JP2006310123A - Planar lighting system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reliable planar lighting system with high intensity by preventing disconnection of a wiring pattern around an LED and increasing heat radiating property of the LED. <P>SOLUTION: The planar lighting system of this invention is provided with a light guide plate, a point light source 50 disposed on a side end face of the light guide plate and a flexible printed circuit board 21 mounting the point light source 50. The flexible printed board 21 comprises a base film 31, a conduction pattern and a cover-lay film 41. The conduction pattern is provided with the wiring pattern 32, land parts 33, 34 and junction parts 36, 35 connecting the wiring pattern 32 with the land parts 33, 34 and wider than the lands 33, 34. Parts of the land parts 33, 34 and the junction parts 36, 35 are exposed from the opening part 42 formed in the cover-lay film 41. The junction parts 36, 35 of wider area than the land part function as wire disconnection prevention parts and heat radiation parts. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a sidelight type planar illumination device, and more particularly to a planar illumination device used as illumination means of a liquid crystal display device.

  Conventionally, as an auxiliary light source for a liquid crystal display device, there is a sidelight type planar illumination device in which a primary light source is disposed on a side end surface of a light guide plate (hereinafter, a side end surface on which a primary light source is disposed is also referred to as a light incident surface). It is widely used in the field of liquid crystal display devices having a relatively small display area. In particular, liquid crystal display devices for small mobile terminals such as mobile phones are white light sources that are excellent in handling, easy to miniaturize, and have high impact resistance as the primary light source for such planar lighting devices. A point light source (hereinafter, also simply referred to as an LED) such as an LED is frequently used.

FIG. 4 is an exploded perspective view schematically showing a configuration example of a sidelight type planar illumination device using LEDs as a primary light source. In FIG. 4, the planar illumination device 100 is disposed on the light source unit 120 including the LED 50 and a flexible printed circuit board (hereinafter also referred to as FPC) 121 on which the LED 50 is mounted, the light guide plate 11, and the back surface 11 b side of the light guide plate 11. The light source unit 120 includes a light diffusing plate 12 and prism plates 13 and 14 that are sequentially stacked on the surface 11a side of the light guide plate 11. It arrange | positions so that the optical surface 11c may be opposed.
Here, the light guide plate 11 is a plate-like light guide formed by preferably injection-molding a translucent resin such as a polycarbonate resin. Generally, the rear surface 11b and / or the front surface 11a of the light guide plate 11 are both. Are formed with optical path changing means (not shown) for changing the traveling direction of light. The reflection plate 15 reflects light leaking from the back surface 11b of the light guide plate 11 to re-enter the light guide plate 11, and the diffusion plate 12 diffuses and equalizes light emitted from the surface 11a of the light guide plate 11. It is. The prism plates 13 and 14 collect light and improve the front luminance of the planar illumination device 100. Each prism plate 13 and 14 has a prism row formed in one direction. The layers are stacked so that their directions are orthogonal to each other.
Further, in the planar illumination device 100, the light incident surface 11 c of the light guide plate 11 diffuses incident light from the LED 50 to the light guide plate 11, so that the light output surface 50 a of the LED 50 is opposed to the light guide plate 11. A light incident prism portion 19 including a plurality of prisms extending in the thickness direction is formed.

  In the planar illumination device 100 configured as described above, the light incident from the light incident surface 11c propagates toward the other side end surface 11d while being totally reflected in the light guide plate 11, and during that time, by the optical path changing means. The light whose path has been changed is emitted from the surface 11a. In this case, for example, when the optical path conversion means is a dot-shaped optical path conversion pattern, the area density of the pattern is sparse on the light incident surface 11c side, and the end By making the surface 11d side dense, planar uniform light emission is realized.

