Flexible circuit board and preparation method therefor

Abstract

A flexible circuit board and a preparation method therefor. The flexible circuit board comprises a group of thermally conductive layers; a first insulating layer, the first insulating layer having a first surface and an opposing second surface, a recessed pattern being arranged on the second surface, and the first surface being in contact with the group of thermally conductive layers; and an electrically conductive circuit, the electrically conductive circuit being arranged within the recessed pattern.

Description

Flexible circuit board and preparation method thereof

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 13, 2023, with application number 202311725589.7 and invention name “Flexible circuit board and its preparation method”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present invention relates to the technical field of flexible circuit boards, and in particular to a flexible circuit board and a preparation method thereof. Background Art

[0003] In the backlight and display technologies of light-emitting diodes such as Mini LED (Mini Light-Emitting Diode) and Micro LED (Micro Light-Emitting Diode), flexible circuit boards play a key role in transmitting power and supporting the above-mentioned light-emitting diodes. The preparation of circuit boards is mainly based on PCB (Printed Circuit Board), specifically, exposure and development are performed on copper-clad boards to prepare circuits. However, chips equipped with Mini LED or Micro LED devices require high precision and need to be prepared using LDI (Laser Direct Imaging) technology, which is very expensive.

[0004] In order to reduce costs, resin substrates have become a new solution as substrates for transmitting electrical energy and supporting the above-mentioned light-emitting diodes. Technical issues

[0005] In the related scheme of preparing circuits on a resin substrate to power multiple LEDs, although the resin substrate can carry more LEDs, the power is greatly improved and the cost is significantly reduced, but the circuit will generate more heat when powering multiple LEDs, and the resin substrate has poor heat dissipation. Technical Solutions

[0006] In a first aspect, the present application provides a flexible circuit board, comprising:

[0007] Thermal conductive layer group;

[0008] a first insulating layer, the first insulating layer having a first surface and a second surface opposite to each other, a recessed pattern being provided on the second surface, and the first surface being in contact with the heat conducting layer assembly;

[0009] A conductive circuit is disposed in the recessed pattern.

[0010] In a second aspect, the present application further provides a method for preparing a flexible circuit board, comprising:

[0011] Providing a first insulating layer, the first insulating layer having a first surface and a second surface opposite to each other, wherein a recessed pattern is provided on the second surface;

[0012] Providing a conductive circuit, and disposing the conductive circuit in the recessed pattern;

[0013] A heat-conducting layer group is provided, and the heat-conducting layer group is bonded to the first surface. Beneficial effects

[0014] The flexible circuit board and its preparation method provided in the embodiments of the present application include a heat-conducting layer group, a first insulating layer, and a conductive circuit. The first insulating layer has a first surface and a second surface facing each other, and a recessed pattern is provided on the first insulating layer. The first surface is in contact with the heat-conducting layer group; the conductive circuit is provided within the recessed pattern. Thus, the use of the first insulating layer to form the first flexible circuit board in this solution can significantly reduce costs compared to using a copper-clad laminate as a flexible circuit board. Since the conductive circuit generates heat during operation, the heat-conducting layer group can dissipate heat from the conductive circuit. Therefore, the flexible circuit board provided in the embodiments of the present application is low-cost and has excellent heat dissipation. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG1 is a schematic diagram of a first structure of a flexible circuit board provided in an embodiment of the present application.

[0016] FIG2 is a schematic diagram of a second structure of a flexible circuit board provided in an embodiment of the present application.

[0017] FIG3 is a schematic diagram of a third structure of a flexible circuit board provided in an embodiment of the present application.

[0018] FIG4 is a schematic diagram of a first process of a method for preparing a flexible circuit board provided in an embodiment of the present application.

[0019] FIG5 is a schematic diagram of a second process of the method for preparing a flexible circuit board provided in an embodiment of the present application.

[0020] FIG6 is a schematic diagram of a first process of a method for preparing a flexible circuit board provided in an embodiment of the present application.

[0021] FIG. 7 is a schematic diagram of a third process flow of the method for preparing a flexible circuit board provided in an embodiment of the present application.

[0022] FIG8 is a schematic diagram of a second process of the method for preparing a flexible circuit board provided in an embodiment of the present application.

[0023] FIG9 is a fourth flow chart of the method for preparing a flexible circuit board provided in an embodiment of the present application.

[0024] FIG10 is a schematic diagram of a third process of the method for preparing a flexible circuit board provided in an embodiment of the present application.

[0025] FIG11 is a fifth flow chart of the method for preparing a flexible circuit board provided in an embodiment of the present application.

[0026] FIG12 is a schematic diagram of a fourth process of the method for preparing a flexible circuit board provided in an embodiment of the present application.

[0027] FIG13 is a sixth flow chart of the method for preparing a flexible circuit board provided in an embodiment of the present application.

[0028] FIG14 is a schematic diagram of the fifth process of the method for preparing a flexible circuit board provided in an embodiment of the present application.

