Patent ID: 12218289

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will now be described in detail with reference to the drawings, which are provided as illustrative examples of the invention so as to enable those skilled in the art to practice the invention. Notably, the figures and examples below are not meant to limit the scope of the present invention to a single embodiment, but other embodiments are possible by way of interchange of some or all of the described or illustrated elements. Moreover, where certain elements of the present invention can be partially or fully implemented using known components, only those portions of such known components that are necessary for an understanding of the present invention will be described, and detailed descriptions of other portions of such known components will be omitted so as not to obscure the invention. In the present specification, an embodiment showing a singular component should not be considered limiting; rather, the invention is intended to encompass other embodiments including a plurality of the same component, and vice-versa, unless explicitly stated otherwise herein. Moreover, applicants do not intend for any term in the specification or claims to be ascribed an uncommon or special meaning unless explicitly set forth as such. Further, the present invention encompasses present and future known equivalents to the known components referred to herein by way of illustration.

Throughout this specification like reference numerals are used to denote like parts. For all figures other thanFIG.1, the reference numeral is preceded by the figure number. For example, an LED chip30is referred to as230inFIG.2,330inFIG.3and so forth.

Packaged White Light Emitting Devices

A packaged white light emitting device220in accordance with an embodiment of the invention will now be described with reference toFIG.2which shows a sectional side view of the device220.

The light emitting device220is a packaged-type device comprising, for example an SMD (Surface Mount Device) package such as an SMD 2835 LED package (lead frame)222. The SMD package222comprises a rectangular base224and side walls226A,226B extending upwardly from opposing edges of the rectangular base224. The interior surfaces of the side walls226A,226B slope inwardly to their vertical axis and together with the interior surface of the solid rectangular base224define a cavity228in the shape of an inverted frustum of a pyramid.

In this embodiment, the cavity228can comprise three InGaN (Indium Gallium Nitride) blue (455 nm) LED dies (solid-state excitation sources)230, and a first photoluminescence layer232comprising a manganese-activated fluoride photoluminescence material filling approximately 70% of the cavity228. The LED dies (chips)230can be serially connected and the rated driving condition is 100 mA, 9 V.

The first photoluminescence layer232contains a majority, at least 75 wt %, of manganese-activated fluoride photoluminescence material compared with other photoluminescence materials that may be in the layer. The first photoluminescence layer232may contain other materials such as light scattering particles or light diffusive material for example. More particularly, in this embodiment, the first photoluminescence layer32only contains K2SiF6:Mn4+(KSF), but not other types of photoluminescence materials. It will be appreciated, however, that other materials such as a light diffusive material can be added into the manganese-activated fluoride photoluminescence material layer232, but the amount of the other materials is typically no more than 30% weight of the manganese-activated fluoride photoluminescence material layer232. Further, in this embodiment, the first photoluminescence layer232is constituted by K2SiF6:Mn4+incorporated (dispersed) in dimethyl silicone. The first photoluminescence layer232is directly in contact with and adjacent the blue LED230. There are no other photoluminescence materials or photoluminescence material containing layers between the first photoluminescence layer232and the blue LED dies230.

Comparing with known constructions, as shown for example inFIG.1, in a conventional single-layer light emitting device, the dispensing process during manufacture involves dispensing a mixture of a manganese-activated fluoride photoluminescence material and other photoluminescence material(s) (typically a green phosphor material) which have equal exposure to excitation light, for example blue excitation light. Since a manganese-activated fluoride photoluminescence material may have a much lower blue light absorption capability than other types of photoluminescence materials (for example, a green/yellow garnet-based phosphors), a greater amount of manganese-activated fluoride photoluminescence material is necessary to convert enough blue light to the required red emission. By contrast, in the light emitting device220according to the invention, the manganese-activated fluoride photoluminescence material in its separate individual layer232is exposed to blue excitation light individually; thus, more of the blue excitation light from the blue LED dies (chips)230can be absorbed by the manganese-activated fluoride photoluminescence material and the remaining blue excitation light can penetrate through to a second photoluminescence layer(s)234for instance. Advantageously, in this light emitting device220, the first photoluminescence layer232can more effectively convert the blue excitation light to red emission without competition from other types of photoluminescence materials present in the second photoluminescence layer234for example. Therefore, the amount/usage of a manganese-activated fluoride photoluminescence material required to achieve a target color point can be significantly reduced compared with known arrangements of a single layer comprising a mixture of photoluminescence materials for instance. Therefore, a benefit of the photoluminescence light emitting device220of the invention is a reduction in the manufacturing cost of the device since less (up to 60% less) manganese-activated fluoride photoluminescence material is required to attain a desired color point compared with known single-layer devices.

In this embodiment, the cavity228also comprises a second photoluminescence layer234dispensed on top of the first photoluminescence layer232that fills the remaining 30% of the cavity228. In this embodiment, the second photoluminescence material layer234comprises a cerium-activated yellow garnet phosphor having a general composition Y3(Al,Ga)5O12:Ce. It will be appreciated that the second photoluminescence layer typically comprises green or yellow phosphors or other minority orange red phosphors that work in conjunction with the first photoluminescence layer to create the desired white point.

In this way, the light emitting device220effectively is able to isolate the manganese-activated fluoride photoluminescence material contained (incorporated (dispersed)) within the first photoluminescence layer232from direct contact with any water/moisture in the surrounding environment. Such a multi-layer or two-layer design of the light emitting device220provides an effective solution to address the poor moisture reliability of manganese-activated fluoride photoluminescence materials in known constructions. Thus, the inclusion of the second photoluminescence material layer234provides the benefit of improved moisture reliability to the light emitting device (i.e. LED package)220.

The first photoluminescence layer232is adjacent (in closer proximity) to the blue LED230than any other photoluminescence material layer including the second photoluminescence material layer234; that is the first photoluminescence layer232is adjacent (proximal—i.e. a proximal layer) to the blue LED230, while the second photoluminescence material layer234is distal (i.e. a distal layer) to the blue LED230.

Referring now toFIG.3, there is shown a packaged white light emitting device320(white light emitting device package) formed according to another embodiment of the invention. This embodiment differs fromFIG.2only in that the light emitting device320further comprises a light transmissive (transparent) passivation layer336disposed on the blue LED die(s)330before the first photoluminescence layer332. In order to fully protect the first photoluminescence layer332from water/moisture, the clear passivation layer336is applied over the floor of the cavity328and LED dies (chips)330as shown inFIG.3. In this embodiment, the passivation layer336can be a layer of dimethyl silicone. This passivation layer336also serves to isolate the bottom electrode (not shown) and blue LED dies330from the first photoluminescence layer332.

Referring toFIG.4, there is shown a packaged white light emitting device420(white light emitting device package) formed according to another embodiment of the invention. In this embodiment the first photoluminescence layer432, containing the manganese-activated fluoride photoluminescence material, comprises a coating layer disposed on and covering an individual LED chip430. As illustrated the first photoluminescence layer432can be generally hemispherical (dome-shaped) in form. Compared with the first photoluminescence layer232of the light emitting device ofFIG.2, the first photoluminescence layer432is more uniform in thickness and this reduces the variation in excitation light photon density received by the manganese-activated fluoride photoluminescence material within different physical location within the layer. Initial test data indicates that such an arrangement can reduce manganese-activated fluoride photoluminescence material usage by up to 80% by weight compared with the known white light emitting devices comprising a single photoluminescence layer (for exampleFIG.1).

The white light emitting device420can be manufactured by firstly depositing the first photoluminescence layer432onto the LED chip430and then filling the cavity428with the other photoluminescence material to form the second photoluminescence layer452.

Packaged White Light Emitting Devices Utilizing CSP LEDs

FIGS.5A and5Bare sectional views of packaged light emitting device in accordance with an embodiment of the invention that utilize CSP (Chip Scale Packaged) LEDs. In the light emitting devices ofFIGS.5A and5B, the first photoluminescence layer532comprises a substantially uniform thickness coating layer that is applied to at least the principle (top) light emitting face of the LED chip530. LED chips with a layer (film) of phosphor on their light emitting faces are often referred to as CSP (Chip Scale Packaged) LEDs. As illustrated inFIG.5A, the device520comprises a CSP LED comprising an LED chip530having a uniform thickness first layer532applied to it top (principle) light emitting face only. As illustrated inFIG.5B, the device520comprises a CSP LED comprising an LED chip530having a uniform thickness first layer532that covers (applied to) the top light emitting face and four side light emitting faces and can, as shown, be in the form of a conformal coating.

