Process for producing metal-ceramic substrate and the metal-ceramic substrate produced using such the process

Abstract

To provide a method for producing a metal-ceramic substrate which is further improved over known the methods, preferably with respect to a good bonding of a metal to void-free, energy-saving and process-safe ceramics.SOLUTION: A method for producing a metal-ceramic substrate, comprises: a step of providing a ceramic element, a piece of metal, and at least one metal layer, in which the piece of metal and the at least one metal layer are comprised of copper; a step of forming an assembly of the ceramic element, the piece of metal, and the at least one metal layer; a step of forming an airtight container surrounding the ceramic element; a step in which at least one metal layer is disposed between the ceramic element and the piece of the metal element in the container; and a step of forming the metal-ceramic substrate by a hot isostatic pressing. The metal-ceramic substrate is provided as a printed circuit board, and only one active metal layer is provided between the piece of the metal and the ceramic element.SELECTED DRAWING: Figure 1d

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a metal-ceramic substrate and to a metal-ceramic substrate manufactured using such a method. [Background technology]

[0002] Metal-ceramic substrates are well known in the prior art (e.g., U.S. Pat. Nos. 5,629,999, 5,729,963, and 5,729,973), for example as printed wiring boards or wiring boards. Typically, conductor bonding areas for electrical components and conductor tracks are arranged on one component side of the metal-ceramic substrate, with the electrical circuits being formed by the interconnection of the electrical components and the conductor tracks. Essential components of a metal-ceramic substrate are an insulating layer, preferably made of ceramic, and at least one metal layer bonded to the insulating layer. Insulating layers made of ceramic have proven to be particularly advantageous in power electronics due to their relatively high dielectric strength. By patterning the metal layer, conductor tracks and conductor bonding areas for electrical components or conductor tracks or conductor bonding areas for electrical components can be realized.

[0003] A requirement for providing such a metal-ceramic substrate is a permanent bond between the metal layer and the ceramic layer. According to the prior art, the so-called direct metal bonding, i.e. DCB or DAB, method is known, as well as the use of solder materials to bond the metal layer to the ceramic layer.

[0004] For example, the active soldering method for joining a metal layer or foil (e.g., a copper layer or foil) to a ceramic material is a method particularly used for producing metal-ceramic substrates. In this method, a bond between a metal foil (e.g., a copper foil) and a ceramic substrate (e.g., an aluminum nitride ceramic) is produced at a temperature of approximately 650-1000°C using a hard solder containing an active metal in addition to a main component such as copper, silver, and / or gold. The active metal is, for example, at least one element selected from the group consisting of Hf, Ti, Zr, Nb, and Ce, and establishes a bond between the solder and the ceramic by chemical reaction, while the bond between the solder and the metal is a hard solder-metal bond.

[0005] Furthermore, methods are known in which hot isostatic pressing is used to bond a metal layer to a ceramic layer to form a metal-ceramic substrate, for example from US Pat. No. 5,629,491 and US Pat. No. 5,629,491. Hot isostatic pressing is also used as a post-treatment to reduce the number of voids that form during bonding when using soldering or direct metal bonding methods. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] German Patent Application Publication No. 102013104739 [Patent Document 2] German Patent Invention No. 19927046 [Patent Document 3] German Patent Application Publication No. 102009033029 [Patent Document 4] German Patent Invention No. 102013113734 [Patent Document 5] Patent No. 4325470 specification Summary of the Invention

[0007] Starting from the prior art, it is an object of the present invention to provide a method for producing metal-ceramic substrates which is further improved over known methods, in particular with regard to a good bonding of the metal to the ceramic which is preferably void-free, energy-saving and process-safe. [Problem to be solved by the invention]

[0008] This object is achieved by providing a method for producing a metal-ceramic substrate according to claim 1 and a metal-ceramic substrate according to claim 15. Further embodiments will become apparent from the dependent claims and the description. [Means for solving the problem]

[0009] According to a first aspect of the present invention, there is provided a method for manufacturing a metal-ceramic substrate, comprising the steps of: providing a ceramic element, a metal piece, and at least one metal layer; forming an assembly of a ceramic element, a metal piece, and at least one metal layer; forming an airtight container surrounding the ceramic element, wherein at least one metal layer is disposed in the container between the ceramic element and the metal piece; forming a metal-ceramic substrate by hot isostatic pressing; A method is provided, comprising:

[0010] In comparison with the methods known from the prior art, according to the present invention, in addition to the metal piece, at least one metal layer is arranged between the metal piece and the ceramic element, and then the metal piece, the at least one metal layer, and the ceramic element are integrally joined. In other words, an additional metal layer is introduced into the container and, together with the metal piece, becomes part of the metallization formed on the metal-ceramic substrate produced in the hot isostatic pressing process. This configuration, in particular, allows a high degree of freedom in the production of the container, since an additional metal layer is introduced between the metal piece and the ceramic element, and this freedom makes it possible to adjust, as required, the properties of the subsequent metallization on the produced metal-ceramic substrate.

