Patent Application
20230294213
The present invention relates to a method for producing a metal-ceramic substrate and to a metal-ceramic substrate produced by such a method.
Carrier substrates for electrical components, for example in the form of metal-ceramic substrates, are sufficiently known from the prior art, for example as printed circuit boards or circuit boards, for example from DE 10 2013 104 739 A1, DE 19 927 046 B4 and DE 10 2009 033 029 A1. Typically, conductor junction areas for electrical components and conductor tracks are arranged on one component side of the metal-ceramic substrate, whereby the electrical components and conductor tracks can be interconnected to form electrical circuits. Essential components of the metal-ceramic substrates are an insulation layer, which is preferably made of a ceramic, and a metal layer or component metallization joined to the insulation layer. Due to their comparatively high insulation strengths, insulation layers made of ceramics have proven to be particularly advantageous in power electronics. By patterning the metal layer, conductor tracks and/or conductor junction areas for the electrical components may be realized.
For such carrier substrates, in particular for metal-ceramic substrates, there is a problem with the insulation layer on the one hand and the metallization on the other hand, in that because of different thermal coefficients of expansion, thermomechanical strains may be induced or caused in the event of heat generation, for example during operation or production of the carrier substrate, which may result in bending or even damage to the carrier substrate.
It has therefore become well-established in prior art to provide backside metallization on a side of the insulation layer opposite the component metallizations to counteract bending by use of the appropriate symmetry, with regard to the thermal expansion coefficients in the stacking direction. However, since component metallization generally has no more than 0.8 mm of a thickness, symmetrical design of the backside metallization would result in a backside metallization formed appropriately to be very thin, not providing the thermal capacity required, which thermal capacity is in particular desired to dissipate heat or to provide a thermal buffer during overload situations.
Starting therefrom, it is the object of the present invention to provide a method for producing a metal-ceramic substrate and a metal-ceramic substrate the thermal shock resistance of which is improved compared to the methods and metal-ceramic substrates known from prior art.
This object will be achieved by providing a method for producing a metal-ceramic substrate as described herein and a metal-ceramic substrate as described herein. Further advantages and features will arise from the subclaims as well as the description and the accompanying figures.
According to a first aspect of the present invention, a method for producing a metal-ceramic substrate will be provided, comprising:
Further advantages and features will arise from the following description of preferred embodiments of the subject matter of the invention, while reference will be made to the accompanying figures. It is within the scope of the invention, to combine individual features of the individual embodiment, wherein in the figures:
Contrary to the methods known from prior art, a mechanical tool and/or a laser is to be used to define the geometry of the side faces, at least in some portions. In other words, the method according to the invention is used to implement a corresponding course of the side faces, for example to improve the thermal shock resistance of the bond between the at least one metal layer and the ceramic element. This has proven to be particularly advantageous when patterning or when forming the side faces is not done within a conventional etching process, in which a curved or oblique etching edge course is produced at the boundary region between the at least one metal layer and the ceramic element, which has an advantageous effect on the thermal shock resistance of the bond between the at least one metal layer and the ceramic layer.
Furthermore, it has proven to be advantageous to use a mechanical tool and/or laser light to define the geometry of the side faces, since this is a more precise and, in particular, more reproducible way of defining the side faces in terms of geometry thereof, in particular compared with etching to produce the side faces. By defining the geometry, in particular, it is to be understood that the action of the mechanical tool and the laser light creates a course of the side face which, in the fabricated metal-ceramic substrate, deviates from a course which is essentially straight and perpendicularly extends to the main extension plane or to the upper surface of the ceramic element. In particular, it is even possible to use a mechanical tool and/or a laser to set up side face courses specifically modulated in which, for example, a radius of curvature of the side face is modulated along a direction running parallel to the main extension plane and/or maxima and minima are locally formed in the course of the side face.
In particular, the fabricated metal-ceramic substrates are printed circuit boards in which the ceramic element serves as an insulation between two metal sections of the at least one metal layer. The individual sections of the at least one metal layer form conductor tracks and/or junctions where electrical or electronic components are attachable, which are carried by the ceramic elements or by the printed circuit board. By forming the side faces, in particular in the context of patterning, the individual metal sections of the at least one metal layer are separated from each another so that so-called insulation trenches will be realized between the individual metal sections, thus electrically insulating the individual metal sections from each other.
