TWI841294B - Flexible printed circuit board and method for producing the same - Google Patents

Abstract

The present invention relates to a flexible printed circuit board and a method for producing the same. The flexible printed circuit board comprises a polyimide substrate, an interface layer, an electrical-conducting layer and a metal layer. The interface layer is disposed between the polyimide substrate and the electrical-conducting layer, and the metal layer is disposed on the electrical-conducting layer. It is unnecessary to produce the flexible printed circuit board with palladium catalyst, thereby lowering manufacturing cost. Besides, the flexible printed circuit board has excellent electrical-conducting properties, and the metal layer has excellent adhering properties to the electrical-conducting layer.

Description

Flexible circuit board and manufacturing method thereof

The present invention relates to a flexible circuit board, and in particular to a flexible circuit board and a manufacturing method thereof which does not require the use of a palladium metal catalyst to form a conductive metal layer.

As electronic products become thinner and lighter, the size of electronic components is shrinking. In order to meet these development trends, flexible circuit boards for conducting current are becoming increasingly important. Conventional flexible circuit boards are made by attaching a metal copper layer to a polyimide substrate, but the use of an adhesive layer cannot meet the needs of thinning applications. Another type of flexible circuit board is to form an electroless plating layer on a polyimide substrate using a chemical plating process, and a metal layer can be further formed by an electroplating process.

It is known that the chemical plating process used to form the metal layer can be a dry method or a wet method. The dry method first forms a siloxane layer on a polyimide substrate, and then uses plasma to connect palladium metal clusters to the end groups of the siloxane, and then the metal layer can be formed by the reduction reaction of the palladium metal catalyst. The wet method first performs a ring-opening reaction on the polyimide, and then uses palladium metal to perform an ion exchange reaction to form a metal layer. Therefore, the chemical plating process must use expensive and scarce palladium metal catalysts, which results in that its manufacturing cost cannot be effectively reduced.

In view of this, there is an urgent need to provide a flexible circuit board and a manufacturing method thereof to improve the defects of the conventional flexible circuit board.

Therefore, one aspect of the present invention is to provide a flexible circuit board, which can replace the electroless plating layer used in chemical plating by improving the bonding between the conductive layer and the polyimide substrate through an interface layer formed by a specific compound, so that the use of a palladium metal catalyst is not required.

Another aspect of the present invention is to provide a method for manufacturing a flexible circuit board, which is to facilitate the formation of an interface layer by surface treatment of a polyimide substrate, so that the conductive layer formed subsequently can be well bonded to the polyimide substrate through the covalent bonding provided by the interface layer, so that the electroplated metal layer can be formed by a general electroplating process.

According to one aspect of the present invention, a flexible circuit board is provided. The flexible circuit board comprises a polyimide substrate, an interface layer, a conductive layer and a metal layer. The interface layer is disposed between the polyimide substrate and the first surface of the conductive layer by covalent bonding, and the metal layer is disposed on the second surface of the conductive layer. The material of the interface layer comprises a first polyamine polymer.

According to some embodiments of the present invention, the aforementioned polyamine polymer has at least 50 amino groups.

According to some embodiments of the present invention, the aforementioned conductive layer includes graphene material.

According to some embodiments of the present invention, the aforementioned conductive layer comprises a plurality of conductive sublayers and at least one interface sublayer. The interface layer is disposed between the polyimide substrate and one of the conductive sublayers by covalent bonding. Each of the at least one interface sublayer is disposed between two adjacent conductive sublayers by covalent bonding, and the material of the at least one interface sublayer comprises a second polyamine polymer.

According to some embodiments of the present invention, the aforementioned metal layer includes nanometal particles and an electroplated metal layer, wherein the nanometal particles are distributed on the second surface, and the electroplated metal layer is disposed on the second surface.

According to another aspect of the present invention, a method for manufacturing a flexible circuit board is proposed. This manufacturing method first performs a surface treatment process on the surface of a polyimide substrate to make the surface have hydrophilic functional groups, and then reacts the hydrophilic functional groups with a first polyamine polymer to form an interface layer. The interface layer is bonded to the polyimide substrate with a first covalent bond. Then, the interface layer is subjected to a bonding reaction with a conductive material to form a conductive layer on the interface layer. The conductive layer is bonded to the interface layer with a second covalent bond. Then, a metal layer is formed on the conductive layer.

According to some embodiments of the present invention, the aforementioned surface treatment process includes applying an alkaline solution to the polyimide substrate.

