WO2017186192A1 - 一种铜银复合粉的制备方法和导电胶 - Google Patents

一种铜银复合粉的制备方法和导电胶 Download PDF

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WO2017186192A1
WO2017186192A1 PCT/CN2017/089121 CN2017089121W WO2017186192A1 WO 2017186192 A1 WO2017186192 A1 WO 2017186192A1 CN 2017089121 W CN2017089121 W CN 2017089121W WO 2017186192 A1 WO2017186192 A1 WO 2017186192A1
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silver
copper
powder
composite powder
preparation
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French (fr)
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李云平
李家翔
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中南大学
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/06—Metallic powder characterised by the shape of the particles
    • B22F1/065—Spherical particles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/14—Treatment of metallic powder
    • B22F1/142—Thermal or thermo-mechanical treatment
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/02—Elements
    • C08K3/08—Metals
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J11/00—Features of adhesives not provided for in group C09J9/00, e.g. additives
    • C09J11/02—Non-macromolecular additives
    • C09J11/04—Non-macromolecular additives inorganic
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J163/00—Adhesives based on epoxy resins; Adhesives based on derivatives of epoxy resins
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J9/00—Adhesives characterised by their physical nature or the effects produced, e.g. glue sticks
    • C09J9/02—Electrically-conducting adhesives
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C9/00—Alloys based on copper
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F2999/00—Aspects linked to processes or compositions used in powder metallurgy
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/02—Elements
    • C08K3/08—Metals
    • C08K2003/0806—Silver
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/02—Elements
    • C08K3/08—Metals
    • C08K2003/085—Copper

Definitions

  • the invention belongs to the technical field of powder metallurgy, and in particular relates to a preparation method of high-conductivity and anti-oxidation copper-silver composite powder and a conductive adhesive.
  • silver and copper are the two metals with the best electrical conductivity and are indispensable materials for the electronics industry. Because silver has extremely high electrical and thermal conductivity and chemical stability (good oxidation resistance at high temperatures), silver powder has been regarded as a conductive filler for a long time as the material of choice for the paste for the electronics industry.
  • silver has some problems that are difficult to avoid by itself, such as the possibility of silver ion migration and high cost under the action of direct current. In particular, the short circuit problem caused by the migration phenomenon of silver ions has become a major problem for electronic products to become smaller and more integrated.
  • copper has a series of advantages such as low price, excellent conductivity and anti-migration performance far higher than silver, and is the preferred alternative material for conductive silver powder.
  • CN101664803A discloses a "preparation method of coated copper-silver bimetallic powder", which is based on the Chinese patent of the publication number CN101294281A, and the ion masking agent can be optimally adjusted by adjusting the pH value of the solution. It exerts its masking activity within the range and promotes the deposition of silver on the copper surface.
  • These methods for preparing copper-silver composite powder are mainly chemical methods, and they have common problems such as low utilization rate of copper-silver reagents, numerous processes, and a large amount of waste liquid discharge.
  • the coating powder prepared by these conventional methods has a low surface silver content, does not have normal temperature oxidation resistance, and causes wasteful waste of silver, and also has a low deposition rate, agglomeration between particles, silver plating and copper.
  • the combination of powder is not strong and so on.
  • the technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a preparation method of copper-silver composite powder.
  • the copper-silver composite powder obtained by the method has good oxidation resistance and is particularly suitable while maintaining high electrical conductivity. It is applied to electronic devices with high ambient temperature, high conductivity requirements and stable service performance, such as electrodes, electromagnetic shielding coatings, conductive adhesives for surface assembly, and conductive connection dispensing.
  • the technical solution proposed by the present invention is:
  • a preparation method of copper-silver composite powder comprising the following steps:
  • the copper-silver alloy powder prepared in the step (1) is subjected to aging treatment in a vacuum or an inert atmosphere to obtain a copper-silver composite powder.
  • the aging temperature is 150 to 350 ° C
  • the aging time is 10 to 600 min
  • the sample is naturally cooled to 50 ° C or less after the aging is completed.
  • the vacuum pressure during the aging treatment is less than 0.1 MPa.
  • the inert gas is argon or nitrogen.
