FPC adapter line resistant to bending and supporting high-frequency signal transmission

Abstract

This invention relates to an FPC adapter cable that is resistant to bending and supports high-frequency signal transmission. It comprises a four-layer flexible printed circuit board (FPC) cable body with a top layer, a first intermediate ground layer, a second intermediate ground layer, and a bottom layer along its thickness direction. The top differential traces reference the second intermediate ground layer, and the bottom differential traces reference the first intermediate ground layer. The two intermediate ground layers are projected and misaligned, with a copper-free cutout area between them. The top and bottom differential traces have serpentine trace segments at predetermined positions near the cable body ends. This invention improves the trace's ductility and bending resistance through the serpentine traces. The misaligned reference ground layers and the cutout design precisely control the differential impedance, achieving impedance accuracy of 90Ω±10Ω and 100Ω±10Ω, while also accommodating a thin design. This solves the problems of existing FPC cables being unresistant to bending and having poor high-frequency signal transmission, making it suitable for multi-interface high-frequency data transmission scenarios.

Description

Technical Field

[0001] This invention relates to the field of FPC adapter cable technology, and in particular to an FPC adapter cable that is resistant to bending and supports high-frequency signal transmission. Background Technology

[0002] The drawbacks of existing electronic wire technology are that it cannot be made thin, impedance cannot be accurately calculated, and adding an outer sheath results in a thicker, more rigid product that cannot be bent at large angles. Soldering is also labor-intensive and costly. Currently, while FPC cables can be made thin, the difficulty in accurately calculating impedance, high-quality transmission of high-frequency signals, and poor bending resistance are drawbacks. A professional cable manufacturer that collaborates with our company previously developed a Type-C-like FPC adapter cable, but its bending resistance was insufficient, and the impedance did not meet requirements, making successful development difficult. Summary of the Invention

[0003] The main objective of this invention is to provide an FPC adapter cable that is resistant to bending and supports high-frequency signal transmission, thereby solving the technical problems of existing FPC cables being not resistant to bending, having difficulty in accurately calculating impedance, and being unable to transmit high-frequency signals with high quality.

[0004] To achieve the above objectives, the present invention provides an FPC adapter cable that is resistant to bending and supports high-frequency signal transmission, including an FPC cable body. The FPC cable body is a four-layer flexible printed circuit board stack-up structure. The four-layer flexible printed circuit board stack-up structure includes, along the thickness direction, a top layer, a first intermediate ground layer, a second intermediate ground layer, and a bottom layer. The differential traces of the top layer use the second intermediate ground layer as the impedance reference ground, and the differential traces of the bottom layer use the first intermediate ground layer as the impedance reference ground. The traces of the first intermediate ground layer and the second intermediate ground layer are staggered in the stacking projection direction, and the substrate area between the first intermediate ground layer and the second intermediate ground layer is a hollow area without copper foil, so that the trace clearance of the second intermediate ground layer is referenced to the trace of the top layer. The differential traces of the top layer and the bottom layer are each provided with serpentine trace segments at preset positions near the ends of the FPC line body.

[0005] Furthermore, the preset position is a region 12mm-18mm away from the end of the FPC line body, and the routing length of the serpentine routing segment is 8mm-12mm.

[0006] Furthermore, both the top-level circuit layer and the bottom-level circuit layer are provided with two sets of differential traces, and each set of differential traces is provided with the serpentine trace segment.

[0007] Furthermore, the differential impedance corresponding to the differential traces of the top layer and the bottom layer is 90Ω±10Ω or 100Ω±10Ω. When the required differential impedance of the first differential trace is 100Ω, the corresponding trace width is 5mil and the trace spacing is 8mil. When the required differential impedance of the second differential trace is 90Ω, the corresponding trace width is 6mil and the trace spacing is 8mil.

[0008] Furthermore, the total thickness of the four-layer flexible printed circuit board stack-up structure is 206 μm; The top layer of the circuit is composed of a 35μm L1 copper conductor on a 25μm PI substrate. The first intermediate layer and the second intermediate layer are composed of 18μm L2 copper conductors and L3 copper conductors respectively set on both sides of a 5μm PI substrate. The bottom circuit layer consists of a 35μm L4 copper conductor on a 25μm PI substrate.

