Highly reliable flexible printed circuit board material and method of making same

Abstract

This invention discloses a highly reliable flexible printed circuit board material and its preparation method, belonging to the field of circuit board material technology. It addresses the technical problem that the flexibility, tensile properties, and heat aging resistance of existing flexible printed circuit board materials need further improvement. Specifically, it includes a flexible substrate layer, a conductive circuit layer, and a functional modification layer located between the flexible substrate layer and the conductive circuit layer. This invention utilizes an amino-terminated polysiloxane containing BHT antioxidant end groups, further introducing fluorocarbon side chains to prepare a fluorinated amino polysiloxane. This is then combined with 3,5-diaminobenzoic acid and 4,4′-biphenyl ether dianhydride to form a siloxane-block polyamic acid with aromatic imide hard segments. This optimizes the layer structure and composition of the layer materials in the flexible printed circuit board, effectively improving not only the flexibility and tensile properties of the flexible printed circuit board material but also its heat aging resistance.

Description

Technical Field

[0001] This invention relates to the field of circuit board materials technology, specifically to a highly reliable flexible printed circuit board material and its preparation method. Background Technology

[0002] Flexible printed circuit boards (FPCs) are a type of electronic interconnect carrier that combines flexibility and wiring density. They are widely used in smartphones, wearable devices, automotive electronics, medical electronics and aerospace. Polyimide has advantages such as good heat resistance and stable electrical properties. Flexible printed circuit boards mostly use polyimide film as flexible substrate, combined with electrolytic copper foil or rolled copper foil to form copper-clad laminate, and then processed by photolithography, etching and other processes to obtain flexible circuits.

[0003] Currently, flexible printed circuit boards using polyimide film as a flexible substrate are prone to problems such as insufficient bending fatigue life, copper foil delamination at the substrate interface, and circuit cracking under long-term repeated bending conditions. Under thermal aging and high humidity environments, substrate embrittlement, mechanical property degradation, and dimensional stability may also occur, thereby affecting the overall conductivity reliability and service life of the board. Modification methods such as introducing siloxane soft segments, fluorine elements, rubber toughening phases, or inorganic fillers into the polyimide system can improve the bending performance of the material while maintaining a certain heat resistance. However, although siloxane soft segments are beneficial to improving flexibility, improper control of their compatibility and phase distribution can easily lead to a decrease in the mechanical strength of the system, insufficient thermal stability, and even migration and interfacial adhesion degradation. Fluorine-containing structures can reduce water absorption and improve dielectric properties, but they often weaken the interfacial bonding force between the resin and the copper foil. Furthermore, excessively high fluorine content may also lead to a decrease in the cohesive strength of the material, thereby inducing interfacial peeling or crack propagation under high-frequency bending conditions.

[0004] To address this technical deficiency, a solution is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a highly reliable flexible printed circuit board material and its preparation method, in order to solve the technical problem that the flexibility, tensile properties and heat aging resistance of flexible printed circuit board materials in the prior art need to be further improved.

[0006] The objective of this invention can be achieved through the following technical solution: a highly reliable flexible printed circuit board material, comprising a flexible substrate layer, a conductive circuit layer, and a functional modification layer located between the flexible substrate layer and the conductive circuit layer; The flexible substrate layer comprises the following components by weight: 70-80 parts of siloxane block polyamic acid, 25-35 parts of thermoplastic polyimide, and 2-3 parts of additives. The functional modified layer comprises the following components by weight: 60-70 parts of thermoplastic polyimide, 18-22 parts of bisphenol A type epoxy resin, and 3-4 parts of additives.

[0007] Furthermore, the method for forming the conductive circuit layer is as follows: a copper foil is laid flat on top of the functional modification layer, hot-pressed, photoresist is coated on the copper foil, then the excess copper foil is etched away, the photoresist is peeled off, and a conductive circuit layer is formed.

[0008] Furthermore, the preparation method of siloxane block polyamic acid is as follows: under the protection of an inert gas atmosphere, fluorine-modified amino polysiloxane, 3,5-diaminobenzoic acid and toluene are mixed and stirred until dissolved. The reaction system is cooled to 20-25℃, 4,4'-biphenyl ether dianhydride is added to the reaction system, and the reaction is kept at the temperature for 6-8 hours. After post-treatment, siloxane block polyamic acid is obtained.

[0009] The synthesis reaction formula for siloxane-block polyamic acid is as follows:

[0010] In the formula:

[0011] Furthermore, the ratio of the fluorinated amino polysiloxane, 3,5-diaminobenzoic acid, and toluene is 9g:3-4g:60-70mL, and the molar amount of 4,4'-biphenyl ether dianhydride is 0.51-0.52 times the molar amount of amino in the mixture composed of amino-terminated polysiloxane and 3,5-diaminobenzoic acid. The post-treatment includes: after the reaction is complete, adding anhydrous ethanol to the reaction system, stirring and dispersing for 20-30 minutes, filtering, washing the filter cake three times with anhydrous ethanol and drying it, transferring the filter cake to a drying oven at 50-60℃ and drying it to constant weight to obtain siloxane block polyamic acid.

