Method for producing metal-ceramic substrate and cermet 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-bonding the at least one metal layer (10) to a bonding surface at 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 in a stacking direction (S) running perpendicular to the main extension plane (HSE), and wherein the bonding surface has a roughness greater than 0.5 [mu]., preferably greater than 1.0 [mu]., and particularly preferably greater than 1.5 [mu].

Description

Technical Field

[0001] The present invention relates to a metal-ceramic substrate and a method for manufacturing a metal-ceramic substrate. Background Technology

[0002] Metal-ceramic substrates as circuit boards or substrates are well known in the prior art, for example from DE 10 2013104 739 A1, DE 19 927 046 B4, and DE 10 2009 033 029 A1. Typically, bonding surfaces for electrical devices and printed conductors are provided on the device side of the metal-ceramic substrate, wherein the electrical devices and printed conductors can be connected together to form an electrical circuit. The main components of the 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 particularly advantageous in power electronic devices due to their relatively high insulating strength. By structuring the metal layer, printed conductors and / or bonding surfaces for electrical devices can then be implemented.

[0003] Successfully providing a metal-ceramic substrate requires a durable bonding of the metal layer to the ceramic layer. Besides the so-called direct metal bonding method, namely DCB or DAB, it is known from the prior art that the metal layer is bonded to the ceramic layer via a soldering material (AMB method).

[0004] Active brazing methods, such as those used to connect metal layers or foils, particularly copper layers or foils, to ceramic materials, should be understood here as a method specifically designed for manufacturing metal-ceramic substrates. Here, a connection is established between a metal foil, such as copper foil, and a ceramic substrate, such as aluminum nitride ceramic, using a hard solder at a temperature of approximately 650-1000°C. This hard solder contains an active metal in addition to its main components, such as copper, silver, and / or gold. This active metal is, for example, at least one element from the group: Hf, Ti, Zr, Nb, Ce. The connection between the solder and the ceramic is established through a chemical reaction, while the connection between the solder and the metal is a metal-to-metal hard solder connection.

[0005] Furthermore, a method is known, for example, from DE 10 2013 113 734 B4 and JP 4-325470, in which bonding of a metal layer to a ceramic layer is achieved by means of hot isostatic pressing to form a metal-ceramic substrate. In addition, hot isostatic pressing is also used in post-processing to reduce the number of shrinkage cavities formed during joining by means of brazing or direct metal bonding methods.

[0006] As known from CN 110 734 297 A, the ceramic element is roughened to 1.5 μm before the bonding method. Summary of the Invention

[0007] Based on the prior art, the object of the present invention is to provide a metal-ceramic substrate that is further improved compared to known metal-ceramic substrates, particularly in terms of bonding performance from the metal layer to the ceramic element and heat dissipation when heat is generated on the device side of the metal-ceramic substrate due to operation.

[0008] The present invention achieves the stated objective by means of the method according to claim 1 and the metal-ceramic substrate according to claim 9. Other embodiments can be derived from the dependent claims and the specification.

[0009] According to a first aspect of the present invention, a method for manufacturing a metal-ceramic substrate is provided, comprising:

[0010] - Provide at least one metal layer,

[0011] - Provides ceramic components, and

[0012] - At least one metal layer is bonded to a bonding surface on the outside of a ceramic element, wherein at least one metal layer and the ceramic element extend along a main extension plane and are disposed vertically overlapping along a stacking direction perpendicular to the main extension plane.

[0013] The bonding surface has a roughness greater than 0.5 μm, preferably greater than 1.0 μm, and particularly preferably greater than 1.5 μm or even greater than 2 μm, and even more preferably greater than 2.5 μm.

[0014] Compared to known metal-ceramic substrates in the prior art, the present invention proposes to create a relatively high surface roughness at the ceramic element. This surface roughness has proven particularly advantageous because it increases the contact area between the metal layer and the ceramic element in the fabricated metal-ceramic substrate. However, the increased contact area also results in lower thermal contact resistance, thereby reducing the overall thermal resistance of the metal-ceramic substrate. This has a beneficial effect on heat dissipation, which is designed to dissipate heat generated by the operation of electrical devices at the device side. Furthermore, the engagement created by the surface roughness has proven advantageous for the bonding layer formed between the metal layer and the ceramic element, as it allows for improved tensile or shear strength. This has a particularly positive impact on the service life of the fabricated metal-ceramic substrate.

[0015] In particular, by increasing the roughness, it is feasible not only to increase the surface area of ​​the interface layer at the bonding surface, thereby improving the adhesion strength in the bonding region, but also because the pulling or peeling forces acting are distributed over a larger surface. On the other hand, when the temperature drops abruptly from one stage to the next, the thermal resistance (R) increases. th =1 / reduction aspect) can also be reduced.