[0029] Implementation Methods of the Application

[0030] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the embodiments described are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative efforts are within the scope of protection of this application.

[0031] In the backlight and display technology of light-emitting diodes such as Mini LED (Mini Light-Emitting Diode) and Micro LED (Micro Light-Emitting Diode), flexible circuit boards play a key role in transmitting electrical energy and carrying the above-mentioned light-emitting diodes. The preparation of circuit boards is mainly based on PCB (Printed Circuit Board), specifically, exposure and development are performed on copper-clad boards to prepare circuits. However, chips equipped with Mini LED or Micro LED devices require high precision and need to be prepared using LDI (Laser Direct Imaging) technology, resulting in high costs. Among them, the circuit board made of PCB can be an aluminum-based circuit board to increase the heat dissipation rate and ensure the reliability of the circuit board.

[0032] To reduce costs, resin substrates have become a new option for transmitting power and supporting the aforementioned LEDs. While the prior art involves fabricating circuits on resin substrates to power multiple LEDs, these substrates can support more LEDs, significantly increasing power and reducing costs. However, these circuits also generate significant heat when powering multiple LEDs, and resin substrates have poor heat dissipation properties.

[0033] The present invention provides a flexible circuit board and a method for manufacturing the same, which has low cost and excellent heat dissipation.

[0034] Please refer to FIG1 , which is a schematic diagram of a first structure of a flexible circuit board provided in an embodiment of the present application.

[0035] The present embodiment provides a flexible circuit board 100, which includes a thermally conductive layer assembly 110, a first insulating layer 120, and a conductive circuit 130. First insulating layer 120 has a first surface and a second surface facing each other. A recessed pattern 121 is provided on the second surface, and the first surface is in contact with thermally conductive layer assembly 110. Conductive circuit 130 is disposed within recessed pattern 121.

[0036] The side of the heat conductive layer group 110 that is bonded to the first surface of the first insulating layer 120 is not conductive, that is, the side of the heat conductive layer group 110 that is bonded to the first surface of the first resin is insulated, which can prevent the heat conductive layer group 110 from causing adverse effects such as short circuits on the conductive circuit 130.

[0037] The first insulating layer 120 may be made of a photocurable resin, such as one or more of epoxy acrylate, polyurethane acrylate, polyester acrylate, and amino acrylate. For example, the first insulating layer 120 may be made of polyester acrylate, a transparent, colorless polymer with excellent film-forming properties, adhesion, gloss retention, weather resistance, corrosion resistance, and flexibility. It is both light-transmissive and provides protection for the thermally conductive layer assembly 110. The conductive trace 130 may be made of a metal, such as copper or silver. The conductive trace 130 may be formed by solidifying a metal melt within the recessed pattern 121.

[0038] In this embodiment, the flexible circuit board 100 is constructed using a first insulating layer 120, significantly reducing costs compared to copper-clad laminates. Since the conductive circuit 130 generates heat during operation, the thermally conductive layer assembly 110 dissipates heat from the conductive circuit 130. Therefore, the flexible circuit board 100 provided in this embodiment is low-cost and has excellent heat dissipation.

[0039] In some embodiments, the recessed pattern 121 on the first insulating layer 120 penetrates the first surface and the second surface, so that the conductive circuit 130 disposed in the recessed pattern 121 contacts the thermal conductive layer assembly 110 , thereby dissipating heat from the conductive circuit 130 and achieving better heat dissipation performance.

[0040] In some embodiments, the thickness of the conductive trace 130 corresponds to the depth of the recessed pattern 121, so that the second surface and the conductive trace 130 form a flat surface. Furthermore, the thickness of the conductive trace 130 is less than or equal to the depth of the recessed pattern 121, so that the conductive trace 130 does not protrude from the second surface, making the second surface a flat surface.

[0041] Thus, the use of the first insulating layer 120 to form the first flexible circuit board in this solution can significantly reduce costs. Since the conductive circuit 130 generates heat during operation, the recessed pattern 121 on the first insulating layer 120 extends through the first surface and the second surface, allowing the conductive circuit 130 disposed within the recessed pattern 121 to contact the heat-conducting layer group 110, thereby dissipating heat from the conductive circuit 130. Therefore, the flexible circuit board 100 provided in the embodiment of the present application is low-cost and has excellent heat dissipation. In some embodiments, please refer to Figure 2, which is a schematic diagram of a second structure of the flexible circuit board provided in the embodiment of the present application. The heat-conducting layer group 110 can be a multi-layer structure. The heat-conducting layer group 110 includes a stacked metal base layer 111 and a second insulating layer 112. The first insulating layer 120 is disposed on the side of the second insulating layer 112 away from the metal base layer 111. Thus, the flexible circuit board 100 includes a metal base layer 111 , a second insulating layer 112 , and a first insulating layer 120 stacked in sequence, and the conductive circuit 130 is disposed in the recessed pattern 121 of the first insulating layer 120 .

