective film. A thermistor in which a chip is sealed with glass is usually called a glass-sealed thermistor. FIG. 2 shows an example of a glass-sealed thermistor. The thermistor element 101 shown in FIG.
The thermistor chip 11 includes a thermistor chip 11, a pair of electrode layers 33 and 35 formed on the thermistor chip 11, and a pair of leads 43 and 45 respectively connected to the electrode layers. , 35,
A part of the lead bodies 43 and 45 is sealed with glass. The lead members 43 and 45 are usually made of a Fe alloy such as a Kovar alloy or a 42 alloy alloy because of appropriate relation with the coefficient of thermal expansion of the sealing glass and low cost.

When used as a high temperature thermistor,
Since the leads 43 and 45 are exposed to high temperatures, surface oxidation occurs. The same applies to storage in a high humidity state. Therefore, it has been proposed to provide an oxidation-resistant plating film of Ni or the like on the lead body. However, metals having good oxidation resistance generally have poor reactivity and low diffusivity into glass. For this reason, metals having good oxidation resistance have low wettability and low adhesion to glass. Therefore, when a lead body having a plating film having good oxidation resistance formed on the entire surface is sealed with glass, the adhesion between the lead body and the sealing glass becomes insufficient. When such a thermistor element is used in a high-temperature and high-humidity environment, moisture and oxygen enter the glass sealing portion from the gap between the heat-resistant plating film and the sealing glass, and the resistance easily changes.

[0006] Under such circumstances, the present inventors firstly,
As shown in FIG. 2, there is proposed a thermistor element in which plating films 431 and 451 are formed only on portions of the lead bodies 43 and 45 exposed from the glass (Japanese Patent Application No. 2-61).
No. 590). However, according to subsequent studies by the present inventors, it has been found that the following problems occur in the thermistor element having such a configuration. In the above proposal, glass sealing is performed before forming a plating film on the lead body. However, since the lead body without the plating film has a relatively good wetting property with respect to glass, it is shown in FIG. Like glass 5
In the portion where the lead bodies 43 and 45 are exposed from the
Is thin and surrounds the lead body. Such a thin glass is easily chipped due to mechanical shock or thermal shock.If chipping occurs in the sealing glass after forming a plating film on the lead body, the lead body without the plating film is exposed. , Deteriorates during use.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances. Even when an impact is applied, there is almost no deterioration of the thermistor characteristics when used under bad conditions such as high temperature and high humidity. An object of the present invention is to provide a method for manufacturing a highly reliable glass-sealed type high temperature thermistor element.

[0008]

This and other objects are achieved by the present invention which is defined below as (1) to (4). (1) a thermistor chip, a pair of electrode layers formed on the thermistor chip, and a pair of leads connected respectively to the electrode layers; the thermistor chip and the electrode layer; Is a method of manufacturing a thermistor element sealed with glass,
The vicinity of the boundary between the lead body and the glass exposed from the glass is covered with a ceramic film, and the ceramic film covers the entire surface of the glass, the thermistor chip, the electrode layer and A method for manufacturing a thermistor element, wherein a part of a lead body is sealed with glass in a non-oxidizing atmosphere, and then the ceramic film is formed by a CVD method. (2) The method for manufacturing a thermistor element according to (1), wherein the ceramic film includes at least one element selected from Al and Si and at least one element selected from O and N. (3) The method for manufacturing a thermistor element according to the above (1) or (2), wherein the thickness of the ceramic film is 3 to 20 μm. (4) The method for manufacturing a thermistor element according to any one of (1) to (3), wherein the lead body is a Kovar alloy or a 42 alloy.

[0009]

[0010]

[0011]

[0012]

[0013]

[0014]

FIG. 1 shows a preferred embodiment of a glass-sealed thermistor element 1 according to the present invention.

In the present invention, the lead members 43, 4 of the glass 5 are used.
The vicinity of the boundary with 5 is covered with a ceramic film 6. Therefore, chipping of the sealing glass 5 near the boundary between the lead bodies 43 and 45 is prevented.

Further, since there is no intervening plating film having low wettability with the glass, the adhesion between the lead members 43 and 45 and the glass 5 is high, and even when used under high temperature and high humidity conditions,
There is almost no intrusion of moisture or oxygen into the glass sealing portion, and the thermistor characteristics do not deteriorate.

