CN109451658B

CN109451658B - Flexible circuit board and preparation method

Info

Publication number: CN109451658B
Application number: CN201811452259.4A
Authority: CN
Inventors: 由龙; 赵伟业; 林翠盈; 顾婧文
Original assignee: Shenzhen Knq Technology Co ltd
Current assignee: Shenzhen Knq Technology Co ltd
Priority date: 2018-11-30
Filing date: 2018-11-30
Publication date: 2021-09-28
Anticipated expiration: 2038-11-30
Also published as: CN109451658A

Abstract

The invention provides a flexible circuit board, which is characterized in that a first covering adhesive film, a shielding film, a base material and a second covering adhesive film are sequentially laminated and combined; the first cover glued membrane, the second covers the glued membrane and all includes the carrier layer and the protective layer of relative setting to and set up the carrier layer with black glue film between the protective layer, wherein, with the total weight of black glue film is 100%, black glue film includes the following weight portions's raw materials component: 55 to 70 percent of modified epoxy resin, 5 to 25 percent of accelerant, 5 to 20 percent of dye and 5 to 10 percent of matte powder. The prepared flexible circuit board has controllable thickness, high product stability, good ductility, enhanced tensile property and difficult damage, and effectively solves the problem that the polyimide film needs to be imported.

Description

Flexible circuit board and preparation method

Technical Field

The invention relates to the technical field of printed circuit board production, in particular to a flexible circuit board for a wireless charger and a preparation method thereof.

Background

With the development of electronic technology, electronic devices such as mobile phones, tablet computers and cameras become an indispensable part of people's daily life, and people have higher and higher requirements for the electronic devices. In order to meet the requirements of people, a wireless charging technology is gradually applied to electronic equipment, and the wireless charging technology can transmit energy through electromagnetic waves, so that the wireless charging of the electronic equipment by a wireless charger is realized, and the convenience of the charging process of the electronic equipment is improved.

The wireless charger is a charger which is connected to a terminal device to be charged without a traditional charging power line, adopts the latest wireless charging technology, transmits electric energy by using an alternating magnetic field generated between coils, and an inductive coupling technology can be a bridge for connecting a charging base station and the device.

At present, a flexible circuit board is generally used for a mobile terminal wireless charger, and a wireless charging coil is generally included in the flexible circuit board, and a carrier Polyimide (PI) film of a metal coil is generally included in the wireless charging coil, and coils on both sides of the PI film are covered with a PI insulator covering film on the outer side of the coil. The PI insulating cover film is large in thickness and occupies the thickness space of the coil. Secondly, the preparation process of the PI insulating film is very complex, a layer of polyethylene (AD) film is usually covered on the black PI film, and the requirements on the cleanliness, static electricity and design precision of external conditions are strict in the film covering process, so that dust and composite bubbles are easily brought in; during production and coating, the thickness of the adhesive layer is only 5um, so that the requirements on equipment precision and external conditions are also strict, the requirement on curing parameters and process temperature control is also high due to the fact that the adhesive is too thin, and in the preparation process, the traditional pressing process can easily cause the cover film to blister and wrinkle and be easily damaged due to extrusion.

Disclosure of Invention

The invention aims to provide a flexible circuit board, and aims to solve the problems that a covering film of the existing flexible circuit board is expensive in raw material, easy to foam, wrinkle and deform in the preparation process and the like.

In order to achieve the purpose, the invention adopts the following technical scheme:

a flexible circuit board is characterized in that a first covering adhesive film, a shielding film, a base material and a second covering adhesive film are sequentially laminated and combined; the first cover adhesive film and the second cover film respectively comprise a carrier layer and a protective layer which are arranged oppositely, and a black adhesive layer arranged between the carrier layer and the protective layer; the black glue layer comprises the following raw material components in parts by weight, wherein the total weight of the black glue layer is 100 percent: 55 to 70 percent of modified epoxy resin, 5 to 25 percent of accelerant, 5 to 20 percent of dye and 5 to 10 percent of matte powder.

Compared with the prior art, the flexible circuit board provided by the invention is sequentially laminated and combined with the first covering adhesive film, the shielding film, the base material and the second covering adhesive film. The first cover adhesive film and the second cover film respectively comprise a carrier layer and a protective layer which are arranged oppositely, and a black adhesive layer arranged between the carrier layer and the protective layer, wherein the black adhesive layer comprises the following raw material components in parts by weight based on the total weight of the black adhesive layer being 100 percent: 55 to 70 percent of modified epoxy resin, 5 to 25 percent of accelerant, 5 to 20 percent of dye and 5 to 10 percent of matte powder. The modified epoxy resin added into the black adhesive layer has good toughness, can improve ductility, keeps toughness in the stretching process, is not easy to break, has certain adhesion, does not need to add an adhesive material during film covering, can ensure that a coating plane is flat and smooth in the coating process, and the obtained filling adhesive material does not have the expansion and shrinkage phenomenon; the added accelerant can promote the forming speed of the filling adhesive, ensures the uniform speed of the filling adhesive when the filling adhesive is solidified, and is not easy to age. The prepared covering adhesive film has viscosity, can directly replace a composite film structure of 5 mu m black Polyimide (PI) +5 mu m polyethylene (AD) (or 8 mu m black PI +5 mu mAD) in the prior art, does not need to add other adhesives in the preparation process, and can effectively avoid the problem that the performance of the flexible circuit board is reduced due to the bad effects of foaming, wrinkling, deformation and the like of the prepared film. The prepared flexible circuit board has controllable thickness, high product stability, good ductility, enhanced tensile property and difficult damage, and effectively solves the problem that the polyimide film needs to be imported.

