Preparation method of low-temperature solderable conductive copper paste

Abstract

The invention discloses a preparation method of low-temperature solderable conductive copper paste, and belongs to the technical field of electronic materials. The conductive copper paste is prepared from the following raw materials: silver-coated copper powder, an organic carrier, an antioxidant, a curing agent, an auxiliary agent, a thixotropic agent, a solvent and an adhesion enhancer. The design of the composite copper powder coated with the silver layer on the surface is matched with the graded particle size, and an organic carrier is combined, so that high conductivity and strong oxidation resistance under low-temperature curing are realized. The preparation method comprises the following steps: treating the copper powder by adopting a dipping-drying process, and coating the surface of the copper powder with the adhesion enhancer and the antioxidant by adopting a chemical method; uniformly mixing the organic carrier, the curing agent, the solvent and the auxiliary agent; and finally, copper powder and a thixotropic agent are added into the mixed organic carrier, and the low-temperature solderable conductive copper paste is prepared through high-speed dispersion and grinding of a three-roller machine. The product can be rapidly cured at 100-180 DEG C, the sheet resistance is smaller than or equal to 20 m omega / square, the welding strength reaches 15 MPa or above, cost is low, production is easy, and wide industrial application value is achieved.

Description

Technical Field

[0001] The present invention relates to the field of electronic material preparation, and in particular to a method for preparing a low-temperature solderable conductive copper paste. Background Art

[0002] Conductive paste, as a key electronic material, is widely used in fields such as solar cells, printed circuit boards (PCBs), radio frequency identification (RFID) tags, flexible electronic devices, and electronic packaging. Traditional conductive paste is mainly silver paste, which has excellent conductivity and mature technology, but the cost of silver raw materials is high and there is a risk of electrochemical migration, which limits its application in low-cost, high-reliability scenarios. Copper, as a conductive material, has similar conductivity to silver, low cost, and good thermal stability, and is considered to be an ideal material to replace silver. However, copper powder is easily oxidized to form an insulating oxide layer (such as CuO, CuO), which leads to a significant decrease in conductivity. In addition, traditional copper paste needs to be sintered at high temperature (usually >300°C) to form a conductive network, which makes it difficult to apply to flexible substrates that are not resistant to high temperatures (such as polyimide, PET, etc.) or heat-sensitive components.

[0003] In the existing technology, some copper pastes delay oxidation by adding antioxidants (such as organic acids, amine compounds) or using surface coating technology (such as silver-plated, nickel-plated copper powder), but such methods may introduce impurity phases, affecting the conductivity and soldering performance of the paste; at the same time, the contact resistance between copper particles is high under the low-temperature curing process (<200°C), which is difficult to meet practical requirements. In addition, conventional conductive pastes need to be sintered at high temperature before undergoing the soldering process, which is a complex process with high energy consumption. Low-temperature solderable copper pastes must also meet the requirements of forming a reliable connection directly with the solder after low-temperature curing. This places higher demands on the wettability, oxidation resistance and interfacial bonding strength of the copper paste. In the existing technology, the combination of copper paste and solder mostly relies on additional flux, which is prone to residual pollution and does not meet environmental protection requirements.

[0004] Therefore, the development of an environmentally friendly conductive copper paste that has low-temperature curing, high conductivity, excellent oxidation resistance, and can achieve reliable soldering without additional flux is of great significance to promoting the development of flexible electronics, low-cost sensors and green manufacturing technologies. Summary of the Invention

[0005] Based on this, in order to solve the problem in the prior art that copper powder in the conductive copper paste is easily oxidized and difficult to weld after low-temperature curing, the present invention provides a method for preparing a low-temperature solderable conductive copper paste. The specific technical solution is as follows:

[0006] A method for preparing a low-temperature solderable conductive copper paste, the method comprising the following steps:

[0007] The copper powder is treated by an impregnation-drying process, and then the copper powder is added to the treatment liquid, stirred at a certain stirring speed, and then vacuum dried to obtain the coated copper powder;

[0008] The organic carrier, curing agent, solvent and auxiliary agent are uniformly mixed to obtain a mixture; then the coated copper powder and thixotropic agent are added to the mixture, and the mixture is subjected to high-speed dispersion treatment and three-roll milling to obtain a low-temperature solderable conductive copper paste.

