Method for chemically plating high-strength and low-resistivity copper wire on surface of polyimide film

Abstract

The invention relates to the technical field of chemical plating of high polymer materials, and discloses a method for chemically plating a high-strength and low-resistivity copper wire on the surface of a polyimide film. The method comprises the following steps: preparing a polyamide acid film, and carrying out graphical treatment on the surface of the polyamide acid film; immersing the substrate into a solution containing a chemical plating catalyst for activation, and enabling the catalyst to cover the graphical processing area; carrying out thermal cyclization treatment on the polyimide film to obtain a polyimide film; and the polyimide film is subjected to copper plating in a chemical plating solution through a gradient concentration control method or a multi-layer alternating method, and the polyimide film with a high-strength and low-resistivity copper wire on the surface is obtained. According to the application, the grain size distribution in the copper plating layer is innovatively controlled through a gradient concentration control strategy and a multi-layer alternating strategy, so that nanometer and micrometer grains coexist to form a nanometer-micrometer double-size structure, a stress transfer network can be constructed through the micrometer grains, electron scattering can be reduced by means of the nanometer grains, and the stress transfer efficiency is improved. Therefore, the strength is improved and the resistivity is reduced.

Description

Technical Field

[0001] This application relates to the field of chemical plating technology for polymer materials, specifically to a method for chemically plating high-strength, low-resistivity copper wires onto the surface of a polyimide film. Background Technology

[0002] Polyimide, as an excellent engineering plastic, possesses superior thermal stability, low dielectric constant, and photo-patterning properties, making it the preferred substrate for high-frequency flexible circuits. As flexible electronic devices develop towards higher density, miniaturization, and higher reliability, higher demands are placed on the comprehensive performance of the metal circuitry on the substrate surface.

[0003] Currently, flexible copper-clad laminates used for flexible current circuits are mainly fabricated by electroplating copper wires onto the surface of polyimide films using subtractive or additive methods. The subtractive method suffers from low material utilization (typically <40%) and severe side etching (linewidth deviation >15%), making it difficult to meet the processing requirements of fine lines below 10µm. Additive electroless plating technology directly constructs conductive lines on the substrate surface through selective chemical deposition, offering significant advantages such as high pattern fidelity (linewidth error <5%) and low material loss (>90% utilization). However, copper wires plated by the additive method have lower strength and are generally of a single grain structure, making it difficult to balance mechanical strength and conductivity. While micron-sized grains can improve the tensile strength of the circuit (up to 450MPa), their coarse grain boundaries lead to increased resistivity (>2.2µΩ·cm); while nanocrystalline structures can reduce resistivity (approximately 1.8µΩ·cm), the risk of brittle fracture caused by the Hall-Petch effect is significantly increased. Related research focuses on improving the performance of conductive copper wires by optimizing plating bath additives. For example, using sodium thiosulfate (0.1-0.5ppm) and polyethylene glycol (50-200ppm) to enhance the density of the coating and improve its strength; however, its static concentration system tends to lead to uniform grain size, making it difficult to balance mechanical strength and conductivity.

[0004] Research has found that when micron- and nano-crystals coexist in a specific ratio in copper plating, a "skeleton-filler" composite structure can be formed. This structure can both build a stress transfer network through micron-crystals (improving ductility by 20%) and reduce electron scattering through nano-crystals. Based on this, developing a method for preparing copper wire plating with a dual nano- and micron-sized structure is of great significance. Summary of the Invention

[0005] This application provides a method for chemically depositing high-strength, low-resistivity copper wires on the surface of a polyimide film, aiming to solve the technical problem that the single grain structure of the copper plating layer in existing flexible copper-clad circuit boards makes it difficult to balance mechanical strength and conductivity.

[0006] To achieve the above objectives, the present application adopts the following technical solution.

[0007] A first aspect of this application provides a method for chemically depositing high-strength, low-resistivity copper wires onto the surface of a polyimide film, comprising:

[0008] S1, Prepare a polyamic acid film and pattern its surface;

[0009] S2, the patterned polyamic acid film is immersed in a solution containing a chemical plating catalyst for activation, so that the catalyst covers the patterned area; then it is subjected to thermal cyclization treatment to obtain a polyimide film;

[0010] S3, the polyimide film is coated with copper in a chemical plating solution by a gradient concentration control method or a multilayer alternating method to obtain a polyimide film with high strength and low resistivity copper wires on the surface.

