Thin and stretchable flexible circuit board and manufacturing method therefor

Abstract

Disclosed are a thin and stretchable flexible circuit board and a manufacturing method therefor. The method comprises: attaching a low-adhesion protective film to a first side of a flexible circuit substrate provided with a circuit layer and two protective film layers, and forming a first circuit substrate, the low-adhesion protective film having a first preset adhesive force; cutting the first circuit substrate to form a meandering circuit, tearing off waste material to form a second circuit substrate; attaching a first elastomer composite film to a second side of the second circuit substrate, and performing adhesion reduction operation on the low-adhesion protective film, so that the low-adhesion protective film has a second preset adhesion force, forming a third circuit substrate, the second preset adhesive force being smaller than the first preset adhesive force; and tearing off the low-adhesion protective film on the third circuit substrate, forming a target circuit board. According to the present invention, on the basis of the low-adhesion protective film, the yield of mass produced products may be improved. Furthermore, on the basis of the elasticity of a composite structure of a polymer film, the meandering circuit may be encapsulated, and different lamination processes can be adapted to, achieving thinning and miniaturization.

Description

Thin stretchable flexible circuit board and manufacturing method thereof Technical Field

[0001] The present invention relates to the field of flexible circuit board manufacturing, and in particular to a thin and stretchable flexible circuit board and a manufacturing method thereof. Background Art

[0002] As an emerging technology, flexible and stretchable electronics are gaining widespread application due to their ability to be compressed, twisted, and conform to complex, non-planar surfaces. Currently, wearable electronic applications have a positive impact on all aspects of daily life, driving economic growth and the rapid development of stretchable electronic devices and related manufacturing technologies. Flexible, soft, and stretchable electronic devices are enabling the next generation of wearable electronic applications, opening up a variety of applications for healthcare, energy, and military purposes.

[0003] A crucial component of flexible and stretchable electronic products is stretchable conductor circuits, ensuring both stretchability and signal and power transmission. Currently, there are numerous methods for fabricating stretchable conductor circuits. One popular approach involves forming metal conductors, such as copper and aluminum, into bendable, stretchable, meandering circuits, which are then encapsulated in a highly elastic polymer (also known as an elastomer). This method requires prefabricating the meandering circuit on a carrier film, bonding the circuit to the elastomer, and then removing the film. To ensure high yield in mass production, the bonding strength between the carrier film and the elastomer must be high before bonding to the elastomer to prevent separation during removal (tearing off) of unwanted waste areas. Furthermore, the bonding strength after bonding must be sufficiently low to ensure that the carrier film can be removed while also preventing separation. However, this current mass production method presents significant challenges, resulting in low yield rates.

[0004] On the other hand, the method currently used to combine meandering circuits with elastomers is usually casting. However, this method requires complex mold design and the resulting stretchable conductor circuits are relatively thick, usually greater than 1mm, which is not conducive to the lightweight and miniaturization of flexible and stretchable electronic products. Technical issues

[0005] In view of this, the present invention provides a thin and stretchable flexible circuit board and a manufacturing method thereof to solve the problems of low mass production yield and large circuit thickness in existing stretchable circuit boards, which are not conducive to the lightweight and miniaturization of products. Technical Solutions

[0006] The present invention provides a method for manufacturing a thin and stretchable flexible circuit board, comprising:

[0007] A flexible circuit substrate having a circuit layer and two protective film layers is provided, and a viscosity-reducing protective film is attached to a first side of the flexible circuit substrate to form a first circuit substrate; wherein the two protective film layers are respectively located on either side of the circuit layer; and the viscosity-reducing protective film has a first predetermined adhesion force;

[0008] From the second side of the first circuit substrate, the two protective film layers in the first circuit substrate are cut to form a meandering circuit between the circuit layer and the two protective film layers after the cut shapes, and waste is removed from the cut first circuit substrate to form a second circuit substrate; wherein the meandering circuit has at least one stretching direction;

[0009] Providing a first elastomeric composite film, laminating the first elastomeric composite film to the second side of the second circuit substrate, and performing a viscosity-reducing operation on the viscosity-reducing protective film on the first side of the second circuit substrate so that the viscosity-reducing protective film has a second predetermined adhesion force, thereby forming a third circuit substrate; wherein the second predetermined adhesion force is less than the first predetermined adhesion force;

[0010] The viscosity-reducing protective film is peeled off from the third circuit substrate to form a target circuit board.

[0011] Optionally, the anti-viscosity protective film includes any one of a UV anti-viscosity film and a thermal anti-viscosity film.

[0012] Optionally, when the viscosity-reducing protective film is the UV viscosity-reducing film, performing a viscosity-reducing operation on the viscosity-reducing protective film on the first side of the second circuit substrate includes:

[0013] performing UV irradiation on the viscosity-reducing protective film on the first side of the second circuit substrate;

[0014] When the viscosity-reducing protective film is the thermal viscosity-reducing film, the viscosity-reducing operation on the viscosity-reducing protective film on the first side of the second circuit substrate includes:

[0015] The viscosity-reducing protective film on the first side of the second circuit substrate is heated.

[0016] Optionally, the first preset adhesive force is greater than 500 gf / inch, and the second preset adhesive force is less than 100 gf / inch.