[0042] It is understood that the metal base layer 111 is made of metal, which has excellent thermal conductivity. To isolate the metal base layer 111 from the conductive circuit 130, at least one second insulating layer 112 is disposed between the metal base layer 111 and the first insulating layer 120. In other words, the second insulating layer 112 is disposed between the metal base layer 111 and the conductive circuit 130. This prevents the metal base layer 111 from causing adverse effects such as short circuits on the conductive circuit 130.

[0043] The metal base layer 111 is made of steel or aluminum, such as 3-series aluminum or 5-series aluminum. 3-series aluminum, also known as aluminum-manganese alloy aluminum plate (Al-Mn), also known as rust-proof aluminum plate, has manganese as the main alloying element, with a content of 1.0-1.5%. It has higher strength than 1-series aluminum plate and has good formability, weldability, and corrosion resistance. 5-series aluminum, also known as aluminum-magnesium alloy aluminum plate (Al-Mg), has magnesium as the main alloying element and has good processing and forming properties, corrosion resistance, and welding properties. The metal base layer 111 can be aluminum foil made of steel, 3-series aluminum, or 5-series aluminum.

[0044] The thickness of the metal base layer 111 is 0.05 mm (millimeter) to 0.3 mm. Precisely because the metal base layer 111 is highly stable, has excellent ductility, and is bendable, the metal base layer 111 can be made into a metal foil and applied to the flexible circuit board 100 of the present application to prepare a bendable flexible circuit board 100. For example, the thickness of the metal base layer 111 is 0.1 mm. When the metal base layer 111 is 0.1 mm thick, it is relatively thin, dimensionally stable, and bendable. It also has a heat dissipation function and can serve as a heat sink for the flexible circuit board 100 in the embodiment of the present application.

[0045] Furthermore, the second insulating layer 112 has both thermal conductivity and insulation properties. The second insulating layer 112 includes a second resin layer and a thermally conductive filler. The thermally conductive filler is dispersed in the second resin layer, resulting in the second insulating layer 112 having both good insulation and high thermal conductivity. When the second insulating layer 112 is disposed between the metal base layer 111 and the conductive trace 130, it can effectively transfer heat generated by the conductive trace 130 to the metal base layer 111, thereby achieving a heat dissipation effect.

[0046] The second resin layer is made of a thermosetting resin. Thermosetting resins have excellent overall properties, including high strength, good heat resistance, excellent electrical properties, corrosion resistance, aging resistance, and good dimensional stability. However, after curing, thermosetting resins form a network structure due to intermolecular crosslinking. This results in high rigidity, high hardness, high temperature resistance, low flammability, and good dimensional stability, but also brittleness. Therefore, various reinforcing materials, such as wood flour, mineral powder, fiber, or textiles, are added to thermosetting resins to reinforce them and create reinforced plastics. Therefore, the second resin layer can include a thermosetting resin and reinforcing materials to ensure high temperature resistance and high strength. The thermosetting resin can be phenolic resin, urea-formaldehyde resin, melamine-formaldehyde resin, epoxy resin, unsaturated resin, polyurethane, polyimide, etc. The second resin layer can be made of FR-4 resin or BT resin. When the second resin layer is made of FR-4 resin or BT resin, the glass transition temperature (Tg) is greater than 130°C, meaning that it exhibits good dimensional stability below 130°C.

[0047] Among them, the thermally conductive filler can be aluminum oxide. The aluminum oxide can be α-aluminum oxide or β-aluminum oxide, or it can be spherical aluminum oxide. It can be understood that the thermally conductive filler is a plurality of aluminum oxide particles, and the plurality of aluminum oxide particles are dispersed in the second resin layer. Since the melting point of aluminum oxide particles is 2054°C, they have good insulating thermal conductivity. When a number of the aluminum oxide particles are dispersed in the second resin layer, the aluminum oxide particles can effectively conduct the heat emitted by the conductive circuit 130 to the metal base layer 111 to enhance heat dissipation. In addition, since the color of aluminum oxide is white, the color of the second resin layer can be whitened, thereby improving the reflection effect of light.

[0048] The second insulating layer 112 comprises, by mass percentage, 60-80% of the second resin layer and 20-40% of the thermal conductive filler. When the second insulating layer 112 has the above composition ratio, it has both dimensional stability and excellent thermal conductivity.

[0049] Furthermore, to enhance the stability and light reflectivity of the second insulating layer 112, the second insulating layer 112 also includes titanium dioxide powder dispersed in the second resin layer. Titanium dioxide, also known as titanium dioxide, has a whitening effect and is highly reflective of light. For example, when the second resin layer comprises epoxy resin and titanium dioxide, the titanium dioxide can fill the gaps in the epoxy resin, thereby increasing the hardness and stability of the second resin layer.

