JPH03263302A - Thermistor element and manufacture thereof - Google Patents

Abstract

PURPOSE:To prevent the deterioration of characteristics under adverse conditions such as high temperature and humidity, and improve reliability, by coating only the parts, of leads, exposed from the glass with a plated film. CONSTITUTION:Plated films 431, 451 are formed only on the parts of leads 43, 45 which parts are exposed from glass 5, and the surfaces of the leads 43, 45 are directly in contact with the glass 5. Since a plated film, whose wettability to glass is low, is not interposed, the adhesion between the leads 43, 45 and the glass 5 are increased, As a result, when the device is used under the condition of high temperature and humidity, water content, oxygen, etc., scarcely permeate into the inside of the glass-sealed part, and thermistor characteristics are not deteriorated. Activation treatment of the lead surface, which is performed to improve the adhesion of the plated film, is executed after glass-sealing, so that chemicals used in the case of activation treatment do not remain in the glass-sealed part, thereby preventing the deterioration of leads, electrodes, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a glass-sealed thermistor element and a manufacturing method thereof.

<Prior Art> A thermistor is a temperature sensor that utilizes the temperature dependence of the electrical resistance of a temperature-sensitive resistor, and is widely used for temperature measurement, temperature control, and the like. Particularly for high-temperature applications, they are used, for example, in automobile exhaust gas temperature detection sensors, oil and gas combustion control sensors, and the like.

As the material for the temperature-sensitive resistor (thermistor chip) of conventional high-temperature thermistor elements, that is, thermistor material, sintered bodies with silicon carbide or boron carbide as conductive paths are used because they exhibit stable electrical resistance at high temperatures. known to be favorable. However, when a thermistor element using these materials is used in the atmosphere at high temperatures, surface oxidation occurs, particularly at temperatures above 500°C. Therefore, it is necessary to provide a protective film.

For forming the protective film, it is easy and reliable to use a method of sealing the chip with glass.

A thermistor whose chip is sealed with glass is usually called a glass-sealed thermistor.

An example of a glass-sealed thermistor is shown in FIG.

The thermistor element 101 shown in FIG. 2 includes a thermistor chip 11, a pair of electrode layers 33.35 formed on the thermistor chip 11, and a pair of lead bodies 43.45 respectively connected to these electrode layers. Thermistor chip 11, electrode layer 33.35, and lead body 4345
A part of it is sealed with glass.

The lead bodies 43, 45 are usually made of a Ni alloy such as Kovar alloy or 42 alloy because of their appropriate relationship with the coefficient of thermal expansion of the sealing glass and their low cost.

When used as a high temperature thermistor, the lead body 43
．． Since No. 45 is exposed to high temperatures, surface oxidation occurs.
The same applies to storage at high temperatures.

For this reason, it has been proposed to provide the lid body with an oxidation-resistant plating film such as N1.

However, metals with good oxidation resistance generally have poor reactivity and low diffusibility into glass.

Therefore, metals with good oxidation resistance have low wettability and low adhesion to glass.

Therefore, when a lead body whose entire surface is coated with a plating film having good oxidation resistance 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 environment, moisture and oxygen are likely to enter the glass sealing portion through the gap between the heat-resistant plating film and the sealing glass, resulting in a resistance change.

<Problems to be Solved by the Invention> The present invention was made in view of the above circumstances, and provides a highly reliable glass seal with almost no deterioration in thermistor characteristics even when used under adverse conditions such as high temperatures. An object of the present invention is to provide a stop-type high-temperature thermistor element and a method for manufacturing the same.

<Means for Solving the Problems> Such objects are achieved by the following inventions (1) to (5).

(1) It has a thermistor chip, a pair of electrode layers formed on the thermistor chip, and a pair of lead bodies each connected to these electrode layers, and the thermistor chip and the electrode layer are connected to a part of the lead body. A thermistor element sealed with glass, wherein only a portion of the lead body exposed from the glass is covered with a plating film.

(2) The thermistor element according to (1) above, wherein the plating film is made of Cr, Cr-based alloy, Ni, or Ni alloy.

(3) The thermistor element according to (1) or (2) above, wherein the lead body is a Kovar alloy or a 42 alloy alloy.

