A method and apparatus for fabricating a flexible circuit

Abstract

The flexible circuit preparation method disclosed by the application first carries out cutting and ultrasonic cleaning pretreatment on the insulating film, then places the insulating film in a potassium hydroxide solution for controllable hydrolysis, generates active functional groups on the surface of the film; after the hydrolysis, the film is immersed in a silver nitrate solution, and ion exchange is carried out for a long time in the dark, so that silver ions are uniformly anchored on the modified surface layer; finally, according to the preset printing information, the actual geometric structure of the film is obtained through visual positioning and position calibration, and the laser direct writing technology is used to reduce the silver ions in situ to a conductive silver layer, so as to generate a flexible circuit. The application has the advantages of short process, low cost, flexible graphic design, strong metal layer adhesion and the like, and is suitable for rapid prototyping and small-batch customized production in the fields of wearable devices, flexible sensors and Internet of Things. Based on the method, the application further discloses a flexible circuit preparation device for preparing a flexible circuit by using the method.

Description

Technical Field

[0001] This application relates to the field of integrated circuit manufacturing technology, and in particular to a method for fabricating flexible circuits. Background Technology

[0002] Flexible printed circuit boards (FPCs) are gradually replacing traditional rigid printed circuit boards (PCBs) in the field of integrated systems due to their excellent versatility and deformability. Conventional FPC manufacturing processes employ subtractive manufacturing, with photolithography as the key technology. This typically involves applying photoresist, pre-baking, positioning exposure, post-baking, development, etching, and stripping on a flexible copper-clad laminate. Obtaining the desired pattern requires large amounts of photoresist, etchant, and metal, making copper pattern production a highly technology- and capital-intensive industry. Currently, there are two main methods for FPC manufacturing: mask manufacturing and printing manufacturing. Printing manufacturing has the advantage of precisely applying ink materials to specific locations on the substrate by adjusting process parameters, eliminating the need for photomasks, templates, and other auxiliary equipment. Based on the ink material, it can be divided into nanoparticle inks and solution inks. Solution inks essentially grow metal patterns in a solution during use, without requiring sintering. Conductive metal patterns are typically silver or copper. While copper patterns offer high short-term economic benefits, they are easily oxidized upon contact with air, leading to reduced conductivity and decreased reliability. Silver, on the other hand, is the metal with the best conductivity and can stably maintain a highly conductive elemental state in a sulfur-free environment. Therefore, silver patterns are the preferred choice for flexible circuit board patterns.

[0003] Currently, the industry still mainly relies on traditional photolithography technology to fabricate flexible circuit patterns. This process has significant limitations: the manufacturing process is lengthy and complex, requiring multiple steps such as photoresist coating, mask exposure, chemical development, etching, and resist removal; it relies on chemical materials such as photoresist, generating a large amount of organic waste liquid, causing environmental pollution; at the same time, the fabrication cost is high, and it is difficult to meet the needs of flexible electronics for three-dimensional curved surfaces, large areas, and personalized fabrication. In particular, for flexible polymer substrates such as PI films, traditional processes often struggle to balance interfacial adhesion and substrate protection, affecting the reliability of the circuit. Summary of the Invention

[0004] This invention discloses a method for fabricating flexible circuits directly on the surface of a PI thin film using laser thermal etching. Based on this method, this invention also discloses an apparatus for applying the method.

[0005] This invention is achieved through the following technical solution: A method for fabricating a flexible circuit, comprising: The insulating film is pretreated, then transferred to an alkaline solution for hydrolysis, followed by sensitization treatment. The hydrolyzed insulating film was transferred to a silver nitrate solution for ion exchange. The printing information is obtained, and the insulating film is laser-printed according to the positions of the insulating film and the laser to generate a flexible circuit.

[0006] Furthermore, the pretreated insulating film specifically includes: Cut the insulating film to the target shape; Ultrasonic cleaning of insulating film for 5-10 minutes, ultrasonic frequency 40-70kHz.

[0007] Furthermore, the alkaline solution is a 5% (w / v) potassium hydroxide solution, and the hydrolysis time of the insulating film is 50-70 minutes; The sensitization treatment specifically includes immersing the hydrolyzed insulating film in a 3-mercaptopropyltrimethoxysilane ethanol solution for 30-40 minutes.

