EP0829897B1 - Electric fuse - Google Patents

Description

The present invention relates to an electrical fuse with a substrate made of an electrically insulating Material, at least two electrical contacts that in the Are spaced from each other on the substrate, and a fusible conductor, which makes the contacts electrically conductive connects and at least partially between the contacts in an electrically insulating potting compound is embedded, with a depression in the substrate between the contacts is arranged.

Known fuses come in different forms and manufactured with varying components and in large Number used in electrical and electronic circuits. There they protect individual components or complete ones Assemblies against excessive current loads due to persistent Overcurrent or short circuit.

The fuse must be built up to the fuse element Provide protection against environmental influences. on the other hand but must also the environment when switching off the fuse before metal vapors or similar be shielded and preserved. In addition, a fuse for the electrical connection contain corresponding connections with the surrounding circuit. Known fuses indicate how to fulfill the named Requires a complex structure that is relative high manufacturing costs and / or space-consuming Sizes required.

From US 5,363,082 is a generic fuse known. A longitudinal groove is formed in the substrate, in which is the fuse element. The fuse element is partial covered with an electrically insulating potting compound. The Tripping characteristics of several identical fuses can vary.

The present invention is therefore the object to create an electrical fuse, the one has a simple design and the reproducibility of the Tripping characteristics of identical fuses improved.

This object is achieved by a backup solved with the features of claim 1.

The invention is based on the knowledge that the Known identical fuses occur different Tripping characteristic is due to the fact that the Not around the fuse element with all fuses is equal to. In particular, there is a risk that the Fusible conductor between the electrical contacts thermally is coupled to the substrate. The points of contact of the Fusible conductors with the substrate cannot be determined beforehand. The spaces between the fuse element and the substrate are small and can become contaminated or otherwise Fill deposits. This also affects the tripping characteristic the fuse. Otherwise, the potting compound cannot completely cover the fuse element, especially where the fuse element is Touched substrate. In other places there are air spaces, which also lead to a thermally inhomogeneous environment and thus lead to different tripping characteristics.

According to the invention, there is between the contacts in the substrate arranged a recess, the fuse element in Area of the depression without contact with the substrate. The depression creates an improved thermal Decoupling of the fuse element from the substrate and guaranteed such a reproducible tripping characteristic. Also allowed it the recess in the substrate that the potting compound can completely surround the fuse element. she reliably creates a reproducible homogeneous environment and improves the reproducibility of the tripping characteristic identical fuses.

• den Schutz des Schmelzleiters vor mechanischen Beanspruchungen und Einflüssen der Umgebung,
• den Schutz der Umgebung vor dem Lichtbogen und verdampfenden Teilen des Schmelzleiters und
• das "Kühlen" des Lichtbogens beim Abschalten der Sicherung, um ein sicheres Ende des Stromflusses durch ein Erlöschen des Lichtbogens zu bewirken.

The fuse element is at least partially covered between the contacts with an electrically insulating casting compound which is connected to the substrate. Covering the fuse element does the following:

• the protection of the fuse element against mechanical stress and environmental influences,
• the protection of the environment from the arc and evaporating parts of the fuse element and
• the "cooling" of the arc when the fuse is switched off, in order to bring about a safe end to the current flow by extinguishing the arc.

Depending on the choice of potting compound, the switch-off characteristic the fuse affects become.

In comparison with known fuses, there is no production the fuse according to the invention by this structure at least a process step, since here the cover is discrete Part not prefabricated and / or by auxiliary materials on the Substrate must be attached. Furthermore, the tightness of the Easy to ensure completion by the potting compound.

Advantageously, as a substrate for an inventive Fuse selected a rectangular plate, so that Fuses of the type described preferably in multiple use finished and separated in a final step, for example by breaking or other separation processes. It but there are also a number of common components that are their material properties for use as a security substrate are suitable.

In a further development, a ceramic substrate for the Structure of a fuse used. Ceramic materials are due to their material properties for use as a security substrate Particularly suitable because they are thermally stable and no conductive even in the presence of arcing Can form bridges, e.g. Carbon bridges.

Great advantages result from the use of a curable Paste as a potting compound. As a flowable medium, a Paste the fuse element completely in one production step and enclose tightly in a subsequent step to be solidified. The hardening or solidification of the Paste has the advantage that the paste reliably melts the fuse element encloses and also for mechanical stability and connection of the arrangement can contribute as it is on adheres securely to the substrate. This is of particular importance Point if it is the fuse element according to claim 9 is a wire. Fusible conductor wires are usually very thin and therefore mechanically less resilient. The hardened paste serves as an important mechanical protection here.

