Bending-resistant flexible circuit board

Abstract

The application relates to the technical field of circuit boards, and discloses a bend-resistant flexible circuit board. The bend-resistant flexible circuit board comprises a first metal layer, a second metal layer and a third metal layer which are stacked and arranged at intervals; the bend-resistant flexible circuit board has a connecting area and a layered area; the first metal layer, the second metal layer and the third metal layer are press-bonded in the connecting area and are arranged at intervals through gaps in the layered area; the second metal layer has a coplanar waveguide unit in the layered area; the coplanar waveguide unit comprises a coplanar waveguide conductor and first grounding electrodes arranged on the two sides of the coplanar waveguide conductor; the first metal layer and the third metal layer are each provided with a first window at positions opposite to the coplanar waveguide conductor; and the first metal layer has a first metal part between adjacent first windows. The bend-resistant flexible circuit board provided by the application can solve the technical problem of large impedance fluctuation of the existing flexible circuit board when being bent by improving the signal line type design of the layered area and adopting the first window structure.

Description

Technical Field

[0001] This application relates to the field of circuit board technology, and in particular to a flexible circuit board that is resistant to bending. Background Technology

[0002] Flexible printed circuits (FPCs) are printed circuit boards made with polyimide or polyester film as the substrate. They are highly reliable and extremely flexible. Due to their advantages such as high wiring density, light weight, thinness, and good bending ability, they are widely used in aerospace, military, mobile communications, laptops, digital cameras and other fields or products.

[0003] To adapt to the development trend of electronic products such as foldable screens and sliding screens, existing technologies provide a bend-resistant flexible circuit board. This bend-resistant flexible circuit board includes multiple metal layers, with a layered structure design in the bending area, meaning the layers are spaced apart to provide good bending performance. However, existing bend-resistant flexible circuit boards have poor anti-interference capabilities; bending easily causes significant impedance changes, affecting signal transmission and, in severe cases, causing product malfunctions. Summary of the Invention

[0004] The purpose of this application is to provide a bend-resistant flexible circuit board to solve the technical problem of large impedance fluctuation when existing flexible circuit boards are bent.

[0005] To address the aforementioned issues, this application provides a bend-resistant flexible circuit board, comprising a first metal layer, a second metal layer, and a third metal layer stacked and spaced apart. The bend-resistant flexible circuit board has a connection area and a layering area. The first metal layer, the second metal layer, and the third metal layer are pressed together in the connection area and separated by gaps in the layering area.

[0006] The second metal layer has a coplanar waveguide unit in the layered region. The coplanar waveguide unit includes a coplanar waveguide strip and a first ground electrode disposed on both sides of the coplanar waveguide strip. The first metal layer and the third metal layer are provided with a first window opposite to the coplanar waveguide strip, and a first metal part is provided between adjacent first windows.

[0007] In one embodiment, the projection of the first window onto the second metal layer covers the coplanar waveguide strip, the width of the coplanar waveguide strip is W1, the width of the first window is W2, the distance between the coplanar waveguide strip and the adjacent first ground electrode is D1, and W2≥W1+2D1+0.4mm.

[0008] In one embodiment, the width of the coplanar waveguide strip is W1, and the distance between the coplanar waveguide strip and the adjacent first ground electrode is D1, where W1 ≥ 6D1.

[0009] In one embodiment, the second metal layer has a stripline unit within the connection area. The stripline unit includes a stripline conductor and second grounding electrodes disposed on both sides of the stripline conductor. The first metal layer and the third metal layer are each provided with a second opening opposite to the stripline conductor.

[0010] In one embodiment, the second window includes a plurality of strip-shaped holes spaced apart along the length of the strip conductor, with a second metal portion between adjacent strip-shaped holes.

[0011] In one embodiment, along the extension direction of the strip conductor, the length of the strip hole is L1, the length of the second metal part is L2, and the ratio of L1 to L2 is 1:0.7 to 1:0.8.

