Silicon nitride ceramic substrate having a surface gradient activation layer and method of manufacturing the same

Abstract

The application belongs to the technical field of advanced ceramic materials and electronic packaging substrates, and particularly relates to a silicon nitride ceramic substrate with a surface gradient activation layer and a preparation method thereof. The silicon nitride ceramic substrate with the surface gradient activation layer comprises a silicon nitride ceramic base and a surface gradient activation layer arranged on at least one side surface of the silicon nitride ceramic base; the surface gradient activation layer comprises one or more of a silicon nitride phase, a silicon-oxygen-nitrogen phase and a silicate or oxynitride phase containing a rare earth element.

Description

Technical Field

[0001] This invention belongs to the field of advanced ceramic materials and electronic packaging substrate technology, specifically relating to a silicon nitride ceramic substrate with a surface gradient activation layer and its preparation method. Background Technology

[0002] Silicon nitride ceramics possess high strength, high fracture toughness, good thermal shock resistance, high thermal conductivity, and thermal expansion properties that are relatively compatible with metals such as copper and aluminum. They are suitable as insulating and heat-dissipating substrates for power semiconductor devices, automotive-grade IGBT modules, SiC / GaN power modules, and other high-reliability electronic components. In practical applications, silicon nitride ceramic substrates typically need to be bonded to copper layers, molybdenum-manganese layers, active metal solder layers, or other metal functional layers to form metallized ceramic substrates. The bonding strength, thermal cycling reliability, and interfacial thermal resistance of the metallization interface directly affect the service life of power devices. Existing silicon nitride ceramic substrates typically focus on improving substrate density and thermal conductivity, resulting in a relatively dense and smooth surface after sintering. However, this surface has low chemical activity, making it prone to problems such as insufficient wetting, localized voids at the interface, and large fluctuations in peel strength when directly performing active metal soldering or thick-film metallization. To improve the metallization bonding strength, methods such as sandblasting, laser roughening, mechanical polishing, acid and alkali etching, or the addition of external transition layers are generally used to treat the ceramic surface.

[0003] However, simple mechanical roughening can easily introduce microcracks and processing damage to the ceramic surface, reducing the substrate strength; strong corrosion treatment can easily cause uncontrollable surface defects; although adding an external glass phase or oxide transition layer can improve wettability, it may increase interfacial thermal resistance and affect heat dissipation performance. For example, CN104409425B discloses a high thermal conductivity silicon nitride ceramic copper-clad laminate and its preparation method, which mainly achieves the welding connection between the silicon nitride ceramic substrate and the oxygen-free copper layer through active metal solder paste under vacuum brazing conditions; CN111192831A discloses a surface metallization method for high thermal conductivity silicon nitride ceramic substrates, which uses ion bombardment surface activation, magnetron sputtering of nano-metal layers, and vacuum bonding pressure to achieve bonding between the silicon nitride ceramic substrate and copper. These methods mainly improve interfacial bonding from the perspective of active solder, metal plating, or bonding process, but it is difficult to controllably adjust the surface structure and activity of the silicon nitride ceramic substrate itself, which leads to problems such as interfacial damage, complex processes, and high equipment requirements. Therefore, there is an urgent need to develop a silicon nitride ceramic substrate and its preparation method that can improve the surface metallization adaptability without significantly damaging the silicon nitride ceramic matrix. Summary of the Invention

[0004] Purpose of the invention: A silicon nitride ceramic substrate with a surface gradient activation layer and its preparation method are provided. While maintaining the compactness, mechanical properties and thermal conductivity of the silicon nitride ceramic matrix, the substrate surface is constructed with a micro-coarsened activation layer that is continuously transitioned to the matrix, thereby improving the wettability, mechanical interlocking and interfacial bonding reliability during the subsequent metallization process.