[0016] Roughening can preferably be any surface structure. Alternatively or supplementarily, it is conceivable that structures, for example, can be formed in a point-like or linear manner, such as in a straight or curved manner, possess the roughness. For example, it is also conceivable that microstructuring, in addition to roughness, is preferred. Microstructuring is preferably understood as a two-dimensional, especially repeating pattern. Here, microstructuring is preferably understood as more global than surface roughness and having a pattern that repeats after a distance along a direction parallel to the main extension plane, wherein the distance is greater than 75 μm, preferably greater than 125 μm, and particularly preferably greater than 150 μm. For example, a moth-eye structure can also be used, specifically embedded in the ceramic element to form a bonding surface. It is particularly emphasized here that the microstructuring is configured such that the increased surface area does not adversely affect the bonding method, for example, by causing an increase in the porosity of the interface layer or an increase in the thickness of the bonding region, which is incompatible, for example, with brazing methods using very thin solder systems, especially relatively thin, especially sputtered active solder layers.

[0017] In particular, the resulting microstructured portions and / or increased roughness are at least locally, preferably entirely, disposed in the outer region of the ceramic element to which at least one metal layer is bonded. This is introduced into the bonding surface provided for bonding, for example, by roughening and / or imprinting. Here, those skilled in the art will preferably understand microstructure as a targeted embedding of surface morphology that follows a pre-given geometry. For example, surface profiles are grooves, channels, columns, rhombuses, prismatic shapes, and / or dome-shaped recesses that are embedded in the outer side of the ceramic element following a specific or arbitrary pattern. Furthermore, it is proposed that, in the bonded state, more than 50%, preferably more than 70%, and particularly preferably more than 85% of the outer side of the ceramic element facing the metal layer is provided with the surface profile.

[0018] Preferably, the arithmetic mean height is determined as a parameter of the roughness. Here, this parameter is the absolute value of the height difference of each point on the surface relative to the arithmetic mean. Alternatively, it may be conceivable to determine the root mean square height (S). Q ), reduce peak height (S) PK ), reduce valley depth (S) VK ) or maximum height (S Z Preferably, Ra is proposed as a measure of roughness. Similarly, R can be envisioned. z or R max To determine the roughness, standard methods are preferred, such as stylus cutting (Tastschnittverfahren), for example by means of a surface roughness measuring instrument (see DIN EN ISO 3274) or confocal microscopy (see ISO 25178-6).

[0019] Preferably, the surface roughness is determined by means of a surface roughness measuring instrument. This simplifies the measurement of the surface roughness of ceramics.

[0020] Preferably, the metal-ceramic substrate is configured as a circuit board, wherein, in its manufactured state, at least one metal layer bonded to the ceramic element is structured. For example, it is proposed that structuring also be performed after the bonding step, for example by laser, etching, and / or machining, to realize terminals and / or printed wires for electrical or electronic devices. Preferably, at the metal-ceramic substrate formed on the ceramic element, an additional metal layer is provided on the side opposite to the metal layer, particularly a back-side metallization and / or cooling element. Here, the back-side metallization is preferably used to suppress warping, while the cooling element is used to effectively dissipate the heat generated by the electrical or electronic devices bonded to the circuit board or metal-ceramic substrate during operation.

[0021] For the materials of at least one metal layer and / or at least one additional metal layer or ceramic element in a metal-ceramic substrate, copper, aluminum, molybdenum, tungsten, nickel and / or their alloys such as CuZr, AlSi or AlMgSi, and laminated materials such as CuW, CuMo, CuAl and / or AlCu or MMC (metal matrix composite), such as CuW, CuM or AlSiC, are contemplated. Furthermore, it is preferred that at least one metal layer at the fabricated metal-ceramic substrate, especially as a device metallization portion, is surface-modified. Surface modification can be achieved, for example, by sealing with noble metals, especially silver and / or gold, or (electroless) nickel or ENIG ("electroless nickel immersion gold"), or by edge encapsulation of the metallization portion to suppress crack formation or propagation.

[0022] Preferably, the ceramic element comprises Al2O3, Si3N4, AlN, HPSX ceramic (i.e., ceramic having an Al2O3 matrix containing x% ZrO2, such as Al2O3 = HPS9 containing 9% ZrO2, or Al2O3 = HPS25 containing 25% ZrO2), SiC, BeO, MgO, high-density MgO (>90% of theoretical density), and TSZ (tetragonal stabilized zirconia) as ceramic materials. It is also conceivable that the ceramic element is configured as a composite or hybrid ceramic, wherein multiple ceramic layers, differing in their material composition, are stacked and bonded together to form a ceramic element in order to combine different desired properties. In particular, it is proposed that the ceramic element comprises silicon nitride and / or preferably is formed of silicon nitride Si3N4 with a content greater than 60%, preferably greater than 70%, and particularly preferably greater than 80%. In particular, it is proposed that the thermal conductivity of the ceramic element is greater than 75 W / mK, preferably greater than 90 W / mK, and especially preferably greater than 105 W / mK, especially based on the measurement of the thermal conductivity of the ceramic by means of laser scintillation combined with density and specific heat.

[0023] Preferably, the roughness value is between 0.5 μm and 8.0 μm, more preferably between 1.0 μm and 5 μm, and particularly preferably between 1.5 μm and 3.0 μm. Particularly preferably, the roughness value is between 1.5 μm and 8 μm, more preferably between 2.0 μm and 3.5 μm, and particularly preferably between 2.2 μm and 3 μm. It is advantageously feasible to also determine an upper limit for the roughness to ensure that the roughened bonding surface can be used by most bonding techniques or methods. It has been proven that, particularly in the range of 1.5 and 3.0, all brazing methods, especially active brazing methods, contribute to successful bonding, especially when using thin solder layer systems, where the solder system, for example as a foil or as a paste, has a layer thickness of less than 20 μm, preferably less than 15 μm, and particularly preferably less than 15 μm.

