DE102013104739B4 - Metal-ceramic substrates and method for producing a metal-ceramic substrate - Google Patents

Abstract

Metal-ceramic substrate comprising at least one ceramic layer (2), which is provided on at least one surface side (2.1) with at least one metallization (3) with a layer thickness (D) of at least 0.1 mm, which is used to form conductor tracks and/or or contact or connection surfaces (5, 5a, 5b) is structured in such a way that in the outer edge area (3') of the structured metallization (3) there is a metallization section (3a, 3b) that extends at least in sections along the outer edge area (3'). reduced layer thickness (DR), the layer-thickness-reduced metallization section (3a, 3b) being provided with a coating of a filling material (6), the filling material (6) being made of a plastic material with a ceramic content and/or graphitized carbon content, characterized that a flush transition between the top of the metallization (3) and the top of the coating of the filler material (6) born ildet is.

Description

The invention relates to metal-ceramic substrates according to the preambles of claims 1 and 13 and a method for producing a metal-ceramic substrate according to the preamble of patent claim 14.

Metal-ceramic substrates in the form of printed circuit boards consisting of a ceramic layer and at least one metallization connected to a surface side of the ceramic layer and structured to form conductor tracks, contacts, contact or connection surfaces are known in a wide variety of designs. Such metal-ceramic substrates are used, for example, to construct power semiconductor modules.

• • - Oxidieren einer Kupferfolie derart, dass sich eine gleichmäßige Kupferoxidschicht ergibt;
• • - Auflegen des Kupferfolie mit der gleichmäßige Kupferoxidschicht auf die Keramikschicht;
• • - Erhitzen des Verbundes auf eine Prozesstemperatur zwischen etwa 1025 bis 1083°C, beispielsweise auf ca. 1071 °C;
• • - Abkühlen auf Raumtemperatur.

The so-called “DCB method” (“direct copper bonding”) is also known for connecting metal foils or metal layers forming the metallization to one another or to a ceramic substrate or a ceramic layer. In this case, metal layers, preferably copper layers or foils, are connected to one another and/or to a ceramic layer, using metal or copper sheets or metal or copper foils which have a layer or a coating (“melting layer”) on their surface sides a chemical compound of the metal and a reactive gas, preferably oxygen. In this example in the U.S. 3,744,120A or in the DE 23 19 854 A In the method described, this layer or this coating (“melting layer”) forms a eutectic with a melting temperature below the melting temperature of the metal (e.g. copper), so that by placing the metal or copper foil on the ceramic layer and heating all the layers, these are connected to one another can, namely by melting the metal layer or copper layer essentially only in the region of the melting layer or oxide layer. Such a DCB method then has the following method steps, for example:

• • - oxidizing a copper foil in such a way that a uniform copper oxide layer results;
• • - Laying the copper foil with the even layer of copper oxide on the ceramic layer;
• • - heating the composite to a process temperature between about 1025 to 1083°C, for example to about 1071°C;
• • - Cooling down to room temperature.

Furthermore, from the publications DE 22 13 115 A and EP 0 153 618 A the so-called active soldering process for connecting metal layers or metal foils forming metallizations, in particular also copper layers or copper foils, to a ceramic material or a ceramic layer is known. In this process, which is also used specifically for the production of metal-ceramic substrates, a connection is made between a metal foil, for example copper foil, and a ceramic substrate, for example aluminum nitride ceramic, at a temperature of between approx. 800-1000°C Manufactured using a brazing alloy 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 from the group Hf, Ti, Zr, Nb, Ce, creates a connection between the brazing alloy and the ceramic by a chemical reaction, while the connection between the brazing alloy and the metal is a metallic brazing connection is.

Methods for the surface connection of an aluminum layer with a ceramic layer are also known under the designation “direct aluminum bonding” (“DAB method”). In principle, adhesive connections or adhesive techniques using plastic adhesives, for example using adhesives based on epoxy resin, can also be used for such a bonding of two layers, and in particular also fiber-reinforced adhesives. In particular, the use of special adhesives that contain carbon fibers and/or carbon nanofibers and/or carbon nanotubes and/or adhesives with which a thermally and/or electrically highly conductive adhesive connection is possible is also known. Said connection technologies can, of course, also be used in combination if several metal layers are provided both on the underside and on the top side of the ceramic layer.

It is known that such metal-ceramic substrates are subject to high thermal cycling stresses in many applications, in which, for example, temperature changes between −40° C. and +125° C. can occur. Due to the different thermal expansion coefficients of the ceramic layer and the metallization or metal layer, considerable mechanical compressive or tensile stresses arise at the transition between these layers during temperature fluctuations, the gradient of which is particularly large in the ceramic material at the edge of the metal layer and leads to cracks in the area of the surface of the ceramic layer .

It is also known that the gradient of the tensile and compressive stresses can be reduced by structuring the metallization or metal layer, which is already often predetermined by the layout required for the circuit.

