Thin multilayer circuit board capable of transmitting force signals and manufacturing method thereof

Abstract

The invention discloses a thin multilayer circuit board capable of transmitting a force signal and a manufacturing method thereof. The method comprises the following steps: providing base material copper and first photosensitive polyimide; combining the base material copper with the first photosensitive polyimide; patterning the formed first photosensitive polyimide on the photosensitive substrate; performing primary circuit manufacturing on the photosensitive base material based on the patterned first photosensitive polyimide to obtain a first circuit substrate; providing second photosensitive polyimide, and combining the second photosensitive polyimide with the first circuit substrate; patterning the second photosensitive polyimide formed on the second circuit substrate; performing secondary circuit manufacturing on the second circuit substrate based on the patterned second photosensitive polyimide to form a hollow circuit structure and obtain a third circuit substrate; and performing surface treatment on the third circuit substrate to obtain a target circuit board. Based on two layers of photosensitive polyimide, the multilayer board is thinned and has the function of transmitting force signals.

Description

Technical Field

[0001] The present invention relates to the field of flexible circuit board manufacturing, and in particular to a thin multilayer circuit board capable of transmitting force signals and a manufacturing method thereof. Background Art

[0002] With the advancement of science and technology and the development of mankind, more and more electronic products are moving towards miniaturization and multi-functionality, such as mobile phones, new energy vehicles, etc. The replacement of these electronic products is dizzying. With the development of flexible circuit boards, multi-layer flexible circuit boards are increasingly used in these electronic products.

[0003] In traditional multi-layer flexible circuit boards, the middle layer is usually a dielectric material (such as polyimide) and glue for bonding, and the outer layer is used to protect the large-area circuit. The protective film is also mostly a combination of polyimide and glue. Since the thickness of the glue layer will occupy more space in the product thickness, it limits the development of thin circuit boards. At the same time, since there is a fixed structure of polyimide and glue between the layers, most of today's flexible circuit boards can only be used as electrical signal connections, which has great limitations on the transmission of multi-dimensional mechanical signals.

[0004] Based on the above-mentioned defects of multi-layer circuit boards, the development of such electronic products using flexible circuit boards is also limited. Summary of the invention

[0005] In view of this, an embodiment of the present invention provides a thin multilayer circuit board that can transmit force signals and a method for manufacturing the same, so as to solve the problem that the existing multilayer circuit boards use polyimide and glue as intermediate dielectric layers and protective films, which limits the thinning of the circuit boards and the transmission of force signals.

[0006] The present invention provides a method for manufacturing a thin multilayer circuit board capable of transmitting force signals, the method comprising:

[0007] Providing a substrate copper and a first photosensitive polyimide respectively;

[0008] Combining the substrate copper with the first photosensitive polyimide to form a photosensitive substrate; and patterning the first photosensitive polyimide on the photosensitive substrate;

[0009] Based on the patterned first photosensitive polyimide, a circuit is fabricated on the photosensitive substrate to obtain a first circuit substrate;

[0010] Providing a second photosensitive polyimide, combining the second photosensitive polyimide with the first circuit substrate to form a second circuit substrate; and patterning the second photosensitive polyimide on the second circuit substrate;

[0011] Based on the patterned second photosensitive polyimide, a second circuit substrate is fabricated, so that a hollow circuit structure is formed on the second circuit substrate, thereby obtaining a third circuit substrate;

[0012] The third circuit substrate is subjected to surface treatment to obtain a target circuit board.

[0013] Optionally, combining the substrate copper and the first photosensitive polyimide together to form a photosensitive substrate comprises:

[0014] The first photosensitive polyimide is printed on one side or both sides of the copper substrate by screen printing or coating to form the photosensitive substrate; or the first photosensitive polyimide is pressed on one side or both sides of the copper substrate by lamination to form the photosensitive substrate.

[0015] Optionally, patterning the laminated first photosensitive polyimide to obtain a photosensitive substrate comprises:

[0016] According to the preset circuit design data, the copper substrate laminated with the first photosensitive polyimide is processed by exposure and development method;

[0017] The substrate copper after exposure and development is baked according to preset baking parameters to complete the patterning of the first photosensitive polyimide and obtain the photosensitive substrate.

[0018] Optionally, patterning the first photosensitive polyimide on the photosensitive substrate includes:

[0019] Pre-curing the first photosensitive polyimide on the photosensitive substrate;

[0020] According to the preset circuit design data, the pre-cured photosensitive substrate is processed by exposure and development method;

[0021] The photosensitive substrate after exposure and development is baked according to preset baking parameters to complete the patterning of the first photosensitive polyimide.

