JP4944428B2 - Light emitting device - Google Patents

Description

  The present invention relates to a light emitting device using an LED chip (light emitting diode chip).

  Conventionally, LED chips emit light by combining LED chips and wavelength conversion materials (for example, fluorescent pigments, fluorescent dyes, etc.) that are excited by light emitted from the LED chips and emit light of a different emission color from the LED chips. Research and development of light-emitting devices that emit light of a color different from the color are being conducted in various places. As this type of light-emitting device, for example, a white light-emitting device (generally called a white LED) that obtains white light (white light emission spectrum) by combining an LED chip that emits blue light or ultraviolet light and a phosphor. Has been commercialized.

  Here, not only white LEDs but also LEDs have advantages such as miniaturization, light weight, and power saving compared to conventional incandescent bulbs and fluorescent lamps. Currently, display light sources, display light sources, It is widely used as an alternative light source for small light bulbs (incandescent light bulbs, halogen light bulbs, etc.), a light source for liquid crystal panels of mobile phones (backlight for liquid crystal panels), and the like.

  In addition, with the recent increase in output of white LEDs, research and development for expanding white LEDs into lighting applications has become active, but the above-mentioned white LEDs require a relatively large light output, such as general lighting. When a single white LED cannot be used to obtain a desired light output, an LED unit having a plurality of surface-mounted white LEDs mounted on a single wiring board is formed. In general, a desired light output is ensured.

  By the way, conventionally, as a surface-mount type light emitting device, it is common to provide external connection electrodes on one side surface of a rectangular plate-shaped package body and the other side surface opposite to the one side surface. Here, many of the package bodies use a resin as a material, but recently, for the purpose of improving the heat dissipation of the light emitting device, a ceramic having a thermal conductivity superior to that of the resin as a material of the package body has been recently used. The ones used are also provided. Here, in the case of using a resin as the material of the package body, there are some in which the external connection electrode is formed by a part of the lead frame, but in the case of using ceramic as the material of the package body, it is easy to process. In general, an external connection electrode made of a conductive thin film is formed on the surface of the package body.

  Recently, for the purpose of further improving heat dissipation, as shown in FIG. 6, the LED chip 1 ′ and the housing recess 21 ′ for housing the LED chip 1 ′ are provided on one surface, and the LED chip 1 ′ is housed. A package body 2 ′ made of ceramic that is mounted on the inner bottom surface of the recess 21 ′, and four external connection electrodes 22 ′ are provided straddling the other surface and side surfaces of the package body 2 ′. One heat-dissipating pad portion 24 'is provided at the center of the other surface of 2', and each external connection electrode 22 'and heat-dissipating pad portion 24' are joined and used via a wiring board and a solder portion. A light emitting device has also been proposed (see, for example, Patent Document 1).

Here, in the light emitting device shown in FIG. 6, a part of each external connection electrode 22 ′ is provided in a notch formed across adjacent side surfaces of the rectangular plate-shaped package body 2 ′. The portion constitutes a solder fillet forming portion 22b ′, and each external connection electrode 22 ′ includes a solder fillet forming portion 22b ′. Therefore, the external connection electrode 22 ′ and the circuit pattern of the wiring board A solder fillet can be formed by appropriately setting the amount of solder used for bonding the solder.
JP 2005-191203 A

  By the way, in the LED unit in which a plurality of surface-mounted light emitting devices are mounted on one wiring board as described above, although the amount of heat generated by each light emitting device is relatively small, As the number of light emitting devices increases, the amount of heat generated increases, so heat tends to accumulate on the wiring board, and the temperature of the entire LED unit tends to rise.

  In addition, in the lighting fixture using the above-mentioned LED unit, the fixture main body tends to be smaller than the fixture main body of the conventional lighting fixture in order to take advantage of the small size of the LED. Other circuit components such as the control unit and the control unit are also arranged close to each other, but since these circuit components act as a heat source for the LED unit, the LED unit is further heated by the heat source around the LED unit. Happens.

  When the LED unit is used for lighting as described above, the expansion and contraction of the LED unit is repeated by repeating the temperature increase after the start of lighting and the temperature decrease after the light is turned off. As a result, as shown in FIG. In the surface mount type light emitting device using ceramic as the material of the package body 2 ′ as in the configuration, a crack is generated in the joint portion made of solder joining the external connection electrode 22 ′ and the circuit pattern of the wiring board. It has become clear that there may be a problem that the external connection electrode 22 ′ is peeled off from the joint.

