Flexible circuit board for microchip and preparation method thereof

Abstract

The invention discloses a flexible circuit board for a microchip and a preparation method thereof, and the method comprises the following steps: selecting a processed composite flexible substrate, and carrying out the surface modification of the composite flexible substrate, so as to obtain a preliminary circuit board; sequentially coating high-adhesion photoresist and high-resolution photoresist on the surface of the primary circuit board, and performing pattern exposure on the primary circuit board coated with the two layers of photoresist by adopting a laser direct imaging technology; carrying out curing treatment on the exposed photoresist layer through a hot pressing process; and forming a conductive layer in the circuit pattern area to prepare the flexible circuit board. According to the invention, the technical problem of circuit processing misalignment of the flexible circuit board in the prior art is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of circuit board preparation, and in particular to a flexible circuit board for a microchip and a preparation method thereof. Background Art

[0002] Flexible circuit board is a kind of highly reliable and extremely flexible printed circuit board made of polyimide or polyester film as the base material. Flexible circuit board is referred to as soft board or FPC, which has the characteristics of high wiring density, light weight and thin thickness.

[0003] In the prior art, the preparation method of the flexible circuit board for microchips includes the steps of substrate preparation, pattern transfer, etching, drilling, electroplating, solder mask, surface treatment and packaging. However, since the flexible substrate of the flexible circuit board for microchips is easy to expand and contract with heat, the size of the mask and the substrate does not match during the preparation process, which makes the circuit processing of the flexible circuit board inaccurate and affects the processing accuracy of the flexible circuit board. Summary of the invention

[0004] The object of the present invention is to provide a flexible circuit board for microchip and a preparation method thereof, which solves the technical problem of misalignment in circuit processing of flexible circuit boards in the prior art.

[0005] To achieve this object, the present invention adopts the following technical solutions: According to a first aspect, the present invention discloses a method for preparing a flexible circuit board for a microchip, comprising: Step S1, selecting a processed composite flexible substrate, and performing surface modification treatment on the composite flexible substrate to obtain a preliminary circuit board; the composite flexible substrate is made of a polyimide-liquid crystal polymer composite material; Step S2, sequentially coating a high-adhesion photoresist and a high-resolution photoresist on the surface of the preliminary circuit board, and performing pattern exposure on the preliminary circuit board coated with two layers of photoresist using laser direct imaging technology; Step S3, curing the exposed photoresist layer by a hot pressing process; Step S4, forming a conductive layer in the circuit pattern area to obtain a flexible circuit board.

[0006] Optionally, the step S1 includes: Step S11, adjusting the composite ratio of polyimide and liquid crystal polymer according to the processing requirements of the flexible circuit board to obtain a processed composite flexible substrate; Step S12, performing plasma treatment on the composite flexible substrate by using a low-temperature plasma device to improve the surface properties of the composite flexible substrate and enhance the adhesion of subsequent photoresist; Step S13, chemically treating the surface of the composite flexible substrate with an aluminum oxide solution or a fluoride solution; Step S14, after the surface chemical treatment, the composite flexible substrate is dried to obtain a preliminary circuit board.

[0007] Optionally, the step S14 includes: S141, selecting a preset temperature and a preset humidity during the drying process; wherein the preset temperature is 80° C. to 100° C., and the preset humidity is 40% to 60%; Step S142, gradually heating up to a preset temperature at a heating rate of 2°C to 3°C per minute, and maintaining a constant temperature for 10 to 15 minutes after reaching the preset temperature; Step S143, during the drying process, the air flow is kept uniform through the air circulation system, and the air flow speed is set to 0.5 meters to 1 meter per second.

[0008] Optionally, the step S11 includes: Step S111, determining the types and molecular structures of polyimide and liquid crystal polymer according to the processing requirements of the flexible circuit board; wherein the polyimide is thermosetting polyimide or soluble polyimide, and the liquid crystal polymer is a wholly aromatic liquid crystal polymer; Step S112, based on the determined polyimide and liquid crystal polymer, adjusting the mass ratio of the polyimide and the liquid crystal polymer to obtain target performance of the composite flexible substrate; wherein the mass percentage of the polyimide and the liquid crystal polymer is (70:30) to (50:50); Step S113, after the polyimide and the liquid crystal polymer are processed into thin films respectively by hot pressing equipment, they are hot pressed and composited at a temperature of 200° C. to 300° C. to obtain a processed composite flexible substrate.

