A method for manufacturing a butterfly-shaped rigid-flex board

Abstract

The present invention discloses a method for manufacturing a butterfly-shaped hard-soft board, comprising the following steps: manufacturing inner circuits of a soft board core board and a hard board core board respectively; the soft board core board comprises a soft board area and a hard-soft board area; laminating a covering film on the entire soft board core board; performing plasma degumming treatment on the surface of the covering film on the soft board core board; pressing the soft board core board and the hard board core board into a production board with pure glue, wherein the stacking order of the production board is the soft board core board, pure glue and hard board core board, and before pressing, windows are opened on the pure glue and hard board core boards corresponding to the soft board area; drilling holes in the production board, and then performing plasma degumming treatment on the production board; forming a layer of polymer conductive film on the hole wall by direct electroplating process; performing post-processing on the production board to obtain a butterfly-shaped hard-soft board. The overall process of the method of the present invention is simple, and effectively improves the yield rate and production efficiency of the product.

Description

Technical Field

[0001] The invention relates to the technical field of printed circuit board manufacturing, and in particular to a method for manufacturing a butterfly-shaped rigid-flexible board. Background Art

[0002] With the recent development of rigid-flex PCBs, more rigid-flex PCBs are becoming smaller and thinner, and most of them are HDI designs.

[0003] Rigid-flex PCB is composed of rigid PCB and flexible PCB selectively laminated together. It has a tight structure and forms conductive connection with metallized holes. Rigid-flex PCB takes into account the regularity and toughness of conventional hard PCB and the flexibility and flexibility of soft PCB. It can be moved, bent, folded, twisted, and realize three-dimensional wiring, which greatly saves the installation space of electronic components and conforms to the development trend of "light, thin, short and small" electronic products. In the past ten years, it has been widely used in many fields such as military industry, aerospace, automotive electronics, medical electronics, and civilian consumer electronics. It has become the fastest-growing type of PCB product and one of the main development directions of PCB in the future.

[0004] Lamination and windowing are the core steps of rigid-flex boards. There are many ways to open windows, among which the most widely used is mechanical controlled depth milling. For the hard board and PP adjacent to the window area and the soft board, the hard board is cut to a certain depth in advance by mechanical methods to form a blind groove, and the PP is cut through and the window is opened; then the hard board layer and the soft board layer are laminated, and other post-processing is carried out normally. Finally, the mechanical controlled depth milling method is used to connect with the blind groove formed by the pre-cutting of the hard board, and the hard board at the window position is removed to expose the soft board. The typical process flow includes the following steps:

[0005] 1. Soft board part: cutting → inner layer pattern → inner layer etching → inner layer AOI → browning → cover film opening → cover film lamination → cover film pressing → OPE punching → browning;

[0006] 2. Hard board part: cutting → inner layer graphics → inner layer etching → OPE punching → inner layer AOI → blind groove → browning;

[0007] 3. Adhesive layer: PP cutting → OPE punching → PP window opening;

[0008] 4. Main process: pressing → X-Ray drilling target hole → milling board edge → drilling → copper sinking, board electricity → outer layer graphics → graphics electroplating → outer layer etching → outer layer AOI → solder mask, characters → surface treatment → electrical testing → molding → mechanical controlled deep milling → FQC → FQA → packaging and shipment.

[0009] In the above production process, the soft board is generally placed in the middle layer of the hard-flex board, and the cover film is only attached to the soft board area on the soft board. This method is not suitable for the structure type of the hard-flex board when the outer layer is a soft board. The hard-flex board with a soft outer layer made by the above method will have the following disadvantages:

[0010] 1. During lamination, PP glue will overflow onto the soft board area of ​​the soft board, affecting the quality of the product. There is also a method of using pure glue instead of PP for lamination, but the mixed pressing process between the pure glue and the soft board and the hard board is prone to stratification, resulting in low yield, which is not conducive to industrial mass production.

[0011] 2. The structure of the cover film laminating the flexible board area will affect the folding life of the rigid-flex board;

[0012] 3. The process is long and complicated, and in the later stage of molding, it is necessary to open the window and uncover the cover to remove the waste part on the hard board. Summary of the invention

[0013] In view of the above-mentioned existing technical defects, the present invention provides a method for manufacturing a butterfly-shaped rigid-flex board, which has a simple overall process and effectively improves the product yield and production efficiency.

