Metal paste for ceramic substrate

Abstract

The invention relates to a metal paste for a ceramic substrate comprising a metal alloy Ni-Cu-Fe powder, a glass powder and additional additives.

Description

[0001] The present invention relates to a metal slurry, a method for obtaining the same and the use thereof.

[0002] describe

[0003] Substrates made of ceramics such as aluminum oxide (Al2O3) or aluminum nitride (AlN) are commonly used as circuit substrates for various electronic components. One method for forming circuits (conductor or metal layers) on, for example, ceramic substrates involves using a conductor or metal paste to form the circuit through a process of screen printing, drying, and firing.

[0004] Conductor or metal paste is generally a paste in which conductive powder and glass powder are dispersed in an organic medium.

[0005] Various metal pastes have been described in the past. For example, EP 2 164 822 B1 discloses a conductive paste for ceramic substrates comprising: a) a conductive metal powder containing silver and palladium; b) a glass powder; and c) an organic solvent, wherein the conductive metal powder has an average particle diameter of no greater than 1.2 μm, and the glass powder is a Bi2O3-SiO2-B2O3 glass powder, with the glass powder content ranging from 1% to 6% by weight, based on the weight of the paste. The paste described in EP 2 164 822 B1 allows the paste applied to the ceramic substrate to be sintered at a temperature of no greater than 650°C, while exhibiting excellent bonding strength to the ceramic substrate. However, the paste utilizes relatively expensive silver and palladium, which hinders its use in mass production.

[0006] WO 2014 / 195097 A1 describes a metal coating on a ceramic substrate. The metal coating is obtained by applying a metal slurry to the ceramic substrate and subsequently sintering it. The slurry may contain Ni powder, Fe powder, Cu powder, a glass powder MnO-SiO2-Al2O3 and an organic solvent. The Fe powder may be at least partially replaced by Ti powder and / or Al powder. Another glass powder described is made of ZnO-SiO2-B2O3-Al2O3-TiO2-ZrO2. The metal slurry is sintered at a temperature of 800°C to 900°C, preferably 830°C to 870°C. However, it turns out that when such a slurry is used, the sintering temperature and sintering time are not optimal.

[0007] It is therefore an object of the present invention to provide a metal paste for ceramic substrates which has an optimal sintering temperature and sintering time and which is at the same time solderable, brazable and bondable without further processing, exhibits oxidation resistance after sintering, as well as ferromagnetic or paramagnetic properties, and is electrically conductive.

[0008] This object is achieved by a metal paste having the features of claim 1 .

[0009] Therefore, a metal paste for a ceramic substrate is provided, comprising:

[0010] -metal alloy Ni-Cu-Fe powder,

[0011] - glass powder, and

[0012] - Additional additives.

[0013] The metal slurry according to the present invention combines several properties. Iron-nickel alloys are used in the chemical industry for their catalytic properties and for their mechanical, thermal, or magnetic properties. Copper-nickel alloys are commonly used in shipbuilding due to their high resistance to corrosion and seawater attack. In addition, these copper-nickel alloys have inherent antifouling properties. In Ni-Cu-Fe alloys, as in the present case, both advantages are combined.

[0014] In one embodiment of the present slurry, 60 to 80 wt %, preferably 65 to 76 wt %, more preferably 68 to 73 wt % (based on the total weight of the slurry) of Ni—Cu—Fe powder is used.

[0015] In one embodiment, the present slurry may additionally contain Fe powder and / or Ni powder and / or titanium (IV) oxide.

[0016] Therefore, in another embodiment, the slurry comprises 0.0 wt% to 5 wt%, preferably 1 wt% to 4 wt%, more preferably 1.2 wt% to 3 wt% (based on the total weight of the slurry) of Fe powder.

[0017] In yet another embodiment, 0.0 wt % to 5 wt %, preferably 1 wt % to 4 wt %, more preferably 1.2 wt % to 3 wt % (based on the total weight of the slurry) of Ni powder is added.