[0012] In one embodiment, the length L1 of the strip hole is ≥ 0.4 mm.

[0013] In one embodiment, the width of the strip conductor is W3, the width of the strip hole is W4, and the distance between the strip conductor and the adjacent second grounding electrode is D2, where W4 ≥ W3 + 2D2 + 0.3 mm.

[0014] In one embodiment, the strip conductor includes a first portion opposite to the strip hole, a second portion opposite to the second metal portion, and a transition connection portion connecting the first portion and the second portion. The width of the first portion is greater than the width of the second portion, and the width of the transition connection portion changes linearly.

[0015] In one embodiment, the width of the coplanar waveguide guide strip is different from the width of the stripline guide strip, and a transition guide strip connects the coplanar waveguide guide strip and the stripline guide strip, the width of which varies linearly.

[0016] The bend-resistant flexible circuit board provided in this application includes a first metal layer, a second metal layer, and a third metal layer stacked and spaced apart. The second metal layer has a coplanar waveguide unit in the layered region. The coplanar waveguide unit includes a coplanar waveguide strip and first ground electrodes disposed on both sides of the coplanar waveguide strip. The first metal layer and the third metal layer are provided with first openings opposite to the coplanar waveguide strip, and there is a first metal part between adjacent first openings. On the one hand, designing coplanar waveguide units in the layered region and using coplanar waveguides to replace the traditional stripline design can ensure the signal transmission performance of the signal lines in the layered region. On the other hand, the coplanar waveguide unit itself forms a complete signal transmission and return path. The clear opening treatment of the first metal layer and the third metal layer opposite to the coplanar waveguide strip and the retention of metal layers between adjacent openings can increase the isolation of the coplanar waveguide unit, so as to play the role of isolating and optimizing return loss, thereby improving the anti-interference capability of the signal lines in the layered region and reducing the impact of bending on signal transmission. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A schematic diagram of the structure of the flexible circuit board with bend resistance provided in this application when it is not bent;

[0019] Figure 2 A schematic diagram of the structure of the flexible circuit board with bend resistance provided in the embodiment of this application when bent;

[0020] Figure 3 This is a schematic diagram of the structure of the coplanar waveguide unit on the second metal layer in the flexible circuit board with bend resistance provided in this application embodiment;

[0021] Figure 4 A schematic diagram of the structure of the first window on the first metal layer / third metal layer in the flexible circuit board with bend resistance provided in this application embodiment;

[0022] Figure 5 This is a schematic diagram of the structure of the stripline unit on the second metal layer in the flexible circuit board with bend resistance provided in this application embodiment;

[0023] Figure 6 A schematic diagram of the structure of the second window on the first metal layer / third metal layer in the flexible circuit board with bend resistance provided in the embodiment of this application;

[0024] Figure 7This is a schematic diagram of the transition conductor in a flexible circuit board that is resistant to bending, provided in an embodiment of this application.

[0025] Explanation of key component symbols:

[0026] 100. Flexible circuit board with bend resistance; 110. Layered area; 120. Connection area;

[0027] 1. First metal layer; 2. Second metal layer; 3. Third metal layer; 4. Coplanar waveguide unit; 41. Coplanar waveguide guide strip; 42. First ground electrode; 51. First window; 52. First metal part; 6. Adhesive; 7. Stripline unit; 71. Stripline guide strip; 72. Second ground electrode; 81. Second window; 82. Second metal part; 9. Transition guide strip. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0029] It should be noted that when a component is referred to as "fixed to" or "set on" another component, it can be directly or indirectly attached to that other component. When a component is referred to as "connected to" another component, it can be directly or indirectly connected to that other component. The terms "upper," "lower," "left," "right," etc., indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are for descriptive convenience only, not indicating or implying that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the patent. The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features. "A plurality" means two or more, unless otherwise explicitly defined.

[0030] In this specification, references to "one embodiment," "some embodiments," or simply "embodiment" mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. Furthermore, in one or more embodiments, specific features, structures, or characteristics may be combined in any suitable manner.

