High-thermal-conductivity polyimide-based adhesive-free flexible copper-clad plate and preparation method thereof

Abstract

The application discloses a high-thermal-conductivity polyimide-based glue-free flexible copper-clad plate and a preparation method thereof. The introduction of amide bonds into a polyimide main chain can improve the chain orientation of polymer macromolecular chains, so that the polyimide molecular chains are highly ordered, and the thermal conductivity of the polyimide is improved. Further, the functionalized hexagonal boron nitride is introduced into the polyimide matrix, and the polyimide matrix can form hydrogen bond action, so that the bridging action of the thermal conduction network is strengthened, thereby achieving a synergistic effect and better improving the thermal conduction capacity of the polyimide film. Through the molecular structure design of the polyimide and the addition of the filler, the polyimide composite film prepared by the application has excellent thermal conductivity, mechanical strength and thermal stability, and the prepared flexible copper-clad plate has a high thermal conductivity, a high peeling strength and a high tin solder bath temperature resistance.

Description

Technical Field

[0001] This invention relates to the technical field of high-performance adhesive-free flexible copper clad laminates, and more specifically, to a high thermal conductivity polyimide-based adhesive-free flexible copper clad laminate and its preparation method. Background Technology

[0002] With the further development of the electronics industry, especially the increasing functionality of smartphones, the electronic circuit board industry has placed higher demands on the heat resistance and heat dissipation of circuit board substrates. Polyimide films, widely used in flexible circuit boards, not only possess excellent electrical insulation properties but also superior flexibility and heat resistance. However, polyimide has a thermal conductivity of only 0.2 W / m·K, making it unsuitable for applications with high heat dissipation requirements, thus limiting its application.

[0003] Existing methods for improving the thermal conductivity of polyimide often involve adding thermally conductive materials. For example, CN202010219309.5 discloses a method for preparing a high-temperature dimensionally stable thermally conductive polyimide film. This involves adding modified nano-boron nitride and modified nano-silica fillers to an aromatic diamine solution, mixing them, then adding aromatic dianhydride and reacting. Next, an octa(aminophenyltrioxosilane) solution is added, and the reaction continues to obtain an intermediate material. The intermediate material is then degassed, coated onto a substrate surface, dried, imidized, and demolded to obtain a high-temperature dimensionally stable thermally conductive polyimide film. However, this patent requires the addition of 15-20% filler to satisfy the thermally conductive island chains, and the thermal conductivity is below 1 W / m·K. To improve thermal conductivity, CN202011254764.5 discloses a polyimide double-sided flexible thermally conductive copper-clad laminate, its preparation method, and its application. This involves patterning and coating a copper foil surface with sodium cholate-modified hexagonal boron nitride nanosheets and a thermoplastic polyimide adhesive, then filling it with a polyimide acid solution containing dihydromyricetin-modified hexagonal boron nitride microsheets to obtain a single-sided polyimide copper foil. Two single-sided polyimide copper foils are then stacked and subjected to hot pressing and thermal imidization to obtain a polyimide double-sided flexible thermally conductive copper-clad laminate. However, this patent requires the addition of a large amount of hexagonal boron nitride microsheets. While this improves the thermal conductivity of the polyimide, it also leads to a decrease in the mechanical properties of the polyimide. For example, the tensile strength of the pure PI film is 119.51 MPa, the elongation at break is 11.84%, and the out-of-plane thermal conductivity is 0.15 W·m. -1 ·K -1 With increasing boron nitride content, the thermal conductivity gradually improves, but the tensile strength and elongation at break of the thermally conductive composite material decrease. When the h-BN@DMY-200℃ content is 30wt%, its tensile strength is 98.85MPa, its elongation at break is 8.93%, and its in-plane thermal conductivity is 2.56W·m. -1 ·K -1 The out-of-plane thermal conductivity is 0.57 W·m. -1 ·K-1 When the h-BN@DMY-200℃ content is 40%, its in-plane thermal conductivity reaches 4.09 W·m. -1 ·K -1 The out-of-plane thermal conductivity reaches 0.67 W·m -1 ·K -1 Similarly, CN201911160557.0 describes a high thermal conductivity polydopamine-modified boron nitride / polyimide composite material and its preparation method. While high thermal conductivity is achieved through modification of boron nitride and its high orientation within the polyimide, the mechanical properties also significantly decrease with increasing boron nitride content. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to address the shortcomings of polyimide in existing flexible copper clad laminates, such as insufficient thermal conductivity, low mechanical strength, and low peel strength from copper. The present invention provides a polyimide-based adhesive-free flexible copper clad laminate with high thermal conductivity.