[0017] Optionally, the first elastomer composite film includes a first polymer film layer having a first melting point and a second polymer film layer having a second melting point, and the second polymer film layer is arranged on one side of the first polymer film layer; wherein the first melting point is lower than the second melting point.

[0018] Optionally, providing a first elastomer composite film, laminating the first elastomer composite film to the second side of the second circuit substrate, and performing a viscosity reduction operation on the viscosity reduction protective film on the first side of the second circuit substrate so that the viscosity reduction protective film has a second preset adhesion force, thereby forming a third circuit substrate, includes:

[0019] performing a viscosity reduction operation on the viscosity reduction protective film on the first side of the second circuit substrate so that the viscosity reduction protective film has the second preset adhesion;

[0020] providing the first elastomeric composite film;

[0021] The side of the first elastomer composite film provided with the first polymer film layer is laminated to the second side of the second circuit substrate after the viscosity reduction operation to form the third circuit substrate.

[0022] Optionally, providing a first elastomer composite film, laminating the first elastomer composite film to the second side of the second circuit substrate, and performing a viscosity reduction operation on the viscosity reduction protective film on the first side of the second circuit substrate so that the viscosity reduction protective film has a second preset adhesion force, thereby forming a third circuit substrate, includes:

[0023] providing the first elastomeric composite film;

[0024] Laminating the side of the first elastomer composite film provided with the first polymer film layer to the second side of the second circuit substrate;

[0025] A viscosity reduction operation is performed on the viscosity reduction protective film on the first side of the second circuit substrate so that the viscosity reduction protective film has the second preset adhesion force, thereby forming the third circuit substrate.

[0026] Optionally, after the viscosity-reducing protective film on the third circuit substrate is removed, the method further includes:

[0027] providing a second elastomeric composite film identical to the first elastomeric composite film;

[0028] The side of the second elastomer composite film provided with the first polymer film layer is attached to the first side of the third circuit substrate after the viscosity-reducing protective film is removed.

[0029] Optionally, the difference between the second melting point and the first melting point ranges from 20 to 100°C.

[0030] Optionally, the difference between the second melting point and the first melting point ranges from 30°C to 60°C.

[0031] Optionally, the thickness of the first polymer film layer is in the range of 30 to 100 μm, and / or the thickness of the second polymer film layer is in the range of 25 to 150 μm.

[0032] Optionally, the winding line includes:

[0033] substrate layer;

[0034] At least one conductive wire layer laminated on one side or both sides of the substrate layer; and

[0035] The two protective film layers after the outer shape cutting are respectively adhered to the outermost conductor layer or the substrate layer through the adhesive layer.

[0036] Optionally, the number of wires in each wire layer is one or more.

[0037] In addition, the present invention also provides a thin and stretchable flexible circuit board, which is manufactured using the aforementioned manufacturing method. Beneficial effects

[0038] The beneficial effects of the present invention are as follows: since the circuit layer and the two protective film layers need to be cut when forming a winding circuit, on the one hand, the two protective film layers need to be cut so that the circuit layer becomes a stretchable winding circuit; on the other hand, the first elastomer composite film needs to be adhered after the winding circuit is formed, so the first side of the flexible circuit substrate having the circuit layer and the two protective film layers is adhered with a viscosity-reducing protective film. The viscosity-reducing protective film can be used as a carrier film when forming the winding circuit, providing support for the entire first circuit substrate when cutting, so as to facilitate better production of the winding circuit; it also provides support when the waste is subsequently torn off and the first elastomer composite film is adhered to form a thin and stretchable flexible circuit board; the viscosity-reducing protective film has viscosity-reducing properties, that is, it can reduce viscosity (i.e., reduce adhesion) through a certain viscosity-reducing operation, so when the winding circuit is produced, When tearing off the waste, the greater adhesion before the viscosity reduction operation can be used to ensure a stronger bonding force between the winding line and the viscosity reduction protective film, ensuring that the winding line is separated from the viscosity reduction protective film when the waste is torn off; then, after laminating the first elastomer composite film, the smaller adhesion after the viscosity reduction operation can be used to ensure that the viscosity reduction protective film can be easily torn off while also ensuring that the winding line is not separated from the first elastomer composite film; thereby, mass production of stretchable flexible circuit boards can be achieved and the mass production yield can be improved; in addition, the first elastomer composite film is a composite structure with multiple layers of polymer films, which can not only encapsulate the winding line based on the elasticity of the polymer film, but also use the characteristics of different polymer films to adapt to different pressing processes, thereby facilitating the reduction of the thickness of the stretchable flexible circuit board and realizing the lightweight and miniaturization of flexible and stretchable electronic products. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The features and advantages of the present invention will be more clearly understood by referring to the accompanying drawings, which are schematic and should not be construed as limiting the present invention in any way. In the accompanying drawings:

[0040] FIG1 shows a flow chart of a method for manufacturing a thin and stretchable flexible circuit board according to a first embodiment of the present invention;

[0041] 2A and 2B respectively show cross-sectional structural views of the first circuit substrate before and after outer shape cutting in the first embodiment of the present invention;

[0042] FIG3 shows a cross-sectional structural diagram of a meandering line in a first embodiment of the present invention;

[0043] FIG4 shows a schematic diagram of a U-shaped meandering line in the first embodiment of the present invention;

[0044] FIG5 is a schematic diagram showing a horseshoe-shaped meandering line in the first embodiment of the present invention;

[0045] FIG6 shows a top view of the structure of the circuit layer after the circuit is formed into a meandering circuit in the first embodiment of the present invention;

[0046] FIG7 shows a cross-sectional structural diagram of the first elastomer composite film in Example 1 of the present invention;

[0047] FIG8 shows a front view structural diagram of a target circuit board in the first embodiment of the present invention;

[0048] FIG9 shows a cross-sectional structural diagram of a target circuit board in the first embodiment of the present invention.

