Anti-wrinkle flexible printed circuit board

Abstract

The utility model discloses an anti -wrinkle flexible printed circuit board, wherein the anti -wrinkle flexible printed circuit board includes: base material layer, be located on the conductive layer of base material layer, be located on the buffer layer of conductive layer, the covering membrane layer is attached to the buffer layer, thus, through setting up the buffer layer between conductive layer and covering membrane layer to utilize the buffer layer interlayer deformation energy to buffer and disperse to interlayer stress, can effectively prevent the wrinkling problem caused by interlayer stress.

Description

Technical Field

[0001] This utility model relates to the field of circuit board technology, and in particular to an anti-wrinkle printed circuit board. Background Technology

[0002] In consumer electronics, industrial control, and smart wearables, keyboards using flexible printed circuit boards (FPCs) have become core input components for various portable devices and precision electronic instruments due to their advantages such as thinness, flexibility, and spatial adaptability. Traditional FPC keyboards typically consist of multiple layers of heterogeneous materials, including a substrate layer, a conductive layer on the substrate layer, and a cover film layer on the conductive layer. However, during the manufacturing process of these FPC keyboards, wrinkling after lamination is a common problem. This is mainly due to the differences in the coefficients of thermal expansion of the different materials. When the lamination temperature fluctuates during production, the expansion and contraction of the various layers of the FPC keyboard are asynchronous. This asynchronous expansion and contraction creates continuous internal stress between the material layers. When the bonding strength in the stress concentration area is insufficient to resist this force, localized warping and wrinkling occur between the cover film and the substrate layer, reducing product yield and reliability. Utility Model Content

[0003] This utility model provides an anti-wrinkle flexible printed circuit board, which solves the problem of wrinkling that occurs after the existing flexible printed circuit boards are fully bonded, thereby improving product yield and reliability.

[0004] To achieve the above objectives, in a first aspect, embodiments of the present invention provide an anti-wrinkle flexible printed circuit board, comprising:

[0005] Substrate layer;

[0006] A conductive layer located on the substrate layer;

[0007] A buffer layer located on the conductive layer;

[0008] A covering film layer attached to the buffer layer.

[0009] Furthermore, the buffer layer is one of the following: white oil layer, clear oil layer, silver paste layer, copper paste layer, carbon paste layer, and graphene layer.

[0010] Furthermore, the components of the white oil layer include modified epoxy resin.

[0011] Furthermore, the thickness of the buffer layer is 9μm-15μm.

[0012] Furthermore, the conductive layer is a silver wire conductive layer; the cover film layer is a white cover film layer.

[0013] Furthermore, the conductive layer has a pad area, and a pad electrically connected to the conductive layer is formed on the pad area. The buffer layer covers the area of ​​the conductive layer other than the pad area.

[0014] Secondly, embodiments of the present invention provide a method for preparing the wrinkle-resistant flexible printed circuit board described above, the method comprising the following steps:

[0015] Provide a substrate layer;

[0016] A conductive layer is formed on the substrate layer;

[0017] A buffer layer is formed on the conductive layer;

[0018] A covering film layer is attached to the buffer layer.

[0019] Further, the step of forming a buffer layer on the conductive layer includes:

[0020] A white ink layer as a buffer layer is printed on the conductive layer using a 200-mesh screen, and the thickness of the printed white ink layer is 9μm-15μm.

[0021] Furthermore, after the step of printing a white oil layer as a buffer layer on the conductive layer using a 200-mesh screen, the method further includes:

[0022] The white oil layer is pre-cured at a first temperature of 75℃~85℃ for 25min~35min.

[0023] After pre-curing, the white oil layer is fully cured at a second temperature of 145℃~160℃ for 50min~70min.

[0024] Plasma cleaning was performed on the fully cured white oil layer.

[0025] Furthermore, the first temperature is 80°C, and the second temperature is 150°C.

[0026] Further, the step of attaching the covering film layer onto the buffer layer includes:

[0027] The cover film layer is bonded to the buffer layer using a pressure of 0.4MPa-0.6MPa.