[0005] Another technical problem to be solved by the present invention is to provide a method for preparing a polyimide-based adhesive-free flexible copper-clad laminate with high thermal conductivity.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A method for preparing a highly thermally conductive polyimide-based adhesive-free flexible copper-clad laminate, comprising the following steps:

[0008] S1. In a protective atmosphere, hexagonal boron nitride is dispersed in a strongly polar aprotic organic solvent for 0.5 to 10 hours. Then, diamine monomer and dianhydride monomer are added to the dispersion containing hexagonal boron nitride at a molar ratio of 1:0.9 to 1.1. The mixture is stirred and reacted at -10 to 40°C for 0.5 to 72 hours to obtain a homogeneous and viscous polyamic acid composite adhesive.

[0009] S2. Coat the copper foil with polyamic acid composite adhesive, then place it in a vacuum oven, evacuate the vacuum, heat up to perform thermal imidization, and after cooling, obtain a high thermal conductivity polyimide-based adhesive-free flexible copper-clad laminate.

[0010] The general structural formula of the diamine monomer is:

[0011]

[0012] The dianhydride monomer is one or more of the following:

[0013]

[0014] Furthermore, the strongly polar aprotic organic solvent includes one or more of N-methylpyrrolidone, dimethyl sulfoxide, dimethyl sulfone, sulfolane, 1,4-dioxane, N,N-dimethylacetamide, N,N-dimethylformamide, m-cresol, and tetrahydrofuran.

[0015] Furthermore, the mass of the hexagonal boron nitride is 1-50% of the total mass of the diamine monomer and the dianhydride monomer.

[0016] Furthermore, the hexagonal boron nitride has a nanosheet structure.

[0017] Furthermore, the hexagonal boron nitride is a functionalized modified hexagonal boron nitride.

[0018] Further, the preparation steps of the functionalized modified hexagonal boron nitride are as follows: hexagonal boron nitride nanosheets are ultrasonically dispersed evenly in Tris-HCl buffer solution, dopamine is added, and the mixture is magnetically stirred for 4 to 10 hours. After the reaction is completed, the mixture is filtered and washed with deionized water until the pH is neutral. After drying, the mixture is collected, which is the functionalized modified hexagonal boron nitride.

[0019] Furthermore, the synthetic steps of the diamine monomer include:

[0020] (1). Synthetic intermediate 1:

[0021] 0.05 mol of 2,8-thiaanthracarboxylic acid was added to a three-necked flask, followed by the addition of dehydrated dichloromethane. Then, 0.150 mol of thionyl chloride was slowly added dropwise under ice bath conditions, followed by the addition of a catalyst. The mixture was stirred and purged with argon gas. After reflux at 75 °C for 12 h, the solvent and excess thionyl chloride were removed by vacuum distillation to obtain intermediate 1. The structure of intermediate 1 is as follows:

[0022]

[0023] (2). Synthetic intermediate 2

[0024] 0.1 mol of 2,3,5,6-tetrafluoro-4-nitroaniline was dissolved in a polar mixed solution, and then 0.02 mol of intermediate one was added. The mixture was stirred at room temperature for 2 h under argon atmosphere, and then heated to 100 °C for 12 h. After cooling, the reaction solution was poured into methanol to precipitate the intermediate. After washing, the precipitate was recrystallized in N,N-dimethylformamide and water, and dried to obtain intermediate 2. The structure of intermediate 2 is as follows:

[0025]

[0026] (3). Synthesis of diamine monomers:

[0027] 0.01 mol of N2,N8-bis(2,3,5,6-tetrafluoro-4-nitrophenyl)thianthrene-2,8-dic-arboxam-ide was added to a three-necked flask, along with anhydrous ethanol. The mixture was stirred and purged with argon gas. After heating to 70°C, a catalyst and a reducing agent were added. The mixture was refluxed for 24 h. The reaction solution was then filtered through a funnel, and the filtrate was placed in a refrigerator for 24 h to crystallize. After filtration, a grayish-white solid was collected and dried in a vacuum drying oven at 80°C for 24 h to obtain the target product.

[0028] Furthermore, the catalyst in synthetic intermediate 1 is N,N-dimethylformamide.

