DE102017210472A1 - Varistor with alloy optimization - Google Patents

Abstract

The invention relates to a varistor (1) with alloy optimization, comprising
A substantially areal extending varistor ceramic (K),
At least one first connection tab (L1),
Wherein the varistor ceramic (K) is in electrical connection with the first connection tab (L1),
Wherein the first connection tab (L1) is arranged parallel to the substantially planarly extending varistor ceramic (K) and extends substantially as far as the edge of the varistor ceramic,
Wherein the first connection lug (L1) has at least one first contact-free region (A1) in the surface, so that there is no direct electrical connection to the varistor ceramic (K) at the location of the first contact-free region (A1),
Wherein a desired Durchlegierungsstelle is formed adjacent to the first non-contact area (A1) or under the first non-contact area (A1).

Description

background

In the field of overvoltage protection, it is known to use varistors for the protection of individual apparatuses and / or complex circuits. In the event of overvoltage, the varistors conduct the voltage to the device / circuit to be protected. A varistor in this case has a varistor ceramic, which is contacted flat from both sides.

If too much current flows through the varistor, e.g. in case of overload, or too long a tracking current, e.g. subsequently to the overload case, the varistor heats up massively, so that it can lead to a process known as alloying through. In addition to the considerable heat development of the varistor is usually destroyed explosively. Here also fires can occur.

In addition, it is also known that varistors tend to cause a leakage current due to aging influences. This leakage current can lead to excessive heating and thus to fires.

In order to counteract these phenomena, separating devices have been proposed in the past which are intended to cut off the varistor in the event of inadmissible heating.

In order to ensure a rapid heat conduction to the separation point and thus a quick shutdown, a lot of effort was made in the past, because the place of Durchlegierens was unknown. The location of the separation point, however, is fixed after production. If a breakdown occurs at a remote location to the separation point, it takes, due to the slow heat conduction, until the separation point is triggered.

In the past, an attempt was made to better define the site of alloying through the design of the varistor ceramic, namely the doping. However, it has been shown that the doping itself leads to an increase in price while on the other hand, the reliability of the place is only slightly affected.

This high cost resulted in complex arrangements with high production and development costs.

Nevertheless, there are still situations where separation does not happen fast enough.

Against this background, the invention has the task of providing a cost-effective solution that can provide a separation quickly and reliably.

Brief description of the invention

The object is achieved by the features of the independent claims. Advantageous embodiments of the invention are specified in the subclaims, the description and the figures.

list of figures

The invention will be explained in more detail with reference to the accompanying drawings with reference to preferred embodiments.

• 1 eine schematische Schnittdarstellung von Ausführungsformen gemäß der Erfindung,
• 2 eine Detail der Ausführungsformen gemäß 1,
• 3 eine weiteres Detail der Ausführungsformen gemäß 1,
• 4 eine schematische Schnittdarstellung von weiteren Ausführungsformen gemäß der Erfindung,
• 5 eine schematische Schnittdarstellung von noch weiteren Ausführungsformen gemäß der Erfindung,
• 6 eine schematische Schnittdarstellung von weiteren Ausführungsformen gemäß der Erfindung,
• 7 eine schematische Schnittdarstellung eines Detail von Ausführungsformen gemäß der Erfindung,
• 8 eine schematische Schnittdarstellung eines Detail von weiteren Ausführungsformen gemäß der Erfindung,
• 9 eine schematische Schnittdarstellung eines Detail von noch weiteren Ausführungsformen gemäß der Erfindung,
• 10 eine schematische Schnittdarstellung von weiteren Ausführungsformen gemäß der Erfindung,
• 11a-d schematische Aufsichten auf ein Detail von Ausführungsformen der Erfindung,
• 12 eine schematische Schnittdarstellung eines Detail von noch weiteren Ausführungsformen gemäß der Erfindung, und
• 13 eine schematische Schnittdarstellung eines Detail von noch weiteren Ausführungsformen gemäß der Erfindung.