[0012] Furthermore, the preparation method of fluorinated amino polysiloxane is as follows: amino-terminated polysiloxane, 2-perfluorooctyl bromide and toluene are mixed and stirred, the reaction system is heated to 80-90℃, and stirred until the system is dissolved. An addition catalyst is added to the reaction system, and the reaction is carried out for 3-5 hours. After post-treatment, fluorinated amino polysiloxane with a molecular weight of 1000-2000 is obtained.

[0013] The synthesis reaction formula for fluorine-modified amino polysiloxanes is as follows:

[0014] In the formula:

[0015] Furthermore, the ratio of the amino-terminated polysiloxane, 2-perfluorooctyl bromide, toluene, and addition catalyst is 10g:3g:80mL:0.2g. The addition catalyst is composed of copper bromide and tris(2-pyridinemethyl)amine in a weight ratio of 1:2. The post-treatment includes: after the reaction is complete, the reaction system is cooled to room temperature, the reaction solution is placed in a dialysis bag with a cutoff of 2000 Da, and then a dialysis bag with a cutoff of 1000 Da is placed outside the dialysis bag with a cutoff of 2000 Da. The two dialysis bags are then dialyzed in toluene for 24 hours, and the toluene is replaced every 2 hours. Then the substance in the dialysis bag with a cutoff of 1000 Da is placed in a rotary evaporator with a water bath temperature of 80-90℃ to remove low-boiling substances under reduced pressure, thereby obtaining fluorinated amino polysiloxane with a molecular weight of 1000-2000.

[0016] Furthermore, amino-terminated polysiloxanes are obtained by the following steps: A1. Under an inert gas atmosphere, 3,5-di-tert-butyl-4-hydroxybenzyl alcohol and tetrahydrofuran were mixed and stirred until the system was dissolved. The reaction system was heated to 50-60℃, and 3-propyl isocyanate methyl diethoxysilane was added to the reaction system. The reaction was kept at the temperature for 50-70 min. After post-treatment, diethoxysilane-modified BHT was obtained. The synthesis reaction formula for diethoxysilane-modified BHT is:

[0017] A2. Mix and stir 2,4,6-trimethyl-2,4,6-triphenylcyclotrisiloxane, tetramethyltetravinylcyclotetrasiloxane, octamethylcyclotetrasiloxane, diethoxysilane-modified BHT and catalyst. Heat the reaction system to 85-95℃ and maintain the temperature for 30-50 min. Add 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane to the reaction system and maintain the temperature for 60-80 min. After post-treatment, amino-terminated polysiloxane is obtained.

[0018] The synthesis reaction formula for amino-terminated polysiloxanes is as follows:

[0019] In the formula:

[0020] Further, in step A1, the molar ratio of 3,5-di-tert-butyl-4-hydroxybenzyl alcohol and 3-propylisocyanate methyl diethoxysilane is 1:1, and the molar ratio of 3,5-di-tert-butyl-4-hydroxybenzyl alcohol to tetrahydrofuran is 1 g: 10 mL. The post-treatment includes: after the reaction is complete, removing low-boiling substances by vacuum distillation to obtain diethoxysilane-modified BHT.

[0021] Further, in step A2, the ratio of 2,4,6-trimethyl-2,4,6-triphenylcyclotrisiloxane, tetramethyltetravinylcyclotetrasiloxane, octamethylcyclotetrasiloxane, diethoxysilane-modified BHT, catalyst, and 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane is 24-26g:7-8g:20g:4-5g:10mL:5-7g. The catalyst is 6-8mol / L sulfuric acid. The post-treatment includes: after the reaction is complete, cooling the reaction system to room temperature, adding cyclohexane and deionized water to the reaction system, stirring and dispersing for 20-30 minutes, allowing it to stand and separate the liquids, washing the organic phase three times with purified water, and then transferring it to a rotary evaporator with a water bath temperature of 60-70℃ to remove low-boiling substances under reduced pressure to obtain amino-terminated polysiloxane.

[0022] This invention also proposes a method for preparing a highly reliable flexible printed circuit board material, comprising the following steps: S1. After crushing the siloxane block polyamic acid, thermoplastic polyimide and additives, pass them through a 100-mesh sieve, then spread them evenly in the mold, hot press for 3-5 minutes, let them cool naturally to room temperature, open the mold, and obtain a flexible substrate layer. S2. After pulverizing the thermoplastic polyimide and passing it through a 100-mesh sieve, mix it with bisphenol A type epoxy resin and additives. Then, spread it evenly into a mold containing a flexible substrate layer to form a layer on top of the flexible substrate layer. Close the mold, hot press for 5-7 minutes, let it cool naturally to room temperature, and open the mold to form a functional modification layer on top of the flexible substrate layer. S3. Lay the copper foil flat on top of the functional modification layer, hot press it, coat the copper foil with photoresist, mask it, expose it with ultraviolet light, develop it, etch away the excess copper foil, peel off the photoresist, and form a conductive circuit layer.

