Conductive paste and preparation method and application thereof

Abstract

The invention relates to the technical field of new materials, in particular to conductive paste and a preparation method and application thereof. The conductive slurry is prepared from the following components in parts by weight: 10 to 13 parts of composite resin, 50 to 78 parts of conductive filler and 14 to 17 parts of solvent, the composite resin comprises polyurethane resin, epoxy resin and polyol resin in a weight ratio of (5-6): (1-2): (4-5); the conductive filler comprises flaky silver powder and spherical silver powder in a weight ratio of (20-33): (30-45); the solvent is selected from one or more of DBE, benzyl alcohol, DMSO and xylene. The conductive paste is high in precision, small in line width, small in edge sawtooth and good in line continuity when being used for manufacturing an FPC circuit board in a silk-screen printing manner.

Description

Technical Field

[0001] The present invention relates to the technical field of new materials, and particularly to a conductive paste, a preparation method thereof and an application thereof. Background Art

[0002] Traditional FPC circuit boards mostly adopt etching processes (also known as subtractive manufacturing processes), which require dozens of processes, such as flexible copper clad laminate manufacturing (FCCL), dry film lamination, exposure, development, etching, stripping, cleaning, etc. The production process is complex and the investment in equipment, site, etc. is relatively large; among them, in the production processes of flexible copper clad laminate manufacturing (FCCL) and etching process (DES), various chemical raw materials will be used, resulting in a large amount of pollutant emissions. The wastewater contains metal ions such as copper and nickel, which are difficult to treat and cause great environmental protection pressure; at the same time, the power consumption and water consumption are huge. In order to solve the above problems, Beijing Dream Ink Technology Co., Ltd. first proposed the eAMP technology, which is a technology that forms a conductive pattern by printing a functional composite conductive paste on the surface of an insulating substrate at one time through a traditional screen printing process. This technology does not require subtractive manufacturing processes, simplifies the production process, greatly reduces the production equipment and required materials, and the production process has almost zero pollution emissions.

[0003] Currently, the conductive paste used for the eAMP technology can generally print circuit patterns with a line width of more than 70 μm. The narrower the line width of the circuit, the higher the performance requirements for the conductive paste. It is urgent to develop a conductive paste that can print fine line circuit (40 - 50 μm) patterns.

[0004] In view of this, the present invention is specifically proposed. Summary of the Invention

[0005] The purpose of the present invention is to provide a conductive paste, which has high precision, small line width, small edge serrations and good circuit continuity when manufacturing an FPC circuit board by screen printing; another purpose of the present invention is to provide a preparation method and an application of the conductive paste.

[0006] Specifically, the present invention provides the following technical solutions:

[0007] The present invention provides a conductive paste, which comprises, by weight:

[0008] 10 - 13 parts of composite resin, 50 - 78 parts of conductive filler, and 14 - 17 parts of solvent;

[0009] The composite resin comprises polyurethane resin, epoxy resin and polyol resin in a weight ratio of (5 - 6) : (1 - 2) : (4 - 5);

[0010] The conductive filler comprises flaky silver powder and spherical silver powder in a weight ratio of (20 - 33) : (30 - 45);

[0011] The solvent is selected from one or more of DBE, benzyl alcohol, DMSO, and xylene.

[0012] The main research and development purpose of the present invention is to reduce the line width of printed fine lines. A large number of monomer and composite compounding methods have been tried. During the research and development process, it was unexpectedly found that in the slurry system for printing, using polyurethane resin, epoxy resin, and polyol resin as composite resins, and a conductive filler composed of flaky silver powder and spherical silver powder, when used in combination, and supplemented with a specific solvent, can effectively reduce the line width of printed fine lines and improve the line continuity.

[0013] Furthermore, controlling the weight ratio of polyurethane resin, epoxy resin, and polyol resin within the range of (5 - 6):(1 - 2):(4 - 5), and controlling the weight ratio of flaky silver powder and spherical silver powder between (20 - 33):(30 - 45), and selecting the solvent from one or more of DBE, benzyl alcohol, DMSO, and xylene can further reduce the line width of printed fine lines and reduce edge serrations.