[0049] The description of each reference numeral is as follows:

[0050] 1. Flexographic board, 2. First elastomer composite film, 3. Second elastomer composite film, 11. Meandering line, 12. Transition zone, 13. Non-stretchable zone, 111. Substrate layer, 112. Wire layer, 113. Protective film layer, 114. Adhesive layer, 21. First polymer film layer, 22. Second polymer film layer, 4. Anti-viscosity protective film. Modes for Carrying Out the Invention

[0051] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making any creative efforts shall fall within the scope of protection of the present invention.

[0052] Example 1

[0053] This embodiment provides a method for manufacturing a thin and stretchable flexible circuit board, as shown in FIG1 , comprising:

[0054] S1: Providing a flexible circuit substrate having a circuit layer and two protective film layers, and attaching a viscosity-reducing protective film to a first side of the flexible circuit substrate to form a first circuit substrate; wherein the two protective film layers are respectively located on either side of the circuit layer; and the viscosity-reducing protective film has a first predetermined adhesion force;

[0055] S2: Cutting the two protective film layers in the first circuit substrate from the second side of the first circuit substrate so that the circuit layer and the two cut protective film layers form a meandering circuit, and removing waste from the cut first circuit substrate to form a second circuit substrate; wherein the meandering circuit has at least one stretching direction;

[0056] S3: Providing a first elastomeric composite film, laminating the first elastomeric composite film to the second side of the second circuit substrate, and performing a viscosity reduction operation on the viscosity reduction protective film on the first side of the second circuit substrate so that the viscosity reduction protective film has a second predetermined adhesion force, thereby forming a third circuit substrate; wherein the second predetermined adhesion force is less than the first predetermined adhesion force;

[0057] S4: peeling off the viscosity-reducing protective film from the third circuit substrate to form a target circuit board.

[0058] In this embodiment, since the circuit layer and the two protective film layers need to be cut when forming a winding circuit, the two protective film layers need to be cut so that the circuit layer becomes a stretchable winding circuit; on the other hand, the first elastomer composite film needs to be adhered after the winding circuit is formed. Therefore, the first side of the flexible circuit substrate having the circuit layer and the two protective film layers is adhered with a viscosity-reducing protective film. The viscosity-reducing protective film can be used as a carrier film when forming the winding circuit, providing support for the entire first circuit substrate when cutting, so as to facilitate better production of the winding circuit; it also provides support when the waste is subsequently torn off and the first elastomer composite film is adhered to form a thin and stretchable flexible circuit board; the viscosity-reducing protective film has viscosity-reducing properties, that is, it can reduce viscosity (i.e., reduce adhesion) through a certain viscosity-reducing operation, so when the winding circuit is produced, When the waste material is torn off, the greater adhesion before the viscosity reduction operation can be used to ensure a stronger bonding force between the winding line and the viscosity reduction protective film, ensuring that the winding line is separated from the viscosity reduction protective film when the waste material is torn off; then, after the first elastomer composite film is attached, the smaller adhesion after the viscosity reduction operation can be used to ensure that the viscosity reduction protective film can be easily torn off while also ensuring that the winding line is not separated from the first elastomer composite film; thereby, mass production of stretchable flexible circuit boards can be achieved and the mass production yield can be improved; in addition, the first elastomer composite film is a composite structure with multiple layers of polymer films, which can not only encapsulate the winding line based on the elasticity of the polymer film, but also use the characteristics of different polymer films to adapt to different pressing processes, thereby facilitating the reduction of the thickness of the stretchable flexible circuit board and realizing the lightweight and miniaturization of flexible and stretchable electronic products.

[0059] The following describes in detail each step of the method for making a thin, stretchable flexible circuit board.

[0060] The flexible circuit substrate having a circuit layer and two protective film layers in this embodiment S1 refers to a circuit board that has undergone the DES process, including dry film development and exposure, etching, film stripping, chemical cleaning, protective film layer application, and lamination. After these processes, a circuit layer that meets the product design is formed on the flexible circuit substrate, and protective film layers are applied to both sides of the circuit layer.

[0061] The primary components of the anti-viscosity protective film in Example S1 include polyester film (PET) and a special acrylic adhesive. It exhibits excellent adhesion and protective properties, and can, under certain conditions, reduce adhesion and friction, achieving specific applications. Anti-viscosity protective films are commonly used in wafer dicing applications, but in this example, they are used in the production of thin, stretchable flexible circuit boards. They serve as a carrier film, providing support for cutting the protective film layer. Furthermore, when the scrap material is removed after the serpentine circuit is produced, they ensure a strong bond between the serpentine circuit and the anti-viscosity protective film, ensuring that the serpentine circuit portion is separated from the anti-viscosity protective film during removal. Furthermore, after laminating the first elastomeric composite film, the reduced adhesion after the anti-viscosity operation ensures that the anti-viscosity protective film can be easily removed while also ensuring that the serpentine circuit portion does not separate from the first elastomeric composite film. This overcomes the difficulties encountered in conventional mass production of flexible and stretchable electronic products, thereby improving production yield.

