Nano-copper sintered ceramic substrate and preparation method thereof

Abstract

The present invention discloses a nano-copper sintered ceramic substrate and its preparation method. From top to bottom, the substrate comprises a copper sheet, a connecting pad, a ceramic substrate, a connecting pad, and a copper sheet, stacked in sequence to form a sandwich structure. A layer of nano-copper particles is deposited on the inner surface of the copper sheet connecting to the connecting pad via magnetron sputtering. Nano-copper paste is screen-printed on the connecting pads on both sides of the connecting pad, the copper sheet, and the ceramic substrate. The advantages of this invention are that it reduces the generation of interfacial voids, improves peel strength, and reduces sintering temperature. The use of silver-free sintering materials reduces manufacturing costs and sintering time.

Description

Technical Field

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

[0002] With the advancement of materials science, the scale effect of nanomaterials during the sintering process has become increasingly prominent. Specifically, as the nanoscale continues to shrink, the sintering temperature also decreases, even reaching temperatures below the material's melting point. Currently, in the field of copper sintering, copper nanomaterials can achieve surface melting at temperatures far below the copper melting point, inducing interdiffusion and the formation of sintering necks, thereby strengthening the bond. However, this approach has generally been applied to chip packaging and has not yet been applied to copper-clad ceramic substrates.

[0003] The silver-containing solder used in existing conventional AMB (active metal brazing) has the characteristics of high cost, high brazing temperature and long time, which is not conducive to large-scale application. If copper solder paste is used, the bonding strength is low, and the copper particles undergo self-oxidation, which is not conducive to the atomic diffusion of densification. Therefore, there is an urgent need to find a nano-copper solder brazing method that can improve activity at the nanoscale and shorten the reaction time. Summary of the Invention

[0004] The purpose of the present invention is to provide a nano-copper sintered ceramic substrate and a preparation method thereof, which can reduce the generation of interface voids, improve peel strength while reducing the sintering temperature, adopt silver-free sintering materials, and reduce manufacturing costs and sintering time.

[0005] The above technical objectives of the present invention are achieved through the following technical solutions:

[0006] A nano-copper sintered ceramic substrate, characterized in that, from top to bottom, a copper sheet, a connecting welding sheet, a ceramic substrate, a connecting welding sheet and a copper sheet are stacked in sequence to form a sandwich structure. A layer of nano-copper particles is provided on the connecting surface between the inner side of the copper sheet and the connecting welding sheet by magnetron sputtering, and nano-copper paste is screen-printed on the connecting surfaces between the two sides of the connecting welding sheet and the copper sheet and the ceramic substrate.

[0007] Preferably, the particle size of the nano-copper particles is 40-60 nm, the thickness of the nano-copper paste on both sides of the connecting solder piece is 10-16 nm, and the thickness of the connecting solder piece is 7-9 μm.

[0008] Preferably, the connecting welding piece is a titanium-copper alloy welding piece.

[0009] Preferably, the preparation method of the nano copper paste is: dissolving Cu(OH)2 and polyvinyl pyrrolidone in 1,3-propylene glycol in an equal mass ratio, rapidly stirring evenly at room temperature, and heating to 190°C. After heating for 150 minutes, the solution is cooled to ambient temperature, and the prepared copper particles are subjected to multiple centrifugal separations and ethanol washings to remove excess solvent and dried. Finally, the dried copper particles are mixed with L-ascorbic acid solvent in a mass ratio of 85:15 to form a nano copper paste.

[0010] Preferably, the L-ascorbic acid solvent is formed by dissolving 10 wt.% of L-ascorbic acid in ethylene glycol at 60°C.

[0011] A method for preparing a nano-copper sintered ceramic substrate, characterized in that it specifically comprises the following steps:

[0012] Step 1: forming a layer of dispersed copper nanoparticles on a copper substrate by a magnetron sputtering process, and spraying an antioxidant on the surface of the copper nanoparticles;

[0013] Step 2: Screen-printing the nano-copper paste on both sides of the titanium-copper solder sheet to form a solder sheet with nano-copper particles;

[0014] Step 3: stacking the copper sheet after sputtering of copper nanoparticles, the nano-copper paste solder sheet, and the ceramic substrate in sequence to form a sandwich hierarchical structure, and heating and draining the liquid under an N2 atmosphere;

[0015] Step 4: After the liquid is drained, the substrate is placed in a N2 atmosphere or vacuum for high-pressure sintering. After the sintering is completed and the solvent has completely evaporated, the substrate is taken out to complete the first sintering of the ceramic substrate.

