A copper-photosensitive polyimide film with excellent interfacial strength and a preparation method and application thereof

Abstract

The application discloses a copper-photosensitive polyimide film with excellent interface strength and a preparation method and application thereof, and relates to the technical field of integrated circuit packaging materials.The copper-photosensitive polyimide film with excellent interface strength prepared by the application reduces the formation of initial holes and pinholes, and reduces the residual stress and the risk of blistering through the improvement of the polar surface energy and the introduction of the uniform nucleation mechanism.Compared with the traditional strong chemical roughening and thick glue layer scheme, the application realizes a better balance among the adhesion strength, the humidity and heat / welding reliability, the micro-line adaptability and the high-frequency dielectric loss.The technology is particularly suitable for application scenarios such as high-density interconnection, 5G / 6G radio frequency flexible antenna, folding display and wearable devices, and these fields have put forward the requirements of compatibility for the thinness, high toughness, high stability and low dielectric loss of the substrate material.

Description

Technical Field

[0001] This invention relates to the field of integrated circuit packaging materials technology, and in particular to a copper-photosensitive polyimide film with excellent interfacial strength, its preparation method and application. Background Technology

[0002] As integrated circuits (ICs) evolve towards higher density, higher performance, and miniaturization, the packaging substrate, as a core component connecting chips to external circuits, directly determines the reliability and signal transmission efficiency of the devices. Polyimide (PI) substrates, due to their excellent high-temperature resistance, low dielectric constant, good mechanical strength, and flexibility, have become an important candidate material for high-end integrated circuit substrates. However, in practical applications, during the metallization process of traditional polyimide substrates, the interfacial bonding force between the metal layer (such as copper foil) and the substrate is insufficient, resulting in poor adhesion. When subjected to thermal or mechanical stress, the metal layer is prone to delamination, warping, or even detachment, severely restricting the reliability and lifespan of the packaged devices.

[0003] Flexible copper clad laminate (FCCL) is a key substrate for flexible circuits, foldable displays, wearable electronics, and high-frequency communication modules, but its performance also faces challenges. Traditional FCCLs, which use adhesives to bond copper and polyimide (PI), are prone to problems such as solder blistering, damp heat failure, and ion residue due to the limited thermal stability and dielectric loss of the organic adhesive layer, leading to decreased product reliability. Furthermore, the adhesive layer can increase the dielectric constant and loss tangent, which is detrimental to the integrity of high-frequency signals.

[0004] To improve the interfacial adhesion between copper and PI, existing technologies often employ methods such as strong chemical roughening, introduction of coupling agents, and stacking of metal adhesion layers. However, these methods generally suffer from the following problems: the weak boundary layer at the interface is not effectively removed, causing the peeling path to extend along the contaminated or degraded layer; excessive roughening increases dielectric loss and line edge roughness, adversely affecting the fabrication of micro-circuits and high-frequency performance; the adhesion modification process conflicts with the development / exposure / release window of photosensitive PI, easily leading to pattern collapse or insufficient development; high-temperature or strong oxidation treatments can damage the PI backbone or photosensitive groups, causing a decrease in material density and mechanical properties.

[0005] In existing technologies, plasma treatment has been widely used for surface modification of polyimide substrates to enhance their interfacial adhesion to metal layers. For example, patent CN113652675B proposes a method for plasma-modified polyimide films. By using a mixed gas of hydrogen and argon for plasma treatment, polar groups such as amide and aldehyde groups are successfully introduced onto the film surface, significantly improving the surface activity and roughness of the polyimide film. This effectively improves the adhesion between the metal layer and the polyimide substrate, providing new possibilities for the application of flexible electronic devices.

[0006] However, there is still room for improvement in the current technology. Therefore, there is an urgent need for a solution that can simultaneously achieve decontamination, functionalization, and moderate roughening under low temperature and short process conditions. This solution must also be compatible with the photolithography process of photosensitive PI. At the same time, it should be able to generate a chemical-physical composite transition layer in situ at the interface, and ultimately significantly improve the interfacial bonding force and service reliability of copper / PI without sacrificing dielectric properties and micro-line fabrication capabilities. Summary of the Invention

[0007] This invention provides a copper-photosensitive polyimide film with excellent interfacial strength, its preparation method and application, to overcome the problem of insufficient adhesion between the metal layer and the substrate in the prior art, and provides a new path for the high-performance and high-reliability manufacturing of high-end integrated circuit substrates.

[0008] To achieve the above objectives, the technical solution of this invention is as follows:

[0009] A first aspect of the present invention provides a method for preparing a copper-photosensitive polyimide film with excellent interfacial strength, comprising:

[0010] 4,4'-diaminodiphenyl ether was added to N,N'-dimethylacetamide solvent in multiple portions, and the mixture was stirred in an ice bath to obtain the first mixture.