[0011] Preferably, the electroless plating solution comprises copper salt, complexing agent, pH adjuster, stabilizer, accelerator, nucleating agent, reducing agent and water;

[0012] The copper salt includes any one of copper sulfate pentahydrate, copper nitrate, or copper chloride;

[0013] The complexing agent includes at least one of ethylenediaminetetraacetic acid, potassium sodium tartrate, sodium citrate, and triethanolamine;

[0014] The pH adjuster includes any one of sodium hydroxide, potassium hydroxide, barium hydroxide, or sodium carbonate;

[0015] The accelerator includes polyethylene glycol or sodium dodecyl sulfate;

[0016] The stabilizer includes any one of 2,2'-bipyridine, thiourea, cyanide, or thiosulfate;

[0017] The nucleating agent includes any one of nickel inorganic salts, chlorine-containing inorganic salts, or potassium ferrocyanide;

[0018] The reducing agent includes any one of sodium hypophosphite, dimethylamine borane, formaldehyde, or acetaldehyde.

[0019] More preferably, the gradient concentration controlled copper plating method includes:

[0020] Prepare multiple sets of chemical plating solutions;

[0021] The concentrations of stabilizer and reducing agent in each group of electroless plating solutions are the same, and there are concentration gradients of stabilizer and reducing agent in multiple groups of electroless plating solutions.

[0022] Following the order of the stabilizer concentration gradient, the polyimide film was plated with copper in each group of electroless plating solutions.

[0023] More preferably, the gradient change is either an increase or a decrease in gradient;

[0024] The electroless plating solution consists of 4 groups, with stabilizer and reducing agent concentrations of 20 mg / L, 15 mg / L, 10 mg / L and 5 mg / L, respectively. The copper plating time in each group of electroless plating solutions is 30 min.

[0025] The copper plating concentrations were decreased in the following order: 20 mg / L, 15 mg / L, 10 mg / L, and 5 mg / L.

[0026] The copper plating concentrations were increased in the following order: 5 mg / L, 10 mg / L, 15 mg / L, and 20 mg / L.

[0027] More preferably, the multi-layer alternating copper plating method includes:

[0028] Prepare two sets of electroless plating solutions;

[0029] The concentrations of stabilizer and reducing agent in each group of electroless plating solutions are the same, but the concentrations of stabilizer and reducing agent in one group of electroless plating solutions are higher than those in the other group.

[0030] The polyimide film was alternately immersed in two sets of chemical plating solutions for copper plating.

[0031] More preferably, the concentrations of the stabilizer and the reducing agent in the two sets of electroless plating solutions are 20 mg / L and 5 mg / L, respectively;

[0032] The copper plating time in each group of chemical plating solutions is 30 minutes.

[0033] Preferably, the polyamic acid film is prepared by a method comprising:

[0034] Under inert gas protection, the diamine monomer is dissolved in a polar organic solvent to obtain solution A; the acid anhydride monomer is added to solution A, and after reaction, a photosensitive polyamic acid solution is obtained.

[0035] The photosensitive polyamic acid solution was filtered, defoamed, and then uniformly coated onto a UV-treated glass slide using a spin coating method.

[0036] The glass sheet is heated at 60-200°C to evaporate the solvent, thereby obtaining a polyamic acid film.

[0037] More preferably, the diamine monomer includes any one of p-phenylenediamine, 4,4'-diaminodiphenyl ether, benzidine, diether diamine, phenylenediamine, and fluorinated diamine;

[0038] The anhydride monomer includes any one of pyromellitic dianhydride, biphenyl dianhydride, hexafluoro dianhydride, biphenyl dianhydride, diether dianhydride, and fluorinated dianhydride;

[0039] The polar organic solvent includes at least one of toluene, m-cresol, xylene, xylenol, N-vinyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, cyclopentanone, N-methyl-2-pyrrolidone, or benzene.

[0040] Preferably, the patterning process includes any one of laser patterning, printing patterning, or photolithography patterning.

[0041] Preferably, in step S2:

[0042] The solution containing the electroless plating catalyst includes any one of silver inorganic salt, palladium inorganic salt, or gold inorganic salt.

[0043] The solution is any one of deionized water, methanol, ethanol, N,N-dimethylacetamide, and N,N-dimethylformamide;

[0044] The activation time is 10–100 s;

[0045] The thermal cyclization treatment includes: maintaining the temperature at 50–100°C for 50–100 min, and then raising the temperature to 100–300°C and maintaining it for 50–150 min.

[0046] Compared with the prior art, the beneficial effects of this application are as follows:

[0047] This application innovatively controls the grain size distribution in the copper plating layer through a gradient concentration control strategy and a multilayer alternation strategy, enabling the coexistence of nano- and micro-grained materials to form a nano- and micro-sized dual-size structure, namely a "skeleton-filler" composite structure. This composite structure can both construct a stress transfer network through micro-grained materials and reduce electron scattering with the help of nano-grained materials, thereby improving strength and reducing resistivity.

