MANUFACTURING PROCESS OF A METAL-CERAMIC SUBSTRATE WITH IMPROVED SURFACE UTILIZATION

Description

[0001] The present invention relates to a metal-ceramic substrate that can be used in a specific method for structuring the metal coating. Furthermore, the present invention relates to a method for producing structured metal-ceramic substrates.

[0002] Typically, metal-ceramic substrates, such as DCB substrates, are patterned using photolithography. First, a light-sensitive film (also known as dry film, dry resist, photoresist, or laminate) is applied (laminated) to the metal coating and covered with a photographic negative (film). Subsequently, all areas of the laminate not covered by the film, i.e., darkened, are exposed to a strong light source. The covered and unexposed areas are removed in the subsequent development step. A reverse procedure is also possible. This exposes the underlying copper, which is then removed by etching in a subsequent process step.

[0003] The structuring of metal-ceramic substrates is typically performed by exposure in automatic continuous exposure units. For this purpose, the substrates coated with metal coatings are placed in an exposure chamber on a film that creates the structure of the substrate's backside.

[0004] This well-known method of structuring metal-ceramic substrates has some disadvantages.

[0005] Firstly, there is the problem of positioning accuracy between substrate and film during exposure. In current state-of-the-art processes, the substrates are pre-positioned before being introduced into the exposure chamber of the automatic continuous exposure unit. However, transferring the pre-positioned substrates into the exposure chamber and setting them down deteriorates the relative positioning accuracy of film to substrate, which can result in errors in the millimeter range. Alternatively, the substrates can be mechanically stopped and positioned during exposure. The disadvantage of this is that the mechanical stop systems can lead to shadowing during the exposure process and thus to a loss of surface area on the substrates.Furthermore, there is the disadvantage that the inaccuracies from film to stop and stop to substrate add up and thus high-precision positioning from substrate to layout is not possible.

[0006] A further disadvantage of conventional methods for structuring metal-ceramic substrates using photolithography is the relatively high energy requirement, since the entire exposure space must be illuminated for structuring.

[0007] The use of conventional films for exposure is also disadvantageous, as the films must first be manufactured, and dimensional accuracy must be checked before each use. Further problems include film wear, which can lead to exposure errors in extreme cases, storage and disposal, and tool management.

[0008] Finally, the conventional state-of-the-art processes are disadvantageous in terms of process economy, i.e., throughput. The production of required films can take up to several working days, and changing between different layouts in corresponding exposure processes involves replacing the film, which also leads to disadvantageous process economy.

[0009] The present invention now has the particular object of solving these disadvantages of the prior art.

[0010] According to the invention, the use of a direct exposure system is recommended for this purpose. This system dispenses with the use of film and projects the light only onto the areas of the metal-ceramic substrate to be exposed. In contrast to known methods for structuring metal-ceramic substrates, direct exposure methods do not require a film to apply the layout to the light-sensitive layer. Instead, they project the layout directly onto the light-sensitive layer of the metal-ceramic substrate using lasers or projectors. Conventional, commercially available direct exposure devices feature an image processing system that detects the position of the substrate to be structured in the exposure chamber and can adapt the creation of the layout on the substrate to this position.

[0011] A corresponding direct exposure system is described, for example, in German patent application DE 10 2009 032 210 A, from which a device is known that has an exposure device and a specimen slide in an exposure chamber. The exposure device and the specimen slide are arranged so that they can move relative to one another. A plate-shaped substrate with a photosensitive layer is provided on the specimen slide, wherein the position of the specimen in the exposure chamber is determined based on its edge. Based on this position of the substrate in the exposure chamber, determined by the edges, a layout is then generated by exposure.

[0012] A corresponding procedure has not yet been carried out on metal-ceramic substrates, since the metal-ceramic substrates known from the prior art are unsuitable for such an application in a direct exposure process similar to DE 10 2009 032 210 A.

[0013] Corresponding metal-ceramic substrates must be suitable for their position in an exposure chamber to be identified, for example, based on the edge of the metal-ceramic substrate, and must also exhibit only minimal deflection or low flatness, since otherwise direct exposure would lead to layout inaccuracies. JP 2012 160642 discloses a ceramic substrate. Metal-ceramic substrate according to the invention

[0014] The present invention is therefore based, first of all, on the object of providing a metal-ceramic substrate which is suitable for being structured in a direct exposure process.

[0015] This object is achieved by a metal-ceramic substrate according to claim 1, in which at least one metal layer is provided on a substantially rectangular ceramic substrate.

[0016] The metal-ceramic substrate according to the invention is then characterized in that the ceramic substrate is at least partially free of metallic coating in the edge region (requirement a). In particular, it is provided that the metal-ceramic substrate, which is at least partially metal-free in the edge region, has no structuring of the metal layer.

[0017] The metal-ceramic substrate according to the invention is further preferably characterized in that the ceramic substrate is flat and the flat metal layer provided thereon does not extend at least partially to the edge of the flat ceramic substrate, thus forming at least a partially metal-free edge region. As shown in the figures described below, the metallization does not cover the entire flat substrate.

[0018] The flatness of the metal-ceramic substrate is less than 1600 µm, preferably less than 1400 µm, more preferably less than 1200 µm, even more preferably less than 1000 µm, even more preferably less than 800 µm, even more preferably less than 500 µm, even more preferably less than 200 µm.