[0022] Optionally, the patterned first photosensitive polyimide is used to perform a circuit manufacturing process on the photosensitive substrate to obtain a first circuit substrate, including:

[0023] Based on the patterned first photosensitive polyimide, a metal copper layer is sputtered on a side of the photosensitive substrate having the first photosensitive polyimide by a vacuum sputtering method;

[0024] Laminating a dry film on the side of the photosensitive substrate on which the metal copper layer is sputtered, and patterning the laminated dry film by exposure and development according to the preset circuit design data;

[0025] Based on the patterned dry film, electroplating copper is performed on the photosensitive substrate laminated with the dry film to form an electroplated copper layer on the side of the photosensitive substrate sputtered with the metal copper layer;

[0026] The photosensitive substrate after the copper electroplating treatment is sequentially subjected to a dry film removal treatment and a flash etching treatment, so that the metal copper layer and the copper electroplating layer on the photosensitive substrate together form a first circuit layer, completing a circuit production to obtain the first circuit substrate.

[0027] Optionally, combining the second photosensitive polyimide and the first circuit substrate together to form a second circuit substrate includes:

[0028] The second photosensitive polyimide is printed on the side of the first circuit substrate having the electroplated copper layer by screen printing or coating to form the second circuit substrate; or, the second photosensitive polyimide is printed on the side of the first circuit substrate having the electroplated copper layer by lamination to form the second circuit substrate.

[0029] Optionally, patterning the second photosensitive polyimide on the second circuit substrate includes:

[0030] pre-curing the second photosensitive polyimide on the second circuit substrate;

[0031] According to the preset circuit design data, the second circuit substrate after pre-curing is processed by exposure and development method; and the second circuit substrate after exposure and development is baked to complete the patterning of the second photosensitive polyimide.

[0032] Optionally, the second circuit substrate is subjected to secondary circuit fabrication based on the patterned second photosensitive polyimide, so that a hollow circuit structure is formed on the second circuit substrate to obtain a third circuit substrate, including:

[0033] Based on the patterned second photosensitive polyimide, the second circuit substrate is subjected to sequential pressing, exposure, development and circuit etching, so that the base copper in the inner layer of the second circuit substrate forms a second circuit layer;

[0034] The second circuit substrate formed with the second circuit layer is subjected to a dry film removal process, so that the first circuit layer and the second circuit layer on the second circuit substrate together form a hollow circuit structure, and the secondary circuit production is completed to obtain the third circuit substrate.

[0035] Optionally, performing surface treatment on the third circuit substrate to obtain a target circuit board includes:

[0036] The third circuit substrate is subjected to chemical nickel-gold coating to obtain the target circuit board.

[0037] Optionally, before laminating the first photosensitive polyimide to one side or both sides of the copper substrate, the method further comprises:

[0038] The substrate copper is laser processed according to preset laser parameters, so that a plurality of exposure alignment holes are formed in the waste area of ​​the substrate copper.

[0039] In addition, the present invention also provides a thin multi-layer circuit board capable of transmitting force signals, which is manufactured using the aforementioned manufacturing method.

[0040] The beneficial effects of the present invention are as follows: firstly, the first photosensitive polyimide provided is combined with the copper substrate. On the one hand, the first photosensitive polyimide can be used as a photosensitive dry film for subsequent patterning due to its own photosensitivity. Based on the patterned first photosensitive polyimide, a subsequent circuit is produced, which can facilitate the formation of a circuit that meets the design requirements; on the other hand, its own single-layer structure can be used as the intermediate dielectric layer of the multilayer board (specifically, a combined structure of polyimide and glue), which will not occupy a large amount of space, and is convenient for the subsequent formation of a miniaturized and multifunctional multilayer circuit board through the combination of other layers; after the first circuit is produced to form the first circuit substrate, it is combined with the second photosensitive polyimide provided, and on the other hand, the photosensitivity of the second photosensitive polyimide can be directly utilized to produce a circuit that meets the design requirements; Patterning is performed to facilitate the subsequent secondary circuit production based on the patterned second photosensitive polyimide. In addition, the two circuit productions achieved by this method can form two layers of circuits with patterns as needed, so that a hollow circuit structure composed of two layers of circuits with patterns can be formed on the second circuit board, that is, the third circuit substrate obtained has a hollow circuit structure, which will deform after being subjected to force, and can facilitate the transmission of three-dimensional mechanical signals; on the other hand, the single-layer structure itself can also be used as the outer layer structure of the multi-layer board, playing the role of a protective film (also a combination structure of polyimide and glue layer), further reducing the space occupied by the traditional multi-layer circuit board in thickness, and further facilitating the formation of a miniaturized and multifunctional multi-layer circuit board;