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• 1 a schematic sectional view of embodiments according to the invention,
• 2 a detail of the embodiments according to 1 .
• 3 a further detail of the embodiments according to 1 .
• 4 a schematic sectional view of further embodiments according to the invention,
• 5 a schematic sectional view of still further embodiments according to the invention,
• 6 a schematic sectional view of further embodiments according to the invention,
• 7 a schematic sectional view of a detail of embodiments according to the invention,
• 8th 1 is a schematic sectional view of a detail of further embodiments according to the invention,
• 9 a schematic sectional view of a detail of still further embodiments according to the invention,
• 10 a schematic sectional view of further embodiments according to the invention,
• 11a-d schematic plan views of a detail of embodiments of the invention,
• 12 a schematic sectional view of a detail of still further embodiments according to the invention, and
• 13 a schematic sectional view of a detail of still further embodiments according to the invention.

Detailed illustration of the invention

Hereinafter, the invention will be illustrated in more detail with reference to the figures. It should be noted that different aspects are described, which can be used individually or in combination. That Any aspect may be used with different embodiments of the invention unless explicitly illustrated as a mere alternative.

Furthermore, in the following, for the sake of simplicity, usually only one entity will be referred to. Unless explicitly stated, however, the invention may also have several of the entities concerned. As such, the use of the words "a," "an" and "an" is to be understood merely as an indication that at least one entity is used in a simple embodiment.

According to embodiments of the invention, for example in 1 . 4-6 . 10 and 12 and 13 are shown in section, has a varistor according to the invention 1 with alloying optimization a substantially areal extending varistor ceramic K on. Furthermore, the varistor 1 at least a first connection tab L1 on, with the varistor ceramic K (at least in sections) in electrical connection with the first connection tab L1 stands. The first connection tab L1 is parallel to the substantially areal extending varistor ceramic K arranged and extends substantially to the edge of the varistor ceramic K , The first connection tab L1 has at least a first non-contact area A1 in the area, so that at the location of the first non-contact area A1 no direct electrical connection to the varistor ceramic K consists. Ie a current can only over other areas of the connection tab L1 or the varistor ceramic K into the areas of the varistor ceramic K under the non-contact area A1 and do not flow there directly.

This causes that in the edge region of the non-contact area A1 on the surface of the varistor ceramic K or any existing metallization M1 a locally higher current density is observed, which also leads to a locally stronger heating, which in turn favors a breakdown as well as a separation. If a metallization is present, the field density within the varistor ceramic K be essentially the same. However, due to the lack of contact, it forms the connection tab L1 in the non-contact area A1 (and especially at the edge) high current densities compared to other locations. If no metallization is present, the electric field lines within the varistor ceramic K are substantially parallel while they are in the area of the non-contact area to the edge of the non-contact area A1 to bend. That is, the field lines are concentrated here on a smaller area, which is accompanied by an increased current flow.

It should be noted that any metallization M1 also under the non-contact area A1 can be present.

In addition, the areas form the connection tab L1 that the varistor ceramic touch a heat sink, so these areas are cooler. That is, a heat input under the non-contact areas A1 is not derived as quickly as in other places. Adjacent to the first non-contact area A1 or below the first non-contact area A1 so a target Durchlegierungsstelle is formed.

The invention makes use of the fact that it has been shown in experiments that the place of Durchlegierens adjusts itself to places that are exposed to a greater thermal load, or where the electric field density is higher than elsewhere. The invention thus allows the site of galling to be placed close to the separation site, allowing for rapid separation (because at a known location). The invention is based on the previous concept, which have the best possible heat conduction from the surfaces of the varistor to the goal. This means that the location of the (local) Durchlegierens (and thus the location of a large (maximum) heating of the varistor is determined by constructive measures, so that the separator AE can be placed in (immediate) proximity.

The varistor 1 may have further connection and / or passivation / insulation layers. Later.

The connection tab L1 (and if necessary, the connection tab L2 ) have substantially the shape of the ceramic K on. This can provide a uniform distribution of current within the ceramic. At the same time it can be prevented that a galling occurs elsewhere.

In advantageous embodiments, which will be described later, the terminal tabs L1 . L2 or a metallization M1 . M2 not led to the very edge. It should be noted that embodiments in which the metallization is not completely led to the edge, are usually formed so that the "recessed" edge region is relatively small. In addition, these embodiments usually have further measures with which the field lines can be selectively influenced at the edge. This can cause flashovers between the two sides of the varistor K or the connection tabs L1 . L2 or a metallization M1 . M2 be prevented.

For technical reasons, the connection tabs L1 . L2 Have recesses, for example, to dissipate a flux during soldering.

