Medium temperature co-fired alumina ceramic substrate matched with tungsten copper paste and preparation method thereof

Abstract

The application discloses a medium-temperature co-fired alumina ceramic substrate matched with tungsten copper paste and a preparation method thereof, and belongs to the technical field of electronic ceramic materials. The method comprises the following steps: taking Al2O3 powder as a matrix, adding sintering aids and rare earth oxides, grinding, mixing and drying to obtain mixed powder; adding a binder to the mixed powder, pressing to obtain a ceramic green body, and then performing glue removal; printing tungsten copper electronic paste on the surface of the glue-removed ceramic green body to form a tungsten copper conductive pattern layer; and placing the ceramic green body with the printed tungsten copper conductive pattern layer in a protective atmosphere for medium-temperature co-firing to obtain the medium-temperature co-fired alumina ceramic substrate matched with the tungsten copper paste. The ceramic substrate obtained by the method has the characteristics of compact structure, excellent mechanical properties, stable dielectric properties and good co-firing interface bonding, and is not prone to defects such as cracking, delamination, blistering and warping in the co-firing process with the tungsten copper paste.

Description

Technical Field

[0001] This invention belongs to the field of electronic ceramic materials technology, specifically relating to a medium-temperature co-fired alumina ceramic substrate matched with tungsten copper paste and its preparation method. Background Technology

[0002] Medium-temperature co-fired ceramics (MTCCs) are ceramic materials with moderate sintering temperatures, falling between high-temperature co-fired ceramics (HTCCs) and low-temperature co-fired ceramics (LTCCs). They possess both excellent mechanical properties and good dielectric properties. Compared to traditional high-temperature co-fired ceramics, MTCCs can effectively lower the sintering temperature, improve co-firing compatibility with high-conductivity metals (such as Au, Ag, and Cu), and significantly reduce production energy consumption and costs. Simultaneously, compared to low-temperature co-fired ceramics, MTCCs exhibit higher mechanical strength and better thermal stability, showing broad application prospects in fields such as electronic packaging substrates, multilayer ceramic devices, and high-reliability electronic modules.

[0003] Alumina ceramics are widely used as high-temperature co-fired ceramic matrix materials due to their high wear resistance, low dielectric loss, and good high-temperature thermal stability. However, traditional alumina ceramics typically require sintering above 1550℃ to achieve densification and obtain excellent mechanical properties. Excessively high sintering temperatures not only increase production costs but also easily lead to thermal stress concentration, cracking, and warping during co-firing with metal conductors, ultimately affecting the product's usability.

[0004] Currently, using sintering aids such as SiO2, TiO2, CaO, and MgO to promote liquid-phase sintering is an important method for reducing the sintering temperature of alumina ceramics. Although this method can achieve low-temperature densification of alumina ceramics, as the content of sintering aids increases, problems such as an increase in grain boundary glass phase, a decrease in microstructure uniformity, and a deterioration in mechanical properties can easily occur.

[0005] Tungsten-copper paste combines the high-temperature resistance of tungsten with the excellent conductivity of copper, making it a commonly used conductive material for medium-temperature co-fired ceramic substrates. However, during co-firing with tungsten-copper paste, the inconsistent sintering shrinkage behavior between the ceramic substrate and the conductive paste can easily lead to defects such as interfacial porosity, delamination, blistering, and cracking, affecting the continuity of the conductive layer and the reliability of the device. Therefore, the co-firing compatibility between the tungsten-copper paste and the alumina ceramic substrate remains a key factor affecting product performance and yield. Developing a medium-temperature co-fired alumina ceramic substrate capable of achieving high-density sintering at around 1400℃, while also possessing high flexural strength, good shrinkage compatibility, and stable interfacial bonding, is of great significance for improving the reliability and application performance of tungsten-copper co-fired devices. Summary of the Invention

[0006] The purpose of this invention is to provide a medium-temperature co-fired alumina ceramic substrate compatible with tungsten-copper paste and its preparation method. This method constructs a silicon-titanium-calcium-magnesium composite sintering aid system and introduces rare earth oxides as co-firing matching control components. This promotes the densification sintering of the alumina ceramic substrate at a lower sintering temperature, improving the substrate's flexural strength. Simultaneously, it controls the shrinkage behavior and interfacial bonding state between the ceramic substrate and the tungsten-copper paste during co-firing, reducing defects such as cracking, delamination, blistering, and warping that occur during co-firing. The resulting alumina ceramic substrate possesses high density, high mechanical strength, and good co-firing compatibility with the tungsten-copper paste.

[0007] In one aspect of the invention, a method for preparing a medium-temperature co-fired alumina ceramic substrate matched with tungsten-copper paste is provided. According to an embodiment of the invention, the method includes the following steps:

[0008] (1) Using Al2O3 powder as the matrix, sintering aids and rare earth oxides are added, ground, mixed and dried to obtain mixed powder;

[0009] (2) Add binder to the mixed powder, press to obtain ceramic green body, and then remove the binder;

[0010] (3) Print tungsten copper electronic paste onto the surface of the ceramic green body after glue removal to form a tungsten copper conductive pattern layer;

[0011] (4) The ceramic green body with the tungsten copper conductive pattern layer is placed in a protective atmosphere for medium-temperature co-firing. The heating rate is 2-8℃ / min, the sintering temperature is 1350-1450℃, and the holding time is 1-3h to obtain a medium-temperature co-fired alumina ceramic substrate that matches the tungsten copper paste.