[0024] Preferably, in addition to roughness, the bonding surface is surface-modulated, preferably having a half-cycle between 5 μm and 1 mm, more preferably between 10 μm and 0.5 mm, and particularly preferably between 200 μm and 100 μm. Here, surface modulation is preferably part of microstructuring. For example, it is wavy surface modulation. Compared to roughness, surface modulation is carried out on a larger scale, and the dimensions are determined to be at least an order of magnitude larger than roughness. Microstructuring preferably involves two-dimensional patterning on the outer side of the ceramic element, while surface modulation involves possible height variations in addition to roughness. It has been shown that by setting corresponding surface modulation in addition to roughness, bond strength can be specifically improved, and in particular tensile strength or adhesive strength is also improved. Preferably, the amplitude of surface modulation 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.

[0025] In particular, those skilled in the art understand surface modulation as the periodicity of protrusions and / or valleys, i.e., regular repetition. In other words, the spacing between two adjacent protrusions remains constant over at least two-thirds of the longitudinal or transverse extension. The periodicity of the protrusions is particularly formed along one direction, preferably only along one direction. In other words, it is not a two-dimensional pattern, or the protrusions and / or valleys are not distributed in a plane. Preferably, the protrusions and / or valleys extend over the entire length or width of the ceramic element, respectively.

[0026] In particular, the amplitude of surface modulation is taken between 1 μm and 40 μm, preferably between 2 μm and 20 μm, and especially preferably between 2.5 μm and 10 μm.

[0027] Preferably, during the preparation step, i.e. prior to actual bonding, the ceramic element is roughened on its outer side to form a bonding surface. It is advantageous to thus selectively set the desired roughness to improve tensile strength.

[0028] Preferably, the ceramic element is roughened mechanically, optically, and / or chemically. For example, it is conceivable to ablate or introduce targeted structures into the surface or outer surface of the ceramic element using a suitable laser, wherein the amount of removal can be controlled, for example, by the residence time of the light on the outer surface. Alternatively, it is conceivable to achieve targeted surface modulation, roughness, and / or microstructuring by sawing or milling, particularly by cutting removal on the outer surface of the ceramic element. Surface modulation using chemical etchants is also conceivable, especially when a corresponding mask facilitates the targeted introduction of surface modulation into the ceramic element. Particularly preferably, surface modulation is achieved by using a sawing tool, particularly a wire saw, when separating the ceramic element from the ceramic bulk. The sawing tool can be, for example, a diamond wire saw or a wafer saw. The characteristics of the wire used for the wire saw can thus advantageously influence the characteristics of the surface modulation. For example, the half-cycle of surface modulation can be set by the wire thickness. It is also conceivable to influence the roughness by the choice of wire material. To set a specific roughness value, it is also conceivable to set a larger roughness for the ceramic element and then set the desired target roughness in a post-processing step such as polishing.

[0029] Microstructuring or surface modulation can also be conceived via laser ablation. Etching or imprinting, especially on green foil prior to sintering, is also conceivable. For example, roughness can be generated by cutting ceramic elements from a ceramic mass, particularly using wire, and / or in a state where the ceramic material is still unhardened, for example, as a foil or as an unsintered blank.

[0030] With appropriate configuration, it is feasible to provide a substantially planar ceramic element whose surface modulation is sufficiently modulated to achieve a significant improvement in resistance to pull-out strength. Preferably, the amplitude of the surface modulation has a first height, and the thickness of the ceramic element measured perpendicular to the main extension plane has a second height, wherein the 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.

[0031] Preferably, surface contouring, especially microstructuring, is achieved by introducing structuring into the powder or powder coating of the green body prior to sintering. Alternatively or additionally, it is conceivable that the powder is sequentially and locally restrictedly applied and hardened by laser sintering on the outer side of the pre-ceramic body or ceramic matrix.

[0032] Preferably, the microstructuring is a repeating pattern that repeats over a large portion of the surface of the ceramic element. In other words, instead of a random and disordered distribution of protrusions that contribute to surface roughness, the desired microstructuring is achieved on the outer side of the ceramic element through targeted placement. It is conceivable that the pattern varies along the ceramic element, particularly increasing, for example, in the region towards the edge of the metal layer or towards the outermost edge of the metal layer in the main extension plane, for example, in terms of the density of recesses per unit area or the size of the recesses. Increased tensile strength is advantageous and desirable in these regions.

[0033] Furthermore, it is preferably proposed that the ceramic element has a first thickness and the metal layer has a second thickness. Here, the first thickness preferably takes a value between 150 μm and 1000 μm, more preferably between 200 μm and 500 μm, and particularly preferably between 200 μm and 400 μm, or even between 400 μm and 600 μm. The second thickness can, for example, be greater than the first thickness, and takes a value greater than 1 mm. Preferably, the second thickness is between 50 μm and 1 mm, more preferably between 100 μm and 500 μm, and particularly preferably between 150 μm and 350 μm. It has been shown, for example, that the ceramic element can be designed to be thicker based on improved thermal resistance without compromising necessary heat transfer. Thus, a particularly insulating and mechanically stable metal-ceramic substrate can be provided for specific applications.