Furthermore, it is preferably conceivable that the course of the side face is defined or determined by a combination of an etching procedure and machining with a mechanical tool and/or laser.
Furthermore, it is particularly preferred that, in addition to the at least one metal layer, a backside metallization is provided on the side of the ceramic element opposite the at least one metal layer. Preferably, the backside metallization is provided to counteract deflection of the metal-ceramic substrate, which would otherwise be expected due to the different thermal expansion coefficients. In addition, in order to be able to provide a buffer during an overload situation, it is preferred that the backside metallization has a thickness appropriately large to provide sufficient heat capacity. In order to counteract bending caused by the comparatively large thickness of the backside metallization, it has proven to be advantageous to design the thickness of the at least one metal layer to be comparably large to the thickness of the backside metallization. Herein, too, the increased thickness of the at least one metal layer has proven to be particularly advantageous for increasing the heat capacity, since this may already cause effective heat dissipation on the component side. Basically, a thicker at least one metal layer and/or backside metallization also has proven to be advantageous as it increases the heat capacity, allowing better cooling and simultaneously increasing mechanical stability. This allows omitting a bottom plate, for example.
Preferably, the at least one metal layer is machined by means of a mechanical tool prior to and/or following joining to the ceramic element, preferably by means of different tools, whereby a plurality of different geometric shapes may be realized. Preferably, machining is performed by means of the mechanical tool and/or by means of the laser light prior to joining the at least one metal layer with the ceramic element and, following joining, the metal layer on the opposite side is machined by means of the same or a different mechanical tool, by means of laser light and/or by means of an etching agent for local removal of metal. Preferably, this is how patterning is performed. Machining of the metal layer is done on the opposite sides, preferably congruently along the stacking direction running perpendicular to the main extension plane.
Materials that are conceivable for use with the at least one metal layer or the backside metallization in the metal-ceramic substrate are copper, aluminum, molybdenum and/or the alloys thereof, as well as laminates such as CuW, CuMo, CuAl, AlCu and/or CuCu, in particular a copper sandwich structure having a first copper layer and a second copper layer, wherein a grain size in the first copper layer is different from the grain size in a second copper layer. Furthermore, it is preferred that the primary metal ply is to be surface-modified, in particular as a component metallization. Among the surface modification procedures that are conceivable are, for example, sealing with a noble metal, in particular silver and/or gold, or ENIG (“electroless nickel immersion gold”), nickel or edge grouting on the at least one metal layer to suppress crack formation or expansion.
Preferably, the ceramic element comprises Al2O3, Si3N4, AlN, an HPSX ceramic (i.e., a ceramic having Al2O3 matrix comprising an x percentage of ZrO2, for example Al2O3 including 9% ZrO2=HPS9 or Al2O3 including 25% ZrO2=HPS25), SiC, BeO, MgO, high-density MgO (>90% of the theoretical density), TSZ (tetragonally stabilized zirconium oxide) or ZTA as a material for the ceramic. It is also conceivable for the ceramic element to be designed as a composite or hybrid ceramic, in which a plurality of ceramic layers, which are different in terms of their material composition, are arranged on top of each other and are joined together to form an insulating layer in order to combine various desirable properties. It is also conceivable for a metallic intermediate layer to be arranged between two ceramic layers, which is preferably thicker than 1.5 mm and/or thicker than the two ceramic layers in total. Preferably, a ceramic that is as thermally conductive as possible is used for the lowest possible thermal resistance.
By “DCB process” (direct copper bond technology) or “DAB process” (direct aluminum bond technology) the person skilled in the art understands such a process which for example is used to join 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 metal or copper foils having a layer or a coating (surface-melt layer) on the their surface sides. In this process, described for example in U.S. Pat. No. 3,744,120 A or in DE23 19 854 C2, this layer or coating (surface-melt layer) forms a eutecticum having a melting temperature below the melting temperature of the metal (e.g., copper), so that by placing the foil on the ceramic and by heating all the layers, they can be joined together, and can be joined together by surface-melting the metal or copper essentially in the region of the surface-melting layer or oxide layer, respectively, only.
