Rigid-flex printed circuit board production method

Abstract

The invention relates to a rigid-flex printed circuit board, in particular to a rigid-flex printed circuit board production method, which comprises the following steps of: providing an upper copper foil layer, an upper bonding layer, an upper flexible circuit board, a middle bonding layer, a lower flexible circuit board, a lower bonding layer and a lower copper foil layer; the flexible end of the upper bonding layer is hollowed out, so that an upper layer cavity is formed; the flexible end of the middle bonding layer is hollowed out, so that a middle-layer cavity is formed; the flexible end of the lower bonding layer is hollowed out, so that a lower layer cavity is formed; an upper metal reinforcement is attached to the bottom surface of the flexible end of the upper flexible circuit board; a lower metal reinforcement is attached to the top surface of the flexible end of the lower flexible circuit board; and laminating the processed layers together and pressing to form a semi-finished rigid-flexible printed circuit board, so that the upper metal reinforcement and the lower metal reinforcement are accommodated in the middle-layer cavity. According to the invention, the middle-layer cavity used for accommodating the metal reinforcement is dug between the upper flexible circuit board and the lower flexible circuit board, so that the fracture phenomenon in the subsequent pressing process is avoided.

Description

Technical Field

[0001] The present invention relates to a rigid-flex printed circuit board, and particularly to a production method of a rigid-flex printed circuit board. Background Art

[0002] The description in this part only provides background information related to the disclosure of the present invention, and does not constitute prior art.

[0003] There is a demand for a rigid-flex printed circuit board product. Among them, the upper and lower flexible circuit boards at the flexible end need to be vertically unfolded in the direction away from the other flexible circuit board respectively to form a three-dimensional circuit structure. In the production of a rigid-flex printed circuit board, it is generally necessary to attach a metal reinforcement at the flexible circuit board of the flexible end to improve the structural performance. The existing method is to attach the metal reinforcement on the outer side of the flexible circuit board. However, in the product where the flexible circuit board needs to be vertically unfolded as described above, when pressing in the case of attaching the metal reinforcement on the outer side, it is easy to cause the fracture of the flexible circuit board, affecting the production efficiency and the yield rate.

[0004] It should be noted that the introduction of the technical background above is only for the convenience of clearly and completely explaining the technical solution of the present invention and facilitating the understanding of those skilled in the art. It cannot be considered that the above technical solutions are well-known to those skilled in the art just because these solutions are described in the background art part of the present invention. Summary of the Invention

[0005] The purpose of the present invention is to provide a production method of a rigid-flex printed circuit board, which can avoid the fracture phenomenon in the subsequent pressing process by digging out a middle cavity with sufficient thickness between the upper flexible circuit board and the lower flexible circuit board and arranging the upper metal reinforcement and the lower metal reinforcement therein.

[0006] To achieve the above purpose, the present invention discloses a production method of a rigid-flex printed circuit board, and the production method of the rigid-flex printed circuit board includes:

[0007] Providing an upper copper foil layer, an upper adhesive layer, an upper flexible circuit board, a middle adhesive layer, a lower flexible circuit board, a lower adhesive layer, and a lower copper foil layer;

[0008] Digging out the flexible end of the upper adhesive layer to form an upper cavity; digging out the flexible end of the middle adhesive layer to form a middle cavity; digging out the flexible end of the lower adhesive layer to form a lower cavity;

[0009] The upper flexible circuit board has a top surface and a bottom surface arranged oppositely, and an upper metal reinforcement is attached to the bottom surface of the flexible end of the upper flexible circuit board; the lower flexible circuit board has a top surface and a bottom surface arranged oppositely, and a lower metal reinforcement is attached to the top surface of the flexible end of the lower flexible circuit board;

[0010] Stack the processed upper copper foil layer, upper adhesive layer, upper flexible circuit board, middle adhesive layer, lower flexible circuit board, lower adhesive layer, and lower copper foil layer together in sequence and perform lamination to form a semi-finished rigid-flex printed circuit board. Among them, the upper metal reinforcement and the lower metal reinforcement are accommodated in the middle cavity.

[0011] As a further description of the above technical solution, the thickness of the middle cavity is greater than the thickness of the upper metal reinforcement or the lower metal reinforcement, and the upper metal reinforcement and the lower metal reinforcement are arranged in a staggered manner so that when the upper flexible circuit board and the lower flexible circuit board are in a parallel state, the upper metal reinforcement and the lower metal reinforcement do not contact each other, and the upper metal reinforcement cannot touch the top surface of the lower flexible circuit board, and the lower metal reinforcement cannot touch the bottom surface of the upper flexible circuit board.

