EP1766648B1 - Safety fuse for a chip - Google Patents

Abstract

To produce a cost-effective fuse in chip design, which is applied to a carrier substrate made of a Al2O3 ceramic having a high thermal conductivity, and which is provided with a fusible metallic conductor and a cover layer, in which the melting point of the metallic conductor may be defined reliably, it is suggested that an intermediate layer having low thermal conductivity be positioned between the carrier substrate and the metallic conductor, the intermediate layer being formed by a low-melting-point inorganic glass paste applied in the screen-printing method or an organic intermediate layer applied in island printing. Furthermore, a method for manufacturing the fuse is specified.

Description

Technical area

The invention relates to a fuse in chip design, which is applied to a carrier substrate made of an Al ₂ O ₃ ceramic, with a fusible metallic conductor, which is applied and structured by thin-film technology and which is provided with a cover layer, and an inexpensive method for production the chip backup.

State of the art

Chip fuses are formed on a ceramic base material by means of methods known to those skilled in the art, for example photolithography. Other support materials, such as FR-4-epoxy or polyimide are known. Chip fuses are typically designed for a voltage of up to 63V.

In order to avoid damage to other electronic components by a disturbance in the electrical power supply, which causes an overvoltage or excessive current flow, it is known to provide a fuse in the power supply. The fuse consists essentially of a carrier material and a metallic conductor, which consists for example of copper, aluminum or silver. The geometry and cross section of the conductor determines the maximum possible current that can flow through this conductor without melting it. If this value is exceeded, the electrical conductor is melted due to the heat generated in it by its electrical resistance and thus The power supply is interrupted before downstream electronic components are overloaded or damaged.

In the methods for the production of chip fuses in thick film technology, in which the fuses and contact layers are applied as pastes by screen printing on a substrate substrate with low thermal conductivity sufficient precision of the geometry of the fusible element layers by the screen printing process due to the process only insufficiently feasible. For higher-quality thick-film fuses, it is therefore necessary to process the fusible element or the fusible metallic conductor by additional laser cutting methods.

Conventionally, the substrate underlays used are all-ceramic glazed ceramic substrates with a high Al ₂ O ₃ antinucleate or low-aluminum oxide ceramic substrates with a low thermal conductivity. Both types of substrate are compared to conventional ceramic substrates, eg. B. from 96% Al ₂ O ₃ in thick film quality, which are used in the manufacture of passive components, considerably more expensive.

In a method for producing a fuse in thin-film technology, a fusible metallic conductor is applied by electrochemical methods or by sputtering. A particularly high precision of the turn-off or melting characteristic is achieved by photolithographic structuring of sputtered layers, wherein a low aluminum oxide substrate with low thermal conductivity serves as a base.

The JP 20031173728 A discloses a manufacturing method for a chip fuse in thin-film technology, wherein a fuse 14 and a cover layer 15 are arranged on a substrate 11. The fuse 14 is patterned by photolithography. The substrate 11 has a low thermal conductivity, in order not to dissipate the heat caused by the electric conductor 14 current in the electrical conductor 14 and thereby promote a melting of the electrical conductor 14. The electrical conductor 14 is in direct contact with the substrate 11.

The JP 2002/140975 A describes a fuse with a metallic conductor 14 made of silver, which is also disposed directly on a substrate 11 with low thermal conductivity, wherein the metallic conductor 14 is electrodeposited or formed as a thick film.

The JP 2003/151425 A discloses a fuse with a glass-ceramic substrate 11 having a low thermal conductivity and a metallic conductor 14 in thick-film technology.

The JP 2002/279883 A also describes a fuse for a chip, in which the fusible region 17 of a conductor 15 is produced by a complex laser processing. This requires additional time and cost intensive processing steps.

The JP 20031234057 A discloses a fuse resistor having a resistor 30 on a substrate 10, wherein between the resistor 30 and the substrate 10, a further heat-storing layer 42 is provided to store the heat generated in the resistor 30 heat. The fusible region is also produced by laser processing.

The JP 08/102244 A describes a fuse 10 in thick film technology with a glass-glaze layer 2 with a low thermal conductivity wherein the glass layer 2 is disposed on a ceramic substrate 1 and on the glass layer 2, a fuse 3 is applied.