[0009] Furthermore, the copper powder is silver-coated copper powder, and the silver content in the silver-coated copper powder is 3wt%-10wt%.

[0010] Furthermore, the silver-coated copper powder includes 5-15 parts of 1000 mesh silver-coated copper powder, 40-60 parts of 3-5 micron silver-coated copper powder; 15-25 parts of 1-3 micron silver-coated copper powder, and 15-30 parts of 300-500 nanometer silver-coated copper powder, with a total mass of 100 parts.

[0011] Furthermore, the treatment liquid is obtained by adding an adhesion enhancer and an antioxidant into an ethanol solution containing 1% to 3% by mass of deionized water.

[0012] Furthermore, the adhesion enhancer is at least one of KH-550, KH-560, and KH-570.

[0013] Furthermore, the antioxidant is at least one of benzotriazole and anhydrous hemic acid.

[0014] Furthermore, the organic carrier is at least one of AG80 epoxy resin, AFG90H epoxy resin, AFG90 epoxy resin, E42 polyurethane modified epoxy resin, E51 epoxy resin, E44 epoxy resin, and DEN439 phenolic epoxy resin.

[0015] Furthermore, the curing agent is at least one of imidazole salts, acid anhydrides, dicyandiamides, and ketimines.

[0016] Furthermore, the solvent is at least one of propylene glycol methyl ether, propylene glycol methyl ether acetate, ethylene glycol butyl ether, ethyl acetate, and amyl acetate.

[0017] Furthermore, the auxiliary agent is at least one of hydrogen-containing silicone oil, vinyl silicone oil, fluorocarbon surfactant, and BYK-333.

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

[0019] The low-temperature solderable conductive copper paste prepared by the present invention has an adjustable viscosity within the range of 30-180 Pa.s, can achieve rapid curing at 100-180°C, has a short-term temperature tolerance of 300°C, a square resistance of ≤20 mΩ / □, and a soldering strength exceeding 15 MPa. This paste effectively addresses the existing issues of copper powder oxidation in conductive copper pastes and the difficulty of soldering after low-temperature curing. Furthermore, the present invention features a simple overall process, low cost, and scalable production, making it widely applicable in industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of the preparation process of the conductive copper paste of the present invention;

[0021] Figure 2 This is a scanning electron microscope image of the conductive copper paste prepared in Example 1 after curing. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with its embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not limit the scope of protection of the present invention.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0024] A method for preparing a low-temperature solderable conductive copper paste according to an embodiment of the present invention comprises the following steps:

[0025] The copper powder is treated by an impregnation-drying process, and then the copper powder is added to the treatment liquid, stirred at a certain stirring speed, and then vacuum dried to obtain the coated copper powder;

[0026] The organic carrier, curing agent, solvent and auxiliary agent are uniformly mixed to obtain a mixture; then the coated copper powder and thixotropic agent are added to the mixture, and the mixture is subjected to high-speed dispersion treatment and three-roll milling to obtain a low-temperature solderable conductive copper paste.

[0027] In one embodiment, the copper powder is silver-coated copper powder, and the silver content in the silver-coated copper powder is 3wt%-10wt%.

[0028] In one embodiment, the silver-coated copper powder includes 5-15 parts of 1000 mesh silver-coated copper powder, 40-60 parts of 3-5 micron silver-coated copper powder; 15-25 parts of 1-3 micron silver-coated copper powder, and 15-30 parts of 300-500 nanometer silver-coated copper powder, with a total mass of 100 parts.

