Method for manufacturing double-sided flexible printed circuit board

Abstract

The present invention relates to a method for manufacturing a double-sided flexible printed circuit board, the method comprising the steps of: forming a hole in a non-conductive film; covering the non-conductive film having the hole with a conductive seed material; applying dry films to both sides of the non-conductive film covered with the conductive seed material; removing portions of the dry films corresponding to a through hole area and a circuit pattern area that are to be plated; forming a plated through hole and circuit pattern by plating the non-conductive film with a conductive material; and removing the remaining dry films and the conductive seed material under the remaining dry films.

Description

Method for manufacturing double-sided flexible printed circuit boards

[0001] The present invention relates to a method for manufacturing a double-sided flexible printed circuit board in which a circuit board is formed on both sides of an insulating film.

[0002] A flexible printed circuit board (FPCB) is a substrate that can be flexibly bent by forming a circuit pattern on a thin insulating film. It is widely used in cases where bending and flexibility are required when mounting components, such as mobile devices such as smartphones and display devices.

[0003] These flexible printed circuit boards are generally manufactured using a flexible copper clad laminate (FCCL) film, which is a copper foil layer laminated on a polyimide film layer, as a substrate (raw material), and the circuit pattern is mainly formed by performing tasks such as laminating, exposing, developing, and etching dry films on the FCCL film.

[0004] Meanwhile, when manufacturing a double-sided flexible printed circuit board to perform circuit connections on both sides of the flexible printed circuit board, a double-sided FCCL substrate is generally used. The double-sided FCCL substrate is in the form of a copper foil layer laminated on both sides of a polyimide film layer.

[0005] By forming a through hole (via hole) in this double-sided FCCL and plating the inner wall of the through hole using electroless copper plating or other methods, the copper layers on both sides are electrically connected, enabling circuit connection on both sides of the flexible printed circuit board.

[0006] Through holes are usually formed through a drilling process using an NC drill or laser. Precision machining is required to avoid damage to both the film and the copper layer, and the more through holes there are, the more time and cost the process takes.

[0007] In addition, a separate process of plating the inner wall of the through hole must be performed for electrical connection of the inner hole, and this process is performed by first conducting electricity on both sides of the inside of the through hole using a method such as electroless plating, and then performing electrolytic plating to increase the thickness of the plating layer inside the through hole.

[0008] However, when looking at the thickness of the entire copper, the upper and lower surfaces of the FCCL with the copper foil layer are represented by the sum of the thickness of the existing copper foil layer, the thickness of the electroless plating layer, and the thickness of the electrolytic plating layer, and the thickness of the inner side wall of the through hole is represented by the sum of the thickness of the electroless plating layer and the thickness of the electrolytic plating layer, so there is a difference in the thickness.

[0009] In addition, due to the formation process of each side and the difference in thickness, a discontinuous connection may be created at the connection between the upper and lower surfaces where the copper layer is located and the plating layer on the inner side wall of the through hole, which may cause a defect.

[0010] As such, the existing process involves multiple steps to form electrically connected through-holes, resulting in high process costs and the need for additional management elements, which inevitably increases manufacturing costs. Furthermore, the price of double-sided FCCLs is relatively high. The above explanation reflects the varying process methods used by each manufacturer, and slight variations may exist.

[0011] Accordingly, research and development of various methods for reducing manufacturing costs are being conducted, but they are not widely used in industrial settings due to problems such as damage to the copper layer, reliability issues, and an increase in the time and cost required for the entire process.

[0012] Meanwhile, the background technology of the present invention is disclosed in Republic of Korea Patent Publication No. 10-2018-0016323 (February 14, 2018).

[0013] The present invention is intended to solve the problems of the conventional double-sided flexible printed circuit board manufacturing method as described above, and the purpose of the present invention is to provide a method for manufacturing a double-sided flexible printed circuit board capable of forming a circuit connected on both sides in a cheaper and simpler manner than the conventional method.

[0014] A method for manufacturing a double-sided flexible printed circuit board according to the present invention is characterized by comprising the steps of: forming a hole in a non-conductive film; covering the non-conductive film in which the hole is formed with a conductive seed material; applying a dry film to each of both surfaces of the non-conductive film covered with the conductive seed material; removing a portion corresponding to a through-hole region and a circuit pattern region to be plated from the dry film; plating a conductive material on the non-conductive film to form a plated through-hole and a circuit pattern; and removing a remaining dry film and a conductive seed material positioned below the remaining dry film.