Various measures are already known for avoiding such cracking and increasing the thermal shock resistance of the metal-ceramic substrate. For example, from the DE 40 04 844 C1 a method for producing a structured copper metallization of a metal-ceramic substrate is already known, in which a structured metallization is created by appropriate etching techniques, which is weakened in places at its edges to reduce the gradient of the tensile and compressive stresses. In its general form, the teaching imparted here also includes previously known configurations of conductor tracks, contact surfaces or similarly structured metallizations as well as edge weakening, as are inevitably obtained when etching structures of metallizations and cannot be avoided.

A power semiconductor module is known from US 2008/0 164 588 A1, which has a ceramic layer, on the upper side of which at least one metallization is provided, which is structured to form contact or connection surfaces. Furthermore, at least one of the metallizations forming a contact or connection area has a metallization section with a reduced layer thickness that extends at least in sections along the outer edge region of the metallization. The entire power semiconductor module is encapsulated on the top.

Furthermore, from the U.S. 6,054,762 A , DE 199 27 046 B4 , EP 0 789 397 A2 a metal-ceramic substrate with a ceramic layer and a metallization located thereon is known, in which a metallization area with a reduced layer thickness is provided at least in sections in the outer edge region of the metallization.

A metal-ceramic substrate with a ceramic layer and contact surfaces arranged on this is known from US 2007/0 224 400 A1, the contact surfaces being provided with a metallization and having a layer thickness of only 20 μm. In individual design variants, a glass layer with a two-layer structure is provided in the outer edge area of the contact surfaces, namely comprising a first glass sub-layer and a second glass sub-layer, which extends over the outer edge area of the contact surfaces onto the underside of the ceramic layer and thus the entire edge area, including covers the front sides of the contact surfaces.

From the generic JP 2002 - 76 197 A and the EP 0 921 565 A2 are known in each case metal-ceramic substrates in which the metallization and the ceramic are covered by a coating of a filling material. In particular from the JP 2002 - 76 197 A it is known to supplement the filling material with a ceramic material.

Proceeding from the prior art mentioned above, the invention is based on the object of demonstrating a metal-ceramic substrate as well as the associated method for producing a metal-ceramic substrate which has improved thermal shock resistance. The object is achieved by a metal-ceramic substrate and a method for its production according to claims 1, 13 . and 14 solved.

According to a first aspect, a metal-ceramic substrate is provided, comprising at least one ceramic layer which is provided on at least one surface side with at least one metallization with a layer thickness of at least 0.1 mm, which is used to form conductor tracks and/or contact or connecting surfaces is structured in such a way that in the outer edge area of the structured metallization there is a metallization section with a reduced layer thickness that extends at least in sections along the outer edge area, the metallization section with the reduced layer thickness being provided with a coating of a filling material, the filling material consisting of a plastic material with a ceramic content and / or graphitized carbon portion is produced, wherein a flush transition between the top of the metallization and the top of the coating layer is formed from the filler material

The essential aspect of the metal-ceramic substrate according to the invention can be seen in the fact that the layer-thickness-reduced metallization section is provided with a coating of a filling material. A noticeable improvement in the resistance to temperature changes is particularly advantageously achieved by the coating according to the invention of the edge region of reduced layer thickness of the structured metallization. The filling material used is preferably compatible with various metallization processes, for example nickel bath, gold bath, silver bath, and is also resistant to acids and alkalis. Finally, the filling material also has a heat resistance of more than 350°C.

In a first variant of the metal-ceramic substrate according to the invention, the layer-thickness-reduced metallization section is particularly advantageously formed by a step-like outer edge section of the metallization, which is preferably coated over the entire surface with the filling material. The reduced layer thickness of the metallization section and the layer The total thickness of the filling material corresponds approximately to the layer thickness of the metallization, ie according to the invention there is a flush transition between the top side of the metallization and the top side of the layer made of the filling material. The layer of the filling material can also extend over the outer edge section into the adjoining etched-free area of the ceramic layer.

In a second embodiment variant of the metal-ceramic substrate according to the invention, the layer-thickness-reduced metallization section is formed by a recess preferably having a trough-like cross-section in the outer edge region of the metallization. The etching of such a recess having a trough-like cross-section advantageously results in a recess edge which effectively prevents the filling material from flowing off the edge into the etched-away region of the ceramic layer. The trough-like recess is preferably completely filled with the filling material.

