Semi-bonded flexible circuit board and manufacturing method thereof

Abstract

The present invention provides a semi-bonded flexible circuit board and a manufacturing method thereof, belonging to the technical field of printed circuit boards. The flexible circuit board comprises M soft boards, one end of which is bonded to form a multi-layer bonded mother board, and the other end of which is provided with N separate sub-boards. The manufacturing method of the flexible circuit board comprises a plurality of steps such as laser depth control processing and electroplating copper blocks. The flexible circuit board of the present invention is a soft board as a whole, which saves more space than the structure of hard boards at both ends and a soft board in the middle commonly used in the industry. The structure, quantity and direction of the sub-boards can be adjusted according to actual conditions to meet the circuit requirements of different positions and directions, and the copper plating design can improve the problem of folding of the board caused by the thinness of the soft board. On the other hand, in the manufacturing method, the present invention forms a conductive structure of multiple copper blocks through a copper plating process to replace the common copper ring structure, and the conductive resistance value increases with the increase of the contact area, thereby improving the high voltage resistance performance of the ultra-long flexible circuit board.

Description

Technical Field

[0001] The invention relates to the technical field of printed circuit boards, and in particular to a semi-adhesive flexible circuit board and a manufacturing method thereof. Background Art

[0002] With the rapid development of electronic technology in recent years, after the integrated assembly of many large industrial control equipment module connectors, the external dimensions of some flexible areas have exceeded 650mm; the flexible area needs to be designed with multiple soft boards, which not only considers the bonding strength and electrical connection reliability between the soft boards, but also ensures the feasibility of assembly in a small space. Usually, soft boards are used to connect and conduct PCB boards. At present, the industry mostly uses a rigid board and a flexible board combined with a separate structure to achieve the connection function, but the rigid board increases the overall board thickness, and when the multiple PCB boards to be connected are not in the same direction, multiple rigid and flexible combined separate boards are required to connect and conduct the PCB boards, resulting in an increase in assembly space.

[0003] In the manufacturing process of multi-layer flexible circuit boards, double-sided electrical connection function is usually achieved by drilling through holes in the flexible board and plating copper through the holes. However, since the single-layer flexible board material is thin, during the drilling and copper plating process, the hole ring is easily broken due to stress, resulting in board folding, and product reliability cannot be guaranteed.

[0004] After the production of multi-layer ultra-long flexible circuit boards, the finished products must pass high-voltage resistance tests. Common test standards include high-voltage resistance of 5kv and on-resistance of less than 150mΩ. However, due to the limitations of the existing process level, in order to ensure that the surface copper meets the etching process, the size range of the hole copper can only be between 25-35um. Since the through hole has the same board area, the smaller the contact area, the smaller the resistance. Therefore, the hole ring with too small a contact area is difficult to withstand high-voltage impact, and the hole ring is prone to breakage during high-voltage testing. Summary of the invention

[0005] In order to overcome the problems existing in the related art, one of the purposes of the present invention is to provide a semi-bonded flexible circuit board, which is a soft board as a whole, which saves more space. The structure, number and direction of the sub-boards can be adjusted according to actual conditions to adapt to the circuit requirements of different positions and directions. The design of the electroplated copper block can improve the problem of board folding caused by the soft board being too thin.

[0006] A semi-bonded flexible circuit board, comprising M soft boards, one end of the soft boards being bonded to form a multi-layer bonded mother board, and the other end of the soft boards being arranged as N separate sub-boards; M and N are both integers greater than 1, and M is greater than or equal to N;

[0007] The flexible board and the adhesive sheet are both provided with a conducting area, and the conducting area is provided with a plurality of square grooves for arranging copper blocks as a conducting structure.

[0008] The overall soft board design is adopted, which saves more space than the commonly used hard board at both ends and soft board in the middle structure in the industry; the setting of multi-layer soft boards can improve the electrical performance and signal transmission capacity of the circuit board. One end of the soft board is glued to form a multi-layer adhesive motherboard, and the motherboard is connected to the PCB board alone. The superposition of the multi-layer soft board and the adhesive sheet increases the rigidity and strength of the overall structure and provides more stable mechanical support. The other end is a plurality of separate sub-boards, and the plurality of sub-boards are respectively connected to a plurality of PCB boards. Since the soft board and the adhesive sheet in the sub-board are both flexible and bendable substrates, the connection direction of the sub-board can be freely adjusted within a certain range, and the structure and hierarchy of the sub-board can also be set as needed. M is greater than or equal to N, ensuring that each sub-board corresponds to at least one soft board, which helps to achieve a more balanced circuit layout and load distribution. This structure not only maintains the original connection function of the circuit board, but also can adapt to complex circuit design requirements, improves the problem that common single boards can only be connected to PCB boards in the same direction, and saves costs;

[0009] The common conduction method between layers in the circuit board is to set up circular conduction holes. The present application optimizes the conduction method to connect through square copper blocks. Since the overall thickness of the copper block is greater than the thickness of the copper layer of the conduction hole, the problem of board folding caused by the thin soft board can be improved. At the same time, the resistance value is increased by increasing the contact area, thereby meeting the high voltage resistance requirements.