[0023] The present invention has the following beneficial effects: This invention significantly improves the flexibility and thermal aging stability of materials through the design and fluorination of amino-terminated polysiloxanes. By introducing antioxidant phenolic groups and fluorinated side chains at the ends of the siloxane backbone, amino-terminated polysiloxanes not only optimize the thermal stability of the material but also enhance its flexibility through reasonable molecular weight control. This allows the material to effectively disperse strain and inhibit the formation of microcracks during repeated bending, thereby greatly improving its flexibility and ductility. Due to the low surface energy and antioxidant properties of the fluorocarbon side chains, the material can combine with hindered phenols at high temperatures, effectively suppressing thermal aging and extending the material's service life.

[0024] This invention also introduces 3,5-diaminobenzoic acid and 4,4′-biphenyl ether diamide structures into fluorinated amino polysiloxanes, forming siloxane block polyamic acid. As the proportion of aromatic imide hard segments gradually increases, the rigidity and heat resistance of the material are effectively improved, further enhancing the structural integrity of the material while maintaining good flexibility. The cooperation between the hard and soft segments provides high-strength support, while the soft segments effectively alleviate stress concentration in the hard segments during repeated stretching, thereby enhancing the material's performance under high strength and high ductility requirements.

[0025] This invention significantly improves the electrical conductivity and long-term conductivity reliability of materials by precisely controlling the structure of the functionally modified layer and the hot-pressing process of copper foil. The functionally modified layer consists of thermoplastic polyimide and epoxy resin. The thermoplastic polyimide acts as a compatibilizer, increasing its compatibility with the flexible substrate layer. The epoxy resin undergoes cross-linking bonding with active sites at high temperatures, forming a stable cross-linked network structure, enabling the material to maintain strong mechanical strength and good thermal stability even at high temperatures. The interface between the copper foil and the functionally modified layer is optimized through the hot-pressing process. Gradual increases in temperature, pressure, and time ensure sufficient bonding at the interface, reducing interfacial voids and stress concentration. The excellent adhesion between the functionally modified layer and the copper foil effectively prevents copper foil delamination and circuit breakage during repeated bending or long-term high-temperature use, improving the bonding strength between the copper foil and the resin, allowing the material to maintain high electrical conductivity and mechanical properties even under thermal aging conditions. Detailed Implementation

[0026] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] In this application, the thermoplastic polyimide is selected from DuPont Chemicals, brand name SP-1; In this application, the bisphenol A type epoxy resin is designated as E-35, and the epoxy value is 0.30-0.40 eq / 100g; In this application, the copper foil has a copper content of 99.96% and a thickness of 0.03 mm. Example

[0028] This embodiment provides a method for preparing a highly reliable flexible printed circuit board material, specifically including the following steps: Step 1: Preparation of amino-terminated polysiloxane Weigh out 23.6 g of 3,5-di-tert-butyl-4-hydroxybenzyl alcohol and 236 mL of tetrahydrofuran and add them to an argon-protected reaction flask. Stir until the system is dissolved. Heat the reaction flask to 50 °C and add 21.7 g of 3-propyl isocyanate methyl diethoxysilane to the reaction flask. Keep the reaction at this temperature for 50 min. Remove the low-boiling substances by vacuum distillation to obtain diethoxysilane-modified BHT. Weigh out 240g of 2,4,6-trimethyl-2,4,6-triphenylcyclotrisiloxane, 70g of tetramethyltetravinylcyclotetrasiloxane, 200g of octamethylcyclotetrasiloxane, 40g of diethoxysilane-modified BHT, and 100mL of 6mol / L sulfuric acid and add them to a reaction flask. Stir the mixture and heat it to 85℃. Keep the mixture at this temperature for 30min. Add 50g of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane to the reaction flask and keep the mixture at this temperature for 60min. Cool the reaction flask to room temperature and add 1L of cyclohexane and 1L of deionized water. Stir and disperse the mixture for 20min. Allow the mixture to stand and separate the liquids. Wash the organic phase three times with purified water and transfer it to a rotary evaporator at a water bath temperature of 60℃. Remove low-boiling substances by vacuum evaporation to obtain amino-terminated polysiloxane.

[0029] In the reaction, the hydroxyl group on the 3,5-di-tert-butyl-4-hydroxybenzyl alcohol molecule condenses with the isocyanate group on the 3-isocyanate methyl diethoxysilane molecule to form a carbamate bond, thus immobilizing the hindered phenol onto the silane to obtain diethoxysilane-modified BHT. Under protic acid catalysis, 2,4,6-trimethyl-2,4,6-triphenylcyclotrisiloxane, tetramethyltetravinylcyclotetrasiloxane, octamethylcyclotetrasiloxane, and diethoxysilane-modified BHT undergo Si-O bond ring-opening / rearrangement equilibrium to form a polysiloxane backbone with a main chain of -Si-O-Si-. 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane is used as a capping agent. After hydrolysis, alkylamine capping is formed on the polysiloxane backbone to obtain amino-capped polysiloxane.