Drawings

Fig. 1 is a schematic structural diagram of a flexible circuit board according to an embodiment of the present invention.

Fig. 2 is a schematic structural diagram of a flexible circuit board according to an embodiment of the present invention.

Fig. 3 is a schematic structural diagram of a substrate of a flexible circuit board according to an embodiment of the present invention.

The reference numbers in the figures denote: 1-covering a glue film; 2-a substrate; 3-a shielding film; 4-covering the adhesive film. 21-a second magnetic core; 22-a coil; 23-a substrate; 24-first magnetic core.

Detailed Description

In order to make the objects, technical solutions and technical effects of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments obtained by a person of ordinary skill in the art without any inventive step in connection with the embodiments of the present invention shall fall within the scope of protection of the present invention.

In the description of the present invention, it is to be understood that the terms "first", "second" and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implying any number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.

The invention provides a flexible circuit board, which is characterized in that a first covering adhesive film, a shielding film, a base material and a second covering adhesive film are sequentially laminated and combined; the first cover adhesive film and the second cover film respectively comprise a carrier layer and a protective layer which are arranged oppositely, and a black adhesive layer arranged between the carrier layer and the protective layer; the black glue layer comprises the following raw material components in parts by weight, wherein the total weight of the black glue layer is 100 percent: 55 to 70 percent of modified epoxy resin, 5 to 25 percent of accelerant, 5 to 20 percent of dye and 5 to 10 percent of matte powder.

Specifically, the black rubber layer comprises the following raw material components in parts by weight: 55 to 70 percent of modified epoxy resin, 5 to 25 percent of accelerant, 5 to 20 percent of dye and 5 to 10 percent of matte powder.

Specifically, the modified epoxy resin is obtained by reacting an organic solvent with a resin to improve the properties of the epoxy resin. The modified epoxy resin obtained by modification can improve the impact toughness, heat resistance and flame resistance of the material, and can prolong the service life and storage life.

Preferably, the modified epoxy resin comprises the following components in parts by weight: 20 to 30 percent of epoxy resin, 40 to 60 percent of diluent and 5 to 10 percent of flame retardant. Specifically, the epoxy resin material has the advantages of high density, water resistance, good leakage resistance, high strength and the like, so that the performance of the black adhesive layer can be more stable by selecting the epoxy resin material AS the main material of the filling adhesive, and in the preferred embodiment of the invention, the resin is preferably AS resin. However, the flame retardant effect of epoxy resin is poor, and the general flame retardant epoxy resin is a resin containing a flame retardant group and prepared from halogen-containing and phosphorus-containing monomers, so that the pollution is large in the preparation process, and the reaction is complex. In order to improve the flame retardant property of the epoxy resin, the prepared black glue layer has better impact toughness, heat resistance and flame resistance, and the service life and the storage life are prolonged. Preferably, the addition amount of the epoxy resin is 20-30%, and if the addition amount of the epoxy resin is increased, the black glue layer is difficult to solidify in the subsequent preparation process, so that the performance of the black glue layer is poor; if the addition amount of the epoxy resin is reduced, the curing is accelerated in the black glue layer forming process, so that the glue body cannot be used due to aging.

Further, a flame retardant is added to the epoxy resin, and the preferable component of the flame retardant is Al (OH)₃Relative density 2.42, Mohs hardness 3.0. It has the features of no toxicity, no smell, high dispersivity, high whiteness, low iron content, etc. and is one kind of inorganic fire retardant with three functions of fire retarding, eliminating smoke, filling, no secondary pollution during burning, no toxic and corrosive gas produced during pyrolysis, heat absorption and water vapor release, and self extinguishing.

The following reactions generally occur when aluminum hydroxide is used as a flame retardant:

the flame retardant effect of the aluminum hydroxide is derived from the principle of three-molecule crystallization moisture desorption heat, on one hand, the aluminum hydroxide is dehydrated and decomposed by heating, the heat absorption capacity reaches 1967.2J/kg, and the temperature rise and the thermal degradation of the polymer can be effectively inhibited. On the other hand, the aluminum hydroxide decomposes to release a large amount of water vapor which can dilute the combustible gas and inhibit the combustion spread, and the double-layer crystal structure of the aluminum hydroxide which is tightly packed can capture hydroxyl radicals which initiate the combustion of the polymer and break off the chain reaction. And moreover, after the aluminum hydroxide is dehydrated, a high-temperature resistant compact dichloro-trioxide protective film is formed on the surface of the polymer, so that air is isolated to prevent flame from spreading. The high-temperature resistant compact aluminum oxide protective film can also promote the carbonization of polymers, adsorb solid particles and inhibit the generation of dense smoke. By adding the flame retardant into the epoxy resin, the flame retardant property of the epoxy resin is improved, and the characteristics of high temperature resistance, good mechanical strength and the like of the epoxy resin can be maintained. If the flame retardant component in the black glue layer is too high, the addition amount of other substances can be reduced to a certain extent, wherein the addition amount of the epoxy resin is mainly reduced, so that the black glue layer is difficult to cure during formation; if the amount of the flame retardant is reduced, the flame retardant effect of the black adhesive layer cannot be further improved.

Further, the diluent is selected from organic solvents for dissolving the epoxy resin. The organic solvent can be selected from aromatic organic solvents and alcohol organic solvents, the preferable organic solvent is toluene and methanol, in the preferable embodiment of the invention, the addition amount of the diluent is preferably a mixed solution of 20-30% of toluene and 20-30% of methanol, the addition of the organic solvent can promote the modification of the resin, and meanwhile, in the later heating process, the organic solvent is easy to volatilize under the action of high temperature and can not affect the material.

