Patent Application
20110006331
1. Field
The present disclosure relates to a light-emitting device, and more particularly, to a method and an apparatus for light-emitting device arrays.
2. Description of Related Technology
A person skilled in the art will appreciate that the concepts disclosed herein are applicable to packages for semiconductor-based light-emitting device, namely a light-emitting diode (LED) device.
LEDs have been used for many years in various light requiring applications, e.g., signaling states for devices, i.e., light on or off, opto-couplers, displays, replacement of bulbs in flashlights, and other applications known in the art. Consequently, LEDs emitting both spectral colors and white light have been developed. There are two primary approaches to producing light with desired properties using LEDs. One is to use individual LED dice that emit the three primary colors—red, green, and blue, and then mix the colors to produce light with the desired properties. The other approach is to use a phosphor material to convert monochromatic light from a blue or ultra-violet color emitting LED die or dice to a light with the desired properties, much in the same way a fluorescent light bulb works. For the purposes of this disclosure a die has its common meaning of a light-emitting semiconductor chip comprising a p-n junction.
Due to LEDs' advantages, i.e., light weight, low energy consumption, good electrical power to light conversion efficiency, and the like, an increased interest has been recently focused on use of LEDs even for high light intensity application, e.g., replacement of conventional, i.e., incandescent and fluorescent light sources, traffic signals, signage, and other high light intensity applications known to a person skilled in the art. It is customary for the technical literature to use the term “high power LED” to imply high light intensity LED; consequently, such terminology is adopted in this disclosure, unless noted otherwise. To increase intensity of the light emitted by the light-emitting device, often more than one light-emitting die is arranged in a package; such a light-emitting device being termed a light-emitting device array. For the purposes of this disclosure, a package is a collection of components comprising the light-emitting device including but not being limited to: a substrate, a die or dice (if an array), phosphors, encapsulant, bonding material(s), light collecting means, and the like. A person skilled in the art will appreciate that some of the components are optional.
There are three main approaches for coating LED die with phosphor(s): freely dispersed coating, conformal coating, and remote coating. Freely dispersed coating is the oldest method that was developed for white light-emitting LEDs.
The two above-described methods deposit the phosphor layer directly on the die or the plurality of dice surface, thus minimizing LED size. However, experimental results confirmed that due to the close proximity between the die or the plurality of dice surface and the phosphor layer, approximately 50-60% light emitted by the die or the plurality of dice is back-scattered by the phosphor layer. This back scattered light may be absorbed by the die or the plurality of dice; consequently, decreasing the efficiency of light-extraction from the light-emitting device.
The absorption of light by the die or the plurality of dice due to back-scattering may be mitigated by moving the phosphor layer to remote location, i.e., location away from the die or the plurality of dice surface. A conceptual cross-section of such exemplary light-emitting device 300 is depicted in
An encapsulant layer 310 is applied on the surfaces of the dice 304, and after the eneapsulant layer 310 is cured, phosphor 312 is dispersed without any mold restriction into the cavity delimited by the substrate 302 and the reflector 306, where the phosphor 312 flows freely until a surface balance is achieved. As a result of this process, the phosphor layer 312 is normally convex. The thickness of the encapsulant layer 310 controls the distance between the plurality of dice surfaces and the phosphor layer, thus reducing the light absorption and increasing the light extraction since only a small part of the light scattered from the remote phosphor layer 312 reaches the plurality of dice 304. Increased distance also improves color uniformity due to averaging of the light leaving the die, or the plurality of dice 304 surfaces.
The remote phosphor approach described in reference to
To mitigate the thermal management issues, an alternative conceptual cross-section of an exemplary light-emitting device 300 with remote phosphor location is depicted in
Although the configuration disclosed in reference to
Accordingly, there is a need in the art for a light-emitting device providing solution to the above identified problems, as well as additional advantages evident to a person skilled in the art.
In one aspect of the disclosure, a light-emitting device with semi-remote phosphor layer location according to appended independent claims is disclosed. Preferred additional aspects are disclosed in the dependent claims.
