WO2018167133A1

WO2018167133A1 - Varistor component having a higher surge current capacity

Info

Publication number: WO2018167133A1
Application number: PCT/EP2018/056365
Authority: WO
Inventors: Michael HOFSTÄTTER
Original assignee: Epcos Ag
Priority date: 2017-03-16
Filing date: 2018-03-14
Publication date: 2018-09-20
Also published as: DE102017105673A1

Abstract

Disclosed is a varistor component having a higher surge current capacity. For this purpose, a varistor component comprises a main part with a first region made of a first varistor material and a second region made of a second varistor material.

Description

description

The invention relates to varistor components which have an increased surge current capacity, and to methods for producing such components and to the use of two different varistor materials in a varistor component.

Varistor components are electrical components with a voltage-dependent electrical resistance. For small applied voltages, a varistor device has a relatively high electrical resistance. With increasing applied voltage, the resistance decreases with one

increasing rate. Within a relatively narrow

Voltage interval then decreases the electrical resistance by several orders of magnitude and can be considered at quasi voltages above this interval as electrically conductive.

Such varistor components can serve as protective elements in electrical or electronic circuits and protect other circuit elements from overvoltages.

Varistor components owe their electrical

Characteristics of a varistor material, which provides the desired current / voltage characteristics. Common varistor materials often include sintered

Ceramics. A varistor component can be a

Have stack structure in which alternating metallization layers and layers of a varistor material. Some of the metallization layers may have a first external one Be connected electrode. Other metallization layers may be connected to a second external electrode. In a voltage interval around a characteristic

Voltage will be the varistor material between the

Metallization surfaces conductive, leaving an undesirable

Power surge from the first electrode to the second electrode, the z. B. can be connected to a ground potential,

can be derived. Varistor components are z. B. from the

Publication Nos. US7,541,910 B2, US7,167,352 B2 or US6,377,439 Bl known.

A characteristic of a varistor component size is the so-called surge current capacity. The

Surge current capacity is essentially a measure of the amount of electrical charge or a measure of the electrical power of a current pulse, which is to be derived. The lower the surge current capability, the higher the likelihood that the varistor device will be damaged upon activation.

Well-known measures to increase the

Surge current capacity is to increase the active volume of a varistor device. The active volume of such a component is essentially that volume of varistor material or in the main body with the varistor material, in which a current flow at

Activation takes place. With increased active volume, the specific power, i. H. the electrical power per unit volume is reduced to the load for the

Reduce component. However, it is not possible to arbitrarily increase the active volume of a varistor device.

There is therefore a desire for varistor components which have an increased surge current capacity.

In the independent claims, such a varistor device or a method for producing such a varistor device and the use

different varistor materials specified in a varistor device. Dependent claims indicate advantageous embodiments.

The varistor device has a main body with a first region of a first varistor material and a region of a second varistor material. The second

Varistor material is from the first varistor material

different. Furthermore, the varistor device has

Metallization surfaces embedded in the body.

It has been recognized that the use of two different varistor materials in a body of a varistor device can improve surge current capability. Metallization surfaces of a varistor device are embedded in a varistor material. Edges of the

Metallization surfaces at interfaces between metal and the surrounding varistor material indicate particularly vulnerable positions within the device. At the points of the edges, the transfer of the charge to be derived from the metal of the metallization surfaces into the varistor material or from the varistor material into the metal of the metallization surfaces of the other polarity takes place. at repeated activity of a varistor device and

possibly already at a first activation with high electrical power cracks can occur at the locations of the edges, on the one hand the electrical

Functionality disturbs and on the other hand the mechanical one

Endanger the stability of the component. Cracks endanger not only the edges of conventional varistors but also the other parts, above all the edges. The provision of two different varistor materials in a varistor device - more precisely, in a main body of a varistor device - can reduce the risk of the formation of such cracks. Accordingly, such

Varistor components have an increased surge current capacity and thus have an increased life. in the

The rest is also the change of the electrical

Characteristics of corresponding varistor components reduced.

The first area of the basic body, the second area of the main body and optionally further areas of the body

Basic body are determined by the associated varistor materials as an interface, z. Legs

Phase boundary separates two adjacent areas. The number of areas in the body can be two, three, four, five, six, seven or more.

The number of different varistor materials can also be two, three, four, five, six, seven or more. The number of areas of the body is greater than or equal to the number of different varistor materials. Two adjoining areas in the

Basic bodies have different varistor Materials on. However, different and not directly adjacent areas may have the same varistor material or consist of the same varistor material. So it is possible that three areas of the

Main body have a total of two different varistor materials.

