Bending-resistant circuit boards and their manufacturing methods

Abstract

This application discloses a bend-resistant circuit board and its manufacturing method. By providing a first self-healing insulating layer, a self-healing conductive layer, and a second self-healing insulating layer with self-healing function in the bending area, this structure can repeatedly self-repair when damage such as cracks or breaks occurs, and can continue to be used normally after self-repair. This significantly increases the number of bends that the bend-resistant circuit board can withstand, thereby improving its service life.

Description

Technical Field

[0001] This application relates to the field of circuit board technology, and in particular to a bend-resistant circuit board and a method for manufacturing the same. Background Technology

[0002] To improve the bending resistance of flexible printed circuit boards (FPCs) and extend their service life, current FPCs typically employ the following techniques: laying copper mesh at the bends, reducing the thickness at the bends, and using a symmetrical structural design.

[0003] Laying a copper mesh at the bend can improve the bending life of the FPC to some extent because the hardness of the copper mesh is less than that of solid copper. However, there is still a risk of breakage after repeated bending. Reducing the thickness at the bend can reduce the stress during bending, but it will affect the structural design of the end product. Using a symmetrical design and placing the bend area in the center of the structure can effectively reduce the stress in the bend area, but it will lead to inflexible wiring.

[0004] Therefore, a new method is needed to improve the bending capacity and service life of FPC. Summary of the Invention

[0005] In view of this, this application proposes a bend-resistant circuit board with self-healing capability, which can repair itself when the bending area of ​​the bend-resistant circuit board is damaged, thereby improving the bending capability and service life of the bend-resistant circuit board.

[0006] In addition, it is necessary to provide a method for manufacturing a bend-resistant circuit board.

[0007] A bend-resistant circuit board includes a first substrate and a second substrate. The first substrate has a first groove, within which a first self-healing insulating layer and a self-healing conductive layer are disposed, at least a portion of the self-healing conductive layer being embedded within the first self-healing insulating layer. The second substrate is disposed on a surface of the first substrate and has a second groove communicating with the first groove. A second self-healing insulating layer is disposed within the second groove, and the second self-healing insulating layer and the first self-healing insulating layer enclose the self-healing conductive layer.

[0008] Both the first and second self-healing insulating layers are formed of self-healing insulating materials. The self-healing insulating material comprises multiple polymer backbones, including hard and soft segments. The hard segments include urethane structures, and the soft segments include coordination structures formed by heterocyclic structures on the soft segments coordinating with metal ions. The self-healing conductive layer comprises a polyurethane elastomer and a conductive filler. The polyurethane elastomer comprises a first polyurethane and a second polyurethane. The first polyurethane has a dynamically cross-linked structure, and the second polyurethane has both a dynamically cross-linked structure and a permanently chemically cross-linked structure. The first polyurethane is obtained by polymerization of a raw material composition including benzophenone compounds, isocyanate compounds, and polyols. The benzophenone compounds include compounds with phenolic hydroxyl or aniline groups, and the isocyanate compounds include compounds with three or more isocyanate groups. The second polyurethane is formed by irradiating the first polyurethane with ultraviolet light. The conductive filler is embedded on the surface of the first polyurethane.

[0009] A method for manufacturing a bend-resistant circuit board includes the following steps: forming a first groove on a first copper-clad laminate; disposing of a self-healing insulating material in the first groove and drying it to form a first self-healing insulating layer; forming a plurality of openings on the first self-healing insulating layer; disposing of a self-healing conductive material in the openings and drying it to form a self-healing conductive layer, thereby obtaining a first substrate; forming a second groove on a second copper-clad laminate; disposing of the self-healing insulating material in the second groove and drying it to form a second self-healing insulating layer, thereby obtaining a second substrate; and pressing the first substrate and the second substrate together such that the second self-healing insulating layer and the first self-healing insulating layer enclose the self-healing conductive layer.

[0010] This application provides a first self-healing insulating layer, a self-healing conductive layer, and a second self-healing insulating layer with self-healing function in the bending area. When damage such as cracks or breaks occurs, the above structure can repeatedly self-repair and continue to be used normally after self-repair, which greatly increases the number of bends that the bend-resistant circuit board can withstand, thereby improving the service life of the bend-resistant circuit board. Attached Figure Description

[0011] Figure 1 This is a cross-sectional view of a bend-resistant circuit board according to one embodiment of this application.

[0012] Figures 2 to 12 For preparation Figure 1 The cross-sectional view of the bend-resistant circuit board shown.

