Flexible circuit board capable of being electrically heated and preparation method and application thereof

Abstract

The invention relates to the technical field of electric heating, in particular to a flexible circuit board capable of being electrically heated and a preparation method and application thereof. The preparation method of the flexible circuit board capable of being electrically heated comprises the steps that the flexible circuit board is provided, and the flexible circuit board comprises a first flexible insulation base material layer, an adhesive layer and a copper circuit layer which are stacked in sequence; providing an electric heating functional layer, wherein the electric heating functional layer comprises a second flexible insulating base material layer and a conductive layer; after a conductive adhesive layer is formed on the surface of a copper circuit layer of the flexible circuit board, the conductive adhesive layer is attached to a part of a conductive layer of the electric heating functional layer, other areas of the conductive layer and the semi-cured adhesive layer which is not covered by the copper circuit layer are pre-bonded, hot-pressed and baked, and then laser tapping resistance adjusting and film covering are carried out to obtain the flexible circuit board. And obtaining the flexible circuit board capable of being electrically heated. The invention provides a method for simply and efficiently forming a well-combined electric heating functional layer on a flexible circuit board.

Description

Technical Field

[0001] The present invention relates to the technical field of electrothermal technology, and particularly relates to an electro-heatable flexible circuit board, a preparation method thereof, and an application thereof. Background Art

[0002] A flexible printed circuit board (FPC), also known as a flexible circuit board or a flexible printed circuit, is a circuit board made of a flexible copper clad laminate (FCCL) with high wiring density, light weight, thin thickness, high temperature resistance, and good bending properties.

[0003] Traditional FPC circuit boards are mainly composed of multiple layers such as copper foil, adhesive layer, flexible insulating substrate layer, and cover film layer; copper foil is used as the material for the circuit conductor, and an organic polymer film (mainly Pi) is used as the flexible insulating substrate layer. A flexible copper clad laminate material (FCCL) is prepared by relying on the adhesive layer coated in the middle and completely cured at high temperature, and then processed into a flexible circuit board FPC through a certain etching process. The outermost layer uses an organic polymer film + semi-cured adhesive as the cover film layer for protecting and isolating the circuit.

[0004] In the prior art, by adding a layer of electro-heatable functional layer on the basis of a traditional FPC circuit board, a flexible circuit board with the functions of "high temperature resistance + flexible bending + electro-heating" and capable of electro-heating can be realized. Its electro-heating temperature can be as high as 150 °C or above, and it can be widely used in temperature uniform control and certain technical applications of setting temperature in fields such as aerospace aircraft equipment structural components, land, sea, and air transportation vehicle structural components, vacuum devices, spacesuits, infrared thermal physiotherapy and health preservation cabins, automotive battery thermal management equipment, automotive seat heating equipment, household floor heating equipment, etc.

[0005] The electro-heatable functional layer of the existing flexible circuit board is composed of a graphene film or a metal film. Due to the advantages of a single film component and no resin, the surface resistance or sheet resistance can be stably controlled during the subsequent hot pressing process, and the consistency of the prepared electro-heatable component samples is relatively good. However, in the prior art, due to reasons such as the bonding force between the copper foil and the adhesive layer of the FCCL material and the processing requirements, the adhesive layer needs to be in a completely cured resin state. After hot pressing, the bonding force between this type of cured adhesive layer and the electro-heatable functional layer is not good, and problems such as blistering and reliability are likely to occur. Therefore, a semi-cured adhesive film with local laser cutting needs to be placed between the electro-heatable functional layer and the cured adhesive layer to tightly hot press and bond the electro-heatable functional layer and the cured adhesive layer on the flexible circuit board. However, this requires adding steps such as "laser cutting, alignment, and pre-pasting", and the alignment and pre-pasting processing links become extremely cumbersome and difficult.

[0006] Therefore, how to make a simple production process and form a well-bonded and stable electro-heatable functional layer on the flexible circuit board is an urgent problem to be solved. Summary of the Invention

[0007] Therefore, the technical problem to be solved by the present invention is to provide a simple and efficient method and application for forming a well - bonded electro - heating functional layer on a flexible circuit board.