[0041] The thin multilayer circuit board capable of transmitting force signals and the manufacturing method thereof of the present invention are based on two layers of photosensitive polyimide as the dielectric layer and the protective film of the multilayer flexible circuit board respectively, and both avoid the use of glue as the bonding material, so that the multilayer flexible circuit board is thinner; at the same time, compared with the traditional pressed polyimide, the photosensitive polyimide has a graphical function and can form a special hollow structure circuit, so that the flexible circuit board can have the function of transmitting three-dimensional mechanical signals, which solves the problem that the traditional multilayer circuit board uses polyimide and glue as the intermediate dielectric layer and the protective film, resulting in the thinning of the circuit board and the transmission of force signals being limited. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The features and advantages of the present invention will be more clearly understood by referring to the accompanying drawings, which are schematic and should not be construed as limiting the present invention in any way. In the accompanying drawings:

[0043] Figure 1 A flow chart showing a method for manufacturing a thin multilayer circuit board capable of transmitting force signals in a first embodiment of the present invention;

[0044] Figure 2 The cross-sectional structure diagram of the substrate copper in the first embodiment of the present invention is shown;

[0045] Figure 3 The cross-sectional structure diagram of the photosensitive substrate obtained after the first photosensitive polyimide is patterned in the first embodiment of the present invention is shown;

[0046] Figure 4 The cross-sectional structure diagram of the photosensitive substrate with a metal copper layer sputtered thereon in the first embodiment of the present invention is shown;

[0047] Figure 5 The cross-sectional structure diagram of the photosensitive substrate after exposure and development in the first embodiment of the present invention is shown;

[0048] Figure 6 The cross-sectional structure diagram of the photosensitive substrate after copper electroplating in the first embodiment of the present invention is shown;

[0049] Figure 7 The cross-sectional structure diagram of the first circuit substrate obtained after completing a circuit manufacturing in the first embodiment of the present invention is shown;

[0050] Figure 8 The cross-sectional structure diagram of the second circuit substrate obtained after the second photosensitive polyimide is patterned in the first embodiment of the present invention is shown;

[0051] Fig. 9 The cross-sectional structure diagram of the second circuit substrate after exposure and development in the first embodiment of the present invention is shown;

[0052] Fig.10The cross-sectional structure diagram of the second circuit substrate after circuit etching in the first embodiment of the present invention is shown;

[0053] Fig.11 The cross-sectional structure diagram of the third circuit substrate obtained after the dry film is removed in the first embodiment of the present invention is shown;

[0054] Fig.12 The cross-sectional structure diagram of the target circuit board obtained in the first embodiment of the present invention is shown.

[0055] The description of each reference numeral is as follows:

[0056] 1. Base copper, 2. First photosensitive polyimide, 3. Metal copper layer, 4. First dry film, 5. Electroplated copper layer, 6. Second photosensitive polyimide, 7. Second dry film, 8. Nickel-gold layer. DETAILED DESCRIPTION

[0057] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0058] Embodiment 1

[0059] This embodiment provides a method for manufacturing a thin multilayer circuit board capable of transmitting force signals. Figure 1 As shown, including:

[0060] S1: providing a substrate copper and a first photosensitive polyimide respectively;

[0061] S2: combining the substrate copper and the first photosensitive polyimide together to form a photosensitive substrate; and patterning the first photosensitive polyimide on the photosensitive substrate;

[0062] S3: Based on the patterned first photosensitive polyimide, performing a circuit manufacturing process on the photosensitive substrate to obtain a first circuit substrate;

[0063] S4: providing a second photosensitive polyimide, combining the second photosensitive polyimide with the first circuit substrate to form a second circuit substrate; and patterning the second photosensitive polyimide on the second circuit substrate;

[0064] S5: performing secondary circuit fabrication on the second circuit substrate based on the patterned second photosensitive polyimide, so that a hollow circuit structure is formed on the second circuit substrate, thereby obtaining a third circuit substrate;

[0065] S6: performing surface treatment on the third circuit substrate to obtain a target circuit board.

