DE102019110106A1 - Method for producing a composite ceramic and composite ceramic produced using such a method - Google Patents

Abstract

A method for producing a composite ceramic (10) comprising- providing a first layer (31) made of a first ceramic material, - arranging the first layer (32) in an oven (20), the first layer (31) in the oven (20) at least is partially surrounded by a powdery or pasty, second layer (32) made of a second ceramic material and - carrying out a hot pressing process to form the composite ceramic (10), which in the manufactured state has a first layer (11) made of the first ceramic material and a second layer ( 12) made of the second ceramic material.

Description

The present invention relates to a method for producing a composite ceramic and a composite ceramic produced using such a method.

Insulation layers made of ceramics for printed circuit boards are well known from the prior art. In this case, metallizations are typically provided on the upper and / or lower side, which serve as conductor tracks or as connection areas for electronic components. The use of AIN is known, for example, in order to effectively dissipate heat generated on the top and / or bottom in order to avoid damage to the circuit board. Despite the material properties of AIN which are favorable for heat dissipation, its use as a ceramic material often proves to be disadvantageous because of its reduced strength compared to other ceramics.

Therefore it is known from the prior art, e.g. B. from the US 0 640 039 A1 , known to design the insulation layer in multiple layers, the individual layers being made from different ceramic materials. Such a composite ceramic allows undesired properties of a ceramic material, such as, for example, reduced strength, to be compensated for by correspondingly pronounced properties of another ceramic material. However, the composite ceramics in the US 0 640 039 A1 produced by an active soldering process, so that a solder layer is formed between the individual layers, which in turn influences the overall properties of the composite ceramic, in particular its electrical insulation properties. Basically, a level of electrical insulation capability of a metal-ceramic substrate is determined on the one hand by the thickness of the insulation layer, which insulates the circuits from a reference potential, and on the other hand by the width of the insulation trenches between the conductor tracks. By introducing a continuous, electrically conductive solder layer underneath the conductor tracks, however, the insulation strength of the circuit is reduced in comparison with an insulation layer containing ceramic without a solder layer. This applies in particular to comparatively thin cover layers in the composite ceramic.

Based on this background, it is the object of the present invention to provide a composite ceramic and a method for its production in which the properties can be adjusted as optimally as possible for use as a printed circuit board, in particular with regard to their electrical insulation properties.

The object is achieved by a method according to claim 1 and a composite ceramic according to claim 10. Further advantages and features emerge from the preferred embodiments of the subject matter according to the invention explained in the following description with reference to the accompanying figures. Individual features of the individual embodiments can be combined with one another within the scope of the invention

• - Bereitstellen einer ersten Schicht aus einem ersten Keramikwerkstoff,
• - Anordnen der ersten Schicht in einem Ofen, wobei die erste Schicht im Ofen zumindest teilweise von einer zweiten pulverförmigen, granulatförmigen oder pastenförmigen Schicht aus einem zweiten Keramikwerkstoff umgeben ist und
• - Durchführen eines Heißpressverfahrens zur Ausbildung der Verbundkeramik, die im gefertigten Zustand eine erste Lage aus dem ersten Keramikwerkstoff und eine zweite Lage aus dem zweiten Keramikwerkstoff aufweist.

A first aspect of the present invention relates to a method for producing a composite ceramic comprising

• - Providing a first layer made of a first ceramic material,
• Arranging the first layer in an oven, the first layer in the oven being at least partially surrounded by a second powdery, granular or pasty layer made of a second ceramic material, and
• - Carrying out a hot pressing process to form the composite ceramic which, in the manufactured state, has a first layer made of the first ceramic material and a second layer made of the second ceramic material.

Compared to the methods known from the prior art, in particular the methods in which the composite ceramic is produced using an active soldering process, it is advantageously possible, by implementing the composite ceramic according to the invention by a hot pressing process, to have a second layer that is as dense and closed as possible Manufacture composite ceramics. The second layer serves in particular as a cover layer for the first layer and the complete and tight covering by means of this cover layer, which is designed as a second layer, ensures, for example, that the dielectric strength of the composite ceramic is as high as possible if the second ceramic material is used for a corresponding increase in the Dielectric strength in the composite ceramic should be provided. Production by means of the hot pressing process results in an immediate, i.e. H. direct connection of the first layer to the second layer, in particular without a solder layer. It is clear to the person skilled in the art that the ceramic materials, i. H. the first ceramic material and the second ceramic material are present as the first and second layers respectively during the manufacturing process and the first layer becomes the first layer and the second layer becomes the second layer through the hot pressing process.

