A method for preparing a copper-clad ceramic substrate

Abstract

The present invention relates to the technical field of copper-clad ceramic substrates, and in particular to a method for preparing a copper-clad ceramic substrate. The method comprises the following steps: S1. Surface treatment of the ceramic substrate; S2. Designing a corresponding steel mesh pattern and making a steel mesh according to circuit design requirements; S3. Directly printing the copper slurry on the treated ceramic substrate by steel mesh printing to form a patterned copper clad layer, and drying it under a nitrogen atmosphere; S4. Repeating step S3 multiple times to obtain a printed sample; S5. Sintering the printed sample, and then polishing and cleaning it to obtain a copper-clad ceramic substrate. The present invention can directly obtain a patterned copper clad layer by steel mesh printing, avoiding the tedious steps of soldering copper foil with solder and subsequent etching. The process is simple and has good formability, and the prepared finished copper clad layer has a strong bonding force with the ceramic substrate.

Description

Technical Field

[0001] The present invention relates to the technical field of copper-clad ceramic substrates, and in particular to a preparation method of a copper-clad ceramic substrate. Background Art

[0002] With the continuous development of fields such as aerospace and electric vehicles, the requirements for core power devices are gradually increasing, and third-generation semiconductors are gradually receiving increasing research and attention. Third-generation semiconductors have higher operating junction temperatures and can maintain good performance above 350°C. Copper-clad ceramic substrates in high-power applications require higher copper thickness and higher temperature reliability to ensure that devices do not fail prematurely.

[0003] At present, the preparation of copper-clad ceramic substrates mainly includes direct copper plating (DPC) process, direct copper bonding (DBC) process, active metal brazing (AMB) process and other methods. Among them, the active metal brazing (AMB) process mainly places active brazing material on the surface of the ceramic carrier by thick film printing, and then places copper foil layers on both sides of the ceramic carrier covered with metal solder to form a copper-brazing material-ceramic-brazing material-copper structure. Then, vacuum sintering is performed to tightly weld the ceramic, brazing material and copper foil. The product is then manufactured through processes such as exposure, development, etching and surface treatment.

[0004] The traditional AMB process is relatively complex and requires precise process control, resulting in high costs. Furthermore, any minor surface defects on the ceramic and copper sheets can cause voids at the soldering interface, affecting bonding strength. Therefore, the development of a new type of copper-clad ceramic substrate that can achieve direct bonding between copper slurry and the ceramic substrate, forming a patterned copper clad layer, has become a research hotspot in the field of electronic packaging materials. This material offers simple processing, high thermal conductivity, good formability, and excellent copper-ceramic bonding strength.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The object of the present invention is to provide a method for preparing a copper-clad ceramic substrate, which can achieve direct bonding between a copper slurry and a ceramic substrate to form a patterned copper clad layer. The process is simple and has good formability. In addition, the prepared finished copper clad layer has a strong bonding force with the ceramic substrate.

[0007] The present invention provides a method for preparing a copper-clad ceramic substrate, comprising the following steps:

[0008] S1. Surface treatment of the ceramic substrate, including cleaning and removing impurities to enhance the bonding strength between the copper slurry and the ceramic substrate;

[0009] S2. Design the corresponding stencil pattern and produce the stencil according to the circuit design requirements;

[0010] S3. The copper paste is printed directly on the treated ceramic substrate by screen printing to form a patterned copper layer and dried under a nitrogen atmosphere;

[0011] S4 repeat step S3 several times to obtain a printed sample; by double-sided printing and drying multiple reciprocating thick copper preparation;

[0012] S5. The printed sample is sintered to achieve a close bond between the copper clad layer and the ceramic substrate. After sintering, post-processing steps such as polishing and cleaning are performed to remove surface impurities and improve surface flatness, ultimately obtaining a copper-clad ceramic substrate.

[0013] Preferably, step S2 includes:

[0014] S21. Design the corresponding stencil pattern based on the circuit design requirements. This includes determining the circuit layout, component placement, and trace routing. The stencil pattern design must take into account the circuit's functionality, performance, and ease of assembly.

