Pressure-sensitive flexible circuit board and manufacturing method thereof

Abstract

The invention provides a pressure-sensitive flexible circuit board and a manufacturing method thereof. The pressure sensing flexible circuit board comprises a flexible circuit substrate, a pressure sensing element and a vibration element, wherein the pressure sensing element and the vibration element are arranged on the flexible circuit substrate. The pressure sensing element includes a first piezoelectric layer; a plurality of first interlayer conductors distributed in the first piezoelectric layer; a first polymer layer adjacent to the first piezoelectric layer; and a first electrode layer disposed on the first piezoelectric layer. The vibration element comprises a plurality of layers of piezoelectric structures; the second electrode layer is arranged on the topmost layer of the multi-layer piezoelectric structure; and a second polymer layer adjacent to the multilayer piezoelectric structure. Each layer of the multilayer piezoelectric structure includes a second piezoelectric layer and a plurality of second interlayer conductors distributed in the second piezoelectric layer. The pressure sensing element and the vibration element are integrated on the flexible circuit substrate, so that the space is saved.

Description

Technical Field

[0001] The present invention relates to a pressure-sensitive flexible printed circuit board and a manufacturing method thereof, and particularly to a pressure-sensitive flexible printed circuit board including a pressure sensing element and a vibration element and a manufacturing method thereof. Background Art

[0002] Flexible pressure sensing and touch control technology has now been widely applied to many electronic products, such as screen touch control and various buttons of smart phones, touch pads of laptop computers, etc. However, compared with mechanical buttons, since the displacement of flexible pressure sensing and touch control technology is relatively small, users may not be able to clearly perceive whether the button has been pressed. Summary of the Invention

[0003] One aspect of the present invention is to provide a pressure-sensitive flexible printed circuit board, which integrates a pressure sensing element and a vibration element on a flexible circuit substrate.

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

[0005] According to one aspect of the present invention, there is provided a pressure-sensitive flexible printed circuit board. The pressure-sensitive flexible printed circuit board includes a flexible circuit substrate, a pressure sensing element and a vibration element disposed on the flexible circuit substrate. The pressure sensing element includes a first piezoelectric layer; a plurality of first interlayer conductors distributed in the first piezoelectric layer; a first polymer layer adjacent to the first piezoelectric layer; and a first electrode layer disposed on the first piezoelectric layer and connected to the plurality of interlayer conductors. The vibration element includes a multi-layer piezoelectric structure; a second electrode layer disposed on the topmost layer of the multi-layer piezoelectric structure; and a second polymer layer adjacent to the multi-layer piezoelectric structure. Each layer of the multi-layer piezoelectric structure includes a second piezoelectric layer and a plurality of second interlayer conductors distributed in the second piezoelectric layer.

[0006] According to an embodiment of the present invention, the pressure sensing element further includes a first conductive post adjacent to the first piezoelectric layer, wherein the first conductive post extends from the first electrode layer into the flexible circuit substrate. The vibration element further includes at least one second conductive post adjacent to the multi-layer piezoelectric structure and the plurality of polymer layers, wherein the second conductive post extends from the second electrode layer into the flexible circuit substrate.

[0007] According to an embodiment of the present invention, the above-mentioned pressure-sensitive flexible printed circuit board further includes a first buffer layer disposed between the flexible circuit substrate and the pressure sensing element; and a second buffer layer disposed between the flexible circuit substrate and the vibration element.

[0008] According to an embodiment of the present invention, the first interlayer conductor and the second interlayer conductor include alloy particles of copper / nickel, copper / silver / nickel, copper / gold / nickel, or a combination of the foregoing.

[0009] According to an embodiment of the present invention, the average size of each of the first interlayer conductor and the second interlayer conductor is 4 μm to 20 μm.

[0010] According to an embodiment of the present invention, each layer of the multi-layer piezoelectric structure further includes a conduction layer disposed on the second piezoelectric layer.

