Front opening flexible circuit board and method of making same

Abstract

The application discloses a front opening cover flexible circuit board and a manufacturing method thereof. The method comprises the following steps: providing a flexible circuit substrate with a completed front opening cover; an outer surface of an opening cover area on the flexible circuit substrate forms a stage difference relative to an outer surface of a non-opening cover area; a first dry film layer is manufactured on the flexible circuit substrate, so that the first dry film layer only covers the opening cover area and at least partially fills the stage difference, to obtain a first circuit substrate; a second dry film layer is manufactured on the first circuit substrate, so that the second dry film layer covers the first dry film layer and offsets the stage difference, to obtain a second circuit substrate; and a circuit is manufactured on the second circuit substrate, to form a circuit layer and simultaneously remove the first dry film layer and the second dry film layer, to obtain a target flexible circuit board. The application solves the problems of dry film fitting cavities and bubbles caused by the stage difference through only two times of dry film manufacturing, greatly improves the product yield of the front opening cover flexible circuit board, and meets the demand for mass production.

Description

Technical Field

[0001] This invention relates to the field of flexible circuit board manufacturing technology, specifically to a front-opening flexible circuit board and its manufacturing method. Background Technology

[0002] As consumer electronics, automotive displays, and smart wearables continue to iterate towards thinner, lighter, longer-lasting, and higher-density circuitry, the design requirements for flexible printed circuits (FPCs) are becoming increasingly stringent. Currently, FPCs need to simultaneously meet two contradictory demands: firstly, functional areas require multi-layered copper foil stacking to carry high current and high-density signals; secondly, bending areas and front-opening areas (front-opening refers to the process where, to create a localized thin bending area, the outer reinforcing layer / covering film / layered material is removed before laminating the outer copper foil, resulting in a "multi-layered functional area" + a single-layer / thinned bending / opening area on the same board surface) require a single-layer thin structure to ensure bending performance. This has led to the development of front-opening FPCs. The structural characteristics of this type of product are: most of the board surface is a multi-layered composite structure, while the open-ended areas retain only a single layer of copper foil and adhesive, resulting in a noticeable stage difference at the open-ended openings after lamination.

[0003] The current standard process flow for FPC is as follows: blanking → adhesive application → punching opening → single-sided copper lamination → fast pressing → laser QR code engraving → chemical cleaning → single-stage dry film pressing → exposure → development and etching (DES) → AOI inspection. In this process, after the fast pressing step, the substrate in the open area formed by the punching opening loses its inner layer support, and lamination deformation creates recessed steps with step differences. During the subsequent single-stage dry film pressing, the dry film cannot fully adhere to the high and low step surfaces due to the step differences, and air is easily trapped in the recessed areas, forming voids / bubbles in the dry film. When the subsequent DES etching process is performed, the circuit pattern cannot be completely transferred at the void / bubble locations, resulting in incomplete copper foil etching or direct circuit breaks in that area. The open circuit defect rate of the finished product has consistently remained at around 2%, severely impacting product yield and mass production. Summary of the Invention

[0004] In view of this, the present invention provides a front-opening flexible circuit board and its manufacturing method to solve the technical problem in the prior art that poor dry film bonding caused by the step difference in the open area leads to circuit etching defects, low yield and inability to mass produce.

[0005] This invention provides a method for manufacturing a front-opening flexible circuit board, the method comprising: A flexible circuit substrate with a pre-opening cover is provided; the flexible circuit substrate has an open cover area and a non-open cover area, and the outer surface of the open cover area forms a stepped difference with respect to the outer surface of the non-open cover area; A first dry film layer is fabricated on the flexible circuit substrate, such that the first dry film layer only covers the opening area and at least partially fills the stage step difference, to obtain the first circuit substrate; A second dry film layer is fabricated on the first circuit substrate, such that the second dry film layer covers the first dry film layer and offsets the stage difference, to obtain the second circuit substrate. The second circuit substrate is used to fabricate circuits, forming a circuit layer, and the first dry film layer and the second dry film layer are removed simultaneously to obtain the target flexible circuit board.

[0006] Optionally, a first dry film layer is formed on the flexible circuit substrate, such that the first dry film layer covers the opening area and at least partially fills the stage step difference, to obtain a first circuit substrate, comprising: Provide the first dry film material; The first dry film material is covered on the entire outer surface of the flexible circuit substrate; The first dry film material on the flexible circuit substrate is patterned to form a first dry film layer that only covers the opening area and at least partially fills the stage difference, thus obtaining the first circuit substrate. The thickness of the first dry film layer is matched with the depth of the stage difference.

[0007] Optionally, the width of the first dry film layer is 3 mm smaller than the width of the flexible circuit substrate.

[0008] Optionally, a clearance distance is reserved between the edge of the first dry film layer covering the opening area and the edge of the opening area, and the clearance distance ranges from 0.1mm to 0.2mm.