[0008] Furthermore, the concentration of the silver nitrate solution is 0.05 mol / L to 0.2 mol / L.

[0009] Furthermore, the ion exchange conditions are as follows: the insulating film is completely immersed in silver nitrate solution and placed in a light-protected environment for at least 24 hours.

[0010] Furthermore, the printed information includes: The printing information includes: the preset geometric structure of the film, the printed image information, the image position information, and the image size information.

[0011] Furthermore, laser printing of the insulating film, based on the positions of the insulating film and the laser, specifically includes: Obtain the endpoint position information of the insulating film; The actual geometric structure of the insulating film is determined based on the endpoint location information; If the actual geometry of the insulating film conforms to the preset geometry, the rotation angle of the insulating film is obtained, and the position of the laser is adjusted according to the printing information. If the actual geometry does not conform to the preset geometry, an alarm message will be output.

[0012] Furthermore, the step of obtaining printing information, after laser printing the insulating film according to the positions of the insulating film and the laser, also includes: Connect the flexible circuit to the test circuit to obtain the electrical performance information of the flexible circuit.

[0013] A flexible circuit fabrication apparatus is used for the fabrication of flexible circuit printed circuit boards. When fabricating a flexible circuit printed circuit board, the flexible circuit fabrication apparatus implements the flexible circuit fabrication method described in any one of the above-mentioned methods.

[0014] Furthermore, the device includes: a cutting device, an ultrasonic cleaning device, a hydrolysis device, an ion exchange device, a laser printing device, and an alarm device.

[0015] The beneficial effects of this invention are as follows: This application utilizes laser thermal etching to fabricate flexible circuits on the surface of insulating films. Through three steps—hydrolysis, silver ion exchange, and laser thermal etching—an environmentally friendly fabrication method for flexible circuits is achieved. Surface hydrolysis is performed using a 5% potassium hydroxide solution. Subsequently, the film is placed in a silver nitrate solution to form a uniform silver ion precursor layer on the surface of the insulating film via ion exchange. Finally, selective thermal etching of the silver-coated film using a laser device forms an electrically conductive silver layer on the surface of the insulating film according to preset printing information, directly fabricating a flexible circuit with conductivity and interfacial adhesion. This method combines the precision of printing technology with the selectivity of laser processing, enabling rapid prototyping of circuit patterns without the need for masks, simplifying the cumbersome multi-step pattern transfer process of traditional photolithography. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the workflow of the present invention; Figure 2a This is a diagram showing the shape of the insulating film after hydrolyzing it in potassium hydroxide solution for 30 minutes according to the present invention. Figure 2b This is a diagram showing the shape of the insulating film after hydrolysis in potassium hydroxide solution for 60 minutes according to the present invention. Figure 2c This is a diagram showing the shape of the insulating film after hydrolyzing it in potassium hydroxide solution for 90 minutes according to the present invention. Figure 2d This is a diagram showing the shape of the insulating film after hydrolyzing it in potassium hydroxide solution for 120 minutes according to the present invention. Figure 3a This is a diagram of the surface shape of the insulating film when the etching depth is 10% during etching. Figure 3b This is a diagram of the surface shape of the insulating film when the etching depth is 20% during etching. Figure 3c This is a diagram of the surface shape of the insulating film when the etching depth is 30% during etching. Figure 3dThis is a diagram of the surface shape of the insulating film when the etching depth is 40% during etching. Figure 3e This is a diagram of the surface shape of the insulating film when the etching depth is 60% during etching. Figure 3f This is a diagram of the surface shape of the insulating film when the etching depth is 80% during etching. Figure 3g This is a diagram of the surface shape of the insulating film when the etching depth is 100% during etching. Figure 4a This is the test circuit in step S4 of the present invention; Figure 4b This is a circuit connection diagram of the flexible circuit prepared by the method described in this invention and connected to the test circuit; Figure 5 This is a schematic diagram of one embodiment of the flexible circuit fabrication apparatus described in this invention.