[0011] According to another aspect of the present invention, a method for manufacturing a pressure-sensitive flexible circuit board is provided. The method includes providing a flexible circuit substrate; forming a first piezoelectric layer and a second piezoelectric layer on the flexible circuit substrate, wherein the first piezoelectric layer and the second piezoelectric layer include a plurality of interlayer conductors; forming a first polymer layer on the flexible circuit substrate, wherein the polymer layer isolates the first piezoelectric layer and the second piezoelectric layer; forming a metal layer on the first polymer layer, the first piezoelectric layer, and the second piezoelectric layer; forming a multi-layer piezoelectric structure on the second piezoelectric layer, wherein each of the multi-layer piezoelectric structures includes a piezoelectric layer and a conduction layer; and forming a metal cover plate on the metal layer and the multi-layer piezoelectric structure to form a pressure sensing element and a vibration element, wherein the pressure sensing element includes the first piezoelectric layer, and the vibration element includes the second piezoelectric layer and the multi-layer piezoelectric structure.

[0012] According to an embodiment of the present invention, before forming the multi-layer piezoelectric structure, the above method further includes patterning the metal layer to form a first electrode layer and a conduction metal layer. The first electrode layer is located on the first piezoelectric layer, and the conduction metal layer is located between the second piezoelectric layer and the multi-layer piezoelectric structure.

[0013] According to an embodiment of the present invention, before forming the metal cover plate, the above method further includes forming a first conductive post adjacent to the first piezoelectric layer, wherein the first conductive post extends from the metal layer into the flexible circuit substrate; and forming at least one second conductive post adjacent to the second piezoelectric layer and the multi-layer piezoelectric structure, wherein the second conductive post extends from the topmost portion of the multi-layer piezoelectric structure through the flexible circuit substrate.

[0014] According to an embodiment of the present invention, the step of forming the multi-layer piezoelectric structure includes forming a second polymer layer adjacent to the piezoelectric layer of each of the plurality of piezoelectric structures.

[0015] Applying the pressure-sensitive flexible circuit board of the present invention and its manufacturing method, the pressure sensing element and the vibration element are integrated on the flexible circuit substrate to save space, and the vibration element including a multi-layer piezoelectric structure is used to achieve the effect of energy saving. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0017] Figure 1 A cross-sectional view of a pressure-sensitive flexible circuit board according to some embodiments of the present invention is shown.

[0018] Figure 2A A side view of a first piezoelectric layer according to some embodiments of the present invention is shown.

[0019] Figure 2B Shown according to Figure 1 An enlarged cross-sectional schematic view of the square A in

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

[0021] The following disclosure provides many different embodiments or exemplifications to implement different features of the invention. The specific exemplifications of the components and configurations described below are for simplifying the present disclosure. These are of course only for illustration and are not intended to be restrictive. For example, the description of the first feature being formed on or above the second feature includes embodiments where the first feature and the second feature are in direct contact, and also includes embodiments where 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 present disclosure repeats element 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, the spatially relative terms, such as "beneath", "below", "lower", "above", "upper", etc., are for ease of describing the relationship between the parts or features depicted in the drawings and other parts or features. The spatially relative terms include different directions of the element during use or operation in addition to the directions depicted in the drawings. The device can be oriented in other ways (rotated 90 degrees or in other directions), and the spatially relative descriptions used in the present disclosure can be interpreted accordingly.

[0023] As used in the present invention, "around", "about", "approximately" or "substantially" generally means within 20%, or within 10%, or within 5% of the stated numerical value or range.

[0024] As described above, the present invention provides a pressure-sensitive flexible circuit board and a manufacturing method thereof, which integrate a pressure sensing element and a vibration element on a flexible circuit substrate to save space; utilize a vibration element including a multi-layer piezoelectric structure to have a larger displacement amount under the same voltage, thereby achieving the effect of energy saving; and utilize metal particles as an interlayer conductor to have a larger contact area and better bonding force, thereby enhancing the vibration resistance of the entire module.

