DE102010025313A1 - Producing structured electrically conductive layer on substrate or layer made of ceramic material, comprises e.g. providing mixture of metallic material and oxide of it, applying mixture on substrate or layer, and structuring - Google Patents

Abstract

Producing structured electrically conductive layer (2) on a substrate (1) or a layer made of ceramic material, comprises: (a) providing a mixture of at least one metallic material and an oxide of it, which form a eutectic system; (b) applying the mixture either as structured or unstructured layer on the substrate or the layer made of the ceramic material, and structuring after temperature step; (c) heating the substrate or the layer made of the ceramic material with the applied layer of the mixture, to a temperature, in which the applied layer is melted, and cooling. An independent claim is also included for a composite material made of a ceramic substrate or a ceramic layer and a structured electrically conductive layer that is produced by the above method.

Description

Technical application

The present invention relates to a method for producing a structured, electrically conductive layer on a substrate or a layer of a ceramic material, in particular using the so-called direct copper bonding (DCB) method. The method is particularly suitable for the production of fine circuit structures on ceramic substrates.

State of the art

• – Oxidieren einer Kupferfolie derart, dass sich eine gleichmäßige Kupferoxidschicht bildet;
• – Auflegen der Kupferfolie auf die Keramikschicht;
• – Erhitzen des Verbundes auf eine Prozesstemperatur zwischen etwa 1025 und 1083°C, z. B. auf ca. 1071°C; und
• – Abkühlen auf Raumtemperatur.

The application of an electrically conductive layer on a ceramic substrate can be done with a technique such as in the DE 23 19 854 A is described. Here, a metal part, for example. A copper plate or copper foil, on the surface sides with a coating of a chemical compound of the metal and a reactive gas, in particular oxygen, provided. This coating forms a eutectic with a thin layer of the adjacent metal having a melting temperature below the melting temperature of the metal. The metal part is then placed on the ceramic substrate and heated together with the ceramic to a temperature above the melting point of the eutectic and below the melting temperature of the metal. As a result, essentially only the eutectic intermediate layer is melted. After cooling, the metal part and the ceramic substrate are then joined together. When copper or a copper alloy is used as the metal, this process is also referred to as DCB bonding or DCB (Direct Copper Bonding) process, but it can also be performed with other metals. The DCB method comprises, for example, the following method steps:

• - Oxidizing a copper foil such that forms a uniform copper oxide layer;
• - placing the copper foil on the ceramic layer;
• - Heating the composite to a process temperature between about 1025 and 1083 ° C, z. B. to about 1071 ° C; and
• - Cool to room temperature.

Subsequently, the metallization applied to the ceramic substrate is patterned in the desired manner.

The prerequisite for the formation of the required in the process intermediate layer of a eutectic mixture is in the DE 23 19 854 A created by a thermal oxidation of the metal part. Another technique for forming the intermediate layer between a copper foil and a ceramic substrate is shown in FIG Y. Yoshino et al., "Interface Structure and Bond Strength of Copper-Bonded Alumina Substrate", Journal of the American Ceramic Society, Vol. 9, 1991, pages 2184-2188 , described. In this technique, as a solid source for the formation of the intermediate layer, a CuO paste is first applied to the ceramic substrate. Subsequently, the copper foil is placed and connected by melting the intermediate layer with the ceramic substrate.

In previously known methods, a copper sheet, which serves as metallization and function carrier for the subsequent circuit, is connected to the ceramic substrate by the DCB technique. The required handleability of the sheet in this technique dictates a minimum thickness of the copper sheet or a corresponding copper foil. By this minimum thickness, however, the achievable in the subsequent etching process structure width of the metallic structures on the ceramic substrate is limited downwards. Therefore, when using such a circuit substrate for components of power electronics, the integration of the driver and the logic of the subsequent circuit is often made separately from the power unit on non-ceramic supports in order to achieve the smallest possible overall size of the component.

So far, different approaches have been pursued to reduce the minimum possible structural width of the metallic layer on the ceramic substrate and thus to allow integration of logic, driver and power unit on a common ceramic circuit substrate with small component size. One approach is to develop improved etching processes that can etch out finer structures from the metallization. In this way, previously structures could be made with a distance corresponding to the thickness of the metallization. In a further approach, after the successful bonding and possibly subsequent etching process, additional, finer metallic structures are applied to regions of the metallization and optionally to regions etched away on the surface of the ceramic substrate. For this purpose, techniques of electroless plating, spraying and thick film technology are used in conjunction with suitable masking.

