Light-emitting device

Abstract

To provide a light-emitting device, having a light-emitting element sealed in a liquid, which can suppress reduction in light extraction efficiency caused by air bubbles contained in the liquid.SOLUTION: A light-emitting device 1 comprises: a light-emitting element 11 which is mounted on a substrate 10; a lens 12 which is placed on the substrate 10 so as to cover the light-emitting element 11; and a sealing liquid 13 which is included in a space inside the lens 12 so as to seal the light-emitting element 11. An inner surface of the lens 12 has a recess 121 which is recessed on the upper side at a position not overlapping an optical axis L of the light-emitting element 11. The position of the recess 121 is higher than a position, on the inner surface, of a point P on the optical axis L. The height of the inner surface monotonously increases from the point P on the optical axis L to the recess 121.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Conventionally, a light-emitting module in which a light-emitting element is sealed by a liquid is known (see, for example, Patent Document 1). In the light-emitting module of Patent Document 1, the internal space of the package is filled with a liquid to seal the light-emitting element.

Prior Art Document

Patent Document

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the light-emitting module of Patent Document 1, it is not easy to completely fill the internal space of the package with a liquid, and there is a risk of air bubbles being mixed in. And since the light emitted from the light-emitting element can be totally reflected at the interface between the air bubble and the liquid, when the air bubble is located directly above the light-emitting element, the light extraction efficiency decreases.

[0005] An object of the present invention is to provide a light-emitting device in which a light-emitting element is sealed with a liquid and can suppress a decrease in light extraction efficiency due to air bubbles contained in the liquid.

Means for Solving the Problems

[0006] [[ID=URL]] One aspect of the present invention provides the following light-emitting device in order to achieve the above object.

[0007] [1] A light-emitting device comprising: a light-emitting element mounted on a substrate; a lens placed on the substrate so as to cover the light-emitting element; and a sealing liquid sealed in the space inside the lens to seal the light-emitting element, wherein the inner surface of the lens has an upwardly recessed recess at a position that does not coincide with the optical axis of the light-emitting element, the position of the recess is higher than the position of a point on the optical axis on the inner surface, and the height of the inner surface increases monotonically from the point on the optical axis to the recess. [2] The light-emitting device according to [1] above, wherein at least a portion of the recess contains air bubbles. [3] The light-emitting device according to [1] or [2] above, wherein the sealing liquid is fluorine oil. [4] The light-emitting device according to [1] or [2] above, wherein the recess is provided in a position where its horizontal position does not overlap with the light-emitting element. [5] The light-emitting device according to [1] or [2] above, wherein the recess has an annular planar pattern surrounding the optical axis. [6] The light-emitting device according to [1] or [2] above, wherein the inner surface of the lens has a projection that curves toward the light-emitting element at a position that coincides with the optical axis. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a light-emitting device in which a light-emitting element is sealed in a liquid, and which can suppress the decrease in light extraction efficiency due to air bubbles contained in the liquid. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1(a) is a vertical cross-sectional view of a light-emitting device according to an embodiment of the present invention. Figure 1(b) is an example of a cross-sectional view of the light-emitting device shown in Figure 1(a) cut along the cutting line AA. [Figure 2] Figure 2 is a vertical cross-sectional view of a light-emitting device equipped with a lens of a conventional shape as a comparative example. [Figure 3] Figures 3(a) and 3(b) show other examples of planar patterns of depressions. [Figure 4]Figure 4(a) is a vertical cross-sectional view of the light-emitting device when the depression has a planar pattern with low symmetry. Figures 4(b) and (c) are examples of cross-sectional views of the light-emitting device shown in Figure 4(a) cut along the cutting line BB. [Modes for carrying out the invention]

[0010] (Configuration of the light-emitting device) Figure 1(a) is a vertical cross-sectional view of a light-emitting device 1 according to an embodiment of the present invention. Figure 1(b) is an example of a cross-sectional view of the light-emitting device 1 shown in Figure 1(a) cut along the cutting line AA.

