WO2021164613A1 - Multi-grade micro-nano mixed metal paste and preparation method therefor - Google Patents

Abstract

A multi-grade micro-nano mixed metal paste, comprising 2-5 grades of 5nm-100μm micro-nano mixed metal particles (6) and flux (7). According to the metal paste (8), the diameters of the metal particles (2, 3, 4) of various grades are further defined, and the multi-grade micro-nano mixed metal paste is prepared by mixing the multi-grade micro-nano metal particles. Also provided is a preparation method for the multi-grade micro-nano mixed metal paste. The metal paste has nano particles evenly distributed, and can satisfy the requirements of low-temperature sintering and high-temperature usage. The preparation method is simple to operate, easy to control, and suitable for large-scale industrial production.

Description

Multi-stage micro-nano mixed metal paste and preparation method thereof Technical field

The invention belongs to the technical field of welding materials. More specifically, it relates to a multi-stage micro-nano hybrid metal paste and a preparation method thereof.

Background technique

Metal nanomaterials (such as copper, silver and nickel) are commonly used as soldering layers in electronic chips, high-speed trains, energy transmission and other fields. They have the advantages of high thermal conductivity (150～300W/m·K) and high service temperature. An ideal high-temperature resistance and high thermal conductivity soldering material, which can be used as the third-generation semiconductor electrode lead-out material and solder for chip packaging to achieve low-temperature (<300°C) interconnection and high-temperature service effects. At present, the commonly used silver nanomaterials are mainly nano-silver materials, but nano-silver materials have disadvantages such as high price, large expansion coefficient, large porosity, and electromigration, and their applications are greatly restricted.

Research has found that nano-copper materials can be used to replace nano-silver materials, and the above-mentioned problems can be solved in a multi-size combination. For example, Chinese patent application CN109935563A discloses a multi-size mixed nano-particle paste and a preparation method thereof. The paste contains mixed copper nanoparticles of various sizes. The gap between the particles is beneficial to realize the connection of nano-copper without pressure assistance, and improve the compactness of the metal layer after sintering. However, this preparation method needs to impart kinetic energy to the small-sized nano-metal particles by means of physical impact, so that they can be driven into the large-sized nano-copper paste, and the nano-metal composite paste of mixed size and size is configured, and the physical impact needs to be strictly controlled and adjusted. In order to control the amount of small-sized nano metal particles, there are problems of uneven particles, complicated operations, and difficult to control.

Therefore, there is an urgent need to provide a multi-stage micro-nano hybrid metal paste with low porosity, high density, uniform mixing, and simple preparation method.

Summary of the invention

The technical problem to be solved by the present invention is to overcome the disadvantages of high price of nano-silver materials in the prior art, large expansion coefficient difference, large porosity, electromigration, etc., the multi-size nano-copper material particles are not uniform, the preparation is relatively complicated, and the quality is difficult to control. Defects and deficiencies provide a multi-level micro-nano hybrid metal paste with low porosity, high density, uniform mixing and simple preparation method.

Another object of the present invention is to provide a method for preparing the multi-stage micro-nano mixed metal paste.

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

A multi-stage micro-nano mixed metal paste, the multi-stage micro-nano mixed metal paste comprising 2 to 5 levels of micro-nano mixed metal particles with a size of 5 nm to 100 μm and a soldering flux;

Wherein, the particle size ratio of the nth level to the (n+1)th level in the micro-nano mixed metal particles is

n=1～4;

The weight ratio of the first-level and second-level particles in the micro-nano mixed metal particles is

The weight ratio of the m-th grade and (m+1)-th grade particles in the micro-nano mixed metal particles is

m=2～4.

The multi-level micro-nano hybrid metal paste of the present invention further limits the diameter of the metal particles at all levels, and adopts the form of mixing multi-level micro-nano metal particles to prepare the multi-level micro-nano hybrid metal paste. The nano-particles are evenly distributed and are used for sintering. The composite section has low porosity, high density, strong thermal shock resistance, high reliability, and can fully meet the requirements of low-temperature sintering and high-temperature service.