The light emitting devices ofFIGS.5A and5Bcan be manufactured by first applying the first photoluminescence layer532to at least the principle light emitting face of the LED chip530, for example using a uniform thickness (typically 20 μm to 300 μm) photoluminescence film comprising the manganese-activated fluoride photoluminescence material. The LED chip530is then mounted to the base524of the package522and the second photoluminescence layer532is then deposited so as to fill the cavity528and cover LED chip530.

FIG.5Cis a sectional view of a further packaged light emitting device in accordance with an embodiment of the invention that utilizes CSP LEDs. In this embodiment, the CSP LED includes first and second photoluminescence layers532,534comprising a coating layer applied to at least the principle (top) light emitting face of the LED chip530. As illustrated inFIG.5C, the first and second photoluminescence layers532,534can be applied to the top light emitting and four side light emitting faces and may be of uniform thickness and in the form of a conformal coating. As shown, the package cavity528may be filled with a light transmissive material (optical encapsulant)538such as a silicone material to provide environmental protection of the CSP LED. The light emitting device ofFIG.5Ccan be manufactured by first manufacturing the CSP LED by applying the first and second photoluminescence layers532,534to light emitting faces of the LED chip530, for example using a first uniform thickness photoluminescence film comprising the manganese-activated fluoride photoluminescence material and then using a second uniform thickness photoluminescence film comprising the other photoluminescence materials. The manufactured CSP LED chip is then mounted to the base524of the package522and a light reflective material542dispensed into the cavity528around the CSP LED up to the level of the first photoluminescence layer532. Finally, the second photoluminescence layer534is deposited so as to fill the cavity528and cover LED chip530.

FIGS.5D to5Hare sectional views of packaged light emitting device in accordance with an embodiment of the invention that utilize CSP (Chip Scale Packaged) LEDs having photoluminescence material that covers the top light emitting face of the LED chip530only and additionally include a light reflective material (layer)542that at least substantially covers the light emitting side faces of the LED chip. The light reflective material542can comprise a white material such as a white silicone material or alike.

The light reflective material layer542ensures that all blue light generated by light emitting side faces of the LED chip530passes into the first photoluminescence layer532comprising a manganese-activated fluoride photoluminescence material. This can be of particular benefit for devices that are configured to generate lower CCT (warm light) light, for example up to 3000K, which require a greater proportion of red light to achieve the desired color temperature. In this way, the inclusion of a light reflective material542that substantially covers the light emitting side faces of the LED chip530can lessen a need of having to include more manganese-activated fluoride photoluminescence material in the photoluminescence layer to compensate for a “dilution” effect by cooler white created by the emission of blue light from the light emitting side faces of the LED chip. That is, the blue light emission from the light emitting side faces of the LED chip can necessitate more manganese-activated fluoride photoluminescence material usage in the photoluminescence layer to generate the desired lower CCT (warm light) light, for example up to 3000K. A desired warmer color temperature can thus be attained without using more manganese-activated fluoride photoluminescence material in the photoluminescence layer due to the inclusion of a light reflective material that substantially covers the light emitting side faces of the LED chip. Since manganese-activated fluoride photoluminescence material is significantly more expensive than other types of photoluminescence materials (for example, green/yellow garnet-based phosphors), reducing the amount of manganese-activated fluoride photoluminescence material to attain a desired color temperature (warm) by using a relatively inexpensive light reflective material in this way provides a significant cost saving and makes the invention more cost effective and economical to manufacture the light emitting device.

A further benefit of having a light reflective material layer that at least substantially covers the light emitting side faces of the LED chip is that this may lead to a more uniform color and uniform color over angle of emitted light.

As shown inFIG.5Dthe light reflective material542comprises a layer of light reflective material542that fills the cavity528to a level that substantially covers the side faces of the LED chip without covering the first photoluminescence layer532, and in at least some embodiments the reflective material542may fill the cavity528to a level that completely covers the side faces of the LED chip without covering the first photoluminescence layer532. That is, the layer of light reflective material542fills the cavity528to a level that at least covers the side faces of the LED chip without covering the first photoluminescence layer532. Consequently, the light reflective material542can be considered to constitute a part of the package522rather than the CSP LED. Optionally, as indicated inFIG.5D, the CSP LED may comprise a light transmissive layer544(indicated by a dashed line) such as a glass or polymer film that covers the first photoluminescence layer532. The second photoluminescence layer534fills the remainder of the cavity528and covers the first photoluminescence layer532.

The light emitting device ofFIG.5Dcan be manufactured by first manufacturing the CSP LED by applying the first photoluminescence layer532to the light emitting top face of the LED chip530, for example applying a uniform thickness photoluminescence film comprising the manganese-activated fluoride photoluminescence material to the LED chip. Optionally, the first photoluminescence layer532may be provided on a light transmissive substrate544(indicated by a dashed line) such as a glass substrate or light transmissive polymer film. Since the first photoluminescence layer532may be thin, a benefit of depositing/fabricating the photoluminescence layer on a substrate can be ease of manufacture when manufacturing the first photoluminescence layer as a separate component and then applying this to the LED chip. The manufactured CSP LED chip is mounted to the base524of the package522and the cavity528filled with a light reflective material542to a level that substantially/completely covers the side faces of the LED chip530without covering the first photoluminescence layer532or light transmissive layer (substrate) when present. A further benefit of the light transmissive layer (substrate)544can be ease of manufacture when filing the cavity with the light reflective material542. More particularly, inclusion of the light transmissive layer (substrate)544effectively increases the thickness of the first photoluminescence layer532thereby allowing for a greater margin of error when filling the cavity528with the light reflective material542to ensure that it is not filled beyond a level that would otherwise obstruct the emission of light from the first photoluminescence layer532or light transmissive layer544(substrate) when present. In this way, since less accuracy is required to fill the cavity528with the light reflective material542to the correct level, this eases the complexity of the manufacturing process thereby diminishing costs.

The light emitting devices520ofFIG.5EandFIG.5Futilize a CSP LED ofFIG.9CandFIG.9Lrespectively and each CSP LED comprises a first photoluminescence layer532that covers the top light emitting face of the LED chip530and a light reflective material542that covers each of the four light emitting side faces. The light emitting devices520ofFIG.5GandFIG.5Hutilize a CSP LED ofFIG.9EandFIG.9Mrespectively and each CSP LED comprises a first photoluminescence layer532that covers the top light emitting face of the LED chip530, a light reflective material542that covers the light emitting side faces, and a second photoluminescence layer534that covers the first photoluminescence layer. The CSP LEDs ofFIGS.9D,9E,9L and9Mare further described below together with their method of manufacture.

The light emitting devices ofFIGS.5E and5Fcan be manufactured by first manufacturing the CSP LEDs as described herein, mounting the CSP LED to the base524of the package522, and then depositing the second photoluminescence layer532so as to fill the cavity528and cover LED chip530.

The light emitting devices ofFIGS.5G and5Hcan be manufactured by first manufacturing the CSP LEDs as described herein, mounting the CSP LED to the base524of the package522, and optionally then filling the cavity528with a light transmissive medium538.

Compared with the light emitting devices ofFIGS.2and3a uniform thickness coating layer can be preferable as it concentrates all of the manganese-activated fluoride photoluminescence material as close to the LED chip as possible and ensures that regardless of physical location within the layer all of the manganese-activated fluoride photoluminescence material receives exposure to substantially the same excitation light photon density. Such an arrangement can maximize the reduction in manganese-activated fluoride photoluminescence material usage. Initial test data indicates that such an arrangement can reduce manganese-activated fluoride photoluminescence material usage by up to 80% by weight compared with the known white light emitting devices comprising a single photoluminescence layer (for exampleFIG.1). The described two-layer light emitting device structure comprising respective first and second photoluminescence layers is not limited to surface mount packaged devices. For instance, it can also be applied in Chip On Board (COB) or Chip Scale Packaged (CSP) applications.

COB (Chip on Board) Packaged White Light Emitting Devices

With reference toFIGS.6A and6B, there is shown a plan view and a cross section side view through A-A (ofFIG.6A) of a COB light emitting device620in accordance with another embodiment of the invention. The light emitting device620has a circular shape; and, can as illustrated, comprise a circular substrate (board)624which is planar and disk shaped. The substrate typically comprises a circuit board such as a Metal Core Printed Circuit Board (MCPCB). Forming a COB arrangement, 7 arrays (rows) of blue LED dies630are evenly distributed on the circular substrate624. The circular substrate624also comprises about its entire perimeter a peripheral (annular) wall626which encloses all the arrays of blue LED dies (chips)630and in conjunction with the substrate624define a volume (cavity)628.