[0009] Optionally, a second dry film layer is formed on the first circuit substrate, such that the second dry film layer covers the first dry film layer and offsets the stage difference, to obtain a second circuit substrate, comprising: Provide a second dry film material based on the preset circuit design data; The second dry film material is pressed onto the entire outer surface of the first circuit substrate, so that the second dry film material covers the first dry film layer under the action of pressing and offsets the stage difference, thereby forming the second dry film layer and obtaining the second circuit substrate.

[0010] Optionally, the preset line design data includes line width and line spacing; When both the line width and the line spacing are less than 25 μm, the thickness of the second dry film layer is less than the line spacing.

[0011] Optionally, the second circuit substrate is used to fabricate a circuit layer and simultaneously the first dry film layer and the second dry film layer are removed to obtain the target flexible circuit board, including: According to the preset circuit design data, the second circuit substrate is subjected to dry film exposure and development so that the second dry film layer only covers the circuit area of ​​the second circuit substrate. The second circuit substrate after dry film exposure and development is etched to remove the exposed conductive layer of the second circuit substrate. According to the preset film removal parameters, an alkaline film removal solution is used to remove the film from the second circuit substrate after etching, so that both the first dry film layer and the second dry film layer on the outer surface of the second circuit substrate are removed to form the circuit layer and obtain the target flexible circuit board.

[0012] Optionally, the preset membrane removal parameters include membrane removal liquid type, membrane removal liquid concentration, membrane removal liquid temperature, membrane removal conveying speed, and membrane removal soaking time.

[0013] Optionally, the type of the membrane removal solution is specifically a sodium hydroxide solution; and / or, the concentration of the membrane removal solution is in the range of 1.5% to 2.5%; and / or, the temperature of the membrane removal solution is in the range of 45℃ to 55℃; and / or, the membrane removal conveying speed is in the range of 0.9m / min to 2.1m / min; and / or, the membrane removal soaking time is greater than 3min.

[0014] In addition, the present invention also provides a front-opening flexible circuit board, which is manufactured using the aforementioned manufacturing method.

[0015] The beneficial effects of this invention are as follows: For a flexible circuit board that has completed the front-opening process, the outer surface of the open area of ​​the flexible circuit board forms a stepped difference relative to the outer surface of the non-open area due to the front-opening process. First, a first dry film layer is fabricated that covers only the open area and at least partially fills the stepped difference. Since this first dry film layer can fill the stepped depression and initially compensate for the stepped difference, it can serve as a flat base for the subsequent fabrication of the second dry film layer. Then, a second dry film layer covering the entire surface is fabricated on top of the filled first dry film layer. Since the second dry film layer is usually fabricated using a lamination process, the lamination action and the support of the first dry film layer for the second dry film layer are utilized. This technology can offset the height difference of the entire board surface, allowing the second dry film layer to adhere completely and tightly to the entire board surface, thereby solving the problems of dry film bonding voids and bubbles caused by stage differences. Finally, by performing circuit fabrication process on the second circuit substrate, it can be ensured that a circuit layer that meets the actual requirements is formed on the second circuit substrate using the second dry film layer. On the other hand, the entire first and second dry film layers can be removed at the same time using the film removal process in the circuit fabrication process. This achieves the simultaneous completion of dry film removal and circuit formation in one film removal process, without the need for additional dry film retention after filling or additional etching steps, and without adding extra process complexity. The front-opening flexible circuit board and its manufacturing method of the present invention solve the problems of dry film bonding voids and bubbles caused by stage differences by only two dry film preparations, effectively avoiding the occurrence of incomplete copper foil etching or open circuit defects in subsequent etching processes, greatly improving the product yield of the front-opening flexible circuit board and meeting the needs of mass production. Attached Figure Description

[0016] The features and advantages of the invention will be more clearly understood by referring to the accompanying drawings, which are schematic and should not be construed as limiting the invention in any way. In the drawings: Figure 1A This diagram shows a cross-sectional view of a flexible circuit board after the front-opening process in a traditional manufacturing technique. Figure 1B This diagram shows a cross-sectional view of a flexible circuit board after it has undergone a front-opening process and a descaling process in a traditional manufacturing technique. Figure 1C This diagram shows a cross-sectional view of a circuit board after the circuit fabrication is completed using a flexible circuit board in a traditional manufacturing process. Figure 2 A flowchart illustrating a method for manufacturing a front-opening flexible circuit board according to Embodiment 1 of the present invention is shown. Figure 3 This shows a cross-sectional view of the circuit board substrate to be opened in Embodiment 1 of the present invention; Figure 4 This is a cross-sectional view of the circuit board to be opened after the adhesive layer is applied in Embodiment 1 of the present invention. Figure 5 This shows a top view of the circuit board to be opened in Embodiment 1 of the present invention after the cover has been opened; Figure 6 This shows a top view of the opening area in the circuit board to be opened in Embodiment 1 of the present invention; Figure 7 This shows a cross-sectional view of the circuit board to be opened in Embodiment 1 of the present invention, which has undergone opening and copper layer covering in sequence. Figure 8 The diagram shows a top view of the flexible circuit board obtained after the front cover is opened in Embodiment 1 of the present invention by laminating a copper layer. Figure 9 This shows a cross-sectional view of the flexible circuit board covered with a first dry film material according to Embodiment 1 of the present invention; Figure 10 This is a top view structural diagram showing the layout relationship between the exposure area and the opening area when the first dry film material is patterned in Embodiment 1 of the present invention. Figure 11 This shows a cross-sectional view of the first circuit board obtained by fabricating the first dry film layer in Embodiment 1 of the present invention. Figure 12 This shows a cross-sectional view of the second circuit substrate obtained by fabricating the second dry film layer in Embodiment 1 of the present invention; Figure 13 This diagram shows a cross-sectional view of the second circuit substrate after dry film exposure and development in Embodiment 1 of the present invention. Figure 14 The diagram shows a cross-sectional view of the target flexible circuit board after etching and film removal processes in Embodiment 1 of the present invention.