[0011] The light-emitting device 1 comprises a light-emitting element 11 mounted on a substrate 10, a lens 12 placed on the substrate 10 so as to cover the light-emitting element 11, and a sealing liquid 13 sealed in the space inside the lens 12 to seal the light-emitting element 11.

[0012] Furthermore, in the light-emitting device 1, the inner surface of the lens 12 has an upper recess 121 at a position that does not coincide with the optical axis L of the light-emitting element 11. At least the horizontal position of the apex (the highest point) of the recess 121 does not coincide with the optical axis L. The recess 121 functions as a pocket for accommodating air bubbles 15 contained in the sealing liquid 13. That is, if the sealing liquid 13 contains air bubbles 15, at least a portion of the recess 121 will contain the air bubbles 15.

[0013] Since the recess 121 is located in a position that does not coincide with the optical axis L of the light-emitting element 11, the air bubble 15 contained in the recess 121 is also located in a position that does not coincide with the optical axis L of the light-emitting element 11. Here, the optical axis L is the axis that points in the direction in which the light-emitting element 11 has the strongest light emission intensity, and is usually an axis that passes through the center of the light-emitting element 11 and points perpendicular to the main surface of the substrate 10.

[0014] As shown in Fig. 1(a), the position of the depression 121 is higher than the position of the point P on the optical axis L of the inner surface of the lens 12. Further, the height of the inner surface of the lens 12 monotonically increases from the point P on the optical axis L to the depression 121. Here, the monotonic increase is a monotonic increase in the broad sense, and the height of the inner surface does not decrease even once between the point P on the optical axis L and the depression 121. That is, when the horizontal distance from the point P on the optical axis L to the depression 121 is x and the height of the inner surface of the lens 12 is f(x), if x1 < x2, then f(x1) ≤ f(x2) holds. Therefore, the bubble 15 contained in the sealing liquid 13 moves to the depression 121 without staying near the optical axis L of the light emitting element 11 by buoyancy and fits into the depression 121.

[0015] Fig. 2 is a vertical cross-sectional view of the light emitting device 5 provided with the lens 51 having a normal shape as a comparative example. As shown in Fig. 2, the space in which the sealing liquid 13 inside the lens 51 is accommodated has a dome shape.

[0016] Therefore, the bubble 15 contained in the sealing liquid 13 easily moves to the center of the space inside the lens 51 by buoyancy. As a result, the bubble 15 is positioned near the optical axis L of the light emitting element 11, and the light emitted from the light emitting element 11 in the direction around the optical axis L is reflected at the interface between the sealing liquid 13 and the bubble 15, so that the light extraction efficiency of the light emitting device 5 decreases.

[0017] In the light emitting device 5 shown in Fig. 2, the light emitted from the light emitting element 11 in the direction around the optical axis L is taken out to the outside through the sealing liquid 13, the bubble 15, and the lens 51. Since the refractive index of the bubble 15 is as low as 1.0, total reflection can occur at the interface between the sealing liquid 13 having a refractive index larger than that of the bubble 15 and the bubble 15.

[0018] On the other hand, in the light emitting device 1 according to the embodiment of the present invention, since the bubble 15 fits into the depression 121, the bubble 15 does not overlap with the optical axis L, and the light emitted from the light emitting element 11 in the direction around the optical axis L does not pass through the bubble 15 and is taken out to the outside through the sealing liquid 13 and the lens 12. Therefore, it is possible to suppress a decrease in the light extraction efficiency due to the bubble 15.

[0019] For example, when a fluorine oil with a refractive index of 1.3 is used as the material of the sealing liquid 13 and quartz with a refractive index of 1.5 is used as the material of the lens 12, total reflection does not occur at the interface between the sealing liquid 13 and the lens 12 because the refractive index of the sealing liquid 13 is smaller than that of the lens 12, and the reflectance is small because the difference in refractive index between the two is small. Therefore, light can be extracted with high efficiency.

