CN210199452U

CN210199452U - Planar lighting device

Info

Publication number: CN210199452U
Application number: CN201921145721.6U
Authority: CN
Inventors: Moriyuki Ebisuka; 海老塚守之; Ippei Kusunoki; 楠木一平
Original assignee: MinebeaMitsumi Inc
Current assignee: MinebeaMitsumi Inc
Priority date: 2018-08-02
Filing date: 2019-07-19
Publication date: 2020-03-27
Anticipated expiration: 2029-07-19
Also published as: CN110792950A; CN110792950B; JP6745300B2; JP2020021666A

Abstract

The utility model provides a can improve the surface form lighting device of installation accuracy. The planar lighting device of the embodiment includes: a plurality of pads, a light source, and an adhesive member. The plurality of pads are provided on the main surface of the wiring substrate. The light source has terminals respectively accommodated in a plurality of cavities arranged on any surface other than the light emitting surface, and the pad and the terminal are bonded via solder accommodated in the cavities. The bonding member is disposed between the main surface and the light source, and bonds the main surface and the light source. The interval between the surface of the light source and the bonding pad is 20 μm or less.

Description

Planar lighting device

Technical Field

The utility model relates to a surface form lighting device.

Background

Conventionally, the following techniques are known: in a mounting method for bonding a pad serving as an electrode provided on a mounting surface of a substrate and a terminal provided on a side surface or a bottom surface of an electronic component other than a light source based on reflow of solder printed on the pad, the mounting surface and the electronic component are bonded via an adhesive or solder arranged at a position different from the terminal of the electronic component, thereby preventing inclination of the electronic component and displacement of a mounting position during reflow.

Patent document 1: japanese laid-open patent publication No. 9-260429

Patent document 2: japanese patent laid-open publication No. 2011-66112

Patent document 3: japanese patent laid-open publication No. 2017-163029

However, in the conventional technique, for example, there is still a concern that the mounting is performed in a state of being inclined with respect to the pad. For example, when the electronic component is a light source, if the electronic component is mounted in a state inclined from the pad at an original angle and the optical axis of the light source is deviated from the original orientation, the desired lighting performance may not be achieved. Thus, improvement in mounting accuracy is expected due to improvement in performance required for electronic components.

SUMMERY OF THE UTILITY MODEL

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a planar lighting device and a mounting method that can improve mounting accuracy.

In order to solve the above problem and achieve the object, a planar lighting device according to an embodiment of the present invention includes: a plurality of pads, a light source, and an adhesive member. The plurality of pads are provided on the main surface of the wiring substrate. The light source has terminals respectively accommodated in a plurality of cavities arranged on any surface other than the light emitting surface, and the pad and the terminal are bonded via solder accommodated in the cavities. The bonding member is disposed between the main surface and the light source, and bonds the main surface and the light source. The interval between the surface of the light source and the bonding pad is 20 μm or less.

According to the utility model discloses an embodiment can improve the installation accuracy.

Drawings

Fig. 1 is a front view showing an example of an external appearance of a planar lighting device according to an embodiment.

Fig. 2 is a sectional view of the planar lighting device according to the embodiment.

Fig. 3 is a view showing an appearance of the LED.

Fig. 4 is a view showing an appearance of the LED.

Fig. 5 is a view showing an appearance of the LED.

Fig. 6 is a view showing an appearance of the LED.

Fig. 7(a) and 7(b) are diagrams for explaining an example of the method 1 for mounting a light source.

Fig. 8(a) and 8(b) are diagrams for explaining an example of the method 2 for mounting a light source.

Fig. 9(a) and 9(b) are diagrams for explaining an example of the method 3 for mounting a light source.

Fig. 10(a) and 10(b) are diagrams for explaining an example of the method 4 for mounting the light source.

Description of reference numerals

1 … planar lighting device; 12 … LED; 14 … FPC; 14a … mounting surface; 50. 55 … bonding pads; 51 … an adhesive; 51a … adhesive means; 60 … solder; 70 … support member; 120 … cavity; 120a … terminal.

Detailed Description

The planar lighting device and the mounting method according to the embodiment will be described below with reference to the drawings. In the drawings, the relationship between the sizes of the respective elements, the ratio of the respective elements, and the like may be different from the actual ones. The drawings often include portions having different dimensional relationships and ratios from each other. In the drawings, for convenience of explanation, a three-dimensional orthogonal coordinate system in which the light emission direction of the planar lighting device is the positive Z-axis direction is illustrated in some cases.