[0016] Step 5: After cooling, take the substrate out of the furnace and repeat steps 1 to 4 to sinter the second side to obtain a double-sided sintered copper clad substrate.

[0017] Preferably, the magnetron sputtering parameters in step 1 are as follows: DC mode, power of 50~300w, target diameter of 2~4 inches, gas of pure Ar, gas pressure of 5-10mTorr, copper substrate temperature of room temperature, deposition rate of 10~50nm / min, and antioxidant of ethanol solution containing 2.5% formic acid.

[0018] Preferably, the specific parameters for drainage in step 3 are: 7×10 4 Pa pure nitrogen atmosphere, heating rate 10℃ / min, debinding temperature 450℃, and holding time 30min.

[0019] Preferably, in step 4, the sintering is carried out at 500-700° C. in a nitrogen atmosphere or at 0.5 MPa under vacuum, and the sintering time is 90 minutes.

[0020] In summary, the present invention has the following beneficial effects:

[0021] The present invention introduces nano-copper sintering technology into copper-clad ceramic substrates to achieve low-temperature sintering under silver-free brazing conditions, while reducing reaction time, reducing energy loss, and improving the preparation efficiency of copper-clad ceramic substrates, which is conducive to large-scale application.

[0022] The nano-copper solder paste used in the present invention has high bonding strength. By pre-screening the nano-copper solder paste on the titanium-copper solder sheet and cooperating with the copper nanoparticles pre-sputtered on the copper sheet, effective sintering interconnection is achieved. Nano-copper has good resistance to electromigration and has electrical conductivity and thermal conductivity comparable to silver. It can well replace the Ag component in the solder paste, greatly reducing costs.

[0023] Since nano-copper itself has active chemical properties and is easily oxidized, which leads to an increase in sintering temperature and reduces conductivity and connection strength, the present application uses a spray-formic acid ethanol solution to soak the pre-sputtered copper nanoparticles on the copper sheet to remove surface oxides. At the same time, L-ascorbic acid is used in the nano-copper paste to inhibit the spontaneous oxidation of the copper particles when they come into contact with air. In addition, the surface of the copper particles is coated with polyvinyl pyrrolidone to further prevent surface oxidation when they come into contact with oxygen and moisture in the reagent, thereby achieving effective bonding between the copper sheet and the soldering sheet.

[0024] The nano-copper solder paste of the present invention mainly utilizes the scale effect to improve the brazing bonding activity. If nano-copper is directly used on a ceramic substrate, the substrate bonding interface strength is very low due to the lack of a reactive intermediate layer (TiN). The present invention avoids the porosity problem caused by silver-copper heterogeneous interface diffusion by combining nano-copper with a titanium-copper alloy solder sheet, and can improve the overall reliability of the substrate.

[0025] The present invention adopts a welding method of combining solder paste with a solder sheet, and the copper nanoparticles on the copper sheet are sprayed with an ethanol solution of formic acid. This method will result in a large number of pores caused by organic volatilization during the sintering and welding process, ultimately resulting in poor welding effect and low interface peeling strength. The present invention adopts a pre-draining method, so that the nano-copper paste is in a pressureless and free state during the process. As the temperature slowly increases, the organic components in the solder paste and the ethanol solution of formic acid are respectively decomposed and volatilized, and finally only the nano-copper particles are left in the weld for sintering connection, thereby greatly reducing the generation of interface voids. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a scanning electron microscope image of the connection interface structure of the nano-copper sintered ceramic substrate prepared in Example 1. DETAILED DESCRIPTION

[0027] The specific embodiments of the present invention will be further described below in conjunction with the accompanying drawings. This embodiment does not constitute a limitation to the present invention.