In particular, it is provided that the first layer is plate-shaped, ie forms a solid body that extends along a main plane of extent, while the second layer preferably consists of one powdery or granular or fitted-shaped second ceramic material is formed. The person skilled in the art preferably understands the hot pressing process to be such a process in which compression is achieved while simultaneously applying pressure and temperature. In the present case, a connection to the first layer is also implemented in particular by means of the hot pressing process. In other words: The composite ceramic is realized by the hot pressing process.

In particular, the prior art knows z. B. uniaxial pressing or isostatic pressing. The composite ceramic is preferably realized by means of hot isostatic pressing (HIP), the so-called “hipping”. For this purpose, for example, an arrangement of the first layer and the second layer is enclosed in a deformable container. For example, this deformable container is formed from a latex material and then this enclosed arrangement is subjected to an appropriate pressure and a certain temperature. After a certain residence time in the furnace, the composite ceramic is then removed again from the furnace. In particular, it is provided that the second layer is formed both on the upper side and also on the underside, ie. H. a sandwich structure is formed for the composite ceramic. For this purpose, in particular the first layer is completely encased by the second layer when it is arranged in the oven. In other words, the first layer is embedded in the second layer. The second layer preferably has free-flowing granules or powder made from the second ceramic material.

According to a preferred embodiment it is provided that the first ceramic material, silicon carbide SiC and / or the second ceramic material is silicon nitride Si ₃ N ₄ . This makes it possible in an advantageous manner, while maintaining the excellent thermal conductivity of silicon carbide, to improve its low dielectric strength by using the second layer made of the ceramic material silicon nitride with a high dielectric strength. In particular, it has been found that a dielectric strength of up to 2 to 3 kV can be achieved in this way, while silicon carbide alone only has a dielectric strength of 10 V.

According to a preferred embodiment, it is provided that the second layer is applied by means of spin coating. In this way, a uniform distribution of the second layer on the first layer can advantageously be realized. The spin coating process is preferably carried out in a preparatory step before the hot pressing process. Typically, such rotary coating processes are a procedure in which a paste made of the second ceramic material is arranged on the first layer and by rotation around an axis of rotation that is perpendicular to the main extension plane HSE the first layer runs, centrifugal forces are generated, which lead to the fact that the paste is evenly distributed on the top of the first layer. In particular, rotation speeds of 1,000 to 4,000 revolutions per minute are used here and the turning or rotating takes place for approx. 10 to 30 seconds. This spin coating process is particularly preferably combined with Y ₂ O ₃ , which was added to the paste made from the second ceramic material.

In particular, it has been found that for spin coating processes with rotation speeds of 800 to 1,200 revolutions per minute, comparatively high dielectric strengths can be achieved.

Provision is preferably made for the second layer in the manufactured composite ceramic to have a second thickness between 10 and 150 μm, preferably between 30 and 50 μm and particularly preferably between 35 and 45 μm. It has been found that especially for second thicknesses between 35 and 45 µm as a cover layer, i.e. H. as a second layer, dielectric strengths between 2 and 3 kV could be achieved for the composite ceramic. Particularly preferably, a second layer is formed on the top and bottom of the composite ceramic, which have essentially the same second thickness. Alternatively, however, it is also conceivable that the second layer on the upper side has a different second thickness than the layer on the lower side.

It is preferably provided that the first layer in the manufactured composite ceramic has a first thickness, the ratio of the second thickness to the first thickness being between 0.05 and 0.2, preferably between 0.05 and 0.15 and particularly preferred takes between 0.075 and 0.13. Correspondingly, the second layer is used to form a cover layer which encases or surrounds the first layer. The first layer, on the other hand, forms a type of core layer of the composite ceramic and essentially contributes to the properties of the composite ceramic. In particular because of the increased thermal conductivity of silicon carbide, for example, it is advantageous to form a thick first layer in order to be able to transport away as much heat as possible.

Preferably it is it is provided that the hot pressing process is carried out at a temperature between 1,500 and 2,000 ° C., preferably between 1,700 and 2,000 ° C. and particularly preferably between 1,850 and 1,950 ° C. In particular, it is provided that the hot pressing process is carried out at a temperature of 1,900 ° C.

