A flexible circuit fine-line silver paste and its preparation method

Abstract

This invention provides a flexible fine-line silver paste and its preparation method, belonging to the field of electronic component technology. The method includes: preparing a saturated polyester resin solution and a polyvinyl butyral thickening resin solution; mixing polyurethane-modified flexible epoxy resin, saturated polyester resin solution, polyvinyl butyral thickening resin solution, thixotropic agent, isocyanate curing agent, and a first solvent, followed by heating and stirring to disperse, to obtain an organic carrier; adding a second solvent and coupling agent to a container and stirring to disperse, then adding a mixture of silver powder and nano-zirconia powder, and sequentially heating, stirring, dispersing, and grinding, before adding it to the organic carrier to disperse, forming a coarse slurry; grinding the coarse slurry multiple times, stirring, and vacuum degassing to obtain a fine-line silver paste. The flexible fine-line silver paste of this invention can meet the printing requirements of fine lines (0.05-0.12 mm) and diffusion (0.01-0.02 mm) in the automotive electronics field, and also meets the requirements of high-density fine-line printing.

Description

Technical Field

[0001] This invention belongs to the field of electronic component technology, and particularly relates to a flexible circuit fine line silver paste and its preparation method. Background Technology

[0002] Printed circuit boards (PCBs) are the carriers for the electrical interconnection of electronic components and are one of the important components of the electronics industry. With the increasing demands for miniaturization and arraying of electronic components, the density of PCBs is constantly increasing to meet these needs. High-density PCBs (HDI-PCBs) have higher line density per unit area, finer lines and space, and higher pad connection density. They are widely used in mobile phones, touch screen devices, laptops, digital cameras, 4G network communications, medical equipment, and various electronic components in aircraft and automobiles. They can also be used to reduce product weight and overall size, as well as enhance the electrical performance of equipment.

[0003] Chinese patent CN108770194B discloses a method for preparing conductive silver paste for printed circuits, which includes the following steps: (1) preparing the required raw materials according to the weight ratio: 10-15 parts of spherical silver powder, 20-30 parts of flake silver powder, 7-10 parts of graphene, 8-12 parts of epoxy-modified polyester resin, 10-15 parts of organic solvent, aluminum nitride, defoamer, and leveling agent; (2) preparation of organic carrier; (3) preparation of conductive silver paste. The silver content of this conductive silver paste for printed circuits is too high. Although the line width meets the requirements for fine line printing of 0.05-0.12 mm, it cannot meet the requirements for diffusion within 0.01-0.02 mm. Moreover, its thixotropy and conductivity cannot meet the requirements for high-density fine line printing.

[0004] Chinese patent CN105070349A discloses a conductive fine line printing silver paste for capacitive touch screens and its preparation and application methods. The raw materials of this conductive fine line printing silver paste for capacitive touch screens include the following components in the following weight ratios: 60-80 parts silver powder, 6-10 parts vinyl resin, 22-25 parts solvent, 0.5-3 parts colorant, and 1-5 parts additives. The silver content of this conductive fine line printing silver paste for capacitive touch screens is too high, and the line width cannot meet the printing requirements of 0.05-0.12 mm and diffusion of 0.01-0.02 mm, nor can it meet the requirements of high-density fine line printing. Summary of the Invention

[0005] One of the objectives of this invention is to provide a method for preparing flexible fine-line silver paste. The flexible fine-line silver paste prepared by this method can meet the printing requirements of silver paste fine lines within 0.05-0.12 mm and diffusion within 0.01-0.02 mm in the automotive electronics field, and can also meet the requirements of high-density fine-line printing.

[0006] The second objective of this invention is to provide a flexible line fine-line silver paste.

[0007] To achieve one of the above objectives, the present invention employs the following technical solution:

[0008] A method for preparing flexible circuit fine-line silver paste, the method comprising the following steps:

[0009] Step S1: Dissolve saturated polyester resin in a first solvent to obtain a saturated polyester resin solution with a mass concentration of 35-45%; dissolve polyvinyl butyral thickening resin in the first solvent to obtain a polyvinyl butyral thickening resin solution with a mass concentration of 15-25%.

[0010] Step S2: Mix polyurethane modified flexible epoxy resin, saturated polyester resin solution, polyvinyl butyral thickening resin solution, thixotropic agent, isocyanate curing agent and first solvent, heat to 60-80℃, and then stir and disperse at a stirring rate of 600-1200 rpm for 20-40 minutes to obtain organic carrier.

