Low-temperature and low-pressure connection method for copper surface in-situ nanocrystallization

Abstract

The invention discloses a low-temperature and low-pressure connection method for copper surface in-situ nanocrystallization, and relates to a copper connection method. The method aims at solving the technical problems that operation of current copper sintering connection is complex, an intermediate layer needs to be added for assistance, the connection strength is low, the interface welding rate is low, the connection temperature and pressure are too high, and the heat preservation time is long. The nanolayer is prepared on the surface of the copper substrate by adopting an in-situ nanocrystallization method, the nanostructure has relatively large surface energy, sintering connection can be realized at low temperature and low pressure, a high-strength joint is formed, and the method can be applied to the fields of copper connection, electronic packaging and the like. And under the condition of 125 DEG C / 10min / 5MPa, the shear strength of the obtained joint can reach 118.9 MPa without additionally adding a nano-particle sintering middle layer, and a connection structure with low connection temperature, short time, low required pressure and high mechanical stability is realized. The method is simple and effective to operate, can realize low-temperature connection of large-size samples, and has a wide application prospect.

Description

Technical Field

[0001] The present invention relates to a method for connecting copper. Background Art

[0002] In fields such as electronic packaging, there is a great demand for the connection of copper. However, due to the high melting point of copper itself, traditional direct copper connection often requires a relatively high temperature. For example, the vacuum diffusion connection of copper requires a temperature of about 600 °C or higher. Using a paste based on copper nanoparticles as an intermediate layer can achieve sintering connection below 300 °C, but the sintering temperature needs to be further reduced, and the connection strength and joint porosity still need to be improved; when connecting large-area samples, there are problems such as difficult evaporation of the solvent in the copper paste, difficult control of the pressure application time and the fluidity of the paste.

[0003] Surface nanocrystallization treatment can improve the surface activity and interfacial bonding ability of materials. Treating copper using surface nanocrystallization treatment technology can form a nanoscale structure in-situ on the surface of copper, increase the specific surface area of copper, improve the surface activity of copper, thereby improving the interfacial bonding ability of copper, and thus achieving reliable connection of copper under low-temperature conditions. This can not only improve the reliability and stability of the joint, but also reduce energy consumption and environmental pollution, and has broad application prospects. Summary of the Invention

[0004] The present invention aims to solve the technical problems of the current copper sintering connection, such as complex operation, the need to add an intermediate layer for assistance, low connection strength, low interfacial welding rate, too high connection temperature and pressure, and long heat preservation time, and provides a low-temperature and low-pressure connection method for in-situ surface nanocrystallization of copper.

[0005] The low-temperature and low-pressure connection method for in-situ surface nanocrystallization of copper in the present invention is carried out according to the following steps:

[0006] 1. Copper in-situ nanocrystallization aid: Prepare a copper in-situ nanocrystallization aid composed of an alkaline reagent, an oxidant, a stabilizer, a humectant, an active agent, and deionized water;

[0007] The alkaline reagent is sodium hydroxide or potassium hydroxide;

[0008] The oxidant is potassium permanganate, potassium persulfate, ammonium persulfate, or sodium persulfate;

[0009] The stabilizer is sodium carbonate, sodium phosphate, or sodium orthosilicate;

[0010] The humectant is glycerol or polyethylene glycol;

[0011] The active agent is fatty alcohol ether sulfate;

[0012] II. The first case: Grind the two copper substrates to be joined on sandpaper, then ultrasonically clean them with absolute ethanol and let them dry naturally. Subsequently, place the copper in-situ nanometrization aid prepared in Step 1 on the surfaces of the two copper substrates to be joined.

[0013] The second case: Place the copper in-situ nanometrization aid prepared in Step 1 on two opposite surfaces of the copper intermediate layer.

[0014] III. In-situ reduction sintering: For the first case of Step II: Put the two copper substrates prepared in Step II into a hot-press sintering furnace. Place the two surfaces of the two copper substrates to be joined opposite to each other with a distance of 5 mm to 50 mm between them. Introduce a reducing gas, then heat up to 50 °C to 90 °C and hold for 2 min to 5 min. Subsequently, heat up to 100 °C to 250 °C and hold for 10 min to 60 min to in-situ produce a nanolayer on the surface of the copper substrate. Then, press the two copper substrates together and apply a pressure of 1 MPa to 10 MPa, and sinter for 1 min to 20 min under the protection of a reducing gas at 100 °C to 250 °C to achieve joining. Subsequently, cool to room temperature and take out the sample.

