METAL-CERAMIC SUBSTRATE AND METHOD FOR PRODUCING A METAL-CERAMIC SUBSTRATE

Description

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

[0002] Substrates for electrical components, for example in the form of metal-ceramic substrates, are well known in the prior art, for example as printed circuit boards or circuit boards, as described in DE 10 2013 104 739 A1, DE 19 927 046 B4 and DE 10 2009 033 029 A1. Typically, contact pads for electrical components and conductor tracks are arranged on one side of the metal-ceramic substrate, and the electrical components and conductor tracks can be interconnected to form electrical circuits. Essential components of the metal-ceramic substrates are an insulating layer, preferably made of a ceramic, and a component metallization bonded to the insulating layer. Due to their comparatively high insulating strength, ceramic insulating layers have proven particularly advantageous in power electronics.By structuring the component metallization, conductor tracks and / or connection surfaces for the electrical components can then be created.

[0003] To bond component metallizations to the ceramic element, a high-temperature process is typically used, such as hot isostatic pressing, diffusion bonding, direct metal bonding, DCB, or active soldering. To form individual conductor tracks or connection pads, the bonded component metallization is structured so that at least a first metal section and a second metal section are created within the component metallization, which are separated and insulated from each other.Since the component metallization and the ceramic element have different coefficients of thermal expansion, thermomechanical stresses develop at the bonding interface between the component metallization and the ceramic element during temperature changes, such as those occurring during bonding or due to electrical components. These stresses can cause the entire metal-ceramic substrate to deflect. To counteract this effect, the prior art involves bonding a back-side metallization to the ceramic element to create symmetry between the component side and the back side of the metal-ceramic substrate.

[0004] From DE 10 2019 135 146 A1, a metal-ceramic substrate is known which has a component metallization and a backside metallization that are bonded to the same ceramic element on opposite sides. Furthermore, recesses are formed in the component metallization and the backside metallization. Further support substrates can be found in EP 2 827 364 A1, EP 1 487 759 A1, EP 2 911 994 A1, JP H08 250 823 A and JP 2013 175 525 A.

[0005] Starting from the prior art, the present invention aims to improve metal-ceramic substrates in such a way that their susceptibility to bending is further reduced and metal-ceramic substrates that are as flat as possible are provided.

[0006] The present invention solves this problem with a metal-ceramic substrate according to claim 1 or 10 and a method for producing a metal-ceramic substrate according to claim 11.

[0007] According to a first aspect, a metal-ceramic substrate is provided, which is intended or designed as a printed circuit board for mounting electrical components, comprising: a component metallization and a backside metallization and a ceramic element arranged along a stacking direction between the component metallization and the backside metallization, wherein the component metallization comprises a first metal section and a second comprising a metal section, wherein the first metal section and the second metal section are separated from each other by an insulating section, and wherein the backside metallization has a material weakening, in particular a material recess, which is arranged congruently with the insulating section when viewed in the stacking direction.

[0008] In contrast to prior art metal-ceramic substrates, the backside metallization is designed to have material weakenings precisely arranged to coincide with the insulating section(s) on the component side. This advantageously increases the symmetry of the material distribution on the component side and the opposite backside. As a result, the overall substrate's susceptibility to deflection is reduced, since the thermomechanical stresses occurring on the component side and backside cancel each other out. This further reduces the tendency to bend and allows for the production of extremely flat metal-ceramic substrates.For this purpose, it is preferably provided that a first thickness of the component metallization essentially corresponds to a second thickness of the backside metallization.

[0009] A congruent arrangement is understood to mean, in particular, that in the case of the imagined projection of the material weakening along the stacking direction or along a direction parallel to the stacking direction, a spatial overlap with the insulation section would be observed. This imagined spatial overlap occurs for more than 50%, preferably more than 75%, and particularly preferably more than 90% of the extent of the material weakening in the backside metallization. The center of the extent of the material weakening can be substantially congruent with the center of the extent of the insulation section or offset laterally from it, i.e., along a direction perpendicular to the stacking direction.

[0010] Furthermore, it is preferably provided that the ceramic element has a third thickness measured along the stacking direction. It is particularly preferred that the third thickness is less than 700 µm, preferably less than 400 µm, and most preferably less than 330 µm. The symmetry between the material weaknesses in the backside metallization and the insulating sections in the component metallization proves to be particularly advantageous for comparatively thin insulating layers or ceramic elements, because these ceramic elements are especially susceptible to bending and even breakage. For example, it is even conceivable that the third thickness of the ceramic element is smaller or thinner than the first thickness of the component metallization and the second thickness of the backside metallization, or the sum of the first and second thicknesses.

[0011] Furthermore, it is preferably provided that the structuring and / or the insertion of the material weakening is carried out after the bonding of the metallization and / or backside metallization to the ceramic element.

[0012] Specifically, it is a metal-ceramic substrate used as a printed circuit board (PCB) where a metallization, i.e., a component metallization, is formed on the component side, which, due to its structuring, has several electrically isolated metallization sections. These metallization sections form, for example, connection pads or conductor tracks of the PCB.

[0013] Preferably, the ceramic element comprises Al₂O₃, Si₃N₄, AIN, an HPSX ceramic (i.e., a ceramic with an Al₂O₃ matrix containing an x ​​percent ZrO₂, for example, Al₂O₃ with 9% ZrO₂ = HPS9 or Al₂O₃ with 25% ZrO₂ = HPS25), SiC, BeO, MgO, high-density MgO (> 90% of the theoretical density), or TSZ (tetragonally stabilized zirconia) as the ceramic material. It is also conceivable that the ceramic element is designed as a composite or hybrid ceramic, in which several ceramic layers, each differing in their material composition, are arranged one above the other and joined together to form an insulating element in order to combine various desired properties.