In a specific embodiment, the addition amount of the modified epoxy resin is 55-70%. If the addition amount of the modified epoxy resin is too high, in the subsequent processing process, due to the fact that the components of the resin are high, the curing effect is poor due to the excessive resin in the heating forming process, and the forming of the black adhesive layer is affected; if the addition amount is too small, the prepared black glue layer has poor toughness, low tensile strength, easy embrittlement in the use process and short service life.

Preferably, the accelerator comprises the following components in parts by weight: 80-90 percent of modified epoxy resin and 3-10 percent of accelerant. Wherein the modified epoxy resin is the modified epoxy resin. The modified epoxy resin is added into the accelerant, so that the substances can be fully and uniformly mixed in a semi-finished product stage, and the reaction speed is uniform in the reaction process of the filling adhesive; if the substances are directly and independently added, the substances are not uniformly mixed when the black glue layer is prepared, and the performance of the product obtained by the reaction is poor. Specifically, the accelerator is added to improve the reaction efficiency and accelerate the generation of the black glue layer. Specifically, the accelerator is an epoxy resin accelerator, which is a substance for accelerating the reaction rate of the hot-melt resin. Furthermore, the accelerator can be selected from organic accelerators preferably, the organic accelerator has high efficiency, the physical and mechanical properties of the black glue layer are improved, and the application is wider. The main organic accelerators include 2-methylimidazole, 2-ethylimidazole, 2-ethyl-4-methylimidazole, 2-isopropylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole and the like, and in a preferred embodiment of the present invention, the accelerator is preferably added with 2-methylimidazole. The accelerant is added into the black glue layer material, so that the reaction of the hot-melt black glue layer can be greatly accelerated, the melting temperature is reduced, the melting time is shortened, and the corresponding properties of the hot-melt resin, such as physical and mechanical properties, chemical properties, appearance and the like, are improved.

In a specific embodiment, the addition amount of the accelerator is 5% to 25%. If the addition amount of the accelerator is small, the curing and forming time of the black adhesive layer is prolonged during reaction and forming, and the colloid substance is easy to age and cannot maintain good performance due to long-time reaction; if the addition amount of the accelerator is large, the formed black glue layer has poor toughness, low tensile strength and poor later-stage use effect.

Preferably, the dye comprises 30-40% of carbon black and 40-60% of diluent. Specifically, carbon black is used as one of the dye substances of the preferred embodiment of the present invention. Since carbon black is a light, loose and extremely fine black powder, the surface area of the powder is very large, and the powder can be mixed with other substances well and attached to the surface of the substance. In a preferred embodiment of the present invention, the selected carbon black particle size is 2um or less. The finer the particle diameter of the carbon black, the higher the degree of light absorption, and the better the blackness thereof can be exhibited. Further, the selected type of the diluent is consistent with the diluent, and the diluent comprises an aromatic organic solvent and an alcohol organic solvent. In a preferred embodiment of the invention, the diluent preferably added is methanol. Because methanol is a simpler alcohol organic solvent, the methanol is kept consistent with the diluent in the using process, and the black glue layer can be ensured not to introduce excessive other impurities.

In a specific embodiment, the addition amount of the dye is 5-20%. If the addition amount is too small, the dye powder cannot be fully mixed with the modified epoxy resin, so that the color of the black glue layer is not uniform, and the color forming effect of the black glue layer is poor; if the addition amount is too large, the content of other components is reduced, so that the prepared black glue layer cannot maintain good tensile strength and is poor in flexibility.

Specifically, the addition amount of the matte powder is 5-10%. Preferably, the matte powder comprises the following components in parts by weight: 80-90% of the modified epoxy resin and 5-10% of matte powder. Wherein the modified epoxy resin is prepared by the method. Because the addition amount of the matte powder in the black glue layer is small, and the particle size of the matte powder is small and light, the matte powder is easy to mix unevenly when being directly added into the black glue layer, so that the glossiness of the black glue layer is poor; therefore, the matte powder is uniformly mixed in the black adhesive layer by mixing the matte powder with the modified epoxy resin, so that the formed black adhesive layer is excellent in color and luster degree, dark in color and free of reflecting black, and the product is excellent in color and luster. Meanwhile, the added matte powder is stable in property, and the stability of the black glue layer is further ensured.

In the black glue layer, the added modified epoxy resin has good toughness, can improve ductility at the same time, keeps the toughness in the stretching process, is not easy to break, has certain adhesiveness, does not need to add an adhesive material additionally during film coating, can ensure that the coating plane is flat and smooth in the coating process, and the obtained black glue layer material does not have the expansion and shrinkage phenomenon; the added accelerant can promote the forming speed of the filling adhesive, ensures the uniform speed of the filling adhesive when the filling adhesive is solidified, and is not easy to age; can directly replace the materials of 5 mu m black polyimide and 5 mu m polyethylene in the ultrathin covering film in the prior art.

Correspondingly, the specific embodiment of the invention also provides a preparation method of the black glue layer. The method comprises the following steps:

s01: weighing the components according to the black adhesive layer;

s02: mixing the weighed modified epoxy resin, the accelerator, the dye and the matte powder to obtain a first mixed material;

s03: placing the first mixed material in a high-speed dispersion machine for dispersion treatment to obtain a second mixed material;

s04: and filtering the second mixed material to obtain the black glue layer.

Specifically, the preferred content and type of the components of the ebonite layer in the step S01 are as described above, and will not be described herein for brevity.

In the step S02, the mixing process may be performed according to a conventional mixing manner, such as stirring, as long as the components are uniformly mixed.