[0011] In hot isostatic pressing, the container, in particular the metal container, is preferably exposed in a heating and pressure device to a gas pressure of 100 to 2000 bar (10,000 to 200,000 kPa), preferably 150 bar to 1,200 bar (15,000 to 120,000 kPa), particularly preferably 300 to 1,000 bar (30,000 to 100,000 kPa) and a process temperature of 300°C up to the melting temperature of the metal piece and / or the additional metal piece, in particular a temperature below the melting temperature of the metal piece and / or the additional metal piece. Thus, it has been found advantageously possible to bond a metal layer, i.e., at least one metal layer and / or metal piece of a metal container and / or additional metal piece, to a ceramic element without reaching the temperatures required for direct metal bonding processes (e.g., DCB or DAB processes) and without using a solder substrate used for active soldering. Furthermore, by utilizing or using an appropriate gas pressure, it may be possible to produce a metal-ceramic substrate that is as void-free as possible, i.e., free of gas between the metal layer and the ceramic element. In particular, the process parameters described in U.S. Patent No. 5,949,497, expressly incorporated herein, for hot isostatic pressing are used.

[0012] In particular, hot isostatic pressing involves heating, particularly sintering and / or annealing, so that the metal piece and / or additional metal piece and / or at least one metal layer of the metal container, particularly the subsequent metallization of the metal-ceramic substrate, do not transition to a molten phase. Therefore, hot isostatic pressing requires lower temperatures than direct metal bonding processes, particularly DCB processes. Furthermore, the use of pressure in hot isostatic pressing has proven advantageous, since it can result in a reduction of air inclusions or pores between the metal piece and / or additional metal piece or at least one metal layer, on the one hand, and the ceramic element, on the other, thereby reducing or completely preventing the formation of bubbles in the resulting metal-ceramic substrate. This has a favorable effect on the quality of the bond between the at least one metal layer or the metal piece and / or additional metal piece of the metal container and the ceramic element. In particular, this results in a "solid-state diffusion bonding" (SDB) process.

[0013] The metal-ceramic substrate is preferably provided as a printed wiring board in the fabricated state with a patterned metallization bonded to a ceramic element. For example, the metal-ceramic substrate may be formed by hot isostatic pressing, as well as by laser, etching, and / or mechanical patterning, for example, to realize conductor tracks and / or conductor joints of an electrical or electronic component. The metal-ceramic substrate fabricated on the ceramic element preferably has a backside metallization and / or a cooling element on the side opposite the metallization or component metallization. The backside metallization preferably functions to accommodate deflection, and the cooling element preferably functions to effectively dissipate heat generated during operation by the electrical or electronic component bonded to the printed wiring board or metal-ceramic substrate.

[0014] Suitable materials for the metal piece, the additional metal piece, and / or the at least one metal layer include copper, aluminum, molybdenum, tungsten, and / or their alloys (e.g., CuZr, AlSi, or AlMgSi), as well as laminates such as CuW, CuMo, CuAl, and / or AlCu, or MMCs (metal matrix composites) such as CuW, CuMo, or AlSiC. Furthermore, the metal piece, the additional metal piece, and / or the at least one metal layer on the produced metal-ceramic substrate are preferably surface-modified, especially as a component metallization. Possible surface modifications include, for example, the addition of noble metals, especially silver and / or gold, or (electroless) nickel or ENIG (electroless nickel immersion gold) on the metallization, or the suppression of crack formation or propagation by sealing with edge grout. For example, the metal piece may be different from the additional metal piece.

[0015] The ceramic element preferably comprises Al2O3, SiN4, AlN, HPSX ceramics (i.e., ceramics with an Al2O3 matrix containing x percent ZrO2, e.g., Al2O3=HPS9 with 9% ZrO2 or Al2O3=HPS25 with 25% ZrO2), SiC, BeO, MgO, high-density MgO (greater than 90% of theoretical density), and TSZ (tetragonally stabilized zirconium oxide). In this context, the ceramic element may be designed as a composite or hybrid ceramic, whereby multiple ceramic layers with different material compositions are arranged one on top of the other to combine various desired properties and are integrally bonded to form the ceramic element.

[0016] The metal strip is preferably thicker or thinner than the at least one metal layer, and is substantially the same thickness as the at least one metal layer. The ratio of the first thickness of the metal strip to the second thickness of the at least one metal layer is preferably 0.01 to 2, preferably 0.1 to 2, and more preferably 0.15 to 0.5 or 2. Furthermore, it has been found that particularly good results are obtained when the first thickness is 0.2 to 0.3 mm, especially when the ratio of the first thickness of the metal strip to the second thickness of the at least one metal layer is 0.01 to 0.5, preferably 0.1 to 0.5, and particularly preferably 0.15 to 0.5. The use of relatively thin metal strips has been found to simplify the manufacturing process, particularly the hermetic sealing of the container, which is required for the use or utilization of hot isostatic pressing. This is particularly distinct from the prior art processes described above, in which suitable sheet metal is bent to form the container and then welded together at its free ends.

[0017] In particular, the atmosphere within the vessel is oxygen-free during the formation of the metal-ceramic substrate. This is preferably achieved by evacuating the oxygen from the vessel prior to sealing the vessel. For example, air is evacuated from the vessel and a vacuum is maintained during the bonding of the metal layer, metal piece, and ceramic element assembly. In particular, the pressure within the vessel is less than 150 mbar (15 kPa), preferably less than 50 mbar (5 kPa), and particularly preferably less than 20 mbar (2 kPa).

