Metal-ceramic substrate and method for producing a metal-ceramic substrate

Abstract

The invention relates to a metal-ceramic substrate and to a method for the production thereof, the substrate including at least one ceramic layer having first and second surface sides, at least one of the surface sides of which is provided with a metallization, wherein the ceramic material forming the ceramic layer contains aluminum oxide, zirconium dioxide and yttrium oxide. The ceramic layer contains aluminum oxide, zirconium dioxide and yttrium oxide in the following proportions, in each case in relation to the total weight thereof: zirconium dioxide between 2 and 15 percent by weight; yttrium oxide between 0.01 and 1 percent by weight; and aluminum oxide between 84 and 97 percent by weight, wherein the average grain size of the aluminum oxide used is between 2 and 8 micrometers and the ratio of the length of the grain boundaries of the aluminum oxide grains to the total length of all the grain boundaries is greater than 0.6.

Claims

1. A metal-ceramic substrate comprising at least one ceramic having first and second surface sides, the at least one ceramic layer being provided with a metallization on at least one of the surface sides, wherein a ceramic material forming the at least one ceramic layer contains aluminium oxide, zirconium dioxide and yttrium oxide, wherein the proportions of the aluminium oxide, the zirconium dioxide, and the yttrium oxide in the at least one ceramic layer are as follows with respect to the total weight thereof: zirconium dioxide between 2% and 15% by weight; yttrium oxide between 0.01% and 1% by weight; and aluminium oxide between 84% and 97% by weight, wherein an average grain size of the aluminium oxide used is between 2 and 8 micrometers and a ratio of a length of grain boundaries of aluminium oxide grains to a total length of all grain boundaries is greater than 0.6.

2. The metal-ceramic substrate according to claim 1, wherein the proportions of the aluminium oxide, the zirconium dioxide, and the yttrium oxide in the at least one ceramic layer are as follows with respect to the total weight thereof: zirconium dioxide between 2% and 10% by weight; yttrium oxide between 0.01% and 1% by weight; and aluminium oxide between 89% and 97% by weight.

3. The metal-ceramic substrate according to claim 1, wherein the at least one ceramic layer comprises a thermal conductivity of more than 25 W/mK.

4. The metal-ceramic substrate according to claim 1, wherein the at least one ceramic layer comprises a bending strength of more than 500 MPa.

5. The metal-ceramic substrate according to claim 1, wherein the at least one ceramic layer has a layer thickness between 0.1 mm and 1.0 mm.

6. The metal-ceramic substrate according to claim 1, wherein the zirconium dioxide in a crystalline phase has a tetragonal crystalline structure, and wherein a proportion of the tetragonal crystalline structure in an overall crystalline structure of the zirconium dioxide is more than 80 percent.

7. The metal-ceramic substrate according to claim 1, wherein the metallization has a layer thickness between 0.05 mm and 1.2 mm.

8. The metal-ceramic substrate according to claim 1, wherein the metallization is structured so as to form contact or bonding faces.

9. The metal-ceramic substrate according to claim 1, wherein the metallization is formed by a layer of copper or a copper alloy and/or a layer of aluminium or an aluminium alloy.

10. A method for production of a metal-ceramic substrate comprising at least one ceramic layer, the at least one ceramic layer having a first and second surface side, comprising the steps of: bonding at least one of the surface sides with at least one metallization, wherein the at least one ceramic layer is produced from a ceramic material comprising aluminium oxide, zirconium dioxide and yttrium oxide, and producing the at least one ceramic layer with proportions of the aluminium oxide, the zirconium dioxide and the yttrium oxide with respect to the total weight of the at least one ceramic layer in proportions as follows: zirconium dioxide between 2% and 15% by weight; yttrium oxide between 0.01% and 1% by weight; and aluminium oxide between 84% and 97% by weight; and utilizing an average grain size of the aluminium oxide between 2 and 8 micrometers and a ratio of a length of grain boundaries of the aluminium oxide grains to a total length of all grain boundaries greater than 0.6.

11. The method according to claim 10, wherein when forming the at least one metallization in a form of a film or layer of copper or a copper alloy, the at least one metallization is bonded to the ceramic layer by a direct copper bonding process, an active solder process, or by adhesion using a synthetic adhesive or a polymer which is suitable for use as an adhesive.

12. The method according to claim 10 wherein when forming the at least one metallization in the form of a film or layer of aluminium or an aluminium alloy, the at least one metallization is bonded to the ceramic layer by a direct aluminium bonding process or by adhesion using a synthetic adhesive or a polymer which is suitable for use as an adhesive.

13. The method according to claim 10, wherein in order to produce the at least one ceramic layer zirconium dioxide, a crystalline phase of which has a mainly tetragonal crystalline structure is used, wherein a proportion of tetragonal crystalline structure in an overall crystalline structure of the zirconium dioxide is more than 80 percent.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described in more detail with the aid of the accompanying drawings and exemplary embodiments.

(2) FIG. 1 is a simplified sectional view through a metal-ceramic substrate in accordance with the invention with one metallization.

(3) FIG. 2 is a simplified sectional view through a metal-ceramic substrate in accordance with the invention with two metallizations.

(4) FIG. 3 is a simplified sectional view of an alternative embodiment of the metal-ceramic substrate of FIG. 2 with two metallizations.

(5) FIG. 4 is a graph of the profile of the thermal conductivity as a function of temperature of a conventional ceramic layer and the ceramic layer with different zirconium oxide proportions used in the metal-ceramic substrate according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(6) FIG. 1 shows a simplified view of a section through a metal-ceramic substrate 1 of the invention comprising at least one ceramic layer 2 with two opposing surface sides, namely a first and a second surface side 2a, 2b.

