AMB copper-clad ceramic substrate and welding method thereof

Abstract

The invention discloses an AMB copper-clad ceramic substrate and a welding method thereof.The welding method comprises the steps that metal powder containing inactive elements Ag and Cu and an active element Ti is mixed with an organic carrier, and active soldering paste is obtained; and coating the active soldering paste on the surface of a ceramic substrate, stacking copper foils on the surface, coated with the active soldering paste, of the ceramic substrate, and performing vacuum sintering to obtain the AMB copper-clad ceramic substrate. According to the AMB copper-clad ceramic substrate and the welding method thereof provided by the invention, the process is improved when the AMB realizes metallization of the ceramic substrate, so that the obtained AMB copper-clad ceramic substrate has the characteristics of high interface bonding force, low warping degree and voidage, excellent cold and hot impact resistance and the like.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductor technology, and particularly relates to an AMB copper-clad ceramic substrate and a welding method thereof. Background Art

[0002] For electronic packaging, the packaging substrate plays a crucial role in connecting the upper and lower parts and the internal and external heat dissipation channels, and also has functions such as electrical interconnection and mechanical support. For a ceramic substrate, since it is not conductive itself, it needs to be copper-clad to meet the requirements of electrical interconnection. In the copper-cladding process, the AMB (Active Metal Brazed Ceramic Substrate) process uses an active metal solder containing a small amount of active elements to achieve the welding between the copper foil and the ceramic substrate. Compared with DPC (Direct Plating on Ceramic Substrate) and DBC (Direct Bonding on Ceramic Substrate), the AMB copper-clad ceramic substrate realizes the bonding by means of a chemical reaction between the ceramic and the active solder paste at high temperature. Therefore, compared with DPC and DBC copper-clad ceramic substrates, it shows higher bonding strength, better resistance to thermal cycling, and higher reliability, and is extremely suitable for connectors or scenarios with high current-carrying capacity and high heat dissipation requirements.

[0003] However, the active solder paste currently used for welding AMB copper-clad ceramic substrates has poor spreading and wetting properties on the ceramic substrate, resulting in problems such as large voids and severe warping between the welded AMB ceramic substrate and the copper foil. In addition, the inherent difference in the coefficient of thermal expansion between the ceramic substrate and the copper will cause large stresses at the copper-ceramic interface when the ceramic copper-clad board withstands thermal cycling, leading to ceramic cracking or copper layer peeling, and further resulting in module failure and reduced reliability.

[0004] The disclosed patent CN115626835A proposes a manufacturing method and product of a ceramic-based copper-clad board. It uses a vapor deposition process technology to metallize the upper and lower surfaces of the ceramic substrate, forming a dense metallized intermediate layer on the surface of the ceramic substrate; then the metallized intermediate layer is thickened by electroplating; finally, the treated ceramic substrate and the copper foil are pressed together and then subjected to high-temperature diffusion welding under the protection of a reducing atmosphere. Although the ceramic-based copper-clad board obtained by this technology has excellent peel strength, the entire process is relatively complex, the cost is relatively high, and it is found that the bonding strength is relatively low after actual simulation tests. Summary of the Invention

[0005] Based on the above technical problems, the present invention provides an AMB copper-clad ceramic substrate and a welding method thereof. By improving the process for metallizing the ceramic substrate in the AMB process, the obtained AMB copper-clad ceramic substrate has the characteristics of high interfacial bonding force, low warpage and void rate, and excellent resistance to thermal shock.

[0006] The present invention proposes a welding method for an AMB copper-clad ceramic substrate, comprising the following steps:

[0007] S1. Mix a metal powder containing inactive elements Ag and Cu and an active element Ti with an organic carrier to obtain an active solder paste;

[0008] S2. Coat the surface of the ceramic substrate with the active solder paste, and then stack a copper foil on the surface of the ceramic substrate coated with the active solder paste. After vacuum sintering, the AMB copper-clad ceramic substrate is obtained.