[0014] Those skilled in the art can set other functional components in the formula according to common knowledge, and all can obtain effects equivalent to those described above in the present invention. However, there are also more optimal technical solutions for other components. Therefore, the present invention further explores and obtains the following preferred solutions.

[0015] Preferably, the polyurethane resin is selected from one or more of 5778, 5715, 5719, 5703, and 5702.

[0016] Preferably, the epoxy resin is bisphenol A epoxy resin, and the bisphenol A epoxy resin is selected from one or more of 1009, 1010, 1256, and 4250.

[0017] Preferably, the polyol resin has a molecular weight of 2000 - 5000, a hydroxyl value of 50 - 60 mg KOH / g, and a functionality of 2.

[0018] Preferably, the average particle size of the flaky silver powder is 3 - 5 μm, and the loose bulk density is 0.5 - 1.0 g / cm 3 .

[0019] Preferably, the average particle size of the spherical silver powder is 1 - 5 μm, and the loose bulk density is 2 - 3 g / cm 3 .

[0020] In the present invention, the polyurethane resin, epoxy resin and polyol resin are screened as above, and the properties of the flaky silver powder and spherical silver powder are screened as above, with better effects. Specifically, the above resins and conductive fillers are supplemented with a specific high-surface-energy solvent, which can make the thixotropy of the slurry within a suitable range (2-2.5), thereby making the convergence effect of the printed circuit better, the sawtooth smaller, and the printed circuit finer.

[0021] Preferably, by weight, the conductive paste further comprises: 4-5 parts of a curing agent;

[0022] The curing agent is an HDI curing agent, and the HDI curing agent is selected from one or more of 3175, 3575, TBN-75PS, TKA-B75S, and TPA-B80X.

[0023] Preferably, by weight, the conductive paste further comprises: 0.1-0.5 part of a toughening agent.

[0024] Preferably, by weight, the conductive paste further comprises: 0.5-1 part of a rheological agent;

[0025] The rheological agent is selected from one or more of fumed silica, polyamide wax, BYK358N, BYK410, and BYK326F.

[0026] Those skilled in the art can combine the above technical solutions according to common sense to obtain a preferred embodiment of the conductive paste of the present invention.

[0027] As a preferred embodiment of the present invention, the conductive paste comprises the following components in parts by weight:

[0028] 5-6 parts of polyurethane resin, 1-2 parts of epoxy resin, 4-5 parts of polyol resin, 14-17 parts of solvent, 4-5 parts of curing agent, 0.1-0.5 part of toughening agent, 0.5-1 part of rheological agent, 20-33 parts of flaky silver powder, and 30-45 parts of spherical silver powder.

[0029] The viscosity of the conductive paste of the present invention is 30-40 Pa·S.

[0030] The present invention also provides a method for preparing the above-mentioned conductive paste, comprising: mixing each component and then grinding.

[0031] Preferably, the preparation method comprises the following steps:

[0032] (1) Mix the polyurethane resin and part of the solvent, and stir at 70-90 °C and 50-500 rpm for 12-48 h to obtain a first premix;

[0033] (2) Mix epoxy resin and a portion of the solvent, and stir at 70 - 90 °C and 50 - 500 rpm for 12 - 48 h to obtain a second premix;

[0034] (3) Mix the first premix, the second premix, and polyol resin, and stir evenly at 700 - 900 r / min to obtain a third premix;

[0035] (4) Mix the third premix, curing agent, toughening agent, rheological agent, conductive filler, and the remaining portion of the solvent, stir evenly at 1400 - 1600 r / min, and then carry out grinding to obtain the product.

[0036] The present invention also discovers that by preparing the conductive paste in the above - mentioned manner, it can further ensure that each component is evenly mixed and guarantee that the product properties do not change differentially.

[0037] Preferably, in step (1), the amount of the portion of the solvent is 45 - 55% of the total amount of the solvent.

[0038] Preferably, in step (2), the amount of the portion of the solvent is 14 - 16% of the total amount of the solvent.