[0018] In yet another embodiment, the slurry comprises 0.0 wt% to 10 wt%, preferably 1 wt% to 8 wt%, more preferably 1.2 wt% to 5 wt% (based on the total weight of the slurry) TiO2.

[0019] In another embodiment, the glass powder is included in the paste in an amount of 3 to 15 wt %, preferably 5 to 10 wt %, more preferably 6 to 8 wt % (based on the total weight of the paste).

[0020] Additional additives may be added in amounts of 15% to 25% by weight of the additional additives.

[0021] In one embodiment, the metal paste has the following composition:

[0022] - 60% to 80% by weight, preferably 65% to 76% by weight, more preferably 68% to 73% by weight (based on the total weight of the slurry) of Ni-Cu-Fe powder;

[0023] 0.0 to 5 wt. %, preferably 1 to 4 wt. %, more preferably 1.2 to 3 wt. % (based on the total weight of the slurry) of Fe powder;

[0024] 0.0 to 5 wt. %, preferably 1 to 4 wt. %, more preferably 1.2 to 3 wt. % (based on the total weight of the slurry) of Ni powder;

[0025] - 0.0% to 10% by weight, preferably 1% to 8% by weight, more preferably 1.2% to 5% by weight (based on the total weight of the slurry) of TiO2;

[0026] 3 to 15 wt. %, preferably 5 to 10 wt. %, more preferably 6 to 8 wt. % (based on the total weight of the paste) of glass powder; and

[0027] 15% to 25% by weight of further additives, the sum of all constituents always totaling 100% by weight.

[0028] In an even further preferred embodiment, the metal paste has the following composition:

[0029] - 60 to 80 wt. % (based on the total weight of the slurry) of Ni—Cu—Fe powder,

[0030] - 0.0 to 5 wt% (based on the total weight of the slurry) of Fe powder;

[0031] - 0.0 wt% to 5 wt% (based on the total weight of the slurry) of Ni powder;

[0032] - 0.0 to 10 wt. % (based on the total weight of the slurry) of TiO2;

[0033] - 3 to 15 wt% (based on the total weight of the paste) of glass powder; and

[0034] 15% to 25% by weight of further additives, the sum of all constituents always totaling 100% by weight.

[0035] In a further preferred embodiment, the metal paste has the following composition:

[0036] - 65 to 76 wt% (based on the total weight of the slurry) of Ni-Cu-Fe powder;

[0037] - 1 to 4 wt% (based on the total weight of the slurry) of Fe powder;

[0038] -1 to 4 wt% (based on the total weight of the slurry) of Ni powder;

[0039] -1 to 8 wt% (based on the total weight of the slurry) of TiO2;

[0040] - 5 to 10 wt% (based on the total weight of the paste) of glass powder; and

[0041] 15% to 25% by weight of further additives, the sum of all constituents always totaling 100% by weight.

[0042] In yet an even further preferred embodiment, the metal paste has the following composition:

[0043] - 68 to 73 wt% (based on the total weight of the slurry) of Ni-Cu-Fe powder;

[0044] - 1.2 to 3 wt% (based on the total weight of the slurry) of Fe powder;

[0045] - 1.2 to 3 wt% (based on the total weight of the slurry) of Ni powder;

[0046] -1.2 to 5 wt% (based on the total weight of the slurry) of TiO2;

[0047] - 6 to 8 wt% (based on the total weight of the paste) of glass powder; and

[0048] 15% to 25% by weight of further additives, the sum of all constituents always totaling 100% by weight.

[0049] As will be discussed further in more detail below, additional additives (inorganic and organic) may include SiO2, binders, dispersants (eg, polymer esters), solvents, and / or diluents.

[0050] The metal paste of the present invention may be sintered at a temperature of 650°C to 1600°C, preferably 800°C to 1500°C, most preferably 900°C to 1400°C for 30 minutes and up to 12 hours, preferably less than 10 hours, most preferably less than 8 hours.

