A method for manufacturing a multilayer flexible board with ultra-thin and ultra-fine lines

Abstract

A method for fabricating an ultra-thin, ultra-dense multilayer flexible circuit board includes the following steps: Step 1: Copper lamination on a carrier board; Step 2: Forming a first substrate; Step 3: Forming a second substrate; Step 4: Forming a third substrate; Step 5: Separating the boards; Step 6: Hole processing; Step 7: Outer layer circuit processing; Step 8: Post-processing. This invention improves and optimizes the manufacturing process of multilayer flexible printed circuit boards by designing additional carrier boards and removable copper foil structures during processing, greatly enhancing the reliability of ultra-thin substrate processing and ultra-dense circuit fabrication, while significantly reducing the difficulty of the processing and increasing production efficiency. This invention is highly practical and has significant potential for widespread application.

Description

Technical Field

[0001] This invention relates to the field of circuit board manufacturing technology, and in particular to a method for manufacturing a multilayer flexible board with ultra-thin and ultra-dense circuitry. Background Technology

[0002] With the rapid development of electronic devices towards thinner, lighter, and more highly integrated designs, the application of multilayer flexible printed circuit boards (PCBs) is becoming increasingly widespread. In traditional manufacturing processes, when using ultra-thin substrates with a thickness of less than 25μm, their extremely low mechanical strength makes them prone to tearing and wrinkling during lamination and pattern transfer, leading to a significant drop in yield. Meanwhile, to meet the demands of high-density wiring, linewidth / spacing designs have been reduced to ultra-fine line levels of 18μm and below. However, limited by the side etching effect and the uniformity of chemical exchange in traditional etching processes, circuit fabrication often suffers from defects such as rough edges, gaps, and even broken lines, severely affecting circuit accuracy and conductivity reliability.

[0003] Furthermore, to achieve multi-layer structures, conventional processes often require the addition of thicker overlays or reinforcing materials, increasing the overall thickness of the finished board and significantly reducing its flexibility. In dynamic bending applications, this structure is prone to stress concentration, leading to circuit breakage or insulation layer separation, significantly weakening the product's flexural life and operational stability. Therefore, achieving high-precision fabrication of ultra-fine circuits on ultra-thin substrates while maintaining flexibility after multi-layer stacking has become a critical technological bottleneck that urgently needs to be overcome in the current flexible board manufacturing field. Summary of the Invention

[0004] Therefore, it is necessary to provide a method for fabricating multilayer flexible boards with ultra-thin and ultra-dense circuitry to address the shortcomings of existing technologies.

[0005] A method for fabricating a multilayer flexible board with ultra-thin and ultra-dense circuitry includes the following steps:

[0006] Step 1: Copper lamination on the carrier board. A double-sided copper-clad core board is selected as the carrier board, and removable copper foil is laminated on the upper and lower surfaces of the carrier board.

[0007] Step 2: First substrate forming: A resin film is pressed onto the outer surface of the upper and lower detachable copper foils to form the first substrate;

[0008] Step 3: Second substrate forming. First, a second copper layer is plated on the outer surfaces of the upper and lower first substrates. Then, the circuit of the second copper layer is processed by pattern electroplating and flash etching to form the second substrate.

[0009] Step 4: Forming the third substrate. Using a fast pressing or pressure transfer method, resin film and copper foil are pressed onto the outer surfaces of the upper and lower second substrates to form the third substrate.

[0010] Step 5: Separate the boards. Separate the upper and lower detachable copper foils from the carrier board to obtain two multilayer pure flexible boards. Use etching solution to etch and remove the outer copper foil of the multilayer pure flexible boards.

[0011] Step 6: Hole machining, using laser to machine blind holes and through holes on the top and bottom surfaces of the multilayer flexible board;

[0012] Step 7: Outer layer circuit processing. Copper is plated on the upper and lower surfaces of the multilayer flexible board, and pattern electroplating and flash etching are used to form the outer layer ultra-fine circuit.

[0013] Step 8: Post-processing, solder mask preparation, surface treatment and shape processing are performed on the multilayer pure flexible board to obtain the final circuit board product.

[0014] Furthermore, in step 1, the removable copper foil includes a surface copper layer and an edge adhesive layer bonded to the surface copper layer, wherein the edge adhesive layer is pressed and bonded to the upper and lower surfaces of the carrier board.

[0015] Furthermore, in step 1, the roughness of the outer surface of the copper layer is greater than the roughness of the inner surface.

[0016] Furthermore, in steps 2 and 4, the resin film is one of epoxy resin film, ABF resin film, and TPI resin film.

[0017] Furthermore, in step 2, after the first substrate is formed by lamination, the outer surface of the first substrate is subjected to surface activity and roughening treatment by means of plasma and chemical desizing.

[0018] Furthermore, in steps 3 and 7, the thickness of both the second copper layer and the outer copper layer is 0.6-0.9 μm.

[0019] Furthermore, in step 4, after the third substrate is formed by lamination, another layer of copper foil is laminated onto the outer surface of the third substrate.