In a further advantageous embodiment variant, the metal-ceramic substrate according to the invention is designed in such a way that the layer-thickness-reduced metallization section is produced by appropriate masking and etching of the metallization and/or by mechanical surface processing, in particular milling, and/or
that the outer edge region includes a central metallization region, which forms a contact or bonding surface for connecting an electrical component, wherein
polyimide, polyamide, epoxy or polyetheretherketone as the plastic material and silicon nitride, aluminum nitride, aluminum oxide or glass as the ceramic component, for example, and/or that the thermal expansion coefficient of the filling material is smaller than the thermal expansion coefficient of the metallization, and/or that the ceramic layer consists of oxide -, Nitride or carbide ceramics such as aluminum oxide or aluminum nitride or silicon nitride or silicon carbide or aluminum oxide is made with zirconium oxide, and / or
that the further surface side of the ceramic layer is provided with at least one further metallization, wherein the aforementioned features can in turn be provided individually or in any combination. Furthermore, the subject of the invention is a metal-ceramic substrate, wherein the metal-ceramic substrate comprises at least one ceramic layer which is provided on at least one surface side with at least one metallization with a layer thickness of at least 0.1 mm, which is used to form Conductor tracks and/or contact or connection surfaces is structured in such a way that a metallization section with a reduced layer thickness that extends at least in sections along the outer edge region is formed in the outer edge area of the structured metallization, the metallization section with the reduced layer thickness being provided with a coating of a filler material, the filler material is made of a plastic material with a ceramic component and/or graphitized carbon component, the layer-thickness-reduced metallization section being formed by a multiplicity of recesses and a flush transition between the upper side of the metallization and the top of the layer is formed from the filling material.

The invention also relates to a method for producing a metal-ceramic substrate comprising at least one ceramic layer which is provided on at least one surface side with at least one metallization with a layer thickness of at least 0.1 mm, in which for the formation of conductor tracks and/or Contact or connection surfaces, the metallization is structured in such a way that a metallization section with a reduced layer thickness that extends at least in sections along the outer edge region is produced in the outer edge region of the structured metallization. According to the invention, the layer-thickness-reduced metallization section is coated with a filler material, the filler material being made of a plastic material with a proportion of ceramic and/or graphitized carbon, with a flush transition between the top of the metallization and the top of the layer of the filler material being formed. Advantageously, the method according to the invention is technically easy to implement, so that no additional effort worth mentioning is required for the production of the metal-ceramic substrates according to the invention.

In an advantageous embodiment variant of the method according to the invention, an etching resist layer is applied to the metallization, namely where the metallization is to remain with the existing layer thickness. The metallization provided with the etching resist layer is then treated with an etching solution to produce the metallization section with reduced layer thickness until recesses of a predetermined depth are etched free in the areas of the metallization exposed by the etching resist layer. The etching resist layer is again removed from the metallization and the etched-open recesses are filled with the filling material, preferably completely. Finally, a further layer of etch resist is applied at least partially over the metallization and over the layer of filler material, specifically where the metallization and layer of filler material remain to form one or more pads and those from the width Areas of the metallization exposed to the etching resist layer are treated with an etching solution and completely removed down to the ceramic layer.

The expressions “approximately”, “substantially” or “roughly” mean deviations from the respective exact value by +/-10%, preferably by +/-5% and/or deviations in the form of changes that are insignificant for the function .

• 1 eine vereinfachte Schnittdarstellung durch eine erste Ausführungsvariante eines erfindungsgemäßes Metall-Keramik-Substrat,
• 2 eine vereinfachte Schnittdarstellung durch eine zweite Ausführungsvariante eines erfindungsgemäßes Metall-Keramik-Substrat,
• 3 eine vereinfachte Schnittdarstellung durch eine dritte Ausführungsvariante eines erfindungsgemäßes Metall-Keramik-Substrat,
• 4 eine vereinfachte Draufsicht auf das Metall-Keramik-Substrates gemäß 1,
• 5 eine vereinfachte Draufsicht auf das Metall-Keramik-Substrates gemäß 2,
• 6 eine vereinfachte Schnittdarstellung durch ein Metall-Keramik-Substrat umfassend eine vollflächig auf einer Keramikschicht aufgebrachte Metallisierung,
• 7 das Metall-Keramik-Substrat gemäß 6 nach Aufbringen einer Ätzresistschicht,
• 8 das Metall-Keramik-Substrat gemäß 7 mit der aufgebrachten Ätzresistschicht und nach dem Freiätzen von Ausnehmungen in der Metallisierung,
• 9 das Metall-Keramik-Substrat gemäß 8 nach dem Entfernen der Ätzresistschicht,
• 10 das Metall-Keramik-Substrat gemäß 9 nach Aufbringen einer weiteren Ätzresistschicht,
• 11 das Metall-Keramik-Substrat gemäß 10 nach Entfernen der randseitigen Metallisierung mittels Ätzen,
• 12 das Metall-Keramik-Substrat gemäß 11 nach Entfernen der weiteren Ätzresistschicht,
• 13 das Metall-Keramik-Substrat gemäß 7 nach Einbringen von kanal- oder bahnartigen Aussparungen in die Metallisierung,
• 14 das Metall-Keramik-Substrat gemäß 13 nach Einbringen einer randseitigen gestuften Ausnehmung in die Metallisierung mittels Ätzen,
• 15 das Metall-Keramik-Substrat gemäß 14 nach Auffüllen der freigeätzten Bereiche mit dem Füllmaterial und anschließenden Entfernen der weiteren Ätzresistschicht,
• 16 das Metall-Keramik-Substrat gemäß 7 nach Einbringen von kanal- oder bahnartigen Aussparungen in die Metallisierung,
• 17 das Metall-Keramik-Substrat gemäß 13 nach Einbringen einer randseitig gestuften Ausnehmung in die Metallisierung mittels Ätzen und Entfernen der randseitigen Metallisierungsabschnitte und
• 18 das Metall-Keramik-Substrat gemäß 17 nach Auffüllen des gestuften Randbereiches und eines Teils der anschließenden Oberfläche der Keramikschicht mit dem Füllmaterial sowie anschließenden Entfernen der weiteren Ätzresistschicht.