[0051] Sintering occurs in an inert or reducing atmosphere, preferably a reducing atmosphere. The reducing atmosphere may contain hydrogen and another inert gas, such as a mixture of hydrogen and nitrogen, preferably a mixture of up to 50 parts hydrogen and 50 parts nitrogen. A reducing atmosphere is preferred over an oxidizing atmosphere.

[0052] Due to these sintering parameters the metal paste is characterized by good adhesion on the ceramic component, good electrical conductivity and good paramagnetic properties.The ceramic component may be a substrate or carrier for a printed circuit board or any other ceramic component, eg a three-dimensional component.

[0053] Ni-Cu-Fe alloy powder

[0054] The Ni-Cu-Fe alloy powder provides magnetic properties and enables bonding, brazing, and welding of metal pastes.

[0055] In one embodiment, the Ni—Cu—Fe alloy powder comprises 15 to 35 wt % Ni (based on the total weight of the Ni—Cu—Fe alloy powder), preferably 18 to 30 wt %, and most preferably 20 to 28 wt %.

[0056] In another embodiment, the Ni—Cu—Fe alloy powder comprises 12 to 26 wt % Cu (based on the total weight of the Ni—Cu—Fe alloy powder), preferably 15 to 25 wt %, and most preferably 18 to 23 wt % Cu.

[0057] In yet another embodiment, the Ni—Cu—Fe alloy powder comprises 45 to 75 wt % (based on the total weight of the Ni—Cu—Fe alloy powder), preferably 50 to 70 wt %, and most preferably 55 to 65 wt % Fe.

[0058] In a preferred embodiment, the Ni—Cu—Fe alloy powder comprises:

[0059] - 15 to 35 wt% Ni, preferably 18 to 30 wt% Ni, most preferably 20 to 28 wt% Ni,

[0060] - 12 to 26 wt% Cu, preferably 15 to 25 wt% Cu, most preferably 18 to 23 wt% Cu, and

[0061] - 45 to 75 wt% Fe, preferably 50 to 70 wt% Fe, most preferably 55 to 65 wt% Fe,

[0062] Based on the total weight of the Ni—Cu—Fe alloy powder. Preferably, the sum of all components always amounts to 100% by weight.

[0063] In a preferred embodiment, the Ni-Cu-Fe alloy powder comprises 15 to 35 wt% Ni, 12 to 26 wt% Cu, and 45 to 75 wt% Fe, based on the total weight of the Ni-Cu-Fe alloy powder. Preferably, the sum of all components always totals 100 wt%.

[0064] In a more preferred embodiment, the Ni-Cu-Fe alloy powder comprises 18 to 30 wt% Ni, 15 to 25 wt% Cu, and 50 to 70 wt% Fe, based on the total weight of the Ni-Cu-Fe alloy powder. Preferably, the sum of all components always totals 100 wt%.

[0065] In a most preferred embodiment, the Ni-Cu-Fe alloy powder comprises 20 to 28 wt% Ni, 18 to 23 wt% Cu, and 55 to 65 wt% Fe, based on the total weight of the Ni-Cu-Fe alloy powder. Preferably, the sum of all components always totals 100 wt%.

[0066] The alloy powder is obtained by mixing the metals, melting the mixture and spraying the melt through an injector (preferably a Laval jet) to obtain the powder. The melt flows through the injector, wherein the melt is surrounded by an inert gas flow having the same flow direction.

[0067] The average particle size d90 of the Ni—Cu—Fe powder is about 3 μm to 60 μm, preferably about 5 μm to 50 μm, more preferably about 8 μm to 40 μm, and most preferably about 10 μm to 18 μm. The average particle size d50 of the Ni—Cu—Fe powder is about 1 μm to 40 μm, preferably about 2 μm to 30 μm, more preferably about 4 μm to 20 μm, and most preferably 4 μm to 12 μm (determined according to ISO 13320 using a Cilas 1064 laser particle size analyzer).

[0068] When Ni—Cu—Fe alloy powder is used, sintering time and temperature can be reduced compared to using a single metal powder (eg, Ni powder, Fe powder, or Cu powder).