Next, a typical configuration of the LED 50 used in the planar lighting device 100 will be described with reference to FIG. In FIG. 5, (a) is a trihedral view showing the outer shape of the LED 50, and (b) is a cross-sectional view taken along the line AA of (a).
The LED 50 includes a lamp house 51 made of, for example, a heat-resistant white resin, and the lamp house 51 is formed with a recess 51a that houses an LED chip 53, which is a semiconductor light emitting element, on the bottom surface of the recess 51a. The lead frames 54 and 55 are formed of a conductive member such as copper. The lead frames 54 and 55 are extended to the outside of the lamp house 51 and integrally formed with the electrode terminals 57 and 58, respectively. The LED chip 53 is mounted on one lead frame 54 and is attached by a gold wire 56. The cathode electrode is electrically connected to the lead frame 54, and the anode electrode is electrically connected to the lead frame 55 (the lamp house 51 is provided with a cathode mark 59 indicating that the electrode terminal 57 is on the cathode side). Is). The recess 51a is filled with a sealing agent 52 made of a transparent resin such as a hard silicone resin or an epoxy resin. The LED 50 uses the surface 50a formed by the sealing agent 52 as a light exit surface, and the LED chip 53. The light emitted from is taken out.

  Next, the configuration of the light source unit 120 will be described with reference to FIG. The FPC 121 forms, for example, a conductive pattern made of a wiring pattern 132 and land portions 133 and 134 on a base film 131 made of polyimide or the like using, for example, copper foil or the like (see FIG. 6A). A coverlay film 141 made of polyimide or the like is laminated and bonded together (see FIG. 6B). Here, as shown in FIG. 6B, the coverlay film 141 is provided to avoid the connection terminal portion 123 for connecting the FPC 121 to an external drive circuit, and the electrode terminals 57 and 58 of the LED 50 are connected. An opening 142 for exposing the land portions 133 and 134 to be exposed is provided. As shown in FIG. 6C, the LED 50 is electrically connected to the wiring pattern 132 by connecting the electrode terminals 57 and 58 and the land portions 133 and 134 by a reflow process that normally uses cream solder. At the same time, it is positioned and fixed with respect to the FPC 121. At that time, the land parts 133 and 134 are usually formed in a shape and size substantially corresponding to the electrode terminals 57 and 58, and thereby, in the reflow process, the self-alignment action due to the surface tension of the molten solder is effective. Therefore, the LED 50 can be positioned with high accuracy.

  Here, the opening portion 142 of the cover lay film 141 is somewhat larger than the area occupied by the land portions 133 and 134 in order to absorb the positional deviation that normally occurs when the cover lay film 141 and the base film 131 are bonded together. It is formed so as to expose a wide area. Therefore, in the FPC 121 configured as described above, not only the land portions 133 and 134 but also a part of the wiring pattern 132 connected to the land portions 133 and 134 is exposed from the opening 142 of the coverlay film 141. As a result of stress concentration when deformation occurs near the land portions 133 and 134 of the FPC 121 being concentrated on the wiring pattern 132 having a narrow line width, there has been a problem that disconnection is likely to occur. Conventionally, as a means for dealing with disconnection of a portion (leading line) exposed from the opening 142 of the wiring pattern 132, for example, it has been proposed to provide a leading line in a plurality of directions from the land part (for example, Patent Document 1). reference).

Furthermore, it is generally known that the LED 50 has a decrease in luminance and a decrease in life due to heat generated by light emission. In order to maintain a stable luminance while maintaining the driving current of the LED 50 within an allowable limit. It is desirable to take some heat dissipation measures for the light source unit 120. In relation to this point, conventionally, it has been proposed to increase the area of the wiring pattern and enhance the heat dissipation of the heat from the LED (for example, see Patent Document 2).
JP 2003-101173 A (Claim 1, FIG. 1) JP 2003-331604 A ([0015], FIG. 6)

  As a means for coping with the disconnection of the lead wire, the means described in Patent Document 1 is such that the stress applied to the FPC is due to, for example, a bending intended in design for incorporation into the apparatus, and its direction is predetermined. If it is decided, it will produce a certain effect. However, the FPC may be subject to unexpected stress during assembly work or rework of the planar lighting device, or may be subject to a drop impact due to an unexpected accident after being incorporated into a device such as a mobile terminal. The means described in Patent Document 1 does not always have a sufficient effect when there is a possibility that force is applied from all directions, and further improvement has been demanded. Further, regarding heat dissipation of heat from the LED, Patent Document 2 describes that the area of the wiring pattern is increased to increase heat dissipation from the LED, but it is described in Patent Document 2. The shape of the wiring pattern is based on the premise that the area of the circuit board is sufficiently large with respect to the area occupied by components (for example, LEDs) mounted thereon. For example, the light source shown in FIG. It is difficult to apply the configuration to the unit 120.