[0012] As a further description of the above technical solution, the thickness of the middle cavity is set to 200 - 220um, the thickness of the upper metal reinforcement is set to 150um, and the thickness of the lower metal reinforcement is set to 150um.

[0013] As a further description of the above technical solution, the thickness of the upper cavity is set to 80um, and the thickness of the lower cavity is set to 80um.

[0014] As a further description of the above technical solution, before the step of "stacking the processed upper copper foil layer, upper adhesive layer, upper flexible circuit board, middle adhesive layer, lower flexible circuit board, lower adhesive layer, and lower copper foil layer together in sequence and performing lamination to form a semi-finished rigid-flex printed circuit board", it further includes the steps of pasting an upper resist layer on the bottom surface of the flexible end of the upper adhesive layer and pasting a lower resist layer on the bottom surface of the flexible end of the lower adhesive layer.

[0015] As a further description of the above technical solution, the upper resist layer is arranged to cover the entire area of the upper cavity, and the lower resist layer is arranged to cover the entire area of the lower cavity.

[0016] As a further description of the above technical solution, the upper metal reinforcement and the lower metal reinforcement are subjected to deburring treatment.

[0017] As a further description of the above technical solution, the upper adhesive layer, the middle adhesive layer, and the lower adhesive layer are all set as low-fluidity adhesive layers to limit glue overflow.

[0018] As a further description of the above technical solution, both the upper flexible circuit board and the lower flexible circuit board are processed by high-ductility rolled copper and graphic electroplating processes, so as to improve the compressive performance of the upper flexible circuit board and the lower flexible circuit board.

[0019] As a further description of the above technical solution, in the step of "stacking and laminating the processed upper copper foil layer, the upper adhesive layer, the upper flexible circuit board, the middle adhesive layer, the lower flexible circuit board, the lower adhesive layer, and the lower copper foil layer together in sequence and performing lamination to form a semi-finished rigid-flex printed circuit board", the lamination is set to a steel-to-steel lamination method, and no auxiliary material can be filled between the steel plate and the rigid-flex printed circuit board. After this step, it further includes steps of drilling, electroplating, processing circuits, processing solder resist, surface treatment, and opening the cover for the semi-finished rigid-flex printed circuit board to form a finished rigid-flex printed circuit board.

[0020] By means of the above technical solution, the beneficial effects of the present invention are as follows:

[0021] In the production method of the rigid-flex printed circuit board of the present invention, a middle cavity with a sufficient thickness can be dug out from the middle adhesive layer between the upper flexible circuit board and the lower flexible circuit board, so that the middle adhesive layer yields space for accommodating the upper metal reinforcement and the lower metal reinforcement, and the upper metal reinforcement and the lower metal reinforcement are installed in the corresponding middle cavities. Compared with the existing method of attaching metal reinforcements to the outer surfaces of the upper flexible circuit board and the lower flexible circuit board, it avoids the situation of touching the metal reinforcements and causing fractures during the subsequent lamination process, and indirectly improves the yield rate.

[0022] To further understand the features and technical content of the present invention, please refer to the following detailed description and diagrams of the present invention. However, the provided diagrams are only for reference and illustration, and are not used to limit the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of this specification or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments recorded in this specification. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0024] Figure 1 It is a schematic diagram of a production method of a rigid-flex printed circuit board provided by an embodiment of this specification;

[0025] In the figure: 1. Upper copper foil layer; 2. Upper adhesive layer; 21. Upper cavity; 22. Upper resist layer; 3. Upper flexible printed circuit board; 31. Upper metal reinforcement; 4. Middle adhesive layer; 41. Middle cavity; 5. Lower flexible printed circuit board; 51. Lower metal reinforcement; 6. Lower adhesive layer; 61. Lower cavity; 62. Lower resist layer; 7. Lower copper foil layer. Specific embodiments

[0026] In order to enable those skilled in the art to better understand the technical solutions in this specification, the following will, in conjunction with the accompanying drawings in the embodiments of this specification, clearly and completely describe the technical solutions in the embodiments of this specification. Obviously, the described embodiments are only a part of the embodiments of this specification, rather than all of them. Based on the embodiments in this specification, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of this specification.

[0027] The following are specific embodiments to illustrate the embodiments of the present invention. Those skilled in the art can understand the advantages and effects of the present invention from the content disclosed in this specification. The present invention can be implemented or applied through other different specific embodiments, and various details in this specification can also be modified and changed based on different viewpoints and applications without departing from the concept of the present invention. In addition, the drawings of the present invention are only for simple schematic illustration and are not drawn according to actual dimensions. The following embodiments will further detail the related technical content of the present invention, but the disclosed content is not intended to limit the protection scope of the present invention.

