Light emitting device and manufacturing method thereof

A light-emitting device and a manufacturing method thereof are provided, which device yields light exhibiting an actual hue with a deviation reduced as much as possible from a designed hue value, wherein the light is a mixture of light emitted from densely-mounted light-emitting elements and excited light from a phosphor contained in a resin sealing the light-emitting elements. The light-emitting device includes a board, light-emitting elements mounted densely on the board so that light-emitting surfaces thereof face opposite to the board, and a seal resin containing a plurality of different phosphors and covering all of the light-emitting elements, wherein the phosphors are excited by light from the light-emitting elements and deposited on upper surfaces of the light-emitting elements. A space between adjacent light-emitting elements has a length of 5 μm or more and 120% or less of a median diameter D50 of a phosphor which has the largest average particle size of the phosphors.

TECHNICAL FIELD

The present invention relates to a light-emitting device and a manufacturing method thereof.

BACKGROUND ART

There are known COB (Chip On Board) light-emitting devices provided with light-emitting elements such as LED (light-emitting diode) elements mounted on a general purpose board such as a ceramic board and a metal board. In such light-emitting devices, LED elements emitting light such as blue light are sealed with a resin containing a phosphor, which is excited by the light from the LED elements to yield light that is mixed therewith to provide light such as white light according to an application.

For example, Patent Literature 1 describes a light-emitting diode provided with a heat dissipation support with high thermal conductivity having a mount surface for die bonding, a circuit board which is placed on the heat dissipation support and has not only a hole for exposing a region of the mount surface but also overhang regions overhanging the perimeter edges of the heat dissipation support, a light-emitting element mounted on the mount surface inside the hole, and a light-transmissive resin body for sealing the upper part of the light-emitting element, wherein through-holes electrically connected to the light-emitting element are formed in the perimeter edges of the overhang regions, which through-holes are provided with external connection electrodes on the upper and lower surfaces thereof.

Further, Patent Literature 2 describes an LED package provided with a cavity including a recessed region formed therein, a protruding heat slug (pedestal) attached to the cavity in such a way as to penetrate the bottom of the recessed region, a submount board mounted on the heat slag, a plurality of LED chips disposed on the submount board, a lead frame electrically connected to each of the LED chips, a phosphor layer embedding each of the LED chips, and a lens formed of a silicone resin filled in the recessed region.

When such light-emitting devices are manufactured, the phosphor dispersed in the resin is settled before the resin is cured, in order to, for example, reduce the variation of chromaticity. For example, Patent Literature 3 describes a production method of a light-emitting element package including the steps of forming a repellent agent pattern on a board, mounting an LED chip inside the repellent agent pattern on the board, applying a seal resin containing a phosphor kneaded therewith to the inside of the repellent agent pattern, and settling the phosphor in the seal resin in a windless condition.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

When a light-emitting device is surmounted by an optical element, such as a lens, to condense emitted light, the emission region of the light-emitting device is desirably as small as possible in order to improve its light condensation property. However, when the emission region is achieved by using only one light-emitting element, a large element is necessarily used to secure desired light emission intensity, leading to disadvantages such as the elevation of manufacturing costs and non-uniform electrical current supply to the light-emitting element, which worsens the light emission efficiency of the element. Therefore, a solution for such problems may be to mount a plurality of light-emitting elements densely, to achieve a compact emission region while securing desired light emission intensity.

However, in regard to light-emitting devices provided with a plurality of light-emitting elements mounted on a board and sealed with a resin containing a phosphor, excited light from which is mixed with light from the light-emitting elements and yields a desired light such as white light, the actual hue of the emitted light may be different from a desired hue thereof. This is because the traveling distance of light in the phosphor layer varies depending on what surface of the light-emitting elements emits the light, owing to the presence of the phosphor also in portions of the seal resin which portions fill the space among the light-emitting elements, since the light-emitting elements are mounted at a certain extent of space among each other in order to prevent short. The traveling distance of light in the phosphor layer varies depending on the position and direction of the emission from the light-emitting elements, thereby causing the intensity variation of light having a color corresponding to the phosphor, resulting in difficulty in adjusting the actual hue of the emitted light to a designed hue value.

