Method for manufacturing a flexible printed circuit board

Abstract

The present invention relates to a flexible printed circuit board (FPCB) and a method for manufacturing the same, and more particularly, to a method for manufacturing a flexible printed circuit board capable of minimizing machining tolerances generated when machining an outline of a board by forming a reference mark in the FPCB in a series of processes for manufacturing the board and by using the reference mark as a reference point for outline machining.

Description

Technical Field

[0001] This disclosure relates to methods for manufacturing flexible printed circuit boards, and more specifically, to methods for manufacturing flexible printed circuit boards that can reduce machining tolerances generated when processing the shape of the flexible printed circuit board. Background Technology

[0002] In recent years, with the market growth of electronic devices such as computers, laptops, and camera devices, the importance of printed circuit boards as essential key components for high integration and packaging has been increasing.

[0003] A printed circuit board (PCB) supports or connects various components based on the circuit design of the wires on the original printed circuit board. PCBs are essential components for configuring electronic products.

[0004] In recent years, with the miniaturization and weight reduction of electronic products, flexible printed circuit boards (FPCBs), made of bendable flexible materials to allow three-dimensional wiring and capable of miniaturization and weight reduction, have attracted attention and have been widely used in small and medium-sized electronic products such as smartphones, camera devices, laptops, and tablets.

[0005] Typically, the aforementioned FPCBs are manufactured through various processes, including cutting, drilling, copper plating, brushing, dry film drying, exposure, etching, PSR, hot pressing, gold plating, BBT, shaping, and final inspection.

[0006] Among these manufacturing processes, the outline machining process processes the shape of the circuit board in accordance with the shape of the product or device (smartphone or laptop) on which the FPCB is finally mounted. The outline machining process performs the outline machining while setting the vias formed on the outside of the circuit board in the printing process as reference points and compensating for the distance from the reference points.

[0007] However, although the FPCB is fixed during the shape processing, errors may occur in the distance from the reference point due to curling caused by bending due to the characteristic flexibility of the board material.

[0008] In this situation, due to a mismatch in reference points during the molding process, the connector (or terminal) may be offset to one side instead of in the center, and as a result, the contact portion of the circuit board with the connector may be misaligned and contact other connectors, leading to a short circuit.

[0009] (Patent Document 1) KR10-1500435B1. Summary of the Invention

[0010] Technical issues

[0011] This disclosure provides a method for reducing machining tolerances that arise when processing the shape of flexible printed circuit boards (FPCBs).

[0012] Solution to the problem

[0013] According to an exemplary embodiment, a method for manufacturing a flexible printed circuit board (FPCB) includes: a cutting step, in which a base film including an insulating layer and at least one thin copper layer is suitably cut into a panel shape conforming to predetermined standards; a drilling step, in which holes are machined through all the insulating layers and thin copper layers of the base film; a copper plating step, in which copper is used to electroplate the inner walls of the holes; a circuit and reference mark forming step, in which predetermined circuit patterns and reference marks are formed on the thin copper layer of the base film; a temporary bonding step, in which a cover film is temporarily bonded to a predetermined area on the top surface of the thin copper layer on which the circuit and reference marks are formed; a full bonding step, in which the temporarily bonded cover film is fully bonded to the base film by applying high temperature and high pressure; a surface electroplating step, in which the surface of the area not covered by the cover film, except for the predetermined area, is electroplated; and a shaping step, in which the shape of the panel-shaped board is machined into a predetermined size and shape. Here, the shaping step machines the shape by using reference marks formed in the FPCB by the circuit and reference mark forming step as reference points.

[0014] The circuit and reference mark formation steps may include: a brushing step to roughen the surface of the thin copper layer; a lamination step to laminate a dry film onto the thin copper layer for close contact; an exposure step to irradiate UV light in the shape of the reference marks and predetermined circuit patterns to be formed on the dry film in close contact with the thin copper layer; a development step to remove the dry film that has not been exposed to UV light and has not been cured; an etching step to oxidize and remove the portion of the thin copper layer other than the circuit patterns and reference marks; and a stripping step to remove the dry film remaining on the surface of the base film to complete the formation of the circuit patterns and reference marks after the etching step.

