# Patent

## Title
Semiconductor light emitting devices including a luminescent conversion element

## Abstract

Methods of packaging a semiconductor light emitting device include dispensing a first quantity of encapsulant material into a cavity including the light emitting device. The first quantity of encapsulant material in the cavity is treated to form a hardened upper surface thereof having a selected shape. A luminescent conversion element is provided on the upper surface of the treated first quantity of encapsulant material. The luminescent conversion element includes a wavelength conversion material and has a thickness at a middle region of the cavity greater than proximate a sidewall of the cavity.

## Background
RELATED APPLICATION
This application claims the benefit of and priority to U. S. Provisional Patent Application No. 60/558,314, entitled “Reflector Packages and Methods for Forming Packaging of a Semiconductor Light Emitting Device,” filed Mar. 31, 2004, and U.S. Provisional Patent Application No. 60/637,700, entitled “Semiconductor Light Emitting Devices Including a Luminescent Conversion Element and Methods for Packaging the Same,” filed Dec. 21, 2004, the disclosures of which are hereby incorporated herein by reference as if set forth in their entirety.


BACKGROUND OF THE INVENTION
This invention relates to semiconductor light emitting devices and fabricating methods therefore, and more particularly to packaging and packaging methods for semiconductor light emitting devices.
It is known to provide semiconductor light emitting device type light sources in packages that may provide protection, color selection, focusing and the like for light emitted by the light emitting device. For example, the light emitting device may be a light emitting diode (“LED”). Various problems may be encountered during packaging of a power LED for use as a light source. Examples of such possible problems will be described with reference to the cross-sectional illustrations of a power LED in FIGS. 1 and 2. As shown in FIGS. 1 and 2, a power LED package 100 generally includes a substrate member 102 on which a light emitting device 103 is mounted. The light emitting device 103 may, for example, include an LED chip/submount assembly 103b mounted to the substrate member 102 and an LED 103a positioned on the LED chip/submount assembly 103b. The substrate member 102 may include traces or metal leads for connecting the package 100 to external circuitry. The substrate 102 may also act as a heatsink to conduct heat away from the LED 103 during operation.
A reflector, such as the reflector cup 104, may be mounted on the substrate 102 and surround the light emitting device 103. The reflector cup 104 illustrated in FIG. 1 includes an angled or sloped lower sidewall 106 for reflecting light generated by the LED 103 upwardly and away from the LED package 100. The illustrated reflector cup 104 also includes upwardly-extending walls 105 that may act as a channel for holding a lens 120 in the LED package 100 and a horizontal shoulder portion 108.
As illustrated in FIG. 1, after the light emitting device 103 is mounted on the substrate 102, an encapsulant material 112, such as liquid silicone gel, is dispensed into an interior reflective cavity 115 of the reflector cup 104. The interior reflective cavity 115 illustrated in FIG. 1 has a bottom surface defined by the substrate 102 to provide a closed cavity capable of retaining a liquid encapsulant material 112 therein. As further shown in FIG. 1, when the encapsulant material 112 is dispensed into the cavity 115, it may wick up the interior side of the sidewall 105 of the reflector cup 104, forming the illustrated concave meniscus.
As shown in FIG. 2, a lens 120 may then be placed into the reflective cavity 115 in contact with the encapsulant material 112. When the lens 120 is placed in the cavity 115, the liquid encapsulant material 112 may be displaced and move through the gap 117 between the lens 120 and the sidewall 105. The encapsulant may, thus, be moved out onto the upper surface of the lens 120 and/or upper surfaces of the sidewall 105 of the reflector cup 104. This movement, which may be referred to as squeeze-out, is generally undesirable for a number of reasons. In the depicted package arrangement, the lens will sit on a lower shelf if the encapsulant is not cured in a domed meniscus shape prior to the lens attach step. This may cause the lens to not float during thermal cycling and fail via delamination of encapsulation to other surfaces or via cohesive failure within the delamination, both of which may affect the light output. The encapsulant material or gel is generally sticky and may interfere with automated processing tools used to manufacture the parts. Moreover, the gel may interfere with light output from the lens 120, for example, by changing the light distribution pattern and/or by blocking portions of the lens 120. The sticky gel may also attract dust, dirt and/or other contaminants that could block or reduce light output from the LED package 100. The gel may also change the shape of the effective lens, which may modify the emitted light pattern/beam shape.
After placement of the lens 120, the package 100 is typically heat-cured, which causes the encapsulant material 112 to solidify and adhere to the lens 120. The lens 120 may, thus, be held in place by the cured encapsulant material 112. However, encapsulant materials having a slight shrinkage factor with curing, such as a silicone gel, generally tend to contract during the heat curing process. In addition, the coefficient of thermal expansion (CTE) effect generally causes higher floating of the lens at elevated temperatures. During cool-down, parts have a tendency to delaminate. As the illustrated volume of encapsulant beneath the lens 120 shown in FIG. 2 is relatively large, this contraction may cause the encapsulant material 112 to delaminate (pull away) from portions of the package 100, including the light emitting device 103, a surface of the substrate 102, the sidewalls 105 of the reflector cup 104 and/or the lens 120 during the curing process. The delamination may significantly affect optical performance, particularly when the delamination is from the die, where it may cause total internal reflection. This contraction may create gaps or voids 113 between the encapsulant material 112 and the light emitting device 103, lens 120, and/or reflector cup 104. Tri-axial stresses in the encapsulant material 112 may also cause cohesive tears 113′ in the encapsulant material 112. These gaps 113 and/or tears 113′ may substantially reduce the amount of light emitted by the light emitting device package 100. The contraction may also pull out air pockets from crevices (i.e, reflector) or from under devices (i.e., die/submount), which may then interfere with optical cavity performance.
During operation of the lamp, large amounts of heat may be generated by the light emitting device 103. Much of the heat may be dissipated by the substrate 102 and the reflector cup 104, each of which may act as a heatsink for the package 100. However, the temperature of the package 100 may still increase significantly during operation. Encapsulant materials 112, such as silicone gels, typically have high coefficients of thermal expansion. As a result, when the package 100 heats up, the encapsulant material 112 may expand. As the lens 120 is mounted within a channel defined by the sidewalls 105 of the reflector cup 104, the lens 120 may travel up and down within the sidewalls 105 as the encapsulant material 112 expands and contracts. Expansion of the encapsulant material 112 may extrude the encapsulant into spaces or out of the cavity such that, when cooled, it may not move back into the cavity. This could cause delamination, voids, higher triaxial stresses and/or the like, which may result in less robust light emitting devices. Such lens movement is further described, for example, in United States Patent Application Pub. No. 2004/0041222. The sidewalls 105 may also help protect the lens 120 from mechanical shock and stress.
SUMMARY OF THE INVENTION
Embodiments of the present invention provide methods of packaging a semiconductor light emitting device. A first quantity of encapsulant material is dispensed into a cavity including the light emitting device (which may be a plurality of light emitting devices, such as light emitting diodes), which may be a reflective cavity. The first quantity of encapsulant material in the reflective cavity is treated to form a hardened upper surface thereof having a selected shape. A luminescent conversion element is provided on the upper surface of the treated first quantity of encapsulant material. The luminescent conversion element includes a wavelength conversion material, such as phosphor and/or nano-crystals, and has a thickness at a middle region of the reflective cavity greater than at a region proximate a sidewall of the reflective cavity.
The thickness of the luminescent conversion element may continuously decrease as the luminescent conversion element extends radially outward from the middle region to the sidewall. The thickness of the luminescent conversion element may vary by more than ten percent of a maximum thickness of the luminescent conversion element. The luminescent conversion element may have a biconvex, plano-convex or concavo-convex shape.
In other embodiments of the present invention, the methods further include dispensing a second quantity of encapsulant material onto the luminescent conversion element to form a convex meniscus of encapsulant material in the reflective cavity providing a desired shape of a lens. The second quantity of encapsulant material is cured to form the lens for the packaged light emitting device from the encapsulant material. In alternative embodiments, the methods include dispensing a second quantity of encapsulant material onto the luminescent conversion element and positioning a lens in the reflective cavity on the dispensed second quantity of encapsulant material. The dispensed second quantity of encapsulant material is cured to attach the lens in the reflective cavity.
In further embodiments of the present invention, providing a luminescent conversion element includes dispensing a second quantity of encapsulant material onto the upper surface of the first quantity of encapsulant material. The second quantity of encapsulant material has the wavelength conversion material therein. The second quantity of encapsulant material is cured to define the luminescent conversion element.