[0012] Furthermore, the method for preparing the medium-temperature co-fired alumina ceramic substrate matched with tungsten-copper paste according to the above embodiments of the present invention may also have the following additional technical features:

[0013] In some embodiments of the present invention, in step (1): the mass ratio of the Al2O3 powder, sintering aid and rare earth oxide is (92-98):(2-8):(0.2-1); and / or, the rare earth oxide is one or more of La2O3, Y2O3, Nd2O3 and CeO2; and / or, the sintering aid is composed of SiO2, TiO2, CaO and MgO, and the mass ratio of SiO2, TiO2, CaO and MgO is (40-60):(20-30):(15-20):(15-20).

[0014] In this invention, Al2O3 powder is used to form the ceramic matrix, providing strength, hardness, insulation, and high-temperature resistance. Sintering aids are used to lower the sintering temperature and promote densification. Rare earth oxides are used to regulate grain boundaries, inhibit abnormal grain growth, and improve microstructure uniformity and material properties. SiO2, TiO2, CaO, and MgO are selected as composite sintering aids. SiO2 can form a low-melting-point liquid phase with CaO and MgO, promoting particle rearrangement and densification; TiO2 can increase the grain boundary diffusion rate and promote sintering neck formation; CaO helps improve the wettability of the liquid phase on Al2O3 particles; and MgO can inhibit abnormal grain growth. The synergistic effect of these components can improve the density and microstructure uniformity of the ceramic while lowering the sintering temperature. Rare earth oxides such as La2O3, Y2O3, Nd2O3, and CeO2 are selected mainly to utilize their segregation and pinning effects at grain boundaries, inhibiting grain boundary migration and abnormal grain growth, and improving grain boundary structure and bonding strength.

[0015] In some embodiments of the present invention, in step (1): the grinding is carried out by ball milling with anhydrous ethanol as the medium for 12-16 hours; and / or, the drying temperature is 60-100°C and the time is 8-12 hours. Through ball milling drying, the Al2O3 powder, sintering aid and rare earth oxide are fully mixed, reducing powder agglomeration, improving the dispersion uniformity of each component, forming a uniform grain boundary liquid phase during sintering, and promoting particle rearrangement and densification.

[0016] In some embodiments of the present invention, in step (2): the binder is one or more of polyvinyl alcohol, polyethylene glycol, and polymethyl methacrylate; and / or, the amount of binder added is 3%-8% of the total mass of the mixed powder.

[0017] In some embodiments of the present invention, in step (2): the pressing pressure is 200-400 MPa; and / or, the heating rate of the glue removal is 1-4℃ / min, the glue removal temperature is 500-650℃, and the holding time is 1-3h. When the pressing pressure is below 200 MPa, the green body density and strength are insufficient; when it is above 400 MPa, density gradients, delamination, or cracking are easily generated. When the glue removal heating rate is below 1℃ / min, the process cycle is too long; when it is above 4℃ / min, the gas generated by the decomposition of organic matter is difficult to be discharged in time, which easily causes blistering and cracking. When the glue removal temperature is below 500℃ or the holding time is less than 1 h, the organic matter is not removed sufficiently; when the temperature is above 650℃ or the holding time exceeds 3 h, energy consumption is easily increased.

[0018] In step (2), adding a binder to the mixed powder can improve the bonding force between powder particles and enhance the strength of the green body; pressing makes the particles tightly arranged, which improves the density of the green body. Subsequently, the organic components are removed by debinding to avoid the generation of pores and cracks during sintering, thus providing a basis for obtaining a uniform and dense ceramic structure.

[0019] In some embodiments of the present invention, in step (3), the tungsten-copper electronic paste includes tungsten-copper powder, an organic carrier, and a binder phase, wherein the mass ratio of the tungsten-copper powder, the organic carrier, and the binder phase is (80-85):(5-15):(5-10). The tungsten-copper powder, as a conductive functional phase, provides good electrical conductivity, thermal conductivity, and thermal matching performance; the organic carrier is used to adjust the paste's flowability and printing performance, and improve the paste's dispersion uniformity; the binder phase is used to enhance the interfacial bonding strength between the metal layer and the ceramic matrix. Through the synergistic effect of these three components, a ceramic metallized structure with strong adhesion, uniform structure, and stable performance can be obtained.

[0020] In some embodiments of the present invention, the mass ratio of tungsten to copper in the tungsten-copper powder is (70-85):(15-30); and / or, the organic carrier is one or more of terpineol, butyl carbitol, ethyl cellulose, fumed silica, and hydrogenated castor oil; and / or, the binder phase is one or more of ethyl cellulose, polyvinyl butyral, acrylic resin, and polyvinylpyrrolidone.

