Flexible circuit board with golden fingers on inner layer and processing method thereof

Abstract

The invention relates to the technical field of multi-layer circuit board production, in particular to a flexible circuit board with a golden finger on the inner layer and a processing method thereof, and the method comprises the steps: attaching an inner layer cover film with a first window on an inner layer substrate on which circuit manufacturing is completed, and attaching a glue blocking film at the first window to cover the golden finger; sequentially laminating the adhesive layer and the conductive layer, and pressing; forming an annular windowing channel for exposing the adhesive layer on the periphery of the edge of the adhesive blocking film; and tearing from the annular windowing channel, removing the glue blocking film and the adhesive layer and the conductive layer above the glue blocking film as an integral structure, and exposing a clean golden finger area. The method has the beneficial effects that a physical barrier is formed in the pressing stage through the glue blocking film, and glue overflowing pollution is completely eradicated from the source; and tearing is guided through an annular channel formed by etching, so that the edge of the window is flat and smooth. According to the invention, the problems of excessive glue pollution, difficulty in uncovering, poor edge quality and low yield in the traditional process are effectively solved.

Description

Technical Field

[0001] This invention relates to the field of multilayer circuit board manufacturing technology, specifically to a flexible circuit board with gold fingers on the inner layer and its processing method. Background Technology

[0002] As electronic devices become thinner, lighter, and denser, the application of flexible printed circuit boards (FPCs) is becoming increasingly widespread. In some special stacking designs, to save space or achieve specific connection methods, it is necessary to design the pluggable gold fingers on the inner layer of the FPC. How to accurately, non-destructively, and contaminantly expose the inner gold fingers from the outer layer material is a key process in the manufacturing of such FPCs.

[0003] In existing technologies, the following technical approaches are mainly used to expose the inner gold fingers: Route 1: Pre-window lamination process. Pre-windows are made on the inner cover film corresponding to the gold finger areas, and then the outer layer material is laminated. However, during the lamination process, the adhesive layer (such as pure adhesive) is highly susceptible to overflow due to high temperature and pressure. This overflow flows into the pre-window area, contaminating the gold finger surface and leading to poor conductivity and reduced solderability. Simultaneously, the alignment accuracy of the window openings on the outer cover film is extremely high; even slight deviations can result in excessive gold finger coverage or exposed copper, affecting product reliability.

[0004] Route Two: Resistant Film Protection and Mechanical Removal Process. To overcome the adhesive overflow problem, the industry has attempted to temporarily cover the windowed areas with resistive films. For example, Chinese invention patent application CN111542179A proposes a method that involves creating windows in the dielectric layer and etching lines at the opening contour during the fabrication of the outer layer circuitry. Finally, the entire board is opened by punching opening grooves and using an adhesive roller for adhesion. While this method avoids adhesive overflow to some extent, the opening process relies on the overall adhesion force of the adhesive roller, resulting in poor controllability. Furthermore, for multi-segmented, elongated gold finger areas, uneven force can easily lead to incomplete opening or tearing of the outer layer circuitry. In addition, the tearing process remains difficult for areas without pre-reserved effective force points.

[0005] Route 3: Laser or blade cutting for window opening. For example, Chinese invention patent application CN110022651B discloses "A method and equipment for processing the inner layer gold fingers of a multilayer board," which involves pre-opening windows in the adhesive layer, laminating to form a space sealed and protected by the outer copper-clad laminate, and finally using an angled blade or laser to cut the windows. However, laser cutting creates a heat-affected zone at the window edge, leading to carbonization and burrs; while blade cutting produces relatively clean edges, for thicker or multilayer structures, the cutting depth control is extremely demanding, easily damaging the inner layer gold fingers. Furthermore, the resulting beveled cross-section, while helpful in reducing air bubbles during subsequent cover film application, relies entirely on the precision of the mechanical cutting for window size and position accuracy, making it difficult to meet increasingly stringent micron-level alignment requirements.