[0030] Step 2: Preparation of fluorine-modified amino polysiloxane Copper bromide and tris(2-pyridinemethyl)amine were mixed evenly at a weight ratio of 1:2 to obtain an addition catalyst; Weigh out 500g of amino-terminated polysiloxane, 100g of 2-perfluorooctyl bromide, and 4000mL of toluene and add them to a reaction flask. Stir the mixture and heat it to 80℃. Keep the mixture warm and stir until the system is dissolved. Add 10g of addition catalyst to the reaction flask and keep the mixture warm for 3 hours. Cool the reaction flask to room temperature and transfer the reaction solution into a dialysis bag with a capacity cutoff of 2000Da. Then, place a dialysis bag with a capacity cutoff of 1000Da over the outside of the dialysis bag with a capacity cutoff of 2000Da. Dialyze both dialysis bags in toluene for 24 hours, replacing the toluene every 2 hours. Then, place the substance in the dialysis bag with a capacity cutoff of 1000Da in a rotary evaporator with a water bath temperature of 80℃ and remove low-boiling substances under reduced pressure to obtain fluorinated amino-modified polysiloxane with a molecular weight of 1000-2000.

[0031] In the reaction, the vinyl side groups on the polysiloxane and the halogens on the 2-perfluorooctyl bromide molecule generate fluorinated alkyl radicals under a catalytic system, resulting in polysiloxanes with perfluoroalkyl side chains. The fluorinated side chains have low surface energy and high bond energy, significantly improving the resistance to chemical, moisture, oxidation, and heat aging. At the same time, it reduces the risk of water absorption and interfacial fouling. The fluorinated side chains work synergistically with the hindered phenols, which truncate the free radical chain reaction, while the fluorinated side chains reduce oxidation susceptibility and surface energy. The combination of these two factors allows the material to maintain good flexibility and strength even after heat aging. By controlling the molecular weight of the fluorinated modified amino polysiloxane to 1000-2000, the material can effectively reduce the risk of migration and form stable flexible blocks.

[0032] Step 3: Preparation of siloxane-block polyamic acid Weigh out 450g of fluorinated amino polysiloxane, 150g of 3,5-diaminobenzoic acid, and 3000mL of toluene and add them to an argon-protected reaction flask. Stir until dissolved. Cool the reaction flask to 20℃. Calculate the amount of 4,4'-biphenyl ether dianhydride to be added based on 0.51 times the molar amount of amino in the mixture of amino-terminated polysiloxane and 3,5-diaminobenzoic acid. Add this to the reaction flask and keep it at this temperature for 6 hours. Add anhydrous ethanol to the reaction flask and stir to disperse for 20 minutes. Filter the mixture. Wash the filter cake three times with anhydrous ethanol and dry it. Transfer the filter cake to a drying oven at 50℃ and dry it to constant weight to obtain siloxane block polyamic acid.

[0033] In the reaction, the terminal amino group of the fluorinated amino polysiloxane and the amino group on the 3,5-diaminobenzoic acid molecule serve as amine sources, and 4,4'-biphenyl ether dianhydride serves as a dianhydride source. The amine and the carbonyl group of the dianhydride undergo nucleophilic ring opening to generate amide and carboxylic acid units, which then grow along the chain to obtain siloxane block polyamic acid with a soft siloxane segment and an aromatic amic acid hard segment.

[0034] The soft segments of siloxane can disperse strain and inhibit the initiation of microcracks when bent, while the high modulus and high heat resistance of the aromatic hard segments provide tensile strength and heat resistance deformation capacity. The carboxyl groups on 3,5-diaminobenzoic acid bring more hydrogen bond / polar interaction sites, which improve interfacial adhesion and cohesive strength, thereby improving the strength and toughness of the material.

[0035] Step 4: Prepare flexible substrate Dibutyl phthalate, zinc stearate, antioxidant 1010, and 2-methylimidazole were mixed in a weight ratio of 7:4:3:2 to obtain the additive. Weigh out the following by weight: 70 parts of siloxane block polyamic acid, 25 parts of thermoplastic polyimide, and 2 parts of additives. After crushing, pass the powder through a 100-mesh sieve and then spread it evenly in a mold. Set the molding pressure to 0.8 MPa and the molding temperature to 160℃. Hot press for 3 minutes, allow it to cool naturally to room temperature, and then open the mold to obtain a flexible substrate layer with a thickness of 0.15 ± 0.01 mm. Weigh out 60 parts by weight of thermoplastic polyimide, pulverize it, pass it through a 100-mesh sieve, mix it with 18 parts of bisphenol A epoxy resin and 3 parts of additives, and then evenly spread it into a mold containing a flexible substrate layer to form a layer on top of the flexible substrate layer. Close the mold, set the molding pressure to 0.8 MPa, the molding temperature to 100℃, hot press for 5 minutes, allow it to cool naturally to room temperature, and then open the mold to form a functional modified layer with a thickness of 0.05±0.01 mm on top of the flexible substrate layer.