[0039] In a specific embodiment, a three - roll mill is used for grinding.

[0040] The present invention also provides the application of the above - mentioned conductive paste in a circuit board; preferably, its application in a flexible circuit board.

[0041] The present invention also provides an electronic device, including a substrate and a conductive circuit located on the substrate, wherein the conductive circuit is formed by printing and heat - curing the above - mentioned conductive paste.

[0042] Preferably, the printing method is screen printing.

[0043] Preferably, the material of the substrate is an elastic material.

[0044] Based on the above - mentioned solution, the beneficial effects of the present invention are as follows:

[0045] The present invention provides a conductive paste, which not only has a low silver content but also a low resistivity (the resistivity is 7.62×10 -7around Ω·cm); Using this conductive paste, circuit patterns with a line width of 40 - 50 μm and unilateral sawteeth ≤ 4 μm can be printed, and the surface of the obtained circuit patterns is flat, and has good adhesion between the substrate and the electroplated copper layer; After the electronic device made of this conductive paste passes through a high-temperature tin bath at 288 °C, there is no melting or embrittlement on the surface, no problem of peeling off of the conductive circuit, and the peeling strength of the conductive circuit can reach more than 7 N / cm; In addition, this conductive paste can be cured at a low temperature (below 200 °C), and the conductive circuit obtained after curing can withstand high temperatures (above 280 °C), and is also resistant to high humidity, salt spray, and can maintain performance under conditions such as thermal shock. Brief Description of the Drawings

[0046] Figure 1 It is a laser microscope picture of the flexible circuit board formed by the conductive paste of Example 1;

[0047] Figure 2 It is a laser microscope picture of the flexible circuit board formed by the conductive paste of Example 2;

[0048] Figure 3 It is a laser microscope picture of the flexible circuit board formed by the conductive paste of Example 3;

[0049] Figure 4 It is a laser microscope picture of the flexible circuit board formed by the conductive paste of Example 4;

[0050] Figure 5 It is a laser microscope picture of the flexible circuit board formed by the conductive paste of Comparative Example 1;

[0051] Figure 6 It is a laser microscope picture of the flexible circuit board formed by the conductive paste of Comparative Example 2;

[0052] Figure 7 It is a laser microscope picture of the flexible circuit board formed by the conductive paste of Comparative Example 3. Detailed Description of the Embodiments

[0053] The following embodiments are some embodiments of the present invention, rather than all embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0054] For those not specified in the embodiments regarding specific technologies or conditions, they shall be carried out according to the technologies or conditions described in the literature in this field or according to the product specifications. For reagents or instruments not specified for the manufacturer, they are all conventional products that can be obtained through regular channels.

[0055] Example 1

[0056] This example provides a conductive paste, and its formula is as follows:

[0057] 5.7 parts of polyurethane resin 5715, 1.6 parts of epoxy resin 1010, 4.4 parts of polyol resin (molecular weight 2000, hydroxyl value 50 - 60 mg KOH / g, functionality 2), 17 parts of DBE, 4.4 parts of 3175, 0.4 part of toughening agent, 0.9 part of BYK358N, 21.9 parts of flaky silver powder, 43.7 parts of spherical silver powder;

[0058] Among them, the average particle size of the flaky silver powder is 3 - 5 μm, and the loose bulk density is 0.5 - 1.0 g / cm 3 ; the average particle size of the spherical silver powder is 1 - 5 μm, and the loose bulk density is 2 - 3 g / cm 3 .

[0059] This embodiment further provides a preparation method of the above conductive paste, which is as follows:

[0060] (1) Mix polyurethane resin 5715 and part of DBE (the dosage is 50% of the total amount of DBE), and stir at 80 °C and 300 rpm for 12 h to obtain the first premix;

[0061] (2) Mix epoxy resin 1010 and part of DBE (the dosage is 15% of the total amount of DBE), and stir at 80 °C and 300 rpm for 12 h to obtain the second premix;

[0062] (3) Mix the first premix, the second premix and the polyol resin, and stir evenly at 800 r / min to obtain the third premix;

[0063] (4) Mix the third premix with 3175, toughening agent, BYK358N, flaky silver powder, spherical silver powder and the remaining part of DBE, stir evenly at 1500 r / min, and then grind with a three-roll mill to obtain.