[0015] In the present invention, the step of removing the residual dry film and the conductive seed material positioned below the residual dry film is characterized in that the residual dry film and the conductive seed material positioned below the residual dry film are removed through etching.

[0016] In the present invention, it is characterized in that at least a portion of the conductive material plated by the etching is etched away.

[0017] In the present invention, it is characterized in that plating of the conductive material is performed taking into consideration the thickness to which the conductive material is to be cut.

[0018] In the present invention, it is characterized in that removal of a portion corresponding to a through-hole area and a circuit pattern area where plating is to be performed in the dry film is performed in consideration of the width to which the conductive material is to be cut.

[0019] In the present invention, the step of covering the non-conductive film with a conductive seed material is characterized by covering the non-conductive film with the conductive seed material through dry plating.

[0020] In the present invention, the step of removing a portion corresponding to the through-hole region and the circuit pattern region is characterized by removing a portion corresponding to the through-hole region and the circuit pattern region from the dry film through exposure and development of the dry film.

[0021] In the present invention, the step of forming the plated through hole and circuit pattern is characterized by performing plating of the conductive material through electroplating.

[0022] In the present invention, the conductive seed material is characterized in that it is one of titanium, nickel, chromium and copper, or an alloy of at least two of titanium, nickel, chromium and copper.

[0023] In the present invention, the conductive seed material is characterized in that it is composed of a plurality of layers.

[0024] In the present invention, the conductive material is characterized in that it is copper.

[0025] In the present invention, the non-conductive film is characterized in that it is a polyimide film.

[0026] The method for manufacturing a double-sided flexible printed circuit board according to the present invention covers a non-conductive film having a hole formed therein with a conductive material, forms an area to be plated, and then forms a plated through hole and a circuit pattern together through a single plating process, thereby omitting a separate hole plating process, thereby having the effect of reducing the time and cost required for manufacturing a double-sided flexible printed circuit board.

[0027] The method for manufacturing a double-sided flexible printed circuit board according to the present invention has the effect of improving the reliability of the through-hole portion by forming plated through-holes and circuit patterns together through a single plating process, thereby preventing the occurrence of discontinuous connection patterns, etc.

[0028] The method for manufacturing a double-sided flexible printed circuit board according to the present invention has the effect of enabling a simpler method than the drilling process used in the case of using a double-sided FCCL for forming through holes or achieving high precision by first forming holes only in a non-conductive film.

[0029] FIG. 1 is a flowchart illustrating a method for manufacturing a double-sided flexible printed circuit board according to one embodiment of the present invention.

[0030] Figures 2 to 7 are exemplary diagrams for explaining a method for manufacturing a double-sided flexible printed circuit board according to one embodiment of the present invention.

[0031] FIGS. 8 to 10 are exemplary views illustrating a method for manufacturing a multilayer flexible printed circuit board by laminating intermediate products of a double-sided flexible printed circuit board manufactured by a double-sided flexible printed circuit board manufacturing method according to one embodiment of the present invention.

[0032] Hereinafter, a method for manufacturing a double-sided flexible printed circuit board according to the present invention will be described with reference to the attached drawings. In this process, the thickness of lines and the sizes of components depicted in the drawings may be exaggerated or omitted for clarity and convenience. Furthermore, the terms described below are defined based on their functions in the present invention and may vary depending on the intentions or practices of the user or operator. Therefore, the definitions of these terms should be based on the contents throughout this specification.

[0033] FIG. 1 is a flowchart for explaining a method for manufacturing a double-sided flexible printed circuit board according to an embodiment of the present invention, and FIGS. 2 to 7 are exemplary diagrams for explaining a method for manufacturing a double-sided flexible printed circuit board according to an embodiment of the present invention. With reference to these, the method for manufacturing a double-sided flexible printed circuit board according to an embodiment of the present invention will be described as follows.