  • the gas atomization method is a nitrogen gas or an argon atomization method.
  • the prepared copper-silver alloy powder has a particle diameter of 120 ⁇ m or less.
  • the copper-silver alloy powder prepared in the step (1) is sieved, and a powder having a particle size distribution of 10 to 25 ⁇ m is selected and subjected to the aging treatment of the step (2).
  • the silver-silver composite powder obtained after the aging treatment is continuously distributed in the copper particles along the copper grain boundary.
  • the present invention also provides a conductive paste, the raw material of which comprises the copper-silver composite powder obtained by the above production method.
  • the raw material thereof comprises a copper-silver composite powder and an organic mixture having a mass ratio of (3 to 6):1, and the organic mixture comprises a mass ratio of (20 to 90): (5 to 50): (10 to 50): (1 to 10) E-51 type epoxy resin, dicyandiamide, diluent 501, 2-ethyl-4-methylimidazole.
  • the copper-silver alloy powder prepared by gas atomization in the present invention is spherical, has a large particle size range (1 to 120 ⁇ m), and has a low silver content.
  • the silver-rich phase preferentially precipitates at defects such as grain boundaries. And form a continuous space network structure, which is conducive to the formation of silver conductive network, and enhances the conductivity performance to a certain extent.
  • the precipitated silver phase covered by defects in the matrix (grain boundary, pores, pores)
  • the preferential oxidation of copper silver powder at the grain boundary and other defects at a higher temperature is effectively suppressed, and the matrix can be significantly improved.
  • Initial oxidation temperature is effectively suppressed, and the matrix can be significantly improved.
  • the copper-silver composite powder obtained by the process of the invention has excellent electrical conductivity and oxidation resistance, is a slurry for the electronic industry, and is an ideal conductive filler, and is particularly suitable for high ambient temperature and high electrical conductivity requirements.
  • Electronic devices with stable performance and packaging such as electrodes, electromagnetic shielding coatings, conductive adhesives for surface assembly, and conductive connection dispensing.
  • silver is uniformly dissolved in the copper matrix in the copper-silver alloy powder. After the aging heat treatment, silver is precipitated from the copper matrix and preferentially precipitates at the grain boundary portion to form a continuous silver network.
  • the aging heat treatment of the present invention causes silver to segregate at a higher energy and unstable grain boundary, and the grain boundary is a position where preferential oxidation of the powder occurs, and the silver distributed along the grain boundary effectively prevents the oxidation of the powder at a lower temperature.
  • the conductive paste prepared by the copper-silver composite powder of the invention not only has the advantages of high electrical conductivity, good moisture resistance, high oxidation resistance, and the silver ion migration resistance is one hundred times higher than that of the pure silver powder conductive adhesive. Copper-silver composite powder can replace existing silver powder in a large range, Copper powder has a wide range of applications.
  • the preparation method of the present invention has simple process steps and does not involve the use of any chemical solvent, thereby avoiding environmental problems caused by a large amount of waste liquid discharge, and the copper-silver reagent in the preparation method has high utilization rate.
  • Example 1 is a microscopic view of the morphology of a copper-silver alloy powder prepared by the atomization method in Example 1.
  • Example 2 is a schematic view showing the distribution of silver in grain along grain boundaries after aging heat treatment according to Example 1 of the present invention.
  • Fig. 3 is a view showing a state of dew condensation in a manner in which deionized water is dropped between electrodes on a glass plate in Example 2 of the present invention.
  • Example 4 is a cross-sectional photograph of a copper-silver composite powder particle having a silver content of 6% obtained after aging for 30 minutes in Example 3 of the present invention.
  • Fig. 5 is a view showing the distribution of silver elements in the cross section of copper-silver composite powder particles having a silver content of 6% obtained after aging for 30 minutes in Example 3 of the present invention.
  • Fig. 6 is a thermogravimetric analysis diagram of copper-silver composite powder and pure copper powder having a silver content of 6% obtained after aging for 30 minutes in Example 3 of the present invention.
  • the various reagents and raw materials used in the present invention are commercially available products or products which can be obtained by a known method.