[0008] The present invention provides a method for preparing an electro - heating flexible circuit board, comprising the following steps:

[0009] (1) Provide a flexible circuit board, which includes a first flexible insulating substrate layer, an adhesive layer, and a copper circuit layer laminated in sequence; wherein, the adhesive layer is a thermosetting resin layer in a semi - cured state, and the copper circuit layer covers part of the adhesive layer;

[0010] (2) Provide an electro - heating functional layer, which includes a second flexible insulating substrate layer and a conductive layer;

[0011] (3) After forming a conductive adhesive layer on the surface of the copper circuit layer of the flexible circuit board, partially attach the conductive adhesive layer to the conductive layer of the electro - heating functional layer, and pre - bond, hot - press, and bake other regions of the conductive layer with the semi - cured adhesive layer not covered by the copper circuit layer to obtain an initially electro - heatable flexible circuit board;

[0012] (4) The initially electro - heatable flexible circuit board is subjected to laser hole - opening and resistance adjustment, and film - covering to obtain the electro - heatable flexible circuit board;

[0013] Wherein, the process of changing the thermosetting resin layer from the initial state to the semi - cured state is achieved by infrared radiation heating.

[0014] Preferably, the preparation process of the flexible circuit board includes the following steps:

[0015] Coat an initial thermosetting resin layer on the copper foil;

[0016] Attach the first flexible insulating substrate layer to the surface of the initial thermosetting resin layer;

[0017] Perform thermosetting by infrared radiation heating to change the initial thermosetting resin layer into a thermosetting resin layer in a semi - cured state;

[0018] Etch the copper foil to obtain the copper circuit layer.

[0019] More preferably, coating the initial thermosetting resin layer on the copper foil is carried out in a roll - to - roll manner.

[0020] Preferably, the relative degree of cure of the thermosetting resin layer in the semi - solid state is 40% - 80%;

[0021] Preferably, the thermal curing process is to achieve the semi-curing of the thermosetting resin layer or the adhesive layer by infrared radiation heating; among them, the temperature of the infrared thermal radiation heating is 100°C - 200°C.

[0022] Preferably, in step (3), the temperature of the pre-lamination is 160°C - 200°C, the pre-lamination speed is 0.1 m / min - 0.5 m / min; the pre-lamination pressure is 1 - 2 MPa.

[0023] Preferably, in step (3), the hot pressing temperature is 160 - 200°C, the hot pressing time is 200 - 300 s; the hot pressing pressure is 1 - 10 MPa.

[0024] Preferably, the bonding strength between the copper circuit layer and the semi-cured thermosetting resin layer in the flexible circuit board is ≥0.3 N / mm.

[0025] Preferably, the bonding strength between the adhesive layer after baking and curing in step (3) and the conductive layer is >0.5 N / mm.

[0026] Preferably, the preparation of the electro-heating functional layer includes the following steps: forming a conductive layer on one side surface of the second flexible insulating substrate layer; among them, the method of forming the conductive layer includes at least one of sputtering and chemical vapor deposition;

[0027] Preferably, the sheet resistance of the conductive layer is 30 Ω / sq - 2000 Ω / sq.

[0028] Preferably, the thickness of the first flexible insulating substrate layer is 5 μm - 100 μm; and / or,

[0029] the thickness of the second flexible insulating substrate layer is 5 μm - 100 μm; and / or,

[0030] the thickness of the semi-cured thermosetting resin layer is 5 μm - 100 μm; and / or,

[0031] the thickness of the copper circuit layer is 12 μm - 60 μm; and / or,

[0032] the thickness of the conductive layer is 0.01 μm - 0.5 μm; and / or,

[0033] The thickness of the conductive adhesive layer is 5 μm - 50 μm.

[0034] Preferably, in step (4), the process of laminating the film includes:

[0035] Covering protective film layers on both side surfaces of the initial electro-heatable flexible circuit board;

[0036] Performing hot pressing and baking and curing treatments on the protective film layers to obtain the electro-heatable flexible circuit board;

[0037] Among them, the thickness of the protective film layer is 12 - 100 μm; the material of the protective film layer is selected from polyimide films.

[0038] Preferably, the material of the flexible insulating substrate layer is selected from polyimide films or polyethylene terephthalate films; and / or, the raw material of the semi-cured thermosetting resin layer is a resin containing epoxy resin and / or acrylic acid; and / or,

[0039] The material of the conductive layer is selected from metal thin films; and / or,

[0040] The material of the conductive adhesive layer is a mixture of conductive particles and thermosetting resin.

