Roll-to-roll die cutting composite process method for FPC (Flexible Printed Circuit) with single-sided board and double-sided pads

Abstract

The invention relates to the field of circuit board manufacturing, and discloses a roll-to-roll die cutting composite process method for a single-sided board double-sided bonding pad FPC (Flexible Printed Circuit), which comprises the following steps of: S1, preparing a PI (Polyimide) bottom film material roll, a copper foil material roll, a circular knife machine and an LDI (Laser Direct Imaging) exposure machine; s2, carrying out bonding pad windowing on the PI bottom film material roll by adopting a first circular knife of a circular knife machine in a roll-to-roll form; s3, in a roll-to-roll mode, the copper foil material roll and the PI bottom film material roll after windowing in the S2 are compounded, and a composite material roll is formed; s4, performing hot press molding on the composite material roll in the S3 in a roll-to-roll form; s5, performing high-temperature curing treatment on the composite material roll in the S4; s6, the composite material roll in the S5 is subjected to chemical cleaning, and the PH value of a cleaning solution is 9.5-10.5; s7, the composite material roll is aligned through visual alignment, then a second circular knife of the circular knife machine is used for windowing the copper foil face of the composite material roll, and the windowing positions of the copper foil face and the PI bottom film face are the same; and S8, exposing the composite material roll in the S7 by adopting an LDI exposure machine.

Description

Technical Field

[0001] The present invention relates to the field of circuit board manufacturing, and particularly to a roll-to-roll die-cutting and compounding process method for a single-sided board double-sided pad FPC. Background Art

[0002] A single-sided board double-sided pad FPC is a flexible circuit board with a special structure. Its "single-sided board" means that the circuit is only laid out on one side, while "double-sided pads" indicate that pads are provided on both the front and back sides of the circuit board; the single-sided board double-sided pad FPC usually uses flexible materials such as polyimide or polyester film as the substrate, with high bendability and flexibility, and can be freely bent, folded, etc. in three-dimensional space; with its own advantages of being thin, light, and small in volume, this FPC can effectively save the internal space of the product and is widely used in electronic devices such as mobile phones, tablet computers, smart watches, etc., meeting the requirements of the devices for miniaturization, light weight, and high integration; at the same time, the design of double-sided pads increases the flexibility and reliability of welding, and can improve the performance and stability of the product; The following problems exist in the current market: Currently, the FPC double-sided pad process generally uses laser windowing or chemical etching methods, which have problems such as high equipment costs (laser equipment) and insufficient windowing accuracy (±25μm error); especially in the new energy field, the requirements for the high-temperature resistance (>200°C) and pad alignment accuracy (±15μm) of FPC are more stringent; The technical problem to be solved by the present invention is: to provide a roll-to-roll die-cutting and compounding process method to reduce production costs. Summary of the Invention

[0003] The technical problem to be solved by the present invention is: to provide a roll-to-roll die-cutting and compounding process method to reduce production costs; in S2, the first round knife of a round knife machine is used to perform pad windowing on the PI base film material roll in a roll-to-roll form, which can achieve continuous production, improve production efficiency, and the precise cutting of the round knife machine can ensure the dimensional accuracy and consistency of pad windowing; it replaces the existing laser windowing or chemical etching method, saving production costs.

[0004] A roll-to-roll die-cutting and compounding process method for a single-sided board double-sided pad FPC includes the following steps: S1. Prepare a PI base film material roll, a copper foil material roll, a round knife machine, and an LDI exposure machine; S2. In a roll-to-roll form, use the first round knife of a round knife machine to perform pad windowing on the PI base film material roll; S3. In a roll-to-roll form, compound the copper foil material roll with the PI base film material roll after windowing in S2 to form a compound material roll; S4. In a roll-to-roll form, perform hot pressing on the compound material roll in S3 to form a shape; S5. Perform high-temperature aging treatment on the composite material roll in S4; S6. Chemically clean the composite material roll in S5, and the pH value of the cleaning solution is 9.5 - 10.5; S7. Use visual alignment to align the composite material roll, and then use the second round knife of the round knife machine to open windows on the copper foil surface of the composite material roll, and the window opening positions on the copper foil surface and the PI bottom film surface are the same; S8. Use an LDI exposure machine to expose the composite material roll in S7; S9. Develop and etch the composite material roll in S8, and perform AOI scanning detection after development and etching; S10. Cover a layer of cover film on the composite material roll after detection in S9, and then wind it up.

