WO2015101135A1

WO2015101135A1 - Polyimide film, flexible circuit board, and method of preparing the same

Info

Publication number: WO2015101135A1
Application number: PCT/CN2014/093186
Authority: WO
Inventors: Fulan TANG; Wei Zhou
Original assignee: Byd Company Limited
Priority date: 2013-12-30
Filing date: 2014-12-05
Publication date: 2015-07-09
Also published as: CN104744696A; CN104744696B

Abstract

A polyimide film contains a chemical plating accelerant including at least one selected from a group consisting of TiO, Ni₂O₃, Co₂O₃, CuSiO₃, NiSiO₃, CoSiO₃, CuB₂O₄, NiB₂O₄, NiC₂O₄, CoO and CoC₂O₄. A method of preparing the polyimide film, a flexible circuit board including the polyimide film, and a method of preparing the flexible circuit board are also provided.

Description

POLYIMIDE FILM, FLEXIBLE CIRCUIT BOARD, AND METHOD OF PREPARING THE SAME

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and benefits of Chinese Patent Application No. 201310746617.3, filed with the State Intellectual Property Office of P. R. China on December 30, 2013. The entire content of the above-identified application is incorporated herein by reference.

FIELD

Embodiments of the present disclosure relate to circuit boards, and more particularly to a polyimide film, a flexible circuit board including the polyimide film, and methods of preparing the polyimide film and the flexible circuit board respectively.

BACKGROUND

Flexible printed circuit (FPC) boards are widely applied in manufacturing printed circuit boards in cellphones, computers, digital cameras, etc., because of their advantages, such as high density, small weight and small thickness. A conventional method for preparing FPC board generally includes steps of: adhering a polyimide film on a surface of a copper foil substrate to obtain a composite substrate； adhering a dry film on the opposite surface of the copper foil substrate； subjecting the dry film to exposure and development processes to remove unsolidified parts of the dry film and to expose corresponding parts of the copper foil substrate； removing the corresponding parts of the copper foil substrate by etching； and removing the dry film to obtain the required circuit. However, this method has various disadvantages, such as complex steps, serious environmental pollution, high cost, and so on.

Chinese patent application publication No. CN1772948A discloses a method for selectively plating a polyimide film. The method includes steps of: immersing a polyimide film in a strong alkali solution to form an imide salt on a surface of the polyimide film； immersing said polyimide film in a silver nitrate solution to obtain a final polyimide film whose surface bond with Ag ions. The Ag ions may be reduced to metal Ag particles by laser irradiation, and thus a micro pattern of a circuit to be printed on the surface of the polyimide film may be controlled by selectively irradiating the surface bonded with Ag ions of the polyimide film by laser. However, this method has complex preparing steps, a high cost, and cannot be used to obtain a circuit board having conduction circuits on both sides.

SUMMARY

Embodiments of the present disclosure seek to solve at least one of the problems existing in the related art, such as complex manufacturing steps, long preparing cycle, high cost, etc.

Embodiments of an aspect of the present disclosure provide a polyimide film. The polyimide film contains a chemical plating accelerant including at least one selected from a group consisting of TiO, Ni₂O₃, Co₂O₃, CuSiO₃, NiSiO₃, CoSiO₃, CuB₂O₄, NiB₂O₄, NiC₂O₄, CoO and CoC₂O₄.

According to embodiments of the present disclosure, the polyimide film may be subjected to an ablation-activation process with a laser to expose the chemical plating accelerant, and then the polyimide film may be chemically plated to dispose metals on the exposed chemical plating accelerant so as to form a circuit. By precisely controlling the ablation-activation process and the structure of the exposed chemical plating accelerant, a required circuit pattern may be obtained. In this way, the polyimide film may be used to form a circuit board with required circuit pattern. In addition, by forming a hole in the polyimide film, metals may be plated on the wall of the hole in the polyimide film by chemical plating instead of black hole treatment. Then, a flexible circuit board having conduction circuits on two surfaces may be obtained.

In some embodiments, the polyimide film according to embodiments of the present disclosure may have a thermal expansion coefficient of 16 μm/ (m·℃) to 25 μm/ (m·℃) , a tensile strength of at least 155 MPa, an elongation at break of at least 20％, and a copper plating speed of at least 3 μm/h.

Embodiments of another aspect of the present disclosure provide a method of preparing a polyimide film. The method may include: subjecting diamine and tetracarboxyl dianhydride to a contact reaction in a solvent to obtain a polyamide acid slurry, and coating the polyamide acid slurry on a substrate and subjecting the polyamide acid slurry to an imidization. In some embodiments, the contact reaction may be carried out in the presence of a chemical plating accelerant containing at least one selected from a group consisting of TiO, Ni₂O₃, Co₂O₃, CuSiO₃, NiSiO₃, CoSiO₃, CuB₂O₄, NiB₂O₄, NiC₂O₄, CoO and CoC₂O₄.

According to embodiments of the present disclosure, in the presence of the chemical plating accelerant containing at least one selected from a group consisting of TiO, Ni₂O₃, Co₂O₃, CuSiO₃, NiSiO₃, CoSiO₃, CuB₂O₄, NiB₂O₄, NiC₂O₄, CoO and CoC₂O₄, by forming the polyamide acid slurry by subjecting the diamine and the tetracarboxyl dianhydride to the contact reaction and subjecting the polyamide acid slurry to the imidization, the polyimide film may be obtained. Moreover, the polyimide film may be subjected to an ablation-activation process with a laser to expose the chemical plating accelerant, and then the polyimide film may be chemically plated to dispose metals on the exposed chemical plating accelerant so as to form a circuit. By precisely controlling the ablation-activation process and the structure of the exposed chemical plating accelerant, a required circuit pattern may be obtained. In this way, the polyimide film may be used to form a circuit board with required circuit pattern. In addition, by forming a hole in the polyimide film, metals may be plated on the walls of the hole in the polyimide film by chemical plating instead of black hole treatment. Then, a flexible circuit board having conduction circuits on two surfaces may be obtained.

