Electronic device and flexible printed circuit board

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2019-113701, filed Jun. 19, 2019, the entire contents of which are incorporated herein by reference.

Embodiments described herein relate generally to an electronic device and a flexible printed circuit board.

As display devices, which are electronic devices such as smartphones, tablet computers and car navigation systems, liquid crystal display devices, organic EL display devices and the like are widely used. The display devices comprise a display panel and a flexible printed circuit board (FPC) mounted on the display panel. The FPC extends outward from the display panel, and is bent in, for example, a rear surface side of the display panel.

The FPC comprises a base film, wiring lines on the base film and a covering film for protecting the wiring lines. For example, such a technique is conventionally known that to form a plurality of grooves are formed in a covering film in order to reduce repulsion occurring in bending of an FPC. However, of the base film, the wiring lines and the covering film described above, the influence of the covering film which causes in the repulsion of the FPC is not significant. Therefore, it is difficult to sufficiently reduce the repulsion of the FPC by forming grooves in the covering film.

Meanwhile, such a display panel is known that comprises a tape carrier package (TCP) with one end connected to the display device and the other end connected to the circuit board. The TCP, as in the case of the FPC described above, comprises a base film, a copper foil on the base film and a resist film covering the copper foil. For example, a plurality of slits which penetrate the base film are formed in a bend portion of the TCP in order to reduce the release force to be applied the junction between the TCP and the display panel.

FIG. 1 is an exploded perspective view showing a display device according to an embodiment.

FIG. 2 is a perspective view of the display device shown in FIG. 1 as viewed from a rear surface side.

FIG. 3 is a cross sectional view of the display device taken along a line A-B in FIG. 2 .

FIG. 4 is a view of a flexible printed circuit board shown in the FIG. 3 .

FIG. 5 is a cross-sectional view of a display device according to the second embodiment.

FIG. 6 is a view showing a flexible printed circuit board shown in FIG. 5 .

FIG. 7 is a cross-sectional view of a display device according to the second embodiment.

FIG. 8 is a view showing a flexible printed circuit board shown in FIG. 7 .

FIG. 9 is a cross-sectional view of a display device according to the fourth embodiment.

FIG. 10 is a view showing a flexible printed circuit board shown in FIG. 9 .

FIG. 11 is a diagram showing the first example of a process of forming grooves in a flexible printed circuit board.

FIG. 12 is a diagram showing the second example of the process of forming grooves in a flexible printed circuit board.

FIG. 13 is a diagram showing the second example of the process of forming grooves in a flexible printed circuit board.

FIG. 14 is a diagram showing the second example of the process of forming grooves in a flexible printed circuit board.

In general, according to one embodiment, an electronic device comprises a panel comprising a mounting edge extending along a first direction and a plurality of pad portions arranged along the mounting edge; a flexible printed circuit board mounted on the panel and overlapping the plurality of pad portions; and a driver IC chip mounted on the flexible printed circuit board and configured as a signal supply source which supplies a signal necessary to drive the panel, the flexible printed circuit board comprising a base member comprising a first surface and a second surface on an opposite side to the first surface, wiring lines placed on a side of the first surface of the base member and a protective layer covering the wiring lines, and including a bent portion which can be bent, the base member comprising a groove portion located in the bend portion and formed in the second surface, the groove portion comprising a plurality of concavity portions extending along a second direction intersecting the first direction and arranged along the first direction, and a thickness of the base member in a site where the groove portion is formed being less than a thickness of the base member in a site overlapping the driver IC chip.

According to another embodiment, a flexible printed circuit board comprises a driver IC chip extending along a first direction; a bend portion being bendable and comprising a base member including a first surface and a second surface on an opposite side to the first surface, wiring lines located on a side of the first surface of the base member and a protective layer covering the wiring lines, the base member comprising a groove portion located in the bend portion and formed in the second surface, the groove portion comprising a plurality of concavity portions extending along a second direction intersecting the first direction, and arranged along the first direction, and a thickness of the base member in a site where the groove is formed being less than a thickness of the base member in a site overlapping the driver IC chip.

Embodiments will be described hereinafter with reference to the accompanying drawings. Note that the disclosure is presented for the sake of exemplification, and any modification and variation conceived within the scope and spirit of the invention by a person having ordinary skill in the art are naturally encompassed in the scope of invention of the present application. Further, a width, thickness, shape, and the like of each element are depicted schematically in the Figures as compared to actual embodiments for the sake of simpler explanation, and they are not to limit the interpretation of the invention of the present application. Furthermore, in the specification and drawings, constituent elements having the same or similar functions as those described in connection with preceding drawings are denoted by like reference numerals and their duplicated detailed explanations may be omitted.