[0034] As illustrated in FIG. 1, a method for manufacturing a double-sided flexible printed circuit board according to one embodiment of the present invention first forms a hole (2) in a non-conductive film (1) (S100). That is, as illustrated in FIG. 2, an area where a through hole is to be formed is formed in advance in the non-conductive film (1).

[0035] At this time, the formation of the hole (2) can be performed in various ways, such as processing by drilling or processing by laser, and unlike the processing of double-sided FCCL, since only the non-conductive film (1) is processed, there are fewer restrictions on the processing method compared to the drilling process when using double-sided FCCL, and it can be performed in a simpler process.

[0036] Meanwhile, various expressions such as through hole, via hole, blind hole, and buried hole are used depending on whether the product is mounted in the hole or whether the hole is exposed to the outside of the finished product (substrate), but since they have the same shape except for the difference in use, they are collectively referred to as through holes in the present invention.

[0037] Here, the non-conductive film (1) may be, for example, a polyimide film, but may also be a film of another insulating material.

[0038] FIG. 2 (a) is a drawing of a non-conductive film (1) viewed from above, and FIG. 2 (b) is a cross-section (a section in the thickness direction of the non-conductive film (1), i.e., a plane perpendicular to the plane of FIG. 2 (a)) obtained by cutting out only the dotted line portion of FIG. 2 (a) for explanation purposes. In the drawings described below, the manufacturing process will be described based on this cross-section, and the implementation of a typical circuit pattern in which a circuit pattern viewed from above is connected in a circular or linear manner corresponds to a matter widely known in the technical field of the present invention, and therefore, a detailed description thereof will be omitted.

[0039] In addition, in this embodiment, only one hole (2) is shown, but multiple holes may be formed as needed.

[0040] Next, a process is performed to cover the film (1) in which the hole (2) is formed with a conductive seed material (3) (S200). At this time, as illustrated in Fig. 3, the entire exposed area of ​​the film (1), including the inner wall of the through hole, can be covered with the conductive seed material (3).

[0041] At this time, the conductive seed material (3) may be a conductive material such as titanium, nickel, chromium, copper, or an alloy thereof.

[0042] In addition, the conductive seed material (3) may be composed of multiple layers, for example, two layers. At this time, the lower layer of the conductive seed material (3) may be made of one of titanium, nickel, chromium, copper, or an alloy thereof to improve bonding strength with the non-conductive film (1) and to ensure clean removal in the soft etching process described later. In addition, the upper layer of the conductive seed material (3) may be made of copper or a copper alloy to secure bonding strength with the lower layer, to facilitate smooth plating of the conductive material (5) described later, and to secure adhesion of the dry film (4).

[0043] Meanwhile, for the convenience of explanation, in the present invention, the direction facing outward from the non-conductive film (1) is referred to as upward. That is, when explaining with reference to FIGS. 3 and 4, etc., the conductive seed material (3) can be referred to as being located above the non-conductive film (1) and below the dry film (4). Since the upper and lower surfaces can be described symmetrically with reference to the drawings, the same criteria can be applied.

[0044] Here, the application of the conductive seed material (3) can be performed by a dry plating method, for example, by an E-Beam, Evaporation, CVD, PVD method, etc. However, it is not limited thereto, and various methods capable of plating the conductive material on the insulating film can be used.

[0045] After the above step (S200), a dry film (4) is applied to both sides of the film (1) covered with the conductive seed material (3) (S300). That is, as shown in Fig. 4, laminating or the like is performed so that the dry film (4) is attached to both sides of the film (1) covered with the conductive seed material (3).

[0046] Next, exposure and development are performed to remove the dry film (4) corresponding to the circuit pattern area (7) and through-hole area (6) where plating is to be performed (S400).

[0047] For example, by irradiating light only to areas where plating does not need to be performed through exposure to cause a polymer reaction, and removing only the areas that did not receive light through development using chemicals, etc., the dry film corresponding to the areas (6, 7) where plating is to be performed can be removed, as shown in Fig. 5.

[0048] At this time, the pattern of the dry film (4) to be removed can be determined by considering the width of the circuit pattern to be cut (reduced) in the etching (soft etching) process described later. That is, the width of the pattern of the dry film (4) to be removed can be determined by adding the width reduced in the soft etching process to the width of the circuit pattern to be manufactured.