The hot pressing process is preferably carried out for more than 4 hours, preferably for more than 6 hours and particularly preferably for more than 8 hours. In particular for dwell times above 6 hours, in particular 8 hours, a significant increase in the dielectric strength can be determined compared to composite ceramics that have not been exposed to the hot pressing process for so long.

In a particularly preferred embodiment of the present invention it is provided that the hot pressing process is carried out in a gas atmosphere, in particular in a nitrogen atmosphere. In particular, the hot pressing takes place with the exclusion of oxygen. As an alternative to nitrogen, the use of argon is also conceivable.

In particular, it is provided that a structured metallization is implemented on the composite ceramic. This allows the composite ceramic in particular to be used as a circuit board. In particular, the properties of high dielectric strength and high thermal conductivity prove to be particularly advantageous for a printed circuit board. The metallization is produced by means of a direct metal connection process and / or an active soldering process. Examples of a direct metal bonding process are a DCB and / or a DAB process.

A direct metal bonding process, such as a “DCB process” (Direct Copper Bond Technology) or DAB process (Direct Aluminum Bond Technology), is understood by those skilled in the art to be such a process, which is used, for example, for joining metal layers or sheets (e.g. copper sheets or foils) are used with one another and / or with ceramic or ceramic layers, namely using metal or copper sheets or metal or copper foils that have a layer or a coating (melted layer) on their surface sides ) exhibit. For example, in the U.S. 3,744,120 A or in the DE23 19 854 C2 described method, this layer or this coating (melting layer) forms a eutectic with a melting temperature below the melting temperature of the metal (e.g. copper), so that by placing the foil on the ceramic and heating all the layers, these can be connected to one another, and by melting the metal or copper essentially only in the area of the melting layer or oxide layer.

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

In particular, the DCB method then z. B. the following process steps:

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

Under an active soldering process, e.g. B. for connecting metal layers or metal foils, in particular also copper layers or copper foils with ceramic material, a method is to be understood which is also used specifically for the production of metal-ceramic substrates. Here, at a temperature between approx. 650-1000 ° C, a connection between a metal foil, for example a copper foil, and a ceramic substrate, for example aluminum nitride ceramic, is produced using a hard solder which, in addition to a main component such as copper, silver and / or Gold, also contains an active metal. This active metal, which is, for example, at least one element from the group Hf, Ti, Zr, Nb, Ce, creates a connection between the solder and the ceramic through a chemical reaction, while the connection between the solder and the metal is a metallic brazed connection .

Alternatively, a DAB process for aluminum metallization and / or a thick film process are also conceivable for the connection.

Another aspect of the present invention is a composite ceramic produced using the method according to the invention. All of the features and advantages described can be applied to composite ceramics and vice versa.

Further advantages and features emerge from the following description of preferred embodiments of the subject matter according to the invention with reference to the attached figures. Individual features of the individual embodiment can be combined with one another within the scope of the invention.

• 1: ein Verfahren zur Herstellung einer Verbundkeramik gemäß einer beispielhaften Ausführungsform der vorliegenden Erfindung und
• 2: eine Leiterplatte mit einer Verbundkeramik gemäß einer beispielhaften Ausführungsform der vorliegenden Erfindung.

It shows:

• 1 FIG. 12 shows a method of manufacturing a composite ceramic according to an exemplary embodiment of the present invention and FIG
• 2 Fig. 3 shows a circuit board with a composite ceramic according to an exemplary embodiment of the present invention.

In the 1 is a composite ceramic 10 illustrated in accordance with an exemplary embodiment of the present invention. In particular, it acts when it comes to composite ceramics 10 around a carrier substrate or an insulation layer, which represents an essential part of a circuit board. To form the circuit board are on a top OS and / or on a bottom US Metallizations 3 or further metallizations 3 ' , in particular metallizations structured by etching, are provided, which provide conductor tracks or metal pads for connecting electronic components. By combining different ceramic materials, it is advantageously possible to create specifically desired properties in the composite ceramic 10 to combine, which would otherwise only be given by a single ceramic material, or undesired properties of a first ceramic material can be compensated for with properties of a second ceramic material.