[0069] Other metal powders

[0070] As described above, in addition to the Ni—Cu—Fe alloy powder, another metal powder may be added.

[0071] Fe powder enables bonding, brazing, and welding of metal pastes.

[0072] The average d50 particle size of the Fe powder is 0.5 to 20 μm, preferably 2 to 15 μm, more preferably 4 to 12 μm, most preferably 7 to 12 μm (determined according to ISO 13320 using a Cilas 1064 laser particle sizer).

[0073] Ni powder enables bonding, brazing, and welding of metal pastes.

[0074] The Ni powder has a d50 particle size of 3 to 20 μm, preferably 5 to 18 μm, most preferably 8 to 15 μm, and a d99 particle size preferably below 90 μm, and preferably below 80 μm (determined according to ISO 13320 using a Cilas 1064 laser granulometer).

[0075] However, it should be understood that the present slurry may also not contain any additional Fe powder and / or Ni powder.

[0076] TiO2 improves the adhesion of metal paste on ceramic substrates. In addition, using TiO2 instead of Ti is more cost-effective.

[0077] glass powder

[0078] Glass is used to create and improve the adhesion of the metal paste to the ceramic substrate. The glass also helps to lower the surface energy of the molten paste.

[0079] Currently used glass powders are based on Zn-Si-BO glass. Specifically, the glass powder contains ZnO, SiO2, and B2O3. Preferably, the amount of ZnO, SiO2, and B2O3 is 60 to 95 weight percent, more preferably 75 to 90 weight percent. The glass may also contain TiO2, ZrO2, Li2O, Na2O, CaO, Al2O3, or mixtures thereof.

[0080] In one embodiment, the glass powder may contain 25 to 45% by weight, preferably 30 to 35% by weight, of ZnO, 10 to 30% by weight, preferably 15 to 20% by weight, of B2O3, 20 to 40% by weight, preferably 25 to 35% by weight, of SiO2, and further oxides such as TiO2, ZrO2, Li2O, Na2O, CaO, and Al2O3. The sum of all components always amounts to 100% by weight. In one embodiment, the compounds TiO2, ZrO2, Li2O, Na2O, CaO, and Al2O3 may each be added in an amount of 0 to 7% by weight.

[0081] Glass melts at a temperature below 1500° C., preferably below 1200° C., and most preferably below 1000° C. Glass powder melts at a lower temperature by maintaining its properties.

[0082] The average particle size d50 is 0.5 to 10 μm, preferably 0.8 to 8 μm, more preferably 1.0 to 5 μm (determined using a Cilas 1064 laser particle sizer according to ISO 13320). Glass powders of this particle size provide optimal printability and sintering activity.

[0083] The glass powder in the slurry may also be mixed with two or more types of glass powders used in combination.

[0084] It should be noted that the present metal paste does not contain any (significant) amount of aluminum (Al). Only trace amounts of less than 1.3% by weight of Al may be present in the glass powder. The addition of Al is undesirable because Al impairs the properties of the paste due to its unfavorable properties in the paste or due to reactions with other compounds of the paste. Furthermore, Al impairs the magnetic properties of the paste.

[0085] Furthermore, CuO or CuO2 is not added to the paste, as the short sintering time is insufficient to completely reduce the oxides to metal, leading to anomalies during sintering and brazing. Tungsten (W) / tungsten oxide (WO2), molybdenum (Mo), or tantalum (Ta) are not added to the paste, as these metals increase the melting point. The paste does not contain lead (Pb).

[0086] As mentioned above, further additives may be included in the metal paste.

[0087] Solvents / diluents

[0088] Solvents and / or diluents are added to adjust the viscosity of the metal slurry for subsequent application, such as application on a ceramic substrate or carrier for a printed circuit board or any other ceramic component (e.g., a three-dimensional component). The slurry can be applied to the substrate or carrier for a printed circuit board or any other ceramic component (e.g., a three-dimensional component) by spraying the slurry onto the substrate or carrier for a printed circuit board or any other ceramic component (e.g., a three-dimensional component) using various printing techniques or by immersing the substrate in the slurry. After application, the solvent and / or diluent are removed during the drying and sintering process.