[0009] In the present invention, a metal powder containing inactive elements Ag and Cu and an active element Ti is made into an active solder paste to realize the connection between the ceramic substrate and the copper foil. Among them, the presence of the active element Ti makes the solder paste have good wettability to the ceramic substrate. After the Ag and Cu alloys melt to form a liquid state, Ti can diffuse to the interface of the ceramic substrate and realize the wetting of the ceramic by reacting with the ceramic substrate, and finally realize the reliable connection between the ceramic and the copper foil.

[0010] Preferably, the inactive elements account for 92.5 - 97.5% of the total mass of the metal powder, and the active element accounts for 2.5 - 7.5% of the total mass of the metal powder;

[0011] Preferably, the mass ratio of the inactive elements Ag and Cu is 100:20 - 45;

[0012] Preferably, the inactive elements further include In, and the mass ratio of Ag and In is 100:1 - 15.

[0013] Preferably, the metal powder includes pure silver powder, pure copper powder, silver-copper alloy powder, pure titanium powder or titanium hydride powder;

[0014] Preferably, the particle size of the metal powder is ≤20 μm.

[0015] Preferably, the organic carrier includes an adhesive and an organic solvent; the adhesive is a polyacrylate, which is formed by copolymerizing a non-hydroxy acrylate monomer, a hydroxy acrylate monomer and a vinyl imidazole monomer; the organic solvent is at least one of ethanol, ethylene glycol, isopropyl alcohol, terpineol, propylene glycol phenyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, alcohol ester twelve or butyl carbitol acetate;

[0016] Preferably, the mass ratio of the adhesive to the organic solvent is 15 - 45:100.

[0017] In the present invention, the binder is selected as a polyacrylate formed by copolymerizing non-hydroxy acrylate monomers, hydroxy acrylate monomers and vinyl imidazole monomers. On the one hand, the compounding of non-hydroxy acrylate monomers, hydroxy acrylate monomers and vinyl imidazole monomers ensures that the polyacrylate has sufficient adhesion ability and low viscosity, which is beneficial to improving the dispersion efficiency of the solder paste and avoiding insufficient fluidity of the solder paste, resulting in difficult soldering. On the other hand, the introduction of hydroxy acrylate monomers and vinyl imidazole monomers endows the polyacrylate with strong polar characteristics, and an effective affinity is formed between the imidazole group and inactive elements Ag and Cu as well as active element Ti, which not only helps the wetting and diffusion of metal powder, but also helps to protect the metal powder, and can effectively prevent the brazing failure caused by the oxidation reaction of active elements during the preparation process, so that the active solder paste has good continuous coating stability.

[0018] Preferably, the non-hydroxy acrylate monomer is at least one of methyl acrylate, ethyl acrylate, n-butyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate or glycidyl methacrylate; the hydroxy acrylate monomer is at least one of 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate or polyethylene glycol methacrylate; the vinyl imidazole monomer is 1-vinyl imidazole or 4-vinyl imidazole;

[0019] Preferably, the molar ratio of the non-hydroxy acrylate monomer, the hydroxy acrylate monomer and the vinyl imidazole monomer is 1:0.2-0.5:0.1-0.3.

[0020] Preferably, the organic carrier further includes a plasticizer, a dispersant or a thixotropic agent;

[0021] Preferably, the plasticizer is at least one of dibutyl phthalate, citrate or epoxidized soybean oil; the dispersant is at least one of stearic acid, oleic acid, linoleic acid, linolenic acid, zinc naphthenate, alkylphenol polyoxyethylene ether, erucamide or glyceryl trioleate; the thixotropic agent is at least one of polyamide, polyamide wax, hydrogenated castor oil, organic bentonite or triethyl citrate.

[0022] Preferably, before the active solder paste is coated on the surface of the ceramic substrate, the ceramic substrate is pretreated, specifically, first treated with an alkaline solution and then immersed in a chloromethyltriethoxysilane solution for treatment;

[0023] Preferably, the alkaline solution is a NaOH or KOH solution with a content of 5-20 wt%.