[0028] Beneficial effects: The present invention provides an anti-wrinkle flexible printed circuit board, comprising a substrate layer, a conductive layer on the substrate layer, a buffer layer on the conductive layer, and a cover film layer attached to the buffer layer. Thus, by setting a buffer layer between the conductive layer and the cover film layer, the buffer layer absorbs the deformation energy between the layers, thereby buffering and dispersing the interlayer stress and effectively preventing wrinkling caused by interlayer stress. Attached Figure Description

[0029] The technical solution and beneficial effects of this utility model will become apparent from the following detailed description of specific embodiments in conjunction with the accompanying drawings.

[0030] Figure 1 This is a schematic diagram of the structure of the anti-wrinkle flexible printed circuit board provided in this embodiment of the utility model;

[0031] Figure 2 This is a flowchart of the method for preparing an anti-wrinkle flexible printed circuit board according to an embodiment of the present invention. Detailed Implementation

[0032] Please refer to the diagram, where the same component symbols represent the same components. The principle of this utility model is illustrated by example in a suitable computing environment. The following description is based on the illustrated specific embodiments of this utility model, and should not be considered as limiting other specific embodiments not detailed herein.

[0033] See Figure 1 A wrinkle-resistant flexible printed circuit board 100 according to an embodiment of the present invention includes a substrate layer 11, a conductive layer 12 located on the substrate layer 11, a buffer layer 13 located on the conductive layer 12, and a cover film layer 14 attached to the buffer layer 13. That is, the buffer layer 13 is located between the conductive layer 12 and the cover film layer 14. Thus, the buffer layer 13 can absorb the deformation energy between the layers to buffer and disperse the interlayer stress, and can effectively prevent wrinkling caused by interlayer stress.

[0034] The substrate layer can be made of PI (polyimide), the conductive layer 12 can be a silver wire conductive layer, and the cover film layer 14 can be a white cover film layer.

[0035] In some embodiments, the buffer layer 13 can be a white oil layer, i.e., the buffer layer 13 is formed by using white oil to create a sandwich structure of conductive layer-white oil layer-covering film layer. Utilizing the flexibility and elasticity of the white oil layer, it can act as a stress buffer layer, absorbing interlayer deformation. The white oil layer comprises modified epoxy resin; that is, the white oil layer serving as the stress buffer layer can be made using a modified epoxy resin system with a viscosity of 2500±500 cps and a contact angle ≤30° with the silver wire conductive layer 12.

[0036] In other embodiments, the buffer layer 13 may also be formed of other materials, such as a clear varnish layer, silver paste layer, copper paste layer, carbon paste layer, or graphene layer, and there is no limitation thereto.

[0037] Optionally, the thickness of the buffer layer 13 is 9μm-15μm, for example, it can be 10μm or 12μm.

[0038] In traditional FPC keyboard structures, the conductive layer and the cover film are directly bonded. The conductive particles in the conductive layer readily react with the ester groups in the cover film, such as polyester PET film, causing the interfacial adhesion to gradually weaken over time, resulting in insufficient interfacial stability. Furthermore, after the bonding process, the FPC keyboard requires a subsequent surface mount technology (SMT) process to solder and assemble electronic components such as resistors, capacitors, and chips. During this SMT process, the reflow soldering equipment generates short-term high-temperature thermal shocks. For the multi-layered structure of traditional FPC keyboards, this rapid heating and cooling process further amplifies the differences in the thermal expansion coefficients of the layers, causing significant differences in interlayer expansion and contraction, resulting in instantaneous tensile stress and making interlayer delamination more likely. In this embodiment of the invention, a white oil buffer layer 13 is provided between the conductive layer 12 and the cover film layer 14 to play a chemical bonding role, thereby enhancing the interfacial bonding force between the conductive layer 12 and the cover film layer 14. At the same time, the white oil buffer layer 13 can also buffer and absorb the tensile stress in the SMT process to solve the problem of interlayer peeling.

[0039] In this embodiment of the invention, the conductive layer 12 has a pad area, which is formed with pads 15 electrically connected to the conductive layer 12. The buffer layer 13 covers the area of ​​the conductive layer 12 other than the pad area. Furthermore, the anti-wrinkle flexible printed circuit board 100 of this invention may further include a solder resist white layer 16 located on the cover film layer 14.

[0040] See Figure 2 This utility model embodiment also provides a method for preparing an anti-wrinkle flexible printed circuit board, used to manufacture the flexible circuit board described in the above embodiment. The preparation method includes the following steps:

[0041] Step S201: Provide a substrate layer. (This is followed by a seemingly unrelated sentence about bonding.) Figure 1 The substrate layer 11 may be, for example, a PI (polyimide) film layer, wherein the substrate layer 11 may be pre-dried.