The invention is explained in more detail below with reference to the figures of exemplary embodiments. Show it:

• 1 a simplified sectional view through a first embodiment of a metal-ceramic substrate according to the invention,
• 2 a simplified sectional view through a second embodiment variant of a metal-ceramic substrate according to the invention,
• 3 a simplified sectional view through a third embodiment of a metal-ceramic substrate according to the invention,
• 4 a simplified top view of the metal-ceramic substrate according to FIG 1 ,
• 5 a simplified top view of the metal-ceramic substrate according to FIG 2 ,
• 6 a simplified sectional view through a metal-ceramic substrate comprising a metallization applied over the entire surface of a ceramic layer,
• 7 according to the metal-ceramic substrate 6 after application of an etching resist layer,
• 8th according to the metal-ceramic substrate 7 with the applied etching resist layer and after the etching of recesses in the metallization,
• 9 according to the metal-ceramic substrate 8th after removing the etch resist layer,
• 10 according to the metal-ceramic substrate 9 after applying another layer of etching resist,
• 11 according to the metal-ceramic substrate 10 after removing the peripheral metallization by etching,
• 12 according to the metal-ceramic substrate 11 after removing the further etching resist layer,
• 13 according to the metal-ceramic substrate 7 after introducing channel or track-like recesses in the metallization,
• 14 according to the metal-ceramic substrate 13 after introducing a stepped recess on the edge into the metallization by means of etching,
• 15 according to the metal-ceramic substrate 14 after filling the etched areas with the filling material and subsequent removal of the further etching resist layer,
• 16 according to the metal-ceramic substrate 7 after introducing channel or track-like recesses in the metallization,
• 17 according to the metal-ceramic substrate 13 after making a recess with stepped edges in the metallization by means of etching and removing the metallization sections at the edges and
• 18 according to the metal-ceramic substrate 17 after filling the stepped edge area and a part of the adjoining surface of the ceramic layer with the filling material and then removing the further layer of etching resist.

1 shows a simplified schematic representation of a section through an embodiment variant of a metal-ceramic substrate 1 according to the invention comprising at least one ceramic layer 2 with two opposite surface sides, namely a first and second surface side 2.1, 2.2.

2 and 3 also show schematic sectional representations of further embodiment variants and FIG. 4 shows a plan view of the first surface side 2.1 of the metal-ceramic substrate 1 according to the invention according to FIGS 1 and 5 a top view of the first surface side 2.1 of the metal-ceramic substrate 1 according to the invention 2 .

In the present exemplary embodiment, the first surface side 2.1 is provided with at least one metallization 3, which is preferably formed or produced by a foil or layer made of copper or a copper alloy and which is applied directly and extensively to the ceramic layer 2. In one embodiment of the invention, the second surface side 2.2 opposite the first surface side 2.1 is provided with a further metallization 4, which is preferably also formed or produced by a foil or layer made of copper or a copper alloy and/or aluminum or an aluminum alloy. The metallizations 3, 4 made of copper or a copper alloy preferably have a layer thickness D of at least 0.1 mm, preferably between 0.3 mm and 0.8 mm and when made of aluminum or an aluminum wire a layer thickness D between 0.1 mm and 25 mm, preferably between 0.3 mm and 3.0 mm.

The metallizations 3, 4 made of copper or a copper alloy are preferably connected over a large area directly to the first or second surface side 2.1, 2.2 of the ceramic layer 2 using the DCB method described above. The ceramic layer 2 is made here, for example, from an oxide, nitride or carbide ceramic such as aluminum oxide (Al2O3) or aluminum nitride (AlN) or silicon nitride (Si3N4) or silicon carbide (SiC) or aluminum oxide with zirconium oxide (Al2O3 + ZrO2) and has a layer thickness for example between 0.1 mm and 1.0 mm, preferably between 0.2 mm and 0.7 mm.