[0066] In this embodiment, the first photosensitive polyimide provided is first combined with the substrate copper. On the one hand, the first photosensitive polyimide can be used as a photosensitive dry film for subsequent patterning due to its own photosensitivity. The subsequent primary circuit production is carried out based on the patterned first photosensitive polyimide, which can facilitate the formation of a circuit that meets the design requirements; on the other hand, its own single-layer structure can be used as the intermediate dielectric layer of the multi-layer board (specifically, a combined structure of polyimide and glue), which will not occupy a lot of space, and is convenient for the subsequent formation of a miniaturized and multifunctional multi-layer circuit board through the combination of other layers; after the primary circuit production is completed to form the first circuit substrate, it is combined with the provided second photosensitive polyimide, and on the other hand, the photosensitivity of the second photosensitive polyimide can be directly used to carry out Graphicalization facilitates the subsequent secondary circuit production based on the patterned second photosensitive polyimide. In addition, the two circuit productions achieved by this method can form two layers of patterned circuits as needed, so that a hollow circuit structure composed of two layers of patterned circuits can be formed on the second circuit board, that is, the third circuit substrate obtained has a hollow circuit structure, which will deform after being subjected to force, and can facilitate the transmission of three-dimensional mechanical signals; on the other hand, its own single-layer structure can also be used as the outer layer structure of the multi-layer board, playing the role of a protective film (also a combination structure of polyimide and glue layer), further reducing the space occupied by the traditional multi-layer circuit board in thickness, and further facilitating the formation of miniaturized and multifunctional multi-layer circuit boards.

[0067] The method for manufacturing a thin multi-layer circuit board capable of transmitting force signals in the present embodiment is based on two layers of photosensitive polyimide as the dielectric layer and protective film of the multi-layer flexible circuit board, respectively, and avoids the use of glue as an adhesive material, thereby making the multi-layer flexible circuit board thinner; at the same time, compared with traditional pressed polyimide, photosensitive polyimide has a graphical function and can form a special hollow structure circuit, thereby enabling the flexible circuit board to have the function of transmitting three-dimensional mechanical signals, solving the problem that the traditional multi-layer circuit board uses polyimide and glue as the intermediate dielectric layer and protective film, resulting in the thinning of the circuit board and the transmission of force signals being limited.

[0068] The following describes in detail each step of the manufacturing method of this embodiment.

[0069] In the present embodiment S1, the thickness of the base copper is in the range of 50 to 150 μm. In the present embodiment, the base copper is specifically 80 μm thick, and its cross-sectional structure is as follows: Figure 2 As shown, in Figure 2 In the figure, 1 is the base copper.

[0070] After S1 and before S2, the method includes:

[0071] The substrate copper is laser processed according to preset laser parameters, so that a plurality of exposure alignment holes are formed in the waste area of ​​the substrate copper.

[0072] By laser-printing a plurality of exposure alignment holes in the waste area of ​​the substrate copper, these exposure alignment holes can be used as alignment references for all subsequent exposure processes to ensure the accuracy of exposure.

[0073] The waste area of ​​the copper substrate is usually the edges of the copper substrate. Specifically, exposure alignment holes can be lasered at the four corners of the copper substrate. The number, aperture and specific position of the exposure alignment holes can be selected and adjusted according to actual conditions. For example, one exposure alignment hole can be lasered at each of the four corners of the copper substrate, and the positions of the four exposure alignment holes are asymmetrical, and the aperture of the exposure alignment holes is 1 mm.

[0074] In the present embodiment S2, the substrate copper and the first photosensitive polyimide are combined together to form a photosensitive substrate, including:

[0075] S21: Printing the first photosensitive polyimide on one side or both sides of the copper substrate by screen printing or coating to form the photosensitive substrate; or, laminating the first photosensitive polyimide on one side or both sides of the copper substrate to form the photosensitive substrate.

[0076] Since photosensitive polyimide has two material forms, film and liquid, for the first photosensitive polyimide in liquid form, the first photosensitive polyimide is printed on one or both sides of the copper substrate by screen printing or coating, which can simply and quickly combine the copper substrate with the first photosensitive polyimide. For the first photosensitive polyimide in film form, the first photosensitive polyimide is printed on one or both sides of the copper substrate by lamination, which can also efficiently and accurately combine the copper substrate with the first photosensitive polyimide.

