Folding circuit board and method of manufacturing the same

Abstract

The application provides a folding circuit board and a preparation method thereof. The application sets unequal-length bendable areas, adapts to the difference of folding radii of each layer, can uniformly disperse stress, thereby can improve the problem of small static folding radius and easy breaking of the multilayer circuit board, and further improves the reliability of the folding circuit board. By setting the unequal-length bendable areas, the reliability can be ensured, the thickness of the folding circuit board can be increased, and the folding circuit board is suitable for thick boards. The application improves the layout utilization rate of the product, improves the material utilization rate, and reduces the cost.

Description

Technical Field

[0001] This application relates to a foldable circuit board and a method for preparing the same. Background Technology

[0002] Flexible printed circuit boards (FPCs) offer many advantages over rigid printed circuit boards. For example, they can be freely bent, rolled, and folded; they can be arranged arbitrarily according to spatial layout and move and stretch freely in three-dimensional space, thus achieving integrated component assembly and wire connection. Using flexible circuit boards, the size of electronic products can be significantly reduced, meeting the needs of high-density, miniaturized, and high-reliability development in electronic products. Therefore, flexible circuit boards are widely used in portable devices (such as mobile phones), computers, tablets, digital cameras, and other electronic products.

[0003] To meet the needs of the rapid development of electronic products, foldable flexible circuit boards with a certain thickness (multi-layer structure) and complex shape have emerged. However, existing technologies are wasteful in terms of layout utilization, easily leading to material waste, increasing enterprise costs, affecting the delivery speed of finished products, and the foldable flexible circuit boards produced are prone to breakage. Summary of the Invention

[0004] In view of this, this application proposes a method for preparing a foldable circuit board, which can improve material utilization, reduce costs, and produce a foldable circuit board that is not easily broken.

[0005] One embodiment of this application provides a method for preparing a folded circuit board, comprising the following steps:

[0006] At least one first copper-clad laminate and at least one second copper-clad laminate are stacked on opposite sides of a first circuit substrate. The first circuit substrate includes a first bendable region and two first connection regions connected to both ends of the first bendable region. The first copper-clad laminate includes a second bendable region and two second connection regions connected to both ends of the second bendable region. The second copper-clad laminate includes a third bendable region and two third connection regions connected to both ends of the third bendable region. The positions of the second bendable region and the third bendable region correspond to the positions of the first bendable region. Along the extending direction of the first circuit substrate, the length a of the second bendable region is greater than the length b of the first bendable region, and the length b of the first bendable region is greater than the length c of the third bendable region. The surfaces of the second bendable region and the third bendable region facing the first circuit substrate are provided with soluble adhesive, and the surfaces of the second connection region and the third connection region facing the first connection region are provided with non-soluble adhesive.

[0007] The first copper-clad laminate, the first circuit board, and the second copper-clad laminate are pressed together, and the first bendable area protrudes towards the direction close to the first copper-clad laminate to form a first protrusion, and the second bendable area protrudes away from the first circuit board to form a second protrusion. The second protrusion is connected to the first protrusion through the soluble adhesive, and the first protrusion is connected to the third bendable area through the soluble adhesive.

[0008] A first circuit layer is formed on the first copper-clad laminate, and a second circuit layer is formed on the second copper-clad laminate;

[0009] Remove the soluble adhesive;

[0010] The second bendable area, the first bendable area, and the third bendable area are bent into an arc shape to obtain the folded circuit board.

[0011] In one implementation, 0 <a-b<0.1mm,0<b-c<0.1mm。

[0012] In one embodiment, the length of the second protrusion along the extending direction is L, where L < 0.1 mm.

[0013] In one embodiment, before removing the soluble adhesive, the preparation method further includes the following steps: forming a first protective layer on the outside of the first circuit layer to obtain a second circuit substrate; and forming a second protective layer on the outside of the second circuit layer to obtain a third circuit substrate.

[0014] In one embodiment, prior to the step of "depositing at least one first copper-clad laminate and at least one second copper-clad laminate on opposite sides of the first circuit substrate," the fabrication method further includes the following step of fabricating the first circuit substrate:

[0015] A first conductive hole is provided on a double-sided copper clad laminate. The double-sided copper clad laminate includes a first substrate layer and two first copper foil layers and second copper foil layers disposed on opposite surfaces of the first substrate layer. The first conductive hole is electrically connected to the first copper foil layers and the second copper foil layers.