[0010] In a preferred technical solution of the present invention, the M soft boards are stacked by adhesive sheets, and the adhesive sheets are bonded in two ways, one is complete bonding, and the other is partial windowing and partial bonding.

[0011] The partially open window and partially bonded design provides greater flexibility and adjustability. The open window area allows specific lines or pads to be exposed for easy welding and electrical connection, while partial bonding maintains the structural integrity of the circuit board.

[0012] In a preferred technical solution of the present invention, the motherboard is composed of M soft boards and M-1 adhesive sheets, and the N sub-boards are composed of M soft boards and MN adhesive sheets;

[0013] The sub-board has two structures, one of which is formed by a single soft board independently, and the other is composed of P soft boards and P-1 adhesive sheets stacked together; P is an integer greater than 1, and P is less than M.

[0014] Two different daughter board structures are provided. The daughter board formed by a single flexible board is suitable for applications that do not require high circuit complexity. The daughter board composed of multiple flexible boards and adhesive sheets is suitable for applications that need to integrate more circuit components. It allows you to choose the appropriate daughter board structure according to different application environments and functional requirements.

[0015] A second object of the present invention is to provide a method for manufacturing a semi-bonded flexible circuit board, comprising the following steps:

[0016] FPC production: M FPCs are stacked at one end to form a multi-layer bonded motherboard, and the other end is set as N separate daughterboards, M≥N>1; windows are opened on the FPCs to set conduction areas, and copper is plated in the conduction areas;

[0017] Making the adhesive sheet: cutting the adhesive layer, drilling positioning holes and making the adhesive sheet;

[0018] Overall lamination: laminating the soft board and the adhesive sheet.

[0019] The copper plating step provides the circuit board with a copper block as a conductive structure, and the traditional conductive hole is no longer designed, which ensures stable signal transmission while reducing the expansion and cracking of the conductive hole; by pre-drilling positioning holes, the adhesive sheet and the soft board are accurately aligned during the lamination process, reducing the adjustment time of the alignment process and improving the overall production efficiency. The precise alignment also ensures the consistency between the layers in the multi-layer structure, reduces the risk of short circuit or open circuit caused by inter-layer misalignment, and reduces the scrap rate; through lamination, the soft board and the adhesive sheet are tightly bonded to form a stable multi-layer structure, which makes the circuit board not easily deformed and damaged when subjected to external forces, thereby enhancing the durability and reliability of the product.

[0020] In a preferred technical solution of the present invention, when M is equal to 3, N is equal to 2, and P is equal to 2, the following specific steps are included:

[0021] S1. The first soft board is made to form the inner layer L1 / 2: After cutting the soft board and applying dry film, a window is opened in the conductive area, and a laser is used to perform controlled depth processing at the window position to form a square groove, and copper is plated in the square groove as a conductive structure;

[0022] S2, making the first adhesive sheet: cutting the adhesive layer and drilling positioning holes, the adhesive layer is preferably a double-sided adhesive-coated PI material;

[0023] S3, the second and third soft boards are made to form the inner layer L3 / 6: two soft boards are cut and dry film is applied, and the two soft boards are pressed together by using the first adhesive sheet;

[0024] S4, making the second adhesive sheet: cutting the adhesive layer, drilling positioning holes, and using laser cutting to retain the adhesive area;

[0025] S5, finished product production: the inner layer L1 / 2 and the inner layer L3 / 6 are pressed together through the second adhesive sheet.

[0026] The parameters of M=3, N=2, and P=2 are selected because they are representative: the circuit board can be provided with multiple sub-boards, and the minimum value is set to 2 sub-boards. The sub-boards have two structures, single-layer and multi-layer, and one sub-board of each structure is provided. Among them, the minimum value of the multi-layer structure of the sub-board is a double-layer soft board, so the minimum value is set to a structure of 2 soft boards and 1 adhesive sheet, and finally 2 sub-boards are pressed together as a whole, which requires a total of 2 adhesive sheets; laser controlled deep processing ensures the precise depth and shape of the square groove, and the electroplated copper block is used as the conductive structure instead of the conductive hole as the conductive structure in the existing technology, so as to improve the folding of the plate caused by thermal expansion cracking of the conductive hole. The problem is that the adhesive sheet is trimmed and cut according to the structural requirements, the adhesive area is reserved, the inner layer L1 / 2 is used as a sub-board of the single-layer soft board structure, and the inner layer L3 / 6 is used as a sub-board of the multi-layer soft board structure. The sub-boards are pre-made, and then multiple sub-boards are pressed together with adhesive sheets to achieve modular design, making the production process more flexible. The number and configuration of sub-boards can be quickly adjusted according to different application requirements, thereby improving design adaptability and production flexibility. The pre-made sub-boards can be carried out in parallel to shorten the overall production cycle. The final multi-layer structure can adapt to more complex circuit designs, provide more inter-layer connection options, and help to achieve a more compact and efficient circuit layout.

