DE10026260B4 - Ceramic component and its use and method for the galvanic generation of contact layers on a ceramic base body - Google Patents

Abstract

Ceramic component with a base body (1) with high electrical resistance which is stable with respect to electroplating baths and which consists of a perovskite compound, with the general chemical formula: M ^II M ^III _1-x Ti ^IV _{x + y} Co ^II _y Co ^III _1-x-2y O ₃ , where the divalent metal M ^{II is} either strontium or barium and the trivalent metal M ^{III is} a rare earth element, where:
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
0.78 <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,
and the surface of which is partially covered by a galvanically applied contact layer (2, 3).

Description

The invention relates to a ceramic Component with a basic body and electroplated contact layers. Also affects the invention the use of the ceramic component.

Ceramic components are known which used as NTC resistors be, which have a high thermal stability and the basic body a Contains mixture of metal oxides. Such components are usually in surface mounting soldered on circuit boards and serve the temperature control of various electronic Components in electrical devices and electrical engineering apparatus.

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

The metal oxide mixtures used as the base body for the components are, for example, from US 3,219,480 known. According to this document, semiconducting oxides of the transition elements and their combinations in the form of a spinel structure are used in the manufacture of the base body. Multi-phase systems, for example nickel-manganese, cobalt-nickel-manganese or also copper-cobalt-nickel-manganese oxide systems, are often used, which are modified by further components such as iron oxide or zinc oxide.

These known metal oxide mixtures have the disadvantage that they low chemical stability have what particularly during the electroplating process for applying an SMD-compatible metallization comes into play. Because the galvanization is usually in caustic bathrooms is carried out, there is a risk that those applied to the base body Electrodes undercut become. This will make the electrical contact between the electrode and the body and thus affects the electrical properties of the component. About that the mechanical stability of the contact layer also suffers.

Furthermore, these have known metal oxide mixtures the disadvantage that they have a relatively low ohmic resistance, which leads to the fact that during the Electroplating not only that applied in the cap area of the components Silver paste but also the rest surface of the component is metallized. This creates short circuits that make the component inoperable.

For this reason they need known ceramic components a passivation layer for covering of the ceramic base body between the contact layers. As a passivation layer, for example glassy layers are used before metallization of the basic body printed or sprayed on and together with the silver paste into the surface of the body of the Component are burned.

The application of a high impedance Passivation layer has the disadvantage that an additional process step is necessary to manufacture the ceramic component.

From the patent DE 197 40 262 C1 is a perovskite ceramic of the general composition M ^II _x M ^III _{1- x} Ti ^IV _{x + y} Co ^II _y Co ^III _1-x-2y O ₃ , known, which has high conductivities, so that galvanization with a metallization of the entire ceramic must be expected.

The aim of the present invention is it is therefore necessary to specify a ceramic component whose base body is opposite the baths used for electroplating is chemically stable and at the same time high electrical Exhibits resistance.

This goal is achieved according to the invention achieved a ceramic component according to claim 1. advantageous Embodiments of the invention and the use of the ceramic Components 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: M ^II _x M ^III _1-x Ti ^IV _{x + y} Co ^II _y Co ^III _1-x-2y O ₃ , where the divalent metal M ^{II is} either strontium or barium and the trivalent metal M ^{III is} a rare earth element, where:
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
0.78 <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,
and the surface of which is partially covered by a galvanically applied contact layer.

The perovskite connection can still further, usual Ingredients contained in small amounts, the properties not affect the connection.

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

Has such a perovskite connection further the advantage that they has a high electrical resistance. This will avoid that at the galvanic application of metal on the base body of the component according to the invention the whole area Metal is deposited.

When using the perovskite connection as a basic body of the ceramic component according to the invention this also results in the advantage that galvanically applied to the base body Contact layers not underestimated become.

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 ^II and Co ^III .

The high electrical resistances result with small values of x and in this case at the same time with a wider range of variation the y parameter 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. At 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 is a ceramic Component particularly advantageous in which the element of the rare Earth the perovskite compound is lanthanum. Lanthanum has experimented as particularly suitable for the Perovskite connection proven.

It is also a ceramic Component particularly advantageous, in which between the base body and the contact layer is a starting layer for the electroplating process. The starting layer for the Has electroplating process the advantage that the Electroplating clearly spatial limited because the metal is preferred in the electroplating process on the starting layer and less on the rest of the surface of the the body separates.