[0016] A first conductive layer is formed on the first copper foil layer, and a second conductive layer is formed on the second copper foil layer;

[0017] Two third protective layers are respectively formed on a portion of the surface of the first conductive layer and the second conductive layer to obtain the first circuit substrate.

[0018] In one embodiment, the first conductive hole is disposed in the first connection area, and the two third protective layers are disposed in the first bendable area. After laminating the first copper-clad laminate, the first circuit board, and the second copper-clad laminate, non-solvable adhesive on the first and second copper-clad laminates respectively covers both ends of the two third protective layers.

[0019] In one embodiment, prior to the step of "forming a first circuit layer on the first copper-clad laminate and forming a second circuit layer on the second copper-clad laminate", the fabrication method further includes: providing at least one second conductive hole to electrically connect the first circuit substrate and the first copper-clad laminate, and providing at least one third conductive hole to electrically connect the first circuit substrate and the second copper-clad laminate.

[0020] In one embodiment, the second conductive via is disposed in the second connection area and the first connection area to electrically connect the first circuit layer and the first conductive layer.

[0021] In one embodiment, the third conductive via is disposed in the third connection area and the first connection area to electrically connect the second circuit layer and the second conductive layer.

[0022] Another aspect of this application provides a folded circuit board prepared by the above-described preparation method. The folded circuit board includes a first circuit board, at least one second circuit board disposed on one side of the first circuit board, at least one third circuit board disposed on the other side of the first circuit board, and a non-soluble adhesive.

[0023] The first circuit board includes a first bendable area and two first connection areas connected to both ends of the first bendable area, wherein the first bendable area protrudes toward the direction close to the second circuit board.

[0024] The second circuit board includes a second bendable region and two second connection regions connected to both ends of the second bendable region. The second bendable region protrudes in a direction away from the first circuit board, and the position of the second bendable region corresponds to the position of the first bendable region.

[0025] The third circuit board includes a third bendable region and two third connection regions connected to both ends of the third bendable region. The position of the third bendable region corresponds to the position of the first bendable region. The length 'a' of the second bendable region is greater than the length 'b' of the first bendable region, and the length 'b' of the first bendable region is greater than the length 'c' of the third bendable region.

[0026] The non-soluble adhesive is sandwiched between the first connection area and the second connection area, and between the first connection area and the third connection area, and exposes a portion of the surface of the first circuit board located in the first bending area.

[0027] In one embodiment, the foldable circuit board further includes a first protective layer, a second protective layer, and two third protective layers. The first protective layer is disposed on the side of the first circuit layer opposite to the first circuit substrate, and the second protective layer is disposed on the side of the second circuit layer opposite to the first circuit substrate. The two third protective layers are respectively disposed on two surfaces of the first circuit substrate near the second circuit substrate and the third circuit substrate, and the two third protective layers are located in the first bendable area.

[0028] This application, by setting flexible areas of unequal length, adapts to the differences in folding radii among different layers, enabling more uniform stress distribution. This improves the problem of small static folding radius and easy breakage in multilayer circuit boards, thereby enhancing their reliability. By setting flexible areas of unequal length, reliability can be guaranteed while allowing for greater thickness of the folded circuit board, making it suitable for thicker boards. This application also improves product layout utilization, increases material utilization, and reduces costs. Attached Figure Description

[0029] Figure 1 This is a cross-sectional view of a double-sided copper-clad laminate provided in one embodiment of this application.

[0030] Figure 2 In order to be in Figure 1 The cross-sectional view shown is taken after the first blind via is formed on the double-sided copper-clad board.

[0031] Figure 3 To Figure 2 The cross-sectional view shown is of the first blind hole after copper plating to form the first conductive hole.

[0032] Figure 4 In order to be in Figure 3 The cross-sectional view shows a structure with a resist film formed on the outer side, and then exposed, developed, etched, and the resist film removed to form the first conductive layer and the second conductive layer.

[0033] Figure 5 In order to be in Figure 4 The cross-sectional view shown is a partial view of the first conductive layer and the second conductive layer after the first protective layer has been applied to their respective surfaces.

[0034] Figure 6 In order to be in Figure 5 The cross-sectional view shown is of a first copper-clad laminate and a second copper-clad laminate stacked on opposite sides of the first circuit board.