[0015] S22. Select the appropriate steel sheet thickness. The thickness of the steel sheet determines the thickness of the copper layer, thereby affecting the performance of the copper-clad ceramic substrate;

[0016] S23. Make the required steel mesh by laser engraving according to the designed steel mesh pattern.

[0017] Preferably, the copper slurry used in step S3 is prepared by the following method:

[0018] (1) pickling the copper powder particles to obtain deoxidized copper particles;

[0019] (2) coating the deoxidized copper particles with a binder to obtain coated copper particles;

[0020] (3) uniformly mixing a plasticizer, a leveling agent, a dispersant, a coupling agent, a curing agent, a sintering temperature regulator, and an organic solvent to obtain an organic solvent system;

[0021] (4) Mixing and stirring the coated copper particles with an organic solvent system to obtain the copper slurry.

[0022] Preferably, the acid used for pickling in step (1) is one of dilute sulfuric acid, hypophosphorous acid, and hypochlorous acid; more preferably, dilute sulfuric acid or hypochlorous acid; the shape of the copper powder particles used is spherical or flaky, and the particle size range is 100-2200nm; more preferably, 300-1500nm, and the particle size can be 300nm, 400nm, 500nm, 800nm, 1000nm, or 1200nm.

[0023] Preferably, the adhesive in step (2) is selected from at least one of polyvinyl alcohol, polyacrylate, polyvinyl acetate, polyvinyl butyral, and methyl cellulose; more preferably, polyvinyl butyral or polyacrylate.

[0024] Preferably, the weight percentages of the components in the organic solvent system obtained in step (3) are as follows: 1%-5% plasticizer, 0.5%-3% leveling agent, 0.5%-3% dispersant, 0.2%-1% coupling agent, 0.5%-3% curing agent, 0.2%-1% sintering temperature regulator, and 91%-96% organic solvent. The mixing method of the organic solvent system is not strictly limited, as long as it can be mixed uniformly, for example, magnetic stirring for 1-3 hours can be used.

[0025] Preferably, the plasticizer used in step (3) is at least one of citrate esters, terephthalate esters and cyclohexanedicarboxylates;

[0026] The leveling agent is one or more of polyethylene oxide, polyether modified silicone, polyether polyol, and polyurethane;

[0027] The dispersant is at least one selected from unsaturated fatty acids having 12 or more and 24 or less carbon atoms;

[0028] The coupling agent is one or more of γ-aminopropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, phosphate, and polyethyleneimine;

[0029] The curing agent is one or more of xylene peroxide, benzoyl peroxide, phenylenediamine, dichloroaniline, and diethylenetriamine;

[0030] The sintering temperature regulator is one or more of sodium chloride, sodium sulfate, ammonium chloride, and a trace amount of rare earth metals (such as yttrium and cerium);

[0031] The organic solvent is at least one alcohol organic solvent.

[0032] Preferably, the dispersant is selected from at least one of linoleic acid and linolenic acid; and the organic solvent is selected from at least one of ethanol, ethylene glycol, propylene glycol, glycerol and diethylene glycol.

[0033] In the organic solvent system, plasticizers are used to improve the fluidity and flexibility of the slurry, making it easier to print and form; levelers are used to ensure the uniformity of the slurry thickness during the printing process; dispersants are used to prevent copper particles from agglomerating during the preparation and printing of copper slurry; coupling agents are used to improve the adhesion between the copper slurry and the ceramic substrate; curing agents are used to promote the hardening or curing process of the slurry and increase the strength of the copper cladding layer; sintering temperature regulators can adjust the sintering temperature of copper and promote the expansion or forming of copper particles to make the sintering process more uniform; and organic solvents are used to adjust the viscosity of the copper slurry.

[0034] Preferably, the stirring in step (4) is carried out using a vacuum deaerator for 10-40 minutes.