[0024] In the present invention, the ceramic substrate is first treated with an alkaline solution to activate the surface, and then treated with chloromethyltriethoxysilane. The chloromethyltriethoxysilane is bonded to the surface of the ceramic substrate through silanol groups, achieving the purpose of grafting chloromethyltriethoxysilane on the surface of the ceramic substrate. At this time, the chloromethyltriethoxysilane, as an organic group, increases the dispersion and wetting effect of the active solder paste on the surface of the ceramic substrate. More importantly, the chloromethyl group can undergo a quaternization reaction with the imidazole group in the aforementioned polyacrylate binder. On the one hand, it promotes the adhesion ability of the metal solder paste on the surface of the ceramic substrate, significantly improves the chemical bonding force between the solder layer and the ceramic surface, and reduces the voids and gaps in the solder bonding layer. On the other hand, the quaternary ammonium salt formed by the quaternization reaction promotes the activation effect of the active solder, thereby further improving the reliability of the welding.

[0025] Preferably, the temperature of the vacuum sintering is 700 - 850 °C, the holding time is 10 - 50 min, and the vacuum degree is ≤ 0.01 Pa.

[0026] Preferably, the ceramic substrate is Si3N4 ceramic or AlN ceramic.

[0027] The present invention also provides an AMB copper-clad ceramic substrate, which is obtained by the above welding method.

[0028] The beneficial effects of the present invention are as follows:

[0029] An AMB copper-clad ceramic substrate and its welding method provided by the present invention prepare a highly reliable AMB copper-clad ceramic substrate through the design of the metal components of the active solder, the selection and preparation of the organic carrier, and the control of the welding process between the ceramic and the copper foil. In the design of the metal components of the active solder, the active element Ti can be fully dissolved in the alloy, which is beneficial to exert the activity of the Ti element and thus improve the reliability of the connection; the selection and preparation of the organic carrier ensure the dispersion and wetting performance of the solder paste and leave no residue after welding, which also improves the reliability of the welding; in the supporting welding process, by chemically modifying the ceramic surface, the adhesion of the solder can be improved, and the high interfacial bonding force between the solder layer and the ceramic surface can be significantly improved. The present invention prepares an active metal solder paste for connecting the ceramic and the copper foil, which can effectively reduce the connection strength between the ceramic and the copper foil, reduce the porosity and warpage, solve the reliability problem of the connection between the ceramic and the copper foil, and improve the market share of the AMB copper-clad ceramic substrate. Description of the Drawings

[0030] Figure 1 It is the interfacial microstructure diagram of the AMB copper-clad ceramic substrate described in Example 1. Detailed Embodiments

[0031] Next, the present invention will detail the technical solution through specific embodiments. However, it should be clearly stated that these embodiments are for illustrative purposes only and should not be construed as limiting the scope of the present invention.

[0032] In the following embodiments, the size of the Si3N4 ceramic used is 100mm×50mm×0.32mm, and the size of the oxygen-free copper foil is 100mm×50mm×0.3mm.

[0033] Example 1

[0034] This example presents a welding method for an AMB copper-clad ceramic substrate, including:

[0035] (1) Place 73.5% of pure silver powder (D50 is 5μm), 23.0% of pure copper powder (D50 is 2μm), and 3.5% of pure titanium powder (D50 is 2μm) in a ball mill tank according to mass percentage. Add acetone and mix until it becomes viscous. The ball-to-material ratio is 2:1. After ball milling at a speed of 160r / min for 3h, take it out and dry it to obtain metal powder; add 23% of polyacrylate, 21% of ethanol, 15% of terpineol, and 41% of diethylene glycol monobutyl ether to a high-speed dispersion mixer, and stir at a speed of 1500r / min for 30min to obtain an organic carrier; add the metal powder and the organic carrier to a three-roll grinder according to a mass ratio of 6:1 and grind evenly to obtain an active solder paste;

[0036] Among them, the polyacrylate is synthesized according to the following method:

[0037] Dissolve the initiator azobisisobutyronitrile in 1,4-dioxane, and then add methyl methacrylate, butyl acrylate, 2-hydroxyethyl methacrylate, and 4-vinylimidazole. The molar ratio of azobisisobutyronitrile, methyl methacrylate, butyl acrylate, 2-hydroxyethyl methacrylate, and 4-vinylimidazole is 0.005:0.6:0.4:0.3:0.2. Heat to 70°C and stir for 12h, then add petroleum ether to precipitate the polymer, that is, obtain the polyacrylate;