In particular, for example, the DCB process then comprises the following process steps:
By an active soldering method, e.g., for joining metal layers or metal foils, in particular also copper layers or copper foils, to ceramic material, a process is meant which is specifically also used for the production of metal-ceramic substrates, a bond between a metal foil, for example copper foil, and a ceramic substrate, for example aluminum nitride ceramic, is produced at a temperature between about 600-1000° C. using a hard solder which, in addition to a main component such as copper, silver and/or gold, also contains an active metal. This active metal, which is for example at least one element selected from the group consisting of Hf, Ti, Zr, Nb, Ce, creates a bond by chemical reaction between the solder and the ceramic, while the bond between the solder and the metal is a hard soldering joint. Alternatively, a thick film process is conceivable to be used for joining.
Hot isostatic pressing is known, for example, from EP 3 080 055 B1, the contents of which are herein explicitly included by reference regarding hot isostatic pressing.
Preferably, in the fabricated state the at least one metal layer is intended to taper at least in some portions when increasing the distance from the ceramic element. This has proven to be advantageous in particular for heat dissipation and allows the electrical components to be arranged as close as possible to the edge of the respective metal section of the at least one metal layer.
Furthermore, it is preferred for the at least one metal layer to have a thickness perpendicular to the main extension plane greater than 1 mm, preferably greater than 1.3 mm and particularly preferably between 1.5 and 3 mm. In particular, for metal-ceramic substrates having thicknesses such large, the use of a mechanical tool or laser light for separating individual sections in the at least one metal layer has proven to be advantageous, since this will create comparatively narrow isolation trenches, whereby the maximally dense pattern of conductive tracks and junctions may be realized. Otherwise, an aspect ratio of less than 1 would be realized by an etching process correspondingly, wherein aspect ratio defines a ratio of depth to width. Accordingly, the thickness of the at least one metal layer above 1 mm would cause a comparatively large distance between the two metal sections which are electrically insulated from each other in the at least one metal layer. In particular, it is advantageous if the recess between two sections of the at least one metal layer has an aspect ratio greater than 1, preferably greater than 1.5 and particularly preferred greater than 2.
Furthermore, it is preferred that machining using the mechanical tool and/or the laser light is carried out prior to joining the ceramic element to the at least one metal layer. In this way, it is advantageously possible to pattern and/or machine that side of the at least one metal layer facing the ceramic element in the joined state. Subsequently, the remaining metallization (preferably in the form of a rib) joining the individual metal sections (in particular on the side or surface side of the at least one metal layer facing away from the ceramic element) may be removed to ensure complete insulation between two adjacent sections of the at least one metal layer.
Furthermore, it is conceivable for the mechanical tool to be an embossing and/or punching device and/or to comprise a milling or sawing blade. The light used may be, for example, continuously emitted or pulsed light. What is preferred is an ultra-short pulse laser light, with light pulses the pulse length or pulse durations of which are shorter than one nanosecond.
Preferably, the geometry of the side face will be determined by tool guiding. For example, a specific lifting movement together with a lateral movement of the mechanical tool will result in a specific course to be printed or inserted into in the side face. Herein, for example, the movement of a tip of the milling tool can determine the curved course.
It is also conceivable for the geometry of the side face to vary along the circumference of the metal layer. In other words, by making use of a mechanical tool and/or a laser beam device to machine the side faces, it is possible to set a geometry that varies in some portions, and a geometry that varies along the direction of circulation around the outermost edge of the at least one metal layer. For example, the geometry can change with respect to a curvature of a curved course or, for example, the type of geometry changes, for example from curved side faces to oblique or stepped side faces.
Furthermore, machining is preferably carried out such that a rib connecting at least two portions of the at least one metal layer is realized. In particular, the rib is dimensioned such that it permits, for example, simple and dimensionally stable handling or transport of the at least one metal layer and thus permits simple arrangement from the ceramic element. It is also conceivable that the rib is not completely removed following joining the at least one metal layer to the ceramic element, but that portions of the rib are provided as a conductor junction area. In other words, the rib is only partially removed, i.e., an overhanging portion of the rib is remains in place, and is intended to create a bond to another metal portion and/or to an electrical component and/or an external control source.