[0014] Suitable materials for component metallization and / or backside metallization include copper, aluminum, molybdenum, tungsten, 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, CuMo, or AlSiC. Preferably, the component metallization is the same as the backside metallization with regard to its material or it differs. Furthermore, it is preferably provided that the component metallization and / or the backside metallization is surface-modified on the manufactured metal-ceramic substrate, particularly as component metallization. Surface modification could, for example, involve sealing with a precious metal, especially silver; and / or gold, or (electroless) nickel or ENIG (electrolytic refractory alloy). electroless nickel immersion gold") or edge sealing on the metallization to suppress crack formation or propagation is conceivable. For example, the metal of the component metallization also differs from the metal of the backside metallization.

[0015] The bonding of the metal layer, i.e. the component metallization and / or the backside metallization, to the ceramic element can be carried out, for example, via a DCB process, an AMB process, diffusion bonding, in particular ADB, and / or hot isostatic pressing.

[0016] A "DCB process" (Direct Copper Bond Technology) or a "DAB process" (Direct Aluminum Bond Technology) is understood by those skilled in the art to be a process used, for example, to bond metal layers or sheets (e.g., copper sheets or foils or aluminum sheets or foils) to each other and / or to ceramics or ceramic layers, using metal or copper sheets or foils that have a layer or coating (fused-on layer) on their surface. In this process, described, for example, in US 3,744,120 A or DE 23 19 854 C2, this layer or coating (fused-on layer) forms a eutectic with a melting point below that of the metal (e.g., copper), so that by placing the foil on the ceramic and heating all layers, they can be bonded together by melting the metal or foil.Copper is essentially only present in the area of ​​the molten layer or oxide layer.

[0017] Preferably, the ceramic layer and the metal layer are joined by means of a direct metal bonding process, hot isostatic pressing, a soldering process and / or a diffusion bonding process.

[0018] In particular, the DCB method then includes, for example, the following process steps: Oxidizing a copper foil to create a uniform copper oxide layer; placing the copper foil onto the ceramic layer; heating the composite to a process temperature between approximately 1025 and 1083°C, e.g., to approximately 1071°C; cooling to room temperature.

[0019] An active soldering process, e.g., for joining metal layers or foils, especially copper layers or foils, to ceramic material, is a process specifically used for producing metal-ceramic substrates. At a temperature between approximately 600 and 1000°C, a bond is created between a metal foil, for example, copper foil, and a ceramic substrate, for example, aluminum nitride ceramic, using a hard solder. This solder contains an active metal in addition to a main component such as copper, silver, and / or gold. This active metal, which is, for example, at least one element from the group Hf, Ti, Zr, Nb, Ce, forms a bond between the solder and the ceramic through a chemical reaction. The bond between the solder and the metal is a metallic brazing joint. Alternatively, a thick-film bonding process is also conceivable.

[0020] Preferably, an ADB (active diffusion bonding) process is used, which includes, for example, the following steps: Providing a ceramic element and a metal layer, providing a gas-tight container that encloses the ceramic element, wherein the container is preferably formed from or comprises the metal layer, forming the metal-ceramic substrate by bonding the metal layer to the ceramic element by means of hot isostatic pressing, In order to form the metal-ceramic substrate, at least in sections an active metal layer or a contact layer comprising an active metal is arranged between the metal layer and the ceramic element to support the bonding of the metal layer to the ceramic element. The container is preferably formed as a metal container consisting of a metal layer and / or a further metal layer. Alternatively, it is also conceivable that a glass container is used.

[0021] In hot isostatic pressing, it is specifically designed that bonding occurs through heating under pressure, ensuring that the metal layer of the metal container, particularly the subsequent metal layer of the metal-ceramic substrate and any eutectic layer present there, does not enter the molten phase. Accordingly, hot isostatic pressing requires lower temperatures than a direct metal bonding process, especially a DCB process.

[0022] In contrast to bonding a metal layer to a ceramic layer using a solder material, which typically involves temperatures below the melting point of at least one metal layer, the present method advantageously eliminates the need for a solder base material and requires only an active metal. Furthermore, the use of pressure during hot isostatic pressing proves beneficial because it reduces air inclusions or voids between the metal layer and the ceramic element. This, in turn, reduces or even eliminates the formation of voids in the resulting metal-ceramic substrate. This positively impacts the bond quality between the metal layer of the metal container and the ceramic element.Furthermore, it is advantageously possible to simplify the "second etching" and avoid solder residues and silver migration.

[0023] The active metal layer comprises a comprehensive contact layer of active metal exceeding 15 wt.%.

[0024] Hot isostatic pressing is known, for example, from EP 3 080 055 B1, the content of which is hereby explicitly referenced with regard to hot isostatic pressing.

[0025] Furthermore, the material weakening is preferably designed as a dome-shaped recess. It is conceivable that an opening of this dome-shaped recess in the backside metallization faces the ceramic element and / or faces away from it. Another possible material weakening feature is a section of material in the backside metallization made of a different material than that used for the backside metallization. For example, suitable filler materials could be inserted into the respective recesses in the backside metallization. These filler materials have coefficients of thermal expansion that do not significantly contribute to the formation, support, or amplification of thermomechanical stresses. Such filler materials increase stability without compromising the desired thermomechanical symmetry between the front and back sides of the component.

[0026] The recesses can also have a circular, rhomboid, square, rectangular or polygonal cross-section in a direction parallel to the main extension plane.

[0027] It is particularly important to note that the congruent arrangement refers to the arrangement of the material weakening. In contrast, it is not necessary, for example, for a backside material weakening to be provided for each sub-area of ​​the component-side insulation section. In other words, according to the invention, the first total area occupied by the insulation sections in the component metallization is larger than the second total area occupied by the material weakenings in the backside metallization. According to the invention, the ratio of the second area to the first area is a value between 0.6 and 0.9, preferably between 0.7 and 0.9, and particularly preferably between 0.75 and 0.9. Here, further material weakenings, in addition to those material weakenings embedded in the backside metallization congruent with the insulation sections, are preferably disregarded.