[0038] (2) Immerse the Si3N4 ceramic and the oxygen-free copper foil in deionized water and ultrasonically clean for 10min respectively, then immerse in absolute ethanol and ultrasonically clean for 10min, take them out and dry; use the screen printing process to evenly coat the above-mentioned active solder paste on the upper and lower surfaces of the Si3N4 ceramic, and the coating thicknesses are 0.02mm respectively. Place two pieces of oxygen-free copper foil on the upper and lower surfaces of the Si3N4 ceramic coated with the active solder paste. After fixing with a fixture, place it in a vacuum brazing furnace (the vacuum degree is 10 -2Sintering is carried out in (Pa), specifically, heating to 220 °C at a heating rate of 10 °C / min, holding for 10 min to remove the organic solvent in the active solder paste, then heating to 790 °C at a heating rate of 5 °C / min, holding for 30 min, and after furnace cooling, the AMB copper-clad ceramic substrate is obtained. The welded specimen and microstructure are as shown in Figure 1 shown.

[0039] Example 2

[0040] This example proposes a welding method for an AMB copper-clad ceramic substrate. Specifically, referring to Example 1, except that in step (1), 73.0% of pure silver powder (D50 is 5 μm), 23.0% of pure copper powder (D50 is 2 μm), and 4.0% of titanium hydride powder (D50 is 15 μm) are placed in a ball mill tank according to mass percentage, acetone is added and mixed until viscous, the ball-to-material ratio is 2:1, ball milled at a speed of 200 r / min for 3 h, taken out and dried to obtain metal powder; 26% of polyacrylate, 6% of dibutyl phthalate, 4% of polyamide wax, 32% of isopropanol, 12% of diethylene glycol monoethyl ether, and 20% of alcohol ester dodecyl are added to a high-speed dispersion mixer according to mass percentage, stirred at a speed of 1500 r / min for 30 min to obtain an organic carrier; the metal powder and the organic carrier are added to a three-roll grinder according to a mass ratio of 6:1 and ground evenly to obtain an active solder paste.

[0041] Example 3

[0042] This example proposes a welding method for an AMB copper-clad ceramic substrate. Specifically, referring to Example 1, except that in step (1), 72.5% of pure silver powder (D50 is 5 μm), 18.0% of pure copper powder (D50 is 2 μm), 3.0% of pure titanium powder (D50 is 2 μm), and 6.5% of pure indium powder (D50 is 10 μm) are placed in a ball mill tank according to mass percentage, acetone is added and mixed until viscous, the ball-to-material ratio is 2:1, ball milled at a speed of 160 r / min for 3 h, taken out and dried to obtain metal powder; 20% of polyacrylate, 19% of ethanol, 25% of butyl carbitol acetate, and 36% of diethylene glycol monobutyl ether are added to a high-speed dispersion mixer according to mass percentage, stirred at a speed of 1500 r / min for 30 min to obtain an organic carrier; the metal powder and the organic carrier are added to a three-roll grinder according to a mass ratio of 6:1 and ground evenly to obtain an active solder paste.

[0043] Example 4

[0044] This embodiment presents a welding method for an AMB copper-clad ceramic substrate. Specifically referring to Embodiment 1, except that in step (2), the Si3N4 ceramic and the oxygen-free copper foil are respectively immersed in deionized water and ultrasonically cleaned for 10 min, then immersed in absolute ethanol and ultrasonically cleaned for 10 min, taken out and dried; the treated Si3N4 ceramic is further immersed in a NaOH solution with a content of 10 wt% and ultrasonically treated for 5 min, taken out and washed with pure water for 2 min, then immersed in an ethanol solution containing 1 wt% chloromethyltriethoxysilane, ultrasonically treated for 20 min, taken out and dried to obtain a pretreated Si3N4 ceramic; the above-mentioned active solder paste is evenly coated on the upper and lower surfaces of the pretreated Si3N4 ceramic by screen printing, and the coating thicknesses are 0.02 mm respectively. Two oxygen-free copper foils are placed on the upper and lower surfaces of the Si3N4 ceramic coated with the active solder paste. After being fixed by a fixture, it is sintered in a vacuum brazing furnace (vacuum degree is 10 -2 Pa). Specifically, it is heated to 220 °C at a heating rate of 10 °C / min and held for 10 min to remove the organic solvents in the active solder paste, then heated to 790 °C at a heating rate of 5 °C / min and held for 30 min. After cooling with the furnace, the AMB copper-clad ceramic substrate is obtained.

