TWI765306B - Flexible printed circuits having high electromagnetic shielding property and preparing methods thereof - Google Patents

Abstract

A flexible printed circuit board having high electromagnetic shielding property comprises a cover film and a flexible copper foil substrate. The cover film comprises a first insulation layer, a second insulation layer, an adhesive layer, a copper foil layer and a first resin layer and a second resin layer. The adhesive layer is disposed between the first insulation layer and the copper foil layer, the copper foil layer is disposed between the adhesive layer and the first resin layer, the first resin layer is disposed between the copper foil layer and the second insulation layer, and the second insulation layer is disposed between the first resin layer and the second resin layer. The cover film has a through hole filing with electro conductive pastes. The present invention further provides a preparing method of the flexible printed circuit board.

Description

Flexible printed circuit board with high electromagnetic shielding performance and preparation method thereof

The present invention relates to the technical field of flexible printed circuit boards, in particular to a flexible printed circuit board with high electromagnetic shielding performance.

Under the current market demand for multi-functional and complex electronic and communication products, thinner and shorter circuit board structures are required, and with the promotion of 5G, there are more and more requirements for flexible printed circuit boards (FPC). The higher the level, the higher the requirements for the speed of signal transmission and the shielding performance of electromagnetic interference. At the same time, low dielectric constant and low dielectric loss are required, so that the electronic products using the FPC can transmit signals normally and improve their reliability.

In order to meet the requirements of high EMI shielding performance, the EMI shielding rate of the FPC needs to be increased, and in order to increase the EMI shielding rate, the thickness of the copper foil of the EMI shielding structure needs to be increased, and the copper foil layer needs to be formed separately. However, its electromagnetic interference shielding value can only reach a maximum of 85dB. Since the electronic products used in 5G applications require an EMI shielding rate greater than 80dB or even 100dB, the FPC prepared using the aforementioned process cannot meet the requirement of high EMI shielding rate, and The manufacturing process needs to form more pores on the circuit board, and at the same time, it will encounter the problem of the expansion of the conductive adhesive layer and the explosion of the board at high temperature.

In order to solve the above-mentioned problems, the present invention provides a flexible printed circuit board with high electromagnetic shielding performance, which includes a cover film and a flexible copper foil substrate combined with the cover film, the cover film system includes: a first insulating layer, which is greater than 4H surface hardness and thickness of 5 microns to 25 microns; the next layer has a thickness of 5 microns to 20 microns and is formed on the first insulating layer; the copper foil layer has a thickness of 2 microns to 105 microns, and is formed on the adhesive layer, so that the adhesive layer is located between the first insulating layer and the copper foil layer; the first resin layer has a thickness of 8 microns to 50 microns, and is formed on the copper foil layer, so that the The copper foil layer is located between the adhesive layer and the first resin layer; the second insulating layer is formed on the first resin layer, so that the first resin layer is located between the copper foil layer and the second insulating layer, and The second insulating layer has a thickness of 7.5 μm to 100 μm, and its dielectric constant at 10 GHz is lower than 4.0, and its dielectric loss at 10 GHz is lower than 0.015; and the second resin layer has a thickness of 8 μm to 50 μm a thickness of micrometers, and is formed on the second insulating layer, wherein the dielectric constants of the first resin layer and the second resin layer at 10 GHz are respectively lower than 4.0, and the dielectric losses at 10 GHz are respectively 0.002 to 0.010, And the water absorption rates are respectively 0.001% to 0.5%; wherein, the cover film has a through hole filled with conductive paste, and based on the total weight of the conductive paste, the conductive paste includes 40% by weight to 75% by weight. Metal particles and 25% to 60% by weight of a thermosetting adhesive, wherein the metal particles are at least one selected from the group consisting of silver, aluminum, and copper, and the thermosetting adhesive includes epoxy resins, Urea-formaldehyde resin, thermosetting phenolic resin, thermosetting At least one of the group consisting of polyester resin, polysulfide rubber, polyvinyl butyral resin, nitrile rubber, isocyanate and thermosetting polyimide resin.

In an embodiment of the flexible printed circuit board of the present invention, the first resin layer and the second resin layer independently comprise a resin selected from the group consisting of fluorine-based resins, epoxy resins, acrylic resins, and urethane-based resins , at least one resin of the group consisting of silicone rubber resin, parylene resin, bismaleimide resin and thermosetting polyimide resin.

In one embodiment of the flexible printed circuit board of the present invention, the copper foil layer is a thin copper layer with a thickness of 2 to 18 microns or a thick copper layer with a thickness of 105 microns.

In one embodiment of the flexible printed circuit board of the present invention, the thin copper layer is a carrier foil.