The JP 10/050198 A discloses a further fuse in thin-film technology with a complex layer structure, in which on the conductor 3 and a glass layer 5, a further elastic silicone layer 6 is formed.

The DE 197 04 097 A1 describes an electrical fuse element with a fusible link in thick film technology and a carrier wherein the carrier consists of a poor thermal conductivity material, in particular of a glass ceramic.

The DE 695 12 519 T2 discloses a surface mounted fuse device wherein a thin film fusible conductor is disposed on a substrate and the substrate is preferably a FR-4 epoxy or a polyamide.

Known are therefore on the one hand a method for the production of chip fuses in thick film technology using special ceramics or Al ₂ O ₃ ceramics and a thermally insulating intermediate layer, on the other hand, chip fuses in thin-film technology using special ceramics or other special support materials.

That's how it describes JP 09 063 454 A a chip fuse according to the preamble of claim 1 with a glass glaze layer (over the entire surface) over the carrier substrate. An island-shaped formation of the glass layer is proposed only for the second, above the fusible conductor attached glass layer. The hole conductor layer used is gold (Au) and silver (Ag). The clamping electrodes are made of silver or silver-palladium.

The JP 09 429 115 A again describes a chip fuse with a full-surface glass glaze layer over the carrier substrate. Aluminum is proposed as the fuse conductor layer. The clamping electrodes consist of at least 3 silver-based layers.

The JP 10 050 198 A also describes a chip fuse with a full-surface glass glaze layer over the carrier substrate and a welterem Structure according to patent D1 with an additional silicone cover.

The JP 09 153 328 also describes a chip fuse with a full-surface glass glaze over the carrier substrate accordingly JP 09 063 454 A with an aluminum fuse conductor layer and silver contacts.

The DE 101 64 240 A1 describes a switching protection device having a laminated copper or copper alloy layer formed around a columnar substrate body. Paragraph [0076] proposes the use of a Cr adhesion layer between the copper layer and the ceramic body. It also describes filling previously patterned grooves in the metallic conductor with organic materials designed to protect the grooves from contamination with foreign materials, the organic fillers having low thermal conductivity. It is therefore a filling of grooves of a current-carrying metallization layer which has been deposited directly on the ceramic carrier substrate.

The DE 691 25 307 T2 describes a fuse Tellbaugruppe with a thin film fuse element and a Glaslsolierungsbeschichtung which are covered only a central portion of the substrate and which is provided with terminal attachment cuts and Kunststoffverhüllung.

DESCRIPTION OF THE INVENTION: Problem, Solution, Advantages

It is therefore an object of the invention to provide a generic fuse, which is inexpensive and can be produced with sufficient precision and their melting characteristics should be precisely defined. Furthermore, a method for producing the fuse is to be specified.

These objects are achieved by the features of claims 1 and 3, respectively

The core idea of the invention is to combine the advantages of a low-cost passive component manufacturing process with the advantages of thin-film technology and precise photolithographic patterning, through the use of a thermally insulating interlayer on Al ₂ O ₃ ceramics in combination with thin-film technology and photolithographic patterning is realized.

The core idea of the invention is thus that between a low-cost ceramic substrate as a carrier with high thermal conductivity and the actual fusible metallic conductor an intermediate layer is provided, which is formed either by a cost-effective method, preferably applied in the island printing process low-melting inorganic glass paste or by an applied in island printing organic layer. Due to the low thermal conductivity of this intermediate layer, the heat arising in the metallic conductor through the current flowing through it is not dissipated downwardly through the carrier substrate with a usually higher thermal conductivity, so that melts in a desired current in the conductor this in the desired manner. This intermediate layer serves as a thermal insulator. Preferably, a low-melting inorganic glass paste is used as the intermediate layer, which is applied in particular by screen printing on the carrier substrate. This offers a significant advantage over other substrates with low thermal conductivity, since the latter are practically only available as custom-made or produced, whereas by applying glass islands as a thermally insulating intermediate layer now inexpensive standard ceramics can be used, even those with only moderate surface finish ( Thick film quality) can be used. In an alternative embodiment, the intermediate layer is an organic intermediate layer, which is applied in particular in island printing and subsequently baked or cured in a manner known to those skilled in the art by the action of heat in the carrier substrate. In this case, any desired shaping of the intermediate layer can also be obtained by the simple island pressure, and the use of Al ₂ O ₃ ceramics as carrier material can be used.