There are further advantages in terms of switching behavior when the potting compound is porous. That closes the possibilities a that the potting compound itself is porous and / or becomes porous when hardened by forming itself Voids solidified. Such a consistency of a substance can be used to extinguish an arc when the fuse is switched off of great benefit because the pores contain the gaseous, hot components of the arc provide enough space for expansion or spread and give areas for precipitation. They thus serve as pressure compensation chambers and thus reduce them the internal pressure of a fuse when switching off. A hollow one Pore content in the potting compound also has thermal Advantages because the gases contained in the cavities represent ideal heat insulation for the fuse element.

Furthermore, the hardened casting compound is thermally stable. The For example, the claims listed above be fulfilled by a non-conductive ceramic paste or through other insulating fillers in natural or through Modified form additives. By the type of cover and the properties of the sealing compound can be the characteristics of the Fuse can be greatly influenced.

The electrical necessary to connect the fuse element Contacts are advantageously made by metallization formed by two edges and / or end faces on the substrate, by, for example, an electrically conductive paste on it Places is applied and baked.

In the fuse according to the invention is the most essential Part, the fuse element, used as a finished element. He is in the form of a wire with defined properties in integrated the structure. This is done with minimal effort, by the wire stretched over the arrangement on the contacts is soldered. It is conceivable to apply a solder paste here on the contacts after metallizing and soldering by infrared or laser treatment. The one so fastened Fusible conductor wire has better thermal properties than for example, an electrically conductive layer, because too a very thin wire is not necessarily on a carrier layer is instructed. A layer formed from a paste is in manufacturing e.g. dependent on at least one carrier film, which in turn the electrical and thermal properties the fuse affects.

According to claim 10, the substrate of the fuse to the Metallized edges or end faces rounded. Thereby can be achieved that the edges of the substrate easier to are metallized. Furthermore, in a metallization process according to claim 7 and / or 8, the amount of to be recorded Paste minimized because no sharp edges are covered Need to become. Ultimately, this measure means that Increase in the width of this backup structure in the area of Total contacts less.

In one development, the substrate points to the one to be metallized Tapered edges or flattened edges on. This measure helps to reduce the height of the connections essential, which means that they protrude from the side the contact via the substrate of the component is avoided. So in the case of an SMD assembly, the component lies overall with the middle part of its substrate on the board of the to be assembled Circuit on. For example, the backup held securely by gluing until the contacts are soldered become. The middle part of the substrate can on the one hand serve as a support and adhesive surface, but also on the other hand the closely spaced soldering areas of the connections separate. It can be advantageous when applying the Solder paste on the board or when soldering not for training come from short-circuit bridges.

Advantageously, in a fuse according to the invention at least one between the fuse element and the sealing compound Cover may be arranged on which the sealing compound is arranged is. For example, a closed cavity are formed, through which the fuse element runs self-supporting. The cavity can also contain porous or granular media, such as. Sand. They are also layered structures to influence the tripping characteristic of the fuse realizable, as with an exemplary embodiment is described below.

Fig. 1a - 1c

eine Draufsicht auf eine erste Ausführungsform einer Sicherung sowie zwei Seitenansichten;

Fig. 2a - 2b

perspektivische Darstellungen verschiedener Ausführungsformen des Substrates der Sicherung von Fig. 1a;

Exemplary embodiments of the invention are explained in more detail below with reference to the drawings. The pictures show:

1a-1c

a plan view of a first embodiment of a fuse and two side views;

2a-2b

perspective representations of various embodiments of the substrate of the fuse of Fig. 1a;

Fig. 1a shows a plan view of a fuse 1, the one Has fuse element 2, which on a substrate 3 between two contacts 4 on opposite edges 5 of the substrate 3 runs under a cover 6 from a potting compound 7.

In a first step, the manufacture of the fuse 1 the contacts 4 on the edges 5 of the ceramic substrate 3 in the form of electrically conductive pastes 8 in a "dip & blot" process applied and baked or sintered so that then on the substrate 3 accessible from the outside, the end faces 9 partially enclosing and solderable contacts 4 arise. A solder paste 10 is then applied to the contacts 4, into which the fusible conductor 2 designed as wire 11 is pushed in. The arrangement is then heated to the extent that the solder paste 10 liquefies and the wire 11th with contacts 4 mechanically permanent and electrically good leading connects. The melting point of the solder paste lies here 10 above the melting point of SMD soldering processes, so that Fuse 1 can be used in SMD processes.

