Flexible printed circuit board and electronic device including the same

A flexible printed circuit board includes a base film; a circuit pattern disposed on one surface of the base film; and a coverlay film covering the circuit pattern. The base film is divided into a flexible area and a rigid area, and the circuit pattern of the flexible area comprises a portion thinner than a portion of the circuit pattern of the rigid area.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application claims the benefit of priority to Korean Patent Application No. 10-2020-0160268, filed on Nov. 25, 2020 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to a flexible printed circuit board and an electronic device including the same.

BACKGROUND

Recently, as electronic devices such as foldable mobile phones and tablets have appeared, there is a need for a flexible printed circuit board having sufficient flexibility to be bendable and/or foldable.

In order to implement an electronic device including a flexible display capable of being bent, folded, or the like, hundreds of thousands of times, the flexible printed circuit board is required to not only be thin and light but also durable. In a situation in which internal components constituting the flexible printed circuit board are thin, there is a need for a technology for repeatedly and continuously distributing external forces applied to a conductive line of the flexible printed circuit board.

SUMMARY

An aspect of the present disclosure may provide a flexible printed circuit board capable of securing reliability in bending and folding even in the case that repeated external forces are applied to the flexible printed circuit board in a situation in which thin and light conductive wires are used.

Another aspect of the present disclosure may provide a flexible printed circuit board simultaneously having improved wiring reliability and improved folding reliability by forming a conductive pattern in a flexible area to have a different thickness from that in a rigid area in the flexible printed circuit board.

Another aspect of the present disclosure may provide a flexible electronic device having improved durability due to folding.

According to an aspect of the present disclosure, a flexible printed circuit board may include: a base film; a circuit pattern disposed on one surface of the base film; and a coverlay film covering the circuit pattern, wherein the base film is divided into a flexible area and a rigid area, and the circuit pattern of the flexible area comprises a portion thinner than a portion of the circuit pattern of the rigid area.

According to another aspect of the present disclosure, a flexible printed circuit board may include: a rigid area comprising a first base film and a first circuit pattern disposed on the first base film; a flexible area comprising a second base film, which is bendable, and a circuit pattern disposed on one outer surface of the second base film; and a coverlay film covering the first and second circuit patterns of the rigid area and the flexible area, wherein the second circuit pattern of the flexible area has a portion thinner than a portion of the first circuit pattern of the rigid area.

According to another aspect of the present disclosure, an electronic device may include: a flexible printed circuit board comprising a flexible area and at least one of a first rigid area or a second rigid area connected to the flexible area; and a display module electrically connected to at least one of the first rigid area or the second rigid area, wherein the flexible printed circuit board includes a base film; a circuit pattern disposed on one upper surface of the base film; and a coverlay film covering the circuit pattern, wherein the base film is divided into the flexible area and the at least one of the first rigid area or the second rigid area, and the circuit pattern of the flexible area comprises a portion thinner than a portion of the circuit pattern of the at least one of the first rigid area or the second rigid area.

DETAILED DESCRIPTION

The exemplary embodiments are subject to various modifications and are provided to assist those skilled in the art in gaining a completely comprehensive understanding. Accordingly, shapes and sizes of elements in the drawings may be exaggerated for clarity, and elements indicated by the same reference numerals in the drawings refer to the same elements.

The terminology used herein is for simply describing various examples only, and is not to be used to limit the disclosure. In this case, expressions in the singular include plural expressions unless otherwise indicated.

Flexible Printed Circuit Board

FIG.1is a cross-sectional view schematically illustrating a flexible printed circuit board according to an exemplary embodiment in the present disclosure.

Referring toFIG.1, the flexible printed circuit board1according to an exemplary embodiment of the present disclosure may include a base film10, a circuit pattern20and a coverlay film70.

The base film10may contain a polyimide (PI) resin having excellent heat resistance, and the material of the base film10is not particularly limited as long as it is a heat-resistant insulating coating resin such as polyethylene terephthalate (PET). In addition, a liquid crystal polymer (LCP) may be used as the base film10for improving flexible characteristics such as bending, folding, or the like.

