Self-reduction anti-oxidation sintering nano-copper soldering paste and preparation method and application thereof

Abstract

The invention belongs to the field of electronic packaging materials, and relates to self-reduction anti-oxidation sintering nano-copper soldering paste and a preparation method and application thereof. The copper soldering paste prepared by the preparation method comprises the pre-oxidized nano-copper particles and at least one reducing organic solvent. The pre-oxidized nano-copper particles ensure the long-term stability of the nano-copper soldering paste disclosed by the invention. When the copper particles are sintered and interconnected with the chip and the substrate, the reducing organic solvent can effectively reduce or avoid further oxidation of the copper particles. And meanwhile, the pre-oxidation layer on the surface of the nano-copper particles is reduced by the reducing organic solvent, and the in-situ generated high-surface-energy nano-copper particles can promote the formation of a sintering neck and the interconnection among the initial copper particles. Therefore, the prepared nano-copper soldering paste has good oxidation resistance, and high-strength and high-reliability sintering welding spots can be achieved in nitrogen and air atmospheres.

Description

Technical Field

[0001] The invention belongs to the field of electronic packaging materials and relates to a nano copper solder paste with self-reducing and anti-oxidation sintering capabilities and a preparation method and application thereof. Background Art

[0002] As the research on third-generation semiconductor materials such as silicon carbide (SiC) and gallium nitride (GaN) gradually matures, the corresponding power devices have been widely used in new infrastructure such as 5G communications, artificial intelligence, ultra-high voltage transmission, rail transportation, and new energy vehicles. The third-generation semiconductor materials have the characteristics of wide bandgap, high breakdown electric field, high thermal conductivity, and high operating temperature. Therefore, when preparing power devices, corresponding high requirements are also put forward for chip interconnection materials. Metal particle sintering technology has the advantages of low-temperature sintering and high-temperature application, and has higher thermal reliability and conductivity than traditional solder. At present, silver solder paste is widely used in power device packaging due to its excellent conductivity and thermal stability. However, silver is expensive and prone to electromigration. Copper is an interconnection material with application prospects because of its conductivity and thermal conductivity comparable to silver, lower cost and good anti-electromigration, and smaller difference in thermal expansion coefficient with the substrate.

[0003] However, copper is easily oxidized at high temperatures, which leads to the degradation of electrical, thermal and mechanical properties, affecting the performance of the device. Therefore, the development of a sintered copper solder paste with good anti-oxidation performance and high service reliability is a current research hotspot to meet the application requirements of high-reliability packaging of power devices. Summary of the invention

[0004] The purpose of the present invention is to provide a self-reducing anti-oxidation sintered copper solder paste, which can effectively prevent the oxidation of copper during the sintering process and achieve good electrical conductivity. The copper solder paste has self-reduction properties and can reduce copper oxides on the surface of particles into copper nanoparticles during the sintering process, while effectively alleviating the oxidation of copper nanoparticles, thereby maintaining the high electrical conductivity of the material. In addition, the present invention also provides a preparation method of the solder paste and its application in electronic device packaging.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] One of the technical solutions of the present invention is to provide a method for preparing a self-reducing anti-oxidation sintered copper solder paste, the steps comprising:

[0007] Pre-oxidation of nano copper particles;

[0008] Mix at least one reducing organic solvent evenly;

[0009] The nano copper particles are added into the mixed organic solvent and stirred evenly to obtain the self-reducing anti-oxidation nano copper solder paste.

[0010] Furthermore, the nano copper particles are ultrasonically cleaned and dispersed in acetone and ethanol in sequence, and then dried by heating at 100-250° C. for 5-30 min in an oxygen atmosphere, and an oxide layer protective layer is formed on the surface of the nano copper particles.

[0011] Furthermore, the average particle size of the nano copper particles is 30 to 100 nm.

[0012] Furthermore, the mass percentages of the nano copper particles and the organic solvent are 40-90% and 10-60% respectively.

[0013] Preferably, the reducing organic solvent is one or more of glycerol, hydrazine hydrate, sodium citrate, polyethylene glycol, triethylene glycol, and ascorbic acid.

[0014] The second technical solution of the present invention: a self-reducing anti-oxidation sintered copper solder paste obtained by the above-mentioned preparation method.

[0015] Technical solution three of the present invention: Application of the above self-reducing anti-oxidation sintered copper solder paste in the field of power device packaging comprises the following steps:

[0016] The self-reducing anti-oxidation nano copper solder paste is applied to the materials to be soldered, and the interconnection is completed under preset conditions.

