DE8908139U1 - Fuse element in thick-film technology components - Google Patents

Description

DiPL-iNQ. BERNHARD RICHTER ^: · ^: : '·'..·*;;-*85oo Nuremberg «ad«, BeethmcretraSe »

PATENT ATTORNEY &tgr;**»*^»«»«»

Telegram: Pjlri Representative at the European Patent Office Telex: 623S4epatiid

European Patent Attorney ^T ' ^w « ^: « "»« ««" ^(C *" ⁺ '"" ^hou ™'

Company SIEGERT GMBH 04.07.1989

Ostlandstrasse 31, 8501 Cadolzburg R/sa

"Security element in components of D'ekcüMchtteehnik"

The invention relates to a fuse element according to the preamble of claim 1. These fuse elements, which function like a fuse, have previously been formed by correspondingly narrow conductor tracks. The main disadvantage of these known fuse elements was that relatively high currents were required to melt these conductor tracks serving as a fuse element, which therefore represented a correspondingly high heat load for the fuse element and the components surrounding this element.

The object of the invention is to create a fuse element for low currents which has a short reaction time and does not significantly influence the environment in terms of heat.

The solution to this problem is initially seen in the features of claim 1. This avoids the disadvantages explained. With the resistors specified in claim 1 even at relatively small temperature increases

the effect that the metal oxides are destroyed at the transitions at their grain boundaries. This prevents the conduction mechanism. The resistance value becomes extraordinarily high (a few 10 kOhms). so that the residual chromium that still flows can be neglected. The temperatures that arise are relatively low, since the currents flowing are very low and therefore the square of the current flowing, which causes heating, and above all the destruction at the grain boundaries, occurs even at relatively low temperature increases. The higher melting temperatures of the known resistors in the form of conductor tracks do not therefore have to be reached. A resistor according to the invention can be applied using screen printing technology. This results in a very high degree of rationalization in the case of production as an (SMD) chip resistor. Several hundred security elements can be manufactured together on a panel substrate (reference is made to claim 9). Furthermore, such security elements can be applied directly to the substrate of a thick-film hybrid circuit using screen printing (see claim 8). This has the advantage of not having to provide and equip an additional component. Such a hybrid circuit can also be manufactured in a panel, which results in a further rationalization effect. The overlaps of the edge areas of the resistor with the conductor tracks can be produced very simply and efficiently. In addition, this ensures perfect contact between the resistor and the conductor tracks.

The features of claims 2 and 3 are also a preferred embodiment of the invention, since the majority of the heat generated in the resistor remains there. This results in a very rapid, thermally largely instantaneous destruction of the transitions at the grain boundaries of the resistor under a corresponding current load.

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Further advantages and features of the invention can be found in the further subclaims, as well as the following description and the associated drawing of embodiments according to the invention. The schematic drawing shows:

Fig. 1: a plan view of a first embodiment.

Fig. 2: a section along the line H-II in Fig. 1 ,

Fig. 3: another embodiment of the

Invention in plan view.

In the example of Fig. 1 and 2, a fuse element is shown as a discrete component in the form of a chip resistor according to the invention. In this example, a poorly heat-conducting layer, i.e. a layer 2 with low thermal conductivity, is applied to a substrate (carrier) 1. The conductor tracks 3, 4 are printed on this layer 2. A printed resistor 5 is also applied, which overlaps the conductor tracks 3, 4 with its two edge areas 5', i.e. is thereby electrically conductively and mechanically firmly connected to the conductor tracks. The conductor tracks 3, 4 and the resistor 5 can be applied using a screen printing process.

The poorly heat-conducting layer 2 can be a corresponding dielectric paste. However, one can also proceed in such a way that

2&sfgr; the conductor tracks and the resistor are printed directly onto the substrate and this is made from a material with poor thermal conductivity, such as a ceramic with poor thermal conductivity, e.g. a low-temperature ceramic. This also ensures that the grain boundary transitions of the resistor are destroyed as quickly as possible

3Q 5 is achieved with corresponding current load.

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Preferred embodiments of the invention are resistance values that are less than 10 kOhm before overload, i.e. before burnout, but after burnout have a resistance value that is greater than 100 kOhm.

The materials for the conductor tracks and the resistors connected to them are known from thick-film technology as conductor track pastes and resistor pastes.

To increase the resistance value and to make the described sudden switch-off effect of the resistor even faster, a geometric narrowing of the resistor can be provided. For this purpose, Fig. 3 shows on a substrate 1, possibly with the above-mentioned layer 2 interposed, the conductor tracks 3, 4, as well as a resistor 5 with a narrowing 7, which in this example is formed by two opposing cuts 8 in the resistor material. The aforementioned narrowing can be created using a screen printing process, or by removing material, such as sandblasting or laser processing.

The following are the data of an embodiment of a security element according to claims 5 and 7:

R = 5 Ghm R after overload ^ 100 kOhm Nominal current 125 mA

Tripping current > 500 mA
Switch-off time < 500 msec.

This safety element has the following
mechanical dimensions (active resistance area):

Length (from electrode to electrode): 0.6 mm

Width: 0.8mm

Necking by laser cutting to: 0.1 mm (narrowing of the width)

Fig. 3 also shows that a resistance element according to the invention can also be provided on a larger substrate that carries a thick-film hybrid circuit. A part of this is shown only schematically, in block form.
9 indicated.

All features shown and their combinations with one another are essential to the invention, unless they are expressly designated as known.

- Expectations -

Claims (7)

&bull; I > BERNHARD RiGHTCR '.." , ·.,'','/> esoo nurnberq &igr;&ogr;, the r» α &tgr;&ggr; «. &igr;-&idiagr;- a ». I ₁ . / α &igr;-&tgr; BttlhovcnitraOt IO PATENT ATTORNEY nuto« <.*,n,. mm 595015 Responsible Representative at the European Patent Office _ _ß &ldquor; Si^ ₁ J European Patent Attorney Company SIEGERT GmbH 04.07.1969 Dstlandstr. 31, 0501 Cadolzburg R~gi S chut &zgr;&eegr;&eegr; s &rgr; r &Ggr;&igr; ch &eegr; : 1. Fuse element as a component in thick-layer technology with conductor track structures printed preferably by screen printing on a carrier [substrate), characterized in that a resistor (5, 6) made of metal oxides bound in glass frit, printed on the carrier or substrate (1) or an intermediate layer (2), serves as the fuse element, which is in electrical contact with at least two conductor tracks (3, 4), the resistor (5, 6) overlapping (5 ¹ ) with the conductor tracks (3, 4). 2. Fuse element according to claim 1, characterized in that the carrier or the substrate (1) consists of a material with low thermal conductivity. 3. A security element according to claim 1 or 2, characterized in that a layer (2) made of a material with low thermal conductivity is applied to the carrier or substrate M), 4. Safety element according to one of claims 1 to 3, characterized in that the resistor (6) in its &bull;^ ⁰ course has a point (7) of small cross-section. 5. Safety element according to claim 4, characterized in that one or two inputs (ε, ν, γ) are provided in the resistor (6), which form and limit the constriction (7). 6. Fuse element according to one of claims 1 to 5, characterized in that it is an integrated element of a printed circuit. 7. Fuse element according to one of claims 1 to 5, characterized in that it is designed as a discrete component, e.g. in the form of a chip resistor.