A super-pure nano copper-based paste and its preparation method and application

Abstract

The present invention relates to an ultra-pure nano copper-based paste and its preparation method and application, belonging to the technical field of electronic materials. It solves the technical problems in the prior art that nano copper powder has disadvantages such as easy agglomeration, easy oxidation, low bulk density, and high sintering temperature. The ultra-pure nano copper-based paste of the present invention comprises ultra-pure nano copper powder, an organic carrier, and a dispersion liquid; wherein, the purity of the ultra-pure nano copper powder is higher than 99.99%; the organic carrier comprises tripropylene glycol butyl ether, hydrogenated castor oil, hydrogenated rosin, succinic acid, and 2-phenylimidazole; the dispersion liquid comprises ethanol, ethylene glycol, stearic acid, and dithiol. In this ultra-pure nano copper-based paste, the ultra-pure nano copper powder is not easy to agglomerate and oxidize, has a high bulk density, the ultra-pure nano copper-based paste has a low sintering temperature and a high sintered body density, and has excellent electrical and thermal conductivity, and can be used as an interconnection material, especially as an encapsulation interconnection material, providing the possibility for the industrial large-scale production of encapsulation interconnection materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of electronic materials, and particularly relates to a super-pure nano copper-based paste, a preparation method thereof and an application thereof, and particularly relates to the application of the super-pure nano copper-based paste as an interconnection material, especially as an encapsulation interconnection material. Background Art

[0002] Encapsulation will affect the safety and reliability of devices. Interconnection materials can effectively achieve the encapsulation connection between chips and substrates, and their selection will affect the performance of devices such as high-frequency resistance, high-voltage resistance and high-temperature resistance.

[0003] The application of third-generation semiconductor power devices has relatively strict requirements for the working environment, and their interconnection materials need to have the performance of "low-temperature interconnection and high-temperature service". In the traditional electronic packaging field, interconnection materials such as solder paste and conductive adhesive are generally used. Tin-lead alloy, as the most traditional interconnection material, has the advantages of excellent welding performance and good economy, but lead is toxic. The main component of lead-free brazing interconnection materials is Sn, and among them, the most representative is the SnAgCu alloy. However, under high-temperature conditions, the brittleness between the connection layers of lead-free brazing interconnection materials increases, the strength decreases, and the melting point of lead-free brazing interconnection materials is relatively low. Conductive adhesives usually contain resins, but since the resins are prone to aging at high temperatures, they cannot meet the working temperatures required by third-generation semiconductor devices.

[0004] The melting point of metal nanoparticles will decrease significantly as their particle size decreases. Therefore, if metal nanoparticles are used as interconnection materials, this property can be utilized to sinter metal nanoparticles at low temperatures, and the sintered interconnection layer has good macroscopic properties, such as good thermal conductivity, electrical conductivity and excellent mechanical properties. Among them, nano silver paste as an interconnection material has attracted the attention of many researchers. However, silver is prone to ion migration, causing chip failure and being expensive, making it difficult to be popularized in mass applications. Nano copper paste has gradually replaced nano silver paste as the preferred choice for interconnection materials due to its advantages such as high thermal conductivity, low coefficient of thermal expansion, resistance to electromigration and low cost. However, on the one hand, the particle size of nano copper powder is small, so it has a high surface energy and is prone to agglomeration; on the other hand, the packing density of nano copper powder is low, so the density of its sintered body is low, which affects its electrical and thermal conductivity; on the other hand, in the preparation process, nano copper powder usually easily remains with metal salts, and it is easy to form a primary battery under the condition of water vapor in the air, and nano copper powder is very easy to oxidize, and the oxides on the surface cause the sintering temperature to be higher than the theoretical temperature. Summary of the Invention

[0005] In view of this, in order to solve the technical problems such as the disadvantages of easy agglomeration, easy oxidation, low packing density and high sintering temperature of nano copper powder in the prior art, the present invention provides a super-pure nano copper-based paste, a preparation method thereof and an application thereof.

[0006] The technical solution adopted by the present invention to solve the above technical problems is as follows.

