Single-sided flexible circuit board and method of manufacturing the same

Abstract

This invention discloses a single-sided flexible circuit board and its fabrication method. The fabrication method includes: obtaining a copper foil, a first cover film, and a second cover film, wherein the first cover film and the second cover film are of the same material and specifications; bonding the first cover film to the matte side of the copper foil and pressing it together; forming a predetermined target circuit on the copper foil to obtain a first product intermediate with a circuit layer; bonding the second cover film to the surface of the circuit layer away from the first cover film and pressing it together to obtain a second product intermediate; and baking and curing the second product intermediate to obtain a single-sided flexible circuit board. This invention uses a first cover film and a second cover film of the same material and specifications bonded to the front and back sides of the circuit layer, forming a symmetrical structural design. During baking and curing, the expansion and contraction deformation of the first and second cover films of the same material and specifications will remain consistent, thereby reducing warping.

Description

Technical Field

[0001] This invention relates to the field of circuit board technology, and in particular to a single-sided flexible circuit board and its preparation method. Background Technology

[0002] Single-sided flexible printed circuit boards (FPCs) are widely used for electrical connections between display modules and glass screens due to their advantages such as simple structure, low cost, and good flexibility. During the assembly of FPCs, the significant differences in the thermal expansion coefficients of the materials in the laminated structure lead to inconsistent shrinkage rates among the layers after high-temperature assembly and subsequent cooling to room temperature. This results in internal stress that cannot be offset, making the FPC prone to warping on one side. Consequently, during the precise assembly of the gold fingers, misalignment between the gold fingers and the glass screen pads can occur, leading to functional defects. Summary of the Invention

[0003] This invention provides a single-sided flexible circuit board and its manufacturing method to solve the problem of warping of single-sided flexible circuit boards.

[0004] In a first aspect, the present invention provides a method for fabricating a single-sided flexible circuit board. The fabrication method includes: Obtain copper foil, a first cover film, and a second cover film, wherein the first cover film and the second cover film are made of the same material and have the same specifications; The first cover film is adhered to the matte surface of the copper foil and pressed together; A predetermined target circuit is formed on the copper foil to obtain a first product intermediate with a circuit layer; The second cover film is adhered to the surface of the circuit layer away from the first cover film and then pressed together to obtain the second product intermediate. The second product intermediate is baked and cured to obtain a single-sided flexible circuit board.

[0005] In one implementation of the first aspect, a predetermined target circuit is formed on the copper foil to obtain a first product intermediate having a circuit layer, comprising: Photoresist is applied to the smooth surface of the copper foil, and the copper foil with photoresist applied is exposed according to the preset target line. The exposed product is developed to retain the photoresist at the pad and circuit area locations, thereby obtaining the third product intermediate. The third product intermediate is sequentially etched and stripped to form a first product intermediate with a circuit layer.

[0006] In one implementation of the first aspect, the copper foil coated with photoresist is exposed according to a preset target line, including: A pre-defined target line film is applied to the photoresist surface on the copper foil, and then exposed to ultraviolet light to transfer the target line onto the photoresist.

[0007] In one implementation of the first aspect, the first cover film is adhered to the matte surface of the copper foil and pressed together, comprising: The first cover film is applied to the matte surface using a laminating machine according to preset laminating parameters, wherein the laminating parameters are: laminating roller temperature of 120±8℃, laminating pressure of 6±0.5kg / cm², laminating speed of 1.2±0.2m / min, feeding tension of 0.8±0.2kg / cm, and roll tension of 1.0±0.2kg / cm. The first cover film and the copper foil are pressed together using a pressing machine according to preset pressing parameters, wherein the pressing parameters are: temperature 180±5℃, pressure 110±5kg / cm², and time 120±5s.

[0008] In one implementation of the first aspect, the second product intermediate is baked and cured to obtain a single-sided flexible circuit board, comprising: The second product intermediate is placed in an oven and baked at 155°C for 90 minutes to complete the curing of the first and second cover films.