[0013] Explanation of main component symbols

[0014] 100 Stretch-resistant road slab

[0015] First substrate 10

[0016] Second substrate 20

[0017] First self-healing insulation layer 30

[0018] Self-healing conductive layer 40

[0019] Second self-healing insulation layer 50

[0020] Adhesive layer 60

[0021] First dielectric layer 11

[0022] First line layer 12

[0023] First protective layer 13

[0024] First groove 101

[0025] Bending area 110

[0026] Non-bending area 120

[0027] First slot 130

[0028] First through channel 140

[0029] Second dielectric layer 21

[0030] Second line layer 22

[0031] Second protective layer 23

[0032] Second groove 201

[0033] Second slot 230

[0034] Second through channel 240

[0035] Opening 301

[0036] First copper-clad laminate 10a

[0037] First copper foil layer 12a

[0038] Second copper-clad laminate 20a

[0039] Second copper foil layer 22a

[0040] The following detailed description, in conjunction with the accompanying drawings, further illustrates the embodiments of this application. Detailed Implementation

[0041] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the embodiments of this application pertain. The terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the embodiments of this application. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0042] It should be noted that all directional indicators (such as up, down, left, right, front, back, etc.) in the embodiments of this application are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicator will also change accordingly.

[0043] It will be understood that when a layer is referred to as "on" another layer, it can be directly on that other layer or there may be an intermediate layer in between. Conversely, when a layer is referred to as "directly on" another layer, there is no intermediate layer. When a component is referred to as "attached to," "mounted to," "set on," or "connected to" another component, it can be directly on that other component or there may be an intervening component. The term "and / or" as used herein includes all and any combination of one or more of the associated listed items.

[0044] Embodiments of this application are described herein with reference to cross-sectional views, which are schematic diagrams of idealized embodiments (and intermediate configurations) of this application. Therefore, variations in the shapes illustrated due to manufacturing processes and / or tolerances are foreseeable. Consequently, embodiments of this application should not be construed as limited to the specific shapes of the areas illustrated herein, but should include, for example, deviations in shape due to manufacturing processes. The areas shown in the figures are merely illustrative, and their shapes are not intended to represent the actual shapes of the illustrated devices, nor are they intended to limit the scope of this application.

[0045] The following detailed description of some embodiments of this application is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0046] Please see Figure 1 The first aspect of this application provides a bend-resistant circuit board 100, which includes a first substrate 10 and a second substrate 20 stacked together. The first substrate 10 has a first groove 101, which extends along the thickness of the first substrate 10 (i.e., ...). Figure 1A first substrate 10 (vertically penetrating the first substrate 10) has a first groove 101 containing a first self-healing insulating layer 30 and a self-healing conductive layer 40, with at least a portion of the self-healing conductive layer 40 embedded within the first self-healing insulating layer 30. A second substrate 20 is disposed on a surface of the first substrate 10 and has a second groove 201 communicating with the first groove 101. A second self-healing insulating layer 50 is disposed within the second groove 201, and the second self-healing insulating layer 50 and the first self-healing insulating layer 30 enclose the self-healing conductive layer 40. That is, the surface of the self-healing conductive layer 40 is either covered by the first self-healing insulating layer 30 or by the second self-healing insulating layer 50.

[0047] Both the first self-healing insulating layer 30 and the second self-healing insulating layer 50 are formed of self-healing insulating material. The polymer backbone of the self-healing insulating material includes hard segments and soft segments. The hard segments include urethane structures, and the soft segments include coordination structures. The coordination structures are formed by the coordination of heterocyclic structures located on the soft segments with metal ions.

[0048] The self-healing conductive layer 40 includes a polyurethane elastomer and a conductive filler. The polyurethane elastomer includes a first polyurethane and a second polyurethane. The first polyurethane includes a dynamically cross-linked structure, and the second polyurethane includes both a dynamically cross-linked structure and a permanently chemically cross-linked structure. The first polyurethane is obtained by polymerization of a raw material composition including benzophenone compounds, isocyanate compounds, and polyols. The benzophenone compounds include compounds having phenolic hydroxyl or aniline groups, and the isocyanate compounds include compounds having three or more isocyanate groups. The conductive filler is embedded in the surface of the first polyurethane.

[0049] In the bend-resistant circuit board 100, the first self-healing insulating layer 30 and the layer in the thickness direction (i.e., Figure 1 The area (vertically) corresponding to the first self-healing insulating layer 30 (i.e., the projection overlaps with the first self-healing insulating layer 30) constitutes the bending area 110 of the bend-resistant circuit board 100, while the remaining area is the non-bending area 120. In the bending area 110, the first self-healing insulating layer 30, the self-healing conductive layer 40, and the second self-healing insulating layer 50 all have self-healing functions.