[0011] 3,3',4,4'-biphenyltetracarboxylic dianhydride was added to the first mixture in multiple portions and mixed thoroughly under ice bath conditions to obtain the second mixture.

[0012] The 2NH2- photosensitive monomer was added to the second mixture in multiple portions and mixed evenly at room temperature to obtain the third mixture.

[0013] The copper plating solution is obtained by mixing copper sulfate pentahydrate, ethylenediaminetetraacetic acid, potassium sodium tartrate, polyethylene glycol, potassium ferrocyanide, 2,2-bipyridine and sodium hydroxide solution evenly in deionized water.

[0014] The third mixture was coated into a thin film, and then dried, exposed to ultraviolet light, subjected to plasma treatment, and rinsed with palladium solution in sequence. Finally, it was thermally cyclized in an inert atmosphere to obtain a photosensitive polyimide film.

[0015] The photosensitive polyimide film is immersed in the copper plating solution containing formaldehyde solution to obtain a copper-photosensitive polyimide film with excellent interfacial strength.

[0016] Preferably, in conjunction with the first aspect, the molar ratio of the 4,4'-diaminodiphenyl ether, the 3,3',4,4'-biphenyltetracarboxylic dianhydride, and the 2NH2-photosensitive monomer is 1:(1-3):1;

[0017] And / or, the solid content of the N,N'-dimethylacetamide solvent is 5% to 25%.

[0018] In conjunction with the first aspect, preferably, when the third mixture is coated into a thin film, the coating method is one of the following: blade coating, casting, and spin coating;

[0019] And / or, when the third mixture is coated into a thin film, the coating amount of the third mixture is 100–300 μL / cm. 2 ;

[0020] And / or, when the third mixture is coated into a thin film, the thickness of the film is 100 to 300 μm.

[0021] In conjunction with the first aspect, preferably, when 3,3',4,4'-biphenyltetracarboxylic dianhydride is added to the first mixture in multiple portions and mixed evenly under an ice bath, the ice bath mixing temperature is 0-5°C and the ice bath mixing time is 0.5-3 hours.

[0022] And / or, when the 2NH2-photosensitive monomer is added to the second mixture in multiple portions and mixed evenly at room temperature, the room temperature mixing temperature is 20-30°C and the room temperature mixing time is 8-15 hours;

[0023] And / or, when copper sulfate pentahydrate, ethylenediaminetetraacetic acid, potassium sodium tartrate, polyethylene glycol, potassium ferrocyanide, 2,2-bipyridine, and sodium hydroxide solution are mixed evenly in deionized water, the mixing temperature is 20-30°C and the mixing time is 24-38 hours.

[0024] And / or, the pH value of the copper plating solution is 13-14;

[0025] And / or, in the copper plating solution containing formaldehyde solution, the amount of formaldehyde solution added is 100-500 μL.

[0026] In conjunction with the first aspect, preferably, when the third mixture is coated into a thin film and then subjected to drying, ultraviolet exposure, plasma treatment, palladium solution rinsing, and thermal cyclization in an inert atmosphere, the drying temperature is 70-80°C and the drying time is 5-30 min.

[0027] And / or, the exposure intensity is 5–20 mW / cm 2 The exposure time is 5 to 20 minutes;

[0028] And / or, the rinsing time is 5 to 20 seconds;

[0029] And / or, the inert atmosphere is nitrogen;

[0030] And / or, the conditions for thermal circulation are: heating to 100, 150, 200, 250 and 300 °C respectively at a heating rate of 2 to 8 °C / min, and holding at each temperature for 60 to 80 min.

[0031] Preferably, in conjunction with the first aspect, the plasma treatment is the introduction of any one or more of Ar / NH3 / CF4 / air;

[0032] And / or, the plasma treatment duration is 10–60 min;

[0033] And / or, the plasma processing power is 100-200W.

[0034] A second aspect of the present invention provides a copper-photosensitive polyimide film with excellent interfacial strength prepared by any of the methods described in the first aspect, wherein the pull-out test data is above 15 MPa.

[0035] A third aspect of the present invention provides the application of a copper-photosensitive polyimide film with excellent interfacial strength prepared by any of the methods described in the first aspect in a flexible polyimide plate.