[0014] In order to solve the above technical problems, the present invention provides a method for manufacturing a butterfly-shaped rigid-flex board, comprising the following steps:

[0015] S1. Making inner circuits of a soft board core board and a hard board core board respectively; the soft board core board includes a soft board area and a soft-hard combination area;

[0016] S2. Laminating the covering film on the entire board of the soft board core board;

[0017] S3, performing plasma debonding treatment on the surface of the covering film on the soft board core board;

[0018] S4, pressing the soft board core board and the hard board core board into a production board with pure glue, wherein the lamination order of the production board is the soft board core board, the pure glue and the hard board core board, and before pressing, opening windows on the pure glue and the hard board core board at the locations corresponding to the soft board area;

[0019] S5, drilling holes in the production board, and then performing plasma degumming treatment on the production board;

[0020] S6, forming a polymer conductive film on the hole wall by direct electroplating process;

[0021] S7. The outer circuit layer and the solder mask layer are sequentially manufactured on the production board, and then the molding process and the surface treatment are performed to obtain a butterfly-shaped rigid-flex board; wherein the molding process is performed by punching the board.

[0022] Furthermore, in step S1, the core board of the flexible board is a double-sided copper-clad board whose substrate is PI, and the core board of the rigid board is a double-sided copper-clad board whose substrate is FR4.

[0023] Furthermore, in step S1, a film is pasted on both sides of the soft board core board and the hard board core board, and then an inner layer circuit is produced on one side of the soft board core board and the hard board core board through exposure, development and etching in sequence, and the copper layer on the other side of the soft board core board corresponding to the blind hole position produced later is etched away to form a laser drilling position; in the stacking structure of step S4, one side of the soft board core board and the hard board core board where the circuit is produced is in contact with pure glue.

[0024] Furthermore, in step S2, a cover film is attached to the side of the flexible core board on which the inner layer circuit is made.

[0025] Furthermore, in step S5, before drilling, a laser is used to control the depth of a blind hole connecting the inner layer circuit of the flexible board core board at the laser drilling position on the outer side of the flexible board core board; the direct electroplating process in step S6 forms a layer of polymer conductive film on the wall of the blind hole.

[0026] Furthermore, in step S4, the hard board core board is first blackened and pre-baked before pressing; and after pressing into a production board, it needs to be de-blackened to expose the surface copper layer; and a pressing gasket is placed at the window of the stacked structure during pressing, and the pressing gasket is removed after pressing.

[0027] Furthermore, in step S4, the pre-baking temperature is 120 degrees and the time is 30 minutes.

[0028] Furthermore, in step S4, the pure glue is a film made of acrylic epoxy resin glue.

[0029] Furthermore, in step S5, after drilling and before plasma debonding, the production board is also baked.

[0030] Furthermore, in step S5, the baking temperature is 120 degrees and the baking time is 3 hours.

[0031] Furthermore, in step S7, when punching the plate, the upper and lower plate edges of the plate are punched first, and then the left and right plate edges of the plate are punched.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The present invention firstly bonds a covering film to the entire core board of the flexible board. Compared with the existing method of only bonding the covering film locally on the flexible board area, the folding life of the rigid-flexible board after lamination can be greatly extended, and the number of dynamic bending times can reach at least 200,000 times; secondly, after bonding the covering film, the covering film is subjected to plasma debonding treatment, which can effectively increase the bonding force between the covering film and the pure glue during lamination, avoid the problem of lamination delamination, improve the lamination quality, and the pure glue lamination method will not cause glue flow, ensuring the size and quality of the window opening; thirdly, after drilling, plasma debonding treatment and direct electroplating process are directly used to form a layer of polymer conductive film on the wall of the hole. Compared with the chemical copper plating process, this method can meet the requirements for forming a conductive layer between different materials in the rigid-flexible board, improve the uniformity of the conductive layer on the hole wall, and also prevent the problems of line failure and hole breakage failure caused by incomplete debonding.