[0050] Furthermore, in order to enhance the flame retardant effect of the second insulating layer 112, the second insulating layer 112 further includes a flame retardant filler dispersed in the second resin layer. The flame retardant filler may be aluminum hydroxide.

[0051] In some embodiments, please refer to Figure 3, which is a schematic diagram of a third structure of a flexible circuit board provided in embodiments of the present application. The flexible circuit board 100 further includes a white ink layer 140 disposed on the second surface of the first insulating layer 120. This white ink layer 140 is used to shield the conductive traces 130. It is understood that when the conductive traces 130 are made of copper, copper has a purple-red or reddish-orange color and does not reflect light. Therefore, in embodiments of the present application, the white ink layer 140 is disposed on the second surface of the first insulating layer 120 to reflect light and increase the reflectivity of the flexible circuit board 100. In some cases, a white first insulating layer 120 has a strong reflectivity to light. If the flexible circuit board 100 further includes the white ink layer 140 to shield the conductive traces 130, the reflectivity of the flexible circuit board 100 can be greater than or equal to 85%.

[0052] In other cases, when the first insulating layer 120 is a transparent resin, the second resin layer, doped with titanium dioxide, has a whitening effect and is highly reflective of light. The first insulating layer 120 superimposed on the second resin layer allows light to pass through while also protecting the second resin layer. In this case, the first insulating layer 120 and the second resin layer jointly reflect light. In this case, the flexible circuit board 100 also includes white ink, which is disposed on the side of the first insulating layer 120 away from the second resin layer to shield the conductive traces 130. As a result, the first insulating layer 120, the second resin layer, and the white ink collectively achieve a light emissivity greater than or equal to 85%.

[0053] The present application also provides a method for preparing a flexible circuit board. Please refer to Figures 1 and 4. Figure 4 is a schematic diagram of the first process of the method for preparing a flexible circuit board provided in the present application.

[0054] The method for preparing the flexible circuit board includes the following steps. It should be noted that the method steps provided in this application are not limited to the steps provided in this embodiment, and the steps in some embodiments can be performed simultaneously.

[0055] The method for preparing the flexible circuit board includes the following steps.

[0056] S101 , providing a first insulating layer 120 , wherein the first insulating layer 120 has a first surface and a second surface opposite to each other, and a recessed pattern 121 is disposed on the second surface.

[0057] S102 , providing a conductive circuit 130 , and disposing the conductive circuit 130 in the recessed pattern 121 .

[0058] S103 , providing a heat-conducting layer assembly 110 , and laminating the heat-conducting layer assembly 110 to the first surface.

[0059] Please refer to Figures 5 and 6. Figure 5 is a second process diagram of the method for preparing a flexible circuit board provided in an embodiment of the present application. Figure 6 is a first process diagram of the method for preparing a flexible circuit board provided in an embodiment of the present application.

[0060] In some embodiments, the recessed pattern 121 penetrates the first surface and the second surface; the conductive circuit 130 is provided, and the conductive circuit 130 is disposed in the recessed pattern 121. The method for preparing the flexible circuit board includes:

[0061] S1. Provide a substrate 150.

[0062] S2. The first surface of the first insulating layer 120 is bonded to the substrate.

[0063] S3 , filling the recessed pattern 121 with a conductive material to form a conductive circuit 130 .

[0064] S4. Provide a heat-conducting layer group 110.

[0065] S5 , laminating the heat conducting layer assembly 110 to the first surface of the first insulating layer 120 .

[0066] S6 , removing the substrate 150 from the second surface of the first insulating layer 120 .

[0067] The substrate 150 may be a hard substrate 150, so that the substrate 150 can support the first insulating layer 120 and can be removed from the second surface of the first insulating layer 120. The substrate 150 may be made of polyethylene glycol terephthalate (PET).

[0068] The side of the heat conductive layer group 110 that is bonded to the first surface of the first insulating layer 120 is not conductive, that is, the side of the heat conductive layer group 110 that is bonded to the first surface of the first resin is insulated, which can prevent the heat conductive layer group 110 from causing adverse effects such as short circuits on the conductive circuit 130.

[0069] The recessed pattern 121 on the first insulating layer 120 can be obtained by stamping the first insulating layer 120 with an imprinting mold 300. Specifically, the imprinting mold 300 can have a protruding pattern. The protruding pattern is the desired circuit pattern. Protruding patterns of different shapes or depths can be prepared according to the desired conductive circuits 130. Subsequently, the imprinting mold 300 is moved toward the side of the first insulating layer 120 away from the substrate 150 for stamping, thereby forming a recessed pattern 121 on the surface of the first insulating layer 120. The recessed pattern 121 matches the protruding pattern on the imprinting mold 300. During the stamping process, the imprinting mold 300 can completely pass through the first insulating layer 120 to abut against the substrate 150, so that the recessed pattern 121 can penetrate the first and second surfaces of the first insulating layer 120.