[0089] There is no particular limitation on the type of organic solvent / diluent. Examples of organic solvents / diluents include, but are not limited to, α-terpineol, butyl carbitol, butyl carbitol acetate, Texanol, octanol, 2-ethylhexanol, and mineral spirits. Preferred solvents / diluents are α-terpineol, butyl carbitol, butyl carbitol acetate, Texanol, octanol, 2-ethylhexanol, and mineral spirits.

[0090] The amount of solvent / diluent in the slurry is from 0.5 wt% to 15 wt%, preferably from 1.0 wt% to 11.0 wt%, more preferably from 1.5 wt% to 8.0 wt%.

[0091] SiO2 in amorphous and / or crystalline form acts as a thickener and determines the thixotropic properties of the metal paste. SiO2 can be added in an amount of 0.1 to 1 wt%, preferably 0.15 to 0.8 wt%, more preferably 0.18 to 0.6 wt%.

[0092] In one embodiment, fumed silica can be used. Fumed silica is a synthetically produced colloidal material with defined properties and particle size that is used as a filler in plastics. It consists entirely of amorphous silicon dioxide particles (SiO2) aggregated into larger units. The primary particle size of fumed silica is about 5 nm to 50 nm, and the BET specific surface area is 50 m 2 / g to 600m 2 / g. The aggregate size is 0.1μm to 100μm.

[0093] Use binding agent to provide the basic viscosity of paste consistency and slurry.Binder can be made up of organic liquid (such as short (C10) chain ether, medium (C50) chain ether or long (C100) chain ether and / or ester, carboxylic acid, fatty acid, cyclic and acyclic, linear or branched polyether or polyester) with low volatility that preferably has O as heteroatom in chain.Binder can also be the mixture of polymer powder dissolved in suitable solvent or the resin dissolved in solvent.The example of suitable polymer is polymethacrylate or nitrocellulose (both linear or branched), but is not limited to these.The example of such resin comprises ethyl cellulose resin, hydroxypropyl cellulose resin, acrylic resin, polyester resin, polyvinyl butyral resin, polyvinyl alcohol resin, rosin modified resin and epoxy resin.

[0094] The binder may be added in an amount of 10 to 20 wt %, preferably 12 to 18 wt %, and more preferably 13 to 16 wt %.

[0095] A dispersant (e.g., polymer ester) is used to improve mixing of all slurry components. The dispersant may be added in an amount of 0.1 to 0.3 wt %, preferably 0.12 to 0.2 wt %, more preferably 0.13 to 0.18 wt %.

[0096] The metal slurry is obtained in a process comprising the steps of:

[0097] - mixing a metal alloy Ni-Cu-Fe powder, optionally Fe powder, optionally Ni powder, optionally titanium(IV) oxide, glass powder and SiO2 to provide a first mixture;

[0098] - adding organic additives, in particular solvents, binders and dispersants, to the first mixture to adjust the viscosity;

[0099] - The mixture was blended until a (smooth) slurry was obtained.

[0100] The compounds of the slurry are provided in the amounts described above.

[0101] The compounds of the slurry are blended or mixed in a suitable blending or mixing device. The rotational speed of the mixing device should be adjusted so that the slurry is preferably not heated during the mixing process.

[0102] As mentioned above, metal pastes are used as conductor layers on ceramic components (eg, ceramic substrates for circuit boards), cooling devices, or 3D elements.

[0103] Suitable ceramic substrates may be oxide ceramics such as Al2O3, Al2O3-ZrO2, Al2O3-SiO2, Al2O3 / ZrO2 / Y2O3 or ZrO2, non-oxide ceramics such as AlN or Si3N4, but may also be dielectric materials or magnetic materials.

[0104] The present metal paste is applied to a ceramic substrate and subsequently sintered at a temperature greater than 650°C, preferably greater than 800°C, and most preferably greater than 900°C.