A first photoluminescence layer632comprising a manganese-activated fluoride photoluminescence material is deposited onto the circular substrate624and, in this embodiment, completely covers the array of blue LEDs630. Similarly, a second photoluminescence material layer634comprising a cerium-activated yellow garnet phosphor having a general composition Y3(Al,Ga)5O12:Ce is deposited onto the first photoluminescence layer632comprising the manganese-activated fluoride photoluminescence material. In this way, the first photoluminescence layer632and the second photoluminescence layer634are located adjacent one another and also contained within the wall626.

The light emitting device620functions and exhibits the same advantages as discussed in relation the light emitting devices ofFIGS.2,3,4,5A to5Efor example. Hence, the statements made in relation to these figures apply equally to the embodiment ofFIGS.6A and6B.

A method of manufacturing the light emitting device, for example, comprises the steps of: providing an array of blue LEDs; dispensing a manganese-activated fluoride photoluminescence material layer (first photoluminescence layer) at least over said array of blue LEDs; and dispensing a second photoluminescence material layer over said manganese-activated fluoride photoluminescence material layer to fill the volume628.

FIG.7is a sectional view of a COB white light emitting device in accordance with an embodiment of the invention. Referring toFIG.7, there is shown a COB packaged white light emitting device720(white light emitting device package) formed according to another embodiment of the invention. In this embodiment the first photoluminescence layer732, containing the manganese-activated fluoride photoluminescence material, comprises a respective individual coating layer disposed on and covering each LED chips730. As illustrated the first photoluminescence layer732can be generally hemispherical (dome-shaped) in form. Compared with the first photoluminescence layer632of the light emitting device ofFIGS.6A and6B, the first photoluminescence layer632is more uniform in thickness and this reduces the variation in excitation light photon density received by the manganese-activated fluoride photoluminescence material within different physical location within the layer. Initial test data indicates that such an arrangement can reduce manganese-activated fluoride photoluminescence material usage by up to 80% by weight compared with the known white light emitting devices comprising a single photoluminescence layer (for exampleFIG.1).

COB White Light Emitting Devices Utilizing CSP LEDs

FIGS.8A to8Fare cross sectional side views COB (Chip On Board) white light emitting device in accordance with embodiments of the invention that utilize CSP (Chip Scale Packaged) LEDs.

In the COB light emitting devices ofFIGS.8A and8Bthe first photoluminescence layer832may comprise a respective uniform thickness coating layer that is applied to at least the principle light emitting face of each LED die (chip). As described herein, LED chips with a uniform thickness layer (film) of phosphor on their light emitting faces are often referred to as CSP (Chip Scale Packaged) LEDs. As illustrated inFIG.8Aeach LED chip830has a uniform thickness layer applied to it top (principle) light emitting face only. As illustrated inFIG.8Beach LED chip830has a uniform thickness layer applied to the top light emitting and four side light emitting faces and is in the form of a conformal coating. The COB light emitting devices ofFIGS.8A and8Bcan be manufactured by first applying the first photoluminescence layer832to at least the principle light emitting face of each of the LED chips830, for example using a uniform thickness (typically 20 μm to 300 μm) photoluminescence film comprising the manganese-activated fluoride photoluminescence material. The LED chips830are then mounted to the base824and the second photoluminescence layer832then deposited over the array of LED chips to fill the volume828. Compared with the light emitting devices ofFIGS.6A and6Ba uniform thickness first photoluminescence layer is preferred as it concentrates all of the manganese-activated fluoride photoluminescence material as close to the LED chip as possible and ensures that regardless of physical location within the layer all of the manganese-activated fluoride photoluminescence material receives exposure to substantially the same excitation light photon density. Initial test data indicates that such an arrangement can reduce manganese-activated fluoride photoluminescence material usage by up to 80% by weight compared with the known white light emitting devices comprising a single photoluminescence layer (for exampleFIG.1).

FIGS.8C to8Fare sectional views of further COB white light emitting devices820in accordance with embodiments of the invention that utilize CSP LEDs having photoluminescence material that covers the top light emitting face of the LED chip830only and a light reflective material (layer)842that covers the light emitting side faces. The light emitting devices820ofFIG.8CandFIG.8Dutilize a CSP LED ofFIG.9CandFIG.9Lrespectively and each comprise a first photoluminescence layer832that covers the top light emitting face of the LED chip830and a light reflective material842that covers each of the four light emitting side faces. The light emitting devices820ofFIG.8EandFIG.8Futilize a CSP LED ofFIG.9EandFIG.9Mrespectively and each comprise a first photoluminescence layer832that covers the top light emitting face of the LED chip830, a light reflective material842that covers the light emitting side faces, and a second photoluminescence layer834that covers the first photoluminescence layer. The CSP LEDs ofFIGS.9D,9E,9L and9Mare further described below together with their method of manufacture.

In the embodiments ofFIGS.8C and8D, the COB packaged white light emitting devices820comprises a plurality (array) of CSP LEDs comprising the first photoluminescence layer832that are mounted on the substrate (board)824. The second photoluminescence layer834is constituted by filling the volume828contained within the peripheral wall826with a light transmissive material (optical encapsulant) containing the second photoluminescence material.

In the embodiments ofFIGS.8E and8F, the COB packaged white light emitting devices820comprises a plurality (array) of CSP LEDs mounted on the substrate (board)824. Since the CSP LEDs include both first and second photoluminescence layers832,834, there is no need for a peripheral wall or light transmissive optical encapsulant. However, in other embodiments, a peripheral wall and optical encapsulant can be provided to provide environmental protection to the CSP LEDs.

CSP (Chip Scale Packaged) Light Emitting Devices

FIGS.9A and9Bshow side views of CSP light emitting devices920in accordance with embodiments of the invention. In each embodiment, a first photoluminescence layer932comprising a manganese-activated fluoride photoluminescence material is applied (deposited) as a uniform thickness layer directly onto and covers at least the principle (e.g. top) light emitting face of a blue LED flip chip (die)930.

As shown inFIG.9A, a second photoluminescence material layer934comprising, for example, a cerium-activated yellow garnet phosphor having a general composition Y3(Al,Ga)5O12:Ce is applied (deposited) as a uniform thickness layer onto and covers the first photoluminescence layer932.

As illustrated inFIG.9B, the LED chip930has uniform thickness first and second photoluminescence layers932,934applied to the light emitting top face (top as shown) and four light emitting side faces and can be in the form of a conformal coating.

FIGS.9C and9Dshow side views of CSP light emitting devices920in accordance with embodiments of the invention. In each embodiment, a first photoluminescence layer932comprising a manganese-activated fluoride photoluminescence material covers (is applied to) the top light emitting face of a blue LED flip chip930and a light reflective material942covers the light emitting side faces. The light reflective material can comprise a white material such as a white silicone material or alike. The light reflective material layer942ensures that all blue light generated by light emitting side faces of the LED chip930passes into the first photoluminescence layer932comprising a manganese-activated fluoride photoluminescence material. This can be of particular benefit for devices that are configured to generate lower CCT (warm light) light, for example up to 3000K, which require a greater proportion of red light to achieve the desired color temperature. In this way, the inclusion of a light reflective material942that substantially covers the light emitting side faces of the LED chip930can lessen a need of having to include more manganese-activated fluoride photoluminescence material in the photoluminescence layer to compensate for a “dilution” effect by cooler white created by the emission of blue light from the light emitting side faces of the LED chip. That is, the blue light emission from the light emitting side faces of the LED chip can necessitate more manganese-activated fluoride photoluminescence material usage in the photoluminescence layer to generate the desired lower CCT (warm light) light, for example up to 3000K. A desired warmer color temperature can thus be attained without using more manganese-activated fluoride photoluminescence material in the photoluminescence layer due to the inclusion of a light reflective material that substantially covers the light emitting side faces of the LED chip. Since manganese-activated fluoride photoluminescence material is significantly more expensive than other types of photoluminescence materials (for example, green/yellow garnet-based phosphors), reducing the amount of manganese-activated fluoride photoluminescence material to attain a desired color temperature (warm) by using a relatively inexpensive light reflective material in this way provides a significant cost saving and makes the invention more cost effective and economical to manufacture the light emitting device.