[0045] Comparative Example 1

[0046] This comparative example presents a welding method for an AMB copper-clad ceramic substrate. Specifically referring to Embodiment 1, except that in step (1), the polyacrylate is synthesized according to the following method:

[0047] The initiator azobisisobutyronitrile is dissolved in 1,4-dioxane, and then methyl methacrylate, butyl acrylate and 2-hydroxyethyl methacrylate are added. The molar ratio of azobisisobutyronitrile, methyl methacrylate, butyl acrylate and 2-hydroxyethyl methacrylate is 0.005:0.6:0.4:0.3. It is heated to 70 °C and stirred for 12 h, and petroleum ether is added to precipitate the polymer, thus obtaining the polyacrylate.

[0048] Comparative Example 2

[0049] This comparative example presents a soldering method for an AMB copper-clad ceramic substrate. Specifically referring to Example 1, except that in step (2), the Si3N4 ceramic and the oxygen-free copper foil are respectively immersed in deionized water and ultrasonically cleaned for 10 minutes, then immersed in absolute ethanol and ultrasonically cleaned for 10 minutes, taken out and dried; the processed Si3N4 ceramic is immersed in a NaOH solution with a content of 10 wt% and ultrasonically treated for 5 minutes, taken out and washed with pure water for 2 minutes, then immersed in an ethanol solution containing 1 wt% methyltriethoxysilane and ultrasonically treated for 20 minutes, taken out and dried to obtain the pretreated Si3N4 ceramic; the above-mentioned active solder paste is evenly coated on the upper and lower surfaces of the pretreated Si3N4 ceramic by screen printing, and the coating thicknesses are 0.02 mm respectively. Two oxygen-free copper foils are placed on the upper and lower surfaces of the Si3N4 ceramic coated with the active solder paste. After being fixed by a fixture, sintering is carried out in a vacuum brazing furnace (vacuum degree is 10 -2 Pa). Specifically, it is heated to 220 °C at a heating rate of 10 °C / min, held for 10 minutes to remove the organic solvent in the active solder paste, then heated to 790 °C at a heating rate of 5 °C / min, held for 30 minutes, and after furnace cooling, the AMB copper-clad ceramic substrate is obtained.

[0050] The AMB copper-clad ceramic substrates obtained in the examples and comparative examples are subjected to the following performance tests:

[0051] Void ratio: The void ratio is tested using an ultrasonic scanning microscope (model SAM301);

[0052] Peel strength: The peel strength is tested using a universal tensile testing machine (model HJS-100KG) with reference to the peel strength test part of the metal-clad thin sheet in the IPC-TM-650 test method manual (etching out 3 mm copper foil);

[0053] Rapid thermal shock performance: Keep at -50 °C for 15 minutes, heat up to 150 °C in 5 minutes, keep at 150 °C for 15 minutes, cool down to -50 °C in 5 minutes, and after 2000 cycles, observe whether the specimen cracks.

[0054] Table 1 Performance results of the AMB copper-clad ceramic substrates in the examples and comparative examples

[0055] Void ratio Peel strength Rapid thermal shock performance Warpage Example 1 0.02％ 28 N / mm No cracking ≤0.1 mm Example 2 0.04％ 31 N / mm No cracking ≤0.1 mm Example 3 0.02％ 26 N / mm No cracking ≤0.1 mm Example 4 0 42 N / mm No cracking ≤0.1 mm Comparative example 1 0.8％ 16 N / mm Cracking occurred ≥0.2 mm Comparative example 2 0.02％ 27 N / mm No cracking ≤0.1 mm

[0056] As can be seen from Table 1 above, the AMB copper-clad ceramic substrate obtained by the present invention has a good surface state, and has the characteristics of high bonding strength, low warpage and void ratio, and excellent thermal shock resistance.

