Flexible circuit board and manufacturing method thereof

Abstract

The invention provides a flexible circuit board and a manufacturing method thereof. The flexible circuit board comprises a first dielectric layer, a second dielectric layer arranged on the first dielectric layer, a signal layer arranged in the second dielectric layer, a third dielectric layer arranged on the second dielectric layer and a plurality of liquid metal composite materials. The signal layer comprises a wire and a liner. And the plurality of liquid metal composite materials are arranged to surround the wire but not surround the liner, so that the signal layer can meet the requirements of high bending times and high-frequency signal transmission.

Description

Technical Field

[0001] The present invention relates to a flexible circuit board and a manufacturing method thereof, and in particular to a flexible circuit board used for high-frequency signal transmission and a manufacturing method thereof. Background Art

[0002] In recent years, the demand for electronic products related to foldable devices (such as laptops and augmented reality (AR) / virtual reality (VR) wearable devices) and foldable screens (such as mobile phones and tablet computers) has gradually increased. Data transmission is still required during the folding operation, but as the products become thinner and the transmission speed increases, the requirements for circuit boards have also increased accordingly, especially for the bending performance and high-frequency signal transmission performance of circuit boards. Summary of the invention

[0003] One aspect of the present invention is to provide a flexible printed circuit board, which sets a signal layer in a dielectric layer and uses liquid metal to surround the wiring of the signal layer to meet the requirements of bending and high-frequency signal transmission.

[0004] Another aspect of the present invention is to provide a method for manufacturing a flexible printed circuit board.

[0005] According to one aspect of the present invention, a flexible circuit board is provided, which includes a first dielectric layer, a second dielectric layer disposed on the first dielectric layer, a signal layer disposed in the second dielectric layer, a third dielectric layer disposed on the second dielectric layer, and a plurality of liquid metal composite materials. The signal layer includes a wiring and a pad. The plurality of liquid metal composite materials are arranged to surround the wiring but not the pad.

[0006] According to an embodiment of the present invention, the plurality of liquid metal composite materials include a plurality of liquid metal composite material side portions and a plurality of liquid metal composite material layers. The plurality of liquid metal composite material side portions extend from the third dielectric layer through the second dielectric layer to the first dielectric layer. The plurality of liquid metal composite material layers are disposed in the first dielectric layer and the third dielectric layer and connect the plurality of liquid metal composite material side portions.

[0007] According to an embodiment of the present invention, the flexible circuit board further includes a plurality of liquid metal protective films respectively disposed on the plurality of liquid metal composite material layers, and the plurality of liquid metal protective films respectively cover surfaces of the plurality of liquid metal composite material layers exposed on the first dielectric layer and the third dielectric layer.

[0008] According to an embodiment of the present invention, the flexible printed circuit board further includes an electronic component disposed on the pad and electrically connected to the pad.

[0009] According to an embodiment of the present invention, the plurality of liquid metal composite materials include liquid metal and cellulose nanofibers.

[0010] According to another aspect of the present invention, a method for manufacturing a flexible circuit board is provided. The method includes providing a substrate, wherein the substrate includes a dielectric layer; forming a first groove in the substrate; forming a signal layer in the first groove; forming a second groove and a third groove in the lower dielectric layer and the upper dielectric layer, respectively, wherein the second groove does not expose the first glue layer, and the third groove does not expose the second glue layer; filling a plurality of liquid metal composite material layers in the second groove and the third groove; forming a fourth groove and a fifth groove on both sides of the signal layer, respectively, and not exposing the signal layer, wherein the fourth groove and the fifth groove extend from the upper dielectric layer through the dielectric layer to the lower dielectric layer; and filling a plurality of liquid metal composite material side portions into the fourth groove and the fifth groove.

[0011] According to an embodiment of the present invention, the substrate includes two metal layers, the dielectric layer is located between the two metal layers, and the first groove does not pass through one of the two metal layers. After forming the signal layer and before forming the lower dielectric layer and the first glue layer, the method further includes removing the two metal layers.