[0009] Furthermore, an adhesive with a thickness of 12.5 μm is provided between the top layer and the first intermediate ground layer, and an adhesive with a thickness of 12.5 μm is provided between the second intermediate ground layer and the bottom layer, resulting in the four-layer flexible printed circuit board stack-up structure with a total thickness of 206 μm.

[0010] Furthermore, a first cover film and a second cover film are respectively provided on both sides of the four-layer flexible printed circuit board stacked structure to form the FPC adapter cable.

[0011] Furthermore, both the first cover film and the second cover film are composed of an adhesive and a polyimide film. The first cover film connects the polyimide film to the top layer of the circuit layer through an adhesive, and the second cover film connects the polyimide film to the bottom layer of the circuit layer through an adhesive.

[0012] Furthermore, the total thickness of the FPC adapter cable is 282 μm, and the thickness of the four-layer flexible printed circuit board stack-up structure is 206 μm. The first cover film connects a 13μm thick polyimide film to the top circuit layer using an adhesive with a thickness of 25μm. The second cover film connects a 13μm thick polyimide film to the underlying circuit layer using an adhesive with a thickness of 25μm.

[0013] Furthermore, the FPC adapter cable includes any one of the following: a Type-C interface adapter cable, a Lightning interface adapter cable, or a Micro interface adapter cable, for high-frequency data transmission.

[0014] The FPC adapter cable provided by this invention, which is resistant to bending and supports high-frequency signal transmission, has the following beneficial effects: (1) By setting serpentine trace segments at preset positions near the ends of the differential traces in the top and bottom trace layers, the ductility of the traces in the fatigue-prone area of ​​bending is effectively increased, the fatigue fracture resistance of the FPC adapter is greatly improved, and its bending life is significantly enhanced, meeting the product's requirements for large-angle and multiple bending applications.

[0015] (2) A four-layer flexible printed circuit board stack-up structure is adopted. The top layer of the circuit board references the second intermediate ground layer, the bottom layer of the circuit board references the first intermediate ground layer, and the two intermediate ground layers are staggered and a hollow area without copper foil is set between them. This increases the thickness of the dielectric layer between the trace and the reference ground, realizes the accurate calculation and control of the FPC adapter impedance, and ensures the differential impedance accuracy of 90Ω±10Ω and 100Ω±10Ω, thereby realizing high-quality and stable transmission of high-frequency signals.

[0016] (3) The FPC adapter cable uses flexible materials such as polyimide and has a fine layer thickness design. The overall thickness is controllable and the texture is soft. It is thinner and easier to bend than traditional electronic wires. At the same time, it avoids the problem of increased thickness and increased hardness after adding an outer sheath to electronic wires. It is suitable for the use scenarios of miniaturized and portable products such as screen sharing devices.

[0017] (4) The four-layer board structure and wiring design take into account both bending resistance and high-frequency signal transmission performance. The overall structure design is reasonable and the process implementation is strong. Compared with the existing unqualified FPC line solutions, it solves the dual technical defects of insufficient impedance and poor bending resistance. Compared with traditional electronic lines, it reduces the labor cost of welding process and improves the production and use cost performance of the product. Attached Figure Description

[0018] Figure 1 This is a thumbnail of a stacked frame table of an FPC adapter cable that is resistant to bending and supports high-frequency signal transmission in one embodiment of the present invention. Figure 2 This is a schematic diagram of the top layer of an FPC adapter cable that is resistant to bending and supports high-frequency signal transmission in one embodiment of the present invention. Figure 3 This is a schematic diagram of the bottom layer of an FPC adapter cable that is resistant to bending and supports high-frequency signal transmission in one embodiment of the present invention. Figure 4 This is a schematic diagram of the first intermediate ground layer of an FPC adapter cable that is resistant to bending and supports high-frequency signal transmission in one embodiment of the present invention; Figure 5 This is a schematic diagram of the second intermediate ground layer of an FPC adapter cable that is resistant to bending and supports high-frequency signal transmission in one embodiment of the present invention; Figure 6This is an FPC differential impedance adjustment table for an FPC adapter cable that is resistant to bending and supports high-frequency signal transmission, according to one embodiment of the present invention.