The starting layer also has the advantage that she because of their for the electroplating necessary good electrical conductivity for one good contacting of the ceramic base body of the component ensures.

There is also a ceramic component particularly advantageous in which the contact layer for surface mounting of the component is suitable. Due to the suitability of the contact layer for the surface Mount (SMD capability) is the whole component for the surface mounting suitable. With the help of surface mounting is a highly rationalized, automated assembly process of the components possible on a circuit board. As a particularly advantageous The contact layer can be, for example, a tin and nickel Contact layer can be used.

There is also a ceramic component particularly advantageous in which the starting layer is made of a silver baking paste on the base body is made. The silver baking paste has the advantage of being a good one Liability on the perovskite connection guaranteed. This will make the mechanical stability of the ceramic component is positively influenced.

It is also a ceramic Component particularly advantageous, the base body on two opposite Sides each have a contact layer, which is electrically located in the interior of the base body conductive Electrodes are contacted, the electrodes being arranged in this way are that they the ohmic resistance measured between the contact layers reduce the component.

Have the electrodes inside the body the advantage that they the relatively high ohmic resistance of the perovskite compound greatly reduce that ceramic component to the respective use of the component matched has electrical resistance. By appropriate design of the conductive Electrodes can be the ohmic resistance of the ceramic component flexible to the intended use of the component customized become.

Advantageously comes as the material for the conductive electrodes Palladium or platinum are used. Have these two precious metals the advantage that they can be sintered in air. Sintering in air is when using the perovskite compound according to the invention as a basic body for the Component absolutely necessary because of a different atmosphere, for example in a protective gas atmosphere from nitrogen gas, the perovskite structure would not be chemically stable.

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

Another advantage of using it of the ceramic according to the invention Component as a thermistor the SMD capability of the component. This enables simple and automated assembly of PCBs possible.

• – bei dem ein Grundkörper verwendet wird, der aus einer Perowskitverbindung besteht, mit der allgemeinen chemischen Formel: M^II _xM^III _1-xTi^IV _x+yCo^II _yCo^III _1-x-2yO₃, bei der das zweiwertige Metall M^II entweder Strontium oder Barium und das dreiwertige Metall M^III ein Element der Seltenen Erden ist, bei der gilt: x = 0 und zugleich y > 0,4 oder 0,09 < x < 0,11 und zugleich y > 0,25 oder 0,78 < x < 0,82 und zugleich y > 0,02 oder 0,68 < x < 0,72 und zugleich y > 0,04,
• – bei dem der Grundkörper direkt mit einem ätzenden Galvanikbad in Kontakt gebracht und galvanisch eine Kontaktschicht erzeugt wird.

The invention further relates to a method for producing contact layers on a ceramic base body

• - in which a base body is used, which consists of a perovskite compound, with the general chemical formula: M ^II _x M ^III _1-x Ti ^IV _{x + y} Co ^II _y Co ^III _1-x-2y O ₃ , where the divalent metal M ^{II is} either strontium or barium and the trivalent metal M ^{III is} a rare earth element, where: 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 0.78 <x <0.82 and simultaneously y> 0.02 or 0.68 <x <0.72 and simultaneously y> 0.04,
• - in which the base body is brought into direct contact with an etching electroplating bath and a contact layer is generated galvanically.

The invention is explained below of an embodiment and the related ones Figures closer explained.

1 shows an example of a ceramic component according to the invention in a schematic perspective view.

2 shows the ceramic component 1 in schematic longitudinal section.

3 shows the area of the contact layer of the component 2 ,

1 shows an inventive ceramic component, the base body 1 has a first contact layer 2 and a second contact layer 3 is arranged. The two contact layers 2 . 3 are electroplated tin layers. With the help of these tin layers, the component can be attached to a printed circuit board in SMD mounting. The basic body 1 is manufactured on the basis of a single-phase perovskite ceramic using the mixed oxide technique as follows:
For the formation of the single-phase perovskite ceramic, mixtures of the starting materials La ₂ O ₂ , SrCO ₃ , TiO ₂ 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 reaction product of the calcination as an aqueous slip with addition subjected to milling for about twenty-four hours by agate balls. After evaporation of the liquid becomes the backlog sieved, and again at 1250 ° C calcined for six hours. Then in aqueous suspension ground to an average grain size <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 at the base body without the intermediate step of applying a passivating protective layer 1 , which is used in this case for a thermistor component. The individual components produced in this way are subjected to sintering at 1350 ° C. for 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 in 2 electrode shown 5 represents the silver baking paste in 3 starting layer shown 4 on which the contact layer is finally galvanically 3 is applied.

