Rigid-flex board production method adopting depth-controlled cover opening process

Abstract

The invention discloses a rigid-flex board production method adopting a depth-controlled cover opening process. The rigid-flex board production method comprises the following steps: setting a flexible board area of a rigid-flex board; pasting a covering film on a soft board area of the soft board layer; taking the hard board layer of which the circuit is manufactured for the first time, and attaching a high-temperature-resistant low-adhesive tape to a corresponding soft board area on one surface of the hard board layer of which the circuit is manufactured to form a filling and adhesive blocking layer; taking a prepreg, and performing windowing treatment on a soft board area of the prepreg; aligning and fixing the upper and lower hard board layers, the upper and lower prepregs and the soft board layer, and pressing to form a laminated structure; secondary circuit manufacturing of the hard board layer is completed; performing depth-controlled uncovering treatment on a soft board area of the hard board layer, wherein the depth of the drilling and milling blind gong is the sum of the thickness of the hard board layer and the thickness of the solder resist ink; the hard board layer located in the soft board area is peeled off, and meanwhile the high-temperature-resistant low-adhesive tape attached to the hard board layer is removed. By adopting the method, the glue overflowing size of the prepreg can be reduced; and the depth of the controlled depth is judged by observing whether the high-temperature-resistant adhesive tape can be observed, so that the production efficiency of products is improved.

Description

Technical Field

[0001] The invention relates to the field of printed circuit board hard-flex board technology, and in particular to a hard-flex board production method using a depth-controlled post-capping process that can meet strict glue overflow size requirements. Background Art

[0002] As electronic products in modern consumer, medical, aviation and other fields gradually develop into thin, integrated and multifunctional ones, the requirements for the production process of printed circuits are getting higher and higher. The soft-rigid combination board in the printed circuit board is a kind of board that has the characteristics of both FPC and PCB. It has a certain flexibility and can be three-dimensionally wired; it also has a certain rigid area, which is very helpful in saving internal space of the product, reducing the volume of the finished product, and improving product performance; the advantages of this product are that it can save more design space, reduce assembly, and transmit signals faster and more stably.

[0003] Due to the bending requirements of the soft board area of ​​the hard-flex board, the semi-cured sheet will be pressurized and glue will overflow during the production process of the soft board area and the hard-flex board combination area of ​​the product. This type of semi-cured sheet material is a rigid material. The overflowing glue area will cause the bending performance of the soft board to become lower. Special consideration should be given to the control of the overflowing glue size in the production and design process. Conventionally, the semi-cured sheet is shrunk and low-flowability or non-flowable semi-cured sheets are selected. By adjusting the lamination and pressing parameters, the overflowing glue size can be ensured to be between 0.5 and 1.5 mm.

[0004] During the production process of the soft board area of ​​the hard-flex board, the hard board isolation layer and the outer hard board layer belong to the same layer of material (FR-4 copper clad board). The hard board isolation layer in this area needs to be peeled off during the production process. There are two production processes: first grooving process and post-capping process. The post-capping process is to peel off the hard board isolation layer after the product is surface treated and before the electrical signal test (electrical test or flying probe test). The existing peeling process uses UV laser cutting, CO2 laser cutting, mechanical blind fishing and other processing technologies to only cut off the two sides of the hard board and expose the soft board area in the middle; however, these post-capping technologies are not easy to control the laser energy or drilling and milling depth, and are prone to damage the soft board area. Summary of the invention

[0005] The present invention aims to provide a novel method for producing a rigid-flexible board to overcome the technical problems existing in the existing decapping process. The technical solution is as follows:

[0006] A method for producing a rigid-flexible board using a depth-controlled post-capping process, comprising:

[0007] Set the soft board area and hard board bonding area of ​​the hard-flex board;

[0008] Take the soft board layer with completed circuits and apply covering film to the soft board areas on both copper foil surfaces;

[0009] Take the hard board layer that has completed the first circuit production, and stick the high temperature resistant low viscosity tape on the soft board area of ​​the copper foil surface where the circuit production is completed; the stuck high temperature resistant low viscosity tape is cut and discharged by CCD alignment laser to form a filling and resistance layer;

[0010] Take the prepreg and make a window treatment on its soft board area;

[0011] Align and fix the upper and lower hard board layers, the upper and lower prepreg sheets, and the soft board layer so that the high temperature resistant low-adhesive tape on the hard board layer and the covering film on the soft board layer face each other, and then press them together to form a laminated structure;

[0012] Complete the secondary circuit production of the hard board layer of the laminated structure;

[0013] The soft board area of ​​the hard board layer under the laminated structure is subjected to a depth-controlled opening process by using a drilling and milling blind gong process. The depth of the drilling and milling blind gong is the sum of the thickness of the hard board layer and the thickness of the solder resist ink, so as to separate the soft board area and the hard board bonding area of ​​the hard board layer;

[0014] The hard board layer located in the soft board area is peeled off, and the high temperature resistant low-adhesion tape attached to the hard board layer is removed at the same time.