[0017] Explanation of reference numerals in the attached figures: 1. Copper layer, 2. Insulating layer, 3. Adhesive layer, 4. Opening, 5. Stage difference, 6. Lamination deformation, 7. First dry film material, 8. First dry film layer, 9. Second dry film layer, 10. Circuit layer, 11. Flexible circuit board, 12. Third dry film layer, 13. Void, 100. Open area, 200. Non-open area, 300. Exposure area. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, 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.

[0019] In this embodiment of the invention, the term "and / or" describes the relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. The character " / " generally indicates that the preceding and following associated objects have an "or" relationship.

[0020] It should be noted that the terms "first," "second," etc., in the specification, claims, and drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0021] In this embodiment of the invention, the term "multiple" refers to two or more, and other quantifiers are similar.

[0022] In addition, the terms used in this document, such as flexible circuit substrate, first circuit substrate, second circuit substrate, target flexible circuit board, open area, non-open area, first dry film layer and second dry film layer, should be understood in the context of this specification. As for the preparation method involved in this application, unless otherwise stated, the order of steps shall be based on the need to achieve the corresponding process effect. Some steps can be completed by conventional flexible circuit board process equipment, as long as the corresponding board surface state can be achieved.

[0023] In the traditional manufacturing process of front-opening circuit boards, the design flow is as follows: blanking → adhesive application → punching → single-sided copper bonding → fast pressing → laser QR code engraving → chemical cleaning → dry film pressing → exposure → DES → AOI inspection. During the fast pressing process, the following issues may occur: Figure 1A As shown in the lamination deformation 5, during the subsequent dry film pressing process, because the original inner layer material in the open area was removed in advance, a recessed step with a significant height difference was formed after the support was lost. During the pressing process, the dry film could not fully conform to the contour of the step and adhere to the inner wall of the recess. Residual air would be trapped in the recessed area of ​​the step, forming dry film voids or bubble defects, such as... Figure 1B The void 13 shown. During subsequent exposure and etching processes, these voids or air bubbles can block the etching solution from etching the copper foil in non-circuit areas, and can also prevent the circuit pattern from being completely transferred, forming... Figure 1C The flexible circuit board shown ultimately suffers from problems such as incomplete copper foil etching or direct circuit breakage, resulting in a low yield rate that cannot meet the requirements of large-scale mass production.

[0024] exist Figures 1A-1C In the diagram, 1 is the copper layer, 2 is the insulating layer (specifically, the PI layer, i.e., polyimide), 3 is the adhesive layer (specifically, epoxy resin adhesive), 5 is the lamination deformation layer, 12 is the third dry film layer, and 9 is the circuit.

[0025] To address this issue, this embodiment provides a front-opening flexible circuit board and its manufacturing method. By employing two dry film fabrication processes to fill and compensate for the stage differences in the open area, the problem of voids and air bubbles during dry film lamination is fundamentally solved. The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0026] Example 1 This embodiment provides a method for manufacturing a front-opening flexible circuit board, such as... Figure 2 As shown, the method includes: S1: Provide a flexible circuit substrate with a front opening completed; the flexible circuit substrate has an opening area and a non-opening area, and the outer surface of the opening area forms a stepped difference with respect to the outer surface of the non-opening area; S2: A first dry film layer is formed on the flexible circuit substrate, such that the first dry film layer only covers the opening area and at least partially fills the stage difference, to obtain the first circuit substrate; S3: A second dry film layer is fabricated on the first circuit substrate, such that the second dry film layer covers the first dry film layer and cancels out the stage difference, to obtain the second circuit substrate. S4: Fabricate the second circuit substrate to form a circuit layer and simultaneously remove the first dry film layer and the second dry film layer to obtain the target flexible circuit board.