Fig. 1 is a front view showing an example of an external appearance of a planar lighting device according to an embodiment. As shown in the example of fig. 1, the planar lighting device 1 of the embodiment has a substantially rectangular shape in a plan view. One end side in the longitudinal direction (X-axis direction) of the planar lighting device 1 is covered with a light-shielding sheet 10 including a first light-shielding sheet 10a and a second light-shielding sheet 10 b. The other end side in the longitudinal direction of the planar lighting device 1 is covered with the light-shielding sheet 100.

The planar lighting device 1 emits light from a light-emitting region (also referred to as a light-emitting region) R not covered with the light-

shielding sheets

10 and 100. That is, the light-emitting region R is defined by the light-

shielding sheets

10 and 100. The planar lighting device 1 of the present embodiment is used as a backlight of a liquid crystal display device. The liquid crystal display device is used in, for example, a smart phone.

As shown in fig. 1, the light-shielding sheet 10 is wider than the light-shielding sheet 100. This is because the Light-shielding sheet 100 covers a Light guide plate, a diffusion sheet, and a prism sheet described later which are present on the Z-axis negative side, that is, on the lower portion of the Light-shielding sheet 100, whereas the Light-shielding sheet 10 covers a relatively wide area including an LED (Light Emitting Diode) described later, an FPC (Flexible Printed Circuit), and the like, in addition to the Light guide plate, the diffusion sheet, and the prism sheet described later which are present on the lower portion of the Light-shielding sheet 10.

Next, the structure of the planar lighting device 1 of the embodiment will be described with reference to fig. 2. Fig. 2 is a sectional view of the planar lighting device according to the embodiment. Fig. 2 is a cross-sectional view of the planar lighting device 1 when viewed from the positive Y-axis direction and cut along the line a-a in fig. 1.

As shown in fig. 2, the planar lighting device 1 includes: the light guide plate includes a first light-shielding sheet 10a, a second light-shielding sheet 10b, a frame 11, an LED12, a light guide plate 13, an FPC14, a prism sheet 15, a diffusion sheet 16, a first coupling member 17, a second coupling member 18, and a land 50.

The frame 11 is a housing made of, for example, a metal material or a resin material, has a side wall 11a and a bottom 11b, and houses the LEDs 12, the light guide plate 13, the FPC14, the prism sheet 15, the diffusion sheet 16, the first connecting member 17, the second connecting member 18, and the lands 50.

The LED12 is, for example, a point-like light source, and in the present embodiment, a plurality of LEDs 12 are arranged along the Y-axis direction, which is the short side direction of the planar lighting device 1. The LED12 is, for example, a pseudo-white LED composed of a blue LED and a phosphor.

The LED12 has: the light-emitting surface 12a, a bottom surface 12b intersecting (e.g., orthogonal to) the light-emitting surface 12a, a back surface 12c which is a surface opposite to the light-emitting surface 12a, and a side surface 12d intersecting the light-emitting surface 12a and the bottom surface 12b (see fig. 3). The light-emitting surface 12a is a surface that emits light in the X-axis direction, which is the light guide plate 13 described later. The bottom surface 12b is a surface facing a mounting surface 14a of an FPC14 described later.

The bottom surface 12b is formed with a recess (cavity) at a position corresponding to a terminal (electrode terminal) of the LED12, and the solder 60 flows into the cavity, whereby the terminal of the LED12 and an FPC14 described later are bonded via a pad 50 described later. That is, the LED12 is a side-view LED in which the bottom surface 12b intersecting the light-emitting surface 12a is attached to the FPC 14.

Next, the LED12 will be further described with reference to fig. 3 to 6. Fig. 3 to 6 are views showing the appearance of the LED 12. Fig. 3 and 4 show perspective views of the LED 12. Fig. 5 is a view of the LED12 viewed from the bottom 12b side, which is the Z-axis negative side. Fig. 6 is a view of the LED12 viewed from the rear surface 12c side, which is the X-axis negative side.

As shown in fig. 3, one LED12 is a substantially rectangular parallelepiped shape having a substantially rectangular shape in a plan view with the Y-axis direction as the longitudinal direction and the X-axis direction as the short-side direction, and has two light-emitting surfaces 12a having substantially the same area at the end portion on the X-axis positive direction side. The number of the light-emitting surfaces 12a of one LED12 is not limited to 2, and may be one or three or more. The areas of the two light-emitting surfaces 12a may be different from each other, not being substantially the same.

As shown in fig. 4 to 6, the LED12 has a cavity 120 formed in a part of a corner portion, which is an intersection of the bottom surface 12b and the back surface 12c, and a terminal 120a is provided on an inner surface of the recess. The cavity 120 may be a part of the bottom surface 12b (or the rear surface 12c), that is, the terminal 120a may be provided on the bottom surface 12b (or the rear surface 12 c).