[0017] Preferably, the preset sintering temperature is 225-325° C., the interconnection time is 1-30 min, and the sintering pressure is less than 5 MPa.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The copper solder paste prepared by the preparation method of the present invention comprises pre-oxidized nano copper particles and at least one reducing organic solvent. The pre-oxidized nano copper particles ensure the long-term stability of the nano copper solder paste of the present invention. When sintering and interconnecting with a chip and a substrate, the reducing organic solvent can effectively reduce or avoid further oxidation of the copper particles. At the same time, the pre-oxidized layer on the surface of the nano copper particles is reduced by the reducing organic solvent, and the high surface energy nano copper particles generated in situ can promote the formation of sintering necks and the interconnection between the initial copper particles. The present invention optimizes the mass fraction of the composite organic solvent and the sintering parameters to finally form a sintered solder joint with high strength, which can meet the application requirements of power device packaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The present invention is a schematic diagram of the self-reducing anti-oxidation sintered copper solder paste prepared by the present invention and its sintering process flow chart.

[0021] Figure 2 The following are XRD patterns of the copper solder joints prepared in the examples and comparative examples.

[0022] Figure 3 These are cross-sectional morphologies of solder joints of the copper solder pastes prepared in Example 2 and Example 8 after sintering in nitrogen and air, respectively. DETAILED DESCRIPTION

[0023] The present invention will be further described below in conjunction with specific embodiments. However, the embodiments do not limit the present invention in any form, but should be understood as a more detailed description of certain aspects, characteristics and implementation schemes of the present invention.

[0024] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0025] Unless otherwise specified, the raw materials and reagents used in the examples of the present invention are conventionally purchased raw materials and reagents. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention.

[0026] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0027] Example 1

[0028] A preparation method of a self-reducing anti-oxidation sintered copper solder paste comprises the following steps:

[0029] Nano copper particles with an average particle size of 50 nm were placed in acetone and ethanol for ultrasonic cleaning and dispersion, and then heated at 150° C. for 15 minutes in air to dry and form a uniform Cu2O oxide layer on the surface to obtain pre-oxidized nano copper particles.

[0030] 15% by mass of polyethylene glycol and 85% by mass of the above-mentioned pre-oxidized nano copper particles are mixed, and the mixture is fully stirred in a vacuum environment to form a self-reducing anti-oxidation sintered copper solder paste.

[0031] Example 2

[0032] A preparation method of a self-reducing anti-oxidation sintered copper solder paste comprises the following steps:

[0033] Nano copper particles with an average particle size of 60 nm were placed in acetone and ethanol for ultrasonic cleaning and dispersion, and then heated at 200° C. for 10 minutes in air to dry and form a uniform Cu2O oxide layer on the surface to obtain pre-oxidized nano copper particles.

[0034] Mixing 90% polyethylene glycol by mass and 10% ascorbic acid by mass at 60° C., dissolving the ascorbic acid, and stirring thoroughly to obtain a uniformly dispersed solution;

[0035] The mixed solution is mixed with the pre-oxidized nano copper particles to make the mass fraction of the nano copper particles 80%, and the mixture is fully stirred to form a self-reducing anti-oxidation sintered copper solder paste.

[0036] Example 3

[0037] A preparation method of a self-reducing anti-oxidation sintered copper solder paste comprises the following steps:

[0038] Nano copper particles with an average particle size of 60 nm were placed in acetone and ethanol for ultrasonic cleaning and dispersion, and then heated at 250° C. for 5 minutes in air to dry and form a uniform Cu2O oxide layer on the surface to obtain pre-oxidized nano copper particles.

[0039] 45% by mass of terpineol, 45% by mass of glycerol and 10% by mass of ascorbic acid were mixed and dissolved at 60° C. and stirred thoroughly to obtain a uniformly dispersed solution;

[0040] The mixed solution is mixed with pre-oxidized nano copper particles to make the mass fraction of the nano copper particles 85%, and the mixture is fully stirred to form a self-reducing anti-oxidation sintered copper solder paste.

[0041] Example 4

[0042] A preparation method of a self-reducing anti-oxidation sintered copper solder paste comprises the following steps:

[0043] Nano copper particles with an average particle size of 100 nm were placed in acetone and ethanol for ultrasonic cleaning and dispersion, and then heated at 250° C. for 5 minutes in an oxygen atmosphere to dry and form a uniform Cu2O oxide layer on the surface to obtain pre-oxidized nano copper particles.

[0044] 45% by mass of triethylene glycol, 45% by mass of glycerol and 10% by mass of ascorbic acid were mixed and dissolved at 60° C. and stirred thoroughly to obtain a uniformly dispersed solution;

[0045] The mixed solution is mixed with pre-oxidized nano copper particles to make the mass fraction of the nano copper particles 85%, and the mixture is fully stirred to form a self-reducing anti-oxidation sintered copper solder paste.