[0057] The above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, making equivalent substitutions or changes, shall be covered by the protection scope of the present invention.

Claims

1. A welding method for an AMB copper-clad ceramic substrate, characterized in that: The steps include: S1, mixing metal powder containing inactive elements Ag and Cu and active element Ti with an organic carrier to obtain an active solder paste; S2, coating the active solder paste on the surface of the ceramic substrate, and then stacking copper foil on the surface of the ceramic substrate coated with the active solder paste, and after vacuum sintering, the AMB copper-clad ceramic substrate is obtained.

2. The welding method of the AMB copper-clad ceramic substrate according to claim 1, characterized in that: The inactive elements account for 92.5-97.5% of the total mass of the metal powder, and the active elements account for 2.5-7.5% of the total mass of the metal powder; Preferably, the mass ratio of the inactive elements Ag and Cu is 100:20-45; Preferably, the inactive element further includes In, and the mass ratio of Ag to In is 100:1-15.

3. The welding method of the AMB copper-clad ceramic substrate according to claim 1 or 2, characterized in that: The metal powder includes pure silver powder, pure copper powder, silver-copper alloy powder, pure titanium powder or titanium hydride powder; Preferably, the particle size of the metal powder is ≤20 μm.

4. The welding method of the AMB copper-clad ceramic substrate according to any one of claims 1 to 3, characterized in that: The organic carrier comprises a binder and an organic solvent; the binder is a polyacrylate, which is formed by copolymerizing a non-hydroxyl acrylate monomer, a hydroxyl acrylate monomer and a vinyl imidazole monomer; the organic solvent is at least one of ethanol, ethylene glycol, isopropanol, terpineol, propylene glycol phenyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, alcohol ester dodecyl or butyl carbitol acetate; Preferably, the mass ratio of the adhesive to the organic solvent is 15-45:

100.

5. The welding method of the AMB copper-clad ceramic substrate according to claim 4, characterized in that: The non-hydroxy acrylate monomer is at least one of methyl acrylate, ethyl acrylate, n-butyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate or glycidyl methacrylate; the hydroxy acrylate monomer is at least one of hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate or polyethylene glycol methacrylate; the vinyl imidazole monomer is 1-vinylimidazole or 4-vinylimidazole; Preferably, the molar ratio of the non-hydroxy acrylate monomer, the hydroxy acrylate monomer and the vinyl imidazole monomer is 1:0.2-0.5:0.1-0.

3.

6. The welding method of the AMB copper-clad ceramic substrate according to claim 4 or 5, characterized in that: The organic carrier also includes a plasticizer, a dispersant or a thixotropic agent; Preferably, the plasticizer is at least one of dibutyl phthalate, citrate or epoxy soybean oil; the dispersant is at least one of stearic acid, oleic acid, linoleic acid, linolenic acid, zinc cyclohexane, alkylphenol polyoxyethylene ether, erucamide or triolein; the thixotropic agent is at least one of polyamide, polyamide wax, hydrogenated castor oil, organic bentonite or triethyl citrate.

7. The welding method of the AMB copper-clad ceramic substrate according to any one of claims 1 to 6, characterized in that: Before applying the active solder paste to the surface of the ceramic substrate, the ceramic substrate is pre-treated, specifically, first treated with an alkaline solution and then immersed in a chloromethyltriethoxysilane solution; Preferably, the alkaline solution is a NaOH or KOH solution with a content of 5-20 wt%.

8. The welding method of the AMB copper-clad ceramic substrate according to any one of claims 1 to 7, characterized in that: The vacuum sintering temperature is 700-850° C., the heat preservation time is 10-50 min, and the vacuum degree is ≤0.01 Pa.

9. The welding method of the AMB copper-clad ceramic substrate according to any one of claims 1 to 8, characterized in that: The ceramic substrate is Si3N4 ceramic or AlN ceramic.

10. An AMB copper-clad ceramic substrate, characterized in that: The welding method is obtained by welding according to any one of claims 1 to 9.

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