[0028] A nano-copper sintered ceramic substrate comprises, from top to bottom, a copper sheet, a connecting solder sheet, a ceramic substrate, a connecting solder sheet, and a copper sheet, which are stacked in sequence to form a sandwich structure. A layer of nano-copper particles is provided on the connecting surface between the inner side of the copper sheet and the connecting solder sheet by magnetron sputtering, and nano-copper paste is screen-printed on the connecting surfaces between the two sides of the connecting solder sheet and the copper sheet and the ceramic substrate.

[0029] The particle size of the nano-copper particles is 40-60 nm, the thickness of the nano-copper paste on both sides of the connecting solder piece is 10-16 nm, and the thickness of the connecting solder piece is 7-9 μm.

[0030] The connecting welding piece is a titanium-copper alloy welding piece.

[0031] The preparation method of nano copper paste is as follows: Cu(OH)2 and polyvinyl pyrrolidone are dissolved in 1,3-propylene glycol in equal mass ratios, quickly stirred evenly at room temperature, and heated to 190°C. After heating for 150 minutes, the solution is cooled to ambient temperature. The prepared copper particles are subjected to multiple centrifugal separations and ethanol washings to remove excess solvent and dried. Finally, the dried copper particles are mixed with L-ascorbic acid solvent in a mass ratio of 85:15 to form a nano copper paste.

[0032] The L-ascorbic acid solvent was prepared by dissolving 10 wt.% of L-ascorbic acid in ethylene glycol at 60°C.

[0033] Example 1

[0034] A method for preparing a nano-copper sintered ceramic substrate comprises the following steps:

[0035] Step 1: Form a layer of dispersed copper nanoparticles on a copper substrate by magnetron sputtering, and spray an ethanol solution containing 2.5% formic acid on the surface of the copper nanoparticles. The magnetron sputtering parameters are as follows: DC mode, power of 100 W, target diameter of 2 inches, pure Ar gas, gas pressure of 5 mTorr, copper substrate temperature at room temperature, and deposition rate of 10 nm / min.

[0036] Step 2: Screen-printing the nano-copper paste on both sides of the titanium-copper solder sheet to form a solder sheet with nano-copper particles;

[0037] Step 3: The copper sheet after sputtering of copper nanoparticles, the nano copper paste solder sheet, and the ceramic substrate are stacked in sequence to form a sandwich structure, and the temperature is increased and the liquid is discharged under N2 atmosphere, specifically 7×10 4 Pa pure nitrogen atmosphere, heating rate 10℃ / min, debinding temperature 450℃, holding time 30min;

[0038] Step 4: After the liquid is drained, the substrate is placed in a nitrogen atmosphere at 500°C or in a vacuum at 0.5 MPa for high pressure sintering for 90 minutes. After the solvent has completely evaporated, the substrate is taken out to complete the first sintering of the ceramic substrate.

[0039] Step 5: After cooling, take the substrate out of the furnace and repeat steps 1 to 4 to sinter the second side to obtain a double-sided sintered copper clad substrate.

[0040] Example 2

[0041] A method for preparing a nano-copper sintered ceramic substrate comprises the following steps:

[0042] Step 1: Form a layer of dispersed copper nanoparticles on a copper substrate by magnetron sputtering, and spray an ethanol solution containing 2.5% formic acid on the surface of the copper nanoparticles. The magnetron sputtering parameters are as follows: DC mode, power of 50W, target diameter of 4 inches, gas of pure Ar, gas pressure of 10mTorr, copper substrate temperature of room temperature, and deposition rate of 10nm / min.

[0043] Step 2: Screen-printing the nano-copper paste on both sides of the titanium-copper solder sheet to form a solder sheet with nano-copper particles;

[0044] Step 3: The copper sheet after sputtering of copper nanoparticles, the nano copper paste solder sheet, and the ceramic substrate are stacked in sequence to form a sandwich structure, and the temperature is increased and the liquid is discharged under N2 atmosphere, specifically 7×10 4 Pa pure nitrogen atmosphere, heating rate 10℃ / min, debinding temperature 450℃, holding time 30min;

[0045] Step 4: After the drainage is completed, the substrate is placed in a nitrogen atmosphere at 600°C or in a vacuum at 0.5 MPa for high pressure sintering for 90 minutes. After the sintering is completed and the solvent has completely evaporated, the substrate is taken out to complete the first sintering of the ceramic substrate.