According to some embodiments of the present invention, the aforementioned conductive layer comprises a graphene material, and before the bonding reaction, the manufacturing method comprises performing a stepwise separation on the graphene raw material to obtain the graphene material.

According to some embodiments of the present invention, before forming the aforementioned metal layer, the manufacturing method may include performing a reduction reaction on the conductive layer.

According to some embodiments of the present invention, the aforementioned binding reaction is performed multiple times.

According to some embodiments of the present invention, before each of the aforementioned bonding reactions, a second polyamine polymer is added to allow the second polyamine polymer to be covalently bonded to the conductive material.

According to some embodiments of the present invention, the operation of forming the metal layer is to first form a plurality of nanometal particles on the conductive layer, and then form an electroplated metal layer on the conductive layer, wherein the nanometal particles are distributed between the electroplated metal layer and the conductive layer.

The flexible circuit board and the manufacturing method thereof of the present invention can improve the bonding between the conductive layer and the polyimide substrate by setting an interface layer between the conductive layer and the polyimide substrate and making the interface layer form a covalent bond with the conductive layer and the polyimide substrate at the same time, and further, the conductive layer can replace the electroless plating layer of the general chemical plating, so the manufacturing of the flexible circuit board of the present invention does not need to use a palladium metal catalyst. Among them, the interface layer is formed by a polyamine polymer, which can provide more amino groups, and further help to improve the reactive bonding between the interface layer and the conductive material, so that the conductivity of the conductive layer can be improved, and its surface roughness can be reduced, which is conducive to the deposition of the metal layer. In addition, the surface of the conductive layer may be provided with nano-metal particles to further enhance the conductivity of the conductive layer, thereby enhancing the electroplating performance and improving the properties of the flexible circuit board.

The making and using of embodiments of the present invention are discussed in detail below. However, it will be appreciated that the embodiments provide many applicable inventive concepts that can be implemented in a wide variety of specific contexts. The specific embodiments discussed are for illustration only and are not intended to limit the scope of the present invention.

Please refer to FIG. 1A, which is a schematic side view of a flexible circuit board according to some embodiments of the present invention. The flexible circuit board 100 includes a polyimide substrate 110, an interface layer 120, a conductive layer 130, and a metal layer 140. The interface layer 120 is disposed between the polyimide substrate 110 and the surface 131 of the conductive layer 130, and the metal layer 140 is disposed on the surface 133 of the conductive layer 130. The material of the polyimide substrate 110 of the present invention is not particularly limited, and it can be a polyimide generally used as a substrate of a flexible circuit board. In some specific examples, the polyimide substrate 110 can be, for example, a polyimide film.

The interface layer 120 is formed of polyamine polymers, wherein the polyamine polymers are grafted onto the surface of the polyimide substrate 110 via covalent bonds. The bonding method is to first perform a surface treatment process on the polyimide substrate 110 so that the surface of the polyimide substrate 110 has hydrophilic functional groups, and then further react these hydrophilic functional groups with the polyamine polymers to form a covalent bond between the two.

In some embodiments, the surface treatment process includes immersing the polyimide film in an alkaline solution to open the imide ring of the polyimide, and further ion exchange can be performed by the added acidic solution to form a hydrophilic functional group (such as -COOH). In some specific examples, the alkaline solution can include potassium hydroxide, other appropriate alkaline solutions, or any mixture of the above solutions, and the acidic solution has no particular limitation, it only needs to be able to perform ion exchange and not corrode the polyimide film. For example, the acidic solution can include hydrogen chloride and/or other appropriate acidic solutions. In some specific examples, in order to reduce the corrosion of the alkaline solution on the polyimide film, the concentration of the alkaline solution can be, for example, 5M. In these specific examples, the immersion time of the polyimide film in the alkaline solution can be greater than 0 minutes and less than or equal to 10 minutes, preferably 1 minute to 7 minutes, and more preferably 3 minutes to 6 minutes. When the immersion time of the polyimide film is within the aforementioned range, the surface of the polyimide film after surface treatment can have an appropriate amount of hydrophilic functional groups and has better hydrophilicity, and the surface of the film will not be corroded by the alkaline solution. In some examples, the reaction mechanism of the aforementioned surface treatment process can be shown as process (a). In process (a), Ar represents a tetravalent group derived from a tetracarboxylic dianhydride compound, and R represents a divalent group derived from a diamine compound, wherein the tetracarboxylic dianhydride compound and the diamine compound are materials well known to those of ordinary skill. (a)