[0005] Preferably, for the composite material roll after winding in S10, use a roll-to-roll method to attach a reinforcing plate to it; after attaching the reinforcing plate, bake it for shaping, the baking temperature is 165 - 175 °C, and the baking time is 45 minutes.

[0006] Preferably, perform antioxidant treatment on the composite material roll after baking and shaping, and the thickness of the antioxidant treatment film is 0.8 - 1.2 μm; then cut the composite material roll into single sheets, and perform packaging after detection.

[0007] Preferably, the temperature for thermocompression forming is 120 - 150 °C, and the pressure is 5 - 8 Mpa.

[0008] Preferably, the high-temperature aging is carried out three times. The first aging temperature is 160 °C and the time is 2 hours; the second aging is 180 °C and the time is 1.5 hours; and the third aging temperature is 170 °C and the time is 2.5 hours.

[0009] Preferably, the first round knife adopts a stepped die-cutting tool die, the angle of the cutting edge is 45 - 60°, and the window opening size compensation amount is +0.05 mm.

[0010] Preferably, in step S3, after forming the composite material roll, use a heating roller to perform thermocompression on it.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows: The roll-to-roll die-cutting composite process method of the single-sided board double-sided pad FPC of the present invention, in S2, uses the first round knife of the round knife machine to open windows on the PI bottom film roll in a roll-to-roll form, which can realize continuous production, improve production efficiency, and the precise cutting of the round knife machine can ensure the dimensional accuracy and consistency of the window opening of the pads; it replaces the existing laser window opening or chemical etching method, saving production costs.

[0012] Additional aspects and advantages of the present invention will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present invention. Description of the Drawings

[0013] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0014] Figure 1 It is a schematic structural diagram of the circular knife machine of the present invention for unwinding with a PI bottom film unwinding roller.

[0015] Figure 2 It is a schematic structural diagram of the circular knife machine of the present invention for unwinding with an etched FPC bare board unwinding roller.

[0016] In the figure: 1. PI bottom film unwinding roller; 2. PI bottom film CCD die; 3. PI bottom film and FPC bare board CCD alignment and compounding roller; 4. FPC outer shape CCD die-cutting roller; 5. Bottom film compounding roller; 6. Deviation rectifier; 7. Collection roller; 8. PI bottom film waste collection roller; 9. FPC bare board waste collection roller; 10. Etched FPC bare board unwinding roller. Detailed Embodiments

[0017] The following will clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0018] Please refer to Figures 1-2 , in the embodiments of the present invention, a roll-to-roll die-cutting and compounding process method for a single-sided board double-sided pad FPC includes the following steps: S1. Prepare a PI bottom film material roll, a copper foil material roll, a circular knife machine, and an LDI exposure machine; S2. In a roll-to-roll form, use the first circular knife of the circular knife machine to open windows for pads on the PI bottom film material roll; S3. In a roll-to-roll form, compound the copper foil material roll with the PI bottom film material roll after windowing in S2 to form a compound material roll; S4. In a roll-to-roll form, perform thermocompression forming on the compound material roll in S3; S5. Perform high-temperature aging treatment on the compound material roll in S4; S6. Chemically clean the composite material roll in S5, and the pH value of the cleaning solution is 9.5 - 10.5; S7. Use visual alignment to align the composite material roll, and then use the second round knife of the round knife machine to open windows on the copper foil surface of the composite material roll, and the window opening positions on the copper foil surface and the PI bottom film surface are the same; S8. Use an LDI exposure machine to expose the composite material roll in S7; S9. Develop and etch the composite material roll in S8, and perform AOI scanning inspection after development and etching; S10. Cover a cover film on the composite material roll after inspection in S9, and then wind it up.

