Copper conductive paste and preparation method and application thereof

Abstract

The invention discloses copper conductive paste as well as a preparation method and application thereof. The copper conductive paste comprises copper powder, organic alcohol amine borate, organic acid, resin and a solvent, the mass ratio of the copper powder to the organic acid to the resin is (50-90): (0-2): (20-50), and the mass of the organic alcohol amine borate is 0.5-10% of the mass of the copper powder; and the C number of the organic acid is 4-20. The preparation method comprises the following steps: firstly, mixing copper powder and resin, adding a solvent, mixing and uniformly stirring; and adding the organic acid and the organic alcohol amine borate, and continuously stirring to obtain the copper conductive paste. The copper conductive paste can be used in cooperation with silver paste to prepare a bending-resistant flexible plate, a silver layer is arranged at the position, needing to be bent, of a substrate, the silver layer is in lap joint with a copper layer or covered with the copper layer, and the copper layer is made of the copper conductive paste. The conductive paste provided by the invention can obviously improve the conductivity of the conductive paste, can be used for curing in the atmosphere, and solves the problem of insufficient bending performance of copper paste through a silver paste printing complementation scheme.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of conductive materials, and particularly relates to a copper conductive paste and a preparation method and application thereof. BACKGROUND

[0002] In the prior art, the process for preparing a flexible screen copper-clad plate is to paste copper, and then to use a chemical etching copper pasting process. However, the copper cladding process has the problems of serious pollution in the later stage and large raw material loss. The silver paste printing process can solve the problem of three wastes, and the process flow is relatively simple, but the silver paste printing process has high cost, and silver ion migration is prone to occur after the silver paste is solidified.

[0003] The silver particles have good ductility, and can maintain a certain flexibility even after low-temperature solidification. The flaky silver particles can form a more stable conductive network and are not prone to breakage when bent. Copper is easy to oxidize, and the surface often needs to be treated for oxidation resistance (such as silver plating or organic coating), but this will increase the interface brittleness. In addition, the copper particles have high hardness, and are prone to cause the breakage of the conductive path due to stress concentration when repeatedly bent. How to improve the bending resistance of the solidified copper paste has also become a problem in its application.

[0004] Japanese Patent JP2660937B2 discloses a method for preparing a copper paste with good weldability by using silver-coated spherical or granular copper powder and a special chemical structure of phenolic resin. The copper paste prepared by the method has good solder wettability, is suitable for welding, and has good conductive performance. However, in order to prevent oxidation of the copper paste, a noble metal silver is used for coating, which has high cost. At the same time, the chemical structure of the phenolic resin is complex. Taiwan, China Patent TW201726279A uses dendritic Sn-coated copper powder and an organic resin to prepare a conductive paste, but the preparation process of the copper powder is complex, and the cost is high. SUMMARY

[0005] In view of the above problems in the prior art, the application provides a copper conductive paste and a preparation method and application thereof. The application can significantly improve the conductive performance of the copper conductive paste, and the copper conductive paste can be solidified at low temperature in the atmosphere. The problem of insufficient bending performance of the copper paste is solved by the scheme of supplementing the silver paste for the part with high bending requirement, and the ion migration speed of copper is 1 / 1000 of that of silver, so that the problem of silver migration after the silver paste is solidified can be solved.

[0006] The technical scheme of the application is as follows:

[0007] The application relates to a copper conductive paste, which comprises the following components: copper powder, organic alcohol amine borate, organic acid, resin and solvent.

[0008] The mass ratio of copper powder, organic acid, and resin is (50-90):(0-2):(20-50), and the amount of organic acid is not zero. The mass of organic alcohol amine borate ester is 0.5-10% of the mass of copper powder.

[0009] The organic acid has a carbon number of 4-20.

[0010] Preferably, the copper powder is pure copper powder, silver-coated copper powder, graphene-coated copper powder, copper-tin alloy powder, copper-nickel alloy powder, or copper-silver alloy powder, and the copper powder is in the shape of spheres, flakes, or dendritic, and the copper powder is micron-sized copper powder.

