JP2897837B2 - Method for manufacturing a thermistor element - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a thermistor element having a negative resistance-temperature characteristic for high temperatures, and more particularly to a method for manufacturing a glass-sealed thermistor element.

<Conventional Technology> 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 and oil / gas combustion control sensors.

As a material for a temperature-sensitive resistor of a conventional high-temperature thermistor element, that is, a thermistor material, a sintered body of a complex oxide such as a fluorite type, a spinel type, a corundum type, a perovskite type, or a rutile type is used.

Since these are sintered composite oxides, their changes over time are not significantly affected by i) having a crystal transformation point below 1000 ° C, and ii) forming a barrier between particles. Many are stable.

In addition, since it is a multi-component composite oxide, its resistance value, etc.
There is large variation in characteristics. Furthermore, in these devices, the value of the thermistor constant B is large, and the temperature coefficient of the resistance of the thermistor is too large, so that the thermistor cannot cover a wide temperature range from room temperature to high temperature. In particular, it did not endure use at a temperature of 500 ° C. or higher.

On the other hand, various thermistor materials containing silicon carbide or boron carbide as a main component are known as thermistor materials usable at 500 ° C. or higher.

However, when a thermistor element using these materials is used at a high temperature in the air, especially at 500 ° C. or higher, 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 the chip with glass for forming the protective film.

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

A glass-sealed thermistor element using various thermistor materials containing silicon carbide or boron carbide as a main component is disclosed in, for example, JP-A-64-64202.

The thermistor element proposed by the present inventors comprises a matrix material containing silicon carbide and / or boron carbide as a conductive path forming material, and further containing aluminum, silicon and at least one oxide of a Group 2A element. Contains, using a thermistor material composed of a sintered body whose content of the silicon carbide is 1.24 or less by volume to the content of the matrix substance, even when used at a temperature of 400 to 800 ° C. It has stability, easy control of resistance value, and easy glass sealing.

In addition, the present inventors, such a thermistor material,
Furthermore, a thermistor element containing a boride of a 4A group element to improve the chip processability has been proposed (Japanese Patent Application No. Hei.
No. 217085).

<Problem to be Solved by the Invention> FIG. 3 shows an example of a glass-sealed thermistor element.

The thermistor element 1 shown in FIG. 3 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 these electrode layers. And the thermistor chip 11, the electrode layers 33 and 35, and a part of the lead bodies 43 and 45 are sealed with glass.

Such a glass-sealed thermistor element is generally manufactured as follows.

First, a sintered body wafer of thermistor material is prepared, and electrode layers are formed on both surfaces of the wafer.

The wafer on which the electrode layer is formed is cut into, for example, a square by using a dicing saw or the like to form chips.

A lead body is connected to the obtained chip. The connection of the lead body is performed by spot welding or the like.

Next, it is inserted into a glass tube and heated to seal the glass, thereby forming a thermistor element.

Since the high-temperature thermistor element is used at a high temperature, a glass having a high glass transition temperature and a high working temperature is used as the sealing glass, and the sealing temperature is, for example, about 750 to 900 ° C.

In each of these steps, the following stress is applied to the electrode layer.

For example, a mechanical stress is mainly applied when forming a chip, a thermal stress and a mechanical stress are applied when connecting a lead body, and a thermal stress is mainly applied when sealing a glass.

Conventionally, as an electrode layer, for example, an electrolytic plating film of Ni or the like as described in JP-A-1-136304 is used, but such an electrode layer has low adhesiveness, as described above. Easy to peel off due to stress. In particular, a thermistor material containing silicon carbide or boron carbide as a main component has a high hardness and is difficult to process. Therefore, a diamond cutter or the like is used for cutting when forming a chip. And peeling is likely to occur.

When peeling occurs in the electrode layer, the resistance of the element significantly changes, so that the product cannot be manufactured, and the production yield decreases.

Under such circumstances, there is a demand for an electrode material that is optimal for a high-temperature glass-sealed thermistor element using a thermistor material containing silicon carbide or boron carbide as a main component.

The present invention improves the production yield of a glass-sealed thermistor element for high temperature using a material containing silicon carbide and / or boron carbide as a thermistor chip material by preventing the electrode layer from peeling off in the manufacturing process. The purpose is to:

<Means for Solving the Problems> Such an object is achieved by the present invention of the following (1) to (5).

(1) Using a thermistor chip containing silicon carbide and / or boron carbide, the electrode forming portion of the thermistor chip is roughened. The electrode forming portion contains a pair of nickel and boron, and has a boron content of 0.1 to An electrode layer of 5 wt% and the balance being substantially nickel is formed by an electroless plating method, and the material for thermistor chip and the material for the electrode layer are mixed between the electrode layer and the thermistor chip. Forming a layer, connecting a pair of leads to each of these electrode layers, and sealing the thermistor chip and the electrode layer and a part of the lead with glass.

(2) The method for manufacturing a thermistor element according to the above (1), wherein the thickness of the electrode layer is 0.1 to 50 μm.

(3) The above (1), wherein the thickness of the mixed layer is 1 to 50 μm.
Or (2) a method for manufacturing a thermistor element.

(4) The method for manufacturing a thermistor element according to any one of (1) to (3), wherein only a portion of the lead body exposed from the glass is covered with a plating film.

(5) The method for manufacturing a thermistor element according to the above (4), wherein the plating film is made of Cr, a Cr-based alloy, Ni or a Ni-based alloy, and the lead body is a Kovar alloy or a 42 alloy.

<Operation> In the thermistor element of the present invention, since the thermistor chip contains silicon carbide and / or boron carbide and the electrode layer contains nickel and boron, the adhesion between the thermistor chip and the electrode layer is extremely high. For this reason, when the thermistor material sintered body on which the electrode is formed is cut into chips, when a lead body is connected by spot welding or the like, and further, when the glass is sealed, the electrode layer hardly peels off. . When the electrode layer is formed by an electroless plating method, the adhesion becomes particularly high.

