Method for producing a metal-ceramic substrate, and metal-ceramic substrate

Abstract

The invention relates to a method for producing a metal-ceramic substrate (1), comprising: - providing at least one metal layer (10) - providing a ceramic element (30), and - joining the at least one metal layer (10) to a joining surface on an outer face of the ceramic element (30), wherein the at least one metal layer (10) and the ceramic element (30) extend along a main plane of extent (HSE) and are arranged one above the other in a stacking direction (S) running perpendicular to the main plane of extent (HSE), wherein the joining surface has a roughness that is greater than 0.5 µm, preferably greater than 1.0 µm, and particularly preferably greater than 1.5 µm.

Description

[0001] Method for producing a metal-ceramic substrate and metal-ceramic substrate

[0002] The present invention relates to a metal-ceramic substrate and a method for producing a metal-ceramic substrate.

[0003] Metal-ceramic substrates are well known as printed circuit boards or circuit boards from the prior art, for example from DE 10 2013 104 739 A1, DE 19 927 046 B4, and DE 10 2009 033 029 A1. Typically, connection pads for electrical components and conductor tracks are arranged on one component side of the metal-ceramic substrate or the metal-ceramic substrate, wherein the electrical components and the conductor tracks can be interconnected to form electrical circuits. Key components of the metal-ceramic substrates are an insulating layer, preferably made of a ceramic, and at least one metal layer bonded to the insulating layer. Due to their comparatively high insulation strengths, insulating layers made of ceramic have proven particularly advantageous in power electronics.By structuring the metal layer, conductor tracks and / or connection surfaces for the electrical components can then be realized.

[0004] A prerequisite for the successful provision of a metal-ceramic substrate is a permanent bond between the metal layer and the ceramic layer. In addition to a so-called direct metal bonding process, i.e., a DCB or DAB process, it is known from the state of the art to bond the metal layer to the ceramic layer using a solder material (AMB process).

[0005] An active soldering process, e.g. for joining metal layers or metal foils, in particular copper layers or copper foils, to ceramic material, is understood here to be a process that is specifically used to produce metal-ceramic substrates. In this process, a bond is created between a metal foil, e.g. a copper foil, and a ceramic substrate, e.g. an aluminum nitride ceramic, at a temperature of approximately 650-1000°C using a brazing alloy that, 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 consisting of Hf, Ti, Zr, Nb, and Ce, creates a bond between the solder and the ceramic through a chemical reaction, while the bond between the solder and the metal is a metallic brazing alloy.

[0006] Furthermore, a process is known, for example, from DE 10 2013 113 734 B4 and from JP 4-325 470, in which a metal layer is bonded to a ceramic layer by means of hot isostatic pressing to form a metal-ceramic substrate. Hot isostatic pressing is also used for post-treatment to reduce the number of voids formed during bonding using a soldering process or a direct metal bonding process.

[0007] From CN 110 734 297 A it is known to roughen the ceramic element up to 1.5 pm before the bonding process.

[0008] Based on the prior art, the present invention has for its object to provide a metal-ceramic substrate which is further improved compared to the known metal-ceramic substrates, in particular with regard to the bonding behavior of the metal layer to the ceramic element and the dissipation of heat when heat is generated on the component side of the metal-ceramic substrate due to operation.

[0009] The present invention solves this problem with a method according to claim 1 and a metal-ceramic substrate according to claim 9. Further embodiments can be found in the dependent claims and the description.

[0010] According to a first aspect of the present invention, there is provided a method for producing a metal-ceramic substrate, comprising:

[0011] Providing at least one metal layer

[0012] Providing a ceramic element, and

[0013] Bonding the at least one metal layer to a bonding surface on an outer side of the ceramic element, wherein the at least one metal layer and the ceramic element extend along a main extension plane and are arranged one above the other along a stacking direction running perpendicular to the main extension plane, wherein the bonding surface has a roughness which is greater than 0.5 pm, preferably greater than 1.0 pm and particularly preferably greater than 1.5 pm or even greater than 2 pm and even particularly preferably greater than 2.5 pm.

[0014] Compared to the metal-ceramic substrates known from the prior art, the invention provides for a comparatively high level of roughness on the ceramic element. This surface roughness proves to be particularly advantageous because it increases the contact area between the metal layer and the ceramic element in the manufactured metal-ceramic substrate. However, an increased contact area simultaneously results in lower thermal contact resistance, as a result of which the thermal resistance of the entire metal-ceramic substrate can be reduced. This has a beneficial effect on heat dissipation, which is intended to dissipate operational heat generated on the component side by electrical components. In addition, an interlocking created by the surface roughness for a bonding layer formed between the metal layer and the ceramic element proves to be advantageous because it increases the peel orShear strength can be achieved. This has a particularly positive effect on the service life of the manufactured metal-ceramic substrate.

[0015] In particular, the increased roughness makes it possible not only to increase the interface surface at the bonding surface, thereby increasing the bond strength in the bonding area because the applied peel or delamination forces are distributed over a larger area. On the other hand, the thermal resistance during the passage of the thermal drop from one phase to the next (R t h=1 / a*A).