[0012] According to an embodiment of the present invention, filling a plurality of liquid metal composite material layers further includes forming a plurality of liquid metal protective films respectively on surfaces of the plurality of liquid metal composite material layers exposed to the upper dielectric layer and the lower dielectric layer.

[0013] According to an embodiment of the present invention, the plurality of liquid metal composite material side portions and the plurality of liquid metal composite material layers are disposed around the signal layer, and the plurality of liquid metal composite material side portions are connected to the plurality of liquid metal composite material layers.

[0014] According to an embodiment of the present invention, the signal layer includes a wiring and a pad. The wiring is surrounded by the multiple liquid metal composite material side portions and the multiple liquid metal composite material layers, while the pad is not surrounded by the multiple liquid metal composite material side portions and the multiple liquid metal composite material layers.

[0015] By using the flexible printed circuit board and its manufacturing method of the present invention, the signal layer is buried in the dielectric layer, and the signal layer wiring is surrounded by the liquid metal composite material, so that the signal layer can meet the requirements of high bending times and high-frequency signal transmission. Furthermore, the electronic components can be directly arranged on the pads of the signal layer, which is beneficial to signal transmission. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present disclosure is better understood by reading the following detailed description in conjunction with the accompanying drawings. It should be noted that, as is standard practice in the industry, many features are not drawn to scale. In fact, for the sake of clarity of discussion, the dimensions of many features may be arbitrarily scaled.

[0017] Figure 1A A perspective view of a flexible printed circuit board according to some embodiments of the present invention is shown.

[0018] Figure 1B A top view of a flexible printed circuit board according to some embodiments of the present invention is shown.

[0019] Figure 2 A cross-sectional view of a flexible printed circuit board according to some embodiments of the present invention is shown.

[0020] 3A to 3H A cross-sectional view of an intermediate stage of a flexible printed circuit board manufacturing process according to some embodiments of the present invention is shown. DETAILED DESCRIPTION

[0021] The following disclosure provides many different embodiments or examples to implement different features of the invention. The specific examples of components and configurations described below are intended to simplify the disclosure. These are of course only examples and are not intended to be limiting. For example, the description of a first feature formed on or above a second feature includes embodiments in which the first feature and the second feature are in direct contact, and also includes embodiments in which other features are formed between the first feature and the second feature, so that the first feature and the second feature are not in direct contact. In addition, the disclosure repeats component symbols and / or letters in various specific examples. The purpose of this repetition is to simplify and clarify the description and does not indicate a relationship between the various discussed embodiments and / or configurations.

[0022] Furthermore, spatially relative terms, such as "beneath," "below," "lower," "above," "upper," etc., are used to facilitate description of the relationship of parts or features illustrated in the drawings to other parts or features. Spatially relative terms encompass different orientations of the elements in use or operation in addition to the orientation depicted in the drawings. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used in the present disclosure may be interpreted so.

[0023] The three-layer stacking design of existing flexible circuit boards requires isolation holes to be set around the signal lines, but the spacing between the isolation holes should reach 1 / 20 of the transmission wavelength to have an isolation effect, so it cannot meet the needs of high-frequency transmission. Furthermore, in order to meet the high number of bending times, the bending area of ​​existing flexible circuit boards usually only includes signal lines and substrates to reduce thickness and increase flexibility. However, this design has signal radiation and crosstalk due to the lack of a shielding layer. Therefore, there is also the option of adding an electromagnetic shielding metal layer to improve the aforementioned problems, but the electromagnetic shielding metal layer (such as a copper layer) will limit the number of bending times and there is a risk of board explosion due to thermal stress. In addition, since the isolation holes usually contain electroplated copper, they may crack when bent, so isolation holes cannot be set in the bending area.

[0024] Therefore, in accordance with the above, the present invention provides a flexible circuit board and a manufacturing method thereof, wherein the signal layer is embedded in the dielectric layer, and the signal layer routing is surrounded by a liquid metal composite material, so that the signal layer can meet the requirements of high bending times and high frequency transmission. Furthermore, the signal layer also includes a pad that is not surrounded by the liquid metal composite material layer, which can be directly electrically connected to the electronic component, thereby facilitating signal transmission.