[0021] In some embodiments of the present invention, in step (3), the thickness of the tungsten copper conductive pattern layer is 5-30 μm; the printing is performed by screen printing. The tungsten copper electronic paste is printed onto the surface of the ceramic green body after adhesive removal, utilizing the fluidity and adhesion of the paste to form the conductive pattern layer.

[0022] In some embodiments of the present invention, in step (4), the protective atmosphere is nitrogen, a hydrogen-nitrogen mixture, or a weak reducing atmosphere. Through co-firing at medium temperature in the protective atmosphere, the alumina ceramic matrix is ​​densified, promoting the sintering and formation of the tungsten-copper conductive layer and its strong bond with the ceramic. Simultaneously, the protective atmosphere prevents metal oxidation and improves the conductivity, adhesion strength, and structural stability of the metallized layer.

[0023] In another aspect of the present invention, the present invention provides a method for preparing a medium-temperature co-fired alumina ceramic substrate that is matched with tungsten copper paste, thereby obtaining a medium-temperature co-fired alumina ceramic substrate that is matched with tungsten copper paste.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] (1) In view of the problems that easily occur during the co-firing of alumina ceramics and tungsten copper slurry, such as shrinkage mismatch, interface cracking, delamination, blistering and unstable bonding of conductive layer, this invention proposes a technical route of "composite sintering aid system to regulate ceramic shrinkage behavior + rare earth oxide to assist interface matching + simultaneous co-firing of tungsten copper slurry". During the sintering process, the composite sintering aid system composed of sintering aids (SiO2, TiO2, CaO, MgO) controls the densification rate and shrinkage initiation temperature of alumina ceramics by adjusting the formation temperature, viscosity and content of liquid phase, so as to make the sintering shrinkage more uniform; rare earth oxides preferentially agglomerate at grain boundaries and ceramic / metal interfaces during the sintering process, which can adjust the distribution and wetting behavior of liquid phase, so that the liquid phase is evenly spread in the interface area, thereby improving the wettability and interface bonding ability of tungsten copper slurry to alumina matrix.

[0026] (2) The densification temperature and shrinkage rate of the alumina substrate are controlled by composite sintering aids and rare earth oxides. At the same time, the sintering behavior of the metal layer is controlled by the ratio of tungsten copper powder to binder phase in tungsten copper paste. Combined with the thickness of the printed layer, the heating rate and the heat preservation system, the two can achieve shrinkage matching during co-firing, reducing warping, cracking and interface delamination.

[0027] During co-firing, the slurry shrinks synchronously with the ceramic substrate and forms a continuous bonding interface, thereby improving the practicality of the co-fired substrate.

[0028] (3) The present invention can achieve simultaneous co-firing of alumina ceramic substrate and tungsten copper paste at 1350-1450℃. The relative density of the obtained ceramic substrate can reach 99.2%, the bending strength can reach 411MPa, the tungsten copper conductive layer and the ceramic substrate interface are continuously bonded, and there are no obvious cracks, delamination, blistering and warping defects.

[0029] (4) The material obtained by the present invention has high density, good mechanical properties, stable conductive layer structure and excellent tungsten copper paste co-fired matching, and can be applied to electronic packaging substrates, multilayer co-fired ceramic devices and high reliability electronic modules. Attached Figure Description

[0030] Figure 1 The image shows a cross-sectional field emission scanning electron microscope (SEM) image of the medium-temperature co-fired alumina ceramic substrate prepared in Example 1 of the present invention and matched with tungsten copper paste.

[0031] Figure 2 This is a cross-sectional SEM image of the medium-temperature co-fired alumina ceramic substrate prepared in Example 2 of the present invention and matched with tungsten copper paste;

[0032] Figure 3 This is a cross-sectional SEM image of the medium-temperature co-fired alumina ceramic substrate prepared in Example 3 of the present invention and matched with tungsten copper paste;

[0033] Figure 4 This is a cross-sectional SEM image of the medium-temperature co-fired alumina ceramic substrate prepared in Comparative Example 1 of the present invention and matched with tungsten-copper paste.

[0034] Figure 5 The images shown are cross-sectional energy dispersive X-ray spectroscopy (EDS) images of the medium-temperature co-fired alumina ceramic substrate prepared in Example 2 of this invention and matched with tungsten copper paste. In the images, a is the overall EDS spectrum, b is the Y element surface distribution pattern, c is the Al element surface distribution pattern, d is the O element surface distribution pattern, e is the Si element surface distribution pattern, f is the Mg element surface distribution pattern, g is the Ca element surface distribution pattern, and h is the Ti element surface distribution pattern.