Preferably, the rib is removed following joining, at least in some portions, for example by laser and/or etching and/or milling and/or spark erosion and/or an electrochemical process. In this way, the final separation of the sections in the at least one metal layer may be realized.
Furthermore, it is conceivable for the mechanical tool to comprise a milling tool, for example a milling head, and a saw blade and/or a punching or embossing member, the shape of which determines the geometry of the side face. This makes it possible to determine the geometry of the side face with the shape of the tool in a simple and easy manner and to define it in a reproducible and precise manner.
Furthermore, it is preferred for the fabricated side face, at least in some portions, to be oblique and/or bent and/or curved and/or stepped. Accordingly, the optimized geometry for the side face can be adjusted to suit the respective application, so that the fabricated metal-ceramic substrate has sufficient thermal shock resistance for a desired comparatively high service life of the metal-ceramic substrate to be guaranteed.
Preferably, the machining is to be performed by means of a plurality different mechanical tools. This allows further refinements in the geometry to be realized, in particular in a versatile manner. For example, different milling or embossing tools having different outer contours are used to realize different geometries or a specific course on the side face.
In particular, the at least one metal layer and/or the at least one additional metal layer are to be patterned prior to joining them to become the pre-composite.
Preferably, the at least one metal layer is divided into a plurality of insulated metal sections and subsequently the geometry of the side face of the insulated metal sections is determined. In other words: Following attaching the at least one metal layer to the ceramic element, the at least one metal layer is first electrically insulated from each other by inserting insulation trenches. The side faces, which extend, for example, essentially perpendicular to the main extension plane, are then brought into the desired geometric shape by the use of mechanical machining and/or laser light.
Alternatively, it is conceivable for the side face and geometry thereof to be determined simultaneously with the creation of the metal sections insulated from each other. This will promote the process, since no additional steps are required.
In particular, machining of the at least one metal layer to define a geometry, at least in some portions, of a side face not running parallel to the main extension plane is largely carried out using laser light. By “largely” it is meant that more than 50%, preferably more than 75% and particularly preferably more than 85% of the expenditure of time required for creating the side face is attributable to laser light machining.
Another object of the present invention is a method for producing a metal-ceramic substrate comprising the steps of:
Another object of the present invention is a metal-ceramic substrate produced by the method according to the invention. All properties and advantages described for the method may analogously apply to the metal-ceramic substrate and vice versa. In particular, the metal-ceramic substrate is a component of a power module and serves as a carrier for electrical or electronic components.
Furthermore, it is particularly preferred that a backside metallization 20 is provided on the ceramic element 30 on the side opposite the at least one metal layer 10, as viewed in the stacking direction S. The backside metallization 20 is provided in particular to counteract bending that would otherwise occur in operation, which is caused by thermomechanical strains that, in turn, result from different expansion coefficients in the at least one metal layer 10 and the ceramic element 30. At the same time, the backside metallization 20 is to provide sufficient heat capacity, which is desired in particular to provide an appropriate buffer in overload situations. In this context, the increased thickness of the at least one metal layer 10 also has proven to be particularly advantageous herein for increasing the heat capacity, since this may already cause effective heat dissipation on the component side. Basically, a thicker at least one metal layer 10 and/or backside metallization 20 also has proven to be advantageous because it increases the heat capacity, allowing better cooling, and at the same time increases the mechanical stability. This allows eliminating the need for a bottom plate, for example.
This requires a certain thickness of the backside metallization 20 to provide the desired heat capacity. In order to simultaneously ensure in turn a symmetrical design of the at least one metal layer 10 and the backside metallization 20, it is preferred for the at least one metal layer 10 to have a thickness D1 extending perpendicularly to the main extension plane HSE, which is greater than 1 mm, preferably greater than 1.3 mm or particularly preferably between 1.5 mm and 3 mm. Using such comparatively large thicknesses of the at least one metal layer 10, it is possible to realize a comparatively high symmetry between the at least one metal layer 10 and the backside metallization 20 and, at the same time, to ensure sufficient heat capacity by virtue of the backside metallization 20. In order to provide the surface of the ceramic element 30 with metal sections as densely as possible for such large thicknesses D1 of the at least one metal layer 10, it is desirable to realize comparatively narrow trenches, i.e., so-called isolation trenches, between the individual metal sections of the at least one metal layer 10.
