EP3814296A1

EP3814296A1 - Ntc compound, thermistor and method for producing the thermistor

Info

Publication number: EP3814296A1
Application number: EP19735512.6A
Authority: EP
Inventors: Michael NADERER
Original assignee: TDK Electronics AG
Current assignee: TDK Electronics AG
Priority date: 2018-06-27
Filing date: 2019-06-25
Publication date: 2021-05-05
Also published as: JP2021520073A; JP7114739B2; US11929193B2; DE102018115513A1; US20210257135A1; CN112334430A; WO2020002336A1

Abstract

The invention relates to an NTC compound for producing a thermistor, containing as the main component a ceramic material of the Mn-Ni-O system, and said ceramic material having a general composition of Νi_xΜn₂O_4-δ, wherein y equals the molar Ni portion in the total metal content of the ceramic material of the Mn-Ni-O system, defined as c(Ni): (c(Ni) + c(Mn), with 0.500 < x < 0.610; 0.197 < y < 0.240.

Description

description

NTC ground, thermistor and method for manufacturing the thermistor

The invention relates to an NTC mass and a thermistor which comprises a ceramic base body which contains the NTC mass. It also relates to a method for producing the thermistor.

For the measurement of temperatures for monitoring and control in a wide variety of applications are predominantly

Thermistors based on sintered NTC masses,

Silicon temperature sensors (KTY), platinum temperature sensors (PRTD) or thermocouples (TC) are used. Due to their cost-effective production and their pronounced negative resistance-temperature characteristics, thermistors whose NTC masses are based on ceramic materials are the

for example, have a spinel structure, the most common. In addition to the constantly increasing requirements regarding the performance and miniaturization of thermistors, the requirements for the

Aging stability of such components increases. A factor that negatively affects the aging stability of a thermistor

can affect is the formation of unwanted

Secondary phases during the manufacture of a ceramic

Base body for the thermistor. Such secondary phases can lead to mechanical problems, in particular to the formation of cracks in the ceramic base body of the thermistor. Furthermore, the formation of the secondary phases changes the

Composition of the ceramic body of the

Thermistors contained NTC ground, which is the

Conductivity and the temperature behavior of the ceramic Change base body. Furthermore, the aging properties also deteriorate because over time

Resistance at 25 ° C of the thermistor changed. This leads to a falsification of the measured temperature.

Typical materials for NTC masses are based on

Ceramic materials from the Ni-Mn-0 system with spinel structure, which have a molar proportion of Ni in the total metal content due to the requirements placed on the components, which prevents the formation of secondary phases during the

Production of the ceramic base body favored for the thermistor. For example, conventional NTC materials have a Ni content in the total metal content, which is defined as c (Ni) :( c (Ni) + c (Mn)), of> 0.240. Because with this Ni content both

Ceramic materials with the desired spinel structure as well as secondary phases, such as NiO, are present side by side in a stable manner, these NTC materials tend to form NiO as an undesirable secondary phase, which has a negative effect on the aging stability of the thermistor.

Based on the above, it is an object of the present invention to provide an NTC composition which comprises a ceramic material from the Ni-Mn-0 system as the main constituent and not to form undesired ones

Side phases tend. Furthermore, a thermistor, which comprises a corresponding ceramic base body, and a

Methods of manufacturing the thermistor are provided.

This object is achieved by the NTC mass described in claim 1. More beneficial

Embodiments of the NTC ground, a thermistor which contains the NTC ground according to the invention and a method for Manufacture of the thermistor can be found in further claims.

NTC mass is to be understood here and below as a ceramic mass that has a negative temperature

has coefficients (NTC) and their electrical

Conductivity improves with increasing temperature.

According to the invention, an NTC composition is provided which contains a ceramic material from the Mn-Ni-0 system as the main component and has a general composition Nz _c Mh2q4- _d ,

where x corresponds to the proportion of nickel in the ceramic material from the Mn-Ni-0 system and y corresponds to the molar proportion of Ni in the total metal content of the ceramic material from the Mn-Ni-0

System defined as c (Ni) :( c (Ni) + c (Mn), corresponds and the following applies:

0.500 <x <0.610

0.197 <y <0.240.