Specifically, the terminal 120a is provided on the circumferential surface of the cavity 120 having a shape in which a semi-cylindrical shape and a semi-conical shape are combined, and the solder 60 is caused to flow into the cavity 120 and electrically connected to the FPC 14. The cavity 120 in which the terminal 120a is provided is not limited to a combination of a semi-cylindrical shape and a semi-conical shape, and may be any recessed shape.

The LED12 may be a top-view LED having the rear surface 12c attached to the FPC 14. The cavity 120 for housing the terminal 120a is not limited to the one formed at the intersection of the bottom surface 12b and the back surface 12c of the LED12, and may be, for example, the back surface 12c, or any surface other than the light-emitting surface 12 a.

As shown in fig. 5, the LED12 may have a terminal 120a housed in the cavity 120 disposed on one end side in the X-axis negative direction with respect to a center line 12m of the LED12 in the X-axis direction (short-side direction) in a plan view, and a light-emitting surface 12a formed on the other end side in the X-axis positive direction.

Referring back to fig. 2, the light guide plate 13 is a plate-like member made of, for example, a transparent material (for example, polycarbonate resin), and is formed to have a substantially rectangular shape in a plan view viewed from the Z-axis negative direction side. The light guide plate 13 has two

main surfaces

13a and 13b and a side surface 13 c.

The side surface 13c is a light incident surface (hereinafter, referred to as light incident surface 13c) that faces the light emitting surface 12a of the LED12 and on which light emitted from the light emitting surface 12a enters. That is, the planar lighting device 1 of the embodiment is a so-called edge-light type lighting device in which a plurality of LEDs 12 are arranged along the edge (light incident surface 13c) of the light guide plate 13.

The main surface 13a is a main surface intersecting the light incident surface 13c, and is an emission surface (hereinafter, referred to as an emission surface 13a) through which light incident from the light incident surface 13c is emitted. The main surface 13b is a main surface (hereinafter, referred to as an opposite surface 13b) located on the opposite side of the emission surface 13 a. An optical path changing pattern formed of, for example, a plurality of dots is formed on the opposite surface 13 b. Thereby, the traveling direction of the light entering the light guide plate 13 is changed, and more light is emitted from the emission surface 13 a.

The light guide plate 13 may be provided with a wedge portion on the side surface 13c, for example. Specifically, the light guide plate 13 may be provided with a wedge portion in which the thickness of the light guide plate 13 decreases from the side surface 13c side toward the X-axis positive direction side, which is the longitudinal direction of the light guide plate 13.

The FPC14 is, for example, a flexible substrate (wiring substrate) on which the LED12 is mounted. The FPC14 is an example of a substrate, and may be a rigid (rigid) substrate. The FPC14 is, for example, long in the Y-axis direction, and has a mounting surface 14a as a main surface on which the LEDs 12 are arranged along the longitudinal direction. A metal pattern such as a wiring is formed on the FPC14, and a pad 50 to be described later connected to the metal pattern is disposed on the mounting surface 14 a.

The FPC14 is connected to a driver circuit, not shown, and controls lighting of the LED12 by the driver circuit. The FPC14 may be provided on the bottom 11b side of the frame 11, or may be provided on the emission surface 13a side of the light guide plate 13. Specifically, the FPC14 may be disposed on the top surface side opposite to the bottom surface 12b of the LED12, that is, on the positive Z-axis direction side. In addition, when a top-view LED is used as the light source, the FPC may be disposed on the side wall 11a of the frame 11.

The prism sheet 15 performs light distribution control of light diffused by a diffusion sheet 16 described later, and causes the light subjected to the light distribution control to exit in the light emission direction, which is the positive Z-axis direction.

The diffusion sheet 16 is provided on the emission surface 13a side of the light guide plate 13, and diffuses light emitted from the emission surface 13 a. Specifically, for example, the diffusion sheet 16 is arranged to cover the emission surface 13a and diffuse the light emitted from the emission surface 13 a.

The first connecting member 17 and the second connecting member 18 are, for example, single-sided tapes or double-sided tapes. The first coupling member 17 optically or structurally couples the LED12 and the light guide plate 13. Specifically, the first connecting member 17 connects the light emitting surface 12a of the LED12 and the light incident surface 13c of the light guide plate 13.

The second coupling member 18 is disposed between the opposite surface 13b of the light guide plate 13 and the FPC14, and fixes the light guide plate 13 to the FPC 14. For example, one surface of the second coupling member 18 is bonded to at least a part of the mounting surface 14a of the FPC14 on the light guide plate 13, and is bonded to at least a part of the opposite surface 13b of the light guide plate 13 on the LED 12.