[0016] The roughening can preferably be an arbitrary surface structure. It is additionally or alternatively conceivable for the roughness to have a structure that can be, for example, point-shaped or line-shaped, for example straight or curved. Also conceivable, for example, is microstructuring, which is preferably present in addition to the roughness. The microstructuring is preferably understood as a two-dimensional, in particular repeating pattern. The microstructuring is preferably to be understood as more global than the surface roughness and has a pattern that repeats after a distance along a direction running parallel to the main extension plane, wherein the distance is greater than 75 pm, preferably greater than 125 pm and particularly preferably greater than 150 pm.For example, it could also be a moth's eye structure that is deliberately embedded into the ceramic element to form the bonding surface. In particular, it is intended that the microstructuring be formed in such a way that an enlarged surface does not adversely affect the joining process, e.g., by the enlarged surface leading to an increase in boundary layer porosity or to an increased thickness of the joining zone, which is, for example, incompatible with soldering processes that use very thin solder systems, especially comparatively thin, especially sputtered active solder layers.

[0017] In particular, the generated microstructuring and / or the increased roughness is provided at least partially, preferably completely, in the area of ​​the outer side of the ceramic element to which the at least one metal layer is to be bonded. It is introduced into the bonding surface intended for bonding, for example by roughening and / or embossing. In this case, the person skilled in the art preferably understands microstructuring to mean a deliberately embedded surface topography that follows a predetermined geometry. For example, the surface profile is groove-, trench-, cylinder-, diamond-, prism-, and / or dome-shaped recesses that are embedded on the outer side of the ceramic element following a specific or arbitrary pattern.Furthermore, it is provided that the outer side of the ceramic element facing the metal layer in the bonded state is provided with a surface profile to more than 50%, preferably more than 70% and particularly preferably more than 85%.

[0018] Preferably, the mean arithmetic height is determined as the roughness parameter. This is the height difference of each point compared to the arithmetic mean of the surface. Alternatively, it is conceivable to determine the mean square height (SQ), a reduced peak height (SPK), a reduced valley height (SVK), or a maximum height (Sz). Preferably, R a is taken as a measure of roughness. R z or R max . Standard methods such as a stylus method, e.g. using a Perthometer (see DIN EN ISO 3274) or confocal microscopy (see ISO 25178-6) are preferred for determining roughness.

[0019] It is preferably provided that the surface roughness is determined with the aid of a Perthometer. In this case, the surface roughness of the ceramic can be measured in a simplified manner. [ Preferably, the metal-ceramic substrate is designed as a circuit board in which, in the manufactured state, the at least one metal layer that is bonded to the ceramic element is structured. For example, it is provided that after the bonding step, structuring is also carried out, for example by lasering, etching and / or mechanical processing, with which conductor tracks and / or connections for electrical or electronic components are realized. It is preferably provided that on a manufactured metal-ceramic substrate, on the ceramic element, on the side opposite the metal layer, a further metal layer, in particular a back-side metallization and / or a cooling element, is provided.The rear-side metallization preferably serves to counteract deflection and the cooling element serves to effectively dissipate heat that is generated during operation by electrical or electronic components that are connected to the circuit board or the metal-ceramic substrate.

[0020] Conceivable materials for the at least one metal layer and / or the at least one further metal layer in the metal-ceramic substrate or ceramic element include copper, aluminum, molybdenum, tungsten, nickel, and / or their alloys, such as CuZr, AlSi, or AlMgSi, as well as laminates such as CuW, CuMo, CuAl, and / or AlCu, or MMC (metal matrix composite), such as CuW, CuM, or AlSiC. Furthermore, it is preferably provided that the at least one metal layer on the manufactured metal-ceramic substrate is surface-modified, in particular as component metallization. A possible surface modification could, for example, be a sealing with a precious metal, in particular silver and / or gold, or (electroless) nickel or EN IG ("electroless nickel immersion gold"), or edge encapsulation on the metallization to suppress crack formation or crack widening.

[0021] The ceramic element preferably comprises Al2O3, SiSn4, AlN, an HPSX ceramic (i.e., a ceramic with an Al2O3 matrix containing an x-percent ZrO2 content, for example Al2O3 with 9% ZrO2 = HPS9 or Al2O3 with 25% ZrO2 = HPS25), SiC, BeO, MgO, high-density MgO (> 90% of the theoretical density), TSZ (tetragonally stabilized zirconium oxide) as the ceramic material. It is also conceivable for the ceramic element to be designed as a composite or hybrid ceramic, in which, in order to combine various desired properties, several ceramic layers, each differing in terms of their material composition, are arranged one above the other and joined together to form a ceramic element. In particular, it is provided that the ceramic element comprises silicon nitride and / or is preferably formed from more than 60%, preferably from more than 70% and particularly preferably from more than 80% of silicon nitride S13N4.In particular, it is provided that a thermal conductivity of the ceramic element is greater than 75 W / mK, preferably greater than 90 W / mK and particularly preferably greater than 105 W / mK, in particular based on thermal conductivity measurements of the ceramic using a laser flash method in combination with density and specific heat.

[0022] It is preferably provided that the roughness assumes a value that lies between 0.5 and 8.0 pm, preferably between 1.0 and 5 pm and particularly preferably between 1.5 and 3.0 pm. It is particularly preferably provided that the roughness assumes a value that lies between 1.5 and 8 pm, preferably between 2.0 and 3.5 pm and particularly preferably between 2.2 and 3 pm. This advantageously makes it possible to also specify an upper limit for the roughness in order to ensure that the roughened bonding surface can be used by the majority of joining technologies or connection methods.It has been found that, particularly in the interval between 1.5 and 3.0, all soldering processes, in particular active soldering processes, are conducive to successful bonding, particularly when thin solder layer systems are used in which the solder system, for example as a film or as a paste, has a layer thickness which is less than 20 pm, preferably less than 15 pm and particularly preferably less than 15 pm.