In one embodiment of the flexible printed circuit board of the present invention, the first insulating layer is a non-ink layer, and the non-ink layer is selected from the group consisting of epoxy resin, polymethyl methacrylate, polyester, polyamide, etc. Imide, polyimide imide, polyether ether ketone, polyether, polyadipidine diamine, polyurethane, polyphenylene sulfide, polyether imide, polyether imide, polypropylene and polystyrene At least one of the formed groups. In another specific embodiment, the polyester system comprises selected from the group consisting of polyethylene terephthalate, polyethylene terephthalate, polyethylene naphthalate and polycarbonate. at least one of the groups.

In an embodiment of the flexible printed circuit board of the present invention, the first insulating layer is an ink layer.

In one embodiment of the flexible printed circuit board of the present invention, the first insulating layer includes a matting powder, and based on the total weight of the first insulating layer, the content of the matting powder is 5 to 5 wt %. 20% by weight.

In an embodiment of the flexible printed circuit board of the present invention, the second insulating layer comprises a group selected from the group consisting of polyolefin, polyphenylene ether, polyphenylene sulfide, polyimide and polyether ether ketone at least one of them.

In one embodiment of the flexible printed circuit board of the present invention, the adhesive layer comprises epoxy resin, acrylic resin, polyvinyl acetate resin, urethane resin, and silicone rubber. At least one of the group consisting of resin, parylene resin, bismaleimide resin and polyimide resin.

In one embodiment of the flexible printed circuit board of the present invention, the flexible copper foil substrate is bonded to the second resin layer of the cover film.

The present invention further provides a preparation method of the flexible printed circuit board, which comprises: forming a through hole with a diameter of 50 to 400 μm through the cover film; filling the through hole with conductive paste; temperature baking the cover film filled with the conductive paste in the through hole, and the baking time is at least 10 minutes; and pressing the baked cover film and the flexible copper foil substrate, for example, with a pressure of 100kgf/cm ² and 180 The baked cover film and the flexible copper foil substrate are pressed together at a temperature of ±5°C. The pre-pressing time is 10 seconds, and the pressing and forming time is 12 seconds. In addition, after completion of pressing, aging was performed at a temperature of 170° C. to 180° C., and the aging time was 60 minutes.

In one embodiment of the preparation method of the present invention, the through hole is formed by laser drilling, the energy of the laser drilling is 4.5W to 15W, and the number of laser drilling is 4 to 15W. 10 times.

In one embodiment of the preparation method of the present invention, before baking the cover film, the cover film and the flexible copper foil substrate are bonded together.

In one embodiment of the preparation method of the present invention, before forming the through hole, the cover film and the flexible copper foil substrate are firstly bonded. In this embodiment, after laminating the cover film and the flexible copper foil substrate and before forming the through hole, the cover film and the flexible copper foil substrate are pressed together, for example, at a pressure of 100kgf/cm ² and a temperature of 180±5°C. The cover film and the flexible copper foil substrate are pressed together at the same temperature, the pre-pressing time is 10 seconds, and the pressing and forming time is 12 seconds. In addition, after completion of pressing, aging was performed at a temperature of 170° C. to 180° C., and the aging time was 60 minutes.

According to an embodiment of the manufacturing method of the flexible printed circuit board of the present invention, the through hole is formed by mechanical drilling. /min, and the retraction amount is 100 to 750mm/min. In this embodiment, after forming the through hole, the cover film and the flexible copper foil substrate are pressed together, for example, the cover film and the flexible copper foil substrate are pressed together at a pressure of 100kgf/cm ² and a temperature of 180±5°C , the pre-compression time is 10 seconds, and the compression molding time is 12 seconds. In addition, after the lamination is completed, aging is performed at a temperature of 170° C. to 180° C., and the aging time is 60 minutes, and the cured cover film is subjected to chemical gold surface treatment.

The cover film used in the flexible printed circuit board of the present invention can provide a high electromagnetic interference shielding performance of up to 100 dB. In addition, the through holes on the cover film can be used as conductive holes, heat conduction holes and air holes at the same time, and it is not necessary to make air holes on the copper foil as in the existing FPC process, which can also improve the explosion caused by the FPC process using the electromagnetic interference shielding film. The problem of the board, and in the case of using a copper foil layer with a thickness of 35 microns, it can improve the problem of heat generation under 5G high-speed transmission.

On the other hand, the cover film of the flexible printed circuit board of the present invention has low dielectric constant and low dielectric loss, and is suitable as a dielectric layer in an FPC for high-frequency and high-speed transmission, and the cover film and the flexible copper foil substrate are connected to each other. Line insulation, also has the effect of electromagnetic interference shielding.

The manufacturing method of the flexible printed circuit board of the present invention does not require an additional process for forming air holes, which can reduce the manufacturing cost, facilitate rapid production and high-density assembly, and increase the design space of the multi-layer structure.