[0018] in: 1. Laser printing device; 2. Cutting device; 3. Alarm device; 4. Ion exchange device; 5. Hydrolysis device; 6. Ultrasonic cleaning device. Detailed Implementation

[0019] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0020] It should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0021] Furthermore, the terms "first" and "second" 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" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0022] Please refer to Figure 1 The present invention discloses a method for fabricating a flexible circuit, comprising: S1, pre-treated insulating film, then transferred to alkaline solution for hydrolysis, followed by sensitization treatment; S2, the hydrolyzed insulating film is transferred to silver nitrate solution for ion exchange; S3: Obtain printing information, and laser print the insulating film according to the positions of the insulating film and the laser to generate a flexible circuit.

[0023] Wherein S1, the pretreated insulating film specifically includes: S11, Cut the insulating film to the target shape; S12, ultrasonically clean the insulating film for 5~10 minutes, ultrasonic frequency 40~70kHz.

[0024] Cutting the insulating film to the target shape is a fundamental step in obtaining flexible circuit boards, reducing material waste. Operators cut the insulating film body according to the required shape, eliminating the need for custom-made molds. Furthermore, the cut insulating film is easier to handle and etch, preventing curling or wrinkling of large sheets during subsequent processing. Specifying the geometric shape of the insulating film also facilitates uniform size and the preparation of standardized fixtures to hold the insulating film. The preferred geometric shape is rectangular, such as a 50*50mm square or an 80*50mm rectangle.

[0025] After cutting, place the insulating film in an ultrasonic cleaner and ultrasonically clean it at a frequency of 40~70kHz for 5~10 minutes. The purpose is to remove surface contaminants such as grease, dust, and other organic residues from the insulating film. The ultrasonic energy of 40~70kHz is relatively low, which can avoid physical damage to the surface of the insulating film caused by high-frequency overheating or low-frequency cavitation. A clean film surface can improve the wettability of the film surface, making it easier to carry out subsequent processing of the insulating film.

[0026] In step S1, the alkaline solution is a 5% (w / v) potassium hydroxide solution, and the hydrolysis time of the insulating film is 50-70 minutes. In a preferred embodiment of the present invention, the selected insulating film is a PI film (polyimide film). After potassium hydroxide hydrolysis, the imide rings on the surface of the PI film are opened, generating hydrophilic macrosine and potassium carboxylate salts, creating active sites on the film surface. Simultaneously, the total hydrolysis of 5% (w / v) potassium hydroxide for 50-70 minutes allows the effect to occur only on the molecular chains on the film surface without corroding the interior of the substrate. Please refer to... Figures 2a to 2d In the fabrication of flexible circuits, the hydrolysis time of potassium hydroxide solution has a crucial impact on the performance of the PI thin film substrate. Insufficient hydrolysis time ( Figure 2a If the polyamate produced by hydrolysis on the film surface is insufficient, subsequent ion exchange will be inadequate, making it difficult to form a circuit with good conductivity. Excessive hydrolysis time will further exacerbate the problem. Figure 2c , Figure 2dThe direct consequence is the deterioration of the film's mechanical properties—a significant reduction in toughness, making it brittle and fragile. Furthermore, over-etched films exhibit noticeable color changes, with decreased transparency and darkening. To determine the optimal conditions, the morphology, hydrophilicity, mechanical strength, and conductivity of the final fabricated circuit were examined after 0.5 hours, 1 hour, 1.5 hours, and 2 hours, respectively. Figures 2a-2d As shown in the figure. Experiments revealed that the mechanical strength continuously decreased with increasing hydrolysis time. An etching time of 1 hour was determined to be the optimal time. Under these conditions, the film surface acquired sufficient active sites to ensure excellent ion exchange and circuit formation, while its mechanical properties remained within a robust range capable of withstanding subsequent processing, thus ensuring the reliability of the final flexible circuit.