[0048] In this application, a gradient concentration control strategy is employed to increase the amount of stabilizer during the nucleation stage, thereby reducing the resistivity of the copper wire. A low concentration of reducing agent is maintained to promote the rapid and stable formation of micron-sized nuclei. Subsequently, the reducing agent concentration is linearly increased, and a diffusion control mechanism is used to induce the epitaxial growth of nanocrystals between micron-sized nuclei, achieving directional control of dual-scale grains. Directional control of dual-scale grains can also be achieved by alternating between high and low concentrations of stabilizer and reducing agent. A multilayer alternation strategy is used to form a multilayer structure by alternating between low and high concentrations of formaldehyde, ultimately resulting in a nano-micron dual-size structure. Attached Figure Description

[0049] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0050] Figure 1 This is a process diagram of copper plating on the surface of a polyimide film in Example 1;

[0051] Figure 2 This is a schematic diagram of the copper particle size distribution of the polyimide film after copper plating in Example 1.

[0052] Figure 3 This is a process diagram of copper plating on the surface of a polyimide film in Example 2;

[0053] Figure 4 This is a schematic diagram of the copper particle size distribution of the polyimide film after copper plating in Example 2;

[0054] Figure 5 This is a process diagram of copper plating on the surface of a polyimide film in Example 3;

[0055] Figure 6 This is a schematic diagram of the copper particle size distribution of the polyimide film after copper plating in Example 3;

[0056] Figure 7 This is a SEM image of the polyimide film after copper plating in Example 1;

[0057] Figure 8 This is a SEM image of the polyimide film after copper plating in Example 2;

[0058] Figure 9 This is a photograph of the polyimide film after copper plating in Example 3.

[0059] Figure 10 The figure shows the test results of the height of the copper wires on the surface of the polyimide film prepared in Example 1;

[0060] Figure 11 Figure showing the height test results of the copper wires on the surface of the polyimide film prepared in Comparative Example 1;

[0061] Figure 12 This is a photograph of the polyimide film with copper wires on its surface in Example 1 before the tear resistance test;

[0062] Figure 13 This is a photograph of the polyimide film with copper wires on its surface from Example 1 after a tear resistance test.

[0063] Figure 14A photograph of the polyimide film with copper wires on its surface prepared for Comparative Example 1 before the tear resistance test;

[0064] Figure 15 The image shows the polyimide film with copper wires on its surface prepared for Comparative Example 1 after a tear resistance test. Detailed Implementation

[0065] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0066] 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.

[0067] In the following description of this embodiment, the term "and / or" is used to describe the association relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, B existing alone, and A and B existing simultaneously. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0068] 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.

[0069] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms "a" and "the" as used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0070] Those skilled in the art should understand that, in the following description of the embodiments of this application, 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 this application.

[0071] Those skilled in the art will understand that the numerical ranges in the embodiments of this application should be understood as each intermediate value between the upper and lower limits of the specifically disclosed range. Each smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this application. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0072] Unless otherwise stated, the technical / scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. While this application describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this application. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0073] In a first aspect, this application provides a method for chemically depositing high-strength, low-resistivity copper wires onto the surface of a polyimide film, comprising:

[0074] S1, Prepare a polyamic acid film and pattern its surface;

[0075] Specifically, the polyamic acid film is prepared by the following method:

[0076] Under inert gas protection, diamine monomer is dissolved in a polar organic solvent to obtain solution A; acid anhydride monomer is added to solution A, and the mixture is stirred for 16-20 hours to obtain a photosensitive polyamic acid solution; wherein the inert gas is nitrogen or argon.

[0077] The photosensitive polyamic acid solution was filtered, defoamed, and then uniformly coated onto a UV-treated glass slide using a spin coating method.

[0078] The glass sheet is heated at 60-200°C to evaporate the solvent, thereby obtaining a polyamic acid film.

[0079] In this application, the diamine monomer may be any one of p-phenylenediamine (PDA), 4,4'-diaminodiphenyl ether (ODA), benzidine, diether diamine, phenylenediamine, and fluorinated diamine;

[0080] The anhydride monomer may be any one of pyromellitic dianhydride (PMDA), biphenyl dianhydride (BPDA), hexafluorodianhydride (6FDA), biphenyl dianhydride, diether dianhydride, or fluorinated dianhydride.

[0081] The polar organic solvent may be any one or more of toluene, m-cresol, xylene, xylenol, N-vinyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, cyclopentanone, N-methyl-2-pyrrolidone, or benzene.

[0082] In this application, a circuit pattern is formed on the surface of polyamic acid through graphic processing.

[0083] The patterning process can be performed using laser patterning, printing patterning, or photolithography. Laser patterning involves irradiating the polyamic acid surface with a UV nanosecond / picosecond laser at a frequency of 50–150 kHz, at an irradiation rate of 100–2000 mm / s. Printing patterning uses 100–400 mesh screen printing. Photolithography patterning uses ultraviolet light with a wavelength of 100–400 nm for exposure time of 15–3000 s.