[0036] Compared with the prior art, the advantages or beneficial effects of the embodiments of the present invention include at least the following:

[0037] This invention provides a composite interface structure with excellent interfacial strength, consisting of a copper-photosensitive polyimide film and a flexible polyimide plate, constructed using plasma multimodal surface engineering technology. This structure utilizes polar functional groups, nano-roughening, and a gradient transition layer. This structure transforms the adhesion mechanism of the copper / polyimide (PSPI) interface from van der Waals forces-dominated physical adsorption to a synergistic effect centered on chemical bonding and coordination bonding, supplemented by nanoscale mechanical interlocking. Cracks deflect and branch at the interface, significantly increasing the interfacial fracture energy. Without the introduction of traditional adhesives, the interfacial peel strength can stably reach 25 MPa. Simultaneously, by precisely controlling the surface roughness and maintaining it within an optimal range, both the mechanical interlocking effect is ensured, while avoiding the increase in high-frequency insertion loss due to excessive roughness. Furthermore, the enhancement of polar surface energy and the introduction of a uniform nucleation mechanism reduce the formation of initial voids and pinholes, lowering residual stress and the risk of blistering. Compared to traditional methods involving strong chemical coarsening and thick adhesive layers, this invention achieves a superior balance between adhesion strength, wet heat / soldering reliability, micro-circuit adaptability, and high-frequency dielectric loss. This technology is particularly suitable for applications such as high-density interconnects, 5G / 6G RF flexible antennas, foldable displays, and wearable devices, which demand a balance of thinness, high toughness, high stability, and low dielectric loss in substrate materials. Attached Figure Description

[0038] Figure 1 The images provided by this invention are SEM images of a plasma-treated, un-thermally cycloidized thin film. The left image shows the film before plasma treatment, and the right image shows the film after plasma treatment.

[0039] Figure 2 The CF4 characterization results of XPS provided by this invention are shown in the figure.

[0040] Figure 3 The figure shows the NH3 characterization results of XPS provided by this invention. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. The described embodiments should not be regarded as limitations on this invention. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0042] In the following description, references to "some embodiments" refer to a subset of all possible embodiments; however, it is understood that "some embodiments" may be the same or different subsets of all possible embodiments and may be combined with each other without conflict. Unless otherwise defined, all technical and scientific terms used in the embodiments of the invention have the same meaning as commonly understood by one of ordinary skill in the art to which the embodiments of the invention pertain. The terminology used in the embodiments of the invention is for the purpose of describing the embodiments of the invention only and is not intended to limit the invention.

[0043] In the following description of this embodiment, the terms "including", "comprising", "having", and "containing" are all open-ended terms, meaning that they include but are not limited to.

[0044] It should be noted that all raw materials / reagents in the embodiments of the present invention can be purchased on the market or prepared according to conventional methods known to those skilled in the art; the term "and / or" in the embodiments of the present invention is only used to describe the relationship between related objects, indicating that there can be three relationships. For example, A and / or B means three cases: A exists alone, B exists alone, and A and B exist simultaneously. A and B can be singular or plural. The character " / " generally indicates that the related objects before and after are in an "or" relationship.

[0045] In the following description of this embodiment, the term "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0046] Those skilled in the art should understand that, in the following description of the embodiments of the present invention, the sequence of numbers does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0047] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0048] Those skilled in the art will understand that the numerical ranges in the embodiments of the present invention should be understood to specifically disclose each intermediate value between the upper and lower limits of the range. Each smaller range between any stated value and an intermediate value within the stated range, as well as any other stated value or an intermediate value within the stated range, is also included within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0049] Unless otherwise stated, the technical / scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may be used in embodiments or test cases of the invention. All references to this specification are generally incorporated herein by reference to disclose and describe methods and / or materials associated with said references. In the event of any conflict with any incorporated reference, the contents of this specification shall prevail.

[0050] It should be noted that all raw materials and / or reagents in the embodiments of the present invention were purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0051] In a first aspect, embodiments of the present invention provide a copper-photosensitive polyimide film with excellent interfacial strength, the preparation method of which includes:

[0052] 4,4'-diaminodiphenyl ether was added to N,N'-dimethylacetamide solvent in multiple portions, and the mixture was stirred in an ice bath to obtain the first mixture.

[0053] 3,3',4,4'-biphenyltetracarboxylic dianhydride was added to the first mixture in multiple portions and mixed thoroughly under ice bath conditions to obtain the second mixture.

[0054] The 2NH2- photosensitive monomer was added to the second mixture in multiple portions and mixed evenly at room temperature to obtain the third mixture.

[0055] The copper plating solution is obtained by mixing copper sulfate pentahydrate, ethylenediaminetetraacetic acid, potassium sodium tartrate, polyethylene glycol, potassium ferrocyanide, 2,2-bipyridine and sodium hydroxide solution evenly in deionized water.