[0015] In one embodiment, the reference mark formed by the circuit and reference mark forming step can be positioned in an area within a predetermined distance from the circuit terminals of the board coupled to the connector.

[0016] In another embodiment, the reference mark formed by the circuit and reference mark forming step can be positioned on the internal region of the circuit terminals of the board coupled to the connector.

[0017] More specifically, the reference mark can be set as an extension portion, which is obtained by extending a pin contact portion area that contacts the connector pins in the internal region of the circuit terminals of the board by a predetermined length.

[0018] According to another exemplary embodiment, a flexible printed circuit board (FPCB) includes circuit terminals coupled to a connector and reference marks, and the reference marks formed in the board serve as reference points when processing the board's outline.

[0019] In one embodiment, a reference mark may be formed on a region within a predetermined distance from the circuit terminals.

[0020] In another embodiment, a reference mark may be formed on the inner region of the circuit terminal.

[0021] The circuit terminal may include an extension portion, which is an area obtained by extending the pin contact portion region that contacts the connector pin by a predetermined length.

[0022] Here, the reference mark can be set as an extension area formed in the circuit terminals of the board.

[0023] The effect of this disclosure

[0024] This disclosure minimizes the possibility of machining tolerances due to curling caused by the board's flexibility during molding by using reference points inside the FPCB to perform profile machining and reducing the distance between the FPCB's connectors (or terminals) and the reference points. Attached Figure Description

[0025] The exemplary embodiments can be understood in more detail from the following description taken in conjunction with the accompanying drawings, in which:

[0026] Figure 1 This is a flowchart illustrating the manufacturing steps of a flexible printed circuit board (FPCB) according to an exemplary embodiment;

[0027] Figure 2 This is a view showing the overall shape of the FPCB;

[0028] Figure 3 This is an enlarged view showing an example of circuit terminals;

[0029] Figure 4 This is a view showing the formation location of reference marks according to an exemplary embodiment; and

[0030] Figure 5 This is a view showing the formation location of reference marks according to another exemplary embodiment. Detailed Implementation

[0031] In the following, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings, enabling those skilled in the art to readily implement the technical concept of the invention. However, this disclosure may be implemented in various forms and should not be construed as limited to the embodiments set forth herein. In the drawings, for clarity, any content unnecessary for describing this disclosure will be omitted, and the same reference numerals denote the same elements in the additional drawings.

[0032] In the following description, embodiments of the inventive concept will be described with reference to the accompanying drawings.

[0033] 1. A method for manufacturing an FPCB according to an exemplary embodiment

[0034] Figure 1 This is a flowchart illustrating a method for manufacturing a flexible printed circuit board (FPCB) according to an exemplary embodiment. (Refer to...) Figure 1 Describe each process.

[0035] 1.1. Cutting step S10

[0036] As the first process used in the production of flexible printed circuit boards (FPCBs), the dicing step involves cutting the base film, which serves as the raw material for the FPCB, based on working standards. Here, the base film comprises an insulating layer (PI) and a thin copper (Cu) layer.

[0037] Here, the base film can have a structure in which a thin copper (Cu) layer is bonded to the top surface of the insulating layer (PI), or a structure in which a thin copper (Cu) layer is bonded to both the top and bottom surfaces of the insulating layer (PI). In the former case, a single-sided FPCB is manufactured, while in the latter case, a double-sided FPCB is manufactured.

[0038] 1.2. Drilling Step S20

[0039] The drilling step is the process of creating holes in the base film by using a drill bit to penetrate all the insulating layers (PI) and thin copper layers of the base film.