A plurality of pads 50 are provided on the mounting surface 14a of the FPC 14. The plurality of pads 50 are arranged linearly along the Y-axis direction, which is the longitudinal direction of the FPC 14. The pad 50 is a conductive electrode made of a metal material such as gold foil or copper foil, and is a portion to be joined to the terminal 120a (see fig. 4 to 6) of the LED12 via the solder 60.

Also, the plurality of pads 50 are respectively bonded to the plurality of terminals 120a of the LED 12. That is, one LED12 is bonded to the same number of pads 50 as the number of terminals 120 a. That is, in the present embodiment, one LED12 is bonded to three pads 50.

In addition, only the pads 50 are provided on the mounting surface 14a of the FPC14, and the wiring electrically connected to the pads 50 is provided on the rear surface side, not shown, opposite to the mounting surface 14a, and the wiring is connected to a driving circuit for driving the LED 12.

< method for mounting LED1 >

Next, the mounting methods 1 to 4 of the LED12 will be described with reference to fig. 7(a), 7(b) to 10(a) and 10(b), respectively. Fig. 7(a) and 7(b) are views for explaining an example of the method 1 for mounting the light source (LED). Fig. 7(a) is a plan view of the FPC14 and the LED12, and fig. 7(b) is a view of the FPC14 and the LED12 corresponding to fig. 7(a) as viewed from the rear surface 12c side. Fig. 8(a), 8(b) to 10(a) and 10(b) are also illustrated from the same viewpoint as fig. 7(a) and 7 (b). In fig. 7(a), 7(b) to 10(a) and 10(b), for simplicity of illustration and description, the cavity 120 and the terminal 120a arranged in the longitudinal direction of the LED12 are illustrated as two examples.

As shown in fig. 7(a) and 7(b), first, in step 1-1, the pads 50 are disposed on the mounting surface 14a of the LED12 of the FPC 14.

Next, in step 1-2, the solder 60 is printed (applied) on the surface of each of the pads 50. The solder 60 may contain about 50% flux, for example.

In step 1-2, an adhesive 51 is applied to the mounting surface 14 a. In this case, the adhesive 51 may be disposed so as to overlap with the midpoint of a line segment connecting the centers 50C of the two pads 50 in a top view (in a plan view), for example, and particularly, the center 51C of the adhesive 51 may be disposed so as to overlap with the midpoint of a line segment connecting the centers 50C of the two pads 50 in a top view (in a plan view). However, the position of application of the adhesive 51 is not limited to this, and for example, the adhesive 51 may be disposed at a position overlapping with the LED12 in at least a top view (a plan view). The adhesive 51 may be disposed at two or more positions. The application of the solder 60 and the adhesive 51 may be performed either first or simultaneously.

Next, in step 1-3, the LEDs 12 are arranged while being controlled in position and posture. Here, the size of the pad 50 disposed on the mounting surface 14a in step 1-1 is larger than the cavity 120 of the LED 12. The center 51C of the adhesive 51 applied in step 1-2 (see step 1-2) is arranged closer to one end of the back surface 12C than the center line 12m in the short side direction of the LED12 in a plan view. Specifically, the adhesive 51 is disposed between the pads 50 adjacent to each other at the center 51C, more specifically, between the terminals 120a (cavities 120) adjacent to each other. In the illustrated example, the land 50 is disposed such that the end portion of the land 50 on the light-emitting surface 12a side is positioned closer to the light-emitting surface 12a than the center line 12m, but the land 50 is not limited to this, and may be disposed such that the land is positioned closer to the back surface 12c than the center line 12m, or may be disposed in the vicinity of the center line 12m so as to substantially coincide with the center line 12m, for example. On the other hand, the end portion of the land 50 on the side opposite to the light-emitting surface 12a (i.e., on the side of the rear surface 12c) may be disposed in the vicinity of the rear surface 12c so as to substantially coincide with the rear surface 12c of the LED12 in a plan view.

The solder 60 printed in step 1-2 is arranged so as to overlap the cavity 120 in a plan view. Specifically, the width b of the solder 60 in the longitudinal direction of the LED12 is smaller than the width a of the cavity 120 in the longitudinal direction of the LED 12. The end of solder 60 on the light-emitting surface 12a side is arranged closer to the back surface 12c than the end of cavity 120 on the light-emitting surface 12a side in the short direction of LED 12. In other words, the solder 60 is not printed between the bottom surface 12b (see fig. 6) of the LED12 (excluding the cavity 120) and the mounting surface 14a of the FPC 14. Thus, the LED12 is disposed over the pad 50 and the adhesive 51 without going over the solder 60. The adhesive 51 deforms in accordance with the posture of the LED12 disposed on the pad 50, and is disposed between the mounting surface 14a and the LED 12.