[0027] In this embodiment, for a flexible circuit board that has completed the front-opening process, the outer surface of the open area of ​​the flexible circuit board forms a step difference relative to the outer surface of the non-open area due to the front-opening process. First, a first dry film layer is fabricated that covers only the open area and at least partially fills the step difference. Since the first dry film layer can fill the step depression and initially compensate for the step difference, it can serve as a flat base for the subsequent fabrication of the second dry film layer. Then, a second dry film layer covering the entire surface is fabricated on top of the filled first dry film layer. Since the second dry film layer is usually fabricated using a lamination process, the lamination action and the supporting effect of the first dry film layer on the second dry film layer are utilized. This can offset the height difference of the entire board surface, allowing the second dry film layer to adhere completely and tightly to the entire board surface, thereby solving the problems of dry film bonding voids and bubbles caused by stage differences. Finally, by performing circuit fabrication process on the second circuit substrate, on the one hand, it can ensure that the second dry film layer forms a circuit layer that meets the actual requirements on the second circuit substrate, and on the other hand, the entire first and second dry film layers can be removed at the same time by using the film removal process in the circuit fabrication process. This achieves the simultaneous completion of dry film removal and circuit formation in one film removal, without the need for additional dry film retention after filling or additional etching steps, and without increasing the complexity of the process.

[0028] The method for manufacturing the front-opening flexible circuit board in this embodiment solves the problems of voids and bubbles in the dry film bonding caused by stage differences by only two dry film preparations. It effectively avoids defects such as incomplete copper foil etching or open circuit defects in subsequent etching processes, greatly improves the product yield of the front-opening flexible circuit board, and meets the needs of mass production.

[0029] It should be understood that the manufacturing method of this embodiment can be used for both single-sided and double-sided flexible circuit board manufacturing. Only the corresponding steps of this method need to be performed on the two boards respectively, which is suitable for a variety of front-opening products with different structures.

[0030] Furthermore, the manufacturing method of this embodiment can be used for both the production of inner layer circuit front opening covers and the production of outer layer circuit front opening covers. Only the relevant process parameters of the first dry film layer need to be adjusted for different stage differences. For the production of inner layer circuit front opening covers, a single-sided copper-clad laminate (CCL) is typically used as the substrate. After punching an opening in the CCL, a single-sided or double-sided CCL circuit board is quickly pressed to form a flexible circuit substrate. For the production of outer layer circuit front opening covers, the inner layer circuit board can be a single-sided, double-sided, or multilayer board (i.e., a combination of single-sided and double-sided CCLs). Using this inner layer circuit board as the substrate, an opening is punched in it, and then a single-sided or double-sided CCL circuit board is quickly pressed to form a flexible circuit substrate.

[0031] For ease of explanation, the following describes each step of the manufacturing method of the front-opening flexible circuit board in this embodiment in detail, taking the production of the inner layer circuit front opening cover as an example.

[0032] In this embodiment S1, a flexible circuit substrate with a front-opening cover is provided, including: S11: Provide a circuit substrate to be opened; the circuit substrate to be opened has a pre-set opening area; S12: Apply an adhesive layer to the circuit substrate to be opened, and punch an opening in the circuit substrate based on the opening area; S13: The punched circuit substrate to be opened is pressed with a copper layer to obtain the flexible circuit substrate with the front opening completed.

[0033] The aforementioned front-opening cover manufacturing method ensures the formation of a circuit board structure consisting of "multi-layer functional areas" + "single-layer / thinned bending open area," thereby meeting the requirements for high bending performance and thinness in the bending area. This is the conventional processing path for realizing functional layered design of current front-opening cover flexible circuit boards. It is precisely this processing path that naturally creates a stage difference between the open area and the non-open area. Therefore, this embodiment can be directly adapted to the existing conventional front-opening cover processing flow without the need to adjust or modify the original front-opening cover preparation process.

[0034] In this embodiment, the substrate of the circuit to be opened is specifically a single-sided copper-clad laminate. The single-sided copper-clad laminate itself includes an insulating substrate layer and a copper foil layer attached to one side of the insulating substrate layer. When punching the opening, the insulating substrate layer of the opening area will be directly punched through, exposing the alignment surface of the copper layer to be bonded. After subsequent fast pressing, only the newly pressed surface copper layer can be retained in the opening area, forming an opening functional area with thinner thickness and better bending performance.

[0035] The cross-sectional structure of the circuit substrate to be opened provided in this embodiment is as follows: Figure 3 As shown, in Figure 3 In the diagram, 1 represents the copper layer, and 2 represents the insulating layer (specifically, the PI layer). The cross-sectional structure after bonding the adhesive layer is shown below. Figure 4 As shown, in Figure 4 In the middle, 3 represents the adhesive layer (specifically, epoxy resin adhesive). Its cross-sectional structure after punching to form an opening is as follows: Figure 5 As shown, in Figure 5 In the middle, 4 represents an opening. The cross-sectional structure of its copper-covered layer is as follows: Figure 7 As shown. In Figure 7 In the process of opening the cover, the outer surface of the central open area 100 is no longer on the same plane relative to the two non-open areas 200 on both sides. A stepped difference 5 is formed between the outer surface of the open area 100 and the outer surface of the non-open areas 200. This stepped difference is precisely the object that needs to be partially filled by the first dry film layer. The layout relationship between the flexible circuit substrate 11 and the open area 100 is as follows: Figure 6 and Figure 7 As shown. The cross-sectional structure of the flexible circuit substrate obtained by lamination after covering with a copper layer is as follows. Figure 8 As shown, in Figure 8 In the middle, 6 represents lamination deformation.