[0029] Furthermore, the polar mixed solution in synthetic intermediate 2 is a solution of N-methylpyrrolidone and pyridine mixed in a mass ratio of 4:1.

[0030] Furthermore, the catalyst for synthesizing the diamine monomer is 10% wt palladium on carbon; the reducing agent is hydrazine hydrate.

[0031] Compared with existing technologies, the beneficial effects are:

[0032] This invention introduces amide bonds into the polyimide backbone to improve the chain orientation of the polymer chains, resulting in a highly ordered arrangement of the polyimide molecular chains. This reduces phonon scattering, allowing heat to be rapidly conducted along the parallel direction of the molecular chains, thus achieving higher thermal conductivity. Furthermore, functionalized hexagonal boron nitride is introduced into the polyimide matrix. On one hand, the modification of hexagonal boron nitride improves its dispersion and compatibility with the polyimide matrix, promoting the interconnection of hexagonal boron nitride within the polymer matrix to form thermally conductive pathways. On the other hand, the functionalized hexagonal boron nitride can form hydrogen bonds with the polyimide matrix, strengthening the bridging effect of the thermally conductive network, thereby achieving a synergistic effect. This further enhances the thermal conductivity and mechanical strength of the polyimide film and reduces its coefficient of thermal expansion.

[0033] Furthermore, the introduction of thiaanthracene structures into polyimide, which contain thioether groups, utilizes the lone pair electrons on the sulfur atoms to give them good affinity with metals, thereby improving the adhesion between polyimide and copper. The amide bonds introduced into polyimide can enhance the adhesion between polyimide and copper and also enhance intermolecular forces, thus reducing the coefficient of thermal expansion of polyimide. The introduction of fluorine atoms into polyimide, due to the high electronegativity of fluorine, results in high-energy CF bonds, making it difficult for fluorine atoms to act as electron donors to form hydrogen bonds with water molecules, which can effectively reduce the water absorption rate and dielectric properties of polyimide films.

[0034] This invention combines the molecular structure design of polyimide with the addition of fillers to produce a polyimide composite film with excellent thermal conductivity, mechanical strength and thermal stability. The resulting flexible copper-clad laminate has high thermal conductivity, peel strength and solder bath temperature resistance. Attached Figure Description

[0035] Figure 1 These are the infrared spectra of the polyimides obtained in Examples 2-5, wherein:

[0036] a corresponds to Example 2;

[0037] b corresponds to Example 3;

[0038] c corresponds to Example 4;

[0039] Figure 2 These are the TMA curves of Examples 2-6 and Comparative Example 1;

[0040] Figure 3 These are the DMA curves of Examples 2-6 and Comparative Example 1;

[0041] Figure 4 This is a thermal conductivity diagram of polyimide materials. Detailed Implementation

[0042] The following examples further explain and clarify the invention, but the specific examples do not limit the invention in any way. Unless otherwise specified, the methods and equipment used in the examples are conventional methods and equipment, and the raw materials used are all commercially available.

[0043] Example 1

[0044] This embodiment provides the diamine monomer N of polyimide. 2 N 8 The preparation method of bis(4-amino-2,3,5,6-tetrafluoroph-enyl)thianthrene-2,8-dicarboxamide (STPNFPDA) includes the following steps:

[0045] 1. Synthetic intermediate thianthrene-2,8-dicarbonyl dichloride:

[0046] 0.05 mol of 2,8-thiaanthracarboxylic acid was added to a three-necked flask, followed by 100 mL of anhydrous dichloromethane. Under ice bath conditions, 0.150 mol of thionyl chloride was slowly added dropwise, followed by 3-4 drops of N,N-dimethylformamide as a catalyst. The mixture was magnetically stirred and purged with argon gas, and the temperature was raised to 75 °C and refluxed for 12 h. The solvent and excess thionyl chloride were removed by vacuum distillation to obtain intermediate one. The structure of intermediate one is as follows:

[0047]

[0048] 2. Synthetic intermediate N 2 N 8 -bis(2,3,5,6-tetrafluoro-4-nitrophenyl)thianthrene-2,8-dicarbox-amide