  The present invention has been made in view of the above problems, and provides a planar illumination device having high luminance and high reliability by preventing disconnection of a wiring pattern around the LED and enhancing heat dissipation of the LED. For the purpose.

  In order to achieve the above object, a planar illumination device according to the present invention includes a light guide plate, a point light source disposed on a side end surface of the light guide plate, and a flexible printed circuit board on which the point light source is mounted. In the planar lighting device, the flexible printed board includes a base film, a conductive pattern, and a coverlay film, and the conductive pattern connects the wiring pattern, the land portion, and the wiring pattern and the land portion. A relay portion having a larger area than the land portion, and the land portion and a part of the relay portion are exposed from an opening formed in the coverlay film.

  According to the present invention, by providing a relay portion having a larger area than the land portion between the land portion and the wiring pattern, a lead line having a narrow line width is not exposed from the opening of the coverlay film. It is possible to prevent disconnection of the portion exposed from the opening portion of the conductive pattern and improve the peel strength of the land portion. In addition, since the heat generated from the point light source can be efficiently radiated by the relay part having a larger area than the land part, the temperature of the point light source is suppressed and the brightness of the surface illumination device is increased. And contributes to stabilization of luminance.

  In one aspect of the present invention, the land portion and the relay portion are connected by overlapping one corner of each, and thereby the shape of the land portion is a shape that does not impair the self-alignment function during solder reflow. Therefore, the point light source can be positioned with high accuracy.

  In addition, the outline of the corner of the relay portion connected to the land portion has one side extending in a direction substantially perpendicular to one of the two adjacent sides of the cover lay film opening, and the opening of the cover lay film. Desirably, the relay portion is formed of one side extending in a direction substantially orthogonal to the other of the two adjacent sides, whereby the shape of the relay portion can be made more effective for preventing disconnection.

  In the aspect of the invention, the point light source includes a light emitting element, a first lead frame and a second lead frame, a first electrode terminal connected to the first lead frame and the second lead frame, and a first lead frame. And the light emitting element is mounted on the first lead frame, and the area of the relay portion connected to the land portion on which the first electrode terminal is mounted is the second electrode terminal. Is wider than the area of the relay portion connected to the land portion on which is mounted.

  Since most of the heat generated from the light emitting element is conducted from the first lead frame on which the light emitting element is mounted to the first electrode terminal, the area of the relay part connected to the land part where the first electrode terminal is disposed is By making the area larger than the area of the relay part connected to the land part on which the second electrode terminal is mounted, the area that can be used as the relay part on the flexible printed circuit board is maximized, and the heat from the point light source Can be radiated more efficiently. In addition, since the relay portion connected to the land portion on which the second electrode terminal is mounted also functions as a heat radiating portion, it is possible to appropriately maintain the temperature balance at the time of solder reflow in the pair of land portions for each point light source. it can.

  Since this invention was comprised in this way, while preventing the disconnection of the wiring pattern in the LED periphery, it can improve the heat dissipation of LED, and it can provide a planar illuminating device with high brightness and high reliability. Become.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the accompanying drawings. However, the drawings are for explanation, and do not necessarily accurately reflect actual shapes and dimensions. FIG. 1 is an exploded perspective view showing a main part of a planar illumination device 10 according to an embodiment of the present invention. The planar illumination device 10 has substantially the same configuration as that of the planar illumination device 100 shown in FIG. 4, and only the configuration of the light source unit 20 is different. The light source unit 20 will be described in detail.