  Further, the inventors of the present application have made researches. In a surface mount type light emitting device in which a resin is used as a material of a package body and an external connection electrode is formed by a lead terminal formed of a part of a lead frame, a lead terminal is used. Since the thermal stress can be absorbed by deforming itself, it has been found that the above-described problems are unlikely to occur. However, in the case of using a ceramic that is superior in heat dissipation as a material of the package body 2 ′ as in the surface-mounted light emitting device shown in FIG. 6, heat between the package body 2 ′ and the wiring board is used. It turns out that a crack occurs in the solder fillet at the joint due to the difference in the expansion coefficient, or that the solder fillet forming portion 22b ′ in the external connection electrode 22 ′ is peeled off from the package body 2 ′. It was.

  The present invention has been made in view of the above-described reasons, and its purpose is to form a solder fillet in a solder fillet due to a difference in thermal expansion coefficient between a package body and a wiring board, or to form a solder fillet in an external connection electrode. An object of the present invention is to provide a light emitting device that can prevent a part from being peeled off from a package body and can improve connection reliability.

The invention according to claim 1, an LED chip and a package body accommodating recess provided on one surface LED chip is a ceramic made of implementation board mounted on the inner bottom surface of the housing recess for housing the LED chip An external connection electrode on the anode side made of a conductive thin film electrically connected to the anode electrode of the LED chip and an external connection on the cathode side made of a conductive thin film electrically connected to the cathode electrode of the LED chip An electrode is provided across the other surface and side surface of the package body, and a heat dissipation pad portion made of a material having a higher thermal conductivity than the package body is provided on the other surface of the package body, The solder fillet forming part provided on the side surface of the package main body of each external connection electrode is a package book on one side of the package main body. Arranged in parallel close to each other in the circumferential direction of the heat radiation pad portion, the overlap projection region of the LED chips in the other surface, and the external connection electrode side from the center of the center of the heat radiation pad portion and the projection region It is characterized by being provided at a position shifted .

  According to the present invention, the solder fillet forming portion provided on the side surface of the package body among each of the external connection electrodes is juxtaposed in the circumferential direction of the package body on one side surface of the package body. Compared with the case where the solder fillet forming parts are provided at the four corners of the package body, the distance between the solder fillet forming parts can be shortened, and the difference in thermal expansion coefficient between the package body and the wiring board on which the light emitting device is mounted. It is possible to reduce the horizontal stress applied to the solder fillet due to the occurrence of cracks in the solder fillet and to prevent the solder fillet forming part of the external connection electrode from peeling from the package body. Connection reliability can be improved.

Further, according to this invention, it can reduce the distance between the heat pad portion release each external connection electrode, due to the difference in thermal expansion coefficient between the package body and the wiring substrate in Handa fillet horizontal stress can be made smaller, and can be from or separated from the cracks in Handa fillet Rihan field fillet forming portion Gapa Kkeji body caused to more reliably prevent, connection reliability applied The sex can be increased.

  According to the first aspect of the present invention, it is possible to prevent the solder fillet from being cracked due to the difference in thermal expansion coefficient between the package body and the wiring board, and the solder fillet forming portion of the external connection electrode from being peeled off from the package body. It is possible to improve the connection reliability.

(Embodiment 1)
As shown in FIG. 1, the light emitting device of this embodiment includes an LED chip 1 and a package body 2 made of a ceramic (for example, alumina) mounting substrate on which the LED chip 1 is mounted. The outer peripheral shape of the package body 2 (that is, the outer peripheral shape of the mounting substrate) is formed in a rectangular shape.

  The LED chip 1 is a GaN-based blue LED chip that emits blue light, and is formed of a GaN-based compound semiconductor material on one surface side of a sapphire substrate, which is a crystal growth substrate, and has a double hetero structure, for example. The light emitting part made of is grown by an epitaxial growth method (for example, MOVPE method or the like). In short, the LED chip 1 is formed on the one surface side of the sapphire substrate that is transparent to the light emitted from the light emitting unit.

  The package body 2 is provided with a housing recess 21 for housing the LED chip 1 at the center of one surface, and an anode electrode (not shown) and a cathode electrode (not shown) of the LED chip 1 are bonded to the bonding wires 14, respectively. Two wiring patterns 23 made of a conductive material (for example, Au, Al, Ag, Rh, etc.) that are electrically connected via 14 are formed. Each wiring pattern 23 has one end exposed on the inner bottom surface of the storage recess 21 and the other end electrically connected to an external connection electrode 22 made of a conductive thin film, which will be described later. Here, the LED chip 1 is formed in a rectangular plate shape, and the storage recess 21 in the package body 2 is opened in a circular shape, and the opening area gradually increases as the distance from the inner bottom surface increases. The LED chip 1 may be flip-chip mounted without using the bonding wires 14, 14. When flip-chip mounting is performed, light emitted from the light emitting portion of the LED chip 1 passes through the sapphire substrate. It is taken out.