[0031] Reference Figure 1This application provides a bend-resistant flexible circuit board 100, including a first metal layer 1, a second metal layer 2, and a third metal layer 3 stacked and spaced apart. The bend-resistant flexible circuit board 100 has a connection area 120 and a layering area 110. The first metal layer 1, the second metal layer 2, and the third metal layer 3 are pressed together in the connection area 120 and separated by gaps in the layering area 110. The second metal layer 2 has a coplanar waveguide unit 4 in the layering area 110. The coplanar waveguide unit 4 includes a coplanar waveguide strip 41 and first ground electrodes 42 disposed on both sides of the coplanar waveguide strip 41. The first metal layer 1 and the third metal layer 3 are each provided with a first opening 51 opposite to the coplanar waveguide strip 41, and a first metal portion 52 is provided between adjacent first openings 51.

[0032] The first metal layer 1, the second metal layer 2, and the third metal layer 3 are all copper layers. The second metal layer 2 serves as a signal layer for arranging signal lines. The first metal layer 1 and the third metal layer 3 are located on opposite sides of the second metal layer 2, serving as reference planes for the second metal layer 2. An insulating layer, such as an insulating dielectric layer or an adhesive layer, is present between adjacent metal layers.

[0033] like Figure 1 and Figure 2 As shown, the layered region 110 can be understood as a bending region. In the layered region 110, the first metal layer 1, the second metal layer 2 and the third metal layer 3 are arranged at intervals. The gap between adjacent metal layers provides deformation space for the metal layers, so that the circuit board has good bending performance at the layered position.

[0034] like Figure 1 and Figure 3 As shown, the first ground electrode 42 is along the width direction of the coplanar waveguide guide strip 41 (e.g., Figure 3 The first ground electrode 42 (in the direction shown by X) is located on both sides of the coplanar waveguide guide strip 41. Adjacent coplanar waveguide units 4 can share a first ground electrode 42. In the coplanar waveguide structure, the coplanar waveguide guide strip 41 provides the signal path, and the first ground electrodes 42 on both sides provide the return path.

[0035] The first metal section 52 can be understood as the area without clear opening. Specifically, copper layers are retained on the first metal layer 1 and the third metal layer 3 opposite to the first grounding electrode 42. This portion of copper layer serves to isolate and optimize return loss.

[0036] The aforementioned flexible circuit board 100 with bend resistance includes a first metal layer 1, a second metal layer 2, and a third metal layer 3 stacked and spaced apart. The second metal layer 2 has a coplanar waveguide unit 4 within the layered region 110. The coplanar waveguide unit 4 includes a coplanar waveguide strip 41 and first ground electrodes 42 disposed on both sides of the coplanar waveguide strip 41. The first metal layer 1 and the third metal layer 3 are each provided with a first opening 51 opposite to the coplanar waveguide strip 41, and a first metal portion 52 is provided between adjacent first openings 51. On the one hand, the coplanar waveguide unit 4 is designed in the layered region 110, using a coplanar waveguide to replace the traditional The stripline design ensures the signal transmission performance of the signal lines within the layered region 110. On the other hand, the coplanar waveguide unit 4 itself forms a complete signal transmission and return path. The first metal layer 1 and the third metal layer 3 opposite to the coplanar waveguide strip 41 are made with clearance window treatment, and metal layers are retained between adjacent windows. This increases the isolation of the coplanar waveguide unit 4, thereby playing a role in isolating and optimizing return loss. This improves the anti-interference capability of the signal lines within the layered region 110, reduces impedance fluctuations caused by changes in the reference plane during bending, and reduces the impact of bending on signal transmission.