[0035] Figure 6 X-ray diffraction (XRD) images of the medium-temperature co-fired alumina ceramic substrates matched with tungsten-copper paste prepared in Examples 1-3 and Comparative Example 1 of this invention;

[0036] Figure 7 This is a SEM image of the co-fired interface of a medium-temperature co-fired alumina ceramic substrate prepared in Example 2 of the present invention and matched with tungsten-copper paste. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0038] Example 1

[0039] A method for preparing a medium-temperature co-fired alumina ceramic substrate matched with tungsten-copper paste includes the following steps:

[0040] (1) Ingredients

[0041] By total mass percentage, Al2O3 powder accounts for 95 wt.%, the SiO2-TiO2-CaO-MgO composite sintering aid system (SiO2, TiO2, CaO, MgO in a mass ratio of 6:2:1:1) accounts for 5 wt.%, and the rare earth oxide Y2O3 accounts for 0.2 wt.% of the Al2O3 powder. Al2O3 serves as the matrix material, SiO2, TiO2, CaO, and MgO together constitute the composite sintering aid system, and Y2O3 acts as a co-firing matching regulator.

[0042] (2) Mixing

[0043] Accurately weigh each component according to the above formula, add them to a zirconia ball mill jar, and ball mill them for 10 hours with anhydrous ethanol as the dispersion medium at a speed of 350 r / min to ensure that each component is evenly dispersed and fully contacted, thereby obtaining a uniform and stable mixed slurry.

[0044] (3) Drying

[0045] The ball-milled slurry was transferred to a vacuum drying oven and dried at 80°C until the ethanol had completely evaporated. The resulting powder was then ground and passed through a 100-mesh sieve to ensure uniform particle size, yielding a mixed powder.

[0046] (4) Molding

[0047] Add an appropriate amount of polyvinyl alcohol (PVA) binder to the sieved mixed powder, and grind and mix thoroughly in a mortar to ensure that the binder evenly coats the powder particles. After passing through a 100-mesh sieve again, prepare ceramic green bodies by dry pressing at a pressure of 300 MPa. The green body dimensions are 20 mm in diameter and 4 mm in thickness.

[0048] (5) De-glue

[0049] A layer of Al2O3 powder is placed on the bottom of the crucible, and the green sample is placed in the alumina crucible to prevent the sample from sticking to the bottom of the crucible during sintering. The crucible is then placed in a muffle furnace for debinding, and the temperature is raised to 500°C at a rate of 2°C / min in air atmosphere and held for 60 minutes to remove the organic PVA added during the molding process.

[0050] (6) Tungsten copper paste printing

[0051] After cleaning the surface of the ceramic green body after debinding, tungsten-copper conductive paste was screen-printed onto the surface of the green body to form a 15μm thick conductive pattern layer. After printing, the sample was dried at 90℃ for 30 minutes to remove organic solvents from the paste. The tungsten-copper conductive paste comprises the following components by weight: 82 parts tungsten-copper powder, 10 parts organic carrier, and 8 parts binder phase. The mass ratio of tungsten powder to copper powder in the tungsten-copper powder is 4:1. The organic carrier comprises the following components by weight percentage: 70 wt% terpineol, 20 wt% butyl carbitol, 2 wt% fumed silica, 3 wt% hydrogenated castor oil, and 5 wt% ethyl cellulose. The binder phase comprises the following components by weight percentage: 50 wt% polyvinyl butyral, 30 wt% acrylic resin, and 20 wt% polyvinylpyrrolidone.

[0052] (7) Co-firing

[0053] The printed ceramic green body was placed in a tube furnace and co-fired in a hydrogen-nitrogen mixed atmosphere (volume ratio of hydrogen to nitrogen: 5:95). The temperature was increased to 1400℃ at 5℃ / min, held for 2 hours, and then cooled to room temperature with the furnace to obtain a medium-temperature co-fired alumina ceramic substrate (denoted as Y-1) that matched the tungsten-copper paste. The dimensions of the co-fired ceramic substrate were 18 mm in diameter, 3 mm in thickness, and 13 μm in conductive layer thickness.

[0054] Example 2

[0055] A method for preparing a medium-temperature co-fired alumina ceramic substrate matched with tungsten-copper paste includes the following steps:

[0056] (1) Ingredients

[0057] By total mass percentage, Al2O3 powder accounts for 95 wt.%, the SiO2-TiO2-CaO-MgO composite sintering aid system (SiO2, TiO2, CaO, MgO in a mass ratio of 6:2:1:1) accounts for 5 wt.%, and the rare earth oxide Y2O3 accounts for 0.5 wt.% of the Al2O3 powder. Al2O3 serves as the matrix material, while SiO2, TiO2, CaO, and MgO together constitute the composite sintering aid system, and Y2O3 acts as a co-firing matching regulator.

[0058] (2) Mixing

[0059] Accurately weigh each component according to the above formula, add them to a zirconia ball mill jar, and ball mill them for 10 hours with anhydrous ethanol as the dispersion medium at a speed of 350 r / min to ensure that each component is evenly dispersed and fully contacted, thereby obtaining a uniform and stable mixed slurry.

[0060] (3) Drying

[0061] The ball-milled slurry was transferred to a vacuum drying oven and dried at 80°C until the ethanol had completely evaporated. The resulting powder was then ground and passed through a 100-mesh sieve to ensure uniform particle size, yielding a mixed powder.