  • a preparation method of the copper-silver composite powder of the invention comprises the following steps:
  • a graphite crucible loaded with 400 g of silver ingot and 3600 g of copper plate was placed in a Hermiga gas atomization apparatus manufactured by PSI, UK, and heated from room temperature to 1150 ° C at a rate of 50 ° C/min to obtain a uniform mixed alloy.
  • the molten metal was atomized by high-pressure nitrogen atomization to obtain a copper-silver alloy powder having a silver content of 10% (having a particle diameter of 120 ⁇ m or less).
  • the copper-silver alloy powder obtained in the step (1) is first sieved to a powder of -100 mesh, and then a standard mesh of 600 mesh and 800 mesh is used to obtain a copper-silver alloy powder having a particle size distribution ranging from 10 to 25 ⁇ m, as shown in FIG. Shown as a nearly spherical powder.
  • step (2) Weigh 20g of step (2) sieved copper-silver alloy powder into a well-sealed furnace, and then use an electric oil pump to pump air to the furnace to a vacuum of -0.05MPa, and then start to heat up to 350 °C After being kept for 180 minutes, it is naturally cooled to 50 ° C, and the copper-silver composite powder is taken out.
  • the schematic diagram of silver in the copper-silver composite powder continuously distributed along the grain boundary of the copper particles in the copper particles is shown in FIG. 2 .
  • E-51 type epoxy resin, dicyandiamide, diluent 501, 2-ethyl-4- according to the mass ratio of 80:8:20:2:0.5 Methylimidazole and KH550 were added and ground in a mortar for 50 min to uniformly mix to obtain an organic mixture.
  • the copper-silver composite powder prepared in this example was mixed with the organic mixture at a mass ratio of 4:1, and ground with a pestle for 30 minutes until the colloid was uniform, thereby obtaining a conductive paste of copper-silver composite powder as a filler.
  • a preparation method of the copper-silver composite powder of the invention comprises the following steps:
  • a graphite crucible carrying 35 g of silver ingot and 380 g of copper plate was placed in a Hermiga gas atomization apparatus manufactured by British PSI Company, heated from room temperature to 1200 ° C at a rate of 50 ° C / min, and melted to obtain a uniform alloy melting.
  • the liquid was atomized by high-pressure nitrogen gas to obtain a copper-silver alloy powder having a silver content of 8.43% (having a particle diameter of 120 ⁇ m or less).
  • the copper-silver alloy powder obtained in the step (1) is first sieved to a powder of -100 mesh, and then a standard mesh of 600 mesh and 800 mesh is used to obtain a copper-silver alloy powder having a particle size distribution ranging from 10 to 25 ⁇ m.
  • step (3) Weigh 10g of copper-silver alloy powder obtained in step (2) into a furnace with better sealing performance, then pump it to the furnace with a vacuum of -0.05MPa, then start heating up to 300 °C and keep warm. After 260 min, it was naturally cooled to below 50 ° C, and the copper-silver composite powder was taken out.
  • E-51 epoxy resin, dicyandiamide, diluent 501, 2-ethyl-4-methylimidazole, KH550 were added to the mortar in a mass ratio of 90:9:18:1:0.5. Grinding for 60 min until homogeneous mixing gave an organic mixture.
  • the copper-silver composite powder prepared in this example was mixed with the organic mixture at a mass ratio of 5:1, and ground with a pestle for 35 minutes until the colloid was uniform, thereby obtaining a conductive paste of copper-silver composite powder as a filler.
  • a uniformly mixed conductive paste was coated on the stainless steel sheet to form a film of 70 ⁇ 6 ⁇ 0.05 mm, followed by a medium temperature curing treatment (curing temperature: 220 ° C, curing time: 50 min).
  • the copper-silver composite powder conductive paste prepared in this embodiment was printed on a glass plate to form two parallel electrodes having a length of 10 mm, a width of 2 mm and a distance of 2 mm.
  • the parallel electrode was placed in a constant temperature environment at 180 ° C to be cured. 50 min, the cured electrode was connected to the loop, and the dew condensation state was simulated by dropping deionized water between the electrodes, as shown in Fig. 3. Finally, the electromigration at different times under the electric field was photographed with a camera.