After the surface treatment process, the hydrophilic functional group and the polyamine polymer are reacted to form a covalent bond between the two. The polyamine polymer used in the present invention is not particularly limited, and it only needs to have a plurality of amine groups ( _-NH2 ) that can react with the hydrophilic functional group. In some embodiments, the polyamine polymer of the present invention may have at least 3 amine groups. Preferably, the polyamine polymer may have at least 50 amine groups. In other embodiments, the molecular weight of the polyamine polymer is greater than 1000 g/mole. For example, the polyamine polymer of the present invention may include but is not limited to polyethyleneimine, other appropriate polyamine polymers, or any mixture of the above materials. In these embodiments, one amine group of the polyamine polymer can react with the hydrophilic functional group to form a covalent bond, while the remaining amine groups do not participate in the reaction, and these remaining amine groups do not react with the hydrophilic functional group of another polyimide polymer chain.

The material of the conductive layer 130 may include graphene material and have functional groups that can react with surface amine groups (—NH ₂ ) of the interface layer 120. In some specific examples, the material of the conductive layer 130 includes graphene oxide, other appropriate conductive materials, or any mixture of the above materials.

The formation of the conductive layer 130 is carried out by reacting the amino groups on the surface of the interface layer 120 with the aforementioned conductive material. The conductive layer 130 is bonded by covalent bonds between the conductive material and the surface amino groups of the interface layer 120. In some embodiments, in order to further improve the coverage of the conductive material on the interface layer 120, the bonding reaction can be performed multiple times. Accordingly, the surface amino groups of the interface layer 120 react and bond with the conductive material, and the continuity of the conductive layer 130 can be improved. In other embodiments, the bonding reaction may be performed multiple times, and before each bonding reaction, an additional polyamine polymer is added to react and bond with the surface groups of the conductive material used in the previous bonding reaction to form a conductive layer 130 composed of multiple stacked sublayers (i.e., the conductive layer 130 is formed by alternately stacking polyamine polymers and conductive materials). The additionally added polyamine polymer may be the same as or different from the polyamine polymer used in the interface layer 120. Preferably, the additionally added polyamine polymer is the same as the polyamine polymer of the interface layer 120.

In some embodiments, in order to enhance the reactivity of the material of the conductive layer 130 and the surface amino groups of the interface layer 120, before the bonding reaction, the conductive raw material is subjected to a distribution step to obtain the conductive material. For example, the distribution step is to apply ultrasound to the graphene raw material to disperse it into graphene materials with smaller particle sizes and narrower distribution ranges, which is conducive to the bonding reaction. In these examples, the particle size range of the graphene material can be 400 nm to 600 nm.

In some embodiments, after the conductive layer 130 is formed, a reduction reaction may be further performed to improve the conductivity of the conductive layer 130. For example, when the conductive layer 130 is formed of graphene oxide, the surface of the formed conductive layer 130 is likely to have epoxy functional groups, so by performing a reduction reaction on the conductive layer 130, it can be restored to a graphene material with a good two-dimensional structure.

The metal layer 140 is formed by immersing the surface 133 of the conductive layer 130 in a solution containing metal ions to deposit the metal layer 140 on the surface 133 by electroplating. In some embodiments, the material of the metal layer 140 may be copper and/or other appropriate metal materials.

In some embodiments, in order to improve the performance of electroplating, the surface 133 of the conductive layer 130 may have nanometal particles. As shown in FIG. 1B , the nanometal particles 141 are distributed on the surface 133, and the metal layer 140 covers the nanometal particles 141 and the conductive layer 130. When the surface 133 of the conductive layer 130 has the nanometal particles 141, the conductivity of the surface 133 can be further improved, which is helpful for the plating of the metal material. In addition, the nanometal particles 141 also help to improve the conductivity of the flexible circuit board 100. In some specific examples, the nanometal particles 141 can be formed by immersing the surface 133 in a solution containing metal ions to form the nanometal particles 141 through a reduction reaction. It is understandable that the material of the nanometal particles 141 is different from the material of the aforementioned metal layer 140. The material of the nanometal particles 141 is not particularly limited, and it only needs to further improve the conductivity of the conductive layer 130 and not affect the formation of the metal layer 140. In some embodiments, the material of the nanometal particles 141 may include but is not limited to silver and/or other appropriate metal materials.