[0025] See also Figure 1A and Figure 1B , Figure 1A and Figure 1B The perspective view and the top view of the flexible printed circuit 100 according to some embodiments of the present invention are respectively shown. The flexible printed circuit 100 includes a first dielectric layer 105, a second dielectric layer 110 and a third dielectric layer 115. In some embodiments, the second dielectric layer 110 is disposed on the first dielectric layer 105, and the third dielectric layer 115 is disposed on the second dielectric layer 110.

[0026] The flexible printed circuit board 100 includes a signal layer trace 130A and a liquid metal composite material 140 surrounding the trace 130A. Figure 1B As shown, the signal layer 130 includes a trace 130A and a pad 130B. It should be understood that Figure 1A The pad 130B is not shown. In some embodiments, the liquid metal composite material 140 only surrounds the trace 130A of the signal layer 130, but does not surround the pad 130B. In some embodiments, the flexible circuit board 100 further includes an electronic component 101. Compared with the existing signal layer that requires the use of vias to electrically connect the electronic component, the pad 130B of the signal layer 130 of the flexible circuit board 100 is exposed to the outside, so the electronic component 101 can be directly set on the pad 130B and electrically connected to the pad 130B, and the electronic component 101 can use the pad 130B to electrically connect the signal layer 130. This is conducive to the design of signal transmission and miniaturization of electronic products.

[0027] See also Figure 2 , Figure 2The flexible printed circuit board 100 according to some embodiments of the present invention is shown along Figure 1A As described above, the second dielectric layer 110 is disposed on the first dielectric layer 105, wherein the first dielectric layer 105 and the second dielectric layer 110 are bonded with the first adhesive layer 112; and the third dielectric layer 115 is disposed on the second dielectric layer 110, wherein the second dielectric layer 110 and the third dielectric layer 115 are bonded with the second adhesive layer 118.

[0028] like Figure 2 As shown, the signal layer 130 is disposed in the second dielectric layer 110. In some embodiments, the signal layer 130 is located between the first adhesive layer 112 and the second adhesive layer 118. The liquid metal composite material 140 includes a liquid metal composite material layer 142, a liquid metal composite material layer 144, a liquid metal composite material side portion 146, and a liquid metal composite material side portion 148. In some embodiments, the liquid metal composite material layer 142 and the liquid metal composite material layer 144 are connected to the liquid metal composite material side portion 146 and the liquid metal composite material side portion 148, so that the liquid metal composite material 140 surrounds the signal layer 130, but does not physically contact the signal layer 130.

[0029] In some embodiments, the liquid metal composite side portion 146 and the liquid metal composite side portion 148 are respectively disposed on both sides of the signal layer 130 , and the liquid metal composite side portion 146 and the liquid metal composite side portion 148 extend from the third dielectric layer 115 through the second dielectric layer 110 to the first dielectric layer 105 , but do not penetrate the first dielectric layer 105 .

[0030] In some embodiments, the liquid metal composite material layer 142 is disposed in the first dielectric layer 105, and the liquid metal composite material layer 144 is disposed in the third dielectric layer 115. In order to protect the liquid metal composite material layer 142 and the liquid metal composite material layer 144 to avoid direct contact with the glue layer 150 and the glue layer 155 (described later), the liquid metal composite material 140 further includes a liquid metal protective film 142A disposed on the liquid metal composite material layer 142 and a liquid metal protective film 144A disposed on the liquid metal composite material layer 144. In some specific examples, the liquid metal protective film 142A covers the surface of the liquid metal composite material layer 142 exposed on the first dielectric layer 105, and the liquid metal protective film 144A covers the surface of the liquid metal composite material layer 144 exposed on the third dielectric layer 115.