[0019] The inventive requirement of a metal-free edge region of the ceramic substrate (requirement a.) enables a precise determination of the position of the metal-ceramic substrate to be structured in the exposure chamber based on the metal-free edge or some points located on the metal-free edge, while the inventive requirement of flatness (requirement b.) makes it possible to achieve a precise layout of the structuring on the metal-ceramic substrate by means of direct exposure.

[0020] The edge region, which is free of metallization within the scope of the present invention, extends laterally up to an imaginary parallel to the ceramic edge, wherein the distance of the parallels to the ceramic edge is a maximum of 1.5 cm, preferably a maximum of 1.4 cm, more preferably a maximum of 1.3 cm, more preferably 1.2 cm, more preferably 1.1 cm, more preferably 1.0 cm, more preferably 0.9 cm, more preferably 0.8 cm, more preferably 0.7 cm, more preferably 0.6 cm, more preferably 0.5 cm, more preferably 0.4 cm, more preferably 0.3 cm, more preferably 0.2 cm, more preferably 0.1 cm.

[0021] In the context of the present invention, the flatness of the metal-ceramic substrate is understood to mean a shape tolerance of the metal-ceramic substrate within which the flat surface of the metal-ceramic substrate must be located. The tolerance limits are determined by two imaginary surfaces parallel to the ideally planar surface of the metal-ceramic substrate. In the case where the actually produced surface of the metal-ceramic substrate pierces through one of the parallel surfaces, the tolerance is exceeded. The tolerance specifies the distance between the two imaginary parallel surfaces. A corresponding arrangement for the inventive definition of flatness is described in Fig. 4, wherein the metal-ceramic substrate 1 is positioned between two ideally flat, parallel imaginary surfaces 10 and 11. These structural requirements of a metal-ceramic substrate are not known from the prior art DE 10 2009 032 210 A for the plate-shaped objects to be structured there, since the prior art DE 10 2009 032 210 A does not aim at structuring metal-ceramic substrates, but rather at structuring PCB circuit boards.

[0022] In PCB circuit boards, low thicknesses of the metal coating are generally realized in a range of 12 to 100 µm, while the metal-ceramic substrates to be used according to the invention have metallization layer thicknesses of generally 200 to 600 µm. Due to the greater thickness of the metal coating and the associated expectation that corresponding metal-ceramic substrates do not have sufficient flatness, the person skilled in the art would not have considered applying the teaching of DE 10 2009 032 210 A to metal-ceramic substrates. Possible deflection directions of metal-ceramic substrates are described, for example, in Figure 5 Figure 5a shows a possible transverse bending and Figure 5b a possible longitudinal bending of the metal-ceramic substrate. Figures 5c to 5e show torsion, saddle, and calotte forms of deflection of the metal-ceramic substrate. Mixed forms are also conceivable.

[0023] In addition to the deflections of metal-ceramic substrates shown above, other deflection forms, such as wave-like ones, are also conceivable. These deflections are determined not only by the layer thickness of the metal coating but also by the thickness of the ceramic substrates used. The manufacturing process of the metal-ceramic substrates—i.e., the way the ceramic substrate is bonded—as well as downstream processing can also influence the deflection. Finally, other influencing parameters include the composition of the ceramic substrate and the metal coating.

[0024] These inherent properties clearly distinguish metal-ceramic substrates from PCB circuit boards, which are significantly less critical than metal-ceramic substrates with regard to radius of curvature as well as hardness, strength, elasticity and spring force.

[0025] A further consideration that would have prevented the skilled person from applying the technical teaching described in DE 10 2009 032 210 A to metal-ceramic substrates is the smaller surface area of the metal-ceramic substrates compared to the surface area of the commonly used PCB circuit boards, which are usually available in sizes of 26 x 24 inches (650 x 610 mm).

[0026] A further consideration that would have prevented the skilled person from applying the teaching of DE 10 2009 032 210 A to metal-ceramic substrates is the oblique edge profile that usually occurs in metal-ceramic substrates, which complicates precise edge detection and precise positioning of the structuring layout (adapted to both sides of the metal-ceramic substrate), particularly in the case of metal-ceramic substrates that are to be structured on both sides.

[0027] Furthermore, DE 10 2009 032 210 A describes edge detection on a rotating wafer, which is not provided for in the context of the present invention.

[0028] What is essential in the method according to the invention described below is that the position of the metal-ceramic substrate in the exposure chamber is determined based on metal-free edges or metal-free points on the edges of the ceramic substrate.

[0029] In the context of the present invention, the following terms are used: Reference edge and reference point: The position of the metal-ceramic substrate is determined based on the position of a metal-free edge of the essentially rectangular substrate (reference edge) and the position of another metal-free point (reference point) on an edge essentially perpendicular to the reference edge. Reference points: The reference edge may also be not completely metal-free. In this case, the reference edge must be determined using the position of at least two reference points located in metal-free areas on an edge of the ceramic substrate. The reference edge is then defined by connecting the two reference points.

[0030] In the following, the metal-ceramic substrates according to the invention, which are used as starting materials in a structuring method according to the invention described further below, are described in more detail. Inventive requirement of the metal-free edge of the ceramic substrate:

[0031] Corresponding devices for the direct exposure of substrates are commercially available, although they have so far only been used for structuring PCB circuit boards, for example.

[0032] These devices are capable of detecting the position of the substrate, including a metal-ceramic substrate, in the exposure chamber and, using coordinate transformation, can ensure alignment of the layout to the precise position of the metal-ceramic substrate. For this purpose, defined locations on the metal-ceramic substrate in the exposure chamber must be captured by an image processing system.

