Composite printing screen plate based on double-layer polyimide film

Abstract

The invention relates to the technical field of precision printing, and discloses a composite screen printing plate based on a double-layer polyimide film, which comprises a precision printing layer, a printing layer, a printing layer and a printing layer, the supporting ink penetrating layer is composed of a second polyimide film and is compounded with the precise printing layer through a middle bonding layer; and the composite reinforced substrate layer is polymer screen cloth and is fixedly connected with the back surface of the supporting ink-permeable layer through a hot melt adhesive layer. According to the invention, the expensive stainless steel wire mesh or steel sheet is replaced by the cheap polyester mesh and the high-molecular adhesive; the material cost is reduced, the preparation process is simplified, and the manufacturing cost and the energy consumption are further reduced; the whole screen functional structure is composed of the polyimide film and the polymer glue layer, and the thermal expansion coefficients of all layers of materials are similar, so that the inherent thermal mismatch problem of a traditional metal-PI composite structure is solved; under the environment of temperature change, all the layers cooperatively deform, and pattern micro-deformation and alignment deviation caused by internal stress are effectively eliminated.

Description

Technical Field

[0001] This invention relates to the field of precision printing technology, specifically a composite printing screen based on a double-layer polyimide film. Background Technology

[0002] Screen printing stencils are key tools in thick-film printing technology, widely used in high-precision manufacturing fields such as electronic packaging, printed circuit board (PCB) manufacturing, photovoltaic cell metallization, flexible electronics, and display panels. Their core function is to precisely deposit functional pastes such as solder paste, conductive silver paste, and insulating paste onto designated locations on the substrate through a preset graphic window. Currently, the mainstream high-precision screen printing stencils in the industry are mainly divided into the following three categories: 1. Emulsion-coated stainless steel wire mesh: A photosensitive emulsion is coated onto a stainless steel wire mesh, and patterns are formed through exposure and development. This type of screen is relatively inexpensive, but the wear resistance of the emulsion layer and the precision of the pattern are limited, and it is usually used in applications where high precision is not required.

[0003] 2. PI (Polyimide) film-stainless steel wire mesh composite plate: A layer of PI film is laminated onto a stainless steel wire mesh, and the pattern is cut out on the PI film by laser. The PI film provides a smooth printing surface and excellent solvent resistance, making it the mainstream choice for high-precision SMT solder paste printing.

[0004] 3. Pure stainless steel sheet screen printing: Patterns are directly formed by chemical etching or laser cutting of thin stainless steel foil. Its pattern precision and stability are extremely high, and it is mainly used in top-tier applications such as semiconductor packaging and ultra-fine circuit printing.

[0005] However, all the above technical solutions share a common and insurmountable core dependency: the necessity of using stainless steel (wire mesh or steel sheet) as the mechanical support framework. This fundamental structural feature leads to a series of significant drawbacks: High cost: High-precision, low-ductility special stainless steel wire mesh or ultra-thin steel sheet materials are expensive, and their processing (such as precision weaving, electroforming, etching) is itself a high-cost process, resulting in the high price of the final screen product, which becomes an important consumable cost burden in the manufacturing process.

[0006] The processes are complex and pose significant environmental challenges: whether it's the stretching and tension control of the wire mesh, or the electroforming (involving electroplating solutions) or etching (using strong acids and alkalis) of the steel sheets, the processes are quite cumbersome and have high requirements for the production environment. In particular, chemical etching / electroforming processes generate large amounts of waste acid and alkali solutions containing heavy metal ions, which are difficult and costly to treat and are environmentally unfriendly.

[0007] Thermophysical property mismatch affects long-term stability: The coefficient of thermal expansion of stainless steel (approximately 17 ppm / ℃) differs significantly from that of polymer PI film (approximately 30–50 ppm / ℃). During the printing process, frictional heat or ambient temperature fluctuations cause internal stress due to the different degrees of expansion / contraction between the metal and polymer layers. Under long-term effects, this can easily lead to micro-peeling at the interface between the PI film and the metal substrate or micro-deformation of the pattern, affecting the long-term stability of printing alignment accuracy (Cp value). This is particularly detrimental to industrial applications requiring continuous production of hundreds of thousands of cycles. Summary of the Invention

[0008] The purpose of this invention is to provide a composite printing screen based on a double-layer polyimide film to solve the problems mentioned in the background art.