[0049] 0.1 mol of 2,3,5,6-tetrafluoro-4-nitroaniline was dissolved in 150 mL of a solution of N-methylpyrrolidone and pyridine in a 4:1 ratio. Then, 0.02 mol of thianthrene-2,8-dicarbonyl dichloride was slowly added. The mixture was stirred at room temperature under argon atmosphere for 2 h, then heated to 100 °C and reacted for 12 h. After cooling, the reaction solution was poured into methanol, the precipitate was filtered off, washed thoroughly with methanol, recrystallized in N,N-dimethylformamide and water, and dried in a vacuum oven at 80 °C for 24 h to obtain intermediate II. The structure of intermediate II is as follows:

[0050]

[0051] 3. Synthesis of diamine monomer N 2 N 8 -bis(4-amino-2,3,5,6-tetrafluoroph-enyl)thian-threne-2,8-dicarboxamide(STPNFPDA):

[0052] 0.01 mol of N 2 N 8 -bis(2,3,5,6-tetrafluoro-4-nitrophenyl)thianthrene-2,8-dicarboxamide was added to a three-necked flask, followed by 450 ml of anhydrous ethanol. The mixture was magnetically stirred and purged with argon gas. After heating in an oil bath to 70°C, 0.1 g of 10% wt palladium on carbon was added, followed by the gradual addition of 10 ml of hydrazine hydrate. The mixture was refluxed for 24 h. The reaction solution was then filtered through a funnel, and the filtrate was placed in a refrigerator for 24 h to crystallize. After filtration, the grayish-white solid was collected and dried in a vacuum oven at 80°C for 24 h to obtain the diamine monomer. The structure of the diamine monomer is as follows:

[0053]

[0054] Example 2

[0055] This embodiment provides a method for preparing a highly thermally conductive polyimide and a polyimide-based adhesive-free flexible copper-clad laminate, the preparation steps of which include:

[0056] S1. Preparation of polyimide

[0057] S11. At room temperature and under an argon atmosphere, 0.85 g of dopamine-functionalized hexagonal boron nitride nanosheets were sonicated in 60.7 ml of N,N-dimethylformamide for 2 h. Then, 0.01 mol of STPNFPDA and 0.01 mol of 1,2,4,5-Benzenetetracarboxylic anhydride (PMDA) were added to N,N-dimethylformamide, and the reaction was stirred for another 6 h to obtain a homogeneous, transparent, viscous polyamic acid solution.

[0058] S12. After removing air bubbles from the polyamic acid solution, coat it onto a glass plate. Then place the glass plate in a vacuum oven, evacuate, and heat. The temperature gradient is controlled as follows: heat from room temperature to 100℃ and hold for 1 hour; heat from 100℃ to 200℃ and hold for 1 hour; heat from 200℃ to 300℃ and hold for 1 hour; heat from 300℃ to 400℃ and hold for 1 hour. After cooling, a polyimide film is obtained, and its infrared spectrum is shown below. Figure 1 As shown in Figure a, its molecular structure is as follows:

[0059]

[0060] S2. Preparation of Flexible Copper Clad Laminates

[0061] After removing air bubbles from the polyamic acid solution obtained in step S11, it is coated onto a copper plate. The copper plate is then placed in a vacuum oven, vacuumed, and heated. The temperature gradient is controlled as follows: from room temperature to 100°C and held for 1 hour, from 100°C to 200°C and held for 1 hour, from 200°C to 300°C and held for 1 hour, from 300°C to 400°C and held for 1 hour. After cooling, a polyimide-based adhesive-free flexible copper-clad laminate is obtained.

[0062] Example 3

[0063] This embodiment provides a method for preparing a highly thermally conductive polyimide and a polyimide-based adhesive-free flexible copper-clad laminate, the preparation steps of which include:

[0064] S1. Preparation of polyimide

[0065] S11. At room temperature and under an argon atmosphere, 0.95 g of dopamine-functionalized hexagonal boron nitride nanosheets were sonicated in 65.7 ml of N,N-dimethylformamide for 2 h. Then, 0.01 mol of STPNFPDA and 0.01 mol of 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) were added to N,N-dimethylformamide, and the reaction was stirred for another 6 h to obtain a homogeneous, transparent, viscous polyamic acid solution.