[0041] In the present invention, the semi-cured thermosetting resin layer is obtained by semi-curing the initial thermosetting resin layer. The raw materials of the initial thermosetting resin layer and the semi-cured thermosetting resin layer are the same.

[0042] The present invention also provides an electrically heatable flexible circuit board, which is prepared by the preparation method described above.

[0043] The present invention also provides an application of the electrically heatable flexible circuit board prepared by the preparation method described above or the electrically heatable flexible circuit board described above in structural elements of spacecraft airborne equipment, structural elements of land, sea and air transportation tools, vacuum devices, spacesuits, infrared thermal physiotherapy health cabins, automotive battery thermal management equipment, automotive seat heating equipment, and household floor heating equipment.

[0044] The technical solution of the present invention has the following advantages:

[0045] The preparation method of the electrically heatable flexible circuit board provided by the present invention includes the following steps: providing a flexible circuit board, the flexible circuit board includes a first flexible insulating substrate layer, an adhesive layer, and a copper circuit layer stacked in sequence; wherein, the adhesive layer is a semi-cured thermosetting resin layer, and the copper circuit layer covers part of the adhesive layer; (2) providing an electrically heatable functional layer, the electrically heatable functional layer includes a second flexible insulating substrate layer and a conductive layer; (3) after forming a conductive adhesive layer on the surface of the copper circuit layer of the flexible circuit board, partially bonding the conductive adhesive layer with the conductive layer of the electrically heatable functional layer, and bonding, hot pressing, and baking other areas of the conductive layer with the semi-cured adhesive layer not covered by the copper circuit layer to obtain an initial electrically heatable flexible circuit board; (4) the initial electrically heatable flexible circuit board is subjected to laser hole opening and resistance adjustment, and film covering to obtain the electrically heatable flexible circuit board. Due to using infrared radiation heating to control the semi-curing degree of the adhesive layer, after the copper circuit is formed on the flexible circuit board, the adhesive layer can still uniformly maintain a semi-cured state and can be directly and well bonded with the conductive layer, and an electrically heatable functional layer with good bonding force and stable performance is prepared.

[0046] Furthermore, in the curing process of the adhesive layer in the preparation method provided by the present invention, infrared radiation heating is used to cure the initial thermosetting resin layer, so that the relative degree of semi-curing of the initial thermosetting resin layer is relatively consistent, and the difference in the relative degree of curing in each region is less than + / - 5%; thus, the difference in the degree of curing in each region is small, which not only maintains a consistent semi-cured state of the adhesive layer, but also maintains consistent and high stability of the bonding force between the copper circuit layer and the adhesive layer and between the conductive layer and the adhesive layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0048] Figure 1 is a flowchart of an embodiment of the present invention;

[0049] Figures 2-5 is a process schematic diagram of the preparation method of the flexible circuit board capable of electric heating of the present invention; Explanation of reference numerals:

[0050] 100. Provide a flexible circuit board; 101. The first flexible insulating substrate layer; 102. The adhesive layer; 103. The copper circuit layer; 104. The conductive adhesive layer; 200. The electric heating functional layer; 201. The conductive layer; 202. The second flexible insulating substrate layer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0051] The following embodiments are provided to better understand the present invention further. They are not limited to the best embodiments, and do not limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior art features falls within the protection scope of the present invention.

[0052] For those steps or conditions not specified in the embodiments, the operations or conditions of the conventional experimental steps described in the literature in this field can be followed. For the reagents or instruments not specified by the manufacturer, they are all conventional reagent products that can be obtained through commercial purchase.

[0053] Embodiment

[0054] This embodiment provides a preparation method of a flexible circuit board capable of electric heating. Refer to Figure 1 , and includes the following steps:

[0055] (1) Provide a flexible circuit board, which includes a first flexible insulating substrate layer, an adhesive layer, and a copper circuit layer stacked in sequence; wherein, the adhesive layer is a thermosetting resin layer in a semi-cured state, and the copper circuit layer covers part of the adhesive layer;

[0056] (2) Provide an electrothermal functional layer, which includes a second flexible insulating substrate layer and a conductive layer;

[0057] (3) After forming a conductive adhesive layer on the surface of the copper circuit layer of the flexible circuit board, bond part of the conductive adhesive layer to the conductive layer of the electrothermal functional layer, and pre-bond, hot-press, and bake other areas of the conductive layer to the semi-cured adhesive layer not covered by the copper circuit layer to obtain an initial electrothermal flexible circuit board;

[0058] (4) The initial electrothermal flexible circuit board is subjected to laser drilling and resistance adjustment, and film covering to obtain the electrothermal flexible circuit board;

[0059] Among them, the process of changing the thermosetting resin layer from the initial state to the semi-cured state is realized by infrared radiation heating.