In the aforementioned operation of forming the metal layer 140 and the nano-metal particles 141 of the present invention, no palladium metal catalyst is required, and no chelating agent and stabilizer in the conventional chemical plating solution are required, so the manufacturing cost of the flexible circuit board 100 can be effectively reduced and environmental pollution can be avoided.

In the flexible circuit board 100 of the present invention, the interface layer 120 formed by the polyamine polymer can provide more amine groups, which is conducive to the reaction bonding of more conductive materials, thereby improving the conductivity of the conductive layer 130 and improving the surface roughness of the conductive layer 130. Therefore, the metal layer 140 can have a better deposition result to improve the characteristics of the flexible circuit board 100.

In some application examples, the flexible circuit board produced by the present invention has a relatively low production cost and good electrical conductivity. Secondly, the interface layer 120 formed by the polyamine polymer can form a good chemical bond with the polyimide substrate 110 and the conductive layer 130, which helps to improve the bonding of each layer.

The following embodiments are used to illustrate the application of the present invention, but they are not used to limit the present invention. Anyone skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention.

Preparation of flexible circuit boards

Preparation Example 1

The polyimide film is first soaked in ethanol for cleaning, and then soaked in a 5M potassium hydroxide aqueous solution at room temperature (e.g., 10°C to 35°C). After 3 to 6 minutes, it is washed with deionized water, and the polyimide film is soaked in a 0.2M hydrogen chloride aqueous solution at room temperature. After 5 minutes, it is washed with deionized water and blown dry with nitrogen. Then, the surface-treated polyimide film is placed in water, and N-(3-dimethyl aminopropyl)-N-ethylcarbodiimide (hereinafter referred to as EDC) is added for reaction. After 10 minutes of reaction, N-hydroxy succinimide (hereinafter referred to as NHS) is added for reaction. After reacting for 30 minutes, add pre-crosslinked polyethyleneimine at room temperature to obtain an aminated polyimide film. After washing with ethanol and drying, an interface layer can be formed on the polyimide film.

Next, graphene oxide is dispersed in an aqueous solution and EDC is added for reaction. After 10 minutes of reaction, NHS is added for reaction. After 30 minutes of reaction, the aminated polyimide film is immersed in a solution at room temperature to obtain a polyimide film grafted with graphene oxide. After baking at 120°C for 1 hour, the grafting of the first layer of graphene oxide is completed. Repeating this process several times will allow the surface of the polyimide film to be completely covered with graphene oxide. When the total number of bonding reactions is four, the surface roughness of graphene oxide decreases from 91.3 nm to 62.3 nm and 43.3 nm, respectively, and finally to 10.7 nm. Afterwards, the polyimide film grafted with graphene oxide is immersed in a reducing agent solution at 90° C. for 2 hours to obtain the conductive layer of Preparation Example 1.

Then, silver nitrate is added to water, and the polyimide film with a conductive layer is immersed in it, and NaBH ₄ is added to reduce the nanosilver on the conductive layer. After the reaction is completed, it is washed with a large amount of water to form nanosilver particles on the surface of the conductive layer.

Pour the base electroplating solution into the Haring test tank and add the electroplating additive. Then, insert the phosphorus copper anode into the Haring test tank, and immediately insert the polyimide film obtained above into the Haring test tank, and make the surface to be plated and the phosphorus copper anode face each other. The DC power supply used in the electroplating process inputs a constant current of 0.219 A to form an electroplated copper layer on the conductive layer. After further drying, the flexible circuit board of Preparation Example 1 can be obtained. The conductivity of the conductive layer prepared in Preparation Example 1 is shown in Table 1, where 4GO represents that the bonding reaction used to form the conductive layer is performed four times; RGO represents the conductive layer after graphene oxide reduction; and Ag5 and Ag30 represent that the reduction time of the nanosilver particles is 5 minutes and 30 minutes respectively.

Preparation Example 2

Preparation Example 2 uses the same preparation method as the preparation method of the flexible circuit board in Preparation Example 1, except that in Preparation Example 2, ethylenediamine is used to replace polyethyleneimine to obtain an aminated polyimide film, and the total number of bonding reactions is six times (the surface roughness of graphene oxide is in descending order of 96.0 nm, 68.1 nm, 52.5 nm, 44.2 nm, 39.4 nm and 34.9 nm). The conductivity of the conductive layer obtained in Preparation Example 2 is shown in Table 1, where 6GO represents six bonding reactions; and the definitions of RGO, Ag5 and Ag30 are as described above and are not further described here.