[0027] In a preferred technical solution of the present invention, the window position is subjected to controlled depth processing using a laser, and the steps include: the upper surface of the first soft board is the A surface, and the lower surface is the B surface, a window is etched in the A surface pad area to expose the soft board interlayer material, and the A surface interlayer material is processed using a laser to form the square groove, and the bottom surface of the square groove is the upper surface of the B surface copper layer.

[0028] Etching windows provides a precise processing area for laser controlled depth processing. The square groove is processed by laser and the depth is controlled until the bottom of the square groove is the upper surface of the B-side copper layer exposed. Copper is then plated in the square groove to ensure circuit continuity.

[0029] In a preferred technical solution of the present invention, the copper plating step in S1 is as follows: the B surface is protected by a dry film, a copper plating process edge is reserved, and a base copper plate is used as a mold to reinforce the copper plating process; a copper block is electroplated in the square groove until the formed copper block fills the square groove, and the thickness of the copper block is required to be ≥90UM; if the thickness requirement cannot be met by a single electroplating, a plurality of positions of the same size are set at the process edge for additional copper plating to form a reference piece, which is used for slicing measurement to confirm the copper thickness after a single copper plating.

[0030] Using the base copper plate as a mold enhances the stability of the soft board electroplating process, prevents deformation of the soft board, and ensures uniform electroplating layer. The thickness of the copper block ensures both the electrical conductivity and mechanical properties while also improving the strength and stability of the soft board. The thickness requirement of greater than or equal to 90UM is to ensure that the copper block can fill the square groove and withstand subsequent use and processing with sufficient strength. The copper block is electroplated synchronously on the reserved process edge as a reference, and the actual thickness of the copper block is confirmed by slicing to ensure product reliability.

[0031] In a preferred technical solution of the present invention, when the copper plating process in S1 is applied on the adhesive sheet, the flexible board and the adhesive sheet are internally conductively connected via the copper blocks on the flexible board and the copper blocks on the adhesive sheet.

[0032] Conventional multi-layer flexible boards and the inner layer of adhesive sheets are connected by vias. The present invention uses multiple copper blocks to replace the common copper ring conduction structure, so the resistance value increases with the increase of contact area, thereby improving the product high voltage resistance test pass rate.

[0033] The beneficial effects of the present invention are:

[0034] The present invention provides a semi-adhesive flexible circuit board, which is a soft board as a whole, and saves more space than the structure of hard boards at both ends and a soft board in the middle commonly used in the industry; the structure, number and direction of the sub-boards can be adjusted according to actual conditions to adapt to the circuit requirements of different positions and directions, improving the problem that common single boards can only be connected to PCB boards in the same direction, saving costs; the design of the copper block can improve the problem of plate folding caused by the soft board being too thin, and at the same time, the resistance value is increased by increasing the contact area to meet the high voltage resistance requirements; the adhesive sheet adopts a double-sided adhesive layer, which is more bendable and has more outstanding bonding performance.

[0035] The present application also provides a method for manufacturing a semi-adhesive flexible circuit board, which improves the problem of board folding caused by the thinness of the flexible board by electroplating copper blocks; the copper plating process forms a conductive structure of multiple copper blocks to replace the common copper ring structure, and the conductive resistance value increases with the increase of contact area, thereby improving the high-voltage resistance of the ultra-long flexible circuit board; through laser depth control technology, the accuracy of the copper plating process is ensured to meet product reliability; the window position of the adhesive sheet is flexibly determined by the position and structure of the sub-board, which improves the structural flexibility to adapt to circuit requirements in different positions and directions; the optimized manufacturing process reduces material waste and reduces production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a structural schematic diagram of a flexible printed circuit board in the prior art;

[0037] Figure 2 It is a structural schematic diagram of a typical embodiment of a semi-bonded flexible circuit board of the present invention;

[0038] Figure 3 It is a structural schematic diagram of a flexible board via hole in the prior art;