[0084] S2, the patterned polyamic acid film is immersed in a solution containing a chemical plating catalyst for activation, so that the catalyst covers the patterned area; then it is subjected to thermal cyclization treatment to obtain a polyimide film;

[0085] The catalyst in the solution containing the electroless plating catalyst includes any one of silver inorganic salt, palladium inorganic salt, or gold inorganic salt; the solution is any one of deionized water, methanol, ethanol, N,N-dimethylacetamide, or N,N-dimethylformamide.

[0086] In this application, the patterned polyamic acid film is immersed in a solution containing a chemical plating catalyst for activation for 10–100 seconds. Activation allows the catalyst to cover the patterned area of ​​the polyamic acid film, enabling the circuit pattern to carry catalyst seeds. The polyamic acid film is then held at 50–100°C for 50–100 minutes, followed by thermal cyclization at 100–300°C for 50–150 minutes, transforming the polyamic acid film into a polyimide film.

[0087] In this application, by selecting different diamine monomers and acid anhydride monomers, pyromellitic polyimides, such as PMDA-ODA type polyimides; biphenyl type polyimides, such as BPDA-PDA or BPDA-ODA type; photosensitive polyimides; and soluble polyimides, such as BPDA-PPD, can be prepared.

[0088] S3, the polyimide film is coated with copper in a chemical plating solution by a gradient concentration control method or a multilayer alternating method to obtain a polyimide film with high strength and low resistivity copper wires on the surface.

[0089] In this application, the electroless plating solution comprises a copper salt, a complexing agent, a pH adjuster, a stabilizer, an accelerator, a nucleating agent, a reducing agent, and water. The copper salt is selected from any one of copper sulfate pentahydrate, copper nitrate, or copper chloride; the complexing agent is selected from at least one of ethylenediaminetetraacetic acid, potassium sodium tartrate, sodium citrate, or triethanolamine; the accelerator is polyethylene glycol or sodium dodecyl sulfate; the stabilizer is selected from any one of 2,2'-bipyridine, thiourea, cyanide, or thiosulfate; the nucleating agent is selected from any one of nickel inorganic salts, chlorine-containing inorganic salts, or potassium ferrocyanide; and the reducing agent is selected from any one of sodium hypophosphite, dimethylamine borane, formaldehyde, or acetaldehyde. The pH adjuster, used to stabilize the pH of the electroless plating solution at 13-14, is selected from any one of sodium hydroxide, potassium hydroxide, barium hydroxide, or sodium carbonate.

[0090] In the electroless plating solution of this application, the preferred concentrations of each component are:

[0091] Copper salt 5-25 g / L, complexing agent 15-31 g / L, stabilizer 5-20 mg / L, accelerator 1-5 g / L, nucleating agent 50-70 mg / L, reducing agent 5-20 mL / L.

[0092] This application describes copper plating in a chemical plating solution using a gradient concentration control method or a multilayer alternating method to control the grain size distribution in the copper plating layer, thereby enabling the coexistence of nano- and micro-grained materials in the copper plating layer to form a nano-micro dual-size structure, i.e., a "skeleton-filler" composite structure.

[0093] In this application, the gradient concentration control method for copper plating includes:

[0094] Prepare multiple sets of electroless plating solutions; ensure that the concentrations of stabilizer and reducing agent are the same in each set of electroless plating solutions, and that the concentration gradients of stabilizer and reducing agent vary across the multiple sets of electroless plating solutions; plate the polyimide film with copper in each set of electroless plating solutions according to the order of the stabilizer concentration gradient change, i.e., the order in which the stabilizer and reducing agent concentration gradient increases or decreases.

[0095] Specifically, four sets of electroless plating solutions were prepared, designated as solutions 1, 2, 3, and 4. The concentrations of stabilizer and reducing agent in solution 1 were 20 mg / L, in solution 2 15 mg / L, in solution 3 10 mg / L, and in solution 4 5 mg / L. The concentrations of all other components were identical in all four solutions.

[0096] The polyimide film was sequentially immersed in chemical plating solutions No. 1, 2, 3, and 4 for 30 minutes each for copper plating; alternatively, the polyimide film with catalyst seeds in the pattern area was sequentially immersed in chemical plating solutions No. 4, 3, 2, and 1 for 30 minutes each for copper plating. A bubble machine was used to bubble the polyimide film during copper plating to promote the redox reaction; the chemical plating solution completely submerged the circuit pattern on the polyimide film.

[0097] This application employs a gradient concentration control strategy to increase the amount of stabilizer during the nucleation stage, thereby reducing the resistivity of the copper wire. A low concentration of reducing agent is maintained to promote the rapid and stable formation of micron-sized nuclei. Subsequently, the reducing agent concentration is linearly increased, and a diffusion control mechanism is used to induce the epitaxial growth of nanocrystals between micron-sized crystals, achieving directional control of dual-scale grains. Specifically, a higher concentration of reducing agent promotes rapid nucleation and formation of nanocrystals (100–200 nm), while a lower concentration of reducing agent forms micron-sized grains (>1 μm), ultimately resulting in a nano-micron dual-size structure.