[0033] For example, the edges of a metal-ceramic substrate can be used as defined locations. However, a metal coating in this edge area interferes with detection, so the ceramic substrate must be at least partially metal-free in the edge area, according to requirement a.

[0034] Therefore, the ceramic substrate is designed in such a way that it has no metal coating at least in some places in the edge area.

[0035] The number of metal-free areas in the edge region of the ceramic substrate can vary within the scope of the present invention, as long as it is ensured that sufficient accuracy is provided in the position detection of the metal-ceramic substrate in the exposure chamber.

[0036] The metal-ceramic substrates to be structured according to the invention can have a relatively small area. Thus, metal-ceramic substrates to be used according to the invention have an area of 100 x 150 mm to 200 x 250 mm, more preferably 115 x 165 mm to 185 x 235 mm, and even more preferably 130 x 180 mm to 170 x 210 mm. With such small metal surfaces to be structured on the ceramic substrate, optimal space utilization is advantageous. The metal-free surfaces along the edges of the ceramic substrate should therefore be selected to be as small as possible to provide sufficient area for structuring, while also being large enough to enable efficient position detection.

[0037] Therefore, it is part of the invention that in the metal-ceramic substrate according to the invention, at least at the locations where a position determination takes place, in the corresponding edge region, the metal coating runs substantially parallel to the ceramic edge and is set back, and a distance of the metal edge of the metal coating from the ceramic edge of generally at least 0.1 cm, more preferably at least 0.2 cm, even more preferably at least 0.3 cm. This distance of the metal coating from the edge of the ceramic substrate can be present if only partial areas of the edge are metal-free or if the entire edge of the ceramic substrate is metal-free (see the embodiments described below).

[0038] Furthermore, it is further preferred if, at least at the points of the edge region at which a position determination takes place, the metal coating runs substantially parallel to the ceramic edge and the metal edge of the metal coating has a distance of at most 0.8 cm, more preferably at least 0.7 cm, even more preferably at least 0.6 cm, from the ceramic edge.

[0039] Larger distances between the metal edge and the ceramic edge are disadvantageous in terms of area utilization, while smaller distances between the metal edge and the ceramic edge lead to inaccurate position detection in the exposure chamber.

[0040] In principle, there are several ways to determine the position of a metal-ceramic substrate in an exposure chamber based on defined locations on the metal-ceramic substrate

[0041] Assuming that the metal-ceramic substrate to be structured lies on a flat slide in the exposure chamber and that both the position determination and the structuring of the metal-ceramic substrate takes place vertically from above, the position detection of at least 3 points of the metal-ceramic substrate is required in order to describe its exact position and its rotation in the plane.

[0042] In the following, configurations of the metal-ceramic substrate are described which are either required or preferred for determining the position of the metal-ceramic substrate in the exposure chamber. First embodiment:

[0043] In one first embodimentThe position of the metal-ceramic substrate 1 in the exposure chamber is determined by detecting two reference edges 3 and 5, which are essentially perpendicular to each other. In this embodiment, the two reference edges 3 and 5 of the ceramic substrate, which are essentially perpendicular to each other, are metal-free. This first embodiment of the metal-ceramic substrate 1 is shown in Figure 1 The reference numbers have the following meaning: 1:Metal-ceramic substrate 2:metal-free edge area of the reference edge 3 3:Reference edge 4:metal-free area of the reference edge 5 5:Reference edge 6:Metal coating

[0044] In this first embodiment, the remaining edges of the ceramic substrate can also be metal-free or non-metal-free. From the perspective of the most optimal use of space for structuring, a design in which the remaining edge regions are not metal-free is preferred.

[0045] If, in the context of the present invention, two metal-free edge regions are arranged perpendicular to each other, the corners at which the perpendicular edges meet can nevertheless be rounded. Second embodiment

[0046] In one second embodimentThe position of the metal-ceramic substrate 1 in the exposure chamber is determined by detecting a completely metal-free reference edge 3 and a point on the reference edge 5, which is substantially perpendicular to the reference edge 3. This point on the reference edge 5, perpendicular to the reference edge 3, is referred to as reference point 7 in the context of the present invention. This second embodiment of the metal-ceramic substrate 1 is shown in the Figure 2 The reference edge 3 is completely, ie continuously, metal-free and the reference edge 5 perpendicular to the reference edge 3 has a partial area 4 which is also metal-free and in which the reference point 7 is located. The reference numbers in Figure 2 have the following meaning: 1:Metal-ceramic substrate 2:metal-free edge area of the reference edge 3 3:Reference edge 4:metal-free partial area at the reference edge 5 5:Reference edge 6:Metal coating 7:Reference point in the metal-free partial area 4 at the reference edge 5

[0047] The position of the metal-free partial region 4 around the reference point 7 can vary within the scope of the present invention; however, a metal-free partial region 4 in the center of the reference edge 5 is preferred in order to accurately determine the position of the metal-ceramic substrate 1 in the exposure chamber. When using a metal-free region 4 around the reference point 7 in the center of the reference edge 5, a possible angular error of the ceramic substrate, i.e., a deviation from the angle of 90° between the two reference edges 3 and 5, is reduced to a minimum. Furthermore, it is also possible for the metal-free region 4 to be placed around the reference point 5 close to the reference edge 3, whereby the reference point 5 and the reference edge 3 in this region can be captured by a single common camera. This reduces the number of cameras required to determine the position of the metal-ceramic substrate 1 in the exposure chamber.In this second embodiment of the metal-ceramic substrate 1 according to the invention, the metal-free reference edge 3 is preferably that edge of the metal-ceramic substrate 1 which has the greatest length, and the metal-free partial region 4 of the reference point 7 is then provided on the shorter reference edge 5 of the metal-ceramic substrate 1. Third embodiment