Preferably, the particle size ratio of the nth level and the (n+1)th level in the micro-nano mixed metal particles is 0.225:(0.5-1), n=1-4.

More preferably, the particle size ratio of the nth level and the (n+1)th level in the micro-nano mixed metal particles is 0.225:1, and n=1˜4. It is found in practice that the multi-level micro-nano mixed metal paste prepared under this ratio has low porosity and high compactness, and each effect is good.

Preferably, the multi-level micro-nano mixed metal paste includes 2 to 3 levels.

More preferably, the multi-stage micro-nano mixed metal paste is grade 3. In practice, it is found that when the multi-level micro-nano mixed metal paste is level 3, the porosity is low, the compactness is high, and the material is saved, and the operation is simple.

Further, the micro-nano mixed metal particles are prepared by a multi-stage chemical reduction method, a mechanical mixing method or a solution mixing method.

The invention can be prepared by a simple multi-stage chemical reduction method, a mechanical mixing method or a solution mixing method, has simple operation, is convenient to control, is suitable for large-scale industrial production, and has huge economic benefits.

Furthermore, the multi-stage chemical reduction method includes the following steps:

Dissolve the soluble copper salt in absolute ethanol, add dispersant and reducing agent in 2 to 5 times, heat up to 60-78°C and complete the reaction, centrifuge, wash, and dry to get it;

Wherein, the weight ratio of the soluble copper salt to the dispersant added for the first time is 1: (0.1 to 3), and the weight ratio of the soluble copper salt to the dispersant added for the second to fourth times is 1: (0 to 3);

The molar ratio of the soluble copper salt to the reducing agent added for the first time is (5～20):1, and the molar ratio of the reducing agent added for the second time to the reducing agent added for the first time is

The molar ratio of the reducing agent added at the (m+1)th time to the reducing agent added at the mth time is

m=2～4;

The first reaction temperature was 60-75°C, and the (n+1)-th reaction temperature was 0-5°C higher than the n-th reaction temperature.

Further, the total added amount of the dispersant does not exceed 5 times the weight of the soluble copper salt; the total added amount of the reducing agent does not exceed 2 times the molar amount of the soluble copper salt.

Furthermore, the soluble copper salt is copper sulfate, copper acetate or copper hydroxide, the dispersant is polyvinylpyrrolidone, nonylphenol polyoxyethylene ether or imidazole, and the reducing agent in question is ascorbic acid, hydrazine hydrate, boron Potassium hydride, sodium borohydride or sodium hypophosphite.

Further, the mechanical mixing method includes the following steps:

Add micro-nano metal particles of different sizes into the mixing container, add spherical, polyhedral or irregularly shaped hard particles, apply static electricity to the mixing container after sealing, and perform mechanical vibration, ultrasonic vibration, continuous impact, flipping, etc. The high-pressure operation makes mixing and separation, and it is obtained.

Furthermore, the hard particles are tungsten carbide, iron-based amorphous alloys or hard PVC transparent hard particles.

Further, the diameter of the hard particles is 10-15 times the largest diameter in the micro-nano mixed metal particles.

Furthermore, the solution mixing method includes the following steps:

Add micro-nano metal particles of different sizes into the mixing container, add absolute ethanol and dispersant, apply static electricity to the mixing container after sealing, and perform mechanical vibration, ultrasonic vibration, continuous impact, overturning, and high-pressure operations to make the mixing uniform. , Centrifugation, magnetic field separation, that is.

Furthermore, the dispersant is polyvinylpyrrolidone.

Further, the weight ratio of the micro-nano mixed metal particles and the flux is (3-5):1.

Preferably, the weight ratio of the micro-nano mixed metal particles and the flux is 4:1. It has been found in practice that the multi-stage micro-nano mixed metal paste prepared under this ratio has low porosity and high compactness, and each effect is good.

Furthermore, the soldering flux is composed of the following raw materials and their weight percentages: 10-30% of active agent, 10-50% of film-forming agent, 1-20% of surfactant and remaining solvent.