In the step S03, the first mixed material is placed in a high-speed disperser and dispersed to obtain a second mixed material. Specifically, in the step of performing dispersion treatment by the high-speed dispersion machine, the rotating speed of the high-speed dispersion machine is 800-; the dispersion time is 3-5 h. If the rotating speed of the high-speed dispersion machine is too low, poor system stability can be caused, a large amount of aggregates are generated, the system viscosity is high, and the filtering performance is poor; if the rotating speed of the high-speed dispersion machine is too high, the material particles are too small, and the later-stage product molding is not facilitated. When the rotating speed of the high-speed dispersion machine is 800-.

Preferably, a constant temperature water tank is added to the high-speed disperser during the dispersing process by the high-speed disperser. Because high-speed dispersion machine operation in-process, high-speed rotatory leads to the material temperature to rise, in order to avoid dispersion in-process high temperature, guarantees the good performance of material, consequently increases the constant temperature basin and cools down in reaction process. In the preferred embodiment of the present invention, the temperature of the constant temperature water tank is 20-25 ℃. If the temperature is too high, the material can be directly molded, and meanwhile, the performance of the black adhesive layer can be influenced by too high temperature, so that the black adhesive layer cannot be used; if the temperature is too low, the reaction rate is too slow and the rate is too low.

Specifically, in step S04, the second mixture is filtered, and in this step, the second mixture is filtered using a filter screen having a pore size of 5 to 10 μm. If the aperture of the filter screen is too large, particles with larger particle sizes exist in the black glue layer, which is not beneficial to forming the black glue layer, and the surface of the formed black glue layer is uneven, which is not beneficial to using later-stage products; if the filtration pore size is too small, the filtration rate is affected and the filtration effect is also likely to be poor.

According to the preparation method of the black adhesive layer, the components are mixed according to the proportion, and then are dispersed by the high-speed dispersing machine and then are filtered, so that the components can be uniformly dispersed, and the beneficial effects of the black adhesive layer are realized, and meanwhile, the black adhesive layer is endowed with stable performance. In addition, the preparation method has simple process, controllable conditions and low equipment requirement, and can be used for industrial production.

Specifically, the first cover adhesive film and the second cover adhesive film stacked on the flexible circuit board respectively comprise a carrier layer and a protective layer which are arranged oppositely, and a black adhesive layer arranged between the carrier layer and the protective layer.

Preferably, the thickness of the black glue layer is 5-15 μm. The thickness of the material is controllable, and the material can be prepared according to actual requirements in the reaction process, so that various requirements are met. If the thickness of the glue layer is too thin, uneven coverage is easily caused in the later-stage overall preparation process of the wireless charging coil, so that the reliability of a product is poor; if the glue layer thickness is too thick, the efficiency of the product is affected, and the glue layer cannot be used for production.

Specifically, the carrier layer mainly provides a substrate for the black glue layer. Preferably, the thickness of the carrier layer is 5 μm to 50 μm. If the thickness of the carrier layer is too thin, the carrier layer is easily damaged in the preparation process, the thin film is uneven, and the performance of the coating film is further influenced.

Preferably, the carrier layer can be any one of a PET release film, a PE release film and an OPP release film. Since the support layer is supported by the black rubber as a support layer, the material preferable as the support layer is required to have high tensile strength, high impact resistance, high toughness, and the like. In a preferred embodiment of the invention, the carrier layer selected is a PET release film.

Specifically, the protective layer covers the surface of the black adhesive, which is far away from the carrier layer, so as to protect the prepared black adhesive layer, and prevent the black adhesive layer from being affected by moisture absorption and the like. Preferably, the thickness of the protective layer is 5-50 μm. If the thickness of the protective layer is too thin, the black glue layer is easy to damage when the surface of the black glue layer is protected, and the protective effect is poor, so that the black glue layer is easy to damage; if the thickness of the protective layer is too thick, material waste is caused in the preparation process, and the cost is further increased. More preferably, the protective layer includes a polyethylene film, a polypropylene film, a polyester film, and a laminated paper. The selected protective layer is insoluble in common solvents at normal temperature, has small water absorption and excellent electrical insulation, and therefore, the protective layer can play a comprehensive protection effect on the black glue layer.

The first covering adhesive film and the second covering adhesive film respectively comprise a carrier layer, a black adhesive layer and a protective layer; the black glue layer has good toughness, so that the prepared first covering glue film and the second covering glue film have good ductility, are not easy to be brittle and are not easy to be broken in the stretching process; meanwhile, the black adhesive layer has good adhesion, so that in the process of preparing the first covering adhesive film and the second covering adhesive film, an adhesive material is not required to be additionally added during film covering, the coating plane can be ensured to be flat and smooth in the coating process, and the obtained first covering adhesive film and the second covering adhesive film cannot expand or contract; the accelerant is added into the black glue layer, so that the forming speed of the black glue layer can be accelerated, the uniform speed in the preparation process of the first covering glue film and the second covering glue film is ensured, meanwhile, the black glue layer is directly coated, the thicknesses of the prepared first covering glue film and the prepared second covering glue film are controllable, and the composite film structure of 5 mu m black Polyimide (PI) +5 mu m polyethylene (AD) (or 8 mu m black PI +5 mu m AD) in the prior art can be completely replaced. Meanwhile, the first cover glue film and the second cover glue film do not need materials such as a black polyimide film and a polyethylene film in the using process, and the problem that the polyimide film needs to be imported is effectively solved.

