Bending-resistant flexible circuit board and preparation method thereof

Abstract

The invention provides a flexing-resistant flexible circuit board and a preparation method thereof. The flexible circuit board comprises at least two circuit substrates and a bonding layer located between the two circuit substrates, and the bonding layer is provided with an opening. A coating is arranged in the area, corresponding to the opening, of the second surface of the base material layer, the friction coefficient of the coating is smaller than or equal to 0.1, and the coating is used for reducing the friction force between the two adjacent base material layers. According to the flexible circuit board, the coating with a small friction coefficient (less than or equal to 0.1) is arranged in the area, corresponding to the opening of the bonding layer, of the base material layer, and the coating can reduce the friction force between the two adjacent base material layers, so that the bulge at the opening can move sideward to release stress, and further the bending resistance of the flexible circuit board can be improved. The coating has good anti-sticking and anti-skid performance, the adhesion problem between the base material layers can be effectively avoided, the product manufacturing yield is increased, and the coating is high in adhesion performance and not prone to falling off.

Description

Technical Field

[0001] The present application relates to the technical field of circuit boards, and in particular to a flex-resistant flexible circuit board and a preparation method thereof. Background Art

[0002] Since flexible printed circuits (FPC, also known as soft boards) have the characteristics of high wiring density, light weight, thin thickness and good bendability, they have been widely used in electronics, automobiles, medical treatment, aerospace and other fields.

[0003] In actual applications, such as in folding mobile phones, tablet computers and other electronic products, FPC needs to have a certain degree of flex resistance. Therefore, when making multi-layer flexible boards, an opening (Airgap) is set in the glue layer to increase its flex resistance. However, during the bending process, the two layers of substrate at the opening will contact each other, generating friction. Due to the effect of friction, the two ends of the opening area will be convex, and the convex part is difficult to move to the side and release stress. Excessive stress will reduce the flex resistance of the FPC. Summary of the invention

[0004] In view of this, the present application proposes a flex-resistant flexible circuit board and a preparation method thereof, so as to improve the flex-resistant performance of the flexible circuit board.

[0005] One embodiment of the present application provides a flex-resistant flexible circuit board, which includes at least two circuit substrates and an adhesive layer located between the two circuit substrates. Each of the circuit substrates includes a substrate layer and a circuit layer formed on the surface of the substrate layer, and the adhesive layer is located between the two substrate layers. The substrate layer includes a first surface and a second surface arranged opposite to each other, and the circuit layer is formed on the first surface. The adhesive layer has an opening that penetrates the adhesive layer in the thickness direction, and a coating is provided in the area of ​​the second surface corresponding to the opening. The friction coefficient of the coating is less than or equal to 0.1, and the coating is used to reduce the friction between two adjacent substrate layers.

[0006] In one embodiment, the coating includes one or more of tungsten disulfide, molybdenum disulfide, and polytetrafluoroethylene.

[0007] In one embodiment, the thickness of the coating is less than or equal to 100 nm.

[0008] In one embodiment, the flexible circuit board further includes a conductive structure, and the conductive structure is used to electrically connect circuit layers of different circuit substrates.

[0009] In one embodiment, the flexible circuit board further includes a protective layer, which is disposed on a surface of the circuit layer facing away from the substrate layer and covers a surface of the substrate layer exposed from the circuit layer.

[0010] An embodiment of the present application provides a method for preparing a flexible circuit board that is resistant to bending and folding, and the preparation method comprises the following steps:

[0011] Providing two copper-clad laminates, the copper-clad laminates comprising a substrate layer and a copper foil layer, the substrate layer comprising a first surface and a second surface arranged opposite to each other, the copper foil layer being formed on the first surface;

[0012] A bonding layer is attached to the surface of one of the copper-clad laminates, the bonding layer is attached to the second surface of the substrate layer, and the bonding layer has an opening penetrating the bonding layer along the thickness direction;

[0013] A coating is provided on the second surface of the substrate layer attached with the adhesive layer in the area corresponding to the opening to obtain a first intermediate; the friction coefficient of the coating is less than or equal to 0.1, and the coating is used to reduce the friction between two adjacent substrate layers;

[0014] Arranging the coating on the second surface of the substrate layer of another copper-clad laminate to obtain a second intermediate;

[0015] Laying the first intermediate and the second intermediate together in a thickness direction and then pressing them together, wherein the adhesive layer is located between two substrate layers, and the coating of the first intermediate corresponds to the coating of the second intermediate;

[0016] The copper foil layer is made into a circuit layer to obtain the flex-resistant flexible circuit board.