Therefore, an object of the present invention is to provide a light-emitting device and a manufacturing method thereof, which device yields light exhibiting an actual hue with a deviation reduced as much as possible from a designed hue value, wherein the light is a mixture of light emitted from a plurality of light-emitting elements mounted densely and excited light from a phosphor contained in a resin sealing the light-emitting elements.

Provided is a light-emitting device including a board, a plurality of light-emitting elements mounted densely on the board, and a seal resin containing a phosphor and covering all of the plurality of light-emitting elements, wherein the plurality of light-emitting elements is mounted on the board so that a space between adjacent light-emitting elements has a length of 5 μm or more and 120% or less of an average particle size of the phosphor.

Further, provided is a light-emitting device including a board, a plurality of light-emitting elements mounted densely on the board so that light-emitting surfaces thereof face opposite to the board, and a seal resin containing a plurality of different phosphors and covering all of the plurality of light-emitting elements, wherein the plurality of different phosphors is excited by light from the plurality of light-emitting elements and deposited on upper surfaces of the plurality of light-emitting elements, wherein a space between adjacent light-emitting elements has a length of 5 μm or more and 120% or less of a median diameter D50 of a phosphor which has the largest average particle size of the plurality of different phosphors.

Preferably, in the above light-emitting device, the median diameter D50 is 20 μm or more and 25 μm or less.

Preferably, the above light-emitting device further includes an optical element mounted on the board so as to cover the seal resin.

Further, provided is a manufacturing method of a light-emitting device, including the steps of mounting a plurality of light-emitting elements densely on a board, and sealing all of the plurality of light-emitting elements with a seal resin containing a phosphor, wherein in the step of mounting, the plurality of light-emitting elements is mounted on the board so that a space between adjacent light-emitting elements has a length of 5 μm or more and 120% or less of an average particle size of the phosphor.

Further, provided is a manufacturing method of a light-emitting device, including the steps of mounting a plurality of light-emitting elements densely on a board so that light-emitting surfaces thereof face opposite to the board, sealing all of the plurality of light-emitting elements with a seal resin containing a plurality of different phosphors excited by light from the plurality of light-emitting elements, and curing the seal resin after the plurality of different phosphors naturally settles out in the seal resin and is deposited on upper surfaces of the plurality of light-emitting elements, wherein in the step of mounting, the plurality of light-emitting elements is mounted so that a space between adjacent light-emitting elements has a length of 5 μm or more and 120% or less of a median diameter D50 of a phosphor which has the largest average particle size of the plurality of different phosphors.

According to the above light-emitting device and manufacturing method thereof, it is possible to yield light exhibiting an actual hue with a deviation reduced as much as possible from a designed hue value, wherein the light is a mixture of light emitted from a plurality of light-emitting elements mounted densely and excited light from a phosphor contained in a resin sealing the light-emitting elements.

DESCRIPTION OF EMBODIMENTS

Hereinafter, with reference to the accompanying drawings, a light-emitting device and a manufacturing method thereof will be explained in detail. However, it should be noted that the present invention is not limited to the drawings or the embodiments described below.

FIG. 1(A)toFIG. 1(C)are a top view and cross-sectional views of a light-emitting device1.FIG. 1(A)is a top view of the light-emitting device1as a completed product,FIG. 1(B)is a cross-sectional view along the line IB-IB inFIG. 1(A), andFIG. 1(C)is a cross-sectional view along the line IC-IC inFIG. 1(A). The light-emitting device1includes LED elements as light-emitting elements, and is used for various illumination apparatuses such as LEDs for illumination and LED light bulbs. The light-emitting device1is provided with a mount board10, a circuit board20, LED elements30, a resin frame40, a seal resin50, and a Zener diode70, as major components.