In a more advantageous embodiment, the

NTC mass according to the invention as a main component

Contain ceramic material from the Mn-Ni-0 system, which has the general composition Nz _c Mh2q4- _d and applies to x and y:

0.520 <x <0.544

0.206 <y <0.214.

This Ni content lies in the optimal stability range of the ceramic material, which is the main component of the

represents NTC mass according to the invention, whereby there is hardly any formation of undesirable secondary phases, even at high sintering temperatures during the manufacturing process of a ceramic base body for a thermistor. In addition, the NTC mass after sintering at temperatures of up to 1340 ° C without significant formation of secondary phases

be cooled.

Furthermore, the ceramic material, which is the main constituent of the NTC composition according to the invention, can have a spinel structure of the general formula AB2O4, where the A positions can be occupied by at least Ni and the B positions can be occupied by at least Mn.

It is noted that the ceramic material that

The main component of the NTC mass is one

can have non-stoichiometric composition.

It is furthermore noted that the NTC mass according to the invention can have an oxygen content of less than four moles per mole of the NTC mass according to the invention, which is illustrated by the expression 4-d in the general empirical formula Ni _x Mn2 <D4-5 should.

Furthermore, the NTC composition according to the invention can additionally contain at least Zr0 ₂ as dopant, where a corresponds to the content of Z rÖ2 and is based on 100 wt% Ni _x Mn2 <D4-5, where:

0.58 wt% <a d 0.72 wt%.

A further stabilization of the NTC mass can be achieved by adding Z rÖ ₂ . The aging stability of a thermistor which comprises a ceramic base body which contains the NTC composition according to the invention can be further improved in this way. In addition, the NTC composition according to the invention can contain at least one B value modifier which is selected from a group of compounds comprising Al2O3 and CuO. B corresponds to the content of Al2O3 and c to the content of CuO and the following applies based on 100 wt% Nz _c Mh2q4- _d :

0 wt% <b d 13, 9 wt%

0 wt% d c d 8.6 wt%

The B value is a constant of a thermistor, which results from the NTC mass used and which shows the slope of a resistance-temperature curve of a thermistor in one

Resistance-temperature diagram indicates that the slope increases with increasing B value. The steeper the resistance-temperature curve, the more it changes

Resistance of a thermistor in a certain temperature range. The B value can be set by B value modifiers, which are present, for example, as metal oxides. Conventionally, the B-value modifier is added in excess and the amount of the B-value modifier added can be up to 20% by weight based on 100% by weight

Base ceramic material amount.

By adding the B value modifier, the B value of a thermistor which comprises a ceramic base body which contains the NTC composition according to the invention can be set within a wide range and comprises B values from 3136 K to 4528 K inclusive. As a result, the resistance-temperature behavior of a thermistor can be adapted to the desired requirements.

Furthermore, by adding the B-value modifier, the specific resistance of a thermistor, the one

includes ceramic base body, the inventive NTC mass contains, can be set in a range comprising 48 Qcm to 51540 Qcm. It must be mentioned that the B value and the specific resistance cannot be set independently of one another. High B values are associated with high specific resistances and low B values with low specific resistances.

The NTC composition according to the invention can be produced by conventional methods. Such a method can include, for example, the substeps:

- Weighing of raw materials

- first wet grinding

- first drying

- first screening

- calcination

- second wet grinding

- second drying

- second screening

It is also an object of the present invention

Providing a method for manufacturing a

Thermistor. This is a ceramic base

prepared which contains the NTC composition according to the invention.

The ceramic base body is shaped and sintered at up to 1340 ° C. On the sintered ceramic

Base bodies are applied to contact electrodes.