[0017] In one embodiment, the coating includes one or more of tungsten disulfide, molybdenum disulfide, and polytetrafluoroethylene.

[0018] In one embodiment, the coating has a thickness less than or equal to 100 nm.

[0019] In one embodiment, the preparation method further comprises: providing a conductive structure to electrically connect the circuit layer.

[0020] In one embodiment, the preparation method further comprises: providing a protective layer on a surface of the circuit layer facing away from the substrate layer, wherein the protective layer covers the surface of the substrate layer exposed from the circuit layer.

[0021] The present application provides a coating with a small friction coefficient (≤0.1) in the area of ​​the opening of the substrate layer corresponding to the adhesive layer. The coating can reduce the friction between two adjacent substrate layers, so that the protrusion at the opening can move to the side to release stress, thereby improving the flex resistance of the flexible circuit board. The coating has good anti-stick and anti-slip properties, can effectively avoid the adhesion problem between the substrate layers, improve the yield of product manufacturing, and the coating has strong adhesion performance and is not easy to fall off. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A cross-sectional view of a flex-resistant flexible circuit board provided in accordance with an embodiment of the present application.

[0023] Figure 2 for Figure 1 The test results of the flexible circuit board shown are simulated by Ansys finite element software.

[0024] Figure 3 This is the test result diagram of the flexible circuit board of the control group subjected to Ansys finite element software simulation test.

[0025] Figures 4 to 8 A cross-sectional view of a method for preparing a flex-resistant flexible circuit board provided in one embodiment of the present application.

[0026] Main component symbols

[0027] Flexible circuit board 100

[0028] Circuit board 10

[0029] Adhesive layer 20

[0030] Coating 30

[0031] Conductive structure 40

[0032] Protective layer 50

[0033] Base material layer 11

[0034] Circuit layer 12

[0035] First surface 111

[0036] Second surface 112

[0037] Opening 21

[0038] Copper clad laminate 10a

[0039] Copper foil layer 12a

[0040] First Intermediate 60

[0041] Film 70

[0042] Second intermediate 80

[0043] The following specific implementation manner will further illustrate the embodiments of the present application in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the technical field of the present application. The terms used herein are only for the purpose of describing specific implementation methods and are not intended to limit the present application embodiments.

[0045] It should be noted that all directional indications in the embodiments of the present application (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0046] Here, the embodiments of the present application are described with reference to the cross-sectional views, which are schematic diagrams of the idealized embodiments (and intermediate configurations) of the present application. Thus, it is foreseeable that the shapes of the diagrams are different due to manufacturing processes and / or tolerances. Therefore, the embodiments of the present application should not be interpreted as being limited to the specific shapes of the regions illustrated here, but should include deviations in shapes such as those produced due to manufacturing. The regions shown in the figures are themselves only schematic, and their shapes are not intended to illustrate the actual shapes of the devices, and are not intended to limit the scope of the present application.

[0047] Some embodiments of the present application are described in detail below in conjunction with the accompanying drawings. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0048] See also Figure 1 In a first aspect, the present application provides a flex-resistant flexible circuit board 100, which includes at least two circuit substrates 10 and an adhesive layer 20 located between the two circuit substrates 10. The two circuit substrates 10 have substantially the same structure, both including a substrate layer 11 and a circuit layer 12 formed on the surface of the substrate layer 11, and the adhesive layer 20 is located between the two substrate layers 11. The substrate layer 11 includes a first surface 111 and a second surface 112 that are arranged opposite to each other, the circuit layer 12 is formed on the first surface 111, and the second surface 112 is closer to the adhesive layer 20 than the first surface 111. The adhesive layer 20 has an opening 21 that penetrates the adhesive layer 20 along the thickness direction, and a coating 30 is provided in an area of ​​the second surface 112 of the substrate layer 11 corresponding to the opening 21. In this embodiment, the second surfaces 112 of the two substrate layers 11 are both provided with a coating 30. The two coatings 30 are arranged opposite to each other, and the orthographic projections of the two coatings 30 on the substrate layer 11 are both located within the range covered by the opening 21. Along the extension direction (i.e. Figure 1 The length of the coating 30 may be equal to or slightly less than the length of the opening 21. The friction coefficient of the coating 30 is less than or equal to 0.1, and the coating 30 is used to reduce the friction between two adjacent substrate layers 11. In the present application, the friction coefficient may be a dynamic friction coefficient or a static friction coefficient, as long as one of the dynamic friction coefficient and the static friction coefficient satisfies the condition of being less than or equal to 0.1.

