Light-emitting device

Abstract

This light-emitting device comprises: a substrate on which a wiring pattern is formed; a light-emitting element mounted on the substrate; a wire providing a connection between the light-emitting element and the wiring pattern; a first protective film containing a translucent organic material and disposed so as to cover the surface of the wire that faces the substrate; and a second protective film formed of a translucent metal oxide and disposed so as to cover the surface on the reverse side of the wire from the substrate.

Description

Light-emitting device

[0001] The present disclosure relates to a light emitting device.

[0002] Various techniques for improving the reliability of light-emitting devices that use light-emitting diode (LED) dies as light-emitting elements are known. The light-emitting device described in JP 2017-126743 A can prevent corrosion of wires connected to light-emitting elements mounted on a mounting surface of a substrate by covering the wires with a protective film made of silica.

[0003] In the light-emitting device described in JP 2017-126743 A, the protective film is placed around the wire after it is connected to the light-emitting element, because if the protective film is placed around the wire before connecting it to the light-emitting element, the flexibility of the wire will decrease. However, as light-emitting devices become smaller, the distance between the mounting surface of the substrate and the wire decreases, making it difficult to place a protective film on the surface opposite the mounting surface of the wire connected to the light-emitting element.

[0004] The object of the present disclosure is to solve such problems and to provide a light emitting device that can effectively protect wires from above and below using different types of materials.

[0005] The light emitting device according to the present disclosure comprises a substrate on which a wiring pattern is formed, a light emitting element mounted on the substrate, a wire connecting the light emitting element and the wiring pattern, a first protective film containing a light-transmitting organic material and arranged to cover the surface of the wire facing the substrate, and a second protective film formed from a light-transmitting metal oxide and arranged to cover the surface of the wire opposite the substrate.

[0006] In the light emitting device according to the present disclosure, the first protective film preferably covers the substrate and connects the substrate to the wire.

[0007] In the light emitting device according to the present disclosure, different types of materials can be used to provide good protection for the wires from above and below.

[0008] 1A is a plan view of a light-emitting device according to an embodiment, and FIG. 1B is a cross-sectional view taken along line A-A in FIG. 1A. FIG. 1A is a partial enlarged view of a portion surrounded by dashed line B in FIG. 1B, and FIG. 1B is a partial enlarged view of a portion where no wire is arranged, corresponding to the portion surrounded by dashed line B. FIG. 2A is a cross-sectional view taken along line C-C in FIG. 2A, and FIG. 2B is a diagram showing a wire protection structure according to a first modified example, FIG. 2C is a diagram showing a wire protection structure according to a second modified example, and FIG. 2D is a diagram showing a wire protection structure according to a third modified example.

[0009] Hereinafter, a light emitting device according to the present disclosure will be described with reference to the drawings. However, it should be noted that the technical scope of the present invention is not limited to the embodiments, but extends to the inventions set forth in the claims and their equivalents.

[0010] 1(a) and 1(b), the light emitting device 1 includes a substrate 10, a pair of wiring patterns 11 and 12, a pair of electrodes 13 and 14, a plurality of LED dies 15, wires 16, a solder resist 17, a reflective frame 18, and a sealing resin 19. The light emitting device 1 is a chip-on-board (COB) type light emitting device.

[0011] The substrate 10 has a rectangular planar shape and includes a mounting substrate 20 and a circuit board 21 arranged in an overlapping manner. The mounting substrate 20 is formed of a metal with high thermal conductivity, such as aluminum, and has a mounting surface 20a on which the LED dies 15 are mounted. The circuit board 21 is bonded to the mounting surface 20a of the mounting substrate 20, and has a circular opening 21a formed in its center. On the upper surface of the circuit board 21, a pair of wiring patterns 11 and 12 are formed, surrounding the opening 21a, as well as a pair of electrodes 13 and 14 arranged near opposite corners and connected to the wiring patterns 11 and 12. When a predetermined threshold voltage is applied between the pair of electrodes 13 and 14 from an external power source, the LED dies 15 emit light, causing the light-emitting device 1 to emit light.