[0015] Furthermore, the size of the covering film is larger than that of a single side of the soft board area by more than 0.5 mm.

[0016] Furthermore, the size of the high temperature resistant low viscosity tape is 0.1 mm to 0.2 mm smaller than that of the soft board area on one side.

[0017] Furthermore, the thickness of the high temperature resistant low viscosity tape is 0.025 mm to 0.075 mm higher than the thickness of the prepreg.

[0018] Furthermore, the cutting method of the high temperature resistant low viscosity tape is:

[0019] Evenly attaching the initially cut high temperature resistant low viscosity tape to the soft board area on the copper foil surface of the hard board layer where the first circuit production is completed;

[0020] With reference to the etched pads or positioning holes on the hard board layer, the high temperature resistant low viscosity tape is completely cut through by laser until the copper foil surface of the hard board layer.

[0021] Furthermore, the high temperature resistant low viscosity tape is a PI tape.

[0022] Furthermore, in the depth-controlled cover opening processing step, the method for confirming the blind gong depth is: when processing the first piece, by observing the color of the drilling and milling surface, determine whether the high-temperature resistant low-viscosity tape is drilled and milled.

[0023] Furthermore, the window size of the prepreg is 0.1 mm to 0.3 mm larger than that of a single side of the soft board area.

[0024] Furthermore, the alignment and fixing method of the laminated structure is: bonding the three layers of material together by means of hot-melt prepreg or riveting and fixing the three layers of material by means of hollow rivets or solid rivets through rivet holes reserved on the three layers of material.

[0025] Furthermore, the secondary circuit production of the hard board layer includes: drilling, copper deposition, copper plating, outer layer circuit etching, outer layer solder mask production, and outer layer surface treatment according to the process flow of the soft-hard combination board, to complete the outer layer circuit production, outer layer solder mask production and outer layer surface treatment of the laminated structure.

[0026] The present invention has the following technical effects:

[0027] 1. After the product is formed, the soft board area can be opened directly through the depth-controlled opening process, which can improve product production efficiency and reduce production processes and production cycles;

[0028] 2. This process is not affected by the size and shape of the soft board area, and has the characteristics of adapting to local conditions and arbitrary deformation of size;

[0029] 3. The high temperature resistant low viscosity tape is attached to the waste area, and the adhesive layer does not contact the gold fingers, pads, etc. of the product, and will not cause secondary contamination of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a schematic diagram of the structure of the soft board layer after the step 1 of the present invention is completed;

[0031] Figure 2 is a schematic diagram of the structure of the hard board layer 3 after completing steps 2-6 of the present invention;

[0032] Figure 3 is a schematic diagram of the structure of the hard board layer 4 after completing steps 2-6 of the present invention;

[0033] Figure 4 is a schematic diagram of the stacked structure before the present invention performs step 8;

[0034] Figure 5 is a schematic diagram of the laminated structure after steps 8 and 9 are completed in the present invention;

[0035] Figure 6 is a schematic diagram of the laminated structure after steps 10 and 11 of the present invention are completed;

[0036] Figure 7 is a schematic diagram of the laminated structure after the step 12 of the present invention is completed;

[0037] Figure 8 It is a schematic diagram of the stacked structure after the step 13 of the present invention is completed. DETAILED DESCRIPTION

[0038] To further illustrate the various embodiments, the present invention provides drawings. These drawings are part of the disclosure of the present invention, which are mainly used to illustrate the embodiments and can be used in conjunction with the relevant descriptions in the specification to explain the operating principles of the embodiments. With reference to these contents, a person of ordinary skill in the art should be able to understand other possible implementations and advantages of the present invention. The components in the figures are not drawn to scale, and similar component symbols are generally used to represent similar components.

[0039] The present invention will now be further described with reference to the accompanying drawings and specific implementation methods.

