COPPER-CERAMIC COMPOSITE

Abstract

The invention relates to a copper-ceramic composite comprising:—a ceramic substrate;—a copper or copper alloy coating in which the copper or copper alloy has grain sizes of 10 μm to 300 μm and a number distribution of the grain sizes with a median d.sub.50 and an arithmetic mean d.sub.arith, the ratio of d.sub.50 to d.sub.arith (d.sub.50/d.sub.arith) being between 0.75 and 1.10.

Claims

1. A copper-ceramic composite comprising a ceramic substrate, and a coating which is present on the ceramic substrate and is composed of copper or a copper alloy, where the copper or the copper alloy has grain sizes in the range from 10 um to 300 μm, and has a number distribution of the grain sizes having a median d.sub.50 and an arithmetic mean d.sub.arith and the ratio of d.sub.50 to d.sub.arith (d.sub.50/d.sub.arith) is in the range from 0.75 to 1.10.

2. The copper-ceramic composite of claim 1, wherein the ratio of d.sub.50 to d.sub.arith (d.sub.50/d.sub.arith) is in the range from 0.78 to 1.05, even more preferably in the range from 0.80 to 1.00.

3. The copper-ceramic composite of claim 1, wherein the copper or the copper alloy has a number distribution of the grain sizes having a d.sub.5 and a d.sub.95 and the ratio of ds to d95 is in the range from 0.1 to 0.4, more preferably in the range from 0.11 to 0.35, even more preferably in the range from 0.12 to 0.30.

4. The copper-ceramic composite claim 1, wherein the grain sizes of the copper or of the copper alloy are in the range from 15 μm to 250 μm, more preferably in the range from 20 μm to 210 μm.

5. The copper-ceramic composite of claim 1, wherein the coating composed of copper or a copper alloy is applied by means of a DCB process to the ceramic substrate.

6. The copper-ceramic composite of claim 1, wherein the coating composed of copper or a copper alloy at least partly has structuring to form electrical contact areas.

7. The copper-ceramic composite of claim 1, wherein the ceramic substrate contains an oxide, a nitride, a carbide or a mixture or composite of at least two of these materials.

8. The copper-ceramic composite of claim 1, wherein the ceramic substrate contains at least 65% by weight of Al.sub.2O.sub.3.

9. The copper-ceramic composite of claim 1, wherein the coating composed of copper or a copper alloy has a thickness in the range of 0.2-1.2 mm over at least 70% of its area; and/or the ceramic substrate has a thickness in the range of 0.2-1.2 mm over at least 70% of its area.

10. A module containing at least one copper-ceramic composite according to claim 1 and at least one or more bond wires.

Description

EXAMPLES

[0126] The following examples show how the grain size distribution in the copper coating influences the thermal shock resistance and the wire bonding behavior of a copper-ceramic composite.

[0127] 5 copper-ceramic specimens which differed in terms of their grain size distributions were produced by a DCB process: [0128] copper-ceramic composite 1, hereinafter “K-K-V 1” (according to the invention) [0129] copper-ceramic composite 2, hereinafter “K-K-V 2” (comparative specimen) [0130] copper-ceramic composite 3, hereinafter “K-K-V 3” (comparative specimen) [0131] copper-ceramic composite 2, hereinafter “K-K-V 4” (comparative specimen) [0132] copper-ceramic composite 3, hereinafter “K-K-V 5” (comparative specimen)

[0133] Both the upper side and the underside of the ceramic substrate were provided with a copper coating in each of these 5 copper-ceramic composites. The copper coating was firstly bonded to one side of the ceramic substrate by means of the SLB process. The opposite side of the ceramic substrate was subsequently provided with a further copper coating by means of the SLB process so as to form a copper-ceramic substrate in which a copper foil is bonded to both sides of the ceramic. One of the two copper coatings was in each case subsequently structured by an etching process in each specimen (same structuring for all specimens).