It is preferred for a region between two metal sections of the at least one metal layer 10 to have an aspect ratio greater than 1, preferably greater than 1.5 and particularly preferably greater than 2. Since such aspect ratios cannot be realized by etching, or can only be realized at great expense, it is advantageous for such patterning of the at least one metal layer 10 to be realized by means of a mechanical tool 40 or by means of laser light. In this context, it is particularly preferred that the at least one metal layer 10 is patterned prior to joining, in particular prior to joining using a DCB, DAB-o-or active soldering method or using hot isostatic pressing, or is machined by means of a mechanical tool 40 and/or by means of laser light. For example, the mechanical tool 40 may be a milling tool and/or a stamping or embossing tool used to pattern the at least one metal layer 10. It is preferred for machining by means of the mechanical tool 40 or the laser light to be carried out such that the at least one metal layer 10 still remains transportable as a component. For this purpose, for example, separating individual metal sections from each other by means of the mechanical tool 40 or the laser light will be omitted, i.e., ribs 14 are realized between the metal sections in the at least one metal layer 10 which are sufficiently thick so that they do not bend during transport or handling by means of a robot, for example.
After the at least one metal layer 10 is arranged on the ceramic element 30, in particular such that the patterned side of the at least one metal layer 10 faces the ceramic element 30, a joining process, such as a direct joining process, a hot isostatic pressing method or an active soldering method, is preferably used to join the at least one metal layer 10 to the ceramic element 30.
In a subsequent process step, it is conceivable for the rib 14 connecting two adjacent metal portions of the at least one metal layer 10 to be partially or completely removed, for example by means of mechanical machining, by means of laser light or a chemical process or etching process. As a result, following joining, metal portions are provided on the ceramic element 10 which are arranged comparatively close to each other, thus providing comparatively narrow isolation trenches. It is also conceivable, for example, to use laser light or a mechanical tool 40 for removing the rib 14 only partially or in some portions, and, for example, to use rib portions laterally projecting from the upper side of the at least one metal layer 10 in the direction of the main extension plane HSE as junction lugs or junction regions, for example, to join different metal portions of the at least one metal layer 10 to each other and/or to realize a bond between components and/or to establish a junction to a an external controller.
Furthermore, it has proven to be advantageous that by using a mechanic tool 40 and/or laser light to form the geometry of the side face 15, this geometry can be created more reproducibly compared to creation thereof by an etching process, and it may also be modified more precisely. In particular, it is even conceivable that by means of the mechanical tool 40 and/or the laser light a radius of curvature along the side face 15 or 20 can be modified or is modified in a direction running parallel to the main extension plane HSE. This is generally not true in the case of isotope-mediated etching, wherein independent matching of the various portions of the side face 15 to each other is not possible or is possible to a limited extent only.
In particular, it has proven to be advantageous that comparatively thin isolation trenches may be realized by this combination of realizing the recess 50 or cavity in the preparation step and subsequently exposing it.
It is preferred for the at least one metal layer 10 to have a plurality of side surface sections 16 that are differently inclined with respect to the main extension plane HSE. In this regard, one of the side surface sections 16 may substantially be vertical or perpendicular to the main extension plane HSE. By setting different inclination angles of the side surface sections 16, it may advantageously be possible to stronger affect the electrical behavior of the adjoining metal sections of the at least one metal layer 10.
In the embodiment of the example of
In particular, in the example embodiment of
The example embodiment of
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2020 119 208.8 | Jul 2020 | DE | national |
This application is a National Stage filing of PCT/EP2021/070217, filed Jul. 20, 2021, which claims priority to DE 10 2020 119 208.8, filed Jul. 21, 2020, both of which are incorporated by reference in their entirety herein.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/070217 | 7/20/2021 | WO |