[0011] In step S2, the mass ratio of the polyurethane modified flexible epoxy resin, saturated polyester resin solution, polyvinyl butyral thickening resin solution, thixotropic agent, isocyanate curing agent and first solvent is 8-15:5-30:10-20:1-6:1-4:30-55.

[0012] Step S3: After adding the second solvent and coupling agent to the container, stir and disperse at a speed of 400-800 rpm for 10-20 minutes. Then add the mixture of silver powder and nano-zirconia powder. Stir and disperse at a speed of 1000-1200 rpm for 1-2 hours at a water bath temperature of 80-85℃. Then seal the container and grind it on a rod mill for 20-28 hours. Then add it to the organic carrier and disperse it at a speed of 800-1600 rpm for 50-70 minutes to form a coarse slurry.

[0013] In step S3, the mass ratio of the silver powder, nano-zirconia powder and organic carrier is 43-51:1-3:47-55;

[0014] The mass of the second solvent is 0.15 to 0.25 times the sum of the masses of the silver powder and the zirconium oxide powder;

[0015] The mass of the coupling agent is 0.01 to 0.03 times the sum of the masses of the silver powder and the zirconium oxide powder;

[0016] In step S3, the silver powder includes flake silver powder and nanoscale silver powder;

[0017] Step S4: Using a three-roll mill, the coarse slurry is ground multiple times, and then vacuum degassed under stirring at a speed of 400-600 rpm to obtain fine silver paste with a fineness of less than 5 μm.

[0018] Furthermore, in step S1, the saturated polyester resin is one or more of ES100, ES110, ES120, ES160, ES210, ES215, ES240, ES300, ES320, ES350, ES360, ES410, ES420, ES450, ES500, ES510, and ES850.

[0019] The polyvinyl butyral thickening resin is any one of B-76, B-08HX, B-14HX, SD-5, and SD-6.

[0020] Furthermore, in steps S1 and S2, the first solvent is one or more of the following: high-boiling-point composite ester DBE, mixed dicarboxylic acid dimethyl ester, EGDA, diethyl succinate, dimethyl adipate, diethyl adipate, and isoflurone.

[0021] In step S3, the second solvent is one or more of methyl formate, ethyl formate, propyl formate, isopropyl formate, butyl formate, isobutyl formate, isoamyl formate, benzyl formate, methyl acetate, sec-butyl acetate, EEP, PGDA, PGA, YDBE, propylene glycol methyl ether acetate, propylene glycol methyl ether, propylene glycol butyl ether, ethylene glycol butyl ether, and ethylene glycol ethyl ether.

[0022] Furthermore, in step S2, the polyurethane modified flexible epoxy resin is one or more of DER791, EPU-105, EPU-133L, EPU-300S, ERS-005, NPER-133L, SL3411, SL3412, and SL3413.

[0023] The thixotropic agent is one of 6900-20X, AKN-7010, BYK-410, Anjeka4410, and Rheotech 2800.

[0024] Furthermore, in step S3, the mass ratio of flake silver powder to nano-sized silver powder in the silver powder is 90-99:1-10.

[0025] Furthermore, in step S3, the mass ratio of flake silver powder to nano-sized silver powder in the silver powder is 93-97:3-7.

[0026] Furthermore, in step S3, the average particle size of the flake-shaped silver powder is 1.2–1.5 μm, and the specific surface area is 1.2–1.8 cm². 2 / g, D100 < 5μm;

[0027] The nanoscale silver powder has an average particle size of 100–200 nm and a specific surface area of ​​6.0–8.0 cm². 2 / g.

[0028] Furthermore, in step S3, the coupling agent is one or more of ZJ-316, ZJ-201, KR-38S, CT-114, NDZ-204, and LD-1070A;

[0029] Furthermore, in step S4, the vacuum degassing is performed at a vacuum level of 0.6–0.8 MPa, a temperature of 20–30°C, and a time of 40–50 minutes. The grinding is repeated 6–10 times.

[0030] To achieve the second objective mentioned above, the present invention employs the following technical solution:

[0031] A flexible circuit fine line silver paste, wherein the flexible circuit fine line silver paste is prepared by the preparation method described above.

[0032] Furthermore, the flexible circuit fine line silver paste has a thixotropic index >4, a silver content of 43-51%, a sheet resistance of 14.6-15.6 mΩ / □, an adhesion of 5B, a hardness of 5H, and a viscosity of 60-80 Pa·s.