[0017]

[Specific Configuration] Hereinafter, a specific configuration of the present invention will be described in detail. The glass-sealed thermistor element 1 of the present invention shown in FIG. 1 includes a thermistor chip 11, a pair of electrode layers 33 and 35 formed on the thermistor chip 11, and a pair of leads respectively connected to these electrode layers. The thermistor chip 11 and the electrode layers 33 and 35 and a part of the lead bodies 43 and 45 are sealed with the glass 5. The vicinity of the boundary between the glass 5 and the lead members 43 and 45 exposed from the glass 5 is covered with the ceramic film 6.

[Thermistor Chip 11] The material of the thermistor chip 11 is not particularly limited, and any material may be used as long as glass sealing is possible. For example, JP
The thermistor material described in JP-A-4-64202, that is, a thermistor material containing silicon carbide and / or boron carbide and a matrix material containing an oxide such as Al or Si can be preferably used. Further, various other thermistor materials containing silicon carbide or boron carbide as a main component may be used. When silicon carbide is contained, the content of silicon carbide is preferably set to 1.24 or less by volume relative to the content of the matrix substance. This is for suppressing foaming in the glass sealing step and facilitating the device formation.

Further, various composite oxide sintered bodies such as a Mn-Ni-based composite oxide, a spinel-based oxide, and an Al ₂ O ₃ -based oxide can also be used.

For the production of the thermistor chip, an ordinary sintering method may be used. For example, after wet mixing various raw material powders, the mixture is press-molded at room temperature, and is subjected to a normal pressure sintering method and a hot press (H) in an oxygen atmosphere or a non-oxidizing atmosphere.
P) After sintering the molded body by a sintering method, a hot isostatic pressure (HIP) method or the like, the molded body is allowed to cool and cut into a predetermined size to obtain a thermistor chip.

The size of the thermistor chip is not particularly limited, but is usually 0.5 to 1.0 mm long and 0.5 to 1.0 mm wide.
0 mm and a thickness of about 0.5 to 1.0 mm.

[Electrode layers 33 and 35] Electrode layers 33 and 35
Is not particularly limited as long as it is an electrode made of a conductive material or an electrode containing a conductive material used for a thermistor element. As the conductive material, a known conductive material may be used, and Au, A
g, Pt, Pd, W, Cu, Ni, Mo, Al, Fe,
Ti, Mn, Nb, Ta, etc., or Pt-Au, P
d-Au, Pt-Pd-Au, Pd-Ag, Pt-Pd
Any of alloys such as -Ag, Fe-Ni-Co, Fe-Ni, and Mo-Mn can be used.

There is no particular limitation on the method of forming the electrode layer. For example, various types of thermal spraying such as gas frame, electric arc, and plasma, or various types of vapor phase such as electrolytic plating, electroless plating, vapor deposition, sputtering, and ion plating. The electrode layer may be formed by a so-called thick film method in which a conductive paste is baked, such as a growth method or a liquid phase growth method. The electrode layer is used to improve the adhesion to the lead body, etc.
It may have a multilayer structure of two or more layers.

The thickness of the electrode layer varies depending on the forming method, but is usually about 0.05 to 200 μm.

[Lead bodies 43 and 45] Lead bodies 43 and 4
Although any conventionally known lead wire can be used as the lead wire 5, 29 wt.
It is preferable to use a Kovar alloy having a composition of% Ni-17 wt% Co-remaining Fe and a 42 alloy alloy having a composition of 41 to 43 wt% Ni-remaining Fe. Kovar alloy has a good thermal expansion characteristic that matches that of hard glass,
This is an alloy used as a hermetic sealing material for hard glass and ceramic. The 42 alloy alloy is used as a hermetic seal such as a transistor, a diode lead, an IC lead frame, and a lead switch lead as a hard or soft glass sealing material.

The lead members 43 and 45 are connected to the electrode layers 3 respectively.
There is no particular limitation on the method of connection to 3, 35, and an appropriate method may be selected from a method using a conductive paste such as a gold paste, a method using spot welding, a method using an ultrasonic bonder, and the like.

[Ceramic Film 6] The ceramic film 6 is provided for preventing the lead bodies 43 and 45 from being oxidized and improving heat resistance, and also for preventing breakage of the sealing glass 5. In the present invention, at least the vicinity of the boundary between the lead members 43 and 45 exposed from the glass 5 and the glass 5 is covered with the ceramic film 6. The ceramic film 6 covers the entire surface of the sealing glass 5 as described above. Note that the lead members 43, 4
In 5, it is preferable that the entire region requiring oxidation resistance and heat resistance is covered with the ceramic film 6 except for the region in contact with an external circuit.