In some embodiments of the present invention, the luminescent conversion element has a biconvex shape. The selected shape is concave and dispensing and curing the second quantity of encapsulant material includes dispensing and curing the second quantity of encapsulant material to form a convex upper surface of the second quantity of encapsulant material.
In further embodiments of the present invention, the luminescent conversion element has a plano-convex shape and the selected shape is concave. Dispensing and curing the second quantity of encapsulant material includes dispensing and curing the second quantity of encapsulant material to form a planar upper surface of the second quantity of encapsulant material. In alternative plano-convex shape embodiments, the selected shape is planar and dispensing and curing the second quantity of encapsulant material includes dispensing and curing the second quantity of encapsulant material to form a convex upper surface of the second quantity of encapsulant material.
In other embodiments of the present invention, the luminescent conversion element has a concavo-convex shape and the selected shape is convex. Dispensing and curing the second quantity of encapsulant material includes dispensing and curing the second quantity of encapsulant material to form a convex upper surface of the second quantity of encapsulant material. In alternative concavo-convex shape embodiments, the selected shape is concave and dispensing and curing the second quantity of encapsulant material includes dispensing and curing the second quantity of encapsulant material to form a concave upper surface of the second quantity of encapsulant material.
In further embodiments of the present invention, treating the first quantity of encapsulant material includes curing the first quantity of encapsulant material. In alternative embodiments, treating the first quantity of encapsulant material includes pre-curing the first quantity of encapsulant material to form a hardened skin on the upper surface thereof and the method further comprises curing the first quantity of encapsulant material after providing the luminescent conversion element. The wavelength conversion material may be phosphor and the first quantity of encapsulant material is substantially free of phosphor.
In other embodiments of the present invention, the luminescent conversion element is a pre-formed insert and the pre-formed insert is placed on the upper surface of the treated first quantity of encapsulant material. The pre-formed insert may be a molded plastic phosphor-loaded piece part. Placing the pre-formed insert on the upper surface may be preceded by testing the pre-formed insert.
In yet other embodiments of the present invention, packaged semiconductor light emitting devices include a body, such as a reflector, having a lower sidewall portion defining a cavity, which may be a reflective cavity. A light emitting device is positioned in the cavity. A first quantity of cured encapsulant material is provided in the cavity including the light emitting device. A luminescent conversion element is on the upper surface of the first quantity of encapsulant material. The luminescent conversion element includes a wavelength conversion material and has a thickness at a middle region of the cavity greater than at a region proximate a sidewall of the cavity. The thickness of the luminescent conversion element may continuously decrease as the luminescent conversion element extends radially outward from the middle region to the sidewall. The thickness of the luminescent conversion element may vary by more than ten percent of a maximum thickness of the luminescent conversion element.
In some embodiments of the present invention, the luminescent conversion element has a biconvex, plano-convex or concavo-convex shape. The light emitting device may be a light emitting diode (LED).
In other embodiments of the present invention, the device has a minimum color temperature no more than 30 percent below a maximum color temperature thereof over a 180 (+/−90 from central axis)-degree range of emission angles. The device may have a primary emission pattern having a total correlated color temperature (CCT) variation of less than about 1000K over a 180 (+/−90 from central axis)-degree range of emission angles. In other embodiments, the device has a primary emission pattern having a total CCT variation of about 500K over a 180 (+/−90 from central axis)-degree range of emission angles or over a 120 (+/−45 from central axis)-degree range of emission angles. In yet other embodiments, the device has a primary emission pattern having a total correlated color temperature (CCT) variation of less than about 500K over a 90 (+/−45 from central axis)-degree range of emission angles.
In yet further embodiments of the present invention, packaged semiconductor light emitting devices include a body having a sidewall portion defining a cavity and a light emitting device positioned in the cavity. A first quantity of cured encapsulant material is in the cavity including the light emitting device and a luminescent conversion element is on an upper surface of the first quantity of encapsulant material. The luminescent conversion element includes a wavelength conversion material. The packaged semiconductor light emitting device exhibits a variation of correlated color temperature (CCT)) across a 180 (+/−90 from central axis)-degree range of emission angles of less than 2000K.



BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 and 2 are cross-sectional side views illustrating a conventional light emitting device package;
FIGS. 3A to 3C are cross-sectional side views illustrating methods of packaging a light emitting device according to some embodiments of the present invention;
FIG. 4A is a top view illustrating a light emitting device package suitable for use with some embodiments of the present invention;
FIG. 4B is a cross-sectional side view illustrating the light emitting device package of FIG. 4A;
FIG. 5A is a top view illustrating a light emitting device package according to some embodiments of the present invention;
FIG. 5B is a cross-sectional side view illustrating the light emitting device package of FIG. 5A;
FIG. 6 is a cross-sectional side view illustrating a light emitting device package according to further embodiments of the present invention;
FIG. 7 is a cross-sectional side view illustrating a light emitting device package according to other embodiments of the present invention;
FIGS. 8A to 8C are cross-sectional side views illustrating methods of packaging a light emitting device according to further embodiments of the present invention;
FIGS. 9A to 9C are cross-sectional side views illustrating methods of packaging a light emitting device according to other embodiments of the present invention;
FIGS. 10A to 10C are cross-sectional side views illustrating methods of packaging a light emitting device according to yet further embodiments of the present invention;
FIG. 11 is a flowchart illustrating operations for packaging a light emitting device according to some embodiments of the present invention;
FIG. 12 is a flowchart illustrating operations for packaging a light emitting device according to some other embodiments of the present invention;
FIG. 13 is a flowchart illustrating operations for packaging a light emitting device according to yet further embodiments of the present invention;
FIG. 14 is a schematic diagram illustrating path length for light traveling through a layer;
FIG. 15 is a polar plot of color-temperature for a light emitting diode(LED) emission pattern;
FIGS. 16A to 16C are cross-sectional side views illustrating methods of packaging a light emitting device including a luminescent conversion element according to further embodiments of the present invention;
FIGS. 17A to 17C are cross-sectional side views illustrating methods of packaging a light emitting device including a luminescent conversion element according to other embodiments of the present invention;
FIGS. 18A to 18C are cross-sectional side views illustrating methods of packaging a light emitting device including a luminescent conversion element according to some other embodiments of the present invention;
FIG. 19 is a flowchart illustrating operations for packaging a light emitting device according to some further embodiments of the present invention;
FIG. 20A is a polar plot of color-temperature for a light emitting diode (LED) emission pattern for a glob-top semiconductor light emitting device without a luminescence conversion element of the present invention;
FIG. 20B is a polar plot of color-temperature for a light emitting diode (LED) emission pattern for a semiconductor light emitting device with a luminescence conversion element according to some embodiments of the present invention;
FIGS. 21A and 21B are digitally analyzed plots of the near field emission pattern of packaged semiconductor light emitting device without a luminescence conversion element; and
FIGS. 22A and 22B are digitally analyzed plots of the near field emission pattern of packaged semiconductor light emitting device including a luminescence conversion element according to some embodiments of the present invention.



DETAILED DESCRIPTION
The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the size and relative sizes of layers and regions may be exaggerated for clarity. Like numbers refer to like elements throughout.
It will be understood that when an element such as a layer, region or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. It will be understood that if part of an element, such as a surface, is referred to as “inner,” it is farther from the outside of the device than other parts of the element. Furthermore, relative terms such as “beneath” or “overlies” may be used herein to describe a relationship of one layer or region to another layer or region relative to a substrate or base layer as illustrated in the figures. It will be understood that these terms are intended to encompass different orientations of the device in addition to the orientation depicted in the figures. Finally, the term “directly” means that there are no intervening elements. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present invention.
Various embodiments of the present invention for packaging a semiconductor light emitting device 103 will be described herein. As used herein, the term semiconductor light emitting device 103 may include a light emitting diode, laser diode and/or other semiconductor device which includes one or more semiconductor layers, which may include silicon, silicon carbide, gallium nitride and/or other semiconductor materials, a substrate which may include sapphire, silicon, silicon carbide and/or other microelectronic substrates, and one or more contact layers which may include metal and/or other conductive layers. In some embodiments, ultraviolet, blue and/or green light emitting diodes (“LEDs”) may be provided. Red and/or amber LEDs may also be provided. The design and fabrication of semiconductor light emitting devices 103 are well known to those having skill in the art and need not be described in detail herein.