(7) The metal-ceramic substrate 1 of the invention in FIG. 1 is provided with at least one metallization 3. In the present embodiment, the first surface side 2a is provided with a first metallization 3 and the second surface side 2b, which is opposite the first surface side 2a, does not have a metallization.

(8) FIG. 2 and FIG. 3 show two alternative variational embodiments of a metal-ceramic substrate 1 of the invention in which the first surface 2a is provided with a first metallization 3 and the second surface 2b, which is opposite the first surface 2a, is provided with a second metallization 4.

(9) The first and/or second metallizations 3, 4 are preferably structured, i.e. form a plurality of contact zones or contact surfaces for the connection of electronic components. FIG. 1 and FIG. 2 respectively show, by way of example, a structured first metallization 3 and FIG. 3 shows a structured first and second metallization 3, 4.

(10) Metal-ceramic substrates 1 of this type are used in a known manner as printed circuit boards for electrical or electronic circuits or circuit modules, in particular for power circuits. In this regard, the structuring of the metallizations 3, 4 is obtained using the usual techniques, such as masking and etching techniques, for example.

(11) In accordance with the invention, the ceramic material used to produce the ceramic layer 2 of the metal-ceramic substrate 1 comprises aluminium oxide (Al.sub.2O.sub.3), zirconium dioxide (ZrO.sub.2) as well as yttrium oxide (Y.sub.2O.sub.3). The aluminium oxide, zirconium dioxide and yttrium oxide in the ceramic layer 2 are present in the following proportions with respect to the total weight of the ceramic layer 2: zirconium dioxide between 2% and 15% by weight; yttrium oxide between 0.01% and 1% by weight; and aluminium oxide between 84% and 97% by weight.

(12) The average grain size of the aluminium oxide used here is between 2 and 8 micrometer. Even better thermal conductivity is obtained in particular with a composition using the following proportions: zirconium dioxide between 2% and 10% by weight; yttrium oxide between 0.01% and 1% by weight; and aluminium oxide between 89% and 97% by weight.

(13) The ceramic layer 2 has a crystalline structure, i.e. it is composed of a plurality of crystallites or grains which border each other directly. Crystallites or grains with different orientations but otherwise identical crystalline structures are separated from each other by so-called grain boundaries. If the ratio of the length of the grain boundaries of the aluminium oxide grains to the total length of the grain boundaries of the grains of all of the constituents is selected so as to be more than 0.6, the thermal conductivity is substantially improved. In addition, the strength of the ceramic layer 2 is substantially increased. The thermal conductivity of the ceramic layer 2 is preferably more than 25 W/mK, i.e. compared with known ceramic layers 2 containing a proportion of zirconium dioxide, resulting in an increase from 8 to 10 percent.

(14) Preferably, the zirconium dioxide used in the crystalline phase has a mainly tetragonal crystalline structure, wherein the proportion of the tetragonal crystalline structure in the overall crystalline structure of the zirconium dioxide is more than 80 percent.

(15) Furthermore, the ceramic layer 2 has a layer thickness between 0.1 mm and 1.0 mm, preferably between 0.2 mm and 0.5 mm, wherein the bending strength of the ceramic layer 2 is, for example, selected so as to be more than 500 MPa.

(16) The metallization 3, 4 is, for example, formed by a film or layer of copper or a copper alloy and/or aluminium or an aluminium alloy, i.e. combinations of a copper or copper alloy and an aluminium or aluminium alloy may also be envisaged. In this regard, the layer thickness of the metallization 3, 4 is between 0.05 mm and 1.2 mm, preferably between 0.1 mm and 0.5 mm.

(17) Various methods, depending on the materials used for the ceramic layer 2 and the metallizations 3, 4, are suitable for forming the extensive bond between the ceramic layer 2 and the first or second metallization 3, 4.

(18) Thus, a metallization 3, 4 in the form of a film or layer of copper or a copper alloy is bonded to the ceramic layer 2 by, for example, adhesion using a synthetic adhesive or a polymer which is suitable for use as an adhesive, preferably using an adhesive which contains carbon fibres, in particular carbon nanofibres. Alternatively, the extensive bond of the ceramic layer can be produced using the DCB process or with the aid of the active solder process.

(19) A metallization 3, 4 produced from aluminium or an aluminium alloy is bonded with the ceramic layer 2 by, for example, a direct aluminium bonding process (DAB process) or by adhesion using a synthetic adhesive or a polymer which is suitable for use as an adhesive, preferably using an adhesive which contains carbon fibres, in particular carbon nanofibres.

(20) FIG. 4 shows, by way of example, a diagram of the profile of the thermal conductivity in W/mK as a function of the temperature in C. for a conventional ceramic layer in accordance with the prior art and the ceramic layer 2 with different proportions of zirconium oxide used in the metal-ceramic substrate according to the invention, namely a ceramic layer with a ZrO.sub.2 proportion of 5%, a ceramic layer with a ZrO.sub.2 proportion of 7% and a ceramic layer with a ZrO.sub.2 proportion of 9%. This shows that the thermal conductivity at room temperature at approximately 24 C. is over 25 W/mK, and thus the thermal conductivity is increased by about 8-10%.

(21) The invention has been described with the aid of exemplary embodiments. It should be understood that many changes and variations are possible without departing from the spirit and scope of the inventive concept underlying the present invention.

LIST OF REFERENCE NUMERALS

(22) 1 metal-ceramic substrate 2 ceramic layer 2a first surface side 2b second surface side 3 first metallization 4 second metallization