The first varistor material and the second varistor material may be materials having different thermal

Expansion coefficients (CTE = coefficient of thermal

Expansion). The relative expansion when the temperature changes differs. It is possible that the varistor materials have sintered materials. A sintering temperature can be in the range around 1000 ° C. During the manufacture of a varistor device, a layer stack is stacked with raw materials and

then sintered. When the layer stack cools, sintering residual stresses can arise. Are the materials chosen so that different thermal

Expansion coefficients are present, the areas of the body can be arranged so that the material with the lower expansion coefficient after cooling is under pressure, while the material with the larger

Expansion coefficient under train is. In the cooled

Condition there are areas where there is a compressive stress, while in other areas a tensile stress is present. It is advantageous, for example, that the range of maximum mechanical stress during activation is under pressure. Now occurs when an activation of the varistor device, so is by the electric

Current and the finite conductivity of the varistor material or the varistor materials dissipated electrical energy in the varistor device. This is accompanied by a Heating of the corresponding areas in the main body. The area whose varistor material has a higher

Expansion coefficient has, and the area whose

Material has a lower coefficient of expansion, so different in response to the heating, that a stress relaxation occurs. Assuming that the two areas in the

Sintering temperature were completely stress-free, then the component relaxes as a whole all the more, the closer the

Activation brings the internal temperature of the varistor device in the direction of the sintering temperature.

As a result, a varistor device is obtained in which the introduced by an activation event

Thermal energy causes a mechanical relaxation of the device, so that the risk of thermally induced stress cracks -. B. at the edges of

Metallization surfaces - is reduced. Additionally or alternatively, the at least two different varistor materials of the first and second regions can also be used in the so-called

Breakthrough field strength (also called varistor field strength) differ. The breakdown field strength is in the

Essentially, the electric field strength at which the varistor material begins to become conductive.

At locations of increased thermal stress, a varistor material with lower breakdown field strength can be arranged. At locations of lower thermal stress, a higher breakdown field strength varistor material may be positioned. The interior of a varistor component is generally more thermally stressed because dissipated Energy in the form of heat worse to the environment

can be derived. External areas of a varistor device are thermally less heavily loaded because the thermal resistance to the environment is reduced. Heat generated in such areas is released more easily. If the activation voltage of the two regions should be substantially the same, an increased breakdown field strength requires a smaller thickness of the layers of the varistor material

between electrode surfaces. Varistor material with lower breakdown field strength (inside the device) causes a greater thickness of the varistor material between the

Metallization. Are the layer thicknesses chosen so that the breakdown voltage in both areas in

Substantially the same, so the same electrical energy is deposited in each case one position in both areas substantially in an activation. A thinner layer (with increased breakdown field strength) has thus increased

Power density. A thicker layer with lower

Breakthrough field strength thus has a lower electrical (heat generation) performance. This heat is more in the

Outside creates from where it can be better dissipated. The thermal load of the entire device is thus reduced.

Compared with conventional varistor components, the surge current capacity can be further improved and the lifetime of the component can be increased. The components are mechanically less stressed and therefore more robust. Based on a defined surge current capacity can

corresponding varistor components with a smaller

Volume and with less varistor material to be built.

Smaller and lighter varistor components are particularly advantageous against the continuing trend towards miniaturization of electrical equipment.

It is possible that the varistor device comprises three regions of at least two different varistor materials. At least two interfaces between different regions of the three regions are arranged in parallel.

It is particularly possible that the boundary surfaces parallel to an outer side of the varistor device, for. B. to the bottom of the varistor device are aligned.

It is possible that at least two metallization surfaces are arranged in parallel. The metallization can be arranged in parallel to other metallization. It may be preferred, the metallization also parallel to an outer side surface, for. B. the underside of the varistor device, align. It is possible that the varistor component has an interface between two regions of different varistor materials. The interface is arranged parallel to at least one metallization. So it is possible that the interfaces between

different areas of the varistor materials and the metallization are all aligned parallel to the bottom of the varistor device. This results in a stack construction that is easy to add

different layers and materials can be produced.

It is possible that the varistor component has an interface between two regions of different varistor Materials includes. The interface may be between two adjacent metallization.

It is also possible that the varistor component a

Metallization surface has, at an interface between two areas of different varistor materials

is embedded.