[0105] As previously mentioned, the metal paste according to the present invention is used to form circuits on ceramic substrates. For this purpose, solder is applied to the sintered metal paste on the ceramic substrate. The present metal paste has been shown to have high wettability, meaning solder can be applied very well to the paste and remains thereon, as well as high resistance to removal, meaning the solder does not remove the paste from the ceramic (i.e., preferably 95% of the paste should remain on the ceramic compound).

[0106] The specific sheet resistance of the conductor track applied to the ceramic is 100 to 220 milliohms / square, preferably 120 to 200 milliohms / square. The sheet resistance can be adjusted by adjusting the sintering conditions.

[0107] The present invention will now be described in more detail with reference to Examples.

[0108] The following examples are included to illustrate certain aspects and embodiments of the present invention as described in the claims. However, those skilled in the art will appreciate that the following descriptions are illustrative only and should not be construed as limiting the present invention in any way.

[0109] An embodiment of the metal paste according to the present invention may have the following composition:

[0110]

[0111] Components and amounts classified by inorganic and organic components:

[0112]

[0113] The sum of all constituents always adds up to 100% by weight.

[0114] The particle sizes of the different compounds used in the slurries were determined in each case in accordance with ISO 13320 using a Cilas 1064 laser particle sizer.

[0115] Preparation of NCF slurry:

[0116] The metal alloy Ni-Cu-Fe powder is obtained by mixing the metals, melting the mixture and granulating it to obtain a powder. The metal slurry is obtained in a method comprising the following steps:

[0117] - mixing a metal alloy Ni-Cu-Fe powder, optionally Fe powder, optionally Ni powder, optionally titanium(IV) oxide, glass powder and SiO2 to provide a first mixture,

[0118] - adding organic additives, in particular solvents, binders and dispersants, to the first mixture to adjust the viscosity,

[0119] - The mixture was blended until a (smooth) slurry was obtained.

[0120] The compounds of the slurry were provided in the amounts as described in the table above.

[0121] Wettability of metal paste

[0122] The ceramic with the paste baked onto it is immersed in a solder bath at a temperature of at least 250°C. The solder bath contains a lead-free solder made of tin, silver, and copper. The ceramic remains in the bath for approximately 10 seconds before being pulled out. When it is first pulled out, it is determined how much solder "sticks" to the paste; the more, the higher the wettability. After removal from the solder bath, more than 80% of the fired paste is wetted.

[0123] Solder leaching resistance

[0124] To determine the solubility of the metallization in the solder, the ceramic was dipped several times and the paste was checked after each dip to see if it remained attached to the ceramic. It is undesirable for the baked paste to alloy with the solder and / or separate. In these experiments, the paste according to the present invention showed little or no reaction with the solder, and more than 80% remained on the ceramic.

[0125] The bonding strength of the metal paste is greater than >5N / mm 2 The bond strength provides information about how strongly the metallization bonds to the ceramic. A nut is attached to the metallization (with glue if the metallization is not brazable or with solder if it is brazable) and then subjected to a tensile stress until the nut pulls off.

[0126] The specific resistance is 100 milliohms / square to 220 milliohms / square, preferably 120 milliohms / square to 200 milliohms / square. The specific resistance is measured using a conductor tape of defined length and width applied to a ceramic support and sintered (see above conditions). After sintering, the layer thickness is measured and the resistance of the conductor tape is measured using a multimeter by 2-point measurement and then standardized to a thickness of 10 μm to generate the specific resistance.

[0127] The durability or life of the metal paste is >500 cycles (as determined by impact testing - in 2 chambers with corresponding temperatures, 40°C for 15 minutes to 125°C in 7 seconds for 15 minutes, transferring the coated ceramic compound between the two chambers).

[0128] The increase in resistance after 1000 cycles was less than 2 ohms.

Claims

1. A metal slurry for a ceramic substrate, comprising: -metal alloy Ni-Cu-Fe powder, - glass powder, and - Additional additives. 2 . The metal paste according to claim 1 , wherein the metal paste comprises Fe powder and / or Ni powder and / or titanium (IV) oxide.