[0036] Based on the above Figures 3-8 It is understandable that the front opening cover does not change a certain local point in isolation, but rather, under a given plate shape and layered layout, it locally thins or opens up a designated area to form an area that needs to be filled in later.

[0037] Preferably, step S2 in this embodiment includes: S21: Provide the first dry film material; S22: Cover the entire outer surface of the flexible circuit substrate with the first dry film material; S23: The first dry film material on the flexible circuit substrate is patterned to form a first dry film layer that only covers the opening area and at least partially fills the stage difference, thus obtaining the first circuit substrate. The thickness of the first dry film layer is matched with the depth of the stage difference.

[0038] During the fabrication of the first dry film layer, the first dry film material is first applied to the entire outer surface of the flexible circuit substrate. This ensures that the first dry film material can fully flow into the recesses of the open area, completing the initial filling of the stage difference and preventing insufficient filling due to pre-reserved spaces. Subsequently, through graphic processing, excess first dry film material in the non-open area is removed, leaving only the first dry film layer in the open area. This achieves the filling function without increasing the thickness of the non-open area, thus avoiding the secondary formation of height differences in the non-open area.

[0039] In step S21, the first dry film material can be a conventional dry film material in the field of PFC manufacturing, and there is no limitation here.

[0040] The thickness of the first dry film layer needs to match the depth of the stage difference. For example, when the stage difference depth is X, the thickness of the first dry film layer is also set to X. This can both reserve space for the pressing of the second dry film layer and basically offset the height difference, ensuring that the overall flatness of the board surface is sufficient when the second dry film layer is pressed.

[0041] In this embodiment, the depth of the stage difference is determined by the thickness of the substrate of the circuit to be opened and the thickness of the adhesive layer. Specifically, the depth of the stage difference is equal to the sum of the thickness of the substrate of the circuit to be opened and the thickness of the adhesive layer. Figure 7 The depth of stage 5 is equal to the thickness of the top copper layer 1 + the thickness of the top insulating layer 2 + the thickness of the adhesive layer 3.

[0042] For example, if the sum of the thickness of the substrate of the circuit to be opened and the thickness of the adhesive layer (the thickness of the uppermost copper layer 1 + the thickness of the uppermost insulating layer 2 + the thickness of the adhesive layer 3) is 40 μm, then the depth of the stage difference is 40 μm. Furthermore, the thickness of the first dry film layer is also 40 μm.

[0043] In step S23, the patterning process can be achieved using conventional exposure and development techniques. Figure 9 The cross-sectional structure after covering with the first dry film material is shown. Figure 10 The diagram illustrates the corresponding layout of the exposed area 300 and the uncovered area 100 during the patterning process. Only the first dry film material above the uncovered area is exposed, while the first dry film material in the non-covered area is not exposed. Subsequent development removes the first dry film material in the non-covered area, resulting in a first dry film layer that only fills the uncovered area. The corresponding cross-sectional structure is shown below. Figure 11 As shown. In Figure 11 In the diagram, 8 represents the first dry film layer that is ultimately formed.

[0044] Furthermore, the width of the first dry film layer is 3 mm smaller than the width of the flexible circuit substrate.

[0045] By limiting the size of the first dry film layer, burrs can be avoided from remaining at the edges of the first dry film layer after development. It can also reduce the possibility of dry film adhering to the roller due to positional deviation during pressing and reduce the risk of forming dry film debris. At the same time, it can ensure that the first dry film layer completely covers the opening area and there will be no problem of incomplete edge filling.

[0046] It should be understood that in actual manufacturing, if the flexible circuit substrate is a roll, and this roll has a corresponding pulling direction during manufacturing, then the dimension of the flexible circuit substrate in the pulling direction is the length, and the dimension in the direction perpendicular to the pulling direction is the width. If the flexible circuit substrate is not a roll, but a single sheet (usually a rectangular sheet), then the aforementioned width includes the dimensions in both the length and width directions of the single sheet.

[0047] Furthermore, in this embodiment, "at least partially filled" means that the first dry film layer does not need to completely fill the stage difference, that is, there is a clearance distance between the edge of the first dry film layer covering the opening area and the edge of the opening area, and the clearance distance is in the range of 0.1mm to 0.2mm.

[0048] By using the aforementioned clearance distance, it is possible to prevent the edge of the first dry film layer from overflowing beyond the opening area due to compression when laminating the second dry film layer. It also fully considers the issue of exposure misalignment, leaving a margin for subsequent exposure misalignment. This ensures that the first dry film layer completely covers all the recessed areas that need to be filled, without missing any steps due to misalignment, thus guaranteeing the filling effect. At the same time, it also ensures that the first dry film layer fully fills the step difference of the entire opening area, without leaving any unfilled gaps, thus balancing the filling effect with the edge bonding accuracy.