[0035] Figure 7 For pressing Figure 6 The diagram shows a first circuit board, a first copper-clad laminate, and a second copper-clad laminate, with the first and second bendable areas protruding.

[0036] Figure 8 In order to be in Figure 7 The cross-sectional view shown is provided with at least one second conductive hole and at least one third conductive hole on the structure shown.

[0037] Figure 9 In order to be in Figure 8 The diagram shows a cross-sectional view after a first circuit layer is formed on a first copper-clad laminate and a second circuit layer is formed on a second copper-clad laminate.

[0038] Figure 10 In order to be in Figure 9 The diagram shows a cross-sectional view after a first protective layer is formed on the first line layer and a second protective layer is formed on the third line.

[0039] Figure 11 To Figure 10 The diagram shows a cross-sectional view of the structure after the soluble adhesive has been removed.

[0040] Figure 12 To Figure 11 The structure shown is a cross-sectional view after being shaped by polygonal lines.

[0041] Explanation of main component symbols

[0042] Folding circuit board 100

[0043] First circuit board 10

[0044] Second circuit board 20

[0045] Third circuit board 30

[0046] Double-sided copper clad laminate 11

[0047] First substrate layer 111

[0048] First copper foil layer 112a

[0049] Second copper foil layer 112b

[0050] First blind hole 113

[0051] First conductive hole 114

[0052] Anti-corrosion film 115

[0053] First conductive layer 116

[0054] Second conductive layer 117

[0055] Third protective layer 118

[0056] First bendable zone 101

[0057] First connection area 102

[0058] First protrusion 103

[0059] First copper-clad laminate 21

[0060] Second substrate layer 211

[0061] First copper layer 212

[0062] First adhesive layer 213

[0063] Second blind hole 214

[0064] Second conductive hole 215

[0065] First line layer 216

[0066] First protective layer 217

[0067] Contact pad 218

[0068] Gold layer 2181

[0069] Second bendable zone 201

[0070] Second connection area 202

[0071] Second protrusion 203

[0072] Second copper-clad laminate 31

[0073] Third substrate layer 311

[0074] Second copper layer 312

[0075] Second adhesive layer 313

[0076] Third blind hole 314

[0077] Third conductive hole 315

[0078] Second line layer 316

[0079] Second protective layer 317

[0080] Third bendable zone 301

[0081] Third connection area 302

[0082] Sol-gel 2131, 3131

[0083] Non-solvable colloids 2132, 3132

[0084] The following detailed description, in conjunction with the accompanying drawings, further illustrates the embodiments of this application. Detailed Implementation

[0085] 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 embodiments of this application belong. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the embodiments of this application.

[0086] 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.

[0087] It will be understood that when a layer is referred to as being "on" another layer, it can be directly on that other layer or there can be intermediate layers in between. Conversely, when a layer is referred to as being "directly" on another layer, there are no intermediate layers.

[0088] Furthermore, the use of terms such as "first" and "second" in this application is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0089] 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.

[0090] 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.

[0091] Please see Figures 1 to 12 One embodiment of this application provides a method for preparing a folded circuit board 100, which includes the following steps:

[0092] For step S00, please refer to... Figures 1 to 5This illustrates a method for fabricating a first circuit board 10 provided in one embodiment of this application.

[0093] like Figure 1 As shown, a double-sided copper-clad laminate 11 is provided, which includes a first substrate layer 111 and a first copper foil layer 112a and a second copper foil layer 112b disposed on opposite surfaces of the first substrate layer 111.

[0094] The material of the first substrate layer 111 includes, but is not limited to, polyimide (PI), polyethylene terephthalate (PET), polyethylene naphthalate glycol ester (PEN), liquid crystal polymer (LCP), and modified polyimide (MPI). In this embodiment, the material of the first substrate layer 111 is PI.

[0095] like Figure 2 As shown, a first blind via 113 can be formed on the double-sided copper-clad laminate 11 by means of, but not limited to, mechanical drilling, laser engraving, etc. The first blind via 113 penetrates the first copper foil layer 112a and the first substrate layer 111, and a portion of the surface of the second copper foil layer 112b near the first substrate layer 111 is exposed through the first blind via 113. The number of first blind vias 113 can be one or more; in this embodiment, the number of first blind vias 113 is two.