[0009] Optionally, step S2 includes: Step S21, coating a high-adhesion photoresist on the surface of the composite flexible substrate by a dynamic rheology controlled spin coating process, and coating a high-resolution photoresist by a plasma-assisted nano-spraying technology; wherein the thickness of the high-adhesion photoresist layer is 2-5 μm, and the thickness of the high-resolution photoresist layer is 1-3 μm; Step S22, using dual-mode laser direct imaging technology to perform pattern exposure to achieve the transfer of the circuit pattern.

[0010] Optionally, the step S22 includes: Step S221, pre-scanning the photoresist with a low-power laser to activate the photosensitive area in the photoresist; Step S222, after the pre-exposure is completed, a high-power laser is used to perform secondary exposure on the key area of ​​the circuit, the microscopic deformation of the substrate is detected in real time, and the laser trajectory is adjusted through a dynamic exposure compensation algorithm to achieve the transfer of the circuit pattern.

[0011] Optionally, step S3 includes: Step S31, by performing zone control on the hot press, the temperature of each zone is monitored in real time, and the temperature is gradually adjusted using a nonlinear temperature rise and fall curve according to the thermal expansion characteristics of the substrate and the curing temperature of the photoresist; Step S32, curing the photoresist layer through a multi-stage temperature gradient heating process.

[0012] Optionally, step S4 includes: Step S41, using low-temperature chemical vapor deposition or physical vapor deposition technology to perform metal deposition at a temperature range of 60° C. to 80° C., and adding a nanoparticle enhancer during the deposition process; Step S42, dispersing the nanoparticles in the metal deposition liquid by using an ultrasonic dispersion method or a surfactant dispersion method, and controlling the deposition rate and the concentration of the nanoparticles to ensure that the nanoparticles are evenly distributed in the metal layer; Step S43, after the metal deposition is completed, the flexible circuit board is subjected to a low-temperature baking and curing treatment, and the baking temperature is controlled within the range of 80°C to 100°C.

[0013] Optionally, in step S42, the concentration of the nanoparticles is 1%-3%, and the deposition rate is 20-50 nm / min.

[0014] According to a second aspect, the present invention discloses a flexible circuit board for a microchip, which is manufactured by the method for manufacturing a flexible circuit board for a microchip as described in the first aspect.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a flexible circuit board for microchips and a preparation method thereof. By selecting a polyimide-liquid crystal polymer composite material as a composite flexible substrate and performing surface modification on the substrate, the flexible circuit board is suitable for the long-term stable working environment of the microchip; laser exposure does not require a complex mask, which reduces the cost and time of making the mask, and further improves the flexibility and efficiency of production. Hot pressing curing can not only improve the adhesion and structural strength of the photoresist layer, but also ensure the stability of the photoresist layer in a high temperature environment, providing a stable foundation for the subsequent deposition of the conductive layer. The method is suitable for a variety of high-precision, high-reliability microchip applications, such as communications, medical equipment, consumer electronics and other fields, meeting the needs of miniaturization, flexibility and high performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0017] The structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification so as to facilitate understanding and reading by persons familiar with the technology. They are not used to limit the conditions under which the present invention can be implemented, and therefore have no substantive technical significance. Any structural modification, change in proportion or adjustment of size shall still fall within the scope of the technical contents disclosed in the present invention without affecting the effects and purposes that can be achieved by the present invention.

[0018] Figure 1 The present invention is a flowchart of a method for preparing a flexible circuit board for a microchip disclosed in Embodiment 1 of the present invention. DETAILED DESCRIPTION

[0019] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] In the description of the present invention, it should be understood that the terms "upper", "lower", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention. It should be noted that when a component is considered to be "connected" to another component, it may be directly connected to the other component or there may be a centrally arranged component at the same time.

[0021] The technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0022] Embodiment 1: The embodiment of the present invention provides a method for preparing a flexible circuit board for a microchip, such as Figure 1 As shown, including: Step S1, selecting a processed composite flexible substrate, and performing surface modification treatment on the composite flexible substrate to obtain a preliminary circuit board; the composite flexible substrate is made of a polyimide-liquid crystal polymer composite material; in this embodiment, by compounding polyimide (PI) and liquid crystal polymer (LCP), while ensuring that the flexible circuit board has high mechanical strength, it can also provide excellent high temperature resistance and corrosion resistance, which is suitable for the long-term stable working environment of the microchip.