[0019] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0021] Reference Figure 2-5 A bend-resistant FPC adapter cable that supports high-frequency signal transmission includes an FPC cable body, wherein the FPC cable body is a four-layer flexible printed circuit board stack structure, and the four-layer flexible printed circuit board stack structure includes, along the thickness direction, a top circuit layer (…). Figure 2 ), First intermediate stratum ( Figure 4 ), the second intermediate stratum ( Figure 5 ) and the underlying circuit layer ( Figure 3 ); The differential traces of the top layer use the second intermediate ground layer as the impedance reference ground, and the differential traces of the bottom layer use the first intermediate ground layer as the impedance reference ground. The traces of the first intermediate ground layer and the second intermediate ground layer are staggered in the stacking projection direction, and the substrate area between the first intermediate ground layer and the second intermediate ground layer is a hollow area without copper foil, so that the trace clearance of the second intermediate ground layer is referenced to the trace of the top layer. The differential traces of the top layer and the bottom layer are each provided with serpentine trace segments at preset positions near the ends of the FPC line body.

[0022] The preset position is a region 12mm-18mm away from the end of the FPC line body, and the length of the serpentine wiring segment is 8mm-12mm.

[0023] Both the top-level and bottom-level line layers are provided with two sets of differential traces, and each set of differential traces is provided with the serpentine trace segment.

[0024] Reference Figure 6 The differential impedance corresponding to the differential traces of the top layer and the bottom layer is 90Ω±10Ω or 100Ω±10Ω. When the required differential impedance of the first differential trace is 100Ω, the corresponding trace width is 5mil and the trace spacing is 8mil. When the required differential impedance of the second differential trace is 90Ω, the corresponding trace width is 6mil and the trace spacing is 8mil.

[0025] Specifically, the design of the differential impedance parameters and corresponding line width and spacing is determined by comprehensively considering the core application scenarios of the FPC adapter cable of this invention, the industry-standard high-speed transmission protocols, the unique four-layer board stack-up structure, the mass production capabilities of FPC manufacturers, and the requirements for bending resistance. The differential impedance is selected as 90Ω±10Ω and 100Ω±10Ω, which is mainly to adapt to the high-frequency data transmission core application scenarios of this invention for Type-C screen sharing devices. The 90Ω differential impedance is for USB 3.0 and USB 3.0.1. The standard differential impedance value specified by mainstream high-speed transmission protocols such as USB4 and Type-C interfaces is 100Ω. This is also the standard differential impedance value commonly used by DisplayPort, HDMI, and other audio / video transmission protocols. By using these two industry-standard impedance values, the FPC adapter cable of this invention is fully compatible with the interface specifications of mainstream Type-C transmission and high-speed data transmission devices on the market. This ensures impedance matching during high-frequency signal transmission, avoiding problems such as signal reflection, transmission loss, and signal distortion caused by impedance discontinuities. This fundamentally guarantees high-quality and stable transmission of high-frequency signals. The impedance tolerance is set at ±10Ω, determined based on the actual mass production capabilities of the FPC manufacturer. Under the four-layer board stack-up structure and routing design of this invention, this tolerance range can be stably achieved during mass production. This satisfies the core requirement of impedance accuracy for high-frequency signal transmission while avoiding the problems of decreased production yield and increased manufacturing costs caused by excessively high accuracy requirements. This directly addresses the technical pain point that this invention initially aimed to solve: the inability to stably achieve precise impedance control in ultra-thin FPC lines. Furthermore, the routing parameters of 5mil line width and 8mil line spacing are matched for a 100Ω target differential impedance, and 6mil line width and 8mil line spacing are matched for a 90Ω target differential impedance. This is entirely based on the invention's unique four-layer board stack-up structure, with the top layer referencing the third ground layer, the bottom layer referencing the second ground layer, and the two ground reference layers arranged in a staggered manner. With the design scheme of the intermediate layer clearance, combined with the fixed dielectric constant of the polyimide (PI) substrate, and the optimal parameter combination determined by precise simulation through professional impedance calculation software, in the ultra-thin laminated structure of this invention with a total thickness of 282μm and a core board thickness of 206μm, this set of line width and spacing parameters can enable the differential traces of the top and bottom layers to form stable impedance loops with their corresponding reference grounds, accurately achieving the target differential impedance value. This completely solves the industry pain point of existing technologies where ultra-thin FPC lines cannot accurately calculate and stably achieve the target impedance, and cannot transmit high-frequency signals with high quality. At the same time, the design of this set of trace parameters also takes into account the core requirement of the invention for bending resistance. The fixed 8mil line spacing design satisfies the coupling of differential signal transmission. The requirements are to reduce crosstalk and radiation loss during high-frequency signal transmission, while also meeting the standard manufacturing capabilities of FPC manufacturers. This avoids increased production difficulty and decreased product yield caused by excessively small line spacing. For the 5mil and 6mil line width designs with different impedance matching, while ensuring accurate impedance matching, it avoids the fatigue fracture problem of copper foil during bending caused by excessively thin line widths, and also avoids the problems of reduced line flexibility and deteriorated bending performance caused by excessively wide line widths. This complements the bend-resistant design of the serpentine wiring segment at the end of this invention, jointly ensuring the bend resistance life and long-term reliability of the FPC adapter cable, fully adapting to the needs of multiple bending and large-angle bending in the retractable use scenario of the screen sharing device.

