A method for separating a flexible circuit board from a profile

Abstract

This invention discloses a method for separating irregularly shaped contours of a flexible circuit board, comprising the following steps: Step 1: Providing a flexible circuit board, which includes a cover film, copper foil circuitry, a PI base film, and a bottom copper foil stacked sequentially from top to bottom. A continuous asymmetric V-shaped groove with a depth of 60%-80% of the PI base film thickness is formed on the PI base film along the irregular contour and thickness direction of the flexible circuit board by laser ablation. Unablated PI base film is retained at the bottom of the groove, maintaining the integrity of the flexible circuit board. Step 2: Applying flexible mechanical composite stress to the flexible circuit board, causing it to undergo a ductile-brittle transition fracture along the V-shaped groove. After mechanical breakage, the board separates into finished product and waste. This method avoids burrs and the thermal impact of laser cutting on the flexible circuit board, preventing carbonization, blackening, and decreased insulation resistance of the PI substrate. It also avoids the re-solidification of the molten material generated by laser ablation.

Description

Technical Field

[0001] This invention relates to the field of flexible circuit board irregular contour separation technology, and more specifically, to a method for separating irregular contours of flexible circuit boards. Background Technology

[0002] With the rapid development of automotive intelligence and large-screen technology, automotive central control displays have been upgraded to full-screen, curved screen, and multi-functional integration. As a core component for signal transmission, the demand for flexible circuit boards is increasing. Automotive flexible circuit boards are mostly double-layer or multi-layer composite structures, and to accommodate the installation space of the central control screen and avoid screw posts and positioning ribs, they need to be processed into various complex irregular shapes.

[0003] Currently, there are two main methods in the industry for separating irregularly shaped flexible circuit boards: 1. Precision steel die punching process: For flexible circuit boards with a thickness greater than 0.2mm or with local reinforcing plates, the high-pressure shearing force applied by the die during punching can easily generate burrs on the edges of the copper foil. If these burrs are not cleaned properly, they can cause short circuits in subsequent circuits. At the same time, the shearing force can cause the adhesive at the interface between the cover film and the PI base film to flow laterally, resulting in interlayer delamination or separation, which affects the flexibility and service life of the flexible circuit board. In addition, steel dies wear out quickly, and the cost of replacing dies is high. This is not suitable for the multi-variety and small-batch production needs of automotive central control flexible circuit boards. Die switching is time-consuming and labor-intensive, which greatly reduces production efficiency and increases production costs.

[0004] 2. Ultraviolet Laser Full-Through Cutting Process: This process was developed to solve the aforementioned punching burr problem. Although it can achieve non-contact, high-precision separation of irregular shapes, it has fatal flaws. The laser energy must be sufficient to cut through the entire layer of PI base film and copper foil, which will form a 100μm-200μm wide heat-affected zone at the cut edge, causing the PI substrate to carbonize and blacken and the insulation resistance to decrease, failing to meet automotive-grade insulation requirements. At the same time, the melt generated by laser ablation will re-solidify, forming hard protruding particles on the cut surface, which can easily scratch the backlight layer of the display screen and generate foreign objects during subsequent assembly, leading to product scrap. In addition, the ultraviolet laser cutting speed is slow and cannot meet the needs of mass production of automotive flexible circuit boards. Summary of the Invention

[0005] The technical problem to be solved by this invention is how to avoid the generation of burrs and the thermal impact of laser cutting on flexible circuit boards, which would cause carbonization, blackening and a decrease in insulation resistance of the PI substrate, while also preventing the molten material generated by laser ablation from re-solidifying.