[0028] According to the invention, it is conceivable that the insulating section in the component metallization extends along a first path, in particular continuously, while on the opposite side, a plurality of separated material weakenings are formed in the backside metallization in an identical arrangement. Furthermore, it is provided that the material weakening on an outer surface of the backside metallization, facing away from the ceramic element, has a first extent that is less than 1.0 mm, preferably less than 0.8 mm, and particularly preferably less than 0.7 mm. It is also provided according to the invention that two adjacent material weakenings are arranged at a first distance from each other that is less than 600 µm, preferably less than 400 µm, and particularly preferably less than 250 µm.Furthermore, it is conceivable that the initial spacing and / or the initial extent differ for several material weakenings. Alternatively, it is conceivable that, for example, the initial extent or the initial spacing of two adjacent material weakenings in the backside metallization is the same.

[0029] Preferably, the insulation section in the component metallization follows a first path in a plane parallel to the main extension plane, and a material weakening or several material weakenings in the backside metallization follow a second path in a plane parallel to the main extension plane, wherein in the stacking direction the second path is identical to the first path, in particular the second path is identical to the first path for more than 50% of its total extension, preferably more than 70% and particularly preferably more than 90% or completely.Thus, the material weakenings and the insulating section are not only congruent with each other in a cross-section perpendicular to the main extension plane, but also with respect to their first and second orientations, along which the insulating sections and material weakenings extend in a plane parallel to the main extension plane. It is conceivable that individual sections or subsections in the backside metallization are omitted with respect to their congruent arrangement with the insulating section(s). In other words, if there is a material weakening in the backside metallization, it is preferably always congruent with an insulating section, whereas for the insulating section, a material weakening in the backside metallization does not necessarily have to be congruent with the insulating section.This can prevent, if necessary, the backside metallization in this metal area from being weakened too much by closely spaced insulation sections.

[0030] The first and / or second profile can have straight or curved sections that are angled or offset from one another. Furthermore, it is preferably provided that the second profile of the material weakening(s) is formed by a series of material weakenings, for example, in the form of a row of holes or a series of dome-shaped recesses, and / or that the backside metallization has a stabilizing area between two material weakenings along the second profile. In particular, a row of holes is formed by a series of adjacent dome-shaped recesses. It is conceivable that a section is formed between two adjacent dome-shaped recesses in which the backside metallization has the second thickness.A residual metallization is provided that is greater than the residual metallization between the recess and the ceramic element. This maintains the stability of the metal-ceramic substrate despite the increased symmetry. Preferably, the first distance between two adjacent material weakenings is less than 600 µm, less than 400 µm, and particularly preferably less than 250 µm. In particular, the recesses are produced by a chemical process, such as etching, by a mechanical process, such as milling, or by an optical process, such as using laser light, especially laser pulses. The use of laser light, in particular, allows for the narrowest possible and most precisely positioned formation of the material weakenings, especially the recesses. The stabilization area is preferably characterized by a less pronounced material weakening.For example, the depth of a recess in the stabilization area may be less, or there may even be no recess in the stabilization area in some areas.

[0031] Preferably, in addition to the material weakening that is aligned with the insulating sections, a further material weakening is provided, which is embedded in an edge region of the backside metallization. In contrast to the material weakening, for the further material weakening, no aligned insulating sections are provided or formed on the opposite side when viewed in the stacking direction.

[0032] For example, it is preferably provided that the further material weakening is arranged in an edge region of the backside metallization that projects in a direction parallel to the main extension plane relative to the component metallization. In this case, the component metallization is smaller than the backside metallization, particularly with regard to its extent along the main extension plane. The further material weakening can form a row of holes or be designed as a flat side surface, i.e., in particular with a comparatively small angle of inclination, which is, for example, at least by a factor of 2, preferably at least by a factor of 3, and most preferably at least by a factor of 5 smaller than a corresponding angle of inclination on the component side.The different dimensions of the component metallization and the backside metallization ensure sufficient distance to the outer edge of the ceramic element on the component side to prevent electrical arcing, while the section of the backside metallization protruding from the component metallization increases the stability of the metal-ceramic substrate in the edge area.

[0033] It has been found that this measure of further material weakening can achieve an additional improvement in the metal-ceramic substrate, which can counteract the susceptibility of the metal-ceramic substrate to deflection and, in particular, further increase its resistance to thermal shock. The further material weakening at the edge can also be designed as a curved flank profile with at least one intermediate maximum. Furthermore, it is preferably provided that the first extent of the further material weakening is smaller than the first extent of the material weakening. If the material weakening and the further material weakening each have different extents, it is preferably provided that the respective average value is taken into account. Furthermore, it is provided that the partial section of the metallization or...The term "backside metallization" refers to a material weakening that extends from the outer perimeter of the backside metallization and covers less than 10%, preferably less than 5%, and particularly preferably less than 2% of the total area of ​​the backside metallization. Furthermore, the additional material weakening is designed to surround, and in particular completely enclose, the area containing the material weakening.

[0034] Furthermore, it is preferably provided that a material weakening, designed as a recess, extends to the ceramic element. This achieves a high degree of symmetry between the component's front and back sides. Alternatively, it is conceivable that residual metallization is formed in the area of ​​the material weakening, so that this residual metallization can contribute to increasing the stability of the entire metal-ceramic substrate. This is particularly advantageous when using very thin insulating layers or ceramic elements, which would otherwise exhibit an increased tendency to break. For example, it is provided that, measured in the stacking direction, the residual metallization has a fourth thickness, wherein the ratio of the fourth thickness to the second thickness is less than 0.5, preferably less than 0.4, and most preferably less than 0.2.