For example, the semiconductor light emitting device 103 may be gallium nitride-based LEDs or lasers fabricated on a silicon carbide substrate such as those devices manufactured and sold by Cree, Inc. of Durham, N.C. The present invention may be suitable for use with LEDs and/or lasers as described in U.S. Pat. Nos. 6,201,262; 6,187,606; 6,120,600; 5,912,477; 5,739,554; 5,631,190; 5,604,135; 5,523,589; 5,416,342; 5,393,993; 5,338,944; 5,210,051; 5,027,168; 5,027,168; 4,966,862 and/or 4,918,497, the disclosures of which are incorporated herein by reference as if set forth fully herein. Other suitable LEDs and/or lasers are described in published U.S. Patent Publication No. US 2003/0006418 A1 entitled Group III Nitride Based Light Emitting Diode Structures With a Quantum Well and Superlattice, Group III Nitride Based Quantum Well Structures and Group III Nitride Based Superlattice Structures, published Jan. 9, 2003, as well as published U.S. Patent Publication No. US 2002/0123164 A1 entitled Light Emitting Diodes Including Modifications for Light Extraction and Manufacturing Methods Therefor. Furthermore, phosphor coated LEDs, such as those described in U.S. application Ser. No. 10/659,241, entitled Phosphor-Coated Light Emitting Diodes Including Tapered Sidewalls and Fabrication Methods Therefor, filed Sep. 9, 2003, the disclosure of which is incorporated by reference herein as if set forth fully, may also be suitable for use in embodiments of the present invention. The LEDs and/or lasers may be configured to operate such that light emission occurs through the substrate. In such embodiments, the substrate may be patterned so as to enhance light output of the devices as is described, for example, in the above-cited U.S. Patent Publication No. US 2002/0123164 A1.
Embodiments of the present invention will now be described with reference to the various embodiments illustrated in FIGS. 3-11. More particularly, some embodiments of a double-cure encapsulation process for use in packaging a light emitting device 103 are illustrated in FIGS. 3A through 3C. Such a double cure encapsulation process may reduce problems associated with shrinkage of encapsulant material during curing. As will be described herein, for some embodiments of the present invention, the double cure process may include three dispense operations and two cure operations. However, it will be understood that more or less dispense operations and cure operations may also be used in packaging the light emitting device in other embodiments of the present invention. As will also be further described herein, embodiments of the present invention also include a multi-dispense operation, leading to a first cure operation followed by another set of dispense and cure operations to attach a lens.
As illustrated in FIG. 3A, a first predetermined amount (quantity) of an encapsulant material, including two encapsulant material portions 112, 114 in the illustrated embodiments, is dispensed within the cavity 115. The encapsulant material 112, 114 may be, for example, a liquid silicon gel, an epoxy or the like. The first portion 112 may be dispensed to wet exposed surface portions of the light emitting device 103, more particularly, the led chip/submount assembly 101 of the light emitting device 103, and the substrate 102. Portions of the reflector cup 104 may also be wet by the initial dispense. In some embodiments of the present invention, the quantity of encapsulant material dispensed as the first portion 112 is sufficient to wet the light emitting device 103 without filling the reflective cavity to a level exceeding the height of the light emitting device 103. In some other embodiments of the present invention, the quantity of encapsulant material dispensed as the first portion 112 is sufficient to substantially cover the light emitting device 103 without forming any air pockets in the encapsulant material 112.
As shown in FIG. 3A, the light emitting device is positioned at about a midpoint 115m of the reflective cavity 115. The encapsulant material may be dispensed from a dispenser 200 at a point 115d displaced from the midpoint 115m towards a sidewall 105 of the reflective cavity 115 so that the encapsulant material 112 is not dispensed directly onto the light emitting device 103. Dispensing encapsulant material 112 directly on the light emitting device 103 may cause trapping of bubbles as the encapsulant material 112 passes over the structure of the light emitting device 103 from above. However, in other embodiments of the present invention, the encapsulant material 112 is dispensed on top of the light emitting device 103 die in addition to or instead of an offset dispense. Dispensing the encapsulant material 112 may include forming a bead of the encapsulant material 112 on an end of a dispenser 200 and contacting the formed bead with the reflective cavity 115 and/or the light emitting device 103 to dispense the bead from the dispenser.
The viscosity and/or other properties of the material used for a dispense may be selected such that, for example, wetting occurs without bubble formation. In further embodiments of the present invention, coatings may be applied to surfaces contacted by the dispensed material to speed/retard the wetting rate. For example, using certain known cleaning procedures that leave microscopic residue, such as an oil film, selected surfaces may be treated and, thus, used to engineer the dynamics of the wetting action.
Due to the surface properties of the inner surface of the reflector cup 104 defining the cavity 115, of the light emitting device 103 and of the encapsulant material 112, dispensed encapsulant material 112, even when dispensed from a point 115d displaced from the midpoint 115m of the cavity 115, may flow within the cavity 115 in a manner that could still cause bubbles in the encapsulant material 112. In particular, the encapsulant material 112 is expected to move or “wick” more rapidly around the inner surface of the reflector cup 104 and the sidewalls of the light emitting device 103 faster than over the top of the light emitting device 103. As a result, a bubble could be trapped on a side of the cavity 115 opposite from the side where the encapsulant material is dispensed when the side flowing encapsulant material meets and then encapsulant material flows over the top of the light emitting device 103, thus being locally dispensed from above with no side outlet for air flow. Accordingly, the quantity of the first portion of dispensed encapsulant material 112 may be selected to reduce or prevent the risk of forming such bubbles. As such, as used herein, reference to “substantially” covering the light emitting device 103 refers to covering enough of the structure of the light emitting device 103 so that such a bubble will not result when the remaining portion 114 of the first quantity of encapsulant material 112, 114 is dispensed.
After the initially dispensed encapsulant material 112 is allowed to settle, the second portion 114 of the first predetermined quantity of encapsulant material is dispensed into the reflective cavity 115. The second portion 114 of the encapsulant material, in some particular embodiments of the present invention, is about twice the first portion 112.
After dispensing all the first quantity of encapsulant material 112, 114, the first quantity of the encapsulant material 112, 114 is cured, for example, by a heat treatment, to solidify the encapsulant material 112, 114. After curing, the level of the encapsulant material 112, 114 within the reflective cavity 115 may drop from the level 114A to the level 114B as a result of shrinkage of the encapsulant material 112, 114.
In some embodiments of the present invention, the first portion 112 is cured before the second portion 114 is dispensed into the reflective cavity 115. For example, it is known to add a light converting material, such as a phosphor, nano-crystals, or the like, to the encapsulant material 112, 114 to affect the characteristics of the light emitted from the package 100. For purposes of the description herein, references will be made to a phosphor as a light converting material. However, it will be understood that other light converting materials may be used in place of phosphor. Depending on the desired color spectrum and/or color temperature tuning for the package 100, phosphor may be most beneficially utilized when positioned adjacent the emitter 103b, in other words, directly on top of the light emitting device 103. As such, it may be desirable to include a phosphor in the second portion 114 while not including a phosphor in the first portion 112. However, as the first portion 112 is below the second portion 114, phosphor may settle from the second portion 114 into the first portion 112, reducing the effectiveness of the phosphor addition in the second portion 114. Accordingly, phosphor can be added to the first portion 112 to limit such settling and/or the first portion 112 can be cured before dispensing the second portion 114. The use of multiple dispenses may also allow the addition of a phosphor preform/wafer of a desired configuration for light conversion. In addition, multiple dispenses may allow for the use of materials having different indexes of refraction to provide, for example, a buried lens (i.e., formed by the interface between two dispenses of materials with different refractive indexes).
As illustrated in FIG. 3B, a second quantity of encapsulant material 116 is dispensed in a predetermined amount onto the cured first quantity of encapsulant material 112, 114 in the reflective cavity 115. In some particular embodiments of the present invention the second quantity 116 is about equal to the first portion 112 of the first quantity of encapsulant material 112, 114. The second quantity 116 may be substantially free of phosphor, however, in other embodiments of the present invention, phosphor may also be included in the second quantity 116.
As shown in FIG. 3C, before the second quantity of encapsulant material 116 is cured, a lens 120 is positioned within the reflective cavity 115 and against the second quantity of encapsulant material 116. The second quantity of encapsulant material 116 is then cured, for example, by heating, to harden the encapsulant material 116 and to attach the lens 120 in the reflective cavity 115. In some embodiments of the present invention, use of a double cure process as described above to encapsulate the light emitting device 103 in the package 100 may reduce delamination of the cured encapsulant material 112, 114, 116 from the light emitting device 103, the lens 120 and/or the reflector cup 104.