[0046] Step 5: After cooling, take the substrate out of the furnace and repeat steps 1 to 4 to sinter the second side to obtain a double-sided sintered copper clad substrate.

[0047] Example 3

[0048] A method for preparing a nano-copper sintered ceramic substrate comprises the following steps:

[0049] Step 1: Form a layer of dispersed copper nanoparticles on a copper substrate by magnetron sputtering, and spray an ethanol solution containing 2.5% formic acid on the surface of the copper nanoparticles. The magnetron sputtering parameters are as follows: DC mode, power of 200 W, target diameter of 3 inches, gas of pure Ar, gas pressure of 8 mTorr, copper substrate temperature of room temperature, and deposition rate of 40 nm / min.

[0050] Step 2: Screen-printing the nano-copper paste on both sides of the titanium-copper solder sheet to form a solder sheet with nano-copper particles;

[0051] Step 3: The copper sheet after sputtering of copper nanoparticles, the nano copper paste solder sheet, and the ceramic substrate are stacked in sequence to form a sandwich structure, and the temperature is increased and the liquid is discharged under N2 atmosphere, specifically 7×10 4 Pa pure nitrogen atmosphere, heating rate 10℃ / min, debinding temperature 450℃, holding time 30min;

[0052] Step 4: After the drainage is completed, the substrate is placed in a nitrogen atmosphere at 600°C or in a vacuum at 0.5 MPa for high pressure sintering for 90 minutes. After the sintering is completed and the solvent has completely evaporated, the substrate is taken out to complete the first sintering of the ceramic substrate.

[0053] Step 5: After cooling, take the substrate out of the furnace and repeat steps 1 to 4 to sinter the second side to obtain a double-sided sintered copper clad substrate.

[0054] Example 4 A method for preparing a nano-copper sintered ceramic substrate comprises the following steps:

[0055] Step 1: Form a layer of dispersed copper nanoparticles on a copper substrate by magnetron sputtering, and spray an ethanol solution containing 2.5% formic acid on the surface of the copper nanoparticles. The magnetron sputtering parameters are as follows: DC mode, power of 300 W, target diameter of 4 inches, gas of pure Ar, gas pressure of 10 mTorr, copper substrate temperature of room temperature, and deposition rate of 50 nm / min.

[0056] Step 2: Screen-printing the nano-copper paste on both sides of the titanium-copper solder sheet to form a solder sheet with nano-copper particles;

[0057] Step 3: The copper sheet after sputtering of copper nanoparticles, the nano copper paste solder sheet, and the ceramic substrate are stacked in sequence to form a sandwich structure, and the temperature is increased and the liquid is discharged under N2 atmosphere, specifically 7×10 4 Pa pure nitrogen atmosphere, heating rate 10℃ / min, debinding temperature 450℃, holding time 30min;

[0058] Step 4: After the liquid is drained, the substrate is placed in a nitrogen atmosphere at 700°C or in a vacuum at 0.5 MPa for high pressure sintering for 90 minutes. After the solvent has completely evaporated, the substrate is taken out to complete the first sintering of the ceramic substrate.

[0059] Step 5: After cooling, take the substrate out of the furnace and repeat steps 1 to 4 to sinter the second side to obtain a double-sided sintered copper clad substrate.