In the present exemplary embodiment, the metallization 3 that is connected to the surface of the first surface side 2.1 is structured in order to form at least one connection region or a connection area 5 for at least one electronic component, in particular a semiconductor component 7 . The structuring of the metallization 3 is preferably carried out by appropriate masking and subsequent etching of an as yet unstructured metallization applied over the entire area to the ceramic layer 2 (see FIG 6 ), with the structuring being at least partially already specified due to the layout required for the circuit. The metallization 3 can thus also be further structured to form conductor tracks, contacts and/or other fastening areas.

In the present exemplary embodiment, the basic idea of the invention is explained in more detail using, for example, a rectangularly structured metallization 3 for forming a connection surface 5, which is completely surrounded by exposed areas 2' of the ceramic layer 2. It goes without saying that, based on this basic idea, a large number of different structurings of the metallization 3 of a metal-ceramic substrate 1 can be produced, which are also supported by the idea according to the invention.

As is already well known, temperature fluctuations cause tensile stresses in the etched-free areas 2' of the ceramic layer 2, while the areas of the ceramic layer 2 connected to the structured metallization 3 are under compressive stress.

As a result, due to the gradient of the tensile and compressive stresses at the transition between the structured metallization 3 and the non-metallized areas 2 ′ of the ceramic layer 2 of the metal-ceramic substrate 1 , cracks can form in the ceramic layer 2 .

In order to reduce these mechanical stresses in the ceramic layer 2 and thus improve the thermal shock resistance, the structured metallization 3 has an outer edge region 3', which surrounds a preferably central metallization region 3" for the planar connection of the electronic component 7, which is structured in such a way that the outer Edge region 3 'of the structured metallization 3 is a metallization section 3a, 3b with a reduced layer thickness DR that extends at least in sections along the outer edge region 3'. According to the invention, this metallization section 3a, 3b with a reduced layer thickness is provided with a layer of a filling material 6. Here, the Layer thickness reduction removes part of the structured metallization 3, so to speak, “filled in” by the layer of the filling material 6, as a result of which an increase in the thermal shock resistance is achieved.

In 1 shows, for example, a first embodiment variant of the metal-ceramic substrate 1 according to the invention, according to which the layer-thickness-reduced metallization section is formed by a stepped outer edge section 3a of the metallization 3, i.e. the layer thickness D of the structured metallization 3 is such in the area of the outer edge region 3' reduced that a step-like edge section 3a is formed, ie a stepped transition S from the central metallization section 3" to the outer edge region 3'. Both the width B and the reduced layer thickness DR are selected depending on the external dimensions and the layer thickness D of the metallization 3 However, for reasons of electrical conductivity, the reduced layer thickness DR should not be less than half the layer thickness D of the metallization 3. For example, with a layer thickness D of the metallization 3 of approximately 0.3 mm, the step-like edge section 3a has a width B between 0.2 mm and 0.3 mm and a reduced layer thickness DR between 0.1 mm and 0.15 mm.

Alternatively or additionally, the layer-thickness-reduced metallization section can also be formed by a multiplicity of recesses of different shape and size.

The recesses can be formed by oval, slit-shaped, diamond-shaped or diamond-shaped indentations and/or by a meandering, stamp-shaped or sawtooth-shaped edge profile of the metallization section with reduced layer thickness. Due to the recesses, the connection is increased tion strength between the filling material 6 and the metallization 3 possible.

The step-like edge section 3a is preferably coated with the filling material 6 in such a way that there is an almost flush transition between the central metallization area 3" of the structured metallization 3 and the surface of the layer of the filling material 6. The surface of the filling material 6 can also be above the level of the Central metallization area 3 "of the structured metallization 3 are also available.

In a second embodiment of the metal-ceramic substrate 1 according to the invention 2 the metallization section with reduced layer thickness is formed by a recess 3b having a trough-like cross section in the outer edge region 3' of the metallization 3, which is produced by appropriate masking and etching of the upper side of the metallization 3. This trough-like recess 3b is preferably completely filled with the filling material 6, so that the trough-like recess 3b is preferably closed flush with the upper side of the metallization 3 by the layer of the filling material 6. The trough-like recess 3b extends along the outer edge region 3' of the structured metallization 3, with a preferably circumferential recess edge 3b' having the layer thickness D of the metallization 3 in the central metallization region 3". Furthermore, the trough-like recess 3b has a layer thickness D of 0 3 mm of the metallization 3 has, for example, a width B' between 0.2 mm and 0.3 mm and a depth T between 0.1 mm and 0.15 mm.

A plastic material, preferably epoxy resins with a proportion of a ceramic material or graphitized carbon, is preferably used as the filling material 6 . For example, polyimide or polyamides can be used as the plastic material and silicon nitride, aluminum nitride, aluminum oxide or glass can be used as the ceramic material, namely ALN, Si ₃ N ₄ , SiC, AL ₂ O ₃ . The thermal expansion coefficient or thermal expansion coefficient of the filling material 6 is preferably selected to be smaller than the thermal expansion coefficient or thermal expansion coefficient of the metallization 3 . Furthermore, the filling material 6 has, for example, a relative permittivity or dielectric constant between 2.5 and 6.5, preferably between 3.2 and 4.0.