1: Flexible printed circuit board

100: cover film

101: The first insulating layer

102: Next layer

103: Copper foil layer

104: The first resin layer

105: Second insulating layer

106: Second resin layer

107: The first release layer

108: The second release layer

109: Through hole

110: conductive paste

110a: Metal particles

110b: Thermosetting Adhesives

200: Flexible copper foil substrate

201: The first copper foil layer

202: The first polyimide adhesive layer

203: Polyimide layer

204: The second polyimide layer

205: Second copper foil layer

Embodiments of the invention are described by way of illustrative reference to the accompanying drawings:

FIG. 1 is a schematic diagram of the structure of the flexible printed circuit board of the present invention.

FIG. 2 is a schematic view of the structure of the cover film of the present invention.

The following describes the implementation of the present invention through specific embodiments, and those skilled in the art can easily understand the advantages and effects of the present invention from the contents disclosed in this specification.

It should be noted that the structures, proportions, sizes, etc. shown in the drawings in this specification are only used to cooperate with the contents disclosed in the specification for the understanding and reading of those who are familiar with the art, and are not intended to limit the implementation of the present invention. Therefore, it has no technical significance. Any modification of the structure, change of the proportional relationship or adjustment of the size should still fall within the scope of the present invention without affecting the effect and the purpose that the present invention can achieve. The technical content disclosed by the invention can be covered within the scope. At the same time, references such as "a", "below" and "above" in this specification are only for the convenience of description, and are not intended to limit the scope of the present invention. Substantially changed technical content should also be regarded as the scope of the present invention. also, All ranges and values herein are inclusive and combinable. Any value or point falling within a range described herein, eg, any integer, can be taken as a minimum or maximum value to derive a lower range, etc.

As shown in FIG. 1, it shows a specific embodiment of the flexible printed circuit board 1 of the present invention, which includes a cover film 100 and a flexible copper foil substrate 200, and the cover film 100 has a conductive paste 110 on the cover film. The hole 109, the conductive paste 110 includes metal particles 110a and a thermosetting adhesive 110b, wherein the metal particles 110a are at least one selected from the group consisting of silver, aluminum and copper, and the thermosetting adhesive 110b includes a selected At least one selected from the group consisting of epoxy resin, urea-formaldehyde resin, thermosetting phenolic resin, thermosetting polyester resin, polysulfide rubber, polyvinyl butyral resin, nitrile rubber, isocyanate and thermosetting polyimide resin.

The conductive paste filled in the through hole of the flexible printed circuit board of the present invention uses a thermosetting adhesive with air permeability, so the through hole can be used as a conductive hole or an air hole at the same time, so as to overcome the problem of using an electromagnetic interference shielding film in the existing FPC process. risk.

In an embodiment, the flexible copper foil substrate 200 is bonded to the second resin layer 106 of the cover film 100 .

In a specific embodiment, the flexible copper foil substrate 200 can be, for example, but not limited to, an adhesive substrate, a non-adhesive substrate, or an LCP substrate with a liquid crystal polymer (LCP) core layer as the main structure; The structure from top to bottom is copper foil layer, adhesive layer, polyimide film, adhesive layer and copper foil layer, but not limited to this; the laminated structure of the adhesive-free substrate is copper foil in sequence from top to bottom layer, polyimide film and copper foil layer, but not limited thereto. In another specific embodiment, the LCP substrate can be an adhesive substrate or a non-adhesive substrate, and the stacked structure of the LCP adhesive substrate is a copper foil layer, an adhesive layer, an LCP film, an adhesive layer, and a copper foil layer in sequence from top to bottom. A foil layer, but not limited to this; the laminated structure of the adhesive-free substrate is a copper foil layer, an LCP film and a copper foil layer in sequence from top to bottom, but not limited to this.

In a specific embodiment, the flexible copper foil substrate 200 includes: a first copper foil layer 201 , a first polyimide adhesive layer 202 , a polyimide layer 203 , and a second polyimide adhesive layer 204 and the second copper foil layer 205 . In another embodiment, the first polyimide adhesive layer 202 is located between the first copper foil layer 201 and the polyimide layer 203, and the polyimide layer 203 is located in the first Between the polyimide adhesive layer 202 and the second polyimide adhesive layer 204 , and the second polyimide adhesive layer 204 is located between the polyimide layer 203 and the second copper foil layer 205 . In this embodiment, the first copper foil layer 201 of the flexible copper foil substrate 200 is in contact with the second resin layer 106 of the cover film 100 .

In a specific embodiment, based on the total weight of the conductive paste, the content of the metal particles is 40% to 75% by weight, for example, 40, 45, 50, 55, 60, 65, 70 or 75% by weight %; based on the total weight of the conductive paste, the content of the thermosetting adhesive is 25% to 60% by weight, for example, 25, 30, 35, 40, 45, 50, 55 or 60% by weight.

In a specific embodiment, the cover film 100 includes a first insulating layer 101, an adhesive layer 102, a copper foil layer 103, a first resin layer 104, a second insulating layer 105, and a second resin layer 106. The adhesive layer 102 is located between the first insulating layer 101 and the copper foil layer 103, the copper foil layer 103 is located between the bonding layer 102 and the first resin layer 104, and the first resin layer 104 is located in the copper foil layer 103 Between the second insulating layer 105 , the second insulating layer 105 is located between the first resin layer 104 and the second resin layer 106 .