[0039] Figure 4 It is a schematic structural diagram of a copper block of a semi-bonded flexible circuit board of the present invention;

[0040] Figure 5 is a schematic structural diagram of another typical embodiment of a semi-bonded flexible circuit board of the present invention;

[0041] Figure 6 It is a structural comparison diagram of the via ring in the prior art and the copper block in the semi-bonded flexible circuit board of the present invention;

[0042] Figure 7 It is a schematic flow chart of a typical embodiment of a method for manufacturing a semi-bonded flexible circuit board of the present invention;

[0043] Figure 8 It is a schematic diagram of laser depth control processing of the manufacturing method of the semi-bonded flexible circuit board of the present invention;

[0044] Fig. 9 It is one of the auxiliary mold schematic diagrams of the method for manufacturing a semi-bonded flexible circuit board of the present invention;

[0045] Fig.10 This is the second schematic diagram of the auxiliary mold of the method for manufacturing the semi-bonded flexible circuit board of the present invention;

[0046] Fig.11 It is a schematic diagram of the process edge slicing area of ​​the manufacturing method of the semi-bonded flexible circuit board of the present invention;

[0047] Fig.12 It is a schematic diagram of double-sided adhesive coating PI-1 of the manufacturing method of the semi-adhesive flexible circuit board of the present invention;

[0048] Fig.13 It is a schematic diagram of the positions of the pads and gold fingers in the method for manufacturing the semi-bonded flexible circuit board of the present invention;

[0049] Fig.14 It is a schematic diagram of double-sided glue coating PI-2 of the manufacturing method of the semi-adhesive flexible circuit board of the present invention;

[0050] Fig.15 It is a schematic diagram of the improvement effect of the folding problem of the semi-bonded flexible circuit board manufacturing method of the present invention;

[0051] Fig.16 It is a physical picture of the finished product of the present invention. DETAILED DESCRIPTION

[0052] The preferred embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although the preferred embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to make the present invention more thorough and complete, and to fully convey the scope of the present invention to those skilled in the art.

[0053] With the rapid development of electronic technology in recent years, after the integrated assembly of many large industrial control equipment module connectors, the external dimensions of some flexible areas have exceeded 650mm; the flexible area needs to be designed with multiple soft boards, which not only considers the bonding strength and electrical connection reliability between the soft boards, but also ensures the feasibility of assembly in a small space. Usually, soft boards are used to connect and conduct PCB boards. At present, the industry mostly uses a rigid board and a flexible board combined with a separate structure to achieve the connection function, but the rigid board increases the overall board thickness, and when the multiple PCB boards to be connected are not in the same direction, multiple rigid and flexible combined separate boards are required to connect and conduct the PCB boards, resulting in an increase in assembly space.

[0054] In the manufacturing process of multi-layer flexible circuit boards, double-sided electrical connection function is usually achieved by drilling through holes in the flexible board and plating copper through the holes. However, since the single-layer flexible board material is thin, during the drilling and copper plating process, the hole ring is easily broken due to stress, resulting in board folding, and product reliability cannot be guaranteed.

[0055] After the production of multi-layer ultra-long flexible circuit boards, the finished products must pass high-voltage resistance tests. Common test standards include high-voltage resistance of 5kv and on-resistance of less than 150mΩ. However, due to the limitations of the existing process level, in order to ensure that the surface copper meets the etching process, the size range of the hole copper can only be between 25-35um. Since the through hole has the same board area, the smaller the contact area, the smaller the resistance. Therefore, the hole ring with too small a contact area is difficult to withstand high-voltage impact, and the hole ring is prone to breakage during high-voltage testing.

[0056] Based on this, the present application provides a semi-adhesive flexible circuit board and a method for manufacturing the same.

[0057] Example 1

[0058] See also Figure 1-Figure 4 The present embodiment provides a semi-bonded flexible circuit board, comprising M soft boards, one end of the soft boards being bonded to form a multi-layer bonded mother board, and the other end of the soft boards being arranged as N separate daughter boards; the M soft boards are bonded by an adhesive sheet; M and N are both integers greater than 1, and M is greater than or equal to N, the soft boards are used to provide electrical connections, and the adhesive sheet preferably has a double-sided adhesive coating layer of polyimide (PI for short), which is used to bond the multi-layer soft boards.