[0033] In summary, the solution proposed in this invention has the following technical effects:

[0034] This invention utilizes a polyurethane-modified flexible epoxy resin and a saturated polyester resin solution to undergo a cross-linking reaction with an isocyanate curing agent at a low unsealing temperature (60–80°C), forming a network structure. This improves the bending, moisture resistance, and chemical corrosion resistance of the silver paste, achieving an adhesion of 5B to the ITO film. The organic binder phase formed by the saturated polyester resin solution further enhances the bending and thixotropic properties of the silver paste after low-temperature curing. The use of a polyvinyl butyral thickening resin solution and a thixotropic agent increases the viscosity and thixotropic properties of the silver paste even with a relatively low silver content. Furthermore, by controlling the addition of flake silver powder, nano-sized silver powder, and the amount added, the viscosity and thixotropic properties of the silver paste are improved without affecting its sheet resistance. This invention improves the printability of the silver paste, enhances its hardness, and controls its fineness through the use of nano-zirconia powder. The flexible circuit fine-line conductive silver paste of this invention has a silver content of 43-51%, is cured at a low temperature of 110℃, achieves an adhesion of 5B to the ITO film, a hardness of 5H, a viscosity of 60-80 Pa·s, and a thixotropic index >4 (5 rpm / 50 rpm). This satisfies both the printing requirements for fine lines (0.05-0.12 mm) and diffusion (0.01-0.02 mm) in the automotive electronics field, and the requirements for high-density fine-line printing. The application of this flexible circuit fine-line conductive silver paste in the HDI-PCB field is of great significance for expanding the application areas of flexible circuit silver paste. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] Example 1:

[0037] Step S1: Dissolve ES100 in DBE to obtain an ES100 solution with a mass concentration of 40%; dissolve B-76 in DBE to obtain a B-76 solution with a mass concentration of 20%.

[0038] Step S2: Mix DER791, ES100 solution, B-76 solution, 6900-20X thixotropic agent, isocyanate curing agent and DBE, heat to 70℃, and then stir and disperse at a stirring rate of 1200 rpm for 40 minutes to obtain organic carrier;

[0039] The mass ratio of DER791, ES100 solution, B-76 solution, 6900-20X thixotropic agent, isocyanate curing agent and DBE is 15:30:20:6:4:55.

[0040] Step S3: After adding methyl formate and ZJ-316 coupling agent to the container, stir and disperse at 600 rpm for 15 minutes. Then add the mixture of silver powder and nano-zirconia powder, and stir and disperse at 1100 rpm for 1.5 hours in a water bath at 82°C. Then seal and grind on a rod mill for 24 hours. Then add it to the organic carrier and disperse at 1200 rpm for 60 minutes to form a coarse slurry.

[0041] The mass ratio of silver powder, nano-zirconia powder, and organic carrier is 51:2:47. The mass of methyl formate is 0.25 times the sum of the masses of silver powder and zirconia powder. The mass of ZJ-316 coupling agent is 0.03 times the sum of the masses of silver powder and zirconia powder. The silver powder includes flake-shaped silver powder and nano-sized silver powder. The mass ratio of flake-shaped silver powder to nano-sized silver powder is 99:1. The average particle size of the flake-shaped silver powder is 1.2 μm, and the specific surface area is 1.2 cm². 2 / g, D100 is 3.5μm, the average particle size of the nano-sized silver powder is 100nm, and the specific surface area is 6.0cm². 2 / g.

[0042] Step S4: Using a three-roll mill, grind the coarse slurry 10 times, and then perform vacuum degassing under stirring at a speed of 500 rpm to obtain fine silver paste with a fineness of 3.5 μm.

[0043] The vacuum degassing process involved a vacuum level of 0.6 MPa, a temperature of 20°C, and a time of 40 minutes.

[0044] Example 2:

[0045] Step S1: Dissolve ES110 in EGDA to obtain an ES110 solution with a mass concentration of 45%; dissolve B-08HX in EGDA to obtain a B-08HX solution with a mass concentration of 25%.

[0046] Step S2: Mix EPU-105, ES110 solution, B-08HX solution, AKN-7010 thixotropic agent, isocyanate curing agent and EGDA, heat to 80℃, and then stir and disperse at a stirring rate of 900 rpm for 30 minutes to obtain organic carrier;

[0047] The mass ratio of EPU-105, ES110 solution, B-08HX solution, AKN-7010 thixotropic agent, isocyanate curing agent and EGDA is 12:20:15:3:2:40.

[0048] Step S3: After adding the second solvent, ethyl formate, and ZJ-201 coupling agent to the container, stir and disperse at 800 rpm for 20 minutes. Then add the mixture of silver powder and nano-zirconia powder, and stir and disperse at 1200 rpm for 2 hours at a water bath temperature of 85°C. Then seal the container, place it on a rod mill and grind it for 28 hours. Then add it to the organic carrier and disperse at 1600 rpm for 70 minutes to form a coarse slurry.