[0056] The third mixture was coated into a thin film, and then dried, exposed to ultraviolet light, subjected to plasma treatment, and rinsed with palladium solution in sequence. Finally, it was thermally cyclized in an inert atmosphere to obtain a photosensitive polyimide film.

[0057] The photosensitive polyimide film is immersed in the copper plating solution containing formaldehyde solution to obtain a copper-photosensitive polyimide film with excellent interfacial strength.

[0058] This invention provides a composite interface structure with excellent interfacial strength, consisting of a copper-photosensitive polyimide film and a flexible polyimide plate, constructed using plasma multimodal surface engineering technology. This structure utilizes polar functional groups, nano-roughening, and a gradient transition layer. This structure transforms the adhesion mechanism of the copper / polyimide (PSPI) interface from van der Waals forces-dominated physical adsorption to a synergistic effect centered on chemical bonding and coordination bonding, supplemented by nanoscale mechanical interlocking. Cracks deflect and branch at the interface, significantly increasing the interfacial fracture energy. Without the introduction of traditional adhesives, the interfacial peel strength can stably reach 25 MPa. Simultaneously, by precisely controlling the surface roughness and maintaining it within an optimal range, both the mechanical interlocking effect is ensured, while avoiding the increase in high-frequency insertion loss due to excessive roughness. Furthermore, the enhancement of polar surface energy and the introduction of a uniform nucleation mechanism reduce the formation of initial voids and pinholes, lowering residual stress and the risk of blistering. Compared to traditional methods involving strong chemical coarsening and thick adhesive layers, this invention achieves a superior balance between adhesion strength, wet heat / soldering reliability, micro-circuit adaptability, and high-frequency dielectric loss. This technology is particularly suitable for applications such as high-density interconnects, 5G / 6G RF flexible antennas, foldable displays, and wearable devices, which demand a balance of thinness, high toughness, high stability, and low dielectric loss in substrate materials.

[0059] It should be noted that the first mixture in this embodiment of the invention is obtained by first adding 4,4'-diaminodiphenyl ether to N,N'-dimethylacetamide solvent in at least three portions, with each addition spaced 2-3 minutes apart, to ensure complete dissolution of the solid. The mixture is then reacted under ice bath conditions at 0-5°C with stirring. Here, stirring can be done using magnetic or mechanical stirring. Initially, the stirring rate can be slightly faster, i.e., 500-800 rpm, to ensure rapid dispersion of the solid reagent. After the reaction stabilizes, the stirring rate can be appropriately reduced, i.e., 200-300 rpm, to avoid temperature fluctuations caused by vigorous stirring.

[0060] The purpose of using an ice bath low-temperature environment in this invention is twofold: firstly, to lower the reaction activation energy and control the reaction rate; and secondly, to suppress side effects and maintain system stability. Specifically, the ice bath reduces the collision frequency and energy of reactant molecules by lowering the system temperature, thereby slowing down the reaction rate and preventing the system temperature from running out of control due to excessively vigorous reactions. The ice bath can also inhibit the oxidation of diamine monomers and the premature cyclization of polyamic acid.

[0061] It should be noted that the reaction between 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) and the first mixture is an exothermic condensation reaction, i.e., the formation of amide bonds and the release of a large amount of heat. If a large amount of BPDA is added at once, the local temperature will rise sharply due to rapid exothermic reaction. However, an ice bath environment of 0-5°C can continuously absorb the heat of reaction, stabilizing the system temperature within the low-temperature range and avoiding a chain reaction of problems caused by excessively high temperatures. For example, it can suppress the hydrolysis side reaction of BPDA.

[0062] It should be noted that the 2NH2- photosensitive monomer in the above steps needs to react with the anhydride group or carboxyl group at the end of the polyamic acid molecular chain to introduce the photosensitive group into the polymer chain.

[0063] It should be noted that copper sulfate pentahydrate is first dissolved in deionized water and stirred until completely dissolved; at this point, the solution is light blue. Then, ethylenediaminetetraacetic acid (EDT) and potassium sodium tartrate are added, and the reaction is continued with stirring. Here, EDTA and potassium sodium tartrate act as complexing agents, reacting with Cu... 2+ A stable chelate is formed, turning the solution color deep blue to avoid Cu 2+ Cu(OH)₂ precipitate was formed under subsequent alkaline conditions. Then, polyethylene glycol, potassium ferrocyanide, and 2,2-bipyridine were added sequentially, stirring until completely dissolved after each addition. Sodium hydroxide solution was then slowly added dropwise while stirring, adjusting the pH of the system to 13-14. Stirring continued until a deep blue copper plating solution was obtained.