[0028] It should be understood that although terms such as "first", "second", and "third" may be used herein to describe various components or signals, these components or signals should not be limited by these terms. These terms are mainly used to distinguish one component from another, or one signal from another. In addition, the term "or" used herein should, depending on the actual situation, possibly include any one or a combination of more of the associated listed items.

[0029] Please refer to Figure 1 , which is a method for producing a rigid-flex printed circuit board according to this embodiment. The method for producing a rigid-flex printed circuit board includes:

[0030] Provide an upper copper foil layer 1, an upper adhesive layer 2, an upper flexible printed circuit board 3, a middle adhesive layer 4, a lower flexible printed circuit board 5, a lower adhesive layer 6, and a lower copper foil layer 7;

[0031] Hollow out the flexible end of the upper adhesive layer 2 to form an upper cavity 21; hollow out the flexible end of the middle adhesive layer 4 to form a middle cavity 41; hollow out the flexible end of the lower adhesive layer 6 to form a lower cavity 62;

[0032] The upper flexible circuit board 3 has a top surface and a bottom surface that are oppositely arranged, and a metal reinforcement 31 is attached to the bottom surface of the flexible end of the upper flexible circuit board 3; the lower flexible circuit board 5 has a top surface and a bottom surface that are oppositely arranged, and a lower metal reinforcement 51 is attached to the top surface of the flexible end of the lower flexible circuit board 5.

[0033] The processed upper copper foil layer 1, upper adhesive layer 2, upper flexible circuit board 3, middle adhesive layer 4, lower flexible circuit board 5, lower adhesive layer 6, and lower copper foil layer 7 are sequentially laminated and bonded together and then pressed to form a semi-finished rigid-flex printed circuit board. Among them, the upper metal reinforcement 31 and the lower metal reinforcement 61 are accommodated in the middle cavity 41.

[0034] With the above structure, a middle cavity 41 with a sufficient thickness is dug out from the middle adhesive layer 4 between the upper flexible circuit board 3 and the lower flexible circuit board 5, so that the middle adhesive layer 4 yields a space for accommodating the upper metal reinforcement 31 and the lower metal reinforcement 51, and the upper metal reinforcement 31 and the lower metal reinforcement 51 are installed in the corresponding middle cavities 41. Compared with the existing method of attaching metal reinforcements to the outer surfaces of the upper flexible circuit board 3 and the lower flexible circuit board 5, both the upper flexible circuit board 3 and the lower flexible circuit board 5 can be respectively mounted with electronic components, increasing the layout space. It also avoids the situation where the insufficient space reserved above and below the upper metal reinforcement 31 and the lower metal reinforcement 51 causes the upper flexible circuit board 3 and the lower flexible circuit board 5 to be broken due to excessive pressure from the metal reinforcements during the subsequent pressing process, indirectly improving the yield rate. Specifically, in the subsequent processing, it is necessary to first remove the adhesive layers on the outer sides of the flexible ends of the upper flexible circuit board 3 and the lower flexible circuit board 5, and perform steel-to-steel pressing operation on the entire semi-finished rigid-flex printed circuit board after laminating. During the pressing process, if the solid metal reinforcements on the outer sides of the upper flexible circuit board 3 and the lower flexible circuit board 5 are excessively physically squeezed, it is very likely that the upper flexible circuit board 3 and the lower flexible circuit board 5 will break. However, in this embodiment, the above-mentioned excessive squeezing of the metal reinforcements on the outer walls of the upper flexible circuit board 3 and the lower flexible circuit board 5 is avoided, and the metal reinforcements are hidden in the middle cavity 41 between the upper flexible circuit board 3 and the lower flexible circuit board 5. On the basis of maintaining the structural strength brought by the reinforcement of the upper flexible circuit board 3 and the lower flexible circuit board 5, it is also possible to protect the integrity of the entire board.