[0019] Specifically, preparing materials and equipment such as PI bottom film rolls, copper foil rolls, round knife machines, and LDI exposure machines is the basis for ensuring the smooth progress of subsequent processes; in S2, use the first round knife of the round knife machine to open pad windows on the PI bottom film roll in a roll-to-roll form. This roll-to-roll operation method can achieve continuous production, improve production efficiency, and the precise cutting of the round knife machine can ensure the dimensional accuracy and consistency of the pad windows; the roll-to-roll method is to use an unwinder to unwind the material, process the material while unwinding, and use a winder to wind up the processed material for use in the next process step; In S3, combine the copper foil roll with the PI bottom film roll with opened windows to form a composite material roll. This step realizes the preliminary combination of materials and lays the foundation for subsequent processes such as forming; immediately following the hot pressing in S4, through hot pressing, the layers of the composite material roll are tightly combined, further enhancing its physical properties and structural stability, and ensuring the quality and reliability of the product; The high-temperature aging treatment in S5 can change the molecular structure inside the material, further improving the material's performance, such as enhancing its flexibility and heat resistance, etc.; in S6, chemically clean the composite material roll with a cleaning solution with a pH value of 9.5 - 10.5. This cleaning process can remove impurities, oil stains and other pollutants on the surface of the composite material roll, ensure the cleanliness of the material surface in subsequent processes, and thus improve the success rate of the process and product quality; S7 uses visual alignment to align the composite material roll, and then uses the second round knife of the round knife machine to open windows on the copper foil surface, and ensures that the window opening positions on the copper foil surface and the PI bottom film surface are the same. The application of visual alignment technology improves the alignment accuracy, ensures the accurate position of the double-sided pads, and provides guarantee for subsequent electrical performance; the reuse of the round knife machine continues the high efficiency of roll-to-roll production; In S8, the composite material roll is exposed using an LDI exposure machine. The LDI exposure machine features high precision and high resolution, enabling accurate transfer of patterns onto the composite material roll, providing an accurate pattern basis for subsequent development and etching; in the development and etching process of S9, the unwanted copper foil is removed to form the required circuit pattern, and after development and etching, AOI scanning detection is carried out, which can promptly detect defects in the circuit pattern, such as short circuits, open circuits, etc., ensuring the product quality and reducing the defective rate; Finally, in S10, a cover film is covered on the composite material roll after detection and then wound up. The cover film plays roles such as protecting the circuit pattern, moisture-proofing, and insulating, and winding up facilitates the storage and transportation of the product.

[0020] Furthermore, for the composite material roll wound up in S10, a reinforcing plate is attached to it in a roll-to-roll manner; after attaching the reinforcing plate, it is baked and shaped. The baking temperature is 165 - 175 degrees Celsius, and the baking time is 45 minutes.

[0021] Specifically, the roll-to-roll method continues the continuous production mode of the previous process, which can effectively improve production efficiency, reduce manual intervention, and reduce errors and quality instability factors caused by manual operation; the attachment of the reinforcing plate can enhance the strength and rigidity of specific parts of the FPC, enabling it to better maintain the structural integrity during subsequent use, especially when subjected to external forces or certain mechanical stresses, and avoiding deformation, fracture, etc., thereby enhancing the reliability and durability of the product; for example, in some electronic devices, the FPC may be frequently bent or squeezed, and the presence of the reinforcing plate can protect the internal circuit from damage; in the baking and shaping process after attaching the reinforcing plate, the baking temperature is set at 165 - 175 degrees Celsius, and the baking time is 45 minutes, so that the adhesive between the reinforcing plate and the composite material roll is fully cured, enhancing the bonding force between the two, ensuring that the reinforcing plate is firmly attached to the composite material roll and playing its due reinforcing role; if the temperature is too low, the adhesive may not be fully cured, resulting in insufficient bonding strength and the easy detachment of the reinforcing plate; while if the temperature is too high, it may damage the materials in the composite material roll, such as the PI base film, copper foil, etc., affecting their electrical and physical properties; similarly, 45 minutes of baking time is also a relatively reasonable duration, which can not only ensure the full curing of the adhesive but also avoid adverse effects on the materials due to excessive baking time.