[0064] Here, EDTA and potassium sodium tartrate act as complexing agents, through interaction with Cu... 2+ Formation of stable chelates, controlling free Cu 2+ Concentration should be adjusted to prevent precipitation under alkaline conditions, while also regulating Cu concentration. 2+ The reduction rate.

[0065] In a specific embodiment, the molar ratio of 4,4'-diaminodiphenyl ether, 3,3',4,4'-biphenyltetracarboxylic dianhydride and 2NH2-photosensitive monomer is preferably 1:(1-3):1; more preferably, the molar ratio of 4,4'-diaminodiphenyl ether, 3,3',4,4'-biphenyltetracarboxylic dianhydride and 2NH2-photosensitive monomer is 1:2:1.

[0066] In a specific embodiment, the solid content of the N,N'-dimethylacetamide solvent is preferably 5-25%.

[0067] It should be noted that when the solid content of N,N'-dimethylacetamide solvent is less than 5%, i.e., excess solvent will dilute the concentration of each component in the system, making it difficult for the grafting reaction between the 2NH2- photosensitive monomer and the polyamic acid chain to proceed uniformly. In some areas, grafting may be insufficient due to too low a concentration of photosensitive monomer, while in others, excessive grafting may occur due to diffusion lag, ultimately resulting in the photosensitive groups being distributed in an island-like pattern on the molecular chain. This inhomogeneity directly affects subsequent photolithography performance. Furthermore, low solid content leads to extremely low solution viscosity, making it difficult to control the thickness during coating. Multiple coatings are required to achieve the target film thickness, but multiple coatings can lead to poor interlayer bonding, and uneven solvent evaporation rates during drying can easily cause pinholes, wrinkles, or cracks.

[0068] It should be noted that when the solid content of N,N'-dimethylacetamide solvent is greater than 25%, it is difficult to form effective convection during reaction stirring, which easily leads to monomer dispersion and grafting reaction only occurring locally, forming photosensitive enrichment areas or photosensitive depletion areas.

[0069] In a specific embodiment, when the third mixture is coated into a thin film, the coating method is preferably one of scraping, casting, or spin coating.

[0070] In a specific embodiment, when the third mixture is coated into a thin film, the coating amount of the third mixture is preferably 100–300 μL / cm. 2 .

[0071] It should be noted that when the coating amount of the third mixture is too large, the penetration depth of ultraviolet light is insufficient, resulting in the inability of the photosensitive groups in the deeper layers of the film to fully cross-link. During development, the uncross-linked resin in the deeper layers will remain, causing tailing or residual layers at the bottom of the pattern, reducing the resolution to below 20μm, which cannot meet the requirements of fine lines. At the same time, in the plasma treatment before copper plating, the surface modification depth of excessively thick films is limited, and there are insufficient deep polar groups, causing the copper layer to only bond with the surface of the film. Meanwhile, interlayer delamination may occur in the interior of the film due to stress concentration, ultimately reducing the adhesion between the copper and PI interfaces.

[0072] When the coating amount of the third mixture is too small, the interaction between molecular chains is weak, the tensile strength decreases, and the elongation at break decreases, making the flexible electronic device prone to brittle fracture during bending. Simultaneously, excessively thin films become more sensitive to environmental humidity and temperature, and are prone to dielectric property fluctuations due to moisture absorption during long-term service. Furthermore, during palladium solution rinsing, palladium ions may penetrate the film and react with the substrate, leading to false bonding between the copper layer and the substrate during subsequent copper plating. Even if the copper layer is successfully deposited, insufficient support from the PI film can cause copper layer detachment during practical applications such as etching and soldering.

[0073] In a specific embodiment, when the third mixture is coated into a thin film, the thickness of the film is preferably 100 to 300 μm.

[0074] It should be noted that a film thickness of 100–300 μm ensures a moderate solvent evaporation rate, avoiding excessively high or low local concentrations. In the subsequent UV exposure step, UV light can penetrate the film uniformly, causing cross-linking reactions of photosensitive monomers at different depths, ensuring consistent cross-linking degrees across all film layers. During the thermal cyclization stage, moisture and residual solvent can be released in an orderly manner, resulting in uniform internal stress distribution and eliminating the risk of localized overheating or cracking.

[0075] In a specific embodiment, 3,3',4,4'-biphenyltetracarboxylic dianhydride is added to the first mixture in multiple portions and mixed evenly under an ice bath. The ice bath mixing temperature is preferably 0-5°C and the ice bath mixing time is preferably 0.5-3 hours.

[0076] In a specific embodiment, the 2NH2-photosensitive monomer is added to the second mixture in multiple batches and mixed evenly at room temperature. The room temperature mixing temperature is preferably 20-30°C and the room temperature mixing time is preferably 8-15 hours.