[0009] In one implementation of the first aspect, the second cover film is adhered to and pressed onto the surface of the circuit layer away from the first cover film to obtain a second product intermediate, comprising: After the second cover film is pressed, a laser windowing operation is performed on the second cover film to obtain a windowed area, thereby exposing the pads on the circuit layer that need to be electrically connected through the windowed area; Carbon black cleaning is performed on the windowed area to remove residual adhesive from the copper surface of the circuit layer. The surface adhesive of the solder pads is removed by sandblasting to obtain the second product intermediate.

[0010] In one implementation of the first aspect, bonding and pressing the second cover film onto the surface of the circuit layer away from the first cover film includes: The second cover film is attached to the circuit layer using the same bonding parameters as those used in the first cover film bonding process; The second cover film is bonded to the circuit layer using the same bonding parameters as the first cover film bonding process.

[0011] In one implementation of the first aspect, bonding and pressing the second cover film onto the surface of the circuit layer away from the first cover film includes: The copper surface of the circuit layer in the first product intermediate is cleaned to remove surface contamination and oxide layer; The copper surface is roughened so that the second cover film can be attached to the roughened copper surface and pressed together.

[0012] In one implementation of the first aspect, the preparation method further includes: The first product intermediate is subjected to open and short circuit testing to determine whether there are defective products in the first product intermediate. If any defective products are found, they shall be marked accordingly.

[0013] Secondly, the present invention provides a single-sided flexible circuit board. The single-sided flexible circuit board includes a first cover film, a circuit layer, and a second cover film stacked sequentially from bottom to top, wherein the second cover film has a window area.

[0014] The beneficial effects of this invention are as follows: For single-sided flexible circuit boards, a copper foil-based circuit layer is used as the intermediate layer, and a first and second cover film of the same material and specifications are respectively pasted on its front and back as protective layers, forming a symmetrical structural design. Based on this, during baking and curing, the expansion and contraction deformation of the first and second cover films of the same material and specifications will be consistent, thereby reducing the occurrence of warping. Attached Figure Description

[0015] Figure 1 This is a flowchart illustrating the steps of a method for fabricating a single-sided flexible circuit board according to an embodiment of the present disclosure.

[0016] Figure 2 This is a schematic cross-sectional view of a single-sided flexible circuit board according to an embodiment of the present disclosure.

[0017] Label Explanation: 1. First covering film; 2. Line layer; 21. Line spacing; 3. Second covering film; 31. Window opening area. Detailed Implementation

[0018] To explain in detail the technical content, objectives, and effects of the present invention, the following description is provided in conjunction with the embodiments and accompanying drawings.

[0019] During the assembly process, single-sided flexible printed circuit boards (FPCs) are prone to curling due to the mismatch of deformation stress in the materials of each layer. This can lead to misalignment of the pads between the gold fingers and the glass screen during the fine assembly of the gold fingers, resulting in functional defects.

[0020] To address at least the aforementioned technical problems, this invention provides a method for fabricating a single-sided flexible circuit board. In this invention, for the single-sided flexible circuit board, a copper foil-based circuit layer 2 is used as the intermediate layer, and a first cover film 1 and a second cover film 3 of the same material and specifications are respectively adhered to its front and back as protective layers, forming a symmetrical structural design. Based on this, during baking and curing, the expansion and contraction deformation of the first cover film 1 and the second cover film 3 of the same material and specifications will remain consistent, thereby reducing the occurrence of warping.

[0021] On the other hand, since processes such as lamination, pressing, and baking / curing affect the expansion and contraction deformation of materials, this invention sets the process parameters involved in the lamination and pressing of the first cover film 1 and the second cover film 3 to be equal, avoiding problems such as asymmetric expansion and contraction of materials caused by differences in production parameters, further improving product dimensional stability and reducing the probability of warping. For the baking process, this invention achieves simultaneous baking and curing of both the first cover film 1 and the second cover film 3 through the same baking and curing process, reducing the probability of warping. Specifically: when manufacturing multi-layer cover films, if the first cover film undergoes complete high-temperature curing first, the product will deform due to heat shrinkage. If the second cover film is then laminated, the inconsistent shrinkage states of the two layers will cause internal stress mismatch, ultimately leading to product warping. This invention simplifies the two high-temperature curing processes of the two cover films into a single high-temperature curing process, achieving simultaneous curing in the same environment, making the shrinkage states of the two cover films as consistent / equivalent as possible, thereby effectively reducing warping problems and improving the overall process stability and product yield.