[0037] In the embodiments provided in this application, such as Figure 1 As shown, the first metal layer 1, the second metal layer 2, and the third metal layer 3 can be formed on different single-layer boards. Adjacent single-layer boards are bonded together with adhesive 6, and a glue-free area is reserved between adjacent single-layer boards at the delamination area 110 to allow gaps to be formed between the single-layer boards. Alternatively, the first metal layer 1, the second metal layer 2, and the third metal layer 3 can also be formed on a multilayer board. Adjacent multilayer boards are bonded together with adhesive 6, and a glue-free area is reserved between adjacent multilayer boards at the delamination area 110 to allow gaps to be formed between the multilayer metal layers.

[0038] In the embodiments provided in this application, such as Figure 1 , Figure 3 and Figure 4 As shown, the projection of the first window 51 on the second metal layer 2 covers the coplanar waveguide strip 41. The width of the coplanar waveguide strip 41 is W1, and the distance between the coplanar waveguide strip 41 and the adjacent first ground electrode 42 is D1. W2≥W1+2D1+0.4mm.

[0039] Optionally, in one embodiment, the first window 51 is extended by 0.2 mm on one side relative to the coplanar waveguide strip 41, and W2 = W1 + 2D1 + 0.4 mm.

[0040] During the fabrication of flexible circuit boards, due to limitations in the manufacturing process, alignment deviations may exist between multiple metal layers. Furthermore, when the flexible circuit board is bent, the metal layers in the layered region 110 deform, also causing alignment deviations. Pre-enlarging the first window 51 can eliminate the impact of interlayer alignment deviations and improve the alignment effect between the first window 51 and the coplanar waveguide strip 41.

[0041] In the embodiments provided in this application, the distance between the coplanar waveguide strip 41 and the adjacent first ground electrode 42 is D1, where 40μm≤D1≤50μm.

[0042] Optionally, in one embodiment, the spacing between the coplanar waveguide strip 41 and the adjacent first ground electrode 42 is 45 μm.

[0043] With the above design, the line spacing between the coplanar waveguide strip 41 and the first grounding electrode 42 is reasonable, which helps to reduce the impedance fluctuation of the signal line in the layered region 110 during the bending process, and the signal return effect is better.

[0044] In the embodiments provided in this application, the width of the coplanar waveguide strip 41 is W1, the distance between the coplanar waveguide strip 41 and the adjacent first ground electrode 42 is D1, and W1≥6D1.

[0045] Optionally, in one embodiment, the linewidth of the coplanar waveguide strip 41 is 6 times the line spacing, W1 = 6D1.

[0046] The design with large line width and small line spacing can improve the anti-interference ability of signal lines and further reduce the impedance fluctuation of signal lines in the layered area 110 during bending.

[0047] When manufacturing flexible circuit boards, the precision of line spacing can be improved by reducing the thickness of the metal layer. For example, the copper layer thickness can be reduced from 1 / 3 oz to 1 / 5 oz, and combined with micro-etching processes, precise line width and spacing can be achieved.

[0048] In the embodiments provided in this application, such as Figure 1 and Figure 5 As shown, the second metal layer 2 has a stripline unit 7 in the connection area 120. The stripline unit 7 includes a stripline conductor 71 and a second grounding electrode 72 disposed on both sides of the stripline conductor 71. The first metal layer 1 and the third metal layer 3 are each provided with a second opening 81 opposite to the stripline conductor 71.

[0049] In the stripline structure, the stripline conductor 71 provides the signal path, and the metal layer near the conductor provides the return path.

[0050] By adopting the above design, by designing stripline unit 7 in connection area 120 and making clearance window treatment on the reference plane opposite to the stripline conductor 71, the impedance fluctuation caused by the change of residual copper ratio during bending can be reduced, thereby improving the anti-interference capability of signal lines in connection area 120 and reducing the impact of bending action on signal transmission.

[0051] In the embodiments provided in this application, such as Figure 6 As shown, the second window 81 includes a plurality of strip-shaped holes spaced apart along the length of the strip conductor 71, and a second metal portion 82 is provided between adjacent strip-shaped holes.

[0052] like Figure 6 As shown, a structural design with windows and solid copper spaced apart is adopted along the length of the strip.