The mount board10is, for example, an almost square-shaped metal board, and includes, in the central region of the upper surface thereof, a mount region on which the LED element30are mounted. The mount board10is composed of, for example, aluminum excellent in thermal resistance and heat dissipativity, so that it also functions as a heat dissipation board for dissipating heat generated by the LED elements30and by a particulate phosphor described later. However, the material for the mount board10may be another metal such as copper, as long as it is excellent in thermal resistance and heat dissipativity.

The circuit board20is, for example, of an almost square shape of the same size as that of the mount board10, and provided with a rectangular opening21in its central region. The circuit board20is attached to and fixed on the mount board10, for example, by an adhesion sheet on the lower surface of the circuit board. The circuit board20is provided with a conductive pattern22A for a ‘+’ electrode and a conductive pattern22B for a ‘−’ electrode, which are formed on the upper surface thereof. Further, the circuit board20is provided with connection electrodes23A and23B for connecting the light-emitting device1to an external power supply, which electrodes are formed at two corners located diagonally on the upper surface of the circuit board20. The connection electrode23A is the ‘+’ electrode, and the connection electrode23B is the ‘−’ electrode, which are connected to and supplied with voltage from the external power supply, to drive the light-emitting device1to emit light. Still further, the circuit board20is provided with a white resist24which is formed on the upper surface thereof and covers the conductive patterns22A and22B except for the region on the surface neighboring and enclosing the perimeter of the opening21and the regions on the connection electrodes23A and23B (seeFIG. 5(A)described later).

The LED elements30are an example of the light-emitting elements, and are, for example, blue LEDs which emit blue light having a wavelength band within the range from about 450 to 460 nm. The width of each LED element30is, for example, about 500 to 600 μm. In the light-emitting device1, a plurality of LED elements30is mounted in a lattice-like arrangement on the central region of the mount board10exposed in the opening21of the circuit board20.FIG. 1(A)illustrates, in particular, an example in which sixteen LED elements30are mounted. The LED elements30are fixed to the upper surface of the mount board10, for example, by a transparent electrically insulative adhesive so that light-emitting surfaces thereof face upward (the side opposite to the mount board10). The LED elements30are provided with a pair of element electrodes on the upper surfaces thereof, and the respective element electrodes of adjacent LED elements30are electrically connected to each other by wires31as depicted inFIG. 1(A). Wires31led out of outermost LED elements30located adjacent to the perimeter of the opening21are connected to the conductive patterns22A and22B of the circuit board20. Thus, the respective LED elements30are supplied with electrical current via the wires31.

The resin frame40is an almost rectangular frame body composed of, for example, a white resin and fitted to the size of the opening21of the circuit board20, and is fixed to a region on the upper surface of the circuit board20, the region neighboring and enclosing the perimeter of the opening21. The resin frame40is a dam member for preventing the outflow of the seal resin50, and reflects light emitted laterally from the LED elements30in the upward direction with respect to the light-emitting device1(the direction opposite to the mount board10with respect to the LED elements30).

In the light-emitting device1, the mount region on the mount board10, the opening21of the circuit board20, and the resin frame40are rectangular, but these may have another shape such as a circular shape.

The seal resin50is injected into the opening21to cover exposed parts of the LED elements30(for example, the upper surfaces of the LED elements30and the side surfaces of the outermost LED elements30, which side surfaces are adjacent to the side of the resin frame40). Thus, the seal resin50covers and protects (seals) all of the LED elements30and the wires31together. For example, as the seal resin50, a colorless and transparent resin such as silicone and epoxy resins, and in particular, a resin with thermal resistance of about 250° C. may be used.

The seal resin50contains a phosphor such as a yellow phosphor (phosphor51inFIG. 2described later) mixed and dispersed therein. The yellow phosphor is a particulate phosphor material, such as YAG (yttrium aluminum garnet), which absorbs blue light emitted by the LED elements30and converts the wavelength thereof into that of yellow light. The light-emitting device1mixes blue light from the LED elements30which are blue LEDs and yellow light yielded through the excitation of the yellow phosphor, and emits the resultant white light.