[0005] Technical solution: A silicon nitride ceramic substrate having a surface gradient activation layer includes: a silicon nitride ceramic substrate and a surface gradient activation layer disposed on at least one side of the silicon nitride ceramic substrate; the surface gradient activation layer includes one or more of silicon nitride phase, silicon oxynitride phase, and silicate or oxynitride phase containing rare earth elements.

[0006] Furthermore, the silicon nitride ceramic matrix is ​​prepared by sintering silicon nitride powder and sintering aids. The sintering aids include one or more of Y2O3, Yb2O3, Lu2O3, MgO, Al2O3, SiO2, and CaO. The total amount of sintering aids is 3-12 wt% of the total mass of the silicon nitride ceramic matrix raw materials. The silicon nitride ceramic matrix is ​​formed by tape casting, dry pressing, cold isostatic pressing, gel casting, or a combination thereof.

[0007] Furthermore, the activation slurry used in the surface gradient activation layer includes: ceramic micro powder, surface activation components, binder and solvent; the ceramic micro powder includes silicon nitride micro powder, boron nitride micro powder, silicon oxide micro powder or combinations thereof; the surface activation components include Y2O3, Yb2O3, MgO, Al2O3, SiO2, rare earth silicate powder or combinations thereof.

[0008] Furthermore, the thickness of the surface gradient activation layer is 0.2-20 μm.

[0009] A method for preparing a silicon nitride ceramic substrate with a surface gradient activation layer, comprising: (1) Mix silicon nitride powder with sintering aid, add dispersion medium and molding aid, and obtain mixed slurry or mixed powder by mechanical stirring and ball milling; (2) The mixed slurry or mixed powder is formed by casting, dry pressing, cold isostatic pressing, gel casting or a combination thereof to obtain silicon nitride ceramic blank; (3) The silicon nitride ceramic blank is degreased and sintered to obtain a dense silicon nitride ceramic matrix; (4) The dense silicon nitride ceramic substrate is subjected to thickness grinding, surface cleaning and drying; (5) An activation precursor layer is formed on at least one side surface of the silicon nitride ceramic substrate; (6) Heat treatment is performed on the silicon nitride ceramic substrate with the activated precursor layer to enable the activated precursor layer to undergo interfacial bonding and in-situ transformation with the surface layer of the ceramic substrate, forming a surface gradient activated layer.

[0010] Furthermore, after step (5) forms the activated precursor layer, the process also includes: The surface of silicon nitride ceramic substrates is pretreated by controlled oxidation, low-damage chemical etching, or plasma activation.

[0011] Further, in step (6), the heat treatment temperature is 850-1350℃ and the holding time is 0.5-6 h; the heat treatment atmosphere is one of nitrogen, argon, air, nitrogen-air mixture, or nitrogen atmosphere containing trace amounts of oxygen or water vapor.

[0012] Furthermore, it also includes: Step 7: After forming the surface gradient activation layer, perform ultrasonic cleaning, light polishing, plasma cleaning, and vacuum drying to remove unbonded particles and obtain a silicon nitride ceramic substrate suitable for metallization.

[0013] Beneficial effects: (1) Instead of using conventional mechanical sandblasting or laser to roughen the surface and improve the bonding ability, this invention constructs a surface gradient activation layer that is continuously transitioned to the substrate on the surface of silicon nitride ceramic, which can reduce surface processing damage and microcracks.

[0014] (2) The surface gradient activation layer has a coarsening structure and chemical activation effect, which can improve the spreading, wetting and interfacial bonding of active metal solder or metallization paste on the silicon nitride surface.

[0015] (3) The thickness of the surface gradient activation layer is controllable and can be controlled within the micrometer range. It does not require the formation of a thick glass layer or a thick oxide layer, which helps to reduce the interfacial thermal resistance and maintain the heat dissipation performance of the silicon nitride ceramic substrate.