[0023] Step S2, coating the surface of the preliminary circuit board with high adhesion photoresist and high resolution photoresist in sequence, and using laser direct imaging technology to perform pattern exposure on the preliminary circuit board coated with two layers of photoresist; in this embodiment, the above two photoresists have different functions, the high adhesion photoresist can effectively enhance the adhesion of the photoresist on the surface of the substrate, avoiding the falling off or peeling of the photoresist in the subsequent process, and the high resolution photoresist has a higher resolution, which can provide a more refined circuit pattern during the pattern exposure process. Through the laser direct imaging technology for pattern exposure, the optimized circuit pattern can be accurately transferred to the photoresist layer. Compared with the traditional photolithography process, laser exposure has higher resolution and flexibility, and is particularly suitable for processing high-density and high-precision microchip circuit design. At the same time, laser exposure does not require a complex mask, which reduces the cost and time of making the mask, and further improves the flexibility and efficiency of production.

[0024] Step S3, curing the exposed photoresist layer by a hot pressing process; in this embodiment, the exposed photoresist layer is cured by a hot pressing process, which helps to enhance the stability of the photoresist and avoid pattern deviation or damage in subsequent processing.

[0025] Step S4, a conductive layer is formed in the circuit pattern area by a low temperature deposition process to obtain a flexible circuit board. In this embodiment, the low temperature deposition technology can complete the deposition of the conductive material at a relatively low temperature, effectively avoiding the damage that the high temperature process may cause to the flexible substrate, such as deformation and softening of the substrate. In addition, low temperature deposition can control the thickness and uniformity of the conductive layer, ensuring the accurate transmission of the circuit pattern and good electrical conductivity. This process is particularly suitable for the high precision requirements of flexible materials and microelectronic products, and can further improve the electrical performance and reliability of the circuit board.

[0026] It should be noted that the present invention provides a method for preparing a flexible circuit board for a microchip, wherein a polyimide-liquid crystal polymer composite material is selected as a composite flexible substrate, and the substrate is subjected to surface modification treatment, so that the flexible circuit board is suitable for the long-term stable working environment of the microchip; laser exposure does not require a complex mask, which reduces the cost and time of making the mask, and further improves the flexibility and efficiency of production. Hot pressing curing can not only improve the adhesion and structural strength of the photoresist layer, but also ensure the stability of the photoresist layer in a high temperature environment, providing a stable foundation for the subsequent deposition of the conductive layer. The method is suitable for a variety of high-precision, high-reliability microchip applications, such as communications, medical equipment, consumer electronics and other fields, meeting the needs of miniaturization, flexibility and high performance.

[0027] In an optional embodiment, step S1 includes: Step S11, according to the processing requirements of the flexible circuit board, adjust the composite ratio of polyimide and liquid crystal polymer to obtain a processed composite flexible substrate; in this embodiment, polyimide has excellent high temperature resistance, chemical stability and mechanical strength, while liquid crystal polymer has low dielectric loss, high dimensional stability and low hygroscopicity. By adjusting the ratio of polyimide and liquid crystal polymer, the best balance can be found between mechanical flexibility, heat resistance and electrical properties. In the flexible circuit board for microchips, it is necessary to take into account the bending ability and structural support of the circuit board. Reasonable regulation of the ratio of polyimide and liquid crystal polymer can improve the overall mechanical properties, so that it can meet the bending requirements without affecting the stability of the electrical connection due to excessive softness.

[0028] Step S12, plasma treatment is performed on the composite flexible substrate by low-temperature plasma equipment to improve the surface properties of the composite flexible substrate and enhance the adhesion of the subsequent photoresist; in this embodiment, plasma treatment can remove organic pollutants on the surface of the material, so that it forms more polar functional groups (such as hydroxyl, carboxyl, etc.), thereby improving the adhesion of the photoresist and reducing the peeling phenomenon caused by poor interface. After plasma modification, the surface of the substrate is more uniform, which is conducive to the uniform coating of the photoresist, improves the accuracy of the photolithography process, and reduces the possibility of circuit breakage or failure. Low-temperature plasma treatment will not destroy the main structure of the polyimide-liquid crystal polymer composite material, and can achieve efficient modification of the surface, which is more gentle and environmentally friendly than traditional mechanical polishing or chemical etching processes.

[0029] Specifically, the low-temperature plasma equipment uses oxygen, nitrogen or argon as the gas source, and the gas flow rate is set between 10 cubic centimeters per minute and 200 cubic centimeters per minute. The vacuum pressure of the low-temperature plasma equipment is controlled between 0.1 Torr and 1 Torr. Excessive pressure will reduce the excitation effect of the plasma, resulting in insufficient surface modification; while too low pressure may cause the plasma to be unstable and unable to produce enough ions and active molecules. In order to effectively modify the surface of the composite flexible substrate, the excitation power of the low-temperature plasma equipment is 50W to 150W, the processing time is set between 30 seconds and 5 minutes, and the processing temperature is 25°C to 60°C.

