Nano-copper sintered ceramic substrate and preparation method thereof

Abstract

The invention discloses a nano-copper sintered ceramic substrate and a preparation method thereof, the nano-copper sintered ceramic substrate comprises a copper sheet, a connecting soldering lug, a ceramic substrate, a connecting soldering lug and a copper sheet from top to bottom, the copper sheet, the connecting soldering lug, the ceramic substrate, the connecting soldering lug and the copper sheet are sequentially stacked to form a sandwich layer structure, and a layer of nano-copper particles is arranged on the connecting surface of the inner side of the copper sheet and the connecting soldering lug through magnetron sputtering. And nano copper paste is printed on the connecting surfaces of the two sides of the connecting soldering lug, the copper sheet and the ceramic substrate through a silk screen. The method has the advantages that generation of interface cavities is reduced, the peeling strength is improved, the sintering temperature is reduced, the silver-free sintering material is adopted, and the manufacturing cost and the sintering time are reduced.

Description

Technical Field

[0001] The 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 development of materials science, the scale effect of nanomaterials in the sintering process has gradually become prominent, that is, as the nanoscale continues to shrink, the sintering temperature continues to decrease, and can even be lower than the melting point of the material. In the current copper sintering field, copper nanomaterials can also achieve surface melting at a temperature far below the melting point of copper, inducing mutual diffusion and the formation of sintering necks, thereby strengthening the bonding strength. However, this is generally used in chip packaging, and has never been used in the application of 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 the peel strength while reducing the sintering temperature, adopt silver-free sintering materials, and reduce the manufacturing cost and sintering time.

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

[0006] 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 welding piece is 10-16 nm, and the thickness of the connecting welding piece is 7-9 μm.

[0007] Preferably, the connecting welding piece is a titanium-copper alloy welding piece.

[0008] Preferably, the preparation method of the nano copper paste is: Cu(OH) 2and polyvinyl pyrrolidone are dissolved in 1,3-propylene glycol in an equal mass ratio, 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 separated by multiple centrifugations and washed with ethanol 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.

[0009] Preferably, the L-ascorbic acid solvent is formed by dissolving 10 wt.% of L-ascorbic acid in ethylene glycol at 60°C.

[0010] A method for preparing a nano-copper sintered ceramic substrate, characterized in that it specifically comprises the following steps: Step 1, forming a layer of dispersed copper nanoparticles on a copper sheet substrate by a magnetron sputtering process, and spraying an antioxidant on the surface of the copper nanoparticles; 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 particles; Step 3: stack 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. 2 Heating and draining under air; Step 4: After draining, place in N 2 High pressure sintering under atmosphere or vacuum, after sintering is completed, the first side of the ceramic substrate is taken out after the solvent has completely evaporated; Step 5, after cooling, take out of the furnace, repeat steps 1 to 4 to sinter the second side, and obtain a double-sided sintered copper-clad substrate.

[0011] 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.

[0012] Preferably, the specific parameters of the discharge in step 3 are: 7×10 4 Pa pure nitrogen atmosphere, heating rate 10℃ / min, debinding temperature 450℃, and holding time 30min.

[0013] 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.

[0014] In summary, the present invention has the following beneficial effects: The present invention introduces nano-copper sintering technology into the copper-clad ceramic substrate to achieve low-temperature sintering without silver brazing, while being able to reduce reaction time, reduce energy loss, and improve the preparation efficiency of the copper-clad ceramic substrate, which is conducive to large-scale application.

[0015] 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 nano particles pre-sputtered on the copper sheet, effective sintering interconnection is achieved. Nano copper has good anti-electromigration ability and has electrical conductivity and thermal conductivity comparable to silver. It can well replace the Ag component in the solder paste, greatly reducing the cost.

[0016] 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-coated 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 in contact with air. In addition, the surface of the copper particles is coated with polyvinyl pyrrolidone to further prevent surface oxidation of the copper particles in contact with oxygen and moisture in the reagent, thereby achieving effective bonding between the copper sheet and the solder sheet.

[0017] The nano copper solder paste of the present invention mainly utilizes the scale effect to improve the brazing bonding activity. If the nano copper is directly used on the 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 the diffusion of the silver-copper heterogeneous interface by combining nano copper with a titanium-copper alloy solder sheet, and can improve the overall reliability of the substrate.

[0018] The present invention adopts a welding method of combining solder paste with 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, resulting in poor welding effect and low interface peeling strength. The present invention adopts a pre-draining method, and the nano copper paste is in a pressure-free 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

[0019] 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

[0020] The specific implementation manner of the present invention is further described below in conjunction with the accompanying drawings, and this embodiment does not constitute a limitation of the present invention.

[0021] A nano-copper sintered ceramic substrate comprises, from top to bottom, a copper sheet, a connecting welding sheet, a ceramic substrate, a connecting welding 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 welding sheet by magnetron sputtering; 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.

[0022] 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.

[0023] The connecting welding piece is a titanium-copper alloy welding piece.

[0024] The preparation method of nano copper paste is as follows: Cu(OH) 2 and polyvinyl pyrrolidone are dissolved in 1,3-propylene glycol in an equal mass ratio, 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 separated by multiple centrifugations and washed with ethanol 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.

[0025] The L-ascorbic acid solvent was prepared by dissolving 10 wt. % of L-ascorbic acid in ethylene glycol at 60°C.