[0049] When the flexible circuit board 100 is bent, since the coating 30 is provided in the area of ​​the substrate layer 11 corresponding to the opening 21, and the friction coefficient of the coating 30 is small (≤0.1), the friction force between the two adjacent substrate layers 11 can be reduced, and the protrusion at the opening 21 can move to the side to release stress, thereby improving the flexing resistance of the flexible circuit board 100.

[0050] In some embodiments, the material of the substrate layer 11 may be, but is not limited to, flexible materials such as polyimide (PI), polyester resin (PET), polyethylene naphthalate di formic acid glycol ester (PEN), polydimethylsiloxane (PDMS). In this embodiment, the material of the substrate layer 11 is PI. In some embodiments, the material of the adhesive layer 20 may be, but is not limited to, BS pure glue (Bonding Sheet).

[0051] In some embodiments, the coating 30 includes tungsten disulfide (WS 2 ), molybdenum disulfide (MoS 2 ), molybdenum disulfide (PTFE). The dynamic friction coefficient of tungsten disulfide is 0.03, and the static friction coefficient is 0.07. The friction coefficient of molybdenum disulfide is 0.03-0.09, and the friction coefficient of polytetrafluoroethylene is ≤0.1. The material of the substrate layer 11 of this embodiment is PI, and its friction coefficient is 0.3-0.5. The friction coefficients of tungsten disulfide, molybdenum disulfide, and polytetrafluoroethylene are all less than the friction coefficient of PI. In addition, the coating 30 made of the above materials has good anti-sticking and anti-slip properties, can effectively avoid the adhesion problem between the substrate layers 11, improve the yield of product manufacturing, and the coating 30 has strong adhesion performance and is not easy to fall off.

[0052] In some embodiments, the thickness of the coating 30 is less than or equal to 100 nm. In this way, the coating 30 can play a role in reducing the friction between two adjacent substrate layers 11 without increasing the thickness of the product.

[0053] like Figure 1 As shown, in some embodiments, the flexible circuit board 100 further includes a conductive structure 40. The conductive structure 40 is used to electrically connect the circuit layers 12 of different circuit substrates 10. The conductive structure 40 can be, but is not limited to, a conductive hole, a conductive column, and the like.

[0054] like Figure 1 As shown, in some embodiments, the flexible circuit board 100 further includes a protective layer 50. The protective layer 50 is disposed on the surface of the circuit layer 12 away from the substrate layer 11, and covers the surface of the substrate layer 11 exposed from the circuit layer 12. In this embodiment, the protective layer 50 is a cover-lay (CVL), and in other embodiments, the protective layer 50 can also be a solder mask. The protective layer 50 is used to protect the circuit layer 12 from being invaded by external water vapor or scratched by foreign objects.

[0055] In some embodiments, a layer may be added on the outside of the circuit layer 12, that is, a dielectric layer and a circuit layer are disposed on the outside of the circuit layer 12, and the dielectric layer is disposed between two adjacent circuit layers. It is understood that the protective layer 50 is disposed on the outside of the outermost circuit layer 12.

[0056] Will Figure 1 The flexible circuit board 100 shown in the figure is compared with the flexible circuit board of the control group (the flexible circuit board of the control group is compared with Figure 1 The difference between the flexible circuit board 100 and the flexible circuit board 100 is that the coating 30 is not provided. Ansys finite element software simulation test is performed to test the stress on the circuit layer 12 of the flexible circuit board 100 when bending. The test results are as follows: Figure 2 and Figure 3 (control group) as shown.

[0057] Depend on Figure 2 It is known that this application Figure 1 After the flexible circuit board 100 is bent, the friction coefficient between two adjacent substrate layers 11 is 0.03, and the stress on the circuit layer 12 is 49.6 MPa. Figure 3 It can be seen that after the flexible circuit board of the control group (without the coating 30) is bent, the stress on the circuit layer is 60.5 MPa. In the control group, the friction coefficient between two adjacent substrate layers is 0.4. Figure 2 and Figure 3 It can be seen that the stress on the flexible circuit board 100 described in the present application is reduced by 18% ((60.5-49.6) / 60.5), indicating that the coating 30 can reduce the friction coefficient between the substrate layers 11, thereby reducing the stress on the release, thereby improving the flexural resistance of the flexible circuit board 100 and improving the flexural life of the flexible circuit board 100.