Alternatively, the seal resin50may contain, for example, a plurality of different phosphors such as green and red phosphors. The green phosphor is a particulate phosphor material such as (BaSr)2SiO4:Eu2, which absorbs blue light emitted by the LED elements30and converts the wavelength thereof into that of green light. The red phosphor is a particulate phosphor material, such as CaAlSiN3:Eu2+, which absorbs blue light emitted by the LED elements30and converts the wavelength thereof into that of red light. In this case, the light-emitting device1mixes blue light from the LED elements30which are blue LEDs and green and red light yielded through the excitation of the green and red phosphors, respectively, and emits the resultant white light.

The phosphor in the seal resin50naturally settles out, and is deposited on the upper surfaces of the LED elements30and the upper surface of the mount board10around the LED elements30. In other words, the seal resin50contains the phosphor, which is excited by light from the LED elements30, so that the concentration thereof increases toward the lower end of the layer of the seal resin50. In the light-emitting device1, since the phosphor in the seal resin50settles out on the side close to the mount board10, heat generated by the LED elements30and the phosphor easily escapes to the outside of the device through the mount board10. Therefore, a decrease in the light emission intensity of the LED elements30owing to heat can be prevented, which is advantageous for improving the light emission intensity.

The Zener diode70is provided on the circuit board20in order to prevent the LED elements30from being broken owing to, for example, static electricity. The Zener diode70is connected to the conductive patterns22A and22B in parallel with the LED elements30(seeFIG. 7(A)described later), and protects the LED elements30by bypassing electrical current caused by voltage inversely applied to the LED elements30.

In the light-emitting device1, the plurality of LED elements30is mounted densely on the mount board10so that the space between adjacent LED elements30has a length of 5 μm or more and 120% or less of the average particle size of the phosphor. This average particle size refers to a median diameter, for example, median diameter D50. The particle size of a particulate phosphor has a distribution over a certain range. The median diameter D50 refers to a diameter at which the particle size distribution of certain particles can be divided into two halves, which are a region of a larger particle size and a region of a smaller particle size, each having the same number of particles. As a phosphor, one having an average particle size of 20 μm to 25 μm is widely used, and a phosphor having a larger particle size leads to higher light emission efficiency and brighter emitted light. Thus, in the light-emitting device1, a phosphor whose average particle size falls within that range may be used as the phosphor contained in the seal resin50. In this case, 120% of the average particle size is about 25 μm to 30 μm. In the light-emitting device1, for example, a phosphor having a median diameter D50 of 25 μm is used, and the plurality of LED elements30is mounted at a space of 30 μm.

When the seal resin50contains a plurality of different phosphors, the plurality of LED elements30is mounted so that the space between adjacent LED elements30has a length of 5 μm or more and 120% or less of the median diameter D50 of a phosphor which has the largest average particle size (median diameter D50) of the plurality of different phosphors. When a plurality of different phosphors is used, the space between the LED elements30may be 30 μm or more, and preferably 60 μm or less at most. Further, when a plurality of different phosphors is used, a phosphor having an average particle size of 20 μm or more and a phosphor having an average particle size of 20 μm or less may be used together. For example, the seal resin50may contain a yellow phosphor having an average particle size of 25 μm, a green phosphor having an average particle size of 25 μm, and a red phosphor having an average particle size of 15 μm.

FIG. 2is an enlarged cross-sectional view of the light-emitting device1.FIG. 2depicts an enlarged region near the LED elements30inFIG. 1(B).FIG. 2also depicts the phosphor51contained in the seal resin50. The reference numeral60indicates the space from the lower to upper end of each LED element30among the LED elements30. This space is hereinafter referred to as “inter-element regions60.” The phosphor51is deposited on the upper surfaces of the LED elements30, just above the inter-element regions60, and on the upper surface of the mount board10in a peripheral region52between the inner wall of the opening21and the outermost LED elements30adjacent to the perimeter of the opening.