A further benefit of having a light reflective material layer that at least substantially covers the light emitting side faces of the LED chip is that this may lead to a more uniform color and uniform color over angle of emitted light.

In the embodiment ofFIG.9C, the CSP light emitting device920comprises a first photoluminescence layer932, comprising in terms of photoluminescence material only a manganese-activated fluoride photoluminescence material, that is applied (deposited) as a uniform thickness layer directly onto the light emitting top face (top face as shown) of a blue LED flip chip930. Optionally, as indicated inFIG.9Cthe first photoluminescence layer932may be provided on a light transmissive substrate944(indicated by a dashed line) such as a glass substrate or light transmissive polymer film. Since the first photoluminescence layer can be of a thickness 20 μm to 300 μm, a benefit of depositing/fabricating the first photoluminescence layer on a substrate can be ease of manufacture when manufacturing the first photoluminescence layer as a separate component and then applying this to the LED chip. A further benefit of the substrate is that this can provide environmental protection to the first photoluminescence layer. The CSP light emitting device920further comprises a light reflective material942that covers the light emitting side faces of the LED flip chip930and constitute a light reflective enclosure (cup) around the periphery of the LED flip chip930. The light reflective material942reflects light that would otherwise be emitted from the side faces of the LED chip back into the LED chip932and this light is eventually emitted from the LED chip through the top light emitting face. As can be seenFIG.9C, the first photoluminescence layer932completely covers the top surface of the LED chip930and the light reflective material942thereby ensuring that all light generated by the CSP light emitting device920is emitted through the first photoluminescence layer932.

The CSP light emitting device920ofFIG.9Dis the same as that ofFIG.9Cexcept that it further comprises a second photoluminescence layer934that is in contact with and covers the first photoluminescence layer932. Optionally, as indicated inFIG.9Dthe photoluminescence layers932,934may be provided on a light transmissive substrate944(indicated by a dashed line) such as a glass substrate or light transmissive polymer film. Since the photoluminescence layers may be thin, a benefit of depositing/fabricating the photoluminescence layers on a substrate can be ease of manufacture when manufacturing the photoluminescence layers as a separate component and then applying this to the LED chip. A further benefit of the substrate is that this can provide environmental protection to the photoluminescence layers.

FIGS.9E to9Killustrate a method of manufacture of the CSP white light emitting device920ofFIG.9D.

First, as shown inFIG.9E, a photoluminescence component (film)946is provided comprising the first and second photoluminescence layers932,934. The photoluminescence film946can be manufactured by for example extrusion, slot die coating or screen printing. As described herein, the photoluminescence layers932,934may be provided on a light transmissive substrate944(not shown) such as a glass substrate or light transmissive polymer film.

Next, with the first photoluminescence layer932oriented uppermost, a measured quantity of a light transmissive material948, such as a curable silicone optical encapsulant, is dispensed on the first photoluminescence layer932at predetermined locations (FIG.9F). To maximize device yield from the photoluminescence film946the locations may, as illustrated, comprise a square array of rows and columns.

An LED flip chip930, with its light emitting face950facing the photoluminescence film (i.e. base940uppermost), is placed on a respective optical encapsulant948and pushed into the optical encapsulant948. The encapsulant948bonds the LED chip to photoluminescence film and forms a thin optical coupling layer between the first photoluminescence932and the top light emitting face950of the LED chip930.

As indicated inFIG.911, there is a square lattice of valleys952between rows and columns of LED dies930. The valleys952are filled with a light reflective material942such as a for example a white silicone material (FIG.91).

Finally, as shown inFIG.9J, individual CSP devices920are produced by cutting along cut lines954. The cut individual CSP devices920can be seen inFIG.9K.

It will be appreciated that a similar method can be used to manufacture the CSP white light emitting device920ofFIG.9Cusing a photoluminescence film comprising only a first photoluminescence layer932.

FIGS.9L and9Mshow side views of CSP light emitting devices920in accordance with embodiments of the invention. In each embodiment, a first photoluminescence layer932comprising a manganese-activated fluoride photoluminescence material covers (is applied to) the top light emitting face of a blue LED chip930, there is a light transmissive region956around the periphery of the LED chip930and a light reflective material942that covers the light transmissive region956and the light emitting side faces of the LED chip. It is to be noted that the first photoluminescence layer932extends beyond the light emitting top face of the LED chip and covers at least the light transmissive region956and may as indicated in the figures additionally cover the light reflective region956. The light reflective material can comprise a white material such as a white silicone material.

The light reflective material layer942ensures that all blue light generated by light emitting side faces of the LED chip930passes into the first photoluminescence layer932comprising a manganese-activated fluoride photoluminescence material. The light transmissive region956increases the amount of blue light generated by light emitting side faces of the LED chip930that reaches the first photoluminescence layer932. As described herein, this can be of particular benefit for devices that are configured to generate lower CCT (warm light) light, for example up to 3000K, which require a greater proportion of red light to achieve the desired color temperature.

In this way, the inclusion of a light reflective material942in combination with the light transmissive portion (layer)956that at least substantially covers the light emitting side faces of the LED chip930can lessen a need of having to include more manganese-activated fluoride photoluminescence material in the photoluminescence layer to compensate for a “dilution” effect by cooler white created by the emission of blue light from the light emitting side faces of the LED chip. That is, the blue light emission from the light emitting side faces of the LED chip can necessitate more manganese-activated fluoride photoluminescence material usage in the photoluminescence layer to generate the desired lower CCT (warm light) light, for example up to 3000K. A desired warmer color temperature can thus be attained without using more manganese-activated fluoride photoluminescence material in the photoluminescence layer due to the inclusion of a light reflective material that substantially covers the light emitting side faces of the LED chip. Since manganese-activated fluoride photoluminescence material is significantly more expensive than other types of photoluminescence materials (for example, green/yellow garnet-based phosphors), reducing the amount of manganese-activated fluoride photoluminescence material to attain a desired color temperature (warm) by using a relatively inexpensive light reflective material in this way provides a significant cost saving and makes the invention more cost effective and economical to manufacture the light emitting device.

In the embodiment ofFIG.9L, the CSP light emitting device920comprises a first photoluminescence layer932, comprising in terms of photoluminescence material only a manganese-activated fluoride photoluminescence material, that can be applied (deposited) as a uniform thickness layer directly onto the light emitting face (top face as shown) of a blue LED flip chip930. The light emitting device further comprises a light transmissive portion (layer)956applied to each of the four light emitting side faces of the LED chip and has a form which extends upwardly and outwardly from the base940of the LED chip. The light transmissive portion956defines a light transmissive region around the periphery of the LED chip and allows light emitted from the sides faces of the LED chip to travel to the first photoluminescence layer932. The CSP light emitting device920further comprises a light reflective material942in contact with the light transmissive region which extends upwardly and inwardly from the base940of the LED chip and defines a light reflective enclosure (cup) around the periphery of the light transmissive portion956. The light reflective portion942reflects light emitted from the side faces of the LED die in an upward direction towards the first photoluminescence layer932. As can be seenFIG.9L, the first photoluminescence layer932completely covers the top surface of the LED die930, light transmissive portion956, and light reflective portion942thereby ensuring that all light generated by the CSP light emitting device920is emitted through the first photoluminescence layer932.

The CSP light emitting device920ofFIG.9Mis the same as that ofFIG.9Lexcept that it further comprises a second photoluminescence layer934that is in contact with and covers the first photoluminescence layer932.

FIGS.9N to9Tillustrate a method of manufacture of the CSP white light emitting device920ofFIG.9M.

First, as shown inFIG.9N, a photoluminescence film946is provided comprising the first and second photoluminescence layers932,934. The photoluminescence film946can be manufactured by for example extrusion, slot die coating or screen printing. As described herein, the photoluminescence layers932,934may be provided on a light transmissive substrate944(not shown) such as a glass substrate or light transmissive polymer film.

Next, with the first photoluminescence layer932oriented uppermost, a measured quantity of a light transmissive material956, such as a curable silicone optical encapsulant, is dispensed on the first photoluminescence layer932at predetermined locations (FIG.9O). To maximize device yield from the photoluminescence film946the locations may, as illustrated, comprise a square array of rows and columns.

An LED flip chip930, with its light emitting face950facing the photoluminescence film (i.e. base940uppermost), is placed on a respective optical encapsulant956and pushed into the optical encapsulant956(FIG.9P). The encapsulant956forms a concave meniscus that extends up and covers each of the light emitting side faces of the LED dies as shown inFIG.9Q.