  FIG. 2 is a plan view showing the configuration of the light source unit 20 in the present embodiment. In the present embodiment, the FPC 21 forms a conductive pattern on a base film 31 made of polyimide or the like, for example, using copper foil or the like (see FIG. 2A), and a cover layer made of polyimide or the like is similarly formed on the upper layer. The film 41 is formed by laminating and bonding (see FIG. 2B), and the conductive pattern formed on the base film 31 includes the wiring pattern 32, the electrode terminal 58 of the LED 50 (see FIG. 5), 57 includes land portions 33 and 34, and relay portions 36 and 35 that connect the wiring pattern 32 and the land portions 33 and 34, respectively. Further, as shown in FIG. 2B, the coverlay film 41 is provided to avoid the connection terminal portion 23 for connecting the FPC 21 to an external drive circuit, and has an opening 42 in the mounting portion of the LED 50. From the opening 42, the land portions 33, 34 and a part of the relay portions 36, 35 connected to the land portions 33, 34 are exposed. Here, the area of each relay part 36, 35 is formed to be larger than at least the area of the land parts 33, 34, and the area of the relay part 35 connected to the land part 34 is connected to the land part 33. It is formed wider than the area of the relay part 36.

FIG. 3 is an enlarged plan view showing the vicinity of one land portion 33, 34 of the FPC 21. Here, with reference to FIG. 3, the shape of the relay parts 36 and 35 and the connection mode of the relay parts 36 and 35 and the land parts 33 and 34 are demonstrated.
In the present embodiment, the portion exposed from the opening 42 of the relay portion 36 includes one side 36b extending in a direction substantially orthogonal to one of the two sides 42a and 42b adjacent to the opening 42, and two adjacent to the opening 42. One side 36a extending in a direction substantially orthogonal to the other side 42b of the sides 42a, 42b, and the relay part 36 and the land part 33 are (virtual) intersections of the two sides 33a, 33b of the land part 33. A certain corner and a corner that is a (virtual) intersection of the two sides 36a and 36b of the relay unit 36 are connected so as to overlap each other. Similarly, a portion exposed from the opening 42 of the relay portion 35 includes a side 35b extending in a direction substantially perpendicular to one of the two sides 42a ′ and 42b adjacent to the opening 42, and two adjacent sides of the opening 42. One side 35a extending in a direction substantially orthogonal to the other side 42b of the sides 42a 'and 42b, the relay part 35 and the land part 34 are (virtual) intersections of the two sides 34a and 34b of the land part 34. And one corner which is a (virtual) intersection of the two sides 35a and 35b of the relay unit 35 are connected so as to overlap each other.

  By configuring the shape of each land portion 33, 34 and the relay portions 36, 35 and the connection manner thereof as described above, a lead line portion having a narrow line width is not provided from the opening 42 of the coverlay film 41. The land portions 33 and 34 can be connected to the wiring pattern 32, and even if the stress due to the bending of the FPC 21 is applied in a loose direction, the relay portions 36 and 35 do not have a bending direction that is likely to break, so that It is possible to effectively prevent disconnection of a portion exposed from the pattern opening 42 (particularly, at a portion where the sides 42a, 42a ′, 42b constituting the opening 42 are in contact with the relay portions 36, 35). .

  Here, as described above, the LED 50 shown in FIG. 5 includes the first lead frame 54 and the second lead frame 55 made of a conductive member such as copper, for example. The lead frame 55 extends outside the lamp house 51 and is formed integrally with the first electrode terminal 57 and the second electrode terminal 58, respectively. The LED chip 53, which is a semiconductor light emitting element, is mounted on a first lead frame 54, and one electrode (for example, a cathode electrode) is connected to the first lead frame 54 and the other electrode (for example, a gold wire 56). , Anode electrodes) are electrically connected to the second lead frame 55, respectively.

