JP2819536B2 - Glass sealed thermistor element for high temperature - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a glass-sealed high temperature thermistor element. More specifically, the present invention can maintain the electric resistance even when used at high temperatures,
The present invention relates to a glass-sealed high-temperature thermistor element having stable thermistor characteristics.

2. Description of the Related Art Conventionally, thermistor elements have been widely used in many fields as temperature sensors for temperature measurement, temperature control, and the like by utilizing the temperature dependence of the electrical resistance of a temperature-sensitive resistor. With the progress of electronic control of devices, a device with high reliability has been required even when used under severe conditions. For example, a thermistor element used for an automobile exhaust gas temperature detection sensor, an oil / gas combustion control sensor, and the like is required to withstand high temperatures and have stable characteristics such as insulating properties.

The thermistor elements include a glass-sealed type and a thin-film type, among which the glass-sealed thermistor element has a thermistor chip having a pair of electrodes each connected to a lead wire sealed in glass. It has a structure.

As a sealing glass used in such a glass-sealed thermistor element, conventionally, K ₂ O, PbO, SiO ₂ system,
Na ₂ O ・ B ₂ O ₃・ SiO ₂ system, K ₂ O ・ Al ₂ O ₃・ B ₂ O ₃・ SiO ₂ system, K ₂ O
・ Alkali-containing glasses such as B ₂ O ₃ and SiO ₂ have been used, but these have an electrical resistance value of 10 ⁶ Ωcm
Since it is difficult to use at high temperatures, especially at 500 ° C or higher, it is difficult to use as a sealing glass for a high-temperature thermistor used at or above this temperature because of problems such as insulation between the lead wires. I could not escape the restrictions.

Problems to be Solved by the Invention Under such circumstances, the present invention can maintain a high electric resistance value even when used at a high temperature of 500 ° C. or higher, and provide a glass seal having stable thermistor characteristics. The purpose of the present invention is to provide a stop type thermistor element.

Means for Solving the Problems The present inventors have conducted intensive research to develop a glass-sealed thermistor element for high temperature, and as a result, the electric resistance value of glass is set to 10 ⁶ Ωcm or more at 500 ° C or more. For this purpose, the inventors have found that it is sufficient to seal with a borosilicate glass having a total amount of alkali metal of not more than 3% by weight in terms of oxide, and have completed the present invention based on this finding.

That is, the present invention provides a glass-sealed high-temperature thermistor element in which a pair of electrode layers are provided on both sides of a thermistor chip, a heat-resistant lead wire made of an iron-based alloy is connected to each of the electrode layers, and the glass is sealed. And a thermistor element characterized by using a borosilicate glass having a total amount of alkali metal of 3% by weight or less as an oxide and an electric resistance value of 10 ⁶ Ωcm or more at 500 ° C. as the glass. Things.

 Hereinafter, the present invention will be described in detail.

The thermistor element of the present invention needs to be sealed with borosilicate glass having a total amount of alkali metal of 3% by weight or less, preferably 1% by weight or less in terms of oxide.

Further, the borosilicate glass used for the glass sealant of the present invention substantially means silicon oxide (SiO ₂ ) and boron oxide (B ₂
O ₃ ), especially those having high temperature resistance,
For example, the glass transition temperature is 500 ° C. or higher, preferably 500 to 70
Those having a temperature in the range of 0 ° C and a working temperature of 1200 ° C or less, preferably in the range of 800 to 1100 ° C are used.

Next, a method for manufacturing the glass-sealed thermistor element of the present invention will be described. First, the coefficient of thermal expansion is 30 × 10 ^−7.
After preparing a wafer having a diameter of about 3 inches and a thickness of about 0.5 mm made of a sintered body of about 90 × 10 ⁻⁷ deg ⁻¹ , an electrode layer is formed on both surfaces of the wafer, and then the electrode layer is formed. One side of the formed wafer is cut with a dicing saw
Cut into squares of about 0.75mm and make into chips.