First, the first embodiment will be described with reference to FIGS. 1 to 4 .

FIG. 1 is an exploded perspective view showing a display device DSP of this embodiment. The main configuration of the present embodiment can be used for electronic devices comprising a flexible printed circuit board, such as display devices. In this specification, the configuration of the present embodiment will be described by taking a display device as an example. The display device can be used for, for example, various devices such as a smartphone, a tablet terminal, a mobile telephone terminal, a notebook-type personal computer, a vehicle-mounted device, and a game console. This embodiment can be applied to various types of display devices including a self-luminous display device such as an organic electroluminescent display device, a micro-LED display device, an electronic paper display device comprising an electrophoretic element and the like, a display device in which micro-electromechanical systems (MEMS) are applied, and a display device in which an electrochromism is applied. Further, the application of the embodiment is not limited to the display devices mentioned above, but examples of the electronic device are a touch panel substrate and a fingerprint sensor substrate. The electronic devices comprise a panel, and a plurality of terminals on which flexible printed circuit boards of this embodiment are implemented are disposed on the panel.

A first direction X, a second direction and a third direction Z illustrated in the figures are orthogonal to each other but may intersect at an angle other than ninety degrees. The first direction X and the second direction Y correspond to a direction parallel to the main surface of the substrate which constitutes the display device DSP, and the third direction Z corresponds to a thickness direction of the display device DSP. In the present specification, a direction forwarding a tip of an arrow, which indicates the third direction Z, is called upward and a direction forwarding oppositely from the tip of the arrow is called downward. Such expression as “a second member on/above a first member” and “a second member under/below a first member”, the second member may be in contact with the first member or may be separated from the first member. A view of an X-Y plane defined by the first direction X and the second direction Y, taken from a tip end side of the arrow indicating the third direction Z is called a plan view.

The display device DSP comprises an active matrix display panel PNL, a cover member CM overlaid on an upper surface PNLa of the display panel PNL, so as to cover the upper surface PNLa, a backlight unit BL disposed to oppose a lower surface PNLb of the display panel PNL so as to illuminate the display panel PNL, a flexible printed circuit board 23 and a circuit board 25 .

The display panel PNL comprises a rectangular plate-shaped first substrate SUB 1 , and a rectangular plate-shaped second substrate SUB 2 opposing the first substrate SUB 1 . The first substrate SUB 1 and the second substrate SUB 2 are attached to each other via a sealing member SE. In FIG. 1 , the sealing member SE is located in a region indicated by hatching. The first substrate SUB 1 and the second substrate SUB 2 are each formed from a transparent insulating substrate such as a glass or resin plate. Further, the first substrate SUB 1 includes a mounting portion MA which does not overlap the second substrate SUB 2 . The display panel PNL includes a mounting edge ME extending along the first direction X. The display panel PNL comprises a plurality of pad portions PD arranged in line along the mounting edge ME.

The display panel PNL includes a display area DA which displays images, located on an inner side of the sealing member SE and a non-display area NDA surrounding the display area DA. The display panel PNL is provided with a transmissive display function which displays images by selectively transmitting light from the backlight unit BL to the display area DA. Note that the display panel PNL may not necessarily be provided with a backlight unit BL, but the display panel PNL of the embodiment may be a transmissive type with a transmissive display function which displays images by selectively transmitting light from a lower surface side of the first substrate SUB 1 , a reflective type with a reflective display function which displays images by selectively transmitting light from an upper surface side of the second substrate SUB 2 , or a transreflective type comprising both of the transmissive display function and the reflective display function.

Here, a detailed explanation of the configuration of the display panel PNL will be omitted, but the display panel PNL may comprise a structure provided for any of a display mode which utilizes a lateral electric field along the main surface of the substrate, a display mode utilizing a longitudinal electric field along a normal to the main surface of the substrate, a display mode utilizing an inclined electric field inclined to a slant direction to the main surface of the substrate, and a display mode utilizing the lateral electric field, longitudinal electric field and inclined electric field appropriately in any combination. Note that the main surface of the substrate is a surface parallel to the X-Y plane defined by the first direction X and the second direction Y.