[0022] In the following, the technical solutions according to this disclosure will be described with reference to specific embodiments and in conjunction with the accompanying drawings.

[0023] Figure 1 This is a flowchart illustrating a method for fabricating a single-sided flexible circuit board according to an embodiment of the present disclosure. (Refer to...) Figure 1 The preparation method includes steps 100 to 108.

[0024] Step 100: Obtain copper foil, first cover film 1 and second cover film 3, wherein the first cover film 1 and the second cover film 3 are made of the same material.

[0025] The material specifications refer to a comprehensive description of the material's type, attributes, and technical parameters. This includes both material composition and specifications. Material composition refers to the material's physical composition, while specifications are specific limitations on quantitative indicators such as size, thickness, and performance grade. When the first cover film 1 and the second cover film 3 have the same material specifications, it means that they must be completely consistent in terms of component types and all key parameters (such as size, thickness, and performance indicators). It should be noted that the material specifications of the first cover film 1 and the second cover film 3 can be selected based on actual circumstances and are not limited here.

[0026] In practical applications, the first covering film 1 and the second covering film 3 can be made of polyimide, and the roll length of both is the same as the roll length of the copper foil.

[0027] Step 102: The first covering film 1 is adhered to the matte surface of the copper foil and pressed together.

[0028] The matte (also called rough) side of the copper foil is the free-growing surface away from the cathode roller, exhibiting a matte texture. The glossy (also called bright) side is the mirror-like surface formed during the production process through contact with the smooth cathode roller, with a smooth and bright surface. In FPC manufacturing, the matte side is used to laminate with the first cover film 1, which serves as the substrate. Its rough structure enhances the anchoring force with the adhesive layer and prevents delamination. The glossy side is used for circuit formation or as exposed pads to meet the needs of subsequent mounting and electrical connections. It should be noted that the process of laminating the first cover film 1 onto the matte copper foil is a false lamination stage. Because the adhesive of the second cover film 3 is not completely cured and shaped at high temperature during the lamination process, it will not warp.

[0029] In some embodiments, the first cover film 1 is adhered to the matte surface of the copper foil and then pressed, comprising: adhering the first cover film 1 to the matte surface using a laminating machine according to preset laminating parameters, wherein the laminating parameters are: laminating roller temperature of 120±8℃, laminating pressure of 6±0.5kg / cm², laminating speed of 1.2±0.2m / min, feeding tension of 0.8±0.2kg / cm, and roll tension of 1.0±0.2kg / cm; the pressing parameters are: temperature of 180±5℃, pressure of 110±5kg / cm², and time of 120±5s. It should be noted that the above pressing parameters need to match the thickness of the first cover film 1 to ensure the pressing effect. Furthermore, the above laminating and pressing parameters can be selected according to actual conditions and are not limited here.

[0030] As can be seen from the above description, by directly attaching the first cover film 1 to one side of the copper foil to make a single-sided substrate, there is no need to purchase a single-sided substrate separately, which shortens the production cycle and reduces material costs.

[0031] Step 104: A preset target circuit is formed on the copper foil to obtain a first product intermediate with circuit layer 2.

[0032] In some embodiments, forming a preset target line on the copper foil to obtain a first product intermediate having a line layer 2 includes: applying photoresist to the light surface of the copper foil and exposing the copper foil with photoresist applied according to the preset target line; developing the exposed product to retain the photoresist at the pad positions and the line area positions, thereby obtaining a third product intermediate; and sequentially etching and stripping the third product intermediate to form the first product intermediate having a line layer 2.

[0033] It should be noted that when bonding photoresist to the smooth surface of copper foil, a suitable photoresist needs to be selected. Specifically, the photoresist with the corresponding resolution and thickness can be selected according to the fineness of the target line. For example, if a fine target line with a width of 30 / 30μm is required, a photoresist with a thickness of 20μm should be selected; if a target line with a width of 50 / 50μm is required, a photoresist with a thickness of 25-30μm should be selected.