[0040] like Figure 1 - Figure 8 As shown, the present invention provides a method for producing a rigid-flexible board using a depth-controlled post-capping process, comprising the following steps:

[0041] 1. Prepare the soft board layer 1 required for the hard-flex board. The soft board layer 1 contains a single-layer or double-layer circuit, including a laminated structure consisting of a flexible substrate 101, copper foil surfaces 102, and 103. According to the design, with the soft board layer 1 as a reference, different areas of the hard-flex board are defined as soft board areas 105 and hard board bonding areas, respectively, wherein the soft board area 105 on the copper foil surfaces 102 and 103 of the soft board layer 1 is affixed with a covering film 2, and the circuits in the hard board bonding area are browned. In specific applications, the flexible substrate of the soft board layer 1 generally adopts materials such as polyimide (PI), and the covering film 2 generally adopts materials such as polyimide film (PI) and polyester film (PET).

[0042] 2. Prepare the hard board layers 3 and 4 required for the rigid-flex board. Drill holes and make the first circuits on each hard board layer 3 and 4. The first circuits are made on the inner side of the lower copper foil surfaces 302 and 402. The lower copper foil surfaces 302 and 402 are respectively opposite to the lower surfaces of the upper copper foil surface 102 and the lower copper foil surface 103 of the soft board layer 1.

[0043] a) Drill holes in the hard board layers 3 and 4 to pre-drill the direction holes, clearance holes, alignment holes 303, 403 and other holes required for assembly;

[0044] b) The inner circuits of the hard board layers 3 and 4 that have completed the drilling process are made: after micro-etching, they are sent to the exposure room, and the first circuit production of the hard board layer is carried out according to the product circuit design. The production process includes micro-etching, dry film pasting, exposure, development, etching, film stripping and other processes.

[0045] In a specific application, the hard board layers 3 and 4 are generally made of hard materials that meet the FR-4 specification.

[0046] 3. Prepare high temperature resistant low viscosity tapes 5 and 6, and cut the high temperature resistant low viscosity tapes 5 and 6 for the first time according to the design pattern size. The currently preferred high temperature resistant low viscosity tape 5 is PI tape, which has the advantages of high temperature resistance, high tensile strength, good chemical resistance, no residual glue, RoHS environmental protection and halogen-free, and is amber in color for easy identification.

[0047] 4. The cut high temperature resistant low viscosity tape 5 is attached to the lower copper foil surface 302 of the hard board layer 3 where the first circuit is made and the area corresponding to the soft board area 105, and then the laminating process is performed to ensure the flatness of the high temperature resistant low viscosity tape 5. Similarly, the cut high temperature resistant low viscosity tape 6 is attached.

[0048] 5. Precise cutting of high temperature resistant low viscosity tape. The hard board layer 3 with the high temperature resistant low viscosity tape 5 is sent to the laser process. According to the design data and referring to the designed etching pads or positioning holes, the high temperature resistant low viscosity tape 5 is completely cut through with CCD alignment laser until the copper foil surface of the hard board layer 3. The laser capability needs to be controlled so that the laser can penetrate the high temperature resistant low viscosity tape 5 but cannot penetrate the hard board layer 3. Preferably, the thickness of the hard board layer cut by the laser does not exceed 0.03 mm to avoid the breakage of the hard board layer 3. Similarly, the laser cutting of the high temperature resistant low viscosity tape 6 is completed. The bonded high temperature resistant low viscosity tapes 5 and 6 are cut by CCD alignment laser, and then the surrounding waste (i.e., waste discharge) is removed to form a filling and adhesive resistance layer in the soft board area 105.

[0049] 6. Tear off the ineffective materials (waste) around the high temperature resistant low viscosity tapes 5 and 6 after completing step 5.

[0050] 7. The prepregs 7 and 8 required for making the hard-flex board are of the same size as the soft board layer 1, and the area corresponding to the soft board area 105 is opened. The opening of the window is based on the boundary line between the soft board area 105 and the hard board area, and the size of the window should be expanded from the soft board area 105 to the hard board area by 0.1mm to 0.3mm.

[0051] 8. The soft board layer 1, the prepregs 7, 8, and the hard board layers 3, 4 are laminated according to the product design, and the three layers of materials are bonded together by hot-melt prepregs 7, 8, or riveted and fixed by hollow rivets or solid rivets through the reserved alignment holes 104, 304, 404 on the three layers of materials. Preferably, in this step, when performing the lamination operation, a special combination PIN (positioning pin) fixture will be put on the alignment holes 104, 304, 404 to prevent alignment deviation.