[0062] It should be noted that the circuit layer of this embodiment includes circuits that already have a serpentine shape (the serpentine shape can be formed using conventional methods, which will not be described in detail here). Because the protective film layer is applied in its entirety to the circuit layer during the actual application process, the serpentine-shaped circuits cannot be stretched or contracted, and thus cannot become truly stretchable serpentine circuits. Therefore, the protective film layer must be subsequently cut to shape the circuits so that they can be stretched or contracted at the serpentine locations.

[0063] Before the outer shape cutting of the present embodiment S2, the cross-sectional structure of the first circuit substrate is shown in FIG2A ; there are various ways to perform the outer shape cutting in the present embodiment S2, such as using a laser for pattern cutting, punching with a mold with a specific pattern, etc. In these methods, it is necessary to cut the protective film layer where the circuit needs to meander, and ensure that it does not affect the anti-viscosity protective film to ensure the integrity and continuity of the anti-viscosity protective film. The cross-sectional structure of the first circuit substrate after the outer shape cutting is shown in FIG2B . In FIG2A and FIG2B , 111 is the base material layer, 112 is the conductor layer, 113 is the protective film layer, 114 is the adhesive layer, and 4 is the anti-viscosity protective film.

[0064] Preferably, as shown in FIG. 2B and FIG. 3 to FIG. 5 , the meandering line 11 produced in the embodiment S2 includes:

[0065] Base material layer 111;

[0066] At least one conductive line layer 112 is formed on one side or both sides of the substrate layer 111;

[0067] The two protective film layers 113 after being cut into shape are respectively adhered to the outermost conductive wire layer 112 or the substrate layer 111 through the adhesive layer 114 .

[0068] The winding circuit of the above structure has both good stretchability and excellent circuit protection performance, which can ensure the functionality of the entire stretchable flexible circuit board and ensure that the metal in the circuit layer will not produce cracks, cracks and other problems that affect functionality during the stretching and rebound process, thereby improving the service life.

[0069] Specifically, the material of substrate layer 111 includes any one of polyimide (PI), polyester resin (PET), LCP, and polybutylene terephthalate (PBT), or a mixture thereof. LCP is a liquid crystal polymer made from materials such as polyphenyl terephthalate (PBT), polymethyl methacrylate (PMMA), and polycarbonate (PC).

[0070] The wire layer 112 is a metal wire layer, and its material is copper or aluminum.

[0071] The material of the protective film layer 113 also includes any one or a mixture of polyimide (PI), polyester resin (PET), LCP, polybutylene terephthalate (PBT), and is used to protect the inner conductor layer and substrate layer of the meandering circuit.

[0072] The material of the adhesive layer 114 includes any one of epoxy resin, acrylic resin, and polyolefin resin, or a mixture of these.

[0073] In a serpentine circuit, the number of conductor layers is one, two or more layers. When it is one layer, it is only formed on one side of the substrate layer; when it is two or more layers, it can be formed on one side of the substrate layer or on both sides of the substrate layer (usually formed on both sides).

[0074] In a serpentine circuit, there are two protective film layers, each bonded to the outermost layer of the serpentine circuit via an adhesive layer (therefore, there are at least two adhesive layers). When a conductor layer is distributed on only one side of the substrate layer, one of the two protective film layers is bonded to the outermost conductor layer via the adhesive layer, and the other of the two protective film layers is bonded to the outermost substrate layer via the adhesive layer. When conductor layers are distributed on both sides of the substrate layer, one of the two protective film layers is bonded to the outermost conductor layer on the first side of the serpentine circuit via the adhesive layer, and the other of the two protective film layers is bonded to the outermost conductor layer on the second side of the serpentine circuit via the adhesive layer.

[0075] In a meandering line, the number of wires in each wire layer is one or more.

[0076] Through one or more wires, it can adapt to the design of different flexible and stretchable electronic products.

[0077] The number of conductor layers and the number of conductors in each conductor layer depend on the specific product design and are not limited here.

[0078] The meandering circuit 11 shown in Figures 2B, 3, and 5 of this embodiment comprises a substrate layer 111, two conductor layers 112, two contour-cut protective film layers 113, and two adhesive layers 114. The two conductor layers 112 are located on either side of the substrate layer 111, and the two contour-cut protective film layers 113 are bonded to the outer sides of the conductor layers 112 via adhesive layers 114, resulting in a double-layer circuit structure. The meandering circuit in Figure 4 is U-shaped, while the meandering circuit in Figure 5 is horseshoe-shaped (the two adhesive layers 114 are not shown in Figures 4 and 5). Each conductor layer contains two conductors.

[0079] In this embodiment, the number of the meandering lines is greater than or equal to one.

[0080] By varying the number of meandering lines, the design of different flexible and stretchable electronic products can also be adapted. The specific number and shape of the meandering lines depend on the specific product design and are not limited here.