[0034] Preferably, at least one metal layer and the ceramic element are connected to each other by means of an active brazing method. Furthermore, it is preferred that at least one metal layer and / or at least one additional metal layer are bonded to the ceramic element by means of an active brazing method, a diffusion bonding method, and / or hot isostatic pressing and / or DCB method.

[0035] Preferably, for bonding, a solder system is disposed between at least one metal layer and the ceramic element, wherein the solder system includes at least one separate active metal layer.

[0036] Furthermore, it is proposed that, in order to achieve bonding, 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 performed.

[0037] For example, a method for manufacturing a metal-ceramic substrate is proposed, comprising:

[0038] - Provide a solder layer, particularly in the form of at least one solder foil or hard solder foil.

[0039] - Coating the ceramic element with at least one active metal layer and / or at least one metal layer and / or at least one solder layer.

[0040] - At least one solder layer is disposed between a ceramic element and at least one metal layer along the stacking direction to form a solder system, the solder system comprising at least one solder layer and at least one active metal layer, wherein the solder material of the at least one solder layer is preferably free of materials that lower the melting point or is phosphorus-free, and

[0041] - At least one metal layer is bonded to at least one ceramic layer via a solder system using an active brazing method.

[0042] In particular, a multi-layered solder system is provided, comprising at least one solder layer, preferably free of elements that lower the melting point, and particularly preferably phosphorus-free, and at least one active metal layer. Separation of the at least one active metal layer from the at least one solder layer has proven particularly advantageous, as it allows for a thinner solder layer, especially when the solder layer is a foil. For solder materials containing active metals, otherwise a relatively large solder layer thickness must be achieved, because the brittle intermetallic phases or high elastic modulus and high yield strength of common active metals, along with their intermetallic phases, hinder the formation of solder paste or solder layers, thus limiting the minimum layer thickness to the manufacturing characteristics of the active metal-containing solder material. Correspondingly, for solder layers containing active metals, the minimum solder layer thickness is determined not by the minimum thickness required for the bonding method, but by the minimum technically achievable layer thickness. Therefore, such a thicker active metal-containing solder layer is more expensive than a thinner one. Those skilled in the art will particularly understand "phosphorus-free" to mean that the phosphorus content in the solder layer is less than 150 ppm, less than 100 ppm, and particularly preferably less than 50 ppm.

[0043] In particular, it is feasible to design the active metal layer to be relatively thin by using a separately implemented active metal layer, thereby achieving a relatively thin thickness of the bonding layer that meets the requirements, especially by averaging different measurements over a defined facet or multiple faces. 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 metals La, Ce, Ca, and Mg are prone to oxidation. Furthermore, it should be pointed out that elements Cr, Mo, and W are not typical active metals, but are suitable as contact layers between Si3N4 and at least one metal layer or solder system or solder material because they do not form an intermetallic phase with at least one metal layer, such as copper, and do not have end-point solid solubility.

[0044] Preferably, the solder layer, especially a phosphorus-free solder layer, comprises a variety of materials in addition to pure metals. For example, indium is a component of the solder material used in the solder layer.

[0045] Furthermore, it is conceivable that solder material, especially active metal, is coated onto the active metal layer and / or at least one metal layer and / or ceramic element by physical and / or chemical vapor deposition and / or electroplating to form the solder layer. It is advantageously feasible to achieve a relatively thin solder layer, especially the active metal layer, in the solder system, particularly in a uniformly distributed manner.

[0046] For example, in the manufacture of metal-ceramic substrates, especially metal-ceramic substrates, other steps are included, including:

[0047] -Provides ceramic components and metal layers,

[0048] - Provides an airtight container surrounding a ceramic element, wherein the container is preferably formed of or includes a metal layer.

[0049] - A metal-ceramic substrate is formed by bonding a metal layer to the ceramic element using hot isostatic pressing.

[0050] To construct the metal-ceramic substrate, an active metal layer or a contact layer containing an active metal is provided at least partially between the metal layer and the ceramic element to assist in bonding the metal layer to the ceramic element. The container is preferably formed of a metal layer and / or additional metal layers to create a metal container. Alternatively, a glass container may be used.

[0051] In particular, hot isostatic pressing (HIP) proposes bonding by heating under pressure, wherein the first and / or second metal layers of the metal container, especially subsequent metal layers of the metal-ceramic substrate, and any eutectic layers that may appear therein, do not enter the molten phase. Correspondingly, the temperature required in HIP is lower than that in direct metal bonding methods, especially in the DCB method.

[0052] Compared to bonding metal layers to ceramic layers using solder materials (where temperatures below the melting point of at least one metal layer are typically used), the current method advantageously eliminates the need for a solder base material and requires only the active metal. The use or utilization of pressure in hot isostatic pressing has also proven advantageous, as it reduces air inclusions or cavities between the first and / or second metal layers on one side and the ceramic element on the other, thereby reducing or even eliminating the frequency of shrinkage cavities in the formed or manufactured metal-ceramic substrate. This has a beneficial effect on the bonding quality between the first and / or second metal layers of the metal layer or metal container and the ceramic element. Furthermore, it is advantageously feasible to simplify the "secondary etching" process and avoid solder residue and silver migration.

