FR2494900A1 - FUSE - Google Patents

Abstract

FUSE CONSTITUTED BY A FUSE CONDUCTOR WITH A SHRINKAGE FORMING A FUSION PLACE AND DEPOSITED ON A BASE. IN THE FUSE ACCORDING TO THE INVENTION, THE FUSION PLACE 3 IS COVERED IN ALL OR PART WITH A LAYER OF A MATERIAL SUITABLE TO COMBINE, FOR EXAMPLE AN ALLOY OF TIN AND LEAD. THIS FUSE IS USED, DEPENDING ON ITS EMBODIMENT, TO OBTAIN A FUSION CHARACTERISTIC VARIING FROM SLOW TO ULTRA-FAST.

Description

The present invention relates to a fuse which is constituted by a base

on which is applied a

  fusible conductor, the latter having a narrowing

  to define the place of fusion.

  Fuses of this type have long been known

  in different embodiments (for example,

  German worm DE-OS 1588333); their common point is to have each an ultrafast fusion feature which can be slightly influenced by a change in the shape of the melting site. The fuse conductor used is either silver or a metal or a low-melting point alloy (German patent DE-PS 744 200). Use

  silk screen printing is known for the application of

  based on the money used as a driver

fuse.

  The methods for modifying an ultrafast fusion characteristic by means of a change in the geometrical shape of the melting point are very limited in number,

  we can not even achieve by this means a characteristic

  only fast melting tick. For this reason, the domain

  Fuses of this type are very restricted.

  The object of the invention is therefore to improve

  a fuse of this type in such a way that it has a

domain: ie-extended application.

  To achieve this object, it is proposed to cover

  all or part of the melting point of a layer of a

able to be allied.

  With the present invention, the corresponding fuse can be imparted with a melt characteristic that varies in the ultrafast to slow range. For this adaptation, it is mainly the characteristic

  of allied material which is decisive, but

  it can be considered as a fundamental rule that the fuse is slower

  the outer layer is easy to combine or the temperature

  overall melting resulting from the alloy is lower; in addition a particularly superficial layer

  thick, because of its relatively large mass,

aunt to a slow break.

  The speed - or slowness - of melting a fuse is assessed by measuring the melting time of the melting point for a determined overcurrent. Unified by the corresponding standards, the melting time is used each time to assess the melting characteristic which is obtained for an overcurrent equal to ten times the nominal current. It is therefore necessary to pay attention to an alloy fuse, to the reduction of the nominal current caused by this alloy, which also entails a reduction of the theoretical test current with a view to

  determination of the standardized melting time. As a result

  As a matter of fact, the fuses according to the invention, with their surface layer in a material capable of being allied, have always, at the standardized point (fixed by the standards) a greater

  inertia that even fuses form under layer super

  ficial. The fuse according to the invention obviously also reacts below and above an overcurrent equal to ten times the nominal current, as long as this nominal current is exceeded significantly. In cases of solicitations not covered by standardization, one can obtain with

  the fuse according to the invention of the fuse

  which depend on the value of the overcurrents. For example, if only half of the melting site is covered over its entire width with a surface layer, relatively high inertia is observed for small overcurrents, while a melting characteristic is observed.

  fast is predominant for very high intensities.

  With the help of the alloying material, its thickness and

  degree of recovery, one can choose an extra number

  ordinary fusion characteristics for the various circuit breakage problems, so that the fuse

  according to the invention can also be used where the characteristics

  slow, moderately slow or slow fusion characteristics

are necessary.

  The covering of the melting site by the surface layer does not always have to be performed, for example, over the entire width; we can also realize

  recovery models for which oFi leaves

  sister an uncovered path in the vicinity of the place of

  fusion. This can be achieved by a recovery

  in the form of lots, consisting of

  with the help of the superficial layer or by covering half of the surface of the melting site, for example half of its length. This guy

  can be further modified by provoking, when reacting

  fuse, by spreading due to the heating of the alloying material and again before the complete melting, a recovery of the entire width of the place of

  merging or leaving an uncovered path.

  Regardless of the recovery model, the application

  of the superficial layer able to be allied can be

  silk screen printing, but it can also be applied to

roll or by another method.

  For example, Sn Pb (tin-lead) alloy has proved to be a particularly easy material to combine for the surface layer, but pure tin or

  other materials used in the art of

  hard tender are just as good. With the lowering

  the melting point of the alloy material, which conducts during alloying with the fuse conductor to a corresponding decrease in its melting temperature at the moment of the alloy, the inertia of the fuse increases

  as well as the thickness of the surface layer

  the same as that of the fuse conductor intervene as other parameters. The more these two layers are thick, the greater the mass of material to be melted, and the more the melting characteristic of the corresponding fuse becomes slow. For the variation of the thickness of the layer and that of the fusible conductor,

  a range of between 0.2 and 100 nm is available.