Correspondingly, the embodiment of the invention also provides a preparation method of the first cover adhesive film and the second cover adhesive film, and the preparation methods are the same and comprise the following steps:

s01, providing a carrier layer;

s02, coating a black glue layer solution on the carrier layer, and baking at 40-120 ℃ to form the black glue layer;

and S03, covering a protective layer on the surface of the black glue layer, which is far away from the carrier layer.

Specifically, the carrier layer in the step S01 is preferably of the same kind and thickness as described above, and will not be described herein again for brevity.

In the above step S02, the preferred type and content of the blackgel layer solution are as described above, and will not be described herein again for brevity. After the black glue layer solution is coated on the carrier layer, baking is carried out at 40-120 ℃, preferably, the baking method is to bake by adopting a tunnel oven, and the tunnel oven is a drying oven which is dried by adopting a long-box hot air circulation and far infrared drying mode, and is characterized in that firstly, a heating element of the tunnel oven is arranged at the top end of the drying oven, so that the heat efficiency is improved; secondly, the oven is provided with an electric appliance control cabinet, the temperature is digitally controlled, and the heating process of the substance can be specifically controlled to be in any constant temperature state; thirdly, the material is cooled by purified wind with vertical laminar flow at the outlet, so that the material is in a strict sterile dust-free state. The tunnel type oven is mainly used for meeting the requirements of high yield, high efficiency and high preparation requirements of the prepared covering adhesive film.

Further, the tunnel type oven is divided into six sections, and the temperature of each section is 40 ℃, 60 ℃, 80 ℃, 120 ℃ and 60 ℃ in sequence; the wind frequency of each air-saving inlet is 25Hz, 20Hz and 25Hz in sequence; the air frequency of the exhaust air is 35 Hz. In a specific embodiment, the set temperature of the tunnel type oven is 40-120 ℃, the black adhesive layer is dried at the temperature, the black adhesive layer can be fully solidified at the temperature and the inherent good characteristics of the black adhesive layer can be kept, if the temperature is too low, the black adhesive layer solution can not be well solidified at the beginning, the solidification is not uniform in the subsequent higher-temperature heating process, the flatness of the prepared material is not good, and the effect is poor; if the temperature is too high, because the black adhesive layer is a hot melt adhesive and is easy to melt under the high-temperature condition, when the temperature is higher than 120 ℃, the black adhesive layer can be changed due to the too high temperature, and the subsequent use of covering the adhesive film is not facilitated.

In the preferred embodiment of the invention, the air inlet frequency of the tunnel type oven is 25Hz, 20Hz and 25Hz in sequence; the air frequency of the exhaust air is 35 Hz. Through the air inlet frequency and the air exhaust frequency of the cooperative tunnel type drying oven, the temperature inside the drying oven is uniform, and the black glue layer is favorably baked. If the wind frequency is too large or too small, the temperature in the oven is uneven, the drying of the black glue layer is affected, and the formation of the black glue layer is not facilitated.

The preparation method for the covering adhesive film only needs to coat the solution of the black adhesive layer on the provided carrier layer and bake the solution at 40-120 ℃ to form the black adhesive layer, and the baking method adopts a tunnel type baking oven to bake, wherein the tunnel type baking oven is divided into six sections, and the temperatures of the sections are sequentially set to be 40 ℃, 60 ℃, 80 ℃, 120 ℃ and 60 ℃; the wind frequency of each air-saving inlet is set to be 25Hz, 20Hz and 25Hz in sequence; the air frequency of the exhaust air is 35 Hz. The preparation of the covering adhesive film is achieved by setting the moderate baking temperature and the air inlet and exhaust frequency.

The preparation method is simple in process and controllable in conditions, and can ensure that the prepared covering adhesive film keeps the beneficial effects and is endowed with excellent stability. In addition, the preparation method has low equipment requirement and can be used for industrial production.

Further, an embodiment of the present invention further provides a flexible printed circuit board, where the flexible printed circuit board is sequentially stacked and combined with a first cover adhesive film, a shielding film, a substrate, and a second cover adhesive film.

Specifically, the first cover adhesive film and the second cover adhesive film are respectively arranged on the surface of the base material and used for protecting the surface of the circuit board so as to ensure the stable performance of the flexible circuit board.

Preferably, the thicknesses of the first covering adhesive film and the second covering adhesive film are both 5-50 μm. As flexible circuit boards become more widely used, their properties, including their thickness, are more and more demanding. In the prior art, the cover film is generally a composite film formed by polyimide and polyethylene, the thinnest composite film at present is 5 μm black Polyimide (PI) +5 μm polyethylene (AD) (or 8 μm black PI +5 μm AD), and when the composite film is prepared, 5 μm black polyimide films need to be imported from abroad, and in the preparation process, 5 μm adhesive film polyethylene needs to be covered to form viscosity for bonding, so that the thickness of the ultrathin composite film prepared is not less than 10 μm. In the invention, the covering adhesive film has adhesiveness, and no additional adhesive is needed, so that the prepared covering adhesive film has the preferable thickness of 5-50 μm, the thickness is controllable, and a thinner covering layer can be obtained, thereby being beneficial to the preparation and the use of the flexible circuit board.

Preferably, the substrate comprises: a substrate, a coil, a magnetic core; the coil is tiled and combined on one surface of the substrate, a through hole is formed in the part, corresponding to the inner side of the coil, of the substrate, the magnetic core comprises a first magnetic core and a second magnetic core, the first magnetic core is combined on the surface, deviating from the coil, of the substrate in a stacking mode, and the second magnetic core is connected with the first magnetic core through the through hole. Meanwhile, the size of the second magnetic core is consistent with that of the through hole; and/or the size of the first magnetic core is consistent with that of the substrate.