[0059] The overall soft board design is adopted, which saves more space than the commonly used hard board at both ends and soft board in the middle structure in the industry; the setting of multi-layer soft boards can improve the electrical performance and signal transmission capability of the circuit board. One end of the soft board is glued to form a multi-layer adhesive motherboard, and the motherboard is connected to the PCB board separately to provide more stable mechanical support. The other end is a plurality of separate daughter boards, and the plurality of daughter boards are respectively connected to a plurality of PCB boards, wherein the connection direction of the daughter board can be freely adjusted, and the structure and hierarchy of the daughter board can also be set as needed, M is greater than or equal to N, ensuring that each daughter board corresponds to at least one soft board, which helps to achieve a more balanced circuit layout and load distribution. This structure not only maintains the original connection function of the circuit board, but also can adapt to the complex circuit design requirements, improves the problem that the common single board can only be connected to the PCB board in the same direction, and saves costs.

[0060] Furthermore, the adhesive sheet is divided into two bonding modes, one is complete bonding, and the other is partial windowing and partial bonding.

[0061] The partially open window and partially bonded design provides greater flexibility and adjustability. The open window area allows specific lines or pads to be exposed for easy welding and electrical connection, while partial bonding maintains the structural integrity of the circuit board.

[0062] Furthermore, the motherboard is composed of M soft boards and M-1 adhesive sheets, and the N daughter boards are composed of M soft boards and MN adhesive sheets; the daughter boards are divided into two structures, one of which is formed by a single soft board independently, and the other is composed of P soft boards and P-1 adhesive sheets glued together; P is an integer greater than 1, and P is less than M;

[0063] Specifically, Figure 2 As shown, the flexible circuit board is composed of the motherboard and three sub-boards, the motherboard is composed of four soft boards and three adhesive sheets, the three sub-boards are respectively a first sub-board, a second sub-board and a third sub-board, wherein the first sub-board and the third sub-board are both independently formed by a single soft board, and the second sub-board is composed of two soft boards and one adhesive sheet; the three sub-boards can connect multiple PCB boards in different directions.

[0064] Two different daughter board structures are provided. The daughter board formed by a single flexible board is suitable for applications that do not require high circuit complexity. The daughter board composed of multiple flexible boards and adhesive sheets is suitable for applications that need to integrate more circuit components. It allows you to choose the appropriate daughter board structure according to different application environments and functional requirements.

[0065] Specifically, a conducting area is provided on both the flexible board and the adhesive sheet, and a plurality of square grooves are provided in the conducting area to arrange copper blocks as conducting structures.

[0066] See also Figure 3The common way of connecting layers in a circuit board is to set circular through holes. In this application, it is optimized to connect through square copper blocks. See Figure 4 , improving the problem of plate bending caused by the thin soft board, and at the same time increasing the resistance value by increasing the contact area to meet the high voltage resistance requirements.

[0067] The present invention provides a semi-adhesive flexible circuit board, which is a soft board as a whole, and saves more space than the structure of hard boards at both ends and a soft board in the middle commonly used in the industry; the structure, number and direction of the sub-boards can be adjusted according to actual conditions to adapt to the circuit requirements of different positions and directions, improving the problem that common single boards can only be connected to PCB boards in the same direction, saving costs; the copper-plated design can improve the problem of board folding caused by the soft board being too thin, and at the same time, the resistance value is increased by increasing the contact area to meet the high voltage resistance requirements; the adhesive sheet adopts double-sided PI coated with glue, which is more bendable and has more outstanding bonding performance.

[0068] Example 2

[0069] See also Figure 5-Figure 6 A semi-bonded flexible circuit board provided in this embodiment includes three soft boards, the soft boards are used to provide electrical connections, one end of the soft boards are bonded to form a multi-layer bonded mother board, and the other end of the soft boards is set as two separate daughter boards; the three soft boards are bonded by an adhesive sheet, and the adhesive sheet is a double-sided PI for bonding the multi-layer soft boards, and the two daughter boards form a separate area.

[0070] The overall soft board design is adopted, which saves more space than the commonly used hard board at both ends and soft board in the middle structure in the industry; the adhesive sheet is double-sided PI coated with glue, which is more flexible and has more outstanding bonding performance; the whole is divided into a motherboard and two daughter boards to meet the circuit requirements of different positions, improving the problem that common single boards can only be connected to PCB boards in the same direction, saving costs.

[0071] From top to bottom, the first soft board constitutes the inner layer L1 / 2, the second soft board constitutes the inner layer L3 / 4, and the third soft board constitutes the inner layer L5 / 6. The first adhesive sheet is double-sided adhesive PI-2, and the second adhesive sheet is double-sided adhesive PI-1. Double-sided adhesive PI-1 bonds the inner layer L3 / 4 and the inner layer L5 / 6 to form the inner layer L3 / 6, and double-sided adhesive PI-2 bonds the inner layer L1 / 2 and the inner layer L3 / 6 as a whole. Double-sided adhesive PI is an adhesive sheet with polyimide (PI for short) as the base material, and both sides of it are adhesive. The numbers in double-sided adhesive PI-1 and double-sided adhesive PI-2 are only used as numbers to distinguish the adhesive sheets and have no special meaning.