[0029] In one embodiment, the treatment liquid is obtained by adding an adhesion enhancer and an antioxidant into an ethanol solution containing 1% to 3% by mass of deionized water.

[0030] In one embodiment, the adhesion enhancer is at least one of KH-550, KH-560, and KH-570.

[0031] In one embodiment, the antioxidant is at least one of benzotriazole and anhydrous hemic acid.

[0032] In one embodiment, the weight ratio of the copper powder, adhesion enhancer, antioxidant and ethanol solution is 100:(0.5-3):(0.5-3):(80-100).

[0033] In one embodiment, the stirring process at a certain stirring speed is performed at a rotation speed of 500 r / min to 1000 r / min, and the stirring time is 30 to 60 min.

[0034] In one embodiment, the vacuum drying temperature is 80°C-90°C.

[0035] In one embodiment, the organic carrier is at least one of AG80 epoxy resin, AFG90H epoxy resin, AFG90 epoxy resin, E42 polyurethane modified epoxy resin, E51 epoxy resin, E44 epoxy resin, and DEN439 novolac epoxy resin.

[0036] In one embodiment, the curing agent is at least one of imidazole salts, acid anhydrides, dicyandiamides, and ketimines.

[0037] In one embodiment, the solvent is at least one of propylene glycol methyl ether, propylene glycol methyl ether acetate, ethylene glycol butyl ether, ethyl acetate, and amyl acetate.

[0038] In one embodiment, the auxiliary agent is at least one of hydrogen silicone oil, vinyl silicone oil, fluorocarbon surfactant, and BYK-333.

[0039] In one embodiment, the weight ratio of the organic vehicle, curing agent, solvent, additive, coated copper powder and thixotropic agent is (10-30): (2-10): (1-5): (1-5): (60-80): (0.5-3).

[0040] In one embodiment, the thixotropic agent is at least one of fumed silica, nano zinc oxide, nano aluminum oxide, and nano quartz powder.

[0041] In one embodiment, the rotation speed of the high-speed dispersion treatment is 100 / min to 500 r / min, and the time is 0.5h to 2h.

[0042] In one embodiment, the three-roll mill grinding time is 0.5h to 2h.

[0043] In one embodiment, the viscosity of the low-temperature solderable conductive copper paste is adjustable within the range of 30-180 Pa.S, the usable temperature is ≤200°C, and rapid curing is achieved at 100-180°C. It can temporarily withstand a temperature of 300°C, the square resistance is ≤20mΩ / □, and the welding strength is above 15MPa.

[0044] In one embodiment, a low-temperature solderable conductive copper paste is used in a soldering process.

[0045] The embodiments of the present invention will be described in detail below with reference to specific examples.

[0046] Example 1:

[0047] A method for preparing a low-temperature solderable conductive copper paste, the method comprising the following steps:

[0048] 1 part KH-550 and 1 part benzotriazole were added to 100 parts of an ethanol solution containing 1.5% by weight of deionized water to obtain a treatment solution, and then 10 parts of 1000-mesh silver-coated copper powder, 50 parts of 5-micron silver-coated copper powder, 20 parts of 3-micron silver-coated copper powder, and 20 parts of 300-nanometer silver-coated copper powder were added to the treatment solution, stirred at a stirring speed of 500 r / min for 30 minutes, and then vacuum-dried at 80°C to obtain coated copper powder.

[0049] According to the weight ratio, 20 parts of E51 epoxy resin, 5 parts of imidazole salt curing agent, 4 parts of propylene glycol methyl ether acetate and 4 parts of hydrogen-containing silicone oil were evenly mixed to obtain a mixture; then 60 parts of coated copper powder and 0.5 parts of fumed silica were added to the mixture, and high-speed dispersion treatment was carried out at a speed of 150 r / min for 1 hour, and then three-roll mill grinding was carried out for 40 minutes to obtain a low-temperature solderable conductive copper paste.

[0050] It should be noted that the silver-coated copper powder used in Example 1 is silver-coated copper powder with a silver content of 5 wt%.