[0049] The mass ratio of silver powder, nano-zirconia powder, and organic carrier is 47:1:52. The mass of methyl formate is 0.20 times the sum of the masses of silver powder and zirconia powder. The mass of coupling agent ZJ-201 is 0.02 times the sum of the masses of silver powder and zirconia powder. The silver powder includes flake-shaped silver powder and nano-sized silver powder. The mass ratio of flake-shaped silver powder to nano-sized silver powder is 95:5. The average particle size of the flake-shaped silver powder is 1.3 μm, and the specific surface area is 1.5 cm². 2 / g, D100 is 4.0μm, the average particle size of the nano-sized silver powder is 150nm, and the specific surface area is 7.0cm². 2 / g.

[0050] Step S4: Using a three-roll mill, the coarse slurry is ground 8 times, and then vacuum degassed under stirring at 600 rpm to obtain a fine silver paste with a fineness of 4.0 μm.

[0051] The vacuum degassing process involved a vacuum level of 0.7 MPa, a temperature of 25°C, and a time of 45 minutes.

[0052] Example 3:

[0053] Step S1: Dissolve ES120 in isoflurane to obtain an ES120 solution with a mass concentration of 35%; dissolve B-14HX in isoflurane to obtain a B-14HX solution with a mass concentration of 15%.

[0054] Step S2: Mix EPU-133L, ES120 solution, B-14HX, BYK-410 thixotropic agent, isocyanate curing agent and isoflurane, heat to 75°C, and then stir and disperse at a stirring rate of 600 rpm for 20 minutes to obtain an organic carrier.

[0055] The mass ratio of EPU-133L, ES120 solution, B-14HX solution, BYK-410 thixotropic agent, isocyanate curing agent and isoflurone is 8:5:10:1:1:30.

[0056] Step S3: After adding propyl formate and KR-38S coupling agent to the container, stir and disperse at 400 rpm for 10 minutes. Then add the mixture of silver powder and nano-zirconia powder, and stir and disperse at 1000 rpm for 1 hour at a water bath temperature of 80°C. Then seal and grind on a rod mill for 20 hours. Then add it to the organic carrier and disperse at 800 rpm for 50 minutes to form a coarse slurry.

[0057] The mass ratio of silver powder, nano-zirconia powder, and organic carrier is 43:2:55. The mass of methyl formate is 0.15 times the sum of the masses of silver powder and zirconia powder. The mass of coupling agent KR-38S is 0.01 times the sum of the masses of silver powder and zirconia powder. The silver powder includes flake-shaped silver powder and nano-sized silver powder, with a mass ratio of 90:10. The average particle size of the flake-shaped silver powder is 1.5 μm, and its specific surface area is 1.8 cm². 2 / g, D100 is 4.5μm, the average particle size of the nano-sized silver powder is 200nm, and the specific surface area is 8.0cm². 2 / g.

[0058] Step S4: Using a three-roll mill, the coarse slurry is ground 6 times, and then vacuum degassed under stirring at 400 rpm to obtain fine silver paste with a fineness of 4.5 μm.

[0059] The vacuum degassing process involved a vacuum level of 0.8 MPa, a temperature of 30°C, and a time of 50 minutes.

[0060] Table 1 Performance index values ​​of fine-line silver pastes in Examples 1-3

[0061] Performance parameters Example 1 Example 2 Example 3 Silver content, % 51 47 43 Viscosity, Pa·s 76.8 68.0 67.2 Thixotropic index, 5 / 50 4.6 4.4 4.1 Shear resistance, mΩ / □ 14.6 15.3 15.6 Flexural strength, secondary 10 10 10 Adhesion 5B 5B 5B hardness 5H 5H 5H 0.05mm printing width, mm 0.0582 0.0588 0.592