Further, the active agent is hydrochloric acid, hydrofluoric acid, orthophosphoric acid, stannous chloride, zinc chloride, ammonium chloride, potassium fluoride, sodium fluoride and other inorganic substances, or rosin, dimethylamine hydrochloride, hydrochloric acid Organic halides such as diethylamine, cyclohexylamine hydrochloride, and aromatic amine hydrohalides, or organic acids such as hydroxy acids and sulfonic acids, or organic amines such as methylamine, dimethylamine, trimethylamine, and ethylamine.

Furthermore, the film forming agent is bisphenol A epoxy resin, organic high polymer, modified cellulose, etc., such as epoxy resin, various synthetic resins, acrylic resins, and the like.

Further, the surfactant is cetyltrimethylammonium bromide, fluoroaliphatic polymer ether, sodium diethyl succinate sulfonate, quaternary ammonium fluoroalkyl compound and the like.

Furthermore, the solvent is terpineol, ethylene glycol, n-butanol, ethanol and the like.

In addition, the present invention also provides a method for preparing the multi-stage micro-nano hybrid metal paste, which is characterized in that it comprises the following steps:

Prepare micro-nano mixed metal particles and flux, stir, sonicate, and mix the micro-nano mixed metal particles and flux evenly to obtain.

The present invention has the following beneficial effects:

(1) The multi-level micro-nano hybrid metal paste of the present invention further limits the diameter of the metal particles at all levels, and prepares the multi-level micro-nano hybrid metal paste in the form of mixing multi-level micro-nano metal particles. The nano-particles are evenly distributed. During sintering, the bonding section has low porosity, high density, strong thermal shock resistance, and high reliability, which can fully meet the requirements of low-temperature sintering and high-temperature service.

(2) The preparation method of a multi-stage micro-nano hybrid metal paste of the present invention can be a multi-stage chemical reduction method, a mechanical mixing method or a solution mixing method. The operation is simple, easy to control, suitable for large-scale industrial production, and has huge advantages. Economic benefits.

Description of the drawings

Figure 1 is a flow chart of the multi-stage chemical reduction method of the present invention;

Among them, 1- containing metal salt solution, 2- primary metal particles, 3- secondary metal particles, 4- tertiary metal particles, 5- reducing agent and dispersant, 6-micro-nano mixed metal particles, 7-assisted Flux, 8-multi-level micro-nano mixed metal paste.

Figure 2 is a flow chart of the mechanical mixing method of the present invention;

Among them, 2-level metal particles, 3-level metal particles, 4-level metal particles, 6-micro-nano mixed metal particles, 7-flux, 8-multi-level micro-nano mixed metal paste, 9-closed mixed Material container, 10-hard particles, 11-mixing table.

Fig. 3 is an SEM observation diagram of the multi-level micro-nano mixed metal paste in Example 1 of the present invention.

4 is a SEM observation diagram of the multi-level micro-nano mixed metal paste of Example 2 of the present invention.

Fig. 5 is an SEM observation diagram of the multi-level micro-nano mixed metal paste in Example 3 of the present invention.

Detailed ways

The present invention will be further described below with reference to the drawings and specific embodiments of the specification, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the technical field.

Unless otherwise specified, the reagents and materials used in the following examples are all commercially available.

Example 1 A multi-stage micro-nano mixed metal paste

The multi-stage micro-nano hybrid metal paste is prepared by the following method:

S1. Preparation of micro-nano mixed metal particles: Dissolve 9g of copper acetate in 900ml of absolute ethanol, add 3.3g of dispersant polyvinylpyrrolidone and 10.56g of reducing agent ascorbic acid for the first time, heat to 70℃ in a water bath, and react to completion; Add 2.4g of the dispersant polyvinylpyrrolidone and 8.1g of the reducing agent ascorbic acid twice, and heat the water bath to 75°C to complete the reaction; add 1.55g of the dispersant polyvinylpyrrolidone and 6g of the reducing agent ascorbic acid for the third time, and heat the water bath to 75°C, After the reaction is complete, centrifuged, washed with deionized water and absolute ethanol, and dried in vacuum for 12-24 hours to obtain micro-nano mixed metal particles with a weight ratio of 1:4:2 at the first level of 45nm, the second level of 200nm, and the third level of 1μm. ；

