WO2024257916A1 - Method for manufacturing double-sided flexible printed circuit board - Google Patents

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 board

The present invention relates to a method for manufacturing a double-sided flexible printed circuit board having circuit boards formed on both sides of an insulating film.

A flexible printed circuit board (FPCB) is a flexible substrate that forms a circuit pattern on a thin insulating film and can be bent flexibly. 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.

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

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 layer laminated on both sides of a polyimide film layer.

Through holes (via holes) are formed in these double-sided FCCLs, and the inner walls of the through holes are plated using electroless copper plating or other methods to electrically connect the copper layers on both sides, thereby enabling circuit connection on both sides of the flexible printed circuit board.

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 longer the process takes and the more costly it becomes.

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 current 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.

However, when looking at the overall thickness of copper, the upper and lower surfaces of the FCCL with the copper layer have the total thickness of the sum of the thickness of the existing copper 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 has the total thickness of 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.

In addition, due to the formation process of each side and the difference in thickness, a discontinuous connection may occur at the connection portion of 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.

In this way, the existing process has several steps to form electrically connected through holes, so it incurs high process costs and requires additional management elements, which inevitably increases manufacturing costs. In addition, there is a problem that the price of double-sided FCCL is relatively high. The above explanation is that each manufacturer has various process methods and there may be some differences.

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 increases in the time and cost required for the entire process.

Meanwhile, the background technology of the present invention is disclosed in Korean Patent Publication No. 10-2018-0016323 (February 14, 2018).

The present invention is intended to solve the problems of the conventional double-sided flexible printed circuit board manufacturing method as described above, and provides 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.

A method for manufacturing a double-sided flexible printed circuit board according to the present invention is characterized by including 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 the non-conductive film with a conductive material 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.

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.

The present invention is characterized in that at least a portion of the conductive material plated by the etching is etched away.

The present invention 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.

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 by which the conductive material is to be cut.

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.

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.

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.

In the present invention, the conductive seed material is characterized by being one of titanium, nickel, chromium and copper, or an alloy of at least two of titanium, nickel, chromium and copper.

In the present invention, the conductive seed material is characterized by being composed of a plurality of layers.

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

In the present invention, the non-conductive film is characterized by being a polyimide film.

The method for manufacturing a double-sided flexible printed circuit board according to the present invention covers a non-conductive film having holes formed therein with a conductive material, forms an area to be plated, and then forms plated through holes 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.

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.

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.

FIG. 1 is a flow chart for explaining a method for manufacturing a double-sided flexible printed circuit board according to one embodiment of the present invention.

FIGS. 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.

FIGS. 8 to 10 are exemplary views for explaining 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 method for manufacturing a double-sided flexible printed circuit board according to one embodiment of the present invention.

Hereinafter, with reference to the attached drawings, one embodiment of a method for manufacturing a double-sided flexible printed circuit board according to the present invention will be described. In this process, the thickness of lines or the size of components illustrated in the drawings may be exaggerated or omitted for the sake of clarity and convenience of explanation. In addition, the terms described below are terms defined in consideration of their functions in the present invention, and may vary depending on the intention or custom of the user or operator. Therefore, the definitions of these terms should be made based on the contents throughout this specification.

FIG. 1 is a flow chart 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 explained as follows.

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).

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.

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 (board), 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.

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

Fig. 2 (a) is a drawing of a non-conductive film (1) viewed from above, and Fig. 2 (b) is a drawing in which only the dotted line portion of Fig. 2 (a) is cut out for explanation and a cross-section thereof (a cross-section in the thickness direction of the non-conductive film (1), i.e., a plane perpendicular to the plane of Fig. 2 (a)) is depicted. In the drawings described below, the manufacturing process will be described based on this cross-section, and the implementation of a conventional 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.

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

Next, a process of covering the film (1) in which the hole (2) is formed with a conductive seed material (3) is performed (S200). At this time, as shown 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).

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

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

Meanwhile, in the present invention, for the convenience of explanation, 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 criterion can be applied.

Here, the application of the conductive seed material (3) can be performed by a dry plating method, and can be performed by, for example, 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.

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).

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

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 were not exposed to 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.

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.

Meanwhile, additional processes (scrubbing, washing, drying, etc.) may be further performed during the laminating, exposure, and developing 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, specific details of performing each process will be omitted.

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 by electroplating (electroplating) to perform the circuit pattern and through-hole plating at the same time.

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 through holes can be performed simultaneously with the formation of the circuit pattern.

Although not shown in Fig. 6, conductive seed material (3) may also be applied to the side of the film (1), so that copper may also be plated on that part. However, since an external processing process such as an altar exists during the actual product manufacturing process, it does not affect the actual product.

Meanwhile, in this embodiment, copper is described as being plated, but if necessary, a conductive material other than copper may be plated to form a circuit pattern (5).

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

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 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) (by controlling the time of electroplating, etc.) in consideration of the thickness of the circuit pattern (5) shaved off in this manner, a circuit pattern (5) having a thickness of a desired specification 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.

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).

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.

Accordingly, as illustrated in Fig. 7, a circuit pattern (5) is formed on both sides of an insulating film (1), and a double-sided flexible printed circuit board intermediate product in the form of a plated through-hole for electrical connection of the circuit pattern (5) formed on both sides can be obtained. In the case of the intermediate product formed in this manner, 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 occur at the connection part.

Afterwards, the product can be completed through processes such as terminal plating and external processing, and components can be mounted as needed. This process can be the same as the manufacturing method of a typical flexible printed circuit board.

FIGS. 8 to 10 are exemplary views for explaining 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 method for manufacturing a double-sided flexible printed circuit board according to one embodiment of the present invention.

As shown in Fig. 8, the intermediate product of the double-sided flexible printed circuit board can be laminated with a non-conductive layer (9) therebetween. The non-conductive layer (9) can be a polyimide film, and in this case, the intermediate product of the double-sided flexible printed circuit board can be attached to the non-conductive layer (9) by utilizing an adhesive material (8). Alternatively, the non-conductive layer can be formed by utilizing the non-conductive adhesive itself.

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

In addition, as illustrated in Fig. 10, lamination in the form of cross-section + double-sided + cross-section is also possible, and various other deformations such as cross-section + double-sided + double-sided + cross-section are also possible.

Even in the case of such multi-layered intermediate products, the product can be completed through processes such as terminal plating and external processing, and components can be mounted as needed. This process can be the same as the manufacturing method of a typical flexible printed circuit board.

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

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 can additionally be equipped with a robot arm, a transfer belt, etc. for transferring a product between each process, and various other equipment can be added in addition. In addition, the control device can include a computer-readable storage medium that stores commands for controlling the manufacturing facility to perform each process, and such storage medium can be coupled with a processor and configured to cause the processor to perform each step of the present invention.

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

Claims (12)

A 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 side 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 performing plating of a conductive material on the above 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 positioned below the residual dry film. In the first paragraph, 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 positioned below the residual dry film removes the residual dry film and the conductive seed material positioned below the residual dry film through etching. In the second paragraph, 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 abraded. In the third paragraph, 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. In the third paragraph, 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 considering a width by which the conductive material is to be cut. In the first paragraph, 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. In the first paragraph, 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. In the first paragraph, 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. In the first paragraph, 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. In the first paragraph, 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. In the first paragraph, A method for manufacturing a double-sided flexible printed circuit board, characterized in that the conductive material is copper. In the first paragraph, 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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