[0050] In the first self-healing insulating layer 30 and the second self-healing insulating layer 50, hydrogen bonds and metal chelate structures are formed between the polymer chains of the self-healing insulating material. When the molecular chains are subjected to external forces (such as stretching or scratching), causing the hydrogen bonds to break and / or the metal chelate structures to be destroyed, the hydrogen bonds and / or chelate structures will reform after a certain period of time, thus completing the self-healing process. Since the hydrogen bonds and metal chelate structures can re-bond after repeated breakage, the first self-healing insulating layer 30 and the second self-healing insulating layer 50 of this application can repeatedly self-heal when they are damaged by bending or other reasons, such as cracks or breaks, and can continue to be used normally after self-healing. Therefore, the number of bends that the bending area 110 can withstand is greatly increased, thereby improving the service life of the bending area 110.

[0051] In the self-healing conductive layer 40, some regions of the surface of the polyurethane elastomer have only a dynamic cross-linking structure and no permanent chemical cross-linking structure, while other regions have both dynamic and permanent chemical cross-linking structures. For clarity and conciseness, this application refers to the polyurethane elastomer with only a dynamic cross-linking structure and no permanent chemical cross-linking structure as the first polyurethane, and the polyurethane elastomer with both dynamic and permanent chemical cross-linking structures as the second polyurethane. In this application, "dynamic cross-linking structure" refers to a structure in which the chemical bonds forming the cross-linking structure between polymer molecular chains can dynamically break and recover with changes in external conditions. For example, under the first condition, polymer molecular chains are connected by chemical bonds to form a cross-linking structure, while under the second condition, the connected chemical bonds break, and when the first condition is restored, the broken chemical bonds reform. "Permanent chemical cross-linking structure" refers to a structure in which the chemical bonds forming the cross-linking structure between polymer molecular chains cannot dynamically break and recover. For example, when external conditions change and cause the chemical bonds forming the cross-linking structure to break, even if the external conditions are restored, the broken chemical bonds cannot reform. The surface without a permanent chemical cross-linking structure (i.e., the surface of the first polyurethane) can subsequently embed conductive fillers, while the surface with a permanent chemical cross-linking structure (i.e., the second polyurethane) cannot embed conductive fillers. Thus, a patterned conductive filler can be formed on the surface of the polyurethane elastomer, and the patterned conductive filler forms a conductive circuit.

[0052] Because the polyurethane elastomer of the self-healing conductive layer 40 has a dynamic cross-linking structure, it possesses self-healing properties (self-healing can be achieved under heating conditions). Therefore, when the self-healing conductive layer 40 of this application suffers damage such as cracks or breaks due to bending or other reasons, it can repeatedly self-heal and continue to be used normally after self-healing. This significantly increases the number of bends that the bending region 110 can withstand, thus improving the bending life of the bending region 110. Furthermore, the first self-healing insulating layer 30 and the second self-healing insulating layer 50 encapsulate the self-healing conductive layer 40, providing a certain degree of protection and further reducing the failure risk of the self-healing conductive layer 40.

[0053] In some embodiments, such as Figure 1 As shown, the first substrate 10 includes a first dielectric layer 11, a first circuit layer 12 located on the surface of the first dielectric layer 11, and a first protective layer 13 covering the first circuit layer 12. The first protective layer 13 may be, but is not limited to, a cover film layer (CVL). A first groove 101 penetrates at least through the first dielectric layer 11 in the thickness direction, and the first protective layer 13 has a first slot 130, with the first slot 130 penetrating a portion of the first protective layer 13 in the thickness direction. In this embodiment, the first circuit layer 12 is located on two opposite surfaces of the first dielectric layer 11, and the first groove 101 penetrates one of the first circuit layers 12 and the first dielectric layer 11, with the bottom wall of the first groove 101 being another first circuit layer 12. In other embodiments, the first substrate 10 may include two or more first dielectric layers 11 and three or more first circuit layers 12. At this time, a first dielectric layer 11 is provided between two adjacent first circuit layers 12, and the first protective layer 13 covers the outermost first circuit layer 12 (that is, the first circuit layer 12 that is furthest from the first groove 101 in the thickness direction).

[0054] Furthermore, the self-healing conductive layer 40 includes impedance lines, power lines, and ground lines. The impedance lines are... Figure 1 The symbol S indicates the power cord. Figure 1 In the diagram, P represents the ground wire. Figure 1 The first slot 130 is represented by G. There can be multiple first slots 130, some of which correspond to the impedance line S (i.e., the orthographic projection of the first slot 130 is located within the orthographic projection of the impedance line), and others correspond to the power line P (i.e., the orthographic projection of the first slot 130 is located within the orthographic projection of the power line). This allows the bending area 110 to have maximum bending capacity and reduces the bending stress in the bending area 110. The depth of the first slot 130 can be half the thickness of the first protective layer 13.

[0055] Furthermore, within the bending region 110, the outermost first circuit layer 12 may have multiple first through slots 140. The first through slots 140 may penetrate the outermost first circuit layer 12 along the thickness direction, so as to make the bond between the first protective layer 13 and the outermost first circuit layer 12 tighter.