[0052] 9. Send the laminated structure after step 8 to a high-temperature vacuum laminating machine or other laminating equipment, laminate it with buffer auxiliary materials according to the design requirements, and then press it according to the laminating parameters of the prepreg.

[0053] 10. Production of secondary circuits on the rigid board layer. According to the design process of the rigid-flex board, drilling, copper deposition, copper plating, outer layer circuit etching, outer layer solder mask production, outer layer surface treatment production, the outer layer circuit production, outer layer solder mask production and outer layer surface treatment of the laminated structure are completed.

[0054] 11. Use the drilling and milling blind gong process to remove the hard board layers 3 and 4 in the soft board area 105. Calculate the depth required for opening the cover by the drilling and milling blind gong process based on the thickness of the hard board layer + the thickness of the solder mask ink, perform drilling and milling, mill out grooves 305 and 405, and separate the hard board layers 3 and 4 in the soft board area 105 from other areas; Confirmation of the drilling and milling blind gong depth: Determine whether the high-temperature resistant and low-viscosity tape is drilled and milled by observing the color of the drilling and milling surface. The confirmation of the drilling and milling blind gong depth is generally confirmed by the first piece processing. The completed milling cutter position can clearly observe the color of the high-temperature resistant and low-viscosity PI tape buried in the inner layer, which is made with the optimal parameters. After the first piece processing is confirmed, the depth required for opening the cover by the drilling and milling blind gong process will be checked, and the drilling and milling blind gong process will be automatically controlled by the checked depth.

[0055] 12. Manually peel off the hard board layers 3 and 4 in the milled soft board area 105, and remove the high temperature resistant low-adhesion tapes 5 and 6 attached to the hard board layers 3 and 4 in the soft board area 105 to complete the cover opening process.

[0056] 13. Shaping. Mill off the excess parts of the product periphery that exceed the size according to the design requirements to mill into the finished product.

[0057] 14. After the product has completed electrical testing or flying probe testing, the NG products will be marked or picked out for processing.

[0058] 15. Products that have completed electrical testing or flying probe testing will undergo appearance inspection and be packaged.

[0059] The present invention uses a method of sticking a high-temperature resistant low-viscosity tape on the soft board area of ​​the hard board copper-clad plate, so that the sum of the thickness of the high-temperature resistant low-viscosity tape and the covering film 2 is slightly higher than the thickness of the semi-cured sheet bonding the soft board and the hard board (about 0.025mm~0.075mm higher), and the cut outer dimensions of the high-temperature resistant low-viscosity tape before assembly are more than 2mm larger than the size of the soft board area on one side. Through the etched pattern or hole positioning, the cut high-temperature resistant low-viscosity tape is manually or mechanically attached to the side of the hard board layer close to the soft board layer that needs to be opened. The attached high-temperature resistant low-viscosity tape is aligned through the hole or etched pattern, and a CCD alignment laser cutting process is adopted to engrave a pattern on the cut high-temperature resistant low-viscosity tape that is 0.1mm~0.2mm smaller than the size of the soft board area on one side, and the edge after laser cutting is Material peeling, in the process of laminating the semi-cured sheet, the thickness of the high temperature resistant low-viscosity tape is higher than the thickness of the surrounding semi-cured sheets, and the high temperature resistant low-viscosity tape is pressed on the surface of the soft board. When the semi-cured sheet overflows during the lamination process, it is blocked by the high temperature resistant low-viscosity tape to prevent excessive overflow of the semi-cured sheet during the lamination process. Referring to the laser cutting alignment accuracy of 0.025mm and the inter-layer misalignment of 0.15mm, it can be ensured that the shape of the high temperature resistant low-viscosity tape and the product's opening process interval are ≤0.3mm, and the actual size of the semi-cured sheet overflowing to the high temperature resistant low-viscosity tape is ≤0.3mm. At the same time, the inner layer of the hard board isolation layer that needs to be opened in the soft board area is protected by this high temperature resistant low-viscosity tape. When the cover is opened by the controlled depth milling process, this layer of high temperature resistant low-viscosity tape protection is added between the milling cutter and the soft board layer FPC. After the product is formed, the product manufacturing process can directly open the cover of the soft board area through the depth-controlled opening process, which can improve product production efficiency and reduce production processes and production cycles; this process is not affected by the size and shape of the soft board area, and has the characteristics of adapting to local conditions and arbitrary deformation of size; the high-temperature resistant low-viscosity tape is a PBT type filler and is attached to the waste area. The adhesive layer does not contact the product's gold fingers, pads, etc., and will not cause secondary pollution of the product.