[0064] Example 2

[0065] This embodiment provides a conductive paste, and its formula is as follows:

[0066] 5.6 parts of polyurethane resin 5778, 1.6 parts of epoxy resin 1256, 4.4 parts of polyol resin (molecular weight 2000, hydroxyl value 50 - 60 mg KOH / g, functionality 2), 17 parts of benzyl alcohol, 4.4 parts of TPA - B80X, 0.4 part of toughening agent, 0.9 part of BYK410, 21.9 parts of flaky silver powder, 43.8 parts of spherical silver powder;

[0067] Among them, the average particle size of the flaky silver powder is 3 - 5 μm, and the loose bulk density is 0.5 - 1.0 g / cm 3; The average particle size of the spherical silver powder is 1 - 5 μm, and the loose bulk density is 2 - 3 g / cm 3 .

[0068] This embodiment further provides a method for preparing the above conductive paste, which is as follows:

[0069] (1) Mix polyurethane resin 5778 and a part of benzyl alcohol (the dosage is 50% of the total amount of the solvent), and stir at 80 °C and 300 rpm for 12 h to obtain a first premix;

[0070] (2) Mix epoxy resin 1256 and a part of benzyl alcohol (the dosage is 15% of the total amount of the solvent), and stir at 80 °C and 300 rpm for 12 h to obtain a second premix;

[0071] (3) Mix the first premix, the second premix, and polyol resin, and stir evenly at 800 r / min to obtain a third premix;

[0072] (4) Mix the third premix with TPA - B80X, toughening agent, BYK410, flaky silver powder, spherical silver powder, and the remaining part of benzyl alcohol, stir evenly at 1500 r / min, and then grind with a three - roll mill to obtain the product.

[0073] Example 3

[0074] This embodiment provides a conductive paste, and its formula is as follows:

[0075] 5.8 parts of polyurethane resin 5719, 1.4 parts of epoxy resin 1009, 4.6 parts of polyol resin (molecular weight is 2000, hydroxyl value is 50 - 60 mg KOH / g, functionality is 2), 14.3 parts of DMSO, 4.6 parts of 3575, 0.5 part of toughening agent, 0.9 part of polyamide wax, 32.9 parts of flaky silver powder, 35 parts of spherical silver powder;

[0076] Among them, the average particle size of the flaky silver powder is 3 - 5 μm, and the loose bulk density is 0.5 - 1.0 g / cm 3 ; The average particle size of the spherical silver powder is 1 - 5 μm, and the loose bulk density is 2 - 3 g / cm 3 .

[0077] This embodiment further provides a method for preparing the above conductive paste, which is as follows:

[0078] (1) Mix polyurethane resin 5719 and a part of DMSO (the dosage is 50% of the total amount of DMSO), and stir at 80 °C and 300 rpm for 12 h to obtain a first premix;

[0079] (2) Mix epoxy resin 1009 and a part of DMSO (the dosage is 15% of the total amount of DMSO), and stir at 80 °C and 300 rpm for 12 h to obtain a second premix;

[0080] (3) Mix the first premix, the second premix, and polyol resin, and stir evenly at 800 r / min to obtain a third premix;

[0081] (4) Mix the third premix, 3575, toughening agent, polyamide wax, flaky silver powder, flaky spherical powder, and the remaining part of DMSO, and stir evenly at 1500 r / min, and then grind with a three-roll mill to obtain the product.

[0082] Example 4

[0083] This example provides a conductive paste, and its formula is as follows:

[0084] 5.8 parts of polyurethane resin 5703, 1.4 parts of epoxy resin 4250, 4.6 parts of polyol resin (molecular weight is 2000, hydroxyl value is 50 - 60 mg KOH / g, functionality is 2), 14.3 parts of xylene, 4.6 parts of TBN-75PS, 0.5 part of toughening agent, 0.9 part of BYK326F, 32.9 parts of flaky silver powder, 35 parts of spherical silver powder;

[0085] Among them, the average particle size of the flaky silver powder is 3 - 5 μm, and the loose bulk density is 0.5 - 1.0 g / cm 3 ; the average particle size of the spherical silver powder is 1 - 5 μm, and the loose bulk density is 2 - 3 g / cm 3 .