[0009] To achieve the above objectives, the present invention provides the following technical solution: A composite printing screen based on a double-layer polyimide film, comprising, from the printing contact surface to the carrier surface, the following components in sequence: The precision printing layer is composed of a first polyimide film on which a precision pattern is provided; The supporting ink-permeable layer is composed of a second polyimide film and is bonded to the precision printing layer through an intermediate adhesive layer. The supporting ink-permeable layer has through-hole ventilation holes and ink-permeable grooves that are centered and aligned with the precision pattern. The line width of the ink-permeable grooves is greater than the line width of the precision pattern. The difference between the line width of the ink-permeable grooves and the line width of the precision pattern forms an ink buffer channel. The composite reinforcing base layer is a polymer mesh fabric, which is bonded to the back of the supporting ink-permeable layer by a hot melt adhesive layer; wherein, part of the hot melt adhesive layer is embedded in the vent holes on the supporting ink-permeable layer to form a mechanical interlocking structure, so as to bond the supporting ink-permeable layer and the composite reinforcing base layer together.

[0010] As a further aspect of the present invention, the thickness of the first polyimide film and the second polyimide film are independently 5 to 50 μm.

[0011] As a further embodiment of the present invention: the intermediate adhesive layer is a pressure-sensitive adhesive layer.

[0012] As a further aspect of the present invention, the line width of the ink-permeable groove is 50 to 200 μm larger than the line width of the precision pattern.

[0013] As a further embodiment of the present invention, the polymer mesh is a polyester mesh.

[0014] As a further aspect of the present invention, the diameter of the vent hole is 100-300 μm.

[0015] A method for preparing a composite printing screen based on a double-layer polyimide film includes the following steps: S1. Base film fixing and initial processing: The second polyimide film of selected thickness is flatly attached to a rigid plate (such as thick glass). Air vents and ink-permeable grooves are processed on the second polyimide film using a laser to obtain a supporting ink-permeable layer; wherein, there are no less than 2 rows of air vents. S2, Initial lamination: The supporting ink-permeable layer is placed together with the rigid plate, and the polymer mesh is placed in the center. The polymer mesh is then hot-pressed with hot melt adhesive, allowing the hot melt adhesive to flow into the vent holes. S3, Secondary Composite and Sealing: On the side of the ink-permeable layer that supports the ink-permeable layer and has ink-permeable grooves, a first polyimide film is hot-pressed with pressure-sensitive adhesive and covered with ink-permeable grooves. S4. Precision pattern processing: The final precision pattern is processed on the first polyimide film using a laser, and the precision pattern is located in the central area of ​​the ink-transparent groove.

[0016] As a further aspect of the present invention: in step S2, the hot-pressing temperature is higher than the melting point of the hot melt adhesive; in step S3, the hot-pressing temperature is lower than the melting point of the hot melt adhesive and the glass transition temperature of the first polyimide film.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention replaces expensive stainless steel wire mesh or steel sheets with inexpensive polyester mesh and polymer adhesive; while reducing material costs, the manufacturing process is simplified, eliminating expensive and complex processes such as mesh stretching, electroforming, and etching, further reducing manufacturing costs and energy consumption. Since the entire screen printing structure is composed of polyimide film and polymer adhesive layer, the thermal expansion coefficients of each layer are similar, overcoming the inherent thermal mismatch problem of traditional metal-PI composite structure; under temperature change environment, each layer deforms synergistically, effectively eliminating the micro-deformation and alignment misalignment of the pattern caused by internal stress. By designing a wide-narrow composite opening structure where the lower support ink-permeable layer has a line width greater than that of the upper precision printing layer, the area between the two forms a natural ink buffer and guiding channel. This structure can effectively store ink and promote the reflow of ink during the printing process, greatly reducing the risk of screen clogging caused by ink particle blockage or surface drying. Detailed Implementation Example