In embodiments of the invention, the varistor 1 between the varistor ceramic K and the first connection tab L1 a metallization M1 on. The metallization provides better current distribution or more uniform potentials with respect to the locations where no target pinhole is formed. Obviously, but also the metallization M1 have a recess / a non-contact area at the location of the desired Durchlegierungsstelle.

In a further embodiment of the invention is - as in 12 and 13 shown - on the varistor ceramic K opposite side of the first connection tab L1 an insulation layer ISO1 intended.

In embodiments of the invention, which in 2 respectively. 3 are shown, the first non-contact area A1 essentially a circular opening. Other forms of non-contact areas, especially those as in the 11a-d shown are not excluded by this.

The use of a variety of non-contact areas allows electrical contact near the location where the varistor 1 will permeate, see , This construction offers further advantages. The middle position forms a heat trap, which favors separation at the site. Furthermore, the reduced cross section increases the current density at these points, which leads to additional heating. The webs can be completely eliminated, in this case, the current is concentrated in the metallization M1 or on the surface of the varistor ceramic K ,

According to another embodiment of the invention is - as in the 1 . 4-6 . 10 and 12 and 13 shown in the area of the first non-contact area A1 a separation unit AE at the first connection tab L1 arranged. The separation unit can be designed, for example, slider-like and a connection wire AD For example, on the connection tab L1 by means of a suitable thermally softenable / decomposable adhesive LOT (eg, a solder) is connected, electrically disconnect by the separation unit AE after softening / decomposing the adhesive LOT between the connection tab L1 and the (detached) lead wire AD pushes. The connecting wire AD can by means of bias first on the connection tab L1 be attached so that in case of softening / decomposition of the terminal tab L1 wegbewegt (away-sprung) is. Without further ado, the separation unit can also be assigned an energy store (not shown), so that by means of the force in the case of softening / decomposition of the thermally softenable / decomposable adhesive LOT the separation unit AE between the connection tab L1 and the (detached) lead wire AD pushes.

In one embodiment, in 12 and 13 is shown, the varistor points 1 a second connection tab L2 on the opposite side of the first connection tab L1 on, with the varistor ceramic K (at least in sections) is in electrical connection with the second connection tab. The second connection tab L1 is parallel to the substantially areal extending varistor ceramic K arranged and extends substantially to the edge of the varistor ceramic K , The second connection tab L2 has at least one second non-contact area A2 in the area, so that at the location of the second non-contact area A2 no direct electrical connection to the varistor ceramic K consists. Ie a current can only over other areas of the connecting tab L1 or the varistor ceramic K into the areas of the varistor ceramic K under the non-contact area A1 and do not flow there directly.

This causes that in the edge region of the non-contact area A2 on the surface of the varistor ceramic K or any existing metallization M2 a locally higher current density is observed, which also leads to a locally stronger heating, which in turn favors a breakdown as well as a separation.

If a metallization is present, the field density within the varistor ceramic K be essentially the same. However, due to the lack of contact, it forms the connection tab L2 in the non-contact area A2 (and especially at the edge) high current densities compared to other locations. Is not metallization M2 present, the electric field lines within the varistor ceramic K are substantially parallel while they are in the area of the non-contact area to the edge of the non-contact area A2 to bend. That is, the field lines are concentrated here on a smaller area, which is accompanied by an increased current flow.

It should be noted that any metallization M2 also under the non-contact area A2 can be present.

In addition, the areas form the connection tab L2 which the varistor ceramic K touch a heat sink so that these areas are cooler. That is, a heat input under the non-contact areas A2 is not derived as quickly as in other places. Adjacent to the second non-contact area A2 or under the second non-contact area A2 so a target Durchlegierungsstelle is formed.

It should already be noted at this point that the design and the spatial arrangement of the first connection tab L1 and the second connection tab L2 can be different.

In embodiments of the invention, the varistor 1 between the varistor ceramic K and the second connection tab L2 a metallization M2 on. Obviously, but also the metallization M2 have a recess / a non-contact area at the location of the desired Durchlegierungsstelle.

In a further embodiment of the invention as in 12 shown on the varistor ceramic K opposite side of the second connection tab L2 an insulation layer ISO2 intended.

Without further ado, for the first connection tab L1 and the second connection tab L2 also a common insulation layer ISO1 be provided as in 13 shown. The insulation layers ISO1 . ISO2 For example, they may be formed of an epoxy material, a thermoset, or a thermoplastic.

