Method for producing a metal-ceramic substrate with at least one via

Abstract

A method for producing a metal-ceramic substrate with at least one electrically conductive via, in which one metal layer, respectively, is attached in a planar manner to a ceramic plate or a ceramic layer to each of two opposing surface sides of the ceramic layer is provided. The method includes introducing a metal-containing, powdery and/or liquid substance into a hole in the ceramic layer delimiting the via prior to the attachment of both metal layers, or subsequent to the attachment of one of the two metal layers to form an assembly. Prior to the attachment of the other one of the two metal layers, and the assembly is subjected to a high-temperature step above 500 C. in which the metal-containing substance wets the ceramic layer at least partially with a wetting angle of less than 90.

Claims

1. A method for producing a metal-ceramic substrate with at least one electrically conductive via, the method comprising: attaching a first metal layer in a planar manner to a first surface side of a ceramic layer and attaching a second metal layer in a planar manner to a second surface side of the ceramic layer opposite the first surface side; introducing a metal-containing powdery substance into a hole in the ceramic layer delimiting the at least one electrically conductive via prior to the attachment of both the first and the second metal layers, or subsequent to the attachment of one of the first and the second metal layers and prior to the attachment of the other one of the first and the second metal layers, to form an assembly; and subjecting the assembly to a high-temperature step above 500 C. in which the metal-containing powdery substance wets the ceramic layer at least partially with a wetting angle of less than 90.

2. The method of claim 1, wherein the first metal layer is attached to the first surface side of the ceramic layer prior to the introduction of the metal-containing powdery substance into the hole delimiting the at least one electrically conductive via.

3. The method of claim 1, wherein the metal-containing powdery substance is a powder mixture comprising copper and at least one compound selected from the group consisting of copper(I) oxide, copper(II) oxide and copper(II) hydroxide.

4. The method of claim 3, wherein grain sizes of the powder mixture are at most 90% of the diameter of the hole delimiting the at least one electrically conductive via.

5. The method of claim 1, wherein the first and the second metal layers are attached to the ceramic layer by means of a direct copper bonding (DCB) method.

6. The method of claim 1, wherein the first and the second metal layers are attached to the ceramic layer by means of an active metal brazing (AMB) method, and wherein the metal-containing powdery substance is an AMB solder.

7. The method of claim 1, wherein one of the first and the second metal layers is attached to the ceramic layer simultaneously with the high-temperature step for wetting the ceramic layer with the metal-containing powdery substance.

8. The method of claim 1, further comprising: subjecting the metal-ceramic substrate to hot isostatic pressing after attaching the first and the second metal layers to the ceramic layer.

9. The method of claim 1, further comprising: grinding the metal-ceramic substrate on opposing external metal surfaces after attaching the first and the second metal layers to the ceramic layer.

10. The method of claim 1, wherein aluminum oxide is admixed as a ceramic filler to the metal-containing powdery substance.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other advantages and features of the invention become apparent from the following description as well of exemplary embodiments of the invention, which shall be understood not to be limiting and which will be explained below with reference to the drawing. In this drawing, the Figures schematically show:

(2) FIG. 1 illustrates four process steps (a-d) of a first exemplary embodiment of a method according to the invention;

(3) FIG. 2 illustrates four process steps (a-d) of a second exemplary embodiment of a method according to the invention; and

(4) FIG. 3 illustrates a metal-ceramic substrate produced with the method of FIG. 2 in a lateral sectional view (a) and a top view (b) sectioned along the section line A-A depicted in the lateral sectional view (a).

DETAILED DESCRIPTION

(5) In the different figures, parts that are equivalent with respect to their function are always provided with the same reference numerals, so that they are also only described once, as a rule.

(6) FIG. 1 illustrates four process steps (a-d) of a first exemplary embodiment of a method according to the invention for the production of a metal-ceramic substrate 1 metallized on both sides with an electrically conductive via 2 shown in an exemplary manner in the four detailed views a) to d). In its entirety, the metal-ceramic substrate 1 has a plurality of the vias 2 shown in view d).

(7) As is apparent from FIG. 1, the metal-ceramic substrate 1 has a ceramic plate or ceramic layer 3, such as Al.sub.2O.sub.3 or AlN ceramics. On the lower surface side of the ceramic layer 3 shown in FIG. 1, a first metal layer 4 has already been attached in a planar manner to the ceramic layer 3 prior to the process step a), for example a copper layer by means of the known DCB method. The ceramic layer 3 further has a hole 5 delimiting the electrical via 2. The hole 5 preferably has a diameter of approximately 50 m to approximately 2000 m. For example, it may be introduced into the ceramic layer 3 by lasering after sintering the ceramic layer 3, or by punching the green compact in a corresponding manner prior to sintering.

(8) In the process step b) shown in FIG. 1, a metal-containing powdery substance 6 was introduced into the hole 5. In the case shown here, the metal-containing substance 6 is a powder mixture composed of copper (Cu) and additionally at least one element from the group consisting of copper(I) oxide (Cu.sub.2O), copper(II) oxide (CuO) and copper(II) hydroxide (Cu(OH).sub.2), wherein the content of copper in the powder mixture is between 0% and approximately 95% and the at least one element from the aforementioned group forms the rest up to 100%.