[0016] (4) The process of the present invention can be adapted to existing industrial processes such as tape casting, gas pressure sintering, grinding and polishing, active metal brazing, and copper metallization, and is suitable for preparing silicon nitride ceramic substrates for power semiconductor packaging. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of a process for preparing a silicon nitride ceramic substrate with a surface gradient activation layer. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0020] This invention belongs to the field of advanced ceramic materials and electronic packaging substrate technology, specifically relating to a silicon nitride ceramic substrate, and more particularly to a silicon nitride ceramic substrate with a gradient activation layer formed on the surface of a dense silicon nitride ceramic substrate to improve the reliability of subsequent metallization bonding, and the same method thereof.

[0021] This invention discloses a silicon nitride ceramic substrate with a surface gradient activation layer and its preparation method. The silicon nitride ceramic substrate includes a silicon nitride ceramic matrix and a surface gradient activation layer disposed on at least one surface of the silicon nitride ceramic matrix. The surface gradient activation layer and the silicon nitride ceramic matrix have a continuous transition structure, and the surface gradient activation layer includes one or more of the following: silicon nitride phase, silicon oxynitride phase, and silicate or oxynitride phase containing rare earth elements. The preparation method includes silicon nitride ceramic matrix preparation, surface activation precursor layer formation, and heat treatment conversion steps. This invention improves wettability and interfacial bonding reliability during subsequent metallization processes by constructing a micron-scale surface gradient activation layer on the surface of silicon nitride ceramic, while avoiding surface damage caused by excessive mechanical roughening. It is suitable for metallized silicon nitride ceramic substrates for power semiconductor packaging.

[0022] A silicon nitride ceramic substrate having a surface gradient activation layer includes a silicon nitride ceramic substrate and a surface gradient activation layer disposed on at least one side of the silicon nitride ceramic substrate; the surface gradient activation layer includes one or more of silicon nitride phase, silicon oxynitride phase, and silicate or oxynitride phase containing rare earth elements.

[0023] The thickness of the surface gradient activation layer is 0.2-20 μm; the surface roughness Ra of the surface gradient activation layer is 0.15-1.50 μm. Micro-pits, island-like protrusions, and continuous or semi-continuous mesh-like roughening structures can be formed in the surface gradient activation layer, providing wetting sites and mechanical anchoring sites during active metal brazing, copper metallization, or thick film metallization processes.

[0024] The silicon nitride ceramic matrix is ​​prepared by sintering silicon nitride powder and sintering aids. The sintering aids include one or more of Y₂O₃, Yb₂O₃, Lu₂O₃, MgO, Al₂O₃, SiO₂, and CaO; the total amount of sintering aids is 3-12 wt% of the total mass of the silicon nitride ceramic matrix raw materials. The silicon nitride ceramic matrix can be formed by tape casting, dry pressing, cold isostatic pressing, gel casting, or a combination thereof.

[0025] like Figure 1The present invention also provides a method for preparing the above-mentioned silicon nitride ceramic substrate, comprising the following steps: (1) Mix silicon nitride powder with sintering aid, add dispersion medium and molding aid, and obtain mixed slurry or mixed powder by mechanical stirring, ball milling or other means; (2) The mixed slurry or mixed powder is formed by dry pressing, casting or other methods to obtain silicon nitride ceramic blanks; (3) The green blank is degreased and sintered to obtain a dense silicon nitride ceramic matrix; (4) The dense silicon nitride ceramic substrate is subjected to thickness grinding, surface cleaning and drying; (5) An activation precursor layer is formed on at least one side surface of the silicon nitride ceramic substrate; (6) Heat treatment is performed on the silicon nitride ceramic substrate with the activated precursor layer to cause interfacial bonding and in-situ transformation between the activated precursor layer and the surface layer of the ceramic substrate, forming a surface gradient activation layer.

[0026] In step (5), the activated precursor layer can be formed by coating, spraying, roller coating, dip coating, or screen printing with an activated slurry. The activated slurry includes ceramic micro powder, surface activating components, binder, and solvent; the ceramic micro powder includes silicon nitride micro powder, boron nitride micro powder, silicon oxide micro powder, or combinations thereof; the surface activating components include Y2O3, Yb2O3, MgO, Al2O3, SiO2, rare earth silicate powder, or combinations thereof.