  • the copper-silver composite powder conductive adhesive prepared in the present embodiment is smeared on the side of the stainless steel test piece (the test piece is polished by 180 mesh water sandpaper and cleaned with acetone), and the two identical test pieces are unilaterally overlapped and clamped.
  • the curing process was started in a drying oven where the temperature was stabilized at 200 ° C, and taken out after 1 h, and placed on a tensile tester to measure the shear strength. Sample preparation and testing are carried out in strict accordance with the GB/T7124-1986 standard.
  • the measured shear strength of the conductive paste is 22 MPa, which satisfies the requirement that the shear strength of the conductive paste for LED packaging is greater than 15 MPa.
  • the preparation method of the copper-silver composite powder of the invention comprises the following steps:
  • the seven silver ingots and the copper plate are respectively 0.1 g and 9.9 g, 0.4 g and 9.6 g, 0.6 g and 9.4 g, 0.8 g and 9.2 g, 1.0 g and 9.0 g, 1.2 g and 8.8 g, 1.4g and 8.6g of graphite crucible were placed in Hermiga gas atomization unit manufactured by British PSI Company, heated from room temperature to 1200 °C at a rate of 50 °C/min, and melted to obtain a uniform alloy melt, which was sequentially formed by high-pressure nitrogen atomization. Copper, silver alloy powders of 1%, 4%, 6%, 8%, 10%, 12% and 14% silver content were obtained.
  • the pure copper powder and the copper-silver alloy powder obtained in the step (1) are first sieved out to a powder of -100 mesh, and then a standard mesh of 600 mesh and 800 mesh is used to obtain a copper-silver alloy powder having a particle size distribution ranging from 10 to 25 ⁇ m. .
  • step (3) Weigh the 8 kinds of powders obtained in step (2) in 3 batches, put 2g of each powder into the furnace with better sealing performance, and then pump the air into the furnace with the electric oil pump to reach -0.08MPa. Then, the temperature was raised to 300 ° C and kept for 10, 30, 60 min, respectively, and then naturally cooled to 50 ° C, and the copper-silver composite powder was taken out.
  • the initial oxidation temperature measured using a thermogravimetric analyzer is shown in Table 1, and the initial oxidation weight gain temperature is defined as a temperature at which the weight gain is 1%. It can be seen from Table 1 that the increase in the silver content and the aging heat treatment can significantly improve the oxidation resistance of the copper-silver composite powder.
  • the electrical conductivity of the powder after oxidation of pure copper powder and different silver content copper-silver composite powder at 200 ° C is shown in Table 2. It can be seen from Table 2 that the heat treatment time and the silver content increase due to the improvement of the oxidation resistance of the powder. It is beneficial to improve the electrical conductivity of the powder at high temperatures. However, if the silver content is too high, the migration of silver ions may be aggravated, so the silver content of the copper-silver composite powder of the present invention is controlled to be 3% to 14%.
  • FIG. 4 A cross-sectional photograph of the copper-silver composite powder particles having a silver content of 6% obtained by aging for 30 minutes in the present embodiment is shown in Fig. 4, and the silver element analysis of the cross section is shown in Fig. 5. It can be seen from Fig. 4 and Fig. 5 that after heat treatment Silver is preferentially precipitated in the grain boundary of the particles and is continuously distributed to form a conductive network mainly composed of silver.
  • thermogravimetric analysis of the copper-silver composite powder and the pure copper powder having a silver content of 6% obtained in the present embodiment for 30 min in the present embodiment is shown in Fig. 6, and the unaged copper-silver alloy powder is compared with the pure copper powder.
  • the anti-oxidation ability is higher.
  • the alloy powder is further improved due to the precipitation of silver along the copper grain boundary in the particle.
  • the powder can be suitable for maintaining high conductivity. Used as a conductive paste at higher temperatures.