[0011] Preferably, the copper powder has a particle size of 1-50 μm. If the copper powder particle size is less than 1 μm, its dispersibility in the resin mixture will decrease, and the amount of resin covering the copper powder surface will increase, leading to a significant reduction in the conductivity of the copper conductive paste. If the particle size is greater than 50 μm, the thickness and line width of the printed circuit lines cannot be controlled during subsequent printing on the circuit board, easily causing short circuits. Ideally, a particle size of 5-30 μm should be selected.

[0012] The organic acid can be at least one of monobasic acid, dibasic acid, and tribasic acid, and can be fatty acid and / or aromatic carboxylic acid.

[0013] Monobasic organic acids include butyric acid, hexanoic acid, octanoic acid, capric acid, lauric acid, myristic acid, palmitic acid, palmitoleic acid, stearic acid, oleic acid, transoleic acid, linoleic acid, α-linolenic acid, γ-linolenic acid, and arachidic acid.

[0014] Dicarboxylic or ternary organic acids include tartaric acid, oxalic acid, malic acid, citric acid, and ascorbic acid (i.e., vitamin C); aromatic organic acids include benzoic acid, salicylic acid, and caffeic acid.

[0015] Further optimization is to select organic acids with 8-20 carbon atoms, which are weaker and less likely to corrode copper powder.

[0016] Preferably, the resin is composed of epoxy resin and polyurethane, wherein the epoxy resin accounts for no less than 60% by mass and the polyurethane accounts for no less than or equal to 40% by mass; the epoxy resin can improve the adhesion of the mixture to the substrate surface and provide bonding, and the resin also contains polyurethane, which helps to adjust the flexibility of the conductive paste after curing.

[0017] The epoxy resin is one of bisphenol A epoxy resin, flexible bisphenol F epoxy resin, bisphenol S type epoxy resin, hydroxymethyl bisphenol A epoxy resin, bisphenol P type epoxy resin, and glycidyl ester type epoxy resin. Bisphenol F epoxy resin with good flexibility is further preferred, as it can improve the flexibility of the cured mixture and enhance adhesion, making it suitable for circuit formation on FPCBs.

[0018] Preferably, the copper conductive paste further includes additives, including dispersants and / or leveling agents. Adding leveling agents, dispersants, and other additives to the conductive paste improves printability and controls the linewidth of the printed conductors.

[0019] Preferably, the organic alcohol amine borate ester is prepared by reacting an organic alcohol amine with boric acid. The organic alcohol amine used to prepare the organic alcohol amine borate ester has 1-3 amino groups and a carbon number of less than 10 and greater than 2. Organic alcohol amines help prevent copper powder from agglomerating during storage and refrigerated transportation. The organic alcohol amines can be compounds with one, two, or three amino groups, and also contain hydroxyl groups, which easily form strong adsorption on the copper powder surface. Examples include diethanolamine, triethanolamine, polydiethanolamine, diethylenetriolamine, benzyl alcohol amine, and polyethylene glycol diamine. To control steric hindrance, short-chain organic alcohols with a carbon number of less than 10 are preferred. With a carbon number greater than 10, the decomposition and volatilization temperature of the organic alcohol increases, and excessive residue during low-temperature curing affects conductivity. The carbon number should be greater than 2; when the carbon number is less than 2, the carbon chain of the alcohol is too short to easily form a complex.

[0020] If the content of organic alcohol amine borate is too high, the steric hindrance will be too great, affecting the proximity of copper powder and reducing conductivity. If the content of organic alcohol amine borate is too low, the surface adsorption of copper powder will be insufficient, and it will not be able to prevent it from being oxidized.

[0021] This invention also relates to a method for preparing copper conductive paste, comprising the following steps:

[0022] S1. Mix copper powder and resin, add solvent, mix and stir evenly;

[0023] S2. Add organic alcohol amine borate and organic acid to the mixture in step S1, and continue stirring to obtain copper conductive paste.

[0024] Preferably, in step S1, an additive is added after the copper powder and resin are mixed;

[0025] In step S1, mix manually until homogeneous, then use a mixer to mix for 30-90 seconds; in step S2, use a mixer to mix for 90-180 seconds.

[0026] This invention also relates to the application of the aforementioned copper conductive paste in PCB (printed circuit board) printing, FPCB (flexible printed circuit board) printing, through-hole circuit formation, and LED substrate circuit formation. The copper conductive paste can be cured at low temperatures in the atmosphere, with the low temperature conditions being 120-200°C. This conductive paste can be used for low-temperature curing in an atmospheric atmosphere without nitrogen protection.