[0035] It is also conceivable that residual metallization exists between the further material weakening formed as a recess and the ceramic element, particularly if the material weakening formed as a recess extends to the ceramic element. This would, for example, differentiate the material weakening from the further material weakening in the edge region.

[0036] Preferably, a first width of the insulation section is defined by a distance between the first metal section and the second metal section, measured along a first direction perpendicular to the first direction, wherein the ratio of a second width of the material weakening, measured along the first direction, to the first width is between 0.1 and 2, preferably between 0.5 and 1.5, and most preferably between 0.75 and 0.9. In particular, it has been shown that a sufficient degree of symmetry with respect to thermodynamic expansion on the component's front and back sides can be achieved if the material weakening on the back side metallization does not extend over the full second width of the insulation section.This allows the stability of the metal-ceramic substrate to be maintained without having to worry that a possible point of failure for the metal-ceramic substrate might arise due to the small amount of material on the back.

[0037] Preferably, the ratio of sections where the first and second profiles do not coincide in the stacking direction to sections where the first and second profiles coincide in the stacking direction is less than 1, preferably less than 0.5, and particularly preferably less than 0.2. It has been found that with an increasing proportion of coincidentally arranged material weaknesses, the overall symmetry on the front and back of the metal-ceramic component can be increased, thereby further improving or reducing the tendency to deflect of the correspondingly designed metal-ceramic substrates.

[0038] Preferably, a heat sink is attached to the backside metallization. In particular, the material weakening is provided, for example, in the form of a recess, embedded in the backside metallization. Thus, the material weakening embedded in the backside metallization is not a recess embedded in the heat sink, which is attached to the backside metallization and is specifically designed to dissipate the heat generated during operation of the specific metal-ceramic substrate to a cooling fluid.

[0039] In particular, it is provided that for each unit of length along the first and / or second path, the insulation section assumes a first volume and the material weakening in the backside metallization assumes a second volume, wherein the first and second volumes are essentially the same in terms of their absolute dimensions but differ in terms of their geometric shapes. This allows, on the one hand, the symmetry between the recesses in the component metallization and the recesses in the backside metallization to be kept as high as possible, and on the other hand, measures can be taken to strengthen the stability in the areas where the insulation section or the material weakening is embedded.In this context, "essentially equal" volumes are preferably understood by those which differ from each other by no more than 10%, preferably no more than 5%, and particularly no more than 2.5% of their mean value. The first and second volumes may differ, for example, in their depth, width, and / or length. Similarly, for recesses of different depths on the side and back of the component, correspondingly different widths or diameters may be used to ensure that the volumes of the recesses in the component metallization and the back-side metallization are essentially the same.

[0040] According to another aspect of the present invention, a metal-ceramic substrate, which is provided as a printed circuit board for mounting electrical components, is provided, comprising: a component metallization and a backside metallization and a ceramic element arranged along a stacking direction between the component metallization and the backside metallization, wherein the component metallization comprises a first metal section and a second metal section, wherein the first metal section and the second metal section are separated from each other by an insulating section and / or a connection area for an electrical component is provided on the first metal section, and wherein the backside metallization has a material weakening, in particular a material recess, which, viewed in the stacking direction, is at least partially congruent with the connection area. All advantages and properties described for the metal-ceramic substrate with the material weakenings congruent with the insulating sections can be transferred analogously to the metal-ceramic substrates with the advantages, properties, and specifications described for the material weakenings congruent with the connection areas, and vice versa.According to the invention, a metal-ceramic substrate is provided that has both material recesses that are congruent with the insulation sections and (further) material recesses that are congruent with the connection area.

[0041] Preferably, the connection area is characterized by a corresponding planar extent that is visibly distinct from conductor tracks because it is wider than conductor tracks in a principal plane of extension. It is conceivable that the material weakening extends over the entire area that is congruent with the connection area. It is also conceivable that the portion of the backside metallization that is congruent with the connection area exhibits material weakening only in certain regions, for example, congruent with an edge section of the connection area. Preferably, the material weakenings that are congruent with the connection area are arranged in a two-dimensional pattern.

[0042] Another object of the present invention is a method for producing a metal-ceramic substrate, in particular for producing a metal-ceramic substrate according to the invention, comprising: Providing a component metallization and a backside metallization, as well as a ceramic element, connecting the component metallization and the backside metallization to the ceramic element, wherein the ceramic element is arranged along a stacking direction between the component metallization and the backside metallization, structuring the component metallization by realizing insulation sections and realizing a material weakening in the backside metallization, wherein the material weakening is arranged coincidentally with the insulation section when viewed in the stacking direction.

[0043] All the advantages, properties, and specifications described for the metal-ceramic substrate can be applied analogously to the process and vice versa.

[0044] Further advantages and features will become apparent from the following description of preferred embodiments of the invention with reference to the accompanying figures. Individual features of the individual embodiments can be combined with one another within the scope of the invention.

[0045] It shows: Fig. 1: a metal-ceramic substrate according to the state of the art, Fig. 2 a metal-ceramic substrate according to a first exemplary embodiment of the present invention in a sectional view Fig. 3 a metal-ceramic substrate according to a second exemplary embodiment of the present invention in a sectional view Fig. 4metal-ceramic substrate according to a third exemplary embodiment of the present invention, Fig. 5 two different material weakenings for the reverse side metallization Fig. 6 a component metallization (bottom) and a backside metallization (top) and a side view (middle) of a metal-ceramic substrate according to a fourth embodiment of the present invention and Fig. 7 a comparison between a recess forming the insulation section and recesses ending in a material weakening for a metal-ceramic substrate according to a fifth exemplary embodiment of the present invention.