[0030] Step S13, chemically treat the surface of the composite flexible substrate with an aluminum oxide solution or a fluoride solution; in this embodiment, the chemical treatment can further remove oxides or pollutants that may remain on the surface, and at the same time form a uniform activation layer, so that the subsequent metal layer (such as copper or other conductive materials) can be more stably attached, avoiding the problem of uneven local deposition caused by surface defects. Appropriate chemical treatment can adjust the roughness of the material surface at the nanometer level, so that it can enhance the adhesion of the photoresist without affecting the accuracy of the final circuit. Through chemical modification, the wetting characteristics of the substrate surface can be optimized, so that it exhibits better fluidity in subsequent coating processes (such as photoresist, conductive layer, etc.), reduces defects, and improves the yield rate.

[0031] In the specific implementation process, the mass concentration of the aluminum oxide solution is 0.1-5%, and the composite flexible substrate is immersed in the aluminum oxide solution for 1 to 10 minutes. The aluminum oxide particles are uniformly dispersed by stirring to ensure uniform surface modification. Alternatively, the concentration of fluoride is 0.5% to 3%, and the composite flexible substrate is immersed in the fluoride solution for 1 to 3 minutes, with mild stirring to enhance the uniformity of the treatment. Immediately after treatment, the surface of the substrate is thoroughly cleaned with deionized water to remove residual aluminum oxide solution or fluoride solution.

[0032] Step S14, after the surface chemical treatment, the composite flexible substrate is dried to obtain a preliminary circuit board. In this embodiment, after the chemical treatment, a small amount of solvent or moisture may remain on the surface of the material. If it is not removed in time, it may cause defects in subsequent processes such as lithography and deposition, such as blistering and delamination. Drying treatment can effectively remove these undesirable factors and improve process stability. Appropriate preheating can release the stress inside the polyimide-liquid crystal polymer composite material and reduce warping or deformation caused by temperature changes during subsequent processing. The dried material has better surface cleanliness and consistency, providing a more stable substrate for subsequent processes such as lithography and conductive layer deposition, thereby improving the yield rate.

[0033] It should be noted that through the reasonable ratio of polyimide-liquid crystal polymer composite materials, key properties such as high flexibility, high mechanical strength, high temperature resistance and low dielectric loss are taken into account, so that the circuit board can operate stably in microchip applications. The low-temperature plasma treatment and chemical modification work together to improve the adhesion of the substrate surface, optimize the adhesion performance of the photoresist and the conductive layer, reduce the production defect rate, and improve the overall yield rate. After drying, the internal stress of the material is released and the dimensional stability is enhanced, so that the flexible circuit board will not be deformed or fail due to environmental changes during long-term use. Low-temperature plasma treatment is an environmentally friendly and efficient surface modification method. Compared with traditional mechanical roughening or strong acid etching processes, it is environmentally friendly, while reducing manufacturing costs and improving the feasibility of industrial applications.

[0034] Specifically, step S11 includes: Step S111, determining the types and molecular structures of polyimide and liquid crystal polymer according to the processing requirements of the flexible circuit board; wherein the polyimide is a thermosetting polyimide or a soluble polyimide, and the liquid crystal polymer is a fully aromatic liquid crystal polymer; in this embodiment, when the operating temperature of the flexible circuit board is required to exceed 300° C., a thermosetting polyimide is selected; when the operating temperature of the flexible circuit board is required to be no more than 300° C., or when the composite flexible substrate needs to be coated over a large area, a soluble polyimide is selected; Step S112, based on the determined polyimide and liquid crystal polymer, regulating the mass ratio of the polyimide and the liquid crystal polymer to obtain the target performance of the composite flexible substrate; wherein the mass percentage of the polyimide and the liquid crystal polymer is (70:30) to (50:50); in this embodiment, the target performance includes heat resistance, flexibility, mechanical strength, dimensional stability and electrical properties; when the mass content of the polyimide is greater than 70%, the heat resistance of the composite flexible substrate can be improved, but the flexibility is reduced; when the mass content of the liquid crystal polymer is greater than 50%, the flexibility of the composite flexible substrate can be enhanced, but the thermal stability and adhesion are affected.