In addition, since the electrode layer containing nickel and boron has high heat resistance, it is suitable as an electrode material for a high-temperature thermistor having a high glass sealing temperature.

<Specific Configuration> Hereinafter, a specific configuration of the present invention will be described in detail.

FIGS. 2 and 3 show a preferred embodiment of the glass-sealed thermistor element of the present invention.

The thermistor element 1 includes a thermistor chip 11, a pair of electrode layers 33 and 35 formed on the thermistor chip 11, and a pair of lead members respectively connected to these electrode layers.
43, 45, thermistor chip 11 and electrode layers 33, 35
And a part of the lead bodies 43 and 45 are sealed with the glass 5.

[Thermistor Chip 11] Since the thermistor element 1 of the present invention is a high-temperature thermistor element, the thermistor chip 11 contains silicon carbide and / or boron carbide that can be used at a high temperature.

Although there is no particular limitation other than containing silicon carbide and / or boron carbide, in the present invention, silicon carbide and / or boron carbide is contained as a conductive path forming substance, and Al, S
It is preferable to use a sintered body containing at least one selected from the group consisting of oxides of i, Mg, Ca, Sr and Ba as a matrix material as a thermistor material.

This thermistor material has high stability particularly in a temperature range of 400 to 800 ° C., is easy to control the resistance value, is easy to seal with glass, and has high chip processing properties.

In this thermistor material, the matrix material is
Usually, it is polycrystalline, and the content of silicon carbide is preferably 1.24 or less by volume relative to the content of the matrix material.

If the volume ratio exceeds 1.24, the resistance value decreases, and foaming occurs in a glass sealing step described later, and it becomes difficult to form an element by glass sealing.

In addition, the volume ratio of silicon carbide / matrix material is 0 to
If 1.24, the ratio of silicon carbide to boron carbide is 1: 0 ~
Various quantitative ratios of 0: 1 may be used.

The volume ratio of silicon carbide, boron carbide, and the matrix substance is defined as the area ratio of each component obtained by subjecting the cut surface of the sintered body to mirror finishing and then observing with an electron microscope.

The matrix material is a sintered body of one or more oxides of Al, Si, Mg, Ca, Sr and Ba.

By using such an oxide sintered body as the matrix material, foaming during glass sealing or the like is reduced.

Such oxides include aluminum oxide (Al ₂ O
₃ , especially α-Al ₂ O ₃ ), or silicon dioxide (SiO ₂ ), or aluminum oxide-silicon dioxide in various quantitative ratios. By using silicon dioxide, cutting workability is improved, and chipping is facilitated. Alternatively, or in addition to these, one or more of oxides of Mg, Ca, Sr and Ba may be used.

By containing these oxides, the electric resistance value can be easily controlled, and the positional variation of the electric resistance value generated in the sintered body wafer can be reduced. Also,
Cutting is also easy.

The oxides of Mg, Ca, Sr and Ba are usually contained in the form of magnesium oxide (MgO), calcium oxide (CaO), strontium oxide (SrO) and barium oxide (BaO).

The amounts of the oxides of Mg, Ca, Sr and Ba may be appropriately determined from the range of 0 to 100% of the matrix material according to the desired electric resistance value.

The matrix material may contain one or more oxides of a Group 4A element in addition to one or more of these oxides.

By containing the oxide of the Group 4A element, the control of the electric resistance value becomes easy, the variation in the sintered body is reduced, and the cutting workability is improved.

As the oxide of the 4A group element (Ti, Zr, Hf), titanium oxide (TiO ₂ ) and zirconium oxide (ZrO ₂ ) are preferable.

The amount of the oxide of these Group 4A elements is preferably 0.5 or less, more preferably 0.3 or less by volume ratio with respect to the content of silicon carbide and boron carbide.

When the volume ratio exceeds 0.5, the oxide of the Group 4A element is reduced by SiC or B ₄ C during firing and has conductivity, so that silicon carbide and boron carbide do not become the main components of the conductive path forming material, and Thermistor characteristics and its stability are reduced.

Specific examples of the oxide sintered body forming such a matrix material include α-Al ₂ O ₃ , SiO ₂ , mullite (3Al ₂ O
₃ · 2SiO _2), steatite (MgO · SiO _2), forsterite (2MgO · SiO _2), zircon (ZrO ₂ · SiO _2), porcelain _{(SiO 2 · Al 2 O 3} ), magnesia (MgO), Al ₂ O ₃・ CaO Al ₂
O ₃・ TiO ₂ , BaO ・ SiO ₂ etc. “Engineering Properties of Ceramics Databook to G
uide Materials Selection for Structural Applicatio
ns "Battele Memorial Institute Columbus Laboratorie
s Complex oxides described in P445 to P447, P459, P469, P472, and P479 to P480.

The chemical formulas of these oxide sintered bodies are those shown in parentheses, respectively, but their compositions may be slightly different in stoichiometry. The average grain size is usually in the range of 0.1 to 250 μm, especially 0.1 to 10 μm.

Silicon carbide in the sintered body is represented by the chemical formula SiC, and its composition may be slightly different in stoichiometry. Further, the average crystal grain size is usually in the range of 0.1 to 15 μm.

The boron carbide in the sintered body is represented by the chemical formula B ₄ C, and its composition may be slightly different in stoichiometry. The average grain size is usually 0.1 to 15 μm
In the range.

These boron carbide, silicon carbide, or boron carbide and silicon carbide form a conductive path in the matrix material and exhibit thermistor characteristics. The conductive path formed from these has stable and good thermistor characteristics at a high temperature of 400 ° C. or higher.