[0006] To overcome the problem of adhesive overflow, the industry has tried using adhesive-resistant films (such as PI protective films) to temporarily cover the windowed areas. However, when removing these protective films, the process is often difficult and inefficient due to excessive adhesion and lack of effective leverage points, sometimes even damaging the inner layer circuitry or gold fingers. Therefore, there is an urgent need for a processing method that can completely solve the problem of adhesive overflow and achieve windowing of the inner layer gold fingers efficiently, accurately, and without damage. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a flexible circuit board with gold fingers in the inner layer and its processing method, so as to solve the problems of gold finger contamination caused by glue overflow during lamination, poor quality of window edge and difficulty in removing the protective layer in the prior art, so as to achieve clean exposure of the gold finger area, flat and controllable window edge and efficient and stable process operation.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a method for processing a flexible circuit board with gold fingers in the inner layer, comprising the following steps: An inner cover film with a first opening is attached to the inner layer substrate after the circuit fabrication is completed, the first opening exposing the gold finger area of ​​the inner layer substrate. A resist film is attached to the first opening of the inner cover film, and the resist film covers the gold finger area. On the inner substrate to which the resist film is attached, an adhesive layer and a conductive layer are sequentially stacked and then pressed together. The conductive layer is patterned and etched to form an annular window channel that exposes the adhesive layer at the periphery of the edge of the resist film; Peel off the annular window opening to remove the resist film and the adhesive layer and conductive layer above it as a whole structure to expose the gold finger area.

[0009] To solve the above-mentioned technical problems, another technical solution adopted by the present invention is to provide a flexible circuit board with gold fingers in the inner layer, which is obtained by the above-mentioned processing method of the flexible circuit board with gold fingers in the inner layer.

[0010] The beneficial effects of this invention are as follows: By pre-attaching a resist film to the inner gold finger area, this invention prevents molten adhesive from overflowing and contaminating the gold finger during the pressing of the adhesive layer and conductive layer, ensuring the cleanliness of the gold finger and the reliability of the electrical connection. Simultaneously, this invention also uses patterned etching of the conductive layer to precisely form an annular window channel exposing the adhesive layer around the edge of the resist film. This provides a controllable separation interface for subsequent operations, allowing the operator to peel off the resist film and the cured adhesive layer and conductive layer as a single composite structure through this channel. This design transforms the previously difficult problem of removing a single-layer protective film into a complete peeling action along a preset path, significantly reducing the operational difficulty and alignment accuracy requirements, and achieving a smooth and even window edge, thus significantly improving product consistency and process yield. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the inner structure cross-section after step S1 is completed in a specific embodiment of the present invention; Figure 2 This is a schematic cross-sectional view of the three-layer slab after pressing in step S2 of Embodiment 1 of the present invention; Figure 3 This is a partial top view of the annular windowed channel formed after selective etching in step S3 of Embodiment 1 of the present invention; Figure 4 This is a top view of the relevant structure of the annular window channel in Embodiment 1 of the present invention; Figure 5 This is a partial structural diagram of the tearing process using the ejector tool in Embodiment 2 of the present invention; Figure 6 This is a schematic diagram of the final product cross-section after the outer cover film on both sides of the outer layer is peeled off in Embodiment 2 of the present invention. 1. Inner substrate; 11. Gold fingers; 2. Inner cover film; 3. Resist film; 4. Adhesive layer; 5. Conductive layer; 51. Annular window channel; 6. Initial positioning pin; 7. Ejector pin; 8. Pre-drilled hole; 9. Outer covering film. Detailed Implementation

[0012] 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.

[0013] The key technical concept of this invention lies in proposing a systematic solution that first protects, then builds, then guides, cleverly peels away, and leaves room for improvement. First, a polyimide protective film is laminated onto the inner gold finger surface, forming a physical barrier during the lamination stage where adhesive overflow is most likely to occur, thus preventing adhesive contamination at the source. Second, with the protective film in place, the outer pure adhesive and copper foil are laminated and the circuit is fabricated, ensuring the integrity of the multilayer board structure. Third, by selectively etching the outer copper foil, a ring-shaped channel exposing the pure adhesive layer is precisely etched around the edge of the protective film, pre-setting a guide path for subsequent separation. Subsequently, using a pre-fabricated semi-exposed hole on the inner substrate and a ejector tool, the protective film is precisely lifted to form a tear-off starting point, allowing the operator to easily tear off the protective film and the cured pure adhesive and copper foil above it as a whole composite structure along the guide channel, perfectly exposing the clean gold fingers. Finally, an outer cover film with a larger opening size is laminated, providing alignment tolerance for the accumulated errors of the previous processes. This completely solves the problem of adhesive overflow contamination, while achieving high quality at the opening edge, efficient and convenient tearing operation, and a breakthrough improvement in overall process yield.