[0060] The following will be described in detail with reference to Figures 2-5 for details.

[0061] Refer to Figure 2 , provide a flexible circuit board 100, which includes a first flexible insulating substrate layer 101, an adhesive layer 102, and a copper circuit layer 103 stacked in sequence; wherein, the adhesive layer 102 is a thermosetting resin layer in a semi-cured state, and the copper circuit layer 103 covers part of the adhesive layer 102;

[0062] In one embodiment, the bonding force between the copper circuit layer 103 and the thermosetting resin layer in the semi-cured state in the flexible circuit board 100 ≥ 0.3 N / mm;

[0063] In one embodiment, the thickness of the first flexible insulating substrate layer 101 is 5 - 100 μm; such as 5, 10, 20, 30, 50, or 60 μm;

[0064] In one embodiment, the thickness of the adhesive layer 102 is 5 - 100 μm; such as 5, 10, 20, 30, 50, or 60 μm.

[0065] In one embodiment, the thickness of the copper circuit layer 103 is 12 - 60 μm; such as 12, 25, 35, or 50 μm.

[0066] In one embodiment, the material of the first flexible insulating substrate layer 101 is selected from a polyimide film or a polyethylene terephthalate film; in a more specific embodiment, the material of the first flexible insulating substrate layer 101 is selected from a polyimide film.

[0067] In one embodiment, the relative degree of cure of the thermosetting resin in the semi-solidified state is 40-80%; for example, 40%, 50%, 60%, 70% or 80%.

[0068] In a specific embodiment, the preparation process of the flexible circuit board 100 includes the following steps: coating an initial thermosetting resin layer on a copper foil; laminating the first flexible insulating substrate layer 101 on the surface of the initial thermosetting resin layer; performing thermal curing by means of infrared radiation heating to change the initial thermosetting resin layer into a semi-cured thermosetting resin layer; etching the copper foil to obtain the copper circuit layer 103.

[0069] In a more specific embodiment, the coating of the initial thermosetting resin layer on the copper foil is carried out in a roll-to-roll manner.

[0070] In a more specific embodiment, the material of the initial thermosetting resin layer is a glue containing acrylic acid or epoxy resin.

[0071] In a specific embodiment, the thermal curing process is to achieve the semi-curing of the adhesive layer 102 by means of infrared radiation heating; wherein, the temperature of the infrared thermal radiation heating is 100°C - 200°C. Compared with the traditional resistance wire heater, the curing difference of each region is greater than + / -15%. By using the infrared radiation heating method to thermally cure the adhesive layer 102, the semi-curing degree of each region of the initial thermosetting resin or the adhesive layer 102 can be better consistent, and the difference in the relative degree of cure is less than + / -5%; in this way, both the consistent semi-cured state of the adhesive layer 102 and the consistent and high stability of the bonding force between the copper circuit layer 103 and the adhesive layer 102 and between the conductive layer 201 and the adhesive layer 102 are maintained, and there will be no problems such as too small local bonding force, delamination and bubbles.

[0072] For the measurement of the degree of cure, methods such as differential scanning calorimetry (DSC) or TMA can be considered;

[0073] Reference Figure 3 , an electric heating functional layer 200 is provided, and the electric heating functional layer 200 includes a second flexible insulating substrate layer 202 and a conductive layer 201;

[0074] In one embodiment, the material of the second flexible insulating substrate layer 202 is a polyimide film;

[0075] In one embodiment, the material of the conductive layer 201 is selected from metal thin films; in a specific embodiment, the material of the conductive layer 201 is selected from nickel-based alloys, iron-based alloys, alnico alloys, copper-nickel alloys, and titanium-iron alloys; nickel-based alloys include nickel-chromium alloys, nickel-chromium-aluminum-iron alloys, nickel-chromium-manganese-silicon alloys, or nickel-manganese-chromium-molybdenum alloys; iron-based alloys include iron-chromium-aluminum alloys or iron-nickel-chromium-molybdenum alloys; in one embodiment, the thickness of the conductive layer 201 is 0.01 - 0.5 μm; for example, 0.01 μm, 0.05 μm, 0.1 μm, 0.2 μm, 0.3 μm, or 0.5 μm.