According to the invention, a method for producing a monolithic thermistor is also provided. The

Thermistor comprises a ceramic base body, which contains the NTC mass according to the invention. The NTC composition according to the invention is used to form the ceramic base body processed into granules and then into the

desired shape pressed to form the ceramic base body. In a next step, the ceramic

Base body sintered at up to 1340 ° C. After that

Electrodes applied to the outside of the ceramic base body to contact it.

According to the invention, a method for producing a thermistor in a multilayer construction is furthermore provided, which comprises a ceramic base body which comprises the

contains NTC mass according to the invention. For this, the

NTC composition according to the invention in a first step to form a green sheet, hereinafter referred to as ceramic sheet,

processed. The NTC composition according to the invention is suspended in a solvent and with the aid of

Provide foil pulling. The ceramic film is then drawn using a suitable method and then printed with metallic internal electrodes. A desired number of such printed ceramic foils is then stacked and pressed in the stack. From the pressed

Film stacks are punched out of the desired base area or number, then debindered and sintered at a maximum of 1340 ° C. Then contacts are applied to the outside of the ceramic base body.

The contacts on the outside of one of the

previous versions manufactured ceramic

The base body can be galvanically reinforced for further stabilization.

The thermistor manufactured according to one of the preceding statements can be coated with a protective layer which contains glass or a polymer. The protective layer protects the Thermistor, especially the ceramic body of the thermistor against corrosion, especially in aggressive

Media, such as acids, which causes the aging stability of the

Thermistor is further improved.

The invention is described in more detail below with reference to exemplary embodiments and associated figures.

Figure 1 shows a schematic cross section of a

Embodiment of a themistor in multi-layer construction.

FIG. 2 shows an image of a cut of the one in FIG. 1

described thermistor.

FIG. 3 shows an enlargement of the cut shown in FIG. 2.

Identical elements, similar or apparently identical elements are provided with the same reference symbols in the figures. The figures and the proportions in the figures are not to scale.

Figure 1 shows a schematic cross section of a

Embodiment of a thermistor in multilayer construction, which comprises a ceramic base body 10, which contains an NTC composition according to the invention.

For the production of the ceramic base body 10, an NTC mass was chosen, which is the main component

Contains ceramic material with the composition Nzo, 529Mh2q4- _d . In addition, the NTC mass contains 0.600% wt Zr0 ₂ as a dopant and 13.14% wt AI2O3 as a B value modifier. For the manufacture of the ceramic base body 10 of the

In a first step the thermistor was processed into a ceramic film. The ceramic film was then printed with an inner electrode metallization made of an AgPd alloy, in order to obtain the first and second

To produce internal electrodes 20 and 30 of the thermistor.

In a further step, a plurality of the ceramic foils were stacked on top of one another such that an alternating sequence of ceramic foils with first inner electrodes 20 and those with second inner electrodes 30 was obtained.

The generated film stack was pressed and from the

a stack of pressed components was punched out, which was sintered at up to 1340 ° C.

In order to connect the first and second internal electrodes 20 and 30 to external contacts 20 "and 30", a metallization made of an AgPd alloy was applied and baked on the end faces, which was galvanically reinforced for further stabilization, as a result of which the component can be contacted. The first internal electrodes 20 are now connected to the external contacts 20 'and the second internal electrodes 30 are connected to the external contacts 30'.

For further protection, the thermistor produced was covered with a protective layer 40 made of glass. After storage for 2000 h at 150 ° C in air without electrical load, the thermistor thus obtained shows a deviation in its resistance position at 25 ° C of only 0.59 ± 0.093%. Based on these

The thermistor manufactured in this way meets the requirements for improving the aging stability of thermistors. Figure 2 shows a section of the thermistor described in Figure 1 in multi-layer construction. The single ones

Components of the thermistor, such as the NTC mass which was produced according to the explanations for FIG

Internal electrodes and the galvanically reinforced external contacts are clearly recognizable.