Next, the case where aluminum oxide (α-Al ₂ O ₃ ) was used as the oxide sintered body of the matrix material,
This will be described in more detail. The composition in the following description is represented by the weight percentage obtained by chemically analyzing the sintered body.

The contents of aluminum oxide, silicon carbide and boron carbide are respectively x wt%, y wt% and z wt%,
When x + y + z = 100 wt%, aluminum oxide,
The composition (x, y, z) of silicon carbide and boron carbide is the first
In the ternary composition diagram shown in the figure, the composition range is surrounded by A (100,0,0), B (0,0,100), C (50,50,0) and does not include the points A and B. . In this case, preferably, the composition range surrounded by D (95,0,5), E (5,0,95), C (50,50,0), F (95,5,0), more preferably Is a composition range surrounded by D (95,0,5), G (50,0,50), C (50,50,0) and F (95,5,0), particularly preferably D (95,0,5). , 0,5), H (80,0,20), I (65,35,0) and F (95,5,0) give favorable results.

Such a composition range is determined by A in FIG.
At (100,0,0) point, that is, at 100 wt% of aluminum oxide or matrix material, high resistance is obtained even at high temperatures, and at point B (0,0,100), that is, at 100 wt% of boron carbide, it becomes difficult to obtain a sintered body. Because. Further, when the temperature is below the BC line, the B constant of the thermistor element becomes large, and it becomes difficult to obtain a sintered body.

When the temperature is below the DF line, a desired resistance value can be obtained due to the effect of B ₄ C and / or SiC addition.
If the number of wires is equal to or greater than the value, sinterability is improved, and a good thermistor material can be obtained.

When the amount of Al ₂ O ₃ is 50 wt% or more at the GC line or more, the sinterability is further improved.

In such a case, one of the effects of adding B ₄ C and / or SiC is to reduce the resistance of Al ₂ O ₃ or the matrix material. Then, the effect of the reduction in resistance appears in a region surrounded by the DGCF, and the resistance value gradually decreases as the amount of B ₄ C and / or SiC increases in this region. However, beyond the GC line, the resistance change saturates, and the resistance value hardly decreases.

For this reason, in the region surrounded by the GEC, it can be used as a thermistor in a normal case, but depending on the raw material used, the resistance value is too low, and it may not be used as a thermistor. Therefore, it is particularly preferable to use a material having a GC line or more in that it is not restricted by the raw material and the resistance can be controlled to a desired value by the amount of addition. In more detail, the raw material SiC includes free C and Si,
O, Al, Fe, Ti, etc. are contained, but those having an SiC content of about 99 wt% or more have a saturation resistance of about 10 ⁴ Ωcm or more, and can be used in a region surrounded by GCE. However, if the purity is lower than the above, the resistance value becomes lower below the GC line. The raw material B ₄ C contains O, N, Fe, etc. as impurities.
It has a saturation resistance of 10 ⁴ Ωcm or more and can be used in the region surrounded by GEC. However, if the purity is less than the above,
The resistance decreases below the GC line.

The area surrounded by DHIF is the area surrounded by J (90,0,10), K (85,0,15), L (80,20,0), and M (70,30,0). Then, a more preferable resistance value can be obtained.

In the above, α-Al ₂ O ₃
Has been described above, and the preferred composition ranges when the contents of α-Al ₂ O ₃ , SiC and B ₄ C are x, y and z, respectively.

When other matrix material is used in place of α-Al ₂ O ₃ , the theoretical density of the other matrix material is ρm, α-
When the theoretical density of Al ₂ O ₃ is ρa, A = 100 / (ρm x /
ρa + y + z), the matrix material is Axρm / ρ
a parts by weight, Ay parts by weight for SiC, and Az parts by weight for B ₄ C may be used. Then, each composition range determined by (Apmx / ρa, Ay, Az) corresponding to (x, y, z) of points A to M in FIG. 1 is a preferable content weight range of each component. It is.

In such a case, the theoretical density of each component is
It is described in the Memorial Institute Columbus Laboratories literature and can be easily calculated therefrom.

alpha-Al ₂ O ₃ is ^{ρa = 3.98g / cm 3, B} 4 C is 2.52 g / cm ^3, SiC is 3.21 g / cm ^3, In addition, for example, 2MgO · SiO ₂ is 3.
It is 71 g / cm ^{3 and the} like.

Since the volume ratio of B ₄ C, SiC and the matrix substance determines the thermistor properties and the foam prevention properties, α-
When the theoretical density of Al ₂ O ₃ is ρ _a , the theoretical density of SiC is ρ _s , and the theoretical density of B ₄ C is ρ _b , B = 100 / (x / ρ _a + y / ρ _s + z / ρ _b ) Then, (Bx / ρ _a , By / ρ _s , Bz / ρ _b ) becomes the volume ratio corresponding to the above (x, y, x).

The sintered body preferably used in the present invention has such a weight ratio composition.
The volume ratio of C / matrix material is 1.24 or less.

The measured density of the sintered body is 75% of the theoretical density of the sintered body.
Above, it is particularly preferable that it is 90 to 100%, and 95 to 100%
Is most preferred. As a result, the change over time in the electrical resistance of the element is improved.

During sintering, part of silicon carbide or boron carbide may be changed to an oxide (silicon oxide, boron oxide), or part of the oxide may be changed to carbide.

However, the content of boron oxide is 0 to 1 wt%, particularly 0.1 to
It is preferably 0.5 wt%. The reason for this is that boron oxide, especially B ₂ O ₃ , becomes vitreous, the glass phase increases and the melting point becomes low, and it becomes difficult to control the electric resistance and the particle size of the sintered body. .