[0012] The LED die 15, also referred to as a light-emitting element, is mounted on the mounting surface 20a of the mounting substrate 20 exposed through the opening 21a. In the light-emitting device 1, 40 LED dies 15 are mounted on the mounting surface 20a. The LED dies 15 are electrically connected between the electrodes 13 and 14 via the wiring patterns 11 and 12 so that five rows of eight LEDs are connected in series in parallel. The LED die 15 is a blue LED die that emits blue light in response to a threshold voltage that is eight times the forward voltage of the LED die 15 being applied between the electrodes 13 and 14. The wire 16, also referred to as a bonding wire, is made of a conductive material and connects adjacent LED dies 15 and between the LED die 15 and the wiring patterns 11 and 12. The wire 16 is preferably made of silver. If the wire 16 is made of silver, the wire 16 has a high reflectivity for light having a wavelength in the blue light region, thereby improving the emission efficiency of the light-emitting device 1. Alternatively, the wire 16 may be a corroding conductive material that is less expensive than gold, such as silver or copper.

[0013] The solder resist 17 is a heat-resistant insulating resin such as epoxy resin, and is arranged to cover the entire surfaces of the pair of wiring patterns 11 and 12, excluding the pair of electrodes 13 and 14. The reflective frame 18 is a white resin made of a synthetic resin such as silicone resin containing a filler such as silica, and is arranged along the outer edge of the opening 21a. The sealing resin 19 is a synthetic resin made of a transparent resin mixed with green phosphor particles such as YAG and red phosphor particles such as CASN, and is arranged inside the reflective frame 18 to seal the LED die 15 and wire 16. The transparent resin is preferably a highly heat-resistant silicone resin. The light-emitting device 1 emits white light by mixing blue light from the LED die 15 with green light and red light obtained by exciting the green phosphor and red phosphor with a portion of the blue light.

[0014] The wire protection structure in the light-emitting device 1 will be described with reference to Figures 2(a), 2(b), and 3(a). In Figures 2(a), 2(b), and 3(a), the positional relationship and size of each component are shown schematically, and the reflective frame 18 and sealing resin 19 are omitted. The LED die 15 has a light-emitting layer 30, an anode 31, and a cathode 32. The wire 16 connects the anode 31 and cathode 32 of a pair of adjacently arranged LED dies 15, and also connects the anode 31 of the LED die 15 to the wiring pattern 11 and the cathode 32 of the LED die 15 to the wiring pattern 12.

[0015] The light emitting device 1 further includes an adhesive 22, a die bond material 23, a first protective film 24, and a second protective film 25. The adhesive 22 is, for example, a silicone resin-based or epoxy resin-based adhesive member, and adheres the circuit board 21 to the mounting substrate 20. The die bond material 23 is, for example, an adhesive member containing a synthetic resin such as a silicone resin-based or polyimide silicone resin-based resin, and mounts the LED die 15 on the mounting substrate 20.

[0016] The first protective film 24 is formed of a member containing a light-transmitting organic material, and is arranged to cover the surface of the wire 16 facing the mounting surface 20a, i.e., the lower surface of the wire. The first protective film 24 is also arranged to cover the mounting surface 20a and at least a portion of the upper and side surfaces of the LED die 15 via the second protective film 25. The first protective film 24 is further arranged to cover at least a portion of the reflector 18. The rigidity of the first protective film 24 may be higher than the rigidity of the sealing resin 19. The first protective film 24 is preferably formed of a synthetic resin containing at least one of an acrylic resin, a fluorine compound, and a silicone resin.

[0017] The second protective film 25 is made of SiO ２ (Silica), Al ２ O ３ , ZrO ２ , TiO ２ , MgO or Nb ２ O ５The second protective layer 25 is formed by sputtering a translucent metal oxide such as SiO 2 or the like, and is disposed so as to cover the surface of the wire 16 opposite the mounting surface 20a, i.e., the upper surface of the wire. The second protective layer 25, together with the first protective layer 24, covers the periphery of the wire 16. The second protective layer 25 is also disposed so as to cover the mounting surface 20a and at least a portion of the upper and side surfaces of the LED die 15. The second protective layer 25 is preferably formed of silica. The refractive index of silica is approximately the same as the refractive index of the transparent resin that constitutes the sealing resin 19, and therefore, stray light of light reflected by the wire 16 can be reduced.