[0053] The above design ensures both the integrity of the signal return path and the compliance of the impedance linewidth design, thereby reducing impedance fluctuations while maintaining the signal transmission performance of the stripline unit 7.

[0054] In the embodiments provided in this application, the length of the strip hole is L1, the length of the second metal part 82 is L2, and the ratio of L1 to L2 is 1:0.7 to 1:0.8.

[0055] The length of the strip hole is its dimension along the length of the strip conductor 71. Optionally, in one embodiment, L1:L2 = 1:0.75.

[0056] The above design, with its reasonable spacing between the window and solid copper, helps to reduce the impedance fluctuation of signal lines within the 120mm connection area.

[0057] In the embodiments provided in this application, the length of the strip hole is L1≥0.4mm.

[0058] Optionally, in one embodiment, L1 = 0.4 mm.

[0059] If the via length is too small, it will affect the design of the window / solid copper spacing structure and the impedance fluctuation of the corresponding signal line. According to experimental tests and simulations, when the via length is greater than 0.4mm, a smaller impedance fluctuation can be obtained.

[0060] In the embodiments provided in this application, the width of the strip conductor 71 is W3, the width of the strip hole is W4, and the distance between the strip conductor 71 and the adjacent second ground electrode 72 is D2, where W4≥W3+2D2+0.3mm.

[0061] Optionally, in one embodiment, the second window 81 is extended by 0.15 mm on one side relative to the strip conductor 71, W4 = W3 + 2D2 + 0.3 mm.

[0062] During the fabrication of flexible circuit boards, alignment deviations may exist between multiple metal layers due to limitations in the manufacturing process. Pre-enlarging the second window 81 can effectively eliminate the impact of interlayer alignment deviations and improve the alignment effect between the second window 81 and the strip conductor 71.

[0063] In the embodiments provided in this application, the distance between the strip conductor 71 and the adjacent second grounding electrode 72 is D2, where 75μm≤D2≤85μm.

[0064] Optionally, in one embodiment, D2 = 80 μm.

[0065] With the above design, the spacing between the strip conductor 71 and the second grounding electrode 72 is reasonable, resulting in less signal transmission interference and helping to reduce signal line impedance fluctuations within the connection area 120.

[0066] In the embodiments provided in this application, the strip conductor 71 includes a first part opposite to the strip hole, a second part opposite to the second metal part 82, and a transition connecting part connecting the first part and the second part. The width of the first part is greater than the width of the second part, and the width of the transition connecting part changes linearly.

[0067] Designing a strip-shaped aperture can widen the impedance linewidth in certain areas while ensuring that the impedance meets the requirements, thereby reducing impedance fluctuations caused by linewidth fluctuations during bending.

[0068] Furthermore, the transition connection is in the shape of an isosceles trapezoid.

[0069] In the embodiments provided in this application, such as Figure 7 As shown, the width of the coplanar waveguide guide strip 41 is different from the width of the stripline guide strip 71, and a transition guide strip 9 connects the coplanar waveguide guide strip 41 and the stripline guide strip 71. The width of the transition guide strip 9 changes linearly.

[0070] By adopting the above design and optimizing the transition structure between signal lines of different line widths, the signal line width can be gradually changed, thereby reducing impedance fluctuations caused by changes in line width.

[0071] Furthermore, the transition guide band 9 is in the shape of an isosceles trapezoid.

[0072] like Figure 7 As shown, the waistline of the isosceles trapezoid connects the coplanar waveguide strip 41 and the strip-shaped line guide strip 71, and is arranged symmetrically.

[0073] The above design, with its regular transition band 9 structure, helps to further reduce impedance fluctuations caused by changes in linewidth. It can be understood that the longer the waist of the isosceles trapezoid, the smaller the impedance change during transitions between different linewidths.

[0074] In the embodiments provided in this application, if signals need to be designed on the surface layer of the circuit board, a microstrip line structure design and a large line width and small line spacing structure can be adopted. When arranging signal lines, it is preferable to arrange the signal lines on the same layer to reduce impedance fluctuations and return losses caused by via connections.

