Metal oxide varistor and method of manufacturing

The present invention concerns a metal oxide varistor and method of manufacturing a metal oxide varistor.

CN 1925072 A discloses a varistor which is arranged in a closed cavity.

If an insulation material is applied to a varistor by dipping or by a spraying process, due to the nature of these

processes, it is not possible to control the dimensions of the final products precisely. Moreover, in order to assemble further components to the varistor, an additional housing is needed .

It is the object of the present invention to provide an improved metal oxide varistor and a method for manufacturing the varistor.

This object is solved by the subject of the independent claims .

A metal oxide varistor is provided which comprises a disc of a varistor material, a first metallization electrode arranged on the disc and an encapsulation of an insulating material in which the disc is at least partly embedded.

The insulating material may be epoxy or silicone.

The disc of varistor material may have any shape. The disc is preferably flat. Thus, a height of the disc, i.e. the distance between the first metallization electrode and a second metallization electrode on an opposite side of the disc, may be smaller than a width of the disc, i.e. the extension of the disc in a direction perpendicular to the height .

The metal oxide varistor may not require an additional housing to insulate the disc of the varistor material.

Instead, the insulation may be provided by the encapsulation of the insulation material.

The encapsulation of the insulating material may be applied on the disc by thermal molding. Thermal molding may allow to apply the insulating material with high precision. Thus, a varistor can be constructed with well-defined dimensions. Moreover, thermal molding may allow to form a thin layer of the insulating material. Thus, a small varistor can be constructed. Accordingly, applying the insulating material by thermal molding may help to miniaturize the varistor.

Thermal molding is a manufacturing method which provided a high flexibility in the manufacturing process. Thus, it may be possible to adapt the application of the insulating material to the desired properties of a varistor.

The encapsulation may cover the first metallization electrode only partly, thereby forming a window in which the first metallization electrode is exposed. Accordingly, the first metallization electrode can be electrically contacted by a contact which is fixed, e.g. soldered, to the first

metallization electrode in the window. A first terminal may be arranged on the first metallization electrode. The first terminal may be a metallic element comprising a metallic structure fixed to the first

metallization electrode. The varistor may be electrically contacted via the first terminal.

The encapsulation may cover the first terminal only partly, thereby forming a window in which the first terminal is exposed. Thus, the first terminal may be electrically contacted in the window.

The encapsulation may completely cover the disc, and the first terminal may comprise a first contact element which protrudes out of the encapsulation. The first terminal may be electrically contacted by contacting the first contact element .

The first contact element may protrudes out of the

encapsulation in a direction parallel to a surface of the disc on which the first metallization is applied.

Alternatively, the first contact element may protrude out of the encapsulation in a direction perpendicular to the surface of the disc on which the first metallization is applied.

The metal oxide varistor may further comprising a second metallization electrode arranged on the disc opposite to the first metallization. A voltage may be applied between the first metallization electrode and the second metallization electrode .

The encapsulation may cover the second metallization

electrode only partly, thereby forming a window in which the second metallization electrode is exposed. A second terminal may be arranged on the second metallization electrode .

The encapsulation may cover the second terminal only partly, thereby forming a window in which the second terminal is exposed .

The encapsulation may completely cover the disc, and the second terminal comprises a second contact element which protrudes out of the encapsulation.

The second contact element may protrude out of the

encapsulation in a direction parallel to a surface of the disc on which the second metallization is applied.

Alternatively, the second contact element may protrude out of the encapsulation in a direction perpendicular to the surface of the disc on which the second metallization is applied.

The encapsulation may comprise a projection for assembling a component to the metal oxide varistor. The projection may be formed by the thermal molding of the insulation material. No additional housing may be required to fix further components to the metal oxide varistor.

The present invention further concerns an assembly comprising the metal oxide varistor with at least one projection and a component which is fixed on the projection. The component may be an SMD component (SMD = surface mounted device) .

According to another aspect, the present invention concerns a method of manufacturing the above-described metal oxide varistor, wherein the encapsulation of the insulating material is applied on the disc by thermal molding. The use of thermal molding for applying the encapsulation provides may advantages. In particular, the insulation material can be applied with high precision, even on small size varistors. Moreover, a projection may be formed by insulation material directly on the encapsulation, thereby allowing to fix further components to the varistor.

In the following, the present invention is described in further detail with respect to the figures which show

preferred embodiments of the invention.

Figures la and lb show a perspective view of a metal oxide varistor according to a first embodiment.

Figures 2a and 2b show a perspective view of a metal oxide varistor according to a second embodiment.

Figures 3a and 3b show a perspective view of a metal oxide varistor according to a third embodiment.

Figures 4a and 4b show a perspective view of a metal oxide varistor according to a fourth embodiment.

Figures 5a and 5b show a perspective view of a metal oxide varistor according to a fifth embodiment.