[0027] The copper conductive paste of this invention exhibits good conductivity, low cost, and ease of operation. Compared to existing copper coating techniques, it can solve the problem of copper powder oxidation at a lower cost. Furthermore, this conductive paste can be screen printed, with a viscosity controllable to 5-10 Pa·s. Printing substrates include glass, flexible polymer films, and rigid polymer circuit boards.

[0028] The present invention also relates to a flexible board, the flexible board comprising a copper layer, the copper layer being made of copper conductive paste.

[0029] Preferably, the flexible board includes a substrate, and a silver layer is provided at the part of the substrate that needs to be bent. The silver layer overlaps with or is covered by the copper layer, and the silver layer is made of silver paste.

[0030] The beneficial effects of this invention are:

[0031] (1) The present invention produces a copper conductive paste with conductivity equivalent to that of silver conductive paste, which helps to reduce the cost of circuit board printing. The copper conductive paste can be cured at low temperature in the atmosphere and will not oxidize even without inert gas protection, thus significantly reducing the process cost.

[0032] (2) Compared with existing electroplating and copper plating processes, the copper conductive paste can be printed using screen printing technology. The copper conductive paste printing process has fewer steps, no wastewater discharge, is environmentally friendly and pollution-free, and the process operation is convenient and simple.

[0033] (3) The present invention combines silver paste and low-temperature curing copper conductive paste, which helps to solve the problem of low-temperature curing copper paste printed circuits being not resistant to bending at a lower cost. At the same time, the ion migration rate of copper is 1 / 1000 that of silver, which can solve the problem of silver migration after the silver paste is cured. Attached Figure Description

[0034] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0035] Figure 1 This is a schematic diagram of the inner and outer folds in the bending resistance test. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0037] A method for preparing a copper conductive paste includes the following steps:

[0038] S1: Mix copper powder with resin, add additives and solvent, stir manually until evenly mixed, then stir for 30 seconds using a rotary mixer at 1400 rpm.

[0039] S2: Add organic acid and organic alcohol amine borate to the mixture in step S1, and stir for 90 seconds using a rotary mixer.

[0040] Among them, the copper powder is micron-sized dendritic copper powder, the resin is composed of epoxy resin and polyurethane, the epoxy resin is bisphenol F epoxy resin, the additives are dispersant and leveling agent, the solvent is terpineol, the organic acid is oleic acid, and the organic alcohol amine borate is diethanolamine borate.

[0041] Examples 1-4 and Comparative Example 1 prepared copper conductive paste according to the formula in Table 1. The copper conductive paste was printed onto the surface of the flexible screen using a screen printing machine. The screen was then dried in an oven at 180°C for 1 hour. After curing, the line length was 1 cm and the line width was 0.1 cm. The resistivity was tested using a two-terminal conductivity meter. The test performance data are also shown in Table 1.

[0042] Table 1

[0043]

[0044] *1: Epoxy resin ratio refers to the mass percentage of epoxy resin in the total resin.

[0045] *2: Polyurethane ratio refers to the mass percentage of polyurethane in the total resin.

[0046] *3: Diethanolamine borate ratio refers to the percentage of diethanolamine borate in the mass of copper powder;

[0047] *4: 100-square experiment, the number of undamaged squares in the 100-square grid.

[0048] Comparison results

[0049] In Example 1, polyurethane accounted for 20 wt% of the total resin weight. In the adhesion test, only 90 out of 100 squares were intact, and the adhesion was significantly lower than that of the sample with 30% polyurethane. In Example 3, the 100-square test showed no damage.

[0050] In Example 2, no polyurethane was added, and the proportion of diethanolamine borate was 2%. In the adhesion test, only 70 out of 100 squares remained intact, indicating a decrease in adhesion compared to Example 1, along with a reduction in flexural strength. Polyurethane plays a role in improving the flexibility of the slurry.

[0051] In Example 3, the proportion of diethanolamine borate was increased to 5%, the volume resistivity was increased to 8E-5Ω·cm, and the adhesion was also very good.