[0049] Figure 11 In this context, d represents the clearance distance, which is 0.1mm to 0.2mm.

[0050] Preferably, step S3 in this embodiment includes: S31: Provide a second dry film material according to the preset circuit design data; S32: The second dry film material is pressed onto the entire outer surface of the first circuit substrate, so that the second dry film material covers the first dry film layer under the action of pressing and offsets the stage difference, thereby forming the second dry film layer and obtaining the second circuit substrate.

[0051] By fabricating a second dry film layer on the first circuit substrate using the above method, since the first dry film layer has already filled the local depressions in the open area, and then the second dry film material is pressed onto the entire surface, it can be laid out on a gentler height transition instead of directly crossing sharp steps. This ensures that the entire board surface remains flat after the second dry film material is pressed on, and there will be no voids or air bubbles caused by the original step differences during the dry film pressing process. This offsets the step differences generated in the aforementioned fast pressing process, ensuring that the formed second dry film layer can closely fit the contour of the entire board surface, providing a foundation for subsequent precise circuit exposure transfer.

[0052] In step S31, the preset circuit design data may include circuit area distribution, line width, line spacing, and layout information related to lamination alignment. This data may vary depending on the actual product design and is not limited here.

[0053] exist Figure 12 In the diagram, 9 represents the second dry film layer. As can be seen, the height difference on the outer surface of the entire first circuit substrate is completely offset by the first and second dry film layers, resulting in the entire board surface being on the same plane. Subsequent circuit fabrication processes based on the first and second dry film layers on this second circuit substrate ensure that, while obtaining the preset circuit pattern, the exposure process will not fail to transfer the circuit pattern completely due to height differences, thus guaranteeing the circuit quality at subsequent stage differences.

[0054] Furthermore, when both the line width and the line spacing are less than 25 μm, the thickness of the formed second dry film layer is less than the line spacing.

[0055] By limiting the thickness of the second dry film layer, problems such as insufficient exposure and inaccurate transfer of circuit patterns due to excessive dry film thickness can be effectively avoided. This meets the requirements for fabricating high-precision fine circuits and ensures a high yield rate for fine circuit formation. If the line width and line spacing are both not less than 25μm, the thickness of the second dry film layer can be set according to conventional processes, which will not be elaborated here.

[0056] It should be understood that for single-sided front-opening production, when making the first dry film layer, it is still necessary to cover both outer surfaces of the flexible circuit substrate with the first dry film layer. This ensures that the entire flexible circuit substrate is subjected to uniform force in the laminating equipment through the pressing of the first dry film material on both outer surfaces, avoiding the impact of unilateral force on the filling effect of the first dry film material on the stage difference, and thus fully ensuring the cancellation effect of the stage difference in subsequent stages. Afterwards, by patterning the two first dry film layers, only the first dry film layer on the single-sided opening area needs to be retained.

[0057] For the production of double-sided front-opening covers, when manufacturing the first dry film layer, it is also necessary to cover the outer surfaces of both sides of the flexible circuit substrate with the first dry film layer. This ensures both the filling effect of the first dry film material on the outer surfaces of both sides on the filling effect of the stage difference between the two sides, and also ensures that the subsequent combination with the second dry film layer can offset the stage difference. Then, by patterning the two first dry film layers, the first dry film layer on the double-sided opening area is retained.

[0058] Furthermore, for the production of a single-sided front-opening cover, when manufacturing the second dry film layer, if circuitry is required on both outer surfaces of the first circuit substrate, the second dry film material is laminated onto both outer surfaces of the first circuit substrate; subsequently, both sides are processed using the circuitry manufacturing process. If only one outer surface of the first circuit substrate requires circuitry, the second dry film material is laminated onto the outer surface of the side of the first circuit substrate where circuitry is required; subsequently, it is processed using the circuitry manufacturing process.

[0059] For the production of double-sided front-opening covers, when making the second dry film layer, the outer surfaces of both sides of the first circuit substrate usually need to be fabricated with circuits. Therefore, the second dry film material is pressed onto both outer surfaces of the first circuit substrate; then both sides are processed by the circuit fabrication process.

[0060] Preferably, step S4 in this embodiment includes: S41: According to the preset circuit design data, the second circuit substrate is exposed and developed by dry film exposure, so that the second dry film layer only covers the circuit area of ​​the second circuit substrate. S42: The second circuit substrate after dry film exposure and development is etched to remove the exposed conductive layer of the second circuit substrate. S43: According to the preset film removal parameters, an alkaline film removal solution is used to remove the film from the second circuit substrate after etching, so that the first dry film layer and the second dry film layer on the outer surface of the second circuit substrate are removed to form the circuit layer and obtain the target flexible circuit board.