[0015] For the second case of Step II: Put the copper intermediate layer prepared in Step II and the two copper substrates to be joined into a hot-press sintering furnace together. The copper intermediate layer is located between the two copper substrates, and the three are placed in parallel. The two surfaces of the copper intermediate layer with the copper in-situ nanometrization aid face the two copper substrates respectively, and there are gaps of 5 mm to 50 mm between the two copper substrates and the copper intermediate layer. Introduce a reducing gas, then heat up to 50 °C to 90 °C and hold for 2 min to 5 min. Subsequently, heat up to 100 °C to 250 °C and hold for 10 min to 60 min to in-situ produce a nanolayer on the surface of the copper intermediate layer. Then, press the three together and apply a pressure of 1 MPa to 10 MPa, and sinter for 1 min to 20 min under the protection of a reducing gas at 100 °C to 250 °C to achieve joining. Subsequently, cool to room temperature and take out the sample.

[0016] The main functions of the copper in-situ nanometrization aid in the present invention are as follows: The oxidant can catalytically generate a high-density copper oxide structure on the copper surface; the alkaline reagent and the stabilizer can ensure the activity of the oxidant; the humectant can ensure the stable existence of the aid at room temperature and preheating temperature without being evaporated dry; the surfactant mainly promotes the high wettability between the aid and the surface of the copper sample. After being treated with the copper in-situ nanometrization aid, a high-density nanolayer can be generated on the copper surface under a reducing atmosphere.

[0017] Surface energy serves as the main source of the driving force for sintering connection. A larger surface energy enables the sintering connection to be successfully completed and obtain a higher connection strength, while nanostructures have a larger specific surface area and higher surface energy. The nanostructures prepared by the present invention are small in size, high in density, and have a large sintering driving force. The combined action of these factors is conducive to achieving high-quality sintering connection of surface-nanocrystallized copper under low temperature and low pressure.

[0018] The method of the present invention can be carried out without adding an intermediate layer material, without using a soldering flux, and without considering issues such as the fluidity of the intermediate layer paste. In-situ nanocrystallization treatment of the copper surface can achieve the connection of large-area samples.

[0019] The connection method of the present invention is simple and effective. It reduces the complex process of preparing solder paste in material preparation; the nanostructures have a high density and a short growth time, resulting in high production efficiency; the temperature, time, and pressure of the sintering connection are all relatively low, and the obtained connection interface has no defects and has a very high connection strength, with great economic value and broad practical application prospects.

[0020] The present invention has the following beneficial effects:

[0021] 1. The operation of the present invention is simple and effective. In-situ reduction generates nanocrystalline copper, which has a high surface energy, a large density, and a large sintering driving force, and is suitable for sintering connection.

[0022] 2. The nanocrystallization treatment time of the present invention is short, and the production efficiency is high.

[0023] 3. The sintering connection temperature, pressure, and time of the present invention are all lower than those of conventional sintering connections based on nanocrystalline copper solder paste.

[0024] 4. The connection joint prepared by the present invention has a high strength and a high interface bonding rate.

[0025] 5. The present invention does not need to add intermediate layers such as metal particles and soldering fluxes during sintering connection, and is suitable for low-temperature connection of large-sized copper samples. Description of the Drawings

[0026] Figure 1 It is the SEM image of the surface morphology of the sample after reduction in Step 3 of Experiment 1;

[0027] Figure 2 It is the SEM image of the cross-sectional morphology of the sample finally obtained in Step 3 of Experiment 1;

[0028] Figure 3 It is the shear strength test curve of the connection joint finally obtained in Experiment 1. Detailed Embodiments

[0029] Detailed Embodiment 1: This embodiment is a low-temperature and low-pressure connection method for in-situ nanocrystallization of the copper surface, and is specifically carried out according to the following steps:

[0030] I. Copper in-situ nanometerization assistant: Prepare a copper in-situ nanometerization assistant composed of an alkaline reagent, an oxidant, a stabilizer, a humectant, an active agent, and deionized water.

[0031] The alkaline reagent is sodium hydroxide or potassium hydroxide.

[0032] The oxidant is potassium permanganate, potassium persulfate, ammonium persulfate, or sodium persulfate.

[0033] The stabilizer is sodium carbonate, sodium phosphate, or sodium orthosilicate.