[0062] Please note that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. The above embodiments only illustrate several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing flexible circuit fine-line silver paste, characterized in that, The preparation method includes the following steps: Step S1: Dissolve saturated polyester resin in a first solvent to obtain a saturated polyester resin solution with a mass concentration of 35-45%; dissolve polyvinyl butyral thickening resin in the first solvent to obtain a polyvinyl butyral thickening resin solution with a mass concentration of 15-25%. Step S2: Mix polyurethane modified flexible epoxy resin, saturated polyester resin solution, polyvinyl butyral thickening resin solution, thixotropic agent, isocyanate curing agent and first solvent, heat to 60-80℃, and then stir and disperse at a stirring rate of 600-1200 rpm for 20-40 minutes to obtain organic carrier. In step S2, the mass ratio of the polyurethane modified flexible epoxy resin, saturated polyester resin solution, polyvinyl butyral thickening resin solution, thixotropic agent, isocyanate curing agent and first solvent is 8-15:5-30:10-20:1-6:1-4:30-55. Step S3: After adding the second solvent and coupling agent to the container, stir and disperse at a speed of 400-800 rpm for 10-20 minutes. Then add the mixture of silver powder and nano-zirconia powder. Stir and disperse at a speed of 1000-1200 rpm for 1-2 hours at a water bath temperature of 80-85℃. Then seal the container and grind it on a rod mill for 20-28 hours. Then add it to the organic carrier and disperse it at a speed of 800-1600 rpm for 50-70 minutes to form a coarse slurry. In step S3, the mass ratio of the silver powder, nano-zirconia powder and organic carrier is 43-51:1-3:47-55; The mass of the second solvent is 0.15 to 0.25 times the sum of the masses of the silver powder and the zirconium oxide powder; The mass of the coupling agent is 0.01 to 0.03 times the sum of the masses of the silver powder and the zirconium oxide powder; In step S3, the silver powder includes flake silver powder and nanoscale silver powder; Step S4: Using a three-roll mill, the coarse slurry is ground multiple times, and then vacuum degassed under stirring at a speed of 400-600 rpm to obtain fine silver paste with a fineness of less than 5 μm.

2. The preparation method according to claim 1, characterized in that, In step S1, the saturated polyester resin is one or more of ES100, ES110, ES120, ES160, ES210, ES215, ES240, ES300, ES320, ES350, ES360, ES410, ES420, ES450, ES500, ES510, and ES850. The polyvinyl butyral thickening resin is any one of B-76, B-08HX, B-14HX, SD-5, and SD-6. In steps S1 and S2, the first solvent is one or more of the following: high-boiling-point composite ester DBE, mixed dicarboxylic acid dimethyl ester, EGDA, diethyl succinate, dimethyl adipate, diethyl adipate, and isoflurone. In step S3, the second solvent is one or more of methyl formate, ethyl formate, propyl formate, isopropyl formate, butyl formate, isobutyl formate, isoamyl formate, benzyl formate, methyl acetate, sec-butyl acetate, EEP, PGDA, PGA, YDBE, propylene glycol methyl ether acetate, propylene glycol methyl ether, propylene glycol butyl ether, ethylene glycol butyl ether, and ethylene glycol ethyl ether.

3. The preparation method according to claim 2, characterized in that, In step S2, the polyurethane modified flexible epoxy resin is one or more of DER791, EPU-105, EPU-133L, EPU-300S, ERS-005, NPER-133L, SL3411, SL3412, and SL3413. The thixotropic agent is one of 6900-20X, AKN-7010, BYK-410, Anjeka4410, and Rheotech 2800.

4. The preparation method according to claim 3, characterized in that, In step S3, the mass ratio of flake silver powder to nano-sized silver powder in the silver powder is 90-99:1-10.

5. The preparation method according to claim 4, characterized in that, In step S3, the mass ratio of flake silver powder to nano-sized silver powder in the silver powder is 93-97:3-7.

6. The preparation method according to claim 5, characterized in that, In step S3, the average particle size of the flake-shaped silver powder is 1.2–1.5 μm, and the specific surface area is 1.2–1.8 cm². 2 / g, D100 < 5μm; The nanoscale silver powder has an average particle size of 100–200 nm and a specific surface area of ​​6.0–8.0 cm². 2 / g.

7. The preparation method according to claim 6, characterized in that, In step S3, the coupling agent is one or more of ZJ-316, ZJ-201, KR-38S, CT-114, NDZ-204, and LD-1070A.

8. The preparation method according to claim 7, characterized in that, In step S4, the vacuum degree of the vacuum degassing is 0.6-0.8 MPa, the temperature is 20-30°C, and the time is 40-50 minutes.

9. A flexible circuit fine-line silver paste, characterized in that, The flexible line fine-line silver paste is prepared using the preparation method described in any one of claims 1 to 8.

10. The flexible line fine-line silver paste according to claim 9, characterized in that, The flexible circuit fine line silver paste has a thixotropic index >4, a silver content of 43-51%, a sheet resistance of 14.6-15.6 mΩ / □, an adhesion of 5B, a hardness of 5H, and a viscosity of 60-80 Pa·s.