  After the completion of a fuse according to the invention,

  it can happen - after a period of time

  strongly long - that constituent elements of the alloy form prematurely, even without reaction of the fuse, a

  alloy with the fusible conductor, following a phenomenon

  leads diffusion. It has already been observed that, under the abovementioned conditions, the tin of a tin-lead alloy penetrates by diffusion into the upper layers of the tin.

  conductive fuse in silver. This phenomenon can occur

  in use and also during storage without passing a current. To eliminate such a phenomenon, which may also be called "aging" it has been provided, in an improvement of the invention, to interpose between

  the fusible conductor and the surface layer a pel-

  in a fusible material, not conducting electrical

tricity.

  Experience has shown that this film constitutes

  killed for example by a commercial solder polish, background

  under the action of the temperature rise when the fu-

  sible reacts and that immediately after contacting the material suitable for alloying heated with the fuse conductor takes place. In this way and until this

  instant contact between the two layers and

  aging is prevented - which does not alter

  not the operating characteristic. When using

  of a film of well-defined melting point, for example a wax-based varnish, the resistance to aging persists until a charging regime

  lead to a warm-up as the film melts.

  The invention will be described in more detail with reference to the accompanying drawing by way of non-limiting example and in which: FIG. 1 is a plan view of a first embodiment of the fuse according to the invention, with the place

melting completely covered.

  FIG. 2 is a plan view of a second example

  with the half-covered melting point.

  Figure 3 is a plan view of a third

2494900

  embodiment with the melting point covered

in its middle on all its width.

  FIGS. 4A and 4B are plan views of other exemplary embodiments with an overlap of the melting point leaving an uncovered path.

  The examples of realization represented on the

  FIGS. 1 to 4B of the fuse according to the invention comprise all,

  as a support, a base 1 on which is applied

  a layer 2 of fusible conductor. The base may consist of a ceramic AlA 2 O 3 (alumina) under a commercial thickness of 0.63 mm and the layer 2 of silver fusible conductor. This layer can be applied to the base 1 by gluing a sheet; however, an application by screen printing followed by a firing of the layer 2 of fusible conductor on the

  base 1 is more economical. The width of the fused conductor

  ble 2 is decreased in the vicinity of the medium to form a melting point 3, thereby increasing the resistance

  per unit length of the fusible conductor strip.

  In the vicinity of this melting point 3, the covering of said conductor is made wholly or partly by means of a

  superficial layer 4 able to combine.

  In the exemplary embodiment represented on the

  1, the surface layer 4 covers the entire melting point 3. This type of fuse has substantially

  the same fusion characteristic for all surin-

  Tensities, speed or inertia depending first of all on the choice of the alloy of the superficial layer. More

  the alloy is easy and the more the melting point of the

  bonding is low, the longer the fuse cut is slow.

  For example, if a silver layer of 25 Am thick

  However, with the geometric shape shown in FIG. 1 is "printed" on a ceramic base of Al 2 O 3 and if no surface layer 4 is used, a melt duration of 0.2 ms is observed at the standard point. only for an overcurrent of 31.5 A. If the same layer of silver

  is covered with a surface layer of 0.1 mm

  thickness of Sn / Pb 40/60 alloy having a melting point of 183 ° C., the alloy formation is initiated very early because of the relatively low melting point of this superficial layer so that the whole of the alloy form

  from the surface layer and the layer of ar-

  gent has a melting point lower than that of the pure silver layer .. This allied set produces very quickly

  at a lower nominal current - it is a question of

  decrease in the rated current - so that in accordance with the definition of the standardized

  theoretical test current equal to ten times the rated current

  nal also decreases. Because of this, less energy is available for melting the fuse section, so that the melting time is prolonged. In the present case,

  it is 300 ms for an overcurrent of 25 A, however

  As compared with the previously described example of a fuse with a pure silver layer, the prolongation of the melting time also results from the increase in the mass of material to be melted, resulting from the presence of the

  superficial layer. A reduction in the amount of

  therefore leads to a shorter duration of merger

  than 300 ms, all other conditions being unchanged.

  elderly. Another reduction in the melting time is obtained if instead of the Sn / Pb 40/60 soft solder, for example pure tin, which is used at 23 ° C., is used. No

  only the temperature of fusion of

  overall bonding produces, but also! 2aptitude to the alloy

  tin is less, so that the formation of the

  binding is slowed down and has not progressed as much

  Until the merger. If the tin is deposited under a thick

  0.1 mm equal to that of the Sn / Pb 40/60 soft solder layer of the preceding example, the melting time is 10 ms for a theoretical test current of 28 A. In the example embodiment of Figure 2, only half of the melting site 3 is covered by the surface layer 4. The melting site 3 is covered over its entire width within this half. This type of fuse has a fusing characteristic that depends

  the value of the overcurrent. For the weak surin-

  tensities, a greater inertia is observed than for very strong overcurrents. This is because, for very strong currents, the free part of melting point 3 already reacts before appreciable alloying, and thus a perceptible decrease in nominal current occurs. For a covering according to FIG. 3 with the aid of the superficial layer 4 able to join together, we obtain

  a merging characteristic very close to a characteristic

  fast, therefore included between fast and fast / slow. The nominal current decrease that can be obtained with this embodiment can not, in

  under the small surface covered, to be very small

  tite, which manifests itself correspondingly in the

fusion characteristic.