[0066] S12. After removing air bubbles from the polyamic acid solution, coat it onto a glass plate. Then place the glass plate in a vacuum oven, evacuate, and heat. The temperature gradient is controlled as follows: heat from room temperature to 100℃ and hold for 1 hour; heat from 100℃ to 200℃ and hold for 1 hour; heat from 200℃ to 300℃ and hold for 1 hour; heat from 300℃ to 400℃ and hold for 1 hour. After cooling, a polyimide film is obtained, and its infrared spectrum is shown below. Figure 1 As shown in Figure b, its molecular structure is as follows:

[0067]

[0068] S2. Preparation of Flexible Copper Clad Laminates

[0069] After removing air bubbles from the polyamic acid solution obtained in step S11, it is coated onto a copper plate. The copper plate is then placed in a vacuum oven, vacuumed, and heated. The temperature gradient is controlled as follows: from room temperature to 100°C and held for 1 hour, from 100°C to 200°C and held for 1 hour, from 200°C to 300°C and held for 1 hour, from 300°C to 400°C and held for 1 hour. After cooling, a polyimide-based adhesive-free flexible copper-clad laminate is obtained.

[0070] Example 4

[0071] This embodiment provides a method for preparing a highly thermally conductive polyimide and a polyimide-based adhesive-free flexible copper-clad laminate, the preparation steps of which include:

[0072] S1. Preparation of polyimide

[0073] S11. At room temperature and under an argon atmosphere, 0.94 g of dopamine-functionalized hexagonal boron nitride nanosheets were sonicated in 62.4 ml of N,N-dimethylformamide for 2 h. Then, 0.01 mol of STPNFPDA and 0.01 mol of 4,4'-diphenyl ether dianhydride (ODPA) were added to N,N-dimethylformamide, and the reaction was stirred for another 6 h to obtain a homogeneous, transparent, viscous polyamic acid solution.

[0074] S12. After removing air bubbles from the polyamic acid solution, coat it onto a glass plate. Then place the glass plate in a vacuum oven, evacuate, and heat. The temperature gradient is controlled as follows: heat from room temperature to 100℃ and hold for 1 hour; heat from 100℃ to 200℃ and hold for 1 hour; heat from 200℃ to 300℃ and hold for 1 hour; heat from 300℃ to 400℃ and hold for 1 hour. After cooling, a polyimide film is obtained, and its infrared spectrum is shown below. Figure 1 As shown in Figure c, its molecular structure is as follows:

[0075]

[0076] S2. Preparation of Flexible Copper Clad Laminates

[0077] After removing air bubbles from the polyamic acid solution obtained in step S11, it is coated onto a copper plate. The copper plate is then placed in a vacuum oven, vacuumed, and heated. The temperature gradient is controlled as follows: from room temperature to 100°C and held for 1 hour, from 100°C to 200°C and held for 1 hour, from 200°C to 300°C and held for 1 hour, from 300°C to 400°C and held for 1 hour. After cooling, a polyimide-based adhesive-free flexible copper-clad laminate is obtained.

[0078] Example 5

[0079] At room temperature and under an argon atmosphere, 1.69 g of dopamine-functionalized hexagonal boron nitride was sonicated in 60.7 ml of N,N-dimethylformamide for 2 h. Then, 0.01 mol of STPNFPDA and 0.01 mol of PMDA were added to the N,N-dimethylformamide, and the reaction was continued with stirring for 6 h to obtain a homogeneous, transparent, and viscous polyamic acid solution. After removing air bubbles from the polyamic acid solution, it was coated onto a glass plate. The glass plate was then placed in a vacuum oven, evacuated, and heated for thermal imidization. After cooling, the polyimide film could be removed.

[0080] Example 6

[0081] At room temperature and under an argon atmosphere, 2.54 g of dopamine-functionalized hexagonal boron nitride was sonicated in 60.7 ml of N,N-dimethylformamide for 2 h. Then, 0.01 mol of STPNFPDA and 0.01 mol of PMDA were added to the N,N-dimethylformamide, and the reaction was continued with stirring for 6 h to obtain a homogeneous, transparent, and viscous polyamic acid solution. After removing air bubbles from the polyamic acid solution, it was coated onto a glass plate. The glass plate was then placed in a vacuum oven, evacuated, and heated for thermal imidization. After cooling, the polyimide film could be removed.

[0082] Comparative Example 1

[0083] At room temperature and under an argon atmosphere, 0.01 mol of STPNFPDA and 2.1812 g of 1,2,4,5-pyromellitic dianhydride (PMDA) were added to N,N-dimethylformamide, and the reaction was continued with stirring for 6 hours to obtain a homogeneous, transparent, and viscous polyamic acid solution. After removing air bubbles, the polyamic acid solution was coated onto a glass plate, which was then placed in a vacuum oven. A vacuum was applied, and the temperature was increased. The temperature gradient was controlled as follows: from room temperature to 100°C and held for 1 hour; from 100°C to 200°C and held for 1 hour; from 200°C to 300°C and held for 1 hour; from 300°C to 400°C and held for 1 hour. After cooling, the polyimide film could be removed.

