How to connect electronic components

Abstract

To provide a method for connecting electronic components, capable of manufacturing a sandwich structure having particularly high bonding strength.SOLUTION: A method includes: (1) providing a sandwich structure including two electronic components A and B each including a metal contact surface, and a metal sintering composition positioned between a metal contact surface A' of the electronic component A and a metal contact surface B' of the electronic component B; (2) optionally, drying the metal sintering composition; and (3) sintering the sandwich structure. The metal sintering composition comprises, based on nonvolatile content, 80 wt.% to 100 wt.% of metal particles (i) having a particle size D90 in a range of 1 μm to 20 μm, the metal contact surface A' has an arithmetic mean roughness RaA, the metal contact surface B' has an arithmetic mean roughness RaB and at least one of a ratio RaA / D90 and a ratio RaB / D90 falls within a range of 0.05 to 0.3.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for connecting electronic components. [Background technology]

[0002] As used herein, the term “electronic component” refers to a component used in electronic equipment, each having at least one metallized contact surface or a contact surface made of metal, where metal or metallization may be, for example, alloyed or non-alloyed copper, silver, gold, palladium, aluminum, or nickel. Examples of such electronic components include diodes, LEDs (light-emitting diodes), dies, IGBTs (insulated-gate bipolar transistors), MOSFETs (metal oxide semiconductor field effect transistors), ICs (integrated circuits), sensors, heat sinks, resistors, capacitors, coils, connecting elements (e.g., clips), base plates, antennas, lead frames, PCBs (printed circuit boards), flexible electronics, ceramic substrates, metal-ceramic substrates, such as DCBs (direct copper bonded substrates), IMSs (insulating metal substrates), etc.

[0003] In the fields of power and consumer electronics, sintering of electronic components is a common method. As a bonding material, metal sintering pastes having a main component in which sinterable metal particles are dispersed are often used. A notable example of such metal sinterable pastes is silver sinterable paste, known to those skilled in the art. Sintering bonding is a very simple method for stable bonding of components, where the components to be bonded are transferred to a sandwich structure with their contact surfaces facing each other and a sintering bonding material, such as metal sintering paste, applied between them. The sandwich structure made using metal sinterable paste is then subjected to a drying and sintering process, during which a mechanically strong, electrically and thermally conductive bond is formed between the components. A mechanically strong bond between two components means the fixation of one component to or on a second component via their respective contact surfaces. [Overview of the project]

[0004] The objective of the present invention was to find a method for connecting electronic components that enables the manufacture of sandwich structures having particularly high connection strength.

[0005] This objective was achieved, on the one hand, by fine-tuning the roughness, more precisely the arithmetic mean roughness Ra, of one or both of the metal contact surfaces of the electronic components to be connected, and on the other hand, by using a metal sintered composition containing metal particles having a specific particle size D90. It was found that satisfying a specific quotient Ra / D90 is essential to the present invention. Accordingly, the present invention provides a method for connecting electronic components, comprising: (1) providing a sandwich structure comprising two electronic components A and B, each having a metal contact surface, and a metal sintered composition positioned between the metal contact surface A' of electronic component A and the metal contact surface B' of electronic component B; (2) optionally drying the metal sintered composition; and (3) sintering the sandwich structure. The metal sintered composition contains 80% to 100% by weight (weight%) of metal particles (i) having a particle size D90 in the range of 1 μm to 20 μm, based on its non-volatile content. Metal contact surface A' has an arithmetic mean roughness RaA, and metal contact surface B' has an arithmetic mean roughness RaB, The present invention relates to a method in which at least one of the quotients RaA / D90 and RaB / D90 is in the range of 0.05 to 0.3.

[0006] As used herein, the term "non-volatile content" means a content that does not contain volatile substances, and "volatile substance" means a substance having a boiling point or decomposition point of ≤280°C, and examples include, in particular, such organic solvents. The metal sintered composition does not have to contain the defined volatile substances.

[0007] The metal sintered composition may be a solid composition, such as a metal sintered preform. A metal sintered preform is, for example, a sheet-like piece of a non-sintered metal sintered composition, such as a dried non-sintered metal sintered composition, which is about 5 μm to 300 μm thick. This can be produced, for example, by applying a non-solid metal sintered composition to a flat support, drying it without sintering, and then peeling it off. Such a solid metal sintered composition is characterized by a low content of volatile substances.