[0031] In some embodiments, the liquid metal composite material 140 is a composite material formed by freeze-drying a stable composite material and then forming a composite shielding film by mechanical lamination. Therefore, the liquid metal composite material 140 has a multi-layer electron transmission path and has an electrical conductivity of up to 96,000 S / m. In some embodiments, the electromagnetic shielding effectiveness of the liquid metal composite material 140 can be as high as 65 dB in the frequency range of 4 GHz to 18 GHz. In some embodiments, after heat treatment at 120°C for 8 hours, the electromagnetic shielding effectiveness of the liquid metal composite material 140 can remain stable. Since the liquid metal composite material 140 can be stretched and deformed, the signal layer 130 can meet the requirements of dynamic bending and high bending times. Furthermore, the signal layer 130 is shielded by using the liquid metal composite material 140 as an isolation groove, and the liquid metal composite material 140 also has a heat dissipation effect, which can meet the requirements of millimeter wave high-frequency transmission.

[0032] In some embodiments, the flexible circuit board 100 further includes a glue layer 150, a glue layer 155, a cover film 160, and a cover film 165. The glue layer 150 covers the first dielectric layer 105 and the liquid metal composite material layer 142 (and the liquid metal protective film 142A), and then the cover film 160 is disposed on the glue layer 150; similarly, the glue layer 155 covers the third dielectric layer 115 and the liquid metal composite material layer 144 (and the liquid metal protective film 144A), and then the cover film 165 is disposed on the glue layer 155.

[0033] See also 3A to 3H , which depicts a cross-sectional view of an intermediate stage of a manufacturing process of a flexible printed circuit board (such as the flexible printed circuit board 100) according to some embodiments of the present invention. Figure 3A , providing a substrate 201. The substrate 201 includes a dielectric layer 210, a metal layer 214 and a metal layer 217, wherein the dielectric layer 210 is located between the metal layer 214 and the metal layer 217. In some embodiments, the dielectric layer 210 includes polyimide (PI), liquid crystal polymer (LCP) or other materials with a low dielectric constant (D k ) / Dielectric loss factor (D f ) dielectric material, and the metal layer 214 and the metal layer 217 can be copper. In some specific examples, the substrate 201 can be a flexible copper clad laminate (FCCL).

[0034] Next, see Figure 3B, forming a first groove R1 in the substrate 201. The first groove R1 extends from the metal layer 217 to the dielectric layer 210, but does not extend to the metal layer 214. In some embodiments, the first groove R1 can be formed by laser or other suitable methods. In addition, in some embodiments, the sidewall between the first groove R1 and the substrate 201 can be shadowed to dip-coat graphite on the sidewall to form the conductive layer 220.

[0035] Then, see Figure 3C , forming a signal layer 230 in the first groove R1 (refer to Figure 3B ). In some embodiments, the signal layer 230 may include copper and may be formed by electroplating, and the configuration of the conductive layer 220 is to use conductive graphite to facilitate the electroplating process. After forming the signal layer 230, the metal layer 214 and the metal layer 217 may be removed (see Figure 3B ).

[0036] See also Figure 3D , respectively forming a first glue layer 212 and a second glue layer 218 below and above the dielectric layer 210 and the signal layer 230, and then respectively forming a lower dielectric layer 205 and an upper dielectric layer 215 on the first glue layer 212 and the second glue layer 218. In this way, the dielectric layer 210 is located between the lower dielectric layer 205 and the upper dielectric layer 215. In some embodiments, the first glue layer 212 and the second glue layer 218 include insulating glue (bonding sheet, BS). In some embodiments, the lower dielectric layer 205 and the upper dielectric layer 215 include polyimide, liquid crystal polymer or other materials with low dielectric constant (D k ) / Dielectric loss factor (D f ) dielectric material.

[0037] Next, see Figure 3E , forming a second groove R2 in the lower dielectric layer 205, and forming a third groove R3 in the upper dielectric layer 215. The second groove R2 extends from the surface of the lower dielectric layer 205 toward the signal layer 230, but does not expose the first adhesive layer 212; similarly, the third groove R3 extends from the surface of the upper dielectric layer 215 toward the signal layer 230, but does not expose the second adhesive layer 218. In some embodiments, the second groove R2 and the third groove R3 can be formed by using a fixed depth laser or other suitable methods.

