Circuit board manufacturing method and circuit board

Abstract

The invention discloses a circuit board manufacturing method and a circuit board. The circuit board manufacturing method comprises the following steps: providing a first flexible core board and a second flexible core board; arranging a bonding layer on one surface of the first flexible core plate, and windowing at the bonding layer to form a first windowing area; a foam layer is arranged in the first windowing area; the second flexible core board is stacked on the face, provided with the bonding layer, of the first flexible core board, buffering pads used for stress are arranged on the face, back to the foam layer, of the first flexible core board and the face, back to the foam layer, of the second flexible core board, and the buffering pads avoid the foam layer in the pressing direction; and providing pressure acting on the buffer pad, and laminating the first flexible core board and the second flexible core board to prepare the circuit board. The circuit board manufacturing method is beneficial for preventing the foam filled in the cavity of the manufactured circuit board from being stressed and creeping in the pressing process.

Description

Technical Field

[0001] The present application relates to the technical field of circuit boards, and particularly relates to a method for manufacturing a circuit board and a circuit board. Background Art

[0002] With the gradual development of the communication electronics field towards high-frequency and high-speed signals, higher requirements are put forward for the transmission loss of high-frequency and high-speed signals of signal lines in printed circuit boards. Specifically, compared with the 112G rate, the loss requirements of the 224G high-speed link pose a huge challenge to the materials used for transmission. However, at present, key materials such as substrates and copper foils have reached the technical bottleneck in improving signals. Since the DK (dielectric constant) of air is much lower than that of current high-speed resin materials, in order to reduce the transmission loss of flexible high-speed boards, using a flexible board structure with cavities is one of the research directions. However, the flexible board substrate does not have rigidity, and during the pressing process to form a circuit board, the area corresponding to the cavity in the flexible board structure will sink, which will affect the height of the cavity, resulting in insufficient height of the cavity, and further causing the transmission loss of the manufactured circuit board to not meet the expectations.

[0003] Among them, since the DK of foam is closest to that of air, a method of filling foam in the cavity is proposed in the related art to solve the above problems. However, during the pressing process to form a circuit board, the foam filled in the cavity will be stressed and creep under the action of high pressure, resulting in deformation of the foam filled in the cavity, so that the size and transmission loss of the manufactured circuit board do not meet the requirements. Summary of the Invention

[0004] The present application aims to at least solve one of the technical problems existing in the prior art. For this purpose, the present application provides a method for manufacturing a circuit board and a circuit board, which are beneficial to preventing the foam filled in the cavity of the circuit board from being stressed and creeping during the pressing process.

[0005] According to the circuit board manufacturing method of the first aspect embodiment of the present application, the following steps are included:

[0006] Provide a first flexible core board and a second flexible core board;

[0007] Set an adhesive layer on one side of the first flexible core board, and open a window at the adhesive layer to form a first window area;

[0008] Set a foam layer in the first window area;

[0009] Stack the second flexible core board on the side of the first flexible core board where the adhesive layer is set, and set buffer pads for bearing force on the side of the first flexible core board facing away from the foam layer and the side of the second flexible core board facing away from the foam layer, and the buffer pads avoid the foam layer along the pressing direction;

[0010] Provide pressure acting on the buffer pad to press the first flexible core board and the second flexible core board to obtain a circuit board.

[0011] According to the circuit board manufacturing method of the embodiments of the present application, it has at least the following beneficial effects: When pressing, the first flexible core board, the first window area, and the second flexible core board enclose a cavity, and the foam layer is accommodated in the cavity to prevent depression at the cavity. Among them, buffer pads for receiving force are provided on the side of the first flexible core board facing away from the foam layer and on the side of the second flexible core board facing away from the foam layer. The buffer pads avoid the foam layer along the pressing direction, so that the pressure generated during pressing mainly acts on the area where the first flexible core board contacts the adhesive layer and the area where the second flexible core board contacts the adhesive layer through the buffer pads. At the same time, both the first flexible core board and the second flexible core board are flexible boards (i.e., flexible printed circuit boards), without rigidity and capable of bending and deforming, so that the unloaded areas of the first flexible core board and the second flexible core board corresponding to the foam layer are not easy to transfer the pressure along the pressing direction during pressing to the foam layer, which is conducive to preventing the foam layer from being stressed and creeping during pressing. In addition, since no adhesive layer is provided for bonding on the side of the foam layer facing the first flexible core board and on the side of the foam layer facing the second flexible core board, there is a certain air gap between the foam layer and the first flexible core board and / or between the foam layer and the second flexible core board, which is equivalent to that the cavity inside the obtained circuit board still has a part filled with air, which is further conducive to reducing transmission loss.