[0018] The first thickness (D1) preferably assumes a value between 10 μm and 500 μm, preferably between 50 μm and 400 μm, particularly preferably between 100 μm and 300 μm. Such a small first thickness has proven to be particularly advantageous, since it allows the container to be closed more easily. Finally, it also makes it easier to bend, for example, during the manufacture of the container. The first thickness is preferably less than 100 μm, preferably less than 80 μm, particularly preferably less than 50 μm.

[0019] The second thickness is preferably determined to assume a value between 100 μm and 10,000 μm, preferably between 150 μm and 6,000 μm, and particularly preferably between 600 μm and 5,000 μm. Therefore, to achieve a suitable thickness of metallization in the resulting metal-ceramic substrate, at least one relatively thick metal layer is used. Such a thick metallization has proven advantageous in terms of facilitating heat diffusion within the metallization to which the electrical or electronic component is bonded. As a result, heat dissipation can be more uniformly distributed, and therefore heat can be extracted more efficiently. In this context, a process in which at least one metal layer is introduced into a container formed from a metal strip has proven particularly advantageous, since the resulting thickness ratio can be particularly easily adjusted.

[0020] Preferably, the metal strip and at least one metal layer are made of different metals or materials. For example, the metal strip could be made of nickel, which creates a surface seal for subsequent metallization during the bonding process. The use of two different materials also leads to new overall properties for the metallization, which can open up new application possibilities for the metal-ceramic substrates thus formed.

[0021] Preferably, a functional layer, particularly a functional layer acting as a diffusion barrier, is disposed between the at least one metal layer and the metal piece prior to forming or providing the container. In this case, an additional metal functional layer is applied as an additional metal functional layer, preferably acting as a diffusion barrier between the metal layer and the metal piece. This may be, for example, at least one metal layer and metal piece or a metal foil having a different thermomechanical expansion coefficient than the at least one metal layer or metal piece. It is also conceivable that a functional layer, for example in the form of a carbide, nitride, and / or metal, is applied to the metal piece and at least one metal layer or metal piece or at least one metal layer, for example, by a physical vapor deposition process, and then disposed between the metal piece and at least one metal layer after forming the container. Furthermore, a mixed layer containing both metal and ceramic may also function as the functional layer. For example, this may be a powder mixture containing metal powder, ceramic powder, and / or metal oxide powder. The powder mixture is preferably formed from a composite powder formed, for example, using a mechanofusion process, and contains powder particles in which the metal and ceramic are integrated. In other words, the metal and ceramic are fused into a common powder particle. Alternatively, it is also conceivable to have a porous metal-ceramic composite layer used as the functional layer.

[0022] The use of functional layers has proven particularly advantageous because they limit the characteristic grain growth of a layer, i.e., the grain growth of the metal flakes or at least one metal flake, to that layer. This is because particles cannot grow through the functional layer, which acts as a diffusion barrier. For example, if the at least one metal layer and the metal flakes are made of different metals, interdiffusion between them is prevented, which can adversely affect certain material properties of each layer, particularly thermal and electrical conductivity. Furthermore, if the layers are made of certain different metals (e.g., Cu and Ti), the formation of intermetallic phases between the at least one metal layer and the metal flakes can be suppressed. Suitable materials for the diffusion barrier include metal layers as well as carbide or nitride bonds. The thickness of the functional layer should be less than 100 μm, preferably less than 20 μm, and particularly preferably less than 10 μm.

[0023] It is further conceivable to provide multiple metal layers arranged between the metal piece and the ceramic element, and to arrange functional layers between the individual metal layers of the multiple metal layers as a supplement or alternative to the functional layer between the metal piece and the metal layer.

[0024] Preferably, the metal flakes and / or the at least one metal layer are configured so that different grain sizes are present in the resulting metal-ceramic substrate, with the first metal region formed by the metal flake having a smaller grain size than the second metal region formed by the at least one metal layer. In other words, the resulting metal-ceramic substrate has a smaller grain size in the outer metallization than in the metal region adjacent to the ceramic element, which is the result of bonding the at least one metal layer. Such grain size influence can be achieved by a temperature treatment performed before providing the metal flakes and the at least one metal layer. That is, the at least one metal layer and the metal flake are subjected to different temperature treatments. Alternatively or additionally, it is also conceivable to adjust the proportion of foreign particles or impurities in the metal layer and / or the metal flakes so that a specific grain size is defined during the bonding process performed under the influence of temperature and pressure. In this way, the grain sizes can be appropriately adjusted, at least relative to each other. This has proven to be particularly advantageous, since a coarse grain size, when formed in the second metal region adjacent to the ceramic element, favors thermal shock resistance. At the same time, the use of fine grained metal areas on the outside has proven advantageous, for example, by simplifying wire bonding and / or facilitating automated optical inspection.