[0018] In this embodiment of the invention, a composite printing screen based on a double-layer polyimide film comprises, from the printing contact surface to the bearing surface, the following components in sequence: The precision printing layer consists of a 12μm thick first polyimide film with a precision pattern of 50μm linewidth; the thicknesses of the first and second polyimide films are independently 5 to 50μm. The supporting ink-permeable layer is composed of a 25μm thick second polyimide film, which is laminated with the precision printing layer through an acrylic pressure-sensitive adhesive layer; wherein, the supporting ink-permeable layer has through-vent holes with a diameter of 200μm and ink-permeable grooves with a line width of 150μm that are centered and aligned with the precision pattern. The composite reinforced base layer is a 300-mesh polyester mesh, which is bonded to the back of the supporting ink-permeable layer through a polyamide hot melt adhesive layer.

[0019] A method for preparing a composite printing screen based on a double-layer polyimide film includes the following steps: S1. Base film fixation and initial processing: A 25μm thick second polyimide film is flatly attached to a thick glass. An array of 200μm diameter air vents and 150μm line width ink-permeable grooves are processed on the second polyimide film using an ultraviolet laser. S2, Initial Composite: The supporting ink-permeable layer is placed together with the thick glass, and the polymer mesh is placed in the center. The polyamide hot melt adhesive is then hot-pressed at 180°C and 0.5MPa for 10 seconds, allowing the polyamide hot melt adhesive to flow into the vent holes. S3, Secondary Composite and Sealing: On the side of the ink-permeable layer that supports the ink-permeable layer and has ink-permeable grooves, the first polyimide film is composited by hot pressing with acrylate pressure-sensitive adhesive at 100°C and 0.2MPa for 5 seconds, and the ink-permeable grooves are covered. S4. Precision pattern processing: A laser is used to process a precision pattern with a line width of 50μm on a 12μm thick first polyimide film. Example

[0020] In this embodiment of the invention, a composite printing screen based on a double-layer polyimide film comprises, from the printing contact surface to the bearing surface, the following components in sequence: The precision printing layer consists of a 10μm thick first polyimide film with a precision pattern of 30μm linewidth; the thickness of the first polyimide film and the second polyimide film are independently 5 to 50μm. The supporting ink-permeable layer is composed of a 30μm thick second polyimide film, which is laminated with the precision printing layer through an acrylic pressure-sensitive adhesive layer; wherein, the supporting ink-permeable layer has through-vent holes with a diameter of 150μm and ink-permeable grooves with a line width of 80μm that are centered and aligned with the precision pattern. The composite reinforced base layer is a 300-mesh polyester mesh, which is bonded to the back of the supporting ink-permeable layer through a polyamide hot melt adhesive layer.

[0021] A method for preparing a composite printing screen based on a double-layer polyimide film includes the following steps: S1. Base film fixation and initial processing: A 25μm thick second polyimide film is flatly attached to a thick glass. An array of 200μm diameter air vents and 150μm line width ink-permeable grooves are processed on the second polyimide film using an ultraviolet laser. S2, Initial Composite: The supporting ink-permeable layer is placed together with the thick glass, and the polymer mesh is placed in the center. The polymer mesh is then hot-pressed for 8 seconds at 170°C and 0.6MPa using polyamide hot melt adhesive, allowing the polyamide hot melt adhesive to flow into the vent holes. S3, Secondary Composite and Sealing: On the side of the ink-permeable layer that supports the ink-permeable layer and has ink-permeable grooves, the first polyimide film is composited by hot pressing with acrylate pressure-sensitive adhesive at 90°C and 0.15MPa for 6 seconds, and the ink-permeable grooves are covered. S4. Precision pattern processing: A laser is used to process a precision pattern with a line width of 50μm on a 12μm thick first polyimide film.