[0022] Furthermore, the composite material roll after baking and shaping is subjected to an antioxidant treatment, and the thickness of the antioxidant treatment film is 0.8 - 1.2 μm; then the composite material roll is cut into single sheets, and after detection, it is packaged.

[0023] Specifically, for FPCs, metal parts such as copper foils on their surfaces are prone to oxidation reactions in the air, leading to a decline in electrical performance, such as problems like increased resistance and unstable signal transmission. An antioxidant treatment film with an appropriate thickness can form an effective protective film on the surface of the composite material roll, preventing oxygen from contacting the metal, thereby greatly slowing down the oxidation rate. If the film thickness is too thin, it may not provide sufficient protection and it is difficult to achieve the desired antioxidant effect. If the film thickness is too thick, it may affect the flexibility of the FPC, increase its thickness, and is not conducive to use in some electronic devices with high space requirements. In addition, during the antioxidant treatment process, the uniformity of the film also needs to be strictly controlled. Uneven film thickness may result in insufficient local antioxidant capacity and affect the overall performance of the product. After the antioxidant treatment is completed, the composite material roll is cut into single sheets, which converts the continuous rolled material into individual products. Precise cutting can ensure that the size of each single FPC meets the design requirements, facilitating subsequent assembly and use. At the same time, during the cutting process, attention should be paid to avoiding problems such as burrs and uneven cuts, otherwise it may affect the electrical performance and appearance quality of the FPC. For example, burrs may pierce the cover film, resulting in faults such as short circuits. The inspection link after cutting into single sheets is a key step to ensure product quality. Through comprehensive and detailed inspections, problems such as dimensional deviations, appearance defects, and poor electrical performance can be discovered, and unqualified products can be promptly removed to ensure that the products finally delivered to customers meet the quality standards. The inspection methods can include various means such as appearance inspection, dimensional measurement, and electrical performance testing to ensure a comprehensive evaluation of the product. Reasonable packaging can provide effective protection during product transportation and storage, preventing the product from being physically damaged, getting damp, or contaminated. The selection of packaging materials and the design of packaging methods need to be based on the characteristics and requirements of the FPC. For example, anti-static packaging materials are used to prevent static electricity from damaging the electrical performance of the FPC, and at the same time, ensure that the packaging has sufficient strength and cushioning performance to cope with vibrations and impacts during transportation.

[0024] Furthermore, the temperature for hot pressing forming is 120 - 150 °C, and the pressure is 5 - 8 Mpa.

[0025] Specifically, from the perspective of temperature, the temperature range of 120 - 150 °C has a specific effect; within this temperature range, the adhesive between the PI base film roll and the copper foil roll can reach an appropriate softening state, thus promoting a closer combination of the two; if the temperature is too low, the adhesive cannot be sufficiently softened, making it difficult to achieve a good bonding effect, which may lead to problems such as delamination in the subsequent use of the composite roll, affecting the reliability and stability of the product; for example, in some application scenarios with high requirements for structural strength, the delamination phenomenon will cause the FPC to be unable to withstand the corresponding external force, resulting in product failure; if the temperature is too high, on the one hand, it may cause thermal deformation of materials such as the PI base film and copper foil, affecting the dimensional accuracy and appearance quality of the FPC; on the other hand, too high a temperature may also cause the adhesive to react excessively, changing its chemical properties, reducing the bonding strength, and even possibly having an adverse effect on the electrical properties of the materials, such as reducing the conductivity of the copper foil. A pressure of 5 - 8 Mpa can enable the materials to be in full contact during the hot pressing process, remove impurities such as air, and further enhance the composite effect; appropriate pressure helps the adhesive to better fill the tiny voids on the material surface, forming a more firm bond; if the pressure is too small, the materials cannot be fully bonded, easily resulting in defects such as bubbles and gaps, affecting the product quality; for example, the presence of bubbles may cause local electrical performance instability and even trigger faults such as short circuits; if the pressure is too large, it may damage the materials, such as causing cracks in the PI base film and deformation of the copper foil, which will also affect the performance and service life of the FPC.