[0025] The ratio of the grain size of the first metal region to the grain size of the second metal region is preferably less than 0.3, preferably less than 0.2, and particularly preferably less than 0.15. For example, grain sizes of less than 600 μm, preferably less than 300 μm, and particularly preferably less than 200 μm are considered. When comparing grain sizes, it is preferable to use an average value of, for example, at least 50 grains for each of the first and second metal regions, and the ratio is calculated after these average values. The grain size is preferably determined by the tangent intersection method, in which the extensions of different grain sizes along a predetermined line are determined. To form a metal-ceramic substrate between the container and the ceramic element, preferably between at least one metal layer and the ceramic element and / or between at least one metal layer and the metal piece, an active metal layer and / or an active metal-containing contact layer are preferably disposed in at least some areas. This advantageously facilitates bonding of the at least one metal layer to the ceramic element. In particular, it has been found that in this way a planar, in particular a homogeneously distributed, adhesion-promoting layer can be achieved between the at least one metal layer and the ceramic element. Furthermore, the introduction of an additional adhesion-promoting layer (e.g., an active metal layer or a solder material) between the metal piece and the at least one metal layer can be considered to assist in bonding the metal piece to the at least one metal layer as part of the soldering process. It is also considered possible to use a solder material with a lower process temperature than that used in hot isostatic pressing. This ensures that the metal piece of the container is also bonded to the at least one metal layer during hot isostatic pressing.

[0026] Preferably, the active metal layer and / or the active metal-containing layer become or are part of the assembly upon bonding, in other words, the active metal layer completes the assembly.

[0027] In particular, the active metal layer and / or the contact layer containing active metal preferably has a proportion of active metal of more than 15% by weight, preferably more than 50% by weight, particularly preferably more than 75% by weight, which distinguishes said layer from active metal-containing solder materials, which typically have an active metal content of up to 10% by weight.

[0028] Preferably, only one active metal layer or active metal is provided between the metal piece and the ceramic element. In particular, the joining is performed without a solder substrate, i.e., without a solder substrate. Advantageously, in comparison with joining a metal layer to a ceramic layer using a solder material, which is typically performed at a temperature below the melting temperature of the metal layer, the present method allows the omission of a solder substrate, provided that only an active metal is present.

[0029] Furthermore, compared to production by soldering methods, narrower isolation trenches can be realized, corresponding to the width of isolation trenches achievable in boards produced by the DCB method, for example. In particular, the isolation trenches can be reduced in size by approximately 200 μm, since solder residues that typically protrude into the isolation trench by a maximum of approximately 200 μm when using active soldering methods are not expected to occur in this case. This solder residue is measured from the edge of the etched lateral surface in the direction of the isolation trench. The solder residue is measured as the sum of the opposing metal parts that delimit the isolation trench in a direction parallel to the main extension plane.

[0030] Examples of active metals include titanium (Ti), zirconium (Zr), hafnium (Hf), chromium (Cr), niobium (Nb), cerium (Ce), tantalum (Ta), magnesium (Mg), lanthanum (La), and vanadium (V). It should be noted herein that the metals La, Ce, Ca, and Mg can be easily oxidized. Furthermore, it should be noted that the elements Cr, Mo, and W are not typically active metals, but are suitable as contact layers between SiN4 and at least one metal layer, solder system, or solder material because they do not form intermetallic phases with at least one metal layer (e.g., copper) and do not exhibit edge solubility. In particular, the solder substrate omitted in this process is a metal-based substrate, preferably a silver-based or copper-based substrate. In a silver-based substrate, silver is the major component (i.e., the component with the highest weight percentage), while in a copper-based substrate, copper is the major component. Examples of silver-based substrates include AgCu, especially AgCu28, AgCuIn, AgCuSn, and AgCuGa. Examples of copper-based substrates include CuSn, CuAg, CuIn, CuGa, CuInSn, CuInMb, and CuGaSn. Solder substrates based on NiCrMn or SnCu can also be omitted.

[0031] Furthermore, a contact layer comprising an active metal is to be understood as a layer comprising compounds comprising an active metal, such as TiN, TiC, TiO, etc., especially with different oxidation states or stoichiometric and non-stoichiometric compositions. Also conceivable are alloys comprising one or more active metals.

[0032] As an alternative to solder-free bonding, it is also possible to place a solder substrate or a solder material containing an active metal between the active metal layer, contact layer, or ceramic element and the metal layer and / or between the metal layer and the metal piece. This provides an additional or reinforced bond. In this case, it is possible to perform bonding at a temperature below or above the process temperature of the solder material or solder substrate. Furthermore, it is advantageous to use a silver-free solder material or solder substrate.

[0033] The process temperature of the solder material depends on the solder material used and is usually below 1100°C. This temperature can be reduced to 600°C by adding a material that lowers the melting point. The solder material melts at this temperature. In this case, the solder material melts at the process temperature. In the present invention, bonding between the ceramic element and the metal layer may be performed even if the process temperature has not been reached.

[0034] The metal strip is preferably folded to form a container and / or joined to another metal strip. For example, the metal strip is wrapped around a component including at least one metal layer and a ceramic element. In particular, the folding is performed so that a first end and a second end of the metal strip integrally protrude toward one side, and the first end and the second end of the same metal strip are integrally joined to form the container. Alternatively, the metal strip and the additional metal strip are arranged on opposite sides, and the free ends protruding toward the main extension plane of the component are integrally joined to form the airtight container. The edge regions of the joined metal strip and / or the additional metal strip are preferably joined to each other, particularly in the specified joining area, by laser welding and / or electron beam welding. The metal strip from which the container is manufactured, which constitutes the resulting metallization, preferably comprises nickel, silver, stainless steel, and / or titanium, and is particularly preferably provided as a foil having a first thickness of 0.01 to 1 mm. Such thin metal pieces are particularly easy to fold and join.