In the light-emitting device1, since the space between the LED elements30is slightly wider than the average particle size of the phosphor51, some of the tiny particles of the phosphor invade the inter-element regions60. However, since the space between the LED elements30is set at 120% or less of the average particle size of the phosphor51, the upper ends of the inter-element regions60are blocked and clogged with large particles of the phosphor as indicated by the reference numeral61inFIG. 2. The same is true when the seal resin50contains a plurality of different phosphors whose average particle sizes are different from each other. The seal resin50may invade the inter-element regions60, and bubbles may remain in the inter-element regions60; however, substantially no phosphor51invades the inter-element regions60owing to the upper ends thereof being blocked. Therefore, the phosphor51remains above the upper surfaces of the LED elements30.

If the mount space among the LED elements30were sufficiently wide, allowing the phosphor51to invade the inter-element regions60with a concentration equal to that in the seal resin50above the LED elements30, light emitted from the side surfaces of the LED elements30would exit outwardly from the light-emitting device after traveling a longer path in the layer of the phosphor51which is a yellow phosphor, than light emitted from the upper surfaces thereof, resulting in a stronger intensity of the yellow light. In other words, the intensity of the yellow light varies depending on the position and direction of emission from the LED elements30, resulting in a deviation of the hue of the emitted light from its designed hue value.

However, in the light-emitting device1, only particles having a small particle size out of the particles of the phosphor51invade the inter-element regions60, and the concentration of the phosphor51in the inter-element regions60is lower than that in the seal resin50above the LED elements30. Therefore, the light emission of the phosphor51in the inter-element regions60is much weaker than that of the phosphor51above the LED elements30, light emitted from the side surfaces of the LED elements30hardly undergo change in its hue until it reaches a level higher than the LED elements30after passing through the inter-element regions60. In other words, in the light-emitting device1, since light emitted from the side surfaces of the LED elements30and that from the upper surfaces thereof travel the same distance in the layer of the phosphor51above the LED elements30before they are emitted outwardly, the distance in the phosphor layer which is traveled by emitted light is kept constant regardless of the position and direction of emission from the LED elements30. Therefore, in the light-emitting device1, light emitted laterally from the LED elements30is not an origin of the variation of the hue, is also unlikely to cause a deviation of the actual hue of the emitted light from a desired hue thereof, and thereby results in emitted light with uniform chromaticity.

Further, in the light-emitting device1, the LED elements30are mounted so that the light-emitting surfaces thereof are placed on the upper side, and thus, even if part of the phosphor is deposited in the inter-element regions60, such phosphor particles are relatively away from the light-emitting surfaces of the LED elements30. Therefore, even if the phosphor which has invaded the inter-element regions60is excited, it does not affect the variation of the hue (color irregularities) of the emitted light.

FIG. 2depicts a large number of particles of the phosphor51which has invaded the peripheral region52between the inner wall of the opening21and the outermost LED elements30adjacent to the perimeter of the opening. A large number of particles of the phosphor51may invade the peripheral region52, unlike the inter-element regions60, as long as the phosphor51is settled and placed in such a way that the thickness of the phosphor51in the peripheral region52is comparable to that on the upper side of the LED elements30. However, it is preferable that the width of the peripheral region52be narrower than the width of each LED element30, and wider than the height of the circuit board20. For example, when the width of each LED element30is about 500 to 600 μm and the height of the circuit board20is about 100 μm, it is preferable that the width of the peripheral region52be about 200 to 400 μm. It is also preferable that the height of the circuit board20be the same as or smaller by about 10% than that of the LED elements30.

Alternatively, in order to eliminate the variation of the hue by making emitted light travel a constant distance in the phosphor layer, the peripheral region52may be filled with a transparent or white resin which contains no phosphor.