[0025] Please refer to Figure 1 , which shows a cross-sectional view of a pressure-sensitive flexible circuit board 100 according to some embodiments of the present invention. The pressure-sensitive flexible circuit board 100 includes a flexible circuit substrate 110, a pressure sensing element 150, and a vibration element 190. The pressure sensing element 150 and the vibration element 190 are both disposed on the flexible circuit substrate 110. In some embodiments, the flexible circuit substrate 110 includes a flexible substrate 112 and an upper circuit layer 115 and a lower circuit layer 118 respectively disposed on the upper surface and the lower surface of the flexible substrate 112.

[0026] In some embodiments, the pressure-sensitive flexible circuit board 100 further includes a steel sheet 101 and a substrate layer 103, and the flexible circuit substrate 110 is disposed on the steel sheet 101 and the substrate layer 103. In some embodiments, the pressure-sensitive flexible circuit board 100 further includes a first buffer layer and a second buffer layer (not shown in the figure), wherein the first buffer layer is disposed between the flexible circuit substrate 110 and the pressure sensing element 150, and the second buffer layer is disposed between the flexible circuit substrate 110 and the vibration element 190.

[0027] The pressure sensing element 150 includes a first piezoelectric layer 120, a first polymer layer 130, and a first electrode layer 135. The first piezoelectric layer 120 is disposed on the upper circuit layer 115 of the flexible circuit substrate 110, and the first polymer layer 130 is also disposed on the upper circuit layer 115 and adjacent to the first piezoelectric layer 120. The first electrode layer 135 is disposed on the first piezoelectric layer 120 and the first polymer layer 130. The setting of the first polymer layer 130 enables the pressure-sensitive flexible circuit board 100 to have better stress resistance and vibration resistance. Generally, no circuit is designed on the first electrode layer 135.

[0028] In some embodiments, the first piezoelectric layer 120 includes a ceramic material, such as Pb 2 Ti x Oy (where x is from 1 to 3, and y is from 1 to 3). In the foregoing embodiments, the thickness of the first piezoelectric layer 120 is about 50 μm to about 150 μm. In some embodiments, the first piezoelectric layer 120 further includes metals such as silver and / or nickel, which can be plated on the ceramic material, and the thickness of the plating layer is not greater than 100 nm to reduce the conduction resistance between the first piezoelectric layer 120 and the first electrode layer 135.

[0029] Please refer to Figure 2A and Figure 2B , Figure 2A which shows a side view of the first piezoelectric layer 120, and Figure 2B which shows an enlarged cross-sectional schematic view of the square A according to Figure 1 . As Figure 2A shown, the pressure sensing element 150 further includes a first interlayer conductor 125 distributed in the first piezoelectric layer 120, and an insulating layer 122 disposed on the first piezoelectric layer 120. In some embodiments, the insulating layer 122 includes epoxy resin, preferably epoxy resin having a low coefficient of thermal expansion (CTE). The insulating layer 122 can be selected as a material that is easily bonded to the ceramic material, so that the first piezoelectric layer 120 and the first electrode layer 135 form a stable structure and can withstand pressure, vibration or stress during application.

[0030] As Figure 2B shown, the first interlayer conductor 125 is conductively connected to the first piezoelectric layer 120 and the first electrode layer 135, and the insulating layer 122 is located between the first piezoelectric layer 120 and the first electrode layer 135. In some embodiments, the thickness of the insulating layer 122 is about 1.5 μm to about 8 μm. In some embodiments, the first interlayer conductor 125 includes alloy particles of copper / nickel, copper / silver / nickel, copper / gold / nickel or a combination of the foregoing. In some embodiments, the average size (e.g., the average particle diameter of the particles) of the first interlayer conductor 125 is about 4 μm to about 20 μm. Since the first interlayer conductor 125 is manufactured by pressing metal particles, it can have a large contact area and good bonding force, which helps to improve the vibration resistance of the element.

[0031] The first electrode layer 135 is mainly used to sense and collect pressure or touch signals. Therefore, the first electrode layer 135 is usually disposed at the center of the button of the touch element or near the center of the button, so that the first electrode layer 135 can collect charges to the greatest extent. In some embodiments, the first electrode layer 135 can be a comb-shaped electrode, and the line width of its electrodes can be, for example, about 50 μm to about 500 μm, and the line pitch can be, for example, about 50 μm to about 300 μm. The first electrode layer 135 must be grounded to provide a circuit for charges, ensuring correct electrical signal transmission and electrostatic dissipation.