[0035] According to a preferred embodiment of the present invention, the container is formed by a metal piece and / or an additional metal piece. Alternatively, the container may comprise, for example, a ceramic element, at least one metal layer, and an assembly of metal pieces. For example, the container is a glass container.

[0036] Another object of the invention is a metal-ceramic substrate manufactured by the method according to the invention. All the properties and advantages described with respect to the method for manufacturing a metal-ceramic substrate are equally applicable to the metal-ceramic substrate and vice versa.

[0037] In particular, the proposed method provides metal-ceramic substrates with fewer voids or fewer voids or pores due to the prevailing pressure conditions compared to metal-ceramic substrates manufactured by the AMB or DCB methods. Furthermore, the metal layer thickness of the metallization has a consistent profile that follows the profile of the ceramic surface. Furthermore, the method for manufacturing a metal-ceramic substrate simplifies the second etching step, since the silver-containing solder base material can be omitted. As a result, narrower isolation trenches can be realized, for example, in dimensions corresponding to the width of isolation trenches achievable in substrates manufactured by the DCB method. In particular, the isolation trenches can be reduced in size by approximately 200 μm, since solder residues that typically protrude into the isolation trench by a maximum of 100 μm per side are not expected to occur in this case. This solder residue is measured from the edge of the etched side in the direction of the isolation trench. The solder residue is measured as the sum of the opposing metal portions that bound the isolation trench in a direction parallel to the main extension plane. Furthermore, fringe formation at the interface between the metallization and the ceramic element is suppressed. The presence of silver in the solder material makes etching difficult and manifests itself as fringe-like courses parallel to the main extension plane. Furthermore, the uniform thickness of the metallization across the entire metal-ceramic substrate allows the etching process to be performed uniformly across the entire area of ​​the metal-ceramic substrate without the need for metallization thickness adjustment. The uniform thickness is achieved because the pressure used in hot isostatic pressing uniformly presses the metallization against the profile of the ceramic element. Advantageously, the uniform material distribution in the metallization also allows for a uniform etch profile across the entire metal-ceramic substrate.

[0038] In particular, the metallization and the ceramic element are arranged one on top of the other along a stacking direction extending along the main extension plane and perpendicular to the main extension plane, and a bonding layer is formed in the carrier substrate to be manufactured between the metallization and the ceramic element, the adhesion-promoting layer of the bonding layer having a sheet resistance of more than 5 Ω / sq, preferably more than 10 Ω / sq, particularly preferably more than 20 Ω / sq.

[0039] Compared to carrier substrates known from the prior art, the sheet resistance of the adhesion-promoting layer of the bonding layer is greater than 5 Ω / sq, preferably greater than 10 Ω / sq, and particularly preferably greater than 20 Ω / sq. The determined sheet resistance is directly related to the proportion of active metal in the adhesion-promoting layer or the layer thickness of the adhesion-promoting layer, which is important for bonding the metallization to the ceramic element. The sheet resistance increases with a decrease in the active metal content in the bonding layer. Correspondingly, a high sheet resistance corresponds to a low active metal content in the bonding layer. It has been found that an increase in the active metal content leads to the formation of brittle intermetallic phases, which impairs the peel strength of the metallization on the ceramic element. In other words, the sheet resistances defined in the claims lead to an improvement, i.e., an increase, in the peel strength of the bonding layer by suppressing the formation of brittle intermetallic phases. Thus, selectively adjusting the sheet resistances defined in the claims allows for particularly strong bonding of the metallization to the ceramic element.

[0040] To determine the sheet resistance, the metal layers and optionally the solder base layers are first removed from the carrier substrate to be fabricated, for example by etching, and then the sheet resistance is measured by a four-point measurement of the top or bottom surface of the carrier substrate from which at least one metal layer and solder base layer has been removed.

[0041] In particular, the sheet resistance of a material sample is understood as the resistance relative to the surface area. Surface resistance is usually expressed in units of Ω / sq. The physical unit of sheet resistance is Ω.

[0042] Preferably, the thickness of the bonding layer, measured in the stacking direction and averaged over multiple measurement points in one or more predetermined areas extending parallel to the main stretching plane, assumes a value of less than 1 μm, preferably less than 0.7 μm, particularly preferably less than 0.5 μm. When referring to multiple areas, in particular, the metallization is subdivided into areas of as equal size as possible, and at least one thickness value, preferably multiple measurements, are recorded in each of these areas that subdivide at least one metal layer. The thicknesses thus determined at different points are then arithmetically averaged.

[0043] In this way, a relatively thin bonding layer is formed between the metallization and the ceramic element compared to carrier substrates known in the prior art. To determine the relevant thickness of the bonding layer, the measured thickness is averaged over a large number of measurement points within a given or defined area. This is advantageous because it takes into account the fact that ceramic elements are generally undulating, i.e., that the ceramic elements can be said to be corrugated. In particular, those skilled in the art will understand that a corrugation refers to a modulation of the generally flat course of a ceramic element, as seen over several millimeters or centimeters along a direction extending parallel to the main extension plane. Therefore, such undulations are different from the surface roughness of the ceramic element, which is usually additionally present on the ceramic element. By incorporating such generally unavoidable undulations of the ceramic element into the thickness determination, it is possible to ensure that the bonding layer may vary due to the undulations, particularly in the valley regions of the ceramic element, compared to the peak regions of the ceramic element.