As shown in FIG. 2C, the LED 50 is mounted on the FPC 21 with the first electrode terminal 57 disposed on the land portion 34 and the second electrode terminal 58 disposed on the land portion 33. In addition, the first and second electrode terminals 57 and the respective land portions 34 and 33 are electrically connected and positioned and fixed by a reflow process using cream solder.
Here, the land portions 33 and 34 are preferably formed in a shape and size substantially corresponding to the electrode terminals 58 and 57, and thereby, in the reflow process, the self-alignment action due to the surface tension of the molten solder is performed. Effectively, the LED 50 can be positioned with high accuracy. In particular, since the positioning accuracy in the direction orthogonal to the light incident surface 11c of the light guide plate 11 is important for increasing the brightness and stabilizing the brightness of the planar illumination device 10, the electrode terminals 58 shown in FIG. It is desirable that the width W1 of 57 and the width W of the land portions 33 and 34 shown in FIG. In relation to this point, the shape of the land portions 33 and 34 and the relay portions 36 and 35 and the connection mode thereof in the present embodiment impairs the outline forming the width W of each land portion 33 and 34 as described above. Therefore, the disconnection can be prevented, which is advantageous. Similarly, the outline forming the width in the direction orthogonal to the width W of each land portion 33, 34 is not impaired.

  Further, the relay portions 35 and 36 in the present embodiment are formed so as to have a larger area than the land portion, and are generated by the light emission of the LED 50 and are radiated from the heat transmitted to the electrode terminals 57 and 58. It also functions. Here, in the LED 50, the diameter of the gold wire 56 that connects the electrode of the LED chip 53 and each lead frame 54, 55 is as thin as 20 to 30 μm, and heat conduction through the gold wire 56 hardly occurs. Therefore, most of the heat from the LED chip 53 that is a light emitting element and also a heat source is transmitted to the first lead frame 54 on which the LED chip 53 is mounted, and is integrally formed with the first lead frame 54. The first electrode terminal 57 has a higher temperature than the second electrode terminal 58. Therefore, like the relay portions 35 and 36 in the present embodiment, the area of the relay portion 35 connected to the land portion 34 where the first electrode terminal 57 is placed and fixed is arranged and fixed. By making the area larger than the area of the relay part 36 connected to the land part 33, the area that can be used as the relay parts 35 and 36 determined by the outer shape of the FPC 21, the arrangement of the wiring pattern 32, etc. is utilized to the maximum extent. The heat from the LED 50 can be efficiently radiated. At this time, the relay portion 36 connected to the land portion 33 on which the second electrode terminal 58 is disposed and fixed has at least a larger area than the land portion 33 and has a constant heat radiation action at the time of solder reflow. This is useful for making the temperature change of the pair of land portions 33 and 34 constant as much as possible.

  The configuration of the planar illumination device according to the present invention is not limited to the configuration of the planar illumination device 10 shown in FIG. 1, but the shape of the light guide plate 11, its main surfaces 11 a and 11 b, side end surfaces 11 c 11 d, etc. The structure or the presence / absence of use of the reflecting plate 15, the diffusing plate 12, and the prism plates 13 and 14 can be arbitrarily selected. Moreover, in this embodiment, although the light source part 20 shall drive two LED50 in series, it cannot be overemphasized that this invention is not limited to the number and connection form of LED to be used.

Hereinafter, the result of trial evaluation of the planar illumination device corresponding to the planar illumination device 10 shown in FIG. 1 will be described. The configuration of the planar illumination device of this example is as follows. The light guide plate 11 was prepared by injection molding a polycarbonate resin into a 30 mm × 40 mm (thickness 6 mm) plate shape. Circular dot patterns were provided on the front and back surfaces 11a and 11b, and a light incident prism portion 19 composed of a fine prism array with a pitch of 0.15 mm was provided on the light incident surface (side end surface on the 30 mm side) 11c. Moreover, the reflecting plate 15 (ESR: manufactured by 3M), the diffusion plate 12 (50 LSE: manufactured by Kimoto), and the prism plates 13 and 14 (BEFII: manufactured by 3M) were arranged as shown in FIG. The FPC 21 is formed by a base film 31 made of polyimide resin, a conductive pattern made of copper foil, and a coverlay film 41 made of polyimide resin. The land portions 33 and 34 are plated with solder, and the connection terminal portion 23 is plated with gold. did. The conduction pattern was configured so that two LEDs 50 were connected in series, and the size of the relay portion 35 connected to the land portion 34 was 4 × 2.5 mm. The total thickness of the FPC 21 including the adhesive layer for bonding was about 0.2 mm. As the LED 50, NESW008 manufactured by Nichia Corporation was used.
A method of creating the light source unit 20 is as follows. First, cream solder (LFM-48X: manufactured by Nippon Almit Co., Ltd.) was applied to the land portions 33 and 34 of the FPC 21 with a thickness of about 100 μm by a screen printing method, and the LED 50 was mounted on the land by a fully automatic chip mounter. Next, soldering was performed by allowing the FPC 21 mounted with the LED 50 to pass through a nitrogen-substituted reflow furnace. The reflow conditions were preheating temperature: about 170 ° C. and solder temperature: about 230 ° C.

