EP3956275A1

EP3956275A1 - Method for producing a composite ceramic, and composite ceramic produced using such a method

Info

Publication number: EP3956275A1
Application number: EP20719992.8A
Authority: EP
Inventors: Karsten Schmidt; Lei Liu; Xinhe Tang; Yang Zhong
Original assignee: Rogers Germany GmbH
Current assignee: Rogers Germany GmbH
Priority date: 2019-04-17
Filing date: 2020-04-15
Publication date: 2022-02-23
Also published as: WO2020212438A1; DE102019110106A1

Abstract

The invention relates to a method for producing a composite ceramic (10), having the steps of: - providing a first layer (31) made of a first ceramic material, - arranging the first layer (32) in a furnace (20), wherein the first layer (31) is at least partly surrounded by a pulverulent or pasty second layer (32) made of a second ceramic material in the furnace (20), and - carrying out a hot pressing method in order to form the composite ceramic (10) which has a first layer (11) made of the first ceramic material and a second layer (12) made of the second ceramic material in the finished state.

Description

Method for producing a composite ceramic and composite ceramic produced using such a method

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 side 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 US 0 640 039 A1, known to design the insulation layer in several layers, the individual layers are each made of different ceramic materials. Such a composite ceramic makes it possible to compensate for undesired properties of a ceramic material, such as, for example, a reduced strength, through correspondingly pronounced properties of another ceramic material. However, the composite ceramics in US Pat. No. 0 640 039 A1 are manufactured using 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 Height of the electrical insulation capacity of a metal-ceramic substrate on the one hand by the thickness of the insulation layer, which isolates the circuits from a reference potential and on the other hand by a width of the insulation trenches between the conductor tracks. By introducing a continuous, electrically conductive solder layer below the conductor tracks, however, the insulation strength of the circuit is reduced in comparison to 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 set 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

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 ceramics are produced using an active soldering process, it is advantageously possible to create a second layer that is as dense and closed as possible by making the composite ceramic according to the invention using a hot pressing process in the 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 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 the dielectric strength in the composite ceramic should be provided. As a result of the production by means of the hot pressing process, a direct, ie direct, connection of the first layer to the second layer, in particular without a solder layer, is realized. It is clear to the person skilled in the art that the ceramic materials, ie the first ceramic material and the second ceramic material, are present as the first or second layer during the manufacturing process and, through the hot pressing process, the first layer is formed from the first layer and the second layer from the second layer becomes.

It is preferably provided that during hot pressing a gas pressure and / or a mechanical pressure is provided which acts on the first and second layers in the furnace. The person skilled in the art understands a hot pressing method to mean the action of a pressure, for example a gas pressure or a mechanical pressure, which acts on the ensemble of the first layer and the second layer while heat is supplied or heating takes place. For example, the mechanical pressure is carried out by a corresponding Pressvor direction in which the first layer and the second layer are arranged.

In particular, it is provided that a mechanical pressure acting on the first layer and the second layer is implemented by means of a pressing device, the first layer and the second layer being arranged in the pressing device. The pressing device allows the desired pressure to be transferred to the ensemble of first layer and second layer during pressing. The pressing device preferably has a protruding contour on its inside which comes into contact with the second layer, and the second layer is at least locally displaced by the protruding contour. It is thereby advantageously possible to implement structuring in the cover layer. In other words: it is implemented like a composite ceramic in which the second layer has a modulated thickness or does not cover the first layer in sections. As a result, a height profile is specifically implemented on the outside of the composite ceramic. In particular, this creates areas in which, when the metal is globally bound to the composite ceramic, there is no or only a weak local connection. In these areas, the metal is occasionally removed during subsequent structuring, especially during second etching.

In particular, it is provided that the first layer is formed in the form of a plate, d. H. forms a solid body which extends along a main extension plane, while the second layer is preferably formed from a powdery or granular or fitted second ceramic material. The person skilled in the art preferably understands the hot pressing process to be such a process in which compression is achieved with the simultaneous application of pressure and temperature. In the present case, a connection to the first layer in particular is realized 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 implemented by means of hot isostatic pressing (HIP), known as “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 is a closed arrangement subjected to a corresponding 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 lower side, ie a sandwich structure is formed for the composite ceramics. 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 nitrite S13N4. 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 this allows a dielectric strength of up to 2 to 3 kV, 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. As a result, a uniform distribution of the second layer on the first layer can advantageously be achieved. The spin coating process is preferably carried out in a preparatory step before the hot pressing process. Typically, such rotary coating processes are a process in which a paste made of the second ceramic material is placed on the first layer and centrifugal forces are generated by rotation around an axis of rotation that runs perpendicular to the main plane of extension HSE of the first layer cause the paste to be evenly distributed on 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 Rotation takes place for approx. 10 to 30 seconds. This rotary coating process is particularly preferably combined with Y2O3, which was added to the paste made from the second ceramic material.