Preferably, the base material includes, but is not limited to, a flexible copper foil substrate (FCCL), and the flexible copper foil can be used for preparing a traditional three-layer flexible printed circuit board substrate (3L-FCCL) and can also be used for preparing a two-layer flexible printed circuit board substrate (2L-FCCL). Therefore, the prepared flexible circuit board is lighter and thinner and has better flexibility. Further, the substrate has a coil-shaped wiring pattern, and the pitch between the wirings is not less than 10 μm. The circuit spacing is large, and the problems of unstable resistance and large fluctuation of the traditional flexible circuit board due to the fact that the circuit spacing is too small in the using process are solved.

Preferably, the magnetic core material includes, but is not limited to, ferrite. Because the ferrite has high resistivity, high dielectric property and higher magnetic conductivity, the ferrite is used as a magnetic core material in the using process of the flexible circuit board, so that the prepared flexible circuit board has higher magnetic conductivity and dielectric property and better performance.

Specifically, the shielding film is used for shielding external interference on the magnetic field inside the flexible circuit board so as to ensure that the magnetic field inside the flexible circuit board is stable. In a preferred embodiment of the invention, the material of the barrier film is preferably graphite.

Preferably, the flexible circuit board has a thickness of not less than 10 μm. If the prepared circuit board is too thin, the product has poor structural stability, is easy to damage and has short service life, and the characteristics of the circuit board are easy to influence, so that the performance of the circuit board is unstable, the fluctuation is large, and the use is influenced. Preferably, the circuit board can be used in wireless chargers, display screens, transfer screens and other devices.

In summary, the flexible circuit board prepared by the invention is sequentially laminated with the first cover adhesive film, the shielding film, the base material and the second cover adhesive film; the first cover adhesive film and the second cover film respectively comprise a carrier layer and a protective layer which are arranged oppositely, and a black adhesive layer arranged between the carrier layer and the protective layer; the black glue layer comprises the following raw material components in parts by weight, wherein the total weight of the black glue layer is 100 percent: 55 to 70 percent of modified epoxy resin, 5 to 25 percent of accelerant, 5 to 20 percent of dye and 5 to 10 percent of matte powder. The modified epoxy resin added into the black glue layer has good toughness, can improve ductility, keeps toughness in the stretching process, is not easy to break, has certain adhesion, does not need to add an adhesive material during film covering, can ensure that a coating plane is flat and smooth in the coating process, and the obtained black glue layer material does not have the expansion and shrinkage phenomenon; the added accelerant can promote the forming speed of the black glue layer, ensures the uniform speed of the black glue layer when the black glue layer is solidified, and is not easy to age. The prepared covering adhesive film has viscosity, can directly replace a composite film structure of 5 mu m black Polyimide (PI) +5 mu m polyethylene (AD) (or 8 mu m black PI +5 mu m AD) in the prior art, does not need to add other adhesives in the using process, and can effectively avoid the problem that the performance of the flexible circuit board is reduced due to the bad effects of foaming, wrinkling, deformation and the like of the prepared covering adhesive film. The prepared flexible circuit board has controllable thickness, high product stability, good ductility, enhanced tensile property and difficult damage, and effectively solves the problem that the polyimide film needs to be imported.

The following examples are given to further illustrate

Referring to fig. 1 or fig. 2 in the specification, an embodiment of the present invention provides a flexible printed circuit board, in which a first cover adhesive film 4, a shielding film 3, a substrate 2, and a second cover adhesive film 1 are sequentially stacked.

Referring to fig. 3, an embodiment of the present invention provides a schematic structural diagram of a substrate 2 of a flexible circuit board, where the substrate 2 includes: a substrate 23, a coil 22, a first magnetic core 24, a second magnetic core 21; the coil 22 is tiled and combined on one surface of the substrate 23, a through hole is formed in a portion of the substrate 23 corresponding to the inner side of the coil 22, the magnetic core includes a first magnetic core 24 and a second magnetic core 21, the first magnetic core 24 is laminated and combined on a surface of the substrate 23 departing from the coil 22, and the second magnetic core 21 is connected with the first magnetic core 24 through the through hole.

Example 1

The content of the components of the filling adhesive for the wireless charging coil diaphragm and the preparation method thereof. Wherein, the filling glue component used for the wireless charging coil diaphragm comprises the following components in percentage by weight in the following table 1. Wherein, the modified epoxy resin comprises the following components: 30% resin AS-60, 30% toluene, 30% methanol, 10% aluminum hydroxide; the accelerator used comprises the components: 90% of modified epoxy resin and 10% of 2-methylimidazole. The dye used comprises the components: 40% carbon black, 60% methanol. The matte powder comprises the following components: 90% of modified epoxy resin and 10% of matte powder.

The preparation method of the filling adhesive for the wireless charging coil diaphragm comprises the following steps: respectively weighing required substances according to the composition ratio of the components at normal temperature and normal pressure, stirring and mixing 55% of modified epoxy resin, 15% of accelerator, 20% of dye and 10% of matte powder to obtain a first mixed material, and then placing the first mixed material into a high-speed dispersion machine for dispersion treatment to obtain a second mixed material; and filtering the second mixed material to obtain the filling adhesive.

The wireless charging coil diaphragm obtained by further preparation comprises a 5-micrometer PET release film and a 5-micrometer polyethylene film which are oppositely arranged, and a 5-micrometer filling adhesive layer arranged between the PET release film and the polyethylene film, wherein the filling adhesive layer is the filling adhesive obtained by the preparation.