[0077] In a specific embodiment, when copper sulfate pentahydrate, ethylenediaminetetraacetic acid, potassium sodium tartrate, polyethylene glycol, potassium ferrocyanide, 2,2-bipyridine, and sodium hydroxide solution are mixed evenly in deionized water, the mixing temperature is preferably 20-30°C, and the mixing time is preferably 24-38 hours.

[0078] In a specific embodiment, the pH value of the copper plating solution is preferably 13-14.

[0079] In a specific embodiment, the amount of formaldehyde solution added to the copper plating solution containing formaldehyde solution is preferably 100-500 μL.

[0080] In a specific embodiment, the third mixture is coated into a thin film and then subjected to drying, ultraviolet exposure, plasma treatment, and palladium solution rinsing in sequence. During thermal cyclization in an inert atmosphere, the drying temperature is preferably 70-80°C and the drying time is preferably 5-30 minutes.

[0081] In a specific embodiment, the exposure intensity is preferably 5–20 mW / cm². 2 The preferred exposure time is 5 to 20 minutes.

[0082] In a specific embodiment, the rinsing time is preferably 5 to 20 seconds.

[0083] In a specific embodiment, the inert atmosphere is preferably nitrogen.

[0084] In a specific embodiment, the preferred conditions for thermal circulation are: heating to 100, 150, 200, 250, and 300°C respectively at a heating rate of 2–8°C / min, and holding at each temperature for 60–80 min.

[0085] In a specific embodiment, plasma treatment is preferably carried out by introducing one or more of Ar / NH3 / CF4 / air.

[0086] In a specific embodiment, the plasma treatment time is preferably 10 to 60 minutes.

[0087] In a specific embodiment, the plasma processing power is preferably 100-200W.

[0088] Secondly, embodiments of the present invention provide a copper-photosensitive polyimide film with excellent interfacial strength prepared by any of the methods described in the first aspect, with a pull-out test data of 15 MPa or higher.

[0089] Thirdly, embodiments of the present invention provide an application of a copper-photosensitive polyimide film with excellent interfacial strength prepared by any of the methods described in the first aspect in a flexible polyimide plate.

[0090] The technical method of the present invention will be further described below with reference to specific embodiments.

[0091] Example 1

[0092] Example 1 provides a method for preparing a copper-photosensitive polyimide film with excellent interfacial strength, the method comprising the following steps:

[0093] Step S1: Add 1399.05 mg of N,N'-dimethylacetamide (DMAc) solvent to a 25 mL round-bottom flask, followed by 50.06 mg of 4,4'-diaminodiphenyl ether (ODA). After stirring to dissolve, stir at 200 rpm for 20 min in an ice-water bath at 5-8 °C to ensure complete dissolution of ODA. Next, add 110.33 mg of BPDA in three portions, with each addition at least 10 min apart, to avoid excessively vigorous reaction leading to explosive polymerization. Maintain the ice-water bath environment and 200 rpm stirring speed throughout the process. Continue stirring in the ice-water bath for 2 h to stabilize the reaction system. Then, 86.5 mg of 2NH2-photosensitive monomer (dimethyl 4-(5-(4-((4,4”-diamino-[1,1':3',1”-triphenyl]-5'-yl)oxy)butoxy)-2-nitrophenyl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylic acid ester) was added, the ice-water bath was removed, and stirring was continued at room temperature for 12 h (with ice packs used to assist in temperature control) to finally obtain a photosensitive polyamic acid (PAA) solution.

[0094] Step S2: Filter 100 μL of dilute PAA solution using an oily filter membrane with a pore size of 0.22 μm to remove impurities. Thin film preparation is performed using a blade coating method. Specifically, a 3 cm × 3 cm glass slide is first subjected to UV treatment for 30 min to enhance its surface properties. Then, 200 μL of filtered photosensitive polyamic acid (PS-PAA) dilute solution is uniformly coated onto the surface of the 3 cm × 3 cm glass slide, controlling the coating thickness to 200 μm, while maintaining the substrate temperature at 60 °C to ensure uniform solution distribution and the formation of a uniform film. Subsequently, the coated glass slide is placed on a hot plate and dried at 80 °C for 4 to 6 min to allow the photosensitive polyamic acid PS-PAA film to initially form and remove residual solvent.

[0095] Step S3: After the film is initially formed, it is placed in a high-precision ultraviolet exposure machine for photolithography. During the exposure process, the exposure intensity is set to 10mW / cm². 2 Sufficient energy is ensured to penetrate the film and initiate the cross-linking reaction of the photosensitive monomers. The exposure time is 10 minutes to ensure that the film completes the photochemical reaction uniformly and fully during the photolithography process.