[0081] In this embodiment S2, the serpentine line 11 is a stretchable region of the circuit layer. When the circuit layer is fabricated into a serpentine line 11, the circuit layer on the first circuit substrate further includes a transition region 12 connected to both ends of the serpentine line 11 and an inextensible region 13 connected to each of the transition regions 12 at both ends, as shown in FIG6 (wherein FIG6 shows four serpentine lines 11). The transition region 12 is composed of a circuit board structure that gradually changes from thin to thick. This structure allows the stress to gradually change during stretching, making it less likely to break. The inextensible region 13 is composed of a circuit board structure of fixed size. Its size does not change during stretching. Components with certain functions can be provided according to actual conditions, or components with different functions connected to different serpentine lines can be provided separately. In FIG6, the four transition regions 12 at each end are all connected to the same inextensible region 13.

[0082] Preferably, in this embodiment S3, as shown in Figure 7, the first elastomer composite film 2 includes a first polymer film layer 21 having a first melting point and a second polymer film layer 22 having a second melting point, and the second polymer film layer 22 is arranged on one side of the first polymer film layer 21; wherein the first melting point is lower than the second melting point.

[0083] The above-mentioned first polymer film layer with a lower melting point (i.e., the first melting point) and the second polymer film layer with a higher melting point (i.e., the second melting point) are used as the first elastomer composite film. This film not only has good elasticity to encapsulate winding circuits, but also can adapt to different lamination processes by utilizing the characteristics of different polymer films. The first polymer film layer with a lower melting point flows during lamination, thereby bonding the entire first elastomer composite film to the flexible board (specifically, the second circuit substrate), and can reduce the thickness of the entire first elastomer composite film, which is beneficial to the miniaturization and lightweightness of flexible board electronic products. The second polymer film layer with a higher melting point does not flow during lamination, thereby ensuring the elasticity of the entire first elastomer composite film while also guaranteeing its strength, thereby protecting the flexible board electronic products.

[0084] In a first optional embodiment, S3 includes:

[0085] S3A1: performing a viscosity reduction operation on the viscosity reduction protective film on the first side of the second circuit substrate, so that the viscosity reduction protective film has the second preset adhesion;

[0086] S3A2: providing the first elastomer composite film;

[0087] S3A3: Laminating the side of the first elastomer composite film provided with the first polymer film layer to the second side of the second circuit substrate after the viscosity reduction operation to form the third circuit substrate.

[0088] The first optional embodiment mentioned above is to form the third circuit substrate by first reducing the viscosity and then laminating the first elastomer composite film. This method reduces the adhesion of the viscosity-reducing protective film through the viscosity-reducing operation, so that when the viscosity-reducing protective film is subsequently torn off when the third circuit substrate is formed, it is ensured that the viscosity-reducing protective film can be easily torn off while also ensuring that the winding circuit is not separated from the first elastomer composite film; the side of the first elastomer composite film provided with the first polymer film layer is laminated as the inner layer on the second side of the second circuit substrate, which not only utilizes the film-carrying function of the viscosity-reducing protective film to facilitate the laminating operation, but also does not affect the subsequent tearing of the viscosity-reducing protective film. At the same time, it is also convenient to utilize the lower melting point characteristics of the first polymer film layer to achieve a good bonding effect between the entire first elastomer composite film and the flexible board (specifically the second circuit substrate), thereby achieving the purpose of encapsulating the winding circuit.

[0089] In a second alternative embodiment, S3 includes:

[0090] S3B1: providing the first elastomer composite film;

[0091] S3B2: Laminating the side of the first elastomer composite film provided with the first polymer film layer to the second side of the second circuit substrate;

[0092] S3B3: performing a viscosity reduction operation on the viscosity reduction protective film on the first side of the second circuit substrate so that the viscosity reduction protective film has the second preset adhesion force, thereby forming the third circuit substrate.

[0093] The above-mentioned second optional embodiment is to form the third circuit substrate by first laminating the first elastomeric composite film and then reducing the viscosity. Similar to the first optional embodiment, the viscosity reduction operation can reduce the adhesion of the viscosity-reducing protective film, so that when the viscosity-reducing protective film is subsequently removed after the third circuit substrate is formed, the viscosity-reducing protective film can be easily torn off while also ensuring that the winding circuit is not separated from the first elastomeric composite film; the side of the first elastomeric composite film provided with the first polymer film layer is laminated as the inner layer on the second side of the second circuit substrate, which not only facilitates the laminating operation, but also does not affect the subsequent removal of the viscosity-reducing protective film, and at the same time achieves a good bonding effect between the entire first elastomeric composite film and the flexible board (specifically, the second circuit substrate), thereby achieving the purpose of encapsulating the winding circuit.

[0094] In addition, compared with the first optional embodiment, the above-mentioned second optional embodiment can also avoid the impact caused by the flexible plate being separated from the anti-viscosity protective film due to movement, transportation, etc. after the anti-viscosity operation, and the adhesive on the anti-viscosity protective film reacting with the first elastomer composite film when performing the anti-viscosity operation, thereby further improving the mass production yield of flexible and stretchable electronic products.

[0095] Of course, if after the de-viscosity operation, the flexible board will not be separated from the de-viscosity protective film due to movement, transportation, etc., and the adhesive on the de-viscosity protective film will not react with the first elastomer composite film when the de-viscosity operation is performed, then the first optional embodiment or the second optional embodiment can be selected according to actual conditions to form the third circuit substrate.

[0096] Preferably, the anti-viscosity protective film includes any one of a UV anti-viscosity film and a thermal anti-viscosity film.

