Flexible coplanar waveguide low-profile high-speed transmission circuit and fabrication method of the same

Abstract

To provide a flexible coplanar waveguide low-profile high-speed transmission circuit and a fabrication method of the same.SOLUTION: A transmission circuit includes a first flexible substrate, a second flexible substrate, a circuit layer, a first electromagnetic interference shielding film and a second electromagnetic interference shielding film. In a fabrication method, first, the circuit layer is disposed between the first flexible substrate and the second flexible substrate, and the first flexible substrate, the second flexible substrate and the circuit layer are crimped. Then, the first electromagnetic interference shielding film is adhered to first flexible substrate, and the second electromagnetic interference shielding film is adhered to the second flexible substrate. The flexible coplanar waveguide low-profile high-speed transmission circuit satisfies following equation. In the equation, DT is the distance between signal transmission wiring and ground wiring in the circuit layer, TS is the thickness of each of the first and second flexible substrates, and DK is the dielectric constant of each of the first and second flexible substrates.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a thin flexible high-speed transmission circuit and a manufacturing method thereof, and more particularly to a thin flexible coplanar waveguide high-speed transmission circuit and a manufacturing method thereof. [Background technology]

[0002] In recent years, with the advancement of science and technology, portable electronic products such as tablet computers (tablet PCs), notebook computers (NBs), smartphones, and other portable devices have frequently appeared in daily life, and the demand for high-speed signal transmission, for example, the demand for high-speed signal transmission between multiple chips in a device or the demand for high-speed signal transmission between multiple devices, is increasing.

[0003] However, transmission circuits used in portable devices are usually bendable to accommodate the shape of the portable electronic product and reduce its size. Furthermore, as wireless communications in devices reach relatively high frequencies, the wavelength of the signal in the connecting wiring becomes shorter, making it more susceptible to various internal and external electromagnetic interference (EMI) problems. Multilayer printed circuit boards with microchips are often used for high-speed signal transmission, and to reduce EMI, the signal layer is typically attached to a ground layer or sandwiched between two ground layers. However, this structure makes it difficult to adjust the shape and bend the board, and is prone to loose connections between layers and even damage such as cracked copper wires.

[0004] Therefore, there is a need for a novel flexible coplanar waveguide thin transmission line structure that not only meets the bendable demands of portable devices, but also has relatively high electromagnetic interference resistance capabilities. Summary of the Invention [Problem to be solved by the invention]

[0005] The embodiments of the present invention provide a thin high-speed transmission circuit using a flexible coplanar waveguide, which has a relatively thin thickness that meets the demand for bendability and has a relatively good electromagnetic interference resistance capability, and a manufacturing method thereof. [Means for solving the problem]

[0006] According to some embodiments of the present invention, a thinned flexible coplanar waveguide transmission line structure of the present invention includes a circuit layer including a signal transmission line and two ground lines, the signal transmission line being located between the two ground lines, a first flexible substrate provided on a first surface of the circuit layer, a second flexible substrate provided on a second surface of the circuit layer opposite to the first surface and also provided on the first flexible substrate, a first Electromagnetic Interference (EMI) shielding film provided on the first flexible substrate and located on two opposing surfaces of the first flexible substrate together with the circuit layer, and a second EMI shielding film provided on the second flexible substrate and located on two opposing surfaces of the second flexible substrate together with the circuit layer, wherein the thinned high-speed transmission circuit of the coplanar waveguide satisfies the following equation:

[0007]

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[0008] DT is the distance between the signal transmission wiring and one of the ground wirings, TS is the thickness of each of the first flexible substrate and the second flexible substrate, and DK is the dielectric constant of the flexible substrate.

[0009] In some embodiments, the first flexible substrate and the second flexible substrate are Liquid Crystal Polymer (LCP) flexible substrates.

[0010] In some embodiments, the circuit layer directly contacts the first flexible substrate and the second flexible substrate.

[0011] In some embodiments, each of the first and second electromagnetic interference shielding films includes at least one shielding metal layer and at least one adhesive layer for adhering the first and second electromagnetic interference shielding films to the first and second flexible substrates.

[0012] In some embodiments, the first flexible substrate and the second flexible substrate each have a substrate thickness between 30 microns (um) and 200 microns (um).

[0013] In some embodiments, the circuit layer has a circuit layer thickness that is 35 microns.

[0014] In some embodiments, the dielectric constant DK is between 2.7 and 4.

[0015] In some embodiments, the signal transmission wiring includes a pair of differential signal transmission wiring.