[0020] The depression 121 is more preferably provided at a position where the horizontal position does not overlap with the light-emitting element 11 (at least, the horizontal position of the apex of the depression 121 does not overlap with the light-emitting element 11). Thereby, the horizontal position of the bubble 15 accommodated in the depression 121 can be made not to overlap with the light-emitting element. As a result, the decrease in the light extraction efficiency due to the bubble 15 can be more effectively suppressed.

[0021] The shape of the horizontal cross-section of the sealing liquid 13 shown in Fig. 1(b) corresponds to the planar pattern of the depression 121. In the example shown in Fig. 1(b), the planar pattern of the depression 121 is an annular shape, but the planar pattern of the depression 121 is not limited to this. Here, the planar pattern refers to a pattern in a direction parallel to the surface of the substrate 10.

[0022] Note that even if the sealing liquid 13 enters between the inner surface of the lens 12 (the inner surface of the depression 121) and the bubble 15 in a state where the bubble 15 is gathered in the depression 121, it is generally considered that there is almost no influence on the light extraction efficiency. However, since the bubble 15 approaches the upper surface of the light-emitting element 11 by the volume of the sealing liquid 13 that has entered between the inner surface of the lens 12 and the bubble 15, depending on the amount of the bubble 15 between the inner surface of the lens 12 and the bubble 15, it may affect the light extraction efficiency. When there is a corner on the inner surface of the depression 121, the sealing liquid 13 accumulates at the corner due to surface tension, and the amount of the sealing liquid 13 that enters between the inner surface of the lens 12 and the bubble 15 may increase. Therefore, as shown in Fig. 1(a), the shape of the depression 121 in the vertical cross-section of the lens 12 is preferably composed of a curve.

[0023] Figures 3(a) and 3(b) are other examples of cross-sectional views of the light-emitting device 1 shown in Figure 1(a), cut along the cutting line AA, and show other examples of the planar pattern of the depression 121 corresponding to the cross-sectional shape of the sealing liquid 13.

[0024] The planar pattern of the recess 121 shown in Figure 3(a) is a rectangular annular pattern. As shown in Figure 3(a), the planar pattern of the recess 121 may also be a polygonal annular pattern. The planar pattern of the recess 121 shown in Figure 3(b) is a pattern consisting of two parallel lines. As shown in Figure 3(b), the planar pattern of the recess 121 may not be annular.

[0025] Figure 4(a) is a vertical cross-sectional view of the light-emitting device 1 when the depression 121 has a planar pattern with low symmetry. Figures 4(b) and (c) are examples of cross-sectional views of the light-emitting device 1 shown in Figure 4(a) cut along the cutting line BB.

[0026] The patterns shown in Figures 4(b) and 4(c) do not have rotational symmetry around the center of the lens 12, unlike the patterns shown in Figures 1(b), 3(a), and 3(b). Thus, the planar pattern of the recess 121 may have low symmetry.

[0027] A particularly preferred planar pattern for the recess 121 is an annular pattern surrounding the optical axis L of the light-emitting element 11, as shown in Figures 1(b) and 3(a). In this case, no matter which direction the air bubbles 15 contained in the sealing liquid 13 move, they can easily enter the recess 121.

[0028] The amount of air bubbles 15 contained in the sealing liquid 13 may vary depending on the viscosity of the sealing liquid 13. In such cases, the depth and width of the depression 121 can be adjusted according to the viscosity of the sealing liquid 13 to adequately accommodate the air bubbles 15.

[0029] As shown in Figure 1(a), it is preferable that the inner surface of the lens 12 has a projection 122 that curves toward the light-emitting element 11 at a position that coincides with the optical axis L of the light-emitting element 11. The projection 122 can facilitate the movement of the air bubble 15 from the vicinity of the optical axis L of the light-emitting element 11 to the recess 121.