[0134] In each of these 5 copper-ceramic composites, the thickness of the copper coating was 0.3 mm and the length×width of the copper coating was: 181×132 mm.sup.2. In the example, the copper is pure copper.

[0135] Furthermore, all 5 specimens contained an Al.sub.2O.sub.3 ceramic substrate (Al.sub.2O.sub.3 content: 96% by weight), thickness of the ceramic substrate: 0.38 mm; length×width of the ceramic substrate: 190×140 mm.sup.2.

[0136] The copper coating was selected so that the effect according to the invention, namely good temperature change resistance, was realized after the two-stage SLB bonding (copper-ceramic substrate according to the invention) and good bonding of wires to the metal coating was realized after the two-stage SLB bonding (copper-ceramic substrate according to the invention).

[0137] FIG. 5 shows an optical micrograph of the surface of the copper coating of K-K-V 1, by means of which the copper grain sizes of the example K-K-V 1 were determined.

[0138] The grain size ranges and the symmetry values of the grain size distributions of the specimens K-K-V 1 to K-K-V 5 are listed in table 1.

[0139] Both the thermal shock resistance and also the wire bonding properties were determined for each of these 5 specimens.

[0140] The thermal shock resistance was determined as follows:

To determine the thermal shock resistance of the copper-ceramic substrate, an individual substrate is preferably broken out from a large card. The individual substrate was subjected in an apparatus known to those skilled in the art to a temperature change cycle which was made up of: [0141] storage at 150° C. (preferably in a first chamber of a temperature change cabinet) for 15 minutes [0142] storage at −40° C. (minus 40° C.) (preferably in a second chamber of the temperature change cabinet) for 15 minutes, [0143] with a transfer time of 15 seconds occurring in the transfer from one chamber into the other chamber.

[0144] Over the course of 5 cycles (storage at 150° C. to −40° C. and back corresponding to one cycle), the bonding area at the interface between copper and ceramic was in each case examined for delamination by means of an ultrasonic microscope.

[0145] The wire bonding properties were determined as follows:

To determine the wire bonding properties of the copper-ceramic substrate, an individual substrate is preferably broken out from a large card. A wire (in the example a copper wire, for example, according to methods known to those skilled in the art) was bonded to the individual substrate on the copper surface of the bonded copper-ceramic substrate in an apparatus known to those skilled in the art. In the context of the invention, it could be established, according to the invention, that, when the product parameters and the subsequent DCB process were selected according to the invention, the specimen K-K-V 1 had significantly improved wire bonding properties compared to the specimens K-K-V 2 and K-K-V 3.

[0146] The results are summarized in the following table 1:

TABLE-US-00001 TABLE 1 Thermal shock resistance and wire bonding properties of the copper-ceramic composites Thermal shock Wire resistance bonding Specimen Grain size range: 32-192 μm ++ ++ K-K-V 1 Symmetry value d.sub.50/d.sub.arith: 0-93 (according to the invention) Specimen Grain size range: 18-167 μm − ++ K-K-V 2 Symmetry value d.sub.50/d.sub.arith: 0-62 (comparison) Specimen Grain size range: 23-201 μm ++ − K-K-V 3 Symmetry value d.sub.50/d.sub.arith: 1.37 (comparison) Specimen Grain size range: 43-470 μm + + K-K-V 4 Symmetry value d.sub.50/d.sub.arith: 0.89 (comparison) Specimen Grain size range: 4-175 μm + + K-K-V 5 Symmetry value d.sub.50/d.sub.arith: 0.94 (comparison)

[0147] Furthermore, the influence of the breadth of the grain size distribution on thermal shock resistance and wire bonding was examined. The results are shown in table 2.

TABLE-US-00002 TABLE 2 Influence of the breadth of the grain size distribution Breadth of the distribution Thermal shock Wire d.sub.5/d.sub.95 resistance bonding 0.27 + + 0.03 − + 0.50 + −

[0148] As table 2 shows, further optimization of the thermal shock resistance and of the wire bonding behavior can be achieved when the breadth of the grain size distribution is in the range according to the invention.