[0016] According to some embodiments of the present invention, a method for manufacturing a thinned high-speed transmission circuit using a flexible coplanar waveguide of the present invention includes: providing a first flexible substrate, a second flexible substrate, and a circuit layer, wherein the circuit layer includes a signal transmission line and two ground lines, and the signal transmission line is located between the two ground lines; interposing the circuit layer between the first flexible substrate and the second flexible substrate; performing a compression step of compressing the first flexible substrate, the second flexible substrate, and the circuit layer; attaching, to the first flexible substrate, a first electromagnetic interference shielding film, which is provided together with the circuit layer on two opposing surfaces of the first flexible substrate, and attaching, to the second flexible substrate, a second electromagnetic interference shielding film, which is provided together with the circuit layer on two opposing surfaces of the second flexible substrate,

[0017]

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[0018] DT is the distance between the signal transmission wiring and one of the ground wirings, TS is the thickness of each of the first and second flexible substrates, and DK is the dielectric constant of the flexible substrate.

[0019] In some embodiments, the first flexible substrate and the second flexible substrate are liquid crystal polymer flexible substrates. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a schematic diagram illustrating a transmission circuit according to an embodiment of the present invention. [Figure 2] 1 is a schematic diagram illustrating a transmission circuit according to an embodiment of the present invention. [Figure 3] 1 is a flowchart illustrating a method for manufacturing a transmission circuit according to an embodiment of the present invention. [Figure 4] 1 illustrates a first flexible substrate, a second flexible substrate, and a circuit layer according to an embodiment of the present invention. [Figure 5] 1 illustrates a step of compressing a first flexible substrate, a second flexible substrate, and a circuit layer according to an embodiment of the present invention. [Figure 6] 4 illustrates a step of bonding a first electromagnetic interference shielding film and a second electromagnetic interference shielding film together according to an embodiment of the present invention. [Figure 7] 1 is a connection schematic diagram showing a transmission circuit according to an embodiment of the present invention; [Figure 8] 10A and 10B show relationship curves for different dielectric constants and thicknesses of flexible substrates of a transmission circuit according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] The following detailed description will be given in accordance with the drawings in the embodiments, but the provided embodiments are not intended to limit the scope of the present invention, and the description of the structural operations is not intended to limit the execution order thereof, and any structure in which elements are recombined, or a device having equivalent effects, is within the scope of the present invention. Note that the drawings are for illustrative purposes only and are not drawn to scale.

[0022] The terms "first," "second," etc. used in this specification do not imply any particular order or ranking, but are used only to distinguish between elements or operations described with the same technical terms.

[0023] 1, the transmission circuit 100 includes a first flexible substrate 111, a second flexible substrate 112, a first electromagnetic interference shielding film 121, a second electromagnetic interference shielding film 122, and a circuit layer 130. The circuit layer 130 includes a circuit for transmitting data, which is interposed between the first flexible substrate 111 and the second flexible substrate 112. In some embodiments, the circuit layer 130 directly contacts the first flexible substrate 111 and the second flexible substrate 112, although embodiments of the present invention are not limited thereto.

[0024] In some embodiments, the circuit layer 130 transmits data using a coplanar waveguide (CPW) structure. The circuit layer 130 includes two ground lines 131 and one signal line 132. The signal lines 132 are interposed between the ground lines 131 and are arranged parallel to each other to form a coplanar waveguide structure. In some embodiments, the ground lines 131 and the signal lines 132 can be formed by etching a copper layer.

[0025] In some embodiments, first flexible substrate 111 and second flexible substrate 112 are liquid crystal polymer (LCP) flexible substrates, although embodiments of the present invention are not limited thereto. In other embodiments of the present invention, first flexible substrate 111 and second flexible substrate 112 may be other flexible substrate materials, such as polyimide (PI) or modified polyimide (MPI).

[0026] The first electromagnetic interference shielding film 121 is disposed on the first flexible substrate 111 and is bonded to the outer surface of the first flexible substrate 111. That is, the first electromagnetic interference shielding film 121 and the circuit layer 130 are disposed on two opposing surfaces of the first flexible substrate 111, with the first electromagnetic interference shielding film 121 disposed on the outer surface of the first flexible substrate 111 and the circuit layer 130 disposed on the inner surface of the first flexible substrate 111. In some embodiments, the first electromagnetic interference shielding film 121 and the circuit layer 130 are both in direct contact with the first flexible substrate 111, but embodiments of the present invention are not limited thereto.