The display device DSP comprises a flexible printed circuit board 23 mounted on the mounting portion MA of the display panel PNL. The flexible printed circuit board 23 overlaps the pad portions PD. A width L 1 of one end portion of the flexible printed circuit board 23 is less than a width L 2 of the first substrate SUB 1 . Further, the flexible printed circuit board 23 includes a plurality of wiring lines 23 b arranged along the first direction X, and the wiring lines 23 b are respectively connected to the pad portions PD. On the flexible printed circuit board 23 , a driver IC chip 24 is mounted as a signal supply source to supply signals necessary to drive the display panel PNL. Moreover, as will be described below, a spacer 103 abutting against the backlight unit BL is disposed around the driver IC chip 24 . A flexible circuit board 25 is jointed to an extending end of the flexible printed circuit board 23 . On the circuit board 25 , a capacitor 28 , connectors 26 and 27 , and the like are mounted.

The cover member CM is formed from, for example, a glass plate or an acrylic transparent resin, and has a rectangular plate shape. On a peripheral portion of the cover member CM, a frame-shaped light-shielding layer RS is formed.

The backlight unit BL comprises a case 18 , a plurality of optical members (not shown) arranged in the case 18 , a light source unit 22 which supplies light to enter the optical members, a frame-shaped double-faced tape TP 1 and the like. The light source unit 22 comprises a plurality of light sources 21 arranged at regular intervals along the first direction X, and a wiring substrate 40 which extends along the first direction X to support the light source 21 . The wiring substrate 40 includes a connecting end portion 40 c integrally formed therewith.

FIG. 2 is a perspective view of the display device DSP shown in the FIG. 1 as viewed from a rear surface side.

The flexible printed circuit board 23 is bent over to the rear surface side of the display panel PNL. In the example illustrated, the flexible printed circuit board 23 bent over opposes a bottom surface 17 of the backlight unit BL. Further, as in the case of the flexible printed circuit board 23 , the connecting end portion 40 c is also bent over to the rear surface side of the display panel PNL to oppose the bottom surface 17 of the backlight unit BL. The connecting end portion 40 c is connected to the connector 27 .

FIG. 3 is a cross-sectional view of the display device DSP taken along line A-B shown in FIG. 2 .

The display panel PNL comprises a liquid crystal layer LC in an inner side surrounded by the first substrate SUB 1 , the second substrate SUB 2 and the sealing member SE. Further, the display panel PNL comprises a first polarizer PL 1 and a second polarizer PL 2 . The first polarizer PL 1 is adhered to a lower surface of the first substrate SUB 1 . The second polarizer PL 2 is adhered to a upper surface of the second substrate SUB 2 .

The cover member CM is adhered to the display panel PNL with an adhesive AD. The light-shielding layer RS is located on an lower surface of the cover member CM so as to be in contact with the adhesive AD. The light-shielding layer RS is located in the non-display area NDA. Note that the light-shielding layer RS may be formed on the upper surface of the cover member CM.

An anisotropic conductive film 3 adheres the display panel PNL and the flexible printed circuit board 23 together and electrically connects them to each other. In other words, the anisotropic conductive film 3 is interposed between the flexible printed circuit board 23 and the mounting portion of the first substrate SUB 1 . While the anisotropic conductive film 3 being interposed between the flexible printed circuit board 23 and the display panel PNL, the flexible printed circuit board 23 and the display panel PNL are pressed from above and below along the third direction Z, followed by heating, thus connecting them electrically and physically to each other.

The flexible printed circuit board 23 includes a base member 23 a , wiring lines 23 b and a protective layer 23 c covering the wiring lines 23 b . The base member 23 a comprises a first surface SF 1 and a second surface SF 2 on an opposite side to the first surface SF 1 . The wiring lines 23 b are located on a first surface SF 1 side of the base member 23 a . The base member 23 a and the protective layer 23 c are formed of, for example, a synthetic resin such as of polyimide or polyurethane. The wiring lines 23 b are formed from, for example, a copper foil. The driver IC chip 24 is mounted on a protective layer 23 c side and is electrically connected to the wiring lines 23 b via openings (not shown) or contact pads provided in the protective layer 23 c . Further, the flexible printed circuit board 23 is fixed to the bottom surface 17 of the backlight unit BL by a double-faced tape TP 2 . Further, the flexible printed circuit board 23 includes the spacer 103 , by which structure, the driver IC chip 24 does not abut directly the backlight unit BL. As shown in FIG. 4 , part (a), the spacer 103 surrounds the driver IC chip 24 .