[0034] For example, a photoresist matching the product is used and applied to the exposed copper surface of the copper foil using an RTR laminator; then, according to the preset circuit pattern data, the photoresist surface is exposed to ensure precise pattern transfer; subsequently, a development process is performed to retain the photoresist in the pads and circuit areas, while completely removing the photoresist in other areas; finally, etching parameters are set according to the thickness of the pure copper foil, and the copper foil is etched on one side to form the circuit pattern required by the design, and the residual photoresist is removed after etching is completed.

[0035] As described above, by applying photoresist to the smooth surface of copper foil and then sequentially performing exposure, development, etching, and stripping processes, the target circuit pattern is precisely transferred onto the copper foil, ultimately forming a first product intermediate with circuit layer 2.

[0036] In some embodiments, exposing a copper foil coated with photoresist according to a preset target line includes: covering the photoresist surface on the copper foil with a preset target line film and exposing it with ultraviolet light to transfer the target line onto the photoresist.

[0037] As described above, ultraviolet light exposure precisely transfers the target circuit pattern from the target circuit film onto the photoresist, providing an accurate selective protective layer for subsequent development and etching, thereby ensuring that the circuit conforms to the design requirements is formed on the copper foil.

[0038] Step 106: The second cover film 3 is attached to the surface of the circuit layer 2 away from the first cover film 1 and pressed together to obtain the second product intermediate.

[0039] In some embodiments, attaching and pressing the second cover film 3 onto the surface of the circuit layer 2 away from the first cover film 1 includes: attaching the second cover film 3 onto the circuit layer 2 using the same bonding parameters as in the bonding process of the first cover film 1; and pressing using the same pressing parameters as in the pressing process of the first cover film 1, so that the second cover film 3 is bonded to the circuit layer 2.

[0040] As described above, using uniform process parameters to complete the bonding and pressing of the protective layer ensures consistent material expansion and contraction deformation, further alleviating the warping problem of single-sided FPC.

[0041] In some embodiments, the process of attaching and pressing the second cover film 3 onto the surface of the circuit layer 2 away from the first cover film 1 may further include: cleaning the copper surface of the circuit layer 2 in the first product intermediate to remove surface contamination and oxide layer; and roughening the copper surface to attach the second cover film 3 onto the roughened copper surface for pressing.

[0042] As can be seen from the above description, cleaning and roughening the copper surface enhances the adhesion when the second cover film 3 is subsequently applied to the copper surface.

[0043] In some embodiments, the second cover film 3 is adhered to and pressed onto the surface of the circuit layer 2 away from the first cover film 1 to obtain a second product intermediate, including: after pressing the second cover film 3, performing a laser windowing operation on the second cover film 3 to obtain a windowed area 31, thereby exposing the pads on the circuit layer 2 that need to be electrically connected through the windowed area 31; performing carbon black cleaning on the windowed area 31, while removing residual adhesive on the copper surface of the circuit layer 3; and removing the surface adhesive of the pads by sandblasting to obtain the second product intermediate.

[0044] As described above, laser windowing precisely exposes the pads that require electrical connection. Then, carbon black cleaning and sandblasting cleaning are used to remove adhesive residue and contaminants from the surface of the pads, resulting in a clean and residue-free pad surface, which provides a reliable guarantee for subsequent component assembly or electrical connection.

[0045] Step 108: Bake and cure the second product intermediate to obtain a single-sided flexible circuit board.

[0046] In some embodiments, the second product intermediate is baked and cured to obtain a single-sided flexible circuit board, including: placing the second product intermediate into an oven and baking it at a temperature of 155°C for 90 minutes to complete the curing of the first cover film 1 and the second cover film 3. It should be noted that the above baking conditions (such as baking temperature and baking time) can be selected according to actual conditions and are not limited here.

[0047] As can be seen from the above description, compared with two high-temperature curing processes, the present invention simplifies the two high-temperature curing processes of the two-layer cover film into a single high-temperature curing process, avoiding the product shrinkage caused by the first high temperature, which in turn causes warping due to mismatch in the deformation of the second cover film, thus improving process stability.

[0048] In some embodiments, the preparation method may further include: performing open / short circuit detection on the first product intermediate to determine whether there are defective products in the first product intermediate; if there are defective products, then distinguishing and marking the defective products. It should be noted that a non-erasable pen can be used to mark the defective products, and a hole can be punched at the marked position as a secondary confirmation mark; after this step is completed, the defective products will continue to flow normally on the production line and will not be rejected temporarily. After the molding process is completed and before final shipment, the defective products with the destruction mark will be picked out uniformly.