[0034] In the present invention, when the inner layer circuit is made on one surface of the soft board core board, the copper layer at the position of the blind hole made later on the other surface is etched away together, so that when the blind hole is laser drilled after lamination, the steps of film pasting, window opening (exposure and development) and etching removal can be reduced once, thereby effectively improving the production efficiency; and before lamination, windows are opened on both the pure glue and the hard board core board at the positions corresponding to the soft board area, thereby reducing the window opening and uncovering process in the later molding process; and the molding adopts the punching plate method, which can improve the accuracy of the board molding compared with the gong plate method, and the shape tolerance after punching the plate can be controlled within ±2mils, which meets the accuracy requirements required for molding. In addition, a symmetrical punching plate method of punching the upper and lower board edges first and then the left and right board edges is adopted to reduce quality problems such as board surface bursting caused by punching the plate; and the surface treatment is placed after the molding treatment, thereby avoiding the quality problem of the coating formed during the surface treatment bursting due to the relationship between the punching plate. DETAILED DESCRIPTION

[0035] In order to more fully understand the technical content of the present invention, the technical solution of the present invention will be further introduced and illustrated in conjunction with specific embodiments below.

[0036] Example

[0037] The method for manufacturing a butterfly-shaped rigid-flex board shown in this embodiment includes the following processing steps in sequence:

[0038] (1) Cutting: Cut soft board core board, pure glue board and hard board core board according to the panel size of 520mm×620mm; among them, the soft board core board is a double-sided copper clad board with a substrate of PI and a substrate thickness of 1mil. The soft board core board includes a soft board area and a soft-hard combination area. In the production process of the butterfly-shaped soft-hard combination board, blind holes connecting the upper and lower layers of the circuits need to be made on the soft board core board. The hard board core board is a double-sided copper clad board with a substrate of FR4 and a substrate thickness of 8mils. The thickness of the copper layer on both surfaces of the soft board core board and the hard board core board is Hoz (i.e. 1 / 2oz); the pure glue is a film made of acrylic epoxy resin glue, which will not produce glue flow when pressed and heated.

[0039] (2) Inner layer circuit production (negative film process): Inner layer pattern transfer, use a vertical coating machine to coat the photosensitive film, the film thickness of the photosensitive film is controlled to 8μm, and a fully automatic exposure machine is used to complete the inner layer circuit exposure on one surface of the flexible board core board and the hard board core board respectively with a 5-6 grid exposure ruler (21 grid exposure ruler). The film on the other surface of the hard board core board is fully exposed, and the film on the other surface of the flexible board core board is fully exposed except for the part corresponding to the blind hole position produced later; Inner layer etching, the soft board core board and the hard board core board after exposure and development are etched out of the inner layer circuit, that is, during etching, the copper layer on the other side of the flexible board core board corresponding to the blind hole position produced later is etched away to form a laser drilling position, and the inner layer line width is measured to be 3mil; Inner layer AOI, then check the inner layer circuit for defects such as open short circuit, circuit gap, circuit pinhole, etc., and scrap the defective products, and send the defective products to the next process.

[0040] (3) Browning: Through chemical reaction, a brown oxide layer is generated on the surface of the copper layer of the flexible board core board, which increases the roughness of the copper surface and enhances the bonding force with the covering film during pressing.

[0041] (4) Covering film: A covering film is pasted on the entire board on the side of the flexible board core board where the inner layer circuit is made. The covering film is made of polyimide (PI material).

[0042] Before bonding, according to the shape of the soft board area, a window treatment is performed on the cover film of the same size as the soft board core board corresponding to the soft and hard bonding area.

[0043] (5) Rapid pressing: Through high temperature and high pressure, the adhesive layer (epoxy resin) of the covering film is completely bonded to the soft board core in a short time to achieve the effect of protecting the soft board core; the parameters of rapid pressing are: temperature 180°C, pressure 100KG, pressing time 1-2min; then the soft board core is baked at 150°C for 1h to completely cure the covering film.

[0044] (6) Plasma degumming: Plasma degumming is performed on the surface of the covering film on the core board of the soft board.

[0045] (7) Opening windows: Open windows in the corresponding soft board areas on the pure glue and hard board core boards to form hollow areas.

[0046] (8) Blackening: Blackening treatment is performed on the hardboard core board.

[0047] (9) Pre-baking: Pre-bake the hardboard core board to remove moisture and stress on the board surface. The pre-baking temperature is 120 degrees and the time is 30 minutes.

[0048] (10) Lamination: The browning speed is based on the browning thickness of the bottom copper. The soft board core board, pure glue and hard board core board are stacked in sequence as required, wherein the side of the soft board core board and the hard board core board with the inner layer circuit is in contact with the pure glue. Then, appropriate lamination conditions are selected according to the Tg of the sheet material to press the stacked boards to form a production board. During the lamination, a pressing gasket is placed at the window of the stacked board structure to balance the pressing pressure and avoid bending or even bursting of the board due to uneven force. The pressing gasket is removed after lamination.