(4) A method for manufacturing the thermistor element according to any one of (1) to 3) above, comprising sealing a part of the thermistor chip, electrode layer, and lead body with glass in a non-oxidizing atmosphere. After that, a plating film is formed on a portion of the lead body that is not sealed with glass.

(5) The method for manufacturing a thermistor element according to the above (4), which includes a step of performing an activation treatment on the surface of the lead body between glass sealing and forming a plating film.

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

In the present invention, the plating films 431 and 451 are
．． Formed only on the exposed part of the glass 5 of 45,
The surface of the lead body 43, 45 is configured to be in direct contact with the glass 5.

Since there is no plating film that has low wettability with the glass, the adhesion between the lead body 43, 45 and the glass 5 is high, and even when used under high temperature conditions, there is no moisture, oxygen, etc. inside the glass sealing part. There is almost no intrusion, and the thermistor characteristics do not deteriorate.

In addition, since the activation treatment on the surface of the lead body, which is performed to improve the adhesion of the plating film, is performed after the glass sealing, chemicals used during the activation treatment do not remain inside the glass sealing part. , There is no deterioration of the lead body, electrodes, etc. due to this.

By the way, JP-A-60-124803 proposes plating the lead wire (lead body) with a heat-resistant metal (platinum). The publication uses a thermistor element (thermistor chip) whose crystal structure changes when it is sealed with glass in an oxygen-free atmosphere, and the thermistor element with electrodes is sandwiched between lead wires and sealed with glass. Let's do it. If air glass sealing is performed in a state where the electrode and the lead wire are not bonded together in this way, poor conductivity will occur due to oxidation of the surface of the lead wire. For this reason, the lead wires are plated with a heat-resistant metal. According to the publication, plating is applied only to the portion covered by the sealing glass.

On the other hand, since the thermistor element of the present invention has a structure in which the thermistor chip and the electrode layer are bonded, problems such as poor conductivity do not occur even if no plating film is provided on the glass sealing part.

Specific composition> Hereinafter, a specific configuration of the present invention will be explained in detail.

A glass-sealed thermistor element 1 of the present invention shown in FIG.
A pair of electrode layers 33.35 formed on 1 and a pair of lead bodies 43.4 respectively connected to these electrode layers.
5, thermistor chip 11 and electrode layer 33°3
5 and a portion of the lead body 43, 45 are sealed with glass 5.

Then, only the portions of the lead bodies 43 and 45 that are exposed from the glass 5, that is, only the portions that are not sealed by the glass, are covered with plating films 431 and 451, respectively.

[Thermistor Chip 11] There is no particular restriction on the material of the thermistor chip 11, and any material may be used as long as it can be sealed with glass.

For example, the thermistor material described in Japanese Patent Application Laid-Open No. 64-64202 can be preferably used.

Further, various other thermistor materials containing silicon carbide or boron carbide as a main component may also be used.

Furthermore, Mn-Ni composite oxide, spinel oxide,
Various composite oxide sintered bodies such as Ag2O3-based oxides can also be used.

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

Note that the dimensions of the thermistor chip are usually 0.5 to 1
．． 0mm, width 0.5-1.0mm, thickness 0.5-1.0
It is about mm.

[Electrode layer 33.35] The electrode layer 33.35 may be any electrode made of a conductive material used in a thermistor element or an electrode containing a conductive material, and is not particularly limited. .

As the conductive material, any known conductive substance may be used, such as Au, Ag, Pt, Pd, W% Cu, Ni
, Mo, Aj2, Fe, Ti, Mn
, Nb, Ta, etc., or Pt-Au.

Pd-Au, Pt-Pd-Au, Pd-Ag
, Pt-Pd-Ag, Fe-N1-Go, F
Alloys such as e-Ni and Mo-Mn can be used.

There are no particular restrictions on the method of forming the electrode layer, and examples include various thermal spraying methods such as gas flame, electric arc, and plasma, electrolytic plating, electroless plating, vapor deposition, sputtering, etc.
The electrode layer may be formed by various types of vapor phase growth methods such as ion blasting, liquid phase growth methods, or even a so-called thick film method in which conductive paste is fired.

Note that the electrode layer may have a multilayer structure of two or more layers in order to improve adhesion to the lead body.

The thickness of the electrode layer varies depending on the formation method, but is usually 0.
．． It is about 05-2001zll+.