[0062] (4) Molding

[0063] Add an appropriate amount of PVA binder to the sieved mixed powder, and grind and mix thoroughly in a mortar to ensure that the binder evenly coats the powder particles. After passing through a 100-mesh sieve again, prepare ceramic green bodies by dry pressing at a pressure of 300 MPa. The green body dimensions are 20 mm in diameter and 4 mm in thickness.

[0064] (5) De-glue

[0065] A layer of Al2O3 powder is placed on the bottom of the crucible, and the green sample is placed in the alumina crucible to prevent the sample from sticking to the bottom of the crucible during sintering. The crucible is then placed in a muffle furnace for debinding, and the temperature is raised to 500°C at a rate of 2°C / min in air atmosphere and held for 60 minutes to remove the organic PVA added during the molding process.

[0066] (6) Tungsten copper paste printing

[0067] After cleaning the surface of the ceramic green body after debinding, tungsten-copper conductive paste was screen-printed onto the surface of the green body to form a 15μm thick conductive pattern layer. After printing, the sample was dried at 90℃ for 30 minutes to remove organic solvents from the paste. The tungsten-copper conductive paste comprises the following components by weight: 82 parts tungsten-copper powder, 10 parts organic carrier, and 8 parts binder phase. The mass ratio of tungsten powder to copper powder in the tungsten-copper powder is 4:1. The organic carrier comprises the following components by weight percentage: 70 wt% terpineol, 20 wt% butyl carbitol, 2 wt% fumed silica, 3 wt% hydrogenated castor oil, and 5 wt% ethyl cellulose. The binder phase comprises the following components by weight percentage: 50 wt% polyvinyl butyral, 30 wt% acrylic resin, and 20 wt% polyvinylpyrrolidone.

[0068] (7) Co-firing

[0069] The printed ceramic green body was placed in a tube furnace and co-fired in a hydrogen-nitrogen mixed atmosphere (volume ratio of hydrogen to nitrogen: 5:95). The temperature was increased to 1400℃ at 5℃ / min, held for 2 hours, and then cooled to room temperature with the furnace to obtain a medium-temperature co-fired alumina ceramic substrate (denoted as Y-2) with tungsten-copper paste matching. The dimensions of the co-fired ceramic substrate were 18 mm in diameter, 3 mm in thickness, and 13 μm in conductive layer thickness.

[0070] Example 3

[0071] A method for preparing a medium-temperature co-fired alumina ceramic substrate matched with tungsten-copper paste includes the following steps:

[0072] (1) Ingredients

[0073] By total mass percentage, Al2O3 powder accounts for 95 wt.%, the SiO2-TiO2-CaO-MgO composite sintering aid system (SiO2, TiO2, CaO, MgO in a mass ratio of 6:2:1:1) accounts for 5 wt.%, and the rare earth oxide Y2O3 accounts for 1.0 wt.% of the Al2O3 powder. Al2O3 serves as the matrix material, while SiO2, TiO2, CaO, and MgO together constitute the composite sintering aid system, and Y2O3 acts as a co-firing matching regulator.

[0074] (2) Mixing

[0075] Accurately weigh each component according to the above formula, add them to a zirconia ball mill jar, and ball mill them for 10 hours with anhydrous ethanol as the dispersion medium at a speed of 350 r / min to ensure that each component is evenly dispersed and fully contacted, thereby obtaining a uniform and stable mixed slurry.

[0076] (3) Drying

[0077] The ball-milled slurry was transferred to a vacuum drying oven and dried at 80°C until the ethanol had completely evaporated. The resulting powder was then ground and passed through a 100-mesh sieve to ensure uniform particle size, yielding a mixed powder.

[0078] (4) Molding

[0079] Add an appropriate amount of PVA binder to the sieved mixed powder, and grind and mix thoroughly in a mortar to ensure that the binder evenly coats the powder particles. After passing through a 100-mesh sieve again, prepare ceramic green bodies by dry pressing at a pressure of 300 MPa. The green body dimensions are 20 mm in diameter and 4 mm in thickness.

[0080] (5) De-glue

[0081] A layer of Al2O3 powder is placed on the bottom of the crucible, and the green sample is placed in the alumina crucible to prevent the sample from sticking to the bottom of the crucible during sintering. The crucible is then placed in a muffle furnace for debinding, and the temperature is raised to 500°C at a rate of 2°C / min in air atmosphere and held for 60 minutes to remove the organic PVA added during the molding process.

[0082] (6) Tungsten copper paste printing

[0083] After cleaning the surface of the ceramic green body after debinding, tungsten-copper conductive paste was screen-printed onto the surface of the green body to form a 15μm thick conductive pattern layer. After printing, the sample was dried at 90℃ for 30 minutes to remove organic solvents from the paste. The tungsten-copper conductive paste comprises the following components by weight: 82 parts tungsten-copper powder, 10 parts organic carrier, and 8 parts binder phase. The mass ratio of tungsten powder to copper powder in the tungsten-copper powder is 4:1. The organic carrier comprises the following components by weight percentage: 70 wt% terpineol, 20 wt% butyl carbitol, 2 wt% fumed silica, 3 wt% hydrogenated castor oil, and 5 wt% ethyl cellulose. The binder phase comprises the following components by weight percentage: 50 wt% polyvinyl butyral, 30 wt% acrylic resin, and 20 wt% polyvinylpyrrolidone.