[0096] like Figure 3 As shown, a first conductive hole 114 is formed by filling or electroplating a conductive material into the first blind hole 113. In this embodiment, the first conductive hole 114 is formed by plating copper into the first blind hole 113. The first conductive hole 114 is electrically connected to the first copper foil layer 112a and the second copper foil layer 112b.

[0097] like Figure 4 As shown, circuitry is fabricated on the first copper foil layer 112a and the second copper foil layer 112b to form the first conductive layer 116 and the second conductive layer 117.

[0098] Specifically, a resist film 115 is formed on the outer side of the first copper foil layer 112a and the second copper foil layer 112b respectively (for example, the resist film 115 is laminated onto the outer side of the first copper foil layer 112a and the second copper foil layer 112b). Then, exposure, development, etching, and removal of the resist film 115 are performed to form the first conductive layer 116 and the second conductive layer 117 respectively. The steps of lamination, exposure, development, etching, and film removal are common techniques in the art and will not be described in detail here.

[0099] like Figure 5 As shown, a third protective layer 118 is respectively formed on a portion of the surface of the first conductive layer 116 and the second conductive layer 117 to obtain a first circuit board 10. Along the extending direction of the first circuit board 10, the third protective layer 118 is approximately located in the middle region. In this embodiment, the third protective layer 118 is a cover-lay (CVL). In other embodiments, the third protective layer 118 can also be a solder resist layer. The third protective layer 118 is used to protect the first conductive layer 116 and the second conductive layer 117 from external moisture intrusion or scratches from foreign objects.

[0100] Along the extending direction of the first circuit board 10, the first circuit board 10 can be divided into a first bendable region 101 and two first connection regions 102 connected to the first bendable region 101. The first bendable region 101 is located approximately in the middle of the first circuit board 10, and the two first connection regions 102 are located at opposite ends of the first bendable region 101. In this embodiment, the third protective layer 118 is disposed in the first bendable region 101 and partially extends to the first connection region 102. Further, the first conductive hole 114 is disposed in the first connection region 102.

[0101] Step S10, please refer to Figure 6 At least one first copper-clad laminate 21 and at least one second copper-clad laminate 31 are respectively stacked on opposite sides of the first circuit substrate 10. In this embodiment, there is one first copper-clad laminate 21 and one second copper-clad laminate 31. In other embodiments, there may be multiple first copper-clad laminates 21 and multiple second copper-clad laminates 31. In this embodiment, the first copper-clad laminate 21 is located on the upper side of the first circuit substrate 10, and the second copper-clad laminate 31 is located on the lower side of the first circuit substrate 10.

[0102] The first copper-clad laminate 21 includes a second substrate layer 211, a first copper layer 212 disposed on one side of the second substrate layer 211, and a first adhesive layer 213 disposed on the other side of the second substrate layer 211. The first adhesive layer 213 is disposed close to the first circuit board 10. Along the extending direction of the first copper-clad laminate 21, the first copper-clad laminate 21 includes a second bendable region 201 and two second connecting regions 202 connected to the second bendable region 201. The second bendable region 201 is approximately located in the middle of the first copper-clad laminate 21, and the two second connecting regions 202 are respectively located at both ends of the second bendable region 201. The position of the second bendable region 201 corresponds to the position of the first bendable region 101. Specifically, the orthographic projection of the first bendable region 101 on the first copper-clad laminate 21 is located within the second bendable region 201. The first adhesive layer 213 is composed of a soluble adhesive 2131 and a non-soluble adhesive 2132. The soluble adhesive 2131 is generally disposed in the second bendable area 201 of the first copper-clad laminate 21, and the non-soluble adhesive 2132 is generally disposed in the second connecting area 202. The soluble adhesive 2131 can be removed by a removal agent, and the non-soluble adhesive 2132 can be, but is not limited to, epoxy resin or acrylic adhesive. In this embodiment, the soluble adhesive 2131 is a hydrolyzable UV protective ink. For example, it is composed of modified silicone acrylic resin, epoxy resin, isoborneol acrylate, tris(hydroxymethane) chlorinated rubber, grass green pigment, silicone coupling agent, defoamer, leveling agent, polymerization inhibitor, calcium carbonate, etc. It can cure quickly in a short time and has the properties of being residue-free and easy to peel off. The removal agent is, for example, a stripping solution with NaOH as the main component.