[0046] In Figure 1A metal-ceramic substrate 1 according to the prior art is schematically depicted. Such a metal-ceramic substrate 1 is preferably a carrier for electrical components. It is particularly provided that the metal-ceramic substrate 1 comprises a ceramic element 30 and a component metallization 10, wherein the ceramic element 30 and the component metallization 10 extend along a principal extension plane HSE. The component metallization 10 is connected to the ceramic element 30, and the component metallization 10 and the ceramic element 30 are arranged one above the other in a stacking direction S perpendicular to the principal extension plane HSE.In particular, it is provided that the component metallization 10 has a plurality of metal sections, for example a first metal section 11, a second metal section 12 and a second third metal section 13, which are arranged, for example, electrically insulated from each other and next to each other along a direction parallel to the main extension plane HSE.

[0047] In particular, it is common practice in the prior art to first bond the component metallization 10 to the ceramic element 30, especially by means of a direct metal bonding process and / or an active soldering process or AMB process and / or an ADB process and / or hot isostatic pressing. Such bonding processes are high-temperature processes in which the arrangement of ceramic element 30 and the component metallization 10 is exposed to an elevated temperature, especially temperatures above 500 °C. After the bonding process, structuring is then carried out, for example by means of an etching process, to create electrically isolated metal sections, in particular a first metal section 11 and a second metal section 12, which can be used as conductor tracks and / or connection surfaces, so-called pads, for electrical circuits.

[0048] A backside metallization 20 is preferably attached to the ceramic element 30 on the side opposite the component metallization 10. This backside metallization is preferably attached to the ceramic element 30 simultaneously with the component metallization 10, i.e., in a single step. Alternatively, the component metallization 10 and the backside metallization are attached sequentially. Such a backside metallization 20 serves in particular to compensate for thermomechanical stresses in the metal-ceramic substrate 1, which arise due to the different thermomechanical expansion coefficients of the component metallization 10 and the ceramic element 30.

[0049] The component metallization 10 is designed to have at least one first metal section 11, one second metal section 12, and / or one third metal section 13. After structuring, the first metal section 11, the second metal section 12, and / or the third metal section 13 are separated from each other by insulating sections 15 to form corresponding conductive traces and / or connection surfaces that are electrically insulated from one another. For this purpose, a structure is embedded in the component metallization 10, for example, by a chemical process, a mechanical process, and / or an optical process. A recess in the component metallization 10 required for the structure extends at least to the ceramic element 30 to provide the necessary electrical insulation.Such insulation sections 15 are formed in a trench-like manner within the component metallization 10 and are also colloquially referred to as insulation trenches. The corresponding first sections VE1 of the trench-like insulation sections 15 follow a specific pattern depending on the application of the metal-ceramic substrate 1 intended as a printed circuit board. In particular, the first section of the insulation sections 15 is individually configured for each series of manufactured metal-ceramic substrates 1 for the respective application.

[0050] To ensure the desired symmetry between a component side BS and a rear side RS of the metal-ceramic substrate 1, thereby allowing corresponding thermomechanical stresses occurring in the metal-ceramic substrate 1 to compensate for each other, the rear side metallization 20 and the component metallization 10 are designed to have essentially comparable thicknesses. These thicknesses are measured along a direction following the stacking direction S.

[0051] In Figure 2 A metal-ceramic substrate 1 according to a first exemplary embodiment of the present invention is shown. In order to reduce the susceptibility of the metal-ceramic substrates 1 to deflection, it is provided that, in addition to the insulating sections 15 in the component metallization 10, material weakenings 25 are embedded in the backside metallization 20. In the Figure 2In the illustrated embodiment, the material weakenings 25 are recesses in the backside metallization 20, which extend in particular to the ceramic element 20 and lead to complete isolation of partial sections of the backside metallization 30. In particular, it is provided that the material weakening 25 is arranged substantially congruently with the isolation section 15 when viewed in the stacking direction S. This advantageously further increases the symmetry between component side BS and backside RD and thus further reduces the susceptibility to deflection of the metal-ceramic substrate 1. It is further provided that the component metallization 10 has a first thickness D1 and the backside metallization 20 has a second thickness D2, wherein the first thickness D1 and the second thickness D2 are substantially equal."Substantially" means that deviations between the first thickness D1 and the second thickness D2 are less than 10%, preferably less than 5%, and most preferably less than 2.5% of the mean value of the first thickness D1 and / or the second thickness D2.

[0052] Furthermore, the ceramic element 30 is provided to have a third thickness D3. Preferably, the third thickness D3 is less than 700 µm, more preferably less than 400 µm, and most preferably less than 330 µm. This results in comparatively thin insulating layers or ceramic elements 30, which are correspondingly more susceptible to deflection. By increasing the symmetry through the additional incorporation of the congruently arranged material weakening 25, it is thus advantageously possible to counteract deflection in such metal-ceramic substrates 1 where a comparatively thin insulating layer, i.e., a comparatively thin ceramic element 30, is used.

[0053] Furthermore, it is provided that the insulation section has a first width B1 and the material weakening 25 has a second width B2. Preferably, the second width B2 is smaller than the first width B1. In particular, it is conceivable that the ratio of the second width B2 to the first width B1 assumes a value between 0.1 and 2.0, preferably between 0.5 and 1.5, and most preferably between 0.75 and 0.5. In the Figure 2 In the illustrated embodiment, the side surfaces of the backside metallization 20 in the area of ​​the material weakening 25 formed as a recess run essentially perpendicular to the main extension plane HSE. Preferably, however, it is provided that the formed side surfaces are curved or inclined, particularly if the material weakening 25 embedded in the backside metallization 20 is realized by an etching process.

[0054] The first width of the insulating section 15 is determined, in particular, by the minimum distance between two opposing metal sections 11, 12, 13 at the location of the insulating section 15 to be measured. A first direction R1, along which the first width B1 is determined, lies within the principal extension plane HSE and, in particular, is perpendicular to the direction along which the insulating section 15 extends in the principal extension plane HSE according to a first profile VE1. This first profile VE1 is defined by the corresponding pattern provided for the respective metal-ceramic substrate 1. The size of the second width B2 is preferably determined at the same position on the back side RS along the same first direction R1.