[0036] Step 6: Forming of conductive circuit layer Copper foil is laid flat on top of the functional modification layer. The molding pressure is set to 0.9 MPa and the molding temperature is 260℃. The hot pressing is carried out for 30 minutes to fix and bond the copper foil to the top of the functional modification layer. Photoresist is coated on the copper foil, and after masking, it is exposed to ultraviolet light and developed. Excess copper foil is etched away, and the photoresist is peeled off to form a conductive circuit layer, thus obtaining a flexible printed circuit board material. Example

[0037] This embodiment provides a method for preparing a highly reliable flexible printed circuit board material, specifically including the following steps: Step 1: Preparation of amino-terminated polysiloxane Weigh out 23.6 g of 3,5-di-tert-butyl-4-hydroxybenzyl alcohol and 236 mL of tetrahydrofuran and add them to an argon-protected reaction flask. Stir until the system is dissolved. Heat the reaction flask to 55 °C and add 21.7 g of 3-propyl isocyanate methyl diethoxysilane to the reaction flask. Keep the reaction at this temperature for 60 min. Remove the low-boiling substances by vacuum distillation to obtain diethoxysilane-modified BHT. Weigh out 250g of 2,4,6-trimethyl-2,4,6-triphenylcyclotrisiloxane, 75g of tetramethyltetravinylcyclotetrasiloxane, 200g of octamethylcyclotetrasiloxane, 45g of diethoxysilane-modified BHT, and 100mL of 7mol / L sulfuric acid and add them to a reaction flask. Stir the mixture and heat it to 90℃. Keep the temperature for 40min. Add 60g of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane to the reaction flask and keep the temperature for 70min. Cool the reaction flask to room temperature and add 1L of cyclohexane and 1L of deionized water. Stir and disperse for 25min. Let the mixture stand and separate the liquids. Wash the organic phase three times with purified water and transfer it to a rotary evaporator with a water bath temperature of 65℃. Remove low-boiling substances by vacuum evaporation to obtain amino-terminated polysiloxane.

[0038] Step 2: Preparation of fluorine-modified amino polysiloxane Copper bromide and tris(2-pyridinemethyl)amine were mixed evenly at a weight ratio of 1:2 to obtain an addition catalyst; Weigh out 500g of amino-terminated polysiloxane, 100g of 2-perfluorooctyl bromide, and 4000mL of toluene and add them to a reaction flask. Stir the mixture and heat it to 85℃. Keep the mixture warm and stir until the system is dissolved. Add 10g of addition catalyst to the reaction flask and keep the mixture warm for 4 hours. Cool the reaction flask to room temperature and transfer the reaction solution into a dialysis bag with a capacity cutoff of 2000Da. Then, place a dialysis bag with a capacity cutoff of 1000Da over the outside of the dialysis bag with a capacity cutoff of 2000Da. Dialyze both dialysis bags in toluene for 24 hours, replacing the toluene every 2 hours. Then, place the substance in the dialysis bag with a capacity cutoff of 1000Da in a rotary evaporator at a water bath temperature of 85℃ and remove low-boiling-point substances under reduced pressure to obtain fluorinated amino-polysiloxane with a molecular weight of 1000-2000.

[0039] Step 3: Preparation of siloxane-block polyamic acid Weigh out 450g of fluorinated amino polysiloxane, 175g of 3,5-diaminobenzoic acid, and 3750mL of toluene and add them to an argon-protected reaction flask. Stir until dissolved. Cool the reaction flask to 23℃. Calculate the amount of 4,4'-biphenyl ether dianhydride to be added based on 0.515 times the molar amount of amino in the mixture of amino-terminated polysiloxane and 3,5-diaminobenzoic acid. Add this to the reaction flask and keep it at this temperature for 7 hours. Add anhydrous ethanol to the reaction flask and stir to disperse for 25 minutes. Filter the mixture. Wash the filter cake three times with anhydrous ethanol and dry it. Transfer the filter cake to a drying oven at 55℃ and dry it to constant weight to obtain siloxane block polyamic acid.

[0040] Step 4: Prepare flexible substrate Diisobutyl phthalate, calcium stearate, antioxidant 1010, and 2-methylimidazole were mixed in a weight ratio of 7:4:3:2 to obtain the additive. Weigh out the following components by weight: 75 parts of siloxane block polyamic acid, 30 parts of thermoplastic polyimide, and 2.5 parts of additives. After crushing, pass the powder through a 100-mesh sieve and then spread it evenly in a mold. Set the molding pressure to 0.85 MPa and the molding temperature to 170℃. Hot press for 4 minutes, allow it to cool naturally to room temperature, and then open the mold to obtain a flexible substrate layer with a thickness of 0.15 ± 0.01 mm. Weigh out 65 parts by weight of thermoplastic polyimide, pulverize it, pass it through a 100-mesh sieve, mix it with 20 parts of bisphenol A epoxy resin and 3.5 parts of additives, and then evenly spread it into a mold containing a flexible substrate layer to form a layer on top of the flexible substrate layer. Close the mold, set the molding pressure to 0.85 MPa, the molding temperature to 115℃, hot press for 6 minutes, allow it to cool naturally to room temperature, and then open the mold. A functional modified layer with a thickness of 0.05 ± 0.01 mm is formed on top of the flexible substrate layer.