Embodiments of a further aspect of the present disclosure provide a method of preparing a flexible circuit board. The method includes: subjecting a surface of a polyimide film to a laser irradiation, with the polyimide film being the above-identified polyimide film or prepared by the above-identified method of preparing a polyimide film, and subjecting the surface of the polyimide film to chemical plating.

In some embodiments, two surfaces of the polyimide film may be irradiated with laser, and the two surfaces may be chemically plated subsequently.

According to embodiments of the present disclosure, with the polyimide film having the chemical plating accelerant (containing at least one selected from a group consisting of TiO, Ni₂O₃, Co₂O₃, CuSiO₃, NiSiO₃, CoSiO₃, CuB₂O₄, NiB₂O₄, NiC₂O₄, CoO and CoC₂O₄) , by subjecting the polyimide film to an ablation-activation process with a laser so as to expose the chemical plating accelerant, and then chemically plating the polyimide film to plate metals on the exposed chemical plating accelerant, the flexible circuit board may be obtained. By precisely controlling the ablation-activation process and the structure of the exposed chemical plating accelerant, a required circuit pattern may be obtained. In addition, by forming a hole in the polyimide film, metals may be plated on the part of walls (where the chemical plating accelerant is exposed) of the hole in the polyimide film by chemical plating. Then, two surfaces of the polyimide film may be conducted with each other, and a flexible circuit board having conduction circuits on two surfaces may be obtained.

In some embodiments, the flexible circuit board may have strong copper adhesion and excellent solder resistance. In addition, the flexible circuit board may have required surface impedance, volume impedance, and insulation resistance between wires.

Embodiments of a further aspect of the present disclosure provide a flexible circuit board. The flexible circuit board is prepared by the above method of preparing a flexible circuit board.

According to embodiments of the present disclosure, the flexible circuit board may have strong copper adhesion and excellent solder resistance. In addition, the flexible circuit board may have required surface impedance, volume impedance, and insulation resistance between wires.

Additional aspects and advantages of embodiments of present disclosure will be given in part in the following descriptions, become apparent in part from the following descriptions, or be learned from the practice of the embodiments of the present disclosure.

DETAILED DESCRIPTION

Reference will be made in detail to embodiments of the present disclosure. The embodiments described herein are explanatory, illustrative, and used to generally understand the present disclosure. The embodiments shall not be construed to limit the present disclosure. In the specification, unless specified or limited otherwise, terms such as “first” and “second” are used herein for purposes of description and are not intended to indicate or imply relative importance or significance. For the purpose of the present description and of the following claims, the definitions of the numerical ranges always include the extremes unless otherwise specified. In addition, the term “comprising” also includes the terms “essentially consisting of” or “consisting of” .

Embodiments of an aspect of the present disclosure provide a polyimide film. The polyimide film contains a chemical plating accelerant, and the chemical plating accelerant contains at least one selected from a group consisting of TiO, Ni₂O₃, Co₂O₃, CuSiO₃, NiSiO₃, CoSiO₃, CuB₂O₄, NiB₂O₄, NiC₂O₄, CoO and CoC₂O₄.

In some embodiments, the chemical plating accelerant may contain at least one selected from a group consisting of Co₂O₃, CoSiO₃, Ni₂O₃, CuSiO₃, NiSiO₃, CuB₂O₄, NiB₂O₄ and NiC₂O₄. In some embodiments, the chemical plating accelerant may contain at least one selected from a group consisting of Co₂O₃, CoSiO₃, CuSiO₃ and Ni₂O₃. Therefore, the polyimide film may have better performances.

In some embodiments, the chemical plating accelerant is uniformly distributed in the polyimide film.

In some embodiments, based on 100 weight parts of the polyimide in the polyimide film, the chemical plating accelerant has a content of 5 weight parts to 20 weight parts. In some embodiments, based on 100 weight parts of the polyimide in the polyimide film, a content of the chemical plating accelerant is 10 weight parts to 16 weight parts.

According to some embodiments of the present disclosure, the polyimide film may be used to prepare flexible circuit board, and the polyimide film may have a thickness as that of a polyimide film used for preparing a conventional flexible circuit board. In some embodiments, the polyimide film has a thickness of 15 μm to 160 μm. In some embodiments, the polyimide film has a thickness of 25 μm to 50 μm.

According to some embodiments of the present disclosure, the polyimide film may contain other additives which may be generally used in the polyimide film. In some embodiments, the additive may include at least one of inorganic filler, antioxidant, and flame retardant agent.

In some embodiments, the polyimide film further includes an inorganic filler. With the inorganic filler, the strength, tensile performance, and wear resistance of the polyimide film maybe improved. In some embodiments, the inorganic filler may be various commonly used ones in the related art. For example, the inorganic filler may contain at least one selected from a group consisting of calcium carbonate, calcium sulfate, talc, titanium dioxide, wollastonite, diatomaceous earth, kaoline, mica, aluminum oxide, carbon black, and silicon dioxide. In some embodiments, the inorganic filler may contain at least one selected from a group consisting of talc, titanium dioxide, mica, and silicon dioxide. The talc and mica may be both in the form of powders.

According to some embodiments of the present disclosure, the amount of the inorganic filler in the polyimide film may be well known in the related art. In some embodiments, based on 100 weight parts of the polyimide in the polyimide film, the inorganic filler has a content of 5 weight parts to 50 weight parts. In some embodiments, based on 100 weight parts of the polyimide in the polyimide film, the inorganic filler has a content of 10 weight parts to 30 weight parts.

Embodiments of another aspect of the present disclosure provide a method of preparing a polyimide film. The method may include: subjecting diamine and tetracarboxyl dianhydride to a contact reaction in a solvent so as to obtain a polyamide acid slurry, and coating the polyamide acid slurry on a substrate and subjecting the polyamide acid slurry to an imidization. In some embodiments, the contact reaction may be carried out in the presence of a chemical plating accelerant containing at least one selected from a group consisting of TiO, Ni₂O₃, Co₂O₃, CuSiO₃, NiSiO₃, CoSiO₃, CuB₂O₄, NiB₂O₄, NiC₂O₄, CoO and CoC₂O₄.