[0034] The humectant is glycerol or polyethylene glycol.

[0035] The active agent is fatty alcohol polyether sulfate.

[0036] II. The first case: Grind the two copper substrates to be joined on sandpaper, then ultrasonically clean them with absolute ethanol and air-dry them naturally. Subsequently, place the copper in-situ nanometerization assistant prepared in step I on the surfaces of the two copper substrates to be joined.

[0037] The second case: Place the copper in-situ nanometerization assistant prepared in step I on two opposite surfaces of the copper intermediate layer.

[0038] III. In-situ reduction sintering: For the first case of step II: Put the two copper substrates prepared in step II into a hot-press sintering furnace, place the two surfaces of the two copper substrates to be joined opposite to each other with a distance of 5 mm to 50 mm between the two surfaces, introduce a reducing gas, then heat up to 50°C to 90°C and hold for 2 min to 5 min, and then heat up to 100°C to 250°C and hold for 10 min to 60 min to in-situ prepare a nanolayer on the surface of the copper substrate; subsequently, fit the two copper substrates together and apply a pressure of 1 MPa to 10 MPa, and sinter for 1 min to 20 min under the protection of a reducing gas at 100°C to 250°C to achieve connection, and then cool to room temperature and take out the sample.

[0039] For the second case of Step 2: Put the copper intermediate layer prepared in Step 2 and the two copper substrates to be joined into a hot-pressing sintering furnace. The copper intermediate layer is located between the two copper substrates, and the three are placed in parallel. The two surfaces of the copper intermediate layer containing the in-situ copper nano-sizing agent face the two copper substrates respectively. A gap of 5 mm to 50 mm is left between the two copper substrates and the copper intermediate layer. Introduce a reducing gas, then heat up to 50 °C to 90 °C and keep warm for 2 min to 5 min, and then heat up to 100 °C to 250 °C and keep warm for 10 min to 60 min to in-situ prepare a nano-layer on the surface of the copper intermediate layer; then fit the three together and apply a pressure of 1 MPa to 10 MPa, and sinter for 1 min to 20 min under the protection of a reducing gas at 100 °C to 250 °C to achieve the connection, and then cool to room temperature and take out the sample.

[0040] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is that: in the copper in-situ nano-sizing agent described in Step 1, the concentration of the alkaline reagent is 0.1 mol / L to 0.5 mol / L, the concentration of the oxidant is 1 mol / L to 5 mol / L, the concentration of the stabilizer is 0.02 mol / L to 0.2 mol / L, the concentration of the humectant is 0.5 mol / L to 1 mol / L, and the concentration of the surfactant is 0.005 mol / L to 0.05 mol / L. Others are the same as Specific Embodiment 1.

[0041] Specific Embodiment 3: The difference between this embodiment and Specific Embodiment 1 or 2 is that: in the first case of Step 2, the copper substrates to be joined are pure copper, copper alloy or other metals with copper plating on the surface. Others are the same as Specific Embodiment 1 or 2.

[0042] Specific Embodiment 4: The difference between this embodiment and Specific Embodiment 3 is that: in the first case of Step 2, the copper substrates to be joined are ceramics, carbon materials or polymers with copper plating on the surface. Others are the same as Specific Embodiment 3.

[0043] Specific Embodiment 5: The difference between this embodiment and Specific Embodiment 4 is that: in the first case of Step 2, the method of placing the copper in-situ nano-sizing agent prepared in Step 1 on the surfaces of the two copper substrates to be joined is brushing, spraying, spin coating, scraping, wiping or soaking. Others are the same as Specific Embodiment 4.

[0044] Specific Embodiment 6: The difference between this embodiment and Specific Embodiment 5 is that: in the second case of Step 2, the copper intermediate layer is copper foil, copper mesh or copper foam. Others are the same as Specific Embodiment 5.

[0045] Embodiment 7: The difference between this embodiment and Embodiment 6 is that: in the second case of Step 2, the method of placing the copper in-situ nanometerization assistant prepared in Step 1 on two opposite surfaces of the copper intermediate layer is brushing, spraying, spin coating, scraping, wiping or soaking. Others are the same as Embodiment 6.

[0046] Embodiment 8: The difference between this embodiment and Embodiment 7 is that: in both cases of Step 3, the reducing gas is hydrogen, formic acid, carbon monoxide, a mixture of hydrogen / argon or a mixture of nitrogen / formic acid. Others are the same as Embodiment 7.