[0032] In some embodiments, the pressure sensing element 150 further includes a first conductive post 140. The first conductive post 140 is adjacent to the first piezoelectric layer 120 but does not physically contact the first piezoelectric layer 120. The first conductive post 140 extends downward from the upper surface of the first electrode layer 135 to the upper circuit layer 115 of the flexible circuit substrate 110 but does not penetrate the flexible substrate 112. In some embodiments, the pressure sensing element 150 further includes a first cover plate 145 on the first electrode layer 135 and the first conductive post 140.

[0033] The vibration element 190 includes a multi-layer piezoelectric structure 180, a second electrode layer 170, a first polymer layer 130, and a second polymer layer 155. The multi-layer piezoelectric structure 180 is disposed on the upper circuit layer 115 of the flexible circuit substrate 110. The second electrode layer 170 is disposed on the multi-layer piezoelectric structure 180. Generally, no circuits are designed on the second electrode layer 170. The first polymer layer 130 and the second polymer layer 155 are adjacent to the multi-layer piezoelectric structure 180. The arrangement of the second polymer layer 155 can protect the multi-layer piezoelectric structure 180, enabling the vibration element 190 of the pressure-sensitive flexible circuit board 100 to have better stress and vibration resistance.

[0034] The multi-layer piezoelectric structure 180 includes a plurality of second piezoelectric layers and a plurality of conductive layers. As Figure 1 shown, the multi-layer piezoelectric structure 180 includes a second piezoelectric layer 160A, a second piezoelectric layer 160B, a second piezoelectric layer 160C, a conductive layer 165A, and a conductive layer 165B, where the second piezoelectric layer 160A is located on the upper circuit layer 115, the conductive layer 165A is located on the second piezoelectric layer 160A, the second piezoelectric layer 160B is located on the conductive layer 165A, the conductive layer 165B is located on the second piezoelectric layer 160B, and the second piezoelectric layer 160C is located on the conductive layer 165B. The second electrode layer 170 is disposed on the second piezoelectric layer 160C of the multi-layer piezoelectric structure 180 and the second polymer layer 155. In some embodiments, the area of the second electrode layer 170 covering the multi-layer piezoelectric structure 180 is more than 85% of the area of the second piezoelectric layer to achieve a stronger piezoelectric effect.

[0035] In some embodiments, the second piezoelectric layer (such as the second piezoelectric layer 160A, the second piezoelectric layer 160B, and the second piezoelectric layer 160C) includes a ceramic material, such as Pb 2 Ti x O y(where x is from 1 to 3, and y is from 1 to 3). In the foregoing embodiments, the thickness of the second piezoelectric layer (such as the second piezoelectric layer 160A, the second piezoelectric layer 160B, and the second piezoelectric layer 160C) is about 50 μm to about 150 μm. In some embodiments, the second piezoelectric layer (such as the second piezoelectric layer 160A, the second piezoelectric layer 160B, and the second piezoelectric layer 160C) further includes metals such as silver and / or nickel, which can be plated on the ceramic material, and the thickness of the plating layer is not greater than 100 nm to reduce the conduction resistance between the multi-layer piezoelectric structure 180 and the second electrode layer 170.

[0036] Similar to the first piezoelectric layer 120, the second piezoelectric layer (such as the second piezoelectric layer 160A, the second piezoelectric layer 160B, and the second piezoelectric layer 160C) includes an interlayer conductor disposed in the second piezoelectric layer (not shown in the figure), and an insulating layer disposed on the second piezoelectric layer (not shown in the figure). In some embodiments, the insulating layer includes epoxy resin, preferably epoxy resin having a low coefficient of thermal expansion, to match the multi-layer piezoelectric structure 180. In some embodiments, the thickness of the insulating layer is about 1.5 μm to about 8 μm. The insulating layer can effectively adhere to the ceramic material, so that the second piezoelectric layer (such as the second piezoelectric layer 160A, the second piezoelectric layer 160B, and the second piezoelectric layer 160C) forms a stable structure with the conduction layer 165A, the conduction layer 165B, and the second electrode layer 170 respectively, and the multi-layer piezoelectric structure 180 can withstand pressure, vibration, or stress during application.

