WO2001090025A2

WO2001090025A2 - Ceramic component and use thereof

Info

Publication number: WO2001090025A2
Application number: PCT/DE2001/001738
Authority: WO
Inventors: Adalbert Feltz; Axel Pecina
Original assignee: Epcos Ag
Priority date: 2000-05-26
Filing date: 2001-05-08
Publication date: 2001-11-29
Also published as: DE10026260B4; DE10026260A1; WO2001090025A3; AU2001265768A1

Abstract

The invention relates to a ceramic component comprising a base body (1) consisting of a perovskite compound having the following general formula: MIIxMIII1-xTiIVx+yCoIIyCoIII1-x-2yO3, wherein the bivalent metal MII is either strontium or barium and the trivalent metal MIII is a rare earth element, wherein 0 ≤ x < 0,85; 0 < y < (1-x)/2 and x+y ≤ 1, and the surface of said component is partially covered by a galvanically applied contact layer (2,3). The invention also relates to the use of said ceramic component. The chemically stable perovoskite compound makes it possible to avoid passivation during the galvanisation process of the contact layer.

Description

description

Ceramic component and its use

The invention relates to a ceramic component with a base body and galvanically applied contact layers. In addition, the invention relates to the use of the ceramic component.

Ceramic components are known which are used as NTC resistors, which have high thermal stability and whose base body contains a mixture of metal oxides. Components of this type are usually soldered onto boards in surface mounting and are used for temperature control of various electronic components in electrical devices and electrical engineering apparatus.

The possibility of surface mounting (SMD capability) of the components is achieved by contacting the base body by baking a silver paste on the base body and then galvanizing the silver paste in a nickel and tin bath. The outermost tin contact layer guarantees the SMD capability.

The metal oxide mixtures used as base bodies for the components are known, for example, from US Pat. No. 3,219,480. According to this document of the ^'basic body of semiconducting oxides of the transition elements, and combinations thereof in the form of a spinel structure is considered excluded in manufacture. In many cases there are multiphase systems, e.g. nickel

Manganese, cobalt-nickel-manganese or copper-cobalt-nickel-manganese oxide systems, which are modified by other components such as iron oxide or zinc oxide.

The known metal oxide mixtures have the disadvantage that they have low chemical stability, which is particularly important during the electroplating process SMD-capable metallization comes into play. Since the electroplating is usually carried out in caustic baths, there is a risk that the electrodes applied to the base body will be undercut. As a result, the electrical contact between the electrode and the base body and thus the electrical properties of the component are impaired. In addition, the mechanical stability of the contact layer also suffers.

Furthermore, the known metal oxide mixtures have the disadvantage that they have a relatively low ohmic resistance, which means that not only the silver paste applied in the cap area of the components but also the remaining surface of the component is metallized during the galvanizing. This creates short circuits that render the component inoperable.

For this reason, the known ceramic components require a passivation layer to cover the ceramic base body between the contact layers. Glass-like layers can be used as the passivation layer, for example, which are printed or sprayed on before the metallization of the base body and are baked together with the silver paste into the surface of the base body of the component.

The application of a high-resistance passivation layer has the disadvantage that an additional process step for the production of the ceramic component is necessary.

The aim of the present invention is therefore to provide a ceramic component whose base body is chemically stable with respect to the baths used for the galvanization.

This goal is achieved according to the invention by a ceramic component according to claim 1. Advantageous configurations gene of the invention and the use of the ceramic component can be found in the further claims.

The invention provides a ceramic component with a base body, which consists of a perovskite compound, with the general chemical formula:

'

where the divalent metal M ^{11 is} either strontium or

Barium and the trivalent metal M ^{111 is} a rare earth element, where: 0 <x <0.85; 0 <y <(lx) / 2 and x + y <1, and the surface of which is partially covered by a galvanically applied contact layer.

The perovskite compound can also contain other, conventional constituents in small amounts which do not impair the properties of the compound.

The ceramic component according to the invention has the advantage that a protective layer covering the part of the base body that is not to be electroplated is not required, since the perovskite compound has a high chemical stability and is insensitive to the caustic baths used in electroplating.

When the perovskite connection is used as the base body of the ceramic component according to the invention, this also has the advantage that contact layers which are applied galvanically to the base body are not undercut.

Since the sum of x and y can result in a maximum of 1 due to the perovskite structure, the stoichiometric parameter x determines the proportion of cobalt that is installed instead of titanium, and at the same time the division into Co ¹¹ and Co ¹¹¹ . Furthermore, a ceramic component is particularly advantageous, in which either for the perovskite connection

x = 0 and at the same time y> 0.4 or 0.09 <x <0.11 and at the same time y> 0.25 or 0.18 <x <0.32 and at the same time y> 0.2 or 0.78 <x <0.82 and at the same time y> 0.02 or 0.68 <x <0.72 and at the same time y> 0.04

applies.