[0070] The conductive circuit 130 is made of metal, which can be copper or silver. The conductive circuit 130 can be formed by photon sintering and solidification of metal particles in the recessed pattern 121. The thickness of the conductive circuit 130 can be 20μm-50μm, and the length and width of the conductive circuit 130 can be 100μm-200μm. Compared with the thickness of the circuit obtained by the traditional copper foil corrosion solution, the thickness of the conductive circuit 130 is increased. When the width of the entire conductive circuit 130 remains unchanged, it is equivalent to increasing the cross-sectional area of ​​the conductive circuit 130, thereby increasing the current carrying capacity to meet the application requirements of Mini LED or Micro LED of different sizes.

[0071] Thus, the use of the first insulating layer 120 to form the first flexible circuit board in this solution can significantly reduce costs. Since the conductive circuit 130 generates heat during operation, the recessed pattern 121 on the first insulating layer 120 extends through the first and second surfaces, allowing the conductive circuit 130 disposed within the recessed pattern 121 to contact the heat-conducting layer assembly 110, thereby dissipating heat from the conductive circuit 130. Therefore, the flexible circuit board produced by the method for preparing a flexible circuit board provided in the embodiments of the present application is low-cost and has excellent heat dissipation.

[0072] In some embodiments, referring to Figures 2, 7, and 8, Figure 7 is a schematic diagram of a third process flow of a method for preparing a flexible circuit board according to an embodiment of the present application, and Figure 8 is a schematic diagram of a second process flow of a method for preparing a flexible circuit board according to an embodiment of the present application. Providing a thermally conductive layer assembly 110 includes the following steps.

[0073] S401 , providing a metal base layer 111 .

[0074] S402 , coating one side of the metal base layer 111 with a thermally conductive insulating adhesive.

[0075] S403 , curing the thermally conductive insulating adhesive to form a second insulating layer 112 on the metal base layer 111 .

[0076] The step of laminating the heat-conducting layer group 110 to the first surface of the first insulating layer 120 includes: S501 , laminating a heat-conducting insulating adhesive to the first surface of the first insulating layer 120 .

[0077] It is understood that the metal base layer 111 is made of metal, which has excellent thermal conductivity. To isolate the metal base layer 111 from the conductive circuit 130, at least one second insulating layer 112 is disposed between the metal base layer 111 and the first insulating layer 120. In other words, the second insulating layer 112 is disposed between the metal base layer 111 and the conductive circuit 130. This prevents the metal base layer 111 from causing adverse effects such as short circuits on the conductive circuit 130. Furthermore, the metal base layer 111 has strong dimensional stability, further enhancing thermal conductivity.

[0078] The material of the metal base layer 111 is steel or aluminum, such as 3 series aluminum or 5 series aluminum. The thickness of the metal base layer 111 is 0.05 mm to 0.3 mm. Precisely because the metal base layer 111 has strong stability, excellent ductility and can be bent, the metal base layer 111 can be made into a metal foil and applied to the flexible circuit board of the present application to prepare a flexible circuit board that can be bent. It can be understood that the second insulating layer 112 has both thermal conductivity and insulation properties. The second insulating layer 112 includes a second resin layer and a thermally conductive filler, and the thermally conductive filler is dispersed in the second resin layer so that the second insulating layer 112 not only has good insulation but also has high thermal conductivity. When the second insulating layer 112 is arranged between the metal base layer 111 and the conductive circuit 130, the second insulating layer 112 can effectively conduct the heat generated by the conductive circuit 130 to the metal base layer 111, thereby achieving a heat dissipation effect.

[0079] Among them, the material of the second resin layer includes thermosetting resin. The thermally conductive filler can be aluminum oxide. The aluminum oxide can be α-aluminum oxide or β-aluminum oxide, or it can be spherical aluminum oxide. It can be understood that the thermally conductive filler is a plurality of aluminum oxide particles, and the plurality of aluminum oxide particles are dispersed in the second resin layer. Since the melting point of aluminum oxide particles is 2054°C, they have good insulating thermal conductivity. When a number of the aluminum oxide particles are dispersed in the second resin layer, the aluminum oxide particles can effectively conduct the heat emitted by the conductive circuit 130 to the metal base layer 111 to enhance heat dissipation. In addition, since the color of aluminum oxide is white, the color of the second resin layer can be whitened, thereby improving the reflection effect of light.

[0080] Furthermore, in order to enhance the stability and light reflectivity of the second insulating layer 112, the second insulating layer 112 further includes titanium dioxide powder dispersed in the second resin layer. Titanium dioxide, also known as titanium dioxide, has a whitening effect and has strong light reflectivity.

[0081] Furthermore, in order to enhance the flame retardant effect of the second insulating layer 112, the second insulating layer 112 further includes a flame retardant filler dispersed in the second resin layer. The flame retardant filler may be aluminum hydroxide.