(9) Then, this assembly consisting of the ceramic layer 3, the metal layer 4 attached to a surface side of the ceramic layer 3 and the powder mixture 6 is subjected to a high-temperature step above 500 C., e.g. to a conventional DCB high-temperature step, in which the metal-containing substance 6 wets the inner wall of the hole 5 at least partially with a wetting angle of less than 90, so that a material bond is formed between the ceramic layer 3 and the metal of the powder mixture 6. Process step c) in FIG. 1 depicts the state after this high-temperature step, in which the powder mixture 6 has reacted to form a (porous) copper body 7.

(10) In a further high-temperature step, e.g. a DCB high-temperature step, a second metal layer 8 is then attached in a conventional manner to a surface side of the ceramic layer 3 opposing the first metal layer 4. In the process, the copper body 7 produces an electrically conductive connection between the two metal layers 4 and 8, as is shown in process step d) of FIG. 1.

(11) FIG. 2 illustrates four process steps (a-d) of a second exemplary embodiment of a method according to the invention for the production of a metal-ceramic substrate 10 metallized on both sides with an electrically conductive via 11 shown in an exemplary manner in the four detailed views a) to d). In its entirety, the metal-ceramic substrate 10 has a plurality of the vias 11 shown in view d).

(12) As is apparent from FIG. 2, the metal-ceramic substrate 10 has a ceramic plate or ceramic layer 3, such as Al.sub.2O.sub.3 or AlN ceramics. On the lower surface side of the ceramic layer 3 shown in FIG. 2, a first metal layer 4 has already been attached in a planar manner to the ceramic layer 3 prior to the process step a), for example a copper layer by means of the known DCB method.

(13) As is also apparent from process step a) of FIG. 2, the ceramic layer 3 has a hole 12 delimiting the electrical via 11, which in the case shown here has a considerably smaller diameter than the hole 5 shown in FIG. 1.

(14) The main difference between the method shown in FIG. 2 and the method shown in FIG. 1 is that the hole 11 of the ceramic layer 3 in process step b) of FIG. 2 was treated with brine 13 instead of with a metal-containing powder mixture 6, in particular with a copper hydroxide or copper acetate brine 13, for example by spraying, immersing the ceramic layer 3 into the brine 13 or the like. Due to the surface tension, the brine 13 is drawn into the hole 12, as is shown in process step b) of FIG. 2.

(15) Then, as shown in process step c) of FIG. 2, an additional thermal conversion step for converting the brine 13 into copper oxide 14 is carried out in a temperature range of approximately 100 C. to approximately 200 C. prior to the high-temperature step (not shown in FIG. 2) for forming a copper body 7 in the hole 12 from the copper oxide 14.

(16) In a further high-temperature step, e.g. a DCB high-temperature step, a second metal layer 8 is finally attached in a conventional manner to a surface side of the ceramic layer 3 opposing the first metal layer 4. In the process, the copper body 7 produces an electrically conductive connection between the two metal layers 4 and 8, as is shown in process step d) of FIG. 2.

(17) FIG. 3 illustrates the metal-ceramic substrate 10 produced with the method of FIG. 2 in a lateral sectional view (a) and a top view (b) sectioned along the section line A-A depicted in the lateral sectional view (a).

(18) As is apparent from view (a) of FIG. 3, a semiconductor component 15 is attached to the upper metal layer 8. A plurality of vias 11, each with relatively small diameters, is disposed in a clustered manner underneath the semiconductor component 15. The clustering of the vias 11 makes it possible to ensure the same current-carrying capacity per unit area. The heat dissipation from the semiconductor component 15 can also be improved thereby. Preferably, the vias 11 are therefore disposed underneath the semiconductor component 15, whose outline is shown in view (b) of FIG. 3 as an aid for better illustration.

(19) The above-described inventive method for producing a metal-ceramic substrate with at least one electrically conductive via is not limited to the embodiments disclosed herein, but also includes embodiments having the same effects. For example, it is conceivable directly to use, instead of the liquid sole shown in FIG. 2, a liquid AMB solder if the metallization of the ceramic layer is carried out by means of the AMB method known per se, for example.

(20) Furthermore, the above-described invention can in principle be applied to any type of ceramic substrate, for example AlN (aluminum nitride), Si.sub.3N.sub.4 (silicon nitride), Al.sub.2O.sub.3 (aluminum oxide) and the like, which can be coated with a metal layer, e.g. Cu (copper) or Al (aluminum) or an alloy thereof. In the process, the metallization can be applied to two opposing surface sides of the substrate by means of different methods, e.g. by AMB (active metal brazing), DCB (direct copper bonding), DAB (direct aluminum bonding), thick-film methods and the like. DCB and AMB ceramic substrates are particularly preferred. Here, the term substrate is used as a synonym for all of the above-mentioned types of substrate.

(21) In a preferred embodiment, the metal-ceramic substrate produced by means of the method according to the invention is used for the fabrication of electric circuits, particularly of power circuits.

(22) With the above range of variations and applications in mind, it should be understood that the present invention is not limited by the foregoing description, nor is it limited by the accompanying drawings. Instead, the present invention is limited only by the following claims and their legal equivalents.

LIST OF REFERENCE NUMERALS

(23) 1 Metal-ceramic substrate 2 Via 3 Ceramic layer 4 First metal layer 5 Hole 6 Powdery metal-containing substance 7 Copper body 8 Second metal layer 10 Metal-ceramic substrate 11 Via 12 Hole 13 Brine 14 Brine converted into copper oxide 15 Semiconductor component