[0097] Preferably, when the viscosity-reducing protective film is the UV viscosity-reducing film, in S3, performing a viscosity-reducing operation on the viscosity-reducing protective film on the first side of the second circuit substrate includes:

[0098] performing UV irradiation on the viscosity-reducing protective film on the first side of the second circuit substrate;

[0099] When the viscosity-reducing protective film is the thermal viscosity-reducing film, in S3, performing a viscosity-reducing operation on the viscosity-reducing protective film on the first side of the second circuit substrate includes:

[0100] The viscosity-reducing protective film on the first side of the second circuit substrate is heated.

[0101] Both UV and thermal adhesive reduction films have good adhesion and protective properties, and can reduce adhesion through simple adhesive reduction operations (including UV irradiation and heating), thereby reducing the difficulty of mass production of flexible and stretchable electronic products.

[0102] Preferably, the first preset adhesive force is greater than 500 gf / inch, and the second preset adhesive force is less than 100 gf / inch.

[0103] The first preset adhesion force in the above range can ensure that when the waste is torn off after the winding circuit is produced, the larger adhesion force can ensure a stronger bonding force between the winding circuit and the anti-viscosity protective film, and ensure that the winding circuit portion is separated from the anti-viscosity protective film when the waste is torn off; the second preset adhesion force in the above range can ensure that after the first elastomer composite film is attached, the smaller adhesion force can be used to ensure that the anti-viscosity protective film can be easily torn off while also ensuring that the winding circuit is not separated from the first elastomer composite film, thereby enabling mass production of stretchable flexible circuit boards and improving mass production yield.

[0104] Both UV and thermal anti-viscosity films can be selected according to actual conditions. For example, the UV anti-viscosity film can use the SL-9715UV-3 model anti-viscosity film, and the thermal anti-viscosity film can use the SL-9900J model anti-viscosity film.

[0105] In this embodiment, the above-mentioned laminating of the anti-viscosity protective film and the laminating of the first elastomer composite film can both adopt conventional laminating operation methods, and the above-mentioned waste material tearing off and tearing off the anti-viscosity protective film can both adopt conventional tearing operation methods. The specific details of the laminating and tearing operation methods are not repeated here.

[0106] Preferably, in S4, after the viscosity-reducing protective film is removed from the third circuit substrate, the method further includes:

[0107] providing a second elastomeric composite film identical to the first elastomeric composite film;

[0108] The side of the second elastomer composite film provided with the first polymer film layer is attached to the first side of the third circuit substrate after the viscosity-reducing protective film is removed.

[0109] By laminating a second elastomer composite film identical to the first elastomer composite film to the first side of the third circuit substrate after removing the viscosity-reducing protective film, both sides of the entire third circuit substrate can be encapsulated, further enhancing the protection of the winding circuit and improving product quality.

[0110] The specific operation method of laminating the second elastomer composite film is the same as the specific operation method of laminating the first elastomer composite film, and the specific details are not repeated here.

[0111] Preferably, in the first and second elastomer composite films, the difference between the second melting point and the first melting point is in the range of 20-100°C.

[0112] Preferably, the difference between the second melting point and the first melting point is in the range of 30-60°C.

[0113] The above-mentioned difference in melting points can better meet different lamination processes, ensuring that the first polymer film layer with a lower melting point flows during lamination, thereby bonding the entire first elastomer composite film to the flexible board (specifically, the second circuit substrate), and facilitating the miniaturization and lightweighting of flexible board electronic products. It also ensures that the second polymer film layer with a higher melting point does not flow during lamination, thereby ensuring the elasticity of the entire first elastomer composite film while also ensuring its strength.

[0114] Preferably, in the first elastomer composite film and the second elastomer composite film, the thickness of the first polymer film layer is in the range of 30 to 100 μm, and / or the thickness of the second polymer film layer is in the range of 25 to 150 μm.

[0115] The first polymer film layer and the second polymer film layer within the above-mentioned thickness range can not only ensure that the two polymer film layers fully exert their own characteristics, but also maximize the reduction of the thickness of the entire first elastomer composite film and the second elastomer composite film, which helps to make flexible and stretchable electronic products lighter and smaller.

[0116] Preferably, in the above-mentioned first elastomer composite film and the second elastomer composite film, the tensile modulus of the first polymer film layer and the tensile modulus of the second polymer film layer are both less than 10 MPa; and / or, the elongation at break of the first polymer film layer and the tensile modulus of the second polymer film layer are both greater than or equal to 200%.

[0117] The tensile modulus and elongation at break within the above range can effectively ensure good stretchability of the entire target circuit board.

[0118] In an optional embodiment, the first polymer film layer and the second polymer film layer are both made of one or more copolymer modifications of polyesters, polyimides, polyamides, polyolefins, polyurethanes, polycarbonates and polyacrylonitrile-butylene-styrene copolymers.

[0119] The first polymer film layer and the second polymer film layer of the above material can rebound after stretching. Unlike new conductive materials such as conductive polymers, composite materials of conductive particles and elastomers, and liquid metals (usually alloys containing gallium and indium), their conductive properties will not decrease with the increase of tensile elongation. Their tensile properties are stable, which is conducive to the production of flexible and stretchable electronic products with excellent tensile properties.

[0120] Preferably, after laminating the second elastomer composite film, the method further comprises:

[0121] The third circuit substrate on which the second elastomer composite film is bonded is baked.