The thermistor material preferably further contains a boride of a Group 4A element. Borides of Group 4A elements have an effect of improving chip workability.

Titanium boride (Ti)
B ₂ ) and zirconium boride (ZrB ₂ ) are preferred, especially Ti
B ₂ is optimal.

By containing these, the occurrence of chipping is remarkably reduced, and the life of the diamond grindstone at the time of processing is remarkably improved.

Borides of these 4A group elements are contained in the thermistor material.
It is preferably contained in an amount of 0.01 to 10 wt% in terms of a 4A group element.

This is because if it is less than 0.01 wt%, there is no improvement in processability, and if it exceeds 10 wt%, its conductivity degrades the characteristics of SiC and B ₄ C as a conductive path forming material, and the high temperature thermistor characteristics and This is because the stability decreases.

In this case, the content of boride of the 4A group element is 0.1 to 8 wt.
%, Especially 0.5 to 6% by weight, more preferably 1 to 5% by weight.

The borides of these Group 4A elements are usually present at the grain boundaries or within the grains.

Their presence can be confirmed with an analytical electron microscope, and their contents may be measured by quantitative analysis using an X-ray diffraction method.

The thermistor material may further contain one or more group 3A elements as accessory components.

The group 3A element may be contained as a simple metal, a compound, or a composite of these.

As group 3A elements, Y and Ce are particularly preferable, and when they are contained as compounds, oxides of these elements (Y ₂ O ₃ ,
CeO ₂ ) or carbide is preferred.

By containing the group 3A element in an amount of preferably 0.01 to 10 wt% in terms of element, the control of the electric resistance value becomes easy and the positional variation of the electric resistance value in the sintered body wafer can be reduced.

In addition, instead of or in addition to the 3A group element, iron is preferably used as a subcomponent, preferably a simple metal, an oxide (Fe ₂ O ₃ ),
It may be contained in one or more types of carbides.

 Fe also has the same effect as Group 3A elements.

 The content of Fe is preferably 0.01 to 10% by weight in terms of element.

In the case of Group 8 elements other than iron, for example, Co, Ni, Ru, etc.,
At an operating temperature of 500 ° C or more, the amount of oxygen vacancies easily changes,
When the content increases, the electrical resistance deteriorates with time. For this reason, the inclusion of metals, oxides, carbides, etc., of Group 8 elements other than iron is not excluded, but 1 wt% in element conversion.
Hereinafter, it is particularly preferably 0 to 0.5% by weight.

As described above, the above-described effects of Group 3A elements and Fe can also be realized by oxides of Al, Si, Mg, Ca, Sr, and Ba and Group 4A element oxides. And, as described above, the preferable content thereof is all or a part of the matrix material, and is preferably 0.01% by weight or more in terms of element.

Further, these elements, preferably Mg, Ca, Sr, Ba,
One or more of Ti and Zr may be a simple element or a carbide. Preferably, at a content of 0.01 to 10% by weight in terms of element, the resistance value can be easily controlled and the variation is small. Become.

Further, if necessary, other subcomponents can be contained, for example, in the form of a simple substance, an oxide, a carbide, or the like.

First, the elements of group 5A and 6A have no effect on their content, but their inclusion is not necessarily excluded.
However, since addition of a large amount degrades the thermistor characteristics, it is preferable that the amount does not exceed 10 wt% in terms of element, especially 1 w
Preferably it does not exceed t%.

Next, it is preferable that a Group 1A element, for example, Na, Li, etc., is not particularly contained. This is because when a voltage is applied to the thermistor element, these ions move and diffuse, and the resistance easily deteriorates with time. Further, at the time of glass sealing, these are liable to be diffused into the glass, and characteristic deterioration is likely to occur.

The content of the 1A group element is 0 to 1% by weight, especially 0% by element conversion.
It is preferably about 0.001% by weight.

Also, the inclusion of a 7A group element is not preferred. This is because the valence of the group 7A element is liable to change, and the characteristics are likely to change with time.

The content of the 7A group element is 0 to 1% by weight, especially 0% by element conversion.
It is preferably about 0.05% by weight.

Further, since the group 1B element and the group 2B element also easily change with time, it is preferably 0 to 1% by weight, particularly preferably 0 to 0.05% by weight in terms of element.

In addition, Ga, In, and Tl, which are Group 3B elements other than B and Al,
The content may be about 0 to 1 wt% or less.

However, 4B group, 5B group, 6B group, 7B other than C, Si, O, N
Since group elements and the like are not preferable in terms of characteristics, the content is preferably 0 to 1% by weight.

In addition, a small amount of nitride, silicide, boride, and the like may be contained as accessory components.

The total of these subcomponents is preferably 10% by weight or less.

When these subcomponents in the sintered body are contained as compounds, their compositions may be stoichiometrically slightly different in composition. In addition, the average particle diameter is usually in the range of 1 to 5 μm in the case of a simple metal, and in the case of a compound,
Usually, it is in the range of 0.1 to 5 μm.

Further, if necessary, the above-mentioned subcomponents or compounds which change to these by sintering, such as carbonates and organometallic compounds, are added.

 Such a sintered body is obtained as follows.

Predetermined amounts of a matrix material powder such as aluminum oxide and a silicon carbide powder and / or a boron carbide powder are prepared, and a solvent such as ethanol or acetone is added thereto and wet-mixed by a ball mill or the like. As the raw material powder of the above oxide such as aluminum oxide (Al ₂ O ₃ ), one having an average particle size of 0.1 to 5 μm and a purity of 99.5 wt% or more is generally used.

In addition, as a raw material of the oxide, a compound which becomes an oxide by sintering such as a carbonate or an organometallic compound may be used.