[0072] Specifically, the double-sided adhesive PI-1 is fully bonded, and the double-sided adhesive PI-2 is partially windowed and partially bonded.

[0073] The fully bonded design makes the overall structure more stable, and the partial window design is to accommodate the placement of sub-boards at required locations for electrical connection or component installation.

[0074] In this embodiment, the sub-boards are divided into two structures, wherein the first sub-board is independently formed by the first soft board, and the second sub-board is composed of the second and third soft boards and the second adhesive sheet stacked together.

[0075] Two different sub-board structures enable the product to select the most suitable structure according to specific application requirements, thereby improving product adaptability.

[0076] Specifically, the flexible board and the adhesive sheet are both provided with conducting areas. According to requirements, a square groove is provided in the conducting area of ​​the first sub-board, and a square copper block is arranged in the square groove as a conducting structure.

[0077] The common drilling via copper plating connection method is optimized to connect through copper plating blocks, which can improve the problem of board bending caused by the thinness of the soft board. At the same time, the common via ring is improved to a copper block to increase the contact area, such as Figure 6 As shown, the resistance value is increased to meet the high voltage resistance requirement.

[0078] When in use, the two sub-boards can be connected to different PCB boards respectively, and the motherboard is connected to other PCB boards in another direction.

[0079] The present invention provides a semi-adhesive flexible circuit board, which is a soft board as a whole, and saves more space than the structure of hard boards at both ends and a soft board in the middle commonly used in the industry; the structure, number and direction of the sub-boards can be adjusted according to actual conditions to adapt to the circuit requirements of different positions and directions, improving the problem that common single boards can only be connected to PCB boards in the same direction, saving costs; the copper-plated design can improve the problem of board folding caused by the soft board being too thin, and at the same time, the resistance value is increased by increasing the contact area to meet the high voltage resistance requirements; the adhesive sheet adopts double-sided PI coated with glue, which is more bendable and has more outstanding bonding performance.

[0080] Example 3

[0081] See also Figure 5-Figure 16 This embodiment provides a method for manufacturing a semi-bonded flexible circuit board of embodiment 2, comprising the following steps:

[0082] S1, inner layer L1 / 2 soft board production:

[0083] S11. Cut the first flexible board to the required size, open windows at the locations where copper plating is required using laser direct imaging technology, and protect other locations by applying dry film. After the inner layer circuit is completed, remove the copper foil not protected by the dry film by acid etching to form the inner layer circuit pattern. After passing the automatic optical inspection, perform browning treatment to enhance the adhesion between the copper surface and the subsequent laminated materials.

[0084] S12, the browned product is subjected to controlled deep processing by laser, the upper surface of the first flexible board is set as the A surface, and the lower surface is set as the B surface, and a window is etched in the pad area of ​​the A surface to expose the PI material in the interlayer of the flexible board, and the PI material exposed on the A surface is burned by laser technology until the bottom copper layer of the B surface is exposed, such as Figure 8 As shown;

[0085] S13, attaching the L1 / 2 soft board after laser processing to the traction board. The function of the traction board is to assist the subsequent processing and ensure that the soft board remains stable during the processing. Then, the impurities and oxide layer on the surface of the soft board are removed by sandblasting technology, especially the surface carbon black, which has a certain influence on the bonding force between the subsequent copper plating layer and the soft board substrate. No grinding brush is used during the sandblasting process to avoid damage to the surface of the soft board.

[0086] S14, the B side is again protected by a dry film to expose the process edge for copper plating; because the soft board is too thin and easy to be folded, it is impossible to clamp the board for copper plating during the electroplating process, and an auxiliary mold is needed for reinforcement. In order to prevent the folded board from being scrapped due to swinging when the overhead crane is moving, the auxiliary mold uses a base copper plate, which is 10mm larger on one side than the soft board, so that it can be riveted with the soft board during copper plating. The auxiliary mold is as follows Figure 9-10 As shown; the auxiliary mold and the soft board with dry film pasted are riveted and reinforced with an iron clamp. Since the soft board process edge has been copper-plated in the previous process, the auxiliary mold also uses a copper edge, which is an excellent conductor. The base copper plate is a copper plate used to assist the electroplating process. During the electroplating process, the base copper plate is used as an auxiliary mold to be riveted and reinforced with the soft board to be copper-plated to ensure the stability of the electroplating process and the uniformity of the copper layer. The base copper plate provides a conductive medium and physical support, so that the copper ions in the electroplating solution can form a uniform copper layer;