The previous approaches to producing a finely structured, electrically conductive layer on a ceramic substrate, however, are expensive.

The object of the present invention is to specify a simple method for producing a finely structured, electrically conductive layer on a substrate or a layer of a ceramic material. The applied layer should on the one hand enable finer structures than in the previous DCB process and, on the other hand, better than thick-film technologies Having adhesion to the layer or the substrate of the ceramic material.

Presentation of the invention

The object is achieved by the method according to claim 1. Advantageous embodiments of the method are the subject of the dependent claims or can be found in the following description and the embodiment.

The proposed method provides a mixture of at least one metallic material and an oxide of the metallic material forming a eutectic system. The mixture is applied either as a structured layer on the substrate or the layer of the ceramic material or applied as an unstructured layer on the substrate or the layer of the ceramic material and patterned only after the subsequent temperature step. The substrate or layer of the ceramic material, hereinafter also referred to as a ceramic support, with the applied layer of the mixture is then heated to a temperature at which the deposited layer melts and forms a eutectic mixture, and then for solidification cooled. The proposed method thus uses the DCB technique or a - in the case of other metallic materials than copper - the DCB technique analogous technique for producing the metallization, but without applying a foil or plate of a metallic material on the ceramic support. Rather, the metallization required for the DCB bonding process and the required amount of oxygen are provided by applying the metal / metal oxide mixture in one step on the ceramic support. These can be conventional application methods such as screen printing or the like, but also spray technologies.

In an alternative of the method, the mixture is already applied as a structured layer on the ceramic support. This can be done, for example, via a suitable masking or a suitable screen printing process. By the subsequent temperature step, which is carried out due to the eutectic system at temperatures well below the melting point of the metal used, the layer connects to the ceramic substrate while maintaining the structures. In this method alternative, the required fine structures are thus already applied in the DCB bonding process, so that no further processing steps for the application of finer structures or the etching of the applied layer are more necessary.

In a second alternative, the mixture is first applied over the entire surface of the ceramic support and connected via the temperature step with the ceramic support. The thickness of the applied layer can be chosen to be small enough to produce the required fine structures of the layer on the ceramic substrate in a subsequent patterning process, in particular an etching process with appropriate masking techniques.

Preferably, the mixture is applied as a pasty mass or paste on the ceramic carrier. In addition to the metal and metal oxide, the mixture may additionally contain ceramic powder. These may be powders of the ceramic material of the ceramic carrier, mixtures of different ceramics, or other ceramic powders coated with the ceramic material of the carrier. An example is ceramic powder of Al ₂ O ₃ in a ceramic carrier of this or another material. Other ceramic powders may, for example, consist of AlN or Si ₃ N ₄ , which, however, then have to have a coating of Al ₂ O ₃ . The ceramic admixture is used to adjust the flow properties at the bonding temperature and the resulting thermal expansion coefficient and the thermal conductivity of the metallic structures, in particular conductor tracks and conductor surfaces. Characteristic of the proposed method is that the admixed ceramic powder in the DCB process firmly bonds to the metallization and thus becomes an integral part of the electrically conductive structure.

With the proposed method finer structures of the electrically conductive layer can be realized on the ceramic support, as was previously possible in DCB process. With the method, a higher integration density can be achieved in the further processing of the substrate for the production of power electronic modules, which enables integration of driver and logic part on the ceramic carrier or power substrate. Compared to conventional circuit carrier technologies such as thick-film technology, the method achieves a far greater adhesion of the metallization to the ceramic carrier and a higher purity of the metallization - and the resulting better technical properties, in particular lower thermal and electrical resistance.

To produce thicker electrically conductive layers on the ceramic carrier, the individual process steps can also be carried out several times in succession. After temperature step and the subsequent cooling is then again applied a new layer of the mixture to the underlying layer and in in the same way connected in a temperature step with the underlying layer. Alternatively, prior to the temperature step, multiple layers of the mixture may be layered on top of each other by repeating the deposition steps to form a thicker layer. In this case, only one final temperature step is required to bond the layers to each other and to the ceramic support.