[0027] In addition, after the activation precursor layer is formed, step (5) can also be performed by controlling oxidation, low-damage chemical etching or plasma activation to pretreat the surface of the silicon nitride ceramic substrate, and then heat treatment in step (6) to form a surface gradient activation layer.

[0028] In step (6), the heat treatment temperature is preferably 850-1350℃, and the holding time is preferably 0.5-6 h; the heat treatment atmosphere is one of nitrogen, argon, air, nitrogen-air mixture, or nitrogen atmosphere containing trace amounts of oxygen or water vapor. By controlling the heat treatment temperature, time, and atmosphere, the thickness, roughness, and chemical composition of the surface gradient activation layer can be adjusted.

[0029] After forming the surface gradient activation layer, further post-processing such as ultrasonic cleaning, light polishing, plasma cleaning, and vacuum drying can be performed to remove unbonded particles and obtain a silicon nitride ceramic substrate suitable for metallization.

[0030] Example 1: Casting of silicon nitride ceramic substrate and its surface activation treatment Weigh out 92 parts by mass percentage of silicon nitride powder, 4 parts by mass of Y2O3 powder, 2 parts by mass of MgO powder, and 2 parts by mass of Al2O3 powder. Add ethanol, dispersant, plasticizer, and binder, and mix by ball milling to obtain a casting slurry. After degassing the slurry, cast it into a tape to obtain a silicon nitride green tape.

[0031] Silicon nitride green tape is cut, stacked, and hot-pressed to obtain silicon nitride ceramic green body. After low-temperature debinding, the green body is subjected to gas pressure sintering in a nitrogen atmosphere at a temperature of 1750-1900℃ for 2-8 hours to obtain a dense silicon nitride ceramic matrix.

[0032] The sintered silicon nitride ceramic substrate was ground to a thickness of 0.20-0.80 mm, followed by ultrasonic cleaning and drying. An activation slurry, comprising silicon nitride micro powder, Y₂O₃ micro powder, SiO₂ micro powder, MgO micro powder, polyvinyl alcohol binder, and an ethanol-water mixed solvent, was then sprayed onto both sides of the substrate. After spraying, the substrate was dried to form an activation precursor layer on its surface.

[0033] A silicon nitride ceramic substrate with an activated precursor layer is placed in a nitrogen-trace oxygen mixed atmosphere and kept at 950-1250℃ for 0.5-3 h. After cooling, it is ultrasonically cleaned to remove unbonded particles, thus obtaining a silicon nitride ceramic substrate with a surface gradient activated layer.

[0034] Example 2: Dry pressing of silicon nitride ceramic substrate and single-sided activation treatment Weigh out 90-96 parts of silicon nitride powder, 2-6 parts of Yb₂O₃ powder, 0.5-3 parts of MgO powder, and 0.2-2 parts of SiO₂ powder by mass percentage. After wet ball milling, drying, and granulation, a mixed powder is obtained. The mixed powder is then dry-pressed and subjected to cold isostatic pressing to obtain a silicon nitride ceramic green body.

[0035] After degreasing, the green body is sintered under nitrogen pressure to obtain a silicon nitride ceramic matrix. One side of the matrix surface is lightly ground and plasma cleaned, and then an activation precursor layer is formed by screen printing. The activation precursor layer contains silicon nitride fine powder, rare earth oxides, and silicon oxide.

[0036] The sample was heat-treated at 900-1300℃ to bond the activated precursor layer with the substrate surface and transform it into a surface gradient activation layer with a thickness of 0.2-20 μm, thus obtaining a silicon nitride ceramic substrate suitable for metallization bonding on one side.

[0037] The aforementioned metallized silicon nitride ceramic substrate is used in power semiconductor packaging, automotive-grade power modules, IGBT modules, SiC power modules, or GaN power modules.