[0096] Step S4: Then place the thin film in a plasma surface treatment instrument for 900 seconds at 200W, and introduce air.

[0097] Step S5: Immerse the treated polymer film in a 0.1 mol / L PdCl2 / EtOH solution for 10 seconds, then clean it with anhydrous ethanol and dry it with compressed air.

[0098] The preparation method of 0.1 mol / L PdCl2 / EtOH solution is as follows: Dissolve 1.7743 g of PdCl2 solid in an appropriate amount of ethanol, stir until completely dissolved, transfer to a 100 mL volumetric flask and dilute to the mark with ethanol, shake well to obtain 0.1 mol / L PdCl2 / EtOH solution.

[0099] Step S6: For the conversion process from PAA to PI, a thermal cyclization treatment is performed using a baking machine. The specific steps are as follows: the temperature is gradually increased to 60℃ for 30 min, 150℃ for 30 min, 200℃ for 30 min, 250℃ for 30 min, and 300℃ for 30 min, and the thermal cyclization reaction is completed, finally obtaining a photosensitive polyimide film.

[0100] Step S7: Next, perform copper plating. Add 1 mL of NaOH to the bubbling 40°C copper plating solution. Observe the pH test paper; it should turn purple-red (pH = 14). Then, immerse the photosensitive polyimide film in the copper plating solution, adding formaldehyde in two batches (more formaldehyde can be added). Immerse until the sample is coated with copper, approximately 2 minutes. Then remove the sample from the copper plating solution, finally obtaining a copper-photosensitive polyimide film with excellent interfacial bonding strength.

[0101] Preparation of copper plating solution:

[0102] To prepare the copper plating solution, first take 1L of deionized water and add 24g CuSO4·5H2O and 21g EDTA sequentially, stirring until completely dissolved to form a copper complex. Then add 10g potassium sodium tartrate, 1g polyethylene glycol (PEG 20000), 70mg potassium ferrocyanide, and 8mg 2,2-bipyridine, stirring until fully dissolved. Finally, slowly add 16g NaOH (or an appropriate amount of NaOH solution) while stirring, adjusting the pH to 13-14. Stir at room temperature for 24 hours at a speed of 200 rpm / min to obtain the copper plating solution.

[0103] Comparative Example 1

[0104] As a control experiment of Example 1, the preparation was carried out using a method that was basically the same as that of Example 1, except that the gas introduced in step S4 was Ar / NH3.

[0105] Comparative Example 2

[0106] As a control experiment of Example 1, the preparation was carried out using a method that was basically the same as that of Example 1, except that the gas Ar / CF4 was introduced in step S4.

[0107] It should be noted that Ar is introduced for 3 minutes first, followed by CF4 for 12 minutes.

[0108] Comparative Example 3

[0109] As a control experiment of Example 1, the thin film was prepared using a method that was basically the same as that of Example 1, except that in step S4, the thin film was not subjected to plasma treatment.

[0110] Test Example 1

[0111] This embodiment provides a SEM test experiment for surface morphology.

[0112] The SEM morphology of the copper-photosensitive polyimide film PS-PAA with excellent interfacial strength prepared in Example 1 after exposure and plasma treatment (right) is compared with that without plasma treatment (left). The results are as follows. Figure 1 As shown.

[0113] Depend on Figure 1 It is evident that plasma-treated surfaces exhibit significant changes. Plasma treatment primarily alters the surface properties of materials through the interaction of high-energy plasma with the material surface, thereby increasing the number of surface-active groups. For photosensitive polyimide films, plasma treatment can introduce polar groups, increasing surface energy and thus improving wettability, adhesion, and reactivity. This treatment can significantly enhance the bonding strength between the film and subsequent coatings or plating layers, while also removing surface impurities and further optimizing the film's surface properties.

[0114] Test Example 2

[0115] This embodiment provides a test experiment for XPS.

[0116] A comparison of the Ar / CF4 ratio of the copper-photosensitive polyimide film PS-PAA with excellent interfacial strength prepared in Example 1 after exposure and plasma treatment with the untreated film is shown in the following results. Figure 2 As shown.

[0117] Depend on Figure 2 It can be seen that, compared with the untreated film, the film treated with Ar-CF4 plasma showed a significant F1s characteristic peak in XPS analysis, indicating that fluorine was successfully introduced.

[0118] Test Example 3

[0119] This embodiment provides a test experiment for XPS.

[0120] A comparison of the Ar / NH3 ratio of the copper-photosensitive polyimide film PS-PAA with excellent interfacial strength prepared in Example 1 after exposure and plasma treatment with the untreated film is shown in the following results. Figure 3 As shown.