[0086] This example further provides a preparation method of the above conductive paste, which is specifically as follows:

[0087] (1) Mix polyurethane resin 5703 and a part of xylene (the dosage is 50% of the total amount of xylene), and stir at 80 °C and 300 rpm for 12 h to obtain a first premix;

[0088] (2) Mix epoxy resin 4250 and a part of xylene (the dosage is 15% of the total amount of xylene), and stir at 80 °C and 300 rpm for 12 h to obtain a second premix;

[0089] (3) Mix the first premix, the second premix, and polyol resin, and stir evenly at 800 r / min to obtain a third premix;

[0090] (4) Mix the third premix with TBN-75PS, toughening agent, BYK326F, flaky silver powder, spherical silver powder, and the remaining xylene, stir evenly at 1500 r / min, and then grind with a three-roll mill to obtain.

[0091] Comparative Example 1

[0092] This comparative example provides a conductive paste, which is different from that of Example 2 in that in the formula, the addition amount of polyurethane resin is 6.5 parts, the addition amount of epoxy resin is 3.1 parts, and the addition amount of polyol resin is 2 parts.

[0093] Comparative Example 2

[0094] This comparative example provides a conductive paste, which is different from that of Example 2 in that in the formula, the loose bulk density of flaky silver powder is 2.0 - 2.5 g / cm 3 , and the addition amount is 41.3 parts, and the addition amount of spherical silver powder is 24.4 parts.

[0095] Comparative Example 3

[0096] This comparative example provides a conductive paste, which is different from that of Example 2 in that in the formula, benzyl alcohol is replaced by diethylene glycol monoethyl ether acetate.

[0097] Test Example

[0098] In this test example, first use a viscosity tester to test the viscosity of the conductive pastes of each example and comparative example, then use a viscometer to calculate the thixotropy coefficient after testing the viscosity of the conductive pastes of each example and comparative example, and then form conductive lines (thickness 5 - 6 μm) on the surface of the substrate (composed of a 25-μm-thick PI film and a 2-4-μm bottom coating formed on the surface of the PI film, and the conductive paste is formed on one side of the bottom coating) by screen printing, cure at 180 °C for 0.5 h, and then form a copper plating layer (thickness 18 μm) on the surface of the conductive lines by electroplating. After post-treatment, a number of flexible printed circuit boards are obtained; perform performance tests on each flexible printed circuit board, specifically as follows:

[0099] (1) Perform resistivity tests on each flexible printed circuit board, and the specific test method is: use a four-probe ohmmeter to test the resistance, and then calculate it as the resistivity.

[0100] (2) Observe each flexible printed circuit board with a laser microscope, specifically see Figure 1-7 , where Figure 1 is the flexible printed circuit board formed by the conductive paste of Example 1, Figure 2 is the flexible printed circuit board formed by the conductive paste of Example 2, Figure 3 is the flexible printed circuit board formed by the conductive paste of Example 3, Figure 4The flexible printed circuit board formed by the conductive paste of Example 4 Figure 5 The flexible printed circuit board formed by the conductive paste of Comparative Example 1 Figure 6 The flexible printed circuit board formed by the conductive paste of Comparative Example 2 Figure 7 The flexible printed circuit board formed by the conductive paste of Comparative Example 3

[0101] (3) Adhesion tests were respectively carried out on the conductive lines of each flexible printed circuit board. This test was carried out before the electroplated copper layer step. The specific test method was as follows: Use 3M 600# adhesive tape to adhere to the surface of the conductive line. After standing for 1 minute, quickly remove the 3M 600# adhesive tape with external force, and observe whether there is peeling on the appearance of each conductive line; if there is no peeling, the adhesion is good; if peeling occurs (including partial peeling), the adhesion is poor.