Next, in step 1-4, the temperature is increased so as to be equal to or higher than the melting point of the solder 60 for reflow of the solder 60. Here, the adhesive 51 has a thermosetting property that is cured at a low temperature lower than the melting point of the solder 60. Therefore, when the temperature rises and reaches a temperature at which the adhesive 51 is solidified, the adhesive 51 starts to solidify before the solder 60 melts and flows. The adhesive 51 is cured to reduce the distance between the LED12 and the pad 50 at a predetermined shrinkage rate, thereby becoming an adhesive member 51 a. In this case, also assuming that the LED12 is fixed in a state inclined from a desired posture by the arrangement of the adhesive member 51a, when the adhesive 51 is arranged on the center 51C (see step 1-2) on the one end side of the back surface 12C in plan view from the center line 12m in the short side direction of the LED12 as described in step 1-3, the contraction force of the adhesive 51 is stably transmitted to the LED12, and the position and posture of the LED12 are easily stably held by the pad 50 and the adhesive member 51 a. As described in step 1-2, when the adhesive 51 or the center 51C of the adhesive 51 is disposed so as to overlap the midpoint of the line segment connecting the centers 50C of the two pads 50 in a plan view, the contraction force of the adhesive 51 is stably transmitted to the LED 12. As described in steps 1 to 3, the center 51C of the adhesive 51 (adhesive member 51a) is disposed between the adjacent pads 50, and more preferably between the adjacent terminals 120a, so that the position and posture of the LED12 can be easily and stably held regardless of the size of the pad 50 with respect to the terminal 120a, the application of the solder 60, and the like.

When the temperature rises to reach the melting point temperature of the solder 60, the solder 60 melts. The melted solder 60 is accommodated in the cavity 120 of the LED12, and the terminal 120a is bonded to the pad 50. At this time, the melted solder 60 does not substantially enter between the LED12 and the pad 50, but may slightly enter depending on the surface state of the pad 50.

As described above, when the solder 60 before melting contains flux, the volume of the solder 60 contained in the cavity 120 may be smaller than the volume of the solder 60 before melting, and the cavity 120 may not be filled with the solder 60. Therefore, for example, as illustrated in step 1 to step 3, the solder 60 may be applied so as to extend to the back surface 12c side in a plan view to a position not overlapping the cavity 120. In this case, the end of the solder 60 may be disposed on the land 50 and may extend up to the mounting surface 14 a.

As described above, according to the mounting method 1 of the light source (LED), the pad 50 holds the LED12 before curing of the adhesive 51, and the pad 50 and the adhesive member 51a hold the LED12 after curing. In addition, the solder 60 accompanying the volume change at the time of reflow does not interfere with the posture holding of the LED 12. Therefore, the mounting accuracy of the LED12 with respect to the FPC14 is improved.

In addition, the distance between the bottom surface 12b (see fig. 6) of the LED12 mounted by the light source (LED) mounting method 1 and the pad 50 is substantially 0. Even when the solder 60 slightly intrudes between the LED12 and the pad 50, the general particle diameter of the particles contained in the solder 60 can be set to 20 μm or less (preferably 10 μm or less, more preferably 5 μm or less), for example. As described above, there is no actual gap between the bottom surface 12b of the LED12 and the land 50, and the bottom surface 12b of the LED12 and the land 50 are configured to be in close contact with each other (the actual gap is set to 0), whereby the positional accuracy (dimensional accuracy) of the LED12 in the height direction (Z-axis direction) can be improved. Further, the LED12 may be held so that the distance between the bottom surface 12b of the LED12 and the pad 50 exceeds 20 μm.

< method for mounting LED 2 >

Fig. 8(a) and 8(b) are views for explaining an example of the method 2 for mounting the light source (LED). As shown in fig. 8(a) and 8(b), first, in step 2-1, the pads 50 and the support member 70 are disposed on the mounting surface 14a of the LED12 of the FPC 14. The support member 70 is an insulating member having a predetermined thickness. For example, a resin member that is less likely to change in volume during reflow can be used as the support member 70. The support member 70 may be a conductive member other than a metal member insulated from the LED12 and the mounting surface 14 a.

Next, in step 2-2, solder 60 is printed (applied) on the surface of each of the pads 50, and an adhesive 51 is applied to the mounting surface 14 a. The position of applying the adhesive 51 may be, for example, a position overlapping with the LED12 in a top view (a plan view), and may be the same as in step 1-2 of fig. 7(a) and 7 (b). The step 2-2 is the same as the step 1-2 of fig. 7(a) and 7(b) except for the position of applying the adhesive 51, and therefore, detailed description thereof is omitted.