[0035] Preferably, when printing the copper paste on the ceramic substrate in step S3, the copper paste is first printed on the front side of the ceramic substrate and dried, and then printed on the back side of the ceramic substrate and dried.

[0036] Preferably, the sintering temperature in step S5 is 400-600° C., the holding time is 15-45 minutes, and the sintering atmosphere is an inert atmosphere.

[0037] In summary, the present invention has the following advantages:

[0038] Traditional copper-clad ceramic substrates are basically prepared by connecting copper foil and ceramic substrate through solder. Its disadvantages are: the required sintering temperature is relatively high (above 800°C), and processes such as exposure, development, etching and surface treatment are required to obtain imaged copper-clad ceramics.

[0039] The technical solution of the present invention, by adding a plasticizer, a curing agent, and a binder, produces a copper paste with a certain degree of plastic formability, ensuring the quality of the copper paste during multiple printings on ceramic substrates, preventing the printed layer from collapsing and achieving good control of formability. Furthermore, the present invention employs a method of repeated printing and drying cycles, enabling printing thicknesses exceeding 800 μm. This allows for direct production of a patterned copper clad layer through stencil printing, avoiding the tedious steps of soldering copper foil with solder and subsequent etching.

[0040] The copper-clad ceramic substrate prepared by the present invention has a lower sintering temperature (400°C-600°C), which makes the final product have lower residual stress and better flatness. The added binder enables the copper slurry to be better bonded to the ceramic substrate under low-temperature sintering, effectively improving the connection quality and enhancing the reliability of the copper-clad ceramic substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0042] Figure 1 This is a flow chart for preparing a copper-clad ceramic substrate in Example 1 of the present invention;

[0043] Figure 2 This is a flow chart of the preparation of the copper slurry in Example 1 of the present invention;

[0044] Figure 3 Schematic diagram of the structure of the copper-clad ceramic substrate prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0045] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0046] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like to indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operate in a specific direction, and therefore should not be understood as limiting the present invention.

[0047] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the said features. In the description of the present invention, "multiple" means two or more, unless otherwise clearly and specifically defined. In addition, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be a communication between the two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0048] Example 1

[0049] A method for preparing a copper-clad ceramic substrate, such as Figure 1 The specific process is as follows:

[0050] S1. Perform ultrasonic cleaning on the ceramic substrate to remove surface impurities.

[0051] S2. Steel mesh pattern design and production

[0052] S21. Design the corresponding stencil pattern based on the circuit design requirements. This includes determining the circuit layout, component placement, and trace routing. The stencil pattern design must take into account the circuit's functionality, performance, and ease of assembly.

[0053] S22. Select a steel sheet having a thickness of 300μm;

[0054] S23. Make the required steel mesh by laser engraving according to the designed steel mesh pattern.

[0055] S3.Stencil printing and drying

[0056] Pour the copper slurry into the hopper of the stencil printer, place the treated ceramic substrate on the platform of the printer, and print the copper slurry on the front of the ceramic substrate using the stencil printer to form a patterned copper coating, which is then dried under a nitrogen atmosphere. Then, the copper slurry is printed on the back of the ceramic substrate using the stencil printing method, which is then dried under a nitrogen atmosphere.

[0057] S4 repeat step S3, perform double-sided printing and drying three times to achieve the preparation of thick copper on the ceramic substrate to obtain a printed sample;

[0058] S5. Place the printed sample in a drying oven for sintering, raise the temperature to 400°C at a rate of 3°C / min, and maintain for 30 minutes in a nitrogen atmosphere; after sintering, remove the sample for polishing and cleaning to remove surface impurities, and obtain a copper-clad ceramic substrate (such as Figure 3 shown).