[0014] This invention provides a method for processing a flexible circuit board with gold fingers in the inner layer, comprising the following steps: An inner cover film with a first opening is attached to the inner layer substrate after the circuit fabrication is completed, the first opening exposing the gold finger area of ​​the inner layer substrate. A resist film is attached to the first opening of the inner cover film, and the resist film covers the gold finger area. On the inner substrate to which the resist film is attached, an adhesive layer and a conductive layer are sequentially stacked and then pressed together. The conductive layer is patterned and etched to form an annular window channel that exposes the adhesive layer at the periphery of the edge of the resist film; Peel off the annular window opening to remove the resist film and the adhesive layer and conductive layer above it as a whole structure to expose the gold finger area.

[0015] The beneficial effects of this invention are as follows: By pre-attaching a resist film to the inner gold finger area, this invention prevents molten adhesive from overflowing and contaminating the gold finger during the pressing of the adhesive layer and conductive layer, ensuring the cleanliness of the gold finger and the reliability of the electrical connection. Simultaneously, this invention also uses patterned etching of the conductive layer to precisely form an annular window channel exposing the adhesive layer around the edge of the resist film. This provides a controllable separation interface for subsequent operations, allowing the operator to peel off the resist film and the cured adhesive layer and conductive layer as a single composite structure through this channel. This design transforms the previously difficult problem of removing a single-layer protective film into a complete peeling action along a preset path, significantly reducing the operational difficulty and alignment accuracy requirements, and achieving a smooth and even window edge, thus significantly improving product consistency and process yield.

[0016] Furthermore, in the above-mentioned processing method for a flexible circuit board with gold fingers in the inner layer, the step of peeling off from the annular window channel specifically involves: using a jig to lift the adhesive-resistant film below the annular window channel to form a peeling starting point.

[0017] As described above, the above method uses a jig to lift the adhesive film from below to form a tearing start point, avoiding the circuit damage or film tearing that may be caused by manual tweezers, and significantly reducing the difficulty of operation.

[0018] Furthermore, in the above-mentioned processing method for a flexible circuit board with gold fingers in the inner layer, before bonding the resist film, the method further includes the step of: processing a pre-made hole on the inner layer substrate at the end position of the gold finger; after bonding the resist film, the projection of the resist film covers the first part of the pre-made hole and exposes the second part of the pre-made hole. The specific steps of tearing from the annular window channel are as follows: a jig passes through the pre-made hole and lifts the adhesive-resistant film below the annular window channel to form a tearing starting point.

[0019] As described above, the ejector pin of the fixture passes through the pre-made hole and lifts the adhesive-resistant film below the annular window channel, which is more convenient and faster than adhesive peeling. Furthermore, because the pre-made hole is divided into two parts, with the middle part corresponding to the annular window channel, the ejector pin can quickly align and lift the adhesive-resistant film at the annular window channel, further reducing the precision requirements for operation.

[0020] Furthermore, in the above-mentioned processing method for a flexible circuit board with gold fingers in the inner layer, the diameter of the pre-made hole is 1.5mm to 2.5mm.

[0021] As described above, this method limits the diameter of the pre-made hole to the range of 1.5mm to 2.5mm. This size ensures that the ejector pin of the fixture has sufficient operating space to pass through and act on the resist film, while avoiding weakening the structural strength of the inner substrate or occupying too much non-functional area due to excessive hole diameter. It ensures the peeling function while taking into account the structural integrity of the substrate and the utilization rate of the panel space.

[0022] Furthermore, in the above-mentioned processing method for a flexible circuit board with gold fingers in the inner layer, the patterned etching includes: On the conductive layer, an opening of a first width is etched into the inner region corresponding to the edge of the resist film pattern; On the conductive layer, corresponding to the outer region of the edge of the resist film pattern, an opening of a second width is etched. The opening of the first width connects with the opening of the second width, together forming the annular window channel.