Figures 6a and 6b show a perspective view of a metal oxide varistor according to a sixth embodiment.

Figures la and lb show a perspective view of a metal oxide varistor. In Figure lb an encapsulation 1 is shown transparent in order to visualize the elements inside the encapsulation 1.

The varistor comprises a disc 2 of a varistor material. The disc 2 has a cuboid shape. The disc 2 has a top face and a bottom face which is opposite of the top face. A base area of the disc 2 is roughly quadratic. A height of the disc 2 perpendicular to the base area is significantly smaller than the side lengths of the roughly quadratic base area. Thus, the disc 2 is flat. The present invention is not limited to discs 2 having this shape. Instead, the disc 2 may have any other shape.

On the top face of the disc 2, a first metallization

electrode 3 is arranged. On the bottom face of the disc 2, a second metallization electrode 4 is arranged.

The disc 2 and the metallization electrodes 3, 4 are at least partly embedded in the encapsulation 1. In the embodiment shown in Figures la and lb, the disc 2 and the metallization electrodes 3, 4 are completely embedded in the encapsulation 1. The encapsulation 1 consists of an insulating material.

The varistor further comprises a first terminal 5 arranged on the first metallization electrode 3. The first terminal 5 comprises a flat metal structure 5a which is soldered to the first metallization electrode 3. The first terminal 5 further comprises a contact element 5b which protrudes away from the disc 2. The contact element 5b is arranged at an edge of the flat metal structure 5a. The contact element 5b is

perpendicular to the flat metal structure 5a. The contact element 5b is also perpendicular to the first metallization electrode 3. The encapsulation 1 covers the flat metal structure 5a of the terminal 5 completely. The contact element 5b protrudes out of the encapsulation 1. An electrical potential can be applied to the contact element 5b. The electrical potential is applied by the contact element 5b via the flat metal structure 5a to the first metallization electrode 3.

Further, the varistor comprises a second terminal 6 which is fixed to the second metallization electrode 4. The second terminal 6 comprises a flat metal structure 6a and a contact element 6b. The flat metal structure 6a is soldered to the second metallization electrode 4. The contact element 6b is arranged on an edge of the flat metal structure 6a and protrudes away from the flat metal structure 6b. The flat metal structure 6a of the second terminal 6 is completely covered by the encapsulation 1. The contact element 6a of the second terminal 6 protrudes out of the encapsulation 1. The contact element 6b of the second terminal 6 is perpendicular to the contact element 5b of the first terminal 5.

The encapsulation 1 of the insulating material is applied by thermal molding. The encapsulation 1 covers the disc 2, the two metallization electrodes 3, 4 and the flat metal

structures 5a, 5b of the terminals 5, 6 completely. Only the contact elements 5b, 6b protrude out of the encapsulation 1.

As the encapsulation 1 of the insulating material is applied by thermal molding, it can be applied with a high precision. Further, the encapsulation 1 does not require a lot of space. Thus, applying the encapsulation 1 by thermal molding allows to construct a varistor having a small size. Figures 2a and 2b show a varistor according to a second embodiment. In Figure 2b, the encapsulation 1 is shown transparent. The second embodiment differs from the first embodiment only in the design of the first terminal 5. In particular, the contact element 5b of the first terminal 5 is not perpendicular to the first metallization electrode 3 in the second embodiment. Instead, the contact element 5b protrudes out of the encapsulation 1 and the contact element 5b is parallel to the first metallization electrode 3.

In the second embodiment, the encapsulation 1 also covers the disc 2, the two metallization electrodes 3, 4 and the flat metal structures 5a, 6a of the terminals 5, 6 completely. The encapsulation 1 is also applied by thermal molding. Thus, the second embodiment also provides the advantages of a high precision manufacturing process and a small size varistor.

The second embodiment shows that the encapsulation 1 being applied by thermal molding can be combined with any kind of design of the two terminals 5, 6. The terminals 5, 6 can be identical to each other or can differ from each other.

Figures 3a and 3b show a varistor according to a third embodiment. In Figure 3b, the encapsulation 1 is shown transparent .

The disc 2 of the varistor material, the second metallization electrode 4 and the second terminal 6 of the varistor

according to the third embodiment are identical to the corresponding elements of the varistor according to the first embodiment and to the varistor according to the second embodiment . The first metallization electrode 3 is applied to the top face of the disc 2. A first terminal 5 is fixed to the first metallization electrode 3. The first terminal 5 differs from the first terminal 5 of the previous embodiments. The first terminal 5 according to the third embodiment does not

comprise a contact element 5b which protrudes out of the encapsulation 1. Instead, the first terminal 5 consists of a flat metal structure 5a which is soldered onto the first metallization electrode 3.