[0098] In this application, the multilayer alternating copper plating method includes:

[0099] Prepare two sets of electroless plating solutions; ensure that the concentrations of stabilizer and reducing agent in each set of solutions are the same, with one set having a higher concentration of stabilizer and reducing agent than the other; alternately immerse the polyimide film in the two sets of solutions for copper plating.

[0100] Specifically, two sets of electroless plating solutions are prepared, denoted as electroless plating solution A and electroless plating solution B. The concentrations of stabilizer and reducing agent in electroless plating solution A are both 20 mg / L, and the concentrations of stabilizer and reducing agent in electroless plating solution B are both 5 mg / L. The concentrations of the remaining components in the two sets of electroless plating solutions are the same.

[0101] The polyimide film is first immersed in chemical plating solution A for 30 minutes, then in chemical plating solution B for 30 minutes, forming the first cycle. This cycle is repeated three times. Alternatively, the polyimide film is first immersed in chemical plating solution B for 30 minutes, then in chemical plating solution A for 30 minutes, forming the first cycle. This cycle is repeated three times. During copper plating, a bubble machine is used to promote the redox reaction. The chemical plating solution completely submerges the circuit pattern on the polyimide film.

[0102] Among them, higher concentrations of reducing agents promote rapid nucleation and formation of nanocrystals (100-200 nm), while lower concentrations of reducing agents form micron-sized grains (>1 micron). The multilayer alternation strategy forms a structure of alternating nano-layers and micron-layers, ultimately forming a nano-micron dual-size structure.

[0103] The nano-micro dual-size structure of this application can both construct a stress transfer network through micron grains and reduce electron scattering by using nano grains, thereby improving strength and reducing resistivity.

[0104] The present application will be further illustrated by the following examples.

[0105] Example 1

[0106] This embodiment provides a method for chemically depositing high-strength, low-resistivity copper wires onto the surface of a PMDA-ODA type polyimide film, including:

[0107] S1, 7.18 g of 4,4'-diaminodiphenyl ether was added to a reactor equipped with a stirrer under inert gas protection, followed by 90.40 g of N,N-dimethylacetamide. The mixture was stirred for 30 min to completely dissolve the 4,4'-diaminodiphenyl ether. 7.82 g of pyromellitic dianhydride was then added to the mixture, and the reaction was stirred for 18 h to obtain a polyamic acid solution.

[0108] The polyamic acid solution was filtered and defoamed, and then uniformly coated onto a UV-treated glass slide using a spin coating method. The slide was then placed in a forced-air drying oven and dried at 100°C for 5 hours to evaporate the solvent, thus obtaining a polyamic acid film.

[0109] The polyamic acid film was patterned on its surface by using a laser with a frequency of 80kHz at a speed of 200mm / s, resulting in a circuit pattern of 1.5cm×3mm.

[0110] S2, the polyamic acid film after surface patterning is immersed in a silver nitrate solution with a concentration of 0.08 g / mL for activation for 15 s. After the surface patterning area is completely covered with silver nitrate, the polyamic acid film is placed in an oven and kept at 80℃ for 50 min, then heated to 180℃ and kept at 180℃ for 100 min for thermal ringing treatment to obtain a polyimide film with silver nitrate in the circuit pattern area.

[0111] S3. Four sets of electroless plating solutions, numbered 1, 2, 3, and 4, were prepared in four 500mL beakers. The concentrations of copper sulfate pentahydrate, sodium tartrate, polyethylene glycol, and potassium ferrocyanide in each solution were 20 g / L, 15 g / L, 3 g / L, and 70 mg / L, respectively. Specifically, in solution 1, the concentrations of 2,2-bipyridine (stabilizer) and formaldehyde (reducing agent) were 20 mL / L; in solution 2, the concentrations of 2,2-bipyridine and formaldehyde were 15 mL / L; in solution 3, the concentrations of 2,2-bipyridine and formaldehyde were 10 mL / L; and in solution 4, the concentrations of 2,2-bipyridine and formaldehyde were 5 mL / L.

[0112] like Figure 1As shown, the polyimide film is first plated with copper in No. 1 for 30 minutes, then in No. 2 for 30 minutes, then in No. 3 for 30 minutes, and finally in No. 4 for 30 minutes to obtain a polyimide film with high-strength, low-resistivity copper wire material on its surface.

[0113] Example 1 has a polyimide film containing high-strength, low-resistivity copper wire material on its surface. A schematic diagram of the copper particle size distribution is shown below. Figure 2 As shown. By Figure 2 It can be seen that the particle size distribution of the copper layer gradually increases from near the base layer to far away from the base layer, forming nano-sized grains containing micro-sized grains, thus achieving the coexistence of nano-sized and micro-sized grains.