[0058] See also Figures 4 to 8 In a second aspect, the present application provides a method for preparing a flex-resistant flexible circuit board 100, which includes steps S10 to S60. It is understandable that the numbering of the steps is intended to clearly describe the specific preparation method, and is not intended to limit the order of the steps.

[0059] See also Figure 4 , step S10, providing two copper clad laminates 10a. The copper clad laminates 10a include a substrate layer 11 and a copper foil layer 12a disposed on one surface of the substrate layer 11, that is, the copper clad laminates 10a are single-sided copper clad laminates. The substrate layer 11 includes a first surface 111 and a second surface 112 disposed opposite to each other, and the copper foil layer 12a is formed on the first surface 111.

[0060] See also Figure 5 In step S20, an adhesive layer 20 is laminated on the surface of one of the copper clad laminates 10a. The adhesive layer 20 may be but is not limited to BS pure adhesive. The adhesive layer 20 is laminated on the second surface 112 of the substrate layer 11. The adhesive layer 20 has an opening 21 that penetrates the adhesive layer 20 along the thickness direction.

[0061] Please continue reading Figure 5 In step S30, a coating 30 is provided on the second surface 112 of the substrate layer 11 bonded with the adhesive layer 20 in the area corresponding to the opening 21 to obtain a first intermediate 60. The friction coefficient of the coating 30 is less than or equal to 0.1, and the coating 30 is used to reduce the friction between two adjacent substrate layers 11.

[0062] like Figure 5 As shown, in step S30, the area of ​​the adhesive layer 20 near the opening 21 may be covered with a film 70 for shielding, so as to prevent the coating 30 from contaminating the adhesive layer 20 during spraying.

[0063] In some embodiments, the coating 30 includes tungsten disulfide (WS 2 ), molybdenum disulfide (MoS 2 ), molybdenum disulfide (PTFE) or more. In this embodiment, the coating 30 is WS 2 WS 2 The second surface 112 of the substrate layer 11 in the area to be bent can be sprayed with dry cold air under a pressure of 0.8 MPa without baking. 2 It can also be mixed with isopropyl alcohol to apply the paste onto the second surface 112 of the substrate layer 11 .

[0064] See also Figure 6 In step S40, a coating 30 is provided on the surface of the substrate layer 11 of another copper clad laminate 10a to obtain a second intermediate 80. The materials of the coatings 30 on the two copper clad laminates 10a can be the same or different, and the present application does not limit this.

[0065] like Figure 6 As shown, in step S40, a film 70 may be covered near the area of ​​the substrate layer 11 where the coating 30 is provided to shield the substrate layer 11, so as to prevent the coating 30 from contaminating the substrate layer 11 during spraying.

[0066] In some embodiments, the thickness of the coating 30 is less than or equal to 100 nm. In this way, the coating 30 can play a role in reducing the friction between two adjacent substrate layers 11 without increasing the thickness of the product.

[0067] See also Figure 7 , step S50, the first intermediate 60 and the second intermediate 80 are stacked and pressed together in the thickness direction, wherein the adhesive layer 20 is located between the two substrate layers 11, and the coating 30 of the first intermediate 60 corresponds to the coating 30 of the second intermediate 80. The coating 30 of the second intermediate 80 also corresponds to the opening 21 of the adhesive layer 20. The two coatings 30 are arranged opposite to each other, and the orthographic projections of the two coatings 30 on the substrate layer 11 are both located within the range covered by the opening 21. Along the extension direction of the first intermediate 60 or the second intermediate 80 (i.e. Figure 7 The length of the coating 30 may be equal to or slightly smaller than the length of the opening 21.

[0068] See also Figure 8 In step S60, the copper foil layer 12a is formed into a circuit layer 12. The circuit layer 12 can be formed by laminating, exposing, developing, etching, and stripping the copper foil layer 12a. The laminating, exposing, developing, etching, and stripping are common technical means in the art and will not be described in detail herein.

[0069] In some embodiments, Figure 8 As shown, after the circuit layer 12 is manufactured, a conductive structure 40 may be provided by laser drilling, electroplating a conductive material (for example, but not limited to copper) in the hole, and the like to electrically connect the circuit layer 12 .

