Fuse in chip design

Abstract

To produce a cost-effective fuse in chip design, which is applied to a carrier substrate made of a Al.sub.2O.sub.3 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.

Claims

1. A fuse in chip design, comprising: a substrate having a first surface facing in a first direction; an intermediate layer disposed on the first surface of the substrate and leaving exposed portions of the first surface of the substrate; an adhesive layer completely covering and in contact with the intermediate layer and the exposed portions of the first surface of the substrate; a fusible metallic conductor covering and in contact with at least a portion of the adhesive layer; a cover layer coated over at least a part of the fusible metallic conductor and over and in contact with at least a portion of the adhesive layer, the cover layer leaving exposed a first area having a first surface facing in the first direction comprising portions of the fusible metallic conductor and portions of the adhesive layer that remain uncovered on a first side of the cover layer, and a second area having a first surface facing in the first direction comprising portions of the fusible metallic conductor and portions of the adhesive layer that remain uncovered on a second side of the cover layer; a first contact plated directly to the first surface of the first area; and a second contact plated directly to the first surface of the second area.

2. The fuse in chip design according to claim 1, wherein the substrate comprises an aluminum oxide ceramic.

3. The fuse in chip design according to claim 1, wherein the intermediate layer comprises at least one of an inorganic glass paste or an inorganic material.

4. The fuse in chip design according to claim 1, wherein the metallic conductor is formed by a low-resistance metal layer.

5. The fuse in chip design according to claim 1, wherein the metallic conductor comprises at least one of: Cu, Au, Ag, Sn, a Cu alloy, an Au alloy, an Ag alloy, or a Sn alloy.

6. The fuse in chip design according to claim 1, wherein the metallic conductor is structured using a positive or a negative lithography method.

7. The fuse in chip design according to claim 1, wherein the cover layer comprises at least one layer comprising at least one of: a polyamide, a polyimide, a polyamide imide, or an epoxide.

8. The fuse in chip design according to claim 1, further comprising an inorganic barrier layer between at least the cover layer and the metallic conductor.

9. The fuse in chip design according to claim 1, wherein the contacts comprise at least one of: copper, nickel, tin, or a tin alloy.

10. The fuse in chip design according to claim 1, wherein the intermediate layer has a thermal conductivity lower than that of the substrate.

11. A method for manufacturing a fuse in chip design, comprising the steps of: forming an intermediate layer on a first surface of a substrate while leaving exposed portions of the first surface of the substrate, the first surface of the substrate facing in a first direction; forming an adhesive layer in direct contact with and completely covering the intermediate layer and exposed portions of the first surface of the substrate; forming a fusible metallic conductor on and in direct contact with at least a portion of the adhesive layer; coating a cover layer over at least a part of the fusible metallic conductor and over and in contact with at least a portion of the adhesive layer, the cover layer leaving exposed a first area having a first surface facing in the first direction comprising portions of the fusible metallic conductor and portions of the adhesive layer that remain uncovered on a first side of the cover layer and a second area having a first surface facing in the first direction comprising portions of the fusible metallic conductor and portions of the adhesive layer that remain uncovered on a second side of the cover layer; plating a first contact directly to the first surface of the first area; and plating a second contact directly to the first surface of the second area.

12. The method according to claim 11, wherein the substrate comprises an aluminum oxide ceramic.

13. The method according to claim 11, wherein the intermediate layer comprises at least one of an inorganic glass paste or an inorganic material.

14. The method according to claim 11, wherein the metallic conductor is formed by a low-resistance metal layer.

15. The method according to claim 11, wherein the metallic conductor comprises at least one of: Cu, Au, Ag, Sn, a Cu alloy, an Au alloy, an Ag alloy, or a Sn alloy.

16. The method according to claim 11, wherein the metallic conductor is formed using positive or a negative lithography.

17. The method according to claim 11, wherein the cover layer comprises at least one layer comprising at least one of: a polyamide, a polyimide, a polyamide imide, or an epoxide.

18. The method according to claim 11, further comprising an inorganic barrier layer between at least the cover layer and the metallic conductor.

19. The method according to claim 11, wherein the contacts comprise at least one of: copper, nickel, tin, or a tin alloy.

20. The method according to claim 11, wherein the intermediate layer has a thermal conductivity lower than that of the substrate.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 shows the manufacturing process of a fuse in six steps.

(2) FIG. 2 shows an inorganic barrier layer covering a metallic conductor.

DETAILED DESCRIPTION

(3) The core idea of the present invention thus comprises providing an intermediate layer, between a cost-effective ceramic substrate as a carrier having high thermal conductivity and the actual fusible metallic conductor, which is produced either through a cost-effective method, preferably low-melting-point inorganic glass pastes applied in the island printing method or an organic layer applied in island printing. Because of the low thermal conductivity of this intermediate layer, the heat arising in the metallic conductor due to the current flowing through it is not dissipated downward through the carrier substrate, which typically has a higher thermal conductivity, so that the conductor fuses in the desired way at a defined current strength therein. This intermediate layer is used as the thermal insulator. A low-melting-point inorganic glass paste is preferably used as the intermediate layer, which is particularly applied to the carrier substrate in the screen-printing method. This offers a significant advantage in relation to other substrates having low thermal conductivity, since the latter may be provided and/or manufactured practically only as special productions, while in contrast, through the application of glass islands as the thermally insulating intermediate layer, cost-effective standard ceramics may now be used, even those only having moderate surface composition (thick-film quality) being able to be used. In an alternative embodiment, the intermediate layer is an organic intermediate layer, which is particularly applied in island printing and subsequently baked and/or cured in the way known to those skilled in the art through the effect of heat in the carrier substrate. In this case, through island printing, which is simple to perform, arbitrary shaping of the intermediate layer may also be obtained, and Al.sub.2O.sub.3 ceramics may be used as the carrier material.