[0023] Preferably, the bonding surface is surface modulated in addition to the roughness, preferably with a half period lying between 5 pm and 1 mm, preferably between 10 pm and 0.5 mm, and particularly preferably between 200 pm and 100 pm. The surface modulation is preferably part of the microstructuring. For example, it is a wave-like surface modulation. In contrast to the roughness, the surface modulation occurs on a larger scale and is at least one order of magnitude larger than the roughness. The microstructuring preferably refers to a two-dimensional pattern on the outer surface of the ceramic element, while the surface modulation relates to a change in height, which can be present in addition to roughness.It has been found that, in addition to roughness, the bond strength can be specifically improved by adjusting appropriate surface modulation, and in particular, the peel strength or adhesion can also be increased. It is preferably provided that the amplitude of the surface modulation assumes a value that is greater than 1 μm, preferably greater than 2 μm, particularly preferably greater than 5 μm, or even greater than 10 μm, or even particularly preferably greater than 15 μm.

[0024] In particular, a person skilled in the art understands surface modulation to mean a periodic, i.e., regular, repetition of elevations and / or valleys. In other words, the distance between two adjacent elevations remains constant over at least two-thirds of the longitudinal or transverse extent. The periodicity of the elevations forms in particular along one direction, preferably only along one direction. In other words, it is not a two-dimensional pattern, and the elevations and / or valleys are not distributed in one plane. Preferably, the elevation and / or valleys each extend over the entire length or width of the ceramic element.

[0025] In particular, the amplitude of the surface modulation assumes a value between 1 pm and 40 pm, preferably between 2 and 20 pm and particularly preferably between 2.5 and 10 pm.

[0026] Preferably, in a preparatory step, i.e., before the actual bonding, the ceramic element is roughened on the outside to form the bonding surface. This advantageously makes it possible to specifically adjust the desired roughness in order to improve the peel strength.

[0027] Preferably, the ceramic element is roughened mechanically, optically, and / or chemically. For example, it is conceivable for a targeted structure to be fired or embedded into the surface or outer side of the ceramic element using suitable laser light, wherein, for example, abrasion can be controlled by a dwell time of the light on the outer surface. Alternatively, it is also conceivable for a targeted surface modulation, roughness, and / or microstructuring to be realized by sawing or milling, in particular by machining the outer side of the ceramic element. Surface modulation using a chemical etching agent is also conceivable, particularly if appropriate masking contributes to a targeted surface modulation being embedded in the ceramic element.The surface modulation is particularly preferably created by using a sawing tool, in particular a wire saw, to separate the ceramic element from a ceramic block. The sawing tool can be, for example, a diamond wire saw or a wafer saw. The properties of a wire used as a wire saw can then advantageously influence the properties of the surface modulation. For example, half a period of the surface modulation can be set by adjusting the wire thickness. It is also conceivable that the roughness can be influenced by the choice of wire material. To set a specific roughness value, it is also conceivable that the ceramic element is set to a greater roughness and then the desired target roughness is set in a post-processing step, for example polishing.

[0028] It is also conceivable that the microstructuring or surface modulation could be performed by laser ablation. Etching or embossing, particularly of the green foils prior to sintering, is also conceivable. For example, it is also conceivable that the roughness could be created by cutting the ceramic element out of a ceramic block, particularly using a steel wire and / or in a state in which the ceramic material is still uncured, e.g., as a foil or as an unsintered blank.

[0029] By appropriate adjustment, it is possible to provide a substantially flat ceramic element whose surface modulation is sufficiently modulated to realize a significant improvement in peel strength. Preferably, an amplitude of the surface modulation has a first height and a thickness of the ceramic element measured perpendicular to the main extension plane has a second height, wherein a ratio of the first height to the second height is less than 0.5, preferably less than 0.2, and particularly preferably less than 0.1.

[0030] Preferably, a surface profiling, in particular a microstructuring, is created by structuring prior to sintering, i.e., in a powder, c or a powder coating of the green body. Alternatively or additionally, it is conceivable that powder is successively applied locally and cured on the outside of a pre-ceramic or a ceramic base body by laser sintering.

[0031] Preferably, the microstructuring is a repeating pattern that is repeated over a large part of the surface of the ceramic element. In other words, it is not a random and disordered distribution of elevations that contributes to surface roughness, but rather a desired microstructuring on the exterior of the ceramic element is realized through targeted placement. It is conceivable that the pattern changes along the ceramic element, in particular, for example, increasing towards the edge of the metal layer or the outermost edge region of the metal layer in the main extension plane, for example with regard to the density of recesses per unit area or with regard to the size of the recesses. In these areas, increased peel strength is advantageous and desirable.

[0032] Furthermore, it is preferably provided that the ceramic element has a first thickness and the metal layer has a second thickness. The first thickness preferably assumes a value between 150 pm and 1000 pm, preferably between 200 pm and 500 pm and particularly preferably between 200 pm and 400 pm or even between 400 pm and 600 pm. The second thickness can, for example, be greater than the first thickness and, for example, assume a value that is greater than 1 mm. The second thickness is preferably between 50 pm and 1 mm, preferably between 100 pm and 500 pm and particularly preferably between 150 pm and 350 pm. It has been shown, for example, that due to the improved thermal resistance, the ceramic elements can be made thicker without jeopardizing the required heat transfer. This makes it possible to provide particularly insulation-resistant and mechanically stable metal-ceramic substrates for certain applications.