Next, in step 2-3, the LED12 is disposed while controlling the position and posture of the LED 12. The LEDs 12 are disposed over the pads 50, adhesive 51, and support members 70 without going over the solder 60. For example, if the thicknesses of the pad 50 and the support member 70 are different, the LED12 is disposed in a posture corresponding to the difference in the thicknesses. Then, the adhesive 51 deforms in accordance with the posture of the LED12, and is disposed between the mounting surface 14a and the LED 12.

Next, in step 2-4, the temperature is increased so as to be equal to or higher than the melting point of the solder 60 for reflow of the solder 60. When the temperature at which the adhesive 51 is solidified is reached, the adhesive 51 starts to solidify before the solder 60 melts and flows. When the temperature further rises to reach the melting point temperature of the solder 60, the solder 60 melts. The melted solder 60 is accommodated in the cavity 120 of the LED12, and the terminal 120a is bonded to the pad 50. At this time, the melted solder 60 does not enter between the LED12 and the pad 50 or slightly enters. Since the steps 2 to 4 are the same as the steps 1 to 4 in fig. 7(a) and 7(b), detailed description thereof is omitted.

As described above, according to the mounting method 2 of the light source (LED), the pad 50 and the support member 70 hold the LED12 before curing the adhesive 51, and the pad 50, the support member 70, and the adhesive member 51a hold the LED12 after curing. In addition, the solder 60 accompanying the volume change at the time of reflow does not interfere with the posture holding of the LED 12. Therefore, the mounting accuracy of the LED12 with respect to the FPC14 is improved. In fig. 8(a) and 8(b), the supporting member 70 is illustrated as having a height higher than that of the land 50, but the present invention is not limited thereto. For example, the height of the support member 70 may be smaller than the height of the land 50, and the heights of the support member 70 and the land 50 may be the same. The LED12 is held in a posture corresponding to the height of the support member 70 and the pad 50.

The distance between the bottom surface 12b (see fig. 6) of the LED12 mounted by the light source (LED) mounting method 2 and the pad 50 can be set to 20 μm or less, for example. Further, the LED12 may be held so that the distance between the bottom surface 12b of the LED12 and the pad 50 exceeds 20 μm.

In the mounting method 2, for example, even when the interval between the adjacent pads 50 is narrow and the adhesive 51 cannot be disposed between the adjacent pads 50, and for example, the adhesive 51 has to be disposed on the light emitting surface 12a side of the pads 50 in a plan view, the LED12 can be held appropriately. In this case, the LED12 is likely to be inclined so that the distance between the rear surface 12c and the mounting surface 14a becomes smaller on the light-emitting surface 12a side than on the mounting surface 14a due to shrinkage caused by curing of the adhesive 51. At this time, if the support member 70 is disposed in advance on the mounting surface 14a, the inclination of the LED12 accompanying the curing of the adhesive 51 can be suppressed. In fig. 8(a) and 8(b), the support member 70 is illustrated as two members, but the present invention is not limited thereto, and may be formed as a continuous single member, for example. In fig. 8(a) and 8(b), a part of the support member 70 is disposed so as not to overlap with the LED12 in a plan view, but the support member 70 is not limited to this, and the support member 70 may be disposed so that the entire region of the support member 70 overlaps with the LED12 in a plan view.

< method for mounting LED 3 >

Fig. 9(a) and 9(b) are views for explaining an example of the method 3 for mounting the light source (LED). As shown in fig. 9(a) and 9(b), first, in step 3-1, the pads 55 are disposed on the mounting surface 14a of the LED12 of the FPC 14. The land 55 is a composite member in which a covering layer 57 (solder layer) is laminated on a land layer 56. The pad 50 described in fig. 7(a), 7(b), 8(a), and 8(b) can be used as the pad layer 56, for example. The coating layer 57 can be formed, for example, by tin plating or solder coating. The coating layer 57 has a smaller flux content than the solder 60, and has a smaller volume change during reflow.

Next, in step 3-2, solder 60 is printed (applied) on the surface of each of the pads 55, and the adhesive 51 is applied to the mounting surface 14 a. The adhesive 51 can be disposed in the same manner as in, for example, step 1-2 of fig. 7(a) and 7(b) or step 2-2 of fig. 8(a) and 8 (b).