The contact layer is particularly advantageous 3 a layer stack of a nickel layer, which is directly on the starting layer 4 is applied, and a tin layer which closes the contact layer to the outside. The nickel layer prevents the silver from stripping, which is located directly on the ceramic base body 1 located.

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: Sr _0.7377 La _0.2623 Ti ^IV _0.7577 Co ^II _0.020 Co ^III _0.2223 O ₃

• – der elektrische Widerstand R des Heißleiters ist abhängig von der Temperatur T und folgt im für die Anwendung interessanten Bereich einer Exponentialfunktion: R(T) = R25exp(B(1/T – 1/298K))
• – Die Konstante B (in K) beschreibt dabei die Empfindlichkeit des Heißleiters für die Temperaturmessung.
• – Der Nennwiderstand R₂₅ gibt den elektrischen Widerstand des Bauelements bei einer Temperatur von 25 °C an.
• – Die Streubreite Vk wird in Prozent angegeben und beschreibt die herstellungsbedingte Variation der Konstante B sowie des Nennwiderstands R₂₅ des Bauelements.

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

• - The electrical resistance R of the thermistor is dependent on the temperature T and follows an exponential function in the area of interest for the application: R (T) = R 25 exp (B (1 / T - 1 / 298K))
• - The constant B (in K) describes the sensitivity of the thermistor for the temperature measurement.
• - The nominal resistance R ₂₅ indicates the electrical resistance of the component at a temperature of 25 ° C.
• - The spread Vk is given in percent and describes the production-related variation of the constant B and the nominal resistance R _{25 of} the component.

With the component described in this example, a specific resistance ρ ₂₅ 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 shows more characteristic parameters of that described in this example Component listed.

The values given in the table show parameters comparable to known components, whereby it becomes clear that through the perovskite structure has no disadvantages in terms of electrical Data of the component must be accepted.

Claims (12)

Ceramic component with a base body that is stable with respect to electroplating baths ( 1 ) with high electrical resistance, consisting of a perovskite compound, with the general chemical formula: M ^II M ^III _1-x Ti ^IV _{x + y} Co ^II _y Co ^III _1-x-2y O ₃ , where the divalent metal M ^{II is} either strontium or barium and the trivalent metal M ^{III is} a rare earth element, where: 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 0.78 <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, and the surface of which is partially covered by an electroplated contact layer ( 2 . 3 ) is covered. Ceramic component according to claim 1, wherein the Element of the rare earth is lanthanum. Ceramic component according to one of the preceding claims, in which between the Basic body ( 1 ) and the contact layer ( 2 . 3 ) a starting layer ( 4 ) for the electroplating process. Ceramic component according to Claims 1 to 3, in which the contact layer ( 2 . 3 ) is suitable for surface mounting of the component. Ceramic component according to Claims 1 to 4, in which the contact layer ( 2 . 3 ) consists of nickel and tin. Ceramic component according to Claims 3 to 5, in which the starting layer ( 4 ) by applying a silver baking paste to the base body ( 1 ) is manufactured. Ceramic component according to claim 1 to 6, the base body ( 1 ) one contact layer each on two opposite sides ( 2 . 3 ), which with inside the base body ( 1 ) electrically conductive electrodes ( 5 ) are contacted, the electrodes ( 5 ) are arranged so that they the the between the contact layers ( 2 . 3 ) reduce the measured ohmic resistance of the component. Use of a ceramic component according to claim 1 to 7 as thermistor. Process for the galvanic generation of contact layers on a ceramic base body - in which a base body is used which consists of a perovskite compound, with the general chemical formula: M ^II _x M ^III _1-x Ti ^IV _{x + y} Co ^II _y Co ^III _1-x-2y O ₃ , where the divalent metal M ^{II is} either strontium or barium and the trivalent metal M ^{III is} a rare earth element, where: 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 0.78 <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, - in which the base body directly with an etching electroplating bath brought into contact and a contact layer is generated galvanically. Method according to the preceding claim, - in which a starting layer before the galvanic generation of the contact layer on the areas of the base body is generated on which the contact layers are to be produced. Method according to the previous claim, - in which the starting layer is produced by applying a silver baking paste becomes. Method according to one of claims 9 to 11, - in which the contact layer by successive galvanic application a nickel layer and a tin layer is produced.