In one embodiment, the first insulating layer has a thickness of 5 microns to 25 microns, eg, 5, 10, 15, 20 or 25 microns; the second insulating layer has a thickness of 7.5 microns to 100 microns , for example, 7.5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or 100 microns; the adhesive layer has 5 microns to 20 The thickness of microns, for example, 5, 10, 15 or 20 microns; the copper foil layer has a thickness of 2 microns to 105 microns, for example, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20 , 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100 or 105 microns; the first resin layer has a thickness of 8 to 50 microns , for example, 8, 15, 20, 25, 30, 35, 40, 45 or 50 microns; the second resin layer has a thickness of 8 to 50 microns, for example, 8, 15, 20, 25, 30, 35 , 40, 45 or 50 microns.

In an embodiment, the surface hardness of the first insulating layer is greater than 4H.

In one embodiment, the dielectric constant of the second insulating layer at 10 GHz is lower than 4.0, and the dielectric loss at 10 GHz is lower than 0.015.

In an embodiment, the dielectric constants of the first resin layer and the second resin layer at 10 GHz are each lower than 4.0, the dielectric losses at 10 GHz are each 0.002 to 0.010, and the water absorption rates are each 0.001% to 0.5%.

In a specific embodiment, the first resin layer and the second resin layer are independently selected from the group consisting of fluorine-based resins, epoxy resins, acrylic resins, urethane-based resins, silicone rubber-based resins, polypara At least one resin of the group consisting of xylene-based resin, bismaleimide-based resin and thermosetting polyimide resin.

In one embodiment, the copper foil layer is a thin copper layer having a thickness of 2 microns to 18 microns or a thick copper layer up to 105 microns is used. In another embodiment, the thin copper layer is a carrier foil.

In a specific embodiment, the first insulating layer is a non-ink layer, and the non-ink layer comprises epoxy resin, polymethyl methacrylate, polyester, polyimide, polyimide imine, polyether ether ketone, polysaccharide, polyadipidine diamine, polyurethane, polyphenylene sulfide, poly At least one of the group consisting of ether, polyetherimide, polypropylene and polystyrene. In another specific embodiment, the polyester system comprises selected from the group consisting of polyethylene terephthalate, polyethylene terephthalate, polyethylene naphthalate and polycarbonate. at least one of the groups.

In an embodiment, the first insulating layer is an ink layer.

In the specific embodiment in which the first insulating layer is a non-ink layer, the preparation method of the cover film includes: coating a first resin layer on the second insulating layer; pressing a copper foil layer on the first resin on the other surface of the layer; coating the second resin layer on the other surface of the second insulating layer; attaching the lower release layer on the surface of the second resin layer; coating the adhesive layer on the other surface of the copper foil layer a surface; and pressing and curing the first insulating layer on the adhesive layer to obtain the cover film of the present invention.

In the specific embodiment in which the first insulating layer is an ink layer, the preparation method of the cover film includes: coating the first insulating layer on the upper release layer, and winding for standby; coating the first resin layer on the upper release layer. on the second insulating layer; pressing a copper foil layer on the other surface of the first resin layer; coating a second resin layer on the other surface of the second insulating layer; attaching a lower release layer to the The surface of the second resin layer; coating the adhesive layer on the other surface of the copper foil layer; and pressing and curing the adhesive layer on the first insulating layer on the upper release layer to obtain the cover film of the present invention.

As can be seen from the above, the step of forming the upper release layer can be omitted by using the non-ink layer as the cover film of the first insulating layer.

In a specific embodiment, the first insulating layer includes a matting powder, and based on the total weight of the first insulating layer, the content of the matting powder is 5% to 20% by weight, such as 5, 10% by weight. , 15, 20% by weight. In this embodiment, the glossiness or hardness of the first insulating layer can be adjusted by adding matting powder.

In a specific embodiment, the matting powder system is selected from calcium sulfate, carbon black, silicon dioxide, titanium dioxide, zinc sulfide, zirconia, calcium carbonate, silicon carbide, boron nitride, alumina, talc, nitride Inorganic powder of at least one of the group consisting of aluminum, glass powder, quartz powder, emery and clay; or polyimide-based organic powder; or containing compounds selected from halogen-containing compounds, phosphorus-containing compounds, A flame retardant compound of at least one of the group consisting of a nitrogen-containing compound and a boron-containing compound. In another specific embodiment, the matting powder system is selected from polyimide organic powders. In yet another embodiment, the matting powder system is selected from at least one flame retardant compound selected from the group consisting of halogen-containing compounds, phosphorus-containing compounds, nitrogen-containing compounds and boron-containing compounds.

In one embodiment, the second insulating layer includes at least one selected from the group consisting of polyolefin, polyphenylene ether, polyphenylene sulfide, polyimide, and polyether ether ketone.