[0007] The ultra-pure nano copper-based paste of the present invention comprises ultra-pure nano copper powder, an organic carrier and a dispersion liquid;

[0008] The purity of the ultra-pure nano copper powder is higher than 99.99%;

[0009] The organic carrier comprises tripropylene glycol butyl ether, hydrogenated castor oil, hydrogenated rosin, succinic acid and 2-phenylimidazole;

[0010] The dispersion liquid comprises ethanol, ethylene glycol, stearic acid, cysteine and dithiol.

[0011] Preferably, the mass percentage of the ultra-pure nano copper powder is 20-40 wt%, the mass percentage of the organic carrier is 5-12 wt%, and the mass percentage of the dispersion liquid is 55-70 wt%.

[0012] Preferably, the ultra-pure nano copper powder is spherical or quasi-spherical, and the average size range is 20-50 nm.

[0013] Preferably, in the organic carrier, the mass percentages of the components are as follows: tripropylene glycol butyl ether 60-70 wt%, hydrogenated castor oil 3-5 wt%, hydrogenated rosin 10-14 wt%, succinic acid 2-6 wt%, 2-phenylimidazole 12-16 wt%.

[0014] Preferably, in the dispersion liquid, the mass percentages of the components are as follows: ethanol 78-86 wt%, ethylene glycol 9-14 wt%, stearic acid 4-9 wt%, dithiol 0.01-0.20 wt%.

[0015] Preferably, the dithiol is a dithiol of C2-C 12 and more preferably, the dithiol is a dithiol of C3-C6.

[0016] The present invention also provides a preparation method of the above ultra-pure nano copper-based paste, comprising the following steps:

[0017] Step 1: Weigh raw materials according to the mass percentages of the components in the organic carrier, mix them evenly to obtain the organic carrier;

[0018] Step 2: Weigh raw materials according to the mass percentages of the components in the dispersion liquid, mix them evenly at 60-75 °C to obtain the dispersion liquid;

[0019] Step 3: First place the ultra-pure nano copper powder in absolute ethanol, after centrifugal washing, add it to the dispersion liquid prepared in Step 2, disperse it evenly, and then add the organic carrier prepared in Step 1 to the dispersion liquid, stir until it becomes paste-like to obtain the ultra-pure nano copper-based paste.

[0020] Preferably, in the first step, it is uniformly mixed by stirring, the stirring temperature is 50 - 120 °C, the stirring time is 5 - 300 min, and the stirring speed is 1000 - 12000 rpm.

[0021] Preferably, in the second step, it is uniformly mixed by stirring.

[0022] Preferably, in the third step, it is uniformly dispersed by ultrasonic.

[0023] The present invention also provides the application of the above ultra - pure nano - copper - based paste as an interconnection material.

[0024] Preferably, the interconnection material is a packaging interconnection material.

[0025] The principle of the present invention is as follows:

[0026] (1) The present invention uses ultra - pure nano - copper powder as the raw material. The purity higher than 99.99% can greatly reduce the content of metal salts in the nano - copper powder, block the process of primary battery oxidation, and thus solve the problems of easy oxidation and high sintering temperature of nano - copper powder;

[0027] (2) The present invention adds 2 - phenylimidazole (in an appropriate amount) to the organic carrier to act with copper, which improves the dispersion degree of copper, so as to solve the problem that nano - copper powder is prone to agglomeration and affects the reliability of the interconnection material. However, the boiling point of 2 - phenylimidazole is relatively high and it is easy to remain in the sintered body. Therefore, the present invention adds hydrogenated rosin to react with 2 - phenylimidazole, and when heated, the two react to form a rosin body and overflow, reducing the organic matter residue in the sintered body;

[0028] (3) The present invention adds dithiol to the organic carrier, which can reduce the distance between copper powder particles and can enhance the connection strength between copper - copper particles through the chemical bonding of copper and sulfur, thereby increasing the packing density of copper powder in the ultra - pure nano - copper - based paste and improving the density of the sintered body;

[0029] (4) The wettability of ultra - pure nano - copper is poor. The present invention first washes the ultra - pure nano - copper powder with absolute ethanol and adds a large amount of ethanol to the dispersion liquid to improve the wettability of ultra - pure nano - copper.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] In the ultra - pure nano - copper - based paste of the present invention, the ultra - pure nano - copper powder is not easy to agglomerate, not easy to oxidize, has a high packing density, the sintering temperature of the ultra - pure nano - copper - based paste is low, the density of the sintered body is high, and it has excellent electrical and thermal conductivity.