S2. Flux preparation: add 12% rosin (active agent), 35.5% bisphenol A type epoxy resin (film former) and 2% cetyltrimethylammonium bromide (surfactant) to the balance In terpineol (solvent), mix evenly to obtain flux;

S3. Preparation of multi-stage micro-nano mixed metal paste: The micro-nano mixed metal particles obtained in step S1 and the flux obtained in step S2 are mixed according to a weight ratio of 4:1, stirred, sonicated, and mixed uniformly to obtain.

The SEM image observation and measurement of the multi-level micro-nano mixed metal paste obtained in Example 1 are performed, and the results are shown in FIG. 3.

Example 2 A multi-stage micro-nano mixed metal paste

The multi-stage micro-nano hybrid metal paste is prepared by the following method:

S1. Preparation of micro-nano mixed metal particles: Weigh the first-level 35nm, second-level 150nm, and third-level 700nm copper nanoparticles with different sizes, with a weight ratio of 0.26:1:1, totaling 0.8g, and add them to the mixing container. 0.1g magnetic spherical hard iron-based amorphous alloy particles with a diameter of 0.5mm, apply static electricity to the mixing container after sealing, and perform mechanical vibration, ultrasonic vibration, continuous impact, overturning, and high-pressure operations to mix, screen, and The magnetic spherical hard iron-based amorphous alloy particles are separated by the magnetic field, and it is obtained;

S2. Flux preparation: add 12% rosin (active agent), 35.5% acrylic resin (film former) and 2% sodium diethyl succinate (surfactant) to the balance of ethylene glycol (solvent) Medium, mix evenly, get flux;

S3. Preparation of multi-stage micro-nano mixed metal paste: The micro-nano mixed metal particles obtained in step S1 and the flux obtained in step S2 are mixed according to a weight ratio of 4:1, stirred, sonicated, and mixed uniformly to obtain.

The SEM image observation and measurement of the multi-level micro-nano mixed metal paste obtained in Example 2 are performed, and the results are shown in FIG. 4.

Example 3 A multi-stage micro-nano mixed metal paste

The multi-stage micro-nano hybrid metal paste is prepared by the following method:

S1. Preparation of micro-nano mixed metal particles: Weigh the first-level 25nm and second-level 110nm nano-copper particles with a weight ratio of 0.26:1, add them to the mixing container, and add 0.1g of spherical hard particles with a diameter of 0.5mm Tungsten carbide particles, after sealing, apply static electricity to the mixing container, and at the same time perform mechanical vibration, ultrasonic vibration, continuous impact, overturning, and high-pressure operations to make it uniform, and then sieving and separating spherical hard tungsten carbide particles, that is;

S2. Flux preparation: Add 12% rosin (active agent), 35.5% bisphenol A type epoxy resin (film former) and 2% fluoroaliphatic polyether (surfactant) to the balance of ethylene glycol ( In the solvent), mix evenly to obtain a flux;

S3. Preparation of multi-stage micro-nano mixed metal paste: The micro-nano mixed metal particles obtained in step S1 and the flux obtained in step S2 are mixed according to a weight ratio of 4:1, stirred, sonicated, and mixed uniformly to obtain.

The SEM image observation and measurement of the multi-level micro-nano mixed metal paste obtained in Example 3 are carried out, and the results are shown in FIG. 5.