[0006] The technical problem to be solved by the present invention is achieved through the following technical solution: To solve the above-mentioned technical problems, the present invention provides a method for separating irregular contours of flexible circuit boards, which includes the following steps: Step 1: Provide a flexible circuit board, which includes a cover film, copper foil circuit, PI base film and bottom copper foil stacked sequentially from top to bottom. Along the irregular contour of the flexible circuit board and along its thickness direction, a continuous asymmetric V-shaped trench with a depth of 60%-80% of the thickness of the PI base film is formed by laser ablation on the PI base film. The bottom of the trench retains the unablated PI base film and keeps the flexible circuit board in its intact shape. Step 2: Apply flexible mechanical composite stress to the flexible circuit board, causing the flexible circuit board to undergo ductile-brittle transition fracture along the V-shaped groove, and after mechanical breakage, it separates into finished product and waste.

[0007] In a preferred embodiment of the method for separating the irregular contour of the flexible circuit board provided by the present invention, the sidewall of the V-shaped groove near the copper foil line has an angle of 30°-45° with the vertical direction, and the sidewall of the V-shaped groove away from the copper foil line has an angle of 15°-25° with the vertical direction.

[0008] As a preferred embodiment of the method for separating the irregular contour of the flexible circuit board provided by the present invention, the laser device for laser ablation adopts a pulsed fiber laser with a wavelength of 1064nm. The parameters of the pulsed fiber laser are set as follows: pulse width 100ns, repetition frequency 50kHz, average power 6W-10W, scanning speed 2000mm / s-400mm / s, and focused spot diameter 25μm.

[0009] In a preferred embodiment of the method for separating the irregular contour of the flexible circuit board provided by the present invention, the relationship between the laser ablation depth D and the total thickness H of the flexible circuit board satisfies: ,and The matching between laser scanning speed v and pulse energy E satisfies: .

[0010] As a preferred embodiment of the method for separating the irregular contour of the flexible circuit board provided by the present invention, step 2 specifically involves providing a pair of parallel pressure rollers and a winding system. The pressure rollers include an upper roller and a lower roller. The upper roller is a smooth metal roller, and the lower roller is a silicone rubber roller with an arc-shaped groove (Shore hardness A30-A40). The groove depth is 0.5mm and the width is 2mm. The groove trajectory is precisely matched with the trajectory of the V-shaped groove. The force application method is as follows: the upper roller applies a pressure of 0.2MPa-0.5MPa perpendicular to the surface of the flexible circuit board, and the winding system applies a tensile force along the length direction of the flexible circuit board. The tensile force is 0.5N-1.0N per centimeter of width. The linear velocity difference between the upper roller and the lower roller is 1%-3%. Flexible mechanical composite stress is applied to the flexible circuit board, causing the flexible circuit board to undergo a ductile-brittle transition fracture along the V-shaped groove. After mechanical breakage, it is separated into finished product and waste.

[0011] As a preferred embodiment of the method for separating the irregular contour of the flexible circuit board provided by the present invention, it further includes step 3: blowing the cross-section and surface of the flexible circuit board with an ion air gun (wind speed 15-20m / s).

[0012] As a preferred embodiment of the method for separating the irregular contour of the flexible circuit board provided by the present invention, it further includes step 4: after the flexible circuit board is mechanically broken, the cross-section is non-destructively inspected using an optical coherence tomography (OCT) module with an inspection accuracy of 1μm to identify whether there are incompletely broken bridging points; for the identified bridging points, secondary local laser irradiation is used for repair, the laser pulse energy is reduced to 30% of the original laser grooving energy, single-point irradiation is used, and the irradiation time of single-point irradiation is 50ns-100ns.

[0013] As a preferred embodiment of the method for separating the irregular contour of the flexible circuit board provided by the present invention, it further includes step 5: performing oxygen plasma cleaning on the flexible circuit board, with a cleaning power of 300W and a cleaning time of 10-15 seconds.

[0014] In a preferred embodiment of the method for separating the irregular contour of the flexible circuit board provided by the present invention, the thickness of the cover film is 10μm-20μm, the thickness of the copper foil circuit is 18μm-35μm, the thickness of the PI base film is 50μm-200μm, the thickness of the bottom copper foil is 18μm-35μm, and the total thickness of the flexible circuit board is 80μm-400μm.