So it is possible that the metallization on

Phase boundaries are embedded between different varistor materials. But one or more Metallisierungsflächen can also completely within a single

Embedded varistor material. The location of

Interfaces between different varistor materials do not limit the position of the metallization surfaces. The location of the metallization areas does not limit the location of the interfaces between areas of different varistor materials. With regard to the economics of manufacturing processes, however, it may be advantageous to arrange metallization layers at phase boundaries between regions of different varistor materials. Accordingly, it is possible that a metallization surface is embedded at the interface between two regions of different varistor materials.

It is possible that the varistor device has a third region. The third region comprises or consists of a varistor material. The second area is arranged between the first area and the third area. The three areas with the middle third area thus make a Sandwich construction made of different varistor materials. Metallization surfaces can be arranged in each of the three areas and in all three areas. It is possible that the material of the first region and the material of the third region are the same. Varistor components as suggested above may thus be so-called multilayer varistor components (MLV: multilayer varistor components). Their basic body contains alternately arranged varistor layers and metallization surfaces.

It is possible that the varistor component has a first

Contact electrode and a second contact electrode comprises. At least one metallization surface is the first

Contact electrode interconnected. At least one

Metallization surface is connected to the second contact electrode.

The contact electrodes serve to interconnect the

Varistor device with an external circuit environment, eg. B. to protect against overvoltages.

The contact electrodes can be arranged at opposite ends of the varistor component. You can

only side surfaces of a z. B. cuboid varistor device touch. However, it is also possible that the contact electrodes in addition over the edges

extend out and in addition to the side surfaces (left, right) and parts of the lower or upper side or parts of

Overlap front and back. It is important to ensure that the two contact electrodes do not touch each other directly, as they would be short-circuited with it and the

Component would be functionless. It is possible that the different materials of the regions are in at least one material parameter

differ. The material parameter can be selected from: coefficient of thermal expansion,

Breakdown field strength, sintering temperature, grain size,

specific gravity, chemical composition, mechanical strength, current and voltage characteristics, grain shape, texture, thermal conductivity and thermal diffusivity.

The varistor materials may be selected from varistor materials consisting of a zinc oxide, e.g. B. ZnO, with bismuth (Bi), or a zinc oxide with praseodymium (Pr) exist. Other possible materials on which the varistor materials may be based are an iron oxide, e.g. B. Fe3Ü ₄ or Fe ₂ Ü3, a nickel oxide, z. As NiO or a cobalt oxide, for. B. CoO.

Iron oxide, e.g. B. Fe3Ü ₄ or Fe ₂ Ü3, Snue _2, Ti0 _2, a nickel oxide, z. As NiO and / or a cobalt oxide, for. B. CoO can

in particular serve as dopants. Other possible

Starting materials for the varistor materials can

Barium titanate (BaTiOs) or strontium titanate (SrTiOs). A zirconium oxide, z. B. Zr0 ₂ or an alumina, for. B. Al ₂ O ₃ or a manganese oxide, for. B. MnO can more

Be starting materials or dopants for the varistor materials.

Exemplary formulations would be: 95 mole percent ZnO, Sb ₂ O ₃ , B1 ₂ O ₃ in the range between 0.5 and 5 mole percent, C0 ₃ O ₄ ,

Mn ₂ 0 ₃ , Si0 ₂ , Cr ₂ 0 ₃ in the range 0.05 to 2 mole percent and B ₂ 0 ₃ , Al ₂ O ₃ , NiO less than 0.1 mole percent.

The varistor materials may also contain Y ₂ O ₃ in the range 0.05-2 mole percent. As materials for the metallization come

especially metals with a high melting point in order to minimize diffusion processes during sintering

restrict. Appropriate materials for the

Metallization surfaces may thus comprise tungsten or consist of tungsten. Ag, Pt, Pd, Cu, Ni, and also alloys such as e.g. AgPd can also be used as materials for the

Metallization surfaces come into question. For the contact electrodes metals with high

Conductivity, e.g. Aluminum, silver, gold, copper, platinum, palladium, nickel, tin and also alloys such as e.g. AgPt and the like come into question. It is possible that the contact electrodes via a solder layer with the

Metallisierungsflächen connected and interconnected.

A method for manufacturing a varistor device with increased surge current capacity comprises the steps:

Providing a base of a first varistor material as a first region,

- Arrange a material from a second, from the first

Varistor material different varistor material than a second area on or over the first area,

- Embedding metallization in the materials of the two areas.

The metallization surfaces can also be embedded at the location of the phase boundaries between the different regions of different materials.

In addition, the use of second different varistor materials in different areas of a Varistor device specified to the

To increase surge current capacity of the components.

Essential aspects and details of concrete embodiments will be explained in more detail with reference to the schematic figures.

Show it:

1 shows a possible stack construction of a (multilayer)

Varistor component MLV.