[0084] (7) Co-firing

[0085] The printed ceramic green body was placed in a tube furnace and co-fired in a hydrogen-nitrogen mixed atmosphere (volume ratio of hydrogen to nitrogen: 5:95). The temperature was increased to 1400℃ at 5℃ / min, held for 2 hours, and then cooled to room temperature with the furnace to obtain a medium-temperature co-fired alumina ceramic substrate (denoted as Y-3) with tungsten-copper paste matching. The dimensions of the co-fired ceramic substrate were 18 mm in diameter, 3 mm in thickness, and 13 μm in conductive layer thickness.

[0086] Comparative Example 1

[0087] A method for preparing a medium-temperature co-fired alumina ceramic substrate matched with tungsten-copper paste includes the following steps:

[0088] (1) Ingredients

[0089] By total mass percentage, Al2O3 powder accounts for 95 wt.%, and the SiO2-TiO2-CaO-MgO composite sintering aid system (SiO2, TiO2, CaO, and MgO in a mass ratio of 6:2:1:1) accounts for 5 wt.%. Among them, Al2O3 is the matrix material, and SiO2, TiO2, CaO, and MgO together constitute the composite sintering aid system.

[0090] (2) Mixing

[0091] Accurately weigh each component according to the above formula, add them to a zirconia ball mill jar, and ball mill them for 10 hours with anhydrous ethanol as the dispersion medium at a speed of 350 r / min to ensure that each component is evenly dispersed and fully contacted, thereby obtaining a uniform and stable mixed slurry.

[0092] (3) Drying

[0093] The ball-milled slurry was transferred to a vacuum drying oven and dried at 80°C until the ethanol had completely evaporated. The resulting powder was then ground and passed through a 100-mesh sieve to ensure uniform particle size, yielding a mixed powder.

[0094] (4) Molding

[0095] Add an appropriate amount of PVA binder to the sieved mixed powder, and grind and mix thoroughly in a mortar to ensure that the binder evenly coats the powder particles. After passing through a 100-mesh sieve again, prepare ceramic green bodies by dry pressing at a pressure of 300 MPa. The green body dimensions are 20 mm in diameter and 4 mm in thickness.

[0096] (5) De-glue

[0097] The green sample is placed in an alumina crucible, and a layer of Al2O3 powder is placed on the bottom of the crucible to prevent the sample from sticking to the bottom of the crucible during sintering. The crucible is then placed in a muffle furnace for debinding, and the temperature is raised to 500°C at a rate of 2°C / min in air atmosphere and held for 60 minutes to remove the organic PVA added during the molding process.

[0098] (6) Tungsten copper paste printing

[0099] After cleaning the surface of the ceramic green body after debinding, tungsten-copper conductive paste was screen-printed onto the surface of the green body to form a 15μm thick conductive pattern layer. After printing, the sample was dried at 90℃ for 30 minutes to remove organic solvents from the paste. The tungsten-copper conductive paste comprises the following components by weight: 82 parts tungsten-copper powder, 10 parts organic carrier, and 8 parts binder phase. The mass ratio of tungsten powder to copper powder in the tungsten-copper powder is 4:1. The organic carrier comprises the following components by weight percentage: 70 wt% terpineol, 20 wt% butyl carbitol, 2 wt% fumed silica, 3 wt% hydrogenated castor oil, and 5 wt% ethyl cellulose. The binder phase comprises the following components by weight percentage: 50 wt% polyvinyl butyral, 30 wt% acrylic resin, and 20 wt% polyvinylpyrrolidone.

[0100] (7) Co-firing

[0101] The printed ceramic green body was placed in a tube furnace and co-fired in a hydrogen-nitrogen mixed atmosphere (hydrogen-nitrogen volume ratio of 5:95). The temperature was increased to 1400℃ at 5℃ / min, held for 2 hours, and then cooled to room temperature with the furnace to obtain a medium-temperature co-fired alumina ceramic substrate (denoted as Y-0) with tungsten-copper paste matching. The dimensions of the co-fired ceramic substrate were 18mm in diameter, 3mm in thickness, and 13μm in conductive layer thickness.

[0102] The performance of the medium-temperature co-fired alumina ceramic substrates matched with the tungsten-copper pastes prepared in Examples 1-3 and Comparative Example 1 was tested:

[0103] (1) The relative density of the samples was determined by Archimedes' water displacement method. The relative density of Y-1 prepared in Example 1 reached 98.3%, the relative density of Y-2 prepared in Example 2 reached 99.2%, the relative density of Y-3 prepared in Example 3 reached 98.6%, and the relative density of Y-0 prepared in Comparative Example 1 was 97.6%.