[0032] The preparation method of the ultra - pure nano - copper - based paste of the present invention is simple in operation, low in cost, and excellent in the performance of the preparation materials.

[0033] The ultra-pure nano copper-based paste of the present invention can be used as an interconnection material, especially as a packaging interconnection material, providing the possibility for large-scale industrial production of packaging interconnection materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present invention and the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0035] Figure 1 SEM photograph of the sintered body of the ultra-pure nano copper-based paste containing pentanedithiol in Example 1 of the present invention.

[0036] Figure 2 SEM photograph of the sintered body of the ultra-pure nano copper-based paste without pentanedithiol in Comparative Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0037] In order to further understand the present invention, the following describes the preferred implementation embodiments of the present invention. However, it should be understood that these descriptions are only for further explaining the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0038] The ultra-pure nano copper-based paste of the present invention includes ultra-pure nano copper powder, an organic carrier, and a dispersion liquid, and can also consist only of the above components.

[0039] In the present invention, the purity of the ultra-pure nano copper powder is higher than 99.99%. The ultra-pure nano copper powder is spherical or quasi-spherical, and the average size range is preferably 20 - 50 nm.

[0040] In the present invention, the organic carrier includes tripropylene glycol butyl ether, hydrogenated castor oil, hydrogenated rosin, succinic acid, and 2-phenylimidazole, and can also consist only of the above components; in the organic carrier, the mass percentages of the components are: tripropylene glycol butyl ether 60 - 70 wt%, hydrogenated castor oil 3 - 5 wt%, hydrogenated rosin 10 - 14 wt%, succinic acid 2 - 6 wt%, and 2-phenylimidazole 12 - 16 wt%.

[0041] In the present invention, the dispersion liquid includes ethanol, ethylene glycol, stearic acid, and dithiol, and can also consist only of the above components; in the dispersion liquid, the mass percentages of the components are: ethanol 78 - 86 wt%, ethylene glycol 9 - 14 wt%, stearic acid 4 - 9 wt%, and dithiol 0.01 - 0.20 wt%. The dithiol is preferably a dithiol having C2 - C 12 dithiol, more preferably a dithiol having C3 - C6. The dispersion liquid contains 78 - 86 wt% ethanol, which can increase the wettability of the ultra-pure nano copper powder.

[0042] In the present invention, preferably, the mass percentage of the ultra-pure nano copper powder is 20-40 wt%, the mass percentage of the organic carrier is 5-12 wt%, and the mass percentage of the dispersion liquid is 55-70 wt%.

[0043] The preparation method of the ultra-pure nano copper-based paste of the present invention comprises the following steps:

[0044] Step 1: Weigh the raw materials according to the mass percentages of the components in the organic carrier, and mix them evenly to obtain the organic carrier;

[0045] Step 2: Weigh the raw materials according to the mass percentages of the components in the dispersion liquid, and mix them evenly at 60-75 °C to obtain the dispersion liquid;

[0046] Step 3: First place the ultra-pure nano copper powder in absolute ethanol, after centrifugal washing, add it to the dispersion liquid prepared in Step 2, disperse it evenly, and then add the organic carrier prepared in Step 1 to the dispersion liquid, and stir until it becomes paste-like to obtain the ultra-pure nano copper-based paste.

[0047] In the above Step 1, it is preferably mixed evenly by stirring, but other well-known mixing methods in the art are also applicable to the present invention. The stirring temperature is preferably 50-120 °C, the stirring time is preferably 30-300 min, more preferably 30-100 min, the stirring speed is preferably 1000-12000 rpm, more preferably 3000-6000 rpm, and the stirring equipment usually selects a high-speed shearing machine.

[0048] In the above Step 2, it is preferably mixed evenly by stirring, but other well-known mixing methods in the art are also applicable to the present invention. The dispersion liquid is carried out at 60-75 °C to ensure the dissolution of stearic acid. The dispersion liquid has the best effect when it is prepared and used immediately.

[0049] In the above Step 3, it is preferably dispersed evenly by ultrasonic waves, but other well-known dispersion methods in the art are also applicable to the present invention.

[0050] The ultra-pure nano copper-based paste of the present invention can be used as an interconnection material, especially for encapsulation interconnection materials.