[0040] This step may be omitted when the base film has a single-sided structure in which the thin copper layer is bonded only to the top surface of the insulating layer (PI).

[0041] 1.3. Copper plating step S30

[0042] The copper plating step is a process of applying conductivity by electroplating copper, which acts as a conductor, onto the inner wall of the hole in which it was drilled during the drilling step.

[0043] This step is used to electrically connect the upper and lower thin copper layers relative to the insulating layer (PI) when the base film has a double-sided structure. Similar to drilling step S20, this step can be omitted when the base film has a single-sided structure.

[0044] 1.4. Circuit and Reference Mark Formation Step S40

[0045] The circuit and reference mark formation steps include: a brushing step S41, roughening the surface of the thin copper layer to allow the dry film (photosensitive film) to properly bond to the base film; a lamination step S42, using heat and pressure to laminate the dry film onto the thin copper layer for close contact; an exposure step S43, irradiating UV light into the shape of the reference mark and predetermined circuit pattern to be formed on the dry film of the thin copper layer tightly attached to the base film to form the circuit and reference mark; a development step S44, removing the dry film that has not been exposed to UV light and has not been cured; an etching step S45, treating the base film after the development step with chemicals to oxidize and remove the exposed portions of the thin copper layer, i.e., portions that do not correspond to the circuit and reference mark; and a stripping step S46, removing the dry film remaining on the surface of the base film to complete the formation of the circuit pattern and reference mark.

[0046] Here, since the dry film cured by UV light in exposure step S43 is resistant to the chemicals in etching step S45, the thin copper layer under the dry film is retained as the circuit and reference mark to be formed.

[0047] Typical FPCB manufacturing processes form only circuit patterns on a base film through brushing, lamination, exposure, development, etching, and stripping. However, in an exemplary embodiment, reference marks are additionally formed during the circuit formation process described above. These reference marks formed in this process are used as reference points when processing the outline in the outline processing step S100, which will be described later.

[0048] Here, the position of the reference mark to be formed by the above process can be set according to the following two embodiments.

[0049] <Implementation Method 1>

[0050] Figure 2 This is a view showing the overall appearance of a flexible printed circuit board 100, including typical FPCB circuit terminals 110 coupled to connectors, and Figure 3 This is an enlarged view showing the FPCB circuit terminal 110.

[0051] In the case of implementation method 1, such as Figure 4As shown, reference mark 120 can be formed adjacent to the FPCB circuit terminal. In exposure step S43, when UV light is irradiated on the dry film of the thin copper layer in close contact with the base film, a predetermined circuit pattern and reference mark can be formed on the thin copper layer by irradiating UV light in the following shape: the shape is realized as including, in addition to the predetermined circuit pattern, a reference mark located at any position in the area within a predetermined interval distance from the FPCB circuit terminal.

[0052] <Implementation Method 2>

[0053] Embodiment 2 can form a reference mark to be positioned in the FPCB circuit terminal. The predetermined circuit pattern and reference mark can be formed by the same method as in Embodiment 1, where UV light is irradiated in the shape of the predetermined circuit pattern and reference mark in exposure step S43, but Embodiment 2 differs from Embodiment 1 in shape.

[0054] Although in Implementation 1 the reference mark is implemented by setting its shape to be adjacent to the FPCB circuit terminal, however... Figure 5 As shown, in Embodiment 2, the reference mark is implemented by the shape provided in the FPCB circuit terminal.

[0055] In this case, specifically, when the shape including the predetermined circuit pattern and the reference mark is realized, the pin contact portion area of ​​the terminal pin 112 in the FPCB circuit terminal is realized by extending the shape of the extension portion with a predetermined length in its width direction, and is set as the reference mark 120. That is, when UV light is irradiated onto the thin copper layer of the base film having the shape including the predetermined circuit pattern and the extension portion, the predetermined circuit pattern and the reference mark set in the FPCB circuit terminal can be formed on the thin copper layer.