As indicated inFIG.9Q, there is a square lattice of valleys952between rows and columns of LED dies930. The valleys952are filled with a light reflective material942such as a for example a white silicone material (FIG.9R).

Finally, as shown inFIG.9S, individual CSP devices920are produced by cutting along cut lines954. The cut individual CSP devices920can be seen inFIG.9T.

It will be appreciated that a similar method can be used to manufacture the CSP white light emitting device920ofFIG.9Lusing a photoluminescence film comprising only a first photoluminescence layer932.

The light emitting devices920ofFIGS.9A to9D,9L and9Mfunction and exhibit the same advantages as discussed in relation the light emitting device ofFIG.2for example. Hence, the statements made in relation toFIG.2apply equally to the embodiment ofFIGS.9A to9D,9L and9M.

Experimental Test Data

In this specification, the following nomenclature is used to denote white light emitting devices: Com. # denotes a comparative (known) white light emitting device comprising a single-phosphor layer and Dev. # denotes a two-phosphor layer white light emitting device in accordance with an embodiment of the invention.

Comparative white light emitting devices (Com. #) and white light emitting devices in accordance with the invention (Dev. #) each comprise SMD 2835 packaged devices containing three serially connected1133(11 mil×33 mil) blue LED chips of dominant wavelength λd≈455 nm. Each device is a nominal 0.9 W (Drive The rated driving condition is 100 mA and a forward drive voltage Vfof 9 V) device and is intended to generate white light with a target Correlated Color Temperature (CCT) of 2700K and a general color rendering index CRI Ra>90.

The phosphors used in the test devices are KSF (K2SiF6:Mn4+) from Intematix Corporation, green YAG phosphor (Intematix NYAG4156—(Y, Ba)3-x(Al1-yGay)5O12:CexPeak emission wavelength λpe=550 nm) and CASN (Ca1-xSrxAlSiN3:Eu λpe≈615 nm). The CASN is included to achieve the 2700K color target and general CRI Ra>90.

For the single-layer comparative devices, Com. #, the three phosphors (KSF, YAG and CASN) were mixed in a phenyl silicone and the mixture dispensed into the 2835 package to fill the cavity. The single-phosphor layer is then cured in an oven.

For the two-layer devices (Dev. #): KSF phosphor is mixed into a phenyl silicone and dispensed into the 2835 package to partially fill the LED cavity. The KSF phosphor layer is cured in an oven. YAG phosphor is mixed with a phenyl silicone and then dispensed on top of KSF layer to fully fill the LED cavity and the cured in an oven. The KSF phosphor layer can additionally include CASN and/or YAG.

Experimental Test Data—Optical Performance

The test method involves measuring total light emission of the packaged white light emitting devices in an integrating sphere.

TABLE 1 tabulates phosphor composition of a comparative device Com.1 (single-layer device) and a two-layer device Dev.1 in accordance with the invention. TABLE 2 tabulates total phosphor usage for the single-layer device (Com.1) and the two-layer device (Dev.1). The phosphor weight values (weight) in TABLES 1 and 2 are normalized to the weight of KSF in the single phosphor layer of comparative device Com.1.

As can be seen from TABLE 1, in terms of phosphor composition: Com. 1 comprises a single phosphor layer comprising a mixture of 69.9 wt % (weight=1.000) KSF, 28.1 wt % (weight=0.400) YAG and 2.1 wt % (weight=0.030) CASN. Dev.1 comprises a two-layered phosphor structure having a 1stphosphor layer comprising a mixture of 95.2 wt % (weight=0.457) KSF and 4.8 wt % (weight=0.023) CASN and a 2ndphosphor layer comprising 100.0 wt % (weight=0.561) YAG.

TABLE 1Phosphor composition of a single-layer LED (Com.1) and a two-layer LED (Dev.1)1stphosphor layer2ndphosphor layerKSFYAGCASNYAGCASNDeviceweight1wt %2weight1wt %2weight1wt %2weight1wt %2weight1wt %2Com.11.00069.90.40028.00.0302.1————Dev.10.45795.2——0.0234.80.561100.0——1weight-phosphor weight normalized to weight of KSF of single phosphor layer of comparative device (Com.1)2wt %-phosphor weight percentage of total phosphor content of the layer

TABLE 2Phosphor usage of a single-layer LED (Com.1) and a two-layer LED (Dev.1)Phosphor usageKSFYAGCASNTOTALDeviceweight1%wt %3weight1%wt %3weight1%wt %3weight1Com.11.000100.069.90.400100.028.00.0301002.11.430Dev.10.45746.043.90.561129.053.90.023762.21.0411weight-phosphor weight normalized to weight of KSF of single phosphor layer of comparative device (Com.1)3wt %-phosphor weight percentage of total phosphor content of device

TABLE 3 tabulates the measured optical performance of the light emitting devices Com.1 and Dev.1. As can be seen from TABLE 3 the color point of light generated by the devices are very similar with the flux generated by the two layer-device of the invention (Dev.1) being 4.1 lm greater (3.4% brighter: Brightness—Br) than the single-layer comparative device (Com.1). However, as can be seen from TABLE 2, compared with the single-layer device Com.1, KSF usage of the two-layer device Dev.1 in accordance with the invention is reduced from a normalized weight (weight) 1.000 to 0.457, that is a 54% reduction in KSF usage compared with Com.1. Moreover, CASN usage of the two-layer device Dev.1 is also reduced from a normalized weight 0.030 to 0.023, that is a 24% reduction in CASN usage compared with Com.1. While there is an increase of 29% (0.561 from 0.400) in YAG usage, total phosphor usage is reduced from weight=1.430 to 1.041, that is a reduction of 28% total phosphor usage. As noted above, YAG is inexpensive compared with both KSF (typically 1/100 to 1/150 of the cost) and CASN (typically at least 1/20 of the cost). Consequently, since YAG is a fraction of the cost of KSF or CASN, the overall cost of the device is dramatically reduced in this way. As well as the cost saving afforded by the reduction in KSF and CASN content, two-layer devices in accordance with the invention are easier to manufacture as they use less total phosphor material which means that the phosphor material loading in silicone is reduced and this reduction can increase the reliability/stability of the dispensing process.

It is believed that the reason for the increase in YAG usage is that due to less blue excitation light reaching the 2ndphosphor layer, more YAG phosphor is required to generate green light to attain the selected color target. As discussed above, it is believed that since the KSF layer contains substantially only KSF (individual KSF layer), KSF usage is reduced, because the KSF can absorb blue excitation light without having to compete with the YAG phosphor as is the case in the known single-layer devices comprising a single layer having a mixture of phosphors.

TABLE 3Measured optical performance of a single-layer device (Com.1)and a two-layer device (Dev.1)CIECRIDevicexyFlux (lm)Br (%)RaΔRaR9ΔR9Com.10.45440.4183121.7100.090.30.057.60.0Dev.10.45480.4208125.8103.490.90.657.4−0.2

TABLE 4 tabulates phosphor composition of a comparative device Com.2 (single-layer device) and two-layer devices Dev.2 to Dev.5 in accordance with the invention for increasing proportion (wt %) of KSF in the 1stphosphor layer. TABLE 5 tabulates total phosphor usage for the single-layer device (Com.2) and the two-layer devices (Dev.2 to Dev.5). The phosphor weights in TABLES 4 and 5 are normalized to the weight of KSF in the comparative device Com.2.

As can be seen from TABLE 4, in terms of phosphor composition: Com.2 comprises a single phosphor layer comprising a mixture of 68.9 wt % (weight=1.000) KSF, 29.0 wt % (weight=0.421) YAG and 2.1 wt % (weight=0.031) CASN. Devices Dev.2 to Dev.5 comprise a 1stphosphor layer having an increasing proportion (wt %) of KSF in the 1stphosphor layer (76.8 wt % to 100 wt %). More specifically: Dev.2 comprises a two-layered structure having a 1stphosphor layer comprising a mixture of 76.8 wt % (weight=0.770) KSF, 3.2 wt % (weight=0.032) CASN and 20.0 wt % (weight=0.200) YAG, and a 2ndphosphor layer comprising 100.0 wt % YAG (weight=0.345); Dev.3 comprises a two-layered structure having a 1stphosphor layer comprising a mixture of 86.4 wt % (weight=0.665) KSF, 3.6 wt % (weight=0.028) CASN and 10.0 wt % (weight=0.077) YAG and a 2ndphosphor layer comprising 100.0 wt % YAG (weight=0.506); Dev.4 comprises a two-layered structure having a 1stphosphor layer comprising a mixture of 96.0 wt % (weight=0.639) KSF, 4.0 wt % (weight=0.0270) CASN and a 2ndphosphor layer comprising 100.0 wt % YAG (weight=0.580); and Dev.5 comprises a two-layered structure having a 1stphosphor layer comprising 100.0 wt % (weight=0.551) KSF and a 2ndphosphor layer comprising a mixture of 96.0 wt % YAG (weight=0.595) and 4.0 wt % (weight=0.025) CASN.