Silicon carbide (SiC) powder generally has an average particle size of 0.5 to
A powder having a thickness of 5 μm and a purity of usually 98 wt% or more is used.

Boron carbide (B ₄ C) powder generally has an average particle size of 0.5 to
Use a material having a purity of 5 wt.

The boride of the 4A group element may be added as, for example, TiB ₂ powder, and generally has an average particle size of 0.1 to 5 μm and a purity of 98 wt.
% Or more may be used.

Further, the boride of the 4A group element, when a boron-containing substance such as boron carbide is contained in the raw material, its oxide,
You may add in the form of a simple substance etc.

At this time, for example, by controlling the sintering conditions as described later, for example, B ₄ C and TiO ₂ react to generate, for example, TiB ₂ .

In such a case, for example, for Al ₂ O ₃ matrix materials are mixed to B ₄ C and / or SiC in the conductive path forming material, and baked by the addition of TiO ₂ this as 4A group element source, the TiB ₂ 9 (Al ₂ O ₃ ) 2 (B ₂ O ₃ ), B
_{13 C 2, TiC, Ti 3} Al, Ti, Ti 2 Si, 3 (Al 2 O 3) 2 (SiO 2)
May be by-produced.

These by-products may be contained in an amount of about 10% by weight or less, particularly about 1% by weight or less.

These may be added as powders having the purity and particle size according to the above.

 The amount of the solvent is about 100 to 120% by weight of the powder.

If necessary, a dispersant or the like may be further added.

Thereafter, the above mixture is pressure-formed at room temperature, and is subjected to a normal pressure sintering method, a hot press (HP) sintering method, a hot isostatic pressure (HIP) method or the like in an oxygen atmosphere or a non-oxidizing atmosphere. The compact is sintered and allowed to cool to obtain a thermistor material.

The pressure at the time of pressure molding is about 500 to 2000 kg / cm ² .

The non-oxidizing atmosphere at the time of sintering may be an inert gas such as N ₂ , Ar, He, H, CO, various hydrocarbons, etc., or a mixed atmosphere thereof, or even a vacuum atmosphere. Good.

In the case of the normal pressure sintering method, atmospheric pressure may be used, and the sintering temperature is 1400 ~
1900 ° C, especially 1600-1900 ° C, more preferably 1750-1800
Effective at ° C.

When the temperature is lower than 1400 ° C., it is not sufficiently densified even after sintering for a long time, and when the temperature is higher than 1900 ° C., oxides such as Al ₂ O ₃ and SiC and / or B ₄ C Interactions become more intense.

 The sintering time is usually 0.5 to 20 hours.

In the case of the HP sintering method, the pressing pressure is 150 to 250 kg / cm ² , and the sintering temperature is 1400 to 1800 ° C, particularly 1500 to 1800 ° C, more preferably 1650 to 1750 ° C.

If the temperature is lower than 1400 ° C, a dense sintered body cannot be obtained,
If the temperature is higher than 1800 ° C, the above matrix material such as Al ₂ O ₃ and S
Interaction with iC and / or B ₄ C becomes severe.

 The sintering time is generally between 1 and 30 hours.

In the case of the HIP sintering method, a green compact of the raw material powder is pre-sintered in an oxygen atmosphere or a non-oxidizing atmosphere (for example, in a vacuum to 1200 ° C., and thereafter preferably in an Ar atmosphere),
Next, the pre-sintered body is sintered in a HIP furnace. The pre-sintering temperature is preferably 1400 to 1650 ° C., and the time is preferably 1 to 50 hours.

The sintering temperature in the HIP method is 1200 to 1500 ° C., the sintering time is 1 to 50 hours, the pressure is 1000 to 1500 kg / cm ² , and the sintering may be performed in an oxygen atmosphere or an inert atmosphere such as Ar.

In this case, at room temperature, oxygen gas, Ar gas, etc. should be 300 ~ 400kg / c
Pressurize to m ² and then apply pressure by heating as described above.

The sintering conditions described above are common to both the case where a boride of a group 4A element is used in advance and the case where a boride of the group 4A element is generated. Occasionally, a boride of a group 4A element may be formed according to the following profile.

 In the room temperature sintering method, the heating rate is 1 to 100 ° C / min, the sintering temperature is 1600 to 1900 ° C, and the holding time at the sintering temperature is 0.5 to 20 hours.

 In the HP method, the heating rate is 1 to 100 ° C / min, the sintering temperature is 1400 to 1800 ° C, and the holding time at the sintering temperature is 1 to 30 hours.

 Furthermore, in the HIP method, the heating rate is 1 to 100 ° C / min, the pre-sintering temperature is 1400 to 1650 ° C, the holding time at the pre-sintering temperature is 1 to 50 hours, the sintering temperature is 1200 to 1500 ° C, and the The holding time is 1 to 50 hours.

As described above, by particularly increasing the holding time at the sintering temperature, the generation of boride of the Group 4A element is promoted, and particularly, the grain size of the matrix material is coarsened in a range of about 10 times or less, and chip processing is performed. The performance is improved.

The thermistor material thus produced has a resistance of 500
It is about 10 ² to 10 ⁷ Ωcm at ° C., and there is almost no change in resistance value even when used or stored in a temperature range of 400 to 800 ° C. Also, the value of B is 1000-5000K at 50-480 ° C.

Such a thermistor material contains a boride of a Group 4A element in an amount of 0.01 to 10% by weight, as described above, so that chip workability is remarkably improved.

As the thermistor characteristics, glass sealing characteristics, and the like, characteristics equivalent to those described in JP-A-64-64202 can be obtained.