In a specific embodiment, the adhesive layer comprises epoxy resin, acrylic resin, polyvinyl acetate resin, urethane resin, silicone rubber resin, parylene resin , at least one of the group consisting of bismaleimide resin and polyimide resin.

In a specific embodiment, the cover film 100 further includes a first release layer 107 and a second release layer 108, the first release layer 107 is attached to the first insulating layer 101, and the second release layer 107 The mold layer 108 is attached to the second resin layer 106 . In another embodiment, the thicknesses of the first release layer 107 and the second release layer 108 are respectively 25 μm to 130 μm, for example, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125 or 130 microns.

In a specific embodiment, the first release layer 107 and the second release layer 108 are each selected from one of a release film, a release paper and a carrier film. In another specific embodiment, the release film is at least one selected from the group consisting of PET fluorine release film, PET silicone oil release film, PET matte release film and PE release film. In this embodiment, the thickness of the release film is from 25 microns to 100 microns. In another specific embodiment, the release paper is one of single-sided PET coated paper or double-sided PET coated paper. In this embodiment, the thickness of the release paper is from 25 microns to 130 microns.

The present invention further provides a method for preparing the flexible printed circuit board 1, which includes: forming a through hole with a diameter of 50 to 400 μm through the cover film; filling the through hole with conductive paste; Baking the cover film filled with the conductive paste in the through hole at a temperature of at least 10 minutes; and pressing the baked cover film with a pressure of 100kgf/cm ² and a temperature of 180±5°C For the flexible copper foil substrate, the pre-pressing time is 10 seconds, and the pressing and forming time is 12 seconds. After the pressing is completed, it is cured at a temperature of 170°C to 180°C, and the curing time is 60 minutes.

In the preparation method of the present invention, the conductive paste is partially cured by the low temperature baking, and the gas in the flexible printed circuit board can escape from the through holes due to the incomplete curing of the conductive paste. In addition, in the preparation method of the present invention, through the high temperature lamination step, the moisture contained in the flexible printed circuit board is evaporated into gas, and the gas can escape through the through holes on the cover film to avoid the occurrence of board explosion during the process. problem, and the flexible printed circuit board can be cured at the same time.

In an embodiment, when the through hole is formed, the cover film may be a sheet type or a roll to roll (RTR) type.

In an embodiment, the through hole is formed by laser drilling, the energy of the laser drilling is 4.5W to 15W, and the number of times of the laser drilling is 4 to 10 times.

In a specific embodiment, before baking the cover film, the cover film and the flexible copper foil substrate are bonded together.

In a specific embodiment, before forming the through hole, the cover film and the flexible copper foil substrate are firstly bonded. In this embodiment, after laminating the cover film and the flexible copper foil substrate and before forming the through hole, the cover film and the flexible copper foil substrate are pressed together with a pressure of 100kgf/cm ² and a temperature of 180±5°C , the pre-pressing time is 10 seconds, and the pressing and forming time is 12 seconds. After the pressing is completed, it is aged at a temperature of 170°C to 180°C, and the curing time is 60 minutes.

In a specific embodiment, the through hole is formed by mechanical drilling, the speed of the mechanical drilling is 50 to 155kr/min, the feed rate is 25 to 70mm/min, and the retraction amount is 100 to 750mm /min. In this embodiment, after the through hole is formed, the cover film and the flexible copper foil substrate are pressed together with a pressure of 100kgf/cm ² and a temperature of 180±5°C. The pre-pressing time is 10 seconds, and the pressing and forming time is It is 12 seconds. After the lamination is completed, the aging is carried out at a temperature of 170 ° C to 180 ° C, and the curing time is 60 minutes, and the surface treatment of the cured cover film is carried out. During the treatment, a metal plating layer is formed on the surface of the cover film to prevent oxidation of the metal in the through hole of the cover film.

The stack structure of the flexible printed circuit board of the present invention is shown in FIG. 1 . The first insulating layer 101 and the bonding layer 102 are used as the outer surface of the flexible printed circuit board. The first insulating layer is a black insulating layer with matte powder, which can shield the circuit design. The first release layer 107 can not only be beneficial for rolling and storage, but also provide stiffness, which is beneficial to the subsequent processing of the flexible printed circuit board 1 . In addition, the first insulating layer 101 , the adhesive layer 102 and the first release layer 107 of the present invention do not affect the signal transmission and shielding performance of the flexible printed circuit board 1 .

The following describes the performance of the flexible printed circuit board of the present invention through examples and comparative examples.

Since the first insulating layer and the adhesive layer in the cover film of the present invention do not substantially affect the performance of the flexible printed circuit board 1 , the structures of the first insulating layer and the adhesive layer will be omitted in the following embodiments 1 to 12. Specifically, the preparation methods of the cover films of Examples 1 to 12 include: coating a first resin layer on the second insulating layer; laminating a copper foil layer on the other surface of the first resin layer; and coating The second resin layer is on the other surface of the second insulating layer; after drying and winding, the cover films used in Examples 1 to 12 of the present invention are obtained.