According to some embodiments of the present disclosure, by subjecting the diamine and the tetracarboxyl dianhydride to the contact reaction, the polyamide acid slurry containing the chemical plating accelerant which contains at least one selected from a group consisting of TiO, Ni₂O₃, Co₂O₃, CuSiO₃, NiSiO₃, CoSiO₃, CuB₂O₄, NiB₂O₄, NiC₂O₄, CoO and CoC₂O₄ may be obtained. Then, by subjecting the polyamide acid slurry to imidization, the polyimide film may be obtained. Using this polyimide film, a flexible circuit board having high metal-substrate adhesion and improved insulation capability between wires may be obtained simply and rapidly.

In some embodiments, the chemical plating accelerant may contain at least one selected from a group consisting of Co₂O₃, CoSiO₃, Ni₂O₃, CuSiO₃, NiSiO₃, CuB₂O₄, NiB₂O₄ and NiC₂O₄. In some embodiments, the chemical plating accelerant may contain at least one selected from a group consisting of Co₂O₃, CoSiO₃, Ni₂O₃, and CuSiO₃. Therefore, the polyimide film may be used to prepare flexible circuit boards with improved performances.

In some embodiments, based on 100 weight parts of a sum of the diamine and the tetracarboxyl dianhydride, the chemical plating accelerant may have an amount of 5 weight parts to 20 weight parts. In some embodiments, the chemical plating accelerant may have an amount of 10 weight parts to 16 weight parts.

According to some embodiments of the present disclosure, the polyimide film may be subjected to an ablation-activation process with a laser to expose the chemical plating accelerant, and then the polyimide film may be chemically plated to dispose metals on the exposed chemical plating accelerant, and therefore a circuit may be obtained. By precisely controlling the ablation-activation process and the structure of the exposed chemical plating accelerant, a flexible circuit board with a required circuit pattern may be obtained. The distribution of chemical plating accelerant in the polyimide film may play an important role in obtaining a required polyimide film. In some embodiments, the chemical plating accelerant has a particle diameter of 0.2 μm to 2 μm. In some embodiments, the chemical plating accelerant has a particle diameter of 0.5 μm to 1.5 μm. With the above particle diameter, the chemical plating accelerant may be distributed in the polyimide film more uniformly, and thus a better flexible circuit board may be obtained.

In some embodiments, the chemical plating accelerant may be mixed with reaction agents (the diamine and the tetracarboxyl dianhydride) completely. Thus, the chemical plating accelerant may be distributed uniformly in the obtained polyamide acid slurry. In this way, a polyimide film having more uniform chemical plating accelerant distribution may be obtained.

According to some embodiments of the present disclosure, the contact reaction may be carried out in the presence of additives which may be generally used in the polyimide film. In some embodiments, the additive may include at least one of inorganic filler, antioxidant, and flame retardant agent.

In some embodiments, the contact reaction may be carried out in the presence of an inorganic filler. With the inorganic filler, the strength, tensile performance, and wear resistance of the polyimide film maybe improved. In some embodiments, the inorganic filler may be various commonly used ones in the related art. For example, the inorganic filler may contain at least one selected from a group consisting of calcium carbonate, calcium sulfate, talc, titanium dioxide, wollastonite, diatomaceous earth, kaoline, mica, aluminum oxide, carbon black, and silicon dioxide. In some embodiments, the inorganic filler may contain at least one selected from a group consisting of talc, titanium dioxide, mica, and silicon dioxide. The talc and mica may be both in the form of powders.

According to some embodiments of the present disclosure, there are no special limits to the amount of the organic filler, and the amount of the organic filler may be adjusted according to required properties of the polyimide film, such as strength. In some embodiments, based on 100 weight parts of a sum of the diamine and the tetracarboxyl dianhydride, the inorganic filler has an amount of 5 weight parts to 50 weight parts. In some embodiments, based on 100 weight parts of a sum of the diamine and the tetracarboxyl dianhydride, the inorganic filler has an amount of 10 weight parts to 30 weight parts.

According to some embodiments of the present disclosure, the particle diameter may be well known to those skilled in the related art. In some embodiments, the inorganic filler has a particle diameter of 0.2 μm to 5 μm.

According to some embodiments of the present disclosure, the contact reaction may be carried out in a solvent, such as a polar solvent. There are no special limits to the solvent, provided the contact reaction between the diamine and the tetracarboxyl dianhydride is capable of forming a polyamide acid. In some embodiments, the solvent may contain at least one selected from a group consisting of N, N-dimethyl formamide, N, N-dimethyl acetamide, N-methyl pyrrolidone, tetrahydrofuran, and methnol.

According to some embodiments of the present disclosure, there are no special limits to the amount of the solvent, and the amount of the solvent may be adjusted according to a required viscosity of the polyamide acid slurry. In some embodiments, based on 100 weight parts of a sum of the diamine and the tetracarboxyl dianhydride, the solvent has an amount of 350 weight parts to 600 weight parts.

In some embodiments, before the contact reaction, the inorganic filler and the chemical plating accelerant may be distributed uniformly in the solvent by, for example, mechanical stirring, to form a mixture. Then the diamine may be dissolved in the mixture, and then the tetracarboxyl dianhydride may be added. In some embodiments, the tetracarboxyl dianhydride may be added at a low temperature (for example, 5℃ to 20℃) under stirring. In this case, the molecular weight and viscosity of the polyamide acid slurry may be well controlled.

In some embodiments, a molar ratio between the diamine and the tetracarboxyl dianhydride is from 1: 0.85 to 1: 1.1. In some embodiments, the molar ratio between the diamine and the tetracarboxyl dianhydride is from 1: 0.9 to 1: 1.05. therefore, a polyimide film obtained in the imidization step may have better mechanical properties.