  As a comparative example, a planar illumination device corresponding to the planar illumination device 100 shown in FIG. 4 was created. The planar lighting device of the comparative example is the same as the planar lighting device of the present embodiment, except for the configuration of the FPC 121 (land size: 0.8 × 1.0 mm).

  Using the planar lighting devices of the present example and the comparative example configured as described above, the LED 50 (two lamps in series) is driven at 20 mA, left for 1 hour in an atmosphere of no air at 25 ° C., and then the LED chip. A temperature of 53 was measured. As a measuring method, a general Vf method was used as a temperature measuring method for semiconductor elements.

  As a result of the above measurement, the temperature of the LED chip 53 of the surface illumination device of the comparative example was 82 ° C., whereas in the surface illumination device of this example, the temperature of the LED chip 53 was 70 for both the two lamps. The temperature dropped to ° C. In addition, it was confirmed that the FPC 21 of the present example did not cause any disconnection in a normal use state with some repeated bending.

It is a disassembled perspective view which shows the principal part of the planar illuminating device in one Embodiment of this invention. It is a top view which shows the light source part of the planar illuminating device shown in FIG. 1, (a) is the state in which the coverlay film is not laminated | stacked on FPC, (b) is the state in which the coverlay film was laminated | stacked on FPC, c) is a diagram showing a state in which the LED is mounted on the FPC. It is a top view which expands and shows the land part vicinity of FPC shown in FIG.2 (b). It is a disassembled perspective view which shows the structural example of the conventional planar illuminating device. It is a figure which shows the structure of the typical LED used for a planar illuminating device, (a) is a three-plane figure, (b) is sectional drawing along the AA cut line shown to (a). It is a top view which shows the light source part of the conventional planar illuminating device shown in FIG. 4, (a) is the state in which the coverlay film is not laminated | stacked on FPC, (b) is the state in which the coverlay film was laminated | stacked on FPC. (C) is a figure which shows the state by which LED was mounted in FPC.

Explanation of symbols

10: planar illumination device, 11: light guide plate, 11c: light incident surface, 21: flexible printed circuit board (FPC), 31: base film, 32: wiring pattern, 33, 34: land portion, 35, 36: relay portion

Claims (4)

In a planar lighting device having a light guide plate, a point light source disposed on a side end surface of the light guide plate, and a flexible printed board on which the point light source is mounted,
The flexible printed board includes a base film, a conductive pattern, and a coverlay film,
The conductive pattern includes a wiring pattern, a land portion, and a relay portion that connects the wiring pattern and the land portion and has a larger area than the land portion,
A planar illumination device, wherein the land portion and a part of the relay portion are exposed from an opening formed in the coverlay film.   The planar lighting device according to claim 1, wherein the land portion and the relay portion are connected by overlapping each corner.   The outline of one corner of the relay portion connected to the land portion is adjacent to one side extending in a direction substantially perpendicular to one of two adjacent sides of the opening of the coverlay film and the opening of the coverlay film. The planar illumination device according to claim 1 or 2, comprising one side extending in a direction substantially orthogonal to the other of the two sides. The point light source includes a light emitting element, a first lead frame and a second lead frame, and a first electrode terminal and a second electrode terminal connected to the first lead frame and the second lead frame, respectively.
The light emitting element is mounted on the first lead frame;
An area of the relay portion connected to the land portion where the first electrode terminal is disposed is larger than an area of the relay portion connected to the land portion where the second electrode terminal is disposed. The planar illumination device according to any one of claims 1 to 3.

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