In a third embodiment of the metal-ceramic substrate 1 according to the invention 3 the layer-thickness-reduced metallization section is again in the form of a step-like outer edge section 3a of the structured metallization 3 analogous to FIG. Here, however, unlike the first embodiment variant, the layer of filling material 6 extends over the outer edge region 3' of the metallization 3 into the etched-free region 2' of the ceramic layer 2, i.e. the transition region between the outer edge section 3a of the structured metallization 3 and the etched-away region 2 'The ceramic layer 2 is completely sealed with the filling material 6 or filled. In this embodiment variant, a part of the layer made of the filling material 6 is connected over a large area both to the structured metallization 3 and to the ceramic layer 2 .

Furthermore, the invention is a method for producing a metal-ceramic substrate 1 described above, the main process steps in the 5 until 15 are shown as examples.

In 6 A cross section through a metal-ceramic substrate 1 is shown as an example, which consists essentially of a ceramic layer 2 and a metallization 3 that is connected to the first surface side 2a of the ceramic layer 2 over its entire surface and is still unstructured. The metallization 3, which is preferably made of copper or a copper alloy, is connected to the ceramic layer 2 using the DCB method described above. It goes without saying that a metallization 3 made of aluminum or an aluminum alloy can also be provided, which is connected over a large area to the ceramic layer 2 via a direct aluminum bonding method. Other connection methods described at the outset, such as an active soldering method or a suitable adhesive method, can also be used. In 6 only a first metallization 3 is provided as an example. Further metallizations 4 have been omitted for reasons of clarity.

According to 7 In a first method step, an etching resist layer 8 is applied to the still unstructured metallization 3, specifically where the metallization 3 made of copper or a copper alloy with a layer thickness D is to remain. The etching resist layer 8 is produced by means of techniques known per se. For example, by applying a photoresist layer with appropriate masking of the surface of the metallization 3, subsequent exposure and curing of the photoresist layer.

In 7 those areas of the metallization 3 which are not covered by the etching resist layer 8 and which are to be removed by etching in the subsequent second method step are already indicated by dashed lines. For this purpose, in the second step, the metallization 3 provided with the etch resist layer 8 is subjected to an etchant for a predetermined period of time. The length of time depends on the etchant and is dimensioned in such a way that recesses 9 of the desired depth T are etched out of the metallization 3 . 8 shows the metal-ceramic substrate 1 provided with the etching resist layer 8 after the etching step has been carried out and the recesses 9 exposed by the etching.

In a subsequent third method step, the etching resist layer 8 is now removed from the surface of the metallization 3, using solvents known per se. In the present exemplary embodiment, the metal-ceramic substrate 1 is treated with the etchant until the recess 9 has been made with the desired depth T in the metallization 3, with the reduced layer thickness DR in the area of the recess 9 being at least half the original layer thickness D of metallization is 3. Finally, the metal-ceramic substrate 1 processed in this way is subjected to further surface cleaning.

In a fourth method step, the etched-free recesses 9 in the metallization 3 are filled with the filling material 6 and a layer is thereby formed, which preferably completely fills the recesses 9 . A screen printing method or stencil printing method, for example, is suitable for applying the filling material 6 . Excess filling material can also be removed using a squeegee. If necessary, the printing process has to be repeated several times in order to obtain a homogeneous filling of the recesses 9 . After the filling material 6 has hardened, the surface of the metallization 3 and the filled recesses 9 can be mechanically processed. 9 shows the metal-ceramic substrate 1 after the recesses 9 have been filled and the filling material or the insulating layer 6 has hardened. In the present exemplary embodiment according to FIG structured metallization 3 from.

According to a fifth method step, a further etching resist layer 10 is applied to the metallization 3 and the layer of the filling material 6, namely where the part of the metallization 3 made of copper or a copper alloy that forms the central metallization region 3" and the layer of the filling material 6 The further etching resist layer 10 is again produced by means of techniques known per se. 10 shows the metal-ceramic substrate 1 with the further etching resist layer 10.

Subsequently, in a sixth step according to 11 the area of the metallization 3 that is not covered by the further etching resist layer 10 is removed by etching, namely completely up to the ceramic layer 2 and the etched-free areas of the ceramic layer 2 are thereby formed. In the present exemplary embodiment, only the connection surface 5 covered with the further etching resist layer 10 remains.

Finally, according to a seventh step 12 the further etching resist layer 10 is removed by a suitable solvent, and the remaining stepped metallization 3 with the applied layer of the filling material 6 forms the connection surface 5 according to the invention. This creates a step-like transition to the etched-free area of the ceramic layer 2 in the outer edge area 3' of the metallization 3.