[0082] In some cases, an organic solvent, a thermosetting resin, aluminum oxide, and titanium dioxide are mixed to form a thermally conductive insulating adhesive, which is then coated on the metal base layer 111. Finally, after the organic solvent evaporates, a second insulating layer 112 is formed on the metal base layer 111. The organic solvent must have volatility, fluidity, dispersibility, and solubility. The organic solvent is used for thermosetting resins. The organic solvent can be a medium-to-low boiling point solvent, for example, a boiling point of 140°C or less. The organic solvent can be one or more of isopropyl alcohol, xylene, cyclohexane, and ethyl acetate. Among them, the boiling point of isopropyl alcohol is 82.5°C, the boiling point of xylene is 137°C to 140°C, the boiling point of cyclohexane is 80.7°C, and the boiling point of ethyl acetate is 76.5°C to 77.5°C. For example, the organic solvent is xylene, which has a strong solubility and can prevent the thermosetting resin from precipitating again from the organic solvent, thereby improving the fluidity of the coating of the thermally conductive insulating adhesive on the metal base layer 111. Alternatively, the organic solvent may include isopropyl alcohol, xylene, cyclohexane, and ethyl acetate. Due to their low boiling point, low viscosity, and rapid evaporation, these solvents aid in diluting and dispersing the material and accelerate drying of the coating. It is worth noting that since aluminum oxide and titanium dioxide are insoluble in these organic solvents, the thermally conductive insulating adhesive must be stirred before coating to ensure a uniform distribution of the aluminum oxide and titanium dioxide in the organic solvent.

[0083] The thermally conductive insulating adhesive may be coated on one side of the metal base layer 111 by applying the thermally conductive insulating adhesive on the metal substrate 150 using a roller coating process.

[0084] Since the main component of the thermally conductive insulating adhesive is a thermosetting resin, the thermally conductive insulating adhesive can be cured to form the second insulating layer 112 by heating. On the one hand, this can accelerate the volatilization of the organic solvent in the thermally conductive insulating adhesive, and on the other hand, it can increase the degree of cross-linking of the thermosetting resin, so that the state of the thermosetting resin is changed from a viscous flow state or a highly elastic state to a glassy state.

[0085] In some embodiments, referring to FIG. 8 , the step of forming a second insulating layer 112 on a metal base layer 111 includes providing a transmission assembly 200 comprising spaced-apart guide rollers 210 and a rubber extrusion roller assembly 220; wrapping the metal base layer 111 around the guide roller 210 and pulling one end of the metal base layer 111; coating the metal base layer 111 with a thermally conductive insulating adhesive as it passes through the rubber extrusion roller assembly 220 under the action of the traction force; and curing the thermally conductive insulating adhesive to form the second insulating layer 112. Because the metal base layer 111 is highly stable, ductile, and bendable, metal foil can be used as the metal base layer 111 in the flexible circuit board of this application to prepare a bendable flexible circuit board. Therefore, the metal base layer 111 in this application can be wrapped around the guide roller 210 for processing.

[0086] The rubber squeezing roller assembly 220 includes a first roller 221 and a second roller 222. The first roller 221 and the second roller 222 are tangential to each other, and the first roller 221 can drive the second roller 222 to roll. The first roller 221 and the second roller 222 are positioned horizontally. Under the action of traction, the metal base layer 111 abuts against the side of the first roller 221 away from the second roller 222, driving the first roller 221 to rotate. Due to gravity and squeezing force, the thermally conductive insulating adhesive flows between the first roller 221 and the second roller 222 and along the first roller 221 onto the metal base layer 111. Finally, the first roller 221 presses the thermally conductive insulating adhesive onto the metal substrate.

[0087] The transmission assembly 200 also includes a transmission roller 230 for changing the direction of the metal substrate 111. The transmission roller 230 is spaced apart from the guide roller 210 and the squeeze roller assembly 220. The metal substrate 150 passes through the guide roller 210 and the squeeze roller assembly 220 before abutting against the transmission roller 230 to change its direction and then undergo curing in the hot drying tunnel.

[0088] In some embodiments, please refer to Figures 9 and 10. Figure 9 is a fourth flow chart of the method for preparing a flexible circuit board provided in an embodiment of the present application, and Figure 10 is a third process chart of the method for preparing a flexible circuit board provided in an embodiment of the present application.

[0089] The step of filling the recessed pattern 121 with a conductive material to form the conductive circuit 130 includes: S301 , filling the recessed pattern 121 with a copper paste 160 ; S302 , heating and sintering the copper paste 160 into a copper wire to form the conductive circuit 130 .

[0090] The copper paste 160 may be applied to the recessed pattern 121 by a scraper 400 .

[0091] The copper paste 160 may be nano-copper particles. In the embodiment of the present application, the conductive circuit 130 is directly formed by heating and sintering the copper paste 160. Compared to the traditional process of applying photoresist, exposing, developing, etching, and removing the resist on the copper-clad laminate, the embodiment of the present application does not require a large copper layer, and the process steps are reduced, with increased precision to meet the application requirements of Mini LED or Micro LED.

