EP0578134A2 - Method of manufacturing electrical fuses and fuses which are manufactured according to this method - Google Patents

Abstract

An electrical thick-film fuse 10 and a method for producing such a fuse are described. In this case, a conductive paste is printed onto a substrate 12 in order to produce a resistance film (layer) 24. However, a dielectric film 22 is expediently deposited onto this substrate first, in the manner of a pedestal, onto which the resistance film 24 is subsequently deposited such that it overlaps. Two electrodes 14, 16, which are at a distance d from one another, are deposited onto this resistance film 24, between which electrodes 14, 16 a web of the resistance film 24 is left, which forms a thick-film fuse element (melting conductor). The width of the web is set by means of lasers. <IMAGE>

Description

The invention relates to a method for producing electrical thick-film fuses, each with a thick-film fusible conductor arranged between two electrodes, which is applied together with the electrodes to a substrate. The invention further relates to a thick film fuse produced by such a method.

Thick-layer fuses differ from conventional wire fuses primarily in that the wire-shaped fuse element is replaced by a thick-layer fuse element. The way such a fuse continues to function is to provide galvanic isolation in the event of a short circuit or defined overcurrent loads.

The problem with the manufacture of such thick-film safeguards is first of all adhering to the tolerances specified with regard to the safety characteristics, which complicates the fact that the actual safety behavior can only be checked directly on a respective thick-film safeguard if its destruction is accepted. In addition, the securing characteristics achieved in each case depend to a large extent, in particular, on the layer thickness scatter and the scatter occurring with regard to the width of the thick-film fuse element. Compliance with reproducible security characteristics is therefore no longer particularly easy, especially when smaller security structures are to be implemented.

The aim of the invention is to provide a further method of the type mentioned at the outset, by means of which, in particular, predefinable security characteristics such as e.g. the current / time behavior can be implemented in a simple and reproducible manner within the narrowest possible tolerance range. Furthermore, a thick-film fuse that can be produced in this way and has correspondingly predefinable characteristics is to be created.

The object is achieved in the method according to the invention in that a resistance layer is produced on the substrate by printing a conductive paste, that the two electrodes are preferably applied to the resistance layer at a distance from one another, and that the width measured transversely to the distance between the electrodes is one between the Electrodes left, the web of the resistance layer forming the thick-film fusible conductor is set by laser, a dielectric layer preferably being applied to the substrate first in the manner of a platform, and then the resistance layer overlapping the dielectric platform is produced.

After the web width has been set by lasering, the respective securing characteristics can be reproduced very precisely, even for relatively small web widths. In any case, the laser enables precise structuring or shaping of the section of the resistance layer lying between the two electrodes. Due to the dielectric intermediate layer or layers which are expediently provided between the substrate and the resistance layer, the annoying heat dissipation to the substrate is substantially reduced, and as a result of the now areal dissipation of the waste heat from the securing web for the securing characteristics, such as in particular the current / time behavior , primarily the web width is decisive is. Because of the resistance layer applied in an overlapping manner to the dielectric platform, the respective thickness fluctuations are reduced to a minimum, at least in the region of interest between the two electrodes. The fact that the electrodes are preferably applied to the resistance layer means that these electrodes have no influence whatsoever on the production of this layer, which additionally facilitates the achievement of a surface resistance that is as uniform as possible.

The resistance layer and / or the dielectric layer or dielectric layers are preferably applied using the screen printing method, the screen resting on the dielectric pedestal when the resistance layer is applied, so that practically the same balance of forces is achieved as when printing large areas in the interior thereof. After the electrodes have been subsequently applied to the resistance layer, this means that there is no interference with the doctor blade pressure.

In the simplest case, to produce the web, two laser cuts lying on a common straight line are to be carried out. However, in order to obtain a minimum amount of the web in the direction of the electrode spacing, which is not always the case with a simple laser cut, the laser in question is preferably moved over a corresponding distance in the longitudinal direction of the web and then to form a U- shaped section expediently returned parallel to the first section. Such a U-shaped laser cut can in turn be carried out on both web sides, the web length depending on the displacement of the laser in the web direction and on the laser track width.

In a particularly simple variant of the method, the web width obtained by lasering the resistance layer is set directly to a predetermined width value. Accordingly, an absolute beam positioning is provided, which can be implemented, for example, by a closed control loop to which the relevant setpoint for the web width is specified. The surface resistance of the resistance layer in the land area is assumed to be constant. This variant is particularly suitable for larger web widths that are, for example, above 80 μm.