[0060] The above embodiment and the copper-clad ceramic substrate sintered with AgCuTi active brazing material in the prior art were used as a comparative example to conduct performance testing. The specific data are shown in Table 1 below:

[0061] Table 1

[0062] Depend on Figure 1 As can be seen from the above table, the nano-copper sintered ceramic substrate prepared by the present invention has significantly reduced voids on the welding interface. Since the interface voids not only pose a hidden danger of local discharge, but also reduce the bonding strength at the interface, resulting in fluctuations in the number of temperature cycles of the substrate, it can be clearly seen from the data in Table 1 that the performance of the nano-copper sintered ceramic substrate prepared by the present invention is comprehensively improved compared with the comparative example. At the same time, due to the use of a silver-free soldering process, the production cost is lower. The characteristics of nano-copper can also reduce the brazing temperature and shorten the production time. In combination with the process steps of antioxidant treatment and pre-drainage, the phenomenon of solder migration is reduced, and the generation of interface voids is reduced, thereby achieving a comprehensive improvement in performance, process, and cost savings.

[0063] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art may make various modifications or equivalent substitutions to the present invention within the essence and protection scope of the present invention, and such modifications or equivalent substitutions should also be deemed to fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing a nano-copper sintered ceramic substrate, characterized in that: The nano-copper sintered ceramic substrate is composed of a copper sheet, a connecting pad, a ceramic substrate, a connecting pad, and a copper sheet stacked from top to bottom to form a sandwich structure. A layer of nano-copper particles is deposited on the inner side of the copper sheet and the connecting pad by magnetron sputtering. Nano-copper paste is screen-printed on the connecting pads on both sides of the connecting pad and the copper sheet and ceramic substrate. The nano-copper paste is prepared by dissolving Cu(OH)2 and polyvinyl pyrrolidone in 1,3-propylene glycol in an equal mass ratio, rapidly stirring the mixture at room temperature, and heating the mixture to 190°C for 150 minutes. The solution is then cooled to ambient temperature, and the prepared copper particles are subjected to multiple centrifugation and ethanol washing to remove excess solvent and dried. Finally, the dried copper particles are mixed with L-ascorbic acid solvent in a mass ratio of 85:15 to form the nano-copper paste. The L-ascorbic acid solvent is formed by dissolving 10 wt.% of L-ascorbic acid in ethylene glycol at 60° C.; The method for preparing the nano-copper sintered ceramic substrate specifically comprises the following steps: Step 1: forming a layer of dispersed copper nanoparticles on a copper substrate by a magnetron sputtering process, and spraying an antioxidant on the surface of the copper nanoparticles, wherein the antioxidant is an ethanol solution containing 2.5% formic acid; Step 2: Screen-printing the nano-copper paste on both sides of the titanium-copper soldering sheet to form a soldering sheet with nano-copper paste; Step 3: stacking the copper sheet after sputtering of copper nanoparticles and spraying of antioxidant, the solder sheet with nano-copper paste, and the ceramic substrate in sequence to form a sandwich structure, and heating and draining the liquid under N2 atmosphere; Step 4: After the liquid is drained, the substrate is placed in a N2 atmosphere or vacuum for high-pressure sintering. After the sintering is completed and the solvent has completely evaporated, the substrate is taken out to complete the first sintering of the ceramic substrate. Step 5: After cooling, take the substrate out of the furnace and repeat steps 1 to 4 to sinter the second side to obtain a double-sided sintered copper clad substrate.

2. The method for preparing a nano-copper sintered ceramic substrate according to claim 1, wherein: The particle size of the nano copper particles is 40-60 nm, the thickness of the nano copper paste on both sides of the connecting solder piece is 10-16 nm, and the thickness of the connecting solder piece is 7-9 μm.

3. The method for preparing a nano-copper sintered ceramic substrate according to claim 1, wherein: The magnetron sputtering parameters in step 1 are as follows: DC mode, power of 50-300 W, target diameter of 2-4 inches, pure Ar gas, gas pressure of 5-10 mTorr, copper substrate temperature of room temperature, and deposition rate of 10-50 nm / min.

4. The method for preparing a nano-copper sintered ceramic substrate according to claim 1, wherein: The specific parameters for the drainage in step 3 are: 7×10 4 Pa pure nitrogen atmosphere, heating rate 10℃ / min, debinding temperature 450℃, and holding time 30min.

5. The method for preparing a nano-copper sintered ceramic substrate according to claim 1, wherein: In step 4, the sintering is carried out at 500-700° C. in a nitrogen atmosphere or at a high pressure of 0.5 MPa under vacuum for 90 minutes.

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