The flexible printed circuit board 23 includes a bend portion BA which can be bent. The flexible printed circuit board 23 is bent so that the protective layer 23 c opposes the display panel PNL and the backlight unit BL. That is, the protective layer 23 c is located in an inner peripheral side of the bend area BA, and the base member 23 a is located in an outer circumferential side of the bend area BA. The flexible printed circuit board 23 contains, in the bend portion BA, a bend start point P 1 on a display panel PNL side and a bend end point P 2 on a side distant from the display panel PNL with respect to the bend start point P 1 . The bend area BA corresponds to a region between the bend start point P 1 and the bend end point P 2 . That is, the flexible printed circuit board 23 has a curvature between the bend start point P 1 and the bend end point P 2 . In the example illustrated, the bend start point P 1 overlaps the mounting edge ME along the third direction Z.

The base member 23 a comprises a groove GR located in the bend portion BA and formed in a second surface SF 2 . One groove GR overlaps the bend start point P 1 and the bend end point P 2 . That is, the groove GR overlaps the mounting edge ME along the third direction Z. As illustrated in the figure, the groove GR may be formed to the outside of the bend area BA. The groove GR extends out to a display area DA side further from the bend start point P 1 to overlap the first substrate SUB 1 along the third direction Z. Further, the groove GR does not penetrate the base member 23 a . As will be described below with reference to FIG. 4 , the groove GR is formed to comprise an irregular bottom surface with convex portions CV.

A protection resin RE 1 is formed between the second substrate SUB 2 and the flexible printed circuit board 23 . The protection resin RE 1 covers the anisotropic conductive film 3 , the pad portions PD and the wiring lines and the like on the first substrate SUB 1 . A protection resin RE 2 is formed on a protective layer 23 c side of the flexible printed circuit board 23 . The protection resin RE 2 is in contact with the display panel PNL, the anisotropic conductive film 3 and the protective layer 23 c.

FIG. 4 is a diagram showing the flexible printed circuit board 23 shown in FIG. 3 . FIG. 4 , part (a) shows a developed plan view of the flexible printed circuit board 23 , and FIG. 4 , part (b) shows a developed cross sectional view of the flexible printed circuit board 23 taken along the second direction Y, and FIG. 4 , part (c) shows a developed cross sectional view of the flexible printed circuit board 23 taken along the first direction X.

As shown in FIG. 4 , part (a), the bend start point P 1 and the bend end point P 2 extend along the first direction X. The driver IC chip 24 extends along the first direction X. The groove GR includes a plurality of concavity portions CC. The concavity portions CC extend along the second direction Y and arranged along the first direction X. Further, the groove GR includes a plurality of convex portions CV. The convex portions CV extend along the second direction Y and arranged along the first direction X. Each convex portion CV is located between each respective adjacent pair of concavity portions CC. These the concavity portions CC and the convex portions CV are formed by making the groove GR along the second direction Y while forming the groove GR with laser. In this embodiment, the groove GR has a width (a first width) W 11 along the second direction Y. The width W 11 is 0.05 to 5 mm. The width W 11 should preferably be, particularly, 1.0 to 3.5 mm, and 2.5 mm is recommended. Further, the groove GR has a width (a second width) W 12 along the first direction X. The width W 12 is 5 to 60 mm.

The flexible printed circuit board 23 comprises a first side SD 1 and a second side SD 2 extending along the second direction Y. In the example illustrated, the first side SD 1 and the second side SD 2 extend substantially parallel to each other, but one or both may be inclined to the second direction Y. The base member 23 a includes a first frame area AR 1 between the first side SD 1 and the respective groove GR and a second frame area AR 2 between the second side SD 2 and the respective groove GR. The groove GR is located between the first frame area AR 1 and the second frame area AR 2 . That is, the groove GR does not overlap the first frame area AR 1 and the second frame area AR 2 , or do not extend to the first side SD 1 and the second side SD 2 . Note that the groove GR may extend to the first side SD 1 and the second side SD 2 . The groove GR overlaps the mounting edge ME of the display panel PNL. The first frame area AR 1 has a width (a third width) W 13 along the first direction X. The second frame area AR 2 has a width (a fourth width) W 14 along the first direction X. The widths W 13 and W 14 each are 0.2 to 5 mm. The widths W 13 and W 14 should preferably be 0.2 to 1.0 mm. The widths W 13 and W 14 may be equal to or different from each other. The wiring lines 23 b should preferably not overlap the first frame area AR 1 and the second frame area AR 2 .