[0044] Despite this unevenness, the average thickness is significantly lower than that known from prior art carrier substrates. This is achieved, in particular, or by way of example, by disposing the required active metal layer separately, i.e., in addition to the solder substrate, between the ceramic element and the metallization. A relatively thin active metal layer is preferably achieved by applying the active metal to the solder substrate and / or at least one metal layer and / or ceramic element by chemical and physical vapor deposition or chemical or physical vapor deposition (e.g., sputtering), thereby resulting in a relatively thin bonding layer, in particular a homogeneous and thin adhesion-promoting layer. It is also conceivable to provide the active metal layer on the solder substrate, the ceramic element, and / or at least one metal layer by vacuum plasma and / or vacuum vapor deposition. It is also conceivable to provide the active metal layer by electroplating. It is particularly preferred that the active metal layer be provided as a foil.

[0045] The formation of a relatively thin bonding layer reduces the effort required to remove the bonding layer again, for example, during a "second etching" of the carrier substrate, particularly in certain areas for the metallization and patterning of the bonding layer. This patterning, which is used to electrically isolate the metal portions of at least one metal layer from each other, is preferably performed by etching and / or mechanical processing steps and / or laser light. It has also been found advantageous to reduce the number of possible defects in the bonding layer, for example, due to material defects in the solder material. For example, defects in the bonding layer or material defects in the solder material are understood to be large particles in the solder material (e.g., paste), such as active metal particles, which can form large particles in the bonding layer and do not melt completely, thereby interfering with the minimization of the solder spacing as a spacer, or large particles in the solder material (e.g., paste), such as active metal particles, which can form large particles in the bonding layer or do not melt completely, thereby interfering with the minimization of the solder spacing as a spacer. Application, in particular by sputtering, is a simple way to ensure that relatively large particles do not become part of the active metal layer, in particular the subsequent bonding layer. Finally, it is advantageous to homogeneously form a thin bonding layer on the carrier substrate to be manufactured.

[0046] It is particularly preferred to use the following method for determining and selecting the measurement area that contributes to the determination, regardless of the size of the carrier substrate. In a first step, at least one metal layer of the carrier substrate is divided into nine equally sized rectangles, particularly squares (i.e., divided into multiple areas). In each of these defined measurement areas, two or three cross-sectional images are generated, which are used to determine the average thickness of the metallization in each of these cross-sectional images. The cross-sectional images are preferably generated by an SEM process, for example, at a magnification of 5000x set on the SEM instrument. Then, in a second step, the average of the 18 or 27 thicknesses recorded in the cross-sectional images distributed over all nine rectangular measurement areas is obtained. In this way, the average thickness is advantageously reliably representative of the bonding layer between the metallization and the ceramic element. In other words, the procedure described in this section provides an average thickness determined for the metallization in a uniformly distributed measurement area. The procedure described herein for selecting the measurement areas contributing to the determination of the average thickness value is also applicable to the determination of the sheet resistance.

[0047] Preferably, both or one of the bonding layer and the other bonding layer is an adhesion promoting layer containing an active metal. In particular, the bonding layer is formed solely by an adhesion promoting layer containing an active metal. In this case, the adhesion promoting layer in the bonding layer contains constituents of the ceramic element, such as nitrogen, oxygen, or carbon, and other constituents of the ceramic in the bonding. Correspondingly, the adhesion promoting layer contains, for example, titanium nitride, titanium oxide, and / or titanium carbide. In this case, the thickness of the bonding layer measured in the stacking direction and averaged over measurement points on a surface or multiple surfaces parallel to the main extension plane is less than 0.003 mm, preferably less than 0.001 mm, particularly preferably less than 0.0005 mm or less than 0.0004 mm. In particular, in the case of these bonding layers in which the solder base material and / or silver component are omitted, a correspondingly thinner bonding layer can be formed.

[0048] Other advantages and features will become apparent from the following description of preferred embodiments of the object of the present invention, which refers to the accompanying drawings. [Brief explanation of the drawings]

[0049] [Figure 1a] 1 illustrates a method for manufacturing a metal-ceramic substrate according to a first exemplary embodiment of the present invention. [Figure 1b] 1 illustrates a method for manufacturing a metal-ceramic substrate according to a first exemplary embodiment of the present invention. [Figure 1c] 1 illustrates a method for manufacturing a metal-ceramic substrate according to a first exemplary embodiment of the present invention. [Figure 1d] 1 illustrates a method for manufacturing a metal-ceramic substrate according to a first exemplary embodiment of the present invention. [Figure 1e] 1 illustrates a method for manufacturing a metal-ceramic substrate according to a first exemplary embodiment of the present invention. [Figure 2] FIG. 10 is a schematic diagram of a vessel for a process according to a third exemplary embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0050] 1a to 1e illustrate a method for manufacturing a metal-ceramic substrate 1 according to a first exemplary embodiment of the present invention, and FIG. 1e illustrates the resulting metal-ceramic substrate 1. Such a metal-ceramic substrate 1 preferably serves as a carrier or printed wiring board for electronic or electrical components that can be bonded to a metallization 20 of the metal-ceramic substrate 1. The metallization 20 is preferably patterned to form appropriate conductor tracks and / or conductor bonding areas. Thus, the metallization 20, which extends substantially along the main extension plane HSE, and the ceramic elements 10 are preferably arranged one above the other and bonded or joined to each other along a stacking direction S that extends perpendicular to the main extension plane HSE. In addition to the metallization 20, the metal-ceramic substrate 1 preferably includes a backside metallization or additional metallization 20′ arranged and bonded to the ceramic elements 10 on the side opposite the metallization 20 in the stacking direction S. For example, the additional metallization 20′ and / or the additional cooling element may be used, inter alia, to counteract bending of the metal-ceramic substrate 1 and / or to dissipate heat input caused by electrical or electronic components on the metal-ceramic substrate 1. An example of a metal-ceramic substrate 1 with a patterned metallization 20 is shown in FIG.