[0047] The present invention is verified by the following tests:

[0048] Test 1: This test is a low-temperature and low-pressure connection method for in-situ nanometerization of the copper surface. Specifically, it is carried out according to the following steps:

[0049] I. Copper in-situ nanometerization assistant: Prepare a copper in-situ nanometerization assistant composed of an alkaline reagent, an oxidant, a stabilizer, a humectant, an active agent and deionized water;

[0050] In the copper in-situ nanometerization assistant, the alkaline reagent is sodium hydroxide with a concentration of 0.2 mol / L; the oxidant is sodium persulfate with a concentration of 3 mol / L; the stabilizer is sodium carbonate with a concentration of 0.1 mol / L; the humectant is glycerol with a concentration of 0.8 mol / L; the active agent is fatty alcohol ether sulfate with a concentration of 0.05 mol / L;

[0051] II. Polish the two copper substrates to be joined on sandpaper, then ultrasonically clean them with absolute ethanol for 10 min, air-dry them naturally, and then soak the surfaces to be joined of the two copper substrates in the copper in-situ nanometerization assistant prepared in Step I for 5 s;

[0052] The copper substrates to be joined are pure copper;

[0053] III. In-situ reduction sintering: Place the two copper substrates prepared in Step II horizontally in a hot press sintering furnace, place the two surfaces to be joined of the two copper substrates opposite to each other and the two surfaces are 20 mm apart. The copper substrate located above is fixed by a fixture, introduce the reducing gas formic acid, then heat up to 75 °C and hold for 3 min, then heat up to 200 °C and hold for 30 min, in-situ prepare a nano-layer on the surface of the copper substrate, cool down to room temperature, and the surface morphology of the sample is shown in Figure 1 , it can be seen from the figure that a high-density and uniformly distributed copper nano-layer is prepared on the surface of the copper substrate. It shows that the copper in-situ nanometerization assistant can generate a high-density copper oxide structure on the copper surface and be transformed into a high-density copper nanometerization layer under a reducing atmosphere.

[0054] Subsequently, the two copper substrates were horizontally placed in a hot press sintering furnace. The two surfaces to be joined of the two copper substrates were placed opposite to each other and in contact, and a pressure of 10 MPa was applied. Sintering was carried out for 5 min under the protection of 150 °C and the reducing gas formic acid to achieve the connection. Subsequently, it was cooled to room temperature and the sample was taken out.

[0055] Figure 2 Figure SEM of the cross-sectional morphology of the sample finally obtained in Step 3 of Experiment 1. The dark part in the upper left corner is the resin for embedding the sample. It can be seen that an excellent joint interface has been formed in the connection area, and the two copper substrate base materials have been integrated microscopically, and no observable defects exist at the interface.

[0056] Figure 3 Figure of the shear strength test curve of the joint finally obtained in Experiment 1. The measured room temperature shear strength is as high as 99.9 MPa.

[0057] Experiment 2: The difference between this experiment and Experiment 1 is that in Step 3, a pressure of 1 MPa was used and sintering was carried out at 200 °C for 5 min. Others are the same as Experiment 1. The measured room temperature shear strength of the sintered sample is 91.9 MPa.

[0058] Experiment 3: The difference between this experiment and Experiment 1 is that in Step 3, a pressure of 5 MPa was used and sintering was carried out at 125 °C for 10 min. Others are the same as Experiment 1. The measured room temperature shear strength of the sintered sample is 118.9 MPa.

[0059] The above characterization results show that nanometer treatment of the copper surface can grow nanostructures on the copper surface. Nanometerization increases the specific surface area of the copper surface, thereby increasing the surface energy of the copper surface, endowing greater bonding activity, and facilitating the formation of an excellent joint interface.