[0027] The sensitization treatment after hydrolysis involves immersing the insulating film, which has been soaked in an alkaline solution, again in a 5 mmol / L 3-mercaptopropyltrimethoxysilane (MPTMS)-ethanol solution for 30–40 min, to generate thiol groups (-SH) on the film surface. The methoxy group of MPTMS first generates a silanol group (Si-OH) in the aqueous solution. The Si-OH then undergoes dehydration condensation with the hydroxyl groups (-OH) on the film surface, causing the thiol groups (-SH) to adhere to the insulating film covalently. The sulfur element in the thiol group effectively captures and immobilizes silver ions on the insulating film through ionic bonds and coordination complexation.

[0028] In step S2, the concentration of the silver nitrate solution is 0.1 mol / L. Potassium ions are exchanged using silver ions. The ion exchange conditions are as follows: the insulating film is completely immersed in the silver nitrate solution and placed in a light-protected environment for at least 24 hours. Under light-protected conditions, silver is uniformly distributed on the film surface in the form of a compound. Silver ion exchange can be carried out at room temperature, reducing production energy consumption and equipment costs. During subsequent laser printing, the silver ions are reduced on the film surface to form elemental silver. The printing information in this invention includes: The printing information includes: the preset geometric structure of the film, printed image information, image position information, and image size information. The preset geometric structure of the film is the film structure at the time of cutting. During the subsequent printing process, it must be ensured that the film's geometry has not undergone deformation, curling, or wrinkling during hydrolysis and ion exchange. The image information is the image printed on the insulating film, specifically a circuit diagram or image of the silver ion conductive channels on the film. The source of the printed image can be a CAD design drawing or a circuit design SS diagram. Step S3 specifically includes: Obtain the endpoint position information of the insulating film; The actual geometric structure of the insulating film is determined based on the endpoint location information; If the actual geometry of the insulating film conforms to the preset geometry, the rotation angle of the insulating film is obtained, and the position of the laser is adjusted according to the printing information. If the actual geometry does not conform to the preset geometry, an alarm message will be output.

[0029] Before printing, it is necessary to determine whether the length and width of the film meet the expectations based on the endpoint information. Once the film itself expands (endpoint spacing is greater than preset), curls (endpoint number increases), or wrinkles (endpoint spacing decreases) due to hydrolysis or ion exchange, the endpoint position information and number can be determined to judge the actual shape and position of the film. Based on the relative position of the endpoints, it can be determined whether the current film is placed at a certain rotation angle. After determining the rotation angle, the laser moves on the horizontal plane according to the printing image information (the distribution position of the image on the film), image position information (the overall position of the image on the film), and image size information (the overall size of the image on the film, the overall area of ​​the distributed area on the film), so that the laser emitted by the laser can perform thermal etching on the film, thereby forming the printed image.

[0030] The localized high heat from the laser reduces silver from a compound state to its elemental state, simultaneously forming a fixed alloy structure with the substrate surface, making it less prone to detachment during bending. Laser printing offers the advantages of precision and controllability, allowing operators to achieve micron-level linewidth printing.

[0031] In a preferred embodiment of the present invention, the laser is 20 cm above the thin film, the laser power is 0.5 watts, and the laser movement speed is 2 mm / s. Please refer to [reference needed]. Figures 3a to 3g Under the same laser power, when the engraving depth is 20%, traces are formed on the film but no deformation occurs. When the engraving depth is 30%~100%, the film deforms. When the engraving depth is 10%, the film does not deform, but no printing traces are left. Therefore, at an engraving depth of 20%, silver elemental conductive channels can be formed on the film, while effectively avoiding problems such as film carbonization, perforation, decreased mechanical strength, and film deformation caused by excessive ablation, thus combining processing effect and substrate-friendly performance.

[0032] After printing the flexible circuit board, its electrical performance also needs to be tested. S4 connects the flexible circuit to the test circuit to obtain the electrical performance information of the flexible circuit.

[0033] Please refer to Figures 4a-4bThe simplified test circuit includes a power supply, an LED, a switch, and a resistive element. It is fixed to the flexible circuit at both ends by an electrical clamp. If the LED lights up, it indicates that the generated flexible circuit has conductivity. In other feasible embodiments of the present invention, users can measure the resistivity, impedance, and other electrical values ​​of the flexible circuit board according to other forms of test circuits.