[0018] A method for manufacturing the light emitting device 1 will now be described. First, in an aggregate substrate preparation step, an aggregate substrate is prepared in which multiple substrates 10 are integrated. Next, in a light emitting element mounting step, multiple LED dies 15 are mounted via die bonding materials 23 at predetermined positions on the mounting surfaces 20a of the multiple substrates 10 included in the aggregate substrate. Next, in a wire bonding step, wire bonding is performed between the multiple LED dies 15, between the multiple LED dies 15 and the wiring pattern 11, and between the multiple LED dies 15 and the wiring pattern 12. Next, in a reflective frame placement step, a reflective frame 18 is placed to surround the mounting surface 20a.

[0019] Next, in a second protective film disposing step, the second protective film 25 is disposed so as to cover the upper surfaces of the mounting surface 20a and the LED die 15 and wires 16. The second protective film 25 is disposed over the entire surface of the mounting surface 20a in a plan view by sputtering a target made of a translucent metal oxide while masking the surfaces of the aggregate substrate other than the mounting surface 20a. Because the target is a translucent metal oxide, a stable and strong second protective film 25 is disposed over the entire surface of the mounting surface 20a. In the second protective film disposing step, the target used for sputtering is preferably silica.

[0020] Next, in the first protective film arrangement step, the first protective film 24 is arranged to cover the mounting surface 20a and the upper and side surfaces of the LED die 15. The first protective film 24 is arranged by applying raw material for the first protective film 24 to the mounting surface 20a from above and then solidifying the raw material applied to the mounting surface 20a. The first protective film 24 is arranged to cover the mounting surface 20a and to connect the mounting surface 20a and at least a portion of the lower surface of the wire 16 in a planar manner.

[0021] In the first protective film disposing step, the raw material of the first protective film 24 preferably contains a light-transmitting organic material. When the raw material of the first protective film 24 contains an organic material, the raw material can be solidified at a lower temperature than inorganic materials, making it easier to solidify the raw material. Furthermore, the raw material of the first protective film 24 before solidification is preferably liquid. When the raw material of the first protective film 24 before solidification is liquid, the mounting surface 20a can be stably covered. Furthermore, the raw material of the first protective film 24 is more preferably a light-transmitting material formed from a synthetic resin containing at least one of an acrylic resin, a fluorine compound, and a silicone resin. When the raw material of the first protective film 24 is a light-transmitting material formed from a synthetic resin containing at least one of an acrylic resin, a fluorine compound, and a silicone resin, the mounting surface 20a and the lower surface of the wire 16 can be stably connected.

[0022] Next, in a sealing resin disposing step, sealing resin 19 is disposed in the area surrounded by the reflective frame 18. Then, in a cutting step, the collective substrate is cut to manufacture a plurality of light emitting devices 1.

[0023] In the light-emitting device 1, a first protective film 24 made of an organic material such as synthetic resin is disposed on the surface facing the mounting surface 20a of the wire 16, thereby protecting the surface facing the mounting surface 20a of the wire 16. Furthermore, a second protective film 25 made of an inorganic material such as silica is disposed on the surface opposite the surface facing the mounting surface 20a of the wire 16, thereby protecting the surface opposite the surface facing the mounting surface 20a of the wire 16. Furthermore, in the light-emitting device 1, the first protective film 24 covers the mounting surface 20a and connects the mounting surface 20a and the wire 16, thereby fixing the wire 16 integrally with the mounting surface 20a and further improving the reliability of the wire 16.

