A light-emitting device includes a substrate including a wiring on a surface thereof, a light-emitting element mounted on the substrate, a lens disposed on the substrate so as to cover the light-emitting element, an annular protrusion provided on the substrate and around the light-emitting element, and a sealing liquid disposed in a space defined under the lens to seal the light-emitting element. A shape of the sealing liquid is maintained between the substrate and a region of an inner surface of the lens above the light-emitting element by surface tension such that the sealing liquid is surrounded by an air layer in the space. A shape of a portion of the sealing liquid in contact with the substrate is maintained by the protrusion. The sealing liquid has a shape that widens laterally in a direction from the substrate to the lens.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present patent application claims the priority of Japanese patent application No. 2023/031264 filed on Mar. 1, 2023, and the entire contents of Japanese patent application No. 2023/031264 are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a light-emitting device.

BACKGROUND ART

A light-emitting module is known in which a light-emitting element is sealed in a liquid (see, e.g., Patent Literature 1). In the light-emitting module of Patent Literature 1, the inner space of a package is filled with the liquid to seal the light-emitting element.

CITATION LIST

Patent Literatures

Patent Literature 1: JP 2016/207754 A

SUMMARY OF INVENTION

When a substrate of the light-emitting element is formed of a material having a large refractive index difference from air, such as sapphire, total reflection occurs at the interface between the substrate and the surrounding air. In such cases, by filling a space inside a lens with a low-refractive-index liquid such as fluorine-based oil to seal the light-emitting element, total reflection at the surface of the substrate can be reduced and light extraction efficiency can be improved.

On the other hand, however, it also causes an increase in the amount of light extracted from the side surface of the substrate of the light-emitting element, resulting in a wide light distribution.

It is an object of the invention to provide a light-emitting device in which a light-emitting element is sealed with a liquid and which can achieve narrow light distribution while increasing light extraction efficiency.

According to an aspect of the invention, provided is a light-emitting device as defined below.

(1) A light-emitting device, comprising:a substrate comprising a wiring on a surface thereof;a light-emitting element mounted on the substrate;a lens disposed on the substrate so as to cover the light-emitting element;an annular protrusion provided on the substrate and around the light-emitting element; anda sealing liquid disposed in a space defined under the lens to seal the light-emitting element,wherein a shape of the sealing liquid is maintained between the substrate and a region of an inner surface of the lens above the light-emitting element by surface tension such that the sealing liquid is surrounded by an air layer in the space,wherein a shape of a portion of the sealing liquid in contact with the substrate is maintained by the protrusion, andwherein the sealing liquid has a shape that widens laterally in a direction from the substrate to the lens.

(2) The light-emitting device defined in (1), wherein at least a portion of the region of the inner surface of the lens above the light-emitting element protrudes downward, and wherein at least a portion of a lower end of the protruding portion of the region faces an upper surface of the light-emitting element.

(3) The light-emitting device defined in (1) or (2), wherein the protrusion constitutes part of the wiring.

(4) The light-emitting device defined in (1) or (2), wherein the sealing liquid comprises a fluorine-based oil.

(5) The light-emitting device defined in (1) or (2), wherein the sealing liquid has a viscosity of not less than 0.3 Pa·s.

(6) The light-emitting device defined in (1) or (2), wherein the protrusion has a height of not less than 10 μm.

(7) A light-emitting device, comprising:a substrate comprising a wiring on a surface thereof;a light-emitting element mounted on the substrate;a lens disposed on the substrate so as to cover the light-emitting element; anda sealing liquid disposed in a space defined under the lens to seal the light-emitting element,wherein a shape of the sealing liquid is maintained between side and upper surfaces of the light-emitting element and a region of an inner surface of the lens above the light-emitting element by surface tension such that the sealing liquid is surrounded by an air layer in the space, andwherein the sealing liquid has a shape that widens laterally in a direction from the substrate to the lens.

Advantageous Effects of Invention

According to an embodiment of the invention, it is possible to provide a light-emitting device in which a light-emitting element is sealed with a liquid and which can achieve narrow light distribution while increasing light extraction efficiency.