[0084] Comparative Example 2

[0085] At room temperature and under an argon atmosphere, 2.54 g of unfunctionalized hexagonal boron nitride was sonicated in 60.7 ml of N,N-dimethylformamide for 2 h. Then, 0.01 mol of STPNFPDA and 0.01 mol of PMDA were added to the N,N-dimethylformamide, and the reaction was continued with stirring for 6 h to obtain a homogeneous, transparent, and viscous polyamic acid solution. After removing air bubbles from the polyamic acid solution, it was coated onto a glass plate. The glass plate was then placed in a vacuum oven, evacuated, and heated for thermal imidization. After cooling, the polyimide film could be removed.

[0086] Comparative Example 3

[0087] At room temperature and under an argon atmosphere, 3.81 g of dopamine-functionalized hexagonal boron nitride was sonicated in 60.7 ml of N,N-dimethylformamide for 2 h. Then, 0.01 mol of STPNFPDA and 0.01 mol of PMDA were added to the N,N-dimethylformamide, and the reaction was continued with stirring for 6 h to obtain a homogeneous, transparent, and viscous polyamic acid solution. After removing air bubbles from the polyamic acid solution, it was coated onto a glass plate. The glass plate was then placed in a vacuum oven, evacuated, and heated for thermal imidization. After cooling, the polyimide film could be removed.

[0088] Experimental Example

[0089] 1. Infrared spectroscopy detection

[0090] from Figure 1 As can be seen in the infrared spectrum, the polyimide prepared in Examples 2-4 of this invention has a wavelength of 1780 and 1710 cm⁻¹. -1 Nearby are the asymmetric and symmetric stretching vibrations of the carbonyl group on the imine ring, 1610 cm⁻¹. -1 The characteristic absorption peak of the amide bond is located nearby, at 1360 cm⁻¹. -1 Nearby is the stretching vibration of the imide ring, 1300 cm. -1 The vibration is an NH bond bending vibration, occurring at 3500–3000 cm⁻¹. -1The characteristic absorption peaks of hydroxyl and -NH are present between these peaks, indicating that polydopamine-coated hexagonal boron nitride / polyimide composites have been successfully synthesized.

[0091] 2. Performance Testing

[0092] The thermal conductivity, coefficient of thermal expansion, and glass transition temperature of the polyimide in Examples 2-5 and Comparative Examples 1-3 were tested respectively. The peel strength between the polyimide and the copper plate was also tested. The test results are shown in Tables 1 and 2 below:

[0093] Table 1

[0094]

[0095] Table 2

[0096] Flexible copper clad laminate Peel strength (N / mm) Solder bath temperature (°C) Example 2 0.69 350 Example 3 0.81 350 Example 4 0.74 350

[0097] From Table 1-2 and Figure 2-4 It is evident that, with the increase of functionalized hexagonal boron nitride content in the polyimide film prepared by this invention, the bridging synergy between the thermally conductive powder and the molecular chains significantly improves the thermal conductivity of the polyimide film. Furthermore, within a certain content range, it maintains the good mechanical properties, heat resistance stability, and low water absorption rate of the polyimide. After lamination with a copper plate, it exhibits good adhesive strength, preventing problems such as base film curling and peeling caused by heat.

[0098] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a highly thermally conductive polyimide-based adhesive-free flexible copper-clad laminate, characterized in that, The preparation steps include: S1. In a protective atmosphere, hexagonal boron nitride is dispersed in a strongly polar aprotic organic solvent for 0.5–10 h. Then, diamine monomer and dianhydride monomer are added to the dispersion containing hexagonal boron nitride at a molar ratio of 1:0.9–1.