[0026] See attached document Figure 1 The four-layer flexible printed circuit board stacked structure is further provided with a first cover film and a second cover film on both sides, which constitute the FPC adapter cable.

[0027] Both the first cover film and the second cover film are composed of an adhesive and a polyimide film. The first cover film connects the polyimide film to the top layer of the circuit layer through an adhesive, and the second cover film connects the polyimide film to the bottom layer of the circuit layer through an adhesive.

[0028] The total thickness of the FPC adapter cable is 282 μm, and the thickness of the four-layer flexible printed circuit board stack-up structure is 206 μm. The first cover film connects a 13μm thick polyimide film to the top circuit layer using an adhesive with a thickness of 25μm. The second cover film connects a 13μm thick polyimide film to the underlying circuit layer using an adhesive with a thickness of 25μm.

[0029] The total thickness of the four-layer flexible printed circuit board stack-up structure is 206 μm; The top layer of the circuit is composed of a 35μm L1 copper conductor on a 25μm PI substrate. The first intermediate layer and the second intermediate layer are composed of 18μm L2 copper conductors and L3 copper conductors respectively set on both sides of a 5μm PI substrate. The bottom circuit layer consists of a 35μm L4 copper conductor on a 25μm PI substrate.

[0030] A 12.5 μm thick adhesive is provided between the top layer and the first intermediate ground layer, and a 12.5 μm thick adhesive is provided between the second intermediate ground layer and the bottom layer, resulting in the four-layer flexible printed circuit board stack-up structure with a total thickness of 206 μm.

[0031] In one embodiment, the FPC adapter cable includes any one of a Type-C interface adapter cable, a Lightning interface adapter cable, or a Micro interface adapter cable, and is used for high-frequency data transmission.

[0032] In summary, this invention proposes an FPC adapter cable that is resistant to bending and supports high-frequency signal transmission. The cable body comprises a four-layer flexible printed circuit board (FPC) stack structure, with a top layer, a first intermediate ground layer, a second intermediate ground layer, and a bottom layer along its thickness direction. The top differential traces reference the second intermediate ground layer, and the bottom differential traces reference the first intermediate ground layer. The two intermediate ground layers are projected and misaligned, with a copper-free cutout area between them. The top and bottom differential traces have serpentine trace segments at predetermined positions near the cable body ends. This invention improves the trace's ductility and bending resistance through the serpentine traces, and precisely controls the differential impedance using the four-layer staggered reference ground and the cutout design, achieving impedance accuracy of 90Ω±10Ω and 100Ω±10Ω, while also considering a thin design. This solves the problems of existing FPC cables being not resistant to bending and having poor high-frequency signal transmission, making it suitable for multi-interface high-frequency data transmission scenarios.