[0061] After the second dry film layer is laminated to obtain the second circuit substrate, the above-described circuit fabrication method can accurately transfer the preset circuit pattern, ensuring the integrity and accuracy of the circuit pattern in the open area. This avoids problems such as circuit breaks, incomplete lines, or unclear exposure caused by differences in the original stage steps. Furthermore, it eliminates the need to modify the original etching and film removal processes, thus avoiding additional processing complexity and production costs, and demonstrating strong processing adaptability. Regarding film removal, since both the first and second dry film layers are conventional dry film materials that can be dissolved and removed by alkaline film removal solution, both layers can be removed simultaneously in a single process, eliminating the need for step-by-step processing and resulting in higher processing efficiency. The final target flexible circuit board not only retains the structural advantages of "multi-layer functional areas + single-layer / thinned bending open area" but also ensures the integrity and consistency of the circuits in the open and closed areas, preventing quality defects caused by height differences in the circuits.

[0062] Specifically, the dry film exposure and development in step S41 and the etching process in step S42 can be completed using conventional processes in the FPC manufacturing field, and no further limitations are specified here. The cross-sectional structure of the second circuit substrate after dry film exposure and development is shown below. Figure 13 As shown, in Figure 13 In this process, the exposed area of ​​the second dry film layer 9 is the area that needs to be etched away in the subsequent etching process, while the area covered by the second dry film layer 9 is the area that needs to be retained in the subsequent etching process, which is the circuit layer 10 to be fabricated. Based on this second circuit substrate, the synergistic effect of the first and second dry film layers reduces the board surface step difference, and the protective pattern before etching is more stable, thus helping to reduce circuit interruptions caused by lamination bubbles or protective discontinuities.

[0063] Furthermore, in step S43, the preset membrane removal parameters include membrane removal liquid type, membrane removal liquid concentration, membrane removal liquid temperature, membrane removal conveying speed, and membrane removal soaking time.

[0064] The above parameters together determine the film removal intensity, film removal uniformity, and the adequacy of removing the double-layer dry film. By controlling the above process parameters in the film removal process, it can be ensured that both the first and second dry film layers are completely removed, and no dry film debris will remain in the open or closed areas. This avoids residual debris affecting the conductivity, insulation performance, or subsequent bonding processing of the circuit board, and ensures the yield of the final product.

[0065] The film removal conveying speed can be selected in conjunction with the line compensation design, while the film removal soaking time can be adjusted in a coordinated manner to ensure the finished product line width requirements and the residual film removal requirements.

[0066] Preferably, the type of the membrane removal solution is sodium hydroxide solution; and / or, the concentration of the membrane removal solution is in the range of 1.5% to 2.5%; and / or, the temperature of the membrane removal solution is in the range of 45℃ to 55℃; and / or, the membrane removal conveying speed is in the range of 0.9m / min to 2.1m / min; and / or, the membrane removal soaking time is greater than 3min.

[0067] By using the above parameter range, the dissolution effect of sodium hydroxide solution on the two dry film layers can be further guaranteed. While removing the dry film, it will not corrode the exposed copper layer of the circuit, thus balancing the film removal efficiency and the circuit protection effect. The specific parameters can be flexibly adjusted according to the actual board size and the total thickness of the dry film.

[0068] For example, in this embodiment, the concentration of the stripping solution is 2% (all concentrations of the stripping solution in this document refer to the mass percentage of the stripping solution), the temperature of the stripping solution is 50°C, the delivery speed of the stripping solution is 1.5 m / min, and the stripping treatment time is 4 min. The stripping solution in this embodiment can also be other alkaline stripping solutions, as long as they can achieve the stripping treatment of the second circuit substrate after etching.

[0069] The cross-sectional structure of the final target flexible circuit board formed in this embodiment is as follows: Figure 14 As shown, from Figure 14 It can be seen that both the first and second dry film layers were completely removed in one go, and the circuit layers in the open and closed areas were complete and continuous, without any quality defects caused by stage differences.

[0070] In this embodiment, the front-opening flexible circuit board is manufactured using the above-described method. The finished product retains the structural relationship between the open and closed areas that a front-opening product should have, and a circuit layer is formed on the corresponding conductive layer. Since the first dry film layer and the second dry film layer only serve the functions of local filling and full-area circuit dry film bearing during the manufacturing process, respectively, and are removed after the circuit is formed, the finished product does not additionally retain these two temporary dry film structures.

[0071] The front-opening flexible circuit board manufactured using the above method, through the sequence of "partial pre-filling - full-surface lamination - development etching - double-layer film removal," achieves the formation of the circuit layer on a relatively flat process surface without altering the final front-opening structure. This reduces the adverse effects of the front-opening stage difference directly on the dry film lamination of the circuit. By using only two dry film fabrications, the problems of voids and bubbles in dry film bonding caused by stage differences are solved, effectively avoiding incomplete copper foil etching or open circuit defects in subsequent etching processes. Furthermore, it eliminates the need for additional complex processes, resulting in low processing costs, good adaptability, and the ability to meet the production requirements of high-precision front-opening flexible circuit boards. It also significantly improves the product yield of front-opening flexible circuit boards, satisfying mass production needs.