[0008] The metal sintered composition is preferably a non-solid composition having a distinct liquid, particularly paste-like consistency, to varying degrees. A preferred example is a so-called metal sintered paste. In a preferred embodiment, the present invention therefore provides a method for connecting electronic components, comprising: (1) providing a sandwich structure comprising two electronic components A and B, each having a metal contact surface, and a non-solid metal sintered composition positioned between the metal contact surface A' of electronic component A and the metal contact surface B' of electronic component B; (2) optionally, but preferably, drying the non-solid metal sintered composition; and (3) sintering the sandwich structure. Non-solid metal sintered compositions, (i) Metal particles having a particle size D90 in the range of 1 μm to 20 μm, in an amount of 50% to 90% by weight, preferably 60% to 85% by weight, and particularly 70% to 85% by weight, (ii) at least one organic solvent in an amount of 10% to 50% by weight, preferably 15% to 40% by weight, and particularly 15% to 30% by weight, (iii) comprising at least one component other than components (i) and (ii) in an amount of 0% to 20% by weight, preferably 0% to 10% by weight, particularly 0% to 5% by weight, specifically 0.1% to 5% by weight, or even slightly 0.2% to 3% by weight, Metal contact surface A' has an arithmetic mean roughness RaA, and metal contact surface B' has an arithmetic mean roughness RaB, The present invention relates to a method in which at least one of the quotients RaA / D90 and RaB / D90 is in the range of 0.05 to 0.3.

[0009] Drying is understood to mean the removal of volatile substances, particularly organic solvents, from the applied, in particular, non-solid metal sintered composition. Steps (1), (2), and (3) form a (1)-(2)-(3) type process sequence, with step (2) as an optional step. In one embodiment of the method according to the present invention, step (1) may include drying, and therefore step (2) may be omitted. In another embodiment, step (1) may not include drying, or may include drying only partially, and the optional step (2) may be omitted or given preferential treatment. If step (2) is omitted here, it may be done in the course of step (3), or may overlap with this step. There may also be cases where drying is not necessary and therefore omitted.

[0010] Electronic components A and B each have at least one metal contact surface A' or B' of one of the types already described above, unless they are already made of metal. This sandwich structure is formed via metal contact surfaces A' and B' within the scope of the method according to the present invention.

[0011] The metal contact surface A' preferably has an arithmetic mean roughness RaA in the range of 0.1 μm to 2.5 μm, with a range of 0.5 μm to 2.0 μm, and a particularly preferred range of 0.75 μm to 1.5 μm. The same applies to the arithmetic mean roughness RaB of the metal contact surface B', which is also preferably in the range of 0.1 μm to 2.5 μm, particularly preferably in the range of 0.5 μm to 2.0 μm, and particularly in the range of 0.75 μm to 1.5 μm.

[0012] As already stated, the essential condition of the present invention is that at least one of the quotients RaA / D90 and RaB / D90 is in the range of 0.05 to 0.3.

[0013] Ra represents the arithmetic mean roughness according to the version of DIN EN ISO 4287 valid on the filing date. For example, the mean roughness Ra can be determined using a confocal microscope μsurf custom (NanoFocus AG, Germany). For this purpose, 3D images of the surface are taken at the metal contact surfaces A' and / or B'. The microscope 3D images can be analyzed using the software μSoft Analysis Premium (7.4.8872; NanoFocus AG, Germany). For this purpose, any deflection of the metal contact surfaces A' and / or B' in the 3D images must first be corrected. Then, the mean roughness Ra can be determined from the surface roughness profile using a Gaussian filter.

[0014] An arithmetic mean roughness RaA or RaB in a desired preferred range of 0.1 μm to 2.5 μm can be set using a suitable technique. Examples of suitable techniques include polishing, blasting, polishing, chemical etching, and laser structuring.

[0015] Abrasive grinding (wet or dry) can be performed, for example, by a rotary grinding wheel or grinding belt that can be moved vertically or horizontally in a manually operated or automated system. Examples of abrasive materials include diamond and cubic boron nitride. The particle size of the abrasive material may be in the range of, for example, 30 μm to 150 μm and can be selected according to the desired material removal.