[0030] The light-emitting element 11 is typically an LED chip. While the light-emitting element 11 is typically a flip-chip type, it may also be a face-up type. The emission wavelength of the light-emitting element 11 is not particularly limited; for example, it may be a wavelength in the visible region or a wavelength in the ultraviolet region. Furthermore, the light-emitting element 11 may be a light-emitting element other than an LED, such as a laser diode (LD).

[0031] The substrate 10 has wiring 14 made of Cu or the like on its surface. If the light-emitting element 11 is a flip-chip type element, it is connected to the wiring 14 by a conductive bonding member made of AuSn or solder or the like.

[0032] The external shape of the lens 12 is typically dome-shaped, as shown in Figure 1(a), but is not limited to this. For example, the material of the lens 12 can be quartz, alumina, fluororesin, or the like.

[0033] The sealing liquid 13 consists of a liquid that transmits light emitted by the light-emitting element 11, such as fluorine oil or water. Furthermore, it is preferable that the sealing liquid 13 has heat dissipation properties, moisture resistance, the ability to efficiently introduce light to the lens 12, and the property of holding the lens 12 by surface tension until the lens 12 is fixed to the substrate 10. For example, fluorine oil with moisture resistance is particularly preferred as a material for the sealing liquid 13.

[0034] If the viscosity of the sealing liquid 13 is too high, the air bubbles 15 will have difficulty moving, making it difficult to move them to the depressions 121. For this reason, the viscosity of the sealing liquid 13 is preferably 1000 Pa·Sec or less.

[0035] A typical procedure for sealing the sealing liquid 13 inside the lens 12 is as follows: First, the lens 12 is turned upside down to allow the sealing liquid 13 to flow into the inner space. Next, the substrate 10 on which the light-emitting element 11 is mounted is brought close to the lens 12 containing the sealing liquid 13, and the lens 12 and substrate 10 are fixed together with the light-emitting element 11 immersed in the sealing liquid 13. The lens 12 and substrate 10 are fixed together, for example, with a resin material such as silicone or with solder.

[0036] (Effects of the embodiment) According to the light-emitting device 1 of the above embodiment of the present invention, by providing a recess 121 in the lens 12, the air bubbles 15 contained in the sealing liquid 13 are kept in a position that does not overlap with the optical axis L of the light-emitting element 11, thereby suppressing the decrease in light extraction efficiency due to the air bubbles 15.

[0037] Although embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the invention. Furthermore, the components of the above embodiments can be arbitrarily combined without departing from the spirit of the invention.

[0038] Furthermore, the above embodiments do not limit the invention as defined in the claims. It should also be noted that not all combinations of features described in the embodiments are necessarily essential for solving the problem of the invention. [Explanation of Symbols]

[0039] 1. Light-emitting device 10 circuit boards 11 Light-emitting element 12 lenses 121 Indentation 122 Protrusion 13 Sealing liquid 15 bubbles

Claims

1. A light-emitting element mounted on a circuit board, A lens placed on the substrate so as to cover the light-emitting element, A sealing liquid with a viscosity of 1000 Pa·Sec or less is sealed inside the space on the lens and seals the light-emitting element, Equipped with, On the inner surface of the lens, at a position that does not overlap with the optical axis of the light-emitting element, there is a recessed area that is recessed upwards, having a curved shape in its vertical cross-section and an annular planar pattern surrounding the optical axis. The position of the recess is higher than the position of the point on the optical axis on the inner surface, The height of the inner surface increases monotonically from the point on the optical axis to the recess. The air bubbles contained in the sealing liquid are contained within the depression. Light-emitting device.

2. The sealing liquid is a fluorine oil, The aforementioned lens is made of quartz. The light-emitting device according to claim 1.

3. The recess is provided in a position where its horizontal position does not overlap with the light-emitting element. The light-emitting device according to claim 1 or 2.

4. The position on the inner surface of the lens that coincides with the optical axis is curved toward the light-emitting element. The light-emitting device according to claim 1 or 2.

Images