TABLE 4Phosphor composition of a single-layer LED (Com.2) and two-layer LEDs (Dev.2 to Dev.5) with increasingwt % KSF content in 1stlayer1stphosphor layer2ndphosphor layerKSFYAGCASNYAGCASNDeviceweight1wt %2weight1wt %2weight1wt %2weight1wt %2%4weight1wt %2Com.21.00068.90.42129.00.0312.1—————Dev.20.77076.80.20020.00.0323.20.345100.063.3——Dev.30.66586.40.07710.00.0283.60.506100.086.8——Dev.40.63996.0——0.0274.00.580100.0100.0——Dev.50.551100.0————0.59596.0100.00.0254.01weight-phosphor weight normalized to weight of KSF of single phosphor layer of comparative device (Com.1)2wt %-phosphor weight percentage of total phosphor content of the layer4%-percentage of total YAG content in 2ndphosphor layer

TABLE 5Phosphor usage of a single-layer LED (Com.1) and a two-layer LED (Dev.1)Phosphor usageKSFYAGCASNTOTALDeviceweight1%wt %3weight1%wt %3weight1%wt %3weight1Com.21.00010040.30.71510028.80.05210030.92.482Dev.20.7707744.00.92512952.90.0541043.11.749Dev.30.6656739.10.99013858.10.047902.81.702Dev.40.6396438.20.98513859.00.045872.71.669Dev.50.5515534.41.00914163.00.042812.61.6021weight-phosphor weight normalized to weight of KSF of single phosphor layer of comparative device (Com.1)3wt %-phosphor weight percentage of total phosphor content of device

TABLE 6 tabulates the measured optical performance of the light emitting devices Com.2 and Dev.2 to Dev.5. As can be seen from TABLE 6 the optical performance/color point of the devices are very similar with the flux generated by the two layer-devices of the invention (Dev.2 to Dev.5) being between about 0.7% and 2.0% brighter (Brightness—Br) than the single-layer comparative device (Com.2). However, as can be seen from TABLE 5, compared with the single-layer device Com.2, KSF usage of the two-layer devices Dev.2 to Dev.5 in accordance with the invention is reduced by 23% up to 45% depending on the proportion (wt %) of KSF in the 1stphosphor layer. It will be noted from TABLE 5 that the greatest reduction in KSF usage is when the 1stphosphor layer, in terms of total phosphor content of the layer, exclusively comprises KSF (i.e. Dev.5-100 wt % KSF in 1stphosphor layer). This being said, it will be appreciated that even for a device having about a 75% wt % proportion of KSF of a total phosphor content in the 1stphosphor layer (Dev.2), the saving in KSF usage is still about 25% which is substantial when the high cost of KSF is taken into account, resulting in nearly a 25% reduction in the overall cost of the manufacturing of the device.

As evidenced in TABLE 5, increasing the proportion (wt %) of KSF in the 1stphosphor layer has the effect of (i) reducing KSF usage (23% to 45%), (ii) reducing CASN usage, (iii) increasing YAG usage, and (iv) reducing total phosphor usage. These effects together provide a significant cost reduction.

It will be further noted that in devices in accordance with the invention, the 2ndphosphor layer can comprise from about 60% (Dev.2) to 100% (Devs.4 and 5) YAG (green photoluminescence material) of the total YAG content of the device.

TABLE 6Optical performance of single-layer LED (Com.2) and two-layer LEDs (Dev.2 to Dev.5)CIECCTFluxLEBrCRIDevicexy(K)(lm)(lm/W)(%)RaΔRaR9ΔR9Com.20.45910.41692759110.1345.4100.093.50.065.50.0Dev.20.45910.41732763111.2347.2100.992.5−1.061.4−4.1Dev.30.45870.41702767111.7345.8101.493.0−0.564.1−1.4Dev.40.45890.41752766110.9345.3100.793.50.067.52.0Dev.50.45990.41352722112.8341.7102.494.81.379.013.5
Experimental Test Data—Thermal Performance

TABLE 7 tabulates the thermal stability of the single-layer light emitting device Com.1 and two-layer light emitting device Dev. 1. As can be seen from TABLE 7, compared with the single-layer device Com.1, the two-layer devices Dev.1 in accordance with the invention exhibits greater thermal stability in terms of light emission and emission color stability.

For example, the average flux generated by Dev.1 drops 12.3% (116.5 lm to 102.1 lm) when operated at 85° C. (H) compared with being operated at 25° C. (C). In comparison the average flux generated by Com.1 drops 12.7% (From 115.9 lm to 101.2 lm) when operated at 85° C. (H) compared with being operated at 25° C. (C).

In terms of luminous efficacy (LE), the average value of LE of Dev.1 drops 10.4% (From 123.1 lm/W to 110.4 lm/W) when operated at 85° C. (H) compared with being operated at 25° C. (C). In comparison, the average value of LE of Com.1 drops 11.6% (From 122.9 lm/W to 108.6 lm/W) when operated at 85° C. (H) compared with being operated at 25° C. (C). This demonstrates the superior thermal stability of a device formed in accordance with the invention since the drop in average LE of 10.4% (Dev.1) is less than the drop of 11.6% (Com.1).

In terms of general color rendering index CRI Ra, the average value of CRI Ra of Dev.1 increases by an amount of only 1.5 (From 93.2 to 95.2) when operated at 85° C. (H) compared with being operated at 25° C. (C). In comparison, the average value of CRI Ra of Com.1 increases by an amount 2.0 (From 91.2 to 93.3) when operated at 85° C. (H) compared with being operated at 25° C. (C). This demonstrates the superior thermal stability of a device formed in accordance with the invention since the increase of average CRI Ra of 1.5 (Dev.1) is less than the increase of 2.0 (Com.1).

In terms of color rendering index CRI R8, the average value of CRI R8 of Dev.1 increases by an amount of only 0.6 (From 97.1 to 97.7) when operated at 85° C. (H) compared with being operated at 25° C. (C). In comparison, the average value of CRI R8 of Com.1 increases by an amount 1.2 (From 82.6 to 83.9) when operated at 85° C. (H) compared with being operated at 25° C. (C). This demonstrates the superior thermal stability of a device formed in accordance with the invention since the increase of average CRI R8 of 0.6 (Dev.1) is less than the increase of 1.2 (Com.1).

In terms of color rendering index CRI R9, the average value of CRI R9 of Dev.1 increases by an amount of only 2.3 (From 83.3 to 85.5) when operated at 85° C. (H) compared with being operated at 25° C. (C). In comparison, the average value of CRI R9 of Com.1 increases by an amount 5.7 (From 57.4 to 63.1) when operated at 85° C. (H) compared with being operated at 25° C. (C). This demonstrates the superior thermal stability of a device formed in accordance with the invention since the increase of average CRI R9 of 2.3 (Dev.1) is less than the increase of 5.7 (Com.1).