Under a composite ceramic 10 or hybrid ceramic is to be understood here in particular as a carrier substrate which in the manufactured state has at least one first layer 11 from the first ceramic material and a second layer 12 having from the second ceramic material. Here is the first layer 11 directly to the second layer 12 connected and the composite ceramics 10 extends in a main plane of extent HSE . The first location 11 and the second layer 12 are then along a perpendicular to the main extension plane HSE running stack direction S. arranged one above the other. In the in 1 illustrated embodiment is a first layer 11 and a second layer 12 intended. Preferably the first layer 11 of two second layers 12 surrounded or sheathed. In other words: the first layer 11 is between two second layers 12 arranged to form a sandwich structure (not shown). It is also possible that the first location 11 between a second layer 12 and one from the second layer 12 different third layer (not shown) is arranged. It is particularly preferred that the first ceramic material differ from the second ceramic material. This makes it possible in an advantageous manner to have positive specifications or properties of the first ceramic material and the second ceramic material in the composite ceramic 10 to combine.

In particular, the first ceramic material is silicon carbide SiC and the second ceramic material is silicon nitride Si ₃ N ₄ . While the first ceramic material z. B. has a comparatively low dielectric strength and a comparatively high thermal conductivity as silicon carbide, it is advantageous through the implementation of the second layer 12 with the second ceramic material silicon nitride Si ₃ N ₄ possible, a significantly higher dielectric strength for the composite ceramic 10 to be realized than would be the case for a pure carrier layer or insulation layer made of silicon carbide. In other words: by encapsulating or sheathing the first layer 11 made of silicon carbide SiC with the second layer 12 A composite ceramic can be made from silicon nitride Si ₃ N ₄ 10 produce that has a high dielectric strength and a high thermal conductivity.

It is provided in particular that the second layer 12 a second thickness D2 and the first layer 11 a first thickness D1 , where a ratio of the first thickness D1 to the second thickness D2 assumes a value between 0.5 and 0.2, preferably between 0.05 and 0.15 and particularly preferably between 0.075 and 0.13. In other words: the second layer 12 forms a top coating for the first layer designed as a core layer 11 . In particular, it is provided that on the top OS and bottom US the composite ceramics 10 by means of a direct metal bonding process, e.g. B. a DCB or DAB process, and / or metallization by an active soldering process 3 at the top OS and / or bottom US is realized, which can then be structured by a suitable etching process, so that a circuit board is obtained on which electronic components or electronic components can be mounted.

In 2 is a method for producing a composite ceramic 10 , for example a composite ceramic 10 out 1 , shown. It is provided that a first layer 31 is provided from a first ceramic material. This is the first layer 31 preferably plate-shaped or as a solid body that extends along the main plane of extent HSE extends, formed. The first layer 31 The first ceramic material is then placed in an oven 20th arranged. In particular, the first layer 31 in the oven 20th arranged in such a way that they are covered by a powdery, pasty and / or granular second layer 32 is at least partially, preferably completely, surrounded by a second ceramic material. In other words: the first layer 31 will be in a second shift 32 embedded from a powder or granules from the second ceramic material.

A composite ceramic is then produced by a hot pressing process, preferably hot isostatic pressing 10 produced, the first layer in the finished state 11 from the first ceramic material and the second layer 12 having from the second ceramic material. In the case of hot isostatic pressing, it is then preferably provided that the arrangement from the first layer is formed at a temperature of about 1900 ° C for about 8 hours 31 and second layer 32 is subjected to a pressure of 2.5 to 3.5 MPa. In particular, the hot isostatic pressing takes place in a gas atmosphere 35 , which consists in particular of nitrogen. Preferably done hot isostatic pressing or the hot pressing process with exclusion of oxygen.

It has proven to be advantageous if, with the specified parameters, a second thickness D2 for the second layer 12 is realized, which is between 10 and 150 μm, preferably between 30 and 35 μm and particularly preferably between 35 and 45 μm. This enables dielectric strengths of 2.6 to 3 kV for the composite ceramic 10 realize. In particular, it is provided that both on the top OS as well as at the bottom US the composite ceramics 10 a second layer each 12 is formed with one of the corresponding second thicknesses. Preferably both are second thicknesses D2 the same size.