[0114] Example 2

[0115] This embodiment provides a method for chemically depositing high-strength, low-resistivity copper wires onto the surface of a BPDA-ODA type polyimide film, including:

[0116] S1, 6.88 g of 4,4'-diaminodiphenyl ether was added to a reactor equipped with a stirrer under inert gas protection, followed by 83.33 g of N,N-dimethylacetamide. The mixture was stirred for 30 min to completely dissolve the 4,4'-diaminodiphenyl ether. Then, 10.12 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride was added, and the mixture was stirred for 18 h to obtain a polyamic acid solution.

[0117] The polyamic acid solution was filtered and defoamed, and then uniformly coated onto a UV-treated glass slide using a spin coating method. The slide was then placed in a forced-air drying oven and dried at 100°C for 5 hours to evaporate the solvent, thus obtaining a polyamic acid film.

[0118] The surface of the polyamic acid film is patterned by screen printing with a mesh size of 150, and circuit patterns are printed on its surface.

[0119] S2 is the same as in Example 1.

[0120] S3 differs from Example 1 in that the copper plating order in the four groups of chemical plating solutions is different, while the rest is the same as in Example 1.

[0121] like Figure 3 As shown, the polyimide film is first plated with copper in No. 4 for 30 minutes, then in No. 3 for 30 minutes, then in No. 2 for 30 minutes, and finally in No. 1 for 30 minutes to obtain a polyimide film with high-strength, low-resistivity copper wire material on its surface.

[0122] Example 1 has a polyimide film containing high-strength, low-resistivity copper wire material on its surface. A schematic diagram of the copper particle size distribution is shown below. Figure 4 As shown. By Figure 4It can be seen that the particle size distribution of the copper layer gradually decreases from near the base layer to far away from the base layer, forming micron-sized grains containing nano-sized grains, thus achieving the coexistence of nano-sized and micron-sized grains.

[0123] Example 3

[0124] This embodiment provides a method for chemically depositing high-strength, low-resistivity copper wires on the surface of a photosensitive polyimide film, including:

[0125] Preparation of photosensitizing diamine: 15.3 g of compound A, 1.5 g of compound B, and 20 ml of N,N-dimethylacetamide were added to a two-necked flask and stirred until homogeneous. Then, 8.4 g of cesium carbonate and 1.6 g of cesium iodide were added, and the mixture was heated under nitrogen protection for 24 h. After the reaction was completed, the reaction solution was cooled to room temperature, filtered, and the filtrate was collected and dried under vacuum to obtain crystals. The crystals were recrystallized from methanol to obtain a yellow solid compound C, i.e., the photosensitizing diamine. The preparation process is shown below:

[0126]

[0127] S1, 1.08 g of p-phenylenediamine and 96.12 g of photosensitizing diamine were added to a reactor equipped with a stirrer under inert gas protection, followed by 476.05 g of N,N-dimethylacetamide. The mixture was stirred for 30 min to completely dissolve 4,4'-diaminodiphenyl ether. 21.80 g of pyromellitic dianhydride was then added, and the mixture was stirred for 18 h to obtain a photosensitizing polyamic acid solution.

[0128] The photosensitive polyamic acid solution was filtered and defoamed, and then uniformly coated onto a UV-treated glass slide using a spin coating method. The slide was then placed in a forced-air drying oven and dried at 100°C for 5 hours to evaporate the solvent, thus obtaining a polyamic acid film.

[0129] The polyamic acid film was exposed to ultraviolet light at a wavelength of 225 nm for 60 seconds to form a circuit pattern on the surface of the polyimide film by photolithography.

[0130] S2 is the same as in Example 1.

[0131] S3. Prepare two sets of electroless plating solutions, labeled A and B, in two 500mL beakers. The concentrations of copper sulfate pentahydrate, sodium tartrate, polyethylene glycol, and potassium ferrocyanide in both solutions are 20g / L, 15g / L, 3g / L, and 70mg / L, respectively. Specifically, electroless plating solution A contains 5mL / L of 2,2-bipyridine as a stabilizer and 5mL / L of formaldehyde as a reducing agent, while electroless plating solution B contains 20mL / L of both 2,2-bipyridine and formaldehyde.

[0132] like Figure 5 As shown, the polyimide film is first immersed in chemical plating solution A for 30 minutes to be plated with copper, and then immersed in chemical plating solution B for 30 minutes to be plated with copper, which is one cycle; the cycle is repeated 3 times to obtain a polyimide film with high-strength and low-resistivity copper wire material on the surface.