The advantage of the invention is that a cost-effective standard ceramic, a thermally insulating intermediate layer which can be produced cost-effectively by screen printing can be combined with the advantage of thin-film technology and photolithographic structuring.

As a result, highly precise and cost-effective fuses in miniaturized version for securing electronic assemblies against fault currents can be produced.

Advantageously, the carrier substrate used for the fuse an alumina substrate that is available from virtually all manufacturers of such ceramic substrates inexpensively and in any shape and size and z. B. is used in mass production of resistance manufacturers use. Such aluminum oxide ceramic substrates can already be provided by the manufacturer with notches in the form of the chips to be produced later from the substrate. In the case of both embodiments described above, the intermediate layers are applied, for example, in the region of the pre-bites given by the manufacturer, in order to separate the carrier substrate in a known manner without damaging the intermediate layers by breaking processes during a subsequent dicing process of the chips.

In order to improve the adhesion of the metallic conductor to the intermediate layer, an inorganic or an organic adhesion promoter layer may be applied directly on the intermediate layer by spraying or by sputtering.

Advantageously, the metallic conductor is formed by a low-resistance metal layer in order to be able to set the melting point of the fuse accurately.

According to the invention, this metal layer is applied by sputtering to the intermediate layer or the adhesion promoter layer. If the sputtered metal layer were applied to a carrier substrate which had been glazed over the whole area, this would lead to a reduced adhesion, so that delamination of the metal layer in the pre-contact region could occur in a singulation process by means of breaking. By applying the metal layer on a thermally insulating island in the form of an intermediate layer with low thermal conductivity ensures the good adhesion of the metal layer in the contact area on the rougher aluminum oxide, as smooth surfaces are generated by these glass islands in the field of fuse, whereby the photolithographic structuring of the fuse particularly precise can be done because in contrast carrier substrates of thermally poorly conducting ceramics have higher surface roughness, which are unfavorable for a precise photolithographic patterning.

For structuring the metallic conductor in the form of the desired fuse, it is proposed that this be done by positive or negative lithography. In a positive lithography process, for example, a metal layer is deposited over the whole area on the layer arranged thereunder, for example copper, and then the desired structure is photolithographically etched into the layer. In a negative lithography process is applied to the underlying layer, i. H. the intermediate layer or the adhesion promoter layer, first a photoresist is deposited, for example sprayed on, and then patterned in the desired manner by photolithography. Subsequently, a metal layer, for example a sputtered copper film, is deposited thereon and the remaining lacquer areas are removed thereon with the metal film.

In order to protect the fuse, one or more cover layers is applied to cover the metallic conductor or preferably the entire fuse, which may, inter alia, also be formed by an inorganic barrier layer. The organic cover layer is in particular a polyamide, polyimide or an epoxide and can also be configured as a multilayer.

For contacting the fuse, the end contacts of the metallic conductor are formed by electrodepositing a metallic barrier layer, typically nickel, and the final solderable or bondable layer, typically of tin or tin alloys.

Advantageous embodiments of the invention are each characterized in the subclaims.

Short description of the drawing

• Fig. 1: den Herstellungsprozess einer Schmelzsicherung in sechs Schritten.

The invention will be explained in more detail with reference to a drawing. It shows:

• Fig. 1 : the manufacturing process of a fuse in six steps.

At the in FIG. 1 First, a manufacturing process of a fuse 100 is deposited on a carrier substrate 10 (step a)), preferably an alumina ceramic, a thermally insulating intermediate layer 11 in island form (step b)). An adhesion layer 12 for improving the adhesion of the metallic conductor 13 to the substrate is applied to this intermediate layer 11 and the surrounding carrier substrate 10 (step c)). Subsequently, the metallic conductor 13 is applied to the adhesion layer 12, for example sputtered on a copper layer and photolithographically structured in the desired manner (step d)).