For example, as for the relationship between the composition ratio of the thermistor material and the resistivity (ρ), the change in ρ depending on the amount of addition is not steep, and it becomes easy to obtain a desired resistance by changing the composition ratio. Elemental electric resistance (kΩ) 2A group 100-400 3A group 130-140 4A group 60-300 Fe20-80 Not only thermistor material of the above-mentioned composition but also those containing silicon carbide and / or boron carbide as the main component Then, the effect of the present invention is realized.

There is no particular limitation on the dimensions of the thermistor chip.
The length is about 0.5 to 1.0 mm, the width is about 0.5 to 1.0 mm, and the thickness is about 0.5 to 1.0 mm.

[Electrode Layers 33, 35] In the present invention, the electrode layers 33, 35 contain nickel and boron.

In the present invention, it is preferable that the electrode layer has a boron content of 0.1 to 5 wt%, particularly 0.2 to 3 wt%, and the balance is substantially nickel. When the boron content is less than the above range, the strength of the electrode layer is insufficient, the electroless plating is difficult, and further, the heat resistance becomes insufficient and the properties are likely to be deteriorated during glass sealing. . If the boron content exceeds the above range, the conductivity is insufficient, and the hardness of the electrode layer becomes too high, so that peeling is likely to occur when the sintered body of the thermistor material is chipped.

Various methods can be used to form such an electrode layer, but in order to obtain high adhesion to the thermistor material as described above, it is particularly preferable to use an electroless plating method.

The electroless plating may be carried out in a usual manner using various kinds of ordinary plating baths, for example, according to the description of “Plating Practical Handbook” (Nikkan Kogyo Shimbun), pp. 121-127. The surface of the sintered body of the thermistor material to be plated is preferably subjected to a general surface activation treatment.

When the electrode layer is formed by the electroless plating method, at least an electrode forming portion on the surface of the sintered body of the thermistor material is roughened before plating. By forming the electrode layer on the roughened surface of the sintered body, the adhesion of the electrode layer becomes extremely high.

Although there is no particular limitation on the method of surface roughening, it is preferable to use a chemical etching method. For example, good surface roughening can be performed by immersion in an alkali molten salt. In this case, it is preferable to use a Na-based salt as the alkali molten salt, and it is particularly preferable to use NaOH. There are no particular restrictions on various conditions such as processing temperature and processing time, and they may be appropriately selected according to the composition of the thermistor material to be processed.

In addition, chemical etching using various acids such as hydrochloric acid and sulfuric acid is also suitable. Further, the surface can be roughened by dry etching such as plasma etching or sand blasting.

The degree of surface roughening can be confirmed with a scanning electron microscope or the like.

When the electrode layer is formed by electroless plating on the surface of the sintered body of thermistor material thus roughened, the electrode layer is placed in minute recesses or pores on the surface of the sintered body formed by the roughening process. Component material invades.

For this reason, a mixed layer in which both the material constituting the electrode layer and the material constituting the sintered body are present is formed between the electrode layer and the sintered body. In this case, the electrode layer is a portion that is substantially continuous and does not include the constituent material of the sintered body. Being substantially continuous means that there may be discontinuous portions due to film defects such as pinholes. Further, the sintered body in this case is a portion where the material constituting the electrode layer does not exist.

Such a state can be observed by a scanning electron microscope or the like, and can be confirmed by an electron beam probe microanalyzer (EPMA). The magnification at this time may be, for example, about 500 to 5000 times.

The thickness of the electrode layer is preferably 0.1 to 50 μm, particularly preferably 1 to 10 μm. If the thickness is less than the above range, it is difficult to form a uniform electrode layer, and a thickness exceeding the above range is unnecessary.

The thickness of the mixed layer is preferably 1 to 50 μm, particularly preferably 5 to 20 μm. When the thickness is less than the above range, the adhesion of the electrode layer is insufficient. If the thickness exceeds the above range, the effective thickness of the chip cannot be sufficiently obtained, and a thickness exceeding the above range is not necessary for improving the adhesion.

Note that an electrolytic plating film of Cr or an alloy thereof, or Ni or an alloy thereof may be provided on the electrode layer. Since the surface of such an electrolytic plating film is relatively rough, the adhesion to the lead body is improved.

[Lead bodies 43 and 45] As the lead wires used as the lead bodies 43 and 45, any of conventionally known lead wires can be used. However, in terms of the coefficient of thermal expansion, cost, etc., 29% by weight of Ni-17% by weight of Co It is preferable to use a Kovar alloy having a composition of Fe and a 42 alloy alloy having a composition of 41 to 43 wt% Ni-remaining Fe.

The Kovar alloy has an excellent thermal expansion characteristic that is similar to that of hard glass, and is an alloy used as a hermetic sealing material for hard glass and ceramic. The 42 alloy alloy is used as various hermetic seals, such as transistors, diode lead wires, IC lead frames, and lead switch leads, as a hard or soft glass sealing material.

There is no particular limitation on the method of connecting the lead bodies 43 and 45 to the electrode layers 33 and 35, respectively, and an appropriate method is 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. do it.

[Plating Films 431, 451] When the lead bodies 43, 45 are used as a high-temperature thermistor, they are exposed to high temperatures, so that surface oxidation occurs. The same applies to storage in a high humidity state.

For this reason, on the lead body surface, to improve oxidation resistance
It is preferable to form a plating film of Cr or a Cr-based alloy, or Ni or a Ni-based alloy.

The plating film may be applied to the entire surface of the lead body. However, like the plating films 431 and 451 shown in FIG. Preferably, it is formed only in the unsealed portion.

 Hereinafter, the reason will be described.

Kovar alloys, 42 alloy alloys, and the like suitable for the lead material contain Fe and have insufficient oxidation resistance, but have good adhesion to glass.

On the other hand, 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.

When a lead body having a plated film with low wettability 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.

Therefore, it is preferable that the plating film of the lead body be formed on a portion other than the glass sealing portion.