Fig. 2 stack layers with metallization within individual areas.

3 shows a layer stack with at least one

Metallization surface at a phase boundary

between the first area and the second one

Area .

Fig, a stack of layers with an arbitrarily aligned

Interface between the first area and the second area.

5 shows a layer stack with an arbitrary orientation of metallization surfaces to the base of the device.

6 shows a varistor component with contact electrodes. 7 shows a varistor illumination device with five

different areas. 8 shows a varistor component in which a phase boundary between different regions also has a metallization surface at the same time. FIG. 1 shows a schematic layer stack of a varistor component V, which is designed as a multilayer varistor component MLV. The varistor component V has a

Basic body GK with a first area Bl and a second area B2. The first region Bl has a first varistor material Ml. The second region B2 has a second varistor material M2. Metallization surfaces MF are embedded in the main body GK. Varistor layers VL are between the

Metallization surfaces MF arranged. An interface separates the first area Bl from the second area B2. The varistor materials M1, M2 of the two areas B1, B2 are such that they differ in at least one material parameter. FIG. 1 shows the possibility of the phase boundary

between the areas Bl, B2 to run within a varistor layer VL. That is, a varistor layer VL may comprise a single varistor material, and it may also be possible for a varistor layer VL to contain two sub-layers with different varistor materials, as shown between the two upper metallization surfaces MF.

FIG. 2 shows a layer stack of a varistor component V, in which the main body GK has three regions B1, B2, B3. At the lower end of the third region B3 is arranged. At the upper end of the first area Bl is arranged. In between, the second area B2 is arranged. Each area can have its own varistor material, which differs at least from the varistor material of a directly adjacent area. The materials Ml and M2 Therefore, they differ in at least one parameter. The materials M2 and M3 differ in at least one parameter. The materials Ml and M3 may be different. But it is also possible that the first area Bl and the third area B3 consists of the same varistor material.

FIG. 3 shows the possibility of a metallization surface MF at an interface between two different ones

Areas here between the first area Bl and the second area B2 to arrange. Arranging a

Metallization surface at an interface is not necessary even within a single varistor device. Thus, the phase boundary between the second region and the third region does not extend at the same height as a metallization surface, but between two

Metallization surfaces.

The layers of the metallization areas do not limit the layers of the interfaces. The layers of the interfaces do not limit the positions of the metallization surfaces.

However, it may be advantageous in the production, if metallization surfaces at interfaces between

different areas are embedded.

FIG. 4 shows that the orientation of boundary surfaces does not restrict the alignment of metallization surfaces. Thus, metallization MF and interfaces, z. B.

be aligned between the first area Bl and the second area B2 at an arbitrary angle to each other. Similarly, FIG. 5 shows that the orientation of the component as a whole V or the alignment of interfaces between the first region and the second region does not force a specific orientation of the metallization surfaces MF.

But to simplify manufacturing steps can

Metallization surfaces, interfaces and sub-

Tops of components an excellent alignment with each other, for. B. have a parallel orientation to each other.

FIG. 6 shows the possibility of contact electrodes

To arrange side surfaces of the varistor component V. Thus, one side may have a first electrode El and the preferably opposite side a second electrode E2, so that the varistor component V, for. B. as

Voltage protection element is connected to an external circuit environment. At least one, preferably several

Metallization surfaces MF1, MF2, MF3 are connected to the first electrode El. One, but preferably a plurality of metallization surfaces MF4, MF5, MF6 are connected to the second electrode E2. Preferably none

Metallization surface is connected to both the first electrode El and the second electrode E2. When the varistor component V is activated, an electric current flows from a set of metallization surfaces, which are connected to one of the two contact electrodes, to the respective other set of metallization surfaces, here in the vertical direction through the varistor layers VL. Edges K of the metallization surfaces MF are particularly at risk in conventional varistor components; In their vicinity, stress cracks can form and spread. The usage different varistor materials in the same body of a varistor component reduces the risk of cracks, especially at critical areas such as edges K and especially edge areas of the body.

The uppermost regions Bl and the lowermost region B3 may comprise or consist of the same varistor material M1. This differs from the varistor material M2 of the second region B2.