FIG. 3is a side view of a light-emitting device1′ with a lens80attached thereto. When the light-emitting device1is used as an illumination apparatus, it is provided with, as illustrated inFIG. 3, the lens80mounted on the upper surface of the circuit board20so as to cover, for example, the seal resin50. The lens80is an example of the optical element, which condenses light emitted from the plurality of LED elements30in the light-emitting device1and emits the light in an upward direction from the light-emitting device1′. In order to facilitate mounting the lens80, the area of the region not covered with the seal resin50on the circuit board20may be widened to secure a flat region that is surmounted by the lens80. Since the light-emitting device1allows a plurality of LED elements30that is mounted densely, thereby enabling narrowing an emission region (emission area) without decreasing the number of the elements, it can achieve effective injection of the emitted light from the LED elements30into the lens80.

Depending on applications of the light-emitting device1, an optical element other than the lens80, such as a filter, may be mounted on the circuit board20. For example, a plate-like optical element instead of the lens80may be used, so that light from the LED elements30in the light-emitting device1is emitted therethrough.

FIG. 4is a graph indicating a relation between the mount space among the LED elements30and the illuminance of the light-emitting device1′. The horizontal axis of the graph is a mount space d (μm) among the LED elements30, and the vertical axis is a relative illuminance I with respect to the illuminance of emitted light from the light-emitting device1′ when the mount space d is 0 mm. Each LED element30is of a rectangular shape of 1 mm square and the incident edge of the lens80is of a circular shape of 10 mm in diameter.FIG. 4indicates maximum values (Max), average values (Ave), and minimum values (Min) of the relative intensity I of the emitted light through the lens80, when the mount space d is 30 μm and 50 μm. As indicated inFIG. 4, the minimum values of the relative intensity I for the mount spaces d of 30 μm and 50 μm are about 20% lower than that for the mount space d of 0 μm owing to a variation caused by the incorporation of the lens80. However, the maximum values of the relative intensity I and the average values thereof are almost constant regardless of the mount spaces d in the illustrated range.

A narrower mount space d among the LED elements30is preferable because it leads to a smaller emission point for condensing light by using the lens80. However, the mount space d is desirably secured so as to be, for example, at least about 5 μm so that no short occurs across adjacent LED elements30. Further, a too large mount space d causes a larger emission diameter of the plurality of LED elements30relative to the diameter of the incident edge of the lens80, leading to light loss, which results in the decrease of the illuminance of light emitted from the light-emitting device1′. For example, when the lens80used for the measurement illustrated inFIG. 4is used, the upper limit of the mount space d is preferably about 50 μm.

Still further, a too large mount space d causes the variation of the hue of the emitted light, owing to the phosphor51invading the inter-element regions60, as described above. The mount space between adjacent LED elements30may not be necessarily narrower than the particle size of the phosphor, and may be a length of 120% or less of the average particle size of the phosphor. In the present description, densely mounting the LED elements30means that the mount space between adjacent LED elements30is set at 5 μm or more and 120% or less of the median diameter D50 of the phosphor (a phosphor having the largest average particle size, when a plurality of different phosphors is used). In actual fact, in the case where a phosphor having an average particle size (median diameter D50) of 25 μm, for example, is used in the light-emitting device1, it is confirmed that the variation of the hue of the emitted light is not substantially caused, as long as the mount space between the LED elements30is not more than 30 μm, which corresponds to 120% of the average particle size of the particles of the phosphor.

FIG. 5(A)toFIG. 8(C)are top views and cross-sectional views depicting manufacturing steps of the light-emitting device1.FIG. 5(B),FIG. 5(C),FIG. 6(B),FIG. 6(C),FIG. 7(B),FIG. 7(C),FIG. 8(B), andFIG. 8(C)depict cross-sections along the line VB-VB and the line VC-VC inFIG. 5(A), the line VIB-VIB and the line VIC-VIC inFIG. 6(A), the line VIIB-VIIB and the line VIIC-VIIC inFIG. 7(A), and the line VIIIB-VIIIB and the line VIIIC-VIIIC inFIG. 8(A), respectively.