[0023] As described above, this method precisely constructs an annular windowed channel surrounding the adhesive resist film by etching openings on both the inner and outer sides. This channel fully exposes the underlying adhesive layer, providing a clear path guide for the peeling operation. The design of etching the inner and outer sides separately allows for independent control of the channel width and position, accommodating gold finger areas of different sizes and shapes, ensuring the accuracy and integrity of the peeling path.

[0024] Furthermore, in the above-mentioned processing method of the flexible circuit board with gold fingers in the inner layer, the first width is 0.10mm to 0.20mm, the second width is 0.15mm to 0.25mm, and the width of the annular window channel is the sum of the first width and the second width.

[0025] As described above, this method limits the inner and outer etching widths within an optimized range, resulting in an annular window channel with a suitable width. This width ensures smooth separation of the overall structure along the channel during the tearing process, avoiding excessive tearing resistance or circuit tearing due to an overly narrow channel. It also guarantees the smoothness of the window edge after tearing, keeping burr height to an extremely low level, thus improving the product's appearance quality and electrical reliability.

[0026] Furthermore, in the above-mentioned processing method for a flexible circuit board with gold fingers in the inner layer, the width of the annular window channel is 0.30-0.45mm.

[0027] As described above, the width of the annular window channel is preferably 0.30-0.45 mm. Within this preferred range, the smoothness of the tearing operation and the flatness of the window edge are optimally balanced. Experiments have verified that this method can effectively ensure that the tearing force is stable at 3.5±0.5N and the burr height at the window edge is less than 10μm, providing an optimal process parameter window for large-scale mass production.

[0028] Furthermore, in the above-mentioned processing method of a flexible circuit board with gold fingers in the inner layer, the adhesion force between the resist film and the inner substrate is less than the bonding force between the resist film and the cured adhesive layer.

[0029] As described above, it is ensured that the separation interface occurs precisely between the polyimide protective film and the inner cover film during peeling, guaranteeing that the surface of the gold fingers is clean after peeling, and that the upper composite structure can be completely peeled off without leaving any residue.

[0030] Furthermore, in the above-described processing method for a flexible circuit board with gold fingers in the inner layer, after removing the overall structure to expose the gold finger area, the method further includes the step of: An outer cover film is attached to the outside of the conductive layer. The outer cover film has a second opening corresponding to the gold finger area. The size of the second opening is larger than the size of the first opening.

[0031] As described above, this method creates a stepped protective structure of "large window within small window" by laminating an outer cover film with a larger opening. This design provides sufficient alignment tolerance for potential cumulative errors in subsequent processes. Even if a slight offset occurs during the lamination of the outer cover film, it will not cover the effective contact area of ​​the gold fingers, significantly improving the lamination yield and appearance consistency of the final product.

[0032] Another technical solution adopted by the present invention is to provide a flexible circuit board with gold fingers in the inner layer, which is obtained by the above-mentioned processing method of the flexible circuit board with gold fingers in the inner layer.

[0033] As described above, the flexible circuit board with gold fingers on the inner layer, manufactured using the aforementioned processing method, has a clean and uncontaminated inner gold finger area, smooth and burr-free window edges, and a precise stepped fit between the outer cover film and the inner window. This product exhibits excellent electrical connection reliability, mechanical stability, and appearance consistency, meeting the stringent requirements of high-density, high-reliability electronic devices for flexible circuit boards.

[0034] Please see Figures 1-4 Example 1 of this application is as follows: This embodiment provides a flexible circuit board with gold fingers in the inner layer, wherein the inner layer is designed with gold fingers 11; the processing method of the flexible circuit board with gold fingers in the inner layer includes the following steps: S1: Inner Layer Fabrication and Pre-protection An inner layer substrate 1 with pre-formed graphics is provided, and the surface of the inner layer substrate 1 has gold fingers 11. A pre-cut window is made on the inner layer cover film 2 corresponding to the gold finger area. The inner layer cover film 2 with the pre-cut window is pressed and cured onto the surface of the inner layer substrate 1, so that the gold fingers 11 are exposed through the window in the cover film. Subsequently, a layer of adhesive resist film 3 (PI protective film tape) is applied directly to the window area of ​​the inner layer cover film 2, the PI protective film tape completely covering the window area of ​​the cover film, and its edge overlapping the inner layer cover film 2 by at least 0.5 mm. Multiple segments of the PI protective film are combined into a single long strip design to form a sealed protection for the gold fingers.