[0015] The present invention has the following beneficial effects: By using laser shallow grooving, the ablation area is confined to the shallow layer of the PI substrate film, without damaging the copper foil circuitry, resulting in no carbonization or slag, thus ensuring the insulation performance and circuit integrity of the flexible circuit board, thereby solving the thermal damage problem of laser full-cutting. Through flexible mechanical stress-controlled fracture, a near-brittle fracture of the flexible circuit board is achieved, resulting in a smooth, burr-free, and delamination-free cross-section, meeting automotive-grade edge quality requirements, thus solving the burr and delamination problems of precision punching. Asymmetric V-shaped grooves guide the crack direction, preventing the crack from touching the copper foil circuitry, ensuring that the separation process does not damage the circuitry, and adapting to various complex irregular contours for precise separation. This method can use conventional fiber lasers and customized flexible pressure rollers, requiring no expensive equipment, suitable for mass production and multi-variety production, with low mold switching costs. It avoids burr generation and the thermal impact of laser cutting on the flexible circuit board, preventing carbonization, blackening, and decreased insulation resistance of the PI substrate, while also preventing the re-solidification of the molten material generated by laser ablation. Detailed Implementation

[0016] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0017] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the embodiments, and are only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0018] Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first," "second," or "third" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0019] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below. The present invention will be described in detail below with reference to embodiments, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0020] This invention provides a method for separating irregular contours of flexible printed circuit boards, which includes the following steps: Step 1: Provide a flexible circuit board, which includes a cover film, copper foil circuit, PI base film and bottom copper foil stacked sequentially from top to bottom. Lay the flexible circuit board to be processed flat on the vacuum adsorption platform, start vacuum adsorption and ensure that the flexible circuit board is flat without wrinkles and displacement. Along the irregular contour of the flexible circuit board and along its thickness direction, a continuous asymmetric V-shaped groove with a depth of 60%-80% of the thickness of the PI base film is formed by laser ablation. The bottom of the groove retains the unablated PI base film (the bottom of the groove retains 20%-40% of the thickness of the unablated PI hinge layer, without damaging any copper foil circuit) and keeps the flexible circuit board in its complete shape. After the laser scanning is completed, turn off the vacuum adsorption and transfer the flexible circuit board to the breaking device station. At this time, the flexible circuit board is completely intact, with only the continuous V-shaped groove. Step 2: Apply flexible mechanical composite stress to the flexible circuit board, causing the flexible circuit board to undergo ductile-brittle transition fracture along the V-shaped groove, and after mechanical breakage, it separates into finished product and waste.

[0021] By using laser shallow grooving, the ablation area is confined to the shallow layer of the PI substrate film, without damaging the copper foil circuitry, resulting in no carbonization or slag, thus ensuring the insulation performance and circuit integrity of the flexible circuit board, thereby solving the thermal damage problem of laser full-cutting. Through flexible mechanical stress-controlled fracture, a near-brittle fracture of the flexible circuit board is achieved, resulting in a smooth, burr-free, and delamination-free cross-section, meeting automotive-grade edge quality requirements, thus solving the burr and delamination problems of precision punching. Asymmetric V-shaped grooves guide the crack direction, preventing the crack from touching the copper foil circuitry, ensuring that the separation process does not damage the circuitry, and adapting to various complex irregular contours for precise separation. This method can use conventional fiber lasers and customized flexible pressure rollers, requiring no expensive equipment, suitable for mass production and multi-variety production, with low mold switching costs. It avoids burr generation and the thermal impact of laser cutting on the flexible circuit board, preventing carbonization, blackening, and decreased insulation resistance of the PI substrate, while also preventing the re-solidification of the molten material generated by laser ablation.

[0022] Furthermore, the sidewall of the V-shaped groove near the copper foil line has an angle of 30°-45° with the vertical direction to prevent cracks from extending towards the copper foil line. The sidewall of the V-shaped groove away from the copper foil line has an angle of 15°-25° with the vertical direction to guide cracks to extend preferentially towards the non-line side, thus thoroughly protecting the integrity of the copper foil line.