In 3 is a method for producing a composite ceramic 10 illustrated in accordance with a second preferred embodiment of the present invention. In addition to the hot pressing process used for 2 has been described, it is provided here, in a preparatory step by means of a spin coating, a further second layer 32 ' made from a silicon nitride paste. Thereby the silicon nitride paste is on the first layer 31 applied from silicon carbide and the silicon carbide layer for rotation around an axis of rotation R. driven. At around 1,000 to 4,000 revolutions per minute for 10 to 40 seconds, the centrifugal forces created by the rotation ensure that the paste is evenly on the top OS the first layer 31 , in particular the first layer consisting of silicon carbide 31 , is distributed. Then the first layer 31 on which the second layer 32 applied as a paste using the spin coating process, in the oven 20th embedded and additionally from the second layer 32 surrounded by the second ceramic material, in particular completely encased or embedded in the powder or granules. The hot pressing process is then carried out as described above.

In 4th various examples of composite ceramics are shown, which are produced using one of the methods from 2 or. 3 were manufactured. The parameters for the hot pressing process or the hot pressing process can be found in column B. Essential parameters of the hot pressing process are the temperature used and the length of time in the furnace while the hot pressing process is carried out. In column A, if carried out, the parameters for the spin coating are entered. Essential parameters for the spin coating process are the number of revolutions per minute and the duration of the implementation of the spin coating process. In column D is the second thickness D2 , ie the second thickness D2 the second layer 12 in the manufactured composite ceramic 10 specified. This is between 20 and 100 µm. Column C shows the dielectric strength of the composite ceramic 10 . In particular, the table shows that particularly high dielectric strengths of up to three kV can be achieved if the arrangement from the first layer is made using a rotation coating process at 1,000 revolutions per minute for at least 10 seconds in a subsequent hot pressing process 31 and second layer 32 exposed to a temperature of 1,900 ° C for about 8 hours. This means that layer thicknesses between 35 and 40 µm and dielectric strengths between 2 and 3 kV can be achieved.

List of reference symbols

3

Metallization

3 '

further metallization

10

Composite ceramics

11

first position

12

second layer

20th

oven

31

first layer

32

second layer

32

another second layer

35

Gas atmosphere

R.

Rotation matter

D1

first thickness

D2

second thickness

S.

Stacking direction

HSE

Main plane of extent

OS

Top

US

bottom

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was 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.

Patent literature cited

• US 0640039 A1 [0003]
• US 3744120 A [0019]
• DE 2319854 C2 [0019]

Claims (10)

A method for producing a composite ceramic (10) comprising - providing a first layer (31) made of a first ceramic material, - Arranging the first layer (32) in an oven (20), the first layer (31) in the oven (20) at least partially from a powdery and / or granular and / or paste-like, second layer (32) made of a second ceramic material is surrounded and - Carrying out a hot pressing process to form the composite ceramic (10) which, in the manufactured state, has a first layer (11) made of the first ceramic material and a second layer (12) made of the second ceramic material. Procedure according to Claim 1 , wherein the first ceramic material is SiC and / or the second ceramic material is Si ₃ N ₄ . Method according to one of the preceding claims, wherein the second layer (32) is applied by means of spin coating. Method according to one of the preceding claims, wherein in the manufactured composite ceramic (10) the second layer (12) has a second thickness (D2) between 10 µm and 150 µm, preferably between 30 and 50 µm and particularly preferably between 35 µm and 45 µm . Method according to one of the preceding claims, wherein in the produced composite ceramic (10) the first layer (11) has a first thickness (D1), a ratio of the second thickness (D2) to the first thickness (D1) having a value between 0.05 and 0.2, preferably between 0.05 and 0.15 and particularly preferably between 0.075 and 0.13. Process according to one of the preceding claims, wherein the hot pressing process is carried out at a temperature between 1500 and 2000 ° C, preferably between 1700 ° C and 2000 ° C and particularly preferably between 1850 ° C and 1950 ° C. Method according to one of the preceding claims, wherein the hot pressing process is carried out for more than 4 hours, preferably for more than 6 hours and particularly preferably for more than 8 hours. Method according to one of the preceding claims, wherein the hot pressing method is carried out in a gas atmosphere (35), in particular a nitrogen atmosphere. Method according to one of the preceding claims, wherein a structured metallization (3, 3 ') is realized on the composite ceramic (10). Composite ceramic (10) produced by a method according to one of the preceding claims.

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