1. The mixture is stirred and reacted at -10–40 °C for 0.5–72 h to obtain a homogeneous, viscous polyamic acid composite adhesive. S2. Coat the copper foil with polyamic acid composite adhesive, then place it in a vacuum oven, evacuate the vacuum, heat up to perform thermal imidization, and after cooling, obtain a high thermal conductivity polyimide-based adhesive-free flexible copper-clad laminate. The general structural formula of the diamine monomer is: ； The dianhydride monomer is one or more of the following: 。 2. The method for preparing the high thermal conductivity polyimide-based adhesive-free flexible copper-clad laminate according to claim 1, characterized in that, The strongly polar aprotic organic solvent includes one or more of N-methylpyrrolidone, dimethyl sulfoxide, dimethyl sulfone, sulfolane, 1,4-dioxane, N,N-dimethylacetamide, N,N-dimethylformamide, m-cresol, and tetrahydrofuran.

3. The method for preparing the high thermal conductivity polyimide-based adhesive-free flexible copper-clad laminate according to claim 1, characterized in that, The mass of the hexagonal boron nitride is 1-50% of the total mass of the diamine monomer and the dianhydride monomer.

4. The method for preparing the high thermal conductivity polyimide-based adhesive-free flexible copper-clad laminate according to claim 1, characterized in that, The hexagonal boron nitride has a nanosheet structure.

5. The method for preparing the high thermal conductivity polyimide-based adhesive-free flexible copper-clad laminate according to claim 1, characterized in that, The hexagonal boron nitride is a functionalized hexagonal boron nitride.

6. The method for preparing the high thermal conductivity polyimide-based adhesive-free flexible copper-clad laminate according to claim 5, characterized in that, The preparation steps of the functionalized modified hexagonal boron nitride are as follows: hexagonal boron nitride nanosheets are ultrasonically dispersed evenly in Tris-HCl buffer solution, dopamine is added, and the mixture is magnetically stirred for 4-10 hours. After the reaction is completed, the mixture is filtered and washed with deionized water until the pH is neutral. After drying, the mixture is collected, which is the functionalized modified hexagonal boron nitride.

7. The method for preparing the high thermal conductivity polyimide-based adhesive-free flexible copper-clad laminate according to claim 1, characterized in that, The steps for synthesizing diamine monomers include: (1). Synthetic intermediate 1: 0.05 mol of 2,8-thiaanthracarboxylic acid was added to a three-necked flask, followed by the addition of dehydrated dichloromethane. Then, 0.150 mol of thionyl chloride was slowly added dropwise under ice bath conditions, followed by the addition of a catalyst. The mixture was stirred and purged with argon gas. After reflux at 75 °C for 12 h, the solvent and excess thionyl chloride were removed by vacuum distillation to obtain intermediate 1. The structure of intermediate 1 is as follows: (2). Synthetic intermediate 2 0.1 mol of 2,3,5,6-tetrafluoro-4-nitroaniline was dissolved in a polar mixed solution, and then 0.02 mol of intermediate 1 was added. The mixture was stirred at room temperature for 2 h under argon atmosphere, and then heated to 100 °C for 12 h. After cooling, the reaction solution was poured into methanol to precipitate the intermediate. After washing, the precipitate was recrystallized in N,N-dimethylformamide and water, and dried to obtain intermediate 2. The structure of intermediate 2 is as follows: (3). Synthesis of diamine monomers: 0.01 mol of N2,N8-bis(2,3,5,6-tetrafluoro-4-nitrophenyl)dibenzo[b,b′]thionanthracene-2,8-dicarboxamide was added to a three-necked flask, along with anhydrous ethanol. The mixture was stirred and purged with argon gas, heated to 70 °C, and then a catalyst and reducing agent were added. The mixture was refluxed for 24 h. The reaction solution was then filtered through a funnel, and the filtrate was placed in a refrigerator for 24 h to crystallize. After filtration, the grayish-white solid was collected and dried in a vacuum drying oven at 80 °C for 24 h to obtain the target product.

8. The method for preparing the high thermal conductivity polyimide-based adhesive-free flexible copper-clad laminate according to claim 7, characterized in that, The catalyst described in intermediate 1 is N,N-dimethylformamide.

9. The method for preparing the high thermal conductivity polyimide-based adhesive-free flexible copper-clad laminate according to claim 7, characterized in that, The polar mixed solution mentioned in synthetic intermediate 2 is a solution of N-methylpyrrolidone and pyridine mixed in a mass ratio of 4:

1.

10. The method for preparing the high thermal conductivity polyimide-based adhesive-free flexible copper-clad laminate according to claim 7, characterized in that, The catalyst for synthesizing the diamine monomer is 10 wt% palladium on carbon; the reducing agent is hydrazine hydrate.

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