[0133] Example 3 has a polyimide film containing high-strength, low-resistivity copper wire material on its surface. A schematic diagram of the copper particle size distribution is shown below. Figure 6 As shown. By Figure 6 It can be seen that the copper layer particle size distribution is uniformly distributed from near the base layer to far away from the base layer, forming a layer of nano-scale grains and a layer of micro-scale grains, realizing the coexistence of nano-scale and micro-scale grains.

[0134] Comparative Example 1

[0135] A method for electroplating copper wires on the surface of a PMDA-ODA type polyimide film is provided, comprising:

[0136] S1, the difference from Example 1 is that the size of the circuit pattern generated on its surface by the graphic processing is 2cm×2mm, and the rest is the same as Example 1;

[0137] S2 is the same as in Example 1;

[0138] In S3, an electroplating solution was prepared in a 1000mL beaker. The concentrations of copper sulfate pentahydrate, sulfuric acid, sodium chloride, and polyethylene glycol in the electroplating solution were 180g / L, 45g / L, 3g / L, and 15g / L. The cathode current density was 10A / dm2. The electroplating system consisted of a phosphor bronze ball as the anode and a laser-patterned polyimide film with activator seeds on its surface as the cathode. The copper plating operation was carried out for 30 minutes in a copper plating solution with bottom magnetic stirring at 40℃ to obtain a polyimide film with copper wire material on its surface.

[0139] The polyimide film of Example 1 was subjected to scanning electron microscopy at room temperature, and its SEM image at 80,000x magnification is shown below. Figure 7 As shown. From Figure 7 It can be seen that a nano-micro dual-size structure was formed through gradient control. This structure improves the density of the copper layer and enhances its strength in use.

[0140] The polyimide film of Example 2 was subjected to scanning electron microscopy at room temperature, and the SEM image at 50,000x magnification is shown below. Figure 8 As shown. From Figure 8 It can be seen that a nano-micro dual-size structure was formed through gradient control. This structure improves the density of the copper layer and enhances its strength in use.

[0141] A physical image of the polyimide film of Example 3 at room temperature is shown below. Figure 9 As shown. From Figure 9 It can be seen that the copper lines on its surface are clear and stable, and high-strength, low-resistivity copper wire materials have been successfully prepared on the surface of polyimide film.

[0142] The resistivity of the polyimide films with copper wires on their surfaces prepared in Example 1 and Comparative Example 1 was tested, as follows:

[0143] The height of the copper wires on the polyimide film was measured using a protractor, the cross-sectional area of ​​the copper wires was calculated, and then their resistivity was calculated. The formula for calculating resistivity is shown below:

[0144] ρ=R×A / L

[0145] Where ρ is resistivity, A is the cross-sectional area of ​​the conductor, R is the resistance of the conductor, and L is the length of the conductor.

[0146] The height test results of the copper wires on the surface of the polyimide film prepared in Example 1 are as follows: Figure 10 As shown, its height is 0.1870 μm; its width is 3 mm; its length is 1.5 cm; and its resistance is measured to be 0.497 Ω. Its resistivity is calculated to be 1.85 x 10⁻⁶. -8 Ω·m, close to the resistivity of copper itself (1.75 x 10⁻⁶). -8 The height of the copper wires on the surface of the polyimide film prepared in Comparative Example 1 is as follows (Ω·m). Figure 11 As shown, its height is 0.8187 μm; its width is 2 mm; its length is 2 cm; and its resistance is measured to be 0.881 Ω. Its resistivity is calculated to be 7.21 x 10⁻⁶. -8 Ω·m. Test results show that the resistivity of the copper wire in the polyimide film prepared in Comparative Example 1 is much higher than that of the copper wire in Example 1.

[0147] The polyimide films with copper wires on the surface prepared in Example 1 and Comparative Example 1 were subjected to tear resistance tests. Figure 12 This is a photograph of the polyimide film with copper wires on its surface in Example 1 before the tear resistance test. Figure 13 Here is a picture of the product after the tear resistance test. From Figure 12 and Figure 13 It can be seen that after the tear resistance test, the copper wires on the surface of the polyimide film did not change significantly, indicating that the copper wires on the surface of the polyimide film in Example 1 have high strength.

[0148] Figure 14 This is a photograph of the polyimide film with copper wires on its surface prepared in Comparative Example 1 before the tear resistance test. Figure 15 Here is a picture of the product after the tear resistance test. From Figure 14 and Figure 15It can be seen that after the tear resistance test, the copper wires on the surface of the polyimide film detached significantly. The strength of the copper wires on the surface of the polyimide film in Comparative Example 1 was significantly lower than that in Example 1.

[0149] Although this application has been described in detail in this specification with general descriptions and specific embodiments, some modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, such modifications or improvements made without departing from the spirit of this application are all within the scope of protection claimed in this application.