In particular for medium web widths, such as those up to about 40 μm, the web width obtained by lasering the resistance layer is expediently adjusted via a resistance comparison of the thick-film fuse. For example, alignment lasers with direct controls for constant resistances can be used. The target value for the resistance can either be calculated in advance or determined by experiments.

In particular for smaller web widths, the web width to be set and / or the resulting target resistance of a respective thick film fuse is preferably determined as a function of the surface resistance measured for the resistance layer region between the electrodes. This can be determined during the manufacture of the securing web, for example, by measuring the resistances of the respective thick-film fuse resulting for different initial web widths and determining the surface resistance of the resistance layer area remaining between the electrodes as a function of the initial different web widths and the assigned resistance measurement values.

The thick-film fuse according to the invention, which can be produced in particular by the described method, comprises a thick-film fusible conductor arranged between two electrodes, which is applied together with the electrodes to a substrate, with at least one dielectric layer preferably being applied to the substrate, the respective top layer being built like a platform and being platform-like thereon A layer of resistance is arranged overlapping the layer, to which are assigned two electrodes spaced apart from one another, between which a web of the resistance layer forming the thick-film fusible conductor is left. The two electrodes are expediently applied to the resistance layer.

Fig. 1

eine schematische Teilschnittdarstellung des Grundaufbaus einer Dickschichtsicherung,

Fig. 2

eine schematische Draufsicht auf die in Figur 1 gezeigte Dickschichtsicherung, wobei der zwischen den beiden Elektroden vorzusehende Sicherungssteg noch nicht realisiert ist,

Fig. 3

eine schematische Draufsicht eines durch seitliche Laserschnitte erhaltenen Sicherungssteges der Widerstandsschicht,

Fig. 4

eine perspektivische Darstellung des Stegbereiches,

Fig. 5

ein Strom/Zeit-Diagramm zur Darstellung der betreffenden Sicherungscharakteristika in Abhängigkeit von der Stegbreite,

Fig. 6

eine Draufsicht auf die unsymmetrische Minimalanordnung zur Ermittlung des Flächenwiderstandes mit eingezeichnetem Laser-Verfahrweg,

Fig. 7

eine rein schematische Darstellung der Schnittlinien bzw. Laser-Verfahrwege, wie sie sich für eine R_F-Bestimmung gemäß Figur 6 sowie die darauffolgende Herstellung des Sicherungssteges gemäß Figur 3 ergeben, wobei abweichend von der Ausführungsform gemäß Fig. 6 jedoch eine symmetrische Ausführung der Schnitte gewählt wurde, und

Fig. 8

eine Draufsicht der Dickschichtsicherung entsprechend den Figuren 2 und 7, wobei durch eine entsprechende Laserstrukturierung bereits ein Sicherungssteg realisiert ist, dessen Stegbreite in Abhängigkeit von dem zuvor ermittelten Flächenwiderstand eingestellt wurde.

The invention is described below with reference to exemplary embodiments with reference to the drawing; in this shows:

Fig. 1

2 shows a schematic partial sectional view of the basic structure of a thick-film fuse,

Fig. 2

2 shows a schematic top view of the thick-film fuse shown in FIG. 1, the fuse web to be provided between the two electrodes not yet being implemented,

Fig. 3

2 shows a schematic top view of a securing web of the resistance layer obtained by lateral laser cuts,

Fig. 4

a perspective view of the web area,

Fig. 5

a current / time diagram to represent the relevant fuse characteristics as a function of the web width,

Fig. 6

1 shows a top view of the asymmetrical minimum arrangement for determining the surface resistance with the laser travel path shown,

Fig. 7

a purely schematic representation of the cutting lines or laser travel paths, as they result for an R _F determination according to FIG. 6 and the subsequent production of the securing web according to FIG. 3, but deviating from the embodiment according to FIG. 6, however, a symmetrical execution of the cuts was chosen, and

Fig. 8

2 shows a plan view of the thick-film fuse in accordance with FIGS. 2 and 7, with a securing web having already been implemented by means of a corresponding laser structuring, the web width of which was set as a function of the previously determined surface resistance.

According to the basic structure of a thick-film fuse 10 shown in FIG. 1, a dielectric layer 22 can expediently be applied to a substrate 12 in the manner of a platform. In the present case, a further underlying dielectric layer 20 is provided.