[0033] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. An FPC adapter cable that is resistant to bending and supports high-frequency signal transmission, characterized in that, It includes an FPC line body, which is a four-layer flexible printed circuit board stack-up structure. The four-layer flexible printed circuit board stack-up structure includes, along the thickness direction, a top circuit layer, a first intermediate ground layer, a second intermediate ground layer, and a bottom circuit layer. The differential traces of the top layer use the second intermediate ground layer as the impedance reference ground, and the differential traces of the bottom layer use the first intermediate ground layer as the impedance reference ground. The traces of the first intermediate ground layer and the second intermediate ground layer are staggered in the stacking projection direction, and the substrate area between the first intermediate ground layer and the second intermediate ground layer is a hollow area without copper foil, so that the trace clearance of the second intermediate ground layer is referenced to the trace of the top layer. The differential traces of the top layer and the bottom layer are each provided with serpentine trace segments at preset positions near both ends of the FPC line body.

2. The FPC adapter cable with bend resistance and support for high-frequency signal transmission according to claim 1, characterized in that, The preset position is a region 12mm-18mm away from the end of the FPC line body, and the length of the serpentine wiring segment is 8mm-12mm.

3. The FPC adapter cable with bend resistance and support for high-frequency signal transmission according to claim 1, characterized in that, Both the top-level and bottom-level line layers are provided with two sets of differential traces, and each set of differential traces is provided with the serpentine trace segment.

4. The FPC adapter cable with bend resistance and support for high-frequency signal transmission according to claim 1, characterized in that, The differential impedance corresponding to the differential traces of the top layer and the bottom layer is 90Ω±10Ω or 100Ω±10Ω. When the required differential impedance of the first differential trace is 100Ω, the corresponding trace width is 5mil and the trace spacing is 8mil. When the required differential impedance of the second differential trace is 90Ω, the corresponding trace width is 6mil and the trace spacing is 8mil.

5. The FPC adapter cable with bend resistance and support for high-frequency signal transmission according to any one of claims 1-4, characterized in that, The total thickness of the four-layer flexible printed circuit board stack-up structure is 206 μm; The top layer of the circuit is composed of a 35μm L1 copper conductor on a 25μm PI substrate. The first intermediate layer and the second intermediate layer are composed of 18μm L2 copper conductors and L3 copper conductors respectively set on both sides of a 5μm PI substrate. The bottom circuit layer consists of a 35μm L4 copper conductor on a 25μm PI substrate.

6. The FPC adapter cable with bend resistance and support for high-frequency signal transmission according to claim 5, characterized in that, A 12.5 μm thick adhesive is provided between the top layer and the first intermediate ground layer, and a 12.5 μm thick adhesive is provided between the second intermediate ground layer and the bottom layer, resulting in the four-layer flexible printed circuit board stack-up structure with a total thickness of 206 μm.

7. The FPC adapter cable with bend resistance and support for high-frequency signal transmission according to claim 1, characterized in that, The four-layer flexible printed circuit board stacked structure is further provided with a first cover film and a second cover film on both sides, forming the FPC adapter cable.

8. The FPC adapter cable with bend resistance and support for high-frequency signal transmission according to claim 7, characterized in that, Both the first cover film and the second cover film are composed of an adhesive and a polyimide film. The first cover film connects the polyimide film to the top layer of the circuit layer through an adhesive, and the second cover film connects the polyimide film to the bottom layer of the circuit layer through an adhesive.

9. The FPC adapter cable with bending resistance and support for high-frequency signal transmission according to claim 8, characterized in that, The total thickness of the FPC adapter cable is 282 μm, and the thickness of the four-layer flexible printed circuit board stack-up structure is 206 μm. The first cover film connects a 13μm thick polyimide film to the top circuit layer using an adhesive with a thickness of 25μm. The second cover film connects a 13μm thick polyimide film to the underlying circuit layer using an adhesive with a thickness of 25μm.

10. The FPC adapter cable with bending resistance and support for high-frequency signal transmission according to claim 1, characterized in that, The FPC adapter cable includes any one of the following: Type-C interface adapter cable, Lightning interface adapter cable, or Micro interface adapter cable, and is used for high-frequency data transmission.

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