The plating films 431 and 451 may be made of any material as long as it has an antioxidant effect, and an appropriate material may be selected in consideration of the lead material used.

For example, when the lead body is a Ni alloy such as the above Kovar alloy or 42 alloy, the plating film material may be Cr, Cr
Preferred are Cr-based alloys such as -Ni, Ni-based alloys such as Ni-Ni-B alloys, and Ni-P. In particular, Cr or a Cr-based alloy is preferred because of its high oxidation resistance and heat resistance.

The thickness of the plating film may be appropriately selected depending on the material to be used, the manufacturing conditions or the use conditions of the thermistor element, and is preferably, for example, about 0.1 to 10 μm, particularly preferably about 0.5 to 2 μm.

The plating film is preferably formed by an electrolytic or electroless plating method.

For example, the plating film of Cr or a Cr-based alloy is preferably formed by an electrolytic plating method. Also, Cr or Cr
When the plating film of the base alloy is formed by the electrolytic plating method,
It is preferably formed on a Ni base film formed by an electroless plating method. By providing such a base film, a uniform plating film having almost no defects such as pinholes can be formed.

The plating film of Ni or a Ni-based alloy is preferably formed by an electroless plating method.

There is no particular limitation on the plating bath used, and it may be appropriately selected according to the desired plating film composition.

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

The activation treatment is performed to promote the growth of the plating film in the electroless plating method. Generally, the lead body surface is cleaned by the steps of degreasing by alkali immersion or the like, washing with water, pickling with hydrochloric acid, and washing with water. After the activation, general sensitization and activation are performed.

Note that the activation treatment is preferably performed after sealing the glass. If the activation treatment is performed after the glass sealing, the chemicals and the like used in the activation treatment do not remain in the glass sealing portion, and there is no deterioration of the lead body and the electrodes.

[Sealing Glass 5] As the glass 5, the glass transition temperature is 600 ° C. or more, particularly about 600 to 700 ° C., and the working temperature is 1000 ° C. or less, especially
It is preferable to use glass at 800 to 1000 ° 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.
It is preferable to use a borosilicate glass containing an alkaline earth metal.

In addition, because it causes a decrease in insulation resistance at high temperatures,
The alkali components such as Na and K contained in the glass 5 are 1 wt.
% Is preferable.

[Method of Manufacturing Thermistor Element] An example of a method of manufacturing the thermistor element 1 will be briefly described below.

For example, a wafer of the above sintered body having a diameter of about 3 inches and a thickness of about 0.5 mm is manufactured. The above-described 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 of about 0.75 mm on a side using a dicing saw or the like to form chips.

The chip obtained in this way has a diameter of 0.2 to 0.5 mm,
A lead body having a length of about 20 to 100 mm is connected using the method described above.

Such a chip is about 1.5 to 2.5 mm in diameter and 5 mm in length.
And sealed in a glass tube at a temperature of about 750 to 900 ° C.

Note that the glass sealing is preferably performed in a non-oxidizing atmosphere. The non-oxidizing atmosphere may be an inert gas such as N ₂ , Ar, or He, H, CO, various hydrocarbons, or a mixed atmosphere thereof, or may be a vacuum or other various atmosphere.

In a non-oxidizing atmosphere during glass sealing, 0.5
% Or less of O ₂ may be contained.

After the glass sealing, preferably, the above-mentioned plating film is formed on the surface of the lead body.

After glass sealing, if necessary,
Aging is preferably performed for about 100 hours. The atmosphere during aging is not particularly limited, but is preferably performed in a non-oxidizing gas atmosphere. When a plating film is formed, aging may be performed before or after the plating film is formed.

<Example> Hereinafter, the present invention will be described in more detail by showing specific examples of the present invention.

Example 1 A sintered body for a thermistor chip containing B ₄ C was produced as described below.

(Thermistor chip raw material) Al ₂ O ₃ (Average particle diameter 1.2 μm, purity 99.9 wt% or more) 86 parts by weight B ₄ C (Average particle diameter 1.2 μm, purity 98 wt% or more) 14 parts by weight TiO ₂ (average particle diameter 0.5 μm, purity 99% by weight or more) 0.2 parts by weight The above-mentioned raw materials were wet-mixed with acetone by a ball mill for 20 hours.

The mixed slurry was dried and granulated and filled in a graphite mold having an inner diameter of 77 mm.

 This was sintered by hot pressing in an Ar atmosphere.

 After cooling, the sintered body was taken out of the mold.

As a result of X-ray diffraction of the sintered body, it was confirmed that Al ₂ O ₃ and B ₄ C were present.

It was also confirmed that TiB ₂ was present in the grain boundaries and in the grains.

Further, coarsening of the grain size of Al ₂ O ₃ was observed.

Simultaneously with generation of TiB _2, traces of TiC, Ti, Ti ₃ A
_{l, B 13 C 2, 9} (Al 2 O 3) 2 (B 2 O 3) or the like byproduct of was observed.

After processing these sintered bodies to 50 × 50 × 0.5 mm, both surfaces were subjected to Pd activation treatment, and then an electrode layer made of a Ni—B alloy was formed by an electroless plating method.

 The conditions of the plating bath were as follows.

NiSO ₄ 200 g / l Dimethylamine borane 2 g / l Boric acid 30 g / l Sodium citrate 40 g / l pH 7.5 60 ° C. The plating bath conditions are for the electrode layer of sample No. 2 shown in Table 1 below. Yes, in other samples with different B contents, the B content was changed by adjusting the dimethylamine borane amount and pH.

 Table 1 below shows the composition and thickness of the electrode layer.