[0033] Preferably, the at least one metal layer and the ceramic element are bonded to one another using an active soldering process. Furthermore, it is preferably provided that the at least one metal layer and / or the at least one further metal layer are bonded to the ceramic element using an active soldering process, a diffusion bonding process, and / or hot isostatic pressing and / or a DGB process.

[0034] It is preferably provided that a solder system is arranged between the at least one metal layer and the ceramic element for bonding, wherein the solder system comprises at least one separate active metal layer.

[0035] Furthermore, it is provided that, in addition to the active metal layer, a solder base material is provided as a component of the solder system for bonding and / or hot isostatic pressing is carried out. For example, it is provided that a method for producing a metal-ceramic substrate is provided, comprising:

[0036] - Providing a soldering layer, in particular in the form of at least one soldering foil or brazing foil,

[0037] - coating the ceramic element and / or the at least one metal layer and / or the at least one solder layer with at least one active metal layer,

[0038] - Arranging the at least one solder layer between the ceramic element and the at least one metal layer along a stacking direction to form a solder system comprising the at least one solder layer and the at least one active metal layer, wherein a solder material of the at least one solder layer is preferably free of a melting point-lowering material or of a phosphorus-free material, and

[0039] - Bonding the at least one metal layer to the at least one ceramic layer via the soldering system by means of an active soldering process.

[0040] In particular, a multi-layer soldering system comprising at least one solder layer, preferably free of melting point-lowering elements, particularly preferably a phosphorus-free solder layer, and at least one active metal layer is provided. The separation of the at least one active metal layer and the at least one solder layer proves to be particularly advantageous because it enables comparatively thin solder layers to be realized, especially when the solder layer is a foil. For solder materials containing active metals, comparatively large solder layer thicknesses must otherwise be realized due to the brittle intermetallic phases or the high modulus of elasticity and high yield strength of common active metals and their intermetallic phases, which hinder the forming of the solder paste or solder layer, whereby the minimum layer thickness is limited by the manufacturing properties of the solder material containing active metal.Accordingly, for solder layers containing active metals, the minimum solder layer thickness is not determined by the minimum thickness required for the joining process, but rather by the minimum technically feasible solder layer thickness. As a result, this thicker, active-metal-containing solder layer is more expensive than thinner layers. The term "phosphorus-free" is understood by those skilled in the art to mean, in particular, that the phosphorus content in the solder layer is less than 150 ppm, less than 100 ppm, and particularly preferably less than 50 ppm.

[0041] In particular, the use of a separately applied active metal layer makes it possible to make it comparatively thin, thereby achieving the claimed comparatively thin thicknesses of the bonding layer, in particular averaged over various thickness values ​​within the specified area(s). Examples of active metals are 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 that the metals La, Ce, Ca, and Mg can easily oxidize. Furthermore, it should be noted that the elements Cr, Mo, and W are not classic active metals, but are suitable as a contact layer between SiSn4 and the at least one metal layer or the solder system or solder material, since they do not form intermetallic phases with the at least one metal layer, for example, copper, and do not have edge solubility.

[0042] Preferably, the solder layer, especially the phosphorus-free solder layer, comprises several materials in addition to the pure metal. For example, indium is a component of the solder material used in the solder layer.

[0043] Furthermore, it is conceivable that the solder material, in particular the active metal, for forming the solder layer is applied to the active metal layer and / or the at least one metal layer and / or to the ceramic element by physical and / or chemical vapor deposition and / or galvanically. This advantageously makes it possible to realize comparatively thin solder layers, in particular active metal layers, in the soldering system, particularly with a homogeneous distribution.

[0044] For example, in the production of the metal-ceramic substrate, in particular the metal-ceramic substrate, further steps are provided, comprising:

[0045] - Providing a ceramic element and a metal layer,

[0046] - providing a gas-tight container enclosing the ceramic element, wherein the container is preferably formed from the metal layer or comprises the metal layer,

[0047] - Forming the metal-ceramic substrate by bonding the metal layer to the ceramic element by means of hot isostatic pressing, wherein, to form the metal-ceramic substrate, an active metal layer or a contact layer comprising an active metal is arranged at least in sections between the metal layer and the ceramic element to assist in bonding the metal layer to the ceramic element. The container is preferably formed as a metal container made of a metal layer and / or a further metal layer. Alternatively, it is also conceivable that a glass container is used. In hot isostatic pressing, it is particularly provided that the bonding takes place by heating under pressure, during which the first and / or second metal layer of the metal container, in particular the subsequent metal layer of the metal-ceramic substrate and any eutectic layer occurring there, do not enter the melting phase.Accordingly, hot isostatic pressing requires lower temperatures than direct metal bonding processes, particularly DCB processes.