1 2 [Lead body 43.45] Any conventionally known lead wire can be used as the lead body 43.45, but in terms of thermal expansion coefficient, cost, etc., 29 wt% Ni-17 wt% Co - Kovar alloy with a composition of residual Fe and 4 to 43 wt% Ni
- It is preferable to use a 42 alloy alloy having a composition of residual Fe.

Kovar alloy has thermal expansion characteristics that closely match that of hard glass, and is an alloy used as a hermetic sealing material for hard glass and ceramics. 42 alloy is also used as a hard or soft glass material for transistors, diode lead wires, IC lead frames, etc.
It is used as a variety of hermetic seals, such as reeds for reed switches.

There are no particular restrictions on the method of connecting the lead bodies 43, 45 to the electrode layers 33, 35, and an appropriate method can be selected from among a method using a conductive paste such as gold paste, a method using spot welding, a method using an ultrasonic bong, etc. do it.

[Plating film 431. ．． 4511 Plating films 431 and 451 are provided to prevent oxidation and improve heat resistance of lead body 4345.

The plating film may be made of any material as long as it has the effect of preventing oxidation and improving heat resistance, and an appropriate material may be selected in consideration of the material of the lead body used.

For example, when the lead body is made of Ni alloy such as the Kovar alloy or 42 alloy, the plating film material is Cr.
, Cr-based alloys such as Cr-Ni, Ni, N1-B alloys, N
Ni-based alloys such as 1-P are preferred, and Cr or Cr-based alloys are particularly preferred because of their high oxidation resistance and heat resistance.

The thickness of the plating film may be appropriately selected depending on the material used and the manufacturing conditions or usage conditions of the thermistor element, but it is preferably about 0.1 to 1 Op, particularly about 0.5 to 2 Op, for example.

The plated film is preferably formed by electrolytic or electroless plating.

For example, the plated film of Cr or Cr-based alloy is preferably formed by electrolytic plating. Furthermore, when a plated film of Cr or Cr-based alloy is formed by electrolytic plating, it is preferably formed on a NiT base film formed by electroless plating. By providing such a base film, it is possible to form a homogeneous plated film with almost no defects such as pinholes.

The plated film of Ni or Ni-based alloy is preferably formed by electroless plating.

The plating bath to be used is not particularly limited and may be appropriately selected depending on the intended plating film composition.

In the present invention, it is preferable to perform activation treatment on the surface of the lead body after the glass sealing and before the formation of the plating film.

Activation treatment is performed to promote the growth of the plated film in electroless plating, and is usually performed by degreasing by immersion in alkali, washing with water, pickling with hydrochloric acid, etc., and washing with water to improve the surface of the lead body. After cleaning, general sensitization and activation are performed.

[Glass for sealing 5] The glass 5 has a glass transition temperature of 600°C or higher, particularly about 600 to 700°C, and a working temperature of 1000°C.
Hereinafter, it is particularly preferable to use glass having a temperature of 800 to too0°C.

The composition of the glass 5 is not particularly limited as long as the glass transition temperature and working temperature are within the above ranges, but it is preferable to use borosilicate glass containing an alkaline earth metal.

Note that alkaline components such as Na, etc. contained in the glass 5 should be
It is preferable that it is t% or less.

5 6 [Thermistor Element Manufacturing Method] An example of the manufacturing method of the thermistor element I will be briefly described below.

For example, a wafer of the aforementioned sintered body having a diameter of about 3 inches and a thickness of about 0.5++u++ is produced. Electrode layers are formed on both sides of this wafer.

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

The chip thus obtained has a diameter of 0.2 to 0.5 mm.
Lead bodies having a length of about 20 to 1100 II mm are connected using the method described above.

Such a chip is inserted into a glass tube having a diameter of about 1, about 5 to 2.5 mm, and a length of about 5 mm, and is sealed with glass at a temperature of about 750 to 900°C.

In the present invention, glass sealing is performed in a non-oxidizing atmosphere.

The non-oxidizing atmosphere may be an inert gas such as N2, Ar, He, etc., H, Go, various hydrocarbons, a mixed atmosphere thereof, or a vacuum.

In addition, 0.5% is added to the non-oxidizing atmosphere during glass sealing.
The following 02 may be included.

After sealing with glass, a plating film is formed on the surface of the lead body in a portion not sealed with glass, preferably after an activation treatment, to obtain a thermistor element.