The sintered body used at this time is not particularly limited, and those conventionally used as thermistor materials, for example, Mn
O ₂ -NiO system, Al ₂ O ₃ -TiO system, ZrO ₂ system, Al ₂ O ₃ -CrO ₃ type, Fe
_{A 2} O ₃ type, spinel type, SiC type or the like can be used, but a sintered body containing at least one selected from carbide, nitride, boride and silicide is particularly preferable. Among such thermistor materials, especially the coefficient of thermal expansion is
30 × 10 ^{−7 to} 90 × 10 ⁻⁷ deg ⁻¹ , preferably 50 × 10 ⁻⁷ to 70 × 1
Those in the range of 0 ^-7 deg ^-1 are preferred. If the coefficient of thermal expansion deviates from the above range, it is difficult to select a material for a lead wire or a sealing glass suitable for a high temperature thermistor element, which is not preferable.

Examples of the carbide include SiC, B ₄ C, TiC, ZrC, M
o ₂ , NbC, Cr ₃ C ₂ etc. are nitrides such as BN, Ti
N, NbN, Cr ₂ N, etc., as borides, for example, CrB, Zr
B, MoB, WB, etc., and silicides such as MoSi ₂ , CrS
i ₂ , TiSi ₂ , WSi _{2 and the} like.

A sintered body containing at least one selected from the group consisting of carbides, nitrides, borides and silicides is effective in stabilizing the B constant in a high temperature range and sealing at high temperatures in an inert gas. Is advantageous.

Such materials include, for example, Al ₂ O ₃ —SiC, Al ₂ O
₃ -B ₄ C _{system, Al 2 O 3 -SiC-B} 4 C _{-based, Al 2 O 3 -B 4 C} -BN based, Al ₂
Examples thereof include those containing Al ₂ O ₃ , such as an O ₃ — (TiN, NbN) system and an Al ₂ O ₃ —TiSi ₂ system. Among these materials, those having an Al ₂ O ₃ content of 50 to 95% by weight are preferred. When SiC is contained, its content is preferably 50% by weight or less, and if it exceeds 50% by weight, there is a possibility that a large amount of foaming occurs during glass sealing.

On the other hand, there is no particular limitation on the electrode layer, and any electrode can be selected and used from an electrode made of a conductive material or an electrode containing a conductive material conventionally used in thermistor elements.

As the conductive material, a known conductive substance, for example,
Au, Ag, Pt, Pd, W, Cu, Ni, Mo, Al, Fe, Ti, Mn, etc., or Pt-Au, Pd-Au, Pt-Pd-Au, Pd-Ag, Pt
Any of alloys such as -Pd-Ag, Fe-Ni-Co, Fe-Ni, and Mo-Mn can be used.

These conductive materials may be formed into an electrode layer by vapor phase plating, liquid phase plating, thermal spraying, or foil and brazing. In addition, these conductive materials, a binder and a solvent, more preferably an appropriate oxide is added to these, mixed to form a conductive paste, the conductive paste is applied to a thermistor chip and baked, The layer may be formed by a so-called thick film method. In addition, it is preferable to use a glass fritless paste containing no glass component as the paste. When a material containing glass frit is used, foaming is likely to occur at the time of connection, and there is a possibility that connectivity and adhesion may be reduced. The thickness of such an electrode layer is usually selected in the range of 5 to 200 μm.

Next, the chips obtained in this way have a diameter of 0.2 to 0.2 mm.
After connecting the lead wire of 0.5mm, length about 20-100mm,
This is usually inserted into a glass tube having a diameter of 1.5 to 2.5 mm and a length of about 5 mm, sealed in an inert atmosphere such as an argon gas atmosphere at a temperature of about 800 to 1000 ° C., and further, if necessary, 500 10 to 100 at a temperature in the range of ~ 750 ° C
By performing aging for about a time, a glass-sealed thermistor element can be obtained.