[0052] In Example 4, the proportion of diethanolamine borate was increased to 6%. Compared with Example 3, the adhesion also decreased. The excessive addition of diethanolamine borate formed steric hindrance on the surface of copper powder, which reduced the bonding strength between the resin and the copper powder and reduced the adhesion.

[0053] Comparative Example 1, which did not contain diethanolamine borate, had a significantly higher volume resistivity than the conductive paste prepared with diethanolamine borate.

[0054] Following the resin and additive ratio in Example 3, copper powder of different shapes was used to prepare copper conductive paste using the same method, and its volume resistivity was tested. Specific data are shown in Table 2.

[0055] Table 2

[0056]

[0057] *1: Diethanolamine borate ratio refers to the percentage of diethanolamine borate in the mass of copper powder.

[0058] In Examples 5 and 6, spherical and flake copper powders were used, while in Example 7, dendritic copper powder of the same particle size was used. The conductive paste prepared in Example 7 showed a significant decrease in volume resistivity. Due to its unique morphology, the dendritic copper powder had more contact points when filled into the conductive paste, resulting in more conductive pathways than flake and spherical powders, thus exhibiting better conductivity. Simultaneously, the specific surface area of ​​regularly shaped flake and spherical powders was smaller than that of dendritic copper powder of the same particle size, reducing the number of adsorption sites for diethanolamine borate esters and making them prone to excess adsorption. Excess diethanolamine borate esters would be distributed in the conductive paste, negatively impacting conductivity.

[0059] In Example 8, dendritic copper powder with a particle size of 3 μm was used. Compared to Example 7, the volume resistivity increased, and the copper powder particle size decreased. The steric hindrance provided by diethanolamine borate was stronger, which improved the dispersion effect of the copper powder. However, when the steric hindrance is too large, the copper powder is difficult to approach, the contact surface is reduced, and the formation of conductive pathways is also reduced, resulting in poor conductivity. At the same time, the smaller copper powder particle size and the larger specific surface area will also promote the oxidation of the copper powder and reduce conductivity.

[0060] In Example 9, dendritic copper powder with a diameter of 10 μm was used. Compared with Example 7, the volume resistivity was reduced. However, in Example 10, the particle size of the copper powder was increased to 15 μm, and the volume resistivity was increased. This is because the increased particle size of the copper powder reduced its specific surface area. As a non-conductive diethanolamine borate ester, the remaining surface adsorption capacity would reduce the conductivity of the copper powder.

[0061] Following the resin and copper powder ratios in Example 3, the proportions and types of organic acids were adjusted, and copper conductive paste was prepared using the same method. Its volume resistivity was then tested. Specific data are shown in Table 3.

[0062] Table 3

[0063]

[0064] Example 11 uses formic acid, which causes the slurry to gel and turn blue, making it impossible to test the conductivity properly.

[0065] The valeric acid selected in Example 12 and the citric acid selected in Example 13 can achieve a volume resistivity similar to that of Example 3. However, the slurry selected in Example 12 turned green after being left to stand, indicating poor stability.

[0066] Example 14: Increase the proportion of oleic acid. In Example 3, the volume resistivity increased with increasing oleic acid proportion.

[0067] In Example 15, the proportion of oleic acid added was 0. Compared with Example 3, the volume resistivity also increased when no oleic acid was added at all.

[0068] Therefore, organic acids can reduce the oxidation of copper powder surface, and organic alcohol amine borate esters can be adsorbed onto the surface of copper powder to reduce copper oxidation. Thus, the combination of organic acids and diethanolamine borate esters can reduce the oxidation of copper powder and produce conductive paste with excellent conductivity.

[0069] The copper conductive paste prepared in Example 3 was used in conjunction with commercially available flexible silver paste, as follows: Silver paste was first printed on PET, dried in a 150°C oven for 10 minutes, and then the copper conductive paste prepared in Example 3 was printed on, with the copper directly covering the silver paste. The mixture was then dried in a 180°C oven for 1 hour. The resulting product at the bend is denoted as copper layer + silver layer + PET.

[0070] In addition, silver paste is first printed onto PET, and then dried in a 150°C oven for 20 minutes. The resulting product with the corresponding bend in the film is denoted as silver layer + PET.

[0071] The copper conductive paste prepared in Example 3 was printed on PET and dried in an oven at 180°C for 1 hour. The film at the bend of the resulting product is denoted as copper layer + PET.