Example 4 A multi-stage micro-nano mixed metal paste

The multi-stage micro-nano hybrid metal paste is prepared by the following method:

S1. Preparation of micro-nano mixed metal paste:

Weigh the first-level 35nm, the second-level 150nm, the third-level 700nm, the fourth-level 3μm, and the fifth-level 13μm copper nanoparticles with a weight ratio of 0.26:1:1:0.5:0.5, and a total of 0.8g. Add five grades of micro-nano metal particles of different sizes into the mixing container, add 100ml of absolute ethanol and 3g of polyvinylpyrrolidone dispersant, apply static electricity to the mixing container after sealing, and perform mechanical vibration, ultrasonic vibration, continuous impact, and inversion at the same time , High-pressure operation makes mixing, centrifugation, magnetic field separation, that is;

S2. Add 12% rosin (active agent), 35.5% acrylic resin (film former) and 2% cetyltrimethylammonium bromide (surfactant) to the remaining ethylene glycol (solvent) and mix Uniform, get flux;

S3. Preparation of multi-stage micro-nano mixed metal paste: The micro-nano mixed metal particles obtained in step S1 and the flux obtained in step S2 are mixed according to a weight ratio of 4:1, stirred, sonicated, and mixed uniformly to obtain.

Comparative Example 1 A metal paste

The difference from Example 1 is that Comparative Example 1 replaces the micro-nano mixed metal particles with single nano-copper particles with a size of 45 nm, and other parameters and operations refer to Example 1.

Comparative Example 2 A metal paste

The difference from Example 1 is that Comparative Example 2 replaces the micro-nano mixed metal particles with single nano-copper particles with a size of 200 nm, and other parameters and operations refer to Example 1.

Comparative Example 3 A metal paste

The difference from Example 1 is that Comparative Example 3 replaces the micro-nano mixed metal particles with single micron copper particles with a size of 1 μm. Refer to Example 1 for other parameters and operations.

Comparative Example 4 A metal paste

The difference from Example 2 is that in Comparative Example 4, the micro-nano mixed metal particles are replaced by single nano-copper particles with a size of 35 nm. Refer to Example 2 for other parameters and operations.

Comparative Example 5 A metal paste

The difference from Example 2 is that in Comparative Example 5, the micro-nano mixed metal particles are replaced with single nano-copper particles with a size of 150 nm, and other parameters and operations refer to Example 2.

Comparative Example 6 A metal paste

The difference from Example 2 is that Comparative Example 6 replaces the micro-nano mixed metal particles with single nano-copper particles with a size of 700 nm, and other parameters and operations refer to Example 2.

Comparative Example 7 A metal paste

The difference from Example 3 is that Comparative Example 7 replaces the micro-nano mixed metal particles with single nano-copper particles with a size of 25 nm, and other parameters and operations refer to Example 3.

Comparative Example 8 A metal paste

The difference from Example 3 is that Comparative Example 8 replaces the micro-nano mixed metal particles with single nano-copper particles with a size of 110 nm, and other parameters and operations refer to Example 3.

Experimental example 1 Metal paste sintered film and measurement of porosity

The metal pastes prepared in Examples 1 to 3 and Comparative Examples 1 to 8 were coated on the substrate and laser sintered. The sintering thickness was all 50 μm. Each group tested 5 in parallel at the same time. The copper nanoparticles were sintered by Image J computer software The SEM image of the film was processed to calculate the average porosity. The results are shown in Table 1.

Table 1 Porosity of metal paste sintered film

Group	Metal paste particle size	Average porosity (%)
Example 1	45nm, 200nm, 1μm	10.4
Comparative example 1	45nm	12.2
Comparative example 2	200nm	14.6
Comparative example 3	1μm	26.4
Example 2	35nm, 150nm, 700nm	10.6
Comparative example 4	35nm	12.0
Comparative example 5	150nm	14.5
Comparative example 6	700nm	21.6
Example 3	25nm, 110nm	11.6
Comparative example 7	25nm	12.1
Comparative example 8	110nm	14.3

It can be seen from Table 1 that the average porosity of the multi-level micro-nano mixed metal paste prepared in Examples 1 to 3 of the present invention is below 12%, with high density, high reliability, and uniform distribution of metal nanoparticles of various sizes; Ratios 1 to 8 use single-sized nano-copper particles, and the average porosity is significantly reduced.

The above-mentioned embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above-mentioned embodiments, and any other changes, modifications, substitutions, combinations, etc. made without departing from the spirit and principle of the present invention Simplified, all should be equivalent replacement methods, and they are all included in the protection scope of the present invention.