[0038] The above detailed embodiments are a description of the present invention. It should not be considered that the specific embodiments of the present invention are limited to these descriptions. For those skilled in the art, several simple deductions and substitutions can be made without departing from the concept of the present invention, and all of these should be considered to fall within the protection scope of the present invention.

Claims

1. A silicon nitride ceramic substrate having a surface gradient activation layer, characterized in that, include: A silicon nitride ceramic substrate and a surface gradient activation layer disposed on at least one side of the silicon nitride ceramic substrate; the surface gradient activation layer includes one or more of silicon nitride phase, silicon oxynitride phase, and silicate or oxynitride phase containing rare earth elements.

2. The silicon nitride ceramic substrate with a surface gradient activation layer according to claim 1, characterized in that, The silicon nitride ceramic matrix is ​​prepared by sintering silicon nitride powder and sintering aids. The sintering aids include one or more of Y2O3, Yb2O3, Lu2O3, MgO, Al2O3, SiO2, and CaO. The total amount of sintering aids is 3-12 wt% of the total mass of the silicon nitride ceramic matrix raw materials. The silicon nitride ceramic matrix is ​​formed by tape casting, dry pressing, cold isostatic pressing, gel casting, or a combination thereof.

3. The silicon nitride ceramic substrate with a surface gradient activation layer according to claim 1, characterized in that, The activation slurry used in the surface gradient activation layer includes: ceramic micro powder, surface activation components, binder and solvent; the ceramic micro powder includes silicon nitride micro powder, boron nitride micro powder, silicon oxide micro powder or combinations thereof; the surface activation components include Y2O3, Yb2O3, MgO, Al2O3, SiO2, rare earth silicate powder or combinations thereof.

4. The silicon nitride ceramic substrate with a surface gradient activation layer according to claim 1, characterized in that, The thickness of the surface gradient activation layer is 0.2-20 μm.

5. A method for preparing a silicon nitride ceramic substrate with a surface gradient activation layer, characterized in that, include: (1) Mix silicon nitride powder with sintering aid, add dispersion medium and molding aid, and obtain mixed slurry or mixed powder by mechanical stirring and ball milling; (2) The mixed slurry or mixed powder is formed by casting, dry pressing, cold isostatic pressing, gel casting or a combination thereof to obtain silicon nitride ceramic blank; (3) The silicon nitride ceramic blank is degreased and sintered to obtain a dense silicon nitride ceramic matrix; (4) The dense silicon nitride ceramic substrate is subjected to thickness grinding, surface cleaning and drying; (5) An activation precursor layer is formed on at least one side surface of the silicon nitride ceramic substrate; (6) Heat treatment is performed on the silicon nitride ceramic substrate with the activation precursor layer to enable the activation precursor layer to undergo interfacial bonding and in-situ transformation with the surface layer of the ceramic substrate, forming a surface gradient activation layer.

6. The method for preparing a silicon nitride ceramic substrate with a surface gradient activation layer according to claim 5, characterized in that, After step (5) forms the activated precursor layer, the process also includes: The surface of silicon nitride ceramic substrates is pretreated by controlled oxidation, low-damage chemical etching, or plasma activation.

7. The method for preparing a silicon nitride ceramic substrate with a surface gradient activation layer according to claim 5, characterized in that, In step (6), the heat treatment temperature is 850-1350℃ and the holding time is 0.5-6 h; the heat treatment atmosphere is one of nitrogen, argon, air, nitrogen-air mixture, or nitrogen atmosphere containing trace amounts of oxygen or water vapor.

8. The method for preparing a silicon nitride ceramic substrate with a surface gradient activation layer according to claim 5, characterized in that, It also includes: Step 7: After forming the surface gradient activation layer, perform ultrasonic cleaning, light polishing, plasma cleaning, and vacuum drying to remove unbonded particles and obtain a silicon nitride ceramic substrate suitable for metallization.

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