[0049] (11) Edge removal: The production board is edged and then de-blackened to expose the surface copper layer.

[0050] (12) Laser drilling: A laser is used to control the depth of a blind hole connected to the inner layer circuit of the flexible board core board at the laser drilling position on the outside of the flexible board core board.

[0051] (13) Outer layer drilling: Based on existing drilling technology, drilling is performed on the production board according to design requirements to drill conductive holes for connecting the circuits on the flexible board core board and the rigid board core board up and down.

[0052] (14) Baking: The production board is baked at a temperature of 120 degrees for 3 hours.

[0053] (15) Glue removal: The production board is subjected to plasma degumming treatment to remove drilling contamination and glue flow in the holes.

[0054] (16) Direct electroplating: A direct electroplating process is then used to form a polymer conductive film with a thickness of about 0.2 mils on the hole walls of the blind hole and the through hole to facilitate subsequent copper electroplating. Of course, the direct electroplating process can also use a carbon pore treatment process, that is, after being treated with a carbon conductive liquid, a carbon conductive layer is deposited on the hole wall.

[0055] In the above, the direct electroplating process adopts the Ecopact CP process of Atotech, that is, the direct electroplating process specifically includes the following steps:

[0056] a. Clean and roughen the board surface by micro-etching;

[0057] b. Wetting and cleaning the glass fiber and resin surface by water washing, so that the pore walls on the plate have a hydrophilic surface;

[0058] c. Forming a uniform and dense layer of MnO2 on the substrate of the pore wall through oxidation treatment, which serves as a catalyst for the formation of conductive polymer polythiophene;

[0059] d. Under the catalysis and reaction of MnO2, a polymer conductive film layer is formed on the substrate of the pore wall, and the polymer conductive film layer is the polymer polythiophene.

[0060] (17) Production of outer circuits (positive film process): Transfer of outer pattern, using a fully automatic exposure machine and positive circuit film, with a 5-7 grid exposure ruler (21 grid exposure ruler) to complete the outer circuit exposure, after development, the outer circuit pattern is formed on the production board; electroplating of the outer pattern, and then copper plating and tin plating respectively on the production board, setting the electroplating parameters according to the required copper thickness, copper plating is 1.8ASD current density electroplating for 60 minutes on the whole board, tin plating is 1.2ASD current density electroplating for 10 minutes, tin thickness 3-5μm; then stripping, etching and tin stripping in turn, etching the outer circuit on the production board; outer layer AOI, using an automatic optical inspection system, by comparing with the CAM data, to detect whether the outer circuit has defects such as open circuit, gap, incomplete etching, short circuit, etc.

[0061] (18) Solder mask and silk screen characters: After silk screen printing solder mask ink on the surface of the multilayer board, it is sequentially subjected to pre-curing, exposure, development and thermal curing treatments to solidify the solder mask ink into a solder mask layer; specifically, the solder mask ink and the characters on the TOP surface are added with a "UL mark", thereby coating a layer on the circuits and substrates that do not require soldering to prevent bridging between circuits during soldering, provide a permanent electrical environment and resist chemical corrosion, and at the same time beautify the appearance.

[0062] (19) Molding: According to the existing technology, the SET board is formed by punching, and the appearance tolerance can be controlled within ±2mils to obtain a butterfly-shaped soft-hard combination board. The precision of the gong board using a forming milling cutter cannot meet the tolerance requirement.

[0063] In the above, when punching the board, according to the appearance characteristics of the butterfly-shaped rigid-flex board, the first mold corresponding to the upper and lower board edges of the SET board and the second mold corresponding to the left and right board edges can be made respectively, and then the first mold is used to punch the upper and lower board edges of the board, and then the second mold is used to punch the left and right board edges of the board, forming a symmetrical punching structure, reducing quality problems such as board surface cracking caused by punching.

[0064] (20) Surface treatment (nickel-gold immersion): The copper surface of the pad at the solder mask opening on the board is chemically treated to evenly deposit a nickel layer and a gold layer of a certain required thickness. The nickel layer thickness is 3-5 μm; the gold layer thickness is 0.05-0.1 μm.