[0035] Step S113, after the polyimide and the liquid crystal polymer are processed into thin films respectively by hot pressing equipment, they are hot pressed and composited at a temperature of 200° C. to 300° C. to obtain a processed composite flexible substrate. In this embodiment, according to the requirements of the flexible circuit board, the thickness of the composite flexible substrate is in the range of 10 to 50 μm.

[0036] It should be noted that by controlling the liquid crystal polymer content at 30% to 50%, it can be ensured that the composite material still maintains good morphological stability in a high temperature environment, while taking into account the interfacial bonding force of polyimide and liquid crystal polymer, ensuring that the material will not affect the reliability of the flexible circuit board due to decreased adhesion. Through high-temperature hot pressing, the molecular chain segments of polyimide can be cross-linked and cured to improve the heat resistance of the substrate. Liquid crystal polymers can form an oriented structure at high temperatures, which enhances the mechanical strength and flexibility of the material. Since the composite thickness of polyimide and liquid crystal polymer is in the range of 10 to 50 μm, the balance between flexibility and mechanical strength of the material is guaranteed, so that it has sufficient support and can adapt to the development needs of miniaturized flexible circuit boards.

[0037] In summary, after surface modification of the composite flexible substrate, the adhesion of the photoresist is improved, the peeling and uneven coating are avoided, and the accuracy of pattern transfer is ensured. The surface microstructure of the substrate is optimized, the uniformity of photoresist coating is improved, and pattern distortion is reduced. The surface-modified composite flexible substrate is more suitable for high-precision pattern transfer, ensuring the high-resolution requirements in applications such as microchips. The modified surface improves the compatibility between the photoresist and materials such as the conductive layer, avoiding problems in subsequent processes, thereby improving the overall quality and stability of flexible circuit board manufacturing.

[0038] Specifically, step S14 includes: S141, set the preset temperature and preset humidity during the drying process; wherein the preset temperature is 80°C to 100°C, and the preset humidity is 40% to 60%; in this embodiment, the temperature range of 80°C to 100°C is selected, which can not only effectively remove the solvent and moisture that may remain on the surface of the composite flexible substrate, but also avoid thermal damage to the substrate caused by excessively high temperatures. Excessive temperatures may cause material deformation, thermal stress concentration, or loss of some physical properties, while this temperature range helps to improve the stability of the material. The humidity is set between 40% and 60%, which can avoid excessive drying of the substrate surface caused by too low humidity, thereby causing problems such as cracks and embrittlement, and prevent softening of the substrate or uneven surface drying due to excessive humidity. This humidity condition helps to evenly dry the material and ensure the stability of the substrate after drying.

[0039] Step S142, gradually heating up to a preset temperature at a heating rate of 2°C to 3°C per minute, and maintaining a constant temperature for 10 to 15 minutes after reaching the preset temperature; in this embodiment, gradually heating up to a preset temperature, with a heating rate controlled at 2°C to 3°C / minute, can effectively avoid the accumulation of thermal stress caused by a sudden temperature rise.

[0040] Step S143, during the drying process, the air circulation system is used to maintain uniform airflow, and the airflow speed is set to 0.5 to 1 meter per second. In this embodiment, the airflow speed is controlled within the range of 0.5 to 1 meter per second, which can not only ensure the efficiency of air flow, but also avoid damage to the surface caused by excessive airflow.

[0041] It should be noted that controlling the temperature and humidity conditions and the heating rate can avoid uneven thermal stress and surface damage to the substrate during the drying process, ensuring the long-term reliability of the flexible circuit board substrate. The precisely controlled airflow speed and real-time feedback adjustment system can ensure the uniformity of the airflow during the drying process, avoid local uneven drying, and ensure the high-precision execution of subsequent processes such as lithography and conductive layer deposition. Through real-time monitoring and feedback adjustment of temperature and humidity, the stability of temperature and humidity is ensured throughout the drying process, which improves the automation level of the production process, reduces the need for manual intervention, and ensures the consistency of production efficiency and finished product quality.

[0042] In an optional embodiment, step S2 includes: Step S21, on the surface of the composite flexible substrate, a high-adhesion photoresist is coated by a dynamic rheology control spin coating process, and a high-resolution photoresist is coated by a plasma-assisted nano-spraying technology; wherein the thickness of the high-adhesion photoresist layer is 2-5 μm, and the thickness of the high-resolution photoresist layer is 1-3 μm; in this embodiment, a dynamic rheology control spin coating process is adopted, and the coating method of the photoresist is dynamically adjusted according to the characteristics of the substrate to ensure uniformity of the glue layer and improve the accuracy of the photolithography pattern. The plasma-assisted nano-spraying technology is adopted to enhance the film quality of the high-resolution photoresist, so that it can support ultra-fine circuit processing.