[0122] By baking, the first polymer film layer with a lower melting point in the first elastomer composite film and the second elastomer composite film can be further solidified, so that the bonding strength between the first elastomer composite film and the flexible plate, and between the second elastomer composite film and the flexible plate is better.

[0123] The target circuit board finally produced in this embodiment has a main view structure as shown in FIG8 and a cross-sectional view structure as shown in FIG9 , which includes a flexible board 1 having a meandering circuit 11 and a first elastomer composite film 2 and a second elastomer composite film 3 located on both sides of the flexible board 1 .

[0124] It should be understood that, since in actual production, the target circuit board is produced in a batch production process, the flexible board 1 in FIG9 has multiple winding lines (specifically, 4); and when the second elastomer composite film 3 is pressed onto the third circuit substrate, the first polymer film layer in the second elastomer composite film 3 flows due to the pressing, and will merge into one with the first polymer film layer in the first elastomer composite film 2 and the first polymer film layer in the second elastomer composite film 3 on the adjacent flexible board. Therefore, the first polymer film layer 21 in FIG9 is actually an integrated structure of the first polymer film layer in the first elastomer composite film 2 and the first polymer film layer in the second elastomer composite film 3.

[0125] To further illustrate this solution, four embodiments were produced. Samples of the target circuit board in this solution were produced in each of the four embodiments (their cross-sectional structures are shown in FIG8 ), and the maximum elongation and number of stretching cycles of each sample were compared.

[0126] The cross-section of the winding line 11 in the sample produced in Example 1 is shown in Figure 4. The first polymer film layer in the first elastomer composite film and the second elastomer composite film adopts TPU (i.e., polyurethane) film, and the corresponding first melting point is 100°C, the tensile modulus is 0.4 MPa, and the thickness is 60 μm; the second polymer film layer in the first elastomer composite film and the second elastomer composite film also adopts TPU (i.e., polyurethane) film, and the corresponding second melting point is 150°C, the tensile modulus is 4 MPa, and the thickness is 60 μm.

[0127] The cross section of the meandering line 11 in the sample prepared in Example 2 is shown in FIG5 . The first polymer film layer in the first elastomer composite film and the second elastomer composite film, as well as the second polymer film layer are the same as those in Example 1 and are not listed here.

[0128] The cross-section of the winding line 11 in the sample prepared in Example 3 is shown in Figure 4. The first polymer film layer in the first elastomer composite film and the second elastomer composite film adopts PDMS (i.e., polydimethylsiloxane) film, and the corresponding first melting point is 120°C, the tensile modulus is 0.1 MPa, and the thickness is 60 μm; the second polymer film layer in the first elastomer composite film and the second elastomer composite film also adopts PDMS (i.e., polydimethylsiloxane) film, and the corresponding second melting point is 170°C, the tensile modulus is 0.4 MPa, and the thickness is 100 μm.

[0129] The cross section of the meandering line 11 in the sample prepared in Example 4 is shown in FIG5 . The first polymer film layer in the first elastomer composite film and the second elastomer composite film, as well as the second polymer film layer are the same as those in Example 3 and are not listed here.

[0130] After the samples in each embodiment were prepared, the maximum elongation and the number of stretching cycles of each sample were evaluated and compared. The evaluation method is as follows:

[0131] The evaluation process of maximum elongation is:

[0132] (1) Measure the length L0 of the stretchable area of ​​the sample, clamp the inextensible areas at both ends of the sample on the tensile testing machine fixture to maintain the natural shape of the sample;

[0133] (2) Stretch the sample at a rate of 500 mm / min until the sample breaks. At this time, the elongation length of the stretchable zone of the sample is L;

[0134] (3) Calculate the maximum elongation of the sample using the formula: L / L0×100%.

[0135] The evaluation process of the number of stretching cycles is:

[0136] (1) Measure the length L0 of the stretchable zone of the sample, and then fix both ends of the sample on the fixture of the tensile fatigue testing machine to maintain the natural shape of the sample;

[0137] (2) Connect the resistance test electrodes to the two sections of the meandering line to test whether the metal wires in the meandering line are broken;

[0138] (3) Stretch the sample cyclically, with each stretch making the stretchable area of ​​the sample extend 100% of its length, and stretch 45 times per minute until the test is damaged or the wire is broken.

[0139] The maximum elongation and the number of stretching cycles of the samples in each embodiment were evaluated according to the above evaluation method. The comparison results of the maximum elongation and the number of stretching cycles of each sample obtained after evaluation are shown in Table 1 below.

[0140] Table 1 Maximum elongation and number of stretching cycles of each sample in the four examples

[0141] Example 1 Example 2 Example 3 Example 4 Maximum elongation 224234176188 Number of stretching cycles 2000200030003000

[0142] From the above comparison results, it can be seen that the thin stretchable flexible circuit board produced by the production method in this scheme has excellent stretchability.

[0143] Example 2

[0144] This embodiment provides a thin and stretchable flexible circuit board, which is manufactured using the manufacturing method described in the first embodiment.

[0145] Compared with traditional stretchable circuit boards, the thin stretchable flexible circuit board produced in this embodiment can not only reduce the difficulty of mass production and improve the yield of mass-produced products based on the anti-viscosity protective film; it can also encapsulate winding circuits based on the elasticity of the composite structure of the polymer film and adapt to different pressing processes, thereby facilitating the reduction of the thickness of the stretchable flexible circuit board and realizing the lightweight and miniaturization of flexible and stretchable electronic products.