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Abstract

一种高导电抗氧化铜银复合粉的制备方法，包括以下步骤：（1）采用气雾化法制备铜银合金粉，所述铜银合金粉中银的质量百分数为3%〜14%；（2）将步骤（1）制备的铜银合金粉在真空或惰性气氛中进行时效处理得到铜银复合粉。以及一种包括上述铜银复合粉的导电胶。上述铜银合金粉用气雾化制备，为球形，粒径范围选择性大，银含量低，经时效处理后富银相在晶界等缺陷处优先析出并形成连续空间网络结构，有利于银导电网络的形成，在一定程度上增强了导电性能。同时，由于基体内缺陷（晶界、孔隙、孔洞）等被析出的银相所覆盖，有效抑制了铜银粉末在较高温度下于晶界等缺陷位置的优先氧化，可明显提高基体的起始氧化温度。

Description

一种铜银复合粉的制备方法和导电胶 技术领域
本发明属于粉末冶金技术领域，尤其涉及一种高导电、抗氧化的铜银复合粉的制备方法和导电胶。
背景技术
众所周知，银、铜是导电性能最好的两种金属，是电子工业不可或缺的材料。由于银具有极高的导电导热性能与化学稳定性(高温下抗氧化性能好)，银粉已作为导电填料在很长一段时间内被视为电子工业用浆料的首选材料。然而，银存在一些自身难以避免的问题，如在直流电作用下易发生银离子迁移及成本高等缺点。尤其是银离子的迁移现象而导致的电路短路问题已成为电子产品迈向小型化、高集成化的一大难题。相对于银，铜有价格便宜、优良的导电性、抗迁移性能远远高于银等一系列优点，是导电银粉首选的替代材料。但由于铜粉在制备及服役过程中容易被氧化等问题，其导电性能受到抑制。如何在保持铜粉高导电的基础上提高其抗氧化性能，是关系到其能否作为导电、屏蔽填料的关键技术之一。中国专利公开号CN101294281A，公开了“一种低温浆料用镀银铜粉的制备方法”，该产品的Ag含量普遍高于30％，但在200℃左右有明显氧化，影响该铜银双金属粉的服役稳定性。中国专利公开号CN101664803A公开了“包覆型铜银双金属粉的制备方法”，该方法在基于公开号为CN101294281A的中国专利基础上，通过调节溶液的pH值，离子掩蔽剂能够在最佳的范围内发挥其掩蔽活性，促进银在铜表面沉积。这些制备铜银复合粉的方法主要以化学方法为主，它们存在铜银试剂利用率较低，工序繁多以及大量废液排放等共性问题。此外，这些传统方法制备的点缀结构的镀层粉末，表面含银量低、不具备常温抗氧化性，造成银的无效浪费，同时还存在沉积速度不高、颗粒间团聚较严重、银镀层与铜粉的结合力不强等突出问题。
发明内容
本发明要解决的技术问题是克服现有技术的不足，提供一种铜银复合粉的制备方法，该方法制得的铜银复合粉在保持高导电性能的同时，抗氧化性好，特别适合应用于环境温度较高、导电率要求高、服役性能稳定的电子器件及其包装方面，如电极、电磁屏蔽涂料、表面组装用导电胶、导电连接点胶。
为解决上述技术问题，本发明提出的技术方案为：
一种铜银复合粉的制备方法，包括以下步骤：
(1)采用气雾化法制备铜银合金粉，所述铜银合金粉中银的质量百分数为3％～14％；
(2)将步骤(1)制备的铜银合金粉在真空或惰性气氛中进行时效处理得到铜银复合粉。
上述的制备方法，优选的，所述步骤(2)中，时效处理过程中，时效温度为150～350℃，时效时间为10～600min，时效结束后自然冷却至50℃以下可取样。
上述的制备方法，优选的，所述步骤(2)中，时效处理过程中的真空压力小于0.1MPa。
上述的制备方法，优选的，所述步骤(2)中，所述惰性气体为氩气或氮气。
上述的制备方法，优选的，所述气雾化法为氮气或氩气雾化法。
上述的制备方法，优选的，所述步骤(1)中，制备得到的铜银合金粉的粒径为120微米以下。