The reflector cup 104 shown in FIGS. 3A-3B is further illustrated in FIGS. 4A-4B. FIG. 4A is a top plan view of the reflector cup 104 showing the top surfaces of the upper sidewall 105, the lower sidewall 106 and a substantially horizontal shoulder sidewall portion 108 between the upper sidewall 105 and the lower sidewall 106. FIG. 4B is a cross-sectional view of the reflector cup 104 taken along line B-B of FIG. 4A.
Alternative reflector cup configurations according to various embodiments of the present invention will now be described as well as methods for packaging of a light emitting device using such alternative reflector cup configurations. In various embodiments of the present invention, these alternative reflector cup configurations may reduce the incidence and/or amount of squeeze out of encapsulant material on insertion of a lens into encapsulant material in the reflector cup. FIGS. 5A-5B, 6 and 7 illustrate various alternative reflector configurations as will now be described. FIG. 5A is a top plan view of a reflector cup 4 and FIG. 5B is a cross-sectional view of the reflector cup 4 taken along line B-B of FIG. 5A. FIG. 6 is a cross-sectional view of a reflector cup 4A and FIG. 7 is a cross-sectional view of a reflector cup 4B. Each of the illustrated reflector cups 4, 4A, 4B includes an upper sidewall 5, an angled lower sidewall 6 and a horizontal shoulder portion 8 between the upper sidewall 5 and the lower sidewall 6, together defining a reflective cavity 15. As used herein with reference to the shoulder portion 8, “horizontal” refers to the general direction in which the shoulder portion 8 extends between the lower sidewall portion 6 and the upper sidewall portion 8 (i.e., as compared to the lower 6 and upper 5 sidewall portions), not to the particular angle of the shoulder portion 8 at any intermediate portion thereof (see, e.g., FIG. 7 where the horizontal shoulder portion may actually have some change in vertical height between the lower 6 and upper 5 sidewall portions to accommodate other features thereof). In addition, each of the reflector cups 4, 4A, 4B may include at least one moat 18 surrounding the lower sidewall 6, with the moat 18 being separated from the lower sidewall 6 by a lip (i.e., a projecting edge) 22. The moat 18 is illustrated as formed in the shoulder portion 8.
In the embodiments of FIGS. 5A-5B, the moat 18 could be formed by stamping, in which case the lip 22 between the moat 18 and the lower sidewall 6 may be provided with a sharp edge instead of a flat surface. However, it will be understand that, due to the limitations of the fabricating processes used, the flat surface of the lip 22 schematically illustrated in FIG. 5B may actually have a more rounded profile. Too much of a rounded profile may be undesirable as will be further described with reference to FIGS. 8A-8C.
Further embodiments of a reflector cup 4A will now be described with reference to the cross-sectional view of FIG. 6. As shown in FIG. 6, a first moat 18 is formed between the upper sidewall 5 and the lower sidewall 6, with a first or inner lip 22 separating the lower sidewall 6 and the first moat 18. A second moat 24 is formed between the upper sidewall 5 and the first moat 18. A second or outer lip 26 separates the second moat 24 from the first moat 18.
Yet further embodiments of a reflector cup 4B will now be described with reference to the cross-sectional view of FIG. 7. As shown in FIG. 7, a first moat 18 is formed between the upper sidewall 5 and the lower sidewall 6, with a first or inner lip 22 separating the lower sidewall 6 and the first moat 18. A second moat 24 is formed between the upper sidewall 5 and the first moat 18. A second or outer lip 26′ separates the second moat 24 from the first moat 18. As illustrated in FIG. 7, the second lip 26′ is elevated with respect to the first lip 22.
In particular embodiments of the present invention, the first lip 22 has a peak having a radius of curvature of less than about 50 micrometers (μm) and the second lip 26, 26′ has a peak having a radius of curvature of less than about 50 μm. The first moat 18 and the second moat 24 may be stamped features of the horizontal shoulder portion 8. As shown in FIGS. 6 and 7, the second moat 24 may have a width extending from the second lip 26, 26′ to the upper sidewall portion 5.
In some embodiments of the present invention, the sloped lower sidewall portion 6 may be substantially conical and may have a minimum diameter of from about 1.9 millimeters (mm) for a 500 μm light emitting device chip to about 3.2 mm for a 900 μm light emitting device chip and a maximum diameter of from about 2.6 mm for a 500 μm light emitting device chip to about 4.5 mm for a 900 μm light emitting device chip and a height of from about 0.8 mm to about 1.0 mm. The upper sidewall portion may be substantially oval and have an inner diameter of from about 3.4 mm to about 5.2 mm and a height of from about 0.6 mm to about 0.7 mm. The horizontal shoulder portion may have a width from the lower sidewall portion to the upper sidewall portion of from about 0.4 mm to about 0.7 mm. It will be understood that, as used herein, the terms “oval” and “conical” are intended to encompass circular, cylindrical and other shapes, including irregular shapes based on the fabrication technology used to form the reflector cup 4, 4A, 4B that may, nonetheless, in combination with a substrate 2 or otherwise, operate to provide a reflector for the light emitting device 103 and retain and harden an encapsulant material 12, 14, 16 therein.
In some embodiments of the present invention, the first moat 18 has a width from about 0.3 mm to about 0.4 mm and the second moat 24 has a width of from about 0.3 mm to about 0.4 mm. As illustrated in FIG. 6, the edge of the first moat 18 may be a first lip 22 having a height relative to a bottom end (i.e., a top surface of the substrate 2) of the lower sidewall portion 6 of from about 0.79 mm to about 0.85 and the edge of the second moat 24 may be a second lip 26 having a height relative to bottom end of the lower sidewall portion 6 of from about 0.79 mm to about 0.85 mm. In other embodiments of the present invention as illustrated in FIG. 7, the first lip 22 has a height relative to a bottom end of the lower sidewall portion of from about 0.79 mm to about 0.85 mm and the second lip 26′ has a height relative to a bottom end of the lower sidewall portion of from about 0.9 mm to about 1.0 mm.
The reflector cups 4, 4A, 4B, in various embodiments of the present invention may, provide for meniscus control when packaging the light emitting device 103 in a reflector cup 4, 4A, 4B. As will be further described, when combined with the double cure methods described above, a distinct convex meniscus may also be provided for different dispenses of encapsulant material and, as a result, the incidence of doming failure may be reduced. In other embodiments of the present invention, the provided meniscus control may reduce the difficulty of lens placement at a desired depth and/or angle, reduce lens wicking or squeeze-out of encapsulant material onto the top of the lens and/or allow for configuration of the optical characteristics of the packaged light emitting device. For example, phosphor may be concentrated in the center (midpoint) of the package by doming (convex meniscus) of phosphor loaded encapsulant material over the midpoint of the package.
Different optical patterns (viewing angles, custom color spectrums, color temperature tuning and the like) may be provided by using multiple meniscus control techniques in combination with dispensing and/or curing variations in the process. For example, a high peaked dome of a phosphor loaded material may provide greater color spectrum uniformity of white temperature light emission with less shift to yellow towards the edges of the reflector cup by providing a more uniform length of the light path through the phosphor loaded material from the light emitting device. Similarly, where desired, a greater color spectrum variation from white at the midpoint to yellow at the edges may be provided by a flatter dome. In some other embodiments of the present invention, where protection related functionality is provided by features other than a lens, meniscus control may allow for packaging a light emitting device without a lens by using the encapsulant material as the lens, with the meniscus being configured to provide the desired lens shape.
FIGS. 8A-8C illustrate methods of packaging a light emitting device, using the structural characteristics of a reflector cup for meniscus control, according to some embodiments of the present invention. The operations illustrated in FIGS. 8A-8C utilize the reflector cup 4 illustrated in FIGS. 5A-5B and the double curing operations also previously described. As shown in FIG. 8A, a first quantity 14 of encapsulant material is deposited in the reflective cavity 15 of the package 10A. In some embodiments of the present invention, the first quantity 14 may be dispensed using a separate (wetting) dispense and second dispense. With proper control of the amount of encapsulant material dispensed, surface tension will cause the liquid encapsulant material 14 to cling to the lip 22, forming a convex meniscus as illustrated in FIG. 8A at a height indicated at 14A. Thus, the lip 22 may be used to prevent the dispensed encapsulant material 14 from contacting and wicking up the upper sidewall 5 and forming a concave meniscus as shown in FIG. 1.