  A sealing portion 28 made of a transparent resin such as a silicone resin that seals the LED chip 1 and the bonding wires 14 and 14 is formed in the housing recess 21 of the package body 2.

  In addition, the light emitting device of this embodiment includes a color conversion unit (not shown) having a yellow phosphor that emits light when excited by the light emitted from the LED chip 1, and the light emitted from the LED chip 1. And white light composed of the combined light of the light emitted from the yellow phosphor. The color conversion unit described above may be configured, for example, by dispersing a yellow phosphor in a transparent resin such as a silicone resin that seals the LED chip 1 in the housing recess 21 of the package body 2. A mixture of a transparent material such as a silicone resin and a yellow phosphor is molded into a sheet shape and fixed to the one surface side of the package body 2 so as to close the opening surface of the housing recess 21. Good. Note that the transparent material used as the material of the color conversion portion is not limited to the silicone resin, and for example, an acrylic resin, an epoxy resin, glass, or the like may be employed. Further, the phosphor mixed with the transparent material used as the material of the color conversion portion is not limited to the yellow phosphor. For example, white light can be obtained by mixing a red phosphor and a green phosphor.

  Further, at the center of the other surface of the package body 2 (the lower surface in FIG. 1B), a heat dissipation material made of a material having higher thermal conductivity than the package body 2 (for example, Au, Al, Ag, Rh, etc.). A pad portion 24 is provided. The heat dissipating pad portion 24 is formed in a rectangular shape having a larger planar size than the LED chip 1, and the heat dissipating pad 24 and the LED chip 1 are arranged in the thickness direction of the LED chip 1 at the center of the heat dissipating pad 24. The positional relationship is such that the projected areas overlap.

  By the way, each of the external connection electrodes 22 described above is provided across the other surface and side surface of the package body 2. Here, each of the external connection electrodes 22, 22 has an L-shaped cross section, and the main connection portions 22 a, 22 a provided on the other surface of the package body 2 and the solder fillet provided on the side surface of the package body 2. The parts 22b and 22b for use are continuously formed integrally. In the present embodiment, the solder fillet forming portions 22b and 22b provided on the side surface of the package body 2 among the external connection electrodes 22 and 22 are one side surface of the package body 2 (the right side surface in FIG. 1A). Are arranged side by side in the circumferential direction of the package body 2. That is, in the present embodiment, two main connection portions 22a and 22a are arranged in parallel along one side of the other surface of the package body 2, and two solder fillet forming portions 22b and 22b are the one side surface of the package body 2. In the circumferential direction of the package main body 2, they are arranged close to each other. Here, the two solder fillet forming portions 22b and 22b are juxtaposed in such a manner that they are close to each other at positions away from both ends in the longitudinal direction of the one side surface.

  In the present embodiment, the planar size (chip size) of the LED chip 1 is 1 mm □, the planar size of the package body 2 is 7 mm □, the thickness is 2 mm, and the planar size of the heat dissipation pad portion 24 is 3 mm □, externally. The length (the horizontal dimension in FIG. 1C) of the main connection portion 22a of the connection electrode 22 is 1 mm, the width dimension (vertical dimension in FIG. 1C) is 1.5 mm, for external connection The solder fillet forming portion 22b of the electrode 22 has a height dimension (horizontal dimension in FIG. 1 (d)) of 1 mm and a width dimension (vertical dimension in FIG. 1 (d)) of 1.5 mm. These numerical values are examples and are not particularly limited.

  For example, as shown in FIG. 2, the above-described light emitting device is used by being mounted on one surface side of the wiring board 3. In FIG. 2, only one light emitting device is illustrated, but a plurality of light emitting devices are mounted on the wiring board 3.

  The wiring board 3 is formed of a metal material (for example, a resin layer 32 made of an insulating resin such as a glass epoxy resin on one surface of a metal plate 31 made of a metal material having a high thermal conductivity such as Cu or Al. , Cu, etc.) is formed, and the circuit pattern 33 is connected to the external connection electrode 22 of the light emitting device via the joint portion 4 made of solder. Here, a part other than the part interposed in the gap between the package body 2 and the wiring board 3 in the joint 4 constitutes the solder fillet 4b.

  Further, the wiring board 3 is thermally coupled to the metal plate 31 and the heat dissipating pad portion 24 disposed at the central portion of the other surface of the package body 2 via the joint portion 5 made of solder. . That is, the heat generated in the light emitting device can be transferred to the metal plate 31 through the heat radiating pad portion 24 and the joining portion 5 to be dissipated, so that the temperature rise of the light emitting device and the LED chip 1 can be suppressed.