Before or after separating the wire 11 into individual Fusible conductor pieces per fuse 1 is the cover 6 Arrangement applied a pasty, curable potting compound 7, which the fusible conductor 2 between the contacts 4 gas and covers pressure-tight. The potting compound 7 is portioned for example by a dosing device, in a screen printing or stencil printing. Main characteristics of the Potting compound 7 are in addition to the paste-like shape and the hardenability also mechanical and thermal stability as well as good electrical insulation. In addition, the casting compound 7 also have a high pore content to gaseous components when the fuse is switched off and metal vapors offer a large area of precipitation can.

Through distinguishable coloring of the hardened casting compound 7 is a basic identification of the fuse for Differentiation, for example, of the tripping characteristic in "quick" or "slow" or to identify the nominal current possible during production, since the dimensioning already makes it possible here and the material selection set these properties are. A general basic identification of these components is because of their small size makes sense due to a color coding.

Fig. 1b shows a side view of the fuse 1, from a End face 9 seen here to illustrate the simple and flat construction. The fuse element 2 is on the contact 4 been electrically conductively attached by a solder paste 10. The cover 6 extends on the top of the fuse 1 almost to the edges 5.

1c shows a view of the long side of the fuse 1 from FIG Fig. 1a. The distance between the contacts 4 is that Hole or pad distance according to the voltage level of the fuse IEC standard was chosen. So that distance turn out very small.

The distance of the fusible conductor 2 from the surface is also further of the substrate 3 very low. So that runs Fusible conductor 2 at the boundary between two half-spaces, where one through the potting compound 7 and the other through the substrate 3 is formed, as can also be seen from FIG. 1b. These half-spaces are mutually different in terms of their thermal properties align as much as possible at low cost.

The measures or properties mentioned are supported by a modified from the basic form shown in Fig. 1a-1c Shape of the substrate realized, as shown in Fig. 2b - 2d are.

2a-2b show ceramic plates 12 with a progressive Number of design measures, their advantages be described using this selection of sketches. The different shapes of the substrates 3 result from a progressive realization of further creative Activities:

The elongated recess 14 or depression 15 in the central surface 16 of the plate 12 of FIG. 2a serves to improve the thermal decoupling of the fusible conductor, since the fusible conductor is embedded in the casting compound over its free length.
The tapering or flattening 17 shown in an enlarged representation in FIG. 2b at the end of the substrate 3 or at the edges 5 fulfills the task of not allowing the edge metallizations of the contacts 4 to protrude, ie the fuse lies only with the middle part 18 of the ceramic substrate 3.

Claims (11)

1. An electrical fuse (1) including a substrate (3) of an electrically insulating material, at least two electrical contacts (4), which are arranged at a distance from one another on the substrate (3), and a fusible conductor (2), which electrically conductively connects the contacts (4) and is at least partially embedded between the contacts (4) in an electrically insulating encapsulating composition (7), a recess (15) being disposed in the substrate (3) between the contacts (4), characterised in that the fusible conductor (2) is arranged between the contacts above the recess (15) without contacting the substrate (3), which permits the fusible conductor to be completely surrounded by encapsulating composition in the vicinity of the recess.
2. A fuse as claimed in Claim 1, characterised in that the substrate (3) is a small rectangular plate (12).
3. A fuse as claimed in one or both of the preceding claims, characterised in that the substrate (3) consists of a ceramic material.
4. A fuse as claimed in one or more of the preceding claims, characterised in that the encapsulating composition (7) consists of a settable paste, which adheres to the substrate after the setting process.
5. A fuse as claimed in one or more of the preceding claims, characterised in that the encapsulating composition is porous.
6. A fuse as claimed in one or more of the preceding claims, characterised in that the encapsulating composition (7) is thermally stable.
7. A fuse as claimed in one or more of the preceding claims, characterised in that the contacts (4) are constituted by metallizing opposing edges (5) and/or end faces (9) of the substrate (3).
8. A fuse as claimed in one or more of the preceding claims, characterised in that the contacts (4) are produced by bakable pastes (8).
9. A fuse as claimed in one or more of the preceding claims, characterised in that the fusible conductor (2) is in the form of a wire (11).
10. A fuse as claimed in one or more of the preceding claims, characterised in that the substrate (3) is rounded at the edges (5) or end faces (9) to be metallized.
11. A fuse as claimed in one or more of the preceding claims, characterised in that the substrate (3) has chamfers or bevels (17) at the edges (5) or end faces (9) to be metallized.

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