[0016] During blasting, the metal contact surface in question can be treated by impacting it with particles such as sand or glass beads. A suitable diameter for the blasting particles is, for example, 40 μm to 70 μm. The blasting agent is preferably projected at high speed onto the surface to be treated using a compressed air blasting system having a pressure in the range of, for example, 2 bar to 10 bar.

[0017] Polishing results in surface smoothing, i.e., reduction of the arithmetic mean roughness. For this purpose, for example, an abrasive having a small particle size of less than 20 μm can be used.

[0018] Chemical etching using, for example, iron(III) chloride can also remove material and thus can produce the desired arithmetic mean roughness Ra without mechanically deforming the metal contact surfaces under discussion. For this purpose, the surface is immersed in an etching solution for several minutes to several days and then the surface is chemically attacked to remove the material.

[0019] In step (1) of the method according to the invention, the electronic components A and B are first brought into contact with each other. The contact is effected via a metal sintered composition which, as described above, may already be dry. For this purpose, a sandwich structure is provided in which the metal sintered composition is located between the electronic components A and B. The sandwich structure is an arrangement in which the two electronic components A and B are located one above the other and are arranged substantially parallel to each other.

[0020] The sandwich structure can be manufactured by a method known from the prior art. A related metal contact surface A' or B' of one of the electronic components A or B is provided with a metal sintered composition. Subsequently, the other component B or A is placed on the metal sintered composition applied to the metal contact surface A' or B' of the electronic component A or B with its metal contact surface B' or A'.

[0021] The metal sintered composition can be applied to the related metal contact surface A' or B' of the electronic component A or B by a conventional method. In the case of a non-solid metal sintered composition, for example, by a printing method such as screen printing or stencil printing. Alternatively, the application can also be carried out by dispensing technology, spraying, pin transfer or dipping. In the case of a solid metal sintered composition, the application can be carried out by placing or loading the solid metal sintered composition onto the related metal contact surface A' or B'.

[0022] The wetting layer thickness of the non-solid metal sintered composition is preferably in the range of 20 μm to 400 μm. The preferred wetting layer thickness depends, for example, on the selected application method. When the non-solid metal sintered composition is applied, for example, by screen printing, a wetting layer thickness of, for example, 20 μm to 60 μm may be preferred. For example, when the application is carried out by stencil printing, the preferred wetting layer thickness may be in the range of 20 μm to 400 μm. For example, in dispensing technology, the preferred wetting layer thickness may be in the range of 20 μm to 400 μm depending on the application tool used. For example, when using a hollow needle, the preferred wetting layer thickness may be in the range of 20 μm to 100 μm, or when using a slot die that also functions as a doctor blade, the preferred wetting layer thickness may be in the range of 50 μm to 400 μm.

[0023] Following the application of the metal sintered composition to the metal contact surface A' or B' of the electronic component A or B, this metal contact surface A' or B' of the electronic component A or B with the optionally partially or completely dried metal sintered composition is brought into contact with the corresponding metal contact surface B' or A' of the electronic component B or A connected via the metal sintered composition. Thus, between the connected electronic components A and B, there is a layer of the non-dried, partially or completely dried metal sintered composition that forms a sandwich structure.

[0024] According to a preferred embodiment, the content of the organic solvent in the dried metal sinterable composition is, for example, 0 wt% to 5 wt% based on the initial proportion of the organic solvent in the metal sintered composition. In other words, during drying according to this preferred embodiment, for example, 95 wt% to 100 wt% of the organic solvent originally present in the metal sintered composition is removed during drying.

[0025] The drying temperature in step (2) is preferably within the range of 100 °C to 150 °C. A typical drying time is, for example, within the range of 5 minutes to 45 minutes. To shorten the drying time, a vacuum, for example, at a pressure within the range of 100 mbar to 300 mbar can be used.

[0026] After the completion of step (1) or step (2), the sandwich structure is finally subjected to a sintering process.

[0027] In this specification, sintering is understood to mean the joining of two electronic components A and B by heating a metal sintered composition while preventing the metal particles from reaching the liquid phase. The solid mechanical connection formed is both electrically and thermally conductive, i.e., the metal sintered body formed between components A and B consists substantially or entirely of metal of metal particles (i).

[0028] This sintering step (3) of the method according to the present invention is preferably carried out under pressure. In the case of pressure sintering, the process pressure is preferably less than 30 MPa, more preferably less than 15 MPa. For example, the process pressure is in the range of 1 MPa to 30 MPa, more preferably in the range of 5 MPa to 15 MPa.