In Examples 1 to 12, the first resin layer and the second resin layer are thermosetting polyimide resins, the dielectric constant at 10 GHz is 2.8, the dielectric loss is 0.003, the water absorption rate is 0.08%, and the Thermosetting polyimide resin is composed of 70% polyimide resin, 8% sintered silica, 3% epoxy resin, 15% phosphorus-based flame retardant and 4% fluorine-based resin; the second insulating layer is The polyimide film (SKCKOLONPI, model FS) had a dielectric constant of 3.1 and a dielectric loss of 0.005 at 10 GHz. In addition, based on the total weight of the conductive paste, the conductive pastes used in Examples 1 to 12 included 70% by weight of silver particles and 30% by weight of epoxy resin, and the silver particles were a combination of flake particles and spherical particles. mixture.

The flexible printed circuit boards of Examples 1 to 4 were prepared by the following method: forming through holes with a diameter of 100 microns from the release layer on the cover film to the direction of the second resin layer by laser drilling. The hole conditions are described in Table 1 below; fill the conductive paste in the through hole; bake at a temperature of 50°C to 60°C, and the baking time is at least 10 minutes; from the cover film after baking The lower release layer is peeled off, and the second resin layer of the cover film is attached to the flexible copper foil substrate; and the pressure is 100kgf/cm ² and the temperature of 180±5℃ is pressed, and the pre-pressing time is 10 Second, the compression molding time is 12 seconds, after the compression is completed, the aging is performed at a temperature of 170°C to 180°C, and the aging time is 60 minutes.

The flexible printed circuit boards of Examples 5 to 8 were prepared by the following methods: peel off the lower release layer from the cover film, and attach the second resin layer of the cover film to the flexible copper foil substrate; The pressure of cm ² and the temperature of 180±5°C are used to press the cover film and the flexible copper foil substrate. The pre-pressing time is 10 seconds, and the pressing time is 12 seconds. After the pressing is completed, the temperature is 170°C to 180°C. Carry out curing, and the curing time is 60 minutes; through laser drilling from the release layer on the cover film to the direction of the second resin layer to form through holes with a diameter of 100 microns, and the conditions for forming through holes are described below. In Table 1; fill the conductive paste in the through hole; bake at a temperature of 50°C to 60°C, and the bake time is at least 10 minutes; and at a pressure of 100kgf/cm ² and a temperature of 180±5°C Pressing is performed, the pre-pressing time is 10 seconds, and the pressing and forming time is 12 seconds. After the pressing is completed, the aging is performed at a temperature of 170°C to 180°C, and the aging time is 60 minutes.

The flexible printed circuit boards of Examples 9 to 12 were prepared by the following methods: the lower release layer was peeled off from the cover film, and the second resin layer was attached to the flexible copper foil substrate; A through hole with a diameter of 100 microns is formed from the release layer on the cover film to the second resin layer. The conditions for forming the through hole are described in Table 1 below; with a pressure of 100kgf/ ^cm2 and a temperature of 180±5℃ The cover film and the flexible copper foil substrate are temperature-bonded, the pre-compression time is 10 seconds, and the compression molding time is 12 seconds. After the lamination is completed, it is cured at a temperature of 170°C to 180°C, and the curing time is 60 minutes; Perform gold surface treatment on the matured cover film; fill the conductive paste in the through hole; bake at a temperature of 50°C to 60°C, and the baking time is at least 10 minutes; and at 100kgf/cm ² The pressure and the temperature of 180±5℃ are pressed, the pre-pressing time is 10 seconds, and the pressing time is 12 seconds. After the pressing is completed, the temperature is 170℃ to 180℃, and the aging time is 60 minutes. .

Table 1: Conditions for forming through holes in Examples 1 to 12

The flexible printed circuit boards of Comparative Examples 1 and 2 use a cover film and a flexible copper foil substrate. The stacking structure from top to bottom is: insulating layer, resin layer and flexible copper foil substrate. The cover film of Comparative Examples 1 and 2 The cover films of Asia Electric Materials Model HFC120 and HFC035 are used. The flexible printed circuit boards of Comparative Examples 3 and 4 use electromagnetic interference shielding films and flexible copper foil substrates. The stacking structure from top to bottom is: copper foil layer, conductive adhesive layer and flexible copper foil substrate. The electromagnetic interference shielding film of 4 is the cover film of Tatsuta model SF-PC 8600 and SF-PC3300 respectively. The flexible copper foil substrates of Comparative Examples 1 to 4 used the same flexible copper foil substrates as those of Examples 1 to 12 of the present invention, and their structures were the same as the flexible copper foil substrates 200 shown in FIG. 1 of the present invention.