[0076] In one embodiment, the thickness of the second flexible insulating substrate layer 202 is 5 - 100 μm; for example, 5 μm, 10 μm, 30 μm, 50 μm, or 80 μm.

[0077] In a specific embodiment, the preparation of the electrothermal functional layer 200 includes the following steps: forming a conductive layer 201 on one side surface of the second flexible insulating substrate layer 202; wherein, the method of forming the conductive layer 201 includes at least one of sputtering and chemical vapor deposition.

[0078] In one embodiment, the sheet resistance of the conductive layer 201 is 30 - 2000 Ω / sq.

[0079] Reference Figure 4 , coating a conductive adhesive layer 104 on the surface of the copper circuit layer 103;

[0080] In one embodiment, the thickness of the conductive adhesive layer 104 is 5 - 50 μm, for example, 5, 10, 30, 50 μm;

[0081] In a specific embodiment, the material of the conductive adhesive layer 104 is a mixture of conductive particles and a thermosetting resin, wherein the conductive particles are selected from, but not limited to, silver, nickel, tin, copper, and titanium, with an average particle size of 10 - 200 nm; wherein the thermosetting resin is selected from, but not limited to, epoxy resins or epoxy-modified resins, with a glass transition temperature Tg of 150 - 200 °C; the mass ratio of the conductive particles to the thermosetting resin is (70 - 99.5):(0.5 - 30), and the volume resistivity is 0.5 -3 *10 -5 Ω·cm.

[0082] In a specific embodiment, the conductive adhesive layer 104 covers a part of the copper circuit layer 103.

[0083] In a more specific embodiment, the line width of the conductive adhesive layer 104 is in a ratio of (0.4 - 0.6):1 to the line width in the copper circuit layer 103, and the adhesive line of the conductive adhesive layer 104 is located in the middle of the corresponding copper wire in the copper circuit layer 103.

[0084] ReferenceFigure 5 , part of the conductive adhesive layer 104 is adhered to the conductive layer 201, and other areas of the conductive layer 201 are pre-bonded, hot-pressed, and baked and cured with the semi-cured adhesive layer 102 not covered by the copper circuit layer 103 to obtain an initial electrically heatable flexible circuit board.

[0085] In one embodiment, in step (3), the pre-bonding temperature is 160 - 200 °C, the pre-bonding speed is 0.1 - 0.5 m / min; the pre-bonding pressure is 1 - 2 MPa; for example, 1 MPa, 1.5 MPa, or 2 MPa.

[0086] In a specific embodiment, the pre-bonding process is carried out by a laminating machine.

[0087] In one embodiment, in step (3), the hot-pressing temperature is 160 - 200 °C, the hot-pressing time is 200 - 300 s; the hot-pressing pressure is 1 - 10 MPa; for example, 1 MPa, 2 MPa, 5 MPa, 8 MPa, or 10 MPa.

[0088] In a specific embodiment, the hot-pressing process is realized by an FPC fast press.

[0089] In one embodiment, the bonding strength between the adhesive layer 102 after hot-pressing and baking and curing and the conductive layer 201 > 0.5 N / mm.

[0090] In this application, the bonding strength is measured by a peeling tester.

[0091] In a specific embodiment, the curing degree of the adhesive layer 102 after hot-pressing and baking and curing is greater than 99%;

[0092] The initial electrically heatable flexible circuit board is subjected to laser hole opening and resistance adjustment, and laminating to obtain the electrically heatable flexible circuit board. Among them, the resistance adjustment is carried out according to the actual target resistance requirement. The laminating process is to cover the protective film layer on both surfaces of the initial electrically heatable flexible circuit board; the protective film layer is subjected to hot-pressing and baking and curing treatment to obtain the electrically heatable flexible circuit board; among them, the thickness of the protective film layer is 12 - 100 μm; the material of the protective film layer is selected from polyimide films.

[0093] Obviously, the above embodiments are merely examples for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or variations derived therefrom are still within the protection scope of the present invention.