[0029] Actual sintering is carried out at temperatures such as 200°C to 280°C.

[0030] The sintering time is, for example, in the range of 2 to 60 minutes, preferably 2 to 10 minutes.

[0031] The sintering process can be carried out in an atmosphere that is not subject to any particular restrictions. On the one hand, sintering can be carried out in an oxygen-containing atmosphere. On the other hand, sintering can also be carried out in an oxygen-free atmosphere or in a vacuum. Within the scope of the present invention, an oxygen-free atmosphere is understood to mean an atmosphere in which the oxygen content is 300 ppm by weight or less, preferably 100 ppm by weight or less, and more preferably 50 ppm by weight or less.

[0032] Sintering is carried out using conventional equipment suitable for sintering, particularly pressure sintering, and the above-mentioned process parameters can be set in such equipment.

[0033] A further essential condition of the present invention is that the metal particles (i) contained in the metal sintered composition used in the method according to the present invention have a particle size D90 in the range of 1 μm to 20 μm, preferably >1 μm to 20 μm, and in particular the particle size D90 is in the range of 2 μm to 15 μm, or especially particularly 3 μm to 10 μm. The particle size D10 is preferably in the range of 0.2 μm to 2 μm, especially preferably in the range of 0.5 μm to 2 μm, and especially in the range of 0.7 μm to 1.5 μm.

[0034] As used herein in relation to metal particles (i), the term "particle size D90" means a primary particle size that can be determined by laser diffraction and is less than 90% of the volume fraction of the particle, and as used herein in relation to metal particles (i), the term "particle size D10" means a primary particle size that can be determined by laser diffraction and is less than 10% of the volume fraction of the particle. Laser diffraction measurements can be performed according to a wet determination method using a corresponding particle size analyzer, for example, a Mastersizer 3000 or Mastersizer 2000 from Malvern Instruments. In the wet determination method, for example, 1 g of type (i) metal particles can be dispersed in 200 ml of ethanol using ultrasound as part of sample preparation.

[0035] The metal of the metal particle (i) may be, for example, copper, or in particular silver. Coated metal particles are also possible, for example, in which a coating of silver or copper surrounds a core of another metal. The metal of the core may be a less noble metal such as nickel or copper.

[0036] The metal particles (i) may be metal flakes (metal platelets), spherical metal particles, or a mixture of metal flakes and spherical metal particles. Metal flakes alone are preferred. The aspect ratio of the metal flakes can be, for example, >5:1, for example >5:1 to several hundred:1. The aspect ratio of the spherical metal particles is 5:1 to 1:1, particularly 3:1 to 1:1. The aspect ratio of the particles is the quotient of their maximum length and minimum length, and thus represents the shape of the particles. In the case of metal flakes, the quotient of the maximum length and the minimum length is the quotient of the maximum length and the platelet thickness. This can be determined by evaluating electron microscope images by determining the dimensions of a statistically significant number of individual particles using a scanning electron microscope.

[0037] The metal flakes can have a specific surface area in the range of, for example, 1 m 2 / g to 5 m 2 / g. The spherical metal particles can have a specific surface area in the range of, for example, 1 m 2 / g to 8 m 2 / g. The specific surface area (m 2 / g) can be determined by BET measurement according to DIN ISO 9277:2014-01 (static volumetric method, gas used: nitrogen).

[0038] The metal flakes can have a tap density in the range of, for example, 1 g / cm 3 to 5 g / cm 3 . The spherical metal particles can have a tap density in the range of, for example, 3 g / cm 3 to 6 g / cm 3 . The tap density is the density of a solid that has been further compressed by tamping or vibration compared to its bulk density. The tap density (g / cm 3 ) can be determined according to DIN EN ISO 787-11:1995-10.

[0039] The metal particles (i) are usually coated. In this case, the weight given here includes the weight of the coating on the metal particles (i).