[0012] According to some embodiments of the present application, the setting of the foam layer in the first window area includes:

[0013] At least two positioning parts extending in a direction perpendicular to the pressing direction are spaced apart from each other at the side edge of the foam layer, and the positioning parts are bonded to the area of the first flexible core board exposed in the first window area.

[0014] According to some embodiments of the present application, before setting the foam layer in the first window area, an alignment mark for positioning one of the positioning parts is preset in the area of the first flexible core board exposed in the first window area.

[0015] According to some embodiments of the present application, the adhesive layer is made of pure glue.

[0016] According to some embodiments of the present application, the foam layer is made of a foam material added with a toughening agent.

[0017] According to some embodiments of the present application, the size of the first window area is d1 larger than the size of the foam layer on each side, where 0.1 mm ≤ d1 ≤ 0.15 mm.

[0018] According to some embodiments of the present application, the buffer pad is of an integral structure, and the buffer pad is windowed to form a second windowing area for avoiding the foam layer. The size of the second windowing area is larger than the size of the foam layer by d2 on each side, where 0.1 mm ≤ d2 ≤ 0.15 mm.

[0019] According to some embodiments of the present application, the width of the foam layer is L, where L ≥ 60.55 mm.

[0020] According to some embodiments of the present application, the thickness of the adhesive layer is H1, and the thickness of the foam layer is H2, where -0.015 mm ≤ H1 - H2 ≤ 0.015 mm.

[0021] The circuit board according to the embodiments of the second aspect of the present application is manufactured by using the circuit board manufacturing method according to the embodiments of the first aspect of the present application above.

[0022] The additional aspects and advantages of the present application will be partly given in the following description, partly will become obvious from the following description, or will be understood through the practice of the present application. Description of the Drawings

[0023] The above and / or additional aspects and advantages of the present application will become obvious and easy to understand from the description of the embodiments in conjunction with the following drawings, where:

[0024] Figure 1 is a schematic structural diagram when the area corresponding to the cavity of the flexible board structure with a cavity is sunken;

[0025] Figure 2 is a schematic flow diagram of a circuit board manufacturing method according to an embodiment of the present application;

[0026] Figure 3 is an exploded schematic diagram of a circuit board according to an embodiment of the present application;

[0027] Figure 4 is a schematic structural diagram when riveting is performed on a circuit board according to an embodiment of the present application;

[0028] Figure 5 is Figure 4 a partial structural diagram of the structure shown in;

[0029] Figure 6 is a top view schematic diagram of a first flexible core board and a foam layer according to an embodiment of the present application;

[0030] Figure 7 is Figure 6 a partial structural diagram of the structure shown in;

[0031] Figure 8 is a top view schematic diagram of a buffer pad and a foam layer according to an embodiment of the present application;

[0032] Figure 9 is Figure 8 a partial structural schematic diagram of the structure shown in

[0033] Figure 10 a loss schematic diagram of a circuit board with different widths of cavities under the same line width and line spacing design.

[0034] Reference numerals:

[0035] rivet hole a;

[0036] the first flexible core board 100, the inner layer 110, the outer layer 120;

[0037] the second flexible core board 200;

[0038] the adhesive layer 300, the first windowed area 310;

[0039] the foam layer 400, the positioning portion 410;

[0040] the buffer pad 500, the second windowed area 510;

[0041] the signal line 600;

[0042] the alignment mark 700;

[0043] the rivet 800. Detailed implementation manners

[0044] The embodiments of the present application will be described in detail below. Examples of the embodiments are shown in the drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the drawings are exemplary and are only used to explain the present application and should not be construed as a limitation of the present application.