[0077] In this embodiment, the first photosensitive polyimide can be located on one side of the copper substrate to form a multilayer circuit board based on the treatment of the single side of the copper substrate; or it can be located on both sides of the copper substrate to form a multilayer circuit board based on the treatment of both sides of the copper substrate. When located on both sides of the copper substrate, the subsequent treatment of each side of the copper substrate is the same.

[0078] The first photosensitive polyimide of this embodiment can be selected according to actual needs. The thickness range is 5 to 25 μm, and 18 μm is selected in this embodiment. For the first photosensitive polyimide in the form of a film material, its specific target thickness needs to be selected before lamination; and for the first photosensitive polyimide in the form of a liquid, the target thickness can be obtained by adjusting the operating parameters during screen printing or coating.

[0079] In the present embodiment S2, patterning the first photosensitive polyimide on the photosensitive substrate includes:

[0080] S22: pre-curing the first photosensitive polyimide on the photosensitive substrate;

[0081] S23: According to the preset circuit design data, the pre-cured photosensitive substrate is processed by an exposure and development method;

[0082] S24: baking the photosensitive substrate after exposure and development according to preset baking parameters to complete the patterning of the first photosensitive polyimide.

[0083] Pre-curing can volatilize part of the solvent in the first photosensitive polyimide, which helps to improve the efficiency of subsequent patterning. Based on the photosensitive properties of the first photosensitive polyimide itself, direct exposure and development can be used to remove part of the polyimide to form the required pattern. Finally, baking can be used to completely cure the first photosensitive polyimide with the pattern, truly completing its patterning and facilitating subsequent circuit production.

[0084] Among them, the preset circuit design data includes the specific layout of the circuit in the two circuit production processes. Exposure and development are performed based on the circuit layout in the first circuit production process, which can facilitate the first photosensitive polyimide to form the required pattern, and then facilitate the subsequent formation of the first circuit layer that meets the design requirements (that is, the circuit structure formed by the metal copper layer and the electroplated copper layer).

[0085] The specific operating parameters of pre-curing are set and adjusted according to the actual situation, and the specific operating parameters of baking (ie, preset baking parameters) are the same and are not limited here.

[0086] In this embodiment, the first photosensitive polyimide is printed or pressed on one side of the copper substrate as an example. The cross-sectional structure of the photosensitive substrate obtained after the first photosensitive polyimide is patterned is as follows: Figure 3 As shown, in Figure 3 In the figure, 2 is the first photosensitive polyimide.

[0087] This embodiment S3 includes:

[0088] S31: sputtering a metal copper layer on a side of the photosensitive substrate having the first photosensitive polyimide by vacuum sputtering based on the patterned first photosensitive polyimide;

[0089] S32: Laminating a dry film on the side of the photosensitive substrate on which the metal copper layer is sputtered, and patterning the laminated dry film by exposure and development according to the preset circuit design data;

[0090] S33: Based on the patterned dry film, electroplating copper is performed on the photosensitive substrate laminated with the dry film to form an electroplated copper layer on the side of the photosensitive substrate sputtered with the metal copper layer;

[0091] S34: sequentially performing a dry film removal treatment and a flash etching treatment on the photosensitive substrate after the copper electroplating treatment, so that the metal copper layer and the copper electroplating layer on the photosensitive substrate jointly form a first circuit layer, completing a circuit production, and obtaining the first circuit substrate.

[0092] Due to the dielectric material properties of the first photosensitive polyimide itself, its own single-layer structure can be directly used as the intermediate dielectric layer of the multilayer board, without the need to combine all the glues to serve as the intermediate dielectric layer of the multilayer board, and it will not occupy a large amount of space; at this time, the vacuum sputtering method is directly used to sputter the metal copper layer on one side of the first photosensitive polyimide, which is equivalent to directly pressing a single-sided board on the photosensitive substrate without the participation of glue, thereby facilitating the formation of a thinner multilayer circuit board; in addition, since the first photosensitive polyimide on the photosensitive substrate has been patterned, the metal copper layer is sputtered based on the patterned first photosensitive polyimide, which can facilitate the subsequent combination of a circuit production process to form the first circuit layer, and expose the area where the inner layer of the substrate copper needs to be exposed, thereby facilitating the formation of a hollow circuit structure, which is helpful to form a multilayer board with a transmission force signal function. After the metal copper layer is sputtered on the photosensitive substrate, the first circuit layer that meets the design requirements can be efficiently and accurately formed by pressing the dry film, exposing and developing, electroplating copper, removing the dry film and flash etching, etc., with a simple production process and high production accuracy.