Claims

1. A low-temperature and low-pressure connection method for in-situ nano-crystallization of copper surface, characterized in that The low-temperature and low-pressure connection method of in-situ nano-crystallization of the copper surface is carried out in the following steps:

1. Copper in-situ nano-forming additive: Prepare a copper in-situ nano-forming additive consisting of an alkaline reagent, an oxidant, a stabilizer, a moisturizer, an active agent and deionized water; The alkaline reagent is sodium hydroxide or potassium hydroxide; The oxidant is potassium permanganate, potassium persulfate, ammonium persulfate or sodium persulfate; The stabilizer is sodium carbonate, sodium phosphate or sodium orthosilicate; The moisturizing agent is glycerin or polyethylene glycol; The active agent is fatty alcohol ether sulfate; 2. The first case: the two copper substrates to be connected are polished on sandpaper, then ultrasonically cleaned with anhydrous ethanol, dried naturally, and then the copper in-situ nano-crystallization additive prepared in step 1 is placed on the surfaces of the two copper substrates to be connected; The second case: the copper in-situ nano-crystallization additive prepared in step 1 is placed on two opposite surfaces of the copper intermediate layer; 3. In-situ reduction sintering: For the first case of step 2: put the two copper substrates prepared in step 2 into a hot pressing sintering furnace, place the two surfaces of the two copper substrates to be connected opposite to each other and the two surfaces are 5mm to 50mm apart, introduce reducing gas, then heat to 50℃ to 90℃ and keep warm for 2min to 5min, then heat to 100℃ to 250℃ and keep warm for 10min to 60min, and prepare a nano layer in situ on the surface of the copper substrate; then fit the two copper substrates together, apply a pressure of 1MPa to 10MPa, sinter at 100℃ to 250℃ and under the protection of reducing gas for 1min to 20min to achieve connection, then cool to room temperature and take out the sample; For the second situation of step two: the copper intermediate layer prepared in step two and the two copper substrates to be connected are placed in a hot pressing sintering furnace together, the copper intermediate layer is located between the two copper substrates, the three are placed in parallel, and the two surfaces of the copper intermediate layer with the copper in-situ nano-additive are facing the two copper substrates respectively, and a gap of 5mm to 50mm is left between the two copper substrates and the copper intermediate layer. Reducing gas is introduced, and then the temperature is raised to 50℃ to 90℃ and kept warm for 2min to 5min, and then the temperature is raised to 100℃ to 250℃ and kept warm for 10min to 60min, and a nanolayer is prepared in situ on the surface of the copper intermediate layer; then the three are bonded to each other, and a pressure of 1MPa to 10MPa is applied, and they are sintered at 100℃ to 250℃ and under the protection of reducing gas for 1min to 20min to achieve connection, and then cooled to room temperature and the sample is taken out.

2. A low-temperature and low-pressure connection method for in-situ nano-crystallization of a copper surface according to claim 1, characterized in that The concentration of the alkaline agent in the copper in-situ nano-forming additive described in step 1 is 0.1mol / L to 0.5mol / L, the concentration of the oxidant is 1mol / L to 5mol / L, the concentration of the stabilizer is 0.02mol / L to 0.2mol / L, the concentration of the moisturizer is 0.5mol / L to 1mol / L, and the concentration of the active agent is 0.005mol / L to 0.05mol / L.

3. A low-temperature and low-pressure connection method for in-situ nano-crystallization of a copper surface according to claim 1, characterized in that In the first case of step 2, the copper substrate to be connected is pure copper, copper alloy or other metal with copper plating on the surface.

4. A low-temperature and low-pressure connection method for in-situ nano-crystallization of a copper surface according to claim 3, characterized in that In the first case of step 2, the copper substrate to be connected is a ceramic, carbon material or polymer with copper plated on the surface.

5. The low-temperature and low-pressure connection method for in-situ nano-crystallization of a copper surface according to claim 1, characterized in that In the first case of step 2, the method of placing the copper in-situ nano-forming additive prepared in step 1 on the surfaces of two copper substrates to be connected is brushing, spraying, spin coating, scraping, rubbing or dipping.

6. A low-temperature and low-pressure connection method for in-situ nano-crystallization of a copper surface according to claim 1, characterized in that The copper intermediate layer in the second case of step 2 is copper foil, copper mesh or foam copper.

7. A low-temperature and low-pressure connection method for in-situ nano-crystallization of a copper surface according to claim 6, characterized in that In the second case of step 2, the method of placing the copper in-situ nano-forming additive prepared in step 1 on two opposite surfaces of the copper intermediate layer is brushing, spraying, spin coating, scraping, rubbing or dipping.

8. The low-temperature and low-pressure connection method for in-situ nano-crystallization of a copper surface according to claim 1, characterized in that In both cases of step 3, the reducing gas is hydrogen, formic acid, carbon monoxide, a mixture of hydrogen / argon or a mixture of nitrogen / formic acid.

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