[0037] Similar to the first piezoelectric layer 120, the interlayer conductor of the second piezoelectric layer 160A conducts and connects the second piezoelectric layer 160A and the conduction layer 165A; the interlayer conductor of the second piezoelectric layer 160B conducts and connects the second piezoelectric layer 160B and the conduction layer 165B; and the interlayer conductor of the second piezoelectric layer 160C conducts and connects the second piezoelectric layer 160C and the second electrode layer 170. In some embodiments, the interlayer conductor includes alloy particles of copper / nickel, copper / silver / nickel, copper / gold / nickel, or a combination of the foregoing. In some embodiments, the average size of the interlayer conductor (such as the average particle size of the particles) is about 4 μm to about 20 μm. Since the interlayer conductor is manufactured by pressing metal particles, it can have a large contact area and good bonding force, which helps to improve the vibration resistance of the component.

[0038] The vibration element 190 can be a multi-layer parallel structure or a same-layer parallel structure, which can be designed according to application requirements, preferably a multi-layer parallel structure. In some embodiments, the multi-layer piezoelectric structure 180 is a structure with three or more layers to increase the magnitude of the total output voltage. In some embodiments, an electric field can be applied on both sides of the second electrode layer 170 to generate a stronger piezoelectric effect. The multi-layer piezoelectric structure 180 of the vibration element 190 can have a larger displacement amount (for example, more than 30% increase) under the same voltage, so it can have an energy-saving effect.

[0039] In some embodiments, the vibration element 190 further includes a second conductive post 185A and a second conductive post 185B. The second conductive post 185A and the second conductive post 185B are adjacent to the second piezoelectric layer 160A to the second piezoelectric layer 160C of the multi-layer piezoelectric structure 180. The second conductive post 185A and the second conductive post 185B extend from above the second electrode layer 170 through the lower circuit layer 118 of the flexible circuit substrate 110 to the substrate layer 103. In some embodiments, the vibration element 190 further includes a second cover plate 188 disposed on the multi-layer piezoelectric structure 180.

[0040] Figures 3A to 3D Shown is a cross-sectional view of an intermediate stage of the process of the pressure-sensitive flexible circuit board 100 according to some embodiments of the present invention. Hereinafter, Figures 3A to 3D the manufacturing process of the pressure-sensitive flexible circuit board 100 is described.

[0041] First, please refer to Figure 3A , and provide the flexible circuit substrate 110. The flexible circuit substrate 110 includes a flexible substrate 112, an upper circuit layer 115, and a lower circuit layer 118, wherein the upper circuit layer 115 is disposed on the upper surface 112A of the flexible substrate 112, and the lower circuit layer 118 is disposed on the lower surface 112B of the flexible substrate 112.

[0042] Next, please refer to Figure 3B , and form a first piezoelectric layer 120 and a second piezoelectric layer 160A on the upper circuit layer 115 of the flexible circuit substrate 110. The aforementioned first piezoelectric layer 120 further includes an interlayer conductor 125 distributed in the first piezoelectric layer 120 and an insulating layer 122 disposed on the first piezoelectric layer 120 (refer to Figure 2A and Figure 2B ). Similarly, the aforementioned second piezoelectric layer 160A further includes an interlayer conductor distributed in the second piezoelectric layer 160A and an insulating layer disposed on the second piezoelectric layer 160A.

[0043] Please continue to refer to Figure 3BThe first polymer layer 130 is formed on the flexible circuit substrate 110, and the first polymer layer 130 separates the first piezoelectric layer 120 and the second piezoelectric layer 160A. Then, the metal layer 310 is formed on the first polymer layer 130, the first piezoelectric layer 120, and the second piezoelectric layer 160A.