[0051] In the method for producing such a metal-ceramic substrate 1, as shown schematically in FIGS. 1a to 1e, a ceramic element 10, a metal piece 40, and at least one metal layer 30 are first provided. In this context, an active metal layer 15 is preferably arranged between the ceramic element 10 and the at least one metal layer 30. In particular, the active metal layer 15 is arranged between the ceramic element 10 and the at least one metal layer 30 in the stacking direction S. Furthermore, at least one additional metal layer 30′ and one additional active metal layer 15′ are preferably provided, with the additional active metal layer 15′ being arranged between the at least one additional metal layer 30′ and the ceramic element 10 in the stacking direction S. In this context, the metal piece 40 preferably has a first thickness D1, the at least one metal layer 30 preferably has a second thickness D2, and the at least one additional metal layer 30′ preferably has a third thickness D3. It is particularly preferred that the second thickness D2 and the third thickness D3 are substantially equal to each other. It is also contemplated that the third thickness D3 may be greater than the second thickness D2, or vice versa. A correspondingly large third thickness D3 may provide a sufficiently large thermal capacity in the fabricated metal-ceramic substrate 1, by providing a properly formed additional metallization 20′, to act as a buffer for heat dissipation in overload situations.

[0052] In the example shown in FIG. 1 a, a construction 50 including at least one metal layer 30, an active metal layer 15, a ceramic element 10, an additional active metal layer 15′, and at least one additional metal sheet 30′ is disposed on a metal piece 40.

[0053] In a subsequent process step, the metal piece 40 is folded to encompass or surround the construct 50, which is comprised of the metal layer 30, the additional metal layer 30′, the active metal layer 15, the additional active metal layer 15′, and the ceramic element 10. In particular, the embodiment of FIG. 1b shows the metal piece 40 folded or covering the construct 50 such that the first and second ends of the metal piece 40 protrude from the same side as viewed from the construct 50. In other words, the metal piece 40 is dimensioned so that, when covering the construct 50, the first and second ends of the metal piece 40 protrude from the same side, particularly the side opposite the folded portion. When folded, the metal piece 40 has first and second ends that are particularly open (preferably protruding) in three directions. In particular, the first and second ends of the metal piece 40 protrude from the construct 50 so that the first and second ends of the metal piece 40 can be integrally joined. 1c illustrates this, in which a component 50 consisting of at least one metal layer 30, active element 15, ceramic element 10, additional active metal layer 15′, and at least one additional metal layer 30′ is enclosed within a container of metal piece 40 to form assembly 18. Electron beam welding or laser beam welding bonds or joins first and second ends of metal piece 40 together, particularly forming an airtight container in which metal piece 40 surrounds or contains component 50, and particularly forming continuous planar contact between metal piece 40 and the individual components and elements of component 50 disposed within the container.

[0054] The airtight container is preferably evacuated. Alternatively, air may remain in the container, or a defined gas atmosphere (e.g., nitrogen) may be present. The assembly 18, in which the structure 50 is placed in the container, is then subjected to hot isostatic pressing to bond the metal piece 40 and the at least one metal layer 30 to the ceramic element 10. It has been found that hot isostatic pressing can be used to bond both the at least one metal layer 30 to the ceramic element 10 and the metal piece 40 to the at least one metal piece 30. In this way, the metal piece 40 of the container becomes part of the subsequent metallization 20 on the metal-ceramic substrate 1. The procedure of using the additional metal piece 40 in addition to the at least one metal layer 30 has been found to be advantageous, particularly since it allows the use of a metal piece 40 with a relatively thin first thickness D1. This significantly simplifies the formation of the airtight container. Furthermore, the use of at least one metal layer 30 as well as different metal pieces 40 allows the metallization 20 to be formed of two different metals and / or metal structures.

[0055] In particular, a first metal region 21 and a second metal region 22 are formed after bonding, the first metal region originating from the metal piece 40 and the second metal region 22 originating from the at least one metal layer 30. Preferably, the ratio of the first thickness D1 of the metal piece 40 to the second thickness D2 of the at least one metal layer 30 is between 0.01 and 2, preferably between 0.1 and 2, more preferably between 0.15 and 0.5 or 2. It has also been found that particularly good results are obtained when the first thickness D1 is between 0.2 and 0.3 mm, in particular when the ratio of the first thickness D1 of the metal piece 40 to the second thickness D2 of the at least one metal layer 30 is between 0.01 and 0.5, preferably between 0.1 and 0.5, particularly preferably between 0.15 and 0.5 or 0.5. After bonding, particularly as part of a hot isostatic pressing process, the metal piece 40 and at least one metal layer 30 bonded to the ceramic element 10 are preferably provided by patterning with a laser beam, etching, and / or machining. As a result, metal portions separated from each other are formed in the metallization 20. For example, in FIG. 1e, a curved or bent etched edge profile can be seen, which is formed in both the metallization 20 and the backside metallization 20′. The so-called separation grooves realized by patterning serve to provide the metal portions bonded to the ceramic element 10 with the preferred function of conductive paths and / or conductor bonding areas.