[0022] To better illustrate the technical effects of the present invention, the following experiments are conducted: A method for manufacturing a stainless steel wire mesh using a shielding method, disclosed in patent CN111070856A, is used as a comparative example. The comparative example uses a traditional stainless steel wire mesh. Example 1: Preparation of a composite screen printing stencil for PCB solder paste printing; Example 2: Preparation of a composite screen printing stencil for fine grid lines in photovoltaic cells; The screen printing plates prepared in Examples 1, 2 and the comparative examples were analyzed from the aspects of material cost, pattern accuracy and stability, ink permeability and anti-clogging mesh, structural durability, process environmental protection and applicable scenarios, as shown in Table 1 below.

[0023] Table 1. Web Version Performance Analysis Table

[0024] Through the above two cross-domain implementation examples and their direct data comparison with traditional technologies, it can be clearly confirmed that: (1) Performance reliability: In the two high-end manufacturing fields of PCB and photovoltaic, which have very different printing requirements, the present invention has achieved a comprehensive improvement or significant optimization of key performance indicators (accuracy, stability, ink penetration).

[0025] (2) Economic efficiency: More than 40% material cost savings have been achieved in both areas, which means huge economic benefits for the manufacturing industry that needs to use screen printing plates on a large scale and at high frequency.

[0026] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A composite printing screen based on a double-layer polyimide film, characterized in that, From the printed contact surface to the bearing surface, the following are included in sequence: The precision printing layer is composed of a first polyimide film on which a precision pattern is provided; The supporting ink-permeable layer is composed of a second polyimide film and is bonded to the precision printing layer through an intermediate adhesive layer. The supporting ink-permeable layer has through-hole ventilation holes and ink-permeable grooves that are centered and aligned with the precision pattern. The line width of the ink-permeable grooves is greater than the line width of the precision pattern. The difference between the line width of the ink-permeable grooves and the line width of the precision pattern forms an ink buffer channel. The composite reinforcing base layer is a polymer mesh fabric, which is bonded to the back of the supporting ink-permeable layer by a hot melt adhesive layer; wherein, part of the hot melt adhesive layer is embedded in the vent holes on the supporting ink-permeable layer to form a mechanical interlocking structure, so as to bond the supporting ink-permeable layer and the composite reinforcing base layer together.

2. The composite printing screen based on a double-layer polyimide film according to claim 1, characterized in that, The thicknesses of the first polyimide film and the second polyimide film are independently 5–50 μm.

3. The composite printing screen based on a double-layer polyimide film according to claim 1, characterized in that, The intermediate adhesive layer is a pressure-sensitive adhesive layer.

4. A composite printing screen based on a double-layer polyimide film according to claim 1, characterized in that, The line width of the ink-permeable groove is 50-200 μm larger than that of the precision pattern.

5. A composite printing screen based on a double-layer polyimide film according to claim 1, characterized in that, The polymer mesh is a polyester mesh.

6. A composite printing screen based on a double-layer polyimide film according to claim 1, characterized in that, The diameter of the vent is 100–300 μm.

7. A method for preparing a composite printing screen based on a double-layer polyimide film as described in any one of claims 1 to 6, characterized in that, Includes the following steps: S1. Base film fixation and initial processing: The second polyimide film of selected thickness is flatly attached to a rigid plate. Air vents and ink-permeable grooves are processed on the second polyimide film using a laser to obtain a supporting ink-permeable layer. S2, Initial lamination: The supporting ink-permeable layer is placed together with the rigid plate, and the polymer mesh is placed in the center. The polymer mesh is then hot-pressed with hot melt adhesive, allowing the hot melt adhesive to flow into the vent holes. S3, Secondary Composite and Sealing: On the side of the ink-permeable layer that supports the ink-permeable layer and has ink-permeable grooves, a first polyimide film is hot-pressed with pressure-sensitive adhesive and covered with ink-permeable grooves. S4. Precision pattern processing: The final precision pattern is processed on the first polyimide film using a laser, and the precision pattern is located in the central area of ​​the ink-transparent groove.

8. A composite printing screen based on a double-layer polyimide film according to claim 7, characterized in that, In step S2, the hot-pressing temperature is higher than the melting point of the hot melt adhesive; in step S3, the hot-pressing temperature is lower than the melting point of the hot melt adhesive and the glass transition temperature of the first polyimide film.

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