The preparation method for the wireless charging coil diaphragm comprises the following steps: providing a PET release film, coating a filling adhesive solution on the PET release film, baking the filling adhesive solution into a filling adhesive layer, and covering a polyethylene film on the surface of the filling adhesive layer, which is far away from the PET release film; wherein the specific baking conditions are as follows: setting the temperatures of all sections of the tunnel type drying oven to be 40 ℃, 60 ℃, 80 ℃, 120 ℃ and 60 ℃ in sequence; the wind frequency of each air-saving inlet is 25Hz, 20Hz and 25Hz in sequence; the air frequency of the exhaust air is 35 Hz.

And further preparing a flexible circuit board of the wireless charger, wherein the flexible circuit board is sequentially combined with a 15-micrometer first wireless charging coil diaphragm, a 5-micrometer graphite shielding film, a 5-micrometer base material and a 15-micrometer second wireless charging coil diaphragm in a stacking manner, and the first wireless charging coil diaphragm and the second wireless charging coil diaphragm are prepared from the filling glue.

Example 2

The preparation method of the filling adhesive for the wireless charging coil diaphragm comprises the following steps: under normal temperature and normal pressure, respectively weighing required substances according to the composition proportion of the components, stirring and mixing 66% of modified epoxy resin, 20% of accelerator, 10% of dye and 10% of matte powder to obtain a first mixed material, and then placing the first mixed material into a high-speed dispersion machine for dispersion treatment to obtain a second mixed material; and filtering the second mixed material to obtain the filling adhesive.

The wireless charging coil diaphragm obtained by further preparation comprises a 5-micrometer PET release film and a 5-micrometer polyethylene film which are arranged oppositely, and an 8-micrometer filling adhesive layer arranged between the PET release film and the polyethylene film, wherein the filling adhesive layer is the filling adhesive obtained by the preparation.

And further preparing a flexible circuit board of the wireless charger, wherein the flexible circuit board is sequentially combined with a first 18-micrometer wireless charging coil diaphragm, a 5-micrometer graphite shielding film, a 5-micrometer substrate and a second 18-micrometer wireless charging coil diaphragm in a stacking manner, and the first wireless charging coil diaphragm and the second wireless charging coil diaphragm are prepared from the filling glue.

Example 3

The preparation method of the filling adhesive for the wireless charging coil diaphragm comprises the following steps: under normal temperature and normal pressure, respectively weighing required substances according to the composition proportion of the components, stirring and mixing 60% of modified epoxy resin, 15% of accelerator, 20% of dye and 5% of matte powder to obtain a first mixed material, and then placing the first mixed material into a high-speed dispersion machine for dispersion treatment to obtain a second mixed material; and filtering the second mixed material to obtain the filling adhesive.

The wireless charging coil diaphragm obtained by further preparation comprises a 5-micrometer PET release film and a 5-micrometer polyethylene film which are arranged oppositely, and a 10-micrometer filling adhesive layer arranged between the PET release film and the polyethylene film, wherein the filling adhesive layer is the filling adhesive obtained by the preparation.

And further preparing a flexible circuit board of the wireless charger, wherein the flexible circuit board is sequentially combined with a 20-micron first wireless charging coil diaphragm, a 5-micron graphite shielding film, a 5-micron base material and a 20-micron second wireless charging coil diaphragm in a stacking manner, and the first wireless charging coil diaphragm and the second wireless charging coil diaphragm are prepared from the filling glue.

TABLE 1 weight parts ratio of each component (%)

The filling adhesives for wireless charging coil diaphragms prepared in examples 1-3 were subjected to performance tests, the test methods are as follows.

The coatings obtained in the above examples were tested as follows:

(1) glue thickness: the thickness of the glue layer of the filling glue prepared in the embodiment 1-3 is measured by a precision micrometer;

(2) tensile strength: the filling adhesive prepared in the above examples 1 to 3 was measured for tensile strength using a universal tensile machine;

(3) solder resistance: the filling adhesive prepared in the above examples 1-3 was reacted in a tin furnace at 300 ℃ for 1 hour and 2 hours, respectively, and the morphology of the filling adhesive was observed;

(4) and (3) testing the peel strength: the filling adhesive prepared in the embodiment 1-3 is bonded with stainless steel, pulled at a constant speed by a universal tensile machine, and the peel strength of the filling adhesive is measured for 1 hour and 2 hours respectively;

(5) glue overflow amount: the underfill prepared in the above examples 1 to 3 was placed in a metallographic microscope to observe the amount of the overflowing resin.

The results are given in table 2 below:

TABLE 2 comparison of Properties of filled gums prepared in examples 1-3

As shown in Table 2, the underfill prepared in each of examples 1 to 3 was analyzed for properties of the adhesive thickness, tensile strength, solder resistance, peel strength, and flash amount 5. Wherein, industry standards specify: the thickness of the prepared glue is 10 +/-2 mu m; the solder resistance test is that the reaction is carried out for 1 hour and 2 hours at 300 ℃, and the obtained glue is qualified if the glue does not bubble; the peel strength is that the filling adhesive is bonded with the stainless steel, and is pulled at a constant speed for 1 hour and 2 hours by a universal pulling machine, and the obtained peel strength is more than or equal to 0.8N/mm, namely the product is qualified; the glue overflow amount is observed in a metallographic microscope, and the glue overflow amount is not more than 0.1mm, namely the glue is qualified.

Specifically, for the determination and analysis of the thickness of the filled adhesive, the thickness of the filled adhesive prepared in example 1 is 12 μm; the thickness of the filling adhesive prepared in example 2 is 12 μm; the thickness of the underfill prepared in example 3 was 11 μm. Compared with the adhesive layer thickness of the industrial standard, the adhesive layer material prepared by the invention has moderate thickness, meets the industrial standard, and is more favorable for preparing the wireless charging coil diaphragm and the flexible circuit board.