上述的制备方法，优选的，将步骤(1)制备的铜银合金粉进行筛分，筛选出粒径分布为10～25微米的粉末再进行步骤(2)的时效处理。
上述的制备方法，优选的，时效处理后得到的铜银复合粉中银在铜颗粒内沿铜晶界呈连续状分布。
本发明还提供一种导电胶，其原材料包括由上述的制备方法获得的铜银复合粉。
上述的导电胶，优选的，其原材料包括质量比为(3～6):1的铜银复合粉和有机混合物，所述有机混合物包括质量比为(20～90):(5～50):(10～50):(1～10)的E-51型环氧树脂、双氰双胺、稀释剂501、2-乙基-4-甲基咪唑。
与现有技术相比，本发明的优点在于：
(1)本发明先利用气雾化制备的铜银合金粉为球形，粒径范围选择性大(1～120μm)，银含量低，经时效处理后富银相在晶界等缺陷处优先析出并形成连续空间网络结构，有利于银导电网络的形成，在一定程度上增强了导电性能。同时，由于基体内缺陷(晶界、孔隙、孔洞)等被析出的银相所覆盖，有效抑制了铜银粉末在较高温度下于晶界等缺陷位置的优先氧化，可明显提高基体的起始氧化温度。鉴于此，本发明的工艺制得的铜银复合粉末兼有优良的导电性与抗氧化性，是电子工业用浆料、理想的导电填料，特别适合于环境温度较高、导电率要求高、服役性能稳定的电子器件及其包装方面，如电极、电磁屏蔽涂料、表面组装用导电胶、导电连接点胶。
(2)本发明的制备方法的中间产品铜银合金粉中银均匀固溶在铜基体中，时效热处理后，银从铜基体中析出，且优先在晶界部位析出，并形成连续银网络。本发明时效热处理使得银偏析在能量较高、不稳定的晶界处，而晶界正是粉末优先氧化发生的位置，这些沿晶界分布的银有效避免了粉末在较低温度氧化的发生。
(3)本发明的铜银复合粉末制得的导电胶不仅具有导电率高、耐湿性好、抗氧化性高等优点，耐银离子迁移性是纯银粉导电胶的百倍。铜银复合粉在较大范围内可取代现有的银粉、 铜粉，具有很广泛的应用价值。
(4)本发明的制备方法工艺步骤简单，不涉及任何化学溶剂的使用，从而避免产生大量废液排放引起的环境问题，同时该制备方法中的铜银试剂利用率高。
附图说明
图1为实施例1中雾化法制备的铜银合金粉末的形貌显微图。
图2为本发明实施例1经时效热处理后银在颗粒沿晶界的分布示意图。
图3为本发明实施例2中在玻璃板上的电极间滴入去离子水的方式模拟结露状态图。
图4为本发明实施例3中时效30min后得到的银质量含量为6％的铜银复合粉颗粒断面照片。
图5为本发明实施例3中时效30min后得到的银质量含量为6％的铜银复合粉颗粒断面的银元素分布图。
图6为本发明实施例3中时效30min后得到的银质量含量为6％的铜银复合粉与纯铜粉在空气中的热重分析图。
具体实施方式
为了便于理解本发明，下文将结合说明书附图和较佳的实施例对本发明作更全面、细致地描述，但本发明的保护范围并不限于以下具体的实施例。
除有特别说明，本发明中用到的各种试剂、原料均为可以从市场上购买的商品或者可以通过公知的方法制得的产品。
实施例1：
一种本发明的铜银复合粉的制备方法，包括以下步骤：
(1)将一个载有400g银锭和3600g紫铜板的石墨坩埚放入英国PSI公司制造的Hermiga气雾化装置中，自室温以50℃/min的速率加热至1150℃，熔化得到均一的混合合金熔液，使用高压氮气雾化将混合合金熔液雾化得到银含量为10％的铜银合金粉末(粒径为120微米以下)。
(2)将步骤(1)得到的铜银合金粉先筛分出-100目的粉末，继而使用600目和800目的标准筛获取粒径分布范围为10～25μm的铜银合金粉末，如图1所示为近球形粉末。
(3)称取20g步骤(2)筛分过的铜银合金粉放入密封性较好的炉子内，再使用电动油泵抽气至炉内真空度达到-0.05MPa，然后开始升温至350℃并保温180min，再自然冷却到50℃，取出铜银复合粉，铜银复合粉中银在铜颗粒内沿铜颗粒内晶界呈连续状分布的示意图如图2所示。