The material M2 of the second region may have a higher coefficient of thermal expansion CTE than the material Ml of the regions Bl and B3. Upon cooling after a sintering process, the material M2 of the second region B2 tends to contract more strongly with increasing cooling. However, this stretching is hindered by the material M1 and M2. Through this stretch disability

arise the described voltages. In the cooled

Condition, the second material of the second region relative to the material of the first and the third region is therefore under a tensile stress, while the first material of the first and the third region is under a compressive stress relative to the material of the second region. at

Activation, d. H. when heating the body through

Dissipating electrical energy, in turn, the second varistor material M2 of the second region expands relatively stronger than the first material Ml of the first and the third region. Analogous to the above, the strains are coupled in the. Thus, on the one hand, the tensile stress builds up in the second material of the second region and, on the other hand, the

Compressive stress in the first material of the second and third range from. In the activated, ie heated state, the mechanical loads are thereby - and in particular relatively to the voltages in activated conventional devices - reduced.

FIG. 7 shows a possible embodiment in which a first area Bl, a third area B3 and a fifth area B5 consist of a first material M1. The

Varistor material of the second region B2 and the fourth region B4 is a second varistor material M2. The second and the fourth area represent thereby of the

thermal stress seen the outer areas of the

Varistor device V represents. The third area B3 represents the interior of the varistor device. The

Breakthrough field strength in the third region B3, that is to say in the first material M1, is preferably lower than in the second varistor material M2. As a result, the layer thickness in the second region and in the fourth region can be reduced and thus the electrical power density in the second and in the fourth region can be increased. Since the second and fourth regions have a reduced thermal resistance to the top and bottom of the device for delivering the heat to an external environment, the thermal load of the entire device is more homogeneous, resulting in a reduced susceptibility to error and improved homogeneity of the electrical

Features over time leads.

FIG. 8 again shows the possibility

Metallisierungsflächen MF at phase boundaries between the first and the second or the second and the third

To arrange area.

The varistor device, the manufacturing method and the use are not limited by the technical details shown. Varistor components can be additional layers, Metallisierungsflächen and varistor material layers, and have additional contact electrodes.

Manufacturing methods may include additional steps, particularly regarding the embedding of

Metallization layers in varistor material include.

Reference sign list

Bl, B2, ... first, second, ... range

El first contact electrode

E2 second contact electrode

GK basic body

K edges of the metallization surfaces

Ml, M2, M3 first, second, third varistor material

MF metallization surface

MF1, MF2, ... first, second, ... metallization surface

MLV multilayer varistor component

V varistor component

VL varistor position

Claims

claims

1. Varistor device (V) with increased

Shock current capacity, comprising

a base body (GK) having a first region (Bl) of a first varistor material and a second region (B2) of a second, different from the first varistor material,

- Embedded in the basic body (GK)

Metallization surfaces (MF).

2. Varistor component according to the preceding claim,

comprising three areas (Bl, B2) of at least two

various varistor materials, wherein at least two interfaces between the three areas (Bl, B2) are arranged in parallel.

3. Varistor component according to one of the preceding claims, wherein at least two metallization (MF) are arranged in parallel.

4. Varistor component according to one of the preceding claims, comprising an interface between two areas (Bl, B2) of different varistor materials, which is arranged parallel to a metallization (MF).

5. Varistor component according to one of the preceding claims, comprising an interface between two areas (Bl, B2) of different varistor materials, which lies between two adjacent metallization (MF).

6. varistor component according to one of the preceding claims, comprising a metallization (MF), at the Interface between two areas (Bl, B2)

embedded in different varistor materials.

7. Varistor component according to one of the preceding claims, comprising a third region (B3) made of a varistor material,

wherein the second region (B2) is disposed between the first region (Bl) and the third region (B3).

8. Varistor component according to the preceding claim,

wherein the material of the first region (Bl) and the material of the third region (B3) are the same.

9. varistor component according to claim 1, wherein the varistor component (V) is a multilayer varistor component having a multiplicity of alternately arranged varistor layers (VL) and metallization surfaces (MF).

10. Varistor component according to one of the preceding claims, further comprising a first contact electrode (El) and a second contact electrode (E2), wherein at least one

Metallization surface (MF) with the first contact electrode (El) is connected and at least one metallization surface (MF) with the second contact electrode (E2) is connected.

11. Varistor component according to claim 1, wherein the different materials of the regions (Bl, B2) differ in at least one material parameter which is selected from: thermal expansion coefficient, breakdown field strength, sintering temperature, grain size,

12. A method for producing a varistor device (V) with increased surge current capacity, comprising

steps

Providing a base of a first varistor material as a first region (Bl),

Arranging a material of a second varistor material different from the first varistor material as a second region (B2) on or over the first region (Bl),

- Embedding metallization (MF) in the

Materials of the two areas (Bl, B2).

13. Use of two different varistor materials in different areas (Bl, B2) of a varistor component (V) in order to increase the surge current capacity.