[0045] In the description of the present application, it should be understood that if orientation descriptions are involved, such as the orientation or positional relationship indicated by up, down, front, back, left, right, etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation of the present application.

[0046] In the description of the present application, if words such as several, greater than, less than, exceeding, above, below, within, etc. appear, where the meaning of several is one or more, the meaning of multiple is two or more, greater than, less than, exceeding, etc. are understood as not including the present number, and above, below, within, etc. are understood as including the present number.

[0047] In the description of the present application, if terms such as first and second appear, they are only used for the purpose of distinguishing technical features, and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features or implicitly specifying the sequence of the indicated technical features.

[0048] In the description of the present application, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and those skilled in the art can reasonably determine the specific meanings of the above terms in the present application in combination with the specific content of the technical solution.

[0049] As the communication electronics field gradually develops towards higher frequencies and speeds of signals, higher requirements are put forward for the transmission loss of high-frequency and high-speed signals of signal lines in printed circuit boards. Specifically, compared with the 112G rate, the loss requirements of the 224G high-speed link pose a huge challenge to the materials used for transmission. However, the current key materials such as substrates and copper foils have reached a technical bottleneck in improving signals. Since the DK (dielectric constant) of air is much lower than that of the current high-speed resin materials, in order to reduce the transmission loss of high-speed flexible boards, using a flexible board structure with cavities is one of the research directions. However, the flexible board substrate does not have rigidity. Referring to Figure 1 , during the process of laminating to form a circuit board, the area of the flexible board structure corresponding to cavity A ( Figure 1 at position B in

[0050] will be sunken, which will affect the height of cavity A, resulting in insufficient height of cavity A, and further causing the transmission loss of the manufactured circuit board to not meet the expectations.

[0051] Therefore, it is urgent to optimize the existing circuit board manufacturing method to solve the above technical problems. The optimized circuit board manufacturing method of the present application will be described in detail below with reference to the accompanying drawings.

[0052] Referring to Figures 2 to 9 , according to the circuit board manufacturing method of the embodiment of the present application, it includes the following steps:

[0053] S100: Provide a first flexible core board 100 and a second flexible core board 200;

[0054] S200: Set an adhesive layer 300 on one side of the first flexible core board 100, and open a window at the adhesive layer 300 to form a first window area 310;

[0055] S300: Set a foam layer 400 within the first window area 310;

[0056] S400: Stack the second flexible core board 200 on the side of the first flexible core board 100 where the adhesive layer 300 is provided. On the side of the first flexible core board 100 facing away from the foam layer 400 and the side of the second flexible core board 200 facing away from the foam layer 400, set buffer pads 500 for bearing force. The buffer pads 500 avoid the foam layer 400 along the pressing direction;

[0057] S500: Provide a pressure acting on the buffer pads 500, and press the first flexible core board 100 and the second flexible core board 200 to obtain a circuit board.

[0058] It should be noted that the above pressing direction is the X direction in the attached drawing.

[0059] During pressing, the first flexible core board 100, the first window area 310, and the second flexible core board 200 enclose to form a cavity, and the foam layer 400 is accommodated in the cavity to prevent depression at the cavity. Among them, buffer pads 500 for bearing force are provided on both the side of the first flexible core board 100 facing away from the foam layer 400 and the side of the second flexible core board 200 facing away from the foam layer 400. The buffer pads 500 avoid the foam layer 400 along the pressing direction, so that the pressure generated during pressing mainly acts on the area where the first flexible core board 100 contacts the adhesive layer 300 and the area where the second flexible core board 200 contacts the adhesive layer 300 through the buffer pads 500. At the same time, both the first flexible core board 100 and the second flexible core board 200 are flexible boards (i.e., flexible printed circuit boards), without rigidity and capable of bending and deforming, so that the non-loaded areas of the first flexible core board 100 and the second flexible core board 200 corresponding to the foam layer 400 are not likely to transfer the pressure along the pressing direction during pressing to the foam layer 400, which is conducive to preventing the foam layer 400 from being stressed and undergoing creep during pressing. In addition, since no adhesive layer 300 is provided for bonding on both the side of the foam layer 400 facing the first flexible core board 100 and the side of the foam layer 400 facing the second flexible core board 200, there is a certain air gap between the foam layer 400 and the first flexible core board 100 and / or between the foam layer 400 and the second flexible core board 200, which is equivalent to that the cavity inside the obtained circuit board still has a part filled with air, and thus is conducive to further reducing the transmission loss.