Before the formation of the electrode layer, the surface of the thermistor chip was subjected to a surface roughening treatment. The surface roughening treatment was performed by immersing in a NaOH bath at 450 ° C. for 10 minutes. Also, for comparison,
A sintered body in which an electrode layer was formed without performing a roughening treatment was also manufactured.

After forming the electrode layer, the peel strength of the electrode layer was measured as follows.

First, the sintered body on which the electrode layer was formed was cut into 2 mm squares,
The L-shaped lead was soldered. Next, the lead body was pulled in a direction perpendicular to the electrode layer surface, and the force at the time when the electrode layer was peeled off from the sintered body was taken as the peel strength, and evaluated by a relative value.

 Table 1 shows the results.

Each of the above sintered bodies is cut by a peripheral slashing machine,
A 0.75 × 0.75 × 0.5 mm thermistor chip was obtained.

Next, the electrode layers of these thermistor chips have a diameter of 0.
A 3 mm, 65 mm long lead made of Kovar alloy was connected by spot welding.

After connecting the lead body, the resistance value was measured. This resistance value is _Ro
And

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

Next, the surface of the part of the lead body that was not covered with glass was subjected to surface treatment with an aqueous solution of iron chloride, and further, general sensitization and activation were performed.

After the activation treatment, a 1.5-μm-thick Cr plating film was formed by electrolytic plating on the surface of the lead body not covered with glass.

Thus, a thermistor element sample as shown in FIG. 2 was produced.

Measuring the resistance values of these thermistor elements were determined difference between the resistance value R _o before sealing. The difference was defined as ΔR, and the rate of change of the resistance value was calculated from (ΔR / R _o ) × 100 (%).

100 samples were measured for each thermistor element sample, and the ratio of those having a resistance change rate of 10% or more is shown in Table 1 as a defective product rate.

For comparison, a thermistor element having a Ni electrode layer was manufactured. The Ni electrode layer was formed by an electrolytic plating method using a Watts bath. The configuration other than the electrode layers was the same as above.

For these, the peel strength was measured in the same manner as described above, and the resistance change rate after glass sealing was measured.

 Table 1 shows the results.

In Samples Nos. 1 to 4, a mixed layer having a thickness of about 10 to 15 μm in which both the material forming the thermistor chip and the material forming the electrode layer existed between the thermistor chip and the electrode layer. An EPMA photograph near the boundary between the thermistor chip of Sample No. 2 and the electrode layer is shown in FIG.

From the results shown in Table 1 above, the effect of the book is clear.

That is, the electrode layer containing Ni and B has extremely high adhesion to the thermistor chip containing B ₄ C, and the characteristics are hardly degraded by the steps of chipping, connecting the lead body, and sealing the glass. .

For comparison, a thermistor element sample No. 7 was prepared by combining a thermistor chip made of a sintered Mn-Ni-Cr composite oxide with the Ni-B electrode layer of sample No. 2.

Further, a thermistor element sample No. 8 was prepared by combining the thermistor chip made of the Mn-Mi-Cr composite oxide sintered body with the Ni electrode layer of the sample No. 6.

In these samples, peeling of the electrode layer occurred when the lead member was connected, and the defective product rate at this time was 50% or more.

Example 2 A thermistor element sample No. 101 was produced in the same manner as in Sample No. 2 in Table 1 above. However, in sample No. 101, a plating film was formed on the entire surface of the lead body before glass sealing.

For sample Nos. 2 and 101,
5 ° C., the resistance value was measured after storage for 1000 hours at 85% RH, the change in resistance [Delta] R, the initial resistance value as R _o, was calculated by _{(ΔR / R o) × 100} (%).

As a result, in Sample No. 2 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 3% or less. In Sample No. 101 on which a plating film was formed, a resistance increase of 50% or more was observed.

The effects of the present invention are evident from the results of the above embodiments.

<Effects of the Invention> According to the present invention, in a glass-sealed thermistor element for high temperature using a material containing silicon carbide and / or boron carbide as a thermistor chip material, reliability and production yield are dramatically improved. Can be done.

[Brief description of the drawings]

FIG. 1 is a graph showing Al ₂ O ₃ —B ₄ C in the thermistor material of the present invention.
FIG. 3 is a ternary diagram showing a composition range of -SiC. FIG. 2 and FIG. 3 are cross-sectional views showing one example of the thermistor element of the present invention. FIG. 4 is a drawing substitute photograph showing a metal structure, and is an EPMA photograph showing an electrode layer and a mixed layer. DESCRIPTION OF SYMBOLS 1 ... Thermistor element 5 ... Glass 11 ... Thermistor chip 33, 35 ... Electrode layer 43, 45 ... Lead body 431, 451 ... Plating film

Claims (5)

(57) [Claims] 1. A thermistor chip containing silicon carbide and / or boron carbide is used. The electrode forming part of the thermistor chip is roughened. The electrode forming part contains a pair of nickel and boron, and the boron content is reduced. An electrode layer of 0.1 to 5 wt%, the balance being substantially nickel, is formed by an electroless plating method. A method of manufacturing a thermistor element in which a mixed layer is formed, a pair of leads are connected to these electrode layers, and the thermistor chip and the electrode layer and a part of the lead are sealed with glass. 2. The method according to claim 1, wherein said electrode layer has a thickness of 0.1 to 50 μm. 3. The method for manufacturing a thermistor element according to claim 1, wherein said mixed layer has a thickness of 1 to 50 μm. 4. The method for manufacturing a thermistor element according to claim 1, wherein only a portion of said lead body exposed from said glass is covered with a plating film. 5. The plating film according to claim 1, wherein said plating film is Cr, a Cr-based alloy, Ni or Ni.
5. The method for manufacturing a thermistor element according to claim 4, wherein said lead body is made of a Kovar alloy or a 42 alloy alloy.