[0023] Furthermore, the laser equipment for laser ablation uses a pulsed fiber laser with a wavelength of 1064nm. The parameters of the pulsed fiber laser are set as follows: pulse width 100ns, repetition frequency 50kHz, average power 6W-10W, scanning speed 2000mm / s-400mm / s, and focused spot diameter 25μm, which far exceeds the ultrafast laser cutting speed and is suitable for mass production.

[0024] Furthermore, the relationship between the laser ablation depth D and the total thickness H of the flexible circuit board satisfies: ,and The matching between laser scanning speed v and pulse energy E satisfies: This is to avoid burning the underlying copper foil.

[0025] Further, step 2 specifically involves providing a pair of parallel pressure rollers and a winding system. The pressure rollers include an upper roller and a lower roller. The upper roller is a smooth metal roller, and the lower roller is a silicone rubber roller with an arc-shaped groove (Shore hardness A30-A40). The groove depth is 0.5mm and the width is 2mm. The groove trajectory is precisely matched with the trajectory of the V-shaped groove. The force application method is as follows: the upper roller applies a pressure of 0.2MPa-0.5MPa perpendicular to the surface of the flexible circuit board, and the winding system applies a tensile force along the length direction of the flexible circuit board. The tensile force is 0.5N-1.0N per centimeter of width. The difference in linear velocity between the upper roller and the lower roller is 1%-3%. Flexible mechanical composite stress is applied to the flexible circuit board, causing the flexible circuit board to undergo ductile-brittle transition fracture along the V-shaped groove. After mechanical breakage, it separates into finished product and waste. Bending normal stress, tensile normal stress, and slight in-plane shear force are applied simultaneously to make the flexible circuit board fracture controllably along the laser groove.

[0026] Furthermore, it also includes step 3: using an ion air gun (wind speed 15-20m / s) to blow away trace amounts of PI dust from the cross-section and surface of the flexible circuit board, so as to avoid the dust affecting subsequent assembly.

[0027] Furthermore, step 4 is included: after the flexible circuit board is mechanically broken, an optical coherence tomography (OCT) module is used to perform non-destructive testing on the cross-section with a detection accuracy of 1μm to identify any incompletely broken bridging points; for the identified bridging points, secondary local laser irradiation is used for repair, with the laser pulse energy reduced to 30% of the original laser grooving energy, using single-point irradiation for 50ns-100ns. This breaks away from the traditional dilemma of scrapping boards if they fail to meet the breakage standard, innovatively introducing optical coherence tomography (OCT) technology commonly used in medical ophthalmology, and applying it across disciplines to non-destructive testing of flexible circuit board cross-sections. Combined with secondary local laser repair, this significantly improves yield and reduces production costs.

[0028] Furthermore, it also includes step 5: oxygen plasma cleaning of the flexible circuit board, with a cleaning power of 300W and a cleaning time of 10-15 seconds, isotropically removing burrs to make the edges smoother and avoid scratching the backlight layer of the display screen during subsequent assembly.

[0029] Furthermore, the thickness of the cover film is 10μm-20μm, the thickness of the copper foil circuit is 18μm-35μm, the thickness of the PI base film is 50μm-200μm, the thickness of the bottom copper foil is 18μm-35μm, and the total thickness of the flexible circuit board is 80μm-400μm.

[0030] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0031] Obviously, the embodiments described above are only some embodiments of this application, not all embodiments, and do not limit the patent scope of this application. This application can be implemented in many different forms; on the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of this application more thorough and comprehensive. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing specific embodiments, or make equivalent substitutions for some of the technical features. Any equivalent structures made using the content of this application's specification, directly or indirectly applied to other related technical fields, are similarly within the patent protection scope of this application.