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

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 kind 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.

It is preferably 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. is particularly preferably carried out 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 of more than 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 have proven 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 connection method, such as a “DCB method” (Direct Copper Bond Technology) or DAB method (Direct Aluminum Bond Technology), is understood by the person skilled in the art to be such a method, for example for connecting 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, which have a layer or a coating (melting layer) on their surface sides. In this method described, for example, in US Pat. No. 3,744,120 A or in DE23 19 854 C2, 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 through Laying the film on the ceramic and by heating all layers these can be connected to one another, namely by melting the metal or copper essentially only in the area of the melting layer or oxide layer.

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 Me tallfolien, in particular also of copper layers or copper foils with ceramic material, a method is to be understood, which is specifically used for the manufacture of metal-ceramic substrates. Here, at a temperature between about 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, establishes a connection between them through a chemical reaction the solder and the ceramic, while the connection between the solder and the metal is a metallic braze joint.

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 manufactured 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.

It shows:

1 shows a method for producing a composite ceramic according to an exemplary embodiment of the present invention and

Fig. 2: a circuit board with a composite ceramic according to an exemplary embodiment of the present invention.

In FIG. 1, a composite ceramic 10 according to an exemplary embodiment of the present invention is illustrated. In particular, the composite ceramic 10 is a carrier substrate or an insulation layer which represents an essential component of a printed circuit board. To form the circuit board, on an upper side OS and / or on a lower side US metallizations 3 or further metallizations 3 ', in particular metallizations structured by etching, are provided, the conductor tracks or metal pads for connection. that of electronic components. By combining different ceramic materials, it is advantageously possible to combine specifically desired properties in the composite ceramic 10 that would otherwise only be provided by a single ceramic material or undesired properties of a first ceramic material with properties of a second ceramic material compensate.

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 a first layer 11 made of the first ceramic material and a second layer 12 made of the second ceramic material. The first layer 11 is directly connected to the second layer 12 and the composite ceramic 10 extends in a main plane of extent HSE. The first layer 11 and the second layer 12 are then arranged one above the other along a stacking direction S running perpendicular to the main extension plane HSE. In the exemplary embodiment shown in Figure 1, a first layer 11 and a second layer 12 is provided. The first layer 1 1 is preferably surrounded or sheathed by two second layers 12. In other words: the first layer 11 is arranged between two second layers 12 with the formation of a sandwich structure (not shown). It is also possible that the first layer 11 is arranged between a second layer 12 and a third layer (not shown) that is different from the second layer 12. It is particularly preferably provided that the first ceramic material differs from the second ceramic material. This makes it possible in an advantageous manner to combine positive specifications or properties of the first ceramic material and the second ceramic material in the composite ceramic 10.

In particular, the first ceramic material is silicon carbide SiC and the second ceramic material is silicon nitride S13N4. 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 By realizing the second layer 12 with the second ceramic material Si silicon nitride S13N4, it is possible to realize a significantly higher dielectric strength for the composite ceramic 10 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 made of silicon nitride S13N4, a composite ceramic 10 can be produced which has high dielectric strength and high thermal conductivity.

It is provided in particular that the second layer 12 has a second thickness D2 and the first layer 11 has a first thickness D1, the ratio of the first thickness D1 to the second thickness D2 being 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 11 designed as a core layer. In particular, it is provided that on the upper side OS and lower side US of the composite ceramic 10 by means of a direct metal connection method, e.g. B. a DCB or DAB process, and / o a metallization 3 is realized on the top OS and / o the bottom US by an active soldering process, which can then be structured by an appropriate etching process so that a circuit board is obtained, on which electronic components or electronic components can be mounted.

FIG. 2 shows a method for producing a composite ceramic 10, for example a composite ceramic 10 from FIG. 1. It is provided that a first layer 31 made of a first ceramic material is provided. The first layer 31 is preferably in the form of a plate or is designed as a solid body which extends along the main plane of extent HSE. The first layer 31 of the first ceramic material is then net angeord in an oven 20. In particular, the first layer 31 is arranged in the furnace 20 in such a way that it is at least partially, preferably completely, surrounded by a powdery, paste-like and / or granular second layer 32 made of a second ceramic material. In other words: the first layer 31 is in a second layer 32 made of a powder or granules made of the second ceramic material embedded.