[0102] (4) Peel strength tests were respectively carried out on each flexible printed circuit board. The specific test method was as follows: Use a universal material testing machine for testing.

[0103] (5) Temperature resistance tests were respectively carried out on each flexible printed circuit board. The specific test method was as follows: Immerse each flexible printed circuit board in a 288 °C tin bath for 10 s and repeat the immersion 3 times, and observe whether there is displacement and peeling of each conductive line; if there is no displacement and peeling, the temperature resistance is good; if displacement and peeling occur (including partial displacement and peeling), the temperature resistance is poor.

[0104] (6) The test results are shown in Table 1.

[0105] Table 1 Test Results

[0106]

[0107]

[0108] Finally, it should be noted that: The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: They can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A conductive paste, characterized in that: By weight, it includes: 10-13 parts of composite resin, 50-78 parts of conductive filler, and 14-17 parts of solvent; The composite resin comprises a polyurethane resin, an epoxy resin and a polyol resin in a weight ratio of (5-6):(1-2):(4-5); The conductive filler comprises flaky silver powder and spherical silver powder in a weight ratio of (20-33):(30-45); The solvent is selected from one or more of DBE, benzyl alcohol, DMSO and xylene.

2. The conductive paste according to claim 1, characterized in that: The polyurethane resin is selected from one or more of 5778, 5715, 5719, 5703, and 5702; and / or, The epoxy resin is bisphenol A epoxy resin, and the bisphenol A epoxy resin is selected from one or more of 1009, 1010, 1256, and 4250; and / or, The polyol resin has a molecular weight of 2000-5000, a hydroxyl value of 50-60 mg KOH / g, and a functionality of 2.

3. The conductive paste according to claim 1, characterized in that: The average particle size of the flaky silver powder is 3-5 μm, and the bulk density is 0.5-1.0 g / cm 3 and / or, The average particle size of the spherical silver powder is 1-5 μm, and the bulk density is 2-3 g / cm 3 .

4. The conductive paste according to any one of claims 1 to 3, characterized in that: In parts by weight, the conductive paste further comprises: 4-5 parts of a curing agent; The curing agent is an HDI curing agent, and the HDI curing agent is selected from one or more of 3175, 3575, TBN-75PS, TKA-B75S, and TPA-B80X.

5. The conductive paste according to any one of claims 1 to 4, characterized in that: In parts by weight, the conductive paste further includes: 0.1-0.5 parts of a toughening agent.

6. The conductive paste according to any one of claims 1 to 5, characterized in that: In parts by weight, the conductive paste further comprises: 0.5-1 part of a rheological agent; The rheological agent is selected from one or more of fumed silica, polyamide wax, BYK358N, BYK410, and BYK326F.

7. The method for preparing the conductive paste according to any one of claims 1 to 6, characterized in that: include: The components are mixed and then ground.

8. The preparation method according to claim 7, characterized in that: The preparation method comprises the following steps: (1) mixing a polyurethane resin and a portion of a solvent, and stirring at 70-90° C. and 50-500 rpm for 12-48 hours to obtain a first premix; (2) mixing the epoxy resin and part of the solvent, and stirring at 70-90° C. and 50-500 rpm for 12-48 hours to obtain a second premix; (3) mixing the first premix, the second premix and the polyol resin, and stirring them uniformly at 700-900 r / min to obtain a third premix; (4) mixing the third premix with the curing agent, toughening agent, rheological agent, conductive filler, and the remaining solvent, stirring evenly at 1400-1600 r / min, and then grinding to obtain; Preferably, in step (1), the amount of the partial solvent is 45-55% of the total amount of the solvent; More preferably, in step (2), the amount of the partial solvent used is 14-16% of the total amount of the solvent.

9. Use of the conductive paste according to any one of claims 1 to 6 in a circuit board, preferably in a flexible circuit board.

10. An electronic device comprising a substrate and a conductive circuit located on the substrate, characterized in that: The conductive circuit is formed by printing the conductive paste according to any one of claims 1 to 6 and heating and curing; Preferably, the printing method is screen printing; More preferably, the material of the substrate is elastic material.

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