[0093] In the present embodiment S31, the thickness of the sputtered copper layer is in the range of 300 to 1000 nm, and in the present embodiment, the thickness is specifically 500 nm. The cross-sectional structure of the photosensitive substrate with the copper layer sputtered is as follows: Figure 4 As shown, in Figure 4 In the embodiment S32, a vacuum laminating device is used to laminate a dry film, and the thickness of the dry film ranges from 15 to 40 μm, and in the embodiment, 25 μm is specifically used. After exposure and development, the area to be electroplated on the metal copper layer is exposed. The cross-sectional structure of the photosensitive substrate after exposure and development is as follows: Figure 5 As shown, in Figure 5In the embodiment S33, the thickness of the electroplated copper layer is in the range of 10 to 35 μm, and in the embodiment, 18 μm is specifically selected. The cross-sectional structure of the photosensitive substrate after the electroplated copper treatment is as follows: Figure 6 As shown, in Figure 6 In the embodiment S34, the dry film on the photosensitive substrate is removed by using a film stripping solution, and then the unnecessary metal copper layer on the photosensitive substrate is removed by flash etching. The cross-sectional structure of the first circuit substrate obtained after completing one circuit manufacturing is as follows: Figure 7 shown.

[0094] In the present embodiment S4, the second photosensitive polyimide is combined with the first circuit substrate to form a second circuit substrate, including:

[0095] S41: Print the second photosensitive polyimide on the side of the first circuit substrate having the electroplated copper layer by screen printing or coating to form the second circuit substrate; or print the second photosensitive polyimide on the side of the first circuit substrate having the electroplated copper layer by lamination to form the second circuit substrate.

[0096] After completing the production of one circuit, a second photosensitive polyimide is printed or pressed on the electroplated copper layer of the first circuit substrate using a method similar to that of the first photosensitive polyimide. At this time, the second photosensitive polyimide can also be patterned based on its own photosensitive properties, so as to facilitate the subsequent secondary circuit production based on the patterned second photosensitive polyimide. In addition, the second photosensitive polyimide is printed or pressed on the first circuit layer, which is equivalent to directly combining with the first circuit board having the first circuit layer without the participation of glue, and can be used as a protective film for the entire first circuit layer. Its single-layer structure plays the role of a protective film, further reducing the space occupied by the traditional multi-layer circuit board in thickness, and further facilitating the formation of a miniaturized and multifunctional multi-layer circuit board.

[0097] In the present embodiment S4, patterning the second photosensitive polyimide on the second circuit substrate includes:

[0098] S42: pre-curing the second photosensitive polyimide on the second circuit substrate;

[0099] S43: According to the preset circuit design data, the second circuit substrate after pre-curing is processed by exposure and development method; and the second circuit substrate after exposure and development is baked to complete the patterning of the second photosensitive polyimide.

[0100] Similar to the method of patterning the first photosensitive polyimide, the patterning of the second photosensitive polyimide is performed through the above steps. On the one hand, the efficiency of patterning can be improved, and on the other hand, the patterning of the second photosensitive polyimide can be accurately completed, so that the base copper in the entire second circuit substrate and the pads used for welding on the outer layer of the second circuit substrate can be exposed according to actual needs, thereby improving the accuracy of subsequent secondary circuit production on the basis of playing the role of a protective film.

[0101] The second photosensitive polyimide of this embodiment can be selected to have a suitable thickness according to actual needs, and the thickness range is 5 to 25 μm, and specifically 10 μm in this embodiment.

[0102] The cross-sectional structure of the second circuit substrate obtained after the second photosensitive polyimide is patterned in this embodiment is as follows: Figure 8 As shown, in Figure 8 In the figure, 6 is a second photosensitive polyimide.

[0103] This embodiment S5 includes:

[0104] S51: based on the patterned second photosensitive polyimide, sequentially performing dry film pressing, exposure and development, and circuit etching on the second circuit substrate, so that the base copper on the inner layer of the second circuit substrate forms a second circuit layer;

[0105] S52: performing a dry film removal process on the second circuit substrate formed with the second circuit layer, so that the first circuit layer and the second circuit layer on the second circuit substrate together form a hollow circuit structure, completing secondary circuit production, and obtaining the third circuit substrate.