As shown in FIG. 4 , part (b), the base member 23 a has a thickness T 1 in a site where a groove GR is formed, and a thickness T 2 in a site overlapping the driver IC chip 24 . In this example, the thickness T 2 is 35 μm. The thickness T 1 is less than the thickness T 2 . The groove GR comprises an edge portion (a first edge portion) EG which extends along the first direction X and overlaps the display panel PNL. A distance (a first distance) DT 1 taken along the second direction Y between the edge portion EG and the mounting edge ME is 0 to 1.0 mm. The distance DT 1 should preferably be, particularly, 0.025 to 0.3 mm, and 0.175 mm is recommended. The protection resin RE 2 includes an end portion E 1 on an opposite side to the display panel PNL. A distance (a second distance) DT 2 taken along the second direction Y between the end portion E 1 and the mounting edge ME is 0 to 1.5 mm. The distance DT 2 should preferably be, particularly, 0.3 to 1.0 mm. Further, the anisotropic conductive film 3 includes an end portion E 2 in contact with the protection resin RE 2 . A distance DT 3 taken along the second direction Y between the end portion E 2 and the mounting edge ME is 0 to 0.3 mm. The distance DT 3 should preferably be, particularly, 0 to 0.15 mm.

As shown in FIG. 4 , part (c), the concavity portions CC and the convex portions CV are formed in the bottom surface of each groove GR, that is, the surface of a first surface SF 1 side of the base member 23 a . A depth DP 1 taken between the second surface SF 2 and the deepest portion of the concavity portions CC is 0.5 to 32 μm. The depth DP 1 should preferably be, particularly, 5 to 25 μm. Further, a range RG defined between a top portion TP of the convex portions CV and a deepest portion BT of the concavity portions CC is 0.5 to 32 μm. The range RG should preferably be, particularly, 5 to 25 μm. The base member 23 a has a thickness T 1 in a site where each groove GR is formed and a thickness T 3 in a site overlapping the first frame area AR 1 and the second frame area AR 2 . The thickness T 1 is less than the thickness T 3 .

Here, an effect of this embodiment will be described.

The driver IC chip 24 is mounted on the flexible printed circuit board 23 . With this structure, as compared to the case where the driver IC chip 24 is not mounted, the thickness of the flexible printed circuit board 23 need to be increased to improve the strength of the substrate, in which case the repulsion against the bending may increase. Further, in order to narrow the frame of the display device DSP, the bending curvature of the bend portion BA tends to increase, and steeper bending is required. Therefore, the repulsion against the bending of the flexible printed circuit board 23 may further increase. On the other hand, with the narrowed frame, an adhesion area between the display panel PNL and the backlight unit BL is decreased, and therefore the adhesivity between the display panel PNL and the backlight unit BL is lowered. In other words, by narrowing the frame, as the repulsion of the flexible printed circuit board 23 increases, the adhesivity decreases in reverse, which may cause separation of the junction between the backlight unit BL and the display panel PNL, separation or deformation of parts in the backlight unit BL and the like.

According to this embodiment, the flexible printed circuit board 23 comprises a groove GR formed in the base member 23 a . With this structure, the flexible printed circuit board 23 can be form to include a thin film portion, which can reduce the rigidity of the flexible printed circuit board 23 . Thus, the flexible printed circuit board 23 can be bent easily, and the repulsion of the flexible printed circuit board 23 , which occurs by banding can be decreased. Therefore, the separation of the junction between backlight unit BL and the display panel PNL due to the repulsion of the flexible printed circuit board 23 , separation of the double-faced tape TP 2 , separation and deformation of the internal parts of the backlight unit BL and the like can be suppressed. Further, in the case of a display device DSP which does not require a backlight unit BL, separation of the flexible printed circuit board 23 and separation and deformation of members to which the flexible printed circuit board 23 is joined, and the like can be suppressed. Further, the parts conventionally required to adhere the flexible printed circuit board 23 against repulsion can be cut down, which can make it possible to reduce the production cost and reduce of the number of processing steps in the assembling.

Further, as the repulsion to the bending of the flexible printed circuit board 23 is reduced, the flexible printed circuit board 23 can be bent further steeper, thereby making it possible to reduce the outward swelling of the flexible printed circuit board 23 . Thus, the frame of the display device DSP can be narrowed.