[0048] In comparison to the bonding of a metal layer to a ceramic layer by means of a solder material, which usually requires temperatures below the melting temperature of the at least one metal layer, the present procedure advantageously dispenses with the need for a solder base material, and only requires an active metal. The use or utilization of pressure during hot isostatic pressing also proves advantageous because it can reduce air inclusions or cavities between the first metal layer and / or the second metal layer on the one hand and the ceramic element on the other. As a result, the frequency of voids forming in the formed or manufactured metal-ceramic substrate can be reduced or even avoided. This has a beneficial effect on the quality of the bond between the metal layer or the first and / or second metal layer of the metal container and the ceramic element.In addition, it is advantageously possible to simplify the “second etching” and avoid solder residues and silver migration.

[0049] It is also conceivable that during hot isostatic pressing an additional solder material is introduced between the ceramic element and the at least one metal layer, wherein a melting temperature of the additional solder material can be lower than the temperature at which the hot isostatic pressing is carried out, ie lower than the melting temperature of the at least one metal layer.

[0050] It is preferably provided that during hot isostatic pressing, the metal container is exposed in a heating and pressure device to a gas pressure between 100 and 2000 bar, preferably between 150 and 1200 bar, and particularly preferably between 300 and 1000 bar, and a process temperature of 300°C up to a melting temperature of the at least one metal layer, in particular up to a temperature below the melting temperature. It has advantageously been found that it is thus possible to bond a metal layer, i.e. a first and / or second metal layer of the metal container, to the ceramic element without the required temperatures of a direct metal bonding process, for example a DCB or a DAB process, and / or without a solder base material that is used in active soldering. In addition, the use or application of an appropriate gas pressure allows the possibility of producing a bond as void-free as possible, i.e.to produce a metal-ceramic substrate without gas inclusions between the metal layer and the ceramic element. In particular, process parameters mentioned in DE 2013 113 734 A1 are used, and are hereby explicitly referenced.

[0051] According to a further aspect of the present invention, a metal-ceramic substrate is provided, preferably produced using a method according to the invention, comprising: a component metallization and a ceramic element (30), wherein the at least one metal layer and the ceramic element extend along a main extension plane and are arranged one above the other along a stacking direction running perpendicular to the main extension plane, wherein the component metallization is bonded to the ceramic element at a bonding surface, wherein the bonding surface has a roughness that is greater than 1.5 pm, preferably greater than 2 pm and particularly preferably greater than 2.5 pm. All advantages and properties described for the method can be transferred analogously to the metal-ceramic substrate and vice versa.

[0052] According to a preferred embodiment of the present invention, it is provided that a bonding layer is formed between the at least one metal layer and the ceramic element in the manufactured metal-ceramic substrate, wherein an adhesion promoter layer of the bonding layer has a surface resistance which is greater than 5 ohms / sq, preferably greater than 10 ohms / sq and particularly preferably greater than 20 ohms / sq.

[0053] The sheet resistance is directly related to the active metal content in the bonding layer, which is crucial for bonding the at least one metal layer to the ceramic element. The sheet resistance increases with a decreasing active metal content in the bonding layer. A correspondingly high sheet resistance therefore corresponds to a low active metal content in the bonding layer. The sheet resistance does not depend on a single parameter, but can be influenced by the interaction of several parameters. For example, the purity of the active metal, the thickness of the bonding layer and / or the surface roughness of the ceramic element all contribute to determining the sheet resistance. In particular, high sheet resistances can only be achieved through the interaction of at least two parameters.

[0054] It has been found that with an increasing proportion of active metal, the formation of brittle, intermetallic phases is promoted, which in turn is detrimental to the peel strength of the metal layer on the insulation layer. In other words: the claimed sheet resistances describe bonding layers whose peel strength is improved, i.e. increased, due to the reduced formation of brittle intermetallic phases. By specifically adjusting the claimed sheet resistances, particularly strong bonds between the at least one metal layer and the ceramic element can be achieved. Such an increased bond strength has a beneficial effect on the service life of the metal-ceramic substrate. To determine the sheet resistance, it is provided that the metal layer and, if applicable,a solder base layer is removed again, for example by etching. Using a four-point measurement, a sheet resistance is then measured on the outside or underside of the metal-ceramic substrate freed from the at least one metal layer and the solder base layer. In particular, the sheet resistance of a material sample is to be understood as its resistance relative to a square surface area. It is customary to designate the surface resistance with the unit ohm / sq(square). The physical unit of sheet resistance is ohm. Preferably, it is provided that a thickness of the bonding layer measured in the stacking direction, averaged over several measuring points within a predetermined area or in several areas that run or run parallel to the main extension plane, assumes a value that is less than 0.20 mm, preferably less than 10 pm and particularly preferably less than 6 pm.When multiple surfaces are mentioned, this means in particular that the at least one metal layer is divided into surfaces of as equal size as possible, and in each of these surfaces dividing the at least one metal layer, at least one value, preferably several measured values, for the thickness are recorded. The thicknesses thus determined at different points are arithmetically averaged. Compared to the metal-ceramic substrates known from the prior art, a comparatively thin bonding layer is thus formed between the at least one metal layer and the ceramic element. In this case, it is provided that, in order to determine the relevant thickness of the bonding layer, the measured thicknesses are averaged over a plurality of measuring points that lie within a predetermined or fixed surface or the plurality of surfaces. This advantageously takes into account the fact that the ceramic element is generally subject to undulation, i.e.The ceramic element is to be considered to have a waviness. In particular, the person skilled in the art understands waviness to be a modulation of the generally flat course of the ceramic element, viewed over several millimeters or centimeters along a direction parallel to the main plane of extension. This distinguishes such an undulation from a surface roughness of the ceramic element, which is generally also present on the ceramic element. By including such a generally unavoidable undulation of the ceramic element in the determination of the thickness, it is taken into account that the bonding layer may vary due to the undulation, in particular it may be larger in valley areas of the ceramic element than in peak areas of the ceramic element.