Table 2 and Table 3 respectively show the thickness and performance of each layer of the cover films in the flexible printed circuit boards of Examples 1 to 12 and the cover films or electromagnetic interference shielding films in the flexible printed circuit boards of Comparative Examples 1 to 3.

Table 2: Thickness and properties of each layer of the cover films in the flexible printed circuit boards of Examples 1 to 9

Table 3: Thickness and performance of each layer of the cover film or EMI shielding film in the flexible printed circuit boards of Comparative Examples 1 to 3

The test methods for the properties in Tables 2 and 3 above are described below. Resistance value: In accordance with the "Test Guidelines for Items of Flexible Board Assembly" (TPCA-F-002), use a multimeter to measure. Peel Strength: Measured using a universal tester in accordance with IPC-TM-650 2.4.9 (or in accordance with TPCA-F-002). Electromagnetic Interference Shielding: Measured in accordance with International Electrotechnical Commission (IEC) standards. Surface mount welding technology test: The surface mount welding technology test is measured in accordance with TPCA-F-002 or IPC-TM-650 2.4.13. The temperature of the paste soldering technology refers to the temperature at which the product of the example or the comparative example is bleached for 30 seconds, and this temperature is the maximum temperature at which the solderability of the product meets the specification. Dielectric Properties: Measured using a network analyzer and resonant cavity per IPC-TM-650 2.5.5.13.

It can be seen from the above Tables 2 and 3 that the EMI shielding values of Examples 1 to 12 of the present invention are higher than those of Comparative Examples 1 to 4, and the EMI shielding values of Examples 1 to 12 are at least 75, which have High EMI shielding performance. In addition, the dielectric constants and dielectric losses of Examples 1 to 12 of the present invention are higher than those of Comparative Examples 1 to 4, and are suitable as the dielectric layers of flexible printed circuit boards for high-frequency and high-speed transmission. Moreover, the thickness range of the flexible printed circuit board of the present invention is wide, and a thicker dielectric layer can be used to reduce the signal transmission loss at high frequencies.

In addition, the highest temperature tested by the surface mount technology (SMT) of Examples 1 to 12 of the present invention is 288°C, which has good solder heat resistance, and can pass the FPC or PCB process without causing the board to explode. question.

In the existing flexible printed circuit board process, after etching the circuit on the copper foil substrate, it is necessary to attach a pre-hole and punched cover film, and after the cover film and the copper foil substrate are pressed and cured, and then the electromagnetic interference is attached. For the shielding film, after pressing and curing the electromagnetic interference shielding film, air-conducting holes are formed on the flexible printed circuit board, so as to perform the step of baking and dehumidification. Compared with the existing flexible printed circuit board manufacturing process, the flexible printed circuit board prepared by using the cover film of the present invention can prepare a circuit board with low dielectric constant and dielectric loss in fewer steps, reducing the process of multi-layer structure and The process can further improve the cracking problem encountered in the process of using the shielding film, and the flexible printed circuit board has good mechanical properties, which can meet the needs of processing processes such as through-hole and hole-filling.

The above-mentioned embodiments are only illustrative, and are not intended to limit the present invention. Any person skilled in the art can carry out the above-mentioned embodiments without departing from the spirit and scope of the present invention. Line modifications and changes. Therefore, the scope of the right protection of the present invention is defined by the scope of the patent application attached to the present invention, as long as the effect and implementation purpose of the present invention are not affected, it shall be included in the technical content disclosed herein.

1: Flexible printed circuit board

100: cover film

101: The first insulating layer

102: Next layer

103: Copper foil layer

104: The first resin layer

105: Second insulating layer

106: Second resin layer

107: The first release layer

109: Through hole

110: conductive paste

110a: Metal particles

110b: Thermosetting Adhesives

200: Flexible copper foil substrate

201: The first copper foil layer

202: The first polyimide adhesive layer

203: Polyimide layer

204: The second polyimide layer

205: Second copper foil layer

Claims (17)