按照质量比为80:8:20:2:0.5的量将E-51型环氧树脂、双氰双胺、稀释剂501、2-乙基-4- 甲基咪唑、KH550添加在研钵中研磨50min至均匀混合得到有机混合物。再将本实施例制备得到的铜银复合粉与该有机混合物按质量比为4:1的比例混合，用研棒研磨30min至胶体均匀，进而获得铜银复合粉为填料的导电胶。将混合均匀的导电胶涂覆在不锈钢片上，形成70×6×0.05mm的薄膜，之后实行中温固化处理(固化温度200℃，固化时长1h)。再使用数字电阻测试仪测其线条两端的电阻，按照“ρ＝R×(W×H)/L计算电阻率(ρ为导电胶的体电阻率；R为导电胶的电阻；W、H、L依次为导电胶层的宽度、厚度和长度)”，测量五次求得平均值为85μΩ·cm，这表明本实施例的铜银复合粉末制成的导电胶和银粉导电胶导电性能相当(≤100μΩ·cm)。
实施例2：
一种本发明的铜银复合粉的制备方法，包括以下步骤：
(1)将一个载有35g银锭和380g紫铜板的石墨坩埚放入英国PSI公司制造的Hermiga气雾化装置中，自室温以50℃/min的速率加热至1200℃，熔化得到均一的合金熔液，使用高压氮气雾化形成得到银含量为8.43％的铜银合金粉末(粒径为120微米以下)。
(2)将步骤(1)得到的铜银合金粉先筛分出-100目的粉末，继而使用600目和800目的标准筛获取粒径分布范围为10～25μm的铜银合金粉末。
(3)称取10g步骤(2)得到的铜银合金粉放入密封性较好的炉子内，再使用电动油泵抽气至炉内真空度达到-0.05MPa，然后开始升温至300℃并保温260min，再自然冷却到50℃以下，取出铜银复合粉。
按照质量比为90:9:18:1:0.5的量将E-51型环氧树脂、双氰双胺、稀释剂501、2-乙基-4-甲基咪唑、KH550添加在研钵中研磨60min至均匀混合得到有机混合物。再将本实施例制备得到的铜银复合粉与该有机混合物按质量比为5:1的比例混合，用研棒研磨35min至胶体均匀，进而获得铜银复合粉为填料的导电胶。将混合均匀的导电胶涂覆在不锈钢片上，形成70×6×0.05mm的薄膜，之后实行中温固化处理(固化温度220℃，固化时长50min)。
将本实施例制成的铜银复合粉末导电胶体放置在100℃、90％RH(相对湿度)环境中1200h后测定其电阻率，并按“电阻变化率＝(恒温恒湿放置后的电阻-初期电阻)/初期电阻×100％”计算电阻变化率，实际测得该导电胶电阻变化率为3％，小于10％的实用化目标。
将本实施例制成的铜银复合粉末导电胶体印刷在玻璃板上，构成长为10mm、宽为2mm且相距2mm的两个平行电极，将此平行电极放置在180℃的恒温环境中保温固化50min，再将固化后的电极接入回路，通过在电极间滴入去离子水的方式模拟结露状态，如图3所示，最后用相机拍下在电场作用下不同时间的电迁移情形。在通电60min后导电胶两极间、从负极向正极并无明显树枝状析出物，说明铜银复合粉胶体的银离子迁移率极低。因此该胶体服 役稳定性高，安全可靠。
将本实施例制成的铜银复合粉末导电胶抹在不锈钢试片(试片是经过180目水磨砂纸打磨并用丙酮清洗的)一侧，将两片同样的试片单边搭接夹紧后送入温度已稳定在200℃的干燥箱中开始固化处理，1h后取出，放到拉伸试验机上测其剪切强度。试样制备及测试严格按照GB/T7124-1986标准执行，测得的该导电浆料的剪切强度为22MPa，满足LED封装用导电浆料的剪切强硬大于15MPa的要求。
实施例3：
本发明的铜银复合粉的制备方法，包括以下步骤：
(1)将七个装有银锭和紫铜板分别为0.1g和9.9g、0.4g和9.6g、0.6g和9.4g、0.8g和9.2g、1.0g和9.0g、1.2g和8.8g、1.4g和8.6g的石墨坩埚放入英国PSI公司制造的Hermiga气雾化装置中，自室温以50℃/min的速率加热至1200℃，熔化得到均一合金熔液，使用高压氮气雾化形成依次得到1％、4％、6％、8％、10％、12％和14％银质量含量的铜银合金粉末。