[0040] The coating described above may be a layer that adheres firmly to the surface of the metal particles (i). Typically, this is an organic coating. The content of the organic coating may be in the range of 0.5% to 2.0% by weight, for example, based on the metal. Generally, such an organic coating may contain 90% to 100% by weight of one or more fatty acids and / or fatty acid derivatives or amines. Examples of fatty acid derivatives include fatty acid salts and fatty acid esters in particular. Examples of fatty acids include caprylic acid (octanoic acid), capric acid (decanoic acid), lauric acid (dodecanoic acid), myristic acid (tetradecanoic acid), palmitic acid (hexadecanoic acid), margaric acid (heptadecanoic acid), stearic acid (octadecanoic acid), oleic acid (9-octadecenoic acid), arachidic acid (eicosanoic acid / eicosanoic acid), behenic acid (docosanoic acid), and lignoceric acid (tetracosanoic acid).

[0041] Type (i) metal particles are commercially available. Metal flakes are commercially available from companies such as Metalor or Ames Goldsmith. Spherical metal particles are commercially available, for example, from Ames Goldsmith.

[0042] Component (i) of the metal sintered composition may be a single metal particle type of type (i) or a combination of two or more metal particle types of type (i), the decisive factor being that component (i) of the metal sintered composition is characterized by a particle size D90 in the range of 1 μm to 20 μm, and preferably contains only one type of metal, specifically silver.

[0043] The component (ii) optionally included in the metal sintered composition, and in any case included in the non-solid metal sintered composition, is at least one organic solvent. Examples of suitable organic solvents include terpineol, N-methyl-2-pyrrolidone, ethylene glycol, dimethylacetamide, 1-tridecanol, 2-tridecanol, 3-tridecanol, 4-tridecanol, 5-tridecanol, 6-tridecanol, isotridecanol, 2-ethyl-1,3-hexanediol, 2-(2-ethylhexyloxy)-ethanol, benzyl alcohol, diethylene glycol monobutyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, dibasic esters (preferably glutaric acid, adipic acid or succinic acid dimethyl esters, or mixtures thereof), glycerol, diethylene glycol, triethylene glycol, and aliphatic, particularly saturated aliphatic hydrocarbons having 5 to 32 carbon atoms, more preferably 10 to 25 carbon atoms, and even more preferably 16 to 20 carbon atoms.

[0044] The preferred optional component (iii) included in the metal sintering composition is at least one component other than the metal particles (i) and the organic solvent (ii). Examples include metal particles other than type (i), pyrolytic metal precursors (metal precursor compounds), additives such as surfactants, defoamers and wetting agents, and polymers, such as cellulose derivatives, such as methylcellulose, ethylcellulose, ethylmethylcellulose, carboxycellulose, hydroxypropylcellulose, hydroxyethylcellulose and hydroxymethylcellulose.

[0045] Based on the metal sintered composition, the total weight percent of components (i) to (iii) is 100% by weight. Therefore, a non-solid metal sintered composition can be prepared by mixing components (i) and (ii) or (i) to (iii). Conventional apparatus known to those skilled in the art, such as a stirrer, a three-roll mill, a jet mixer and / or a dispersion mixer, can be used.

[0046] The method according to the present invention makes it possible to obtain a sintered sandwich structure characterized by high connection strength and low porosity of the metal sintered body connecting electronic components A and B of the sintered sandwich structure. The low porosity may be particularly low in the direct proximity region between the metal sintered body and the metal contact surfaces A' and / or B'. This is considered to be measurable as shear strength, if not the key to high connection strength. [Examples]

[0047] Examples 1-4 and Comparative Examples 5 and 6 of the present invention, general procedure: 1. Preparation of copper-ceramic substrate (27mm x 38mm) Examples 1, 2, and 4 of the present invention used copper-ceramic substrates having a copper contact surface modified with respect to arithmetic mean roughness Ra. The corresponding modifications were carried out by chemical etching using an aqueous iron(III) chloride solution (see Table 2).

[0048] In Example 3 of the present invention, the copper contact surface was modified by grinding with respect to the arithmetic mean roughness Ra. For this purpose, a copper-ceramic substrate was fixed to an automated system by vacuum suction, and its surface was machined longitudinally with a rotary diamond grinding wheel having a particle size of 126 μm while adding a cooling lubricant.

[0049] In comparative examples V5 and V6, instead of grinding, blasting was performed using glass beads with a diameter in the range of 40 μm to 70 μm at an air pressure of 4 bar.

[0050] 2. Manufacturing of silver sinterable paste First, an organic solvent and ethyl cellulose were homogenized at 80°C to form a solvent system. Next, silver particles were gradually added to the solvent system and completely dispersed. The raw materials used can be found in Table 1 (in weight percent).