[0035] Figure 1 The diagram shows a cross-sectional view of the inner layer structure after step S1 is completed (where the inner layer substrate 1 (double-sided substrate) includes polyimide (PI) and CU on both sides, and the inner layer cover film 2 (including adhesive layer (AD) and polyimide PI) is located above the inner layer substrate 1).

[0036] S2: Outer layer lamination On the entire surface of the inner substrate 1, which is covered with a polyimide protective film, a pure adhesive film 4 and a conductive layer 5 (pure copper foil) are sequentially stacked. Then, high-temperature and high-pressure pressing is performed to cure the pure adhesive film, bonding the pure copper foil, adhesive layer 4, inner cover film 2, and inner substrate 1 into a single unit, forming a three-layer slab. The PI protective film acts as a resist film during the pressing process, effectively preventing molten pure adhesive from flowing into the gold finger area below.

[0037] Figure 2 The figure shown is a cross-sectional schematic diagram of the three-layer slab after pressing in step S2.

[0038] S3: Outer Layer Patterning and Selective Etching Drilling is performed on the pure copper foil side of the three-layer slab completed in S2, followed by copper plating for hole metallization. Then, the outer layer circuit pattern is formed through pattern transfer and etching processes. The etching in this step is a critical selective etching process, specifically including: On the copper surface corresponding to the PI protective film area, an etching with a width of 0.10-0.20 mm (preferably 0.15 mm) is performed along the inner side of the edge of the PI protective film pattern to remove the copper layer in that area, but retain the copper layer above the main area of ​​the PI protective film.

[0039] In the outer area without the PI protective film, an etching with a width of 0.15-0.25 mm (preferably 0.20 mm) is performed along the outer edge of the protective film pattern.

[0040] After the above two etching processes, an annular window channel 51 with a width of 0.30-0.45 mm (preferably 0.35 mm) is formed around the edge of the polyimide protective film. The copper layer inside the annular window channel 51 is completely removed, exposing the pure adhesive film that has been cured underneath.

[0041] Figure 3 This is a partial top view of the annular windowed channel formed after selective etching in step S3; Figure 4 This is a partial top view of the annular window channel (peel-off channel) formed after selective etching in step S3.

[0042] S4: Tear-open window A specialized ejector tool is fabricated, equipped with precision ejector pins corresponding to the positions of the gold fingers. The board with the outer layer etched is positioned on the ejector tool, ensuring the ejector pins are precisely aligned and applied to the predetermined peeling end of the PI protective film. The ejector pins are driven upwards, lifting the PI protective film at the peeling end and separating it from the underlying inner layer cover film 2, forming a peeling initiation point. Subsequently, along this initiation point, manually or with the aid of tools, the PI protective film, the cured pure adhesive film above it, and the unetched copper layer on the pure adhesive film are peeled off as a single composite structure, thus fully exposing the clean inner layer gold fingers underneath.

[0043] S5: Final protective layer bonding An outer cover film is applied as a final protective layer to the exposed gold finger area and its surroundings. The opening size of the outer cover film is at least 0.3 mm larger on one side than the pre-opening size of the inner cover film 2, thereby providing alignment tolerance and ensuring that the outer cover film does not cover the effective contact area of ​​the gold finger due to lamination deviation.

[0044] Please see Figure 5 and Figure 6 Example 2 of this application is as follows: This embodiment provides a flexible circuit board with gold fingers in the inner layer; the processing method of the flexible circuit board with gold fingers in the inner layer includes the following steps: 1. On the inner layer substrate 1 (double-sided substrate) after the inner layer circuit etching and browning are completed, a polyimide cover film (27.5μm thick: PI-12.5μm + AD-15μm) with pre-processed openings (the openings are 0.05mm larger than the gold finger pattern on each side as compensation for excess adhesive) is applied to the etched circuitry of the inner layer. A TPX release film is used as an auxiliary material for lamination. After curing, the gold finger opening area of ​​the inner layer substrate 1 is formed. Subsequently, a 25μm thick, slightly tacky resist film 3 (PI protective film tape) is precisely applied using a transfer film to cover the entire gold finger opening area, with the tape edge overlapping the inner layer cover film 2 by 0.8mm. Before lamination, a 2.0mm diameter pre-drilled hole 8 is processed at the edge of the PI protective film tape on the product process edge after the inner layer cover film is applied. During lamination, the PI protective film covers approximately 2 / 3 of this hole area.