[0121] Depend on Figure 3 It can be seen that, compared with the untreated film, the film treated with Ar-NH3 plasma showed obvious amine characteristic peak C-NH2 in XPS analysis.

[0122] Test Example 3

[0123] This embodiment provides a pull-out test for a copper-photosensitive polyimide film with excellent interfacial strength.

[0124] The results obtained from the preparation of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 are shown in Table 1.

[0125] Table 1 Summary of pull-out tests of PS-PAA prepared in Example 1

[0126]

[0127] As shown in Table 1, there is a significant difference in the pull-out test results between plasma-treated and plasma-treated samples, with plasma treatment showing a markedly better effect.

[0128] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a copper-photosensitive polyimide film with excellent interfacial strength, characterized in that, include: 4,4'-diaminodiphenyl ether was added to N,N'-dimethylacetamide solvent in multiple portions, and the mixture was stirred in an ice bath to obtain the first mixture. 3,3',4,4'-biphenyltetracarboxylic dianhydride was added to the first mixture in multiple portions and mixed thoroughly under ice bath conditions to obtain the second mixture. The 2NH2-photosensitive monomer was added to the second mixture in multiple portions and mixed evenly at room temperature to obtain the third mixture. The copper plating solution is obtained by mixing copper sulfate pentahydrate, ethylenediaminetetraacetic acid, potassium sodium tartrate, polyethylene glycol, potassium ferrocyanide, 2,2-bipyridine and sodium hydroxide solution evenly in deionized water. The third mixture was coated into a thin film, and then dried, exposed to ultraviolet light, subjected to plasma treatment, and rinsed with palladium solution in sequence. Finally, it was thermally cyclized in an inert atmosphere to obtain a photosensitive polyimide film. The photosensitive polyimide film is immersed in the copper plating solution containing formaldehyde to obtain a copper-photosensitive polyimide film with excellent interfacial strength; The molar ratio of the 4,4'-diaminodiphenyl ether, the 3,3',4,4'-biphenyltetracarboxylic dianhydride, and the 2NH2-photosensitive monomer is 1:(1-3):1; The solid content of the N,N'-dimethylacetamide solvent is 5-25%; When the third mixture is coated into a thin film, the coating method is one of the following: blade coating, casting, or spin coating. When the third mixture is coated into a thin film, the coating amount of the third mixture is 100–300 μL / cm. 2 ; When the third mixture is coated into a thin film, the thickness of the film is 100–300 μm; When 3,3',4,4'-biphenyltetracarboxylic dianhydride is added to the first mixture in multiple portions and mixed evenly under an ice bath, the ice bath mixing temperature is 0-5°C and the ice bath mixing time is 0.5-3 hours. When the 2NH2-photosensitive monomer is added to the second mixture in multiple batches and mixed evenly at room temperature, the room temperature mixing temperature is 20-30℃ and the room temperature mixing time is 8-15h. When copper sulfate pentahydrate, ethylenediaminetetraacetic acid, potassium sodium tartrate, polyethylene glycol, potassium ferrocyanide, 2,2-bipyridine, and sodium hydroxide solution are mixed evenly in deionized water, the mixing temperature is 20-30℃ and the mixing time is 24-38h. The pH value of the copper plating solution is 13-14; In the copper plating solution containing formaldehyde solution, the amount of formaldehyde solution added is 100-500 μL.

2. The method for preparing a copper-photosensitive polyimide film with excellent interfacial strength according to claim 1, characterized in that, The process involves coating the third mixture into a thin film, followed by drying, ultraviolet exposure, plasma treatment, and palladium solution rinsing. Then, during thermal cyclization in an inert atmosphere, the drying temperature is 70–80°C, and the drying time is 5–30 minutes. And / or, the exposure intensity is 5–20 mW / cm 2 The exposure time is 5 to 20 minutes; And / or, the rinsing time is 5 to 20 seconds; And / or, the inert atmosphere is nitrogen; And / or, the conditions for thermal circulation are as follows: heating to 100℃, 150℃, 200℃, 250℃, and 300℃ respectively at a heating rate of 2 to 8℃ / min, and holding at each temperature for 60 to 80 min.

3. The method for preparing a copper-photosensitive polyimide film with excellent interfacial strength according to claim 1, characterized in that, The plasma treatment involves introducing one or more of Ar, NH3, CF4, or air. And / or, the plasma treatment duration is 10–60 min; And / or, the plasma processing power is 100-200W.

4. A copper-photosensitive polyimide film with excellent interfacial strength prepared by the method according to any one of claims 1-3.

5. The application of a copper-photosensitive polyimide film with excellent interfacial strength prepared by any one of claims 1-3 in a flexible polyimide board.

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