Silver paste printing process with line width and line distance of 175 microns

Abstract

The invention discloses a 175-micron line width and line distance silver paste printing process, which can stably realize the 175-micron line width and line distance and the error of less than or equal to 5 microns through screen printing plate opening reserved shrinkage amount and scraper parameter optimization, and meets the requirements of high-precision electronic components. The substrate plasma pretreatment and the silver paste leveling agent addition solve the problems of line breakage and burrs of narrow line width printing, and the circuit qualification rate is greater than or equal to 95%; the process is modified based on existing screen printing equipment (only the parameters of a screen printing plate and a scraper need to be adjusted), brand new equipment investment is not needed, cost is controllable, and industrial mass production is easy.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flexible circuit board, in particular to a 175-micron line width and line spacing silver paste printing process. BACKGROUND

[0002] Currently, the line width and line spacing of silver paste printing is commonly 200-500 microns. For high-precision electronic components (such as micro-FPC and high-density solar cell grid lines), the line width and line spacing need to be further reduced to improve the component integration and reduce energy consumption.

[0003] If the line width and line spacing are directly compressed to 175 microns in the prior art, two major problems will occur: 1. Printing quality problem: the silver paste is prone to "line breakage" and "edge burr" (due to uneven adhesion of the squeegee to the substrate caused by too narrow line width); 2. Performance defects: too narrow line spacing easily leads to "short circuit" of adjacent lines (silver paste overflow after solidification), or too narrow line width leads to reduced conductivity (insufficient silver paste thickness).

[0004] In view of the defects that the prior art cannot stably realize 175-micron line width and line spacing silver paste printing, the present application provides a technical solution that takes into account printing quality and conductivity. SUMMARY

[0005] To solve the above technical problems, the present application provides a 175-micron line width and line spacing silver paste printing process, comprising the following steps: S1, substrate pretreatment: selecting PET or PI substrate, removing surface dirt and impurities by plasma cleaning machine to ensure that the surface tension of the substrate is greater than or equal to 38 mN / m; S2, silver paste selection and modulation: selecting conductive silver paste prepared from spherical silver powder with a particle size of 2-5 microns, adding 0.5-1% of silicone leveling agent, adjusting the viscosity of the silver paste to 15000-20000 cP to ensure the balance of the flowability and formability of the silver paste; S3, preparation of screen printing plate: using a composite steel screen, the screen printing plate is made by a photosensitive adhesive plate making method, the opening size of the screen printing plate corresponding to the line is 155-160 microns, and the tension of the screen printing plate is controlled at 28-32 N / cm; S4, printing parameter setting: using a squeegee type screen printing machine, the squeegee angle is 0-15°, the printing speed is 80-100 mm / s, and the printing pressure is 0.4-0.7 MPa to ensure that the silver paste uniformly fills the opening of the screen printing plate without overflow; S5, curing treatment: after printing, the solvent in the silver paste is removed by pre-baking, and then high-temperature curing is performed to fully sinter the silver powder, and the curing environment is protected by inert gas to avoid oxidation of silver.

[0006] In step S1, the power of the plasma cleaning machine is 300-400W, the processing time is 20-30s, and the surface tension of the substrate is ensured to be greater than or equal to 38mN / m to ensure the adhesion of the silver paste.

[0007] In step S3, the mesh number of the composite steel wire mesh is 400.

[0008] In step S4, the scraper material is polyurethane, and the hardness is 70-80 Shore A.

[0009] In step S5, the pre-baking temperature is 80-90℃, the pre-baking time is 3-5min, the high-temperature curing temperature is 120-130℃, the high-temperature curing time is 20-30min, and the inert gas is nitrogen.

[0010] Through the above technical solution, the present application has the following advantages: 1. Precision advantage: through the screen opening reserved shrinkage, scraper parameter optimization, 175μm line width line distance can be stably realized, the error is less than or equal to 5μm, and the demand of high-precision electronic components is met; 2. Quality advantage: substrate plasma pretreatment + silver paste leveling agent addition solves the problems of "broken line" and "burr" in narrow line width printing, and the line qualification rate is greater than or equal to 95%; 3. Practicality advantage: the process is based on the modification of existing silk screen printing equipment (only the screen and scraper parameters need to be adjusted), no new equipment investment is needed, the cost is controllable, and industrial mass production is easy. DETAILED DESCRIPTION

[0011] The technical solutions in the embodiments of the present application will be described clearly and completely below.