[0045] 2. On the entire surface of the board with the protective film applied, a 25μm thick adhesive layer 4 (pure adhesive film) and a 12μm thick conductive layer 4 (calendered copper foil) are laminated, and then the board is placed in a vacuum press at 180℃ and 30kgf / cm². 2 Press the adhesive under these conditions for 90 minutes to allow the pure adhesive to fully cure.

[0046] 3. The laminated board is drilled, copper-plated, and electroplated throughout. Then, dry film exposure is used for pattern transfer. After DES line etching, circuit patterns are fabricated on the outer copper foil. Using acidic copper chloride etching solution, selective etching is achieved by precisely controlling exposure and etching parameters: a 0.15mm wide annular copper-free area is etched inside the polyimide protective film pattern, and a 0.20mm wide copper-free area is etched outside, thus forming a pure adhesive exposure channel with a total width of 0.35mm.

[0047] 4. After aligning the initial positioning holes of the FPC panel with the initial positioning pins 6 of the fixture, fix the FPC onto the dedicated ejector fixture. The ejector pins 7 on the fixture are precisely aligned with the exposed area of ​​the pre-drilled holes 8. The ejector pins protrude 1.5~2mm from the fixture plane. Press down on the side of the FPC with the pre-drilled holes to smoothly lift the PI protective film. The operator uses tweezers to hold the lifted end of the PI protective film and applies gentle force at an angle of approximately 150 degrees to peel off the protective film, along with the cured pure adhesive and copper foil on top, revealing the clean gold fingers.

[0048] Figure 5 This is a partial structural diagram of the tearing process using a pin fixture in step 4.

[0049] 5. Finally, attach the outer cover film 9 (12.5μm PI + 25μm adhesive), whose window size is 0.4mm larger on each side than the inner cover film 2, to complete the final protection.

[0050] Figure 6This is a schematic diagram of the final product cross-section after the outer cover film 9 on both sides of the outer layer is peeled off in an embodiment of the present invention; Testing showed that the flexible circuit board produced in this embodiment had clean gold finger surfaces, free of any adhesive residue, and its contact resistance met requirements. The insertion and extraction force test passed 5000 cycles. The peeling process achieved a yield rate of over 99.5%, and its efficiency was approximately 300% higher than traditional manual methods.

[0051] In summary, the flexible circuit board with gold fingers in the inner layer and its processing method provided by the present invention have the following significant advantages: 1. Fundamentally eliminate glue overflow and contamination, ensuring the integrity of the gold finger's function. Traditional pre-windowed lamination processes cannot prevent adhesive flow from contaminating the gold fingers. This invention addresses this by directly bonding a polyimide (PI) protective film to the gold finger surface, creating a perfect physical barrier during subsequent pure adhesive film lamination, thus eliminating the risk of adhesive overflow at the source. Experimental verification shows that gold fingers prepared using this method achieve a 100% clean and contamination-free surface, requiring no subsequent cleaning and ensuring excellent and stable electrical contact performance.

[0052] 2. Achieve high-quality window edges, improving product reliability and consistency. Traditional laser cutting methods generate a heat-affected zone, leading to edge carbonization and burrs (typically 15-30 μm); while simple mechanical peeling methods easily cause edge tearing and irregularities (burrs can reach 50-100 μm). This invention uses selective etching to form precise tearing channels, allowing the tearing process to naturally separate along the material interface. The resulting window edges are smooth and flat, with burr height controlled within 10 μm, greatly reducing stress concentration and potential short-circuit risks caused by edge defects, significantly improving product consistency and reliability.

[0053] 3. Breakthrough improvements in process stability and yield. Traditional methods suffer from yield limitations due to uncertainties in laser alignment accuracy, thermal deformation, or manual tearing, typically resulting in yields below 93%, and sometimes even below 60%. This invention innovatively introduces a tearing scheme using pre-drilled holes and ejector pins, achieving a 100% tearing success rate and stable tearing force (3.5±0.5N). Combined with a guided tearing channel, the overall process yield consistently reaches over 99%, providing a crucial guarantee for large-scale mass production.