The metallization M1 . M2 may be formed of a copper (containing) foil, a metallic vapor or the like.

In embodiments of the invention, which in 2 respectively. 3 are shown, the second non-contact area A2 essentially a circular opening. Other forms of non-contact areas, especially those as in the 11a-d shown are not excluded by this.

The use of a variety of non-contact areas allows electrical contact near the location where the varistor 1 will permeate, see , This construction offers further advantages. The middle position forms a heat trap, which promotes alloying at the site. Furthermore, the reduced cross section increases the current density at these points, which leads to additional heating. The webs can be completely eliminated, in this case, the current is concentrated in the metallization M2 or on the surface of the varistor ceramic K ,

According to another embodiment of the invention is - as in the 12 shown in the area of the second non-contact area A1 a (further) separation unit AE at the first connection tab L1 arranged. The separation unit can be designed, for example, slider-like and a connection wire AD For example, on the connection tab L2 by means of a suitable thermally softenable / decomposable adhesive LOT (eg, a solder) is connected, electrically disconnect by the separation unit AE after softening / decomposing the adhesive LOT between the connection tab L1 and the (detached) lead wire AD pushes. The connecting wire AD can by means of bias first on the connection tab L2 be attached so that in case of softening / decomposition of the terminal tab L2 wegbewegt (away-sprung) is. Without further ado, the separation unit may also be assigned an energy store (not shown), so that by means of the force in the case of softening / decomposition of the thermally softenable / decomposable adhesive LOT the separation unit AE between the connection tab L2 and the (detached) lead wire AD pushes.

As previously described, the designer has no limits and so can the first non-contact area A1 on the first tab L1 and the second non-contact area A2 on the second tab L2 are arranged opposite or not opposite.

An opposing arrangement may be advantageous in individual cases, since only a narrowly limited pass-through channel will be formed, which runs essentially perpendicular to the varistor ceramic surface. That is, by providing differently placed and shape non-contact areas, both the current flow and the thermal behavior can be selectively influenced, so that the condition for the detachment of a separation unit AE can be targeted. For example, in the embodiment of the 1 (and the 2 and 3 ) the locations of the non-contact areas A1 . A2 placed differently. In the embodiment of the 5 and 6 is just a recess A1 intended. In the embodiments of the 4 . 10 . 12 and 12 are, however, the non-contact areas A1 . A2 arranged opposite.

On the other hand, e.g. Redundancy is added by providing two target pass-through locations and two disconnect units, thus increasing security.

Punches on the edge of the varistor ceramic K can by targeted design of the varistor ceramic K be prevented.

For example, the varistor ceramic K - as in 9 shown - have a substantially constant thickness, wherein the varistor ceramic K has an increased thickness at the edge. Increasing the varistor thickness at the edge reduces the field strength in these areas. Thus, there is less heating in the edge area and the varistor 1 alloyed in another area. Here is the width of the edge cant a preferably less than 10% of the varistor (area) width, in particular less than 1% of the varistor (area) width. In addition, the edge cant b less than 20% of the varistor thickness, especially less than 5%.

Alternatively or additionally, the varistor ceramic K at the edge of a recess, in particular a concave or convex indentation as in 7 shown have.

Alternatively or additionally, the varistor ceramic K have a slope on the edge, as in 8th shown.

Alternatively or additionally, the varistor ceramic K at the edge an isolation ISO1 have, as in 13 shown.

In embodiments of the invention, a plurality of non-contact areas are on a terminal tab L1 . L2 provided, so locally a power distribution and, consequently, a local heating can be achieved during operation. That is, by means of a variety of non-contact areas, the field distribution can be designed specifically, so that it comes to local Feldüberhöhungen. This can also be accompanied by the current density distribution in the varistor ceramic K be affected, so it comes to local current density peaks. As a result, the location of the thinning out and an increased heat development can be influenced in a targeted manner.

As can be seen from the figures, the non-contact area can be designed differently.

Thus, the non-contact area can be formed as a recess in eg a stamped sheet, see for example 1 . 4-u nd 5.

However, it is also possible by a bulge as in 6 . 10 . 12 and 13 shown to design the non-contact area as a bulge.