[0026] Furthermore, high-temperature curing is carried out three times. The first curing temperature is 160 °C and the time is 2 hours; the second curing is at 180 °C and the time is 1.5 hours; and the third curing temperature is 170 °C and the time is 2.5 hours.

[0027] Specifically, the first curing is set at a temperature of 160 °C and a time of 2 hours. This relatively low temperature and long time arrangement in this stage are to allow the materials in the composite roll to initially undergo physical and chemical changes; at 160 °C, the molecular chains inside the materials begin to gradually become active, and components such as the adhesive also begin to slowly carry out cross-linking reactions, laying the foundation for the subsequent more in-depth curing process; the relatively long 2-hour time can ensure that this initial change occurs more uniformly throughout the composite roll, avoiding the situation of insufficient local reaction. The second curing temperature is increased to 180 °C and the time is shortened to 1.5 hours. The higher temperature makes the molecular chain activity more intense, further accelerating and deepening the cross-linking reaction of the adhesive, and further improving the performance of the material. There will be a significant enhancement in aspects such as hardness and strength. The shorter time setting is to ensure sufficient reaction while avoiding excessive thermal damage to the material caused by too high temperature and too long time, and preventing the decline of properties such as the flexibility of the material. For example, if the time is too long at 180 °C, the PI base film may become brittle, affecting the performance of the FPC in bending and other usage scenarios. The third curing temperature is 170 °C and the time is 2.5 hours. This stage is to further consolidate and optimize the effects of the previous two curings. The temperature of 170 °C can make the reaction inside the material more sufficient and stable, and the longer 2.5-hour time can make the performance of the material more uniform and stable, eliminating the possible minor differences in the previous two curings. Through these three curing processes with different temperatures and times, the materials in the composite material roll can reach a relatively ideal state, and its comprehensive performance is significantly improved, including better mechanical properties, electrical properties, and properties such as temperature resistance and aging resistance.

[0028] Furthermore, the first round die uses a stepped die-cutting tool die, the angle of the cutting edge is 45 - 60°, and the window size compensation amount is +0.05 mm.

[0029] Specifically, the stepped die-cutting tool die enables step-by-step and precise cutting when performing pad windowing on the PI base film roll. Compared with ordinary tool dies, the stepped tool die can process the material in stages according to different cutting depths and requirements. This helps to reduce the impact force on the PI base film during the cutting process and reduce the risk of defects such as deformation and tearing of the material. At the same time, the stepped design can better adapt to the multi-layer structure of the PI base film, ensuring that the edges of the window are more neat and smooth, providing a good foundation for the subsequent lamination with the copper foil roll. When the angle of the cutting edge is within the range of 45 - 60°, if the angle of the cutting edge is too small, although the cutting will be sharper, the durability of the tool die will be reduced, and problems such as wear and chipping are likely to occur, increasing the production cost and the frequency of replacing the tool die. On the contrary, if the angle of the cutting edge is too large, the pressure required for cutting will increase, which may cause indentation and deformation of the PI base film, affecting the accuracy and quality of the windowing. Within the angle range of 45 - 60°, it is possible to achieve relatively easy and precise cutting while ensuring the durability of the tool die, making the size and shape of the window meet the design requirements. The window opening size compensation is +0.05mm, which is considered based on various factors in the actual production process; in subsequent process steps, such as compounding with copper foil rolls, hot pressing, and high-temperature curing, the material will be affected by factors such as temperature and pressure, and may shrink or expand to a certain extent; by reserving a compensation of +0.05mm, the influence of these factors on the window opening size can be offset to a certain extent, ensuring that the pad window opening size of the final product meets the design standard; without this compensation, it may result in too small a window opening size, affecting subsequent electrical connection and soldering processes; or too large a window opening size, reducing the stability and reliability of the pads.

[0030] Further, in step S3, after forming the composite roll, a heating roller is used to perform hot pressing on it.