[0041] Step 6: Forming of conductive circuit layer Copper foil is laid flat on top of the functional modification layer. The molding pressure is set to 1.0 MPa and the molding temperature is 270℃. The hot pressing is carried out for 40 minutes to fix and bond the copper foil to the top of the functional modification layer. Photoresist is coated on the copper foil, and after masking, it is exposed to ultraviolet light and developed. Excess copper foil is etched away, and the photoresist is peeled off to form a conductive circuit layer, thus obtaining a flexible printed circuit board material. Example

[0042] This embodiment provides a method for preparing a highly reliable flexible printed circuit board material, specifically including the following steps: Step 1: Preparation of amino-terminated polysiloxane Weigh out 23.6 g of 3,5-di-tert-butyl-4-hydroxybenzyl alcohol and 236 mL of tetrahydrofuran and add them to an argon-protected reaction flask. Stir until the system is dissolved. Heat the reaction flask to 60 °C and add 21.7 g of 3-propyl isocyanate methyl diethoxysilane to the reaction flask. Keep the reaction at this temperature for 70 min. Remove the low-boiling substances by vacuum distillation to obtain diethoxysilane-modified BHT. Weigh out 260g of 2,4,6-trimethyl-2,4,6-triphenylcyclotrisiloxane, 80g of tetramethyltetravinylcyclotetrasiloxane, 200g of octamethylcyclotetrasiloxane, 50g of diethoxysilane-modified BHT, and 100mL of 8mol / L sulfuric acid and add them to a reaction flask. Stir the mixture and heat it to 95℃. Keep the mixture at this temperature for 50min. Add 70g of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane to the reaction flask and keep the mixture at this temperature for 80min. Cool the reaction flask to room temperature and add 1L of cyclohexane and 1L of deionized water. Stir and disperse the mixture for 30min. Allow the mixture to stand and separate the liquids. Wash the organic phase three times with purified water and transfer it to a rotary evaporator at a water bath temperature of 70℃. Remove low-boiling substances by vacuum evaporation to obtain amino-terminated polysiloxane.

[0043] Step 2: Preparation of fluorine-modified amino polysiloxane Copper bromide and tris(2-pyridinemethyl)amine were mixed evenly at a weight ratio of 1:2 to obtain an addition catalyst; Weigh out 500g of amino-terminated polysiloxane, 100g of 2-perfluorooctyl bromide, and 4000mL of toluene and add them to a reaction flask. Stir the mixture and heat it to 90℃. Keep the mixture warm and stir until the system is dissolved. Add 10g of addition catalyst to the reaction flask and keep the mixture warm for 5 hours. Cool the reaction flask to room temperature and transfer the reaction solution into a dialysis bag with a capacity cutoff of 2000Da. Then, place a dialysis bag with a capacity cutoff of 1000Da over the outside of the dialysis bag with a capacity cutoff of 2000Da. Dialyze both dialysis bags in toluene for 24 hours, replacing the toluene every 2 hours. Then, place the substance in the dialysis bag with a capacity cutoff of 1000Da in a rotary evaporator with a water bath temperature of 90℃ and remove low-boiling-point substances under reduced pressure to obtain fluorinated amino-polysiloxane with a molecular weight of 1000-2000.

[0044] Step 3: Preparation of siloxane-block polyamic acid Weigh out 450g of fluorinated amino polysiloxane, 200g of 3,5-diaminobenzoic acid, and 4500mL of toluene and add them to an argon-protected reaction flask. Stir until dissolved. Cool the reaction flask to 25℃. Calculate the amount of 4,4'-biphenyl ether dianhydride to be added based on 0.52 times the molar amount of amino in the mixture of amino-terminated polysiloxane and 3,5-diaminobenzoic acid. Add this to the reaction flask and keep it at this temperature for 8 hours. Add anhydrous ethanol to the reaction flask and stir to disperse for 30 minutes. Filter the mixture. Wash the filter cake three times with anhydrous ethanol and dry it. Transfer the filter cake to a drying oven at 60℃ and dry it to constant weight to obtain siloxane block polyamic acid.