  For all the examples of realization mentioned previously

  surface layer 4 covers each time

  entire width of the place of fusion 3, even if, in

  lengthwise, only part of the

  said place is covered. Unlike what pre-

  In FIGS. 4A and 4B there is shown an island-shaped overlap consisting of surface elements and closed elements, with the result that an uncovered path remains for the current, adjacent to these elements.

of surface.

  For a definitive determination of the characteris-

  In the case of smelting, the dimensions of the elementary domains 5 and 5t are used and also, indirectly, the thickness of the layer. During a reaction of the fuse, the heating of the alloying material leads more precisely to a spreading of the surface elements 5 and 5 ', of smaller dimensions at the beginning, so that according to the distance chosen beforehand the elements that have spread out come in contact or not. For the exemplary embodiment shown in FIG. 4A, the thickness of the layer, the dimensions of the surface elements 5 as well as their distances are chosen from such

  that, even in the case of a reaction, no

  merge of elementary domains-does not occur. The melting point 3 is not completely covered, either

  no time, in the sense of the width. According to the

  constancy we are with this fuse in the presence of a

  fusion feature that is close to being ultrafast.

  The fusing characteristic of the fuse according to the

  4B is a little slower because in this case the elementary domains 5 'of the alloying material are larger overall and furthermore the confusion during the reaction of the fuse is

  desired. In this way, the current paths are not

  covered originally existing between the elements of

  face 51 are closed so that it also occurs in

  these elements an alloy, even if it starts later.

  For all the examples of realization one can inter-

  wedge between the fusible conductor 2 and the superficial layer

  4 a film 6 electrically non-conductive (Figure 1, below the raised portion of the surface layer 4) for the purpose of separation which can be

  necessary to prevent the aging of two

  2 and 4 from each other. This operation may be necessary especially for superficial layers

which are easily combined.

  The surface layer can be applied at a thickness of 0.2 to 10 μm. Because of the setting up

  of the melting point of the material of the outer layer

  In this case, its thickness can be varied to determine the characteristic of the fuse. For example for a ceramic base of A1203 and a silver fuse conductor of

  Am thick, we obtain for example a characteristic

  very fast melting point if the surface layer is pure tin applied to a thickness of 30 WlM, and on the other hand a slow melting characteristic if the surface layer consists of a 40/60 Sn / Pb weld applied at a thickness of 100 Mm, if it is admitted that between the silver layer and the surface layer considered a -derder varnish is interposed as separating film.

  By reiterating the examples of realization, we recon-

  only the fuse according to the invention, and its

  can take many forms and can be

  perform almost every fusion characteristic, followed by

  the needs, by the combination of several

meters.

  It goes without saying that the present invention has not been described.

  that as indicative and not limiting and that it is susceptible of various variants without going beyond its framework,

Claims (7)

  1 - Fuse, consisting of a base and a conductor   fuse applied thereto, having a narrowing   conduct of the conductor for the formation of the melting point, characterized in that said melting point (3) is covered wholly or partly with a layer (4) of a material fit to ally.   2 - Fuse according to claim 1, characterized in that the surface layer 54) is constituted by   SnPb alloy (lead and tin).   3 - Fuse according to one of claims 1 and 2,   characterized in that a film of fused material   non-electrically conductive is interposed between   the fuse conductor (2) and the surface layer (4).   4l - Fuse according to one of claims 1 to 3,   characterized in that the thicknesses of the fuse conductor layer (2) and the surface layer (4) are each from 30 to 40 Hem.   Fuse according to one of Claims 1 to 4,   characterized in that the melting point (3) is covered   over half of its total width by the super-layer (4).   6 - Fuse according to one of claims 1 to 4,   characterized in that about one third of the center of the fusilli   ble (3) is covered over its entire width by the layer. superficial (4).   7 - Fuse according to one of claims 1 to 4,   characterized in that the melting site (3) is covered by closed surface elements forming batches (5, 5t) of the surface layer while leaving a uncovered path.   8 - Fuse according to claim 7, characterized in   the surface elements (5, 5 ') of the superimposed layer are shaped like circles.   9 - Fuse according to one of claims 7 and 8,   characterized in that the distance between the surface elements (5) is sufficiently small so that, in the case of a complete melting at the melting point (3), the elementary domains become confused by of warming.   - Fuse according to one of claims 7 and 8,   characterized in that the distance between the surface elements (51) is chosen so large that,   in the case of a merger of the place of merger (3), the   surface elements (5 ') remain separated from each other   despite the warm-up and some staggering.