Such a perovskite connection has the advantage that it has a high electrical resistance. This prevents metal being deposited over the entire surface during the galvanic application of metal to the base body of the component according to the invention.

The high electrical resistances result from small values of x and in this case at the same time a larger range of variation of the y parameters in the range of high y values, e.g. for x = 0 in the range y> 0.4; for x = 0.1 in the range y> 0.25; for x = 0.2 and 0.3 in the range y> 0.2. With high x values, the range of variation of the y parameters is severely limited and the required high resistances are already achieved with small y values, e.g. for x = 0.8 already from a y of approx. 0.02; for x = 0.7 already from y = approx.0.04.

Furthermore, a ceramic component is particularly advantageous in which the rare earth element of the perovskite compound is lanthanum. In experiments, lanthanum has proven to be particularly suitable for the perovskite compound.

In addition, a ceramic component is particularly advantageous in which there is a starting layer for the electroplating process between the base body and the contact layer. The starting layer for the electroplating process has the advantage that the electroplating is clearly limited in space. det, since the metal in the electroplating process preferentially deposits on the starting layer and less on the remaining surface of the base body.

Furthermore, the starting layer has the advantage that, because of its good electrical conductivity, which is necessary for electroplating, it ensures good contacting of the ceramic base body of the component.

Furthermore, a ceramic component is particularly advantageous in which the contact layer is suitable for surface mounting the component. Due to the suitability of the contact layer for surface mounting (SMD capability), the entire component is suitable for surface mounting. With the help of surface mounting, a highly rationalized, automated assembly process of the components on a printed circuit board is possible. A contact layer consisting of tin and nickel can be used as a particularly advantageous contact layer, for example.

Furthermore, a ceramic component in which the starting layer is produced by a silver baking paste on the base body is particularly advantageous. The silver baking paste has the advantage that it ensures good adhesion to the perovskite compound. This has a positive influence on the mechanical stability of the ceramic component.

In addition, a ceramic component is particularly advantageous, the base body of which has a contact layer on each of two opposite sides, which is contacted with electrically conductive electrodes located in the interior of the base body, the electrodes being arranged in such a way that they measure the one measured between the contact layers reduce the ohmic resistance of the component.

The electrodes in the interior of the base body have the advantage that they have the relatively high ohmic resistance of the perovskite Reduce the connection so far that the ceramic component has an electrical resistance that is adapted to the respective use of the component. The ohmic resistance of the ceramic component can be flexibly adapted to the intended area of use of the component by suitable design of the conductive electrodes.

Palladium or platinum is advantageously used as the material for the conductive electrodes. These two precious metals have the advantage that they can be sintered in air. Sintering in air is absolutely necessary when using the perovskite compound according to the invention as the base body for the component, since the perovskite structure would not be chemically stable in another atmosphere, for example in a protective gas atmosphere made of nitrogen gas.

In addition, the invention specifies the use of the ceramic component according to the invention as a thermistor. Because of the very well-defined resistance of the component according to the invention, in particular when inside the

Component conductive electrodes are arranged, the component according to the invention is particularly suitable for applications as a thermistor. Because of the protective function they perform, thermistors are subject to particularly high requirements with regard to component stability.

Another advantage of using the ceramic component according to the invention as a thermistor is the SMD capability of the component. This enables simple and automated assembly of printed circuit boards.

The invention is explained in more detail below on the basis of an exemplary embodiment and the associated figures.

Figure 1 shows an example of a ceramic component according to the invention in a schematic perspective view. FIG. 2 shows the ceramic component from FIG. 1 in a schematic longitudinal section.

FIG. 3 shows the area of the contact layer of the component from FIG. 2.

FIG. 1 shows a ceramic component according to the invention, which has a base body 1 on which a first contact layer 2 and a second contact layer 3 are arranged.

The two contact layers 2, 3 are galvanically applied tin layers. With the help of these tin layers, the component can be attached to a printed circuit board in SMD mounting. The base body 1 is produced on the basis of a single-phase perovskite ceramic using the mixed oxide technique as described below:

For the formation of the single-phase perovskite ceramic, mixtures of the starting materials La2θ2, SrCθ3, Tiθ2 and cobalt oxide, the content of metal cations of which was determined analytically, are converted by calcination at 1250 ° C. The single-phase nature of the perovskite ceramic has the advantage that the component has very good aging stability, since no phases can be converted into one another within the system. The calcination usually takes six hours.