Secondly, for the determination and analysis of the filled adhesive tensile strength, the filled adhesive tensile strength prepared in the example 1 is 12N/mm; the tensile strength of the filled adhesive prepared in example 2 is 13.4N/mm; the tensile strength of the filled adhesive prepared in example 3 is 15.47N/mm; therefore, the prepared filling adhesive can keep toughness in the stretching process and is not easy to be broken by pulling; meanwhile, the preparation method can be better applied to the preparation of the wireless charging coil diaphragm and the flexible circuit board.

And (3) analyzing the solder resistance of the filling adhesive, wherein the solder resistance refers to that the filling adhesive is qualified after reacting for 1 hour and 2 hours at 300 ℃ and does not bubble. The filled adhesives prepared in the example 1, the example 2 and the example 3 are respectively reacted for 1 hour and 2 hours at the temperature of 300 ℃, and the obtained filled adhesives are not foamed and are qualified. Therefore, the prepared filling adhesive has good welding resistance, the coating plane can be ensured to be flat and smooth in the coating process, and the expansion and shrinkage phenomena of the prepared filling adhesive material can be avoided; meanwhile, the preparation method can be better applied to the preparation of the wireless charging coil diaphragm and the flexible circuit board.

And (3) analyzing the peel strength of the filling adhesive, wherein the industrial standard specifies that the peel strength is that the filling adhesive is bonded with stainless steel, and the filling adhesive is pulled at a constant speed for 1 hour and 2 hours by a universal pulling machine, and the obtained peel strength is not less than 0.8N/mm, namely the filling adhesive is qualified. According to the data of Table 2, the peel strength of the underfill prepared in example 1 was 1N/mm after pulling for 1 hour; the peel strength of the resulting underfill prepared in example 2 was 1.34N/mm; the peel strength of the resulting underfill prepared in example 3 was 1.12N/mm; after 2 hours of pulling, the peel strength of the underfill prepared in example 1 was 1.1N/mm; the peel strength of the resulting underfill prepared in example 2 was 1.47N/mm; the peel strength of the resulting underfill prepared in example 3 was 1.25N/mm; after pulling for 1 hour and 2 hours, the peel strengths of the filled adhesives prepared in examples 1-3 are all more than or equal to 0.8N/mm and meet the standard. Therefore, the prepared filling adhesive has strong adhesion, so that the prepared wireless charging coil diaphragm and the prepared flexible circuit board have excellent performance.

And analyzing the glue overflow amount of the filling glue, observing the prepared filling glue in a metallographic microscope, and determining that the glue overflow amount is less than or equal to 0.1 mm. The filling adhesives prepared in the embodiments 1-3 are respectively observed in a metallographic microscope, the adhesive overflow amount of the filling adhesives is respectively 0.06mm, 0.03mm and 0.04mm, and the filling adhesives meet the standard that the adhesive overflow amount is less than or equal to 0.1mm in the industry, so that the prepared wireless charging coil diaphragm and the prepared flexible circuit board have excellent performance.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.

Claims

1. The flexible circuit board is characterized in that the flexible circuit board is sequentially laminated with a first covering adhesive film, a shielding film, a base material and a second covering adhesive film; the first cover glued membrane, the second covers the glued membrane and all includes the carrier layer and the protective layer of relative setting to and set up the carrier layer with black glue film between the protective layer, wherein, with the total weight of black glue film is 100%, black glue film includes the following weight portions's raw materials component: 55-70% of modified epoxy resin, 5-25% of accelerant, 5-20% of dye and 5-10% of matte powder; the modified epoxy resin comprises the following raw material components in parts by weight, based on 100% of the total weight of the modified epoxy resin:

20 to 30 percent of epoxy resin

40 to 60 percent of diluent

5 to 10 percent of flame retardant; and, the flame retardant is selected from Al (OH)₃；

Wherein the thickness of the black glue layer is 5-15 μm.

2. The flexible circuit board of claim 1, wherein the accelerator comprises the following components in parts by weight, based on 100% of the total weight of the accelerator:

80 to 90 percent of modified epoxy resin

3 to 10 percent of accelerant.

3. The flexible circuit board of claim 1, wherein the dye comprises the following components in parts by weight, based on 100% of the total weight of the dye:

30 to 40 percent of carbon black

40 to 60 percent of diluent.

4. The flexible circuit board of claim 1, wherein the matte powder comprises the following components in parts by weight, based on 100% of the total weight of the matte powder:

80 to 90 percent of modified epoxy resin

5 to 10 percent of matte powder.

5. The flexible circuit board of any one of claims 1 to 4, wherein the thickness of the first cover adhesive film is 5 μm to 50 μm; and/or

The thickness of the second covering adhesive film is 5-50 mu m.

6. The flexible circuit board according to any one of claims 1 to 4, wherein the base material comprises: a substrate, a coil, a magnetic core; the coil is tiled and combined on one surface of the substrate, a through hole is formed in the part, corresponding to the inner side of the coil, of the substrate, the magnetic core comprises a first magnetic core and a second magnetic core, the first magnetic core is combined on the surface, deviating from the coil, of the substrate in a stacking mode, and the second magnetic core is connected with the first magnetic core through the through hole.

7. The flexible circuit board of claim 6, wherein the size of the second magnetic core is consistent with the size of the through hole; and/or the presence of a gas in the gas,

the size of the first magnetic core is consistent with that of the substrate.

8. The flexible circuit board according to any one of claims 1 to 4, wherein the thickness of the flexible circuit board is not less than 10 μm.