The dispensed encapsulant material 14 is cured, for example, by heating, and may shrink down to a height indicated at 14B. As shown in FIG. 8B, a second quantity 16 of encapsulant material is then dispensed into the cavity 15 on the cured first quantity 14 of encapsulant material. In some embodiments, as illustrated in FIG. 8B, the second quantity 16 of encapsulant material may also cling to the same edge of the lip 22 to form a convex meniscus. In other embodiments, the lip 22 may have an inner and outer edge thereon and the second quantity 16 of encapsulant material may cling to the outer edge and the first quantity 14 may cling to the inner edge. Thus, the second quantity 16 of encapsulant material may also not contact or wick up the upper sidewall 5 to form a concave meniscus.
Referring to FIG. 8C, the lens 20 is inserted into reflective cavity 15 and brought into contact with the uncured liquid encapsulant material 16. As such, the encapsulant material 16 may be squeezed out from underneath the lens 20. However, in some embodiments of the present invention, instead of squeezing out onto the exposed upper surfaces of the reflector cup and the lens (as shown in FIG. 2), the excess of the encapsulant material 16 is squeezed into and received by the moat 18, thus limiting wicking of the encapsulant material 16 up the sidewall 5 even after the lens 20 is inserted and the convex meniscus shown in FIG. 8B is displaced. The encapsulant material 16 is then cured to attach the lens 20 in the package 10A and to solidify the encapsulant material 16.
FIGS. 9A-9C illustrate methods of packaging a light emitting device, using the structural characteristics of a reflector cup for meniscus control, according to some embodiments of the present invention. The operations illustrated in FIGS. 9A-9C utilize the reflector cup 4A illustrated in FIG. 6 and the double curing operations also previously described. As shown in FIG. 9A, a first quantity 14 of encapsulant material is deposited in the reflective cavity 15 of the package 10B. In some embodiments of the present invention, the first quantity 14 may be dispensed using a distinct first (wetting) dispense and a second dispense after wetting of the light emitting device. With proper control of the amount of encapsulant material dispensed, surface tension will cause the liquid encapsulant material 14 to cling to the inner lip 22, forming a convex meniscus as illustrated in FIG. 9A at a height indicated at 14A. Thus, the inner lip 22 may be used to prevent the dispensed encapsulant material 14 from contacting and wicking up the upper sidewall 5 and forming a concave meniscus as shown in FIG. 1.
The dispensed encapsulant material 14 is cured, for example, by heating, and may shrink down to a height indicated at 14B. As shown in FIG. 9B, a second quantity 16 of encapsulant material is then dispensed into the reflective cavity 15 on the cured first quantity 14 of encapsulant material. In some embodiments, as illustrated in FIG. 9B, the second quantity 16 of encapsulant material clings to the outer lip 26, forming a convex meniscus. Thus, the outer lip 26 may be used to prevent the dispensed second quantity 16 of encapsulant material from contacting and wicking up the upper sidewall 5 and forming a concave meniscus as shown in FIG. 1.
Referring to FIG. 9C, the lens 20 is inserted into reflective cavity 15 and brought into contact with the uncured liquid encapsulant material 16. As such, the encapsulant material 16 may be squeezed out from underneath the lens 20. However, in some embodiments of the present invention, instead of squeezing out onto the exposed upper surfaces of the reflector cup and the lens (as shown in FIG. 2), the excess of the encapsulant material 16 is squeezed into and received by the second moat 24, thus limiting wicking of the encapsulant material 16 up the sidewall 5 even after the lens 20 is inserted and the convex meniscus shown in FIG. 9B is displaced. The encapsulant material 16 is then cured to attach the lens 20 in the package 10B and to solidify the encapsulant material 16.
FIG. 9C further illustrates that, in some embodiments of the present invention, the cured encapsulant 14 may be used as a stop to provide for level (depth of placement) control for the lens 20. Such control over the positioning of the lens 20 may facilitate the production of parts with more consistent optical performance.
As shown in FIG. 9C, the lens 20 in some embodiments of the present is positioned without advancing into the cavity until it contacts the cured first quantity of encapsulant material 14 as a film of the encapsulant material 16 remains therebetween. Thus, in some embodiments of the present invention, the device is configured so that the lens 20 may be advanced to a position established by the first quantity of encapsulant material 14, which position may be established with or without contact of the lens 20 to the cured encapsulant material 14 in various embodiments of the present invention.
FIGS. 10A-10C illustrate methods of packaging a light emitting device, using the structural characteristics of a reflector cup for meniscus control, according to some embodiments of the present invention. The operations illustrated in FIGS. 10A-10C utilize the reflector cup 4B illustrated in FIG. 7 and the double curing operations also previously described. As shown in FIG. 10A, a first quantity 14 of encapsulant material is deposited in the reflective cavity 15 of the package 10C. In some embodiments of the present invention, the first quantity 14 may be dispensed using a separate (wetting) dispense and a second dispense. With proper control of the amount of encapsulant material dispensed, surface tension will cause the liquid encapsulant material 14 to cling to the inner lip 22, forming a convex meniscus as illustrated in FIG. 10A at a height indicated at 14A. Thus, the inner lip 22 may be used to prevent the dispensed encapsulant material 14 from contacting and wicking up the upper sidewall 5 and forming a concave meniscus as shown in FIG. 1.
The dispensed encapsulant material 14 is cured, for example, by heating, and may shrink down to a height indicated at 14B. As shown in FIG. 10B, a second quantity 16 of encapsulant material is then dispensed into the reflective cavity 15 on the cured first quantity 14 of encapsulant material. In some embodiments, as illustrated in FIG. 10B, the second quantity 16 of encapsulant material clings to the outer lip 26′, forming a convex meniscus. Thus, the outer lip 26′ may be used to prevent the dispensed second quantity 16 of encapsulant material from contacting and wicking up the upper sidewall 5 and forming a concave meniscus as shown in FIG. 1.
Referring to FIG. 10C, the lens 20 is inserted into reflective cavity 15 and brought into contact with the uncured liquid encapsulant material 16. As such, the encapsulant material 16 may be squeezed out from underneath the lens 20. However, in some embodiments of the present invention, instead of squeezing out onto the exposed upper surfaces of the reflector cup and the lens (as shown in FIG. 2), the excess of the encapsulant material 16 is squeezed into and received by the second moat 24, thus limiting wicking of the encapsulant material 16 up the sidewall 5 even after the lens 20 is inserted and the convex meniscus shown in FIG. 10B is displaced. The encapsulant material 16 is then cured to attach the lens 20 in the package 10C and to solidify the encapsulant material 16.
FIG. 10C further illustrates that, in some embodiments of the present invention, the outer lip 26′ may be used as a stop to provide for level (depth of placement) control for the lens 20. Such control over the positioning of the lens 20 may facilitate the production of parts with more consistent optical performance. In this embodiment, the lens placement does not depend on the amount of shrinkage of the encapsulant during the first cure step. For the embodiments illustrated in FIG. 10C, as contrasted with those illustrated in FIG. 9C, the placement of the lens 20 need not be dependent on the amount of shrinkage of the first quantity 14 of encapsulant material as the placement depth is, instead, defined by the height of the outer lip 26′. As such, in some embodiments of the present invention, the placement may be more exact, which may result in improved optical performance of the package 10C.
Methods for packaging a light emitting device using a first (wetting) dispense according to some embodiments of the present invention will now be further described with reference to the flowchart illustrations of FIG. 11. As shown in FIG. 11, operations may begin at Block 1100 by mounting the light emitting device on a bottom surface of a reflective cavity. The mounted light emitting device has an associated height relative to the bottom surface of the reflective cavity. A first quantity of encapsulant material is dispensed into the reflective cavity including the light emitting device (Block 1120).
The first quantity may be sufficient to substantially cover the light emitting device without forming any air pockets in the encapsulant material. In some embodiments of the present invention, the first quantity may be sufficient to wet the light emitting device without filling the reflective cavity to a level exceeding the height of the light emitting device. In other embodiments of the present invention, the time/speed of dispense of the encapsulant material may be changed to reduce the formation of air pockets in the encapsulant material. In yet further embodiments, a single dispense may be used, for example, with a slow dispense rate, from a small dispense needle, low pressure, or the like, allowing an air pocket to potentially form and then cave/collapse before enough encapsulant material has been dispensed to prevent collapse of the air pocket. Thus, the first (wetting) dispense and second dispense may be provided by a continuous dispense at a selected rate of a selected viscosity encapsulant material that allows cave/collapse of a formed air pocket during the dispense operation The first quantity may be sufficient to wet the light emitting device without filling the reflective cavity to a level exceeding the height of the light emitting device.