[0031] Specifically, hot pressing with a heating roller can further strengthen the bonding effect between the copper foil and the PI base film of the composite roll; when forming the composite roll, although the copper foil and the PI base film have been initially adhered, there may be some areas where the adhesion is not tight enough; the use of the heating roller can further melt and flow the adhesive, fill in the tiny gaps, and increase the contact area between the materials, thus achieving a more firm bond; for example, appropriate temperature and pressure can enhance the intermolecular forces between the copper foil and the PI base film, improve the overall structural strength of the composite roll, and reduce the risk of delamination in subsequent process steps. Hot pressing with a heating roller can also have a positive impact on the flatness of the composite roll; during the composite process, due to material non-uniformity or operating factors, there may be minor unevenness on the surface of the composite roll; the pressure of the heating roller can make the surface of the composite roll smoother, which is beneficial for subsequent processes. For example, in steps such as exposure, a smooth surface can ensure the accuracy and consistency of pattern transfer. <{}

[0032] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, in any regard, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, it is intended to encompass all changes falling within the meaning and scope of the equivalent elements of the claims in the present invention.

Claims

1. A roll-to-roll die-cutting and compounding process method for a single-sided panel double-sided pad FPC, characterized in that, It includes the following steps: S1. Prepare a PI base film roll, a copper foil roll, a round knife machine, and an LDI exposure machine; S2. In a roll-to-roll manner, use the first round knife of the round knife machine to open windows for the solder pads on the PI base film roll; S3. In a roll-to-roll manner, laminate the copper foil roll with the PI base film roll after window opening in S2 to form a laminated roll; S4. In a roll-to-roll manner, perform hot pressing and forming on the laminated roll in S3; S5. Perform high-temperature aging treatment on the laminated roll in S4; S6. Chemically clean the laminated roll in S5, and the pH value of the cleaning solution is 9.5 - 10.5; S7. Use visual alignment to align the laminated roll, and then use the second round knife of the round knife machine to open windows on the copper foil surface of the laminated roll, and the window opening positions on the copper foil surface and the PI base film surface are the same; S8. Use the LDI exposure machine to expose the laminated roll in S7; S9. Develop and etch the laminated roll in S8, and perform AOI scanning and detection after development and etching; S10. Cover a cover film on the laminated roll after detection in S9, and then wind it up.

2. The roll-to-roll die-cutting and lamination process method of a single-sided panel double-sided pad FPC according to claim 1, characterized in that, For the laminated roll wound up in S10, stick a reinforcing plate to it in a roll-to-roll manner; after sticking the reinforcing plate, bake and shape it, the baking temperature is 165 - 175 °C, and the baking time is 45 minutes.

3. A roll-to-roll die-cutting and lamination process method for a single-sided panel double-sided pad FPC according to claim 2, characterized in that, Perform antioxidant treatment on the laminated roll after baking and shaping, and the thickness of the antioxidant treatment film is 0.8 - 1.2 μm; After that, cut the laminated roll into single sheets, and perform packaging after detection.

4. A roll-to-roll die-cutting and composite process method for a single-sided panel double-sided pad FPC according to claim 1, characterized in that, The temperature of hot pressing and forming is 120 - 150 °C, and the pressure is 5 - 8 Mpa.

5. The roll-to-roll die-cutting and lamination process method of a single-sided panel double-sided pad FPC according to claim 1, characterized in that, The high-temperature aging is carried out three times. The first aging temperature is 160 °C and the time is 2 hours; the second aging is 180 °C and the time is 1.5 hours; and the third aging temperature is 170 °C and the time is 2.5 hours.

6. The roll-to-roll die-cutting and compounding process method of a single-sided panel double-sided pad FPC according to claim 1, characterized in that The first round knife uses a stepped die-cutting tool die, the angle of the cutting edge is 45 - 60°, and the window opening size compensation amount is +0.05 mm.

7. A roll-to-roll die-cutting and compounding process method for a single-sided panel double-sided pad FPC according to claim 1, characterized in that, In step S3, after forming the laminated roll, use a heating roller to perform hot pressing on it.

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