[0012] The present application provides a 175μm line width line distance silver paste printing process, which comprises the following steps: S1, substrate pretreatment: selecting PET or PI substrate, removing surface dirt and impurities by plasma cleaning machine, and ensuring that the surface tension of the substrate is greater than or equal to 38mN / m; wherein the power of the plasma cleaning machine is 300-400W, the processing time is 20-30s, and the surface tension of the substrate is ensured to be greater than or equal to 38mN / m to ensure the adhesion of the silver paste; S2, silver paste selection and modulation: selecting conductive silver paste prepared from spherical silver powder with a particle size of 2-5μm, adding 0.5-1% of silicone leveling agent, adjusting the viscosity of the silver paste to 15000-20000cP to ensure the balance of silver paste fluidity and formability; S3, screen preparation: using a composite steel wire mesh with a mesh number of 400, making a screen by a photosensitive adhesive plate making method, the opening size corresponding to the line on the screen is 155-160μm, and the screen tension is controlled to be 28-32N / cm; S4, printing parameter setting: using a doctor blade screen printing machine, the doctor blade material is polyurethane, the hardness is 70-80 Shore A, the doctor blade angle is 0-15°, the printing speed is 80-100 mm / s, the printing pressure is 0.4-0.7 MPa, and it is ensured that the silver paste uniformly fills the screen printing plate opening and does not overflow; S5, curing treatment: after printing, pre-baking is performed to remove the solvent in the silver paste, and high-temperature curing is performed to fully sinter the silver powder, and the curing environment is inert gas protection to avoid silver oxidation; wherein the pre-baking temperature is 80-90°C, the pre-baking time is 3-5 min; the high-temperature curing temperature is 120-130°C, the high-temperature curing time is 20-30 min, and the inert gas is nitrogen. Embodiment

[0013] 1. Substrate: PI film with a thickness of 50 μm, plasma cleaning parameters: power 350 W, time 25 s, surface tension up to 40 mN / m; 2. Silver paste: silver powder particle size 3 μm, adding 0.8% leveling agent type BYK-333, the actual viscosity is 18000 cP (25°C, measured by rotary viscometer); 3. Screen printing plate: 400 mesh composite steel wire mesh, opening size 182 μm, tension 30 N / cm; 4. Printing: doctor blade angle 12°, speed 80 mm / s, pressure 0.5 MPa; 5. Curing: 120°C nitrogen environment curing for 30 min; 6. Results: the obtained silver paste line width is 171 μm, the line spacing is 175 μm, there is no broken line and burr, and the resistivity is 2.3 x 10⁻ 8 Ω•m, meeting the FPC conductive requirements.

[0014] The above description of disclosed embodiments enables a person skilled in the art to implement or use the present application. Various modifications to the above-described embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A silver paste printing process with a linewidth and spacing of 175μm, characterized in that, Includes the following steps: S1. Substrate pretreatment: Select PET or PI substrate, remove surface oil and impurities by plasma cleaning machine, and ensure that the surface tension of the substrate is ≥38mN / m. S2. Silver paste selection and preparation: Select conductive silver paste prepared from spherical silver powder with a particle size of 2-5μm, add 0.5-1% of organosilicon leveling agent, and adjust the viscosity of the silver paste to 15000-20000cP to ensure a balance between the fluidity and formability of the silver paste. S3. Screen preparation: A composite steel wire mesh is used to make the screen using the photosensitive emulsion method. The opening size of the corresponding lines on the screen is 155-160μm, and the screen tension is controlled at 28-32N / cm. S4. Printing parameter settings: Use a squeegee screen printing machine with a squeegee angle of 0-15°, a printing speed of 80-100mm / s, and a printing pressure of 0.4-0.7MPa to ensure that the silver paste fills the screen opening evenly without overflowing. S5. Curing treatment: After printing, the solvent in the silver paste is removed by pre-baking, and then cured at high temperature to fully sinter the silver powder. The curing environment is protected by inert gas to avoid silver oxidation.

2. The printing process according to claim 1, characterized in that, In step S1, the plasma cleaner has a power of 300-400W and a processing time of 20-30s, ensuring that the surface tension of the substrate is ≥38mN / m to ensure the adhesion of the silver paste.

3. The printing process according to claim 1, characterized in that, In step S3, the mesh count of the composite wire mesh is 400.

4. The printing process according to claim 1, characterized in that, In step S4, the scraper is made of polyurethane with a hardness of 70-80 Shore A.

5. The printing process according to claim 1, characterized in that, In step S5, the pre-baking temperature is 80-90℃ and the pre-baking time is 3-5 min; the high-temperature curing temperature is 120-130℃ and the high-temperature curing time is 20-30 min; the inert gas is nitrogen.