LIST OF REFERENCE NUMBERS

1

varistor

K

varistor

L1

first connection tab

A1

first non-contact area

M1

metallization

ISO1

insulation layer

AE

separation unit

L2

second connection tab

A2

second non-contact area

M2

metallization

ISO2

insulation layer

AD

Lead wire

LOT

adhesives

a

Width of the edge cant

b

edge overshoot

Claims (19)

Varistor (1) with alloy optimization, comprising A substantially areal extending varistor ceramic (K), At least one first connection tab (L1), Wherein the varistor ceramic (K) is in electrical connection with the first connection tab (L1), Wherein the first connection tab (L1) is arranged parallel to the substantially planarly extending varistor ceramic (K) and extends substantially as far as the edge of the varistor ceramic, Wherein the first connection lug (L1) has at least one first contact-free region (A1) in the surface, so that there is no direct electrical connection to the varistor ceramic (K) at the location of the first contact-free region (A1), Wherein a desired Durchlegierungsstelle is formed adjacent to the first non-contact area (A1) or under the first non-contact area (A1). Varistor with alloy optimization according to Claim 1 , wherein a metallization (M1) is provided between the varistor ceramic (K) and the first connection tab (L1). Varistor with alloy optimization according to Claim 1 or 2 , wherein on the side of the first connection tab (L1) facing away from the varistor ceramic (K) an insulation layer (ISO1) is provided. The alloy with alloy optimization according to one of the preceding claims, wherein the first non-contact region (A1) has a substantially circular opening. Varistor with alloy optimization according to one of the preceding claims, wherein in the region of the first non-contact region (A1), a separation unit (AE) is arranged on the first connection tab (L1). A varistor with alloy optimization according to one of the preceding claims, comprising a second connection tab (L2), wherein the varistor ceramic (K) is in electrical connection with the second connection tab, Wherein the second connection tab (L2) is arranged parallel to the substantially planarly extending varistor ceramic (K) and extends substantially as far as the edge of the varistor ceramic (K), Wherein the second connection lug (L2) has at least one second contact-free region (A2) in the surface, so that there is no direct electrical connection to the varistor ceramic (K) at the location of the second contact-free region (A2). Varistor with alloy optimization according to Claim 6 , wherein a metallization (M2) is provided between the varistor ceramic (K) and the second connection tab (L2). Varistor with alloy optimization according to Claim 6 or 7 , wherein on the side of the second connection tab (L2) facing away from the varistor ceramic (K) an insulation layer (ISO2) is provided. Varistor with alloy optimization according to one of the preceding Claims 6 to 8th wherein the second non-contact region (A2) has a substantially circular opening. Varistor with alloy optimization according to one of the preceding Claims 6 to 9 , wherein in the region of the second contact-free region (A2) a separation unit (AE) is arranged on the second connection tab (L2). Varistor with alloy optimization according to one of the preceding Claims 6 to 10 wherein the first non-contact area (A1) on the first tab (L1) and the second non-contact area (A2) on the second tab (L2) are arranged opposite each other. Varistor with alloy optimization according to one of the preceding Claims 6 to 10 wherein the first non-contact area (A1) on the first tab (L1) and the second non-contact area (A2) on the second tab (L2) are not arranged opposite one another. The varistor with alloy optimization according to one of the preceding claims, wherein the varistor ceramic (K) has a substantially constant thickness, the varistor ceramic (K) having an increased thickness at the edge. Varistor with alloy optimization according to one of the preceding Claims 1 to 13 , wherein the varistor ceramic (K) has a substantially constant thickness, wherein the varistor ceramic (K) has a recess at the edge. Varistor with alloy optimization according to Claim 14 , wherein the indentation is concave or convex. Varistor with alloy optimization according to one of the preceding Claims 1 to 15 wherein the varistor ceramic (K) has a substantially constant thickness, wherein the varistor ceramic (K) has a bevel at the edge. Varistor with alloy optimization according to one of the preceding Claims 1 to 13 wherein the varistor ceramic (K) has a substantially constant thickness, wherein the varistor ceramic (K) has an insulation at the edge. Varistor with alloy optimization according to one of the preceding claims, wherein a plurality of non-contact areas on a terminal tab (L1, L2) are provided, so locally a current distribution and, consequently, a local heating can be achieved during operation. A through-alloy optimization varistor according to one of the preceding claims, wherein the first non-contact region (A1) is a bulge.

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