[0054] 4. Achieve micron-level dimensional accuracy to meet high-density design requirements. The final window size and position of this invention are determined by the PI protective film and the etched copper layer on the protective film. Quantitative data shows that the positional accuracy of the tear-off cover window can reach ±0.1mm, and the contour size deviation is controlled within ±0.05mm. In addition, the "large-over-small" design of the outer cover film (more than 0.3mm larger on each side) provides secondary process tolerance, further ensuring the accurate realization of the high-density interconnect design intent.

[0055] 5. It forms a systematic solution with high industrial application value. This invention is not an improvement on a single step, but rather provides a complete and controllable process flow from "barrier (PI film) - construction (lamination) - guidance (etching channels) - execution (ejector peeling)". This solution transforms quality risks from uncontrollable process steps into engineering problems that can be guaranteed by precision patterning and mechanical fixtures. The technical path is clear, repeatable, and highly compatible with automation, possessing significant advantages for industrial application and promotional value.

[0056] 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 processing a flexible circuit board with gold fingers in the inner layer, characterized in that, Includes the following steps: An inner cover film with a first opening is attached to the inner layer substrate after the circuit fabrication is completed, the first opening exposing the gold finger area of ​​the inner layer substrate. A resist film is attached to the first opening of the inner cover film, and the resist film covers the gold finger area. On the inner substrate to which the resist film is attached, an adhesive layer and a conductive layer are sequentially stacked and then pressed together. The conductive layer is patterned and etched to form an annular window channel that exposes the adhesive layer at the periphery of the edge of the resist film; Peel off the annular window opening to remove the resist film and the adhesive layer and conductive layer above it as a whole structure to expose the gold finger area.

2. The method for processing a flexible circuit board with gold fingers in the inner layer according to claim 1, characterized in that, The specific steps of tearing from the annular window opening are as follows: the adhesive-resistant film below the annular window opening is lifted by a fixture to form the tearing starting point.

3. The method for processing a flexible circuit board with gold fingers in the inner layer according to claim 1, characterized in that, Before bonding the resist film, the method further includes the following steps: machining a pre-formed hole on the inner substrate at the end position of the gold finger; after bonding the resist film, the projection of the resist film covers a first part of the pre-formed hole and exposes a second part of the pre-formed hole; The specific steps of tearing from the annular window channel are as follows: a jig passes through the pre-made hole and lifts the adhesive-resistant film below the annular window channel to form a tearing starting point.

4. The method for processing a flexible circuit board with gold fingers in the inner layer according to claim 3, characterized in that, The diameter of the pre-drilled hole is 1.5 mm to 2.5 mm.

5. The method for processing a flexible circuit board with gold fingers in the inner layer according to claim 1, characterized in that, The patterning etching includes: On the conductive layer, an opening of a first width is etched into the inner region corresponding to the edge of the resist film pattern; On the conductive layer, corresponding to the outer region of the edge of the resist film pattern, an opening of a second width is etched. The opening of the first width connects with the opening of the second width, together forming the annular window channel.

6. The method for processing a flexible circuit board with gold fingers in the inner layer according to claim 5, characterized in that, The first width is 0.10 mm to 0.20 mm, the second width is 0.15 mm to 0.25 mm, and the width of the annular window channel is the sum of the first width and the second width.

7. The method for processing a flexible circuit board with gold fingers in the inner layer according to claim 6, characterized in that, The width of the annular window opening channel is 0.30-0.45mm.

8. The method for processing a flexible circuit board with gold fingers in the inner layer according to claim 1, characterized in that, The adhesion force between the resist film and the inner substrate is less than the bonding force between the resist film and the cured adhesive layer.

9. The method for processing a flexible circuit board with gold fingers in the inner layer according to claim 1, characterized in that, After removing the overall structure to expose the gold finger area, the following steps are also included: An outer cover film is attached to the outside of the conductive layer. The outer cover film has a second opening corresponding to the gold finger area. The size of the second opening is larger than the size of the first opening.

10. A flexible circuit board with gold fingers in the inner layer, characterized in that, It is manufactured by the processing method of the flexible circuit board with gold fingers in the inner layer as described in any one of claims 1 to 9.

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