The lead wire used at this time is not particularly limited, and is conventionally used as a heat-resistant lead wire in a thermistor element, for example, 29% by weight Ni-17% by weight Co-remainder.
Kovar alloy with Fe composition or 41-43 wt% Ni-Fe
Alloys having the composition of 42 alloys, or alloys made of Fe-Cr alloys can be used, and among these, those made of Kovar alloy are preferable in terms of the coefficient of thermal expansion and adhesion to sealing glass. It is suitable. Such a lead wire may be one whose surface has been previously plated with a heat-resistant metal such as platinum.

The lead wire usually has a diameter of 0.2 to 0.5 mm, length
What is in the range of 20 to 100 mm is used, and as a method of connecting this lead wire to the electrode layer, for example, a conductive paste such as a gold paste is used, and a method of electrically contacting and connecting is used. And any method such as a method using an ultrasonic bonder can be used.

The structure of the glass-sealed thermistor element thus manufactured will be described with reference to the accompanying drawings. In the figure, a pair of electrode layers 4 are provided on both sides of a thermistor chip 1, and a lead wire is provided for each of the electrode layers 4. 3 is connected, and the whole except a part of the lead wire is made of borosilicate glass sealant 2.
Shows the structure sealed with.

EXAMPLES Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

The high temperature and high electrical resistance of the thermistor element is calculated by using the following equation. The sample is held at 500 ° C. for 1000 hours, the resistance change due to high temperature storage is ΔR, and the resistance before high temperature storage is R _0. ) = ΔR / R ₀ × 100.

Examples 1 and 2, Comparative Examples 1,2,3 430 g of Al ₂ O ₃ , 70 g of B ₄ C, 0.5 g of MgCO _{3 and} 0.5 g of Y ₂ O ₃ were mixed in a wet ball mill for 20 hours, dried and granulated, and 3 inches in diameter. After being molded into an Ar atmosphere, sintering temperature 1600 ° C, press pressure
Hot press sintering under the condition of 200kg / cm ² for 1 hour to thickness
A composite sintered body having a diameter of 0.5 mm and a diameter of 3 inches was produced.

A Ni electrode layer having a thickness of 1.5 μm was formed on both surfaces of the composite sintered body thus obtained by Ni electroless plating to obtain a wafer. Next, the wafer was cut into a square having a side of 0.75 mm with a diamond blade using an outer peripheral slicing machine to obtain a thermistor chip.

Subsequently, a Kovar alloy lead wire having a diameter of 0.25 mm and a length of 65 mm was connected to this chip by a parallel gap welding method under the following conditions.

(Parallel gap welding conditions) AC voltage 0.7 V Time 30 msec Next, the obtained material was inserted into a tube of borosilicate glass having a composition shown in Table 1 having a diameter of 2.5 mm and a length of 4 mm. After sealing at 800 to 1000 ° C. in an argon gas atmosphere, this was subjected to an aging treatment to produce a glass-sealed thermistor element as shown in the figure.

Table 2 shows the results obtained by examining the electrical resistance at a high temperature.

Effect of the Invention The glass-sealed high temperature thermistor element of the present invention is 500
Even when used at a high temperature of not less than ° C., a high electric resistance value can be maintained and stable thermistor characteristics are provided.

This glass-sealed thermistor element is suitable as a high-temperature sensor such as an automobile exhaust gas temperature detection sensor or an oil / gas combustion control sensor.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an example of a glass-sealed thermistor element of the present invention. In the figure, reference numeral 1 denotes a thermistor chip, 2 denotes a sealing glass, 3 denotes a lead wire, and 4 denotes an electrode layer.

Claims (1)

(57) [Claims] A glass-sealed high-temperature thermistor element comprising a pair of electrode layers provided on both sides of a thermistor chip, a heat-resistant lead wire made of an iron-based alloy connected to each of the electrode layers, and sealing with glass. A thermistor element comprising a borosilicate glass having a total amount of alkali metal of not more than 3% by weight in terms of oxide and an electric resistance value of not less than 10 ⁶ Ωcm at 500 ° C. as the glass.