A flexible printed circuit board with high electromagnetic interference shielding performance includes a cover film and a flexible copper foil substrate combined with the cover film; the cover film system includes: a first insulating layer, which has a surface hardness of greater than 4H and a surface hardness of 5 microns to A thickness of 25 microns; an adhesive layer, which has a thickness of 5 microns to 20 microns, and is formed on the first insulating layer; a copper foil layer, which has a thickness of 2 microns to 105 microns, and is formed on the adhesive layer, The adhesive layer is located between the first insulating layer and the copper foil layer; the first resin layer has a thickness of 8 microns to 50 microns and is formed on the copper foil layer, so that the copper foil layer is located on the adhesive layer and the first resin layer; the second insulating layer is formed on the first resin layer, so that the first resin layer is located between the copper foil layer and the second insulating layer, and the second insulating layer has 7.5 The thickness of micrometer to 100 micrometers, and its dielectric constant at 10GHz is less than 4.0, the dielectric loss at 10GHz is less than 0.015; and the second resin layer has a thickness of 8 micrometers to 50 micrometers, and is formed on On the second insulating layer, the second insulating layer is located between the first resin layer and the second resin layer, wherein the dielectric constants of the first resin layer and the second resin layer at 10 GHz are respectively lower than 4.0 , the dielectric loss at 10GHz is respectively 0.002 to 0.010, and the water absorption rate is respectively 0.001% to 0.5%; wherein, the cover film has a through hole filled with conductive paste, based on the total weight of the conductive paste , the conductive paste comprises 40% to 75% by weight of metal particles and 25% to 60% by weight of a thermosetting adhesive, wherein the metal particles are at least selected from the group consisting of silver, aluminum and copper One, and the thermosetting adhesive is selected from the group consisting of epoxy resins, urea-formaldehyde resins, thermosetting phenolic resins, thermosetting polyester resins, polysulfide rubbers, polyvinyl butyral resins, nitrile rubbers, isocyanates, and thermosetting polyamides At least one of the group consisting of amine resins. The flexible printed circuit board according to claim 1, wherein the first resin layer and the second resin layer independently comprise a resin selected from the group consisting of fluorine resin, epoxy resin, acrylic resin, urethane resin, silicon resin At least one resin of the group consisting of rubber-based resin, parylene-based resin, bismaleimide-based resin and thermosetting polyimide resin. The flexible printed circuit board of claim 1, wherein the copper foil layer is a thin copper layer with a thickness of 2 to 18 microns or a thick copper layer with a thickness of 105 microns. The flexible printed circuit board of claim 3, wherein the thin copper layer is a carrier foil. The flexible printed circuit board as claimed in claim 1, wherein the first insulating layer is a non-ink layer, and the non-ink layer comprises epoxy resin, polymethyl methacrylate, polyethylene terephthalate Diester, polyethylene naphthalate, polycarbonate, polyimide, polyimide, polyether ether ketone, polyether, polyhexamethylenediamine, polycyclohexyl terephthalate At least one of the group consisting of alkane dimethyl ester, polyurethane, polyphenylene sulfide, polyether sulfide, polyetherimide, polypropylene and polystyrene. The flexible printed circuit board according to claim 1, wherein the first insulating layer is an ink layer. The flexible printed circuit board of claim 1, wherein the first insulating layer comprises a matting powder, and based on the total weight of the first insulating layer, the content of the matting powder is 5% to 20% by weight %. The flexible printed circuit board of claim 1, wherein the second insulating layer comprises at least one selected from the group consisting of polyolefin, polyphenylene ether, polyphenylene sulfide, polyimide and polyether ether ketone one. The flexible printed circuit board according to claim 1, wherein the adhesive layer is selected from epoxy resins, acrylic resins, polyvinyl acetate resins, urethane resins, silicone rubber resins, At least one of the group consisting of parylene-based resin, bismaleimide-based resin and polyimide-based resin. The flexible printed circuit board of claim 1, wherein the flexible copper foil substrate is bonded to the second resin layer of the cover film. A method for preparing a flexible printed circuit board as claimed in claim 1, comprising: forming through holes with a diameter of 50 to 400 microns through the cover film; filling the through holes with conductive paste; Bake the cover film filled with the conductive paste in the through hole at a temperature of 60°C for at least 10 minutes; and press the baked cover at a pressure of 100kgf/cm ² and a temperature of 180±5°C For the film and the flexible copper foil substrate, the pre-pressing time is 10 seconds, and the pressing time is 12 seconds. After the pressing is completed, it is aged at a temperature of 170°C to 180°C, and the curing time is 60 minutes. The manufacturing method of a flexible printed circuit board according to claim 11, wherein the through hole is formed by laser drilling, the energy of the laser drilling is 4.5W to 15W, and the number of laser drilling is 4 to 10 times. The method for preparing a flexible printed circuit board according to claim 11, wherein before baking the cover film, the cover film and the flexible copper foil substrate are firstly bonded. The manufacturing method of a flexible printed circuit board according to claim 11, wherein before forming the through hole, the cover film and the flexible copper foil substrate are firstly bonded. The method for preparing a flexible printed circuit board according to claim 14, further comprising laminating the cover film and the flexible copper foil substrate after laminating the cover film and the flexible copper foil substrate and before forming the through hole, and laminating the cover film and the flexible copper foil substrate. After completion, aging is performed at a temperature of 170°C to 180°C. The manufacturing method of a flexible printed circuit board as claimed in claim 14, wherein the through hole is formed by mechanical drilling, the rotating speed of the mechanical drilling is 50-155kr/min, and the feed rate is 25-70mm/min , and the retraction amount is 100 to 750mm/min. The method for preparing a flexible printed circuit board according to claim 16, further comprising pressing the cover film and the flexible copper foil substrate after forming the through hole, and curing at a temperature of 170°C to 180°C after the pressing is completed. , and then perform chemical gold surface treatment on the matured cover film.

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