[0056] In some embodiments, such as Figure 1 As shown, the second substrate 20 includes a second dielectric layer 21, a second circuit layer 22 located on the surface of the second dielectric layer 21, and a second protective layer 23 covering the second circuit layer 22. The second protective layer 23 may be, but is not limited to, a CVL. A second groove 201 penetrates the second dielectric layer 21 along the thickness direction. The second protective layer 23 has a second slot 230, which penetrates the second protective layer 23 along the thickness direction. The depth of the second slot 230 may be half the thickness of the second protective layer 23. In this embodiment, the second substrate 20 includes one second dielectric layer 21 and one second circuit layer 22. In other embodiments, the second substrate 10 may include two or more second dielectric layers 21 and two or more second circuit layers 22. In this case, a second dielectric layer 21 is provided between two adjacent second circuit layers 22, and the second protective layer 23 covers the outermost second circuit layer 22 (that is, the second circuit layer 22 farthest from the second groove 201 in the thickness direction).

[0057] Furthermore, there can be multiple second slots 230, some of which are set to correspond to the impedance line S (that is, the orthographic projection of the second slot 230 is located within the orthographic projection of the impedance line), and other second slots 230 are set to correspond to the power line P (that is, the orthographic projection of the second slot 230 is located within the orthographic projection of the power line). In this way, the bending area 110 can have maximum bending capacity, and the bending stress of the bending area 110 can also be reduced.

[0058] Furthermore, within the bending region 110, the outermost second circuit layer 22 may have multiple second through slots 240. The second through slots 240 may penetrate the outermost second circuit layer 22 along the thickness direction, so as to make the bond between the second protective layer 23 and the outermost second circuit layer 22 tighter.

[0059] In some embodiments, such as Figure 1 As shown, the sum of the thicknesses H of the first self-healing insulating layer 30 and the second self-healing insulating layer 50 is 12μm to 100μm. This ensures that both the first and second self-healing insulating layers 30 and 50 have certain bending properties, while also controlling the overall thickness of the bend-resistant circuit board 100.

[0060] In some embodiments, the heterocyclic structure may be one or more of azopyridine, alkylpyridine, halopyridine, aminopyridine, bromopyridine, methylpyridine, iodopyridine, chloropyridine, hydroxypyridine, benzylpyridine, ethylpyridine, bipyridine, imidazole, pyrazole, and thiophene. The metal ion may be one or more of zinc ions, iron ions, nickel ions, and copper ions.

[0061] In some embodiments, the benzophenone compound may be, but is not limited to, one or more of 4,4'-dihydroxybenzophenone, 2,4-dihydroxybenzophenone, 4,4'-diaminobenzophenone, and 2,4-diaminobenzophenone. Compounds having three or more isocyanate groups may be, but are not limited to, one or more of hexamethylene diisocyanate trimer, isophorone diisocyanate trimer, and dicyclohexylmethane diisocyanate trimer.

[0062] In some embodiments, the materials of the first dielectric layer 11 and the second dielectric layer 21 may be independently selected from polyimide (PI), polyethylene terephthalate (PET), polyethylene naphthalate dimethyl acid glycol ester (PEN), polydimethylsiloxane (PDMS), liquid crystal polymer (LCP), etc. The materials of the first dielectric layer 11 and the second dielectric layer 21 may be the same or different, and this application does not impose any limitations.

[0063] Please see Figures 2 to 12 The second aspect of this application provides a method for manufacturing a bend-resistant circuit board 100, which includes steps S1 to S12. It is understood that the numbering of the steps is intended to clearly describe the specific preparation method and does not imply a limitation on the order of the steps.

[0064] Please see Figure 2 and Figure 3 S1, the first groove 101 can be formed on the first copper-clad laminate 10a by means of laser cutting, but not limited to laser cutting.

[0065] like Figure 2 As shown, the first copper-clad laminate 10a may include a first dielectric layer 11 and a first copper foil layer 12a located on opposite surfaces of the first dielectric layer 11. The first dielectric layer 11 may be, but is not limited to, PI, PET, PEN, PDMS, LCP, etc.

[0066] like Figure 3As shown, the first groove 101 penetrates a first copper foil layer 12a and a first dielectric layer 11 along the thickness direction, and part of the surface of another first copper foil layer 12a can be exposed from the first groove 101.

[0067] Please continue reading. Figure 3 S2, the first copper foil layer 12a is fabricated to form the first circuit layer 12. The first circuit layer 12 can be fabricated using image transfer and etching processes.

[0068] Please see Figure 4 S3, a self-healing insulating material can be placed in the first groove 101 by means of printing and then dried to form a first self-healing insulating layer 30. The self-healing insulating material comprises multiple polymer backbones, which include hard segments and soft segments. The hard segments include urethane structures, and the soft segments include coordination structures formed by the coordination of heterocyclic structures located on the soft segments with metal ions.