As shown in Table 1, the conductive layers of Preparation Example 1 and Preparation Example 2 both have good conductivity, and the conductivity of the conductive layers of Preparation Example 1 and Preparation Example 2 is improved by the placement of the silver nanoparticles and the increase of the reduction reaction time.

Please refer to FIG. 2A to FIG. 2D, which respectively show scanning electron microscope photos of the conductive layer of Preparation Example 1 and Preparation Example 2 of the present case, wherein FIG. 2A and FIG. 2B respectively show the interface layer before the bonding reaction and the conductive layer after the bonding reaction is performed four times in Preparation Example 1, and FIG. 2C and FIG. 2D respectively show the interface layer before the bonding reaction and the conductive layer after the bonding reaction is performed six times in Preparation Example 2. Since Preparation Example 1 uses polyethyleneimine to form the interface layer, it has more amine groups, which helps more graphene oxide to bond to the interface layer during each bonding reaction. Therefore, compared with Preparation Example 2, Preparation Example 1 only needs to perform four bonding reactions to form a continuous conductive layer. In addition, the thickness of the graphene oxide layer of Preparation Example 1 in FIG. 2B is 6.75 μm, and the thickness of the graphene oxide layer of Preparation Example 2 in FIG. 2D is 3.33 μm.

Please refer to FIG. 3A to FIG. 3D, which are scanning electron microscope photos of the metal layer of the preparation example 1 of the present case. FIG. 3A and FIG. 3B are copper directly electroplated on the surface of the conductive layer, while FIG. 3C and FIG. 3D have nanosilver particles on the surface of the conductive layer and the copper metal layer electroplated thereon, wherein the reduction time of the nanosilver particles in FIG. 3C and FIG. 3D is 5 minutes and 30 minutes respectively. The current density of FIG. 3A, FIG. 3C and FIG. 3D is 0.729 A, while the current density of FIG. 3B is 0.129 A.

In Figures 3A and 3B, since the polyethyleneimine interface layer can reduce the roughness of the conductive layer, the copper grains have a tendency to form columns under high current density (0.729 A). As the current density decreases, the grains of the copper metal layer become more dense, and the gaps between the copper grains gradually shrink. In Figures 3C and 3D, the conductivity of the conductive layer is also improved by the placement of nanosilver particles, which helps the growth of electroplated copper grains.

Please refer to FIG. 4A to FIG. 4D, which are scanning electron microscope photos of the metal layer of Preparation Example 2 of this case. FIG. 4A and FIG. 4B are copper directly electroplated on the surface of the conductive layer, while FIG. 4C and FIG. 4D have nanosilver particles on the surface of the conductive layer and the copper metal layer electroplated thereon, wherein the reduction time of the nanosilver particles in FIG. 4C and FIG. 4D is 5 minutes and 30 minutes respectively. The current density of FIG. 4A, FIG. 4C and FIG. 4D is 0.729 A, while the current density of FIG. 4B is 0.129 A.

Compared to FIG3A, since preparation example 2 uses ethylenediamine to form the interface layer, the conductivity of the conductive layer formed is lower, resulting in uneven current density on the surface during electroplating, and thus the surface of the conductive layer in FIG4A is not completely covered by electroplated copper. In FIG4B, although the surface roughness of the electroplated copper has been greatly reduced, there are still gaps between the copper grains. In FIG4C and FIG4D, by setting up nanosilver particles and increasing the reduction time, the copper crystal columns of the electroplated copper become more dense, and the copper grain gaps in FIG4D no longer exist.

Please refer to Figures 5A to 5D, which respectively show the optical microscope photos of the metal layer of Preparation Example 1 of the present case. The current density of Figures 5A, 5C and 5D is 0.729 A, while the current density of Figure 5B is 0.129 A. As the current density decreases, the density of the electroplated copper surface is improved, and the conductivity of the conductive layer is improved by the arrangement of the nanosilver particles, which is conducive to the deposition of the electroplated copper. In Figures 5B and 5D, the deposition results of the electroplated copper obtained by the lower current density are close to the deposition results of the electroplated copper with the nanosilver particles reduced for 30 minutes, so the surface roughness of the conductive layer will affect the deposition morphology of the electroplated copper.