[0053] Alternatively, during hot isostatic pressing, an additional solder material can be introduced between the ceramic element and at least one metal layer, wherein the melting point of the additional solder material can be lower than the temperature at which hot isostatic pressing is performed, i.e., lower than the melting point of at least one metal layer.

[0054] Preferably, during hot isostatic pressing, the metal container is exposed in a heating and pressurizing apparatus to a gas pressure between 100 bar and 2000 bar, preferably between 150 bar and 1200 bar, and particularly preferably between 300 bar and 1000 bar, and a process temperature between 300°C and the melting point of at least one metal layer, especially down to temperatures below the melting point. It has been advantageously proven that this allows for the bonding of metal layers, i.e., the first and / or second metal layers of the metal container, to a ceramic element without the temperatures required by direct metal bonding methods, such as DCB or DAB methods, and / or without the solder base material used in active brazing. Furthermore, the use of corresponding gas pressures allows for the fabrication of a metal-ceramic substrate between the metal layer and the ceramic element with minimal shrinkage, i.e., without gas inclusions. In particular, the process parameters mentioned in DE 2013 113 734 A1 and explicitly referenced herein are used.

[0055] According to another aspect of the invention, a metal-ceramic substrate, preferably manufactured by means of the method according to the invention, is provided, comprising: a device metallization portion and a ceramic element (30), wherein at least one metal layer and the ceramic element extend along a main extension plane and are stacked along a stacking direction perpendicular to the main extension plane, wherein the device metallization portion is bonded to the ceramic element at a bonding surface, wherein the bonding surface has a roughness greater than 1.5 μm, preferably greater than 2 μm, and particularly preferably greater than 2.5 μm. All the advantages and characteristics described with respect to the method can be similarly applied to the metal-ceramic substrate, and vice versa.

[0056] According to a preferred embodiment of the present invention, in the fabricated metal-ceramic substrate, a bonding layer is formed between at least one metal layer and a ceramic element, wherein the bonding layer has an adhesion layer having a sheet resistance greater than 5 Ohm / sq, preferably greater than 10 Ohm / sq, and particularly preferably greater than 20 Ohm / sq.

[0057] The sheet resistance is directly related to the proportion of active metal in the bonding layer, which is crucial for bonding at least one metal layer to the ceramic element. Here, the sheet resistance increases as the proportion of active metal in the bonding layer decreases. A high sheet resistance therefore corresponds to a low proportion of active metal in the bonding layer.

[0058] Here, sheet resistance is not related to a single parameter, but rather is influenced by the interaction of multiple parameters. Thus, the purity of the active metal, the thickness of the bonding layer, and / or the surface roughness of the ceramic element also contribute to determining sheet resistance. In particular, high sheet resistance can only be achieved through the interaction of at least two parameters.

[0059] It has been confirmed that an increase in the proportion of active metal favors the formation of brittle intermetallic phases, which is detrimental to the pull-out strength of the metal layer at the insulating layer. In other words, by describing such a bonding layer with a suitable sheet resistance, its pull-out strength is improved, i.e., increased, due to the reduced formation of brittle intermetallic phases. By selectively setting a suitable sheet resistance, it is possible to achieve a particularly strong bond of at least one metal layer to the ceramic element. This improved bonding strength has a beneficial effect on the lifespan of the metal-ceramic substrate. Here, to determine the sheet resistance, it is proposed to first remove the metal layer and then remove any possible solder base layer on the fabricated metal-ceramic substrate, for example, by etching. Then, the sheet resistance is measured on the outer or underside of the metal-ceramic substrate without at least one metal layer and solder base layer using a four-probe measurement method. In particular, the sheet resistance of the material sample should be understood as its resistance over a square surface area. Surface resistance is generally expressed in Ohm / sq (square). The physical unit of sheet resistance is the ohm. Preferably, the thickness of the bonding layer, measured along the stacking direction, is averaged over multiple measurement points in one or more predetermined planes extending parallel to the main extension plane, and takes a value less than 0.20 mm, preferably less than 10 mm, and particularly preferably less than 6 mm. When referring to multiple planes, this specifically means dividing at least one metal layer into planes of as equal size as possible, and detecting at least one, preferably multiple, thickness values ​​in each of the planes dividing the at least one metal layer. The thicknesses thus determined at different locations are then arithmetically averaged.

[0060] Therefore, compared to metal-ceramic substrates known from the prior art, a relatively thin bonding layer is formed between at least one metal layer and the ceramic element. It is proposed that, to determine the critical thickness of the bonding layer, the thickness is averaged by measuring at multiple points located within a predetermined or specified plane or plurality of planes. It is also advantageously considered that the ceramic element typically undergoes ondulation, that is, the ondulation of the ceramic element. In particular, those skilled in the art understand ondulation as a modulation of the overall flat orientation of the ceramic element, observed within a range of millimeters or centimeters along a direction extending parallel to the main extension plane. Thus, this ondulation is distinguished from the surface roughness of the ceramic element that is usually additionally present at the ceramic element. By incorporating this generally unavoidable ondulation of the ceramic element into the thickness determination, it is considered that the bonding layer may vary due to the ondulation, particularly that it may be larger in the valley regions of the ceramic element than in the peak regions.