[0020] Furthermore, in step 6, after processing blind holes and through holes, residual adhesive inside the holes is cleaned by plasma and chemical descaling, and surface activity and roughening treatment is performed on the upper and lower outer surfaces of the multilayer pure flexible board.

[0021] In summary, the beneficial effects of the method for manufacturing an ultra-thin, ultra-dense multilayer flexible circuit board according to the present invention are as follows: by improving and optimizing the production process of the multilayer flexible printed circuit board, and designing additional carrier boards and detachable copper foils and other structures during the processing, the reliability of ultra-thin substrate processing and ultra-dense circuit fabrication is greatly improved, while the difficulty of the processing is significantly reduced and production efficiency is improved; the present invention is highly practical and has strong promotional significance. Attached Figure Description

[0022] Figure 1 This is a cross-sectional structural diagram of steps 1 and 2 in this invention;

[0023] Figure 2 This is a cross-sectional structural diagram of step 3 in the present invention;

[0024] Figure 3 This is a cross-sectional structural diagram of step 4 in the present invention;

[0025] Figure 4 This is a cross-sectional structural diagram of step 5 in the present invention;

[0026] Figure 5 This is a cross-sectional structural diagram of steps 6 and 7 in this invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0028] like Figures 1 to 5 As shown, the present invention provides a method for fabricating a multilayer flexible board with ultra-thin and ultra-dense circuitry, comprising the following steps:

[0029] Step 1: Press copper onto the carrier board 10. A core board with double-sided copper cladding is selected as the carrier board 10, and a removable copper foil 20 is pressed onto the upper and lower surfaces of the carrier board 10. The removable copper foil 20 includes a surface copper layer 21 and an edge adhesive layer 22 bonded to the surface copper layer 21. The edge adhesive layer 22 is pressed and bonded to the upper and lower surfaces of the carrier board 10.

[0030] Adding a carrier plate 10 with extremely high thickness and strength as the pre-forming load-bearing structure for the multilayer flexible board with ultra-thin and ultra-fine lines can provide a stable and reliable support for each ultra-thin substrate. This not only reduces the risk of damage or defects to the substrate during processing, but also makes it easier to fabricate ultra-fine lines on the substrate.

[0031] Specifically, in this embodiment, the roughness of the outer side of the surface copper layer 21 is greater than the roughness of the inner side, that is, the rough surface of the surface copper layer 21 faces outward. The outward setting of the rough surface enables it to be reliably and firmly pressed with the flexible board substrate, and also facilitates the peeling of the surface copper layer 21 from the edge adhesive layer 22, which is convenient for subsequent board separation operations.

[0032] Step 2: The first substrate 30 is formed by pressing a resin film onto the outer surface of the upper and lower detachable copper foils 20 to form the first substrate 30. After the first substrate 30 is formed by pressing, the outer surface of the first substrate 30 is subjected to surface activity and roughening treatment by plasma and chemical descaling.

[0033] The outer surface of the first substrate 30, after plasma and chemical descaling, can be better plated with copper in subsequent processes, making the bonding between the dielectric layer and the copper plating layer stronger and more reliable. Specifically, in this embodiment, the resin film is one of epoxy resin film, ABF resin film, and TPI resin film. These resin films are all heat-resistant and insulating films, and they contain a high proportion of silicon, thus having better adhesion.

[0034] Step 3: Forming the second substrate 40. First, a second copper layer 41 is plated on the outer surfaces of the upper and lower first substrates 30. Then, the circuit 42 of the second copper layer is processed by pattern electroplating and flash etching to form the second substrate 40. The thickness of the second copper layer 41 is 0.6-0.9μm. Specifically, in this embodiment, the second copper layer 41 is a low-stress copper layer with a thickness of 0.8μm. The low-stress copper layer has high uniformity and can effectively prevent problems such as unevenness, cracks or even peeling of the copper layer.

[0035] Step 4: Forming the third substrate. Using a fast pressing or pressure transfer method, a resin film 50 is pressed onto the outer surface of the upper and lower second substrates 40, and a copper foil 60 is then pressed onto the outer surface of the resin film 50 to form the third substrate. Specifically, in this embodiment, the resin film 50 is one of epoxy resin film, ABF (Ajinomoto laminate) resin film, and TPI (thermoplastic polyimide) resin film.

[0036] Step 5: Separate the boards. Separate the upper and lower detachable copper foils 20 from the carrier board 10 to obtain two multilayer pure flexible boards 100. Use etching solution to etch and remove the copper foil on the outside of the multilayer pure flexible boards 100.

[0037] In this invention, the process used to manufacture the multilayer flexible board is the common SAP (semi-additive process). However, unlike the ordinary SAP process, this invention also includes an operation in steps 1, 4 and 5 of pressing a removable copper foil 20 and a copper foil 60 onto the resin film 50 and then removing them.

[0038] The laminated removable copper foil 20 and copper foil 60 not only protect the vertical adhesive film 50, but also the micro-copper tooth structure on the surface of the copper layer can make the surface of the resin adhesive film 50 have a certain roughness, which greatly increases the bonding force between the copper plating layer and the additive material.