[0055] Furthermore, "congruent" means that along an imaginary projection of the extent of the material weakening 25 onto the extent of the insulation section 15, parallel to the stacking direction S, a spatial overlap would be conceptually evident, which is in particular greater than 50%, preferably greater than 75%, and most preferably greater than 95%. The centers of the extents of the material weakening 25 and the center of the insulation section 15 can be superimposed in the stacking direction or laterally offset from each other, in particular in the main extension plane HSE along a direction perpendicular to the first extent VE1 or perpendicular to the second extent VE2.

[0056] In Figure 3 Figure 1 shows a sectional view through a metal-ceramic substrate 1 according to a second exemplary embodiment of the present invention. This embodiment differs from the previous one. Figure 3essentially from the embodiment of the Figure 2 only insofar as in the exemplary embodiment of the Figure 3The material weakening 25, formed as a recess, does not extend to the ceramic element 30. In particular, it is provided here that residual metallization 40 is provided in the area of ​​the material weakening 25. This residual metallization 40 has a fourth thickness D4, which is smaller than the second thickness D2. Preferably, the ratio of the fourth thickness D4 to the second thickness D2 is less than 0.5, more preferably less than 0.25, and most preferably less than 0.1. This embodiment has the advantage that the residual metallization 40 contributes to the stability of the ceramic element 30, while simultaneously taking into account the symmetry of the component side BS and the rear side RS. It is conceivable that the second thickness D2 is smaller than the first thickness D1 in order to compensate for the presence of the residual metallization 40.Furthermore, it is conceivable that in another embodiment, material weakening 25 provided as a recess in a metal-ceramic substrate 1 extends partly to the ceramic section 30, while other sections exhibit residual metallization 40. In other words, the metal-ceramic substrate 1 comprises material weakenings 25 formed as recesses, some of which extend to the ceramic element 30 and some of which exhibit residual metallization 40.

[0057] Furthermore, it is conceivable that in another embodiment the fourth thickness D4 is different and varied for different material weakenings 25 and is in particular adapted to the extent of the expected thermomechanical stresses for the respective layout / pattern or for the respective planned first profiles VE1 of the insulation sections 15.

[0058] In Figure 4Figure 1 shows a side view (center), a top view of the back side RS (top), and a top view of the component side BS (bottom) of a metal-ceramic substrate 1 according to a third exemplary embodiment of the present invention. In particular, the material weakening 25 in the back-side metallization 20 is designed as a row of holes or as an array of material weakenings 25. Such a row of holes proves particularly advantageous because the metallization maintained between the individual holes increases the stability of the metal-ceramic substrate 1 while simultaneously increasing the symmetry of the material distribution on component side BS and back side RS of the metal-ceramic substrate 1. Preferably, the row of holes is an array of circular and / or dome-shaped recesses.The embodiments of the recess shown in the sectional view extend once to the ceramic element 30 (left) and once the recess ends in the backside metallization (right), i.e. a residual metallization 40 is provided between the recess and the ceramic element 30.

[0059] Furthermore, it is provided that the row of holes or the sequence of material weakening 25 follows a second path VE2, which is in particular identical to a first path VE1, which is defined by the insulation section 15 on the component side BS or in the component metallization 10. The first path VE1 and the second path VE2 can each have angled subsections and / or curved subsections in the main extension plane HSE, which, for example, connect straight subsections. It is also conceivable that the first path VE1 and / or the second path VE2 have branches.

[0060] Furthermore, it is particularly preferred that a first distance AB1 between two adjacent recesses or material weakenings 25 is less than 600 µm, preferably less than 400 µm, and particularly preferably less than 250 µm. In particular, it is preferred that the first distance AB1 between two material weakenings is greater than the first extent E1.

[0061] It is also conceivable that the recesses arranged as a row of holes touch each other or merge into each other and are not separated from each other by a metal section that extends to the outside of the backside metallization.

[0062] Furthermore, it is preferably provided that, in addition to the material weakening 25, a further material weakening 26 is provided, which forms in the edge region of the backside metallization 20. In particular, the further material weakening 26 is formed as a series of further material weakenings 26, especially as a row of holes, wherein the series extends in a frame-like manner along an edge region of the backside metallization 20 or of the metal-ceramic element 1. In particular, it is provided that the course of the further material weakening 26 lies outside a region in which the material weakenings 25 are formed that are congruent with the first course VE1 or the arrangement of the insulating sections 15 on the component side BS.Furthermore, it is provided that the further material weakening 26, in particular configured as further recesses, has a first extent E1 on the outside of the backside metallization 20, which faces away from the ceramic element 30, which is smaller than the first extent E1 of the material weakening 25. Furthermore, the ratio of the first extent E1 of the further material weakening 26 to the first extent E1 of the material weakening 25 assumes a value that is less than 0.7, less than 0.6, and particularly preferably less than 0.5. Preferably, the first extent E1 of the further material weakening 26 is less than 1.2 mm, more preferably less than 0.9 mm, and more preferably less than 0.7 mm. It is also preferably provided that a first distance AB1 between two adjacent further material weakenings 26 is smaller than the distance between two material weakenings 25. The distance of the material weakening 25 or AB1 is determined by the first extent AB1 of the material weakening 26.Further material weakening 26 between each other is determined here from center to center of the respective recess. Furthermore, it is preferably provided that the edge region is understood to be the region that extends from the outer circumference towards the center of the backside metallization 20, wherein the extent of the edge region is limited to a maximum of 10% of the total extent of the backside metallization 20, in particular a maximum of 5% and especially preferably a maximum of 2%.