[0104] (2) The bending strength was tested using the three-point bending method. The bending strength of the Y-1 sample prepared in Example 1 reached 356 MPa, the bending strength of the Y-2 sample prepared in Example 2 reached 383 MPa, the bending strength of the Y-3 sample prepared in Example 3 reached 374 MPa, and the bending strength of the Y-0 sample prepared in Comparative Example 1 was 318 MPa.

[0105] (3) The dimensional changes of the ceramics before and after co-firing were measured using vernier calipers and the linear shrinkage rate was calculated. The linear shrinkage rate of the Y-1 sample prepared in Example 1 reached 15.9%, and the difference between the linear shrinkage rate and that of the tungsten copper slurry reached 0.4%; the linear shrinkage rate of the Y-2 sample prepared in Example 2 reached 16.8%, and the difference between the linear shrinkage rate and that of the tungsten copper slurry reached 0.4%; the linear shrinkage rate of the Y-3 sample prepared in Example 3 reached 16.1%, and the difference between the linear shrinkage rate and that of the tungsten copper slurry reached 0.2%; the linear shrinkage rate of the Y-0 sample prepared in Comparative Example 1 reached 14.8%, and the difference between the linear shrinkage rate and that of the tungsten copper slurry reached 1.4%.

[0106] (4) The sample was analyzed by X-ray diffraction (XRD), the cross-sectional microstructure and co-fired interface microstructure were observed by field emission scanning electron microscopy (SEM), and the sample was analyzed by elemental analysis and surface scanning test by energy dispersive X-ray spectroscopy (EDS).

[0107] like Figure 1 As shown, the Y-1 sample (0.2 wt.% Y2O3) of Example 1 has a denser microstructure after sintering, compared to the comparative example 1 (without added Y2O3). Figure 4 Compared to the previous sample, the Y-1 sample showed a significant reduction in the number of pores and no obvious abnormal grain growth or localized loose areas. This is beneficial for reducing interfacial stress caused by uneven shrinkage of the ceramic matrix during co-firing, thereby reducing the risk of cracking, warping, and delamination between the metal layer and the ceramic substrate. These results indicate that the introduction of an appropriate amount of Y2O3 not only improves the ceramic microstructure but also helps to enhance the co-firing compatibility between the material and the metal paste.

[0108] like Figure 2 As shown, the Y-2 sample (0.5 wt.% Y2O3) of Example 2 exhibits a dense microstructure after sintering, with well-developed grains and a significant reduction in internal porosity. Combined with... Figure 5 (EDS) and Figure 6 XRD analysis revealed that the small amount of Y₂Si₂O₇ phase formed by the reaction of Y₂O₃ and SiO₂ was mainly distributed in the grain boundary region. This grain boundary phase, while promoting ceramic densification, can effectively control sintering shrinkage behavior and reduce interfacial stress concentration during co-firing. Figure 7As shown, the Y-2 sample of Example 2, after co-firing with the tungsten-copper conductor slurry at 1400℃, formed a complete and continuous interface structure. The interface between the conductor layer and the ceramic layer was clear, and the conductor layer and the ceramic matrix were tightly bonded. No obvious abnormal penetration of conductor particles was observed, and no obvious cracking, warping, or delamination was observed at the interface, indicating that no serious interfacial reaction or excessive liquid phase migration occurred during sintering. The above results show that the sample prepared in Example 2 not only has high density and flexural strength, but also exhibits better sintering shrinkage stability and co-firing compatibility with the tungsten-copper conductor slurry, making it suitable as a medium-temperature co-fired ceramic substrate material.

[0109] like Figure 3 As shown, with the addition of Y₂O₃ increasing to 1.0 wt.%, the Y-3 sample (1.0 wt.% Y₂O₃) in Example 3 still maintained a high density, but more coarse and fine grains were observed at the ceramic grain boundaries, indicating an uneven microstructure. Compared with the Y-2 sample, the Y-3 sample had an increased content of Y-Si grain boundary phase, which easily caused local stress concentration and interfacial stress accumulation, making it difficult to form a stable and continuous bonding interface between the ceramic matrix and the tungsten copper conductor layer. Therefore, an appropriate amount of Y₂O₃ is beneficial to improving the co-firing compatibility between alumina ceramics and tungsten copper conductor slurry, while excessive addition will reduce the compatibility.

[0110] like Figure 4 As shown, the Y-0 sample (without added Y2O3) of Comparative Example 1 still exhibits numerous pores and uneven grain size distribution after sintering, with abnormal grain growth observed in localized areas. This indicates that while the SiO2-TiO2-CaO-MgO composite sintering aid system can promote the sintering of alumina ceramics, it is insufficient to obtain a uniform and stable microstructure. The uneven microstructure leads to increased local shrinkage differences in the ceramic matrix during sintering, thereby increasing shrinkage mismatch and interfacial stress during co-firing with the tungsten-copper conductor slurry.