[0049] As described above, by performing open and short circuit detection on the first product intermediate that has formed the circuit layer 2, defective products with open or short circuit defects can be identified in a timely manner, and these defective products can be distinguished and marked, making it easier to pick them out from the final product and improving the reliability and yield of the final product.

[0050] According to another aspect of the present invention, this disclosure also provides a single-sided flexible circuit board. The single-sided flexible circuit board includes a first cover film 1, a circuit layer 2, and a second cover film 3 stacked sequentially from bottom to top, wherein the second cover film 3 is provided with a window area 31.

[0051] To make this application easier to understand, the following is combined with... Figure 2 An example application is provided.

[0052] In this exemplary application, this embodiment is based on Figure 2 The structural design uses 12μm pure copper foil as the substrate material to fabricate circuit layer 2, and selects cover films of the same specifications as the bottom cover film (i.e., the first cover film 1) and the top cover film (i.e., the second cover film 3). The specific fabrication steps are as follows: S1, Material preparation: Select an oxygen-free pure copper foil roll with a width of 250mm and a thickness of 12μm as the copper foil layer, and select a polyimide cover film with a width of 250mm and a length matching the oxygen-free pure copper foil roll as the first cover film 1. The thickness of the first cover film 1 can be 25μm. After checking that there are no scratches or stains on the surface of the roll, the material feeding is completed.

[0053] S2, Applying the first cover film 1: Start the RTR (Roll to Roll) laminator and set the corresponding lamination parameters to accurately apply the first cover film 1 to the matte surface of the copper foil layer. The lamination parameters can be as follows: lamination roller temperature 120℃, lamination pressure 6kg / cm², lamination speed 1.2m / min, feed tension 0.8kg / cm, and roll tension 1.0kg / cm, thereby ensuring a tight, bubble-free bond between the first cover film 1 and the copper foil.

[0054] S3, First RTR pressing: Based on the characteristics of the 25μm polyimide cover film, set the pressing parameters, which can be temperature 180℃, pressure 110kg / cm², and time 120s. Start the RTR press to complete the pressing, so that the first cover film 1 is firmly bonded to the copper foil layer.

[0055] S4, RTR photoresist bonding (dry film bonding): Photosensitive photoresist (dry film) is selected and uniformly bonded to the exposed smooth surface of the copper foil layer using an RTR bonding machine. The bonding temperature can be controlled at 95℃ to ensure that the photoresist is wrinkle-free and has no gaps.

[0056] S5, RTR Exposure: The preset target line film (including line spacing 21 and window area 31 design) is covered on the photoresist surface, and a UV exposure machine is used for exposure. The exposure energy can be set to level 5 according to the 21-level exposure scale to ensure clear pattern transfer.

[0057] S6, RTR Development: The exposed product is sent into the development tank, and a 1% sodium carbonate solution is used as the developer. The development temperature is 30℃, the development speed is 2.0m / min, and the development pressure is 1.4kg / cm2. After development, the photoresist in the pads and circuit areas is retained, while the photoresist in the remaining areas is completely removed, thus obtaining the third product intermediate.

[0058] S7, RTR Etching and Stripping: The third product intermediate is etched on one side using a copper chloride etching solution. The etching temperature can be 50℃, the etching speed 2.0 m / min, and the etching pressure 1.8 kg / cm². After etching, the designed circuit pattern is obtained (i.e., as shown in the image). Figure 2The circuit layer 2 shown includes the line spacing 21. After that, the film can be stripped, for example, by using a 5% sodium hydroxide solution to remove residual photoresist and then drying after cleaning. It should be noted that after etching, all exposed copper foil will be removed, and what remains is the protected circuit, and the gap between the circuits (i.e., the area that has been etched away) is the line spacing 21.

[0059] S8, RTR AOI Inspection: This step involves detecting open and short circuits in defective products. If defective products are found, they are marked. It should be noted that a non-erasable pen can be used to mark defective products, and holes can be punched at the marked locations as a secondary confirmation marker. After this step, the defective products continue to flow along the production line without being removed. They are only removed after the molding process is completed and before final shipment.