[0026] Example 1 A method for preparing a nano-copper sintered ceramic substrate 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 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 100w, target diameter of 2 inches, gas of pure Ar, gas pressure of 5mTorr, copper substrate temperature of room temperature, deposition rate of 10nm / min; 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 particles; Step 3: stack 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. 2 Temperature rise and discharge under atmosphere, specifically 7×10 4 Pa pure nitrogen atmosphere, heating rate 10℃ / min, debinding temperature 450℃, holding time 30min; Step 4: After the liquid is drained, the substrate is placed under nitrogen atmosphere at 500°C or 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 side sintering. Step 5, after cooling, take out of the furnace, repeat steps 1 to 4 to sinter the second side, and obtain a double-sided sintered copper-clad substrate.

[0027] Example 2 A method for preparing a nano-copper sintered ceramic substrate 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 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, deposition rate of 10nm / min; 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 particles; Step 3: stack 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. 2 Temperature rise and discharge under atmosphere, specifically 7×10 4 Pa pure nitrogen atmosphere, heating rate 10℃ / min, debinding temperature 450℃, holding time 30min; Step 4: After the liquid is drained, the substrate is placed under nitrogen atmosphere at 600°C or 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. Step 5, after cooling, take out of the furnace, repeat steps 1 to 4 to sinter the second side, and obtain a double-sided sintered copper-clad substrate.

[0028] Example 3 A method for preparing a nano-copper sintered ceramic substrate 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 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 200w, target diameter of 3 inches, gas of pure Ar, gas pressure of 8mTorr, copper substrate temperature of room temperature, deposition rate of 40nm / min; 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 particles; Step 3: stack 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. 2 Temperature rise and discharge under atmosphere, specifically 7×10 4 Pa pure nitrogen atmosphere, heating rate 10℃ / min, debinding temperature 450℃, holding time 30min; Step 4: After the liquid is drained, the substrate is placed under nitrogen atmosphere at 600°C or 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. Step 5, after cooling, take out of the furnace, repeat steps 1 to 4 to sinter the second side, and obtain a double-sided sintered copper-clad substrate.

[0029] Embodiment 4 A method for preparing a nano-copper sintered ceramic substrate 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 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 300w, target diameter of 4 inches, gas of pure Ar, gas pressure of 10mTorr, copper substrate temperature of room temperature, deposition rate of 50nm / min; 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 particles; Step 3: stack 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. 2 Temperature rise and discharge under atmosphere, specifically 7×10 4 Pa pure nitrogen atmosphere, heating rate 10℃ / min, debinding temperature 450℃, holding time 30min; Step 4: After the liquid is drained, the substrate is placed under nitrogen atmosphere at 700°C or vacuum for high pressure sintering at 0.5 MPa for 90 minutes. After the sintering is completed, the first side of the ceramic substrate is taken out after the solvent has completely evaporated. Step 5, after cooling, take out of the furnace, repeat steps 1 to 4 to sinter the second side, and obtain a double-sided sintered copper-clad substrate.

[0030] 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 perform performance testing, and the specific data are shown in Table 1 below: Table 1 Depend on Figure 1As 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 cause the risk 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 welding process, the production cost is lower, the characteristics of nano-copper can also reduce the brazing temperature, the production time is shorter, and the process steps of antioxidant treatment and pre-drainage are combined to reduce the phenomenon of solder migration and reduce the generation of interface voids, thereby achieving a comprehensive improvement in performance, process, and cost savings.

[0031] 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 nano copper sintered ceramic substrate, characterized in that: From top to bottom, there are copper sheets, connecting welding sheets, ceramic substrates, connecting welding sheets and copper sheets, 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 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.

2. The nano-copper sintered ceramic substrate according to claim 1, characterized in that: 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 welding piece is 10-16 nm, and the thickness of the connecting welding piece is 7-9 μm.

3. The nano-copper sintered ceramic substrate according to claim 1, characterized in that: The connecting welding piece is a titanium-copper alloy welding piece.

4. The nano-copper sintered ceramic substrate according to claim 1, characterized in that: The preparation method of the nano copper paste is as follows: Cu(OH)2 and polyvinyl pyrrolidone are dissolved in 1,3-propylene glycol in an equal mass ratio, quickly stirred evenly at room temperature, and heated 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.

5. The nano-copper sintered ceramic substrate according to claim 4, characterized in that: The L-ascorbic acid solvent is formed by dissolving 10 wt.% of L-ascorbic acid in ethylene glycol at 60°C.

6. A method for preparing a nano-copper sintered ceramic substrate, characterized in that: The specific steps include: Step 1, forming a layer of dispersed copper nanoparticles on a copper sheet substrate by a magnetron sputtering process, and spraying an antioxidant on the surface of the copper nanoparticles; 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 particles; 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 in a N2 atmosphere; Step 4: After the liquid is drained, the ceramic 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 ceramic substrate is taken out to complete the first side sintering; Step 5, after cooling, take out of the furnace, repeat steps 1 to 4 to sinter the second side, and obtain a double-sided sintered copper-clad substrate.

7. The method for preparing a nano-copper sintered ceramic substrate according to claim 6, characterized in that: 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.

8. The method for preparing a nano-copper sintered ceramic substrate according to claim 6, characterized in that: The specific parameters of the discharge in step 3 are: 7×10 4 Pa pure nitrogen atmosphere, heating rate 10℃ / min, debinding temperature 450℃, and holding time 30min.

9. The method for preparing a nano-copper sintered ceramic substrate according to claim 6, characterized in that: In step 4, the sintering is performed at 500-700° C. in a nitrogen atmosphere or at 0.5 MPa under vacuum, and the sintering time is 90 minutes.

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