The ceramic film 6 may be made of any material as long as it has an action of preventing oxidation, improving heat resistance and preventing breakage of the glass 5 and has an insulating property. An appropriate material may be selected in consideration of matching of the adhesive strength and the coefficient of thermal expansion of, for example, at least one element selected from Al and Si and at least one element selected from O and N Are preferred. Specifically, such ceramics are preferably ceramics made of Al ₂ O ₃ , SiO ₂ , Si ₃ N ₄ or AlN, or ceramics containing at least one of these. Of these, Al and Al are particularly preferred due to their high hardness and corrosion resistance.
₂ O ₃ is preferred.

The ceramic film is formed by a CVD method because of its high film formation rate, good step coverage, and the ability to form a dense film. The CVD method to be used is not particularly limited, and may be appropriately selected from various CVD methods such as a thermal CVD method and a plasma CVD method. However, the thermal CVD method is particularly preferable because the film formation rate is high. The conditions of the various CVD methods, such as the source gas and the temperature of the adherend, are not particularly limited, and may be appropriately determined based on an ordinary method. For example, as the source gas, various halides, organometallic compounds, ammonia, and the like may be used.

The thickness of the ceramic film may be appropriately determined according to the forming method, the material used, and the like so that the effects of preventing oxidation, improving heat resistance, and preventing breakage of glass are sufficiently obtained. For example, when formed by the CVD method, the thickness of the ceramic film is preferably set to 3 to 20 μm. When the thickness is less than 3 μm, it is difficult to form a dense and defect-free film. Further, even if the thickness exceeds 20 μm, the above effect is not remarkably improved, and the productivity is reduced because the film formation time is prolonged.

It is preferable to form the ceramic film by controlling the forming conditions so as to generate a residual stress that compresses the glass 5. Such stress prevents peeling of the ceramic film.

[Sealing Glass 5] The glass 5 has a glass transition temperature of 600 ° C. or higher, especially about 600 to 700 ° C.
Further, the working temperature is 1000 ° C. or less, especially 800 to 100
It is preferable to use a glass at 0 ° C. The composition of the glass 5 is not particularly limited as long as the glass transition temperature and the working temperature are within the above ranges, but it is preferable to use a borosilicate glass containing an alkaline earth metal. In addition,
Glass 5 may cause a decrease in insulation resistance at high temperatures.
Is preferably 1 wt% or less.

[Method of Manufacturing Thermistor Element] An example of a method of manufacturing the thermistor element 1 will be briefly described below. First,
A wafer of the sintered body having a diameter of about 3 inches and a thickness of about 0.5 mm is prepared. Electrode layers are formed on both surfaces of the wafer.

The wafer on which the electrode layer has been formed is cut into a square having a side of about 0.75 mm using a dicing saw or the like to form chips.

A lead having a diameter of about 0.2 to 0.5 mm and a length of about 20 to 100 mm is connected to the thus obtained chip by the above-described method. Such a chip is inserted into a glass tube having a diameter of about 1.5 to 2.5 mm and a length of about 5 mm to perform glass sealing. In the present invention, glass sealing is performed in a non-oxidizing atmosphere. The non-oxidizing atmosphere may be an inert gas such as N ₂ , Ar, He, H, CO, or various hydrocarbons, or a mixed atmosphere thereof, or may be a vacuum or other various atmosphere. The non-oxidizing atmosphere at the time of glass sealing may contain 0.5% or less of O ₂ .

After glass sealing, a ceramic film 6 is formed by the above-described CVD method.

Before or after the formation of the ceramic film, aging is preferably performed at 500 to 750 ° C. for about 10 to 100 hours as necessary. The atmosphere during aging is not particularly limited, but is preferably performed in a non-oxidizing atmosphere.

[0038]

EXAMPLES Hereinafter, the present invention will be described in more detail by showing specific examples of the present invention. The following raw material powders were wet-mixed with acetone using a ball mill for 20 hours.

(Raw material powder) Al ₂ O ₃ : 86 parts by weight B ₄ C: 14 parts by weight TiO ₂ : 0.2 part by weight The obtained slurry was dried and granulated, and filled in a graphite mold having an inner diameter of 77 mm.

This was subjected to hot press sintering in an Ar atmosphere, cooled, processed to 50 × 50 × 0.5 mm, electrodes were formed on both sides, and then processed by an outer peripheral slashing machine.
It was made into a chip of 0.75 × 0.75 × 0.5 mm.

Next, a lead body having a diameter of 0.25 mm and a length of 65 mm was connected to the electrode layer by using a spot welding method.