(4) The advantage of the present invention is that a cost-effective standard ceramic, a thermally insulating intermediate layer, which may be manufactured cost-effectively in the screen-printing method, having the advantage of thin-film technology, and photolithographic structuring may be combined. In this way, high-precision and cost-effective fuses for safeguarding electronic assemblies from fault currents may be manufactured in miniaturized embodiments.

(5) An aluminium oxide substrate is advantageously used as the carrier substrate for the fuse, which is available cost-effectively and in any arbitrary shape and size from practically all manufacturers of ceramic substrates of this type and is used, for example, in mass production of resistor manufacturers. Aluminium oxide ceramic substrates of this type may already be provided by the manufacturer with preliminary notches in the shape of the chips to be manufactured later from the substrate. In both of the embodiments described above, the intermediate layers are applied in the region of the preliminary notches predefined by the manufacturer, for example, in order to separate the carrier substrate in a known way without damaging the intermediate layers through fracturing processes during a later isolation process.

(6) In order to improve the adhesion of the metallic conductor to the intermediate layer, an inorganic or an organic adhesion promoter may be applied directly to the intermediate layer in the spray method or through sputtering.

(7) In an advantageous embodiment, the metallic conductor is formed by a low-resistance metal layer in order to be able to set the melting point of the fuse precisely.

(8) In a first embodiment, this metal layer is applied to the intermediate layer and/or the adhesion promoter layer through sputtering. If the sputtered metal layer was applied to a carrier substrate glazed over its entire surface, this would lead to reduced adhesion, so that delamination of the metal layer in the pre-contact region could arise during an isolation process using fracturing. By applying the metal layer onto a thermally insulating island in the form of an intermediate layer having low thermal conductivity, good adhesion of the metal layer to the rougher aluminium oxide ceramic is ensured in the contact region, since smooth surfaces are produced by these glass islands in the region of the fuse, through which the photolithographic structuring of the fuse may be performed especially precisely, since in contrast to this, carrier substrates made of ceramics having poor thermal conductivity have higher surface roughness, which is unfavourable for precise photolithographic structuring.

(9) For structuring the metallic conductor into the form of the desired fuse, it is suggested that this be performed through positive or negative lithography. In a positive lithography process, a metal layer, such as copper, is deposited over the entire area onto the layer positioned underneath and the desired structure is subsequently photo lithographically etched into the layer, for example. In a negative lithography process, first a photo resist is deposited, sprayed, for example, onto the layer lying underneath, i.e., the intermediate layer or the adhesion promoter layer, and subsequently photo lithographically structured in the desired way. Subsequently, a metal layer, such as a sputtered copper film, is deposited thereon and the remaining photo resist regions having the metal film thereon are removed.

(10) To protect the fuse, one or more cover layers are applied to cover the metallic conductor or preferably the entire fuse, which may be formed by an inorganic barrier layer 16, among other things. The organic cover layer is particularly a polyamide, polyimide, or an epoxide, and may also be implemented as multilayered.

(11) For the contacts of the fuse, the end contacts of the metallic conductor are produced through electrode position of a metallic barrier layer, typically made of nickel, and the final layer, which may be soldered or bonded, typically made of tin or tin alloys.

(12) In the following, the present invention will be explained in greater detail on the basis of the drawing.

(13) In the manufacturing process of a fuse 100 shown in FIG. 1, first a thermally insulating intermediate layer 11 is deposited in island form (step b) onto a carrier substrate (step a), preferably an aluminium oxide ceramic. An adhesive layer 12 for improving the adhesion of the metallic conductor 13 to the foundation is applied (step c) to this intermediate layer 11 and the surrounding carrier substrate 10. Subsequently, the metallic conductor 13, such as a copper layer which is sputtered on and photo lithographically structured in the desired way (step d), is applied to the adhesive layer 12.

(14) In this way, through the thickness and width of the web in the central region of the metallic conductor 13, the maximum current strength is predefined, this web fusing if the maximum current strength is exceeded and other electronic components thus being protected from damage. Through the thermally insulating intermediate layer, the heat conduction into the carrier substrate 10 is strongly suppressed, so that the melting point of the fuse 100 may be defined precisely.

(15) Subsequently, the fuse 100 and/or the central region of the metallic conductor 13 is/are coated with an organic cover layer 14, such as a polyamide or an epoxide, in order to protect the fuse 100 from damage. For the contacts, the end contacts 15 of the metallic conductor 13 are electroplated, using nickel and tin, for example.

LIST OF REFERENCE NUMBERS

(16) 100 fuse 10 carrier substrate 11 intermediate layer 12 adhesive layer 13 metallic conductor 14 cover layer 15 end contact