The synthesis of the perovskite compound requires a repetition of the calcination. For this purpose the calcination reaction product is subjected to a grinding process as an aqueous slip with the addition of agate balls for about twenty-four hours. After the liquid has been evaporated off, the residue is sieved and calcined again at 1250 ° C. for six hours. The mixture is then ground in aqueous suspension to an average grain size of <1 μm. After adding suitable proportions of a dispersant and a binding system suitable for the production of ceramic films, the process step of film drawing is carried out and the films are printed with platinum or palladium paste. By stacking the individual foils, laminating the stack and cutting the laminate, one finally arrives directly at the base body 1, without the intermediate step of applying a passivating protective layer, which in this case is used for a thermistor component. The individual components produced in this way are subjected to sintering at 1350 ° C. for a period of at least three hours and then terminated with a silver baking paste.

The silver baking paste determines the position of the contact layers 2, 3 which are applied to the silver baking paste in the subsequent electroplating bath. The platinum or palladium paste represents the electrode 5 shown in FIG. 2. The silver baking paste represents the one shown in FIG

Starts layer 4, on which the contact layer 3 is finally applied galvanically.

In a particularly advantageous manner, the contact layer 3 is a layer stack made of a nickel layer, which is directly on the

Starting layer 4 is applied, and a tin layer closing the contact layer to the outside. The nickel layer prevents the silver, which is located directly on the ceramic base body 1, from alloying.

With the described method, a perovskite connection with the parameters x = 0.7377 and y = 0.02 was realized. This results in the following composition of an exemplary perovskite compound: Sro, 7377 ^La O, 2623 ^τiIV 0.7577 ^CoII 0.020 ^oIII 0.2223 ° 3

Ceramic components and in particular thermistors are characterized by the following sizes:

- The electrical resistance R of the thermistor depends on the temperature T and follows an exponential function in the area of interest for the application:

R (T) = R ₂ 5exp (B (l / Tl / 298K))

- The constant B (in K) describes the sensitivity of the thermistor for the temperature measurement.

- The nominal resistance R25 indicates the electrical resistance of the component at a temperature of 25 ° C.

- The spread Vk is given in percent and describes the manufacturing-related variation of the constant B and the nominal resistance R25 of the component.

In the component described in this example, a specific resistance P25 of 61.5 kΩcm was measured after production. After 144 hours of aging at 150 ° C, the specific resistance had practically not changed and was again 61.5 kΩcm. This shows how great the stability of the single-phase perovskite ceramic is in this example.

The following table lists further characteristic parameters of the component described in this example.

The values given in the table show parameters comparable to known components, which makes it clear that the perovskite structure means that no disadvantages with regard to the electrical data of the component have to be accepted.

The invention is not limited to the exemplary embodiment shown, but is defined in its most general form by claim 1.

Claims

claims

1. Ceramic component with a base body (1), which consists of a perovskite compound, with the general chemical formula:

MlI _χ MlH ₁ _ _x TiIV _{χ + y} coII _y CθIII ₁ _ _x _2y0 ₃ ,

where the divalent metal M ^ is either strontium or barium and the trivalent metal M * ¹ ! is a rare earth element where: 0 <x <0.85; 0 <y <(lx) / 2 and x + y <1,

and the surface of which is partially covered by a galvanically applied contact layer (2, 3).

2. Ceramic component according to claim 1, wherein either for the perovskite connection

x = 0 and at the same time y> 0.4 or

0.09 <x <0.11 and at the same time y> 0.25 or

0.18 <x <0.32 and at the same time y> 0.2 or

0.78 <x <0.82 and at the same time y> 0.02 or

0.68 <x <0.72 and at the same time y> 0.04

applies.

3. Ceramic device according to claim 1 or 2, wherein the rare earth element is lanthanum.

4. Ceramic component according to claim 1 to 3, in which between the base body (1) and the contact layer (2, 3) there is a starting layer (4) for the electroplating process.

5. Ceramic component according to claim 1 to 4, wherein the contact layer (2, 3) is suitable for surface mounting of the component.

6. Ceramic component according to claim 1 to 5, wherein the contact layer (2, 3) consists of nickel and tin.

7. Ceramic component according to claim 4 to 6, in which the starting layer (4) is produced by applying a silver baking paste to the base body (1).

8. Ceramic component according to claim 1 to 7, the base body (1) on two opposite sides each having a contact layer (2, 3) which are in contact with the inside of the base body (1) located, electrically conductive electrodes (5), wherein the electrodes (5) are arranged in such a way that they reduce the ohmic resistance of the component measured between the contact layers (2, 3).

9. Use of a ceramic component according to claim 1 to 8 as a thermistor.