[0048] In one third embodimentThe position of the metal-ceramic substrate 1 in the exposure chamber is determined by detecting three points on two adjacent edges, wherein the adjacent edges are arranged substantially perpendicular to each other. In this case, the position of two reference points 8 and 9 on a reference edge 3 in two metal-free partial areas 2a and 2b of the reference edge 3 is first identified, and the position of the reference edge 3 in the exposure chamber is determined by these two reference points 8 and 9. With the help of the remaining reference point 7 on the reference edge 5 arranged perpendicular to the first reference edge 3, the position of the metal-ceramic substrate 1 in the exposure chamber can then be determined. The two reference points 8 and 9 are located on a reference edge 3 of the ceramic substrate in metal-free partial areas 2a and 2b, respectively. This third embodiment of the metal-ceramic substrate is shown in the Figure 3The reference numbers have the following meaning: 1:Metal-ceramic substrate 2a, 2b:Partially metal-free areas of the first reference edge 3:Reference edge 4:Metal-free partial area at the reference edge 5 5:Reference edge 6:Metal coating 7:Reference point in the metal-free partial area 4 of the reference edge 5 8:Reference point at the reference edge 3 9:Reference point at the reference edge 3

[0049] In this third embodiment, the metal-ceramic substrate 1 is therefore designed such that it has two metal-free partial regions 2a and 2b on the first reference edge 3 and a further metal-free partial region 4 on the reference edge 5, which runs perpendicular to the reference edge 3. In this third embodiment of the metal-ceramic substrate 1 according to the invention, the reference edge 3 with the two metal-free partial regions 2a and 2b is preferably the edge of the metal-ceramic substrate 1 which has the greatest length, and the metal-free partial region 4 of the reference edge 5 lies on the shorter edge of the metal-ceramic substrate 1. This configuration is shown in Figure 3shown. In this embodiment, it is further preferred that the distance between the reference points 8 and 9 is at least 50%, more preferably at least 70%, even more preferably at least 90% of the length of the reference edge 3 of the metal-ceramic substrate 1. The reference points are particularly preferably located in the corners of the reference edge 3 of the metal-ceramic substrate 1. This third embodiment of the present invention has the advantage that the reference edge 3 does not have to be completely metal-free and therefore more area is available overall for structuring the metal coating of the metal-ceramic substrate 1. This is particularly important with relatively small metal surfaces, such as those found in DCB substrates.In this third embodiment, it may further be preferred that the reference point 7 on the reference edge 5 be identified jointly with the adjacent reference point 8 of the reference edge 3 by a single common camera. Therefore, the reference point 7 can be provided close to the reference point 8 of the reference edge 3.

[0050] The metal-free partial regions 2a and 2b typically have a size of 20 to 60 mm 2< , more preferably 30 to 50 mm 2< , even more preferably 35 to 45 mm 2< .

[0051] The first to third embodiments described above define metal-ceramic substrates with the minimum required metal-free edge regions. Furthermore, it is also possible to form further partial regions of the ceramic edges without metal and to determine the position of the metal-ceramic substrate at these additional metal-free regions as well, in order to improve the accuracy of determining the position of the metal-ceramic substrate in the exposure chamber or to obtain further information about the geometric extent of the metal-ceramic substrate. Metal-free regions at the other edges of the metal-ceramic substrate are particularly suitable for this purpose.

[0052] The first to third embodiments described above provide for individual reference points to be determined at the metal-free edges of the ceramic substrate. In a further embodiment, it is possible for each individual point to be calculated from several individual points. By detecting a reference edge, the rotation of the substrate in the xy plane, which is created by the metal-ceramic substrate, is compensated.

[0053] The metal-ceramic substrates of the present invention to be structured accordingly are preferably produced by methods described in German patent applications DE 10 2014 215 377.8 and DE 10 2014 224 588.5. Accordingly, the metal-ceramic substrates to be used according to the invention are preferably produced by a method according to DE 10 2014 215 377.8, which is characterized by the following process steps: (1) Positioning an arrangement comprising at least a first metal layer, at least a second metal layer, and a ceramic substrate arranged between the first and second metal layers on a carrier; (2) Heating the arrangement resulting from process step (1) to a temperature such that the ceramic substrate and the two adjacent metal layers are bonded together to form a double-sided metallized ceramic substrate, wherein the carrier is inclined and / or curved in method step (1) before positioning the arrangement and / or the carrier is inclined in method step (1) after positioning the arrangement on the carrier and / or during method step (2).

[0054] In a further embodiment, the metal-ceramic substrate to be used according to the invention is produced by a method according to DE 10 2014 224 588.5, comprising the following method steps: (1) Positioning an arrangement comprising at least a first metal layer and a ceramic substrate on a carrier; (2) Heating the arrangement resulting from process step (1) to a temperature such that the ceramic substrate and the adjacent at least one metal layer are bonded together to form a metallized ceramic substrate, wherein the carrier in process step (1) has at least one support on at least one of its peripheral edges, on which the arrangement from process step (1) rests with at least one of its outer edges in at least one peripheral partial region of the arrangement, and the at least one support is arranged on the carrier in such a way thatthat the arrangement is inclined when positioned on the support of the carrier and / or the carrier with the at least one support is inclined in method step (1) after positioning the arrangement on the at least one support of the carrier and / or during method step (2), and wherein the carrier has at least one boundary in the form of at least one stop or at least one edge on at least one of its peripheral edges.