When the light-emitting device1is manufactured, first, the mount board10and the circuit board20provided with the opening21are superimposed and bonded to each other, as depicted inFIG. 5(A)toFIG. 5(C). Then, the plurality of LED elements30is mounted on the upper surface of the mount board10exposed within the opening21of the circuit board20, as depicted inFIG. 6(A)toFIG. 6(C), so that the light-emitting surfaces thereof face opposite to the mount board10. At that time, the space between adjacent LED elements30is set at a length of 5 μm or more and 120% or less of the median diameter D50 of the phosphor that is used (a phosphor having the largest average particle size, when a plurality of different phosphors is used). Further, at the same time, the Zener diode70is also mounted between the conductive patterns22A and22B on the upper surface of the circuit board20.

Then, adjacent LED elements30are connected electrically to each other with wires31, and wires31led out of outermost LED elements30adjacent to the perimeter of the opening21are connected to the conductive patterns22A and22B, as depicted inFIG. 7(A)toFIG. 7(C). At the same time, the Zener diode70is also connected to the conductive patterns22A and22B with wires71.

Then, the resin frame40is fixed to a region on the upper surface of the circuit board20, the region neighboring and enclosing the perimeter of the opening21, as depicted inFIG. 8(A)toFIG. 8(C). Then, all of the LED elements30are sealed with the seal resin50containing a phosphor. At that time, while the seal resin50is kept uncured, the phosphor is allowed to naturally settle out in the seal resin50so as to be deposited on the upper surfaces of the LED elements30; and thereafter, the seal resin50is cured. The light-emitting device1illustrated inFIG. 1(A)toFIG. 1(C)is thus completed according to the above steps.

FIG. 9(A)toFIG. 9(C)are a top view and cross-sectional views of a light-emitting device2.FIG. 9(A)is a top view of the light-emitting device2as a completed product,FIG. 9(B)is a cross-sectional view along the line IXB-IXB inFIG. 9(A), andFIG. 9(C)is a cross-sectional view along the line IXC-IXC inFIG. 9(A). The light-emitting device2is provided with a mount board10′, LED elements30, a resin frame40, a seal resin50, and a Zener diode70as major components. The light-emitting device2is different from the light-emitting device1in that it is not provided with the circuit board20which has an opening21and is included in the light-emitting device1.

The mount board10′ is, for example, an electrically insulative board composed of ceramic, and includes, in the central region of the upper surface thereof, a mount region on which the LED elements30are mounted. The light-emitting device2is also provided with a plurality of LED elements30mounted in a lattice-like arrangement in the central region of the mount board10′, as is the case with the light-emitting device1. The mount board10′, as is the case with the circuit board20of the light-emitting device1, is provided with a conductive pattern22A for a ‘+’ electrode and a conductive pattern22B for a ‘−’ electrode, which are formed on the upper surface thereof, and connection electrodes23A and23B which are formed at two corners located diagonally on the upper surface thereof. Further, the mount board10′ is provided with a white resist24which is formed on the upper surface thereof and covers the conductive patterns22A and22B except for the region on the surface neighboring and enclosing the perimeter of the mount region for the LED elements30and the regions on the connection electrodes23A and23B (seeFIG. 10(A)described later).

The resin frame40is an almost rectangular frame body composed of, for example, a white resin and fitted to the size of the mount region of the mount board10′, as is the case with the light-emitting device1. However, the resin frame40may be of another shape such as a circular shape. The seal resin50is injected into a region enclosed by the resin frame40on the mount board10′, to cover and protect (seal) all of the LED elements30together. The seal resin50is a thermally resistive resin, such as a silicone resin, in which a phosphor is mixed and dispersed, as is the case with the light-emitting device1.

The Zener diode70is connected to the conductive patterns22A and22B in parallel with the LED elements30on the mount board10′ (seeFIG. 12(A)described later), and protects the LED elements30by bypassing electrical current caused by voltage inversely applied to the LED elements30.