[0063] In Figure 5Sectional views through two different forms of material weakening 25 are shown. In particular, it is provided that the dome-shaped recesses on an outer surface of the backside metallization 20 facing away from the ceramic element 30 have a first extension E1. Preferably, the first extension E1 is essentially identical for all material weakening 25, especially all dome-shaped recesses. It is also conceivable that the size of the first extension E1 differs between the different dome-shaped recesses that are arranged congruently with the insulating sections 15.

[0064] Preferably, a first extent E1 of the material weakening 25, in particular of the dome-shaped recess, is less than 1.5 mm, more preferably less than 1.0 mm, and most preferably less than 0.75 mm. If the dome-shaped recess extends to the ceramic element 30, it is preferably provided that a second extent E2 of the material weakening 25 on the outside of the backside metallization 20, which faces the ceramic element 30, is less than 1.3 mm, more preferably less than 0.8 mm, and most preferably less than 0.6 mm. In particular, the ratio of the second extent E2 to the first extent E1 is between 0.6 and 0.95, more preferably between 0.7 and 0.9, and most preferably between 0.75 and 0.85.

[0065] In Figure 6Figure 1 shows a component metallization 10 (bottom) and a backside metallization 20 (top), as well as a side view (middle) for a metal-ceramic substrate 1 according to a fourth exemplary embodiment. This embodiment differs from the previous one. Figure 6 from the one Figure 4In particular, the first path VE1 and the second path VE2, which are congruent with each other and each located in a central area of ​​the component metallization 10 and the backside metallization 20 respectively, have several intersecting sub-sections. This is necessary to achieve the desired pattern for forming conductor tracks or connection pads. Specifically, the lower figure shows a first path VE1 along which the insulation section 15 extends in the plane parallel to the main extension plane HSE. In the top view shown here, it can be seen that, to form a pullback, the ceramic element 30 projects from the component metallization 10 in a direction parallel to the main extension plane HSE.

[0066] Essentially, in the exemplary embodiment of the Figure 6The backside metallization 20 is provided with material weakening 25, which is arranged congruently with the first path VE1 of the insulation section 15 on the component metallization 10, and with further material weakening 26, which is arranged in the edge region of the backside metallization 20. It can be seen that the further material weakening 26 in the edge region is not arranged congruently with the entire insulation section 15.

[0067] In the embodiment of the Figure 6It is further provided that the ceramic element 30 projects less than the backside metallization 20 in a direction parallel to the main extension plane HSE than it does to the component metallization 10. This reduces the probability of flashover on the component side BS due to the increased distance to the end of the ceramic element 30, while on the backside RS, the edge region of the backside metallization 20 supports the stabilization of the metal-ceramic substrate 1. In particular, the additional material weakening 26 in the edge region of the backside metallization 20 is located in the area of ​​the backside metallization 20 that projects less than the component metallization 10 in a direction parallel to the main extension plane HSE.In the side view, it can be seen that the backside metallization 20 is larger in its extent in the main extension plane HSE than the component metallization 10 and protrudes in a direction parallel to the main extension plane HSE compared to the component metallization 10.

[0068] Furthermore, it is conceivable (not shown) that the second course VE2 of the material weakenings 25 is arranged completely congruently with the insulation section 15, but that the second course VE2 includes subsections in which a material weakening 25 is omitted. Thus, the first course VE1 is not completely congruent with the second course VE2, since there are subsections of the first course VE1 for which no material weakening 25 is provided on the backside metallization 20. This is particularly useful for areas where a high density of insulation trenches or insulation sections 15 is provided, as the introduction of corresponding material weakenings 25 on the backside RS would lead to a corresponding destabilization of the metal-ceramic substrate 1.

[0069] In Figure 7A schematic comparison is shown between a recess associated with the insulation section 15 and a recess associated with a material weakening 25 for a metal-ceramic substrate 1. In other words: in the middle area of ​​the Figure 7 Top views of the component side BS and the back side RS are shown, revealing a first surface A1 for the recess of the insulation section 15, as well as several material weakenings 25 in the form of dome-shaped recesses, which in the top view of the back side RS form a series of, for example, second surfaces A2 of equal size in total.

[0070] Along the section line AA, also included here, a cross-sectional view through the component metallization (top) and the backside metallization (bottom) is shown. The recess, which is assigned to the insulation section 15 on the component side BS, has a first depth T1, while the material weakening 25, which is designed as a dome-shaped recess, has a second depth T2. For the highest possible symmetry, it is provided that, for a defined unit of length LE, a first volume V1 of the one or more recesses forming the insulation section 15 corresponds in size to a second volume V2, which the recess or the multiple recesses in the backside metallization 10 occupy per unit of length LE in an area in the backside metallization 20 opposite the insulation section 15.The length unit LE is preferably formed by the first distance AB1 between two adjacent material weakenings 25 or extends over 1 cm, preferably 2 cm, and particularly preferably 2.5 cm. It is specifically provided that, despite the volumes being the same size, the shapes of the first volume V1 and the second volume V2 are different. For example, the insulation section 15 is formed by a continuous recess, while the material weakenings 25 on the rear side RS are formed as dome-shaped recesses. Thus, for example, the second depth T2 does not correspond to the first depth T1, and the length of the recess along the first extension VE1 and / or second extension VE2, which is associated with the insulation section 15, does not correspond to the corresponding length of the material weakening 25.If the recess in the material weakening 25 extends to the ceramic element 30, it is preferably provided that, for example, by an increased diameter for the recess in the back side RS, a first area A1 per unit length LE corresponds approximately to the sum of the second area A2 in the back side RS. To accommodate the different shapes of the material weakening 25 compared to the recess forming the insulating section 15, the diameter, i.e., a second width B2, of a dome-shaped recess can, for example, be chosen to be larger than a corresponding first width B1 of the associated insulating section 15. This proves particularly advantageous because it retains more material on the back side RS, thereby increasing the stability of the entire metal-ceramic substrate 1, especially in the area of ​​the insulating section 15.At the same time, however, this avoids reducing the symmetry, which could in turn cause bending, especially during operation of the metal-ceramic substrate 1.