A second quantity of encapsulant material is dispensed onto the first quantity of encapsulant material (Block 1130). The dispensed first and second quantity of encapsulant material are then cured (Block 1140). In some embodiments of the present invention, the first dispensed wetting quantity of encapsulant material may be cured before the remainder of the encapsulant material is dispensed.
The first quantity 12, 14 and the second quantity 16 of the encapsulant material may be the same or different materials. Similarly, the first 12 and second 14 portions of the first quantity of the encapsulant material may be the same or different materials. Examples of materials that may be used as an encapsulant material in various embodiments of the present invention include silicon.
Operations related to packaging a semiconductor light emitting device according to some embodiments of the present invention using meniscus control will now be described with reference to the flowchart illustration of FIG. 12. As shown in FIG. 12, operations may begin at Block 1200 with mounting of the light emitting device 103 in a reflective cavity 15 of a reflector 5. Encapsulant material is dispensed into the reflective cavity 15 including the light emitting device 103 therein to cover the light emitting device 103 and to form a convex meniscus of encapsulant material in the reflective cavity extending from an edge of the moat without contacting the upper sidewall 5 of the reflector 4, 4A, 4B (Block 1210). More generally, operations at Block 1210 provide for formation of a convex meniscus extending from an outer edge of the meniscus that is at a height positioning the outer edge of the meniscus within the reflective cavity 15. For example, selection of materials used for the upper sidewall 5 and the encapsulant material 12, 14, 16 may facilitate formation of a convex, rather than concave, meniscus extending into the reflective cavity 15. The encapsulant material 12, 14, 16 is in the reflective cavity 15 (Block 1220). In embodiments where a lens 20 is included in the package 10A, 10B, 10C, insertion of the lens 20 may include collapsing the convex meniscus and moving a portion of the encapsulant material 12, 14, 16 into the moat 18, 24 with the lens 20 and then curing the encapsulant material 12, 14, 16 to attach the lens 20 in the reflective cavity 15. Alternatively, the encapsulant material 12, 14, 16 may be cured to form a lens for the packaged light emitting device 103 from the encapsulant material 12, 14, 16 and the encapsulant material 12, 14, 16 may be dispensed to form a convex meniscus providing a desired shape of the lens.
Embodiments of methods of packaging a semiconductor light emitting device 103 in a reflector 4, 4A, 4B having a moat 18, 24 positioned between a lower 6 and an upper 5 sidewall thereof, the upper 5 and lower 6 sidewall defining a reflective cavity 15, using a multiple dispense and/or cure operation will now be further described with reference to FIG. 13. As shown in the embodiments of FIG. 13, operations begin at Block 1300 by dispensing a first quantity 14 of encapsulant material into the reflective cavity 15 to form a first convex meniscus. The first quantity 14 of encapsulant material is cured (Block 1310). A second quantity 16 of encapsulant material is dispensed onto the cured first quantity 14 of encapsulant material to form a second convex meniscus of encapsulant material in the reflective cavity 15 extending from an edge of the moat 18, 24 without contacting the upper sidewall 5 of the reflector 4, 4A, 4B (Block 1320).
The second convex meniscus and the first convex meniscus of encapsulant material may both extend from the same edge of the moat 18 as illustrated in FIG. 8B. However, in other embodiments of the present invention, the moat 18, 24 may have an inner edge and an outer edge, such as the first lip 22 and the second lip 26, 26′, and the second convex meniscus of encapsulant material extends from the outer edge (second lip 26, 26′)of the moat 18, 24 and the first convex meniscus of encapsulant material extends from the inner edge (first lip 22) of the moat 18, 24. Thus, using the first lip 22, the inner moat 18 may be configured to limit wicking of encapsulant material 14 outwardly along the horizontal shoulder portion 8 to allow formation of a first convex meniscus of encapsulant material dispensed into the reflective cavity 15. Using the second lip 26, 26′, the outer moat 24 may be configured to limit wicking of encapsulant material outwardly along the horizontal shoulder portion 8 to allow formation of a second convex meniscus of encapsulant material dispensed into the reflective cavity 15.
In some embodiments of the present invention including a lens, the lens 20 is positioned in the reflective cavity 15 proximate the dispensed second quantity 16 of encapsulant material (Block 1330). Positioning the lens 20 may include collapsing the second convex meniscus and moving a portion of the second quantity 16 of encapsulant material into the outer moat 24 with the lens 20 as illustrated in FIGS. 9C and 10C. In addition, as illustrated in FIG. 10C, the second lip 26′ may have a height greater than that of the first lip 22. The height of the second lip 26′ may be selected to provide a desired position for the lens 20 and the lens 20 may be moved into the reflective cavity 15 until it contacts the second lip 26′. In other embodiments of the present invention, as illustrated in FIG. 9C, the lens 20 is advanced into the reflective cavity 15 until it contacts the cured first quantity 14 of encapsulant material and the dispensed first quantity 14 of encapsulant material sufficient to establish a desired position for the lens 20 in the reflective cavity 15. The dispensed second quantity 16 of encapsulant material is cured to attach the lens 20 in the reflective cavity 15 (Block 1340).
The flowcharts of FIGS. 11-13 and the schematic illustrations of FIGS. 8A-8C, 9A-9C and 10A-10C illustrate the functionality and operation of possible implementations of methods for packaging a light emitting device according to some embodiments of the present invention. It should be noted that, in some alternative implementations, the acts noted in describing the figures may occur out of the order noted in the figures. For example, two blocks/operations shown in succession may, in fact, be executed substantially concurrently, or may be executed in the reverse order, depending upon the functionality involved.
As discussed above, different optical patterns (viewing angles, custom color spectrums, color temperature tuning and the like) may be provided by using multiple meniscus control techniques in combination with dispensing and/or curing variations in the process. For example, a high peaked dome of a phosphor loaded material may provide greater color spectrum uniformity of white temperature light emission with less shift to yellow towards the edges of the reflector cup by providing a more uniform length of the light path through the phosphor loaded material from the light emitting device.
Embodiments of the present invention provide one or more light emitting devices (i.e. chips) mounted in an optical cavity with a phosphor-loaded luminescent conversion layer formed in proximity to the light emitting device (i.e. adjacent or in a spaced relationship thereto). Conventional packaging technology teaches that the luminescent conversion layer should have a thickness variation less than or equal to ten percent (10%) of the average thickness of the luminescent conversion layer. However, such a requirement means that light emission from the optical cavity may travel substantially different path lengths through the luminescent conversion layer depending on the angle of emission, resulting in non-uniform wavelength conversion (and therefore non-uniform correlated color temperature or CCT) as a function of viewing angle. For example, light traveling in a direction normal to a luminescent conversion layer having a thickness t will travel through the luminescent conversion layer by a path length (PL) equal to t, the shortest possible path length. However, as shown schematically in FIG. 14, light emitted by a light emitting device 103 and passing through the luminescent conversion layer at an angle of incidence α has a path length equal to the thickness t divided by the cosine of the angle of incidence. Thus, for example, light passing through a luminescent conversion layer at an angle of incidence of 60° would travel through the layer by a path length that is twice the path length of light traveling in a normal direction. FIG. 15 is a polar plot of an emission pattern showing substantial sidelobes at off-axis angles of emission that may result from a conventional glob-top type semiconductor light emitting device including a light emitting diode (LED).
The methods disclosed herein for meniscus control may be employed to form a shaped luminescent conversion region or element that may result in improved color uniformity. Improved color uniformity may be quantified, for example, by improved angular uniformity of correlated color temperature or reduced variation in CCT across all viewing angles. Alternatively, the improved uniformity is evidenced by near field optical measurements as a reduced spatial CCT variation across the emission surface of the LED.
In some embodiments, a phosphor-loaded luminescent conversion region or element is characterized by a non-uniform thickness that is greater in the middle of the optical cavity and smaller near the sidewalls of the optical cavity. In some embodiments, a phosphor-loaded luminescent conversion region or element is thickest at the center of the optical cavity and becomes thinner as it extends radially outward toward the edge of the luminescent conversion region. In some embodiments, the thickness variation of the phosphor-loaded luminescent conversion region is greater than 10% of the maximum thickness of the luminescent conversion region. In some embodiments, the luminescent conversion region or element is shaped in the form of a biconvex, plano-convex or concavo-convex region. In some embodiments, the luminescent conversion element comprises a pre-formed structure, such as a molded plastic phosphor-loaded piece part, that is inserted into the reflective cavity of the package.