Claims (10)

1. A multi-stage micro-nano mixed metal paste, characterized in that the multi-stage micro-nano mixed metal paste includes 2 to 5 levels of micro-nano mixed metal particles with a size of 5 nm to 100 μm and a soldering flux;

   Wherein, the particle size ratio of the nth level to the (n+1)th level in the micro-nano mixed metal particles is

   

   n=1～4;

   The weight ratio of the first-level and second-level particles in the micro-nano mixed metal particles is

   

   The weight ratio of the m-th grade and (m+1)-th grade particles in the micro-nano mixed metal particles is

   

   m=2～4.
2. The multi-stage micro-nano mixed metal paste according to claim 1, wherein the micro-nano mixed metal particles are prepared by a multi-stage chemical reduction method, a mechanical mixing method, or a solution mixing method.
3. The multi-stage micro-nano mixed metal paste according to claim 2, wherein the multi-stage chemical reduction method comprises the following steps:

   Dissolve the soluble copper salt in absolute ethanol, add dispersant and reducing agent in 2 to 5 times, heat up to 60-78°C to complete the reaction, centrifuge, wash, and dry to get it;

   Wherein, the weight ratio of the soluble copper salt to the dispersant added for the first time is 1: (0.1 to 3), and the weight ratio of the soluble copper salt to the dispersant added for the second to fourth times is 1: (0 to 3);

   The molar ratio of the soluble copper salt to the reducing agent added for the first time is (5～20):1, and the molar ratio of the reducing agent added for the second time to the reducing agent added for the first time is

   

   The molar ratio of the reducing agent added at the (m+1)th time to the reducing agent added at the mth time is

   

   m=2～4;

   The first reaction temperature was 60-75°C, and the (n+1)-th reaction temperature was 0-5°C higher than the n-th reaction temperature.
4. The multi-stage micro-nano mixed metal paste according to claim 3, wherein the total added amount of the dispersant does not exceed 5 times the weight of the soluble copper salt; the total added amount of the reducing agent does not exceed the moles of the soluble copper salt 2 times the amount.
5. The multi-stage micro-nano mixed metal paste according to claim 4, wherein the soluble copper salt is copper sulfate, copper acetate or copper hydroxide, and the dispersant is polyvinylpyrrolidone, nonylphenol polyoxyethylene ether Or imidazole, the reducing agent in question is ascorbic acid, hydrazine hydrate, potassium borohydride, sodium borohydride or sodium hypophosphite.
6. The multi-stage micro-nano hybrid metal paste according to claim 2, wherein the mechanical mixing method comprises the following steps:

   Add micro-nano metal particles of different sizes into the mixing container, add spherical, polyhedral or irregularly shaped hard particles, apply static electricity to the mixing container after sealing, and perform mechanical vibration, ultrasonic vibration, continuous impact, flipping, etc. The high-pressure operation makes mixing and separation, and it is obtained.
7. The multi-stage micro-nano hybrid metal paste according to claim 2, wherein the solution mixing method comprises the following steps:

   Add micro-nano metal particles of different sizes into the mixing container, add absolute ethanol and dispersant, apply static electricity to the mixing container after sealing, and perform mechanical vibration, ultrasonic vibration, continuous impact, overturning, and high-pressure operations to make the mixing uniform. , Centrifugation, magnetic field separation, that is.
8. The multi-stage micro-nano mixed metal paste according to any one of claims 1 to 7, wherein the weight ratio of the micro-nano mixed metal particles and the flux is (3 to 5):1.
9. The multi-level micro-nano mixed metal paste according to claim 8, wherein the flux is composed of the following raw materials and their weight percentages: 10-30% of active agent, 10-50% of film-forming agent, and 1 ～20% and solvent balance.
10. The preparation method of the multi-stage micro-nano hybrid metal paste according to claim 9, characterized in that it comprises the following steps:

    Prepare micro-nano mixed metal particles and flux, stir, sonicate, and mix the micro-nano mixed metal particles and flux evenly to obtain.

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