[0027] The first electromagnetic interference shielding film 121 includes a first shielding metal layer 121S and a first adhesive layer 121G. The first shielding metal layer 121S is primarily used to shield external electromagnetic interference and prevent the internal circuit layer 130 from receiving electromagnetic interference when transmitting data. The first adhesive layer 121G is used to attach and fix the first shielding metal layer 121S to the first flexible substrate 111 and to provide additional electromagnetic interference shielding. In some embodiments, the material of the first adhesive layer 121G includes nickel chromium (NiCr) and nickel vanadium (NiV) and has a viscous material that adheres the first electromagnetic interference shielding film 121 to the outer surface of the first flexible substrate 111. The material of the first shielding metal layer 121S includes silver and / or copper to provide the primary electromagnetic interference shielding effect. However, the embodiments of the present invention are not limited thereto, and in other embodiments of the present invention, the first blocking metal layer 121S / first adhesive layer 121G may use other metal materials that have an electromagnetic interference blocking effect.

[0028] The second EMI shielding film 122 is disposed on the second flexible substrate 112 and is bonded to the outer surface of the second flexible substrate 112. That is, the second EMI shielding film 122 and the circuit layer 130 are disposed on two opposing surfaces of the second flexible substrate 112, with the second EMI shielding film 122 disposed on the outer surface of the second flexible substrate 112 and the circuit layer 130 disposed on the inner surface of the second EMI shielding film 122. In some embodiments, the second EMI shielding film 122 and the circuit layer 130 are in direct contact with the second flexible substrate 112, although embodiments of the present invention are not limited thereto.

[0029] The second electromagnetic interference shielding film 122 includes a second shielding metal layer 122S and a second adhesive layer 122G. The second shielding metal layer 122S is primarily used to shield external electromagnetic interference and prevent the internal circuit layer 130 from receiving electromagnetic interference when transmitting data. The second adhesive layer 122G is used to attach and fix the second shielding metal layer 122S to the second flexible substrate 112 and to provide additional electromagnetic interference shielding. In some embodiments, the material of the second adhesive layer 122G includes nickel chromium (NiCr) and nickel vanadium (NiV) and has a viscous material that adheres the second electromagnetic interference shielding film 122 to the outer surface of the first flexible substrate 111. The material of the second shielding metal layer 122S includes silver and / or copper to provide the primary electromagnetic interference shielding effect. However, the embodiments of the present invention are not limited thereto, and in other embodiments of the present invention, the second blocking metal layer 122S / second adhesive layer 122G may use other metal materials that have an electromagnetic interference blocking effect.

[0030] In this embodiment, the circuit layer 130 is located between the first electromagnetic interference shielding film 121 and the second electromagnetic interference shielding film 122, and therefore the first electromagnetic interference shielding film 121 and the second electromagnetic interference shielding film 122 effectively reduce the electromagnetic interference received by the circuit layer 130. The transmission circuit 100 of this embodiment has a relatively good anti-electromagnetic interference effect.

[0031] In addition, in the present embodiment, the first flexible substrate 111 and the second flexible substrate 112 each have a thickness TS, the first electromagnetic interference shielding film 121 and the second electromagnetic interference shielding film 122 each have a thickness TM, and the circuit layer has a thickness TC. In this embodiment, the thickness TS is 30 to 200 microns (um), the thickness TM is 12 to 22 microns (um), and the thickness TC is 10 to 40 microns (um). These thickness designs ensure normal data transmission, and the transmission circuit 100 of the present embodiment has a relatively good electromagnetic interference resistance effect during high-speed transmission compared to conventional transmission line structures. It also has the flexibility to bend widely to meet the needs of various electronic products. In some embodiments, the thickness TS is 30 to 100 microns (um) so that the transmission circuit 100 can be folded multiple times according to user needs. In some embodiments, the thickness TS is 100 to 200 microns (um), which allows the transmission circuit 100 to be easily fixed in the folded state after being folded once.

[0032] Please refer to Fig. 2. A thinned high-speed transmission circuit 200 using a coplanar waveguide according to another embodiment of the present invention is similar to the transmission circuit 100, but differs in that a circuit layer 230 of the transmission circuit 200 performs data transmission using a differential architecture (GSSG). Specifically, the circuit layer 230 includes a ground wiring 231 and a pair of differential signal transmission wirings D1 and D2, which are disposed between the ground wiring 231 and are on the same plane as the ground wiring 231. The transmission circuit 200 has better interference resistance than the transmission circuit 100.