DESCRIPTION OF EMBODIMENTS

FIG.1Ais a vertical cross-sectional view showing a light-emitting device1in an embodiment of the invention. The light-emitting device1includes a substrate10having a wiring14(wirings14a,14b) on its surface, a light-emitting element11mounted on the substrate10, a lens12placed on the substrate10so as to cover the light-emitting element11, an annular protrusion16provided on the substrate10and located around the light-emitting element11, and a sealing liquid13disposed in a space defined under the lens12to seal the light-emitting element11.

In the light-emitting device1, the shape of the sealing liquid13is maintained between the substrate10and a region121of an inner surface of the lens12above the light-emitting element11by surface tension such that the sealing liquid13is surrounded by an air layer15in the space inside the lens12.

A portion of the sealing liquid13in contact with the substrate10tends to stay inside the annular protrusion16due to surface tension. That is, the shape of the portion of the sealing liquid13in contact with the substrate10is maintained by the protrusion16so that the sealing liquid13does not spread to the outside of the protrusion16. A side surface131of the sealing liquid13is formed mainly between the protrusion16and the inner surface of the lens12.

The light-emitting element11is typically an LED chip. The light emitting element11is also typically a flip-chip type element, but may be a face-up type element. The emission wavelength of the light-emitting element11is not particularly limited, and may be, e.g., a wavelength in the visible region or a wavelength in the ultraviolet region. The light-emitting element11may be a light-emitting element other than LED, such as a laser diode (LD).

The substrate10has the wiring14(wirings14a,14b) formed of Cu, etc., on its surface. An n-electrode and a p-electrode of the light-emitting element11are respectively connected to the wirings14aand14b. The light-emitting element11, when being a flip-chip type element, is connected to the wirings14aand14bby a conductive bonding member formed of AuSn or solder, etc.

The sealing liquid13has an inverse tapered shape that broadens laterally from a lower side toward an upper side. Since this increases the angle of incidence of light emitted from the light-emitting element11on the side surface131of the sealing liquid13, i.e., on the interface between the sealing liquid13and the air layer15, the reflectance at the side surface131of the sealing liquid13increases and also total reflection is more likely to occur. Total reflection can occur because the refractive index of the sealing liquid13is greater than that of the air layer15. As a result, it is possible to reduce light extracted laterally from the light-emitting element11and increase light extracted upward, thereby achieving a narrow light distribution.

The inverse tapered shape of the sealing liquid13may be a linear inverse tapered shape with straight sides when viewed in a vertical cross section as shown inFIG.1A, or a non-linear inverse tapered shape with curved sides when viewed in a vertical cross section.

By controlling the taper angle of the side surface131of the sealing liquid13, it is possible to control the direction of light reflection from the side surface131. The taper angle of the side surface131can be controlled by the size of the planar pattern of the protrusion16, the amount of the sealing liquid13, and the shape of a portion of the inner surface of the lens12in contact with the sealing liquid13, etc.

FIG.1Bis a top view showing the substrate10at around the protrusion16. As described above, the protrusion16has an annular planar pattern. The shape of the portion of the sealing liquid13in contact with the substrate10is maintained on the inner side of the annular protrusion16. The planar pattern here means a pattern in a direction parallel to the surface of the substrate10.

The planar pattern of the protrusion16shown inFIG.1Bis a circular annular shape, but it is not limited thereto and it may be another annular shape such as polygonal annular shape. The planar pattern of the protrusion16may be a partially discontinued annular shape as long as it is possible to form and maintain the shape of the sealing liquid13, but a continuous annular shape without disconnection as shown inFIG.1Bis preferable to stably form and maintain the shape of the sealing liquid13.

To more stably maintain the shape of the portion of the sealing liquid13in contact with the substrate10by the protrusion16, the height of the protrusion16is preferably not less than 10 μm. On the other hand, if the protrusion16is too high, absorption of light by the protrusion16may become so large as to affect light extraction efficiency of the light-emitting device1. For this reason, when, e.g., the light-emitting element11is of a flip-chip type, the height of the protrusion16is preferably not more than half the height of the light-emitting element11, e.g., not more than 200 μm.