Further, a thermistor chip having an electrode and a lead body was inserted into borosilicate glass having a diameter of 2.5 mm and a length of 4 mm, and glass-sealed at 850 ° C. in an Ar gas atmosphere.

After glass sealing, a ceramic film is formed on the entire surface of the glass and the surface of the lead body by a thermal CVD method.
Each of the thermistor element samples as shown in FIG.
0 were produced. The material of the lead body, the composition of the ceramic film, and the thickness of each sample are shown in Table 1 below. The element temperature during the formation of the ceramic film was 900 ° C.

For comparison, a sample in which a plating film was formed on the surface of a lead body after glass sealing (No. 6) and a comparative sample in which a plating film was formed on the entire surface of the lead body before glass sealing (No. 6) .7) was prepared. No ceramic film was formed on these comparative samples.

The following measurements were performed for each of these samples. Table 1 shows the results.

(Change in Resistance Value) The resistance value was measured at the initial stage after the thermistor element was manufactured and after storage at 600 ° C. for 2,000 hours, and the change in the resistance value was ΔR, and the initial resistance value was R _{0. 0} ) × 100 [%]

[0047]

[Table 1]

From the results shown in Table 1, the effect of the present invention is clear. That is, in the sample of the present invention on which the ceramic film is formed, the change in resistivity is small even after storage under high temperature and high humidity conditions. On the other hand, in the comparative sample in which the plating film is formed on the entire surface of the lead body including the inside of the glass sealing portion, the resistance after storage under the high temperature and high humidity condition is remarkably increased.

When the above samples were subjected to a cycle test (room temperature and 600 ° C.), the samples of the present invention did not crack the ceramic film and glass, and no oxidation of the lead was observed.

The above-described effect according to the present invention was realized even when the composition of the thermistor chip was changed. In particular, all the compositions described in JP-A-64-64202 were similarly realized.

[0051]

According to the present invention, the sealing glass is not damaged even when an impact is applied during packing, transportation, mounting, etc., and thus the thermistor characteristics when used under bad conditions such as high temperature and high humidity. And a highly reliable glass-sealed thermistor element for high temperature is realized.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a preferred embodiment of a thermistor element of the present invention.

FIG. 2 is a cross-sectional view showing one example of a conventional thermistor element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 101 Thermistor element 11 Thermistor chip 33, 35 Electrode layer 43, 45 Lead body 431, 451 Plating film 5 Glass 6 Ceramic film

──────────────────────────────────────────────────続 き Continuing on the front page (72) Ryuichi Ogiso, Inventor TDK Corporation, 1-13-1 Nihonbashi, Chuo-ku, Tokyo (72) Inventor Shigeru Sakano 1-13-1 Nihonbashi, Nihonbashi, Chuo-ku, Tokyo Inside (72) Inventor: Nobuyuki Miki 1-13-1 Nihonbashi, Chuo-ku, Tokyo TDK Corporation (72) Inventor: Hirotsugu Nohara 1-13-1 Nihonbashi, Chuo-ku, Tokyo Inside TDK Corporation (72) Inventor Masaro Taniguchi 1-13-1 Nihonbashi, Chuo-ku, Tokyo Inside TDK Corporation (56) References JP-A-57-187630 (JP, A) JP-A-3-263302 (JP, A) JP-A-2-155202 (JP, A) JP-A-63-187602 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01K 7 /twenty two

Claims (4)

(57) [Claims] An electronic device comprising: a thermistor chip; a pair of electrode layers formed on the thermistor chip; and a pair of leads connected respectively to the electrode layers. A method for manufacturing a thermistor element in which a portion is sealed with glass, wherein the vicinity of a boundary between the lead body and the glass exposed from the glass is covered with a ceramic film, and the ceramic A film covers the entire surface of the glass, and after sealing a part of the thermistor chip, the electrode layer and the lead body with glass in a non-oxidizing atmosphere, forming the ceramic film by a CVD method. A method for manufacturing a thermistor element. 2. The method according to claim 1, wherein the ceramic film is made of Al and Si.
The method for producing a thermistor element according to claim 1, comprising at least one element selected from the group consisting of O and N and at least one element selected from the group consisting of O and N. 3. The thickness of the ceramic film is 3 to 20 μm.
3. The method for manufacturing a thermistor element according to claim 1, wherein m is m. 4. The lead body is made of a Kovar alloy or 4
4. The method for manufacturing a thermistor element according to claim 1, wherein the thermistor element is a two-alloy alloy.