TABLE 7Thermal stability of a single-layer LED (Com.1) and two-layer LED (Dev. 1)FluxLECIECRIDeviceCondition(lm)(lm/W)xyRaR8R9Com.1Cold (C) 25° C.115.0123.20.45420.407391.082.457.0117.3119.80.45340.408391.382.557.3115.4125.60.45230.410191.483.057.8Average115.9122.90.45330.408691.282.657.4Hot (H)100.4107.10.45790.398592.983.462.285° C.102.9109.60.45700.399193.483.963.2100.2109.10.45620.400893.584.463.9Average101.2108.60.45700.399593.383.963.1Δ C to H−12.7%−13.1%0.0037−0.00881.91.05.2−12.3%−8.5%0.0036−0.00922.11.45.9−13.2%−13.1%0.0039−0.00932.11.46.1Average−12.7%−11.6%0.0040−0.00902.01.25.7Dev.1Cold (C) 25° C.118.5125.00.44560.432292.796.079.4116.7126.20.44670.429893.696.881.7114.4118.20.45120.426594.798.488.9Average116.5123.10.44780.429593.497.183.3Hot (H) 85° C.103.9112.30.44950.424294.596.782.1102.3112.10.45050.421695.497.384.2100.2106.80.45530.418295.799.090.5Average102.1110.40.45020.421395.297.785.6Δ C to H−12.3%−10.1%0.0039−0.00801.80.72.7−12.3%−11.3%0.0038−0.00821.80.52.5−12.4%−9.7%0.0041−0.00831.00.61.6Average−12.3%−10.4%0.0040−0.00801.50.62.3

The reliability, relative brightness, of a light emitting device in accordance with the invention (Dev.1) comprising two-layers is compared with the reliability of a known device (Com.1) comprising a single-layer of mixed photoluminescence materials under Wet High Temperature Operation Life test condition (WHTOL), temperature is 85° C., relative humidity is 85%. The driving condition is 9V and 120 mA. As shown inFIG.10, the two-layer LED's (Dev.1) relative intensity at 336 hrs is 96.4% while the relative intensity of the known single-layer LED (Com. 1) dropped to 91.45% at 336 hrs. It is believed that this improvement in reliability is due to a combination of the reduced usage of KSF phosphor as discussed above and the protection provided by the 2ndphotoluminescence layer covering the manganese-activated fluoride photoluminescence layer (1stlayer).

Another accelerated reliability is a water boiling test. In this test, the LEDs were immersed in 85° C. deionized water for 4 hours. The LED brightness is tested before and after immersion in water. The results of this test are tabulated in TABLE 8. Under these conditions, it is believed that hot water may penetrate the upper photoluminescence layer silicone surface to react with Fluoride photoluminescence material. The two-layer device of the invention provides increased isolation between water and the KSF (manganese-activated fluoride photoluminescence material) in the 1stphosphor layer, resulting in better lumen maintenance than the single-layer device.

TABLE 8Relative brightness of single-layer LEDs (Com.1) and two-single-layer LEDs (Dev.1)under immersion in boiling water (85° C.) for 4 hoursRelative Brightness (%) after 4 hoursSample numberDevice12345678910maxminavgCom.195.496.496.793.994.796.193.594.193.094.696.793.094.8Dev.197.397.197.597.698.098.398.298.098.497.398.497.197.8
Experimental Data—Packaged White Light Emitting Devices Utilizing CSP LEDs

TABLE 9 tabulates the measured optical performance of packaged white light emitting devices Devs. 6 to 8 that utilize CSP LEDs.

Dev.6 has the packaging arrangement ofFIG.5Dand comprises a 2835 package containing a 4343 (43 mil×43 mil≈1.1 mm2) CSP flip chip LED of dominant wavelength λd≈455 nm. The LED flip chip has a single photoluminescence layer which in terms of photoluminescence material (phosphor) consists of only KSF applied to its top light emitting face only. The photoluminescence layer is provided on a glass substrate. The package cavity is filled with a light reflective white silicone to a level that at least substantially or completely covers the side faces of the LED chip without covering the glass substrate. The remainder of the cavity is filled with silicone containing a mixture of broadband green to red emitting photoluminescence materials. The device is a nominal 0.3 W (rated driving condition is 120 mA and a forward drive voltage of 2.75 V) device and is intended to generate white light with a target Correlated Color Temperature (CCT) of 2700K and a general color rendering index CRI Ra≥90 and a CRI R9 of at least 50.

Dev.7 has the packaging arrangement ofFIG.5Fand comprises a 2835 package containing a 4343 (43 mil×43 mil≈1.1 mm2) CSP flip chip LED of dominant wavelength λd≈455 nm. The LED flip chip has a single photoluminescence layer which in terms of photoluminescence material (phosphor) consists of only KSF applied to its top light emitting face only. The photoluminescence layer is provided on a glass substrate. The CSP LED further comprises light reflective material that covers the four light emitting side faces of the LED chip. The package cavity is filled with silicone containing a mixture of broadband green to red emitting photoluminescence materials. The device is a nominal 0.3 W (rated driving condition is 120 mA and a forward drive voltage of 2.75 V) device and is intended to generate white light with a target Correlated Color Temperature (CCT) of 2700K and a general color rendering index CRI Ra≥90 and a CRI R9 of at least 50.

Dev.8 has the packaging arrangement ofFIG.5Aand comprises a 2835 package containing a 4343 (43 mil×43 mil≈1.1 mm2) CSP flip chip LED of dominant wavelength λd≈455 nm. The LED flip chip has a single photoluminescence layer which in terms of photoluminescence material (phosphor) consists of only KSF applied to its top light emitting face only. The photoluminescence layer is provided on a glass substrate. The package cavity is filed with silicone containing a mixture of broadband green to red emitting photoluminescence materials. The device is a nominal 0.3 W (rated driving condition is 120 mA and a forward drive voltage of 2.75 V) device and is intended to generate white light with a target Correlated Color Temperature (CCT) of 4000K and a general color rendering index CRI Ra≥90 and a CRI R9 of at least 50.

TABLE 9Optical performance of 2700K (Devs.6 and 7) and 4000K (Dev.8) packaged white lightemitting device utilizing CSP LEDsIFFluxLECIECCTCRIDevice(mA)VF(V)(lm)(lm/W)xy(K)RaR9Dev.61202.8450.71490.45780.4213281191.757.2652.7528.51600.45980.4191276693.362.1Dev.71202.8052.31550.45760.4193279992.862.5652.7229.41660.45980.4193275094.267.1Dev.81202.8067.22040.38330.3856398989.152.8
Color Temperature Tunable White Light Emitting Devices

While the foregoing description has been in relation to fixed color temperature light emitting devices, embodiments of the invention also find utility in color temperature tunable white light emitting devices. Color temperature tunable white light emitting devices according to the invention comprise first and second LED chips (dies) for generating light of first and second different color temperatures. The LED chips are electrically configured such that electrical power can be applied independently to the first and second LED chips enabling color temperature tuning of light generated by the device. For example, when electrical power is provided to only the first LED chip(s) the device generates light of the first color temperature. When electrical power is provided to only the second LED chip(s) the device generates light of the second color temperature. When electrical power is provided to both the first and second LED chips the device generates light with a color temperature between the first and second color temperatures. The exact color temperature of light generated by the device depends on the ratio of the electrical power provided to the first and second LED chips. In the following description, LED chips with a suffix “a” are used to indicate LED chips that generate light of a first color temperature and LED chips with a suffix “b’ are used to indicate LED chips that generate light of a second different color temperature.

Packaged Color Temperature Tunable White Light Emitting Devices Utilizing CSP LEDs

FIGS.11A to11Eare cross sectional side views of packaged color temperature tunable white light emitting devices1120in accordance with embodiments of the invention that utilize CSP (Chip Scale Packaged) LEDs1158.

Each of the color temperature tunable devices1120ofFIGS.11A to11Ccomprise a package1122(comprising a base1124and side walls1126A,1126B extending upwardly from opposing edges of the base1124), one or more first CSP LEDs1158a(indicated by a heavy solid line), one or more second blue LED chips1130b, and second photoluminescence layer1134that covers the first CSP LED(s)1158aand the second LED chip(s)1130b. The one or more first CSP LEDs1158acomprise a first LED chip1130awith a first photoluminescence layer1132athat covers at least its light emitting top face. The first photoluminescence layer1132acomprises a manganese-activated fluoride photoluminescence material only and can be applied in direct contact with and may be of a substantially uniform thickness.

As shown inFIG.11A, a color tunable light emitting device1120comprises a package1122with one or more first CSP LEDs1158acomprising a first LED chip1130awith a first photoluminescence layer1132covering (applied to) its light emitting top face only. The device further comprises one or more second LED chips1130b. A second photoluminescence layer1134is deposited so as to fill the cavity1128and cover the first CSP LED(s)1158aand cover the second LED chip(s)1130b. The first CSP LED(s)1158ain conjunction with the second photoluminescence layer1134generate white light of a first color temperature while the second blue LED chip(s)1130bin conjunction with the second photoluminescence layer1134generates white light of a second different color temperature. Since light generated by the first CSP LED(s)1158aadditionally includes red light generated by the manganese-activated fluoride phosphor of the first photoluminescence layer1132it will typically be warmer in color (that is lower in color temperature) than the light generated by the second LED chip(s)1130bwhich includes light generated by the second photoluminescence layer1134only.

