COPPER-CERAMIC COMPOSITE

Abstract

The invention relates to a copper-ceramic composite, comprising a ceramic substrate, which contains aluminum oxide, a coating on the ceramic substrate made of copper or a copper alloy, wherein the aluminum oxide has an average grain form factor R.sub.a(Al.sub.2O.sub.3), determined as an arithmetic average value from the form factors of the grains of the aluminum oxide, the copper or the copper alloy has an average grain form factor R.sub.a(Cu), determined as an arithmetic average of the form factors of the grains of the copper or copper alloy, and the average grain form factors of the aluminum oxide and copper or copper alloy meet the following condition: 0.5R.sub.a(Al.sub.2O.sub.3)/R.sub.a(Cu)2.0.

Claims

1. A copper-ceramic composite comprising a ceramic substrate containing aluminum oxide, a coating composed of copper or a copper alloy present on the ceramic substrate, wherein the grains of the aluminum oxide each have a maximum diameter d.sub.Kmax, a diameter d.sub.K,ortho running perpendicular to d.sub.K,max, determined on half the length of d.sub.K,max, and a shape factor R.sub.K(Al.sub.2O.sub.3)=d.sub.K,ortho/d.sub.K,max and the aluminum oxide has an average grain shape factor R.sub.a(Al.sub.2O.sub.3), determined as arithmetic mean of the shape factors R.sub.K(Al.sub.2O.sub.3) of the grains of the aluminum oxide, the grains of the copper or of the copper alloy each have a maximum diameter d.sub.K,max, a diameter d.sub.K,ortho running perpendicular to d.sub.K,max, determined on half the length of d.sub.K,max, and a shape factor R.sub.K(Cu)=d.sub.K,ortho/d.sub.K,max and the copper or the copper alloy has an average grain shape factor R.sub.a(Cu), determined as arithmetic mean of the shape factors R.sub.K(Cu) of the grains of the copper or of the copper alloy, where the average grain shape factors of the aluminum oxide and of the copper or the copper alloy satisfy the following condition:
0.5R.sub.a(Al.sub.2O.sub.3)/R.sub.a(Cu)2.0.

2. The copper-ceramic composite of claim 1, wherein the copper or the copper alloy has grain sizes in the range from 10 m to 300 m, more preferably in the range from 15 m to 250 m, even more preferably in the range from 20 m to 210 m.

3. The copper-ceramic composite of claim 1, wherein the aluminum oxide has grain sizes in the range from 0.01 m to 25 m, more preferably in the range from 0.3 m to 23 m, even more preferably in the range from 0.5 m to 20 m.

4. The copper-ceramic composite of claim 1, wherein the ratio of the average grain shape factor of the aluminum oxide to the average grain shape factor of the copper or of the copper alloy is in the range of 0.75-1.50, more preferably in the range of 0.80-1.20.

5. The copper-ceramic composite of claim 1, wherein the ceramic substrate contains the aluminum oxide in an amount of at least 65% by weight.

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

7. 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.

8. 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.

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

Description

EXAMPLES

[0112] The following examples show how the thermal shock resistance of the copper-ceramic composite can be improved when the average shape factors of the copper and of the Al.sub.2O.sub.3 approximate one another.

[0113] Three copper-ceramic specimens were produced by a DCB process:

[0114] Copper-ceramic composite 1, hereinafter K-K-V 1 (according to the invention)

[0115] Copper-ceramic composite 2, hereinafter K-K-V 2 (comparative specimen)

[0116] Copper-ceramic composite 3, hereinafter K-K-V 3 (comparative specimen)

[0117] In each of these three copper-ceramic composites, both the upper side and also the underside of the ceramic substrate were provided with a copper coating. The copper coating was firstly bonded by means of the SLB process to one side of the ceramic substrate. The opposite side of the ceramic substrate was subsequently provided by means of the SLB process with a further copper coating so as to form a copper-ceramic substrate in which a copper foil is bonded to each of the two sides of the ceramic. One of the two copper coatings on each of the specimens was subsequently structured by an etching process (same structuring for all specimens). In all examples, the substrates comprised 96% by weight of Al.sub.2O.sub.3.

[0118] In each of these three copper-ceramic composites, the ceramic substrate had the following dimensions:

[0119] Thickness of the ceramic substrate: 0.38 mm;

[0120] Lengthwidth of the ceramic substrate: 190140 mm.sup.2

[0121] The copper coating in each case had a thickness of 0.3 mm.

[0122] FIG. 5 shows an SEM image of the surface of the ceramic substrate of K-K-V 1, by means of which the Al.sub.2O.sub.3 grain structure was determined.

[0123] FIG. 6 shows an optical micrograph of the surface of the copper coating of K-K-V 1, by means of which the copper grain structure was determined.

[0124] For each of these three specimens, the thermal shock resistance of the metal-ceramic composite was determined by the following method:

[0125] To determine the thermal shock resistance of the copper-ceramic substrate, an individual substrate was 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 made up as follows: [0126] storage at 150 C. (preferably in a first chamber of a temperature change cabinet) for 15 minutes [0127] storage at 40 C. (minus 40 C.) (preferably in a second chamber of the temperature change cabinet) for 15 minutes, [0128] with a transfer time of 15 seconds occurring in the transport from one chamber into the other chamber.

[0129] During the course of five cycles (storage at 150 C. to 40 C. and back corresponds 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.

[0130] The ratios of the average grain shape factors (i.e. R.sub.a(Al.sub.2O.sub.3)/R.sub.a(Cu)) and also the results of the thermal shock resistance tests for the composites K-K-V 1, K-K-V 2 and K-K-V 3 are summarized in table 1 below:

TABLE-US-00001 TABLE 1 Thermal shock resistance as a function of R.sub.a(Al.sub.2O.sub.3)/R.sub.a(Cu) Thermal shock resistance Specimen K-K-V 1 R.sub.a(Al.sub.2O.sub.3)/R.sub.a(Cu): 1.0 + (according to the invention) Specimen K-K-V 2 R.sub.a(Al.sub.2O.sub.3)/R.sub.a(Cu): 0.2 (comparison) Specimen K-K-V 3 R.sub.a(Al.sub.2O.sub.3)/R.sub.a(Cu): 2.8 (comparison)

[0131] As the examples show, the thermal shock resistance of the copper-ceramic composite can be improved when the average shape of the grains and thus the average grain shape factors of the copper and of the Al.sub.2O.sub.3 approximate one another.