[0069] like Figure 4 As shown, the surface of the first self-healing insulating layer 30 near the opening of the first groove 101 (i.e. Figure 4 The lower surface of the first self-healing insulating layer 30 can be flush with the surface of the first circuit layer 12 (the first circuit layer 12 that is closer to the opening of the first groove 101 in the thickness direction) away from the surface of the first dielectric layer 11.

[0070] In some embodiments, the self-healing insulating material can be prepared by the following steps.

[0071] First, a first solution is provided. The first solution comprises isocyanate monomers and a solvent, wherein the isocyanate monomers constitute 75%-85% by weight in the first solution. The isocyanate monomers may be, but are not limited to, trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylidene diisocyanate, 1,3-butylidene diisocyanate, dodecamethyl diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, 1,3-cyclopentylene diisocyanate, 1,3-cyclohexane diisocyanate, etc. The solvent may be, but is not limited to, tetrahydrofuran (THF).

[0072] Secondly, a second solution is provided. The second solution comprises a diol containing a heterocyclic structure and a solvent, with the diol comprising 85%-95% by weight. The diol is a compound having a functional group capable of coordinating with a metal and capable of polymerizing with isocyanate monomers. Typically, diol compounds are chosen that contain a heterocyclic functional group. The type of heterocyclic structure can be, but is not limited to, azopyridine, alkylpyridine, halopyridine, aminopyridine, bromopyridine, methylpyridine, iodopyridine, chloropyridine, hydroxypyridine, benzylpyridine, ethylpyridine, and bipyridine, etc., and pyrazoles, thiophenes, or imidazoles can also be used. Specifically, poly(propylene glycol) can be selected as the diol. The solvent can be, but is not limited to, THF.

[0073] Then, the first solution and the second solution are mixed and subjected to a polymerization reaction to obtain a polymer precursor containing heterocyclic structures and diols. The polymer backbone of the polymer precursor contains hard segments and soft segments; the hard segments include urethane structures, and the soft segments include heterocyclic structures.

[0074] In some embodiments, the first solution can be preheated in a water bath at 40°C to 70°C, preferably around 60°C, and then the second solution can be slowly added dropwise to the first solution. The reaction can be carried out for 10 to 15 hours, preferably around 12 hours, to obtain the polymer precursor. The polymer precursor can be diluted with a solvent before proceeding to the next reaction.

[0075] Next, a third solution is provided. The third solution comprises a metal salt and a solvent. The metal salt constitutes 20%-30% by weight in the third solution, and the solvent may be, but is not limited to, THF. The metal ion in the metal salt is a transition metal ion, and may be, but is not limited to, one or more of zinc, iron, nickel, and copper ions. The anion in the metal salt may be CF3SO3. - NO 3- SO4 2- and Cl - One or more of them.

[0076] Finally, the polymer precursor is mixed with the third solution and subjected to a chelation reaction, so that the metal ions in the metal salt form a coordination structure with the heterocyclic structure, thereby obtaining a self-healing insulating material.

[0077] In some embodiments, a certain concentration of the polymer precursor is first diluted with a solvent (preferably THF), stirred evenly, and then a third solution is slowly added dropwise to the diluted polymer precursor solution. The reaction is carried out at room temperature for 4 to 8 hours to obtain a self-healing insulating material. The dried self-healing insulating material forms a first self-healing insulating layer 30.

[0078] Please see Figure 5S4, multiple openings 301 can be formed on the first self-healing insulating layer 30 by means of, but not limited to, laser ablation or mechanical cutting. The openings 301 penetrate the first self-healing insulating layer 30 along the thickness direction.

[0079] Please see Figure 6 S5, a self-healing conductive material can be applied within the opening 301 by means of printing, but not limited to printing, and then dried to form a self-healing conductive layer 40, thus obtaining a first substrate 10. The self-healing conductive material includes a polyurethane elastomer and a conductive filler. The polyurethane elastomer includes a first polyurethane and a second polyurethane. The first polyurethane includes a dynamically cross-linked structure, and the second polyurethane includes both a dynamically cross-linked structure and a permanently chemically cross-linked structure. The first polyurethane is obtained by polymerization of a raw material composition including benzophenone compounds, isocyanate compounds, and polyols. The benzophenone compounds include compounds having phenolic hydroxyl or aniline groups, and the isocyanate compounds include compounds having three or more isocyanate groups. The conductive filler is embedded in the surface of the first polyurethane.

[0080] In some embodiments, the self-healing conductive material can be prepared by the following steps.