In the color tunable light emitting device1120ofFIG.11Bthe CSP LED(s)1158acomprise an LED chip1130awith a first photoluminescence layer1132athat covers the light emitting top face and four side light emitting faces of the first LED chip1130a. As indicated the first photoluminescence layer can be in the form of a conformal coating.

As shown inFIG.11Cthe CSP LED(s)1150acomprise the CSP packaging arrangement ofFIG.9Lwith a first photoluminescence layer1132athat covers the light emitting top face and four side light emitting faces of the first LED chip1130a. The CSP LED(s)1150acomprises a light reflective material1142a(1142b) in the same way as shown in the arrangement ofFIG.9L.

The color temperature tunable light emitting devices ofFIGS.11A to11Ccan be manufactured by mounting the CSP LED(s)1158aand second blue LED chip(s)1130bto the base (floor)1124of the package cavity1128and then depositing the second photoluminescence layer1132so as to fill the volume (cavity)1128and cover the CSP LED(s)1158aand LED chip1130b.

The color temperature tunable devices ofFIGS.11D and11Ecomprise one or more first CSP LEDs1158athat generate white light of a first color temperature and one or more second CSP LEDs1158bthat generate white light of a second different color temperature. The first and second CSP LEDs1158a,1158beach respectively comprise an LED chip1130a,1130bwith first photoluminescence layer1132a,1132bapplied to at least its light emitting top face and a second photoluminescence layer1134a,1134bcover the first photoluminescence layer. The first and second photoluminescence layers may be of uniform thickness.

As shown inFIG.11Da color temperature tunable light emitting device1120comprises a package1122with one or more first and second CSP LEDs1158a,1158b. As illustrated, the first and second CSP LEDs1158a,1158bcan, as shown, comprise the CSP packaging arrangement ofFIG.9Bcomprising LED chips1130a,1130bwith first and second photoluminescence layers1132,1134applied to their light emitting top face and four side light emitting faces in the form of a conformal coating. Optionally, the package cavity1128can be filled with a light transmissive material (optical encapsulant)1138such as a silicone material to provide environment protection to the CSP LEDs1158a,1158b.

In another embodiment, as shown inFIG.11E, the first and second CSP LED(s)1158a,1158bcan comprise the CSP packaging arrangement ofFIG.9M.

The color temperature tunable light emitting devices ofFIGS.11D and11Ecan be manufactured by first manufacturing the CSP LEDs1158a,1158b, as herein described (FIGS.9N to9T), mounting the CSP LEDs to the floor of the package cavity1128and then filling the cavity with a light transmissive material (optical encapsulant)1138to provide environment protection to the CSP LEDs1158a,1158b.

COB Color Tunable White Light Emitting Devices Utilizing CSP LEDs

FIGS.12A to12Eare cross sectional side views of COB (Chip On Board) color temperature tunable white light emitting devices in accordance with embodiments of the invention that utilize CSP (Chip Scale Packaged) LEDs.

Each of the color temperature tunable devices ofFIGS.12A to12Ccomprise a substrate1224, one or more first CSP LEDs1258a(indicated by a heavy solid line), one or more second blue LED chips1230b, and second photoluminescence layer1234that covers the first CSP LED(s)1258aand the second LED chip(s)1230b. The one or more first CSP LEDs1258acomprise a first LED chip1230awith a first photoluminescence layer1232athat covers at least its light emitting top face. The first photoluminescence layer1232acomprises a manganese-activated fluoride photoluminescence material only and can be applied in direct contact with and may be of a substantially uniform thickness.

In an embodiment, as shown inFIG.12A, a COB color tunable light emitting device1220comprises a planar substrate (board)1224which may typically comprise a circuit board such as a Metal Core Printed Circuit Board (MCPCB). An array of first CSP LEDs1258aand an array of second blue LED chips1230bare evenly distributed on the substrate1224. To ensure a uniform emission color of light, the CSP LEDs1258aand second LED chips1230bcan be interspersed. Each CSP LED1258acomprises a first LED chip1230awith a with a uniform thickness first photoluminescence layer1132aapplied to its light emitting top face only. The substrate1224further comprises about its entire perimeter a peripheral wall1226which encloses all the arrays of CSP LEDs1258aand LED chips1230band in conjunction with the substrate1224define a volume (cavity)1228. A second photoluminescence layer1134is deposited so as to fill the volume1228and cover the first CSP LED(s)1258aand second LED chip(s)1230b. The first CSP LED(s)1258ain conjunction with the second photoluminescence layer1234generates white light of a first color temperature while the second LED chip(s)1230bin conjunction with the second photoluminescence layer1234generates white light of a second different color temperature.

In the color tunable light emitting device1220ofFIG.12Bthe CSP LED(s)1258acomprise an LED chip1230awith a uniform thickness first photoluminescence layer1232aapplied to its light emitting top face and four side light emitting faces and is in the form of a conformal coating.

As shown inFIG.12Cthe CSP LED(s)1250acan comprise the CSP packaging arrangement ofFIG.9L.

The COB color temperature tunable light emitting devices ofFIGS.12A to12Ccan be manufactured by mounting the first CSP LED(s)1258aand second LED chip(s)1230bto the substrate (board)1224and then depositing the second photoluminescence layer1234so as to fill the volume (cavity)1228and cover the first CSP LEDs1258aand second LED chips1130b.

FIGS.12D and12Eare cross sectional side views of COB (Chip On Board) color temperature tunable white light emitting devices1220that each comprise a plurality of first CSP LEDs1258athat generate white light of a first color temperature and a plurality of CSP LEDs1258bthat generate white light of a second different color temperature. The first and second CSP LEDs1258a,1258beach respectively comprise an LED chip1230a,1230bwith a uniform thickness first photoluminescence layer1232a,1232bapplied to at least its light emitting top face and a second photoluminescence layer1234a.1234bcover the first photoluminescence layer.

In the embodiment shown inFIG.12D, a COB color temperature tunable light emitting device1220comprises a substrate (board)1224with an array of first and second CSP LEDs1258a,1258b. As illustrated, the first and second CSP LEDs1258a,1258bcan comprise the CSP packaging arrangement ofFIG.9Bcomprising LED chips1230a,1230bwith first and second photoluminescence layers1232,1234applied to their light emitting top face and four side light emitting faces in the form of a conformal coating. As indicated inFIG.12Dthere is no need for a peripheral wall, though a peripheral wall may be provided and the volume within the wall filled with a light transmissive material (optical encapsulant) such as a silicone material to provide environmental protection to the first and second CSP LEDs.

In another embodiment, as shown inFIG.12E, the first and second CSP LED(s)1258a,1258bcan comprise the CSP packaging arrangement ofFIG.9M.

The COB color temperature tunable light emitting devices ofFIGS.12D and12Ecan be manufactured by first manufacturing the first and second CSP LEDs1258a,1258bas herein described and then mounting them to the substrate (board)1224.

As used in this document, both in the description and in the claims, and as customarily used in the art, the words “substantially,” “approximately,” and similar terms of approximation are used to account for manufacturing tolerances, manufacturing variations, manufacturing imprecisions, and measurement inaccuracy and imprecision that are inescapable parts of fabricating and operating any mechanism or structure in the physical world.

While the invention has been described in detail, it will be apparent to one skilled in the art that various changes and modifications can be made and equivalents employed, without departing from the present invention. It is to be understood that the invention is not limited to the details of construction, the arrangements of components, and/or the method set forth in the above description or illustrated in the drawings. Statements in the abstract of this document, and any summary statements in this document, are merely exemplary; they are not, and cannot be interpreted as, limiting the scope of the claims. Further, the figures are merely exemplary and not limiting. Topical headings and subheadings are for the convenience of the reader only. They should not and cannot be construed to have any substantive significance, meaning or interpretation, and should not and cannot be deemed to indicate that all of the information relating to any particular topic is to be found under or limited to any particular heading or subheading. Therefore, the invention is not to be restricted or limited except in accordance with the following claims and their legal equivalents.

LIST OF REFERENCE NUMERALS

10Known light emitting device12Package14Cavity16LED die (chip)18Optical encapsulant#20Light Emitting Device#22Package#24Base#26Wall#28Cavity#30LED chip (die)#32First Photoluminescence layer#34Second photoluminescence layer#36Passivation layer#38Light transmissive material#40LED chip base#42Light reflective material#44Light transmissive substrate#46Photoluminescence component (film)#48Light transmissive material#50LED chip light emitting face#52Valleys#54Cut lines#56Light transmissive region (layer)#58CSP LED#=Figure number