[0087] S15. The position of laser controlled depth milling is a square groove, and the square groove is copper plated until the formed copper block fills the square groove. The copper plating thickness requirement is ≥90UM. A single electroplating cannot meet the thickness requirement. After each electroplating, it is necessary to slice and measure to confirm the thickness of the copper block. Therefore, multiple additional copper platings of the same size as the copper plating position are set at the process side to form reference pieces for slicing measurement to confirm the copper thickness and reduce scrap. Fig.11 As shown;

[0088] S16, transferring the copper-plated flexible board to the inner layer circuit production process, etching the inner layer L1 / 2 circuit pattern, and then performing browning treatment after AOI scanning to form an anti-oxidation layer on the copper surface to enhance the adhesion of the copper surface, and then affixing a covering film on the outer surface of the flexible board to protect the circuit from physical damage and chemical corrosion, and at the same time play an insulating role;

[0089] S17, the soft board with cover film protection is treated with immersion gold using electroplating mold and clip riveting to improve the wear resistance, corrosion resistance and solderability of the soft board, thus completing the production of the inner layer L1 / 2 soft board.

[0090] S2, double-sided adhesive PI-1 production:

[0091] Cut according to the actual size specifications of the production information, and drill positioning holes on the cut double-sided glued PI. The positioning holes are used for positioning and alignment during subsequent lamination, such as Fig.12 As shown, the double-sided glue-coated PI-1 does not need laser windowing, and after completion, it will be pressed with the L3 / 4 soft board 2 and the L5 / 6 soft board.

[0092] S3, inner layer L3 / 4 and L5 / 6 soft board production:

[0093] According to the process in S1, the L3 / 4 inner layer circuit and the L5 / 6 inner layer circuit are made. After completion, acid etching is performed to etch away the copper foil not protected by the resist to form the required circuit pattern. After etching, AOI inspection scanning is performed to identify defects in the circuit. Then the L3 / 4 and L5 / 6 soft boards are browned. After completion, they are pressed with double-sided adhesive PI-1 to form the inner layer L3 / 6.

[0094] S4, inner layer L3 / 6 production:

[0095] S41, the inner layer L3 / 6 soft board is drilled according to the production information file to prepare for the subsequent electrical connection, and then the copper deposition process is carried out to deposit a thin copper layer on the hole wall to make the hole conductive, and then transferred to the circuit production link to make pads and gold fingers, such as Fig.13 As shown, the pad is the copper foil area for soldering electronic components, and the gold finger is the conductive edge for connecting or inserting other circuit boards. Due to various factors in the manufacturing process, the actual pad size may deviate from the design size. Therefore, in this embodiment, the gold finger pad size is 5.9mil, and the reserved compensation size is 3.6mil;

[0096] S42, after the inner layer L3 / 6 soft board is finished with circuit fabrication, AOI scanning is performed. If there is no abnormality in the result, browning treatment is performed. The covering film is opened according to the engineering data. The milled covering film is attached to the inner layer L3 / 6 soft board after browning and fixed with a soldering iron.

[0097] S43, carry out the character printing process, and after completion, wait for the total pressing with the inner layer L1 / 2 soft board and the double-sided glue PI-2.

[0098] S5, double-sided adhesive PI-2 production:

[0099] Double-sided adhesive PI-2 is cut by laser according to the production information file, and the double-sided adhesive PI in the separation area is cut off, and the adhesive area is retained, such as Fig.14 shown.

[0100] S6. Overall pressing:

[0101] Use rivets to rivet the soldering iron solder joints, and use a fast press to press the inner layer L1 / 2 soft board, double-sided glue-coated PI-2 and inner layer L3 / 6 soft board. Before pressing, separate areas are separated by release paper. In actual applications, the pressure is set to 100kg / 500s.

[0102] S7, subsequent process:

[0103] The product is tested for electrical performance with a high voltage resistance of 5kv and an on-resistance value of less than 150mΩ. Products that pass the test are cut out using lasers and glue is applied to the separated area to prevent the soft board from cracking.

[0104] Improvement effect comparison:

[0105] Comparison of improvement effects on folding plate problem Fig.15 Therefore, optimizing the common copper-plated connection method of drilling through holes to connecting through copper-plated blocks can improve the problem of board bending caused by the thinness of the flexible board.

[0106] The products were tested for high voltage resistance of 5kv and on-resistance value less than 150mΩ. The results showed that the products in the prior art that used drilled via holes and copper-plated connections had a test pass rate of 0%, while the products in the present invention that used copper blocks for conduction had a test pass rate of 100%. It can be seen from the results that the products before improvement could not pass the tests for high voltage resistance of 5kv and on-resistance value less than 150mΩ, while the products after improvement could pass the tests, and the improvement effect was obvious.