In an alternative embodiment of the method according to the 13 until 15 In a second process step, the metallization 3 provided with the etch resist layer 8 is treated with an etchant and a channel or track-like recess 11 is etched out of the metallization 3, which preferably extends over the entire layer thickness of the metallization 3, ie up to the ceramic layer 2. The channel or web-like recess 11 has a width of 0.3 mm to 2 mm, for example.

The etching resist layer 8 is then at least partially removed. Alternatively, this can also be completely removed and reapplied, so that according to 14 the opposite edge sections of the metallization 3, which are separated from one another by the channel-like or track-like recess 11, are not covered at the edge. In a further method step, the part of the metallization 3 that is not covered is exposed to an etchant in such a way that only part of the metallization 3 is removed and a step-like edge of the metallization 3 is formed.

In the next method step, both the step-like edge of the metallization 3 and the channel-like or track-like recess 11 between the etched-free sections of the metallization 3 are filled with the filling material, thereby forming a gap over the channel-like or track-like recess 11 and the insulation layer 6.

Finally, the etch resist layer 10 is again removed by a suitable solvent and the remaining stepped metallization 3 with the applied insulation layer 6 now forms a plurality of connection surfaces 5, 5a, 5b.

The production of the trough-like recess 3b takes place analogously to the method steps described by appropriate masking and subsequent controlled etching.

Alternatively, the step-like edge section 3a or the trough-like recess 3b can also be produced by a mechanical surface treatment method, for example milling.

In a further alternative embodiment of the method according to the 16 until 18 In a second process step, the metallization 3 provided with the etch resist layer 8 is treated with an etchant and a channel or track-like recess 11 is etched out of the metallization 3, which preferably extends over the entire layer thickness of the metallization 3, ie up to the ceramic layer 2. Then, in order to produce a stepped edge section 3a, the etching resist layer 8 is removed at least in the edge areas adjoining the channel-like or track-like recess 11 and an etchant is applied again. Alternatively, this can also be completely removed and a new, further etching resist layer 10 applied, so that the areas indicated by dashed lines in FIG. 16, edge sections of the metallization 3, can be etched away. For this purpose, in a further method step, the uncovered part of the metallization 3 is treated with an etchant in such a way that only a part of the metallization 3 is removed and a step-like edge section 3a of the metallization 3 is formed and, in a preferred embodiment, also the subsequent edge section the ceramic layer 2 is completely freed from the metallization 3.

In the next process step, both the step-like edge section 3a of the metallization 3 and a part of the surface of the ceramic layer 2 directly adjoining it are filled with the filling material, thereby forming an insulating layer 6 extending over the edge section 3a onto the surface of the ceramic layer. Finally, the etch resist layer 10 is again removed by a suitable solvent and the remaining stepped metallization 3 with the applied insulation layer 6 now forms at least one connection surface 5 .

In an advantageous embodiment variant, the metallizations 3, 4 can be at least partially provided with a metallic surface layer, for example a surface layer made of nickel, gold, silver or a nickel, gold and silver alloy. The layer thickness of the surface layer is between 0.1 microns and 10 microns, for example. Such a metallic surface layer is preferably applied to the ceramic layer 2 after the metallizations 3, 4 have been applied. The surface layer is applied using a suitable method, for example galvanically and/or by chemical deposition and/or by spraying.

In an embodiment variant that is not shown in the figures, a solder stop structure that at least partially surrounds the connection surface 5 can be provided between the connection surface 5 and the filling material 6, which solder stop structure is also produced from the filling material, for example. This is applied to the surface of the metallization 3, for example by means of a screen printing process. Alternatively, the solder stop structure can be produced by a glass-containing paste, which is burned into the metallization and, in the burned-in state, has a small coefficient of expansion compared to a metallization 3 formed from copper or a copper alloy.

reference list

1

metal-ceramic substrate

2

ceramic layer

2'

etched areas

2.1

first surface side

2.2

second surface side

3

structured metallization

3'

outer edge area

3"

central metallization area

3a

Metallization section or step-like edge section

3b

Metallization section or trough-like recess

3b'

recess edge

4

further metallization

5

land

6

filling material

7

semiconductor device

8th

etch resist layer

9

recesses

10

another layer of etch resist

11

channel or web-like recess

S

transition area

D

layer thickness

DR

reduced layer thickness

B

Width of the stepped border section

B'

width of the recess

T

depth of recess

Claims (20)