Embodiments of the invention in which the phosphor-loaded region is shaped to provide improved color uniformity are shown in FIGS. 16A-16C, which illustrate methods of packaging a light emitting device and resulting devices using the structural characteristics of a reflector cup for meniscus control. The operations illustrated in FIGS. 16A-16C utilize the reflector cup 4 illustrated in FIGS. 5A-5B and multiple curing operations similar to those previously described. As shown in FIG. 16A, a first quantity 14 of encapsulant material is deposited in the reflective cavity 15 of the package 10. In some embodiments of the present invention, the first quantity 14 may be dispensed using a separate (wetting) pre-dispense followed by another dispense. With proper control of the amount of encapsulant material dispensed, surface tension will cause the liquid encapsulant material 14 to cling to the lip 22, forming a meniscus as illustrated in FIG. 16A at a height indicated at 14A. The initial meniscus formed by encapsulant material 14 may be concave, convex or substantially flat as illustrated in FIG. 16A.
The dispensed encapsulant material 14 is cured, for example, by heating, and may shrink down to a lower height indicated at 14B. In the illustrated embodiment, the cured encapsulant material 14 shrinks down to form a concave surface 14C, which in three dimensions may be substantially bowl-shaped (i.e. lowest in the center and sloping radially upwards). In some embodiments (in particular embodiments in which the first encapsulant material 14 is dispensed to form a concave surface prior to curing), the encapsulant material 14 may be pre-cured, i.e. exposed to a lower temperature or for shorter cure times, such that the encapsulant material does not completely solidify but rather merely forms a solid “skin” over its surface. The purpose of forming the skin is to prevent subsequently dispensed encapsulant material from intermixing with the first encapsulant material 14. Subsequent encapsulant dispenses may contain wavelength conversion materials (such as phosphors) and, as discussed above, it may be desirable for the phosphor-loaded luminescent conversion region to retain a characteristic shape rather than becoming intermixed with the first encapsulant material 14. Subjecting the first encapsulant layer 14 to a pre-cure instead of a full cure may speed the manufacturing process and may result in an improved interface between the first encapsulant material and subsequent encapsulant regions.
As shown in FIG. 16B, a second quantity 16 of encapsulant material is then dispensed into the cavity 15 onto bowl-shaped surface 14C. The second encapsulant material 16 includes a luminescent wavelength conversion material, such as a phosphor, in the illustrated embodiments. In some embodiments, the first encapsulant material 14 includes no luminescent wavelength conversion material. In other embodiments, the first encapsulant material 14 includes a lower concentration of luminescent wavelength conversion material than the second encapsulant material 16.
In some embodiments, as illustrated in FIG. 16B, the second encapsulant material 16 may also cling to the same edge of the lip 22 to form a convex meniscus. The second encapsulant material 16 is then cured (along with the first encapsulant material 14 if the first encapsulant material 14 was only pre-cured before the second encapsulant material 16 was dispensed). In some embodiments, the second encapsulant material 16 may also be pre-cured, i.e. exposed to a lower temperature or for shorter cure times, in order to prevent or reduce the risk of subsequently dispensed encapsulant material from intermixing with the second encapsulant material 16. However, in other embodiments, the second encapsulant material 16 may be more fully cured in order to solidify the material before the lens 20 is inserted into the cavity 15. As discussed below, once solidified, the second encapsulant material 16 may act as a mechanical stop to assist with correct placement of the lens 20.
The resulting cured (or pre-cured) second encapsulant material 16 defines a luminescent conversion element 19 characterized by a non-uniform thickness that is greatest near the center of the optical cavity and that decreases radially towards the outer edge of the luminescent conversion element 19. In the illustrated embodiment, the luminescent conversion element 19 is a bi-convex structure including a convex upper surface 19A and a convex lower surface 19B.
As mentioned above, while it is possible to form the luminescent conversion element 19 using the meniscus control methods described herein, in other embodiments, the luminescent conversion element 19 may be a pre-formed phosphor-loaded insert that is placed within the reflective cavity 15 of the package 10. Such a structure may have some advantages for device performance and manufacturability. In particular, forming the luminescent conversion element 19 as a pre-formed insert may result in improved quality control as the pre-formed inserts may be individually tested before insertion. In addition, by forming the phosphor-loaded luminescent conversion element 19 as a pre-formed insert, liquid phosphor-loaded material does not have to be used in the final assembly process. This can provide benefits, as phosphor-loaded material can be abrasive and can interfere with the operation of automated machinery. Finally, a cure step may be avoided by forming the phosphor-loaded luminescent conversion element 19 as a pre-formed insert.
In further embodiments, a transparent, convex hemispherical mold (not shown) may be placed over first encapsulant 14 before or after it is cured in order to receive the second encapsulant 16. Upon curing, the second encapsulant 16 will take the shape of the convex hemispherical mold, which may provide improved control over the final shape of the luminescent conversion element 19.
After formation or insertion of the luminescent conversion element 19, a quantity of a third encapsulant material 17 is dispensed within the cavity 15 as further illustrated in FIG. 16B. The third encapsulant material 17 may be an optically transparent material, such as silicone or epoxy, with no luminescent conversion material or a low concentration of luminescent conversion material. Because the third encapsulant material 17 is dispensed following a cure or pre-cure step, the phosphor conversion material embedded in luminescent conversion element 19 may not substantially intermix with the third encapsulant material 17.
In some embodiments, as illustrated in FIG. 16B, the lip 22 may have an inner and outer edge thereon and the third quantity 17 of encapsulant material may cling to the outer edge of the lip 22, forming a convex meniscus above luminescent conversion element 19. Thus, the third encapsulant material 17 may also not contact or wick up the upper sidewall 5 to form a concave meniscus.
Referring to FIG. 16C, the lens 20 is inserted into reflective cavity 15 and brought into contact with the uncured liquid third encapsulant material 17. As such, the third encapsulant material 17 may be squeezed out from underneath the lens 20. However, in some embodiments of the present invention, instead of squeezing out onto the exposed upper surfaces of the reflector cup and the lens (as shown in FIG. 2), the excess of the third encapsulant material 17 is squeezed into and received by the moat 18, thus limiting wicking of the encapsulant material 17 up the sidewall 5 even after the lens 20 is inserted and the convex meniscus of third encapsulant material 17 shown in FIG. 16B is displaced. The encapsulant material 17 is then cured to attach the lens 20 in the package 10 and to solidify the encapsulant material 17.
In some embodiments, the lens 20 is advanced into the reflective cavity 15 until it contacts the luminescent conversion element 19 to establish a desired position for the lens 20 in the reflective cavity 15. In other words, the luminescent conversion element 19 may act as a mechanical stop to assure correct placement of the lens 20. In other embodiments, the lens 20 is advanced into the reflective cavity 15 until it contacts a lip formed in the cavity sufficient to establish a desired position for the lens 20 in the reflective cavity 15, as illustrated in FIG. 10C.
In some embodiments, the first encapsulant material 14 may include a scattering material embedded therein for scattering light passing therethrough, which may better improve angular uniformity of light emission.
In some embodiments, the first encapsulant material 14 may have a high index of refraction for better light extraction from the device 103. If luminescent conversion element 19 has a different index of refraction from that of the first encapsulant material 14, light rays passing through the interface between the two regions may be refracted, altering the light emission patterns of the device. If the index of refraction of the luminescent conversion element 19 is lower than that of first encapsulant material 14, light rays will tend to be refracted away from the normal direction, which may result in a more pronounced path length difference. The shape of luminescent conversion element 19 may be chosen or altered to offset such effects. For example, as discussed above, the luminescent conversion element 19 may be bi-convex, piano-convex or concavo-convex.
An example of forming a plano-convex luminescent conversion element using meniscus control techniques described herein is illustrated in FIGS. 17A-17C. As shown therein, a quantity of first encapsulant material 14 is deposited in the reflective cavity 15 of the package 10. With proper control of the amount of encapsulant material dispensed, surface tension will cause the liquid encapsulant material 14 to cling to the lip 22, forming a convex meniscus as illustrated in FIG. 17A at a height indicated at 14A. After curing, the first encapsulant material 14 relaxes to a height indicated at 14B, forming an approximately flat surface 14C. Second encapsulant material 16 is then dispensed, forming a convex meniscus that clings to an inner or outer edge of lip 22. After curing, the second encapsulant material 16 forms a plano-convex luminescent conversion element 19 having a convex surface 19A above a planar surface 19B. The remaining manufacturing steps are generally the same as were described above in connection with FIGS. 16A-16C.