A further embodiment of the proposed method comprises a combination with the known bonding method, in which a plate or foil made of the metallic material is connected to the ceramic carrier via a corresponding intermediate layer which forms a eutectic mixture. For this purpose, after the application of the mixture to the ceramic carrier, the corresponding metallic foil or plate is placed on a portion of the applied layer, and then the temperature step is carried out. While the area of the deposited layer not covered by the sheet or film directly forms the metallization, the metallization in the other area is formed by the applied plate or foil, where the applied layer of the mixture in a known manner as an intermediate layer for the connection with the Ceramic carrier serves.

The proposed method can be carried out in particular with the parameters of the known DCB bonding process. In this case, the mixture used is a mixture of copper and copper oxide, optionally with admixture of ceramic powder. The mixture consists of at least 2% copper oxide and at least 2% copper. The copper oxide may be CuO or Cu ₂ O. Depending on the chosen method, a slightly liquid binder can also be added. However, the process can also be carried out in an analogous manner with other metals, provided that they form a eutectic system in conjunction with their oxide.

Brief description of the drawings

The present method will be explained in more detail below with reference to exemplary embodiments in conjunction with the figures. Hereby show:

1 schematically a first example of the implementation of the proposed method;

2 schematically a second example of the implementation of the proposed method;

3 schematically a third example of the implementation of the proposed method; and

4 schematically a fourth example of the implementation of the proposed method.

Ways to carry out the invention

In the following, the proposed method will be explained in various embodiments, in which a copper-containing metallization is applied to an Al ₂ O ₃ or an AlN ceramic substrate. With the method, metallic structures can be applied to the ceramic substrate on one or both sides. Furthermore, it is also possible to use a substrate made of another material with a ceramic surface layer instead of the ceramic substrate.

1 shows a first example, in which the metallization is applied to one side of the ceramic substrate. For this purpose, first a Cu / CuO paste, which represents the eutectic system, as a structured layer 2 on the ceramic substrate 1 applied. This can be done, for example, by means of a doctor blade. The paste has an oxygen content of 2-8 wt .-%, so that a copper content of 98-92 wt .-% results. Following the application of the Cu / CuO paste, the ceramic substrate passes through 1 with the applied layer 2 the DCB process being taken from the paste or applied layer 2 the desired structured metallization 3 arises, which is firmly connected to the ceramic support. The process temperature is approximately between 1025 and 1083 ° C, for example. About 1071 ° C. The structure may include, for example, conductor tracks for the subsequent application of the electrical or electronic circuit parts. The dissolution of the structure is largely determined by the application process of the paste. Unlike the known DCB method according to the prior art, the Cu / CuO mixture applied here is not used as an oxygen carrier for bonding a metallization plate, but serves as an independent carrier or conductor track structure of the later circuit.

2 shows an example of a two-sided application of a patterned metallization on a ceramic substrate 1 , The first three steps correspond to those of 1 , so that will not be discussed in more detail here. The application of the Cu / CuO paste can take place here, for example, by means of screen printing. After the formation of the structure metallization 3 on top of the ceramic substrate is turned and the paste in the same way in the desired structure as a layer 2 applied to the back. Subsequently, again the temperature step, which corresponds to the DCB process, so that finally a ceramic substrate 1 with a double-sided structured metallization 3 is obtained.

For the construction of thicker electrically conductive structures or metallizations, in particular thicker interconnect layers, as well as for finally ensuring a solderable surface, the proposed method can be repeated several times. In an alternative, after completing the structured metallization on the ceramic substrate, as in the last step of the embodiment according to FIG 1 a patterned layer of the mixture is again applied to this patterned metallization and joined to the underlying metallization by a DCB process. This can be repeated by a multiple series of printing and high temperature processes until the desired thickness of the resulting metallization on the ceramic substrate is obtained.

In another alternative, as in 3 is shown, only the step of applying the paste is repeated several times and carried out only a final temperature step according to the DCB process. 3 shows the step of applying the structured layer 2 on the ceramic substrate 1 , for example by means of screen printing. Subsequently, by means of screen printing in the desired sections another, possibly structured, layer 4 from the mixture to the underlying layer 2 applied. Again, this can, for example, done by screen printing. Finally, in this example, the final high-temperature step, in which the structured metallization takes place 3 obtained firmly with the underlying ceramic substrate 1 connected is. In this way, higher layer thicknesses of the metallization on the ceramic substrate can be 1 produce.