[0046] Example 5

[0047] A method for preparing a nano copper solder paste is the same as that of Example 4, except that the nano copper particles with an average particle size of 80 nm are replaced with nano copper particles with an average particle size of 30 nm, and the pre-oxidation conditions are 150° C. and 10 min.

[0048] Example 6

[0049] The preparation method of a nano copper solder paste is the same as that of Example 3, except that the mixed organic solvent is replaced by 80% by mass of glycerol and 20% by mass of sodium citrate.

[0050] Example 7

[0051] The preparation method of a nano copper solder paste is the same as that of Example 2, except that the mass fraction of nano copper particles in the solder paste is replaced with 88%.

[0052] Example 8

[0053] The preparation method of a nano copper solder paste is the same as that of Example 1, except that the nano copper particles with an average particle size of 50 nm are replaced by nano copper particles with an average particle size of 200 nm.

[0054] Comparative Example 1

[0055] A method for preparing a nano copper solder paste is the same as that in Example 1, except that polyethylene glycol is replaced with ethylene glycol of equal mass.

[0056] Comparative Example 2

[0057] The preparation method of a nano copper solder paste is the same as that of Example 2, except that the composite organic solvent is replaced by 80% by mass of triethylene glycol and 20% by mass of pinene alcohol, which are mixed and dissolved with each other and stirred thoroughly to obtain a uniformly dispersed solution.

[0058] Comparative Example 3

[0059] The preparation method of a nano copper solder paste is the same as that of Example 3, except that the composite organic solvent is replaced with an equal mass of pinene alcohol.

[0060] Comparative Example 4

[0061] The preparation method of a nano copper solder paste is the same as that of Example 3, except that nano copper particles with the same average particle size are not passivated by oxygen, but are directly mixed with the composite organic solvent.

[0062] Comparative Example 5

[0063] A method for preparing a nano copper solder paste is the same as that of Example 5, except that the composite organic solvent is replaced with an equal mass of triethylene glycol.

[0064] application

[0065] The nano copper solder paste prepared in each embodiment and comparative example was coated on a bare copper DBC substrate, and a 3×3 mm copper sheet was attached, and then sintered in a nitrogen or air atmosphere, wherein the sintering temperature was 300° C., the sintering time was 30 min, and the pressure was 2 MPa.

[0066] Performance Testing

[0067] 1. Test methods

[0068] Oxidation degree of sintered solder joints: XRD (D8 Advance, Bruker) was used to characterize the physical phase of the shear section of the sample.

[0069] Shear strength of sintered solder joints: The shear strength test was carried out at room temperature using a multifunctional push-pull tester (MFM1200, Try precision) at a test speed of 100 μm / s.

[0070] Porosity of sintered solder joints: Based on the SEM morphology of the solder joint cross section, the porosity of the sintered layer was calculated using ImageJ software.

[0071] 2. Test results

[0072] Figure 2 The XRD patterns of the copper solder pastes of the embodiments and comparative examples after sintering are shown to explore the self-reduction ability and antioxidant ability of the solder pastes. Obviously, no oxide diffraction peaks were detected in Example 1 after sintering in nitrogen and air. However, there is still a diffraction peak of Cu2O (111) in Comparative Example 1 without a reducing organic solvent after sintering in nitrogen, indicating that the oxide layer has not been reduced, and the diffraction peaks of Cu2O sintered in air increase and strengthen, indicating that the copper particles are further oxidized. No diffraction peaks of oxides were detected in the solder joints of Examples 2 and 3 after sintering in air, while Comparative Examples 2 and 3 have diffraction peaks of Cu2O (111). Therefore, the reducing organic solvent used in the present invention can effectively reduce its own oxidative passivation layer, inhibit oxidation during the sintering process, and improve the antioxidant ability of the copper solder paste.