Meanwhile, the groove GR of the embodiment is constructed by a plurality of concavity portions CC formed along the second direction Y. The bend area BA is bent along second direction Y. That is, the concavity portions CC are parallel to the bending direction, or perpendicular to the mounting edge ME. The bending direction is defined as a direction indicated by an arrow shown in the bend area BA of FIG. 3 , for example. With this structure, the concentration of stress on the bend area BA is dispersed as compared to the case where the concavity portions CC are formed along the first direction X with laser, thus making it possible to reduce the risk of disconnection of the wiring lines 23 b.

Further, in the example illustrated, the groove GR overlaps the bend start point P 1 and the bend end point P 2 . In the bend start point P 1 and the bend end point P 2 , it is easy for particularly great shearing stress to occur under the influence of bending stress. However, with the groove GR thus formed, the thickness in the bend start point P 1 and the bend end point P 2 of the flexible printed circuit board 23 is less, and therefore the shearing stress can be relaxed. As described, in the points where stress is particularly great, breakage of the flexible printed circuit board 23 and disconnection of the wiring lines 23 b can be suppressed as well.

Further, in this embodiment, the base member 23 a includes the first frame area AR 1 and the second frame area AR 2 , and the groove GR does not overlap the first frame area AR 1 and the second frame area AR 2 . That is, the groove GR does not extend to the first side SD 1 and the second side SD 2 of the flexible printed circuit board 23 . With this structure, a thinned portion is not formed in the first side SD 1 and the second side SD 2 , which can suppress the flexible printed circuit board 23 from breaking from the first side SD 1 or the second side SD 2 .

Next, the second embodiment will be described with reference to FIGS. 5 and 6 .

FIG. 5 is a cross section of a display device DSP according to the second embodiment. The configuration shown in FIG. 5 is different from that of FIG. 3 in that the base member 23 a comprises the first groove GR 1 and the second groove GR 2 .

In the example illustrated, the groove GR is constructed by a first groove GR 1 and a second groove GR 2 . The first groove GR 1 is located in the bend start point P 1 . The second groove GR 2 is located in the bend end point P 2 . That is, the first groove GR 1 overlaps the mounting edge ME along the third direction Z. As illustrated in the figure, the first groove GR 1 and the second groove GR 2 may be formed over to an outside of the bend area BA. The first groove GR 1 extends on an display area DA side further from the bend start point P 1 , and overlaps the first substrate SUB 1 along the third direction Z. Further, the first groove GR 1 and the second groove GR 2 do not penetrate the base member 23 a . As will be described below with reference to FIG. 6 , the first groove GR 1 and the second groove GR 2 are formed to comprise an irregular bottom surface with convex portions CV.

FIG. 6 is a view of the flexible printed circuit board 23 shown in FIG. 5 . FIG. 6 , part (a) shows a developed plan view of the flexible printed circuit board 23 . FIG. 6 , part (b) is a developed cross-sectional view of the flexible printed circuit board 23 taken along the second direction Y. FIG. 6 , part (c) is a developed cross-sectional view of the flexible printed circuit board 23 taken along the first direction X.

As shown in FIG. 6 , part (a), the first groove GR 1 overlaps the bend start point P 1 and extends along the first direction X. The second groove GR 2 overlaps the bend end point P 2 and extends along the first direction X. The first groove GR 1 and the second groove GR 2 each comprise a plurality of concavity portions CC. The concavity portions CC extend along the second direction Y and are arranged along the first direction X. A plurality of the convex portions CV are each formed between each respective adjacent pair of concavity portions CC. The concavity portions CC and the convex portions CV are formed by making the first groove GR 1 and the second groove GR 2 when forming the first groove GR 1 and the second groove GR 2 along the second direction Y with laser. In the second embodiment, the first groove GR 1 has a width (a fifth width) W 15 along the second direction Y. The width W 15 is 0.05 to 2.5 mm. The width W 15 should preferably be, particularly, 0.05 to 1.25 mm. The second groove GR 2 has a width (a sixth width) W 16 along the second direction Y. The width W 16 is 0.05 to 2.5 mm. The width W 16 should preferably be, particularly, 0.05 to 1.25 mm. The first groove GR 1 includes an edge portion EG 1 which extends along the first direction X and overlaps the display panel PNL. The second groove GR 2 includes an edge portion EG 2 which extends along the first direction X and is located on a driver IC chip 24 side. The width W 11 between the edge portion EG 1 and the edge portion EG 2 is equal to the width W 11 of the groove GR taken along the second direction Y, discussed in the first embodiment.