[0056] FIG. 2 is a schematic diagram of a process vessel according to a third exemplary embodiment of the present invention. Herein, FIG. 2 shows an assembly of a metal piece 40, at least one metal layer 30, and a ceramic element 10 before or during hot isostatic pressing (e.g., FIG. 1c). The exemplary embodiment of FIG. 2 differs from the assembly of FIGS. 1a-1e in that a functional layer 60 is disposed between the metal piece 40 and the at least one metal layer 30, which preferably serves as a diffusion barrier between the at least one metal layer 30 and the metal piece 40. This has the effect, for example, of keeping the metal piece 40 and the at least one metal layer 30 separated from each other during hot isostatic pressing. In this case, the functional layer 60 extends completely over the entire surface, i.e., between the at least one metal layer 30 and the metal piece 40. [Explanation of symbols]

[0057] 1 Metal ceramic substrate 10 Ceramic Elements 15 Active metal layer 15' additional active metal layer 18 Aggregate 20 Metallization 20' additional metallization 21 First Metal Region 22 Second Metal Region 30 metal layer 30' additional metal layer 40 metal pieces 50 Constructs 60 Functional Layers D1 First thickness D2 Second thickness D3 Third thickness S Stacking direction HSE main stretching surface

Claims

1. A method for manufacturing a metal-ceramic substrate (1), comprising: providing a ceramic element (10), a metal piece (40), and at least one metal layer (30), wherein the metal piece (40) and the at least one metal layer (30) are comprised of copper; forming an assembly (18) of the ceramic element (10), the metal piece (40), and the at least one metal layer (30); forming an airtight container surrounding the ceramic element (10), wherein the at least one metal layer (30) is disposed in the container between the ceramic element (10) and the metal piece (40); forming said metal-ceramic substrate (1) by hot isostatic pressing; Including, The metal-ceramic substrate (1) is provided as a printed wiring board, A method in which only one active metal layer (15) is provided between said metal piece (40) and the ceramic element (10).

2. The method of claim 1 , wherein the metal strip (40) is thinner than the at least one metal layer (30).

3. 2. The method of claim 1, wherein the ratio (D1 / D2) of the first thickness (D1) of the metal piece (40) to the second thickness (D2) of the at least one metal layer (30) assumes a value between 0.01 and 2.

4. The method of claim 1 , wherein the metal piece (40) is thicker than the at least one metal layer (30).

5. The method according to any one of claims 1 to 4, wherein the atmosphere in the vessel is oxygen-free during the formation of the metal-ceramic substrate (1).

6. The method according to claim 3, wherein said first thickness (D1) assumes a value between 10 μm and 500 μm.

7. The method according to claim 3, wherein said second thickness (D2) assumes a value between 100 μm and 10,000 μm.

8. 8. The method according to claim 1, wherein the metal flakes (40) and / or the at least one metal layer (30) are designed such that different grain sizes are defined in the metal-ceramic substrate (1) to be produced, and a first metal region (21) of a metallization (20) formed with the metal flakes (40) has a smaller grain size than a second metal region (22) of a metallization (20) formed with the at least one metal layer (30).

9. 9. The method of claim 8, wherein the ratio of the grain size of the first metal region (21) to the grain size of the second metal region (22) is less than 0.

3.

10. 10. The method according to claim 1, wherein when forming the metal-ceramic substrate (1) between the at least one metal layer and the ceramic element (10), an active metal layer (15) and / or a contact layer comprising an active metal is arranged in at least some parts to assist bonding of the at least one metal layer (30) to the ceramic element (10).

11. 11. The method of claim 10, wherein the proportion of active metal in the active metal layer (15) and / or the contact layer containing active metal is greater than 15% by weight.

12. The method according to any one of the preceding claims, wherein the metal piece (40) is folded to form the container and / or joined to an additional metal piece.

13. The method according to any one of the preceding claims, wherein a functional layer (60) is inserted between the at least one metal layer (30) and the metal piece (40).

14. A metal-ceramic substrate (1) manufactured by the method according to any one of claims 1 to 13, The metal pieces (40) and / or the at least one metal layer (30) are configured so that different grain sizes are present in the metal-ceramic substrate (1) to be produced, and a first metal region (21) formed by the metal pieces (40) has a smaller grain size than a second metal region (22) formed by the at least one metal layer (30); an active metal layer (15) and / or a contact layer containing an active metal are disposed between the at least one metal layer (30) and the ceramic element (10) in at least some portions thereof to assist in bonding the at least one metal layer (30) to the ceramic element (10); A metal-ceramic substrate (1) in which the sheet resistance of the active metal layer (15) and / or the contact layer containing the active metal is greater than 5 Ω / sq.

Images