[0035] Further, the thickness of the middle cavity 41 is greater than the thickness of the upper metal reinforcement 31 or the lower metal reinforcement 51, and the upper metal reinforcement 31 and the lower metal reinforcement 51 are arranged in a staggered manner, so that in the state where the upper flexible circuit board 3 and the lower flexible circuit board 5 are parallel, the upper metal reinforcement 31 and the lower metal reinforcement 51 do not contact each other, the upper metal reinforcement 31 cannot touch the top surface of the lower flexible circuit board 5, and the lower metal reinforcement 51 cannot touch the bottom surface of the upper flexible circuit board 3. Specifically, through the limitation of the above thickness, the outer surfaces of the upper metal reinforcement 31 and the lower metal reinforcement 51 can be protected from being squeezed and broken, and the inner wall will not be excessively squeezed and broken, further ensuring the integrity of the entire rigid-flex printed circuit board. Specifically, the thickness of the middle cavity 41 is set to 200 - 220um, the thickness of the upper metal reinforcement 31 is set to 150um, and the thickness of the lower metal reinforcement 51 is set to 150um. That is to say, in this embodiment, in addition to accommodating the corresponding upper metal reinforcement 31 and lower metal reinforcement 51, the middle cavity 41 has a relatively large remaining space, avoiding the upper flexible circuit board 3 and the lower flexible circuit board 5 from being damaged by excessive pressure. Of course, in some other embodiments, the thickness of the middle cavity 41 can be set as needed.

[0036] Further, the thickness of the upper cavity is set to 80um, and the thickness of the lower cavity is set to 80um, so that there is a certain controllable gap between the outer walls of the upper metal reinforcement 31 and the lower metal reinforcement 51 and the upper adhesive layer 2 or the lower adhesive layer 6 in this embodiment, avoiding accidental adhesion.

[0037] Further, before the step of "stacking and laminating the processed upper copper foil layer 1, upper adhesive layer 2, upper flexible circuit board 3, middle adhesive layer 4, lower flexible circuit board 5, lower adhesive layer 6, and lower copper foil layer 7 together in sequence and performing lamination to form a semi-finished rigid-flex printed circuit board", it further includes the steps of pasting an upper resist layer 22 on the bottom surface of the flexible end of the upper adhesive layer 2 and pasting a lower resist layer 62 on the bottom surface of the flexible end of the lower adhesive layer 6. Specifically, through the setting of the upper resist layer 22, it can be avoided that the upper flexible circuit board 3 accidentally adheres to the upper adhesive layer 2 before the flexible end of the upper adhesive layer 2 is cut, affecting the product quality. The same applies to the lower resist layer 62.

[0038] Further, the upper resist layer 22 is arranged to cover the entire area of the upper cavity 21, and the lower resist layer 62 is arranged to cover the entire area of the lower cavity 61. Specifically, through the setting that the upper resist layer 22 has a sufficient extension length, it can ensure the full coverage of the upper flexible circuit board 3 and avoid any possibility of adhesion. The same applies to the lower resist layer 62.

[0039] Further, the upper metal reinforcement 31 and the lower metal reinforcement 51 are deburred to make the surfaces and edges of the upper metal reinforcement 31 and the lower metal reinforcement 51 smoother and flatter, avoiding the upper metal reinforcement 31 or the lower metal reinforcement 51 touching the corresponding upper flexible circuit board 3 or lower flexible circuit board 5 in case of an accident, resulting in scratches or even cracks on the inner upper flexible circuit board 3 and lower flexible circuit board 5.

[0040] Further, after the step of "stacking and laminating the processed upper copper foil layer 1, upper adhesive layer 2, upper flexible circuit board 3, middle adhesive layer 4, lower flexible circuit board 5, lower adhesive layer 6, and lower copper foil layer 7 together and pressing them to form a semi-finished rigid-flex printed circuit board", it further includes steps of drilling, electroplating, circuit processing, solder resist processing, surface treatment, and opening the cover on the semi-finished rigid-flex printed circuit board to form a finished flexible-rigid printed circuit board. Specifically, drilling means drilling on the rigid board end at the other end of the flexible end of the semi-finished rigid-flex printed circuit board, and then forming a layer of conductive metal on the surface, and then performing circuit processing to meet the electrical connection requirements, coating a solder resist layer and then surface treatment, cutting and forming after opening the cover, and cleaning to produce the finished flexible-rigid printed circuit board.

[0041] The content disclosed above is only the preferred and feasible embodiments of the present invention, and does not limit the scope of the patent application of the present invention. Therefore, all equivalent technical changes made by using the content of the specification and drawings of the present invention are included in the scope of the patent application of the present invention.

[0042] The various embodiments in this specification are described in a progressive manner. For the same or similar parts between the various embodiments, reference can be made to each other. Each embodiment focuses on the differences from other embodiments.

[0043] Although the present application is depicted through embodiments, those of ordinary skill in the art know that the present application has many variations and changes without departing from the spirit of the present application. It is hoped that the appended embodiments include these variations and changes without departing from the present application.