[0070] In some embodiments, Figure 1 As shown, a protective layer 50 may be further provided on the surface of the circuit layer 12 away from the substrate layer 11, and the protective layer 50 covers the surface of the substrate layer 11 exposed from the circuit layer 12. In this embodiment, the protective layer 50 is a cover-lay (CVL), and in other embodiments, the protective layer 50 may also be a solder mask.

[0071] The present application sets a coating 30 with a small friction coefficient (≤0.1) in the area of ​​the substrate layer 11 corresponding to the opening 21 of the adhesive layer 20. The coating 30 can reduce the friction between two adjacent substrate layers 11, so that the protrusion at the opening 21 can move to the side to release stress, thereby improving the flex resistance of the flexible circuit board 100. The coating 30 has good anti-stick and anti-slip properties, can effectively avoid the adhesion problem between the substrate layers 11, improve the yield of product manufacturing, and the coating 30 has strong adhesion performance and is not easy to fall off.

[0072] The above descriptions are some specific implementations of the present application, but they are not limited to these implementations in actual application. For ordinary technicians in this field, other variations and changes made according to the technical concept of the present application should all fall within the protection scope of the present application.

Claims

1. A flex-resistant flexible circuit board, characterized in that: The flexible circuit board includes at least two circuit substrates and an adhesive layer located between the two circuit substrates; each of the circuit substrates includes a base material layer and a circuit layer formed on the surface of the base material layer, the adhesive layer is located between the two base material layers, the base material layer includes a first surface and a second surface arranged opposite to each other, and the circuit layer is formed on the first surface; the adhesive layer has an opening that penetrates the adhesive layer along the thickness direction, and a coating is provided in the area of ​​the second surface corresponding to the opening, the friction coefficient of the coating is less than or equal to 0.1, and the coating is used to reduce the friction between two adjacent base material layers.

2. The flex-resistant flexible circuit board according to claim 1, characterized in that: The coating includes one or more of tungsten disulfide, molybdenum disulfide, and polytetrafluoroethylene.

3. The flex-resistant flexible circuit board according to claim 1, characterized in that: The thickness of the coating layer is less than or equal to 100 nm.

4. The flex-resistant flexible circuit board according to claim 1, characterized in that: The flexible circuit board also includes a conductive structure, and the conductive structure is used to electrically connect circuit layers of different circuit substrates.

5. The flex-resistant flexible circuit board according to claim 1, characterized in that: The flexible circuit board further comprises a protection layer, which is arranged on a surface of the circuit layer away from the substrate layer and covers a surface of the substrate layer exposed from the circuit layer.

6. A method for preparing a flex-resistant flexible circuit board, characterized in that: The preparation method comprises the following steps: Providing two copper-clad laminates, the copper-clad laminates comprising a substrate layer and a copper foil layer, the substrate layer comprising a first surface and a second surface arranged opposite to each other, and the copper foil layer being formed on the first surface; A bonding layer is attached to the surface of one of the copper-clad laminates, the bonding layer is attached to the second surface of the substrate layer, and the bonding layer has an opening penetrating the bonding layer along the thickness direction; A coating is provided on the second surface of the substrate layer attached with the adhesive layer in the area corresponding to the opening to obtain a first intermediate; the friction coefficient of the coating is less than or equal to 0.1, and the coating is used to reduce the friction between two adjacent substrate layers; Arranging the coating on the second surface of the substrate layer of another copper-clad laminate to obtain a second intermediate; Laying the first intermediate and the second intermediate together in a thickness direction and then pressing them together, wherein the adhesive layer is located between two substrate layers, and the coating of the first intermediate corresponds to the coating of the second intermediate; The copper foil layer is made into a circuit layer to obtain the flex-resistant flexible circuit board.

7. The preparation method according to claim 6, characterized in that: The coating includes one or more of tungsten disulfide, molybdenum disulfide, and polytetrafluoroethylene.

8. The preparation method according to claim 6, characterized in that: The thickness of the coating layer is less than or equal to 100 nm.

9. The preparation method according to claim 6, characterized in that: The preparation method further comprises: providing a conductive structure to electrically connect the circuit layer.

10. The preparation method according to claim 9, characterized in that: The preparation method further comprises: providing a protective layer on the surface of the circuit layer away from the substrate layer, wherein the protective layer covers the surface of the substrate layer exposed from the circuit layer.

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