Here, the maximum current is predetermined by the thickness and width of the web in the central region of the metallic conductor 13 at the crossing of this bridge melts and thus other electronic components are protected from damage. The heat transfer into the carrier substrate 10 is strongly suppressed by the thermally insulating intermediate layer, so that the melting point of the fuse 100 can be precisely defined.

Subsequently, the fuse 100 or the middle region of the metallic conductor 13 is coated with an organic cover layer 14, for example a polyamide or an epoxy, in order to protect the fuse 100 against damage. For contacting the end contacts 15 of the metallic conductor 13 are galvanized, for example with nickel and tin.

LIST OF REFERENCE NUMBERS

100

fuse

10

carrier substrate

11

interlayer

12

adhesive layer

13

metallic conductor

14

topcoat

15

end contact

Claims (4)

1. A fuse (100) in chip design, which is on a carrier substrate (10) made of a ceramic, which is an aluminium oxide ceramic in thick-film quality or in thin-film quality, with a fusible metallic conductor (13) which is applied and structured by means of thin-film technology and which is provided with a cover layer (14), wherein between carrier substrate (10) and metallic conductor (13) an intermediate layer (11) having low thermal conductivity is arranged, the carrier substrate (10) is an Al₂O₃ ceramic with high thermal conductivity, and the fusible metallic conductor (13) is applied by sputteriing or vapour deposition methods and is structured by means of lithography technology,
   the metallic conductor (13) is formed by a low-resistance metal layer, namely by Cu, Au, Ag, Sn alloy or a low-resistance Cu, Au, Ag, Sn alloy, and the metal layer is sputtered on by the vacuum method or is vapour-deposited,
   the metallic conductor (13) is structured with a positive or negative lithography method,
   a cover layer (14) is formed on the metallic conductor (13) by an inorganic or organic layer, in particular by a polyamide, polyimide, polyamide imide or an epoxide and in particular is constructed having several layers,
   characterized in that
   the intermediate layer (11) is a low-melting-point inorganic glass paste, applied by the screen printing method, or is an organic intermediate layer (11) applied by island printing,
   end contacts (15) of the fuse (100) are formed by immersion or preferably by galvanic deposition, in particular of copper, nickel, tin and tin alloys, and an adhesive layer (12) is arranged on the intermediate layer (11),
   the metallic conductor (13) is applied onto the adhesive layer (12).
2. The fuse according to Claim 1, characterized in that an inorganic barrier layer is formed between the cover layer (4) and the metallic conductor (13).
3. A method for the production of a fuse (100) in chip design, consisting of a carrier substrate (10), an intermediate layer (11) with low thermal conductivity, an adhesive layer (12) which is arranged on the intermediate layer (11), and a fusible metallic conductor (13), which is applied and structured by means of thin-film technology and which is provided with a cover layer (14), wherein

   - the intermediate layer (11) is applied on the carrier substrate (10) of an Al₂O₃ ceramic in thick-film quality or thin-film quality with a high thermal conductivity,

   - the intermediate layer (11) is formed by a low-melting-point inorganic glass paste applied by the screen printing method or an organic intermediate layer (11) applied by island printing,

   - the metallic conductor (13) is applied onto the intermediate layer (11), wherein the metallic conductor (13) is applied onto the adhesive layer (12) and

   - the cover layer (14) is applied onto the metallic conductor (13),

   - the metallic conductor (13) is formed by a low-resistance metal layer, wherein the metal layer is sputtered on by the vacuum method or is vapour-deposited, and the metal layer is formed by Cu, Au, Ag, Sn alloy or a low-resistance Cu, Au, Ag, Sn alloy,

   - the metallic conductor (13) is structured by a positive or negative lithography process,

   - the cover layer (14) is formed by an inorganic or organic layer, in particular by a polyamide, polyimide, polyamide imide or an epoxide and may also be constructed having several layers, and

   - end contacts (15) of the fuse (100) are formed by immersion or preferably by galvanic deposition, in particular of copper, nickel, tin or tin alloys.
4. The method according to Claim 3, characterized in that an inorganic barrier layer is formed between the cover layer (14) and the metallic conductor (13).

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