Next, in step 3-3, the LED12 is disposed while controlling the position and posture of the LED 12. The pads 55 disposed in step 3-1 and the solder 60 printed in step 3-2 are disposed so as to overlap the cavities 120 in a plan view. Specifically, the width of the pad 55 and the solder 60 in the longitudinal direction of the LED12 is smaller than the width of the cavity 120 in the longitudinal direction of the LED 12. The end portions of the pads 55 and the solder 60 on the light-emitting surface 12a side are arranged on the back surface 12c in the short direction of the LED12, compared with the end portion of the cavity 120 on the light-emitting surface 12a side. Therefore, the LED12 is disposed so that the solder 60 contacts the cavity 120 or the terminal 120 a. The adhesive 51 deforms in accordance with the posture of the LED12, and is disposed between the mounting surface 14a and the LED 12. At this time, if the LED12 is disposed so that a part of the pad 55 is accommodated in the cavity 120, the thickness of the adhesive 51 is smaller than the thickness of the pad 55. In particular, as shown in the drawing, when a part of the pad layer 56 in the pad 55 is accommodated in the cavity 120, the thickness of the adhesive 51, that is, the distance between the mount surface 14a and the LED12 is smaller than the thickness of the pad layer 56.

Next, in step 3-4, the temperature is increased so that the melting points of the solder 60 and the coating layer 57 are equal to or higher than the melting points of the solder 60 and the coating layer 57 for reflow of the solder 60 and the coating layer 57. When the temperature reaches the temperature at which the adhesive 51 is cured, the adhesive 51 is cured before the solder 60 and the coating layer 57 are melted, and the adhesive member 51a having high dimensional stability is produced. When the temperature further rises to reach the melting point temperature of the solder 60 and the coating layer 57, the solder 60 and the coating layer 57 melt. The melted solder 60 and the coating layer 57 are contained in the cavity 120 of the LED12 as the solder 60a mixed to an extent that is not recognized, and the terminal 120a and the pad layer 56 are joined. At this time, the melted solder 60a does not enter between the LED12 and the pad layer 56, or slightly enters.

As described above, according to the mounting method 3 of the light source (LED), the posture of the LED12 is held by the land 55 before curing of the adhesive 51, and the posture of the LED12 is held by the adhesive member 51a after curing of the adhesive 51. Therefore, the mounting accuracy of the LED12 with respect to the FPC14 is improved.

Further, according to the method 3 for mounting a light source (LED), the coating layer 57 is disposed in advance in anticipation of the volume reduction of the solder 60 before and after melting. This makes the connection between the terminal 120a and the pad layer 56 via the solder 60a composed of the components derived from the solder 60 and the coating layer 57 more reliable.

The distance between the bottom surface 12b (see fig. 6) of the LED12 mounted by the light source (LED) mounting method 3 and the pad layer 56 can be set to 20 μm or less, for example. In particular, when a part of the pad layer 56 is housed in the cavity 120, the distance between the bottom surface 12b of the LED12 and the pad layer 56 can be set to 0 or less, that is, the distance between the bottom surface 12b of the LED12 and the mount surface 14a can be set to the thickness of the pad layer 56 or less (the actual gap is set to 0). In addition, the solder can be reliably suppressed from entering the interface between the bottom surface 12b of the LED12 and the mounting surface 14a of the FPC 14. This further improves the positional accuracy of the LED12 in the height direction. Further, the LED12 may be held so that the distance between the bottom surface 12b of the LED12 and the pad layer 56 exceeds 20 μm.

< method for mounting LED 4 >

Fig. 10(a) and 10(b) are diagrams for explaining an example of the method 4 for mounting the light source (LED). As shown in fig. 10(a) and 10(b), first, in step 4-1, the pads 50 and the support member 70 are disposed on the mounting surface 14a of the LED12 of the FPC 14. The step 4-1 is the same as the step 2-1 shown in fig. 8(a) and 8(b), and therefore, detailed description thereof is omitted.

Next, in step 4-2, solder 60 is printed (applied) on the surface of each of the pads 50, and an adhesive 51 is applied to the mounting surface 14 a. The step 4-2 is the same as the step 2-2 of fig. 8(a) and 8(b), except for the range of applying the solder 60.

Next, in step 4-3, the LED12 is disposed while controlling the position and posture of the LED 12. Since the solder 60 has a larger size than the cavity 120 of the LED12 in a plan view, the LED12 is disposed above the adhesive 51, the solder 60, and the support member 70. The adhesive 51 deforms in accordance with the posture of the LED12, and is disposed between the mounting surface 14a and the LED 12. At this time, since the solder 60 is disposed on the surface of the pad 50, the thickness of the adhesive 51 is larger than the thickness of the pad 50.

Next, in step 4-4, the temperature is increased so as to be equal to or higher than the melting point of the solder 60 for reflow of the solder 60. When the temperature reaches the temperature at which the adhesive 51 is cured, the adhesive 51 is cured before the solder 60 melts and flows, and the adhesive member 51a is produced. When the temperature further rises to reach the melting point temperature of the solder 60, the solder 60 melts. The melted solder 60 is accommodated in the cavity 120 of the LED12, and the terminal 120a is bonded to the pad 50.