Metal-ceramic substrate comprising at least one ceramic layer (2), which is provided on at least one surface side (2.1) with at least one metallization (3) with a layer thickness (D) of at least 0.1 mm, which is used to form conductor tracks and/or or contact or connection surfaces (5, 5a, 5b) is structured in such a way that in the outer edge area (3') of the structured metallization (3) there is a metallization section (3a, 3b) that extends at least in sections along the outer edge area (3'). reduced layer thickness (DR), the layer-thickness-reduced metallization section (3a, 3b) being provided with a coating of a filler material (6), the filler material (6) being made of a plastic material with a ceramic content and/or graphitized carbon content, characterized That ge a flush transition between the top of the metallization (3) and the top of the coating of the filling material (6). forms is. metal-ceramic substrate claim 1 , characterized in that the layer-thickness-reduced metallization section (3a, 3b) is formed by a stepped outer edge section (3a) of the metallization (3). metal-ceramic substrate claim 2 , characterized in that the coating of the filling material (6) extends over the outer edge section (3a) into a subsequent etched-free area (2') of the ceramic layer (2). metal-ceramic substrate claim 1 , characterized in that the layer-thickness-reduced metallization section (3a, 3b) is formed by a recess (3b) having a trough-like cross section in the outer edge region (3') of the metallization (3). metal-ceramic substrate claim 4 , characterized in that the trough-like recess (3b) is completely filled with the filling material (6). Metal-ceramic substrate according to one of Claims 1 until 5 , characterized in that the layer-thickness-reduced metallization section (3a, 3b) is produced by appropriate masking and etching of the metallization (3) and/or by mechanical surface processing. Metal-ceramic substrate according to one of Claims 1 until 6 , characterized in that the outer edge region (3') includes a central metallization region (3"), which forms a contact or bonding surface for connecting an electrical component (7). Metal-ceramic substrate according to one of Claims 1 until 7 , characterized in that the plastic material is polyimide, polyamide, epoxide or polyether ether ketone and the ceramic component is silicon nitride, aluminum nitride, aluminum oxide or glass. Metal-ceramic substrate according to one of Claims 1 until 8th , characterized in that the thermal expansion coefficient of the filling material (6) is smaller than the thermal expansion coefficient of the metallization (3). Metal-ceramic substrate according to one of Claims 1 until 9 , characterized in that the ceramic layer (2) is made of oxide, nitride or carbide ceramics such as aluminum oxide or aluminum nitride or silicon nitride or silicon carbide or aluminum oxide with zirconium oxide. Metal-ceramic substrate according to one of Claims 1 until 9 , characterized in that a further surface side (2.2) of the ceramic layer (2) is provided with at least one further metallization (4). Metal-ceramic substrate according to one of Claims 1 until 11 , characterized in that the metallizations (3, 4) are connected to the ceramic layer (2) by means of a "direct copper bonding" method. Metal-ceramic substrate comprising at least one ceramic layer (2), which is provided on at least one surface side (2.1) with at least one metallization (3) with a layer thickness (D) of at least 0.1 mm, which is used to form conductor tracks and/or or contact or connection surfaces (5, 5a, 5b) is structured in such a way that in the outer edge area (3') of the structured metallization (3) there is a metallization section (3a, 3b) that extends at least in sections along the outer edge area (3'). reduced layer thickness (DR), the layer-thickness-reduced metallization section (3a, 3b) being provided with a coating of a filling material (6), the filling material (6) being made of a plastic material with a ceramic content and/or graphitized carbon content, with the metallization with reduced layer thickness ing section (3a, 3b) is formed by a multiplicity of recesses, characterized in that a flush transition is formed between the upper side of the metallization (3) and the upper side of the coating of the filling material (6). Method for producing a metal-ceramic substrate (2) comprising at least one ceramic layer (2), which is provided on at least one surface side (2.1) with at least one metallization (3) with a layer thickness (D) of at least 0.1 mm, in which, in order to form conductor tracks and/or contact or connection surfaces (5, 5a, 5b), the metallization (3) is structured in such a way that in the outer edge region (3') of the structured metallization (3) there is at least a section along the outer Metallization section (3a, 3b) with a reduced layer thickness (DR) extending from the edge area (3') is produced, the metallization section (3a, 3b) with the reduced layer thickness being coated with a filling material (6), the filling material (6) being made of a plastic material with a Ceramic portion and / or graphitized carbon portion is made, characterized in that a flush transition between the top of the metallization (3) and the upper side of the coating of the filling material (6) is formed. procedure after Claim 14 , characterized in that an etching resist layer (8) is applied to the metallization (3), specifically where the metallization (3) is to remain with the existing layer thickness (D). procedure after claim 15 , characterized in that the with the etch resist layer (8) provided metallization (3) to produce the layer-thickness-reduced metallization section (3a, 3b) is applied with an etching solution until recesses (9) of a predetermined depth (T) in the etching resist layer ( 8) released areas of the metallization (3) are etched free. procedure after Claim 16 , characterized in that the etching resist layer (8) is removed again from the metallization (3). procedure after Claim 16 or 17 characterized in that the etched-out recesses (9) are filled with the filling material (6). procedure after Claim 18 , characterized in that a further etching resist layer (10) is applied at least partially to the metallization (3) and to the coating of the filling material (6), specifically where the metallization (3) is used to form one or more connection surfaces (5 , 5a, 5b) remains. procedure after claim 19 , characterized in that the areas of the metallization (3) released by the further etching resist layer (10) are exposed to an etching solution and completely removed down to the ceramic layer (2).

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