[0038] See also Figure 3F , fill the liquid metal composite material into the second groove R2 and the third groove R3 (refer to Figure 3E) to form a liquid metal composite material layer 242 and a liquid metal composite material layer 244 respectively. In some embodiments, the liquid metal composite material includes cellulose nanofibers and liquid metal. Since the liquid metal composite material has the property of being stretchable and deformable, it can be changed according to the appearance of the second groove R2 and the third groove R3. In some embodiments, a liquid metal protective film 242A is formed on the surface of the liquid metal composite material layer 242, and a liquid metal protective film 244A is formed on the surface of the liquid metal composite material layer 244 to achieve a packaging effect.

[0039] See also Figure 3G , forming a fourth groove R4 and a fifth groove R5 on both sides of the signal layer 230, but not exposing the signal layer 230. The fourth groove R4 and the fifth groove R5 extend from the upper dielectric layer 215 to sequentially pass through the second adhesive layer 218, the dielectric layer 210 and the first adhesive layer 212 to the lower dielectric layer 205, but do not penetrate the lower dielectric layer 205. In some embodiments, the fourth groove R4 and the fifth groove R5 expose the liquid metal composite material layer 242 and the liquid metal composite material layer 244.

[0040] Next, see Figure 3H , fill the fourth groove R4 and the fifth groove R5 with liquid metal composite material (refer to Figure 3G ) to form a liquid metal composite material side portion 246 and a liquid metal composite material side portion 248 respectively. Since the liquid metal composite material has the characteristic of being stretchable and deformable, it can be changed according to the appearance of the fourth groove R4 and the fifth groove R5. The liquid metal composite material side portion 246 and the liquid metal composite material side portion 248 connect the two ends of the liquid metal composite material layer 242 and the liquid metal composite material layer 244. In some embodiments, the top of the liquid metal composite material side portion 246 and the liquid metal composite material side portion 248 is at the same height as the top surface of the liquid metal composite material layer 244. Therefore, in some embodiments, after the liquid metal composite material side portion 246 and the liquid metal composite material side portion 248 are formed, a liquid metal protective film 244A can be formed to cover the top surface of the liquid metal composite material layer 244 and the top of the liquid metal composite material side portion 246 and the liquid metal composite material side portion 248.

[0041] Then, selectively set the glue layer and the cover film on Figure 3H Above and below the structure shown, for example Figure 2 The flexible printed circuit board 100 is shown.

[0042] As described above, the flexible printed circuit board and the manufacturing method thereof provided by the present invention utilize the signal layer to be embedded in the dielectric layer, and utilize the liquid metal composite material to surround the wiring of the signal layer, so that the signal layer can meet the requirements of high bending times and high frequency transmission. Furthermore, the signal layer also includes a pad that is not surrounded by the liquid metal composite material, which can be directly electrically connected to the electronic component, thus facilitating signal transmission and miniaturization of electronic products.

[0043] Although the present invention has been disclosed as above with several embodiments, they are not intended to limit the present invention. Those skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the definition of the attached claims.

[0044]

Explanation of symbols

[0045] 100: Flexible printed circuit board

[0046] 101: Electronic components

[0047] 105: first dielectric layer

[0048] 110: Second dielectric layer

[0049] 112: First adhesive layer

[0050] 115: The third dielectric layer

[0051] 118: Second adhesive layer

[0052] 130:Signal layer

[0053] 130A: Routing

[0054] 130B:Padding

[0055] 140:Liquid Metal Composite Materials

[0056] 142,144: Liquid metal composite layer

[0057] 142A,144A: Liquid metal protective film

[0058] 146,148: Liquid metal composite side

[0059] 150,155: Adhesive layer

[0060] 160,165: Covering film

[0061] 201:Substrate

[0062] 205: lower dielectric layer

[0063] 210: Dielectric layer

[0064] 212: First adhesive layer

[0065] 214,217:Metal layer

[0066] 215: upper dielectric layer

[0067] 218: Second adhesive layer

[0068] 220: Conductive layer

[0069] 230:Signal layer

[0070] 242,244: Liquid metal composite layer

[0071] 242A,244A: Liquid metal protective film

[0072] 246,248: Liquid metal composite side

[0073] A-A': hatch line

[0074] R1: First groove

[0075] R2: Second groove

[0076] R3: The third groove

[0077] R4: The fourth groove

[0078] R5: The fifth groove.