[0051] The terms used in the present invention generally have the meanings commonly understood by those of ordinary skill in the art, unless otherwise specified.

[0052] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below in conjunction with embodiments.

[0053] In the following embodiments, various processes and methods not described in detail are conventional methods well known in the art. The materials, reagents, devices, instruments, equipment, etc. used in the following embodiments can be obtained from commercial sources without special instructions.

[0054] Example 1

[0055] Mix 19 g of tripropylene glycol butyl ether, 1.2 g of hydrogenated castor oil, 3.7 g of hydrogenated rosin, 0.7 g of succinic acid, and 4.2 g of 2-phenylimidazole in a beaker, and use a high-speed shearer to process for 45 min (the components are mixed evenly) at a rotation speed of 6000 rpm and a temperature of 70 °C, and then cool to room temperature to obtain an organic carrier.

[0056] Mix 14 g of absolute ethanol, 2 g of ethylene glycol, 1 g of stearic acid, and 0.020 g of pentanedithiol, and heat up to 60 °C until the stearic acid is completely dissolved (the components are mixed evenly) to obtain a dispersion.

[0057] First, place 6 g of ultra-pure nano copper powder in 45 ml of absolute ethanol, centrifuge and wash to obtain ultra-pure nano copper powder with improved wettability. Then place the ultra-pure nano copper powder with improved wettability in the above dispersion, and ultrasonically disperse it evenly. Finally, take 1.5 g of the above-prepared organic carrier and place it in the dispersion, and stir at normal temperature and pressure until it becomes a paste to obtain an ultra-pure nano copper-based paste.

[0058] Take the ultra-pure nano copper-based paste prepared in Example 1 and sinter it in a hydrogen atmosphere at 300 °C for 2 h. Measure the resistivity according to the method of GB / T 351-2019 of the national standard, and its resistivity is 15 μΩ·cm; its scanning electron microscope is as attached Figure 1 .

[0059] Comparative Example 1

[0060] Mix 19 g of tripropylene glycol butyl ether, 1.2 g of hydrogenated castor oil, 3.7 g of hydrogenated rosin, 0.7 g of succinic acid, and 4.2 g of 2-phenylimidazole in a beaker, and use a high-speed shearer to process for 45 min (the components are mixed evenly) at a rotation speed of 6000 rpm and a temperature of 70 °C, and then cool to room temperature to obtain an organic carrier.

[0061] Mix 14 g of absolute ethanol, 2 g of ethylene glycol, and 1 g of stearic acid, and heat up to 60 °C until the stearic acid is completely dissolved (the components are mixed evenly) to obtain a dispersion.

[0062] First, place 6 g of ultra-pure nano copper powder in 45 ml of absolute ethanol, centrifuge and wash to obtain ultra-pure nano copper powder with improved wettability. Then place it in the above dispersion, and ultrasonically disperse it evenly. Finally, take 1.5 g of the above-prepared organic carrier and place it in the dispersion, and stir at normal temperature and pressure until it becomes a paste to obtain an ultra-pure nano copper-based paste.

[0063] The paste prepared in Comparative Example 1 was sintered in a hydrogen atmosphere at 300 °C for 2 h, and the resistivity was measured according to the method of GB / T 351-2019 of the national standard. Its resistivity was 39 μΩ·cm, and its scanning electron microscope is as attached Figure 2 .

[0064] From Figure 1 and Figure 2 it can be seen that the sintered body of the ultra-pure nano copper-based paste prepared in Example 1 is relatively dense, and the sintered body of the ultra-pure nano copper-based paste prepared in Comparative Example 1 contains more pores. It shows that adding dithiol in Example 1 of the present invention can reduce the distance between copper powders, and can enhance the connection strength between copper-copper particles through the chemical bond between copper and sulfur, thereby increasing the packing density of copper powders in the copper paste and improving the density of the sintered body.

[0065] Comparative Example 2

[0066] 19 g of tripropylene glycol butyl ether, 1.2 g of hydrogenated castor oil, 3.7 g of hydrogenated rosin, 0.7 g of succinic acid and 4.2 g of 2-phenylimidazole were mixed and placed in a beaker, and treated with a high-speed shear machine at a rotation speed of 6000 rpm and a temperature of 70 °C for 45 min (each component was mixed evenly), and then cooled to room temperature to obtain an organic carrier.