The circuit pattern20may include a copper foil on one surface of the base film10to form a wire through which an electric signal is transferred. As for the circuit pattern20, a rolled annealed (RA) copper foil may be used as a copper foil for signal transfer, particularly for a reduced thickness. If necessary, however, an electrodeposited (ED) copper foil may be used, and a method of forming the copper foil is not particularly limited.

The base film10, a first circuit pattern20and a second circuit pattern40may constitute a flexible copper clad laminate (FCCL) film which is bendable or foldable. The flexible printed circuit board1manufactured of such a flexible copper clad laminate film may be applied to a microelectronic device such as a camera of a mobile communication terminal or a next-generation electronic device such as a laptop PC or a foldable terminal.

The flexible printed circuit board1of present exemplary embodiment is divided into a flexible area300and rigid areas200and400, and the second circuit pattern40is not disposed on the opposite surface of the base film10of the flexible area300on which the circuit pattern20is formed. That is, the flexible area300is a single-sided flexible printed circuit board (FPC), while the rigid areas200and400are double-sided FPC. Such configuration may allow reliability of folding to be secured in the flexible area300in which bending or folding is performed and reliability of wiring to be secured in the rigid area in which an electrical signal is exchanged with external electronic modules.

Meanwhile, the FCCL film may constitute a flexible area300of the flexible printed circuit board1according to the present exemplary embodiment, and the rigid areas200and400may be formed by building up an insulating layer220and a wiring layer240on the FCCL film. The rigid areas200and400may be formed at both ends of the flexible area300and may constitute a first rigid area200and a second rigid area400, respectively. If required by an electronic device, the rigid areas200and400may not be included in the flexible printed circuit board1, or only one of the first rigid area200and the second rigid area400may be formed in the flexible printed circuit board1.

Each of the first rigid area200and the second rigid area400is for relatively describing an area which is more difficult to bend or fold than the flexible area300. It should be understood that the first rigid area200and the second rigid area400are not to be interpreted as being areas which are not bendable or foldable.

A rigid-flexible printed circuit board including the first rigid area200, the second rigid area400and the flexible area300is an example of the flexible printed circuit board1according to the present disclosure.

The first rigid area200and the second rigid area400are multilayer circuit boards in which the insulating layers220and the wiring layers240are built up on the flexible copper clad laminate film, and the number of layers may be selected as needed. A method of forming the rigid areas is not limited thereto.

The coverlay film70is a sheet used as a solder resist of the flexible printed circuit board1and may be connected to the first circuit pattern20by an adhesive. At this time, prepreg obtained by impregnating a thermosetting resin in a base material such as glass fiber and curing the same to a B-stage (a semi-cured state of the resin) may be used as the adhesive; however, the material of the adhesive is not limited thereto.

Meanwhile, the circuit pattern22of the flexible area300has a portion thinner than the circuit pattern24of the rigid area200. Hereinbelow, an exemplary embodiment for each circuit pattern will be described in detail.

FIG.2is a cross-sectional view of a circuit pattern of Example 1 of the flexible printed circuit board ofFIG.1, andFIG.3is an enlarged schematic view illustrating portion I ofFIG.2.

Referring toFIGS.1to3, the flexible printed circuit board1includes the first rigid area200and the flexible area300, and the circuit pattern22of the flexible area300has a portion thinner than the circuit pattern24of the rigid area200.

In the present exemplary embodiment, a thickness tF of the circuit pattern22of the flexible area300is overall formed to be uniformly small, as compared to a thickness tR of the circuit pattern24of the rigid area200.

When bending or folding the flexible printed circuit board1, compressive force is generated inwardly within the bended portion of the flexible printed circuit board1, while tensile force is generated outwardly within the bend. When the thickness of the circuit pattern22of the flexible area300is uniform overall as compared to the circuit pattern24of the rigid area200, it may be possible to reduce the tensile force generated outwardly within the bend. As used herein, the term “bending” may be defined as a partially folded state. Upon bending, a curvature R begins to be formed in the flexible area300of the flexible printed circuit board1.