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

It has proven to be advantageous if, with the specified parameters, a second thickness D2 is realized for the second layer 12, 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. In particular, it is provided that a second layer 12 with one of the corresponding second thicknesses is formed both on the upper side OS and on the lower side US of the composite ceramic 10. Both second thicknesses D2 are preferably dimensioned to be the same.

FIG. 3 shows a method for producing a composite ceramic 10 according to a second preferred embodiment of the present invention. In addition to the hot pressing process which has been described for FIG. 2, provision is made here to produce a further second layer 32 'from a silicon nitride paste in a preparatory step by means of a rotary coating. The silicon nitride paste is applied to the first layer 31 of silicon carbide and the silicon carbide layer is driven to rotate about an axis of rotation R. At around 1,000 to 4,000 revolutions per minute for 10 to 40 seconds, it is ensured that the resulting from the rotation Centrifugal forces the paste is evenly distributed on the top OS of the first layer 31, in particular the first layer 31 made of silicon carbide. At closing, the first layer 31, on which the second layer 32 was applied as paste by means of the spin coating process, is embedded in the furnace 20 and additionally surrounded by the second layer 32 made of the second ceramic material, in particular completely encased or in the powder or Granules embedded. The hot pressing process is then carried out as described above.

In FIG. 4, various examples of composite ceramics are shown, which were produced using one of the methods from FIGS. 2 or 3. 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 Rotationsbe coating process are the number of revolutions per minute and the duration of the implementation of the rotary coating process. In column D, the second thickness D2, i.e. H. the second thickness D2 of the second layer 12 in the manufactured composite ceramic 10 is indicated. This is between 20 and 100 pm. 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 a rotation coating process with 1,000 revolutions per minute is used for at least 10 seconds in a subsequent Hot-pressing process, the arrangement of the first layer 31 and second layer 32 is 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.

Reference list:

3 metallization 3 'further metallization

10 composite ceramics

11 first layer

12 second layer

20 oven

31 first layer

32 second layer

32 further second layer

35 gas atmosphere

R a matter of rotation

D1 first thickness

D2 second thickness

S stack direction

HSE main extension plane OS upper side

US bottom

Claims

Expectations

1. A method for producing a composite ceramic (10) and in particular for producing a metal-ceramic substrate, 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 finished state has a first layer (11) made of the first ceramic material and a second layer (12) made of the second ceramic material.

2. The method according to claim 1, wherein the first ceramic material is SiC and / or the second ceramic material is S13N4.

3. The method according to any one of the preceding claims, wherein the first layer (31) is plate-shaped.

4. The method according to any one of the preceding claims, wherein a gas pressure and / or a mechanical pressure is provided during hot pressing, which acts on the first layer (31) and second layer (32) in the furnace (20).

5. The method according to any one of the preceding claims, wherein a pressing device on the first layer (31) and second layer (32) we kender mechanical pressure is realized, wherein the first layer (31) and the second layer (32) between in the pressing device is arranged.

6. The method according to any one of the preceding claims, wherein the pressing device has a protruding contour on its inner side coming into contact with the second layer (32) and the second layer (32) is at least locally displaced by the protruding contour. .

7. The method according to any one of the preceding claims, wherein the second layer (32) is applied by means of spin coating.

8. The method according to any one of the preceding claims, wherein in the manufactured composite ceramic (10), the second layer (12) has a second thickness (D2) between 10 pm and 150 pm, preferably between 30 and 50 pm and particularly preferably between 35 pm and 45 pm.

9. The method according to any one of the preceding claims, wherein in the manufactured composite ceramic (10), the first layer (11) has a first thickness (D1), a ratio of the second thickness (D2) to the first thickness (D1) egg NEN Assumes a value between 0.05 and 0.2, preferably between 0.05 and 0.15 and particularly preferably between 0.075 and 0.13.

10. The method according to any one of the preceding claims, wherein the hot pressing process at a temperature between 1500 and 2000 ° C, preferably between 1700 ° C and 2000 ° C and particularly preferably between 1850 ° C and 1950 ° C is carried out.

11. The method according to any 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.

12. The method according to any one of the preceding claims, wherein the hot pressing process in a gas atmosphere (35), in particular a nitrogen atmosphere, is carried out.

13. The method according to any one of the preceding claims, wherein a structured metallization (3, 3 ‘) is realized on the composite ceramic (10).

14. Composite ceramic (10) produced with a method according to one of the preceding claims.

15. Metal-ceramic substrate with a composite ceramic according to claim 14.