[0060] Although the present invention has been specifically shown and described in conjunction with the preferred embodiments, it should be understood by those skilled in the art that various changes may be made to the present invention in form and details without departing from the spirit and scope of the present invention as defined by the appended claims, all of which are within the scope of protection of the present invention.

Claims

1. A method for producing a rigid-flexible board using a depth-controlled post-capping process, characterized in that: include: Set the soft board area and hard board bonding area of ​​the hard-flex board; Take the soft board layer with completed circuits and apply covering film to the soft board areas on both copper foil surfaces; Take the hard board layer that has completed the first circuit production, and stick the high temperature resistant low viscosity tape on the soft board area of ​​the copper foil surface where the circuit production is completed; the stuck high temperature resistant low viscosity tape is cut and discharged by CCD alignment laser to form a filling and resistance layer; Take the prepreg and make a window treatment on its soft board area; Align and fix the upper and lower hard board layers, the upper and lower prepreg sheets, and the soft board layer so that the high temperature resistant low-adhesive tape on the hard board layer and the covering film on the soft board layer face each other, and then press them together to form a laminated structure; Complete the secondary circuit production of the hard board layer of the laminated structure; The soft board area of ​​the hard board layer under the laminated structure is subjected to a depth-controlled opening process by using a drilling and milling blind gong process. The depth of the drilling and milling blind gong is the sum of the thickness of the hard board layer and the thickness of the solder resist ink, so as to separate the soft board area and the hard board bonding area of ​​the hard board layer; The hard board layer located in the soft board area is peeled off, and the high temperature resistant low-adhesion tape attached to the hard board layer is removed at the same time.

2. The method for producing a rigid-flexible board using a depth-controlled post-capping process according to claim 1, characterized in that: The size of the covering film is larger than that of the soft board area by more than 0.5 mm.

3. The method for producing a rigid-flexible board using a depth-controlled post-capping process according to claim 1, characterized in that: The size of the high temperature resistant low viscosity tape is 0.1 mm to 0.2 mm smaller than that of a single side of the soft board area.

4. The method for producing a rigid-flexible board using a depth-controlled post-capping process according to claim 1, characterized in that: The thickness of the high temperature resistant low viscosity tape is 0.025 mm to 0.075 mm higher than the thickness of the prepreg.

5. The method for producing a rigid-flexible board using a depth-controlled post-capping process according to claim 1, characterized in that: The cutting method of the high temperature resistant low viscosity tape is as follows: Evenly attaching the initially cut high temperature resistant low viscosity tape to the soft board area on the copper foil surface of the hard board layer where the first circuit production is completed; With reference to the etched pads or positioning holes on the hard board layer, the high temperature resistant low viscosity tape is completely cut through by laser until the copper foil surface of the hard board layer.

6. The method for producing a rigid-flexible board using a depth-controlled post-capping process according to claim 1, characterized in that: The high temperature resistant low viscosity tape is a PI tape.

7. The method for producing a rigid-flexible board using a depth-controlled post-capping process according to claim 6, characterized in that: In the depth-controlled cover opening processing step, the method for confirming the blind gong drilling and milling depth is: when processing the first piece, by observing the color of the drilling and milling surface, determine whether the high-temperature resistant low-viscosity tape is drilled and milled.

8. The method for producing a rigid-flexible board using a depth-controlled post-capping process according to claim 1, characterized in that: The window size of the prepreg is 0.1 mm to 0.3 mm larger than that of the soft board area on one side.

9. The method for producing a rigid-flexible board using a depth-controlled post-capping process according to claim 1, characterized in that: The alignment and fixing method of the laminated structure is: using a hot-melt prepreg to bond the three layers of material together or using hollow rivets or solid rivets to rivet and fix through the rivet holes reserved on the three layers of material.

10. The method for producing a rigid-flexible board using a depth-controlled post-capping process according to claim 1, characterized in that: The secondary circuit production of the hard board layer includes: drilling, copper deposition, copper plating, outer layer circuit etching, outer layer solder mask production, and outer layer surface treatment according to the process flow of the soft-hard combination board, completing the outer layer circuit production, outer layer solder mask production and outer layer surface treatment of the laminated structure.

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