[0044] See also Figure 3C , the patterned metal layer 310 is formed to form the first electrode layer 135 on the first piezoelectric layer 120 and the conductive layer 165A on the second piezoelectric layer 160A. Then, the second piezoelectric layer 160B, the conductive layer 165B, the second piezoelectric layer 160C and the second electrode layer 170 are sequentially laminated on the conductive layer 165A to complete the multilayer piezoelectric structure 180. It should be understood that, similar to the second piezoelectric layer 160A, the second piezoelectric layer 160B and the second piezoelectric layer 160C also include a second interlayer conductor and an insulating layer. Furthermore, in the process of forming the multilayer piezoelectric structure 180, the second polymer layer 155 adjacent to the multilayer piezoelectric structure 180 is formed.

[0045] See also Figure 3D , a drilling copper plating process is performed to form a first conductive column 140, a second conductive column 185A and a second conductive column 185B. The first conductive column 140 is arranged adjacent to the first piezoelectric layer 120, and the first conductive column 140 extends from the upper surface of the first electrode layer 135 through the first polymer layer 130 to the upper circuit layer 115 of the flexible circuit substrate 110, but does not penetrate the flexible substrate 112. The second conductive column 185A and the second conductive column 185B are respectively arranged adjacent to the second piezoelectric layer 160A to the second piezoelectric layer 160C of the multilayer piezoelectric structure 180, and are respectively located on both sides of the second piezoelectric layer 160A to the second piezoelectric layer 160C. The second conductive column 185A and the second conductive column 185B extend from above the second electrode layer 170 to penetrate the second polymer layer 155, the first polymer layer 130 and the lower circuit layer 118 of the flexible circuit substrate 110. At this point, the pressure sensing element 150 and the vibration element 190 of the pressure sensitive flexible printed circuit board 100 are substantially completed.

[0046] Then, the first cover plate 145 is disposed on the first electrode layer 135 of the pressure sensing element 150, and the second cover plate 188 is disposed on the second electrode layer 170 of the vibration element 190. And this structure is disposed on the steel sheet 101 and the substrate layer 103, and the Figure 1 The pressure-sensitive flexible printed circuit board 100 is shown.

[0047] The present invention provides a pressure-sensitive flexible circuit board and a manufacturing method thereof, to integrate a pressure sensing element and a vibration element on a flexible circuit substrate. The vibration element is arranged to include a multi-layer piezoelectric structure, so that it can have a larger displacement amount under the same voltage, and metal particles are used as an interlayer conductor between the piezoelectric layer and the electrode or the conduction layer. Thereby, the effects of saving space, energy conservation and improving the vibration resistance ability can be achieved.

[0048] Although the present invention has been disclosed above with several embodiments, it is not intended to limit the present invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to that defined by the appended claims.

[0049]

Symbol Explanation

[0050] 100: Pressure-sensitive flexible circuit board

[0051] 101: Steel sheet

[0052] 103: Substrate layer

[0053] 110: Flexible circuit substrate

[0054] 112: Flexible substrate

[0055] 115: Upper circuit layer

[0056] 118: Lower circuit layer

[0057] 120: First piezoelectric layer

[0058] 122: Insulating layer

[0059] 125: First interlayer conductor

[0060] 130: First polymer layer

[0061] 135: First electrode layer

[0062] 140: First conductive post

[0063] 145: First cover plate

[0064] 150: Pressure sensing element

[0065] 155: Second polymer layer

[0066] 160A, 160B, 160C: Second piezoelectric layer

[0067] 165A, 165B: Conduction layer

[0068] 170: Second electrode layer

[0069] 180: Multi-layer piezoelectric structure

[0070] 185A, 185B: The second conductive post

[0071] 188: The second cover plate

[0072] 190: The vibration element

[0073] 310: The metal layer

[0074] A: The square frame.