Claims

1. A method for producing a rigid-flexible printed circuit board, characterized in that: The method for producing a rigid-flexible printed circuit board comprises: Providing an upper copper foil layer, an upper adhesive layer, an upper flexible circuit board, a middle adhesive layer, a lower flexible circuit board, a lower adhesive layer, and a lower copper foil layer; The flexible end of the upper adhesive layer is hollowed out to form an upper cavity; the flexible end of the middle adhesive layer is hollowed out to form a middle cavity; the flexible end of the lower adhesive layer is hollowed out to form a lower cavity; The upper flexible circuit board has a top surface and a bottom surface that are arranged oppositely, and an upper metal reinforcement is attached to the bottom surface of the flexible end of the upper flexible circuit board; the lower flexible circuit board has a top surface and a bottom surface that are arranged oppositely, and a lower metal reinforcement is attached to the top surface of the flexible end of the lower flexible circuit board; The processed upper copper foil layer, the upper adhesive layer, the upper flexible circuit board, the middle adhesive layer, the lower flexible circuit board, the lower adhesive layer, and the lower copper foil layer are stacked together in sequence and pressed together to form a semi-finished rigid-flexible printed circuit board, wherein the upper metal reinforcement and the lower metal reinforcement are accommodated in the middle layer cavity.

2. The method for producing a rigid-flexible printed circuit board according to claim 1, characterized in that: The thickness of the middle-layer cavity is greater than the thickness of the upper metal reinforcement or the lower metal reinforcement, and the upper metal reinforcement and the lower metal reinforcement are staggered so that when the upper flexible circuit board is parallel to the lower flexible circuit board, the upper metal reinforcement and the lower metal reinforcement do not contact each other, the upper metal reinforcement cannot touch the top surface of the lower flexible circuit board, and the lower metal reinforcement cannot touch the bottom surface of the upper flexible circuit board.

3. The method for producing a rigid-flexible printed circuit board according to claim 1, characterized in that: The thickness of the middle cavity is set to 200-220um, the thickness of the upper metal reinforcement is set to 150um, and the thickness of the lower metal reinforcement is set to 150um.

4. The method for producing a rigid-flexible printed circuit board according to claim 1, characterized in that: The thickness of the upper cavity is set to 80 um, and the thickness of the lower cavity is set to 80 um.

5. The method for producing a rigid-flexible printed circuit board according to claim 1, characterized in that: Before the step of "stacking and laminating the processed upper copper foil layer, the upper adhesive layer, the upper flexible circuit board, the middle adhesive layer, the lower flexible circuit board, the lower adhesive layer and the lower copper foil layer in sequence to form a semi-finished rigid-flexible printed circuit board", it also includes the steps of laminating an upper resistive layer on the bottom surface of the flexible end of the upper adhesive layer and laminating a lower resistive layer on the bottom surface of the flexible end of the lower adhesive layer.

6. The method for producing a rigid-flexible printed circuit board according to claim 5, characterized in that: The upper resist layer covers the entire area of ​​the upper cavity, and the lower resist layer covers the entire area of ​​the lower cavity.

7. The method for producing a rigid-flexible printed circuit board according to claim 1, characterized in that: The upper metal reinforcement and the lower metal reinforcement are subjected to burr-free treatment.

8. The method for producing a rigid-flexible printed circuit board according to claim 1, characterized in that: The upper adhesive layer, the middle adhesive layer and the lower adhesive layer are all configured as adhesive layers with low fluidity to limit glue overflow.

9. The method for producing a rigid-flexible printed circuit board according to claim 1, characterized in that: The upper flexible circuit board and the lower flexible circuit board are both processed by high-ductility rolled copper and pattern electroplating processes, so that the compression resistance of the upper flexible circuit board and the lower flexible circuit board is improved.

10. The method for producing a rigid-flexible printed circuit board according to claim 1, characterized in that: In the step of "stacking and laminating the processed upper copper foil layer, the upper adhesive layer, the upper flexible circuit board, the middle adhesive layer, the lower flexible circuit board, the lower adhesive layer and the lower copper foil layer in sequence to form a semi-finished rigid-flexible printed circuit board", the pressing is set to a steel-to-steel pressing method, and no auxiliary materials can be filled between the steel plate and the rigid-flexible printed circuit board. After the step, it also includes the steps of drilling, electroplating, processing circuits, processing solder resist, surface treatment and uncovering the semi-finished rigid-flexible printed circuit board to form a finished flexible printed circuit board.

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