The coverlay film70maintains substantially the same thickness in the rigid areas200and400and the flexible area300, such that a height hC of the coverlay film of the flexible area300is smaller than a height hR of the coverlay film of the rigid area200, thereby aiding to distribute the tensile force applied outwardly within the bend.

Further, the rigid area200includes a transition region T, in which the circuit pattern22of the flexible area300is connected to the circuit pattern24of the rigid area200, and a margin portion50having substantially the same thickness as the circuit pattern22of the flexible area300is provided in the transition region T. One or ordinary skill in the art would understand that the expression “substantially the same” refers to being the same by allowing process errors, positional deviations, and/or measurement errors that may occur in a manufacturing process.

As the circuit pattern22of the flexible area300, a circuit pattern22of the margin portion is uniformly formed to be thinner overall than the circuit pattern24in the rigid area200.

In the margin portion50, an end of the margin portion50is a boundary between the circuit pattern24of the rigid area200and the circuit pattern22of the flexible area300and corresponds to a manufacturing error. By allowing the margin portion50to have an allowable length, bending of the circuit pattern22of the flexible area300may be relatively easily initiated at the end of the margin portion50.

FIG.4is a cross-sectional view of a circuit pattern of Example 2 of the flexible printed circuit board ofFIG.1, andFIG.5is an enlarged schematic view illustrating portion II ofFIG.4.

Referring toFIGS.1,4and5, the flexible printed circuit board1includes the first rigid area200and the flexible area300, and the circuit pattern22of the flexible area300has a portion thinner than the circuit pattern24of the rigid area200.

The portion in the circuit pattern22of the flexible area, thinner than the circuit pattern24of the rigid area200, is a square groove246formed in the circuit pattern22of the flexible area300.

As compared to the circuit pattern22of the flexible area300ofFIGS.2and3, a thickness-reinforcing circuit pattern245is formed in an upper portion of the circuit pattern22of the flexible area300of the present exemplary embodiment such that an overall thickness of the circuit pattern in the flexible area300becomes similar to that of the circuit pattern24of the rigid area200.

The thickness-reinforcing circuit pattern245of the flexible area300may be manufactured by selecting a rolled annealed copper foil relatively thicker than the circuit pattern22of the flexible area300ofFIGS.2and3and etching to form the square grooves246at regular intervals.

When bending or folding the flexible printed circuit board1, compressive force is generated inwardly within the bended portion of the flexible printed circuit board1, and tensile force is generated outwardly within the bended portion. A thickness difference at a stepped portion formed in the circuit pattern22of the flexible area300due to the square groove246may reduce the tensile force generated outwardly within the bended portion.

Alternately, the thickness may be increased by selecting a rolled annealed copper foil having a thickness not different from that of the circuit pattern22of the flexible area300ofFIGS.2and3and forming the thickness-reinforcing circuit pattern245thicker than the circuit pattern22of the flexible area300on an upper portion of the rolled annealed copper foil to form an electrodeposited copper foil.

The thickness-reinforcing circuit pattern245of the flexible area300having the square groove246may effectively reduce the tensile force generated outwardly within the bended portion by having a smaller average thickness than that of the thickness-reinforcing circuit pattern245of the rigid area200. In addition, the coverlay film70of the flexible area300may be disposed at a lower level than the coverlay film70of the rigid area200according to the square groove246of the thickness-reinforcing circuit pattern245.

Such a lamination method can be applied to the method of forming the circuit pattern24of the rigid area200of the exemplary embodiments ofFIGS.1to3. The descriptions of the exemplary embodiments ofFIGS.1to3may also be applied to the present exemplary embodiment within a range which does not contradict each other.

FIG.6is a cross-sectional view of a circuit pattern of Example 3 of the flexible printed circuit board ofFIG.1, andFIG.7is an enlarged schematic view illustrating portion III ofFIG.6.