According to some embodiments of the present disclosure, the diamine and the tetracarboxyl dianhydride may be those well known in the related art. In some embodiments, the diamine may contain at least one selected from a group consisting of p-phenylenediamine, 3, 4'-diaminodiphenyl ether, 4, 4'-diaminodiphenyl ether, 4, 4'-diaminodiphenyl sulfone, 1, 4-bi (4-aminophenoxy) benzene, 2, 2'-bi [4- (4-aminophenoxy) phenyl] propane, and bi [4- (4-aminophenoxy) phenyl] sulfone. In some embodiments, the tetracarboxyl dianhydride may contain at least one selected from a group consisting of pyromellitic dianhydride, diphenyl ether tetracarboxylic dianhydride, biphenyl tetracarboxylic diandhydride, dibenzophenonetetracarboxylic dianhydride, and 2, 2'-bi [4- (3, 4-dicarboxylphenoxyl) phenyl] propane dianhydride.

According to some embodiments of the present disclosure, the polyamide acid slurry may have a viscosity varied in a large range. In some embodiments, the polyamide acid slurry has a viscosity of 60,000 cp to 100,000 cp at 25℃. In some embodiments, the viscosity of the polyamide acid slurry may be smaller than 100,000 cp, which may facilitate to coat the polyamide acid slurry uniformly on the substrate and to remove the solvent in the imidization step. Meanwhile, the viscosity of the polyamide acid slurry may be at least 60,000 cp, which may facilitate to ensure a chemical resistance of the prepared polyimide film.

In some embodiments, the polyamide acid slurry obtained by the contact reaction may be coated on the substrate (for example, glass plate, stainless steel plate) by a conventional coating manner in the related art (for example, using a spreading machine, or by blade coating) , and then subjected to imidization.

There are no special limits to the thickness of the polyamide acid slurry coated on the substrate or the thickness of the obtained polyimide film, which may be any conventional thickness known in the related art. In some embodiments, the polyimide film has a thickness of 15 μm to 160 μm. In some embodiments, the polyimide film has a thickness of 25 μm to 50 μm. Then market requirements for the polyimide film may be satisfied. The thickness of the polyamide acid slurry coated on the substrate may be adjusted according to a required thickness of the polyimide film. In some embodiments, the polyamide acid slurry coated on the substrate has a thickness of 100 μm to 1500 μm. In this case, the polyimide film has a thickness of 15 μm to 160 μm.

According to some embodiments of the present disclosure, the method of preparing the polyimide film includes an imidization step which is used to convert the polyamide acid slurry into a polyimide film. The imidization may be any conventional imidization method known in the related art. In some embodiments, the imidization may include a first imidization and a second imidization. In the first imidization, the solvent in the polyamide acid slurry coated on the substrate may be removed and an initial imidization may be achieved, which is beneficial to the second imidization. In some embodiments, the first imidization may include heating the polyamide acid slurry from a first temperature of 30℃ to 45℃ to a second temperature of 160℃ to 180℃with a first temperature increasing rate of 6℃/min to 10℃/min. The first temperature of 30℃ to 45℃ may be an initial temperature of an oven, or adjusted by presetting. Heating the polyamide acid slurry from the first temperature of 30℃ to 45℃ may facilitate to discharge the solvent, heating the polyamide acid slurry with a first temperature increasing rate of 6℃/min to 10℃/min may ensure a sufficient time for discharging the solvent and reduce the discharging time, and heating the polyamide acid slurry to the second temperature of 160℃ to 180℃ may ensure that the solvent is removed completely and meanwhile the polyamide acid slurry has a relatively low temperature. If the polyamide acid slurry has a too high temperature when the first imidization ends, the first imidization may cause a significant amount of imidization, and therefore the properties of obtained polyimide film may be reduced.

The polyamide acid slurry obtained from the first imidization may be taken out directly or removed by coiling, cooled to room temperature, and subjected to the second imidization. In the second imidization, the final polyimide film is formed. In some embodiments, the second imidization may include heating the polyamide acid slurry from a third temperature of 20℃ to 40℃ to a fourth temperature of 320℃ to 350℃ with a second temperature increasing rate of 4℃/min to 6℃/min, and keeping the polyamide acid slurry at the fourth temperature for 50 min to 70 min. The third temperature may be the room temperature, and needs not to be set as the initial temperature in the oven. After the first imidization, an initial polyimide film may be formed. And then initial polyimide film is taken out of the oven and cooled to the room temperature, and subjected to the second imidization. In the second imidization, by using a relatively lower temperature increasing rate of 4℃/min to 6℃/min and keeping the polyamide acid slurry at the fourth temperature for 50 min to 70 min after heating the polyamide acid to the fourth temperature of 320℃ to 350℃, the imidization is completed and the polyimide film may be obtained. With these two imidizations, the polyamide acid slurry coated on the substrate may be converted into a polyimide film having no air bubbles, no cracks, and excellent tensile properties.

In some embodiments, the polyimide film according to embodiments of the present disclosure may have a thermal expansion coefficient of 16 μm/ (m·℃) to 25 μm/ (m·℃) , a tensile strength of at least 155 MPa, and an elongation at break of at least 20％.

For the aim of the present invention, other additives or components can be optionally added to the above polyamide acid slurry to adapt it so as to satisfy specific practical requirements. The polyimide film thus obtained should therefore be considered as being included in the scope of the present invention.

According to some embodiments of the present disclosure, at least a part of a surface or at least a part of two surfaces of the polyimide film may be irradiated with the laser according to a required circuit pattern to be formed, polymer resins in the substrate corresponding to the irradiated part of the polyimide film may be ablated by the laser and the chemical plating accelerant evenly distributed in the polyimide film corresponding to the irradiated part of the polyimide film may be exposed. The exposed chemical plating accelerant forms a structure which is corresponding to the required circuit pattern and is similar to a porous honeycomb, which facilitates to bond with metals in the subsequent chemical plating process.