Accordingly, the flexible circuit board and its manufacturing method of the present invention can form a conductive layer well on the polyimide substrate by using the covalent bonding of the interface layer through the provision of the interface layer, thereby eliminating the need for a chemical plating process, so the manufacturing method of the present invention does not need to use a palladium catalyst. Among them, the interface layer can be formed by a polyamine polymer, which helps to improve the reactive bonding between the interface layer and the conductive material, thereby improving the conductivity of the conductive layer, and can improve the deposition result of the metal layer, so that better surface quality can be obtained. Furthermore, the surface of the conductive layer can have nanometal particles, which further improves the conductivity of the conductive layer, thereby helping to improve the performance of electroplating and the properties of the flexible circuit board obtained. In addition, each layer in the flexible circuit board of the present invention has good bonding properties and therefore has good tensile strength.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the present invention. Anyone with ordinary knowledge in the technical field to which the present invention belongs can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be defined by the scope of the attached patent application.

100: Flexible circuit board 110: Polyimide substrate 120: Interface layer 130: Conductive layer 131,133: Surface 140: Metal layer 141: Nanometal particles A: Region

In order to have a more complete understanding of the embodiments of the present invention and its advantages, please refer to the following description and the corresponding drawings. It must be emphasized that the various features are not drawn to scale and are only for illustration purposes. The contents of the relevant drawings are described as follows: FIG. 1A is a schematic side view of a flexible circuit board according to some embodiments of the present invention. FIG. 1B is an enlarged view of area A of FIG. 1A. FIG. 2A to FIG. 2D are scanning electron microscope photos of the conductive layer of Preparation Example 1 and Preparation Example 2 of the present case, respectively. FIG. 3A and FIG. 3B and FIG. 4A and FIG. 4B are scanning electron microscope photos of the metal layer of Preparation Example 1 and Preparation Example 2 of the present case, respectively. Figures 3C and 3D and Figures 4C and 4D respectively show scanning electron microscope photographs of the metal layer of Preparation Example 1 and Preparation Example 2 of this case, wherein nanosilver particles are provided on the surface of the conductive layer. Figures 5A to 5D respectively show optical microscope photographs of the metal layer of Preparation Example 1 of this case.

Domestic storage information (please note in the order of storage institution, date, and number) None Foreign storage information (please note in the order of storage country, institution, date, and number) None

100: Flexible circuit board

110: Polyimide substrate

120: Interface layer

130: Conductive layer

131,133:Surface

140:Metal layer

A: Area

Claims (7)

A flexible circuit board comprises: a polyimide substrate; an interface layer, wherein a material of the interface layer comprises a first polyamine polymer; a conductive layer, wherein the interface layer is disposed between the polyimide substrate and a first surface of the conductive layer by covalent bonding, and the conductive layer comprises: a plurality of conductive sublayers, wherein the interface layer is disposed between the polyimide substrate and a first surface of the conductive layer by covalent bonding. disposed between the polyimide substrate and one of the conductive sublayers; and at least one interface sublayer, wherein each of the at least one interface sublayer is disposed between two adjacent conductive sublayers by covalent bonding, and a material of the at least one interface sublayer comprises a second polyamine polymer; and a metal layer disposed on a second surface of the conductive layer. A flexible circuit board as described in claim 1, wherein the conductive layer comprises a graphene material. A flexible circuit board as described in claim 1, wherein the metal layer comprises: a nanometal particle distributed on the second surface; and an electroplated metal layer disposed on the second surface. A method for manufacturing a flexible circuit board includes: performing a surface treatment process on a surface of a polyimide substrate to make the surface have a hydrophilic functional group; performing a reaction on the hydrophilic functional group and a first polyamine polymer to form an interface layer, wherein the interface layer is bonded to the polyimide substrate by a first covalent bond; performing a bonding reaction on the interface layer and a conductive material to form a conductive layer on the interface layer, wherein the conductive layer is bonded to the interface layer by a second covalent bond; and forming a metal layer on the conductive layer; wherein the bonding reaction is performed multiple times, and before each bonding reaction, the manufacturing method further includes adding a second polyamine polymer to covalently bond the second polyamine polymer to the conductive material. The method for manufacturing a flexible circuit board as described in claim 4, wherein the conductive layer comprises a graphene material, and before the bonding reaction, the method further comprises: performing a stepwise process on a graphene raw material to obtain the graphene material. The method for manufacturing a flexible circuit board as described in claim 5, wherein before forming the metal layer, the method further comprises: performing a reduction reaction on the conductive layer. The method for manufacturing a flexible circuit board as described in claim 4, wherein the operation of forming the metal layer includes: forming a plurality of nanometal particles on the conductive layer; and forming an electroplated metal layer on the conductive layer, wherein the nanometal particles are distributed between the electroplated metal layer and the conductive layer.