[0065] (21) Electrical test: Test the electrical conductivity of the finished board. The test method used for this board is: flying probe test.

[0066] (22) FQC: Inspect the appearance of the butterfly-type rigid-flex PCB according to the customer's acceptance standards and our inspection standards. If there are any defects, repair them in time to ensure that we provide customers with excellent quality control.

[0067] (23) FQA: Re-test the appearance, hole copper thickness, dielectric layer thickness, green oil thickness, inner layer copper thickness of the circuit board to see if they meet customer requirements.

[0068] (24) Packaging: According to the packaging method and packaging quantity required by the customer, the butterfly-shaped rigid-flex board is sealed and packed, and desiccant and humidity card are placed before shipment.

[0069] The technical solutions provided by the embodiments of the present invention are introduced in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the embodiments of the present invention. The description of the above embodiments is only applicable to help understand the principles of the embodiments of the present invention. At the same time, for those skilled in the art, according to the embodiments of the present invention, there will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for manufacturing a butterfly-shaped rigid-flex board, characterized in that: The following steps are involved: S1. Making inner circuits of a soft board core board and a hard board core board respectively; the soft board core board includes a soft board area and a soft-hard combination area; S2. Laminating the covering film on the entire board of the soft board core board; S3, performing plasma debonding treatment on the surface of the covering film on the soft board core board; S4, pressing the soft board core board and the hard board core board into a production board with pure glue, wherein the lamination order of the production board is the soft board core board, the pure glue and the hard board core board, and before pressing, opening windows on the pure glue and the hard board core board at the locations corresponding to the soft board area; S5, drilling holes in the production board, and then performing plasma degumming treatment on the production board; S6, forming a polymer conductive film on the hole wall by direct electroplating process; S7. The outer layer circuit and the solder mask layer are sequentially manufactured on the production board, and then the molding process and the surface treatment are performed to obtain a butterfly-shaped rigid-flex board; wherein the molding process is performed by punching the board, and when punching the board, the upper and lower board edges of the board are punched first, and then the left and right board edges of the board are punched.

2. The method for manufacturing a butterfly-shaped rigid-flex PCB according to claim 1, characterized in that: In step S1, the core board of the flexible board is a double-sided copper-clad board with a substrate of PI, and the core board of the rigid board is a double-sided copper-clad board with a substrate of FR4.

3. The method for manufacturing a butterfly-shaped rigid-flex PCB according to claim 1, characterized in that: In step S1, a film is applied to both sides of the flexible board core board and the rigid board core board, and then an inner layer circuit is produced on one side of the flexible board core board and the rigid board core board through exposure, development and etching in sequence, and the copper layer on the other side of the flexible board core board corresponding to the position of the blind hole produced later is etched away to form a laser drilling position; in the stacked board structure of step S4, one side of the flexible board core board and the rigid board core board where the circuit is produced is in contact with pure glue.

4. The method for manufacturing a butterfly-shaped rigid-flex PCB according to claim 3, characterized in that: In step S2, a cover film is attached to the surface of the flexible core board on which the inner layer circuit is formed.

5. The method for manufacturing a butterfly-shaped rigid-flex PCB according to claim 4, characterized in that: In step S5, before drilling, a laser is used to control the depth of a blind hole connecting the inner layer circuit of the flexible board core board at the laser drilling position on the outer side of the flexible board core board; the direct electroplating process in step S6 forms a layer of polymer conductive film on the wall of the blind hole.

6. The method for manufacturing a butterfly-shaped rigid-flex PCB according to claim 1, characterized in that: In step S4, before the hard board core board is pressed, the hard board core board is first blackened and pre-baked; after being pressed into a production board, it needs to be de-blackened to expose the surface copper layer; and during pressing, a pressing gasket is placed at the window of the stacked board structure, and the pressing gasket is removed after pressing.

7. The method for manufacturing a butterfly-shaped rigid-flex board according to claim 6, characterized in that: In step S4, the pre-baking temperature is 120 degrees and the time is 30 minutes.

8. The method for manufacturing a butterfly-shaped rigid-flex PCB according to claim 1, characterized in that: In step S5, after drilling and before plasma debonding, the production board is also baked.

9. The method for manufacturing a butterfly-shaped rigid-flex board according to claim 8, characterized in that: In step S5, the baking temperature is 120 degrees and the time is 3 hours.