The first groove GR 1 and the second groove GR 2 are located between the first frame area AR 1 and the second frame area AR 2 . That is, the first groove GR 1 and the second groove GR 2 do not overlap the first frame area AR 1 and the second frame area AR 2 , and do not extend over to the first side SD 1 and the second side SD 2 . The width W 13 of the first frame area AR 1 and the width W 14 of the second frame area AR 2 are respectively equal to the widths W 13 and W 14 discussed in the first embodiment.

As shown in FIG. 6 , part (b), the base member 23 a has a thickness T 11 in a site where the first groove GR 1 is formed, and has a thickness T 12 in a site where the second groove GR 2 is formed. Further, it has a thickness T 2 in a site overlapping the driver IC chip 24 . The thicknesses T 11 and T 12 are each thinner than the thickness T 2 . The thicknesses T 11 and T 12 may be equal to or different from each other. A distance DT 1 between the edge portion EG 1 and the mounting edge ME taken along the second direction Y is equal to the distance DT 1 discussed in the first embodiment. A distance DT 2 between the end portion E 1 of the protection resin RE 2 and the mounting edge ME taken along the second direction Y is equal to the distance DT 2 discussed in the first embodiment. A distance DT 3 between the end portion E 2 of the anisotropic conductive film 3 and the mounting edge ME taken along the second direction Y is equal to the distance DT 3 discussed in the first embodiment.

As shown in FIG. 6 , part (c), the concavity portions CC and the convex portions CV are formed in the bottom surface of the first groove GR 1 , that is, a surface on a first surface SF 1 side of the base member 23 a . A depth DP 1 between the second surface SF 2 and the deepest portion of the concavity portions CC is equal to the depth DP 1 discussed in the first embodiment. Further, a range RG between the deepest portion of the concavity portions CC and a top portion of the convex portions CV is equal to the range RG discussed in the first embodiment. The second groove GR 2 is similar to the first groove GR 1 .

For this reason, advantages similar to those of the first embodiment can be obtained in the second embodiment.

The third embodiment will be described with reference to FIGS. 7 and 8 .

FIG. 7 is a cross section of a display device DSP according to the third embodiment. The configuration shown in FIG. 7 is different from that of FIG. 5 in that the base member 23 a comprises a first groove GR 1 , but does not comprise a second groove GR 2 . The configuration of the first groove GR 1 shown in FIG. 7 is similar to the configuration of the first groove GR 1 shown in FIG. 5 .

FIG. 8 is a diagram illustrating the flexible printed circuit board 23 shown in FIG. V. FIG. 8 , part (a) is a developed plan view of the flexible printed circuit board 23 , and FIG. 8 , part (b) is a developed cross-sectional view of the flexible printed circuit board 23 taken along the second direction Y. FIG. 8 , part (c) is a developed cross-sectional view of the flexible printed circuit board 23 taken along the first direction X. The configuration of a first groove GR 1 shown in FIG. 8 is equal to the configuration of the first groove GR 1 shown in FIG. 6 . The width W 15 of the first groove GR 1 is 0.05 to 5 mm. The width W 15 should preferably be, particularly, 0.05 to 1.25 mm. The bend start point P 1 is a site where the repulsion is at maximum in the bend area BA, and therefore, by setting the first groove GR 1 in the bend start point P 1 , the repulsion of the flexible printed circuit board 23 can be effectively relaxed.

Thus, advantages similar to those of the first embodiment can also be obtained in the third embodiment.

Next, the fourth embodiment will be described with reference to FIGS. 9 and 10 .

FIG. 9 is a cross section of a display device DSP according to the fourth embodiment. The configuration shown in FIG. 9 is different from that of FIG. 5 in that the base member 23 a comprises a second groove GR 2 , but does not comprise a first groove GR 1 . The configuration of the second groove GR 2 shown in FIG. 9 is similar to the configuration of the second groove GR 2 shown in FIG. 5 .