The encapsulation 1 does not cover the first terminal 5 completely. The encapsulation 1 covers the first terminal 5 only partly. The encapsulation 1 forms a window 7 on the first terminal 5 where the first terminal 5 is free from the encapsulation 1. Further elements for contacting the varistor can be fixed to the first terminal 5 in the window 7 in the encapsulation 1.

In particular, a joint can be soldered to the first terminal 5 at the window 7 by a low temperature solder. In case of an overheating, the low temperature solder will melt and

disconnect the varistor.

The encapsulation 1 covers the varistor completely except for the window 7 on the first terminal 5. The encapsulation 1 is applied via thermal molding. Thus, the encapsulation 1 is applied with high precision and minimal space requirements.

Figures 4a and 4b show a varistor according to a fourth embodiment. In Figure 4b, the encapsulation 1 is shown transparent . The disc 2 of the varistor material and the metallization electrodes 3, 4 according to the fourth embodiment are identical to the corresponding elements of the varistor according to the previous embodiments.

Each of the first terminal 5 and the second terminal 6 consists of a flat metal structure 5a, 6a. The flat metal structure 5a of the first terminal 5 is soldered to the first metallization electrode 3. The flat metal structure 6a of the second terminal 6 is soldered to the second metallization electrode 4. None of the first terminal 5 and the second terminal 6 comprises a contact element 5b, 6b protruding out of the encapsulation 1.

The encapsulation 1 forms a first window 7 on the top face of the varistor and a second window 7 on the bottom face of the varistor. The encapsulation 1 does not cover the first terminal 5 and the second terminal 6. The first window 7 in the encapsulation 1 is larger than the window 7 in the encapsulation according to the third embodiment.

Further elements can be fixed to the first terminal 5 and the second terminal 6 at the windows 7 for electrically

contacting the varistor. In particular, a joint can be soldered to the first terminal 5 in the first window 7 by a low temperature solder. A further joint can be soldered to the second terminal 6 in the second window 7 by a low

temperature solder. In case of an overheating of the

varistor, the low temperature solder connections will melt and, thereby, disconnect the varistor. Figures 5a and 5b show a varistor according to a fifth embodiment. In Figure 5b, the encapsulation 1 is shown transparent .

The varistor according to the fifth embodiment differs from the varistor according to the fourth embodiment in that the varistor does not comprise a first terminal 5 and a second terminal 6 at all. Instead, a first window 7 is formed in the encapsulation 1 on the top face of the varistor such that the first metallization electrode 3 is exposed below the first window 7. A second window 7 is formed in the encapsulation 1 on the bottom face of the varistor such that the second metallization electrode 4 is exposed below the second window 7.

A contactor can be soldered directly to each of the first metallization electrode 3 and the second metallization electrode 4. The contactor may allow to electrically contact the varistor. The contactor can be soldered to the respective metallization electrode 3, 4 by a low temperature solder.

The encapsulation 1 covers the disc 2 partly. The

encapsulation 1 forms windows 7 on each of the metallization electrodes 3, 4. The encapsulation 1 is applied by thermal molding .

Figures 6a and 6b show a varistor according to a sixth embodiment. In Figure 6b, the encapsulation 1 is shown transparent .

The varistor according to the sixth embodiment is based on the varistor to the third embodiment. Additionally, the varistor according to the sixth embodiment comprises two projections 8, 9. Each of the projections 8, 9 is configured for assembling a component to the varistor.

The projections 8, 9 are formed by the encapsulation 1. The projections 8, 9 are arranged on the top face of the

varistor. One of the projections 8 has a cuboid shape and the other projection 9 has a cylindrical shape. The projections 8, 9 may also have any other shape. The projections 8, 9 are fixtures on the encapsulation 1 for assembling with other components. Thus, no additional housing is required for combining the varistor with other components. Instead, the varistor and the other component can form an assembly wherein the other component is fixed on the projection 8, 9 of the encapsulation 1 of the varistor.

The encapsulation 1 is applied by thermal molding. Thus, the encapsulation 1 can be applied very precisely. Thereby, a reliable fixature can be formed.

As the encapsulation 1 is applied by thermal molding, it is easily possible to modify the molding process such that the projections 8, 9 are arranged at a different position or such that the number and/or the shape of the projections 8, 9 is varied. Thus, the thermal molding provides a large

flexibility in the design of the encapsulation 1, thereby allowing to adapt the encapsulation 1 to all kinds of configurations of components that shall be fixed to the varistor .

One or more projections 8, 9 as shown in Figures 6a and 6b can also be added to each of the varistors according to the other embodiments. Reference numerals

1 encapsulation

2 disc

3 first metallization electrode

4 second metallization electrode

5 first terminal

5a flat metal structure

5b contact element

6 second terminal

6a flat metal structure

6b contact element

7 window

8 proj ection

9 proj ection