[0075] In summary, the bend-resistant flexible circuit board 100 provided in this application, by designing coplanar waveguide units 4 in the layered region 110, designing first openings 51 based on coplanar waveguide guide strips 41, retaining first metal portions 52 between adjacent first openings 51, and optimizing the line width and spacing design of the coplanar waveguide guide strips 41, can reduce impedance fluctuations caused by changes in the reference plane during bending and improve the anti-interference capability of signal lines within the layered region 110; and by designing stripline units 7 in the connection region 120, designing second openings 81 based on stripline guide strips 71, and... Optimizing the line width and spacing design of the strip conductor 71 can widen the impedance line width, thereby reducing impedance fluctuations caused by line width fluctuations during bending and improving the anti-interference capability of signal lines in the connection area 120. In addition, the signal lines in the layer area 110 and the connection area 120 are designed with different types and line widths to meet the overall impedance requirements of the circuit board. Furthermore, the connection between signal lines with different line widths is achieved by isosceles trapezoidal transition conductors 9, which can reduce impedance fluctuations caused by line width changes and improve the anti-interference capability of signal lines at the junction of the connection area 120 and the layer area 110.

[0076] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A flexible circuit board resistant to bending, characterized in that, The flexible circuit board includes a first metal layer, a second metal layer, and a third metal layer stacked and spaced apart. The flexible circuit board has a connection area and a layered area. The first metal layer, the second metal layer, and the third metal layer are pressed together in the connection area and separated by gaps in the layered area. The second metal layer has a coplanar waveguide unit within the layered region. The coplanar waveguide unit includes a coplanar waveguide strip and first ground electrodes disposed on both sides of the coplanar waveguide strip. The first metal layer and the third metal layer each have a first opening opposite to the coplanar waveguide strip, and a first metal portion is provided between adjacent first openings. The width of the coplanar waveguide strip is W1, and the distance between the coplanar waveguide strip and the adjacent first ground electrode is D1, where W1 ≥ 6D1. The second metal layer has a stripline unit within the connection area. The stripline unit includes a stripline conductor and second grounding electrodes disposed on both sides of the stripline conductor. The first metal layer and the third metal layer each have a second opening opposite to the stripline conductor. The second opening includes a plurality of strip-shaped holes spaced apart along the length direction of the stripline conductor, and a second metal portion is provided between adjacent strip-shaped holes. The stripline conductor includes a first portion opposite to the strip-shaped holes, a second portion opposite to the second metal portion, and a transition connection portion connecting the first portion and the second portion. The width of the first portion is greater than the width of the second portion, and the width of the transition connection portion changes linearly.

2. The flexible circuit board resistant to bending according to claim 1, characterized in that, The projection of the first window onto the second metal layer covers the coplanar waveguide strip, the width of the coplanar waveguide strip is W1, the width of the first window is W2, the distance between the coplanar waveguide strip and the adjacent first ground electrode is D1, and W2≥W1+2D1+0.4mm.

3. The flexible circuit board resistant to bending according to claim 1, characterized in that, Along the extension direction of the strip conductor, the length of the strip hole is L1, the length of the second metal part is L2, and the ratio of L1 to L2 is 1:0.7 to 1:0.

8.

4. The flexible circuit board resistant to bending according to claim 3, characterized in that, The length L1 of the strip hole is ≥ 0.4 mm.

5. The flexible circuit board resistant to bending according to claim 3, characterized in that, The width of the strip conductor is W3, the width of the strip hole is W4, and the distance between the strip conductor and the adjacent second grounding electrode is D2, where W4 ≥ W3 + 2 D2 + 0.3 mm.

6. The flexible circuit board resistant to bending according to claim 1, characterized in that, The width of the coplanar waveguide guide strip is different from the width of the stripline guide strip, and a transition guide strip connects the coplanar waveguide guide strip and the stripline guide strip, the width of which varies linearly.

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