[0034] Please refer to Figure 5 Based on the above-described flexible circuit fabrication method, this invention also discloses a flexible circuit fabrication apparatus using the aforementioned method. The apparatus includes: a cutting device 2 for cutting an insulating film; an ultrasonic cleaning device 6 for cleaning the insulating film; a hydrolysis device 5 and an ion exchange device 4 for generating silver ions on the surface of the insulating film; a laser printing device 1 for generating silver elemental pathways on the surface of the insulating film; and an alarm device 3 that emits a warning sound. When fabricating a flexible circuit board, the apparatus implements the flexible circuit fabrication method described above.

[0035] This invention fabricates flexible circuits on the surface of insulating films using laser thermal etching. Through three steps—hydrolysis, silver ion exchange, and laser thermal etching—it achieves environmentally friendly fabrication of flexible circuits. Surface hydrolysis is performed using a 5% potassium hydroxide solution. The film is then placed in a silver nitrate solution to form a uniform silver ion precursor layer on the surface of the insulating film via ion exchange. Finally, selective thermal etching of the silver-coated film using a laser device forms an electrically conductive silver layer on the surface of the insulating film according to preset printing information, directly fabricating a flexible circuit with conductivity and interfacial adhesion. This method combines the precision of printing technology with the selectivity of laser processing, enabling rapid prototyping of circuit patterns without the need for masks, simplifying the cumbersome multi-step pattern transfer process of traditional photolithography.

[0036] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for fabricating a flexible circuit, characterized in that, include: The insulating film is pretreated, then transferred to an alkaline solution for hydrolysis, followed by sensitization treatment. The hydrolyzed insulating film was transferred to a silver nitrate solution for ion exchange. The printing information is obtained, and the insulating film is laser-printed according to the positions of the insulating film and the laser to generate a flexible circuit.

2. The flexible circuit fabrication method according to claim 1, characterized in that, The pretreated insulating film specifically includes: Cut the insulating film to the target shape; Ultrasonic cleaning of insulating film for 5-10 minutes, ultrasonic frequency 40-70kHz.

3. The flexible circuit fabrication method according to claim 1, characterized in that, The alkaline solution is a 5% (w / v) potassium hydroxide solution, and the hydrolysis time of the insulating film is 50-70 minutes; The sensitization treatment specifically includes immersing the hydrolyzed insulating film in a 3-mercaptopropyltrimethoxysilane ethanol solution for 30-40 minutes.

4. The method for fabricating a flexible circuit according to claim 1, characterized in that, The concentration of the silver nitrate solution is 0.05 mol / L to 0.2 mol / L.

5. The method for fabricating a flexible circuit according to claim 1 or 4, characterized in that, The ion exchange conditions are as follows: the insulating film is completely immersed in silver nitrate solution and placed in a light-proof environment for at least 24 hours.

6. The method for fabricating a flexible circuit according to claim 1, characterized in that, The printed information includes: The printing information includes: the preset geometric structure of the film, the printed image information, the image position information, and the image size information.

7. The method for fabricating a flexible circuit according to claim 6, characterized in that, Laser printing of insulating films, based on the positions of the insulating film and the laser, specifically includes: Obtain the endpoint position information of the insulating film; The actual geometric structure of the insulating film is determined based on the endpoint location information; If the actual geometry of the insulating film conforms to the preset geometry, the rotation angle of the insulating film is obtained, and the position of the laser is adjusted according to the printing information. If the actual geometry does not conform to the preset geometry, an alarm message will be output.

8. The method for fabricating a flexible circuit according to claim 1, characterized in that, The step of obtaining printing information, after laser printing the insulating film according to the positions of the insulating film and the laser, further includes: Connect the flexible circuit to the test circuit to obtain the electrical performance information of the flexible circuit.

9. A flexible circuit fabrication apparatus, characterized in that, The flexible circuit fabrication apparatus is used in the fabrication of flexible circuit printed circuit boards, and when fabricating the flexible circuit printed circuit board, it implements the flexible circuit fabrication method as described in any one of claims 1 to 8.

10. The flexible circuit fabrication apparatus according to claim 9, characterized in that, The device includes: a cutting device, an ultrasonic cleaning device, a hydrolysis device, an ion exchange device, a laser printing device, and an alarm device.

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