[0039] Step 6: Hole processing. Blind holes and through holes are processed on the upper and lower surfaces of the multilayer pure flexible board 100 using a laser. After processing the blind holes and through holes, residual adhesive in the holes is cleaned by plasma and chemical descaling. At the same time, the upper and lower outer surfaces of the multilayer pure flexible board 100 are subjected to surface activity and roughening treatment.

[0040] Step 7: Outer layer circuit processing. The outer layer copper 70 is plated on the upper and lower surfaces of the multilayer pure flexible board 100, and the outer layer ultra-fine circuit 80 is formed by pattern electroplating and flash etching. The thickness of the outer layer copper 70 is 0.6-0.9μm.

[0041] Step 8: Post-processing, solder resist preparation, surface treatment and shape processing are performed on the multilayer pure flexible board 100 to obtain the final circuit board product.

[0042] In summary, the beneficial effects of the method for manufacturing an ultra-thin, ultra-dense multilayer flexible circuit board according to the present invention are as follows: by improving and optimizing the manufacturing process of the multilayer flexible printed circuit board, and designing additional carrier board 10 and detachable copper foil 20 and other structures during the processing, the reliability of ultra-thin substrate processing and ultra-dense circuit manufacturing is greatly improved, while the difficulty of the processing process is significantly reduced and the production efficiency is improved; the present invention is highly practical and has strong promotional significance.

[0043] The embodiments described above illustrate only one implementation of the invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the inventive concept, and these all fall within the scope of protection of the invention. Therefore, the scope of protection of the invention patent should be determined by the appended claims.

Claims

1. A method for fabricating a multilayer flexible board with ultra-thin, ultra-dense circuitry, characterized in that, Includes the following steps: Step 1: Copper lamination on the carrier board. A double-sided copper-clad core board is selected as the carrier board, and removable copper foil is laminated on the upper and lower surfaces of the carrier board. Step 2: First substrate forming: A resin film is pressed onto the outer surface of the upper and lower detachable copper foils to form the first substrate; Step 3: Second substrate forming. First, a second copper layer is plated on the outer surfaces of the upper and lower first substrates. Then, the circuit of the second copper layer is processed by pattern electroplating and flash etching to form the second substrate. Step 4: Forming the third substrate. Using a fast pressing or pressure transfer method, resin film and copper foil are pressed onto the outer surfaces of the upper and lower second substrates to form the third substrate. Step 5: Separate the boards. Separate the upper and lower detachable copper foils from the carrier board to obtain two multilayer pure flexible boards. Use etching solution to etch and remove the outer copper foil of the multilayer pure flexible boards. Step 6: Hole machining, using laser to machine blind holes and through holes on the top and bottom surfaces of the multilayer flexible board; Step 7: Outer layer circuit processing. Copper is plated on the upper and lower surfaces of the multilayer flexible board, and pattern electroplating and flash etching are used to form the outer layer ultra-fine circuit. Step 8: Post-processing, solder mask preparation, surface treatment and shape processing are performed on the multilayer pure flexible board to obtain the final circuit board product.

2. The method for fabricating a multilayer flexible board with ultra-thin and ultra-dense circuitry as described in claim 1, characterized in that: In step 1, the removable copper foil includes a surface copper layer and an edge adhesive layer bonded to the surface copper layer, wherein the edge adhesive layer is pressed and bonded to the upper and lower surfaces of the carrier board.

3. The method for fabricating a multilayer flexible board with ultra-thin and ultra-dense circuitry as described in claim 1, characterized in that: In step 1, the roughness of the outer surface of the copper layer is greater than the roughness of the inner surface.

4. The method for fabricating a multilayer flexible board with ultra-thin and ultra-dense circuitry as described in claim 1, characterized in that: In steps 2 and 4, the resin film is one of epoxy resin film, ABF resin film, and TPI resin film.

5. The method for fabricating a multilayer flexible board with ultra-thin and ultra-dense circuitry as described in claim 1, characterized in that: In step 2, after the first substrate is formed by lamination, the outer surface of the first substrate is subjected to surface activity and roughening treatment by plasma and chemical desizing.

6. The method for fabricating a multilayer flexible board with ultra-thin and ultra-dense circuitry as described in claim 1, characterized in that: In steps 3 and 7, the thickness of both the second copper layer and the outer copper layer is 0.6-0.9 μm.

7. The method for fabricating a multilayer flexible board with ultra-thin and ultra-dense circuitry as described in claim 1, characterized in that: In step 4, after the third substrate is formed by lamination, another layer of copper foil is laminated onto the outer surface of the third substrate.

8. The method for fabricating a multilayer flexible board with ultra-thin and ultra-dense circuitry as described in claim 1, characterized in that: In step 6, after the blind holes and through holes are machined, the residual adhesive inside the holes is cleaned by plasma and chemical descaling, and the upper and lower outer surfaces of the multilayer pure flexible board are simultaneously subjected to surface activity and roughening treatment.

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