[0043] It should be noted that since the thickness of the high-adhesion photoresist layer is 2~5μm, the adhesion of the layer to the substrate is enhanced, and the overall heat resistance and chemical corrosion resistance are improved. Since the thickness of the high-resolution photoresist layer is 1~3μm, it provides ultra-fine photolithography patterns, and its thinner layer can achieve higher exposure resolution, ensure high-precision molding of photolithography patterns, and realize sub-micron-level circuit processing.

[0044] Step S22, dual-mode laser direct imaging technology is used to perform pattern exposure to achieve the transfer of circuit patterns. In this embodiment, dual-mode exposure is used to effectively reduce alignment errors and achieve sub-micron circuit pattern transfer. The exposure speed is greatly improved, so that the flexible circuit board can meet the needs of large-scale production, especially for high-precision microchip applications.

[0045] It should be noted that traditional mask lithography (such as contact or projection lithography) is affected by factors such as mask accuracy and optical distortion, making it difficult to achieve ultra-high-precision circuit patterns. However, dual-mode laser direct imaging technology directly controls laser beam exposure through a computer, without the need for a mask, and can achieve sub-micron exposure accuracy, making it very suitable for the manufacture of high-density flexible circuit boards. Laser direct imaging technology does not require a mask, and can modify exposure data through software to quickly adapt to different design requirements, greatly improving production flexibility and reducing manufacturing costs.

[0046] Specifically, step S22 includes: Step S221, pre-scan the photoresist with a low-power laser to activate the photosensitive area in the photoresist; in this embodiment, the photosensitive area includes the photosensitizer in the photoresist and its reaction area after being stimulated. The pre-scanning function of the low-power laser is to activate the photosensitive area of ​​the photoresist to ensure that the surface of the photoresist can uniformly respond to subsequent high-power laser exposure. This process helps to remove non-uniform or over-cured areas that may exist on the surface of the photoresist, enhance the uniformity of the photoresist layer, and thus improve the accuracy of pattern transfer. In the specific implementation process, the power range of the low-power laser is 0.1mW / cm² to 10mW / cm², and the scanning speed of the low-power laser is 1μm / s to 10μm / s.

[0047] Step S222, after the pre-exposure is completed, the key area of ​​the circuit is subjected to secondary exposure by using a high-power laser, the microscopic deformation of the substrate is detected in real time, and the laser trajectory is adjusted by a dynamic exposure compensation algorithm to achieve the transfer of the circuit pattern. In this embodiment, the secondary exposure of the high-power laser is aimed at the key area of ​​the circuit, ensuring that the accuracy of the key circuit part can be fully guaranteed, and avoiding the phenomenon of pattern blur or distortion in complex circuit patterns. Through the fine high-power laser secondary exposure, the fine line width and spacing can be effectively processed to ensure the high-precision transfer of the pattern, which is particularly suitable for high-density and complex microchip circuit design. In the specific implementation process, the dynamic exposure compensation algorithm is a commonly used algorithm in this field and will not be repeated here. The key area of ​​the circuit includes the core functional area of ​​the microchip, the fine line width area, the through hole and the metal interconnection area. The core functional area of ​​the microchip includes logic gates, storage units, power distribution networks and high-speed signal transmission channels. In the specific implementation process, the power range of the high-power laser is 10mW / cm² to 200mW / cm², and the scanning speed is 0.1μm / s to 1μm / s.

[0048] In an optional embodiment, step S3 includes: Step S31, by performing zoning control on the hot press, the temperature of each area is monitored in real time, and the temperature is gradually adjusted using a nonlinear temperature rise and fall curve according to the thermal expansion characteristics of the substrate and the curing temperature of the photoresist; in this embodiment, the polyimide-liquid crystal polymer composite material may expand to varying degrees when heated. If the temperature changes in each area are uneven, it is easy to cause local stress concentration and affect the circuit accuracy. Zoning control can ensure that the entire substrate is heated evenly, reduce deformation, and improve dimensional accuracy. The curing of photoresist usually requires precise temperature control, and the nonlinear temperature rise and fall curve can provide slow heating or cooling at the appropriate stage to ensure that the photoresist layer is uniformly cured and reduce cracks or delamination caused by too fast temperature gradient changes.