A resistance layer 24 overlapping this over a large area is arranged above the dielectric pedestal 22. On this resistance layer 24 there are two a distance d from one another having electrodes 14, 16 applied. Both electrodes 14, 16 and the adjacent area B of the resistance layer 24 (see, for example, FIGS. 2 and 8), including the resistance area located between these electrodes, lie above the dielectric pedestal 22.

When the thick-film resistor 10 is finished, a securing web 26 of the resistive layer 24, which forms the thick-film fusible conductor, is left between the two electrodes 14, 16, and thus in an area above the dielectric pedestal 22 (see, for example, FIGS. 3, 4, 7 and 8).

The securing web 26 lying between the two electrodes 14, 16 can have a length l which at least essentially corresponds to the distance d between the two electrodes 14, 16 (cf. e.g. FIGS. 3, 4). However, this web length can also be less than this electrode spacing d, as is the case, for example, in the exemplary embodiment illustrated in FIGS. 7 and 8.

To produce such an electrical thick-film fuse, first the dielectric layer 20 and then the dielectric layer 22 is applied in the manner of a platform. In principle, however, a single layer 22 of this type is also sufficient, such a layer even being completely dispensed with in the case of larger tripping currents.

The resistance layer 24, which overlaps the dielectric pedestal 22 over a large area, is then produced by printing on a conductive paste.

The two lines or electrodes 14, 16 are then applied to this resistance layer 24, the distance d being left between these two electrodes 14, 16 above the dielectric platform 22.

The two dielectric layers 20, 22 and the resistance layer 24 which overlaps them over a large area are each produced using the screen printing process.

The width b _St measured transversely to the distance between the electrodes 14, 16 (cf. FIGS. 3, 4, 7 and 8) of the web 26 of the resistance layer 24 left between the electrodes 14, 16 and forming the thick-film fusible conductor is set by lasers. In this case, the resistance layer 24 is structured in a manner to be described by means of corresponding laser cuts or cuts, which are represented by dashed lines in FIGS. 3, 6 and 7.

When performing these laser cuts, the web width b _{St can,} for example, be set directly to a predetermined width value (see, for example, FIGS. 3, 4).

However, the web width b _St obtained by lasering the resistance layer 24 can also be set by means of a resistance adjustment of the thick-film fuse.

Finally, the web width b _{St to be set} and / or the resulting target resistance R _{Z of} a respective thick-film fuse 10 can also be determined as a function of the surface resistance R _F measured for the resistance layer area between the electrodes 14, 16 (see, for example, FIGS. 6 to 8 ).

According to FIGS. 6, 7 and 8, provision is made here, for example, to measure the resistance of the thick-film fuse resulting for different initial web widths and the surface resistance of the resistance layer area remaining between the electrodes as a function of the initial resistance to determine the surface resistance to determine different web widths or the corresponding laser travel paths as well as the assigned resistance measurement values. In the exemplary embodiment shown in FIGS. 7 and 8, the webs initially generated for determining the sheet resistance have a greater length than the final web forming the thick-film fuse element.

The aligned electrodes 14, 16 have the same defined geometry, i.e. in particular, the same width and a constant distance d causing parallel edges running parallel to each other. The shape of the electrodes shown also ensures, in particular, that the most homogeneous possible electric field strength can be generated at the time of laser structuring within the area in which the securing web is to be realized.

The above-mentioned method steps of setting a constant web width by absolute positioning of the laser beam, setting a constant web resistance and setting an individual web width, which is calculated depending on the local surface resistance in the area of the securing web to be produced, can also be combined with one another. For example, it is possible to set the starting values for the two other method steps by absolute positioning of the laser beam.

In order to avoid a drop-like melting of the pastes in the web area during the laser structuring, the laser cuts are expediently divided into partial cuts, between each of which there is a waiting time and the laser is switched off.