[0045] Step 4: Prepare flexible substrate Dioctyl phthalate, sodium stearate, antioxidant 1010, and 2-methylimidazole were mixed in a weight ratio of 7:4:3:2 to obtain the additive. Weigh out the following by weight: 80 parts of siloxane block polyamic acid, 35 parts of thermoplastic polyimide, and 3 parts of additives. After crushing, pass the powder through a 100-mesh sieve and then spread it evenly in a mold. Set the molding pressure to 0.9 MPa and the molding temperature to 180℃. Hot press for 5 minutes, allow it to cool naturally to room temperature, and then open the mold to obtain a flexible substrate layer with a thickness of 0.15 ± 0.01 mm. Weigh out 70 parts by weight of thermoplastic polyimide, pulverize it, pass it through a 100-mesh sieve, mix it with 22 parts of bisphenol A epoxy resin and 4 parts of additives, and then evenly spread it into a mold containing a flexible substrate layer to form a layer on top of the flexible substrate layer. Close the mold, set the molding pressure to 0.9 MPa, the molding temperature to 130℃, hot press for 7 minutes, allow it to cool naturally to room temperature, and then open the mold to form a functional modified layer with a thickness of 0.05±0.01 mm on top of the flexible substrate layer.

[0046] Step 6: Forming of conductive circuit layer Copper foil is laid flat on top of the functional modification layer. The molding pressure is set to 1.1 MPa, the molding temperature is 280℃, and the hot pressing is carried out for 50 minutes to fix and bond the copper foil to the top of the functional modification layer. Photoresist is coated on the copper foil, and after masking, it is exposed to ultraviolet light and developed. Excess copper foil is etched away, and the photoresist is peeled off to form a conductive circuit layer, thus obtaining a flexible printed circuit board material.

[0047] Comparative Example 1 The difference between this comparative example and Example 3 is that 2-perfluorooctyl bromide was not added in step 2.

[0048] Comparative Example 2 The difference between this comparative example and Example 3 is that in step 2, the molecular weight of the fluorinated amino polysiloxane is 100-1000.

[0049] Comparative Example 3 The difference between this comparative example and Example 3 is that, in step 3, 4,4'-biphenyl ether dianhydride is replaced by an equimolar amount of pyromellitic dianhydride.

[0050] Comparative Example 4 The difference between this comparative example and Example 3 is that thermoplastic polyimide was not added in step 4.

[0051] Performance testing: The method for determining the flexibility of the samples is as follows: set the bending radius R=5mm, the bending angle ±90°, the bending frequency 30 times / min, and determine the number of cycles after the on-resistance of the flexible printed circuit board materials prepared in Examples 1-3 and Comparative Examples 1-4 changes. The tensile strength and tensile fracture strain of the flexible printed circuit board materials prepared in Examples 1-3 and Comparative Examples 1-4 were determined in accordance with the standard GB / T 1040.1-2025 "Determination of tensile properties of plastics - Part 1: General". Referring to Method A in GB / T 7141-2008 "Test Method for Thermal Aging of Plastics", the flexible printed circuit board materials prepared in Examples 1-3 and Comparative Examples 1-4 were subjected to thermal aging treatment at 100°C for 32 hours. The flexibility, tensile strength, and tensile fracture strain of the samples were measured. The specific test data are shown in Table 1 below.

[0052] Table 1 - Performance Test Data of Samples

[0053]

[0054] Data Analysis: The flexible printed circuit board material samples prepared by this invention exhibited a flexibility of 15.1-22.2 × 10⁻⁶ before thermal aging. 3 The tensile strength reached 48.3-55.4 MPa, the tensile fracture strain reached 35-42%, and the flexibility of the specimens before heat aging reached 13.2-19.3 × 10⁻⁶ MPa. 3 The tensile strength reached 42.6-48.6 MPa, and the tensile fracture strain reached 31-37%. All performance test data were superior to those of the comparative example. This indicates that the present invention constructs a siloxane soft segment with high flexibility and excellent heat oxidation resistance by using an amino-terminated polysiloxane containing BHT antioxidant end groups and further introducing fluorocarbon side chains. Then, this soft segment is block copolymerized with an aromatic imide hard segment formed by 3,5-diaminobenzoic acid and 4,4′-biphenyl ether dianhydride, and synergistically formulated with thermoplastic polyimide to form a siloxane block polyamic acid / polyimide matrix with a reasonable match between soft and hard segments. At the same time, a functional modification layer composed of thermoplastic polyimide and epoxy resin is set on the material surface, and an optimized copper foil hot pressing process is used to obtain a dense and firm copper / resin interface. This creates a synergistic effect at three levels: molecular chain flexibility, main chain rigid framework, and interface adhesion. This not only effectively improves the flexibility and tensile properties of the flexible printed circuit board material, but also improves the material's heat aging resistance.

[0055] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A highly reliable flexible printed circuit board material, characterized in that, It includes a flexible substrate layer, a conductive circuit layer, and a functional modification layer located between the flexible substrate layer and the conductive circuit layer; The flexible substrate layer comprises the following components by weight: 70-80 parts of siloxane block polyamic acid, 25-35 parts of thermoplastic polyimide, and 2-3 parts of additives. The functional modified layer comprises the following components by weight: 60-70 parts of thermoplastic polyimide, 18-22 parts of bisphenol A type epoxy resin, and 3-4 parts of additives.