[0051] The performance test of the low-temperature solderable conductive copper paste prepared in Example 1 showed that the curing temperature of the low-temperature solderable conductive copper paste prepared in Example 1 was 150° C., the curing time was 25 min, the square resistance was 12 mΩ / □, and the welding strength reached 16.3 MPa.

[0052] Example 2:

[0053] A method for preparing a low-temperature solderable conductive copper paste, the method comprising the following steps:

[0054] 1 part KH-560 and 2 parts benzotriazole were added to 100 parts of an ethanol solution containing 1.5% by weight of deionized water to obtain a treatment solution, and then 12 parts of 1000-mesh silver-coated copper powder, 50 parts of 5-micron silver-coated copper powder, 18 parts of 2-micron silver-coated copper powder, and 20 parts of 500-nanometer silver-coated copper powder were added to the treatment solution, stirred at a stirring speed of 500 r / min for 30 minutes, and then vacuum-dried at 80°C to obtain coated copper powder.

[0055] According to the weight ratio, 22 parts of E44 epoxy resin, 5 parts of imidazole salt curing agent, 5 parts of ethyl acetate, 2 parts of vinyl silicone oil and 2 parts of BYK-333 were mixed uniformly to obtain a mixture; then 65 parts of coated copper powder and 0.5 parts of fumed silica were added to the mixture, and high-speed dispersion treatment was carried out at a speed of 150 r / min for 1 hour, and then three-roll mill grinding was carried out for 40 minutes to obtain a low-temperature solderable conductive copper paste.

[0056] It should be noted that the silver-coated copper powder used in Example 2 is silver-coated copper powder with a silver content of 5 wt%.

[0057] The performance test of the low-temperature solderable conductive copper paste prepared in Example 2 showed that the curing temperature of the low-temperature solderable conductive copper paste prepared in Example 2 was 150° C., the curing time was 30 min, the square resistance was 14.6 mΩ / □, and the welding strength reached 16.3 MPa.

[0058] Example 3:

[0059] A method for preparing a low-temperature solderable conductive copper paste, the method comprising the following steps:

[0060] 2 parts of KH-550 and 2 parts of benzotriazole were added to 100 parts of an ethanol solution containing 1.5% by weight of deionized water to obtain a treatment solution. 15 parts of 1000-mesh silver-coated copper powder, 50 parts of 5-micron silver-coated copper powder, 15 parts of 3-micron silver-coated copper powder, and 20 parts of 500-nanometer silver-coated copper powder were added to the treatment solution, and the mixture was stirred at a stirring speed of 500 r / min for 35 minutes. The mixture was then vacuum-dried at 80° C. to obtain coated copper powder.

[0061] According to the weight ratio, 25 parts of E51 epoxy resin, 7 parts of dicyandiamide curing agent, 2 parts of propylene glycol methyl ether, 2 parts of ethylene glycol butyl ether, 2 parts of hydrogenated silicone oil and 2 parts of fluorocarbon surfactant are mixed uniformly to obtain a mixture; then 60-80 parts of coated copper powder and 0.5 parts of fumed silica are added to the mixture, and high-speed dispersion treatment is carried out at a speed of 150 r / min for 1 hour, and then three-roll mill grinding is carried out for 40 minutes to obtain a low-temperature solderable conductive copper paste.

[0062] It should be noted that the silver-coated copper powder used in Example 3 is silver-coated copper powder with a silver content of 5 wt%.

[0063] The performance test of the low-temperature solderable conductive copper paste prepared in Example 3 showed that the curing temperature of the low-temperature solderable conductive copper paste prepared in Example 3 was 150° C., the curing time was 28 min, the square resistance was 17.0 mΩ / □, and the welding strength reached 15.2 MPa.

[0064] Comparative Example 1:

[0065] Comparative Example 1 is compared with Example 1, the difference of Comparative Example 1 is that no hydrogen-containing silicone oil is added, and the other parts are the same as Example 1.