[0072] Example 2 A front-opening flexible circuit board is manufactured using the method described in Example 1.

[0073] The flexible circuit board manufactured in this embodiment retains the structural characteristics of "multi-layer functional area + single-layer / thinning bending open area", ensuring that the open area has a low thickness that meets bending requirements. At the same time, it can avoid circuit manufacturing defects caused by stage differences in the open area. The circuits in the open area and the non-open area are complete and continuous, with higher line width and line spacing accuracy. It is more suitable for scenarios with high requirements for bending reliability and circuit fineness. The product lifespan and yield can be effectively guaranteed.

[0074] The manufacturing method used in this embodiment is the same as that described in Embodiment 1. Therefore, for details not covered in this embodiment, please refer to Embodiment 1 and Figures 1 to 12. Figure 14 The specific details will not be repeated here.

[0075] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A method for manufacturing a front-opening flexible circuit board, characterized in that, The method includes: A flexible circuit substrate with a pre-opening cover is provided; the flexible circuit substrate has an open cover area and a non-open cover area, and the outer surface of the open cover area forms a stepped difference with respect to the outer surface of the non-open cover area; A first dry film layer is fabricated on the flexible circuit substrate, such that the first dry film layer only covers the opening area and at least partially fills the stage step difference, to obtain the first circuit substrate; A second dry film layer is fabricated on the first circuit substrate, such that the second dry film layer covers the first dry film layer and offsets the stage difference, to obtain the second circuit substrate. The second circuit substrate is used to fabricate circuits, forming a circuit layer, and the first dry film layer and the second dry film layer are removed simultaneously to obtain the target flexible circuit board.

2. The method for manufacturing a front-opening flexible circuit board according to claim 1, characterized in that, A first dry film layer is fabricated on the flexible circuit substrate, such that the first dry film layer covers the opening area and at least partially fills the stage step difference, to obtain the first circuit substrate, comprising: Provide the first dry film material; The first dry film material is covered on the entire outer surface of the flexible circuit substrate; The first dry film material on the flexible circuit substrate is patterned to form a first dry film layer that only covers the opening area and at least partially fills the stage difference, thus obtaining the first circuit substrate. The thickness of the first dry film layer is matched with the depth of the stage difference.

3. The method for manufacturing a front-opening flexible circuit board according to claim 1, characterized in that, The width of the first dry film layer is 3 mm smaller than the width of the flexible circuit substrate.

4. The method for manufacturing a front-opening flexible circuit board according to claim 1, characterized in that, A clearance distance is provided between the edge of the first dry film layer covering the opening area and the edge of the opening area, and the clearance distance ranges from 0.1mm to 0.2mm.

5. The method for manufacturing a front-opening flexible circuit board according to claim 1, characterized in that, A second dry film layer is fabricated on the first circuit substrate, such that the second dry film layer covers the first dry film layer and offsets the stage difference, to obtain the second circuit substrate, comprising: Provide a second dry film material based on the preset circuit design data; The second dry film material is pressed onto the entire outer surface of the first circuit substrate, so that the second dry film material covers the first dry film layer under the action of pressing and offsets the stage difference, thereby forming the second dry film layer and obtaining the second circuit substrate.

6. The method for manufacturing a front-opening flexible circuit board according to claim 5, characterized in that, The preset line design data includes line width and line spacing; When both the line width and the line spacing are less than 25 μm, the thickness of the second dry film material formed is less than the line spacing.

7. The method for manufacturing a front-opening flexible circuit board according to claim 1, characterized in that, The second circuit substrate is used to fabricate circuits, forming a circuit layer and simultaneously removing the first dry film layer and the second dry film layer to obtain the target flexible circuit board, including: According to the preset circuit design data, the second circuit substrate is subjected to dry film exposure and development so that the second dry film layer only covers the circuit area of ​​the second circuit substrate. The second circuit substrate after dry film exposure and development is etched to remove the exposed conductive layer of the second circuit substrate. According to the preset film removal parameters, an alkaline film removal solution is used to remove the film from the second circuit substrate after etching, so that both the first dry film layer and the second dry film layer on the outer surface of the second circuit substrate are removed to form the circuit layer and obtain the target flexible circuit board.

8. The method for manufacturing a front-opening flexible circuit board according to claim 7, characterized in that, The preset membrane removal parameters include membrane removal liquid type, membrane removal liquid concentration, membrane removal liquid temperature, membrane removal conveying speed, and membrane removal soaking time.

9. The method for manufacturing a front-opening flexible circuit board according to claim 8, characterized in that, The specific type of the film removal solution is sodium hydroxide solution; and / or, the concentration of the film removal solution is in the range of 1.5% to 2.5%; and / or, the temperature of the film removal solution is in the range of 45℃ to 55℃; and / or, the film removal conveying speed is in the range of 0.9m / min to 2.1m / min; and / or, the film removal soaking time is greater than 3min.

10. A front-opening flexible circuit board, characterized in that, It is manufactured using the manufacturing method described in any one of claims 1 to 9.

Images