Referring toFIGS.1,6and7, the flexible printed circuit board1includes the first rigid area200and the flexible area300, and the circuit pattern22of the flexible area300has a portion thinner than the circuit pattern24of the rigid area200.

The portion in the circuit pattern22of the flexible area300, thinner than the circuit pattern24of the rigid area200, is a rounded groove247.

In comparison to the circuit pattern22of the flexible area300ofFIGS.2and3, a thickness-reinforcing circuit pattern245is formed in an upper portion of the circuit pattern22of the flexible area300of the present exemplary embodiment such that an overall thickness of the circuit pattern in the flexible area300becomes similar to that of the circuit pattern24of the rigid area200.

The thickness-reinforcing circuit pattern245of the flexible area300may be manufactured by selecting a rolled annealed copper foil relatively thicker than the circuit pattern22of the flexible area300ofFIGS.2and3and etching to form the rounded grooves247at regular intervals.

When bending or folding the flexible printed circuit board1, compressive force is generated inside the bending of the flexible printed circuit board1, and tensile force is generated outwardly within the bended portion. A thickness difference at a stepped portion formed in the circuit pattern22of the flexible area300due to the rounded groove247may reduce the tensile force generated outwardly within the bended portion.

Alternately, the thickness may be increased by selecting a rolled annealed copper foil having a thickness not different from that of the circuit pattern22of the flexible area300ofFIGS.2and3and forming the thickness-reinforcing circuit pattern245to be thicker than the circuit pattern22of the flexible area300on an upper portion of the rolled annealed copper foil to form an electrodeposited copper foil.

The thickness-reinforcing circuit pattern245of the flexible area300having the rounded grooves247may effectively reduce the tensile force generated outwardly within the bended portion by having a smaller average thickness than that of the thickness-reinforcing circuit pattern245of the rigid area200. In addition, the coverlay film70of the flexible area300may be disposed at a lower level than the coverlay film70of the rigid area200according to the rounded groove247of the thickness-reinforcing circuit pattern245.

The other descriptions of the exemplary embodiments ofFIGS.1to3may also be applied to the present exemplary embodiment within a range which does not contradict each other.

FIG.8is a cross-sectional view of a circuit pattern of Example 4 of the flexible printed circuit board ofFIG.1, andFIG.9is an enlarged schematic view illustrating portion IV ofFIG.8.

Referring toFIGS.1,8and9, the flexible printed circuit board1includes the first rigid area200and the flexible area300, and the circuit pattern22of the flexible area300has a portion thinner than the circuit pattern24of the rigid area200.

The portion in the circuit pattern22of the flexible area300, thinner than the circuit pattern24of the rigid area200, is a triangular groove248.

In comparison to the circuit pattern22of the flexible area300ofFIGS.2and3, a thickness-reinforcing circuit pattern245is formed in an upper portion of the circuit pattern22of the flexible area300of the present exemplary embodiment such that an overall thickness of the circuit pattern in the flexible area300becomes similar to that of the circuit pattern24of the rigid area200.

The thickness-reinforcing circuit pattern245of the flexible area300may be manufactured by selecting a rolled annealed copper foil relatively thicker than the circuit pattern22of the flexible area300ofFIGS.2and3and etching to form the triangular groove248at regular intervals.

When bending or folding the flexible printed circuit board1, compressive force is generated inwardly within the bended portion of the flexible printed circuit board1, and tensile force is generated outwardly within the bended portion. A thickness difference at a stepped portion formed in the circuit pattern22of the flexible area300due to the triangular groove248may reduce the tensile force generated outwardly within the bended portion.

Alternately, the thickness may be increased by selecting a rolled annealed copper foil having a thickness not different from that of the circuit pattern22of the flexible area300ofFIGS.2and3and forming the thickness-reinforcing circuit pattern245thicker than the circuit pattern22of the flexible area on an upper portion of the rolled annealed copper foil to form an electrodeposited copper foil.