According to some embodiments of the present disclosure, the laser may be adjusted according to the compositions of the polymer resin in the polyimide film. In some embodiments, the laser has wavelength of 800 nm to 2500 nm. In some embodiments, the laser has a scanning speed of 500mm/s to 8000mm/s. In some embodiments, the laser has a power of 3W to 20W. In some embodiments, the laser has wavelength of 800 nm to 1200 nm. In some embodiments, the laser has a scanning speed of 800mm/s to 1500mm/s. In some embodiments, the laser has a power of 3W to 5W. According to some embodiments of the present disclosure, if the power of the laser is relatively larger, the polymer in the polyimide film may be significantly ablated by the laser, thus causing a deformation of the polyimide film or forming through holes in the polyimide film. The laser may be adjusted according to the thickness of the polyimide film and the type of the required circuit pattern. In some embodiments, the power of the laser may be 3W to 20W. In some embodiments, the power of the laser may be 3W to 5W. In these embodiments, a clear circuit pattern may be obtained in a shorter time with a smaller energy consumption, without causing a deformation of the polyimide film or forming a hole in the polyimide film due to an extra ablation to the polyimide film.

The laser irradiation may be carried out by using a conventional laser in the related art, such as a CO₂ laser marking machine. By referring to the above-mentioned laser condition and properly setting parameters of the laser, polymers in the corresponding part of the substrate may be ablated and subsequently the required circuit pattern may be formed. There are no special limits to the parameters of the laser, such as the frequency, step size, time delay, filling distance, etc, and the parameters of the laser may be provided according to the laser irradiating condition. In some embodiments, the frequency may be from 30 KHz to 40 KHz. In some embodiments, the step size may be from 3 μm to 9 μm. In some embodiments, the time delay may be from 30μs to 100 μs. In some embodiments, the filling distance may be from 10 μm to 50 μm.

According to some embodiments of the present disclosure, after the laser irradiation, the chemical plating may be performed to plate metals. In some embodiments, when preparing a circuit board having circuit patterns on two surfaces thereof and these circuit patterns capable of electrically capable of conducting with each other, a hole may be formed in the polyimide film before the chemical plating step, and then metals may be plated on the substrate by chemical plating. There are no special limits to the method of forming a hole in the polyimide film, provided the obtained hole ensure that the following chemical plating forms circuits disposed on two surfaces of the substrate and electrically capable of conducting with each other. In some embodiments, during the chemical plating, metals may be disposed in the hole in the polyimide film, which may be connected with two circuits formed on two surfaces of the substrate respectively, thus achieving the electrical conduction between the two circuits formed on the two surfaces.

According to some embodiments of the present disclosure, after forming the hole, there is no need to perform a black hole process on the wall of the hole. In the related art, in order to form a circuit board having two circuits disposed on two surfaces thereof and capable of conducting with each other, after forming a hole, the black hole process is generally needed to form a conductive carbon layer on the wall of the hole, and therefore metals such as copper may be plated on the wall of the hole. According to some embodiments of the present disclosure, after forming a hole, chemical plating accelerants at the wall of the hole may be exposed. Then, with the following chemical plating, metals may be plated on the irradiated part of the substrate and the wall of the hole, thus forming a flexible circuit board having two circuits disposed on two surfaces thereof. Therefore, the operation process for obtaining the flexible circuit board may be simplified.

In some embodiments, after the polyimide film is subjected to the chemical plating, at least one metal may be plated on the substrate. The metal may be any conventional metal known in the related art, such as at least one of copper, nickel, gold, and so on.

According to some embodiments of the present disclosure, the chemical plating may be carried out with any conventional chemical plating method in the related art. In some embodiments, the chemical plating method may include the following steps. Firstly, the irradiated polyimide film may be contacted with a metal solution for chemical plating, and then the metal solution is reduced to metal disposed on the exposed chemical plating accelerant in the polyimide film and covered on the chemical plating accelerant.

In some embodiments, one metal may be plated by contacting the polyimide film with one metal solution for chemical plating. In some embodiments, a plurality of metals may be plated by contacting the polyimide film with a plurality of metal solutions simultaneously or sequentially. In some embodiments, the irradiated polyimide film may be contacted with a copper solution, a nickel solution and a gold solution sequentially, thus forming three metal layers on the substrate, i.e. a Cu layer, a Ni layer, and a gold layer from the inside out.

There are no special limits to the metal solutions for chemical plating, such as copper solution, nickel solution and gold solution which may be any conventional ones in the related art that are known to those skilled in the art. These metal solutions for chemical plating, such as copper solution, nickel solution and gold solution, may be commercially available or self-prepared. In some embodiments, the copper solution may contain 0.12mol/L CuS0₄·5H₂O, 0.14mol/L Na₂EDTA·2H₂O, 10mg/L potassium ferrocyanide, 10mg/L 2, 2-bipyridine, and 0.10mol/L ethanol acid, and have a pH value of 12.5-13 which may be adjusted by using NaOH and H₂SO₄. In some embodiments, the nickel solution may contain 23g/L nickel sulfate, 18g/L sodium hypophosphite, and 15g/L malic acid and have a pH value of 5.2 at 85℃ to 90℃ which is adjusted by using NaOH. In some embodiments, the gold solution may be BG-24 neutral gold solution for plating commercially available from Shenzhen Jinyanchuang Chemical Company, China. The plating gold may be performed by a flash plating process which is known in the related art.

In some embodiments, the obtained copper layer may have a thickness of 0.1-100 μm. In some embodiments, the copper layer may have a thickness of 1-50 μm. In some embodiments, the copper layer may have a thickness of 5-30 μm.

In some embodiments, the obtained nickel layer may have a thickness of 0.1-50 μm. In some embodiments, the obtained nickel layer may have a thickness of 1-10 μm. In some embodiments, the obtained nickel layer may have a thickness of 2-3 μm.

In some embodiments, the obtained gold layer may have a thickness of 0.01-10 μm. In some embodiments, the obtained gold layer may have a thickness of 0.01-2 μm.

In some embodiments, the flexible circuit board may have one circuit formed on one surface thereof by chemical plating. In some embodiments, the flexible circuit board may have two circuits formed on two surfaces thereof and capable of conducting with each other. According to embodiments of the present disclosure, the flexible circuit board may have strong copper adhesion and excellent solder resistance. In addition, the flexible circuit board may have a surface impedance of at least 10¹³Ω, a volume impedance of at least 10¹⁴Ω·cm, and insulation resistance between wires of at least 100MΩ.