[0103] The second copper-clad laminate 31 includes a third substrate layer 311, a second copper layer 312 disposed on one side of the third substrate layer 311, and a second adhesive layer 313 disposed on the other side of the third substrate layer 311. The second adhesive layer 313 is disposed close to the first circuit board 10. Along the extending direction of the second copper-clad laminate 31, the second copper-clad laminate 31 includes a third bendable region 301 and two third connecting regions 302 connected to the third bendable region 301. The third bendable region 301 is approximately located in the middle of the second copper-clad laminate 31, and the two third connecting regions 302 are respectively located at both ends of the third bendable region 301. The position of the third bendable region 301 corresponds to the position of the first bendable region 101. Specifically, the orthographic projection of the third bendable region 301 on the first circuit board 10 is located within the first bendable region 101, that is, within the second bendable region 201. The second adhesive layer 313 is composed of a soluble adhesive 3131 and a non-soluble adhesive 3132. The soluble adhesive 3131 is generally disposed in the third bendable area 301 of the second copper-clad laminate 31, and the non-soluble adhesive 3132 is generally disposed in the third connecting area 302. The soluble adhesive 3131 can be removed by a removal agent. The non-soluble adhesive 3132 can be, but is not limited to, epoxy resin or acrylic adhesive. In this embodiment, the soluble adhesive 3131 is a hydrolyzable UV protective ink. For example, it is composed of modified silicone acrylic resin, epoxy resin, isoborneol acrylate, tris(hydroxymethane) chlorinated rubber, grass green pigment, silicone coupling agent, defoamer, leveling agent, polymerization inhibitor, calcium carbonate, etc. It can cure quickly in a short time and has the properties of being residue-free and easy to peel off. The removal agent is, for example, a stripping solution with NaOH as the main component.

[0104] The materials of the second substrate layer 211 and the third substrate layer 311 include, but are not limited to, PI, PET, PEN, LCP, and MPI. The materials of the second substrate layer 211, the third substrate layer 311, and the first substrate layer 111 may be the same or different. In this embodiment, the material of both the second substrate layer 211 and the third substrate layer 311 is PI.

[0105] like Figure 6 As shown, along the extension direction, the length of the second bendable region 201 is a, the length of the first bendable region 101 is b, and the length of the third bendable region 301 is c, where a > b > c.

[0106] It is understood that the length of each bendable area gradually increases from the inside to the outside depending on the static folding position. In this embodiment, when the bendable area is bent to form an arc (see...), Figure 12), the third bendable region 301, the first bendable region 101 and the second bendable region 201 are arranged in sequence from the inside to the outside, the second bendable region 201 located at the outermost side has the maximum length, the first bendable region 101 has the second largest length, and the third bendable region 301 located at the innermost side has the minimum length. The radius of the arc formed by the second bendable region 201, the radius of the arc formed by the first bendable region 101, and the radius of the arc formed by the third bendable region 301 decrease sequentially from the outside to the inside, and the lengths of the second bendable region 201, the first bendable region 101 and the third bendable region 301 are also set to decrease sequentially from the outside to the inside, which adapts to the difference in the folding radius of each layer, enables the stress to be uniformly dispersed, thereby improving the problems of small static folding radius and easy breakage of the multilayer wiring board, and further enhancing the reliability of the folded wiring board.

[0107] Further, in some embodiments, 0<a-b<0.1mm, 0<b-c<0.1mm. The lengths of the third bendable region 301, the first bendable region 101 and the second bendable region 201 gradually increase from the inside to the outside according to the folding position, and the increased value or proportion can be adjusted by comprehensively considering the folding radius and the actual board thickness.

[0108] Step S20, please refer to Figure 7 , pressing the first copper-clad plate 21, the first circuit substrate 10 and the second copper-clad plate 31, and making the second bendable region 201 protrude in a direction away from the first circuit substrate 10 to form a second protruding portion 203, and the first bendable region 101 protrude in a direction close to the first copper-clad plate 21 to form a first protruding portion 103, so that the non-adhesive-solvable glue 2132 located on the first copper-clad plate 21 covers both ends of the third protective layer 118 located on the first conductive layer 116, and the non-adhesive-solvable glue 3132 located on the second copper-clad plate 31 covers both ends of the third protective layer 118 located on the second conductive layer 117. The second protruding portion 203 and the first protruding portion 103 are connected by the solvable glue 2131, and the first protruding portion 103 and the third bendable region 301 are connected by the solvable glue 3131. The solvable glue 2131 fills the gap between the second protruding portion 203 and the first protruding portion 103 for fixing, and the solvable glue 3131 fills the gap between the first protruding portion 103 and the third bendable region 301 for fixing, so that the positions among the first copper-clad plate 21, the first circuit substrate 10 and the second copper-clad plate 31 are relatively fixed. The solvable glues 2131 and 3131 are removed before molding, which can improve the problem of water trapped in the manufacturing process.