[0092] The step of heating and sintering the copper paste 160 to form copper wires in the flexible circuit board manufacturing method includes performing photon sintering on the copper paste 160 according to the shape of the recessed pattern 121, so that the copper particles in the copper paste 160 are sintered into a whole. The photon sintering can be laser sintering, and the laser power can be greater than or equal to 10 J / cm2 (joules per square).

[0093] It is understandable that laser sintering the copper paste 160 according to the shape of the recessed pattern 121 means that since the copper paste 160 is filled in the recessed pattern 121, the laser only sinters the area where the copper paste 160 is present, and uses a high-energy laser to melt the copper paste 160 into copper paste. Under the same conditions, the energy density of the laser is much higher than that of a muffle furnace or a resistance furnace. When the power of the laser is greater than or equal to 10J / cm2, the sintering temperature of the copper paste 160 is high, the diffusion rate of the copper atoms is faster, and the interface between the copper pastes 160 disappears at high temperatures, that is, the density of the sintered copper is higher, thereby reducing the square resistance of the conductive circuit 130, making its square resistance reach the same order of magnitude as that of the electroplated copper foil, shortening the process time and reducing its cost.

[0094] In some embodiments, please refer to Figures 3, 11, and 12. Figure 11 is a fifth flow diagram of the method for preparing a flexible circuit board provided in an embodiment of the present application, and Figure 12 is a fourth process diagram of the method for preparing a flexible circuit board provided in an embodiment of the present application. Substrate 150 is a transparent substrate 150. The step of forming a first insulating layer 120 on substrate 150 further includes: S201, coating substrate 150 with a photocurable resin; S202, providing an imprinting mold 300; S203, pressing the protruding pattern on the imprinting mold 300 into the photocurable resin; S204, curing the photocurable resin through substrate 150 with light to form the first insulating layer 120.

[0095] As can be seen, the material of the first insulating layer 120 can be a light-curable resin. The light-curable resin can be one or more of epoxy acrylate, polyurethane acrylate, polyester acrylate, and amino acrylate. For example, the material of the first insulating layer 120 is polyester acrylate, which is a transparent and colorless polymer with excellent film-forming properties, adhesion, gloss retention, weather resistance, corrosion resistance, and flexibility.

[0096] Since the substrate 150 is transparent, light may be irradiated on a side of the substrate 150 away from the photocurable resin so that the light passes through the substrate 150 and the photocurable resin is photocured to form the first insulating layer 120 .

[0097] It can be understood that when the photocurable resin is imprinted using the protruding pattern on the imprinting mold 300, the photocurable resin can be cured by light, such as ultraviolet light, to form the first insulating layer 120, presenting an extrusion and molding effect. Compared with steps such as thermal curing, it can save a lot of time and improve efficiency.

[0098] In some embodiments, please refer to Figures 13 and 14. Figure 13 is a sixth flow diagram of the method for preparing a flexible circuit board provided in an embodiment of the present application, and Figure 14 is a fifth process diagram of the method for preparing a flexible circuit board provided in an embodiment of the present application. After removing the substrate 150 from the second surface of the first insulating layer 120, the process further includes S7: providing a white ink mixture; S8: applying the white ink mixture to the second surface of the first insulating layer 120 to cover the conductive traces 130; and S9: curing the white ink mixture to form a white ink layer 140. It is understood that the white ink mixture can be printed onto the second surface of the first insulating layer 120 using a screen printing and thermal curing process, thereby producing a flexible metal substrate 150 circuit with a reflectivity exceeding 85%. The white ink layer 140 may be a solder mask white ink layer 140.

[0099] The flexible circuit board 100 and its preparation method provided in an embodiment of the present application include a thermally conductive layer assembly 110, a first insulating layer 120, and a conductive circuit 130. The first insulating layer 120 has opposing first and second surfaces. A recessed pattern 121 is provided on the first insulating layer 120, extending through both the first and second surfaces, with the first surface being in contact with the thermally conductive layer assembly 110. The conductive circuit 130 is disposed within the recessed pattern 121. Thus, the use of the first insulating layer 120 to form the first flexible circuit board in this embodiment significantly reduces costs. Since the conductive circuit 130 generates heat during operation, the recessed pattern 121 on the first insulating layer 120 extends through both the first and second surfaces, allowing the conductive circuit 130 disposed within the recessed pattern 121 to contact the thermally conductive layer assembly 110, thereby dissipating heat from the conductive circuit 130. Therefore, the flexible circuit board 100 provided in the embodiment of the present application is low-cost and has excellent heat dissipation.

[0100] In the above embodiments, the description of each embodiment has its own focus. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0101] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of technical features indicated. Therefore, features specified as "first" or "second" may explicitly or implicitly include one or more features.

[0102] The flexible circuit board and its preparation method provided in the embodiments of the present application are described in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is intended only to facilitate understanding of the present application. Furthermore, those skilled in the art will appreciate that variations in the specific implementation methods and scope of application may occur based on the principles of the present application. In summary, the contents of this specification should not be construed as limiting the present application.