In addition, before or after forming the plating film, if necessary,
It is preferable to carry out aging at 00 to 750°C for about 10 to 100 hours.

Although there is no particular restriction on the atmosphere during aging, it is preferable to carry out aging in a non-oxidizing atmosphere.

<Examples> Hereinafter, specific examples of the present invention will be shown and the present invention will be explained in further detail.

The following raw material powder was milled in a ball mill using acetone for 20 minutes.
Mixed time-wise.

(Raw material powder) Al1.203 286 parts by weight B4C: 14 parts by weight Tie: 0.2 parts by weight The obtained slurry was dried and granulated, and filled into a graphite mold with an inner diameter of 77 mm.

This was hot press sintered in an Ar atmosphere.

After cooling, it was processed into a size of 50 x 50 x 0.5 mm, electrodes were formed on both sides, and then processed using a peripheral sling machine to give a size of 0.5 mm.
It was made into a chip of 75XO, 75X0.5mm.

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

The materials of the lead bodies used are shown in Table 2 below.

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 the glass was sealed at 850'C in an Ar gas atmosphere.

Next, the surface of the portion of the lead body not covered with glass was subjected to activation treatment.

Activation treatment was performed by surface treatment with an aqueous solution of iron chloride, and in the case of electroless plating, general sensitization and activation were further performed.

After the activation treatment, a plating film with a thickness of 1.5 mm was formed on the surface of the portion of the lead body that was not covered with glass. Table 2 shows the plating method used and the composition of the plating film.

In sample No. 4, Cr was electrolytically plated on a 1.0 pm thick N1-B base film formed by electroless plating.

The conditions of the plating bath used are shown in Table 1 below.

9 0 Table 1 I did it. The results are shown in Table 2.

(Resistance value change) The resistance value was measured at the initial stage after manufacturing the thermistor element and after storage for 1000 hours at 85°C and 85% RH. Calculated by Ro)xlOO(%).

In this way, a thermistor element sample as shown in FIG. 1 was produced.

Note that a comparative sample was prepared in which a plating film was formed on the entire surface of the lead body before glass sealing.

Except for the plating films of these comparative samples, they were produced in the same manner as above.

The effects of the present invention are clear from the results of the measurements shown in Table 2 for each of these samples.

That is, in the sample of the present invention in which a plating film was formed on a portion other than the glass sealing portion of the lead body, the change in resistivity was small even after storage under high temperature conditions.

On the other hand, in a comparative sample in which a plating film was also formed on the portion existing within the glass sealing part of the lead body, the resistance increased significantly after storage under high temperature conditions.

Note that the above effects of the present invention can be achieved even when the composition of the thermistor chip is changed, and in particular,
The same realization was achieved for all the compositions described in the 4202 publication.

3 4 <Effects of the Invention> According to the present invention, lead body deterioration during manufacturing can be suppressed, and the thermistor characteristics are extremely reliable with almost no deterioration even when used under adverse conditions such as high temperatures. A glass-sealed high-temperature thermistor element with high resistance is realized.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a preferred embodiment of the thermistor element of the present invention. FIG. 2 is a sectional view showing an example of a conventional thermistor element. Explanation of symbols 1.101...Thermistor element 5...Glass 11...Thermistor chip 33.35...Electrode layer 43.45...Lead body 431.451...Plating film

Claims (5)

[Claims] (1) It has a thermistor chip, a pair of electrode layers formed on the thermistor chip, and a pair of lead bodies each connected to these electrode layers, and the thermistor chip and the electrode layer are connected to a part of the lead body. A thermistor element sealed with glass, wherein only a portion of the lead body exposed from the glass is covered with a plating film. (2) The thermistor element according to claim 1, wherein the plating film is made of Cr, Cr-based alloy, Ni, or Ni alloy. (3) The thermistor element according to claim 1 or 2, wherein the lead body is made of Kovar alloy or 42 alloy. (4) A method for manufacturing a thermistor element according to any one of claims 1 to 3, comprising: sealing a part of the thermistor chip, electrode layer, and lead body with glass in a non-oxidizing atmosphere; A method for manufacturing a thermistor element, comprising forming a plating film on a portion of the lead body that is not sealed with glass. (5) The method for manufacturing a thermistor element according to claim 4, further comprising a step of performing activation treatment on the surface of the lead body between glass sealing and plating film formation.