[0109] As shown in Figure 7 , along the extending direction, the linear length of the second protruding portion 203 is L. In some embodiments, L<0.1mm.

[0110] Step S30, please refer to Figure 8At least one second blind via 214 is formed on the first copper-clad laminate 21 and the first circuit board 10 by means of mechanical drilling, laser engraving, etc., and at least one third blind via 314 is formed on the second copper-clad laminate 31 and the first circuit board 10. The second blind via 214 and the third blind via 314 are then plated with copper to form a second conductive via 215 and a third conductive via 315. The second conductive via 215 is electrically connected to the first conductive layer 116 of the first circuit board 10 and the first copper-clad laminate 21, and the third conductive via 315 is electrically connected to the second conductive layer 117 of the first circuit board 10 and the second copper-clad laminate 31.

[0111] The second blind via 214 penetrates the first copper-clad laminate 21 and partially exposes the first conductive layer 116. The second blind via 214 is disposed in the second connection area 202. The third blind via 314 penetrates the second copper-clad laminate 31 and partially exposes the second conductive layer 117. The third blind via 314 is disposed in the third connection area 302.

[0112] For step S40, please refer to... Figure 9 The first copper layer 212 is fabricated to form the first circuit layer 216 through image transfer processes and other methods, and the second copper layer 312 is fabricated to form the second circuit layer 316.

[0113] For step S50, please refer to... Figure 10 A first protective layer 217 is formed on the outside of the first circuit layer 216 to obtain the second circuit substrate 20; a second protective layer 317 is formed on the outside of the second circuit layer 316 to obtain the third circuit substrate 30. The first protective layer 217 is used to protect the first circuit layer 216, and the second protective layer 317 is used to protect the second circuit layer 316 from external moisture or scratches from foreign objects. In this embodiment, both the first circuit layer 216 and the second protective layer 317 are cover-lay (CVL) layers; in other embodiments, they can also be solder resist layers. In this embodiment, a portion of the first circuit layer 216 is not covered by the first protective layer 217 and is exposed, forming contact pads 218. The contact pads 218 are used for electrical connection with external components. A gold plating layer 2181 is also formed on the contact pads 218.

[0114] For step S60, please refer to... Figure 11 The soluble colloids 2131 and 3131 can be removed by applying a specific solvent (solution).

[0115] like Figure 11 As shown, the distance H between the highest point of the second circuit board 20 (i.e., the highest point after the second protrusion 203 covers the first protective layer 217) and the horizontal first protective layer 217 without protrusions is 0.08 mm. In some embodiments, H < 0.08 mm.

[0116] For step S70, please refer to... Figure 12 Folded line shaping: The second bendable area 201, the first bendable area 101 and the third bendable area 301 are bent into an arc shape. At this time, the two second connection areas 202 of the second circuit board 20 are approximately parallel to each other, the two first connection areas 102 of the first circuit board 10 are approximately parallel to each other, and the two third connection areas 302 of the third circuit board 30 are approximately parallel to each other, thus obtaining the folded circuit board 100.

[0117] like Figure 12 As shown, one embodiment of this application provides a foldable circuit board 100, which includes a first circuit board 10, at least one second circuit board 20 disposed on one side of the first circuit board 10, and at least one third circuit board 30 disposed on the other side of the first circuit board 10. In this embodiment, the number of the second circuit board 20 and the third circuit board 30 is one.

[0118] The first circuit board 10 includes a first substrate layer 111 and a first conductive layer 116 and a second conductive layer 117 respectively disposed on both sides of the first substrate layer 111. The first circuit board 10 also has a first conductive hole 114 to electrically connect the first conductive layer 116 and the second conductive layer 117. The first circuit board 10 includes a first bendable region 101, which protrudes in an arc shape toward the second circuit board 20, and the first conductive hole 114 is disposed outside the first bendable region 101.