[0072] The bending resistance of the above products was tested, and the specific methods are shown below. The specific results are shown in Table 4.

[0073] (1) Outward fold: bend 180° toward the PET substrate, press a 2kg weight on the fold for 1 minute as one time, and test the film circuit resistance after bending and flattening.

[0074] (2) Inward fold: bend 180° toward the printed line, press a 2kg weight on the fold for 1 minute as one time, and test the resistance of the thin film line after bending and flattening.

[0075] (3) The width of the printed test line is 0.3mm-1mm and the length is 50-100mm.

[0076] Table 4

[0077]

[0078] It should be understood that the specific embodiments described above are merely illustrative or explanatory of the principles of the invention and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of the invention should be included within the protection scope of the invention. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

Claims

1. A copper conductive paste, characterized by, The copper conductive paste comprises the following components: copper powder, organic alcohol amine borate, organic acid, resin and solvent. The mass ratio of the copper powder, the organic acid and the resin is (50-90):(0-2):(20-50), and the amount of the organic acid is not 0, and the mass of the organic alcohol amine borate is 0.5-10% of the mass of the copper powder. The C number of the organic acid is 4-20.

2. The copper conductive paste according to claim 1, wherein The copper powder is pure copper powder, silver-coated copper powder, graphene-coated copper powder, copper-tin alloy powder, copper-nickel alloy powder or copper-silver alloy powder, the shape of the copper powder is spherical, flaky or dendritic, and the copper powder is micron-level copper powder, preferably the particle size of the copper powder is 1-50 μm. The organic acid is at least one of butyric acid, hexanoic acid, octanoic acid, decanoic acid, lauric acid, myristic acid, palmitic acid, palmitoleic acid, stearic acid, oleic acid, elaidic acid, linoleic acid, alpha-linolenic acid, gamma-linolenic acid, arachidic acid, tartaric acid, oxalic acid, malic acid, citric acid, ascorbic acid, benzoic acid, salicylic acid and coffee acid.

3. The copper conductive paste of claim 1, wherein The resin is composed of epoxy resin and polyurethane, the mass ratio of the epoxy resin in the resin is not less than 60%, and the mass ratio of the polyurethane is less than or equal to 40%. The epoxy resin is one of bisphenol A epoxy resin, flexible bisphenol F epoxy resin, bisphenol S type epoxy resin, hydroxymethyl bisphenol A epoxy resin, bisphenol P type epoxy resin and glycidyl ester type epoxy resin.

4. The copper conductive paste of claim 1, wherein The copper conductive paste further comprises an additive, and the additive comprises a dispersant and / or a leveling agent.

5. The copper conductive paste of claim 1, wherein The organic alcohol amine borate is prepared by reacting organic alcohol amine with boric acid, the number of amine groups in the organic alcohol amine is 1-3, the C number of the organic alcohol amine is less than 10 and greater than 2.

6. A process for the preparation of the copper conductive paste according to any one of claims 1 to 5, characterized in that, The method comprises the following steps: S1, mixing the copper powder and the resin, adding the solvent, mixing and stirring uniformly; S2, adding the organic amine borate and the organic acid to the mixture in step S1, and continuing to stir to obtain the copper conductive paste.

7. The preparation method according to claim 6, characterized in that, in step S1, the additive is further added after the copper powder and the resin are mixed. In the stirring process of step S1, the mixture is first manually mixed uniformly, and then stirred with a stirrer for 30-90 seconds; in the stirring process of step S2, the mixture is stirred with a stirrer for 90-180 seconds.

8. Application of the copper conductive paste according to any one of claims 1-5 in PCB printing, FPCB printing, through-hole circuit formation and LED substrate circuit formation, wherein the copper conductive paste can be cured at low temperature in the atmosphere, and the low temperature condition is 120-200 DEG C.

9. A flexible sheet, characterized by The flexible board comprises a copper layer prepared from the copper conductive paste according to any one of claims 1-5.

10. The flexure of claim 9, wherein, The flexible board comprises a substrate, a silver layer is arranged at a position where the substrate needs to be bent, the silver layer is overlapped with the copper layer or covered by the copper layer, and the silver layer is prepared from silver paste.

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