In the case of the thick-film fuses shown, the tripping time is not dependent on the length of the web. Decisive for the fuse characteristics of interest is primarily the current / time behavior, which is primarily determined by the web width.

wobei Q_E die in die Sicherung eingespeiste elektrische Energie beschreibt, die sich in die Nutzenergie Q_N, die zum Aufheizen des Sicherungssteges bis auf die Schmelztemperatur T_S sowie das anschließende Aufschmelzen erforderlich ist, sowie die Abwärme Q_A aufteilt, die während dieser Zeit zu dem aus Keramik bestehenden Substrat 12 hin abfließt.This results, for example, from the following energy balance

${\text{Q}}_{\text{E}}{\text{= Q}}_{\text{N}}{\text{+ Q}}_{\text{A}}\text{,}$

where Q _{E describes} the electrical energy fed into the fuse, which is divided into the useful energy Q _N , which is required to heat the fuse bridge up to the melting temperature T _S and the subsequent melting, and the waste heat Q _A , which during this time flows out of the substrate 12 made of ceramic.

Below a critical tripping current I ₀ , a balance can be established between the electrical energy supplied and the thermal energy flowing away. Only at current values I> I _O is the melting temperature T _{S of} the fuse bar reached, at which the fuse bar can melt, as a result of which electrical isolation occurs.

b_St =

Stegbreite

d =

Dicke der Widerstandsschicht

A =

Materialkonstante

ρ_R =

spezifischer Widerstand

I =

Strom

B =

Materialkonstante

Für die einzustellende Stegbreite b_St ergibt sich somit die folgende Beziehung:

Im allgemeinen wird für die Dickschichtsicherung eine möglichst niederohmige Anordnung bevorzugt. Die für entsprechend kleine Auslöseströme erforderlichen kleinen Strukturen können durch entsprechende Laserschnitte relativ präzise hergestellt werden.The tripping time t results from the following relationship:

b _St =

Web width

d =

Resistance layer thickness

A =

Material constant

ρ _R =

specific resistance

I =

electricity

B =

Material constant

The following relationship thus results for the web width b _{St to} be set:

In general, a low-impedance arrangement is preferred for the thick-film protection. The small structures required for correspondingly small tripping currents can be produced relatively precisely by means of appropriate laser cuts.

The simplest possible security structure would consist of two laser cuts converging on a straight line. In order to rule out any scatter in the triggering time due to undefined web widths, however, a minimum amount of the web is expediently provided in the direction of the electrode spacing, which is achieved according to FIG. 3, for example, in that in the Y direction or in the direction of the electrode spacing the laser is preferably around the twice the laser track width is shifted. The securing web 26 is accordingly produced by U-shaped laser cuts made on both sides, the web length l being determined by the Y displacement and the laser track width. The web extension is among other things reliable galvanic isolation after melting also ensured.

In accordance with the relationship given above, the tripping time t depends on the layer thickness d and the specific paste resistance ρ _{R of} the securing web. Accordingly, these values must either be assumed to be constant or individually determined for each individual web.

wobei l und b₁ jeweils konstant ist.In the case of an individual determination of the sizes mentioned for each individual web, these can be obtained indirectly, for example, by means of a measured variable which includes both information about the layer thickness and also about the specific resistance. The surface resistance R _F , which is defined by the following relationship, is particularly suitable here:

where l and b₁ is constant.

Aufgrund dieser Beziehung ist es möglich, den Auslösestrom I_O unabhängig von jeweiligen Schwankungen des spezifischen Pastenwiderstandes ρ_R und der Schichtdicke d konstant zu halten.While the tripping time t is dependent on both the material constant A and the constant B, the tripping current I _O is dependent only on one of these two constants, namely on the constant B. This follows from the following relationship:

Because of this relationship, it is possible to keep the tripping current I _O constant regardless of any fluctuations in the specific paste resistance ρ _R and the layer thickness d.

The respective fuse characteristics and in particular the respective current / time behavior of the thick-film fuse can now be set in different ways. For example, a constant web width, a constant web resistance or a constant tripping current can be set.

In FIG. 3, the travel paths of a respective laser are shown in dashed lines, which result from an absolute beam positioning for setting a constant web width b _St. This is achieved by means of two lateral, U-shaped laser cuts, the respective laser in turn also being shifted in the Y direction in order to obtain the minimum amount of web design required for a defined web width.

In this exemplary embodiment, before the constant web width is set by a corresponding absolute beam positioning, the web width is determined once in advance. This can be done, for example, by tests or by a calculation based on a desired tripping current I _O , a surface resistance that is assumed to be constant and the constant B that is also known as known. Due to the generation of a resistance layer overlapping the dielectric pedestal, the paste surface resistance can be at least in the web region of interest R _F can easily be kept at an almost constant value.