Of course, these two alternatives can be performed so that the thickness of the patterned metallization 3 only locally in certain places or even continuously increased.

To build thicker wiring layers and finally ensure a solderable surface, the process can also be combined with a conventional DCB process. this is in 4 exemplified. Here, in turn, in a known manner, a structured layer 2 by applying the Cu / CuO paste, for example by screen printing, on the ceramic substrate 1 generated. Subsequently, a section of the structured layer 2 a copper sheet 5 hung up. Finally, in a known manner, the high-temperature step, ie the DCB process, in which the structured metallization forms, which firmly with the ceramic substrate 1 connected is.

The technical advantage of this combination with the conventional DCB process is the fixed and direct connection between the fine structure (driver / logic) and the coarse structure (power section), which no longer requires any other connection elements, such as wire bonds. The power unit does not require as fine structuring as the driver or logic part. In the in 4 Thus, the driver or logic components are applied to the finely structured left part, the power parts on the coarsely structured or structurable right part. On the cost and process side, this embodiment offers the advantage that the high-temperature process only has to be run through once.

LIST OF REFERENCE NUMBERS

1

ceramic substrate

2

structured layer

3

structured metallization

4

another structured layer

5

copper sheet

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 2319854 A [0002, 0004]

Cited non-patent literature

• Y. Yoshino et al., "Interface Structure and Bond Strength of Copper-Bonded Alumina Substrate", Journal of the American Ceramic Society, Vol. 9, 1991, pages 2184-2188 [0004]

Claims (9)

Method for producing a structured, electrically conductive layer ( 3 ) on a substrate ( 1 ) or a layer of a ceramic material, in which - a mixture of at least one metallic material and an oxide of the metallic material is provided, which form a eutectic system, - the mixture either as a structured layer ( 2 ) on the substrate ( 1 ) or the layer of the ceramic material applied or as an unstructured layer on the substrate ( 1 ) or the layer of the ceramic material is applied and structured after the subsequent temperature step, and - the substrate ( 1 ) or the layer of the ceramic material with the applied layer ( 2 ) is heated from the mixture to a temperature at which the applied layer ( 2 ), and then forming the structured, electrically conductive layer ( 3 ) cools down again. A method according to claim 1, characterized in that the mixture additionally contains a proportion of Al ₂ O ₃ and / or on one or more further ceramic materials. A method according to claim 1 or 2, characterized in that the mixture is provided as a powder or paste and applied to the substrate ( 1 ) or the layer of the ceramic material is applied. Method according to one of claims 1 to 3, characterized in that the mixture by means of screen printing or by means of a spraying technique on the substrate ( 1 ) or the layer is applied. Method according to one of claims 1 to 4, characterized in that the sequence of operations is repeated several times from application of the mixture to cooling or structuring, to form a thicker electrically conductive layer ( 3 ) on the substrate ( 1 ) or the layer of the ceramic material, wherein the application of the mixture then in each case at least to portions of the already present electrically conductive layer ( 3 ) he follows. Method according to one of claims 1 to 4, characterized in that the step of applying the mixture as a structured or unstructured layer ( 2 ) is repeated several times before the subsequent temperature step to form a thicker layer ( 2 ) from the mixture on the substrate ( 1 ) or the layer of the ceramic material, wherein the application of the mixture then in each case at least to portions of each already applied applied layer ( 2 ) takes place from the mixture. Method according to one of claims 1 to 6, characterized in that a portion of the structured or unstructured layer ( 2 ) from the mixture before the subsequent temperature step, a film or plate ( 5 ) is applied from the metallic material and through the subsequent temperature step via the molten structured or unstructured layer ( 2 ) as an intermediate layer with the substrate ( 1 ) or the layer of the ceramic material is connected. Method according to one of claims 1 to 7 for the production of printed circuit boards or metallized substrates for electrical or electronic circuits. Composite of a ceramic substrate ( 1 ) or a ceramic layer and a structured, electrically conductive layer ( 3 ) produced according to any one of claims 1 to 7.

Images