[0042] Step S202: A conductive layer is formed on the substrate layer. The conductive layer 12 may be, for example, a silver wire conductive layer, formed by printing silver wires on the substrate layer 11. Afterwards, the resistance of the silver wire conductive layer is tested, and it is then baked. After the conductive layer 12 is formed, pads 15 are formed on the conductive layer 12.

[0043] Step S203: Form a buffer layer on the conductive layer.

[0044] Specifically, white ink can be printed on the conductive layer 12 using a 200-mesh screen to form a buffer layer 13, i.e., the buffer layer 13 is the white ink layer. Of course, other mesh sizes can also be used for printing; there are no limitations. During the printing process, the thickness of the white ink layer is controlled to be 9μm-15μm, for example, 10μm or 12μm. The white ink layer, serving as the buffer layer 13, covers the area of ​​the conductive layer 12 except for the pads 15. After printing the white ink, the following steps can be included: pre-curing the white ink layer at a first temperature of 75℃~85℃ for 25min~35min; after pre-curing, fully curing the white ink layer at a second temperature of 145℃~160℃ for 50min~70min; and then plasma cleaning the fully cured white ink layer. After plasma cleaning, the surface tension of the white ink layer can reach above 72dyn / cm.

[0045] The first temperature can be 80°C, the second temperature can be 150°C, the pre-curing time can be, for example, 30 minutes, and the complete curing time can be, for example, 60 minutes. In other embodiments, the first temperature, the second temperature, the pre-curing time, and the complete curing time can be selected according to actual conditions.

[0046] Step S204: Attach the cover film layer to the buffer layer. Specifically, the cover film layer 14 can be attached to the buffer layer 13 using a pressure of 0.4MPa-0.6MPa.

[0047] The preparation method of this utility model utilizes the buffer layer 13 to absorb interlayer stress, thereby solving the problem of wrinkling that occurs after overall bonding of existing flexible printed circuit boards, improving product yield and reliability. After step S204, a chemical gold plating process can be performed, i.e., gold plating (Au) on the pads 15 to improve their corrosion resistance and reduce contact resistance. Afterwards, processes such as printing black text on the front, printing black ink on the back, applying PI reinforcement, and printing white text on the back can be performed, followed by open / short circuit testing and visual inspection. Before the SMI process, a first LED test is performed, followed by applying blue adhesive to the flexible printed circuit board obtained after the above processes and laminating the blue adhesive, and then a second LED test is performed. After the blue film adhesive lamination process, a 3D profilometer was used for inspection. The inspection results show that the wrinkling height of the flexible printed circuit board produced by this embodiment is ≤15μm (the wrinkling height of the traditional FPC structure is ≥50μm). Moreover, there is no delamination after 200 bending tests. In addition, after dual-light test verification, the wrinkling defect rate of the flexible printed circuit board of this embodiment is reduced to below 0.5%, thereby solving the problem of wrinkling and delamination after the flexible printed circuit board is laminated.

[0048] This document uses specific examples to illustrate the principles and implementation methods of this utility model. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this utility model. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this utility model. Therefore, the content of this specification should not be construed as a description of this utility model.

Claims

1. A wrinkle-resistant flexible printed circuit board, characterized in that, include: Substrate layer; A conductive layer located on the substrate layer; A buffer layer located on the conductive layer; A covering film layer attached to the buffer layer.

2. The anti-wrinkle flexible printed circuit board according to claim 1, characterized in that, The buffer layer is one of the following: white oil layer, clear oil layer, silver paste layer, copper paste layer, carbon paste layer, and graphene layer.

3. The anti-wrinkle flexible printed circuit board according to claim 2, characterized in that, The components of the white oil layer include modified epoxy resin.

4. The anti-wrinkle flexible printed circuit board according to claim 1, characterized in that, The thickness of the buffer layer is 9μm-15μm.

5. The anti-wrinkle flexible printed circuit board according to claim 1, characterized in that, The conductive layer is a silver wire conductive layer; the cover film layer is a white cover film layer.

6. The anti-wrinkle flexible printed circuit board according to claim 1, characterized in that, The conductive layer has a pad area, and a pad electrically connected to the conductive layer is formed on the pad area. The buffer layer covers the area of ​​the conductive layer other than the pad area.

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