The thickness-reinforcing circuit pattern245of the flexible area300having the triangular grooves248may effectively reduce the tensile force generated outwardly within the bended portion by having a smaller average thickness than that of the thickness-reinforcing circuit pattern245of the rigid area200. In addition, the coverlay film70of the flexible area300may be disposed at a lower level than the coverlay film70of the rigid area200according to the triangular groove248of the thickness-reinforcing circuit pattern245.

The other descriptions of the exemplary embodiments ofFIGS.1to3may also be applied to the present exemplary embodiment within a range which does not contradict each other.

Referring again toFIGS.1to9, the flexible printed circuit board1according to an exemplary embodiment of the present disclosure includes the rigid areas200and400, the flexible area300and the coverlay film70.

The rigid areas200and400include the first rigid area200and the second rigid area400with the flexible area300interposed therebetween, and the base film10and the circuit pattern24disposed on the base film10.

The flexible area300has the circuit pattern22disposed on one outer surface in a direction in which the base film10bends.

The coverlay film70covers the circuit patterns22and24in the rigid area200and the flexible area300.

As the circuit pattern22of the flexible area300has the portion thinner than the circuit pattern24of the rigid area200, the tensile force generated outwardly within the bended portion of the flexible circuit board1may be distributed when bending or folding the flexible printed circuit board1.

The circuit patterns22and24may include a rolled annealed copper foil. The circuit pattern24of the rigid area200may be plated with an electrodeposited copper foil to have a thickness-reinforcing circuit pattern245thicker than that of the circuit pattern22of the flexible area300.

The thickness-reinforcing circuit pattern245may be formed in the upper portion of the circuit pattern22of the flexible area300to have a thickness similar to that of the circuit pattern24of the rigid area200.

The height hC of the coverlay film of the flexible area300may be set to be lower than the height hR of the coverlay film of the rigid area200along the portion thinner than the circuit pattern24of the rigid area200.

In the rigid area200, a transition region T, to which the circuit pattern22of the flexible area300is connected, is formed, and a margin portion50, in which a circuit pattern is formed to have substantially the same thickness tF as the circuit pattern22of the flexible area300, may be provided in the transition region T.

The circuit pattern22of the flexible area300and the circuit pattern24of the margin portion is uniformly formed to be thinner than the circuit pattern24in the rigid area200.

The thickness-reinforcing circuit pattern245is disposed on an upper surface of the circuit pattern22of the flexible area300and an upper surface of the circuit pattern22of the margin portion. In the thickness-reinforcing circuit pattern, at least one of the square groove246, the triangular groove248or the rounded groove247may be formed. A shape of the groove is not particularly limited.

The end of the margin portion50is a boundary between the circuit pattern24of the rigid area200and the circuit pattern22of the flexible area300and may be a point at which the circuit pattern22of the flexible area300begins to bend.

Electronic Device

FIG.10is a schematic perspective view of a foldable terminal as an electronic device according to an exemplary embodiment in the present disclosure.

Referring toFIG.10, an electronic device100according to an exemplary embodiment of the present disclosure may include a flexible printed circuit board1and a display module500.

The flexible printed circuit board1includes a flexible area300and at least one of a first rigid area200or a second rigid area400connected to the flexible area300.

The display module500may be bent, folded, or rolled, and accordingly, the flexible area300may be adjusted to have a required length.

Meanwhile, the display module500may be electrically connected to at least one of the first rigid area200or the second rigid area400.

The flexible printed circuit board1according to any of the above-described exemplary embodiments may be applied to the electronic device100according to the present exemplary embodiment.

As set forth above, according to the exemplary embodiments of the present disclosure, the flexible printed circuit board has improved reliability in bending and folding even though repeated external forces are applied to the printed circuit board in a situation in which the thin and light conductive wires are used.

In addition, the flexible printed circuit board is capable of simultaneously having improved folding reliability in a flexible area and improved wiring reliability in a rigid area by forming a conductive pattern in the flexible area of the flexible circuit board to have a different thickness from that in the rigid area.

According to the exemplary embodiments of the present disclosure, an electronic device including the flexible printed circuit board has improved durability due to folding.