[0055] Preferably, a proportion of active metal in the adhesion promoter layer comprising an active metal is greater than 15 wt.%, preferably greater than 20 wt.% and particularly preferably greater than 25 wt.%.

[0056] The bonding layer is preferably formed flatly, in particular without interruption, i.e. continuously, between the at least one metal layer and the ceramic element. It is preferably provided that a ratio of an area in which no bonding layer is formed between the at least one metal layer and the ceramic element to the areas in which a bonding layer is formed between the at least one bonding layer and the ceramic element is less than 0.05, preferably less than 0.02 and particularly preferably less than 0.007. The person skilled in the art will understand in particular that in forming this ratio, the areas which are free of metal of the at least one metal layer due to the structuring are not taken into account.

[0057] Preferably, the thermal conductivity of the ceramic element is greater than 75 W / mK, preferably greater than 90 W / mK, and particularly preferably greater than 105 W / mK. Correspondingly high thermal conductivities also prove particularly advantageous for heat dissipation, particularly in addition to the aforementioned surface roughness. This prevents the heat from accumulating in the ceramic element after rapid heat dissipation via the interface between the ceramic element and the metal layer. This allows corresponding metal-ceramic substrates to be used particularly advantageously for high-performance electronic components that generate very high levels of heat during operation.

[0058] Further advantages and features will become apparent from the following description of preferred embodiments of the subject matter of the invention with reference to the accompanying figures. They show:

[0059] Fig. 1 : Metal-ceramic substrate according to a first exemplary embodiment of the present invention;

[0060] Fig. 2a and 2b show a detailed view of the grain on an outer side of the ceramic element of a metal-ceramic substrate according to a second exemplary embodiment of the present invention

[0061] Fig.3 shows a ceramic element of a metal-ceramic substrate according to a third exemplary embodiment of the present invention and

[0062] Fig. 4a and 4b are sectional views through a metal-ceramic substrate according to the prior art and according to a fourth exemplary embodiment of the present invention.

[0063] Figure 1 shows a metal-ceramic substrate 1 according to a first exemplary embodiment of the present invention. Such metal-ceramic substrates 1 preferably serve as carriers or circuit boards for electronic or electrical components, which can be bonded to the at least one metal layer 10 of the metal-ceramic substrate 1 on its component side. It is preferably provided that the at least one metal layer 10 is structured in order to form corresponding conductor tracks and / or connection surfaces, i.e., in the manufactured metal-ceramic substrate 1, the at least one metal layer 10 comprises a plurality of metal sections that are electrically insulated from one another.The at least one metal layer 10, which extends essentially along a main extension plane HSE, and a ceramic element 30, which extends along the main extension plane HSE, are arranged one above the other along a stacking direction S running perpendicular to the main extension plane HSE and are preferably joined or connected to one another via a bonding layer 12. Preferably, the metal-ceramic substrate 1 comprises, in addition to the at least one metal layer 10, at least one further metal layer 20, which, viewed in the stacking direction S, is arranged on the side of the ceramic element 30 opposite the at least one metal layer 10 and is bonded to the ceramic element 30 via a further bonding layer 12'.

[0064] In this case, the at least one further metal layer 20 serves as a backside metallization, which counteracts a bending of the metal-ceramic substrate 1, in particular of the metal-ceramic element, and / or as an adapter for a heat sink, which is designed to dissipate heat input caused by electrical or electronic components on the metal-ceramic substrate 1, or as a heat sink.

[0065] In particular, the metal-ceramic substrate 1 has a bonding layer 12 arranged between the at least one metal layer 10 and the ceramic element 30. It has proven advantageous if the thickness of the bonding layer 12 measured in the stacking direction S is comparatively thin. Furthermore, a comparatively thin thickness of the bonding layer 12 between the at least one metal layer 10 and the ceramic element 30 proves advantageous if an etching process is provided for the purpose of structuring the at least one metal layer 10. For example, this allows narrower isolation trenches, i.e., distances between individual metal sections of the at least one metal layer 10, to be realized.

[0066] Furthermore, the formation of a thinner bonding layer 12 proves to be advantageous in that it can further reduce the number of possible defects in the bonding layer 12 caused by material defects in a solder material that may be used.

[0067] In the example shown in Figure 1, the bonding layer 12 is in particular an adhesion promoter layer 13 comprising an active metal. In this case, the adhesion promoter layer 13 is preferably formed after bonding from a material composition comprising a compound of components of the ceramic element on the one hand and an active metal on the other. Since these are very brittle compounds, the thinnest possible design of this adhesion promoter layer 13 is advantageous for the adhesive strength of the at least one metal layer 10 on the ceramic element 30. For example, the adhesion promoter layer 13 can form the bonding layer 12 if, for example, an active metal layer, in particular an active metal foil, is arranged between the ceramic element 30 and the metal layer 10 for the bonding process and the bonding process is carried out via hot isostatic pressing.However, the adhesion promoter layer 13 can also be formed, for example, by an active metal layer, in particular an active metal foil, which is arranged between the ceramic element 30 and a solder base layer in order to create the bond between the metal layer 10 and the ceramic element 30 via the system of the active metal layer and the solder base layer. In this case, the adhesion promoter layer 13 forms part of the bonding layer 12.