[0067] 14 g of absolute ethanol, 2 g of ethylene glycol and 1 g of stearic acid were mixed and heated to 60 °C until the stearic acid was completely dissolved (each component was mixed evenly) to obtain a dispersion.

[0068] First, 6 g of ordinary purity nano copper powder (purity lower than 99%) was placed in 45 ml of absolute ethanol, centrifuged and washed to obtain nano copper powder with improved wettability. Then it was placed in the above dispersion and ultrasonicated to make it evenly dispersed. Finally, 1.5 g of the above-prepared organic carrier was taken and placed in the dispersion, and stirred to a paste state under normal temperature and pressure to obtain a nano copper-based paste.

[0069] The paste prepared in Comparative Example 2 was sintered in a hydrogen atmosphere at 300 °C for 2 h, and the resistivity was measured according to the method of GB / T 351-2019 of the national standard. Its resistivity was calculated to be 70 μΩ·cm. The experimental results show that the resistivity of the copper paste sintered body prepared from ultra-pure nano copper powder is lower than that of the copper paste sintered body prepared from ordinary purity copper powder.

[0070] Obviously, the above examples are only examples given for clear illustration, and are not limitations on the examples. For those of ordinary skill in the art, other different forms of changes or modifications can be made on the basis of the above description. It is not necessary and impossible to list all examples here. And the obvious changes or modifications derived therefrom still fall within the protection scope of the present invention.

Claims

1. Ultra-pure nano copper-based paste, characterized in that, It includes ultra-pure nano copper powder, organic carrier and dispersion liquid; The purity of the ultra-pure nano copper powder is higher than 99.99%; The organic carrier includes tripropylene glycol butyl ether, hydrogenated castor oil, hydrogenated rosin, succinic acid and 2-phenylimidazole; The dispersion liquid includes ethanol, ethylene glycol, stearic acid and dithiol; In the dispersion liquid, the mass percentages of each component are: ethanol 78 - 86wt%, ethylene glycol 9 - 14wt%, stearic acid 4 - 9wt%, dithiol 0.01 - 0.20wt%; The dithiol is a dithiol having C2-C 12 .

2. The ultra-pure nano copper-based paste according to claim 1, wherein The mass percentage of the ultra-pure nano copper powder is 20 - 40wt%, the mass percentage of the organic carrier is 5 - 12wt%, and the mass percentage of the dispersion liquid is 55 - 70wt%.

3. The ultra-pure nano copper-based paste according to claim 1, wherein The ultra-pure nano copper powder is spherical or quasi-spherical, and the average size range is 20 - 50nm.

4. The ultra-pure nano copper-based paste according to claim 1, characterized in that, In the organic carrier, the mass percentages of each component are: tripropylene glycol butyl ether 60 - 70wt%, hydrogenated castor oil 3 - 5wt%, hydrogenated rosin 10 - 14wt%, succinic acid 2 - 6wt%, 2-phenylimidazole 12 - 16wt%.

5. The preparation method of the ultra-pure nano copper-based paste according to any one of claims 1-4, characterized in that, It includes the following steps: Step 1: Weigh raw materials according to the mass percentages of each component in the organic carrier, mix them evenly to obtain the organic carrier; Step 2: Weigh raw materials according to the mass percentages of each component in the dispersion liquid, mix them evenly at 60 - 75°C to obtain the dispersion liquid; Step 3: First place the ultra-pure nano copper powder in absolute ethanol, after centrifugal washing, add it to the dispersion liquid prepared in Step 2, disperse it evenly, and then add the organic carrier prepared in Step 1 to the dispersion liquid, stir until it becomes paste-like to obtain the ultra-pure nano copper-based paste.

6. The preparation method of the ultra-pure nano copper-based paste according to claim 5, wherein, In Step 1, it is mixed evenly by stirring, the stirring temperature is 50 - 120°C, the stirring time is 5 - 300min, and the stirring speed is 1000 - 12000rpm; In Step 2, it is mixed evenly by stirring; In Step 3, it is dispersed evenly by ultrasonic wave.

7. Application of the ultra-pure nano copper-based paste according to any one of claims 1 - 4 as an interconnection material.

8. Use of the ultra-pure nano copper-based paste according to claim 7 as an interconnect material, characterized in that, The interconnection material is a packaging interconnection material.

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