Claims

1. A flexible circuit board, further comprising: Thermally conductive layer group; A first insulating layer, the first insulating layer having a first surface and a second surface opposite to each other, a concave pattern being arranged on the second surface, and the first surface being in contact with the heat conducting layer assembly; A conductive circuit is disposed in the recessed pattern.

2. The flexible circuit board according to claim 1, wherein: The concave pattern penetrates the first surface and the second surface.

3. The flexible circuit board according to claim 1, wherein: The thickness of the conductive line corresponds to the depth of the recessed pattern, so that the second surface and the conductive line form a flat surface.

4. The flexible circuit board according to claim 1, wherein: The heat-conducting layer group includes a metal base layer and a second insulating layer which are stacked, and the first insulating layer is arranged on a side of the second insulating layer away from the metal base layer.

5. The flexible circuit board according to claim 4, wherein: The material of the metal base layer is steel or aluminum.

6. The flexible circuit board according to claim 5, wherein: The thickness of the metal base layer is 0.05 mm to 0.3 mm.

7. The flexible circuit board according to claim 4, wherein: The second insulating layer includes a second resin layer and a thermally conductive filler, and the thermally conductive filler is dispersed in the second resin layer.

8. The flexible circuit board according to claim 7, wherein: The material of the second resin layer includes thermosetting resin; the thermal conductive filler is aluminum oxide.

9. The flexible circuit board according to claim 7, wherein: The second insulating layer further includes titanium dioxide powder, and the titanium dioxide powder is dispersed in the second resin layer.

10. The flexible circuit board according to claim 1, wherein: The conductive circuit is formed by solidifying metal melt in the concave pattern.

11. The flexible circuit board according to claim 1, wherein: It also includes a white ink layer, which is arranged on the second surface of the first insulating layer and is used to shield the conductive line.

12. The flexible circuit board according to claim 1, wherein: The first insulating layer is a photocurable resin.

13. A method for preparing a flexible circuit board, comprising: Providing a first insulating layer, the first insulating layer having a first surface and a second surface opposite to each other, and a concave pattern is arranged on the second surface; Providing a conductive circuit, and disposing the conductive circuit in the recessed pattern; A heat-conducting layer group is provided, and the heat-conducting layer group is bonded to the first surface.

14. The method for preparing a flexible circuit board according to claim 13, wherein: The concave pattern penetrates the first surface and the second surface; Providing a conductive circuit, and arranging the conductive circuit in the recessed pattern, the method for preparing the flexible circuit board includes: providing a substrate; Laminating the second surface to the substrate; Filling the concave pattern with a conductive material to form a conductive circuit; After laminating the heat-conducting layer group to the first surface, the method for preparing the flexible circuit board further includes: The substrate is removed from the second surface of the first insulating layer.

15. The method for preparing a flexible circuit board according to claim 13, wherein: The step of providing a heat-conducting layer group comprises: Provide a metal base layer; forming a second insulating layer on the metal base layer; The step of laminating the heat-conducting layer group to the first surface of the first insulating layer comprises: The second insulating layer is bonded to the first surface of the first insulating layer.

16. The method for preparing a flexible circuit board according to claim 15, wherein: A second insulating layer is formed on the metal base layer. The method for preparing the flexible circuit board includes: A transmission assembly is provided, the transmission assembly comprising guide rollers and a rubber squeezing roller assembly spaced apart from each other; Winding the metal base layer on the guide roller and pulling one end of the metal base layer; The metal base layer is coated with heat-conducting insulating glue when passing through the glue squeezing roller assembly under the action of traction; The thermally conductive insulating adhesive is cured to form a second insulating layer.

17. The method for preparing a flexible circuit board according to claim 14, wherein: Filling the concave pattern with a conductive material to form a conductive circuit includes: filling the concave pattern with a copper paste; heating and sintering the copper paste into a copper wire to form a conductive circuit.

18. The method for preparing a flexible circuit board according to claim 17, wherein: The copper paste is heated and sintered to form a copper wire, comprising: performing photon sintering on the copper paste according to the shape of the concave pattern, so that the copper particles in the copper paste are sintered into one body.

19. The method for preparing a flexible circuit board according to claim 14, wherein: The substrate is a transparent substrate, and a first insulating layer is formed on the substrate, including: coating a photocurable resin on the substrate; providing an imprinting mold; pressing a protruding pattern on the imprinting mold into the photocurable resin; and curing the photocurable resin through the substrate to form the first insulating layer.

20. The method for preparing a flexible circuit board according to claim 14, wherein: After removing the substrate from the second surface of the first insulating layer, the method for preparing the flexible circuit board further includes: providing a white ink mixture; setting the white ink mixture on the second surface of the first insulating layer to cover the conductive circuit; and curing the white ink mixture to form a white ink layer.

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