[0071] Furthermore, it is possible to adjust the first volume V1 and / or second volume V2 by means of a corresponding first depth T1 and / or second depth T2, such that the first volume V1 and the second volume V2 are essentially equivalent to each other.

[0072] In this context, "essentially" means that deviations of less than 10%, preferably less than 5% and particularly preferably less than 2.5% of the relevant quantity or of the mean of the values ​​to be compared are to be expected. Reference symbol:

[0073] 1 Metal-ceramic substrate 10 Component metallization 11 First metal section 12 Second metal section 13 Third metal section 15 Insulation section 20 Backside metallization 25 Material weakening 26 Further material weakening 30 Ceramic element 40 Residual metallization S Stacking direction BS Component side RS Backside HSE Main extent plane R1 First direction B1 First width B2 Second width D1 First thickness D2 Second thickness D3 Third thickness D4 Fourth thickness V1 First volume V2 Second volume VE1 First contour VE2 Second contour AB1 First spacing T1 First depth T2 Second depth E1 First extension E2 Second extension

Claims

1. A metal-ceramic substrate (1) provided as a printed circuit board for mounting electrical components, comprising: - a component metallisation (10) and a backside metallisation (20), and - a ceramic element (30) arranged between the component metallisation (10) and the backside metallisation (20) along a stacking direction (S), wherein the component metallisation (10) has a first metal section (11) and a second metal section (12), wherein the first metal section (11) and the second metal section (12) are separated from each other by an isolation section (15), and wherein the backside metallisation (20) has a material weakening (25), in particular a material recess, which, viewed in the stacking direction (S), is arranged at least zonally congruently with the isolation section (15), characterized in that a plurality of separated material weakenings (25) are formed, wherein two adjacent material weakenings (25) are arranged at a first distance from each other which is less than 600 µm, and a first total area occupied by the isolation sections in the component metallisation is greater than a second total area occupied by the material weakening in the backside metallisation, wherein a ratio of the second total area to the first total area assumes a value which lies between 0.6 and 0.9.

2. The metal-ceramic substrate (1) according to claim 1, wherein the material weakening (25) is formed as a dome-shaped recess.

3. The metal-ceramic substrate (1) according to one of the preceding claims, wherein the isolation section (15) in the component metallisation (10) in a plane parallel to the main extension plane (HSE) has a first course (VE1) and the material weakening (25) or several material weakenings (25) in the backside metallisation (20) follow a second course (VE2) in a plane parallel to the main extension plane (HSE), wherein the second course (VE2) is preferably arranged congruently with the first course (VE1) in the stacking direction (S).

4. The metal-ceramic substrate (1) according to claim 3, wherein the second course (VE2) of the material weakening (25) or the material weakenings (25) is formed by a sequence of material weakenings (25), for example in the form of a row of holes, and / or has a stabilization region along the second course (VE2) between two material weakenings (25).

5. The metal-ceramic substrate (1) according to one of the preceding claims, wherein a further material weakening (26) is provided, which is embedded in the backside metallisation (20) in a peripheral region of the backside metallisation (20) and, in particular, is embedded in the component metallisation (10) independently of an isolation section (15).

6. The metal-ceramic substrate (1) according to one of the preceding claims, wherein the material weakening (25) formed as a recess extends in the backside metallisation (20) to the ceramic element (30).

7. The metal-ceramic substrate (1) according to claim 5, wherein a residual metallisation (40) is formed between the further material weakening (26) formed as a recess and the ceramic element (30).

8. The metal-ceramic substrate (1) according to claim 3, wherein a ratio of sections in which the first course (VE1) and the second course (VE2) are not congruent when viewed in the stacking direction (S) to sections in which the first course (VE1) and the second course (VE2) are congruent with each other when viewed in the stacking direction (S), have a value that is less than 1, more preferably less than 0.5, and most preferably less than 0.2.

9. The metal-ceramic substrate (1) according to claim 3, wherein per unit of length (LE) along the first course (VE1) and / or second course (VE2), the isolation section (15) attains a first volume (V1) and the material weakening (25) or the material weakenings in the backside metallisation (20) attains or attain a second volume (V2), wherein the first volume (V1) and the second volume (V2) are essentially equal in terms of their absolute size and are different in terms of their geometric forms.

10. A metal-ceramic substrate (1) provided as a printed circuit board for mounting electrical components, comprising: - a component metallisation (10) and a backside metallisation (20), and - a ceramic element (30) arranged between the component metallisation (10) and the backside metallisation (20) along a stacking direction (S), wherein the component metallisation (10) has a first metal section (11) and a second metal section (12), wherein the first metal section (11) and the second metal section (12) are separated from each other by an isolation section (15) and / or a connection region for an electrical component is provided on the first metal section, and wherein the backside metallisation (20) has a material weakening (25) in the form of a material recess which when viewed in the stacking direction (S), is arranged at least partially congruent with the connection region, characterized in that a plurality of separated material weakenings (25) are formed, wherein the backside metallisation has both material recesses that are congruent with the isolation sections and material recesses that are congruent with the connection region.

11. A method for manufacturing a metal-ceramic substrate (1) according to one of the preceding claims, comprising: - providing a component metallisation (10) and a backside metallisation (30) as well as a ceramic element (20), - bonding the component metallisation (10) and the backside metallisation (30) to the ceramic element (20), wherein the ceramic element (20) is arranged between the component metallisation (10) and the backside metallisation (20) along a stacking direction (S), - structuring the component metallisation (10) by realising isolation sections (15) and - creating material weakening (25) in the backside metallisation (20), wherein the material weakening (25) is arranged so as to be congruent with the isolation section (15) and / or a connection region of the first metal section when viewed in the stacking direction (S).