Claims

1. A pressure-sensitive flexible circuit board, characterized in that, it comprises: a flexible circuit substrate; a pressure sensing element disposed on the flexible circuit substrate, wherein the pressure sensing element comprises: a first piezoelectric layer; a plurality of first interlayer conductors distributed in the first piezoelectric layer; a first polymer layer adjacent to the first piezoelectric layer; and a first electrode layer disposed on the first piezoelectric layer and connected to the plurality of interlayer conductors; and a vibration element disposed on the flexible circuit substrate, wherein the vibration element comprises: a multi-layer piezoelectric structure, and each layer of the multi-layer piezoelectric structure comprises: a second piezoelectric layer; and a plurality of second interlayer conductors distributed in the second piezoelectric layer; a second electrode layer disposed on the topmost layer of the multi-layer piezoelectric structure; and a second polymer layer adjacent to the multi-layer piezoelectric structure.

2. The pressure-sensitive flexible circuit board according to claim 1, characterized in that, the pressure sensing element further comprises: a first conductive post adjacent to the first piezoelectric layer, wherein the first conductive post extends from the first electrode layer into the flexible circuit substrate, and the vibration element further comprises: at least one second conductive post adjacent to the multi-layer piezoelectric structure and the plurality of polymer layers, wherein the at least one second conductive post extends from the second electrode layer through the flexible circuit substrate.

3. The pressure-sensitive flexible circuit board according to claim 1, characterized in that, it further comprises: a first buffer layer disposed between the flexible circuit substrate and the pressure sensing element; and a second buffer layer disposed between the flexible circuit substrate and the vibration element.

4. The pressure-sensitive flexible circuit board according to claim 1, characterized in that, the first interlayer conductors and the second interlayer conductors comprise alloy particles of copper / nickel, copper / silver / nickel, copper / gold / nickel or a combination of the foregoing.

5. The pressure-sensitive flexible circuit board according to claim 1, characterized in that, the average size of each of the first interlayer conductors and the second interlayer conductors is 4 μm to 20 μm.

6. The pressure-sensitive flexible circuit board according to claim 1, characterized in that, each layer of the multi-layer piezoelectric structure further comprises: a conduction layer disposed on the second piezoelectric layer.

7. A method for manufacturing a pressure-sensitive flexible circuit board, characterized in that, it comprises: providing a flexible circuit substrate; forming a first piezoelectric layer and a second piezoelectric layer on the flexible circuit substrate, wherein the first piezoelectric layer and the second piezoelectric layer comprise a plurality of interlayer conductors; forming a first polymer layer on the flexible circuit substrate, wherein the polymer layer isolates the first piezoelectric layer and the second piezoelectric layer; forming a metal layer on the first polymer layer, the first piezoelectric layer and the second piezoelectric layer; forming a multi-layer piezoelectric structure on the second piezoelectric layer, wherein each of the multi-layer piezoelectric structures comprises a piezoelectric layer and a conduction layer; and Form a cover plate on the metal layer and the multi-layer piezoelectric structure to form a pressure sensing element and a vibration element, wherein the pressure sensing element includes the first piezoelectric layer, and the vibration element includes the second piezoelectric layer and the multi-layer piezoelectric structure.

8. The method for manufacturing a pressure-sensitive flexible circuit board according to claim 7, wherein, before forming the multi-layer piezoelectric structure, it further includes: patterning the metal layer to form a first electrode layer and a conducting metal layer, wherein the first electrode layer is located on the first piezoelectric layer, and the conducting metal layer is located between the second piezoelectric layer and the multi-layer piezoelectric structure.

9. The method for manufacturing a pressure-sensitive flexible circuit board according to claim 7, wherein, before forming the cover plate, it further includes: forming a first conductive post adjacent to the first piezoelectric layer, wherein the first conductive post extends from the metal layer into the flexible circuit substrate; and forming at least one second conductive post adjacent to the second piezoelectric layer and the multi-layer piezoelectric structure, wherein the at least one second conductive post extends from the topmost part of the multi-layer piezoelectric structure into the flexible circuit substrate.

10. The method for manufacturing a pressure-sensitive flexible circuit board according to claim 7, wherein, forming the multi-layer piezoelectric structure includes: forming a second polymer layer adjacent to the piezoelectric layer of each of the plurality of piezoelectric structures.

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