[0024] Because the first protective film 24 contains an organic material, it is possible to form the first protective film 24 well on the surface of the wire 16 facing the mounting substrate 20. In particular, as shown in FIG. 3A , when the first protective film 24 is intended to connect the surface of the mounting substrate 20 to the wire 16 so that a film is formed, it is preferable to form the first protective film 24 from an organic material. On the other hand, when the second protective film 25 is intended to be formed uniformly over the entire inside of the opening 21 a of the mounting substrate 20, it is preferable to form the second protective film 25 from a metal oxide. Therefore, by having the first protective film disposed to cover the surface of the wire 16 facing the mounting substrate 20 a contain a light-transmitting organic material and the second protective film disposed to cover the surface of the wire 16 opposite the mounting substrate 20 a be formed from a light-transmitting metal oxide, it is possible to provide good protection for the wire 16 from above and below.

[0025] Fig. 3(b) is a diagram showing a wire protection structure according to a first modified example, Fig. 3(c) is a diagram showing a wire protection structure according to a second modified example, and Fig. 3(d) is a diagram showing a wire protection structure according to a third modified example. Note that Figs. 3(b) to 3(d) are cross-sectional views showing only the portion corresponding to dashed line D in Fig. 3(a). In Figs. 3(b) to 3(d), reference numerals 24b to 24d indicate first protective films, and reference numerals 25b to 25d indicate second protective films.

[0026] As shown in Figure 3 (b), in a cross-sectional view of the wire 16, the first protective film 24b covers a portion of the lower surface of the wire 16, the second protective film 25b covers a portion of the upper surface of the wire 16, and portions of the upper and lower surfaces of the wire 16 are not covered by the protective film.

[0027] As shown in Figure 3 (c), in a cross-sectional view of the wire 16, the first protective film 24c covers a portion of the lower surface of the wire 16 and the lower end of the second protective film 25c, and the second protective film 25c covers a portion of the upper surface of the wire 16, so that the wire 16 is covered with a protective film around its entire circumference.

[0028] As shown in Figure 3 (d), the first protective film 24d covers the entire circumference of the wire 16 when viewed in cross section of the wire 16, and the second protective film 25d covers a portion of the upper surface of the wire 16, so that the wire 16 is covered with a protective film around its entire circumference.

[0029] The wire protection structures according to the first to third modifications may be configured at only a portion of the wire 16. The wire protection structures according to the first to third modifications may be mixed.

Claims

1. A light-emitting device comprising: a substrate on which a wiring pattern is formed; a light-emitting element mounted on the substrate; a wire connecting the light-emitting element and the wiring pattern; a first protective film containing a light-transmitting organic material and arranged to cover a surface of the wire facing the substrate; a second protective film formed from a light-transmitting metal oxide and arranged to cover a surface of the wire opposite the substrate; and a sealant that seals the light-emitting element, the wire, the first protective film, and the second protective film, wherein the rigidity of the first protective film is higher than the rigidity of the sealant.

2. The light-emitting device of claim 1, wherein the first protective film covers a portion of the surface of the wire facing the substrate and a lower end of the second protective film when viewed in cross section of the wire, and the second protective film covers a portion of the surface of the wire opposite the substrate.

3. The light emitting device according to claim 1, wherein the first protective film covers the entire circumference of the wire in a cross-sectional view of the wire, and the second protective film covers a portion of the surface of the wire opposite the substrate.

4. The light emitting device according to any one of claims 1 to 3, wherein the wire is made of silver, and the first protective film is formed of a synthetic resin containing at least one of an acrylic resin, a fluorine compound, and a silicone resin.

5. The light emitting device according to any one of claims 1 to 4, wherein the first protective film covers the substrate and connects the substrate and the wire.

6. The light emitting device according to any one of claims 1 to 5, wherein the first protective film covers the substrate via the second protective film.

7. The light emitting device according to any one of claims 1 to 6, wherein the first protective film covers the light emitting element via the second protective film.

8. The light emitting device according to any one of claims 1 to 7, further comprising a reflective frame disposed on said substrate so as to surround said light emitting element, said first protective film covering a portion of said reflective frame.

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