[0068] In particular, it is intended to provide metal-ceramic substrates 1 which are improved compared to the metal-ceramic substrates 1 known from the prior art, in particular with regard to their heat dissipation and with regard to their peel and shear strength. This is preferably brought about by increasing a roughness Ra of the surface of the ceramic element 30. For example, a roughness Ra of the surface of the ceramic element 30 assumes a value of more than 1.5 pm, preferably greater than 2.0 pm and particularly preferably greater than 2.5 pm. This advantageously makes it possible to enlarge the surface of the ceramic element 30, whereby the contact area between the metal layer 10 and the ceramic element 30 is increased after the bonding process. Since the thermal contact resistance is inversely proportional to this contact area, this leads to a lower thermal contact resistance.As a result, the thermal resistance of the metal-ceramic substrate 1 is reduced, which advantageously reduces heat dissipation, particularly when heat is to be dissipated from the electrical components on the component side of the metal-ceramic substrate 1.

[0069] Furthermore, the increased roughness makes it possible to increase the interlocking of metal layer 10 and ceramic element 30, thereby additionally increasing the peel and shear strength of metal layer 10 relative to ceramic element 30. This advantageously leads to an increase in the service life of metal-ceramic substrate 1. Figure 2a shows a sectional view through a metal-ceramic substrate 1, wherein component metallization and backside metallization are bonded to ceramic element 30, which result from the bonding of metal layer 10 and further metal layer 20. In particular, the embodiment shown in Figure 2a is characterized in that ceramic element 30 is surface-modulated, particularly in the region of the bonding surface.In the exemplary embodiment illustrated in Figure 2a, the bonding surface has a generally undulating profile in a direction running along the main extension plane HSE. Half the period P1 of this undulating profile is designated P1. Preferably, half the period P1 is at a value between 20 pm and 2 mm, preferably between 50 pm and 1 mm, and particularly preferably between 100 pm and 500 pm. In the exemplary embodiment illustrated, half the period P1 is 160 pm.

[0070] The ceramic element 30 has a first thickness D of approximately 280 pm, and an amplitude of the surface modulation is approximately 10 pm. A second thickness of the component metallization and / or the backside metallization is, for example, 500 to 700 pm. In addition, the ceramic element 30 used here has a roughness of approximately 2 pm, in addition to the more global surface modulation.

[0071] The roughness is less visible or recognizable in this Figure 2a compared to the representations in Figures 4a and 4b. The periodicity or surface modulation that is created here is the result of the manufacturing process, in which the ceramic element 30 was separated from a block, in particular from a silicon nitride block. The periodicity and thus also the size of half the period P1 is set, for example, by the thickness of the wire that is used when separating it from the block. Preferably, the thickness of the wire is selected such that it determines the distance between two neighboring peaks, i.e., corresponds to half the periodicity or half the period P1. It has been found that the peel strength or adhesion of the bonded metal layer 10 can be further improved by a corresponding periodicity of the surface, i.e., by the surface modulation of the ceramic element 30.

[0072] Figure 2b shows a comparison of the peel strength or adhesion in N / mm for a metal-ceramic substrate 1 that was joined using a conventional active soldering process. The metal-ceramic substrate 1 used has a first thickness of 320 pm and a second thickness of 800 pm of a copper layer. The ceramic element 30 is made of silicon nitride, and a bonding technology was used for joining in which the active metal is provided as a separate layer alongside a solder base material. The metal-ceramic substrate (2) in this test has a first thickness of 280 pm and a second thickness of 800 pm for the copper layer. The joining technology is the same as that used for the metal-ceramic substrate (1). The result shows that the peel strength or adhesionthe adhesion is significantly improved when a metal-ceramic substrate 1 is produced in which the ceramic element 30 has a surface modulation as shown by way of example in Figure 2a, in particular with the specified half period P1.

[0073] Figure 3 shows a ceramic element 30 for a metal-ceramic substrate 1 according to a third exemplary embodiment of the present invention. In particular, Figure 3 shows a plan view of the ceramic element 30 (bottom) and a sectional view along the drawn line. In contrast to the exemplary embodiment of Figures 2a and 2b, the exemplary embodiment of Figure 3 provides for a surface profile 18 to be embedded in the ceramic element 30. In contrast to the randomly distributed pattern of elevations from the exemplary embodiment of Figures 2a and 2b, the exemplary embodiment of Figure 3 provides for a repeated pattern or a targeted pattern to be provided on the outer side of the ceramic element 30. Such a pattern can be realized, for example, by a corresponding etching or mechanical process after the sintering process.Alternatively, it is conceivable that structuring could be applied to the green compact itself, which would then harden during sintering, creating the desired microstructure. Additive microstructuring through laser sintering, in which powder is applied to a pre-ceramic or ceramic base body, is also conceivable.