[0061] Preferably, in the coating layer containing the active metal, the proportion of the active metal is greater than 15% by weight, more preferably greater than 20% by weight, and particularly preferably greater than 25% by weight.

[0062] Preferably, the bonding layer is planar, particularly uninterrupted, i.e., continuous, and is formed between at least one metal layer and the ceramic element. Preferably, the ratio of the area between at least one metal layer and the ceramic element where no bonding layer is formed to the area between at least one bonding layer and the ceramic element where a bonding layer is formed is less than 0.05, preferably less than 0.02, and particularly preferably less than 0.007. Here, those skilled in the art will particularly understand that, in order to achieve this ratio, areas of metal that do not contain at least one metal layer due to structuring are not considered.

[0063] Preferably, the thermal conductivity of the ceramic element is greater than 75 W / mK, more preferably greater than 90 W / mK, and particularly preferably greater than 105 W / mK. Furthermore, this high thermal conductivity proves particularly advantageous for heat dissipation, especially in addition to the aforementioned surface roughness. This prevents heat accumulation in the ceramic element after rapid heat dissipation via the interface between the ceramic element and the metal layer. Consequently, the corresponding metal-ceramic substrate can be particularly advantageously used in high-power electronic devices that generate extremely high amounts of heat during operation. Attached Figure Description

[0064] Other advantages and features are set forth below in the description of preferred embodiments of the subject matter according to the invention, with reference to the accompanying drawings. The drawings show:

[0065] Figure 1 A metal-ceramic substrate according to an exemplary first embodiment of the present invention is shown;

[0066] Figure 2a and Figure 2b A detailed view of the grains on the outer side of a ceramic element on a metal-ceramic substrate according to an exemplary second embodiment of the present invention is shown.

[0067] Figure 3 A ceramic element on a metal-ceramic substrate according to an exemplary third embodiment of the present invention; and

[0068] Figure 4a and Figure 4b A cross-sectional view is shown through a metal-ceramic substrate according to the prior art and a metal-ceramic substrate according to an exemplary fourth embodiment of the present invention. Detailed Implementation

[0069] Figure 1 The diagram illustrates a metal-ceramic substrate 1 according to an exemplary first embodiment of the present invention. This metal-ceramic substrate 1 is preferably used as a carrier or circuit board for electronic or electrical devices, which can be bonded to at least one metal layer 10 of the metal-ceramic substrate 1 at their device side. Preferably, the at least one metal layer 10 is structured to form corresponding printed conductors and / or connection surfaces; that is, in the fabricated metal-ceramic substrate 1, the at least one metal layer 10 comprises a plurality of electrically insulated metal segments. Here, at least one metal layer 10 extending substantially along the main extension plane HSE and a ceramic element 30 extending along the main extension plane HSE are stacked along a stacking direction S perpendicular to the main extension plane HSE, and are preferably bonded or connected to each other via a bonding layer 12. Preferably, the metal-ceramic substrate 1 includes at least one additional metal layer 20 in addition to the at least one metal layer 10, which is disposed on the side of the ceramic element 30 opposite to the at least one metal layer 10 when viewed in the stacking direction S, and is bonded to the ceramic element 30 via another bonding layer 12'.

[0070] Here, at least one additional metal layer 20 is used as a back-side metallization portion to suppress warping of the metal-ceramic substrate 1, especially the metal-ceramic element 1, and / or as an adapter for a cooling body designed to dissipate heat input caused by electrical or electronic devices on the metal-ceramic substrate 1, or as a cooling body.

[0071] In particular, the metal-ceramic substrate 1 has a bonding layer 12 disposed between at least one metal layer 10 and the ceramic element 30. It has proven advantageous that the bonding layer 12 has a relatively thin thickness measured along the stacking direction S. Furthermore, if an etching process is provided for structuring at least one metal layer 10, the relatively thin thickness of the bonding layer 12 between the at least one metal layer 10 and the ceramic element 30 proves advantageous. For example, this allows for narrower insulating trenches, i.e., the spacing between the individual metal segments of the at least one metal layer 10.

[0072] Furthermore, the thinner bonding layer 12 has proven advantageous, as it can further reduce the number of potential defects in the bonding layer 12 caused by material defects in the solder material that may be used.

[0073] exist Figure 1 In the example shown, the bonding layer 12 is in particular an adhesion layer 13 comprising an active metal. In this case, the adhesion layer 13 is preferably composed of a material composition after bonding, which comprises a compound consisting of a component of the ceramic element on one hand and an active metal on the other. Since this involves a very brittle compound, it is advantageous to design these adhesion layers 13 as thin as possible for the adhesion strength of at least one metal layer 10 on the ceramic element 30. For example, if an active metal layer, especially an active metal foil, is provided for the bonding process between the ceramic element 30 and the metal layer 10, and the bonding process is carried out via hot isostatic pressing, then the adhesion layer 13 can form the bonding layer 12. However, the adhesion layer 13 can also be formed, for example, by an active metal layer, especially an active metal foil, disposed between the ceramic element 30 and the solder base layer, so that bonding between the metal layer 10 and the ceramic element 30 is generated via a system consisting of the active metal layer and the solder base layer. In this case, the adhesion layer 13 forms part of the bonding layer 12.