[0055] The metal-ceramic substrates obtained, for example, from these processes are then modified so that the corresponding areas at the reference edges are metal-free. Options for maintaining the corresponding areas at the reference edges metal-free include: In a first embodiment, the metal layer is made sufficiently small and placed centrally on the ceramic. Depending on the material combination produced, the metal layer can shift several millimeters during bonding due to the inclination of the substrate.

[0056] In a second embodiment, the metal layer is punched out in the corresponding edge areas for image recognition, and the metal layer is aligned to the ceramic using a stop system during bonding. This procedure is particularly suitable for the production of metal-ceramic substrates using the above-mentioned methods described in DE 10 2014 215 377.8 and DE 10 2014 224 588.5. The width of the punch (parallel to the ceramic edge) can be several millimeters, e.g., 5 to 10 mm. A larger punch is unnecessary for image capture and would potentially reduce the usable area.

[0057] In a third embodiment, subsequent removal of the metal layer is possible, but this is not technically or economically feasible.

[0058] In a fourth embodiment, the metal layer is designed so that after bonding, it is at least 0.5 mm smaller than the ceramic and is impacted on the opposite side during bonding. This results in a metal-free edge that can be used for image processing. The metal-ceramic substrates according to the invention are intended to be suitable for structuring by direct exposure.

[0059] For this purpose, the exposure corresponding to the layout to be created must be adjusted to the position of the metal-ceramic substrate in the exposure chamber. The metal-free areas or partial areas of the edges or points described above are captured in the exposure chamber by one or more cameras as described above. The position of the metal-ceramic substrate and the layout are then aligned, for example, using coordinate transformation.

[0060] Such processes are state of the art in printed circuit board (PCB) manufacturing. Reference is made, for example, to DE 10 2009 032 210 A.

[0061] However, when using ceramic circuit boards, for example DCB substrates, there are special features compared to the teaching of DE 10 2009 032 210 A, which have led to the technology of structuring by means of direct exposure not yet being transferred to metal-ceramic substrates, in particular DCB substrates.

[0062] In this regard, the first consideration is the dimensional accuracy of the ceramic substrates in terms of length and width, which typically exhibits a fluctuation of up to 1.5% in technically implemented processes. Further difficulties arise from the lack of angular conformity of the edges of the ceramic substrates used to each other, which in some cases deviates significantly from 90°, as well as the flatness of the ceramic substrates, which in some cases deviates significantly from ideal flatness, particularly in the edge area, which is nevertheless required according to the invention.

[0063] Ceramic substrates resulting from the known processes often have curved or bent edges and therefore cannot be detected with sufficient accuracy using optical edge detection devices.

[0064] Therefore, it is often necessary to machine the ceramic edges prior to the manufacturing step of bonding the metal coating to the ceramic substrate. This machining of the metal-ceramic substrates may be required on one, two, three, or all four edges of the ceramic substrate to ensure sufficient dimensional accuracy and perpendicularity. The number of edges to be machined depends on the number and location of the metal-free edge areas detected.

[0065] The precise ceramic edges required for edge detection according to the invention can be achieved, for example, by creating predetermined break lines using a laser or diamond scribing and then breaking off the edges. This eliminates the edge inaccuracies that arise during the production of the ceramic substrates. In this way, the inaccuracies in the external dimensions of the ceramic substrates can also be significantly reduced.

[0066] In the context of the present invention, ceramic substrates metallized on both sides are used, ie ceramic substrates which have a metal coating to be structured on both sides.

[0067] In addition to the metal-free edge regions, the metal-ceramic substrates according to the invention must also fulfill at least one further structural requirement in order to be structured using direct exposure technology. Inventive requirement for the flatness of the ceramic substrate:

[0068] The metal-ceramic substrates obtained from conventional processes generally do not have a perfectly flat structure. This deflection of the metal-ceramic substrates must be reduced as much as possible during exposure, as otherwise it can lead to errors in image processing during edge detection (blurring) and blurred exposure.

[0069] The required flatness of the metal-ceramic substrate of less than 800 µm, more preferably less than 500 µm, even more preferably less than 200 µm can be achieved in a first embodiment, for example, by fixing the metal-ceramic substrate to be structured between two transparent plates, for example glass plates or foils, and then exposing it.

[0070] In a second embodiment, in order to reduce this deflection, the ceramic substrates can be clamped with frames.

[0071] In a third embodiment of the present invention, the substrates can be suctioned in place using a vacuum. The flatness of the metal-ceramic substrates according to the invention is particularly present when the metal-ceramic substrates are fixed between two glass plates according to the first embodiment, clamped with frames according to the second embodiment, or suctioned in place using a vacuum according to the third embodiment.

[0072] To enable efficient edge detection, the metal-ceramic substrate according to the invention further has a roughness Ra of a maximum of 16 µm, more preferably a maximum of 13 µm, and even more preferably a maximum of 10 µm. Such a roughness can be achieved, for example, by laser processing the metal-ceramic substrate.