[0049] Step S32, curing the photoresist layer by a multi-stage temperature gradient heating process. In this embodiment, the curing process of the present invention adopts an accurate temperature control strategy and a multi-stage temperature gradient heating technology to ensure uniform curing of the photoresist, while reducing substrate deformation and internal stress, and improving the overall quality and long-term reliability of the flexible circuit board. This process scheme is particularly suitable for high-precision microchip applications, can meet stringent manufacturing requirements, and provide a high-quality substrate foundation for subsequent processing.

[0050] Specifically, step S32 includes: Step S321, slowly increase the temperature to 50-70°C, control the heating rate at 1-2°C / min, and maintain it for 5-10 minutes; in this embodiment, this step is a preheating stage, which starts thermal activation of the photoresist and releases the stress inside the substrate.

[0051] Step S322, raising the temperature to the main curing temperature of the photoresist, the main curing temperature range is 100-130°C, and maintaining it for 20-30 minutes; in this embodiment, this step is the main curing stage, the chemical bond cross-linking of the photoresist is fully completed, so that it has higher heat resistance and mechanical stability. The curing rate is optimized, thermal decomposition or local over-curing is avoided, and the stability of the circuit pattern is improved.

[0052] Step S323, using a nonlinear cooling curve, slowly lower the temperature to 70~80℃ and maintain it for 5~10 minutes; wherein the cooling rate is 1~2℃ / min; in the present embodiment, this step is a temperature slow-down stage, which can gradually eliminate the thermal stress of the photoresist and the substrate. In the present embodiment, the nonlinear cooling curve means that the cooling rate during the temperature reduction process is not a constant value, but varies according to specific process requirements and material properties. Specifically, the cooling rate may gradually slow down over time, or be adjusted in certain specific temperature ranges. Compared with linear cooling, nonlinear cooling allows for more sophisticated temperature control, allowing the photoresist and substrate to better adapt to temperature changes during the cooling process and avoid excessive thermal stress.

[0053] Step S324, lowering the temperature to room temperature and cooling naturally for 10 to 15 minutes; wherein the room temperature is 25°C. In this embodiment, this step is a cooling stage, which allows the substrate and the photoresist layer to reach a thermal equilibrium state, ensures the stability of the cured photoresist layer, avoids deformation or stress release during subsequent processing, and enhances the reliability of the flexible circuit board, preventing micro cracks or delamination caused by residual internal stress.

[0054] In an optional embodiment, step S4 includes: Step S41, using low-temperature chemical vapor deposition or physical vapor deposition technology, metal deposition is performed in a temperature range of 60°C to 80°C, and nanoparticle reinforcement is added during the deposition process; in this embodiment, the nanoparticle reinforcement can be metal nanoparticles, carbon nanotubes, aluminum oxide, etc.

[0055] Step S42, using ultrasonic dispersion method or surfactant dispersion method to disperse the nanoparticles in the metal deposition liquid, and controlling the deposition rate and nanoparticle concentration to ensure that the nanoparticles are evenly distributed in the metal layer; in this embodiment, the concentration of the nanoparticles is 1%~3%, and the deposition rate is 20-50 nm / min.

[0056] Step S43, after the metal deposition is completed, the flexible circuit board is subjected to a low-temperature baking and curing treatment, and the baking temperature is controlled within the range of 80°C to 100°C.

[0057] It should be noted that low-temperature deposition technology avoids damage to the substrate caused by high temperature, ensuring the stability of the flexible circuit board; the addition of nanoparticles not only improves the conductivity of the metal layer, but also enhances the adhesion and durability of the metal layer, adapting to the electrical requirements of high-precision microchips. The low-temperature curing process further enhances the bonding between the metal layer and the substrate, improves the long-term reliability of the metal layer, and ensures the stability of the flexible circuit board in complex applications.

[0058] Embodiment 2: The invention discloses a flexible circuit board for a microchip. The flexible circuit board for a microchip is prepared by adopting the preparation method of the flexible circuit board for a microchip in the first embodiment.

[0059] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a flexible circuit board for a microchip, characterized in that: include: Step S1, selecting a composite flexible substrate to be processed, and performing surface modification treatment on the composite flexible substrate to obtain a preliminary circuit board; The composite flexible substrate is made of a polyimide-liquid crystal polymer composite material; Step S2, sequentially coating a high-adhesion photoresist and a high-resolution photoresist on the surface of the preliminary circuit board, and performing pattern exposure on the preliminary circuit board coated with two layers of photoresist using laser direct imaging technology; Step S3, curing the exposed photoresist layer by a hot pressing process; Step S4, forming a conductive layer in the circuit pattern area to obtain a flexible circuit board.