[0056] As described above, unlike the typical case where the reference point is located outside the FPCB when processing the FPCB outline, according to the exemplary embodiment, in a series of processes for forming circuit patterns on the board, the reference point is located in the FPCB by forming a reference point other than the circuit pattern.

[0057] Here, although the reference mark is in Figure 4 It has a circular shape and Figure 5 The reference mark has a rectangular shape, but the exemplary implementation is not limited to this. For example, the reference mark can have various shapes, such as a triangle or a rectangle.

[0058] 1.5. Temporary joining step S50

[0059] The temporary bonding step is a step in which a cover film is temporarily bonded to the FPCB product on which the circuit and reference mark formation step S40 has been fully performed. Here, the cover film is used to protect the circuit and form an insulating layer as a protective film for the FPCB.

[0060] Here, when the cover film is temporarily attached, the predetermined area to be electroplated with gold in the surface electroplating step S70 is excluded in order to expose the circuit, and the predetermined area refers to the soldering area.

[0061] 1.6. Fully Engaged Step S60

[0062] The full bonding step is a step in which the base film is fully bonded to the cover film temporarily bonded in the temporary bonding step by applying high temperature and high pressure. Here, before applying high temperature and high pressure, a typical process (lamination process) is performed in which insert paper is inserted between the thin copper layer etched in step S40 by forming circuit patterns and reference marks to protect the base film from high temperature and high pressure while the cover film is temporarily bonded.

[0063] 1.7. Surface electroplating step S70

[0064] After completing the bonding step S60, a process is performed to electroplate the surface of the area not covered by the cover film—that is, the area where the circuit (thin copper layer) was exposed as the soldering area in the temporary bonding step S50.

[0065] 1.8. Printing Step S80

[0066] After the gold plating step, a process is performed to print product information (such as customer name, final product code, part number, part location, and rated capacity) to be displayed on the FPCB product.

[0067] 1.9. Abnormal State Inspection Step S90

[0068] This step is to check whether the electrical function of the FPCB is normal or abnormal to ensure the characteristics of the electrical signals. Since the FPCB forms a circuit that serves as a wire, this step checks whether the circuit pattern formed in step S40 is normal or abnormal through the circuit and reference marks. The method for checking whether the electrical function of the FPCB is normal or abnormal can be performed by applying current to the FPCB to check whether electrical functions such as open circuit or short circuit are normal or abnormal.

[0069] 1.10. External machining steps S100

[0070] The shape processing step is a process of using molds to process the shape of an FPCB product with a panel shape into a predetermined size and shape.

[0071] Unlike the typical method of processing the shape by using vias formed on the outside of the FPCB as reference points, the shape processing steps according to the exemplary embodiment process the shape by using reference marks formed in the FPCB by the circuit pattern and reference mark forming step S40 as reference points.

[0072] As described above, according to an exemplary embodiment, in a series of processes for forming circuit patterns on an FPCB, specifically, reference marks are additionally formed in the FPCB at a location adjacent to or within the region of the FPCB circuit terminals coupled to terminals (or connectors), and the shape processing is performed by using the reference marks as reference points during shape processing, so as to minimize the tolerances generated during shape processing, thereby improving the production efficiency of FPCB products.

[0073] 2. FPCB according to an exemplary embodiment

[0074] The difference between the FPCB according to the exemplary embodiment and the typical FPCB is that the FPCB according to the exemplary embodiment includes reference marks additionally formed by a series of processes in which a circuit pattern is formed in the FPCB, which serve as reference points when processing the outline as described above, while the typical FPCB performs outline processing by using vias formed on the outside of the FPCB as reference points.

[0075] Reference marks formed in the FPCB can be positioned in an area spaced a predetermined distance from the FPCB circuit terminals, adjacent to the FPCB circuit terminals coupled to the terminals (or connectors), such as... Figure 4 The illustrated embodiment 1, or positioned within the FPCB circuit terminals, such as... Figure 5 The illustrated embodiment 2. Specifically, in embodiment 2, the reference mark can be positioned in the area of ​​the terminal (or connector) in contact with the FPCB circuit terminal.