[0111] The results of Examples 1-3 and Comparative Example 1 show that the appropriate introduction of Y2O3 can synergistically enhance the SiO2-TiO2-CaO-MgO composite sintering aid system, promoting the densification of alumina ceramics at 1400℃, improving the uniformity of the microstructure, and enhancing the flexural strength and sintering shrinkage stability of the material. Compared with the sample without added Y2O3, the difference in linear shrinkage between the ceramic sample with added Y2O3 and the tungsten-copper conductor slurry was significantly reduced. After co-firing, the interface was continuous and intact, with no obvious cracks, pores, or delamination observed, indicating improved co-firing compatibility. Specifically, when the Y2O3 addition amount was 0.5 wt.%, the alumina ceramic exhibited superior comprehensive performance, with a relative density of 99.2%, a flexural strength of 383 MPa, and a linear shrinkage difference of 0.2%, forming a perfectly stable co-firing interface with the tungsten-copper conductor slurry.

[0112] In summary, this invention, through the combined use of a composite sintering aid system and rare earth oxides to regulate the liquid phase distribution, sintering shrinkage behavior, and interfacial wetting state of the ceramic substrate, enables the ceramic substrate to achieve high density and flexural strength, while simultaneously improving its shrinkage matching and interfacial reliability with the tungsten copper conductor paste, demonstrating promising application prospects in medium-temperature co-firing.

[0113] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the structure of the present invention or exceed the scope defined by the present invention, and all such modifications or additions should fall within the protection scope of the present invention.

Claims

1. A method for preparing a medium-temperature co-fired alumina ceramic substrate matched with tungsten-copper paste, characterized in that, Includes the following steps: (1) Using Al2O3 powder as the matrix, sintering aids and rare earth oxides are added, ground, mixed and dried to obtain mixed powder; (2) Add binder to the mixed powder, press to obtain ceramic green body, and then remove the binder; (3) Print tungsten copper electronic paste onto the surface of the ceramic green body after glue removal to form a tungsten copper conductive pattern layer; (4) The ceramic green body with the tungsten copper conductive pattern layer printed on it is placed in a protective atmosphere for medium-temperature co-firing. The heating rate is 3-8℃ / min, the sintering temperature is 1350-1450℃, and the holding time is 1-3h to obtain a medium-temperature co-fired alumina ceramic substrate that matches the tungsten copper paste.

2. The method for preparing a medium-temperature co-fired alumina ceramic substrate matched with tungsten-copper paste according to claim 1, characterized in that, In step (1): The mass ratio of Al2O3 powder, sintering aid, and rare earth oxide is (92-98):(2-8):(0.2-1). And / or, the rare earth oxide is one or more of La2O3, Y2O3, Nd2O3, and CeO2; And / or, the sintering aid is composed of SiO2, TiO2, CaO and MgO, and the mass ratio of SiO2, TiO2, CaO and MgO is (40-60):(20-30):(15-20):(15-20).

3. The method for preparing a medium-temperature co-fired alumina ceramic substrate matched with tungsten-copper paste according to claim 1, characterized in that, In step (1): The grinding process involves ball milling with anhydrous ethanol as the medium for 10-16 hours. And / or, the drying temperature is 60-100℃ and the time is 8-12h.

4. The method for preparing a medium-temperature co-fired alumina ceramic substrate matched with tungsten-copper paste according to claim 1, characterized in that, In step (2): The adhesive is one or more of polyvinyl alcohol, polyethylene glycol, and polymethyl methacrylate; And / or, the amount of binder added is 3%-8% of the total mass of the mixed powder.

5. The method for preparing a medium-temperature co-fired alumina ceramic substrate matched with tungsten-copper paste according to claim 1, characterized in that, In step (2): The pressing pressure is 200-400 MPa; And / or, the heating rate of the glue removal is 1-4℃ / min, the glue removal temperature is 500-650℃, and the holding time is 1-3h.

6. The method for preparing a medium-temperature co-fired alumina ceramic substrate matched with tungsten-copper paste according to claim 1, characterized in that: In step (3), the tungsten copper electronic paste includes tungsten copper powder, organic carrier, and binder phase, and the mass ratio of the tungsten copper powder, organic carrier, and binder phase is (80-85):(5-15):(5-10).

7. The method for preparing a medium-temperature co-fired alumina ceramic substrate matched with tungsten-copper paste according to claim 6, characterized in that: The mass ratio of tungsten to copper in the tungsten-copper powder is (70-85):(15-30). And / or, the organic carrier is one or more of terpineol, butyl carbitol, ethyl cellulose, fumed silica, and hydrogenated castor oil; And / or, the binder phase is one or more of ethyl cellulose, polyvinyl butyral, acrylic resin, and polyvinylpyrrolidone.

8. The method for preparing a medium-temperature co-fired alumina ceramic substrate matched with tungsten-copper paste according to claim 1, characterized in that: In step (3), the thickness of the tungsten copper conductive pattern layer is 5-30 μm; the printing is done by screen printing.

9. The method for preparing a medium-temperature co-fired alumina ceramic substrate matched with tungsten-copper paste according to claim 1, characterized in that: In step (4), the protective atmosphere is nitrogen, a hydrogen-nitrogen mixture, or a weak reducing atmosphere.

10. The medium-temperature co-fired alumina ceramic substrate matched with tungsten-copper paste prepared by the method of any one of claims 1-9.

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