As described above, according to the mounting method 4 of the light source (LED), the solder 60 and the support member 70 hold the posture of the LED12 before the curing of the adhesive 51, and the adhesive member 51a and the support member 70 hold the posture of the LED12 after the curing of the adhesive 51. Therefore, the mounting accuracy of the LED12 with respect to the FPC14 is improved.

Further, according to the method 4 for mounting a light source (LED), it is expected that the volume of the solder 60 is reduced before and after melting, and the solder 60 larger than the cavity 120 is coated in advance. Thereby, the connection between the terminal 120a and the pad 50 via the solder 60 becomes more reliable.

The distance between the bottom surface 12b (see fig. 6) of the LED12 mounted by the light source (LED) mounting method 4 and the mounting surface 14a can be made larger than the thickness of the land 50. For example, the LEDs 12 are arranged in a posture corresponding to the thickness of the support member 70 and the interval between the mounting surface 14a and the upper surface of the solder 60 applied to the pads 50 in step 4-2. That is, by changing the thickness of the solder 60 applied to the pad 50 and the thickness and arrangement of the support member 70, the LEDs 12 can be arranged in a posture corresponding to the changed thickness and arrangement. Therefore, for example, when the thickness of the second coupling member 18 is to be changed in accordance with the adhesive strength required for the second coupling member 18 for fixing the FPC14 to the light guide plate 13 shown in fig. 2, the LED12 can be held in a posture in which the LED12 is stabilized at a predetermined height direction (Z-axis direction) position by setting the thickness of the supporting member 70 in accordance with the thickness of the second coupling member 18. Further, the thickness of the support member 70 may be smaller than or larger than the interval between the upper surface of the solder 60 applied on the land 50 in the process 4-2 and the mounting surface 14 a.

The method of mounting the light source (LED) according to the embodiment is explained above. As described above, according to the method of mounting a light source (LED) of the embodiment, since the LED12 is held by a member having higher dimensional stability than the solder 60 before and after reflow, the mounting accuracy is improved.

In the mounting methods 1 to 4 of the light source (LED) shown in fig. 7(a), 7(b) to 10(a) and 10(b), although the

solder

60 or 60a is described as being accommodated to fill the cavity 120, a gap may be formed in the cavity 120 if the pad 50 or the pad layer 56 and the terminal 120a are appropriately connected.

Further, although the adhesive 51 has been described as having thermosetting properties, it may be formed of any material if it is a material that is cured at a low temperature lower than the melting point of the solder 60, and may be cured at room temperature before reflow, for example.

In fig. 8(a) and 8(b) or fig. 10(a) and 10(b), the land 50 and the support member 70 are illustrated as separate members, but may be formed as a continuous single member.

In the method 3 for mounting a light source (LED) shown in fig. 9(a) and 9(b), for example, the support member 70 shown in fig. 8(a) and 8(b) may be used. This can further improve the mounting accuracy of the LED12, which is an example of an electronic component.

In the above, although the method of mounting the light source (LED12) of the planar lighting device 1 has been described, a member having terminals housed in each of the plurality of cavities can be used as a method of mounting any electronic component.

The present invention is not limited to the above embodiments. The present invention also includes a combination of the above-described constituent elements as appropriate. Further, it is easy for those skilled in the art to derive further effects and modifications. Therefore, the broader aspects of the present invention are not limited to the above embodiments, and various modifications are possible.

Claims

1. A planar lighting device is provided with:

a plurality of pads provided on a main surface of the wiring substrate;

a light source having terminals respectively housed in a plurality of cavities disposed on any surface other than the light-emitting surface, the pad and the terminal being joined via solder housed in the cavities; and

a bonding member disposed between the main surface and the light source to bond the main surface and the light source,

the interval between the surface of the light source and the bonding pad is 20 μm or less.

2. A planar lighting device is provided with:

a plurality of pads provided on a main surface of the wiring substrate;

the terminal is arranged on one end side of the short side direction of the light source in a plan view,

the center of the adhesive member is disposed on the one end side in a plan view.

3. The planar lighting device according to claim 2,

the center of the adhesive member is disposed between the adjacent terminals.

4. The planar lighting device according to claim 2,

5. The planar lighting device according to claim 3,

6. The planar lighting device according to claim 1 or 2,

the adhesive member is disposed so as to overlap, in a plan view, a midpoint of a line segment connecting centers of two adjacent pads.

7. The planar lighting device according to claim 1 or 2,

the pad is smaller than a region overlapping with the cavity in a plan view.

8. The planar lighting device according to claim 1 or 2,

the light source device further includes a support member disposed between the main surface and the light source.

9. The planar lighting device according to claim 8,

the support member is disposed on the other end side opposite to one end side in the short side direction of the light source on which the terminal is disposed.