[0073] Furthermore, it is preferred if the metal-free edges or partial areas are present on both sides of double-sided metallized ceramic substrates.

[0074] In the case of double-sided coated metal-ceramic substrates, the following preferred embodiments should also be mentioned: In the case that the metal-ceramic substrate according to the invention has a ceramic thickness of 0.38 cm, the ratio of the metal coating thickness from the front side to the back side is preferably less than 2.5, more preferably less than 2.25, even more preferably less than 2. It is further preferred that the difference between the metal coatings is less than 200 µm, more preferably less than 175 µm, even more preferably less than 150 µm.

[0075] In the case where the metal-ceramic substrate according to the invention has a ceramic thickness of less than 0.38 cm, the ratio of the metal coating thickness from the front side to the back side is preferably less than 2.0, more preferably less than 1.75, and even more preferably less than 1.5. It is further preferred that the difference between the metal coatings be less than 150 µm, more preferably less than 125 µm, and even more preferably less than 100 µm.

[0076] In the case where the metal-ceramic substrate according to the invention has a ceramic thickness greater than 0.38 cm, the ratio of the metal coating thickness from the front side to the back side is preferably less than 3.0, more preferably less than 2.75, and even more preferably less than 2.5. It is further preferred that the difference between the metal coatings be less than 300 µm, more preferably less than 275 µm, and even more preferably less than 250 µm.

[0077] Overall, it is preferred if the difference between the metal coatings is less than 50%, more preferably less than 45%, even more preferably less than 40%, of the layer thickness of the ceramic substrate. Inventive method for structuring metal-ceramic substrates

[0078] In a further aspect, the present invention relates to a method for producing a structured metal-ceramic substrate as described above.

[0079] The method according to the invention is characterized, first of all, by using a metal-ceramic substrate as described above and subjecting it to structuring by direct exposure. The use of a direct exposure system eliminates the need for a film, as in photolithography, and generates light on the areas to be structured.

[0080] The structuring on the metal coating itself can be achieved through a direct exposure process using laser radiation or projectors. The projector projects a portion of the image and scans the entire surface, resulting in the complete image.

[0081] Devices suitable for direct exposure according to the invention usually comprise an exposure chamber with at least one edge image detection unit, at least one exposure unit and at least one specimen slide on which the metal-ceramic substrate is present.

[0082] In the context of the present invention, an exposure chamber is understood to be a space which has at least one object carrier, an edge image capture unit and an exposure unit.

[0083] The edge image detection unit is a unit capable of detecting the position of an edge of the metal-ceramic substrate.

[0084] The exposure unit is a unit that is capable of exposing a metal-ceramic substrate in such a way that a pattern is created on the metal coating.

[0085] The slide serves to fix the metal-ceramic substrate and can be designed to be movable.

[0086] The position of the metal-ceramic substrate according to the invention in the exposure chamber on the slide is determined by the position of at least (1) two metal-free reference edges that run essentially perpendicular to each other (cf. first embodiment of the metal-ceramic substrate according to the invention) (2) a metal-free reference edge and a reference point in a partial area of the edge essentially perpendicular to the reference edge (cf. second embodiment of the metal-ceramic substrate according to the invention) or (3) two reference points in metal-free partial areas of a first edge, forming a reference edge and a reference point in a metal-free partial area at an edge essentially perpendicular to the reference edge (cf. third embodiment of the metal-ceramic substrate according to the invention) certainly.

[0087] According to the invention, the edge detection is directed at the ceramic edge and not at the edge of the metal coating, since this can change during the method according to the invention due to structuring.

[0088] The positions of the edges or points described above are identified using an image capture unit. Each edge or point can be identified with a single camera, or two points, or all edges and points can be identified together using a single camera. Within the scope of the present invention, the use of separate cameras is preferred, since using a single camera would require the corresponding points for edge detection to be very close together, which would lead to disadvantages due to data extrapolation, or a very large camera field would have to be used, which would lead to a deterioration in image quality and thus in accuracy.

[0089] Alternatively, in all embodiments of the present invention, it is possible for only a single camera to be used to detect the position of the metal-ceramic substrate in the exposure chamber, and for the relative position of the metal-ceramic substrate to be changed from camera to camera either by moving the camera or by moving the metal-ceramic substrate. This embodiment has the advantage that only one camera needs to be used, but at the same time results in a slowdown of the inventive method due to the required relative displacement.

[0090] The accuracy of determining the position of the metal-ceramic substrate in the exposure chamber can be improved by determining the position of additional reference points on the ceramic substrate. Therefore, in a further embodiment, the metal-ceramic substrate according to the invention has additional metal-free regions, the position of which can be used to determine the position of the metal-ceramic substrate. These additional metal-free edge regions can be located on the same first and second edges (cf. the first to third embodiments described above) or on the other two edges.

[0091] An edge detection unit is used to detect the position of the metal-ceramic substrate on the slide. This edge detection unit comprises at least one edge illumination device, for example, arranged in the slide below the slide surface.

[0092] This edge lighting device enables the formation of an illuminated area in at least one edge region of the metal-ceramic substrate. In particular, the lighting unit is designed to illuminate all those areas of the metal-free edge of the ceramic substrate that are used to determine the position of the metal-ceramic substrate. These areas are illuminated with light emitted over the entire area. It may be necessary to use multiple edge lighting devices for the different metal-free areas of the metal-ceramic substrate.