[0051] [Table 1]

[0052] 3. Manufacturing of sandwich structures A specific silver sintered paste (see Table 1) was applied to the copper surface of a copper-ceramic substrate by stencil printing to a wet layer thickness of 150 μm (see Table 2). This was followed by a drying process in a convection oven in a nitrogen atmosphere at 140°C for 20 minutes. The dried silver sintered paste was then mounted onto silicon chips (4 mm × 4 mm) with a silver-metallized bottom surface using a Tresky semi-automatic chip placement machine. For this purpose, the chips were pressed into the dried paste with a force of 2000 g at 80°C for 2000 ms. The resulting sandwich structure was sintered in a hot press in a nitrogen atmosphere (<100 ppm oxygen) at 230°C under a pressure of 10 MPa for 3 minutes.

[0053] 4. Evaluation of connection strength To determine the connection strength, the shear strength of the sandwich structure was determined. For this purpose, a Nordson Dage 4000 Plus test apparatus was used. A shearing chisel was placed on the chip, i.e., on the upper component of the sandwich structure, at a height of 30 μm from the height of the sintered paste, and the chip was sheared at a speed of 300 μm / s at room temperature (21°C). The force until the connection failed was recorded with a 20 kN load cell.

[0054] [Table 2]

Claims

1. A method for connecting electronic components, comprising: (1) providing a sandwich structure comprising two electronic components A and B, each having a metal contact surface, and a metal sintered composition positioned between the metal contact surface A' of electronic component A and the metal contact surface B' of electronic component B; (2) optionally drying the metal sintered composition; and (3) sintering the sandwich structure. The metal sintered composition contains 80% to 100% by weight of metal particles (i) having a particle size D90 in the range of 3.0 μm to 6.3 μm, based on its non-volatile content. The metal contact surface A' has an arithmetic mean roughness RaA, and the metal contact surface B' has an arithmetic mean roughness RaB, A method wherein at least one of the quotients RaA / D90 and RaB / D90 is in the range of 0.05 to 0.

3.

2. The method according to claim 1, wherein the metal sintered composition is a solid composition or a non-solid composition.

3. A method for connecting electronic components, comprising: (1) providing a sandwich structure comprising two electronic components A and B, each having a metal contact surface, and a non-solid metal sintered composition positioned between the metal contact surface A' of electronic component A and the metal contact surface B' of electronic component B; (2) optionally, but preferably, drying the non-solid metal sintered composition; and (3) sintering the sandwich structure. The non-solid metal sintered composition is (i) Metal particles having a particle size D90 in the range of 3.0 μm to 6.3 μm, in an amount of 50% to 90% by weight, preferably 60% to 85% by weight, and particularly 70% to 85% by weight, (ii) at least one organic solvent in an amount of 10% to 50% by weight, preferably 15% to 40% by weight, and particularly 15% to 30% by weight, (iii) comprising 0% to 20% by weight, preferably 0% to 10% by weight, particularly 0% to 5% by weight, specifically 0.1% to 5% by weight, or even slightly 0.2% to 3% by weight, at least one component other than components (i) and (ii), The metal contact surface A' has an arithmetic mean roughness RaA, and the metal contact surface B' has an arithmetic mean roughness RaB, A method wherein at least one of the quotients RaA / D90 and RaB / D90 is in the range of 0.05 to 0.

3.

4. The method according to claim 1, wherein the arithmetic mean roughness RaA is in the range of 0.1 μm to 2.5 μm, preferably in the range of 0.5 μm to 2.0 μm, and particularly in the range of 0.75 μm to 1.5 μm.

5. The method according to claim 1, wherein the arithmetic mean roughness RaB is in the range of 0.1 μm to 2.5 μm, preferably in the range of 0.5 μm to 2.0 μm, and particularly in the range of 0.75 μm to 1.5 μm.

6. The method according to claim 1, wherein the metal of the metal particle (i) is copper or silver.

7. The method according to claim 1, wherein the metal particle (i) includes coated metal particles.

8. The method according to claim 1, wherein the metal particles (i) are metal flakes and / or spherical metal particles.

9. The method according to claim 1, wherein the metal particles (i) are coated.

10. A sintered sandwich structure that can be obtained by the method described in claim 1.

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