[0119] The second circuit board 20 includes a second substrate layer 211 and a first circuit layer 216 disposed on one side of the second substrate layer 211, the first circuit layer 216 being disposed away from the first circuit board 10. The second circuit board 20 also includes a second conductive via 215 to electrically connect the first circuit layer 216 and the first conductive layer 116. The second circuit board 20 includes a second bendable region 201, the second bendable region 201 protruding in an arc shape away from the first circuit board 10, the position of the second bendable region 201 corresponding to the position of the first bendable region 101. The second conductive via 215 is disposed outside the second bendable region 201.

[0120] The third circuit board 30 includes a third substrate layer 311 and a second circuit layer 316 disposed on one side of the third substrate layer 311, the second circuit layer 316 being disposed away from the first circuit board 10. The third circuit board 30 also includes a third conductive via 315 to electrically connect the second circuit layer 316 and the second conductive layer 117. The third circuit board includes a third bendable region 301, the position of which corresponds to the position of the first bendable region 101, and the third conductive via 315 being disposed outside the third bendable region 301.

[0121] Furthermore, such as Figure 12 As shown, the first circuit board 10 further includes two first connection areas 102 connected to the first bendable area 101. The two first connection areas 102 are located at opposite ends of the first bendable area 101, and the first conductive hole 114 is disposed in the first connection area 102. The two first connection areas 102 are generally parallel to each other. A third protective layer 118 is respectively disposed on a portion of the surface of the first conductive layer 116 and the second conductive layer 117. The third protective layer 118 is disposed in the first bendable area 101 and extends partially to the first connection area 102. The second circuit board 20 further includes two second connection areas 202 connected to the second bendable area 201. The two second connection areas 202 are located at opposite ends of the second bendable area 201 and are generally parallel to each other. A first adhesive layer 213 is disposed on the side of the first circuit layer 216 closest to the first circuit board 10, and a first protective layer 217 is disposed on the other side away from the first circuit board 10. The third circuit board 30 further includes two third connection areas 302 connected to the third bendable area 301. The two third connection areas 302 are located at opposite ends of the third bendable area 301 and are substantially parallel to each other. The second circuit layer 316 has a second adhesive layer 313 on the side near the first circuit board 10 and a second protective layer 317 on the side away from the first circuit board 10. The first adhesive layer 213 includes a non-soluble adhesive 2132, and the second adhesive layer 313 also includes a non-soluble adhesive 3132. The non-soluble adhesive 2132 is sandwiched between the first connection area 102 and the second connection area 202, and the non-soluble adhesive 3132 is sandwiched between the first connection area 102 and the third connection area 302, exposing a portion of the surface of the first circuit board 10 located in the first bendable area 101.

[0122] This application, by setting flexible areas of unequal length, adapts to the differences in folding radii among different layers, enabling more uniform stress distribution. This improves the problem of small static folding radius and easy breakage in multilayer circuit boards, thereby enhancing their reliability. By setting flexible areas of unequal length, reliability can be guaranteed while allowing for greater thickness of the folded circuit board, making it suitable for thicker boards. This application also improves product layout utilization, increases material utilization, and reduces costs.

[0123] 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 method for preparing a foldable circuit board, characterized in that, Includes the following steps: At least one first copper-clad laminate and at least one second copper-clad laminate are stacked on opposite sides of a first circuit substrate. The first circuit substrate includes a first bendable region and two first connection regions connected to both ends of the first bendable region. The first copper-clad laminate includes a second bendable region and two second connection regions connected to both ends of the second bendable region. The second copper-clad laminate includes a third bendable region and two third connection regions connected to both ends of the third bendable region. The positions of the second bendable region and the third bendable region correspond to the positions of the first bendable region. Along the extension direction of the first circuit substrate, the length 'a' of the second bendable region is greater than the length 'b' of the first bendable region, and the length 'b' of the first bendable region is greater than the length 'c' of the third bendable region. The surfaces of the second bendable region and the third bendable region facing the first circuit substrate are provided with soluble adhesive, and the surfaces of the second connection region and the third connection region facing the first connection region are provided with non-soluble adhesive. The first copper-clad laminate, the first circuit board, and the second copper-clad laminate are pressed together, and the first bendable area protrudes towards the direction close to the first copper-clad laminate to form a first protrusion, and the second bendable area protrudes away from the first circuit board to form a second protrusion. The second protrusion is connected to the first protrusion through the soluble adhesive, and the first protrusion is connected to the third bendable area through the soluble adhesive. A first circuit layer is formed on the first copper-clad laminate, and a second circuit layer is formed on the second copper-clad laminate; Remove the soluble adhesive; The second bendable area, the first bendable area, and the third bendable area are bent into an arc shape to obtain the folded circuit board. The soluble adhesive is a hydrolyzable UV protective ink.