[0081] First, the raw material composition and catalyst are subjected to a polymerization reaction to obtain a polyurethane with a dynamically crosslinked structure. The raw material composition includes benzophenone compounds, isocyanate compounds, and polyols. In the raw material composition, the molar ratio of benzophenone compounds:isocyanate compounds:polyols is 1:(0.8–3):(0.3–3), preferably 1:(1–2.5):(0.5–2). The benzophenone compounds may be, but are not limited to, one or more of 4,4'-dihydroxybenzophenone, 2,4-dihydroxybenzophenone, 4,4'-diaminobenzophenone, and 2,4-diaminobenzophenone. The isocyanate compounds are preferably compounds having three or more isocyanate groups, such as hexamethylene diisocyanate trimers, isophorone diisocyanate trimers, dicyclohexylmethane diisocyanate trimers, etc. The polyols may be, but are not limited to, polycaprolactone polyols, polybutylene adipate polyols, etc. The catalyst can be any catalyst known in the art suitable for the preparation of polyurethane, such as triethylenediamine, bis(dimethylaminoethyl) ether, etc. The polymerization temperature can be 40°C to 120°C, and the reaction time can be 4 hours to 48 hours. Since the reaction between the hydroxyl or amino groups in benzophenone compounds and compounds having three or more isocyanate groups is reversible, a dynamically cross-linked structure is formed.

[0082] Next, a mask is applied to the surface of the polyurethane and irradiated with ultraviolet light to obtain a polyurethane elastomer with a patterned crosslinked surface. The mask has patterned voids that allow ultraviolet light to pass through. Utilizing the photoradical initiation properties of the benzophenone group, photo-induced self-crosslinking is achieved, thereby further forming a permanent chemical crosslinking structure on the ultraviolet-irradiated surface portion of the polyurethane with a dynamically crosslinked structure. This effectively combines the two different crosslinking structures: the dynamic crosslinking structure and the permanent chemical crosslinking structure. The ultraviolet light wavelength can be 300–500 nm, preferably 365 nm, and the irradiation time can be 5–60 minutes.

[0083] Finally, a filter membrane with deposited conductive filler is placed on a polyurethane elastomer, heated to embed the conductive filler into the polyurethane elastomer, and then cooled to room temperature. The filter membrane is then removed to obtain a self-healing conductive material. The conductive filler can be, but is not limited to, metal nanowires (e.g., silver nanowires), carbon nanotubes, graphene, liquid metal, or metal particles (e.g., copper particles). The conductive filler can be deposited on a polytetrafluoroethylene filter membrane using a vacuum filtration method. The heating temperature can be 100°C, and the time can be 1 hour. Utilizing the adhesiveness of the non-permanently chemically cross-linked portion of the polyurethane elastomer surface, the conductive filler can embed into the polyurethane elastomer surface, thereby obtaining a self-healing conductive material with conductive properties. After drying, the self-healing conductive material forms a self-healing conductive layer 40. The self-healing conductive layer 40 is located near the surface of the opening of the first groove 101 (i.e....). Figure 6 The lower surface of the self-healing conductive layer 40 can be adjacent to the surface of the first self-healing insulating layer 30 near the opening of the first groove 101 (i.e. Figure 6 The lower surface of the first self-healing insulation layer 30 is flush with the middle surface.

[0084] Please see Figure 7 and Figure 8 S6, a second groove 201 may be formed on the second copper-clad laminate 20a by means of, but not limited to, laser cutting.

[0085] like Figure 7 As shown, the second copper-clad laminate 20a may include a second dielectric layer 21 and a second copper foil layer 22a located on one surface of the second dielectric layer 21. The second dielectric layer 21 may be, but is not limited to, PI, PET, PEN, PDMS, LCP, etc.

[0086] like Figure 8 As shown, the second groove 201 penetrates the second dielectric layer 21 along the thickness direction, and a portion of the surface of the second copper foil layer 22a near the first dielectric layer 21 can be exposed from the second groove 201.

[0087] Please continue reading. Figure 8 S7, the second copper foil layer 22a is fabricated to form the second circuit layer 22. The second circuit layer 22 can be fabricated using image transfer and etching processes.

[0088] Please see Figure 9 In step S8, a self-healing insulating material can be placed in the second groove 201 by means of printing, and then dried to form a second self-healing insulating layer 50, thus obtaining a second substrate 20. The preparation method of the self-healing insulating material is the same as that in step S3, and will not be described again here. The surface of the second self-healing insulating layer 50 facing away from the second circuit layer 22 can be flush with the surface of the first dielectric layer 21 facing away from the second circuit layer 22.

[0089] Please see Figure 10 S9, with the first self-healing insulating layer 30 of the first substrate 10 facing the second self-healing insulating layer 50 of the second substrate 20, the first substrate 10 and the second substrate 20 are pressed together so that the first self-healing insulating layer 30 and the second self-healing insulating layer 50 cover the self-healing conductive layer 40.