(2)将纯铜粉和步骤(1)得到的铜银合金粉先筛分出-100目的粉末，继而使用600目和800目的标准筛获取粒径分布范围为10～25μm的铜银合金粉末。
(3)分3批次称取步骤(2)得到的8种粉末、每次每种粉末2g放入密封性较好的炉子内，再使用电动油泵抽气至炉内真空度达到-0.08MPa，然后开始升温至300℃并分别保温10、30、60min，再自然冷却到50℃，取出铜银复合粉。使用热重分析仪测得的起始氧化温度如表1所示，起始氧化增重温度定义为增重量为1％的温度。由表1可知，银含量的增加和时效热处理能显著提高铜银复合粉末的抗氧化能力。本实施例中纯铜粉和不同银含量铜银复合粉在200℃氧化后粉末的电导率见表2所示，由表2可知，热处理时间及银含量的增加，由于粉末抗氧化性的提高，有利于提高粉末在高温下的电导率。但银含量太高可能会引起银离子迁移现象加重，故本发明的铜银复合粉中银含量控制在3％-14％。
表1实施例3制备得到的纯铜粉和铜银复合粉的抗氧化能力
Figure PCTCN2017089121-appb-000001
表2实施例3制备得到的纯铜粉和铜银复合粉的电导率
Figure PCTCN2017089121-appb-000002
本实施例中时效30min得到的银质量含量为6％的铜银复合粉颗粒断面照片如图4所示，断面的银元素分析如图5所示，由图4和图5可知，经热处理后，银优先于颗粒内铜晶界析出并呈连续分布状态，形成以银为主的导电网络。
本实施例中时效30min得到的银质量含量为6％的铜银复合粉与纯铜粉在空气中的热重分析如图6所示，相比于纯铜粉末，未时效的铜银合金粉末的抗氧化能力较高，经时效处理后，合金粉末由于银沿颗粒内铜晶界的析出，粉末的抗氧化性能进一步提高，此时该粉末可在保持高导电率的情况下，适合于在较高温度下作为导电胶使用。

Claims (9)

  1. 一种铜银复合粉的制备方法，其特征在于，包括以下步骤：
    (1)采用气雾化法制备铜银合金粉，所述铜银合金粉中银的质量百分数为3％～14％；
    (2)将步骤(1)制备的铜银合金粉在真空或惰性气氛中进行时效处理得到铜银复合粉。
  2. 如权利要求1所述的制备方法，其特征在于，所述步骤(2)中，时效处理过程中，时效温度为150～350℃，时效时间为10～600min。
  3. 如权利要求1所述的制备方法，其特征在于，所述步骤(2)中，时效处理过程中的真空压力小于0.1MPa。
  4. 如权利要求1所述的制备方法，其特征在于，所述步骤(2)中，惰性气氛是指氩气或氮气。
  5. 如权利要求1所述的制备方法，其特征在于，所述步骤(1)中，制备得到的铜银合金粉的粒径为120微米以下。
  6. 如权利要求1所述的制备方法，其特征在于，将步骤(1)制备的铜银合金粉进行筛分，筛选出粒径分布为10～25微米的粉末再进行步骤(2)的时效处理。
  7. 如权利要求1～6任一项所述的制备方法，其特征在于，时效处理后得到的铜银复合粉中银在铜颗粒内沿铜晶界呈连续分布。
  8. 一种导电胶，其特征在于，其原材料包括由权利要求1～7任一项所述的制备方法获得的铜银复合粉。
  9. 如权利要求8所述的导电胶，其特征在于，其原材料包括质量比为(3～6):1的铜银复合粉和有机混合物，所述有机混合物包括质量比为(20～90):(5～50):(10～50):(1～10)的E-51型环氧树脂、双氰双胺、稀释剂501、2-乙基-4-甲基咪唑。
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