[0093] In order to make the detection of the edges of the metal-ceramic substrate as simple as possible, it is preferably provided that for each edge of the metal-ceramic substrate a separate illumination area is provided to illuminate this edge.

[0094] At a distance from the specimen slide surface on which the metal-ceramic substrate is placed and the side opposite the illumination device, at least one edge image detection unit is provided, which identifies an edge section of the metal-ceramic substrate located in the illumination area and detects the edge section with precise position relative to the specimen slide.

[0095] In principle, at least one light source that emits light over a wide area is sufficient. An advantageous solution provides for the lighting unit to have a diffuser and at least one light source illuminating the respective lighting area.

[0096] A particularly simple way of integrating the illumination unit into the direct exposure device provides that the light sources and the diffuser are integrated into the specimen carrier of the metal-ceramic substrate.

[0097] A further advantageous solution provides that the slide has a slide plate forming a slide surface and that the light from the illumination unit passes through the slide plate.

[0098] In addition, it is possible for the slide plate to act as an optical diffuser, i.e. in addition to holding the object, it also acts as an optical diffuser.

[0099] The edge image capture unit used in the method according to the invention preferably comprises a telecentric lens with an optical axis that deviates by a maximum of 5° from a perpendicular to the slide plane. This prevents faulty edge images caused by obliquely running edge surfaces.

[0100] The position of the reference edge, reference points, or reference points on the metal-ceramic substrate according to the invention can be captured with a single camera or with multiple cameras. It is particularly cost-effective if the position of the respective edges and points can be captured with a single camera.

[0101] Furthermore, to derive or calculate a point or edge, multiple points can be recorded and mathematically combined into one. This results in freely combinable embodiments of the present invention.

[0102] Further details of the direct exposure device can be found in DE 10 2009 032 210 A.

[0103] After determining the position of the metal-ceramic substrate in the exposure chamber, the metal-ceramic substrate is structured by exposure essentially perpendicular to the metal-ceramic substrate from the same side as the edge detection or from both sides simultaneously. In the case of a substrate metal-coated on both sides, the two metal coatings to be structured can be structured by exposure simultaneously or sequentially. Simultaneous exposure of both sides of the ceramic substrate requires a microscope slide that allows simultaneous exposure and structuring from both sides.

[0104] During the determination of the position of the metal-ceramic substrate in the exposure chamber and the subsequent structuring, the metal-ceramic substrate is preferably fixed.

[0105] As already mentioned, DCB substrates typically exhibit some deflection due to their manufacturing process. This deflection must be reduced as much as possible during exposure, as otherwise it can lead to image processing errors when detecting edges (blurring) and blurred exposure. Therefore, according to the invention, a maximum permissible flatness was defined for the metal-ceramic substrates to be used.

[0106] To ensure this flatness is maintained during the edge detection and structuring process by exposure, the following previously described configurations are possible in the method according to the invention: A first possibility to prevent corresponding deflection of the metal-ceramic substrates during edge detection and structuring by exposure is to fix the metal-ceramic substrate between two transparent plates or films, for example, between two glass plates. The disadvantage of this first possibility is the risk of breakage of the glass and ceramic, as well as the risk of shortening, which in turn leads to incorrect exposure. A further disadvantage is the adhesion of contaminants and residues.

[0107] A second option to prevent corresponding deflection of the metal-ceramic substrates during edge detection and structuring by exposure is to clamp or mount the substrates in a frame. However, this carries the risk of mechanical damage to the ceramic substrates. Furthermore, depending on the design, the frames can completely or partially cover the edges of the substrates, which can lead to limitations during edge detection or prevent it altogether. Furthermore, the frame may limit the possible area for structuring.

[0108] A third option for preventing corresponding deflection of the metal-ceramic substrates during edge detection and structuring by exposure is to vacuum-hold the substrates. Clamping down in the embodiments described above exerts mechanical stress on the base material (e.g., point loading of a ceramic corner). This leads to, for example, ceramic particles detaching from the exposed material during the clamping down process and subsequently remaining in the clamping system. The particles can then become mechanically anchored, for example, in the mask during subsequent exposure cycles, thus leading to serial exposure errors. Larger particles can even result in irreparable damage (microcracks in the ceramic; mechanical metal imprints) to the exposed material.

[0109] The disadvantage of this third procedure is that it prevents simultaneous exposure of both sides. Therefore, in this embodiment, a second exposure step is required for the back of the metal-ceramic substrate, which makes precise alignment to a ceramic edge even more important to achieve the highest possible positioning accuracy between the layout on the front and back. It is also important to ensure that the same ceramic edge is captured after the substrate is flipped. Depending on whether the tilting is over the long or short substrate edge, the image processing position must be adjusted for one or the other edge.

[0110] Therefore, in a further embodiment of the present invention, the use of raised exposure nests is proposed. These nests consist of a soft base material, for example a rubber material such as Linatex®, or a foam material, through which the resulting particle can almost never get back onto the material to be exposed or onto the clamping device after the low-voltage process. The particle therefore remains in a non-critical area outside the clamping system and can be easily removed later. Exposure errors are thus effectively minimized. Should, contrary to expectations, a particle nevertheless become lodged between the clamping device and the material to be exposed, mechanical damage to the substrate can be virtually ruled out, since the particle can press into the soft nest during the clamping process and is not necessarily pressed into the substrate surface.