Claims

1. A preparation method of an electrically heatable flexible circuit board, characterized in that, It includes the following steps: (1) Provide a flexible circuit board, which includes a first flexible insulating substrate layer, an adhesive layer, and a copper circuit layer laminated in sequence; wherein, the adhesive layer is a semi-cured thermosetting resin layer, and the copper circuit layer covers part of the adhesive layer; (2) Provide an electrothermal functional layer, which includes a second flexible insulating substrate layer and a conductive layer; (3) After forming a conductive adhesive layer on the surface of the copper circuit layer of the flexible circuit board, bond part of the conductive adhesive layer with the conductive layer of the electrothermal functional layer, and pre-bond, hot-press, and bake the other areas of the conductive layer with the semi-cured adhesive layer not covered by the copper circuit layer to obtain an initial electrothermal flexible circuit board; (4) The initial electrothermal flexible circuit board is subjected to laser drilling and resistance adjustment, and film covering to obtain the electrothermal flexible circuit board; Among them, the process of the semi-cured thermosetting resin layer changing from the initial state to the semi-cured state is realized by infrared radiation heating.

2. The preparation method according to claim 1, characterized in that, The preparation process of the flexible circuit board includes the following steps: Coat an initial thermosetting resin layer on the copper foil; Bond the first flexible insulating substrate layer on the surface of the initial thermosetting resin layer; Perform thermal curing by infrared radiation heating to make the initial thermosetting resin layer become a semi-cured thermosetting resin layer; Etch the copper foil to obtain the copper circuit layer.

3. The preparation method according to claim 2, characterized in that, The relative curing degree of the semi-solidified thermosetting resin layer is 40%-80%; Preferably, the temperature of infrared thermal radiation heating is 100°C-200°C.

4. The preparation method according to claim 1, characterized in that, In step (3), the pre-bonding temperature is 160°C-200°C, the pre-bonding speed is 0.1m / min-0.5m / min, and the pre-bonding pressure is 1-2MPa; and / or, In step (3), the hot-press temperature is 160°C-200°C, the hot-press time is 200s-300s; the hot-press pressure is 1-10MPa.

5. The preparation method according to claim 1, wherein The bonding strength between the copper circuit layer and the semi-cured thermosetting resin layer in the flexible circuit board is ≥0.3N / mm; and / or, The bonding strength between the adhesive layer after baking in step (3) and the conductive layer is >0.5N / mm.

6. The preparation method according to claim 1, characterized in that, The preparation of the electrothermal functional layer includes the following steps: form a conductive layer on one side surface of the second flexible insulating substrate layer; wherein, the method of forming the conductive layer includes at least one of sputtering and chemical vapor deposition; Preferably, the sheet resistance of the conductive layer is 30Ω / sq-2000Ω / sq.

7. The preparation method according to claim 1, characterized in that, The thickness of the first flexible insulating substrate layer is 5-100μm; and / or, The thickness of the second flexible insulating substrate layer is 5-100μm; and / or, The thickness of the semi-cured thermosetting resin layer is 5-100μm; and / or, The thickness of the copper circuit layer is 12μm-60μm; and / or, The thickness of the conductive layer is 0.01μm-0.5μm; and / or, The thickness of the conductive adhesive layer is 5μm-50μm.

8. The preparation method according to claim 1, characterized in that, In step (4), the process of film covering includes: Cover protective film layers on both side surfaces of the initial electrothermal flexible circuit board; Perform hot-press and baking curing treatment on the protective film layers to obtain the electrothermal flexible circuit board; Among them, the thickness of the protective film layer is 12 - 100 μm; the material of the protective film layer is selected from polyimide films.

9. The preparation method according to claim 1, wherein The material of the flexible insulating substrate layer is selected from polyimide films or polyethylene terephthalate films; and / or, the raw material of the semi-cured thermosetting resin layer is a resin containing epoxy resin and / or acrylic acid; and / or, The material of the conductive layer is selected from metal thin films; and / or, The material of the conductive adhesive layer is a mixture of conductive particles and thermosetting resin.

10. An electrically heatable flexible circuit board, characterized in that, The electro-heatable flexible circuit board is prepared by the preparation method according to any one of claims 1 - 9.

11. Application of an electro-heatable flexible circuit board prepared by the preparation method according to any one of claims 1 - 9 or the electro-heatable flexible circuit board according to claim 10 in structural elements of spacecraft airborne equipment, structural elements of land, sea and air transportation vehicles, vacuum devices, spacesuits, infrared thermal physiotherapy health care cabins, automotive battery thermal management equipment, automotive seat heating equipment, and household floor heating equipment.

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