[0076] The reference mark is a thin copper portion that differs from the circuit and is retained during etching step S45. Through a series of processes, the reference mark can be... Figure 4 As shown, it is formed at a location adjacent to the circuit terminals or as... Figure 5 At the location shown in the circuit terminal, the series of processes includes: process S43, irradiating UV light in the shape of a predetermined circuit pattern and reference mark to be formed on a dry film in close contact with a thin copper layer; process S44, peeling off the dry film of the portion not exposed to UV light and not cured; and process S45, oxidizing and removing the portion that does not correspond to the circuit pattern and reference mark.

[0077] According to an exemplary embodiment, the FPCB includes a reference mark set adjacent to or disposed in the FPCB circuit terminals, and the reference mark acts as a reference point during profile processing to reduce the distance between the FPCB product and the reference point more than typically, so as to minimize processing tolerances caused by various factors (such as curling caused by the flexibility of the FPCB as a characteristic of the FPCB) during profile processing.

[0078] As described above, the technical concept of the present invention has been specifically described with reference to the above embodiments. However, it should be noted that the above embodiments are provided for illustration only and not for limiting the present invention. Various embodiments may be provided to enable those skilled in the art to understand the scope of the present invention, but the present invention is not limited thereto.

Claims

1. A method for manufacturing a flexible printed circuit board, comprising: The cutting step involves appropriately cutting the base film, which includes an insulating layer and at least one thin copper layer, into a panel shape that conforms to predetermined standards. The drilling step involves machining holes that pass through all the insulating layers and thin copper layers of the base film; The copper plating step involves electroplating the inner wall of the hole with copper. The circuit and reference mark formation step involves forming a predetermined circuit pattern and reference marks on the thin copper layer of the base film; The temporary bonding step involves temporarily bonding the cover film to a predetermined area on the top surface of the thin copper layer on which the circuit and the reference mark are formed; The complete bonding step involves applying high temperature and high pressure to fully bond the temporarily bonded cover film to the base film; The surface electroplating step involves electroplating the surface of the area not covered by the covering film, except for the predetermined area. The outer shape processing step involves processing the panel-shaped plate into a predetermined size and shape. The shape processing step involves using reference marks formed in the flexible printed circuit board through the circuit and reference mark forming step as reference points to process the shape. The reference mark formed through the circuit and reference mark forming steps is positioned on the internal region of the circuit terminals of the board coupled to the connector, and The reference mark is set as an extension portion, which is obtained by extending a pin contact portion region that contacts the connector pin in the internal region of the circuit terminal of the board by a predetermined length.

2. The method according to claim 1, wherein, The circuit and reference mark formation steps include: The brushing step roughens the surface of the thin copper layer; The lamination step involves laminating a dry film onto the thin copper layer to ensure close contact with the thin copper layer. The exposure step involves irradiating UV light into the shape of reference marks and predetermined circuit patterns to be formed on the dry film in close contact with the thin copper layer. The developing step removes the dry film from the portions that were not exposed to the UV light and were not cured. Etching steps, oxidizing and removing portions of the thin copper layer except for the circuit pattern and the reference marks; and The stripping step removes the dry film remaining on the surface of the base film to complete the formation of the circuit pattern and the reference mark after the etching step.

3. A flexible printed circuit board, comprising: Circuit terminals coupled to the connector; And reference markers, In the process of manufacturing the shape of the flexible printed circuit board, the reference mark formed in the flexible printed circuit board serves as a reference point. The reference mark is formed on the internal region of the circuit terminal, and The reference mark is configured as an extension portion, which is obtained by extending a pin contact portion region that contacts the connector pin in the internal region of the circuit terminal of the flexible printed circuit board by a predetermined length.

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