[0090] In some embodiments, an adhesive layer 60 may be provided between the first substrate 10 and the second substrate 20 to make the connection between the first substrate 10 and the second substrate 20 more secure. It is understood that the adhesive layer 60 has adhesive-free areas at positions corresponding to the first self-healing insulating layer 30 and the second self-healing insulating layer 50, so that the first self-healing insulating layer 30 and the second self-healing insulating layer 50 can contact each other. The adhesive layer 60 may be formed of pure adhesive (AD).

[0091] Please see Figure 11 In step S10, multiple first through-slots 140 can be formed on the outermost first circuit layer 12 and multiple second through-slots 140 can be formed on the outermost second circuit layer 22 by means of, but not limited to, laser cutting. The first through-slots 140 can penetrate the outermost first circuit layer 12 along the thickness direction to facilitate subsequent bonding of the first protective layer 13. The second through-slots 240 can penetrate the outermost second circuit layer 22 along the thickness direction to facilitate subsequent bonding of the second protective layer 23.

[0092] Please see Figure 12 S11, a first protective layer 13 is provided on the surface of the outermost first circuit layer 12, and a second protective layer 23 is provided on the surface of the outermost second circuit layer 22.

[0093] Please see Figure 1S12, a first groove 130 can be formed on the first protective layer and a second groove 230 can be formed on the second protective layer 23 by means of laser cutting, to obtain a bend-resistant circuit board 100. The number of the first groove 130 and the second groove 230 can be multiple, of which a portion of the first groove 130 and the second groove 230 are set to the impedance line S of the self-healing conductive layer 40 (that is, the orthographic projection of the first groove 130 and the second groove 230 are both located within the orthographic projection of the impedance line S), and another portion of the first groove 130 and the second groove 230 are set to the power line P of the self-healing conductive layer 40 (that is, the orthographic projection of the first groove 130 and the second groove 230 are both located within the orthographic projection of the power line P).

[0094] The bend-resistant circuit board 100 and its preparation method in this application embodiment, by providing a first self-healing insulating layer 30, a self-healing conductive layer 40 and a second self-healing insulating layer 50 with self-healing function in the bending area 101, can repeatedly self-repair when damage such as cracks or breaks occurs, and can continue to be used normally after self-repair, thus greatly increasing the number of bends that the bend-resistant circuit board 100 can withstand, thereby improving the service life of the bend-resistant circuit board 100.

[0095] The above description describes some specific embodiments of this application, but in actual applications, the application should not be limited to these embodiments. For those skilled in the art, other modifications and alterations made based on the technical concept of this application should fall within the protection scope of this application.

Claims

1. A bend-resistant circuit board, characterized in that, include: A first substrate has a first groove, and a first self-healing insulating layer and a self-healing conductive layer are disposed in the first groove, with at least a portion of the self-healing conductive layer embedded in the first self-healing insulating layer. and A second substrate is disposed on a surface of the first substrate. The second substrate has a second groove communicating with the first groove. A second self-healing insulating layer is disposed in the second groove. The second self-healing insulating layer and the first self-healing insulating layer cover the self-healing conductive layer. Wherein, both the first self-healing insulating layer and the second self-healing insulating layer are formed of self-healing insulating material, the self-healing insulating material includes multiple polymer backbones, the polymer backbones include hard segments and soft segments, the hard segments include urethane structures, the soft segments include coordination structures, the coordination structures are formed by the coordination of heterocyclic structures located on the soft segments with metal ions; The self-healing conductive layer comprises a polyurethane elastomer and a conductive filler. The polyurethane elastomer comprises a first polyurethane and a second polyurethane. The first polyurethane has a dynamic cross-linking structure, and the second polyurethane has both a dynamic cross-linking structure and a permanent chemical cross-linking structure. The first polyurethane is obtained by polymerization of a raw material composition comprising benzophenone compounds, isocyanate compounds, and polyols. The benzophenone compounds include compounds with phenolic hydroxyl or aniline groups, and the isocyanate compounds include compounds with three or more isocyanate groups. The second polyurethane is formed by irradiating the first polyurethane with ultraviolet light. The conductive filler is embedded in the surface of the first polyurethane.

2. The bend-resistant circuit board as described in claim 1, characterized in that, The first substrate includes a first dielectric layer, a first circuit layer located on the surface of the first dielectric layer, and a first protective layer covering the first circuit layer. The first groove penetrates at least through the first dielectric layer along the thickness direction, and the first protective layer has a first slot. The self-healing conductive layer includes impedance lines and power lines. There are multiple first slots, some of which correspond to the impedance lines and others correspond to the power lines.