[0073] Table 1 Shear performance test results of copper solder joints prepared in various embodiments and comparative examples

[0074] <![CDATA[Shear strength of N2 sintered solder joints (MPa)]]> Air sintered solder joint shear strength (MPa) Example 1 33.81±3.31 23.22±1.57 Example 2 51.30±4.67 46.64±1.81 Example 3 37.72±6.88 38.92±5.21 Example 4 34.25±5.75 31.66±4.93 Example 5 40.78±5.26 32.35±4.81 Example 6 38.94±4.63 29.52±3.58 Example 7 50.94±5.26 46.69±2.61 Example 8 68.60±5.50 41.27±5.62 Comparative Example 1 4.37±1.23 0 (below the detection limit) Comparative Example 2 14.26±3.94 7.33±4.82 Comparative Example 3 11.90±0.35 2.51±0.44 Comparative Example 4 15.25±4.37 13.40±1.29 Comparative Example 5 14.11±2.25 4.82±1.15

[0075] Table 1 shows the shear strength of the solder joints of the copper solder pastes prepared in the examples and comparative examples after sintering in nitrogen and air atmospheres, respectively. It can be seen from the figure that the copper solder pastes prepared by the present invention have a relatively high shear strength, wherein the shear strength of Examples 3, 7 and 8 sintered in nitrogen can reach more than 50 MPa, and even sintered in air can obtain a shear strength of more than 40 MPa. However, Comparative Example 1 using a non-reducing solvent cannot achieve effective sintering connection in air, and Comparative Examples 2 to 5 using a relatively low reducing solvent have a shear strength of only more than 10 MPa sintered in nitrogen, and the solder joint strength after sintering in air is basically lower than 10 MPa, which is not enough to meet the application requirements of power device packaging. It can be seen from the results of Example 2 and Comparative Example 4 that the oxygen passivation layer of the copper particles is reduced by the reducing agent during the sintering process, and the high-energy nano copper particles generated in situ have a promoting effect on sintering, thereby effectively improving the shear strength of the solder joints.

[0076] Figure 3 Figures ab are cross-sectional morphologies of the solder joints of the copper solder paste prepared in Example 2 after sintering in nitrogen and air, respectively. In both atmospheres, the copper solder paste finally formed a dense sintered structure after sintering, and at the same time formed an effective connection with the substrate. The porosity of the solder joints sintered in nitrogen and air was 28.64% and 31.64%, respectively. Figure 3 Figures cd in the figure are cross-sectional morphologies of the solder joints of the copper solder paste prepared in Example 8 after sintering in nitrogen and air. A denser sintering structure is formed in the nitrogen atmosphere, with a porosity of 22.30%. The sintered structure in the air atmosphere is relatively elongated, with a porosity of 22.50%.

[0077] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for preparing a self-reducing anti-oxidation nano copper solder paste, characterized in that: The steps include: (1) pre-oxidizing the nano copper particles; (2) using more than one reducing organic solvent and mixing them uniformly; (3) adding the nano copper particles into the mixed organic solvent and stirring evenly to obtain the self-reducing antioxidant nano copper solder paste; The raw material addition amounts are calculated by mass fraction, including 40-80% of nano copper particles and 20-60% of organic solvent.

2. The method for preparing the self-reducing anti-oxidation nano copper solder paste according to claim 1, characterized in that: The nano copper particles are pre-oxidized in air or oxygen atmosphere at 100-250° C. for 5-30 minutes, and the surfaces are covered with an oxide layer.

3. The method for preparing the self-reducing anti-oxidation nano copper solder paste according to claim 1, characterized in that: The particle size of the nano copper particles is 30 to 200 nm.

4. The method for preparing the self-reducing anti-oxidation nano copper solder paste according to claim 1, characterized in that: The reducing organic solvent is one or more of glycerol, hydrazine hydrate, sodium citrate, polyethylene glycol, triethylene glycol, and ascorbic acid.

5. The method for preparing the self-reducing anti-oxidation nano copper solder paste according to claim 1, characterized in that: The combination of reducing organic solvents is: glycerol and sodium citrate, triethylene glycol, glycerol and ascorbic acid, terpineol, glycerol and ascorbic acid, or polyethylene glycol and ascorbic acid.

6. The method for preparing the self-reducing anti-oxidation nano copper solder paste according to claim 5, characterized in that: Specifically, it is: 80% glycerol and 20% sodium citrate, 45% triethylene glycol, 45% glycerol and 10% ascorbic acid by mass, 45% terpineol, 45% glycerol and 10% ascorbic acid by mass, or 90% polyethylene glycol and 10% ascorbic acid by mass.

7. The self-reducing and anti-oxidation nano copper solder paste prepared by the preparation method according to any one of claims 1 to 6.

8. Application of the self-reducing and anti-oxidation nano copper solder paste according to claim 7 in power device packaging interconnection.

9. The use according to claim 8, characterized in that: The steps include: The self-reducing anti-oxidation nano-copper solder paste is coated on the DBC substrate, and then the Cu simulation chip is attached to complete the Cu-Cu interconnection under preset conditions.

10. The use according to claim 9, characterized in that: The preset conditions include a sintering temperature of 225 to 325° C., an interconnection time of 1 to 60 minutes, and a sintering pressure of less than 5 MPa.

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