[0074] In particular, the present invention provides for a microstructuring to be produced on the surface or outside of the ceramic element 30. In this case, a person skilled in the art understands a microstructuring in particular as having a height profile with a maximum amplitude of between 1 pm and 50 pm, preferably between 1.5 and 10 pm and particularly preferably between 2.0 and 9 pm. The microstructuring is preferably a pattern extending substantially along the main extension plane, which preferably has surface modulation. In the exemplary embodiment shown, the microstructurings run in the main extension plane HSE along a zigzag line (below), the microstructuring being produced substantially by equally spaced depressions, as can be seen in the sectional view (above).However, this geometric shape is merely exemplary of a multitude of other possible surface profilings or structurings. For example, pyramid, cylinder, or dome shapes are also conceivable. Furthermore, intersecting line patterns or parallel line patterns are conceivable. All of these patterns prove particularly advantageous because they increase the surface area of ​​the ceramic element 30 and thus the contact area between the metal layer 10 and the ceramic element 30. Preferably, it is conceivable that a surface profiling is only embedded in the regions in which the later ceramic element 30 is connected to the metal layer 10. In particular, it is envisaged that the microstructuring is realized in addition to the roughness and / or surface modulation.

[0075] Figures 4a and 4b show a comparison between a bonding region between metal layer 10 and ceramic element 30 according to the prior art (top) and according to the present invention (bottom). It can be seen in particular that in the case of the present invention, the interface region, ie the bonding layer, between metal layer 10 and ceramic element 30 is characterized by a tangled structure, which is the result of the roughness S a the surface of the ceramic element 30. It can thus be seen that the bonding layer 12 between the metal layer 10 and the ceramic element 30 engages in the ceramic element 30 in an anchor-like, interlocking manner, thus strengthening the bond between the metal layer 10 and the ceramic element 30. This increases the peel and shear strength.

[0076] List of reference symbols:

[0077] 1 metal-ceramic substrate

[0078] 10 metal layer

[0079] 12 binding layer

[0080] 12' additional binding layer

[0081] 13 Adhesion promoter layer

[0082] 20 additional metal layers

[0083] 30 ceramic elements

[0084] HSE main extension level

[0085] S Stacking direction

[0086] P1 half period D1 first thickness

[0087] D2 second thickness

Claims

Claims 1. A method for producing a metal-ceramic substrate (1) comprising: Providing at least one metal layer (10) Providing a ceramic element (30), and Bonding the at least one metal layer (10) to a bonding surface on an outer side of the ceramic element (30), wherein the at least one metal layer (10) and the ceramic element (30) extend along a main extension plane (HSE) and are arranged one above the other along a stacking direction (S) running perpendicular to the main extension plane (HSE), wherein the bonding surface has a roughness that is greater than 0.5 pm, preferably greater than 1.0 pm and particularly preferably greater than 1.5 pm or even greater than 2 pm and even particularly preferably greater than 2.5 pm.

2. The method according to claim 1, wherein the roughness assumes a value between 0.5 pm and 8 pm, preferably between 1.0 pm and 5 pm and particularly preferably between 1.5 pm and 3 pm.

3. Method according to one of the preceding claims, wherein in a preparatory step the ceramic element (30) is roughened on the outside to form the bonding surface.

4. The method according to claim 3, wherein the ceramic element (30) is roughened mechanically, optically and / or chemically.

5. Method according to one of the preceding claims, wherein the bonding surface is surface modulated in addition to the roughness, preferably with a half period (P1) between 5 pm and 1 mm, preferably between 10 pm and 0.5 mm and particularly preferably between 20 pm and 100 pm.

6. The method according to claim 5, wherein a distance between two elevations of the surface modulation remains constant over at least two thirds of the longitudinal or transverse extent of the ceramic element (30).

7. Method according to one of claims 5 or 6, wherein the ceramic element (30) is surface-modulated in a wave-like manner.

8. The method according to any one of claims 5 to 7, wherein an amplitude of the surface modulation assumes a value between 1 pm and 40 pm, preferably between 2 and 20 pm and particularly preferably between 2.5 and 10 pm.

9. The method according to any one of claims 5 to 8, wherein an amplitude of the surface modulation has a first height and a thickness of the ceramic element (30) measured perpendicular to the main extension plane has a second height, wherein a ratio of the first height to the second height is less than 0.5, preferably less than 0.2 and particularly preferably less than 0.1 10. Method according to one of the preceding claims, wherein the at least one metal layer (10) and the ceramic element (30) are joined together using an active soldering process.

11. The method according to claim 6, wherein for bonding purposes a solder system is arranged between the at least one metal layer (10) and the ceramic element (30), wherein the solder system comprises at least one separate active metal layer.

12. The method according to claim 7, wherein, in addition to the active metal layer, a solder base material is provided as a component of the solder system and / or hot isostatic pressing is carried out for bonding.

13. Metal-ceramic substrate (1), preferably produced by a method according to one of the preceding claims, comprising: - component metallization and - a ceramic element (30), wherein the at least one metal layer (10) and the ceramic element (30) extend along a main extension plane (HSE) and are arranged one above the other along a stacking direction (S) running perpendicular to the main extension plane (HSE), wherein the component metallization is bonded to the ceramic element (30) at a bonding surface, wherein the bonding surface has a roughness that is greater than 1.0 pm, preferably greater than 1.5 pm and particularly preferably greater than 2.0 pm is.

14. Metal-ceramic substrate (1) according to claim 9, wherein the bonding surface is surface-modulated.

15. Metal-ceramic substrate (1) according to claim 13 or 14, wherein an adhesion promoter layer of the bonding layer has a surface resistance which is greater than 5 ohms / sq, preferably greater than 10 ohms / sq and particularly preferably greater than 20 ohms / sq

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