[0107] The present invention discloses a method for manufacturing a semi-bonded flexible circuit board. The method improves the problem of plate folding caused by the thinness of the flexible circuit board by electroplating copper blocks. The copper plating process forms a conductive structure of multiple copper blocks to replace the common copper ring structure, and the conductive resistance value increases with the increase of the contact area, thereby improving the high-voltage resistance of the ultra-long flexible circuit board. The laser depth control technology is used to ensure the accuracy of the copper plating process and meet the product reliability. The window position of the double-sided glue-coated PI is flexibly determined by the position and structure of the sub-board, thereby improving the structural flexibility to adapt to the circuit requirements of different positions and directions. The optimized manufacturing process reduces material waste and reduces production costs.

[0108] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0109] In addition, it should be noted that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of this application.

[0110] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A semi-bonded flexible circuit board, characterized in that: It comprises M soft boards, one end of which is glued to form a multi-layer adhesive mother board, and the other end of which is arranged as N separate sub-boards; M and N are both integers greater than 1, and M is greater than or equal to N.

2. A semi-adhesive flexible circuit board according to claim 1, characterized in that: The M soft boards are bonded together by adhesive sheets, and the adhesive sheets are bonded in two ways, one is complete bonding, and the other is partial windowing and partial bonding.

3. The semi-adhesive flexible circuit board according to claim 1, characterized in that: The motherboard is composed of M soft boards and M-1 adhesive sheets, and the N sub-boards are composed of M soft boards and MN adhesive sheets.

4. The semi-adhesive flexible circuit board according to claim 3, characterized in that: The sub-board has two structures, one of which is formed by a single soft board independently, and the other is composed of P soft boards and P-1 adhesive sheets stacked together; P is an integer greater than 1, and P is less than M.

5. A semi-adhesive flexible circuit board according to any one of claims 2 to 4, characterized in that: The flexible board and the adhesive sheet are both provided with a conducting area, the conducting area is provided with a plurality of square grooves, and copper blocks are arranged in the square grooves as a conducting structure.

6. A method for manufacturing a semi-adhesive flexible circuit board according to claim 1, characterized in that: The following steps are involved: FPC production: M FPCs are stacked at one end to form a multi-layer bonded motherboard, and the other end is set as N separate daughterboards, M≥N>1; windows are opened on the FPCs to set conduction areas, and copper is plated in the conduction areas; Making the adhesive sheet: cutting the adhesive layer, drilling positioning holes and making the adhesive sheet; Overall lamination: laminating the soft board and the adhesive sheet.

7. The method for manufacturing a semi-adhesive flexible circuit board according to claim 6, characterized in that: When M is equal to 3, N is equal to 2, and P is equal to 2, the following steps are included: S1. The first flexible board is made to form the inner layer L1 / 2: After cutting the flexible board and applying dry film, a window is opened in the conductive area, and a laser is used to perform controlled depth processing at the window opening position to form a square groove, and copper is plated in the square groove as a conductive structure; S2, making the first adhesive sheet: cutting the adhesive layer and drilling positioning holes; S3, the second and third soft boards are made to form the inner layer L3 / 6: two soft boards are cut and dry film is applied, and the two soft boards are pressed together by using the first adhesive sheet; S4, making the second adhesive sheet: cutting the adhesive layer, drilling positioning holes, and using laser cutting to retain the adhesive area; S5, finished product production: the inner layer L1 / 2 and the inner layer L3 / 6 are pressed together through the second adhesive sheet.

8. The method for manufacturing a semi-adhesive flexible circuit board according to claim 7, characterized in that: The window position is subjected to controlled depth processing using a laser, and the steps include: the upper surface of the first soft board is the A surface, and the lower surface is the B surface, a window is etched in the A surface pad area to expose the soft board interlayer material, and the A surface interlayer material is processed using a laser to form the square groove, and the bottom surface of the square groove is the upper surface of the B surface copper layer.

9. The method for manufacturing a semi-adhesive flexible circuit board according to claim 7, characterized in that: The copper plating step in S1 includes: applying a dry film to the B surface for protection, reserving a copper plating process edge, and using a base copper plate as a copper plating process reinforcement mold; The square groove is filled by copper plating, and the thickness of the copper block is ≥90UM; The process edge is provided with a plurality of additional copper-plated reference pieces at positions of the same size, which are used for slicing and measuring to confirm the copper thickness after a single copper plating.

10. The method for manufacturing a semi-adhesive flexible circuit board according to claim 7, characterized in that: When the copper plating process in S1 is applied to the adhesive sheet, the flexible board and the adhesive sheet are connected to each other through the copper blocks on the flexible board and the copper blocks on the adhesive sheet.

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