Claims

1. A method for separating irregular contours of a flexible circuit board, characterized in that, It includes the following steps: Step 1: Provide a flexible circuit board, which includes a cover film, copper foil circuit, PI base film and bottom copper foil stacked sequentially from top to bottom. Along the irregular contour of the flexible circuit board and along its thickness direction, a continuous asymmetric V-shaped trench with a depth of 60%-80% of the thickness of the PI base film is formed by laser ablation on the PI base film. The bottom of the trench retains the unablated PI base film and keeps the flexible circuit board in its intact shape. Step 2: Apply flexible mechanical composite stress to the flexible circuit board, causing the flexible circuit board to undergo ductile-brittle transition fracture along the V-shaped groove, and after mechanical breakage, it separates into finished product and waste.

2. The method for separating the irregular contour of a flexible circuit board according to claim 1, characterized in that, The sidewall of the V-shaped groove closest to the copper foil line makes an angle of 30°-45° with the vertical direction, while the sidewall of the V-shaped groove furthest from the copper foil line makes an angle of 15°-25° with the vertical direction.

3. The method for separating the irregular contour of a flexible circuit board according to claim 1, characterized in that, The laser equipment for laser ablation uses a pulsed fiber laser with a wavelength of 1064nm. The parameters of the pulsed fiber laser are set as follows: pulse width 100ns, repetition frequency 50kHz, average power 6W-10W, scanning speed 2000mm / s-400mm / s, and focused spot diameter 25μm.

4. The method for separating the irregular contour of a flexible circuit board according to claim 1, characterized in that, The relationship between the laser ablation depth D and the total thickness H of the flexible circuit board satisfies: ,and The matching between laser scanning speed v and pulse energy E satisfies: .

5. The method for separating the irregular contour of a flexible circuit board according to claim 1, characterized in that, Step 2 specifically involves providing a pair of parallel pressure rollers and a winding system. The pressure rollers include an upper roller and a lower roller. The upper roller is a smooth metal roller, and the lower roller is a silicone rubber roller with an arc-shaped groove (Shore hardness A30-A40). The groove depth is 0.5mm and the width is 2mm. The groove trajectory is precisely matched with the trajectory of the V-shaped groove. The force application method is as follows: the upper roller applies a pressure of 0.2MPa-0.5MPa perpendicular to the surface of the flexible circuit board, and the winding system applies a tensile force along the length of the flexible circuit board. The tensile force is 0.5N-1.0N per centimeter of width. The linear velocity difference between the upper roller and the lower roller is 1%-3%. Flexible mechanical composite stress is applied to the flexible circuit board, causing the flexible circuit board to undergo a ductile-brittle transition fracture along the V-shaped groove. After mechanical breakage, it separates into finished product and waste.

6. The method for separating the irregular contour of a flexible circuit board according to claim 1, characterized in that, It also includes step 3: blowing the cross-section and surface of the flexible circuit board with an ion air gun (wind speed 15-20m / s).

7. The method for separating the irregular contour of a flexible circuit board according to claim 1, characterized in that, The process also includes step 4: After the flexible circuit board is mechanically broken, the cross-section is non-destructively inspected using an optical coherence tomography (OCT) module with an accuracy of 1μm to identify any incompletely broken bridge points; for the identified bridge points, secondary local laser irradiation is used for repair, with the laser pulse energy reduced to 30% of the original laser grooving energy, and single-point irradiation is used, with an irradiation time of 50ns-100ns.

8. The method for separating the irregular contour of a flexible circuit board according to claim 1, characterized in that, It also includes step 5: oxygen plasma cleaning of the flexible circuit board, with a cleaning power of 300W and a cleaning time of 10-15 seconds.

9. The method for separating the irregular contour of a flexible circuit board according to claim 1, characterized in that, The thickness of the cover film is 10μm-20μm, the thickness of the copper foil circuit is 18μm-35μm, the thickness of the PI base film is 50μm-200μm, the thickness of the bottom copper foil is 18μm-35μm, and the total thickness of the flexible circuit board is 80μm-400μm.

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