[0060] S9, RTR Cleaning: The copper surface is cleaned using an RTR horizontal cleaning line to remove the surface oxide layer and contaminants. At the same time, the copper surface is roughened by sodium persulfate micro-etching solution to improve the adhesion of the cover film. The cleaning time can be 30 seconds.

[0061] S10, Applying the second cover film 3: Select a polyimide cover film of the same specifications as the first one, and apply the second cover film 3 to the surface of the circuit layer 2 away from the first cover film 1 using an RTR laminator, thereby forming the top cover film; it should be noted that during the application of the second cover film 3, the corresponding lamination parameters must be completely consistent with the lamination parameters of the first cover film 1, that is, the lamination parameters of the second cover film 3 can be: lamination roller temperature 120℃, lamination pressure 6kg / cm², lamination speed 1.2m / min, feeding tension 0.8kg / cm, and roll tension 1.0kg / cm.

[0062] S11, Second RTR pressing: Press the second cover film 3 with the same pressing parameters as the first cover film pressing (i.e., temperature 180℃, pressure 110kg / cm², time 120s) to make the second cover film 3 firmly bonded to the circuit layer 2.

[0063] S12, RTR laser windowing: The second cover film 3 is removed by laser vaporization using laser technology to expose areas such as the pads that need to be electrically connected (the number of laser cuts is adjusted according to the thickness of the cover film).

[0064] S13, RTR plasma cleaning: Carbon black cleaning is performed on the window area 31 of the second cover film 3 using adhesive removal parameters, while removing adhesive residue from the copper surface of the circuit layer 2; wherein, the adhesive removal parameters can be: cavity temperature 60℃, power 6KW, oxygen / carbon tetrafluoride / nitrogen ratio of 80%:8%:12%.

[0065] S14, RTR sandblasting cleaning: Sandblasting cleaning is used to remove the surface adhesive of the pads; the pressure during the sandblasting cleaning process can be 1.8 kg / cm2 and the speed can be 2 m / min, in order to obtain the second product intermediate.

[0066] S15, Curing: The second product intermediate is placed in an RTR baking oven and baked at 155°C for 90 minutes to complete the curing of the first cover film 1 and the second cover film 3, ensuring the stability of the overall structure. S16, Subsequent Processes: Following standard single-sided FPC production requirements, the following processes are completed sequentially: target punching, plate cutting, electroless metallization, assembly reinforcement, shape machining, electrical testing, and visual inspection, ultimately yielding the final product. Figure 2 The finished overall structure shown.

[0067] Based on the above steps, the single-sided FPC finished product has no warping after testing. The flatness error of the gold finger area (covering film window area 31) is ≤0.1mm. When assembling with the glass screen, the pad alignment accuracy is ≥99.95%, which meets the requirements of high-precision assembly. Compared with the existing technology, the material cost is reduced by 30%, the production cycle is shortened by 25%, and the original dynamic bending function and three-dimensional assembly characteristics of FPC are retained.

[0068] In summary, the single-sided flexible circuit board and its preparation method provided by the present invention are as follows: (1) The present invention provides a method for improving the warpage of single-sided FPC and its preparation method. It starts from both structural design and process parameters. By using symmetrical protective layer design and unified process parameter control, the warpage problem caused by stress mismatch is avoided from the source. At the same time, cost control and retention of core product characteristics are taken into account. (2) The symmetrical structural design completely avoids the risk of warpage: By symmetrically bonding the same thickness and specification of cover film on both sides of the circuit layer 2, and using bonding, pressing, baking and other processes that affect the expansion and contraction of materials with the same parameters, the irreversible stress deformation caused by the difference in thickness and molecular structure of the circuit insulation protective layer material under specific processing environment is effectively avoided. The problem of product warpage is solved from the root, and the functional defect of FPC being unable to be assembled due to warpage is eliminated. (3) Shorten the cycle and reduce the cost: The present invention directly attaches the cover film to the pure copper foil to make a single-sided substrate. There is no need to purchase a single-sided substrate separately. This shortens the production cycle and reduces the material procurement cost, significantly improving the market competitiveness of the product. (4) Unified process parameters ensure stability: The bonding and pressing of the two cover films use completely consistent process parameters, avoiding problems such as material expansion and contraction mismatch caused by differences in production parameters, further improving product dimensional stability and reducing the probability of warping. (5) Simplified process reduces deformation interference: The high-temperature curing process of the first cover film is simplified, avoiding product shrinkage caused by a single high temperature, which in turn causes warping problems due to mismatch in deformation of the second cover film, thus improving process stability.