FIG. 3 shows an enlarged section of the section from FIG. 2. The section shows internal electrodes (gray lines) with the sintered NTC material in between. The structure of the sintered NTC mass has no secondary phases, which significantly improves the aging stability of the thermistor. Furthermore, the sintered NTC mass has a high sintering density and an excellent connection to the

Internal electrodes. This shows the high manufacturing suitability of the NTC mass, which makes it powerful and

have aging-stable thermistors implemented.

LIST OF REFERENCE NUMBERS

10 ceramic base body

20 first inner electrode,

30 second inner electrode,

20 "external contact, connected to the first internal electrodes 30" external contact, connected to the second internal electrodes 40 protective layer

Claims

claims

1. NTC mass for the production of a thermistor, which contains as its main component a ceramic material from the Mn-Ni-0 system which has a general composition of Ni _x NkpCy- _ö ,

where y corresponds to the molar proportion of Ni in the total metal content of the ceramic material from the Mn-Ni-0 system, defined as c (Ni) :( c (Ni) + c (Mn), and the following applies:

0.500 <x <0.610

0.197 <y <0.240.

2. NTC mass according to claim 1, where the following applies to x and y:

0.520 <x <0.544

0.206 <y <0.214.

3. NTC composition according to one of claims 1 or 2, which contains additively at least ZrÖ2 as a dopant, where a corresponds to the ZrÖ2 content and is based on 100% wt Nz _c Mh2q4- _d , where:

0.58 wt% <a d 0.72 wt%.

4. NTC composition according to one of claims 1 to 3, wherein the ceramic material has a spinel structure with the general formula AB2O4, wherein the A positions are occupied by at least Ni and the B positions at least by Mn.

5. NTC composition according to one of claims 1 to 4, which additionally contains at least one B value modifier which is selected from a group comprising CuO and Al2O3.

6. NTC composition according to one of claims 1 to 5, which contains either only CuO or only AI2O3 as a B value modifier, wherein b corresponds to the content of AI2O3 and c to the content of CuO and applies to 100% wt Nί _c Mh2q4- _d :

0 wt% <b d 13, 9 wt%

0 wt% d c d 8.6 wt%.

7. thermistor, comprising a ceramic base body, the ceramic base body containing an NTC composition according to one of claims 1 to 6.

8. Thermistor according to claim 7, wherein the composition is selected so that the thermistor when stored in air at 150 ° C without an electrical load after a maximum of 2000 h

Has aging of 0.59 ± 0.093% based on the resistance at 25 ° C.

9. Thermistor according to one of claims 7 or 8, wherein the thermistor has a B value which is selected from a range comprising 3136 K to 4528 K.

10. Thermistor according to one of claims 7 to 9, wherein the ceramic base body of the thermistor has a specific resistance P _{25 °} c, which is selected from one

Area covering 48 sq. Cm to 51540 sq. Cm.

11. Thermistor according to one of claims 7 to 10, wherein the thermistor has a protective layer containing glass or a polymer.

12. A method for producing a thermistor according to one of claims 7 to 11, comprising the production steps: a) forming a ceramic base body from an NTC composition according to one of claims 1 to 6 by producing one

Granules from the NTC mass, pressing the granules and subsequent sintering of the pressed granules at a maximum of 1340 ° C,

b) application of electrode layers to the sintered ceramic base body,

c) baking the electrode layers in the ceramic base body.

13. A method for producing a thermistor according to one of claims 7 to 11,

comprehensive the manufacturing steps:

a) processing an NTC composition according to one of claims 1 to 6 to a ceramic film,

b) printing the ceramic film with internal electrodes (10, 20),

c) stacking a large number of ceramic foils, d) pressing the stacked ceramic foils,

e) punching out a ceramic component from the pressed, stacked ceramic foils,

f) debinding of the ceramic component,

g) sintering the ceramic component to the ceramic

Main body

h) Application of external contacts (20 ", 30") on the

ceramic body.

14. A method for producing a thermistor according to claim 13, wherein a metal selected from one is used for the first and second inner electrodes (20, 30)

Group comprising Ag, Pd and an alloy of both elements.