Claims

1. A flexible circuit board, characterized in that: Include: a first dielectric layer; A second dielectric layer, disposed on the first dielectric layer; A signal layer, disposed in the second dielectric layer, and comprising a trace and a pad; A third dielectric layer, disposed on the second dielectric layer; as well as A plurality of liquid metal composite materials are arranged to surround the traces but not the pads.

2. The flexible printed circuit board according to claim 1, characterized in that: The plurality of liquid metal composite materials include: a plurality of liquid metal composite side portions, wherein the plurality of liquid metal composite side portions extend from the third dielectric layer through the second dielectric layer to the first dielectric layer; as well as A plurality of liquid metal composite material layers are arranged in the first medium layer and the third medium layer and connected to the plurality of liquid metal composite material side portions.

3. The flexible printed circuit board according to claim 2, characterized in that: The plurality of liquid metal composite materials further comprises: A plurality of liquid metal protective films are respectively arranged on the plurality of liquid metal composite material layers, wherein the plurality of liquid metal protective films respectively cover surfaces of the plurality of liquid metal composite material layers exposed on the first dielectric layer and the third dielectric layer.

4. The flexible printed circuit board according to claim 1, characterized in that: Also includes: The electronic component is disposed on the pad and electrically connected to the pad.

5. The flexible printed circuit board according to claim 1, characterized in that: The plurality of liquid metal composite materials include liquid metal and cellulose nanofibers.

6. A method for manufacturing a flexible circuit board, characterized in that: Include: providing a substrate, wherein the substrate comprises a dielectric layer; forming a first groove in the substrate; forming a signal layer in the first groove; forming a lower dielectric layer and a first adhesive layer under the dielectric layer and the signal layer; forming an upper dielectric layer and a second adhesive layer on the dielectric layer and the signal layer; forming a second groove and a third groove in the lower dielectric layer and the upper dielectric layer respectively, wherein the second groove does not expose the first glue layer, and the third groove does not expose the second glue layer; Filling a plurality of liquid metal composite material layers in the second groove and the third groove; forming a fourth groove and a fifth groove on both sides of the signal layer respectively without exposing the signal layer, wherein the fourth groove and the fifth groove extend from the upper dielectric layer through the dielectric layer to the lower dielectric layer; and A plurality of liquid metal composite material side portions are filled into the fourth groove and the fifth groove.

7. The method for manufacturing a flexible printed circuit board according to claim 6, characterized in that: The substrate includes two metal layers, the dielectric layer is located between the two metal layers, the first groove does not pass through one of the two metal layers, and After forming the signal layer and before forming the lower dielectric layer and the first glue layer, the method further comprises: The two metal layers are removed.

8. The method for manufacturing a flexible printed circuit board according to claim 6, wherein: Filling multiple layers of liquid metal composite material also includes: A plurality of liquid metal protective films are respectively formed on the surfaces of the plurality of liquid metal composite material layers exposed to the upper dielectric layer and the lower dielectric layer.

9. The method for manufacturing a flexible printed circuit board according to claim 6, characterized in that: The plurality of liquid metal composite material side portions and the plurality of liquid metal composite material layers are disposed around the signal layer, and the plurality of liquid metal composite material side portions are connected to the plurality of liquid metal composite material layers.

10. The method for manufacturing a flexible printed circuit board according to claim 6, wherein: The signal layer comprises: a routing line, wherein the routing line is surrounded by the plurality of liquid metal composite material sides and the plurality of liquid metal composite material layers; as well as A liner, wherein the liner is not surrounded by the plurality of liquid metal composite side portions and the plurality of liquid metal composite layers.

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