Claims

1. A method for chemically depositing high-strength, low-resistivity copper wires onto the surface of a polyimide film, characterized in that, include: S1, Prepare a polyamic acid film and pattern its surface; S2, the patterned polyamic acid film is immersed in a solution containing a chemical plating catalyst for activation, so that the catalyst covers the patterned area; then it is subjected to thermal cyclization treatment to obtain a polyimide film; S3, the polyimide film is coated with copper in a chemical plating solution by a gradient concentration control method or a multilayer alternating method to obtain a polyimide film with high strength and low resistivity copper wires on the surface.

2. The method according to claim 1, characterized in that, The electroless plating solution includes copper salt, complexing agent, pH adjuster, stabilizer, accelerator, nucleating agent, reducing agent and water; The copper salt includes any one of copper sulfate pentahydrate, copper nitrate, or copper chloride; The complexing agent includes at least one of ethylenediaminetetraacetic acid, potassium sodium tartrate, sodium citrate, and triethanolamine; The pH adjuster includes any one of sodium hydroxide, potassium hydroxide, barium hydroxide, or sodium carbonate; The accelerator includes polyethylene glycol or sodium dodecyl sulfate; The stabilizer includes any one of 2,2'-bipyridine, thiourea, cyanide, or thiosulfate; The nucleating agent includes any one of nickel inorganic salts, chlorine-containing inorganic salts, or potassium ferrocyanide; The reducing agent includes any one of sodium hypophosphite, dimethylamine borane, formaldehyde, or acetaldehyde.

3. The method according to claim 2, characterized in that, The gradient concentration controlled copper plating method includes: Prepare multiple sets of chemical plating solutions; The concentrations of stabilizer and reducing agent in each group of electroless plating solutions are the same, and there are concentration gradients of stabilizer and reducing agent in multiple groups of electroless plating solutions. Following the order of the stabilizer concentration gradient, the polyimide film was plated with copper in each group of electroless plating solutions.

4. The method according to claim 3, characterized in that, The gradient change is either an increase in gradient or a decrease in gradient; The electroless plating solution consists of 4 groups, with stabilizer and reducing agent concentrations of 20 mg / L, 15 mg / L, 10 mg / L and 5 mg / L, respectively. The copper plating time in each group of electroless plating solutions is 30 min. The copper plating concentrations were decreased in the following order: 20 mg / L, 15 mg / L, 10 mg / L, and 5 mg / L. The copper plating concentrations were increased in the following order: 5 mg / L, 10 mg / L, 15 mg / L, and 20 mg / L.

5. The method according to claim 2, characterized in that, The multi-layer alternating copper plating method includes: Prepare two sets of electroless plating solutions; The concentrations of stabilizer and reducing agent in each group of electroless plating solutions are the same, but the concentrations of stabilizer and reducing agent in one group of electroless plating solutions are higher than those in the other group. The polyimide film was alternately immersed in two sets of chemical plating solutions for copper plating.

6. The method according to claim 5, characterized in that, The two sets of electroless plating solutions have stabilizer and reducing agent concentrations of 20 mg / L and 5 mg / L, respectively. The copper plating time in each group of chemical plating solutions is 30 minutes.

7. The method according to claim 1, characterized in that, The polyamic acid film is prepared by the following method: Under inert gas protection, the diamine monomer is dissolved in a polar organic solvent to obtain solution A; the acid anhydride monomer is added to solution A, and after reaction, a photosensitive polyamic acid solution is obtained. The photosensitive polyamic acid solution was filtered, defoamed, and then uniformly coated onto a UV-treated glass slide using a spin coating method. The glass sheet is heated at 60-200°C to evaporate the solvent, thereby obtaining a polyamic acid film.

8. The method according to claim 7, characterized in that, The diamine monomer includes any one of p-phenylenediamine, 4,4'-diaminodiphenyl ether, benzidine, diether diamine, phenylenediamine, and fluorinated diamine; The anhydride monomer includes any one of pyromellitic dianhydride, biphenyl dianhydride, hexafluoro dianhydride, biphenyl dianhydride, diether dianhydride, and fluorinated dianhydride; The polar organic solvent includes at least one of toluene, m-cresol, xylene, xylenol, N-vinyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, cyclopentanone, N-methyl-2-pyrrolidone, or benzene.

9. The method according to claim 1, characterized in that, The patterning process includes any one of laser patterning, printing patterning, or photolithography patterning.

10. The method according to claim 1, characterized in that, In step S2: The solution containing the electroless plating catalyst includes any one of silver inorganic salt, palladium inorganic salt, or gold inorganic salt. The solution is any one of deionized water, methanol, ethanol, N,N-dimethylacetamide, and N,N-dimethylformamide; The activation time is 10–100 s; The thermal cyclization treatment includes: maintaining the temperature at 50–100°C for 50–100 min, and then raising the temperature to 100–300°C and maintaining it for 50–150 min.

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