[0060] In some of the embodiments, the buffer pads 500 are made of fiber paper material, so that the buffer pads 500 do not have fluidity during pressing and have a good overmolding filling effect in the pressing direction, which is conducive to further preventing the pressure along the pressing direction during pressing from being transmitted to the foam layer 400.

[0061] In some of these embodiments, the first flexible core board 100 and the second flexible core board 200 are made of bendable high-speed materials, so that the first flexible core board 100 and the second flexible core board 200 have good flexure performance. Specifically, materials such as modified epoxy resin (MPI), liquid crystal polymer (LCP), and polytetrafluoroethylene (CF4) can be used, which are not limited herein.

[0062] In some of these embodiments, the foam layer 400 can be made of foam plastics. Specifically, materials such as polyethylene foam plastics and polypropylene foam plastics can be used, which are not limited herein.

[0063] In some of these embodiments, the copper foils on the surfaces of the first flexible core board 100 and the second flexible core board 200 are HVLP copper foils with low roughness.

[0064] Refer to Figure 3 、 Figure 4 and Figure 6 In some of these embodiments, a signal line 600 is provided on the first flexible core board 100. To ensure that the transmission loss of the signal line 600 can meet the requirements, the signal line 600 is designed as a stripline structure. Among them, the first flexible core board 100 has an inner layer 110 and an outer layer 120, the signal line 600 is provided in the inner layer 110 of the first flexible core board 100, and both sides of the signal line 600 are shielded with large copper surfaces.

[0065] In some of these embodiments, before laminating the first flexible core board 100 and the second flexible core board 200, the structures of each layer are fixed by riveting to ensure the alignment accuracy between the structures of each layer.

[0066] Specifically, the first flexible core board 100, the second flexible core board 200, the adhesive layer 300, and the buffer pad 500 stacked in sequence are fixed together by rivets 800. Among them, before riveting, rivet holes a for passing the rivets 800 need to be processed on the first flexible core board 100, the second flexible core board 200, the adhesive layer 300, and the buffer pad 500 by a punching machine or a drilling machine.

[0067] It should be noted that the riveting process can be completed by a riveting machine.

[0068] It should be noted that in some other embodiments, before laminating the first flexible core board 100 and the second flexible core board 200, the structures of each layer can also be fixed by thermal fusion.

[0069] Specifically, thermal fusion can be performed by a PIN alignment thermal fusion machine or a CCD alignment thermal fusion machine.

[0070] Refer to Figures 6 to 9, in some of these embodiments, the step of disposing the foam layer 400 within the first windowing area 310 includes:

[0071] At least two positioning portions 410 extending in a direction perpendicular to the pressing direction are spaced apart at the side edges of the foam layer 400, and the positioning portions 410 are bonded to the area of the first flexible core board 100 exposed within the first windowing area 310, thereby facilitating ensuring the position accuracy of the foam layer 400. When bonding, ensure that no bonding material is disposed at the position where the foam layer 400 contacts the signal line 600.

[0072] Specifically, the bonding material can be epoxy resin glue for bonding.

[0073] It should be noted that in some other embodiments, the bonding material can also be hot melt adhesive. Specifically, after placing the foam layer 400 within the first windowing area 310 and adjusting the position of the foam layer 400, heat is released at the positioning portion 410 with a soldering iron to melt the hot melt adhesive and bond the positioning portion 410 and the first flexible core board 100 together to achieve the positioning of the foam layer 400. Among them, the hot melt adhesive does not have adhesiveness before melting, which is convenient for adjusting the position of the foam layer 400.