[0049] Meanwhile, additional processes (scrubbing, washing, drying, etc.) may be performed during the laminating, exposure, and development processes of the above steps (S300, S400), and since the processes of laminating, exposure, and development correspond to technologies widely known in the technical field of the present invention, the specific details of performing each process will be omitted.

[0050] After the above step (S400), copper plating is performed to form a circuit pattern and through-hole plating is performed (S500). As illustrated in Fig. 5, since the conductive seed material (3) is exposed in the area where plating is to be performed, plating can be performed using an electroplating method to perform circuit pattern and through-hole plating at the same time.

[0051] Through this, as illustrated in Fig. 6, a circuit pattern (5) with both sides electrically connected is formed on both sides of the film (1) (on the conductive seed material (3)). That is, according to the present invention, even without performing a separate plating process to plate through holes for connecting the circuit patterns on both sides of the film (1), plating of the through holes can be performed simultaneously with the formation of the circuit pattern.

[0052] Although not shown in Fig. 6, conductive seed material (3) may also be applied to the side surface of the film (1), so that copper may also be plated on that portion. However, since an external processing process such as a cutting edge is performed during the actual product manufacturing process, this does not affect the actual product.

[0053] Meanwhile, in this embodiment, copper plating was described, but if necessary, a conductive material other than copper may be plated to form a circuit pattern (5).

[0054] Next, the residual dry film (4) remaining on the conductive seed material (3) and the conductive seed material (3) below the residual dry film (4) are removed (S600). For example, the residual dry film (4) can be removed using an alkaline chemical agent, etc.

[0055] Next, in addition to the residual dry film (4), the conductive seed material (3) located below the residual dry film (4) is also removed. This can be achieved by selecting a chemical agent for etching (soft etching) in consideration of the properties of the conductive seed material (3), etc. For example, an acid-based chemical agent can be used. In this process, a part of the surface of the circuit pattern (5) may be shaved off, and by performing the plating of the step (S500) (adjusting the electroplating time, etc.) in consideration of the thickness of the circuit pattern (5) shaved off in this way, a circuit pattern (5) having a desired thickness can be formed. That is, the thickness of the conductive layer formed on the non-conductive film (1) is the sum of the thickness of the circuit pattern (5) from which a part is shaved off and the thickness of the conductive seed material (3), so that a conductive layer having a desired specification can be formed in consideration of this.

[0056] Meanwhile, as described above, the reduction in the width of the circuit pattern (5) can be reflected by changing the width of the pattern of the dry film (4).

[0057] Afterwards, additional processes such as smoothing the surface of the circuit pattern (5) or the insulating film (1), or additionally removing the unremoved dry film (4) or conductive seed material (3) can be performed, and for this purpose, various methods and additional processes already known in the technical field of the present invention can be utilized.

[0058] Accordingly, as illustrated in Fig. 7, a double-sided flexible printed circuit board intermediate product can be obtained in which a circuit pattern (5) is formed on both sides of an insulating film (1) and a plated through-hole exists for electrical connection of the circuit pattern (5) formed on both sides. In the case of the intermediate product formed in this way, the thickness of the circuit pattern (5) formed on both sides and the thickness of the side wall of the through-hole are the same because they are plating layers formed in one process, and they are integrally formed so that no problems with the connection part occur.

[0059] The product can then be completed through processes such as terminal plating and external processing, and components can be mounted as needed. This process can be identical to the manufacturing method for conventional flexible printed circuit boards.

[0060] FIGS. 8 to 10 are exemplary views illustrating a method for manufacturing a multilayer flexible printed circuit board by laminating intermediate products of a double-sided flexible printed circuit board manufactured by a double-sided flexible printed circuit board manufacturing method according to one embodiment of the present invention.

[0061] As illustrated in Fig. 8, an intermediate product of a double-sided flexible printed circuit board can be laminated with a non-conductive layer (9) therebetween. The non-conductive layer (9) may be a polyimide film, and in this case, an adhesive material (8) may be used to attach the intermediate product of the double-sided flexible printed circuit board to the non-conductive layer (9). Alternatively, the non-conductive layer may be formed by using a non-conductive adhesive itself.