[0111] Localized stress on the corners and edges can be counteracted by designing a clamping fixture with a smaller footprint than the metal-ceramic substrate to be exposed. Thus, the low-pressure clamping system would not directly mechanically influence the edge area of the metal-ceramic substrate. The metal-ceramic substrate thus protrudes beyond the clamping system.

[0112] The exposure nest provided according to the invention has holes or capillaries in the soft base material through which a vacuum can be applied to the metal-ceramic substrate. Applying the vacuum then lowers the tension on the metal-ceramic substrate.

[0113] In summary, the method according to the invention therefore comprises in particular the following method steps: (a) providing a metal-ceramic substrate on a slide in a direct exposure device; (b) detecting the position of the metal-ceramic substrate to be patterned on the slide in the exposure chamber; and (c) exposing the metallic coating of the metal-ceramic substrate.

[0114] The method according to the invention can be carried out in an exposure chamber whose slide is designed such that at least 2 metal-ceramic substrates, more preferably at least 4 metal-ceramic substrates, even more preferably at least 6 metal-ceramic substrates, even more preferably at least 8 metal-ceramic substrates, are fixed on the slide and can be structured simultaneously by direct exposure.

[0115] For exposure of the metal-ceramic substrate, it is further preferred if the metal-ceramic substrate is clamped low, thus ensuring sufficient flatness. This clamping can be achieved, for example, with a special microscope slide arrangement.

[0116] The present invention is explained in more detail with reference to the following detailed description of the figures.

[0117] The present invention is explained in more detail with reference to the following figures: The Figures 1 to 3 show embodiments of the metal-ceramic substrate according to the invention, which have already been explained in more detail above. Figure 4 clarifies the inventive understanding of flatness. For the definition of flatness, please refer to the above explanations. Figure 5 shows different deflection orientations of common metal-ceramic substrates.

Claims

1. A metal-ceramic substrate in which at least one metal layer is provided on a substantially rectangular ceramic substrate, the ceramic substrate being at least partially free of metal coating in the edge region, being planar, and the planar metal layer provided thereon not extending, at least in part, to the edge of the planar ceramic substrate, and thus at least the partially metal-free edge region being formed, and the edge region which is free from metalization extending laterally to an imaginary line parallel to the ceramic edge, the distance of the imaginary parallel line to the ceramic edge being at most 1.5 cm, characterized in that the metal-ceramic substrate has a flatness of less than 1600 µm, the flatness of the metal-ceramic substrate being understood to mean a shape tolerance of the metal-ceramic substrate, within which shape tolerance the flat surface of the metal-ceramic substrate must be, the tolerance limits being created by two imaginary surfaces parallel to the ideally planar surface of the metal-ceramic substrate, the tolerance being exceeded in the case in which the actually-realized surface of the metal-ceramic substrate passes through one of the parallel surfaces, and the tolerance indicating the distance between the two imaginary parallel surfaces, and the size of the metal-ceramic substrate being 100 x 150 mm to 200 x 250 mm.

2. The metal-ceramic substrate according to claim 1, characterized in that in the metal-free edge region, the metal coating runs substantially parallel to the ceramic edge and is at a distance of at least 0.1 cm from the ceramic edge.

3. The metal-ceramic substrate according to claim 1 or claim 2, characterized in that in the metal-ceramic substrate, two edges arranged substantially perpendicular to one another are metal-free.

4. The metal-ceramic substrate according to claim 1 or claim 2, characterized in that an edge of the metal-ceramic substrate is metal-free, and the edge perpendicular to this edge of the metal-ceramic substrate comprises a subregion which is also metal-free.

5. The metal-ceramic substrate according to claim 1 or claim 2, characterized in that the metal-ceramic substrate comprises two metal-free subregions at a first edge, and a further metal-free subregion at an edge which runs perpendicular to the first edge.

6. A method for producing a structured metal-ceramic substrate, characterized in that the structuring of the metal layer on the substrate takes place via a direct exposure method, and a metal-ceramic substrate according to any of claims 1 to 5 is used.

7. The method according to claim 6, characterized in that the direct exposure method is carried out by using a direct exposure device comprising an exposure chamber comprising at least one edge image capture unit, at least one exposure unit and at least one specimen slide on which the metal-ceramic substrate is present.

8. The method according to claim 6 or claim 7, characterized by the following method steps: a. providing a metal-ceramic substrate on a specimen slide in a direct exposure device; b. detecting the position of the metal-ceramic substrate to be structured on the specimen slide in the exposure chamber; and c. exposing the metal coating of the metal-ceramic substrate.

9. The method according to claim 8, characterized in that the direct exposure device is designed such that it detects the position of the substrate to be structured on the specimen slide in the exposure chamber based on the position of edges or of points on the metal-free edge(s) of the ceramic substrate.

10. The method according to any of claims 6 to 9, characterized in that the position of the metal-ceramic substrate is determined based on two metal-free edges that run substantially perpendicular to one another.

11. The method according to any of claims 6 to 9, characterized in that the position of the metal-ceramic substrate is determined, based on a metal-free edge and a reference point in a metal-free subregion of the edge, substantially perpendicular to the reference edge.

12. The method according to any of claims 6 to 9, characterized in that the position of the metal-ceramic substrate is determined, based on two points in metal-free subregions of a first edge and of a point in a metal-free subregion at an edge, substantially perpendicular to the first edge.

13. A use of metal-ceramic substrates according to any of claims 1 to 5 in a method for structuring the metal coating(s) of the ceramic substrate.