3. The bend-resistant circuit board as described in claim 1, characterized in that, The second substrate includes a second dielectric layer, a second circuit layer located on the surface of the second dielectric layer, and a second protective layer covering the second circuit layer. The second groove penetrates the second dielectric layer along the thickness direction, and the second protective layer has a second slot. The self-healing conductive layer includes impedance lines and power lines. There are multiple second slots, some of which are set to the impedance lines and others are set to the power lines.

4. The bend-resistant circuit board as described in claim 1, characterized in that, The sum of the thicknesses of the first self-healing insulating layer and the second self-healing insulating layer is 12 μm to 100 μm.

5. The bend-resistant circuit board as described in claim 1, characterized in that, The heterocyclic structure includes one or more of azopyridine, alkylpyridine, halopyridine, aminopyridine, bromopyridine, methylpyridine, iodopyridine, chloropyridine, hydroxypyridine, benzylpyridine, ethylpyridine, bipyridine, imidazole, pyrazole, and thiophene; the metal ion includes one or more of zinc ion, iron ion, nickel ion, and copper ion.

6. The bend-resistant circuit board as described in claim 1, characterized in that, The benzophenone compounds include one or more of 4,4'-dihydroxybenzophenone, 2,4-dihydroxybenzophenone, 4,4'-diaminobenzophenone, and 2,4-diaminobenzophenone; the compounds having three or more isocyanate groups include one or more of hexamethylene diisocyanate trimer, isophorone diisocyanate trimer, and dicyclohexylmethane diisocyanate trimer.

7. A method for manufacturing a bend-resistant circuit board, characterized in that, Includes the following steps: A first groove is formed on the first copper-clad laminate; A self-healing insulating material is placed in the first groove and dried to form a first self-healing insulating layer; wherein, the self-healing insulating material includes multiple polymer backbones, the polymer backbones include hard segments and soft segments, the hard segments include urethane structures, the soft segments include coordination structures, and the coordination structures are formed by the coordination of heterocyclic structures located on the soft segments with metal ions; Multiple openings are formed on the first self-healing insulating layer; A self-healing conductive material is placed inside the opening and dried to form a self-healing conductive layer, resulting in a first substrate. The self-healing conductive material comprises a polyurethane elastomer and a conductive filler. The polyurethane elastomer comprises a first polyurethane and a second polyurethane. The first polyurethane includes a dynamically cross-linked structure, and the second polyurethane includes both a dynamically cross-linked structure and a permanently chemically cross-linked structure. The first polyurethane is obtained by polymerization of a raw material composition comprising benzophenone compounds, isocyanate compounds, and polyols. The benzophenone compounds include compounds with phenolic hydroxyl or aniline groups, and the isocyanate compounds include compounds with three or more isocyanate groups. The conductive filler is embedded in the surface of the first polyurethane. A second groove is formed on the second copper-clad board; The self-healing insulating material is placed in the second groove and dried to form a second self-healing insulating layer, thus obtaining a second substrate. The first substrate and the second substrate are pressed together so that the second self-healing insulating layer and the first self-healing insulating layer cover the self-healing conductive layer.

8. The manufacturing method as described in claim 7, characterized in that, The method for preparing the self-healing insulating material includes the following steps: A first solution is provided, the first solution comprising an isocyanate monomer, the isocyanate monomer comprising 75%-85% by weight in the first solution; A second solution is provided, the second solution comprising a diol containing a heterocyclic structure, the diol comprising 85%-95% by weight in the second solution; The first solution and the second solution are mixed and subjected to a polymerization reaction to obtain a polymeric precursor containing a heterocyclic structure and a diol. The polymeric precursor has a polymeric backbone containing hard segments and soft segments. The hard segments include urethane structures, and the soft segments include heterocyclic structures. A third solution is provided, the third solution comprising a metal salt, the metal salt being present in the third solution at a weight percentage of 20%-30%; The polymer precursor is mixed with the third solution and subjected to a chelation reaction, so that the metal ions in the metal salt form a coordination structure with the heterocyclic structure, thereby obtaining the self-healing insulating material.

9. The manufacturing method as described in claim 7, characterized in that, The preparation method of the self-healing conductive material includes the following steps: A polymer reaction is carried out between a raw material composition and a catalyst to obtain a polyurethane with a dynamic crosslinking structure; wherein the raw material composition includes benzophenone compounds, isocyanate compounds and polyols; A mask is covered on the surface of the polyurethane and irradiated with ultraviolet light to obtain a polyurethane elastomer with a patterned crosslinked surface; wherein the mask has gaps for allowing ultraviolet light to pass through. A filter membrane with deposited conductive filler is coated on the polyurethane elastomer, heated to embed the conductive filler into the polyurethane elastomer, then cooled to room temperature, and the filter membrane is removed to obtain the self-healing conductive material.

10. The manufacturing method as described in claim 7, characterized in that, Also includes: A first protective layer is disposed on the surface of the first substrate, and a second protective layer is disposed on the surface of the second substrate.

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