[0106] Based on the patterned second photosensitive polyimide, the second circuit substrate is pressed into a dry film, and the base copper in the entire second circuit substrate can be exposed according to actual needs, and the base copper position where etching is required can be further selected to be exposed, so as to facilitate the subsequent use of exposure and development, circuit etching and dry film removal processes, so that the base copper forms a second circuit layer; and then combined with the first circuit formed in the previous step to form a hollow circuit structure in the entire multilayer board, so that the target circuit board finally manufactured has the function of transmitting mechanical signals.

[0107] It should be understood that when the first photosensitive polyimide is printed or laminated on both sides of the copper substrate, both sides need to be processed according to the steps S1 to S4 of this embodiment. After step S4, the second circuit substrate is printed or laminated on both sides with the second photosensitive polyimide, and according to step S5, dry film pressing, exposure and development, circuit etching and dry film removal are performed on both sides of the second circuit substrate, and a third circuit substrate with a hollow circuit structure can also be obtained.

[0108] When the first photosensitive polyimide is printed or laminated on only one side of the copper substrate, the side having the first photosensitive polyimide needs to be processed according to the steps S1 to S4 of this embodiment. After step S4, the second circuit substrate has the second photosensitive polyimide printed or laminated on only one side. At this time, in step S5, based on the patterned second photosensitive polyimide, it is necessary to perform dry film pressing, exposure and development, circuit etching and dry film removal on both sides of the second circuit substrate to obtain a third circuit substrate with a hollow circuit structure.

[0109] For printing or laminating the first photosensitive polyimide on one side of the copper substrate, in this embodiment S51, the cross-sectional structure of the second circuit substrate after exposure and development is as follows: Fig. 9 As shown, the cross-sectional structure of the second circuit substrate after circuit etching is as shown Fig.10 As shown, in Fig. 9 and Fig.10 7 is the second dry film (both sides of the second circuit substrate are subjected to dry film pressing, exposure and development, and circuit etching). Similarly, the thickness of the second dry film can be selected according to actual conditions. In this embodiment, 40 μm is specifically selected. In this embodiment S52, the cross-sectional structure of the third circuit substrate obtained after removing the dry film is as follows: Fig.11 shown.

[0110] This embodiment S6 includes:

[0111] The third circuit substrate is subjected to chemical nickel-gold coating to obtain the target circuit board.

[0112] Through chemical nickel-gold, a nickel layer and a gold layer can be formed in the area where the copper is exposed on the third circuit substrate to prevent oxidation of the product surface and obtain a flexible board product that meets actual needs.

[0113] Specifically, the chemical nickel-gold adopts the conventional operation method in the field of flexible board production, and the thickness of the nickel layer and the gold layer finally formed are 0.4 μm and 0.03 μm respectively. The cross-sectional structure of the target circuit board obtained in this embodiment is as follows: Fig.12 As shown, in Fig.12 In the figure, 8 is the nickel-gold layer. Fig.12 It can be seen that the circuit structure in the entire target circuit board presents a special hollow shape, which will deform after being subjected to force. When connected to the sensor, the flexible circuit board can have the function of transmitting three-dimensional mechanical signals.

[0114] Embodiment 2

[0115] The present embodiment provides a thin multi-layer circuit board capable of transmitting force signals, which is manufactured by using the manufacturing method of the thin multi-layer circuit board capable of transmitting force signals described in the first embodiment.

[0116] This embodiment is based on two layers of photosensitive polyimide as the dielectric layer and protective film of the multi-layer flexible circuit board, respectively, and avoids the use of glue as an adhesive material, making the multi-layer flexible circuit board thinner; at the same time, compared with traditional pressed polyimide, photosensitive polyimide has a graphical function and can form a special hollow structure circuit, thereby enabling the flexible circuit board to have the function of transmitting three-dimensional mechanical signals, solving the problem that the traditional multi-layer circuit board uses polyimide and glue as the intermediate dielectric layer and protective film, resulting in the thinning of the circuit board and the transmission of force signals are limited.

[0117] The manufacturing method of the thin multilayer circuit board capable of transmitting force signals in this embodiment is the same as the method steps described in the first embodiment. Therefore, for details not provided in this embodiment, please refer to the first embodiment and the second embodiment. Figures 1 to 12 The specific description of this embodiment will not be repeated in detail.