3. Metal paste according to one of the preceding claims, characterized in that - 60% to 80% by weight, preferably 65% to 76% by weight, more preferably 68% to 73% by weight (based on the total weight of the slurry) of the Ni-Cu-Fe powder; 0.0 to 5 wt. %, preferably 1 to 4 wt. %, more preferably 1.2 to 3 wt. % (based on the total weight of the slurry) of Fe powder; 0.0 to 5 wt %, preferably 1 to 4 wt %, more preferably 1.2 to 3 wt % (based on the total weight of the slurry) of Ni powder; - 0.0% to 10% by weight, preferably 1% to 8% by weight, more preferably 1.2% to 5% by weight (based on the total weight of the slurry) of TiO2; 3 to 15 wt. %, preferably 5 to 10 wt. %, more preferably 6 to 8 wt. % (based on the total weight of the paste) of glass powder; and 15% to 25% by weight of further additives, the sum of all constituents always totaling 100% by weight.

4. The metal paste according to claim 1 , wherein the Ni—Cu—Fe alloy powder comprises 15 to 35 wt.-% Ni, preferably 18 to 30 wt.-%, most preferably 20 to 28 wt.-%, 12 to 26 wt.-%, preferably 15 to 25 wt.-%, most preferably 18 to 23 wt.-% Cu, and 45 to 75 wt.-%, preferably 50 to 70 wt.-%, most preferably 55 to 65 wt.-% Fe, based on the total weight of the Ni—Cu—Fe alloy powder.

5. The metal paste according to claim 1 , wherein the Ni—Cu—Fe powder has an average particle size d50 of about 1 to 40 μm, preferably about 2 to 30 μm, more preferably about 4 to 20 μm, even more preferably 4 to 12 μm.

6. Metal paste according to one of the preceding claims, characterized in that the Fe powder has an average particle size d50 of 0.5 to 20 μm, preferably 2 to 15 μm, more preferably 4 to 12 μm, even more preferably 7 to 12 μm. 7 . The metal paste according to claim 1 , wherein the glass powder comprises ZnO, SiO 2 and B 2 O 3 . 8 . The metal paste according to claim 1 , wherein the glass powder has an average particle size d50 of 0.5 to 10 μm, preferably 0.8 to 8 μm, more preferably 1.0 to 5 μm.

9. Metal paste according to one of the preceding claims, characterized in that a solvent / diluent, in particular an organic solvent / diluent, is added.

10. The metal paste according to claim 9, characterized in that the solvent / diluent is one of the following: α-terpineol, butyl carbitol, butyl carbitol acetate, Texanol, octanol, 2-ethylhexanol and mineral spirits.

11. Metal paste according to one of claims 9 to 10, characterized in that the amount of solvent / diluent in the paste is 0.5 to 15 wt.-%, preferably 1.0 to 11 wt.-%, more preferably 1.5 to 8 wt.-%.

12. A method for obtaining a metal paste according to one of the preceding claims, comprising the following steps: - mixing a metal alloy Ni-Cu-Fe powder, optionally Fe powder, optionally Ni powder, optionally titanium(IV) oxide, glass powder and SiO2 to provide a first mixture; - adding organic additives, in particular solvents / diluents, binders and dispersants, to the first mixture to adjust the viscosity; - The mixture is blended until a (smooth) slurry is obtained.

13. Use of the metal paste according to one of claims 1 to 11 as a conductor layer on a ceramic substrate, on a cooling device or on a 3D component.

14. A ceramic substrate having a conductor layer obtained from the metal paste according to one of claims 1 to 11.

15. A method for obtaining the ceramic substrate according to claim 14, comprising the following steps: The metal paste according to one of claims 1 to 11 is applied to a ceramic substrate and sintered at a temperature greater than 650° C., preferably greater than 800° C., most preferably greater than 900° C., in a reducing atmosphere.

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