[0062] Thereafter, as illustrated in FIG. 9, a hole (10) may be formed to perform multi-layer connection, and plating of the inner wall of the hole (10) may be performed. However, since this process can be carried out using the same method used in the conventional double-sided printed circuit board manufacturing method using a double-sided FCCL substrate, a more detailed description thereof will be omitted.

[0063] In addition, as shown in Fig. 10, it is possible to laminate in the form of cross-section + double-sided + single-sided, and in addition, various other forms of deformation such as cross-section + double-sided + double-sided + single-sided are possible.

[0064] Even for these multi-layered intermediate products, the finished product can be completed through processes such as terminal plating and external processing, and components can be mounted as needed. This process can be identical to the manufacturing method for conventional flexible printed circuit boards.

[0065] Additional processes for product production (e.g., washing process, drying process, etc.) may be added between the aforementioned processes as needed.

[0066] Meanwhile, the present invention can be performed in a flexible printed circuit board manufacturing facility configured to perform each process such as hole processing, dry plating, laminating, exposure, development, etching, electroplating, and attachment, and a control device of such manufacturing facility can control the operation of each process. Such manufacturing facility may additionally be equipped with a robot arm, a transfer belt, etc. for transferring products between each process, and various other equipment may be added. In addition, the control device may include a computer-readable storage medium that stores commands for controlling the manufacturing facility to perform each process, and such storage medium may be coupled to a processor to cause the processor to perform each step of the present invention.

[0067] While the present invention has been described with reference to the embodiments illustrated in the drawings, these are merely exemplary, and those skilled in the art will understand that various modifications and equivalent embodiments are possible. Accordingly, the technical protection scope of the present invention should be defined by the following claims.

Claims

1. Step of forming a hole in a non-conductive film; A step of covering the non-conductive film in which the hole is formed with a conductive seed material; A step of applying a dry film to each of the two sides of the non-conductive film covered with the conductive seed material; A step of removing a portion corresponding to a through-hole area and a circuit pattern area where plating is to be performed in the above dry film; A step of forming a plated through hole and a circuit pattern by plating a conductive material on the non-conductive film; and A method for manufacturing a double-sided flexible printed circuit board, comprising the step of removing a residual dry film and a conductive seed material located below the residual dry film.

2. In paragraph 1, A method for manufacturing a double-sided flexible printed circuit board, characterized in that the step of removing the residual dry film and the conductive seed material located below the residual dry film is performed by etching.

3. In paragraph 2, A method for manufacturing a double-sided flexible printed circuit board, characterized in that at least a portion of the conductive material plated by the etching is etched away.

4. In paragraph 3, A method for manufacturing a double-sided flexible printed circuit board, characterized in that plating of the conductive material is performed taking into account the thickness to which the conductive material is to be cut.

5. In paragraph 3, A method for manufacturing a double-sided flexible printed circuit board, characterized in that removal of a portion corresponding to a through-hole area and a circuit pattern area where plating is to be performed in the dry film is performed in consideration of the width to which the conductive material is to be cut.

6. In paragraph 1, A method for manufacturing a double-sided flexible printed circuit board, characterized in that the step of covering the non-conductive film with a conductive seed material comprises covering the non-conductive film with the conductive seed material through dry plating.

7. In paragraph 1, A method for manufacturing a double-sided flexible printed circuit board, characterized in that the step of removing a portion corresponding to the through-hole area and the circuit pattern area removes a portion corresponding to the through-hole area and the circuit pattern area from the dry film through exposure and development of the dry film.

8. In paragraph 1, A method for manufacturing a double-sided flexible printed circuit board, characterized in that the step of forming the plated through hole and circuit pattern comprises performing plating of the conductive material through electroplating.

9. In paragraph 1, A method for manufacturing a double-sided flexible printed circuit board, characterized in that the conductive seed material is one of titanium, nickel, chromium, and copper, or an alloy of at least two of titanium, nickel, chromium, and copper.

10. In paragraph 1, A method for manufacturing a double-sided flexible printed circuit board, characterized in that the conductive seed material is composed of a plurality of layers.

11. In paragraph 1, A method for manufacturing a double-sided flexible printed circuit board, characterized in that the conductive material is copper.

12. In paragraph 1, A method for manufacturing a double-sided flexible printed circuit board, characterized in that the above non-conductive film is a polyimide film.

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