Also in the light-emitting device2, the plurality of LED elements30is mounted densely on the mount board10so that the space between adjacent LED elements30has a length of 5 μm or more and 120% or less of the median diameter D50 of the phosphor (a phosphor having the largest average particle size, when a plurality of different phosphors is used). Thus, since the phosphor in the seal resin50does not substantially invade the inter-element regions60, the distance in the phosphor layer which is traveled by emitted light is kept constant regardless of the position and direction of emission from the LED elements30. Therefore, the light-emitting device2is also unlikely to cause a deviation of the actual hue of the emitted light from a desired hue thereof, and thereby resulting in emitted light with uniform chromaticity.

Also in the light-emitting device2, a large number of particles of the phosphor51may invade the peripheral region between the resin frame40and the outermost LED elements30, unlike the inter-element regions60, as long as the phosphor is settled and placed in such a way that the thickness of the phosphor in the peripheral region is comparable to that on the upper side of the LED elements30. However, it is preferable that the width of this peripheral region be narrower than the width of each LED element30. Alternatively, this peripheral region may be completely filled with a transparent or white resin.

The light-emitting device2, as is the case with the light-emitting device1′, may be provided with an optical element such as a lens80mounted on the upper surface of the mount board10′ so as to cover the seal resin50.

FIG. 10(A)toFIG. 13(C)are top views and cross-sectional views depicting manufacturing steps of the light-emitting device2.FIG. 10(B),FIG. 10(C),FIG. 11(B),FIG. 11(C),FIG. 12(B),FIG. 12(C),FIG. 13(B), andFIG. 13(C)depict cross-sections along the line XB-XB and the line XC-XC inFIG. 10(A), the line XIB-XIB and the line XIC-XIC inFIG. 11(A), the line XIIB-XIIB and the line XIIC-XIIC inFIG. 12(A), and the line XIIIB-XIIIB and the line XIIIC-XIIIC inFIG. 13(A), respectively.

When the light-emitting device2is manufactured, first, the mount board10′ is prepared which is provided with the conductive patterns22A and22B, the connection electrodes23A and23B, and the white resist24formed thereon, as depicted inFIG. 10(A)toFIG. 10(C). Then, the plurality of LED elements30is mounted in the central region of the mount board10′, as depicted inFIG. 11(A)toFIG. 11(C), so that the light-emitting surfaces thereof face opposite to the mount board10. At that time, the space between adjacent LED elements30is set at a length of 5 μm or more and 120% or less of the median diameter D50 of the phosphor that is used (a phosphor having the largest average particle size, when a plurality of different phosphors is used). Further, at the same time, the Zener diode70is also mounted between the conductive pattern22A and the conductive pattern22B on the upper surface of the mount board10′.

Then, adjacent LED elements30are connected electrically to each other with wires31, and wires31led out of outermost LED elements30adjacent to the perimeter of the mount region are connected to the conductive patterns22A and22B, as depicted inFIG. 12(A)toFIG. 12(C). At the same time, the Zener diode70is also connected to the conductive patterns22A and22B with wires71.

Then, the resin frame40is fixed to the peripheral part of the mount region on the mount board10′, as depicted inFIG. 13(A)toFIG. 13(C). Then, all of the LED elements30are sealed with the seal resin50containing a phosphor. At that time, while the seal resin50is kept uncured, the phosphor is allowed to naturally settle out in the seal resin50so as to be deposited on the upper surfaces of the LED elements30; and thereafter, the seal resin50is cured. The light-emitting device2illustrated inFIG. 9(A)toFIG. 9(C)is thus completed according to the above steps.

The LED elements30are mounted by using wire bonding in the light-emitting devices1and2, but the above configuration is also applicable to a light-emitting device in which LED elements are mounted by using flip chip. In other words, the space among the plurality of LED elements mounted densely on the mount board by using flip chip may have a length of 120% or less of the median diameter D50 of the phosphor that is used (a phosphor having the largest average particle size, when a plurality of different phosphors is used). Then, a deviation of the actual hue of emitted light from a desired hue thereof is unlikely to occur, owing to substantially preventing the phosphor in the seal resin from invading the space among the elements, resulting in emitted light with uniform chromaticity, as is the case with the light-emitting devices1and2.