[0074] Of course, other types of bonding materials can also be used for bonding, which is not limited herein.

[0075] Refer to Figure 6 and Figure 8 , in some of these embodiments, the foam layer 400 is rectangular, and the positioning portions 410 are disposed at the corners of the foam layer 400. Specifically, positioning portions 410 are provided at all four corners of the foam layer 400, thereby facilitating ensuring that the foam layer 400 does not move relative to the first flexible core board 100 before the pressing is completed.

[0076] Refer to Figure 6 and Figure 7 , in some of these embodiments, before disposing the foam layer 400 within the first windowing area 310, a registration mark 700 for positioning one of the positioning portions 410 is preset in the area of the first flexible core board 100 exposed within the first windowing area 310 to facilitate more accurately positioning the foam layer 400.

[0077] Specifically, the positioning portion 410 is rectangular, and the registration mark 700 is an L-shaped registration line to facilitate positioning the positioning portion 410.

[0078] When using hot melt adhesive to bond the positioning portion 410, after aligning the corresponding positioning portion 410 with the registration mark 700, heat is released at the position of the positioning portion 410 with a soldering iron.

[0079] In some of these embodiments, the adhesive layer 300 is made of pure glue. Specifically, the pure glue uses a low DK high-speed material film, which is beneficial to reducing the transmission loss of the manufactured circuit board.

[0080] It should be noted that in some other embodiments, the adhesive layer 300 can also use a prepreg. Among them, the prepreg is mainly composed of resin and reinforcing materials, and the reinforcing materials are divided into several types such as fiberglass cloth, paper base, and composite materials.

[0081] In some of these embodiments, the foam layer 400 is made of a foam material added with a toughening agent, which can enhance the bendability of the foam layer 400, and further enable the manufactured circuit board to have good bendability to adapt to corresponding application scenarios.

[0082] Refer to Figure 5 , in some of these embodiments, considering the alignment accuracy and glue overflow amount of the adhesive layer 300, the size of the first opening area 310 is larger than the size of the foam layer 400 by d1 on each side to ensure that the foam layer 400 will not be affected by the adhesive layer 300 during the lamination process, where 0.1 mm ≤ d1 ≤ 0.15 mm, such as 0.1 mm, 0.11 mm, 0.12 mm, 0.13 mm, 0.14 mm, 0.15 mm, etc.

[0083] Refer to Figure 4 , Figure 5 , Figure 8 and Figure 9 , in some of these embodiments, the buffer pad 500 is an integral structure, and the buffer pad 500 is opened to form a second opening area 510 for avoiding the foam layer 400. Considering the alignment tolerance, the size of the second opening area 510 is larger than the size of the foam layer 400 by d2 on each side to ensure that the buffer pad 500 can avoid the foam layer 400 during lamination, where 0.1 mm ≤ d2 ≤ 0.15 mm, such as 0.1 mm, 0.11 mm, 0.12 mm, 0.13 mm, 0.14 mm, 0.15 mm, etc.

[0084] Refer to Figure 4 , in some of these embodiments, the width of the foam layer 400 is L, where L ≥ 60.55 mm. Through research, it is found that the width of the cavity has an obvious influence on the transmission loss of the manufactured circuit board. Refer to Figure 10, under the same line width and line spacing design, the loss when the width of the cavity is 0.276 inch (7.01 mm) is greater than the loss when the width of the cavity is 2.384 inch (60.55 mm). Therefore, when designing, the width of the foam layer 400 is made greater than or equal to 60.55 mm, which is beneficial to reducing the transmission loss of the manufactured circuit board, and further beneficial to enabling the manufactured circuit board to meet higher signal transmission requirements.