With this setting of a constant web width by means of an absolute jet positioning, it is further assumed that the layer thickness d (cf. for example FIG. 4) does not vary either within the substrate use or within a print batch. If possible, there should be no fluctuations in paste sheet resistance R _F or pressure behavior between different print batches.

FIG. 5 shows the typical current / time behavior of the thick-film fuse as a function of the respective web width b _St , the tripping currents I _{O being} defined by the vertical sections of the various curves.

The melting time or tripping time is shown as a function of the overcurrent. The respective characteristics run in a first area with small fault currents and long melting times almost perpendicular to the current axis. In this area, even the smallest changes in current lead to a relatively large variation in the melting time. In a second area, the respective curves are strongly curved. These curves then change to a horizontal in a third area. The reason for this is, among other things, that heat dissipation to the environment can be neglected in this third area.

It can be seen from FIG. 6 how the laser has to be moved in order to determine the individual sheet resistance R _{F of} the web area for a respective thick-film protection.

Here, the laser is first moved so far that there is an initial web width b. For this initial web width b, the total resistance R 1 of the overall arrangement is measured. Then another laser cut is carried out, after which the web width b 1 is obtained, for which again the total resistance R 2 of the arrangement is measured. The track width of the laser is B _Sp .

gilt.After the first resistance measurement, the laser is shifted by the distance B₂ in the X direction. The distance from the two-sided laser travel paths provided in the longitudinal direction of the web, measured from center to center, is initially B and then B₁, wherein

$\text{B = B₁ + B₂}$

applies.

Der anfänglich erhaltene Steg mit der Breite b weist einen Stegwiderstand auf, der durch zwei zueinander parallel geschaltete Widerstände R_X1 und R_X2 dargestellt werden kann. Für den sich nach der Laserverschiebung B₂ ergebenden Steg mit der Breite b₁ ergibt sich ein Stegwiderstand R_X1, was bedeutet, daß durch diesen Hilfsschnitt der parallele Hilfswiderstand R_X2 entfernt wurde. Die Steglänge l wird hierbei konstant gehalten. Mit L ist die Verfahrstrecke des Lasers in Längsrichtung des Steges bezeichnet.Accordingly, the initial web width b can be represented as follows:

$\text{b = b₁ + b₂}$

The web with the width b initially obtained has a web resistance which can be represented by two resistors R _X1 and R _X2 connected in parallel with one another. For the resulting after the laser shift B₂ web with the width b₁ there is a web resistance R _X1 , which means that the parallel auxiliary resistance R _{X2 was} removed by this auxiliary cut. The web length l is kept constant. L is the travel distance of the laser in the longitudinal direction of the web.

R_X2 durch die folgenden Beziehungen eleminieren:

${\text{R}}_{\text{X1}}\text{= (1 + 1/t) (R₂- R₁)}$

${\text{R}}_{\text{S}}{\text{= R₂ - R}}_{\text{X1}}\text{ (V)}$

Der gesuchte Flächenwiderstand R_F für den relevanten Stegbereich der Widerstandsschicht ergibt sich demnach aus den folgenden Beziehungen:

In Abhängigkeit von den beiden gemessenen Gesamtwiderständen, den Breiten b₁, b₂ der beiden zunächst zueinander parallel liegenden Stege und der Summenbreite b läßt sich der Stegwiderstand R_X1 für den nach der Laserverschiebung B₂ erhaltenen Steg der Breite b₁ wie folgt darstellen:

Übertragen auf die Steuergrößen für die Laser-Verfahrwege bedeutet dies:

woraus folgt:

Demnach kann der Flächenwiderstand für den interessierenden Stegbereich im Verlauf der ohnehin vorzunehmenden Laserstrukturierung bestimmt werden, indem bei zwei unterschiedlichen Stegbreiten die Gesamtwiderstände gemessen werden und aus den erhaltenen Widerstandswerten sowie der betreffenden Laser-Verfahrwege der Wert des Flächenwiderstandes berechnet wird.The measured total resistances R₁, R₂ are now determined not only by the respective land resistances, but also by series resistors, which include, for example, the conductor resistances and the contact resistances in the area of the conductor connections. The serial resistor R _S , which is in series with the land resistors R _X1 , R _X2 , can be used for ${\text{R}}_{\text{X1}}\text{= t}$

Eliminate R _X2 through the following relationships:

${\text{R}}_{\text{X1}}\text{= (1 + 1 / t) (R₂- R₁)}$

${\text{R}}_{\text{S}}{\text{= R₂ - R}}_{\text{X1}}\text{(V)}$

The surface resistance R _F sought for the relevant land area of the resistance layer therefore results from the following relationships:

Depending on the two measured total resistances, the widths b₁, b₂ of the two initially parallel webs and the total width b, the web resistance R _X1 for the web of width b₁ obtained after the laser displacement B₂ can be represented as follows:

Applied to the control variables for the laser travel paths, this means:

From which follows:

Accordingly, the surface resistance for the web region of interest can be determined in the course of the laser structuring which is to be carried out anyway, by measuring the total resistances for two different web widths and calculating the value of the surface resistance from the resistance values obtained and the laser travel paths concerned.

The surface resistance, determined in particular in this way, can now be used to calculate the web width to be set and / or also to calculate a target resistance of a respective thick-film fuse that results for this web width.

For the setting of a constant web resistance, it is also important to implement a safety web that is geometrically as clearly defined as possible. Laser cuts are again preferably carried out for this purpose, as has been described, for example, in connection with FIG. 3. Here, the web length l is a predetermined size.

(I) als auch der Auslösestrom I_O bleiben somit abhängig von Schwankungen der Schichtdicke d und des spezifischen Pastenwiderstandes ρ_R. Eine Streuung dieser Größen kann jedoch durch das beschriebene Herstellungsverfahren zumindest innerhalb enger Grenzen gehalten werden.With such an adjustment to a constant resistance R, the quotient ρ _R / b _St d is kept constant, which means a constant product b _St d in particular with a constant quantity ρ _R. Both the current / time characteristic $\text{t = F}$

(I) and the tripping current I _O thus remain dependent on fluctuations in the layer thickness d and the specific paste resistance ρ _R. A spread of these quantities can, however, be kept at least within narrow limits by means of the production method described.

Instead of calculating the target resistance in advance, it can also be determined by experiment.

zugegriffen wird und im Verlauf der durchgeführten Laserstrukturierung auf die zuvor beschriebene Weise der Flächenwiderstand R_F bestimmt wird, um aus diesem wiederum einen Zielwiderstand R_z für den endgültigen Abgleich zu berechnen.In the exemplary embodiment shown in FIGS. 7 and 8, an adjustment is made to a constant tripping current I ₀ , with reference to the relationship

is accessed and in the course of the laser structuring carried out in the manner described above, the surface resistance R _{F is} determined in order to in turn calculate a target resistance R _z for the final adjustment.

Accordingly, an individual sheet resistance R _F assigned to the respective thick-film fuse is first determined, from which an individual web width b _{St is} calculated based on the specification of a constant tripping current I _O. The value for the individual web width is then converted into an individual target value R _z for the resistance adjustment to be effected by lasers.

individuell für jeden Steg bestimmt werden.In order to be able to determine the target value R _z exactly, the parasitic serial lead and contact transition resistances must in turn be known exactly. In order to be able to take these lead and contact transition resistances into account accordingly, two additional laser cuts are carried out, as already described in connection with FIG. 6 has been. From the total resistances R 1, R 2 measured for the two different web widths, both the serial resistance R _S determined by the supply and contact contact resistances and the sheet resistance can then be determined ${\text{R}}_{\text{F}}{\text{= ρ}}_{\text{R}}\text{/ d}$

can be determined individually for each bar.

The web length l is expediently predetermined by the layout of the interconnect connection.

First, a first laser cut S1 is carried out on both sides of the web to be produced, which leads to an initial web width corresponding to the width of the electrodes 14, 16. For this initial web width, there is a distance B, measured from center to center, of the respective laser travel paths S1. For the initial web obtained in this way, the total resistance R 1 is measured.

Then a second laser cut S2 is carried out from one or both sides of the web, which leads to a narrowing of the web by B₂ and, like the first cut S1, has a U-shaped course. For both cuts S1 and S2, there is a web length l which is approximately equal to the distance between the two electrodes 14, 16. For the web now obtained, for which there is a measured distance B₁ of the two laser travel paths S2 from center to center, the total resistance R₂ of the arrangement is again measured.