Some illustrative and non-limiting examples are provided hereunder for a better understanding of the present invention and for its practical embodiment.

TESTS

Properties of the polyimide film were tested by the following tests. Related results were shown in Table 1.

Thermal expansion coefficient was measured by a method according to ASTM D3386-2000.

Tensile strength was measured by a method according to IPC-TM-650 2.4.19.

Elongation at break was measured by a method according to IPC-TM-650 2.4.19.

Properties of the flexible circuit board were tested by the following tests. Related results were shown in Table 3.

Adhesion was measured by a method according to GB/T 9286-1998.

Soldering resistance was measured by a method according to IPC-TM-650 NO. 2.4.13.

Surface impedance was measured by a method according to IPC-TM-650 2.5.17.

Volume impedance was measured by a method according to IPC-TM-650 2.5.17.

Insulation resistance between wires was measured by a method according to IPC-TM-650 2.6.3.2.

Resistance of a combination of circuits

The resistance of a combination of the two circuits formed on two surfaces of the flexible circuit board was measured by using a universal instrument. For example, one of the two circuits was connected to one detecting terminal of the universal instrument, and the other one of the two circuits was connected to the other one detecting terminal of the universal instrument, and then the resistance of the combination of the two circuits was read on a display screen of the universal instrument. If the resistance was equal to 0 or very small, it was determined that the two circuits on the two surfaces were electrically conductive with each other.

The following materials were used.

Chemical plating accelerant: Co₂O, Ni₂O₃, CuSiO₃ and CoSiO₃ commercially available from Tianyuan Chemical Co., Ltd, China.

Inorganic filler: mica powders, talc powders, and silicon dioxide commercially available from Jinyang Chemical Co., Ltd, China.

P-phenylenediamine was commercially available from Amino Chemical Company.

3, 4'-diaminodiphenyl ether and 4, 4'-diaminodiphenyl ether were commercially available from Changji Chemical Co., Ltd, China.

Pyromellitic dianhydride and 3, 3', 4, 4'-biphenyl tetracarboxylic diandhydride were commercially available from Shijiazhuang Haili Fine Chemical Liability Co., Ltd, China.

3, 3', 4, 4'-diphenyl ether tetracarboxylic dianhydride was commercially available from Shanghai Juhao Fine Chemical Co., Ltd, China.

3, 3', 4, 4'-dibenzophenonetetracarboxylic dianhydride was commercially available from Shanghai Longlei Biotech Co., Ltd, China.

Embodiment 1

13.759 g mica powders having an average particle diameter of 1.5 μm, 13.759 g Co₂O₃ having an average particle diameter of 2 μm, and 353 ml N, N-dimethyl acetamide were mixed and stirred for 35 min to form a first system. 27.3 g 4, 4'-diaminodiphenyl ether and 6.318 g p-phenylenediamine were added in the first system and stirred for 30 min to dissolve the 4, 4'-diaminodiphenyl ether and the p-phenylenediamine completely, thus obtaining a second system. Then, 3, 3', 4, 4'-biphenyl tetracarboxylic diandhydride was slowly added into the second system to increase the viscosity of the reaction system. When the added amount of 3, 3', 4, 4'-biphenyl tetracarboxylic diandhydride was 53g, the viscosity of the reaction system reached 67,000 cp. At this moment, the adding of 3, 3', 4, 4'-biphenyl tetracarboxylic diandhydride was stopped, and a polyamide acid slurry was obtained.

The polyamide acid slurry was vacuumized to discharge air bubbles in the polyamide acid slurry.

The obtained polyamide acid slurry was coated on a glass plate with a blade, and a slurry layer having a thickness of 500 μm was formed. Firstly, the coated glass plate was uniformly heated from 40℃ to 180℃ within 15 min, and then cooled to 25℃. Then, the glass plate was uniformly heated from 25℃ to 340℃ within 1 h, and kept at 340℃ for 1 h. After the glass plate was cooled, a polyimide film was obtained.

The polyimide film had a thickness of 45 μm.

Embodiment 2

14 g mica powders having an average particle diameter of 0.8 μm, 7 g CoSiO₃ having an average particle diameter of 2 μm, and 280 ml N, N-dimethyl acetamide were mixed and stirred for 15 min to form a first system. 35 g 4, 4'-diaminodiphenyl ether was added in the first system and stirred for 30 min to dissolve the 4, 4'-diaminodiphenyl ether completely, thus obtaining a second system. Then, pyromellitic dianhydride was slowly added into the second system to increase the viscosity of the reaction system. When the added amount of the pyromellitic dianhydride was 35g, the viscosity of the reaction system reached 87,000 cp. At this moment, the adding of pyromellitic dianhydride was stopped, and a polyamide acid slurry was obtained.

The obtained polyamide acid slurry was coated on a glass plate with a blade, and a slurry layer having a thickness of 700 μm was formed. Firstly, the coated glass plate was uniformly heated from 40℃ to 180℃ within 15 min, and then cooled to 25℃. Then, the glass plate was uniformly heated from 25℃ to 340℃ within 1 h, and kept at 340℃ for 1 h. After the glass plate was cooled, a polyimide film was obtained.

The polyimide film had a thickness of 60 μm.

Embodiment 3

15.4 g talc powders having an average particle diameter of 0.5 μm, 7.7 g CoSiO₃ having an average particle diameter of 1 μm, and 500 ml N, N-dimethyl acetamide were mixed and stirred for 40 min to form a first system. 31.15 g 3, 4'-diaminodiphenyl ether was added in the first system and stirred for 25 min to dissolve the 3, 4'-diaminodiphenyl ether completely, thus obtaining a second system. Then, 3, 3', 4, 4'-diphenyl ether tetracarboxylic dianhydride was slowly added into the second system to increase the viscosity of the reaction system. When the added amount of 3,3', 4, 4'-diphenyl ether tetracarboxylic dianhydride was 45.85g, the viscosity of the reaction system reached 92,000 cp. At this moment, the adding of 3, 3', 4, 4'-diphenyl ether tetracarboxylic dianhydride was stopped, and a polyamide acid slurry was obtained.