[0059] The copper slurry used in step S3 is prepared by the following method (eg Figure 2 shown):

[0060] (1) Copper powder particles (particle size 300 nm) were mixed with hypochlorous acid solution, ultrasonically treated for 10 min, and the supernatant was removed by centrifugation. Anhydrous ethanol was then added, ultrasonically treated for 6 min, and the supernatant was removed by centrifugation to obtain deoxidized copper particles;

[0061] (2) mixing the above-mentioned deoxidized copper particles with a polyvinyl butyral ethanol solution, wherein the mass ratio of polyvinyl butyral to ethanol is 1:99, ultrasonically treating for 90 minutes, and centrifuging to remove the supernatant to obtain binder-coated copper particles; mixing the binder-coated copper particles with the ethanol solution, ultrasonically treating for 10 minutes, and centrifuging to remove the supernatant to obtain coated copper particles;

[0062] (3) The following raw materials in percentage by weight: 2% tributyl citrate, 1.5% polyethylene oxide, 0.5% linolenic acid, 0.3% γ-aminopropyltriethoxysilane, 1.5% xylene peroxide, 0.5% sodium chloride, and 93.7% ethylene glycol were mixed and magnetically stirred for 3 h to obtain an organic solvent system;

[0063] (4) After mixing the coated copper particles with the organic solvent system, the mixture was stirred in a vacuum degassing machine for 30 minutes to obtain a copper slurry.

[0064] Example 2

[0065] A method for preparing a copper-clad ceramic substrate, the specific process is as follows:

[0066] S1. Perform ultrasonic cleaning on the ceramic substrate to remove surface impurities.

[0067] S2. Steel mesh pattern design and production

[0068] S21. Design the corresponding stencil pattern based on the circuit design requirements. This includes determining the circuit layout, component placement, and trace routing. The stencil pattern design must take into account the circuit's functionality, performance, and ease of assembly.

[0069] S22. Select a steel sheet having a thickness of 300μm;

[0070] S23. Make the required steel mesh by laser engraving according to the designed steel mesh pattern.

[0071] S3.Stencil printing and drying

[0072] Pour the copper paste into the hopper of the stencil printer, place the treated ceramic substrate on the platform of the printer, and use the stencil printer to print the copper paste on the front of the ceramic substrate to form a patterned copper coating. The copper coating is then dried under nitrogen atmosphere. The copper paste is then printed on the back of the ceramic substrate using the stencil printing method and dried under nitrogen atmosphere.

[0073] S4. Repeat step S3, perform double-sided printing and drying three times, and realize the preparation of thick copper on the ceramic substrate.

[0074] S5. Place the printed sample in a drying oven for sintering. Raise the temperature to 500°C at a rate of 3°C / min and hold for 30 minutes in a nitrogen atmosphere. After sintering, remove the sample, polish, and clean it to remove surface impurities, thereby obtaining a copper-clad ceramic substrate.

[0075] The copper slurry used in step S3 is prepared by the following method:

[0076] (1) Copper powder particles (particle size 300 nm) were mixed with a dilute sulfuric acid solution, ultrasonically treated for 10 min, and the supernatant was removed by centrifugation. Anhydrous ethanol was then added, ultrasonically treated for 6 min, and the supernatant was removed by centrifugation to obtain deoxidized copper particles;

[0077] (2) mixing the above-mentioned deoxidized copper particles with a polyacrylate ethanol solution, wherein the mass ratio of polyacrylate to ethanol is 1:99, ultrasonically treating for 90 minutes, and centrifuging to remove the supernatant to obtain binder-coated copper particles; mixing the binder-coated copper particles with the ethanol solution, ultrasonically treating for 10 minutes, and centrifuging to remove the supernatant to obtain coated copper particles;

[0078] (3) The following raw materials in percentage by weight: 2% acetyl tributyl citrate, 1.5% polyurethane, 0.5% linoleic acid, 0.3% polyethyleneimine, 2% benzoyl peroxide, 0.5% sodium sulfate, and 93.2% propylene glycol were mixed and magnetically stirred for 3 h to obtain an organic solvent system;

[0079] (4) After mixing the coated copper particles with the organic solvent system, the mixture was stirred in a vacuum degassing machine for 30 minutes to obtain a copper slurry.