The protrusion16is typically formed as a part of the wiring14(wirings14a,14b). In this case, the wirings14a,14band the protrusion16are formed by patterning one metal film. Thus, the protrusion16is formed of the same material as the wirings14aand14b(e.g., Cu) and has the same thickness as the wirings14aand14b. The protrusion16is not connected to the wirings14aand14bconnected to the light-emitting element11, and is not used as a current path. The protrusion16does not need to be a part of the wiring14and may be a member that is formed of a resin material such as silicone, a ceramic material such as alumina, or a metal material such as Au or Al, and is a fixed to the upper surface of the substrate10.

It is easier to maintain the shape of the sealing liquid13when a distance D between the upper surface of the light-emitting element11and the inner surface of the lens12is smaller, and it is particularly preferable that the distance D be zero, i.e., the upper surface of the light-emitting element11be in contact with the inner surface of the lens12.

The distance D between the upper surface of the light-emitting element11and the inner surface of the lens12can be reduced by forming the inner surface of the lens12so that the region121above the light-emitting element is curved and protrudes downward as shown inFIG.1A. At least a portion of a lower end of the protruding portion of the region121faces the upper surface of the light-emitting element11. That is, at least the portion of the lower end of the protruding portion of the region121and the horizontal position of the upper surface of the light emitting element11overlap.

The taper angle of the side surface131of the sealing liquid13can be controlled also by the size of the protruding portion of the region121. For example, when the size of the planar pattern of the protrusion16and the amount of sealing liquid13are held constant, the larger the protruding portion of the region121, the larger the taper angle of the side surface131.

FIGS.2A and2Bare examples of cross-sectional view showing the light-emitting device1taken along line A-A shown inFIG.1A. The horizontal cross-sectional shape of the air layer15shown inFIGS.2A and2Bcorresponds to the planar pattern of a depression127. In case that the region121of the inner surface of lens12protrudes downward, typically the depression127having an annular shape surrounds the protruding portion of the region121, as shown inFIGS.1A,2A and2B. The depression127is an upwardly recessed portion of the inner surface of the lens12. In this case, the shape of the region121makes it easier to hold the sealing liquid13around the light-emitting element11. The planar pattern of the depression127is, e.g., a circular annular shape as shown inFIG.2Aor a polygonal annular shape as shown inFIG.2B.

FIGS.3A to3C,4A and4Bare vertical cross-sectional views showing modifications of the light-emitting device1which are different in the shape of the region of the inner surface of the lens12above the light-emitting element11.

In the example shown inFIG.3A, the region of the inner surface of the lens12above the light-emitting element11is provided with a flat region123, and the depression127is provided therearound. A step122is formed between the region123and the depression127, and the sealing liquid13tends to stay on the inner side of the step122due to surface tension. In other words, the shape of the portion of the sealing liquid13in contact with the inner surface of the lens12can be maintained by the step122.

In the examples shown inFIGS.3B and3C, the flat region123is provided with one or plural protruding portions124that curve downward and protrude. By providing the protruding portion124, the distance D between the upper surface of the light-emitting element11and the inner surface of the lens12can be reduced. The flat region123may be provided with a stepped protruding portion125as shown inFIG.4A. At least a portion of the lower end of the protruding portion124,125faces the upper surface of the light-emitting element11.

In the example shown inFIG.4B, the flat region123is provided with a depression126tailored to the shape of the light-emitting element11, and the inner surface of the lens12covers the upper surface and an upper portion of the side surface of the light-emitting element11. The position of the flat region123in this case is lower than the position of the upper surface of the light-emitting element11. In this structure, the distance between the light-emitting element11and the inner surface of the lens12can be reduced over a wide range, allowing the shape of the sealing liquid13to be maintained more stably.

The outer shape of the lens12is typically a dome shape as shown inFIG.1A, but is not limited thereto. As the material of the lens12, e.g., quartz, alumina, fluoropolymer, etc. can be used.