The obtained polyamide acid slurry was coated on a glass plate with a blade, and a slurry layer having a thickness of 1100 μm was formed. Firstly, the coated glass plate was uniformly heated from 30℃ to 170℃ within 20 min, and then cooled to 30℃. Then, the glass plate was uniformly heated from 30℃ to 330℃ within 50 min, and kept at 330℃ for 70 min. After the glass plate was cooled, a polyimide film was obtained.

The polyimide film had a thickness of 100 μm.

Embodiment 4

20.17 g silicon dioxide having an average particle diameter of 2 μm, 9.63 g Ni₂O₃ having an average particle diameter of 0.5 μm, and 550 ml mixed solution of tetrahydrofuran and methanol (volume ratio of 1: 1) were mixed and stirred for 30 min to form a first system. 32.78 g 3, 4'-diaminodiphenyl ether was added in the first system and stirred for 25 min to dissolve the 3, 4'-diaminodiphenyl ether completely, thus obtaining a second system. Then, 3, 3', 4, 4'-dibenzophenonetetracarboxylic dianhydride was slowly added into the second system to increase the viscosity of the reaction system. When the added amount of 3, 3', 4, 4'-dibenzophenonetetracarboxylic dianhydride was 47.5 g, the viscosity of the reaction system reached 75,000 cp. At this moment, the adding of 3, 3', 4, 4'-dibenzophenonetetracarboxylic dianhydride was stopped, and a polyamide acid slurry was obtained.

The obtained polyamide acid slurry was coated on a glass plate with a blade, and a slurry layer having a thickness of 1500 μm was formed. Firstly, the coated glass plate was uniformly heated from 45℃ to 160℃ within 12 min, and then cooled to 35℃. Then, the glass plate was uniformly heated from 35℃ to 345℃ within 65 min, and kept at 345℃ for 55 min. After the glass plate was cooled, a polyimide film was obtained.

The polyimide film had a thickness of 145 μm.

Embodiment 5

The polyimide films obtained from Embodiments 1-4 were used to prepare flexible circuit boards with the following steps.

The polyimide film was irradiated with a YLP-20 laser (commercially available from Han’S Laser Technology Co., Ltd, Shenzhen, China) using laser parameters listed in Table 2. Then the irradiated polyimide film was cleaned, and chemically plated for 120 min with a copper solution having a pH value of 12.5 and consisting of CuSO₄·5H₂O (0.12mol/L) , Na₂EDTA·2H₂O (0.14mol/L) , potassium ferrocyanide (10mg/L) , 2, 2'-bipyridine (10mg/L) , and ethanol acid (0.1mol/L) . The copper plating speed was shown in Table 3.

Embodiment 6

A hole having a diameter of 0.5 mm was formed in the polyimide film obtained from Embodiment 1 at places where an electrical conduction between two circuits was required. Then same steps as those in Embodiment 5 were performed, thus obtaining a flexible circuit board having two circuits formed on two surfaces thereof and capable of conducting with each other. Resistances of circuits on both surfaces of the circuit board were 0.05Ω, which indicated that the two circuits on the two surfaces were capable of conducting with each other.

Table 1

Table 2

Table 3

As can be seen from Tables 1 and 3, the polyimide film according to embodiments of the present disclosure may have excellent mechanical and insulation properties. The method of preparing a flexible circuit board using the polyimide film according to embodiments of the present disclosure may be simple, and the obtained flexible circuit board may have large strength and strong adhesion between the circuit and the substrate. As can be seen from Table 2, a flexible circuit board having two circuits formed on two surfaces thereof and capable of conducting with each other may be prepared using the polyimide film according to embodiments of the present disclosure.

It will be understood that the features mentioned above and those still to be explained hereinafter may be used not only in the particular combination specified but also in other combinations or on their own, without departing from the scope of the present invention.

Reference throughout this specification to “an embodiment, ” “some embodiments, ” “one embodiment” , “another example, ” “an example, ” “a specific example, ” or “some examples, ” means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present disclosure. Thus, the appearances of the phrases such as “in some embodiments, ” “in one embodiment” , “in an embodiment” , “in another example, ” “in an example, ” “in a specific example, ” or “in some examples, ” in various places throughout this specification are not necessarily referring to the same embodiment or example of the present disclosure. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

Although explanatory embodiments have been shown and described, it would be appreciated by those skilled in the art that the above embodiments can not be construed to limit the present disclosure, and changes, alternatives, and modifications can be made in the embodiments without departing from spirit, principles and scope of the present disclosure.

Claims

A polyimide film comprising

a chemical plating accelerant comprising at least one selected from a group consisting of TiO, Ni₂O₃, Co₂O₃, CuSiO₃, NiSiO₃, CoSiO₃, CuB₂O₄, NiB₂O₄, NiC₂O₄, CoO and CoC₂O₄.
The polyimide film according to claim 1, wherein the chemical plating accelerant comprises at least one selected from a group consisting of Co₂O₃, CoSiO₃, Ni₂O₃, CuSiO₃, NiSiO₃, CuB₂O₄, NiB₂O₄ and NiC₂O₄.
The polyimide film according to claim 1 or 2, wherein based on 100 weight parts of the polyimide in the polyimide film, the chemical plating accelerant has a content of 5 weight parts to 20 weight parts.
The polyimide film according to claim 3, wherein based on 100 weight parts of the polyimide in the polyimide film, the chemical plating accelerant has a content of 10 weight parts to 16 weight parts.
The polyimide film according to any of claims 1-4, wherein the polyimide film has a thickness of 15 μm to 160 μm.
The polyimide film according to any of claims 1-5, further comprising an inorganic filler, wherein the inorganic filler comprises at least one selected from a group consisting of calcium carbonate, calcium sulfate, talc, titanium dioxide, wollastonite, diatomaceous earth, kaoline, mica, aluminum oxide, carbon black, and silicon dioxide.
The polyimide film according to claim 6, wherein the inorganic filler comprises at least one selected from a group consisting of talc, titanium dioxide, mica, and silicon dioxide.
The polyimide film according to claim 6 or 7, wherein based on 100 weight parts of the polyimide in the polyimide film, the inorganic filler has a content of 5 weight parts to 50 weight parts.
The polyimide film according to claim 8, wherein based on 100 weight parts of the polyimide in the polyimide film, the inorganic filler has a content of 10 weight parts to 30 weight parts.
A method of preparing a polyimide film, comprising