[0080] Comparative Example 1

[0081] A method for preparing a copper-clad ceramic substrate, the technical solution of which is basically the same as that of Example 1, except that: in the copper slurry preparation process used in step S3, no plasticizer tributyl citrate, curing agent xylene peroxide and sintering temperature regulator sodium chloride are added.

[0082] Comparative Example 2

[0083] A method for preparing a copper-clad ceramic substrate, the technical solution of which is basically the same as that of Example 2, except that: in the preparation process of the copper slurry used in step S3, no plasticizer (acetyl tributyl citrate), curing agent (benzoyl peroxide) and sintering temperature regulator (sodium sulfate) are added.

[0084] The experiments showed that the copper paste prepared in Comparative Examples 1-2 had poor formability, could not maintain a patterned shape after screen printing, had a collapsed printed layer, and was not firmly bonded to the ceramic substrate after sintering at 800°C.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a copper-clad ceramic substrate, characterized in that: The following steps are involved: S1. Surface treatment of ceramic substrate; S2. Design the corresponding stencil pattern and produce the stencil according to the circuit design requirements; S3. The copper paste is printed directly on the treated ceramic substrate by screen printing to form a patterned copper layer and dried under a nitrogen atmosphere; S4. Repeat step S3 several times to obtain a printed sample; S5. The printed sample is sintered, then polished and cleaned to obtain a copper-clad ceramic substrate; The copper slurry used in step S3 is prepared by the following method: (1) acid-washing the copper powder particles to obtain deoxidized copper particles; (2) coating the deoxidized copper particles with a binder to obtain coated copper particles; (3) uniformly mixing a plasticizer, a leveling agent, a dispersant, a coupling agent, a curing agent, a sintering temperature regulator, and an organic solvent to obtain an organic solvent system; (4) mixing and stirring the coated copper particles with an organic solvent system to obtain the copper slurry; The mass percentages of the components in the organic solvent system obtained in step (3) are as follows: plasticizer 1%-5%, leveler 0.5%-3%, dispersant 0.5%-3%, coupling agent 0.2%-1%, curing agent 0.5%-3%, sintering temperature regulator 0.2%-1%, and organic solvent 91%-96%; The plasticizer used in step (3) is at least one of citrate esters, terephthalate esters and cyclohexanedicarboxylates; The leveling agent is one or more of polyethylene oxide, polyether modified silicone, polyether polyol, and polyurethane; The dispersant is at least one selected from unsaturated fatty acids having 12 or more and 24 or less carbon atoms; The coupling agent is one or more of γ-aminopropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, phosphate, and polyethyleneimine; The curing agent is one or more of xylene peroxide, benzoyl peroxide, phenylenediamine, dichloroaniline, and diethylenetriamine; The sintering temperature regulator is one or more of sodium chloride, sodium sulfate, ammonium chloride, and rare earth metals; The organic solvent is at least one alcohol organic solvent; The sintering temperature in step S5 is 400-600° C., the holding time is 15-45 minutes, and the sintering atmosphere is an inert atmosphere.

2. The preparation method according to claim 1, characterized in that The acid used for pickling in step (1) is one of dilute sulfuric acid, hypophosphorous acid, and hypochlorous acid; the copper powder particles used are spherical or flaky, and have a particle size range of 100-2200 nm.

3. The preparation method according to claim 1, characterized in that The binder in step (2) is selected from at least one of polyvinyl alcohol, polyacrylate, polyvinyl acetate, polyvinyl butyral, and methyl cellulose.

4. The preparation method according to claim 1, characterized in that The dispersant is selected from at least one of linoleic acid and linolenic acid; and the organic solvent is selected from at least one of ethanol, ethylene glycol, propylene glycol, glycerol and diethylene glycol.

5. The preparation method according to claim 1, characterized in that The stirring in step (4) is carried out by using a vacuum deaerator for 10-40 minutes.

6. The preparation method according to claim 1, characterized in that When printing the copper paste on the ceramic substrate in step S3, the copper paste is first printed on the front side of the ceramic substrate and dried, and then printed on the back side of the ceramic substrate and dried.

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