[0074] In particular, it is proposed to provide a metal-ceramic substrate 1, which is improved, especially in terms of its heat dissipation, tensile strength, and shear strength, compared to metal-ceramic substrates known from the prior art. This is preferably achieved by increasing the surface roughness Ra of the ceramic element 30. For example, the surface roughness Ra of the ceramic element 30 is taken to be greater than 1.5, preferably greater than 2.0, and particularly preferably greater than 2.5. It is advantageously possible to increase the surface area of ​​the ceramic element 30, thereby increasing the contact area between the metal layer 10 and the ceramic element 30 after the bonding process. Since the thermal contact resistance is inversely proportional to this contact area, this results in a lower thermal contact resistance. This reduces the thermal resistance of the metal-ceramic substrate 1, thereby advantageously improving heat dissipation, especially when heat should be dissipated from the electrical components at the device side of the metal-ceramic substrate 1.

[0075] Furthermore, it is feasible to improve the engagement between the metal layer 10 and the ceramic element 30 by increasing the roughness, thereby additionally improving the tensile strength and shear strength of the metal layer 10 relative to the ceramic element 30. This advantageously leads to an increase in the service life of the metal-ceramic substrate 1.

[0076] Figure 2a The figure shows a cross-sectional view through the metal-ceramic substrate 1, wherein a device metallization portion and a back metallization portion are bonded on the ceramic element 30, the device metallization portion and the back metallization portion being formed by bonding a metal layer 10 and another metal layer 20. Figure 2a A key feature of the embodiment shown is that the ceramic element 30, particularly in the region of the bonding surface, is surface-modulated. Figure 2a In the illustrated embodiment, the bonding surface has a generally wavy orientation along the direction of extension of the main extension plane HSE. Here, the half-cycle of this wavy orientation is designated P1. Preferably, the value of the half-cycle P1 is between 20 μm and 2 mm, more preferably between 50 μm and 1 mm, and particularly preferably between 100 μm and 500 μm. In the illustrated embodiment, the half-cycle P1 is 160 μm.

[0077] The ceramic element 30 has a first thickness D of approximately 280 μm and a surface modulation amplitude of approximately 10 μm. The second thickness of the device metallization and / or back-side metallization is, for example, 500 μm to 700 μm. Additionally, the ceramic element 30 used herein has a roughness of approximately 2 μm in addition to the more global surface modulation.

[0078] and Figure 4a and Figure 4b Compared to the diagram in the previous section, in the diagram in the current section Figure 2a The roughness is not as clearly visible or discernible in the middle. The resulting periodicity or surface modulation is a result of the manufacturing process in which the ceramic element 30 is separated from the bulk, particularly from the silicon nitride bulk. The periodicity, and thus the size of the half-cycle P1, is set, for example, by the thickness of the wire used during separation from the bulk. Preferably, the wire thickness is chosen such that it determines the spacing between two adjacent peaks, corresponding to the half-cycle or half-cycle P1. It has been shown that the tensile strength or adhesion strength of the bonded metal layer 10 can be further improved by the corresponding surface periodicity, i.e., by the surface modulation of the ceramic element 30.

[0079] exist Figure 2bThe tensile strength or adhesion strength in N / mm is given for a metal-ceramic substrate 1, in which bonding is performed via a conventional active soldering method. Here, the metal-ceramic substrate 1 uses a substrate with a first copper layer thickness of 320 μm and a second copper layer thickness of 800 μm. The ceramic element 30 is made of silicon nitride, and a bonding technique is used for bonding, in which the active metal is provided as a separate layer alongside the solder base material. The metal-ceramic substrate 2 in this experiment has a first copper layer thickness of 280 μm and a second copper layer thickness of 800 μm. This bonding technique is the same as that used in the metal-ceramic substrate 1. The results show that if the metal-ceramic substrate 1 is manufactured as follows, the ceramic element 30 in the metal-ceramic substrate 1 has the following properties: Figure 2a The surface modulation exemplified herein, especially with the given half-cycle P1, significantly improves the tensile strength or adhesive strength.

[0080] exist Figure 3 The image shows a ceramic element 30 used in a metal-ceramic substrate 1 according to an exemplary third embodiment of the present invention. In particular, Figure 3 A top view (below) and a cross-sectional view along the drawn lines are shown for the ceramic element 30. Figure 2a and Figure 2b In contrast to the embodiments, in Figure 3 In some embodiments, the surface profile 18 is configured to be introduced into or to be introduced into the ceramic element 30. Figure 2a and Figure 2b In contrast to the randomly distributed pattern of the protrusions in the embodiments, in Figure 3 In some embodiments, a repeating or targeted pattern is provided on the outer side of the ceramic element 30. This patterning can be achieved, for example, by corresponding etching or mechanical methods after the sintering process. Alternatively, it is conceivable that structuring has already been performed in the green body, which is then hardened by green body sintering, thereby producing the desired microstructure. It is also conceivable to form the microstructure additively by laser sintering, in which powder is coated onto a pre-ceramic body or ceramic matrix.