subjecting diamine and tetracarboxyl dianhydride to a contact reaction in a solvent to obtain a polyamide acid slurry, and

coating the polyamide acid slurry on a substrate and subjecting the polyamide acid slurry to an imidization,

wherein the contact reaction is carried out in the presence of a chemical plating accelerant comprising at least one selected from a group consisting of TiO, Ni₂O₃, Co₂O₃, CuSiO₃, NiSiO₃, CoSiO₃, CuB₂O₄, NiB₂O₄, NiC₂O₄, CoO and CoC₂O₄.
The method according to claim 10, wherein the chemical plating accelerant comprises at least one selected from a group consisting of Co₂O₃, CoSiO₃, Ni₂O₃, CuSiO₃, NiSiO₃, CuB₂O₄, NiB₂O₄ and NiC₂O₄.
The method according to claim 10 or 11, wherein based on 100 weight parts of a sum of the diamine and the tetracarboxyl dianhydride, the chemical plating accelerant has an amount of 5 weight parts to 20 weight parts.
The method according to claim 12, wherein based on 100 weight parts of a sum of the diamine and the tetracarboxyl dianhydride, the chemical plating accelerant has an amount of 10 weight parts to 16 weight parts.
The method according to any of claims 10-13, wherein the chemical plating accelerant has a particle diameter of 0.2 μm to 2 μm.
The method according to any of claims 10-14, wherein the polyamide acid slurry has a viscosity of 60,000 cp to 100,000 cp.
The method according to any of claims 10-15, wherein based on 100 weight parts of a sum of the diamine and the tetracarboxyl dianhydride, the solvent has an amount of 350 weight parts to 600 weight parts.
The method according to any of claims 10-16, wherein the solvent comprises at least one selected from a group consisting of N, N-dimethyl formamide, N, N-dimethyl acetamide, N-methyl pyrrolidone, tetrahydrofuran, and methnol.
The method according to any of claims 10-17, wherein the contact reaction is carried out in the presence of an organic filler, and the inorganic filler comprises at least one selected from a group consisting of calcium carbonate, calcium sulfate, talc, titanium dioxide, wollastonite, diatomaceous earth, kaoline, mica, aluminum oxide, carbon black, and silicon dioxide.
The method according to claim 18, wherein the inorganic filler comprises at least one selected from a group consisting of talc, titanium dioxide, mica, and silicon dioxide.
The method according to claim 18 or 19, wherein based on 100 weight parts of a sum of the diamine and the tetracarboxyl dianhydride, the inorganic filler has an amount of 5 weight parts to 50 weight parts.
The method according to claim 20, wherein based on 100 weight parts of a sum of the diamine and the tetracarboxyl dianhydride, the inorganic filler has an amount of 10 weight parts to 30 weight parts.
The method according to any of claims 18-21, wherein the inorganic filler has a particle diameter of 0.2 μm to 5 μm.
The method according to any of claims 10-22, wherein a molar ratio between the diamine and the tetracarboxyl dianhydride is from 1:0.85 to 1:1.1.
The method according to claim 23, wherein the molar ratio between the diamine and the tetracarboxyl dianhydride is from 1:0.9 to 1:1.05.
The method according to any of claims 10-24, wherein the diamine comprises at least one selected from a group consisting of p-phenylenediamine, 3, 4'-diaminodiphenyl ether, 4, 4'-diaminodiphenyl ether, 4, 4'-diaminodiphenyl sulfone, 1, 4-bi (4-aminophenoxy) benzene, 2, 2'-bi [4- (4-aminophenoxy) phenyl] propane, and bi [4- (4-aminophenoxy) phenyl] sulfone.
The method according to any of claims 10-25, wherein the tetracarboxyl dianhydride comprises at least one selected from a group consisting of pyromellitic dianhydride, diphenyl ether tetracarboxylic dianhydride, biphenyl tetracarboxylic diandhydride, dibenzophenonetetracarboxylic dianhydride, and 2, 2'-bi [4- (3, 4-dicarboxylphenoxyl) phenyl] propane dianhydride.
The method according to any of claims 10-26, wherein the polyamide acid slurry coated on the substrate has a thickness of 100 μm to 1500 μm.
The method according to any of claims 10-27, wherein the imidization comprises a first imidization and a second imidization,

the first imidization comprises heating the polyamide acid slurry from a first temperature of 30℃ to 45℃ to a second temperature of 160℃ to 180℃ at a rate of 6℃/min to 10℃/min, and

the second imidization comprises heating the polyamide acid slurry from a third temperature of 20℃ to 40℃ to a fourth temperature of 320℃ to 350℃ at a rate of 4℃/min to 6℃/min, and keeping the polyamide acid slurry at the fourth temperature for 50 min to 70 min.
A method of preparing a flexible circuit board, comprising

subjecting a surface of a polyimide film to a laser irradiation with the polyimide film being any one of claims 1-9 or prepared by the method according to any of claims 10-28, and

subjecting the surface of the polyimide film to chemical plating.
The method according to claim 29, wherein the laser has wavelength of 800 nm to 2500 nm.
The method according to claim 29 or 30, wherein the laser has a scanning speed of 500mm/s to 8000mm/s.
The method according to any of claims 29-31, wherein the laser has a power of 3W to 20W.
The method according to any of claims 29-32, further comprising forming a hole in the polyimide film before the chemical plating.
A flexible circuit board prepared by a method according to any of claims 29-33.