[0146] The manufacturing method of the thin stretchable flexible circuit board in this embodiment is the same as the method steps described in Example 1. Therefore, for the details not fully described in this embodiment, please refer to the specific description of Example 1 and Figures 1 to 9, and will not be repeated in this embodiment.

[0147] Although the embodiments of the present invention have been described with reference to the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention. Such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A method for manufacturing a thin and stretchable flexible circuit board, characterized in that: include: A flexible circuit substrate having a circuit layer and two protective film layers is provided, and a viscosity-reducing protective film is attached to a first side of the flexible circuit substrate to form a first circuit substrate; wherein the two protective film layers are respectively located on both sides of the circuit layer; and the viscosity-reducing protective film has a first preset adhesion; From the second side of the first circuit substrate, the two protective film layers in the first circuit substrate are cut into an outer shape, so that the circuit layer and the two protective film layers after the outer shape cutting form a meandering circuit, and the cut first circuit substrate is torn off waste material to form a second circuit substrate; wherein the meandering circuit has at least one stretching direction; Providing a first elastic composite film, laminating the first elastic composite film on the second side of the second circuit substrate, and performing a viscosity reduction operation on the viscosity reduction protective film on the first side of the second circuit substrate so that the viscosity reduction protective film has a second preset adhesion force, thereby forming a third circuit substrate; wherein the second preset adhesion force is less than the first preset adhesion force; The viscosity-reducing protective film is peeled off from the third circuit substrate to form a target circuit board.

2. The method according to claim 1, characterized in that The anti-viscosity protective film includes any one of a UV anti-viscosity film and a thermal anti-viscosity film.

3. The method according to claim 2, characterized in that When the viscosity-reducing protective film is the UV viscosity-reducing film, the viscosity-reducing operation on the viscosity-reducing protective film on the first side of the second circuit substrate includes: Performing UV irradiation on the viscosity-reducing protective film on the first side of the second circuit substrate; When the viscosity-reducing protective film is the thermal viscosity-reducing film, the viscosity-reducing operation on the viscosity-reducing protective film on the first side of the second circuit substrate includes: The viscosity-reducing protective film on the first side of the second circuit substrate is heated.

4. The method according to claim 1, characterized in that The first preset adhesive force is greater than 500 gf / inch, and the second preset adhesive force is less than 100 gf / inch.

5. The method according to claim 1, characterized in that The first elastomer composite film includes a first polymer film layer with a first melting point and a second polymer film layer with a second melting point, and the second polymer film layer is arranged on one side of the first polymer film layer; wherein the first melting point is lower than the second melting point.

6. The method according to claim 5, characterized in that The method of providing a first elastic composite film, laminating the first elastic composite film on the second side of the second circuit substrate, and performing a viscosity reduction operation on the viscosity reduction protective film on the first side of the second circuit substrate so that the viscosity reduction protective film has a second preset adhesion force, thereby forming a third circuit substrate, includes: Performing a viscosity reduction operation on the viscosity reduction protective film on the first side of the second circuit substrate so that the viscosity reduction protective film has the second preset adhesion; providing the first elastomeric composite film; The side of the first elastomer composite film provided with the first polymer film layer is bonded to the second side of the second circuit substrate after the viscosity reduction operation to form the third circuit substrate.

7. The method according to claim 5, characterized in that The method of providing a first elastic composite film, laminating the first elastic composite film on the second side of the second circuit substrate, and performing a viscosity reduction operation on the viscosity reduction protective film on the first side of the second circuit substrate so that the viscosity reduction protective film has a second preset adhesion force, thereby forming a third circuit substrate, includes: providing the first elastomeric composite film; Laminating the side of the first elastomer composite film provided with the first polymer film layer to the second side of the second circuit substrate; A viscosity reducing operation is performed on the viscosity reducing protective film on the first side of the second circuit substrate so that the viscosity reducing protective film has the second preset adhesion force, thereby forming the third circuit substrate.

8. The method according to claim 5, characterized in that After the viscosity-reducing protective film is removed from the third circuit substrate, the method further includes: providing a second elastomeric composite film identical to the first elastomeric composite film; The side of the second elastomer composite film provided with the first polymer film layer is attached to the first side of the third circuit substrate after the viscosity-reducing protective film is torn off.

9. The method according to claim 5, characterized in that The difference between the second melting point and the first melting point ranges from 20 to 100°C.

10. The method according to claim 5, characterized in that The difference between the second melting point and the first melting point ranges from 30 to 60°C.

11. The method according to claim 5, characterized in that The thickness of the first polymer film layer is in the range of 30-100 μm, and / or the thickness of the second polymer film layer is in the range of 25-150 μm.

12. The method according to any one of claims 1 to 11, characterized in that: The winding line comprises: substrate layer; at least one conductive line layer formed on one side or both sides of the substrate layer; and The two protective film layers after the cut shapes are respectively bonded to the outermost conductor layer or the substrate layer through adhesive layers.

13. The method according to claim 12, characterized in that The number of wires in each wire layer is one or more.

14. A thin and stretchable flexible circuit board, characterized in that: The method is produced according to any one of claims 1 to 13.

Images