mit

mit K: Geometriefaktor (Stromdichteverteilung)
Anschließend wird beispielsweise auf der linken Seite des herzustellenden Steges 26 ein weiterer Laserschnitt S3.1 hergestellt, der bereits die endgültige Steglänge l_St festlegt, die kleiner als die Länge l gleich dem Abstand zwischen den beiden Elektroden 14, 16 sein kann. Mit diesem auf der linken Seite durchgeführten Laserschnitt S 3.1 kann vorzugsweise eine im voraus bestimmte Stegbreite eingestellt werden.Starting from the two measured total resistance values, the serial resistance R _S determined by the supply and contact transition resistances can then be determined on the basis of the relationships V. Furthermore, the individual sheet resistance R _F can be determined from the relationship X. Then the individual Web width b _St determines from which the target resistance R _{Z in question} can be calculated using the following relationship:

${\text{R}}_{\text{Z.}}{\text{= R}}_{\text{S}}{\text{+ R}}_{\text{W}}{\text{+ R}}_{\text{St}}\text{(XII)}$

With

with K: geometry factor (current density distribution)
A further laser cut S3.1 is then produced, for example, on the left side of the web 26 to be produced, which laser laser already defines the final web length I _St , which can be smaller than the length I equal to the distance between the two electrodes 14, 16. With this laser cut S 3.1 carried out on the left side, a web width determined in advance can preferably be set.

A further laser cut S 3.2 is then produced on the right side of the web while maintaining the same web length I _St , which is carried out on the basis of a comparison with the target resistance R _Z.

The conductive paste used to produce the resistance layer can be a resistance paste or a conductor paste.

In all versions, the thick-film protection can then be provided with a cover.

A fuse element with an irreversible fuse function that can be produced using thick-film technology is thus created, which can be inexpensively produced in miniature form without sacrificing the respective fuse characteristics, can be integrated in thick-film hybrids and can be implemented as a chip component. The respective tripping current can be set with a high degree of accuracy. Due to the special basic structure, layer thickness scatter is reduced to a minimum. Due to the laser structuring, even extremely narrow webs can be produced with a high degree of accuracy, so that, in particular, even smaller resistance values of the fuses can be achieved with a uniform layer thickness.

Claims (12)

Method for producing electrical thick-film fuses, each with a thick-film fusible conductor arranged between two electrodes, which is applied together with the electrodes to a substrate,
characterized by
that a resistive layer is produced on the substrate by printing a conductive paste, that the two electrodes are preferably applied to the resistive layer at a distance from one another, and that the width, measured transversely to the spacing of the electrodes, of a web of the resistive layer which forms between the electrodes and forms the thick-film fusible conductor is adjusted by lasers. Method according to claim 1,
characterized by
that a dielectric layer is first applied to the substrate in the manner of a pedestal, and that the resistance layer overlapping the dielectric pedestal is then produced. The method of claim 1 or 2,
characterized by
that the resistance layer is applied by screen printing. Method according to one of the preceding claims,
characterized by
that the dielectric layer or the dielectric layers are applied by screen printing. Method according to one of the preceding claims,
characterized by
that the resistance layer is structured accordingly by laser cuts to produce the web. Method according to one of the preceding claims,
characterized by
that the web length is selected at least substantially equal to the electrode spacing. Method according to one of the preceding claims,
characterized by
that the land width obtained by lasering the resistance layer is immediately set to a predetermined width value. Method according to one of the preceding claims,
characterized by
that the adjustment of the web width obtained by lasering the resistance layer takes place via a resistance adjustment of the thick-film fuse. Method according to one of the preceding claims,
characterized by
that the web width to be set and / or the resulting target resistance of a respective thick film fuse is determined as a function of the surface resistance calculated for the resistance layer region between the electrodes. Method according to claim 9,
characterized by
that to determine the sheet resistance, the resistances of a respective thick-film fuse that result for different initial web widths are measured, and that the sheet resistance of the resistance layer area remaining between the electrodes is determined as a function of the initial different web widths and the assigned resistance measurement values. A method according to claim 10,
characterized by
that the width of the rectangular web is first set by lasering the resistance layer in accordance with the width of the electrodes, which preferably have the same geometric shape. Thick film fuse with a thick film fusible conductor (26) arranged between two electrodes (14, 16), which is applied together with the electrodes (14, 16) on a substrate (12),
characterized by
that at least one dielectric layer (20, 22) is preferably applied to the substrate (12), the respective top layer is built up in a platform-like manner and a resistance layer (24) is arranged overlapping on this platform-like layer, which has two electrodes (d) spaced from one another ( 14, 16) are assigned, between which a web (26) of the resistance layer (24) forming the thick-film fusible conductor is left.

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