Copper-ceramic composite

Abstract

A copper-ceramic composite: includes a ceramic substrate containing alumina and a copper or copper alloy coating on the ceramic substrate. The alumina has a mean grain shape factor R.sub.a(Al.sub.2O.sub.3), defined as the arithmetic mean of the shape factors R of the alumina grains, of at least 0.4.

Claims

1. A copper-ceramic composite comprising: a ceramic substrate containing grains of aluminum oxide, and 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 grain diameter d.sub.K,max, a grain 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=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 of the grains, of at least 0.8, wherein the coating composed of copper or a copper alloy is applied to the ceramic substrate by a direct copper bonding (DCB) process, the DCB process comprising: oxidizing a copper foil to form a copper oxide layer on the copper foil; laying the copper foil with the copper oxide layer on the ceramic substrate; heating the ceramic substrate and copper foil with the copper oxide layer to a temperature ranging from 1025° C. to 1083° C.; and cooling the heated ceramic substrate and copper foil with the copper oxide layer to room temperature.

2. The copper-ceramic composite of claim 1, wherein the grains of aluminum oxide range from a d.sub.min of ≥0.01 μm to a d.sub.max of ≤25 μm.

3. The copper-ceramic composites of claim 1, wherein the ceramic substrate contains at least 65% by weight of the grains of aluminum oxide.

4. 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.

5. 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 the ceramic substrate has a thickness in the range of 0.2-1.2 mm over at least 70% of its area.

6. A module containing at least one copper-ceramic composite according to claim 1 and one or more bond wire(s).

7. The copper-ceramic composite of claim 1, wherein the grains of aluminum oxide range from a d.sub.min of ≥0.3 μm to a d.sub.max of ≤23 μm.

8. The copper-ceramic composite of claim 1, wherein the grains of aluminum oxide range from a d.sub.min of ≥0.5 μm to a d.sub.max of ≤20 μm.

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.

10. The copper-ceramic composite of claim 1, wherein the ceramic substrate has a thickness in the range of 0.2-1.2 mm over at least 70% of its area.

11. The copper-ceramic composite of claim 1, further comprising copper-aluminum spinels between the ceramic substrate and the coating.

12. The copper ceramic composite of claim 1, wherein the ceramic substrate and copper foil with the copper oxide layer are heated to a temperature ranging from 1065° C. to 1083° C.

Description

EXAMPLES

(1) The following examples show how the shape factor of the Al.sub.2O.sub.3 grains of the ceramic substrate influences the mechanical strength of a copper-ceramic composite.

(2) Three copper-ceramic specimens which differ in terms of the shape factors of the aluminum oxide in the ceramic substrate were produced by a DCB process: copper-ceramic composite 1, hereinafter “K-K-V 1” (according to the invention) copper-ceramic composite 2, hereinafter “K-K-V 2” (according to the invention) copper-ceramic composite 3, hereinafter “K-K-V 3” (comparative specimen)

(3) In each of these three copper-ceramic composites, both the upper side and also the underside of the ceramic substrate was 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 three examples, the substrates comprised 96% by weight of Al.sub.2O.sub.3, but differ in terms of their grain structure.

(4) In each of these 3 copper-ceramic composites, the ceramic substrate had the following dimensions: thickness of the ceramic substrate: 0.38 mm; length×width of the ceramic substrate: 190×140 mm.sup.2

(5) The copper coating in each case had a thickness of 0.3 mm.

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

(7) The average shape factors R.sub.a(Al.sub.2O.sub.3) of the Al.sub.2O.sub.3 of the specimens K-K-V 1 to K-K-V 3 are listed in table 1.

(8) For each of these 3 specimens, the flexural fracture strength of the ceramic substrate in the copper-ceramic composite was determined.

(9) In the determination of the flexural fracture strength, the force leading to fracture was determined in a three-point bending test. The measurement was based on DIN EN 843-1 (2008), with the specimen geometry deviating from DIN EN 843-1 (2008) in that the specimens had dimensions of 20×40×0.38 mm.sup.3 or 20×40×0.63 mm.sup.3.

(10) The results are summarized in table 1 below:

(11) TABLE-US-00001 TABLE 1 Mechanical strength of the ceramic substrates Mechanical strength Specimen K-K-V 1 Average shape factor R.sub.a(Al.sub.2O.sub.3) ++ (according to the of the Al.sub.2O.sub.3: 0.88 invention) Specimen K-K-V 2 Average shape factor R.sub.a(Al.sub.2O.sub.3) + (according to the of the Al.sub.2O.sub.3: 0.56 invention) Specimen K-K-V 3 Average shape factor R.sub.a(Al.sub.2O.sub.3) − (comparison) of the Al.sub.2O.sub.3: 0.31

(12) As the examples demonstrate, an improvement in the mechanical strength can successfully be achieved with the Al.sub.2O.sub.3 grain structure according to the invention, which has a high proportion of relative round or circular grains.