[0118] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A method for manufacturing a thin multilayer circuit board capable of transmitting force signals, characterized in that: The method comprises: Providing a substrate copper and a first photosensitive polyimide respectively; Combining the substrate copper with the first photosensitive polyimide to form a photosensitive substrate; and patterning the first photosensitive polyimide on the photosensitive substrate; Based on the patterned first photosensitive polyimide, a circuit is fabricated on the photosensitive substrate to obtain a first circuit substrate; Providing a second photosensitive polyimide, combining the second photosensitive polyimide with the first circuit substrate to form a second circuit substrate; and patterning the second photosensitive polyimide on the second circuit substrate; Based on the patterned second photosensitive polyimide, a second circuit substrate is fabricated, so that a hollow circuit structure is formed on the second circuit substrate, thereby obtaining a third circuit substrate; The third circuit substrate is subjected to surface treatment to obtain a target circuit board.

2. The method according to claim 1, characterized in that: The step of combining the substrate copper and the first photosensitive polyimide together to form a photosensitive substrate comprises: The first photosensitive polyimide is printed on one side or both sides of the copper substrate by screen printing or coating to form the photosensitive substrate; or the first photosensitive polyimide is pressed on one side or both sides of the copper substrate by lamination to form the photosensitive substrate.

3. The method according to claim 1, characterized in that: The step of patterning the first photosensitive polyimide on the photosensitive substrate comprises: Pre-curing the first photosensitive polyimide on the photosensitive substrate; According to the preset circuit design data, the pre-cured photosensitive substrate is processed by exposure and development method; The photosensitive substrate after exposure and development is baked according to preset baking parameters to complete the patterning of the first photosensitive polyimide.

4. The method according to claim 3, characterized in that: The first photosensitive polyimide is patterned, and a circuit is fabricated on the photosensitive substrate to obtain a first circuit substrate, comprising: Based on the patterned first photosensitive polyimide, a metal copper layer is sputtered on a side of the photosensitive substrate having the first photosensitive polyimide by a vacuum sputtering method; Laminating a dry film on the side of the photosensitive substrate on which the metal copper layer is sputtered, and patterning the laminated dry film by exposure and development according to the preset circuit design data; Based on the patterned dry film, electroplating copper is performed on the photosensitive substrate laminated with the dry film to form an electroplated copper layer on the side of the photosensitive substrate sputtered with the metal copper layer; The photosensitive substrate after the copper electroplating treatment is sequentially subjected to a dry film removal treatment and a flash etching treatment, so that the metal copper layer and the copper electroplating layer on the photosensitive substrate together form a first circuit layer, completing a circuit production to obtain the first circuit substrate.

5. The manufacturing method according to claim 4, characterized in that: The step of combining the second photosensitive polyimide with the first circuit substrate to form a second circuit substrate comprises: The second photosensitive polyimide is printed on the side of the first circuit substrate having the electroplated copper layer by screen printing or coating to form the second circuit substrate; or, the second photosensitive polyimide is printed on the side of the first circuit substrate having the electroplated copper layer by lamination to form the second circuit substrate.

6. The method according to claim 5, characterized in that: The step of patterning the second photosensitive polyimide on the second circuit substrate comprises: pre-curing the second photosensitive polyimide on the second circuit substrate; According to the preset circuit design data, the second circuit substrate after pre-curing is processed by exposure and development method; and the second circuit substrate after exposure and development is baked to complete the patterning of the second photosensitive polyimide.

7. The method according to claim 4, characterized in that: The second circuit substrate is subjected to secondary circuit manufacturing based on the patterned second photosensitive polyimide, so that a hollow circuit structure is formed on the second circuit substrate to obtain a third circuit substrate, including: Based on the patterned second photosensitive polyimide, the second circuit substrate is subjected to sequential pressing, exposure, development and circuit etching, so that the base copper in the inner layer of the second circuit substrate forms a second circuit layer; The second circuit substrate formed with the second circuit layer is subjected to a dry film removal process, so that the first circuit layer and the second circuit layer on the second circuit substrate together form a hollow circuit structure, and the secondary circuit production is completed to obtain the third circuit substrate.

8. The manufacturing method according to claim 1, characterized in that: The step of performing surface treatment on the third circuit substrate to obtain a target circuit board comprises: The third circuit substrate is subjected to chemical nickel-gold coating to obtain the target circuit board.

9. The production method according to any one of claims 1 to 8, characterized in that: Before combining the substrate copper and the first photosensitive polyimide together, the method further comprises: The substrate copper is laser processed according to preset laser parameters, so that a plurality of exposure alignment holes are formed in the waste area of ​​the substrate copper.

10. A thin multilayer circuit board capable of transmitting force signals, characterized in that: The method is manufactured by the manufacturing method according to any one of claims 1 to 9.

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