2. The method for preparing a folded circuit board as described in claim 1, characterized in that, 0 <a-b<0.1mm,0<b-c<0.1mm。 3. The method for preparing a folded circuit board as described in claim 1, characterized in that, Along the extending direction, the length of the second protrusion is L, where L < 0.1 mm.

4. The method for preparing a folded circuit board as described in claim 1, characterized in that, Before removing the soluble adhesive, the preparation method further includes the following steps: forming a first protective layer on the outside of the first circuit layer to obtain a second circuit substrate; forming a second protective layer on the outside of the second circuit layer to obtain a third circuit substrate.

5. The method for preparing a folded circuit board as described in claim 1, characterized in that, Before the step of "depositing at least one first copper-clad laminate and at least one second copper-clad laminate on opposite sides of the first circuit substrate", the fabrication method further includes the following steps for fabricating the first circuit substrate: A first conductive hole is provided on a double-sided copper clad laminate. The double-sided copper clad laminate includes a first substrate layer and a first copper foil layer and a second copper foil layer disposed on opposite surfaces of the first substrate layer. The first conductive hole is electrically connected to the first copper foil layer and the second copper foil layer. A first conductive layer is formed on the first copper foil layer, and a second conductive layer is formed on the second copper foil layer; Two third protective layers are respectively formed on a portion of the surface of the first conductive layer and the second conductive layer to obtain the first circuit substrate.

6. The method for preparing a folded circuit board as described in claim 5, characterized in that, The first conductive hole is disposed in the first connection area, and the two third protective layers are disposed in the first bendable area; after the first copper-clad laminate, the first circuit board and the second copper-clad laminate are pressed together, the non-solubilized adhesive on the first copper-clad laminate and the second copper-clad laminate respectively covers the two ends of the two third protective layers.

7. The method for preparing a folded circuit board as described in claim 6, characterized in that, Before the step of "forming a first circuit layer on the first copper-clad laminate and forming a second circuit layer on the second copper-clad laminate", the preparation method further includes: providing at least one second conductive hole to electrically connect the first circuit substrate and the first copper-clad laminate, and providing at least one third conductive hole to electrically connect the first circuit substrate and the second copper-clad laminate.

8. The method for preparing a folded circuit board as described in claim 7, characterized in that, The second conductive via is disposed in the second connection area and the first connection area to electrically connect the first circuit layer and the first conductive layer; the third conductive via is disposed in the third connection area and the first connection area to electrically connect the second circuit layer and the second conductive layer.

9. A foldable circuit board prepared by the method for preparing a foldable circuit board according to any one of claims 1 to 8, characterized in that, The folded circuit board includes a first circuit board, at least one second circuit board disposed on one side of the first circuit board, at least one third circuit board disposed on the other side of the first circuit board, and a non-soluble adhesive, wherein, The first circuit board includes a first bendable area and two first connection areas connected to both ends of the first bendable area, wherein the first bendable area protrudes toward the direction close to the second circuit board; The second circuit board includes a second bendable area and two second connection areas connected to both ends of the second bendable area. The second bendable area protrudes in a direction away from the first circuit board, and the position of the second bendable area corresponds to the position of the first bendable area. The third circuit board includes a third bendable area and two third connection areas connected to both ends of the third bendable area. The position of the third bendable area corresponds to the position of the first bendable area. The length a of the second bendable area is greater than the length b of the first bendable area, and the length b of the first bendable area is greater than the length c of the third bendable area. The non-soluble adhesive is sandwiched between the first connection area and the second connection area, and between the first connection area and the third connection area, and exposes a portion of the surface of the first circuit board located in the first bending area.

10. The folding circuit board as described in claim 9, characterized in that, The foldable circuit board further includes a first protective layer, a second protective layer, and two third protective layers. The first protective layer is disposed on the side of the second circuit board away from the first circuit board, the second protective layer is disposed on the side of the third circuit board away from the first circuit board, and the two third protective layers are disposed on two surfaces of the first circuit board near the second circuit board and the third circuit board, and the two third protective layers are located in the first bendable area.

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