[0033] Please refer to FIG. 3. This is a flowchart illustrating a method 300 for manufacturing a transmission circuit 100 according to an embodiment of the present invention. As shown in FIG. 4, the manufacturing method 300 first includes step 310 of providing the first flexible substrate 111, second flexible substrate 112, and circuit layer 130, and step 320 of interposing the circuit layer 130 between the first flexible substrate 111 and the second flexible substrate 112. In this embodiment, the first flexible substrate 111 and the second flexible substrate 112 are liquid crystal polymer flexible substrates, and the circuit layer 130 is a copper layer etched with a circuit pattern. However, this is not limited to this embodiment. Then, as shown in FIG. 5, step 330 of compressing the first flexible substrate 111, second flexible substrate 112, and circuit layer 130 is performed. In this manner, the first flexible substrate 111, second flexible substrate 112, and circuit layer 130 form a three-layer circuit board structure. Next, as shown in FIG. 6 , steps 340 and 350 are performed to attach the first EMI shielding film 121 and the second EMI shielding film 122 to the first flexible substrate 111 and the second flexible substrate 112, respectively. In this embodiment, the first EMI shielding film 121 and the second EMI shielding film 122 have a first adhesive layer 121G and a second adhesive layer 122G, respectively, and can be easily attached to the first flexible substrate 111 and the second flexible substrate 112 via the first adhesive layer 121G and the second adhesive layer 122G. In some embodiments, the first flexible substrate 111 and the second flexible substrate 112 are LCP substrates. The LCP substrate overlaps and bonds to the EMI shielding film, providing excellent thermal stability, low moisture absorption, and good electrical insulation. The LCP substrate serves as a dielectric layer for the EMI shielding film, enhancing the reflection and absorption of electromagnetic waves. For example, in the 5G or millimeter wave frequency range, the above arrangement has significant effects.

[0034] Please refer to FIG. 7, which is a connection schematic diagram showing a transmission circuit 100. The transmission circuit 100 of the embodiment of the present invention can be bent to fit various shapes and spaces of electronic devices. As shown in FIG. 7, in some embodiments, an antenna module 710 needs to receive high-speed / high-frequency electronic signals from an RF chip module 720 using a high-speed transmission line. The transmission circuit 100 of the embodiment of the present invention can be significantly bent into various shapes and can electrically connect the antenna module 710 to the RF chip module 720.

[0035] 1 and 2, in some embodiments, the distance DT between the signal transmission wiring 132 and the ground wiring 131, the thickness TS of the flexible substrate, and the dielectric constant DK of the flexible substrate satisfy the following equation (1):

[0036]

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[0037] When the distance DT, thickness TS, and dielectric constant DK of the flexible substrate satisfy the above formula (1), the transmission circuit 100 / 200 according to the embodiment of the present invention has a relatively good insertion loss characteristic and maintains flexibility. See Figure 8. The horizontal axis is the thickness TS, and the vertical axis is

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[0038] Considering curves 850-870, none of curves 850-870 satisfy the above formula (1), and the corresponding insertion losses are all higher than -1.0 decibels (dB), and therefore do not meet the needs of the present invention. Considering curves 820-840, some of curves 820-840 (shown by dashed lines) do not satisfy the above formula (1), and the corresponding insertion losses are all higher than -1.0 dB, but another part of curves 820-840 (shown by solid lines) satisfy the above formula (1), and therefore the corresponding insertion losses are all -1.0 dB or less. Considering curve 810, curve 810 satisfies the above formula (1), and therefore the corresponding insertion losses are -1.0 dB or less.

[0039] In some embodiments, the dielectric constant DK of the flexible substrate is in the range of 2≦DK<3. In some embodiments, the dielectric constant DK of the flexible substrate is in the range of 3≦DK<4. In some embodiments, the dielectric constant DK of the flexible substrate is in the range of 4≦DK<5. In some embodiments, the dielectric constant DK of the flexible substrate is in the range of 5≦DK<6. In some embodiments, the dielectric constant DK of the flexible substrate is in the range of 6≦DK<7. In some embodiments, the dielectric constant DK of the flexible substrate is in the range of 7≦DK<8.