The sealing liquid13is formed of a liquid transparent to light emitted by the light-emitting element11, such as fluorine-based oils or water. It is preferable that the sealing liquid13also have heat dissipation properties, moisture barrier properties, properties to efficiently introduce light into the lens12, and properties to hold the lens12by surface tension until the lens12is fixed to the substrate10. For example, fluorine-based oils with moisture barrier properties are particularly preferable as the material of the sealing liquid13.

The sealing liquid13having a higher viscosity maintains its shape more easily. For this reason, the viscosity of the sealing liquid13is preferably, e.g., not less than 0.3 Pa's, more preferably, not less than 2.5 Pa·s. The fluorine-based oils have poor wettability and can stably maintain its shape even if the viscosity is low to some extent, hence, it is preferable as the material of the sealing liquid13. In case that the sealing liquid13includes a filler, the viscosity increases but light extraction efficiency decreases, hence, it is preferable that the sealing liquid13do not includes a filler.

A typical procedure for forming the inverse tapered sealing liquid13inside the lens12is as follows. First, the sealing liquid13is dropped from above the light-emitting element11mounted on the substrate10. The light-emitting element11is thereby covered with the sealing liquid13having a dome shape. At this time, when dropping the sealing liquid13onto the light-emitting element11, the amount of the sealing liquid13dropped is such that the sealing liquid13does not wet and spread to the outside of the protrusion16. Next, the lens12is placed over the light-emitting element11covered with the sealing liquid13. At this time, the dome-shaped sealing liquid13is squashed by the inner surface of the lens12and is deformed into an inverse tapered shape as shown inFIG.1A, etc. The lens12and the substrate10are fixed by, e.g., a resin material such as silicone, or solder.

The size of the planar pattern of the protrusion16, the amount of the sealing liquid13, and the shape of the portion of the inner surface of the lens12in contact with the sealing liquid13, etc., are adjusted so that after placing the lens12over the substrate10, the sealing liquid13is surrounded by the air layer15and the shape of the sealing liquid13is maintained between the substrate10and the region121of the inner surface of the lens12above the light-emitting element11by surface tension.

The taper angle of the inversely tapered sealing liquid13can be controlled by the size of the planar pattern of the protrusion16, the amount of the sealing liquid13, and the shape of the portion of the inner surface of the lens12in contact with the sealing liquid13, etc. For example, it is possible to increase the taper angle of the sealing liquid13by reducing the size of the planar pattern of the protrusion16, by increasing the amount of sealing liquid13, or by increasing the size of the protruding portion of the region121of the inner surface of the lens12.

FIG.5is a vertical cross-sectional view showing a light-emitting device2which is a modification of the light-emitting device1. The light-emitting device2differs from the light-emitting device1in that the shape of the lower side of the sealing liquid13is maintained by a side surface111of the light-emitting element11instead of by the protrusion16. In this case, the side surface131of the sealing liquid13is formed mainly between the lower edge (on the substrate10side) of the side surface111of the light-emitting element11and the inner surface of the lens12.

That is, in the light-emitting device2, the shape of the sealing liquid13is maintained between the side surface111and an upper surface112of the light-emitting element11and the region121of the inner surface of the lens12above the light-emitting element11by surface tension such that the sealing liquid13is surrounded by the air layer15in the space inside the lens12. The sealing liquid13has an inverse tapered shape that broadens laterally from the lower side toward the upper side.

Effects of the Embodiment

In the light-emitting device1according to the embodiment of the invention, since the light-emitting element11is sealed with the sealing liquid13having an inverse tapered shape and the sealing liquid13is surrounded by the air layer15, light extracted laterally from the light-emitting element11due to reflection at the side surface131of the sealing liquid13can be reduced and light extracted upward can be increased. It is thereby possible to narrow light distribution of the light-emitting device1and improve light collection efficiency.

Although the embodiment of the invention has been described, the invention is not intended to be limited to the embodiment, and the various kinds of modifications can be implemented without departing from the gist of the invention. In addition, the constituent elements in the embodiment can be arbitrarily combined without departing from the gist of the invention.

In addition, the embodiment described above does not limit the invention according to the claims. Further, please note that not all combinations of the features described in the embodiment are necessary to solve the problem of the invention.

REFERENCE SIGNS LIST