[0069] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention specification and drawings, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for fabricating a single-sided flexible circuit board, characterized in that, include: Obtain copper foil, a first cover film, and a second cover film, wherein the first cover film and the second cover film are made of the same material and have the same specifications; The first cover film is adhered to the matte surface of the copper foil and pressed together; A predetermined target circuit is formed on the copper foil to obtain a first product intermediate with a circuit layer; The second cover film is adhered to the surface of the circuit layer away from the first cover film and then pressed together to obtain the second product intermediate. The second product intermediate is baked and cured to obtain a single-sided flexible circuit board.

2. The preparation method according to claim 1, characterized in that, A predetermined target circuit is formed on the copper foil to obtain a first product intermediate with a circuit layer, comprising: Photoresist is applied to the smooth surface of the copper foil, and the copper foil with photoresist applied is exposed according to the preset target line; The exposed product is developed to retain the photoresist at the pad and circuit area locations, thereby obtaining the third product intermediate. The third product intermediate is sequentially etched and stripped to form a first product intermediate with a circuit layer.

3. The preparation method according to claim 2, characterized in that, The copper foil coated with photoresist is exposed according to the preset target line, including: A pre-defined target line film is applied to the photoresist surface on the copper foil, and then exposed to ultraviolet light to transfer the pre-defined target line onto the photoresist.

4. The preparation method according to claim 1, characterized in that, The process of attaching the first cover film to the matte surface of the copper foil and pressing it together includes: The first cover film is applied to the matte surface using a laminating machine according to preset laminating parameters, wherein the laminating parameters are: laminating roller temperature of 120±8℃, laminating pressure of 6±0.5kg / cm², laminating speed of 1.2±0.2m / min, feeding tension of 0.8±0.2kg / cm, and roll tension of 1.0±0.2kg / cm. The first cover film and the copper foil are pressed together using a pressing machine according to preset pressing parameters, wherein the pressing parameters are: temperature 180±5℃, pressure 110±5kg / cm², and time 120±5s.

5. The preparation method according to claim 1, characterized in that, The second product intermediate is baked and cured to obtain a single-sided flexible circuit board, including: The second product intermediate is placed in an oven and baked at 155°C for 90 minutes to complete the curing of the first and second cover films.

6. The preparation method according to claim 1, characterized in that, The second cover film is adhered to and pressed onto the surface of the circuit layer away from the first cover film to obtain a second product intermediate, comprising: After the second cover film is pressed, a laser windowing operation is performed on the second cover film to obtain a windowed area, thereby exposing the pads on the circuit layer that need to be electrically connected through the windowed area; Carbon black cleaning is performed on the windowed area to remove residual adhesive from the copper surface of the circuit layer. The surface adhesive of the solder pads is removed by sandblasting to obtain the second product intermediate.

7. The preparation method according to claim 1, characterized in that, The process of attaching and pressing the second cover film onto the surface of the circuit layer away from the first cover film includes: The second cover film is attached to the circuit layer using the same bonding parameters as those used in the first cover film bonding process; The second cover film is bonded to the circuit layer using the same bonding parameters as the first cover film bonding process.

8. The preparation method according to claim 1, characterized in that, The process of attaching and pressing the second cover film onto the surface of the circuit layer away from the first cover film includes: The copper surface of the circuit layer in the first product intermediate is cleaned to remove surface contamination and oxide layer; The copper surface is roughened so that the second cover film can be attached to the roughened copper surface and pressed together.

9. The preparation method according to claim 1, characterized in that, Also includes: The first product intermediate is subjected to open and short circuit testing to determine whether there are defective products in the first product intermediate. If any defective products are found, they shall be marked accordingly.

10. A single-sided flexible circuit board, characterized in that, It includes a first cover film, a circuit layer and a second cover film stacked from bottom to top, and the second cover film has a window area.

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