[0040] The present invention has been disclosed above by way of examples, but the above examples are not used to limit the present invention, and anyone skilled in the art can make any changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention is in accordance with that defined by the scope of the patent application to be attached later. [Explanation of symbols]

[0041] 100: Transmission circuit 111: First flexible substrate 112:Second flexible substrate 121: First electromagnetic interference shielding film 121G: First adhesion layer 121S: First blocking metal layer 122: Second electromagnetic interference shielding film 122G: Second adhesion layer 122S: Second blocking metal layer 130:Circuit layer 131: Ground wiring 132: Signal transmission wiring 200: Transmission circuit 230:Circuit layer 231: Ground wiring 300: Manufacturing method 310: Step 320: Step 330: Step 340: Step 350: Step 710: Antenna module 720: RF chip module 810~870: Curve D1, D2: Differential signal transmission wiring DT: distance TS: Thickness TM: Thickness TC: Thickness

Claims

1. A thin high-speed transmission circuit using a flexible coplanar waveguide, a circuit layer including a signal transmission wiring and two ground wirings, the signal transmission wiring being located between the two ground wirings; a first flexible substrate provided on a first surface of the circuit layer; a second flexible substrate provided on a second surface of the circuit layer opposite the first surface; a first EMI (Electromagnetic Interference) shielding film provided on the first flexible substrate and positioned on two opposing surfaces of the first flexible substrate together with the circuit layer; a second electromagnetic interference shielding film provided on the second flexible substrate and positioned on two opposing surfaces of the second flexible substrate together with the circuit layer; Including, The thin high-speed transmission circuit of the flexible coplanar waveguide satisfies the following equation: [Equation 1] A thin high-speed transmission circuit using a flexible coplanar waveguide, wherein DT is the distance between the signal transmission wiring and one of the ground wirings, TS is the thickness of each of the first flexible substrate and the second flexible substrate, and DK is the dielectric constant of the first flexible substrate and the second flexible substrate.

2. 2. The thin high-speed transmission circuit of flexible coplanar waveguide according to claim 1, wherein the first flexible substrate and the second flexible substrate are liquid crystal polymer (LCP) flexible substrates.

3. 2. The thin high-speed transmission circuit using a flexible coplanar waveguide according to claim 1, wherein the circuit layer is in direct contact with the first flexible substrate and the second flexible substrate.

4. Each of the first electromagnetic interference shielding film and the second electromagnetic interference shielding film comprises: at least one blocking metal layer; at least one adhesive layer for attaching the first and second electromagnetic interference shielding films to the first and second flexible substrates; 2. The thin high-speed transmission circuit of claim 1, comprising:

5. 2. The flexible coplanar waveguide thin high-speed transmission circuit according to claim 1, wherein the first flexible substrate and the second flexible substrate each have a substrate thickness of 30 microns (um) to 200 microns.

6. 10. The flexible coplanar waveguide thinned high speed transmission circuit of claim 1, wherein the circuit layer has a circuit layer thickness that is 35 microns.

7. 2. The thin high-speed transmission circuit of claim 1, wherein the dielectric constant DK is 2.7 to 4.

8. 2. The thin high-speed transmission circuit using a flexible coplanar waveguide according to claim 1, wherein the signal transmission wiring includes a pair of differential signal transmission wirings.

9. A method for manufacturing a thin high-speed transmission circuit using a flexible coplanar waveguide, comprising: providing a first flexible substrate, a second flexible substrate, and a circuit layer, the circuit layer including a signal transmission wiring and two ground wirings, the signal transmission wiring being located between the two ground wirings; interposing the circuit layer between the first flexible substrate and the second flexible substrate; performing a compression step of compressing the first flexible substrate, the second flexible substrate, and the circuit layer; attaching a first electromagnetic interference shielding film to the first flexible substrate, the first electromagnetic interference shielding film being provided on two opposing surfaces of the first flexible substrate together with the circuit layer; attaching a second electromagnetic interference shielding film to the second flexible substrate, the second electromagnetic interference shielding film being provided on two opposing surfaces of the second flexible substrate together with the circuit layer; Including, The thin high-speed transmission circuit of the flexible coplanar waveguide satisfies the following equation: [Equation 2] A method for manufacturing a thin high-speed transmission circuit using a flexible coplanar waveguide, wherein DT is the distance between the signal transmission wiring and one of the ground wirings, TS is the thickness of each of the first flexible substrate and the second flexible substrate, and DK is the dielectric constant of the first flexible substrate and the second flexible substrate.

10. 10. The method for manufacturing a thin high-speed transmission circuit using a flexible coplanar waveguide according to claim 9, wherein the first flexible substrate and the second flexible substrate are liquid crystal polymer flexible substrates.

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