The foregoing aspects described herein will become more readily apparent by reference to the following description when taken in conjunction with the accompanying drawings wherein:
Various aspects of the present invention will be described herein with reference to drawings that are schematic illustrations of idealized configurations of the present invention. As such, variations from the shapes of the illustrations as a result, for example, manufacturing techniques and/or tolerances, are to be expected. Thus, the various aspects of the present invention presented throughout this disclosure should not be construed as limited to the particular shapes of elements (e.g., regions, layers, sections, substrates, etc.) illustrated and described herein but are to include deviations in shapes that result, for example, from manufacturing. By way of example, an element illustrated or described as a rectangle may have rounded or curved features and/or a gradient concentration at its edges rather than a discrete change from one element to another. Thus, the elements illustrated in the drawings are schematic in nature and their shapes are not intended to illustrate the precise shape of an element and are not intended to limit the scope of the present invention.
It will be understood that when an element such as a region, layer, section, substrate, or the like, is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present. It will be further understood that when an element is referred to as being “formed” on another element, it can be grown, deposited, etched, attached, connected, coupled, or otherwise prepared or fabricated on the other element or an intervening element.
Furthermore, relative terms, such as “lower” or “bottom” and “upper” or “top,” may be used herein to describe one element's relationship to another element as illustrated in the drawings. It will be understood that relative terms are intended to encompass different orientations of an apparatus in addition to the orientation depicted in the drawings. By way of example, if an apparatus in the drawings is turned over, elements disclosed as being on the “lower” side of other elements would then be oriented on the “upper” side of the other elements. The term “lower” can therefore encompass both an orientation of “lower” and “upper,” depending of the particular orientation of the apparatus. Similarly, if an apparatus in the drawing is turned over, elements described as “below” or “beneath” other elements would then be oriented “above” the other elements. The terms “below” or “beneath” can therefore encompass both an orientation of above and below.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and this disclosure.
As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprise,” “comprises,” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The term “and/or” includes any and all combinations of one or more of the associated listed items.
Various disclosed aspects may be illustrated with reference to one or more exemplary configurations. As used herein, the term “exemplary” means “serving as an example, instance, or illustration,” and should not necessarily be construed as preferred or advantageous over other configurations disclosed herein.
Furthermore, various descriptive terms used herein, such as “on” and “transparent,” should be given the broadest meaning possible within the context of the present disclosure. For example, when a layer is said to be “on” another layer, it should be understood that that one layer may be deposited, etched, attached, or otherwise prepared or fabricated directly or indirectly above or below that other layer. In addition, something that is described as being “transparent” should be understood as having a property allowing no significant obstruction or absorption of electromagnetic radiation in the particular wavelength (or wavelengths) of interest, unless a particular transmittance is provided.
In accordance with one aspect, an exemplary light-emitting device comprises a complex lens. At least one semiconductor die is disposed on a substrate of the light-emitting device. The complex lens is created by forming one first lens comprising a clear transparent material directly on a surface of each one of at least one die, and by forming an outer lens comprising a clear transparent material filled uniformly with phosphor, directly encapsulating the substrate and the at least one die with the formed first lens.
A substantially flat substrate 402 in addition to being a mechanical support is often used as a means for heat dissipation from the light-emitting device. A material is considered to be substantially flat if the irregularities in flatness would not cause light to be reflected by such irregularities. When used in the latter function the substrate 402 is made from a material with high thermal conductivity. Such material may comprise metals, e.g., Al, Cu, Si-based materials, or any other material whose thermal conductivity is appropriate for the light-emitting device in question. A person skilled in the art will appreciate that material appropriate for a light-emitting device with power dissipation of, e.g., 35 milliwatts (mW) is different than material appropriate for a light-emitting device with power dissipation of, e.g., 350 mW.