FIG. 10 is a diagram illustrating the flexible printed circuit board 23 shown in FIG. 9 . FIG. 10 , part (a) is a developed plan view of the flexible printed circuit board 23 , and FIG. 10 , part (b) is a developed cross-sectional view of the flexible printed circuit board 23 taken along the second direction Y. FIG. 10 , part (c) is a developed cross-sectional view of the flexible printed circuit board 23 taken along the first direction X. The configuration of a second groove GR 2 shown in FIG. 10 is equal to the configuration of the second groove GR 2 shown in FIG. 6 . The width W 16 of the second groove GR 2 is 0.05 to 5 mm. The width W 16 should preferably be, particularly, 0.05 to 1.25 mm. The width W 16 should preferably be, particularly, 0.05 to 1.25 mm. Further, a distance DT 4 between the edge portion EG 2 of the second groove GR 2 and the mounting edge ME taken along the second direction Y is 0.05 to 5 mm. A distance DT should preferably be, particularly, 0.75 to 3.75 mm. Here, the bend end point P 2 is located at a site most close to the double-faced tape TP 2 in the bend area BA, and therefore, by setting the second groove GR 2 in the bend end point P 2 , the release force to occur to an adhesion portion between the backlight unit BL and the flexible printed circuit board 23 can be effectively reduced.

For this reason, advantages similar to those of the first embodiment can also be obtained in the fourth embodiment.

FIG. 11 is a diagram showing the first example of a processing step of forming grooves GR in the flexible printed circuit board 23 .

A motherboard 100 to prepare a plurality of flexible printed circuit boards 23 is rolled round a reel. Flexible printed circuit boards 23 are cut out from one motherboard 100 with a punch die. The motherboard 100 includes a base member 23 a , wiring lines 23 b and a protective layer 23 c as those shown in FIG. 3 . A test pad TPD for testing electrical continuity of a flexible printed circuit board 23 is placed outside of the flexible printed circuit board 23 . A plurality of wiring lines 23 b are drawn to the outside of the flexible printed circuit board 23 and connected to the test pads TPD.

In the example illustrated in FIG. 11 , before flexible printed circuit boards 23 are cut out from the motherboard 100 , laser LL is irradiated onto a flexible printed circuit board 23 to form a groove GR. The groove GR is formed between the first frame area AR 1 and the second frame area AR 2 in the bend area BA. The reel may be set in a mounting machine to perform a process to mount a flexible printed circuit board 23 on a display panel PNL, and the step of punching flexible printed circuit boards 23 out from the motherboard 100 may be performed in the mounting machine.

FIG. 12 is a diagram showing the second embodiment of the processing step of forming a groove GR in a flexible printed circuit board 23 .

In the example illustrated in FIG. 12 , laser LL is irradiated onto a single-unit flexible printed circuit board 23 to form the groove GR. More specifically, after a flexible printed circuit board 23 is cut out from a motherboard 100 such as shown in FIG. 11 or immediately before the flexible printed circuit board 23 is mounted to the display panel PNL, the groove GR is formed. The groove GR is formed between the first frame area AR 1 and the second frame area AR 2 in the bend area BA.

FIG. 13 is a diagram showing the third embodiment of the processing step of forming a groove GR in a flexible printed circuit board 23 .

In the example illustrated in FIG. 13 , after mounting the flexible printed circuit board 23 in the display panel PNL, laser LL is irradiated on the base member 23 a to form the groove GR. The groove GR is formed between the first frame area AR 1 and the second frame area AR 2 in the bend area BA. After forming the groove GR, the flexible printed circuit board 23 is bent from the bend portion BA.

FIG. 14 is a diagram showing the fourth embodiment of the processing step of forming a groove GR in a flexible printed circuit board 23 .

In the example illustrated in FIG. 14 , after the flexible printed circuit board 23 is bent, the groove GR is formed in the flexible printed circuit board 23 by laser LL. Or, at the end of the manufacturing process of the display device DSP, the groove GR is formed in the flexible printed circuit board 23 by laser LL. The groove GR is formed between the first frame area AR 1 and the second frame area AR 2 in the bend area BA.

The processing step of forming a groove GR by the laser LL, described above, may be performed by a single-unit laser mechanism, or it may be performed in a mounting machine configured to mount a flexible printed circuit board 23 in a display panel PNL. The laser mechanism can be installed in an arbitrary site in the device of manufacturing display devices DSP. The processing steps shown in FIGS. 11 to 14 can be applied to all the patterns of the grooves GR described above.

As discussed above, according to this embodiment, an electronic device and a flexible printed circuit board, with improved reliability can be obtained.

Note that, in the examples described above, the driver IC chip 24 is mounted on the flexible printed circuit board 23 , but the driver IC chip 24 may be mounted on the display panel PNL. Or, if the strength of the flexible printed circuit board 23 is sufficient, the groove GR may be formed in the first frame area AR 1 and the second frame area AR 2 as well. Further, the pattern of the groove GR can be adjusted to an arbitrary shape and may as well be so other pattern than those discussed above.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.