[0081] In particular, this invention proposes the formation of microstructured portions on the surface or outer side of the ceramic element 30. Here, those skilled in the art will understand microstructured portions in particular as those with a height profile having a maximum amplitude between 1 μm and 50 μm, preferably between 1.5 μm and 10 μm, and particularly preferably between 2.0 μm and 9 μm. The microstructured portions are preferably patterns extending substantially along a main extension plane, and these patterns preferably have surface modulation. In the illustrated embodiment, the microstructured portions extend along a zigzag line in the main extension plane HSE (see below), wherein the microstructured portions are substantially made by recesses implemented at equal intervals, as can be seen in the cross-sectional view (above). However, this geometry is merely exemplary for a large number of other possible surface contouring or structuring. For example, pyramidal, cylindrical, or dome-shaped patterns are also conceivable. Furthermore, intersecting line patterns or parallel extending line patterns are conceivable. All these patterned portions have proven particularly advantageous because they increase the surface area of ​​the ceramic element 30, thereby increasing the contact area between the metal layer 10 and the ceramic element 30. Preferably, it is conceivable that the surface contouring portion is introduced only in the region where the ceramic element 30 is subsequently bonded to the metal layer 10. In particular, it is proposed to achieve microstructuring in addition to roughness and / or surface modulation.

[0082] exist Figure 4a and Figure 4b The figure shows a comparison of the bonding region between the metal layer 10 and the ceramic element 30 according to the prior art (top figure) and according to the present invention (bottom figure). In particular, it can be seen that, in the case of the present invention, the interface region between the metal layer 10 and the ceramic element 30, i.e., the bonding layer, is characterized by a burr structure, wherein the burr structure is a surface roughness S of the ceramic element 30. a As a result, it can be seen that the bonding layer 12 between the metal layer 10 and the ceramic element 30 is anchored and interlocked into the ceramic element 30, thereby enhancing the bonding between the metal layer 10 and the ceramic element 30. This improves tensile strength and shear strength.

[0083] List of reference numerals

[0084] 1. Metal-ceramic substrate

[0085] 10 metal layers

[0086] 12 bonded layers

[0087] 12' additional bonding layer

[0088] 13 Added Layers

[0089] 20. Additional metal layers

[0090] 30 ceramic components

[0091] HSE Main Extension Plane

[0092] S-stack direction

[0093] P1 half-cycle

[0094] D1 First Thickness

[0095] D2 Second Thickness

Claims

1. A method for manufacturing a metal-ceramic substrate (1), comprising: - Provide at least one metal layer (10). - Provides ceramic components (30), and - The at least one metal layer (10) is bonded to the bonding surface on the outside of the ceramic element (30), wherein the at least one metal layer (10) and the ceramic element (30) are stacked along a main extension plane (HSE) and in a stacking direction (S) perpendicular to the main extension plane (HSE). The bonding surface has a roughness greater than 0.5 μm, preferably greater than 1.0 μm, and particularly preferably greater than 1.5 μm or even greater than 2 μm, and even more preferably greater than 2.5 μm.

2. The method according to claim 1, wherein the roughness is between 0.5 μm and 8 μm, preferably between 1.0 μm and 5 μm, and particularly preferably between 1.5 μm and 3 μm.

3. The method according to any one of the preceding claims, wherein in the preparation step, the ceramic element (30) is roughened on the outer side 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. The method according to any one of the preceding claims, wherein, in addition to the roughness, the bonding surface is modulated with a half-cycle (P1) of the following half-cycle, preferably between 5 μm and 1 mm, more preferably between 10 μm and 0.5 mm, and particularly preferably between 20 μm and 100 μm.

6. The method according to claim 5, wherein the spacing between the two protrusions of the surface modulation remains constant over at least two-thirds of the longitudinal or transverse extension of the ceramic element (30).

7. The method according to any one of claims 5 or 6, wherein the ceramic element (30) is modulated with a wavy surface.

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

9. The method according to any one of claims 5 to 8, wherein the amplitude of the surface modulation has a first height, and the thickness of the ceramic element (30) measured perpendicular to the main extension plane has a second height, wherein the 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. The method according to any one of the preceding claims, wherein the at least one metal layer (10) and the ceramic element (30) are connected to each other by means of an active brazing method.

11. The method of claim 6, wherein, for bonding, a solder system is disposed 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 of claim 7, wherein, for bonding, a solder base material is provided as part of the solder system in addition to the active metal layer, and / or hot isostatic pressing is performed.

13. A metal-ceramic substrate (1), preferably manufactured by the method according to any one of the preceding claims, comprising: - Device metallization, and - A ceramic element (30), wherein at least one metal layer (10) and the ceramic element (30) are stacked along a main extension plane (HSE) and along a stacking direction (S) perpendicular to the main extension plane (HSE), wherein the device metallization is bonded to the ceramic element (30) at a bonding surface, wherein the bonding surface has a roughness greater than 1.0 μm, preferably greater than 1.5 μm, and particularly preferably greater than 2.0 μm.

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

15. The metal-ceramic substrate (1) according to claim 13 or 14, wherein the bonding layer has a sheet resistance greater than 5 Ohm / sq, preferably greater than 10 Ohm / sq, and particularly preferably greater than 20 Ohm / sq.

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