To improve light extraction from the light-emitting device 400, the surface of the substrate 402 exposed to the light emitted from the plurality of dice 404, i.e., the upper surface, may be treated, to acquire a specific reflectivity. In one aspect, such a treatment may comprise e.g., polishing, buffing, or any other process known to a person skilled in the art. In one aspect, such a treatment comprises polishing, buffing, or any other process known to a person skilled in the art.
In an alternative aspect, the desired reflectivity is achieved by applying a layer of reflective material 418 on the upper surface of the substrate 402. To maximize luminous efficiency, material with high reflectivity, e.g., noble metals like Pt, Au, Ag, or other materials, like Al, are used for this purpose. Reflective layers employing such materials possess predominantly specular reflectivity, unless specific technological process designed to increase diffusive reflectivity is followed.
In yet another aspect, further improvement in luminous efficiency as well as in spatial light distribution may be obtained by employing reflective surfaces possessing diffusive reflectivity. Consequently, in an alternative, the reflective layer 418 comprises a material with high diffusive reflectivity applied onto select region(s) of the upper surface of the substrate 402. As shown in
Although most surfaces poses a mixture of diffuse and specular reflective properties, a person skilled in the art will appreciate that the terms specular and diffuse refer to predominant mode of reflection. Thus, as disclosed above, polished or buffed metallic objects and/or layers of metallic material posses specular reflectivity; matte surfaces posses diffuse reflectivity.
Further details regarding use of reflective surfaces possessing diffusive reflectivity is disclosed in a co-pending application Ser. No. ______, filed on XX/XX/XXXX, entitled REFLECTIVE SURFACE SUB-ASSEMBLY FOR A LIGHT-EMITTING DEVICE.
As depicted in
In an alternative aspect, an over-molding, using, e.g., a prefabricated stainless steel mold form may be used. In accordance with this aspect, exposed surfaces of the die 404 may be covered with the clear transparent material comprising the lens 420, as depicted in
Although the shape of the lens 420 depicted in
Once the plurality of lenses 420 are formed on the upper surface of each of the plurality of dice 404, clear transparent material is mixed with phosphor in a ratio determined by desired optical characteristics, e.g., correlated color temperature (CCT), color rendering index CRI, and other optical characteristics known to a person skilled in the art. It is further desirable that the refractive index of the clear transparent material to be mixed with phosphor should be the same or slightly smaller than the refractive index for the clear transparent material used for the plurality of lenses 420. An outer lens 422 comprising the mixture of the clear transparent material and phosphor is then formed directly encapsulating on a sub-assembly comprising the substrate 402 with the optional upper surface treatment, e.g., reflective layer 418, and the die or the plurality of dice 404 with formed plurality of lenses 420.
The shape of the formed outer lens 422 is determined with design criteria for the light-emitting device 400 and/or technological capabilities of the manufacturer. Accordingly, thermal management, desired distribution of the light emitted by the light-emitting device 400 may be considered as examples of such design criteria.
Regarding the thermal management, an outer lens 422 that has a high surface-to-volume ratio, which, together with the mixture of the clear transparent material and phosphor comprising the outer lens 422 being in contact with the substrate 402 provides thermal management, comparable with the remote phosphor placement on the thermally conductive flat plate like sapphire, as described above in reference to
Regarding the desired distribution of the light, several consideration affect the design of the outer lens 422, e.g., distribution of the light emitted by the individual die or dices 404, shape of the lens(es) 420, scattering effect in the material of the lens 422, shape of the desired illuminated plane, and the like. Consequently, different shapes of the outer lens 422, from simple concave, convex, i.e., hemispherical lens to sophisticated free-formed lens may be required.
The various aspects of this disclosure are provided to enable one of ordinary skill in the art to practice the present invention. Modifications to various aspects of a presented throughout this disclosure will be readily apparent to those skilled in the art, and the concepts disclosed herein may be extended to other applications. Thus, the claims are not intended to be limited to the various aspects of the reflective surfaces for a light-emitting device array presented throughout this disclosure, but are to be accorded the full scope consistent with the language of the claims. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 U.S.C. §112, sixth paragraph, unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited using the phrase “step for.”