  In the light emitting device of the present embodiment described above, the solder fillet forming portion 22b provided on the side surface of the package body 2 among the external connection electrodes 22 is close in the circumferential direction of the package body 2 on one side surface of the package body 2. Accordingly, the distance between the solder fillet forming portions 22b is compared with that in which the solder fillet forming portions 22b 'are provided at the four corners of the package body 2' as in the conventional configuration shown in FIG. The horizontal stress applied to the solder fillet 4b due to the difference in coefficient of thermal expansion between the package body 2 and the wiring board 3 (stress in a plane parallel to the other surface of the package body 2) can be reduced. The solder fillet 4b is cracked or the solder fillet forming portion 22b of each external connection electrode 22 is formed in the package body 2 It is possible to prevent the or al peeling, it is possible to improve the connection reliability.

(Embodiment 2)
The basic configuration of the light emitting device according to the present embodiment is substantially the same as that of the first embodiment. As shown in FIG. It is formed over the inner peripheral surface of the place 21 and the one surface of the package body 2, and the only difference is that the height dimension of the solder fillet forming portion 22 b of each external connection electrode 22 is increased. It is.

(Embodiment 3)
The configuration of the light emitting device of this embodiment is substantially the same as that of the first embodiment. As shown in FIGS. 4 and 5, the heat radiating pad portion 24 is placed on the projection area of the LED chip 1 on the other surface of the package body 2. The difference is that they are provided at positions that overlap and are shifted to the respective external connection electrodes 22 side. In addition, the same code | symbol is attached | subjected to the component similar to Embodiment 1, and description is abbreviate | omitted.

  In the light emitting device of this embodiment, the planar size of the heat dissipation pad portion 24 is the same as that of the heat dissipation pad portion 24 of the first embodiment, and the center of the heat dissipation pad portion 24 extends from the center of the projection area of the LED chip 1 to the package body. The distance between the heat radiation pad portion 24 and each external connection electrode 22 is shortened by shifting to the one side of the other surface 2.

  Therefore, in the light emitting device according to the present embodiment, the distance between the heat radiation pad portion 24 and each external connection electrode 22 can be shortened as compared with the first embodiment, and the thermal expansion between the package body 2 and the wiring board 3 can be achieved. The stress in the horizontal direction applied to the solder fillet 4b due to the rate difference can be further reduced, and it is more reliable that the solder fillet 4b is cracked or the solder fillet forming portion 22b is separated from the package body 2. And the connection reliability can be further improved.

  In the present embodiment, a part of the wiring pattern 23 is exposed and the other part is embedded in the package body 2 as in the first embodiment, but the wiring pattern 23 is embedded in the package body 2 as in the second embodiment. It may be routed without being embedded in.

The light-emitting device of Embodiment 1 is shown, (a) is a schematic plan view, (b) is a schematic sectional view, (c) is a schematic bottom view, and (d) is a schematic right side view. It is a schematic sectional drawing of the state which mounted the light-emitting device same as the above on a wiring board. The light-emitting device of Embodiment 2 is shown, (a) is a schematic plan view, (b) is a schematic sectional view, (c) is a schematic bottom view, and (d) is a schematic right side view. The light-emitting device of Embodiment 3 is shown, (a) is a schematic plan view, (b) is a schematic sectional view, (c) is a schematic bottom view, and (d) is a schematic right side view. It is a schematic sectional drawing of the state which mounted the light-emitting device same as the above on a wiring board. A prior art example is shown, (a) is a schematic sectional view, and (b) is a schematic bottom view.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 LED chip 2 Package main body 14 Bonding wire 21 Storage recess 22 External connection electrode 22a Main connection part 22b Solder fillet formation part 23 Wiring pattern 24 Heat radiation pad part 28 Sealing part

Claims (1)

Comprising a LED chip, and a package body accommodating recess provided on one surface LED chip is a ceramic made of implementation board mounted on the inner bottom surface of the housing recess for housing the LED chip, an anode electrode of the LED chip The external connection electrode on the anode side made of a conductive thin film electrically connected to the electrode and the external connection electrode on the cathode side made of a conductive thin film electrically connected to the cathode electrode of the LED chip are on the other surface of the package body. A light-emitting device provided on the other surface of the package body with a heat-dissipating pad portion made of a material having a higher thermal conductivity than the package body, and each external connection electrode The solder fillet forming part provided on the side surface of the package body is one side surface of the package body in the circumferential direction of the package body. Are juxtaposed in contact with, the heat radiation pad section overlaps the projected area of the LED chip in the other surface, and the center of the heat radiation pad portion at a position shifted to the external connection electrode side from the center of the projection area A light emitting device characterized by being provided .

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