2. The high-reliability flexible printed circuit board material according to claim 1, characterized in that, The method for forming the conductive circuit layer is as follows: copper foil is laid flat on top of the functional modification layer, hot-pressed, photoresist is coated on the copper foil, then the excess copper foil is etched away, and the photoresist is peeled off to form the conductive circuit layer.

3. The high-reliability flexible printed circuit board material according to claim 1, characterized in that, The preparation method of siloxane block polyamic acid is as follows: under the protection of an inert gas atmosphere, fluorine-modified amino polysiloxane, 3,5-diaminobenzoic acid and toluene are mixed and stirred until dissolved. The reaction system is cooled to 20-25℃, 4,4'-biphenyl ether dianhydride is added to the reaction system, and the reaction is kept at the temperature for 6-8 hours. After post-treatment, siloxane block polyamic acid is obtained.

4. The high-reliability flexible printed circuit board material according to claim 3, characterized in that, The ratio of the fluorinated amino polysiloxane, 3,5-diaminobenzoic acid, and toluene is 9g:3-4g:60-70mL, and the molar amount of 4,4'-biphenyl ether dianhydride is 0.51-0.52 times the molar amount of amino in the mixture composed of amino-terminated polysiloxane and 3,5-diaminobenzoic acid.

5. The high-reliability flexible printed circuit board material according to claim 3, characterized in that, The preparation method of fluorinated amino polysiloxane is as follows: amino-terminated polysiloxane, 2-perfluorooctyl bromide and toluene are mixed and stirred, the reaction system is heated to 80-90℃, and stirred until the system is dissolved. An addition catalyst is added to the reaction system, and the reaction is carried out for 3-5 hours. After post-treatment, fluorinated amino polysiloxane with a molecular weight of 1000-2000 is obtained.

6. The high-reliability flexible printed circuit board material according to claim 5, characterized in that, The ratio of amino-terminated polysiloxane, 2-perfluorooctyl bromide, toluene, and addition catalyst is 10g:3g:80mL:0.2g, and the addition catalyst is composed of copper bromide and tris(2-pyridinemethyl)amine in a weight ratio of 1:

2.

7. The high-reliability flexible printed circuit board material according to claim 5, characterized in that, Amino-terminated polysiloxanes are obtained by the following steps: A1. Under an inert gas atmosphere, 3,5-di-tert-butyl-4-hydroxybenzyl alcohol and tetrahydrofuran were mixed and stirred until the system was dissolved. The reaction system was heated to 50-60℃, and 3-propyl isocyanate methyl diethoxysilane was added to the reaction system. The reaction was kept at the temperature for 50-70 min. After post-treatment, diethoxysilane-modified BHT was obtained. A2. Mix and stir 2,4,6-trimethyl-2,4,6-triphenylcyclotrisiloxane, tetramethyltetravinylcyclotetrasiloxane, octamethylcyclotetrasiloxane, diethoxysilane-modified BHT and catalyst. Heat the reaction system to 85-95℃ and maintain the temperature for 30-50 min. Add 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane to the reaction system and maintain the temperature for 60-80 min. After post-treatment, amino-terminated polysiloxane is obtained.

8. The high-reliability flexible printed circuit board material according to claim 7, characterized in that, In step A1, the molar ratio of 3,5-di-tert-butyl-4-hydroxybenzyl alcohol and 3-propylisocyanate methyl diethoxysilane is 1:1, and the molar ratio of 3,5-di-tert-butyl-4-hydroxybenzyl alcohol and tetrahydrofuran is 1g:10mL.

9. The high-reliability flexible printed circuit board material according to claim 7, characterized in that, In step A2, the ratio of 2,4,6-trimethyl-2,4,6-triphenylcyclotrisiloxane, tetramethyltetravinylcyclotetrasiloxane, octamethylcyclotetrasiloxane, diethoxysilane-modified BHT, catalyst, and 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane is 24-26g:7-8g:20g:4-5g:10mL:5-7g, and the catalyst is 6-8mol / L sulfuric acid.

10. A method for preparing a high-reliability flexible printed circuit board material as described in any one of claims 1-9, characterized in that, Includes the following steps: S1. After crushing the siloxane block polyamic acid, thermoplastic polyimide and additives, pass them through a 100-mesh sieve, then spread them evenly in the mold, hot press for 3-5 minutes, let them cool naturally to room temperature, open the mold, and obtain a flexible substrate layer. S2. After pulverizing the thermoplastic polyimide and passing it through a 100-mesh sieve, mix it with bisphenol A type epoxy resin and additives. Then, spread it evenly into a mold containing a flexible substrate layer to form a layer on top of the flexible substrate layer. Close the mold, hot press for 5-7 minutes, let it cool naturally to room temperature, and open the mold to form a functional modification layer on top of the flexible substrate layer. S3. Lay the copper foil flat on top of the functional modification layer, hot press it, coat the copper foil with photoresist, mask it, expose it with ultraviolet light, develop it, etch away the excess copper foil, peel off the photoresist, and form a conductive circuit layer.

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