2. The method for preparing a flexible circuit board for a microchip according to claim 1, characterized in that: The step S1 comprises: Step S11, adjusting the composite ratio of polyimide and liquid crystal polymer according to the processing requirements of the flexible circuit board to obtain a processed composite flexible substrate; Step S12, performing plasma treatment on the composite flexible substrate by using a low-temperature plasma device; Step S13, chemically treating the surface of the composite flexible substrate with an aluminum oxide solution or a fluoride solution; Step S14, after the surface chemical treatment, the composite flexible substrate is dried to obtain a preliminary circuit board.

3. The method for preparing a flexible circuit board for a microchip according to claim 2, characterized in that: The step S14 comprises: S141, setting a preset temperature and a preset humidity during the drying process; wherein the preset temperature is 80° C. to 100° C., and the preset humidity is 40% to 60%; Step S142, gradually heating up to a preset temperature at a heating rate of 2°C to 3°C per minute, and maintaining a constant temperature for 10 to 15 minutes after reaching the preset temperature; Step S143, during the drying process, the air flow is kept uniform through the air circulation system, and the air flow speed is set to 0.5 meters to 1 meter per second.

4. The method for preparing a flexible circuit board for a microchip according to claim 2, characterized in that: The step S11 comprises: Step S111, determining the types and molecular structures of polyimide and liquid crystal polymer according to the processing requirements of the flexible circuit board; wherein the polyimide is thermosetting polyimide or soluble polyimide, and the liquid crystal polymer is a wholly aromatic liquid crystal polymer; Step S112, based on the determined polyimide and liquid crystal polymer, adjusting the mass ratio of the polyimide and the liquid crystal polymer to obtain target performance of the composite flexible substrate; wherein the mass percentage of the polyimide and the liquid crystal polymer is (70:30) to (50:50); Step S113, after the polyimide and the liquid crystal polymer are processed into thin films respectively by hot pressing equipment, they are hot pressed and composited at a temperature of 200° C. to 300° C. to obtain a processed composite flexible substrate.

5. The method for preparing a flexible circuit board for a microchip according to claim 1, characterized in that: The step S2 comprises: Step S21, coating a high-adhesion photoresist on the surface of the composite flexible substrate by a dynamic rheology controlled spin coating process, and coating a high-resolution photoresist by a plasma-assisted nano-spraying technology; wherein the thickness of the high-adhesion photoresist layer is 2-5 μm, and the thickness of the high-resolution photoresist layer is 1-3 μm; Step S22, using dual-mode laser direct imaging technology to perform pattern exposure to achieve the transfer of the circuit pattern.

6. The method for preparing a flexible circuit board for a microchip according to claim 5, characterized in that: The step S22 comprises: Step S221, pre-scanning the photoresist with a low-power laser to activate the photosensitive area in the photoresist; Step S222, after the pre-exposure is completed, a high-power laser is used to perform secondary exposure on the key area of ​​the circuit, the microscopic deformation of the substrate is detected in real time, and the laser trajectory is adjusted through a dynamic exposure compensation algorithm to achieve the transfer of the circuit pattern.

7. The method for preparing a flexible circuit board for a microchip according to claim 1, characterized in that: The step S3 comprises: Step S31, by performing zone control on the hot press, the temperature of each zone is monitored in real time, and the temperature is gradually adjusted using a nonlinear temperature rise and fall curve according to the thermal expansion characteristics of the substrate and the curing temperature of the photoresist; Step S32, curing the photoresist layer through a multi-stage temperature gradient heating process.

8. The method for preparing a flexible circuit board for a microchip according to claim 1, characterized in that: The step S4 comprises: Step S41, using low-temperature chemical vapor deposition or physical vapor deposition technology to perform metal deposition at a temperature range of 60° C. to 80° C., and adding a nanoparticle enhancer during the deposition process; Step S42, dispersing the nanoparticles in the metal deposition liquid by using an ultrasonic dispersion method or a surfactant dispersion method, and controlling the deposition rate and the concentration of the nanoparticles to ensure that the nanoparticles are evenly distributed in the metal layer; Step S43, after the metal deposition is completed, the flexible circuit board is subjected to a low-temperature baking and curing treatment, and the baking temperature is controlled within the range of 80°C to 100°C.

9. The method for preparing a flexible circuit board for a microchip according to claim 8, characterized in that: In step S42, the concentration of the nanoparticles is 1% to 3%, and the deposition rate is 20-50 nm / min.

10. A flexible circuit board for a microchip, characterized in that: The flexible circuit board for microchip is prepared by the method for preparing the flexible circuit board for microchip according to any one of claims 1 to 9.

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