[0085] Referring to Figure 5 , in some of these embodiments, the thickness of the adhesive layer 300 is H1, and the thickness of the foam layer 400 is H2, where -0.015 mm ≤ H1 - H2 ≤ 0.015 mm, such as -0.015 mm, -0.01 mm, -0.005 mm, 0 mm, 0.005 mm, 0.01 mm, 0.015 mm, etc. When designing, considering that if the foam layer 400 is too thick relative to the adhesive layer 300 after lamination, it will cause the problem of pressure loss during lamination, and if the foam layer 400 is too thin relative to the adhesive layer 300, it will cause insufficient cavity thickness and affect the transmission loss of the manufactured circuit board. Therefore, the absolute value of the difference between the thickness of the adhesive layer 300 and the thickness of the foam layer 400 is 0 mm to 0.015 mm.

[0086] Specifically, when -0.015 mm ≤ H1 - H2 < 0 mm, the thickness of the adhesive layer 300 is less than the thickness of the foam layer 400, and when 0 mm < H1 - H2 ≤ 0.015 mm, the thickness of the adhesive layer 300 is greater than the thickness of the foam layer 400.

[0087] In some of these embodiments, to balance the requirements of the bendability and transmission loss of the manufactured circuit board, the thickness range of the foam layer 400 is 0.1 mm to 0.3 mm, such as 0.1 mm, 0.2 mm, 0.3 mm, etc.

[0088] The circuit board according to the embodiment of the present application is manufactured by using the above circuit board manufacturing method.

[0089] In the description of this specification, if descriptions of reference terms such as "one embodiment", "some embodiments", "schematic embodiments", "examples", "specific examples", and "some examples" are involved, it means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic descriptions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0090] Although embodiments of the present application have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present application. The scope of the present application is defined by the claims and their equivalents.

Claims

1. A method for manufacturing a circuit board, characterized in that, The method includes the following steps: Providing a first flexible core board and a second flexible core board; Providing an adhesive layer on one side of the first flexible core board, and forming a first opening area by opening a window in the adhesive layer; Providing a foam layer in the first opening area; Stacking the second flexible core board on the side of the first flexible core board provided with the adhesive layer, and providing buffer pads for bearing force on the side of the first flexible core board facing away from the foam layer and the side of the second flexible core board facing away from the foam layer, wherein the buffer pads avoid the foam layer along the pressing direction; Providing a pressure acting on the buffer pads, and pressing the first flexible core board and the second flexible core board to obtain a circuit board.

2. The circuit board manufacturing method according to claim 1, characterized in that, The step of providing the foam layer in the first opening area includes: Providing at least two positioning parts extending along a direction perpendicular to the pressing direction at intervals on the side edges of the foam layer, and bonding the positioning parts to the area of the first flexible core board exposed in the first opening area.

3. The circuit board manufacturing method according to claim 2, wherein, Before providing the foam layer in the first opening area, presetting an alignment mark for positioning one of the positioning parts in the area of the first flexible core board exposed in the first opening area.

4. The circuit board manufacturing method according to claim 1, characterized in that, The adhesive layer is made of pure glue.

5. The circuit board manufacturing method according to claim 1, wherein The foam layer is made of a foam material added with a toughening agent.

6. The circuit board manufacturing method according to claim 1, wherein The size of the first opening area is larger than the size of the foam layer by d1 on each side, wherein 0.1 mm ≤ d1 ≤ 0.15 mm.

7. The method for manufacturing a circuit board according to claim 1, characterized in that, The buffer pad is of an integral structure, and a second opening area for avoiding the foam layer is formed by opening a window in the buffer pad. The size of the second opening area is larger than the size of the foam layer by d2 on each side, wherein 0.1 mm ≤ d2 ≤ 0.15 mm.

8. The circuit board manufacturing method according to claim 1, wherein, The width of the foam layer is L, wherein L ≥ 60.55 mm.

9. The method for manufacturing a circuit board according to claim 1, characterized in that, The thickness of the adhesive layer is H1, and the thickness of the foam layer is H2, wherein -0.015 mm ≤ H1 - H2 ≤ 0.015 mm.

10. A circuit board, characterized in that, Manufactured by using the circuit board manufacturing method according to any one of claims 1 to 9.

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