[0066] The performance test of the comparative sample prepared in Comparative Example 1 showed that the curing temperature was 150° C., the curing time was 30 min, and the square resistance was 12.7 mΩ / □, but soldering was not possible.

[0067] Comparative Example 2:

[0068] Compared with Example 1, Comparative Example 2 is different in that a single specification of silver-coated copper powder is used, that is, a single 3-5 micron silver-coated copper powder is used in Comparative Example 2, and the rest is the same as Example 1.

[0069] The comparative sample prepared in Comparative Example 2 was subjected to performance testing, and the results showed that the curing temperature was 150° C., the curing time was 25 min, the square resistance was 36.0 mΩ / □, and the welding strength was 14.1 MPa.

[0070] Comparative Example 3:

[0071] Compared with Example 1, the difference of Comparative Example 3 is that the content of the added silver-coated copper powder is different. Other aspects are the same as Example 1. The weight ratio of the silver-coated copper powder added in Comparative Example 3 is as follows:

[0072] 10 parts of 1000 mesh silver-coated copper powder, 19 parts of 3-5 micron silver-coated copper powder; 15 parts of 1-3 micron silver-coated copper powder and 15 parts of 300-500 nanometer silver-coated copper powder.

[0073] The comparative sample prepared in Comparative Example 3 was subjected to performance testing. The results showed that the curing temperature was 150° C., the curing time was 30 min, the square resistance was 0.7 mΩ / □, and soldering was impossible.

[0074] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0075] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A method for preparing a low-temperature solderable conductive copper paste, characterized in that: The preparation method comprises the following steps: The copper powder is treated by an impregnation-drying process, and then the copper powder is added to the treatment liquid, stirred at a certain stirring speed, and then vacuum dried to obtain the coated copper powder; The organic carrier, curing agent, solvent and auxiliary agent are uniformly mixed to obtain a mixture; then the coated copper powder and thixotropic agent are added to the mixture, and the mixture is subjected to high-speed dispersion treatment and three-roll milling to obtain a low-temperature solderable conductive copper paste.

2. The preparation method according to claim 1, characterized in that The copper powder is silver-coated copper powder, and the silver content in the silver-coated copper powder is 3wt%-10wt%.

3. The preparation method according to claim 2, characterized in that The silver-coated copper powder includes 5-15 parts of 1000 mesh silver-coated copper powder, 40-60 parts of 3-5 micron silver-coated copper powder, 15-25 parts of 1-3 micron silver-coated copper powder, and 15-30 parts of 300-500 nanometer silver-coated copper powder, with a total mass of 100 parts.

4. The preparation method according to claim 1, characterized in that The treatment liquid is obtained by adding an adhesion enhancer and an antioxidant into an ethanol solution containing 1% to 3% by mass of deionized water.

5. The preparation method according to claim 4, characterized in that The adhesion enhancer is at least one of KH-550, KH-560, and KH-570.

6. The preparation method according to claim 4, characterized in that The antioxidant is at least one of benzotriazole and anhydrous hemic acid.

7. The preparation method according to claim 1, characterized in that The organic carrier is at least one of AG80 epoxy resin, AFG90H epoxy resin, AFG90 epoxy resin, E42 polyurethane modified epoxy resin, E51 epoxy resin, E44 epoxy resin, and DEN439 novolac epoxy resin.

8. The preparation method according to claim 1, characterized in that The curing agent is at least one of imidazole salts, acid anhydrides, dicyandiamides, and ketimines.

9. The preparation method according to claim 1, characterized in that The solvent is at least one of propylene glycol methyl ether, propylene glycol methyl ether acetate, ethylene glycol butyl ether, ethyl acetate, and amyl acetate.

10. The preparation method according to claim 1, characterized in that The auxiliary agent is at least one of hydrogen silicone oil, vinyl silicone oil, fluorocarbon surfactant, and BYK-333.

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