Using similar techniques, the luminescent conversion element 19 may be formed as a plano-convex region with a planar region above a convex surface (FIG. 18A), a concavo-convex region with a convex surface above a concave surface (FIG. 18B) or a concavo-convex region with a concave surface above a convex surface (FIG. 18C). As discussed above, in each embodiment, the luminescent conversion element 19 includes a wavelength conversion material, such as a phosphor material. The first encapsulant material 14 and the third encapsulant material 17 may have no wavelength conversion material or a lower concentration of wavelength conversion material compared to the luminescent conversion element 19. Although the embodiments of FIGS. 16A-C, 17A-C and 18A-C are illustrated in connection with a reflector cup 4 as illustrated in FIGS. 5A-B, the techniques described above are applicable to other reflector cup designs, including reflector cups that include multiple moats and reflector cups that do not include a moat.
Embodiments of methods of packaging a semiconductor light emitting device 103 in a reflector 4 having a lower 6 and an upper 5 sidewall defining a reflective cavity 15 and incorporating a phosphor-loaded luminescent conversion element 19 with a non-uniform thickness will now be further described with reference to FIG. 19. As shown in the embodiments of FIG. 19, operations begin at Block 1900 by dispensing a first quantity 14 of encapsulant material into the reflective cavity 15 to form a first meniscus. The meniscus may have a convex, concave or substantially planar shape depending on the desired final shape of the luminescent conversion element 19. The shape of the meniscus is determined by the physical dimensions of the reflector 4 and the quantity of encapsulant dispensed into the cavity. The first quantity 14 of encapsulant material is then cured or pre-cured (Block 1910). Next, Branch A of the flowchart of FIG. 19 may be followed if it is desired to form the luminescent conversion element 19 using meniscus control methods. Branch B may be followed if it is desired to form luminescent conversion element 19 using a pre-formed insert.
Following Branch A, a second quantity 16 of encapsulant material containing a concentration of wavelength conversion material that is greater than that of first encapsulant material 14 is dispensed onto the cured first encapsulant material 14 (Block 1920).
The second encapsulant material 16 is then cured or pre-cured to form a luminescent conversion element 19 (Block 1930).
If Path B is followed, then a pre-formed luminescent conversion element 19 is inserted into the cavity 15 in contact with first encapsulant material 14 (Block 1950). In some embodiments, the step of curing the first quantity of encapsulant material may be performed after insertion of the pre-formed luminescent conversion element 19.
After formation or insertion of luminescent conversion element 19 (Block 1930 or Block 1950), third encapsulant material 17 is dispensed within cavity 15 (Block 1960). In some embodiments of the present invention including a lens, the lens 20 is positioned in the reflective cavity 15 proximate the dispensed third quantity 17 of encapsulant material (Block 1970). Positioning the lens 20 may include collapsing a meniscus of third encapsulant material 17 and moving a portion of the third quantity 17 of encapsulant material into a moat 18, 24 with the lens 20 as illustrated in FIGS. 9C, 10C, 16C and 17C. In addition, as illustrated in FIG. 10C, the package may include a second lip 26′ having a height greater than that of the first lip 22. The height of the second lip 26′ may be selected to provide a desired position for the lens 20 and the lens 20 may be moved into the reflective cavity 15 until it contacts the second lip 26′. In other embodiments of the present invention, as illustrated in FIGS. 9C, 16C and 17C, the lens 20 is advanced into the reflective cavity 15 until it contacts the luminescent conversion element 19 sufficient to establish a desired position for the lens 20 in the reflective cavity 15. The dispensed third quantity 17 of encapsulant material is cured to attach the lens 20 in the reflective cavity 15 (Block 1980).
The flowchart of FIG. 19 and the schematic illustrations of FIGS. 16A-16C, 17A-17C and 18A-18C illustrate the functionality and operation of possible implementations of methods for packaging a light emitting device according to some embodiments of the present invention. It should be noted that, in some alternative implementations, the acts noted in describing the figures may occur out of the order noted in the figures. For example, two blocks/operations shown in succession may, in fact, be executed substantially concurrently, or may be executed in the reverse order, depending upon the functionality involved.
Emission patterns for light emitting device packages will now be further discussed with reference to FIGS. 20A, 20B and 21. FIG. 20A is a polar plot of color-temperature for a glob-top light emitting diode (LED) emission pattern without a luminescent conversion element of the present invention generated using a goniometer. FIG, 20B is a polar plot of color-temperature for a light emitting diode (LED) emission pattern with a luminescent conversion element according to some embodiments of the present invention. A comparison of FIG. 20B to FIG. 20A shows an improvement in uniformity provided by the luminescent conversion region (i.e., the radius of the emission pattern is more uniform in FIG. 20B). As seen in FIG. 20B, the packaged semiconductor light emitting device has a minimum color temperature (5.3 kK at about −85°) approximately 26 percent below a maximum color temperature (7.2 kK at about 0°) thereof over the measured 180 (+/−90 from normal or central axis)-degree range of emission angles. Various embodiments of the present invention may provide a minimum color temperature no more than 30 percent below a maximum color temperature for the semiconductor light emitting device package over a measured 180 (+/−90 from normal or central axis)-degree range of emission angles or over a measured 120 (+/−45 from normal or central axis)-degree range of emission angles.
FIGS. 21A and 21B and 22A and 22B further illustrate improvement in color uniformity obtained according to some embodiments of the present invention. FIGS. 21A and 21B are digitally analyzed plots of the near field emission pattern of a first packaged device including a substrate/reflector assembly in which a Model C460XB900 light emitting diode manufactured by Cree, Inc. was mounted. 0.0030 cc Silicone (example: vendor e.g. Nye Synthetic Lubricants ) mixed with 4% YAG doped with Ce Phosphor (example: from Philips) was pre-dispensed over the light emitting device, followed by a dispense of 0.0070 cc of the same encapsulant. Next, the dispensed encapsulant was cured for 60 minutes at a temperature of 70C. A second quantity of 0.0050 cc of clear encapsulant material was then dispensed into the optical cavity and a lens was positioned in the optical cavity in contact with the second quantity of encapsulant. The second quantity of encapsulant was then cured for 60 minutes at a temperature of 70C. The resulting structure was then energized and the near field emission pattern was recorded and analyzed. The emission pattern shows a total CCT variation of approximately 2000K over the measured 180 (+/−90 from normal or central axis)-degree range of emission angles.
FIGS. 22A and 22B are digitally analyzed plots of the near field emission pattern of a second packaged device including a substrate/reflector assembly in which a C460XB900 light emitting diode manufactured by Cree, Inc. was mounted. 0.0020 cc of clear silicone (example: vendor e.g. Nye Synthetic Lubricants ) was pre-dispensed over the light emitting device, followed by a first dispense of 0.0035 cc of the same encapsulant. The first encapsulant (including the pre-dispensed encapsulant) contained no wavelength conversion material. Next, the first encapsulant was cured for 60 minutes at a temperature of 70C. to form a concave meniscus. A second quantity of 0.0045 cc encapsulant material containing a wavelength conversion phosphor, namely 7% by weight of YAG doped with Ce Phosphor (example: from Philips) was then dispensed into concave meniscus formed by the first encapsulant. The second encapsulant was then cured for 60 minutes at a temperature of 70C. to form a luminescent conversion element having a thickness that was greatest at the center of the optical cavity and that decreased radially outward. A third quantity of 0.0050 cc encapsulant (which did not contain any wavelength conversion material) was then dispensed into the optical cavity and a lens was positioned in the optical cavity in contact with the third quantity of encapsulant. The third quantity of encapsulant was then cured for 60 minutes at a temperature of 70C. The resulting structure was then energized and the near field emission pattern was recorded and analyzed. The emission pattern shows a total CCT variation of approximately 500K over the same range of emission angles.
In some embodiments of the present invention, a CCT variation of less than about 1000K is provided over a measured 180, 120 or 90 (centered on normal or central axis)-degree range of emission angles. In other embodiments of the present invention, a CCT variation of less than about 2000K is provided over a measured 180, 120 or 90 (centered on normal or central axis)-degree range of emission angles. In yet further embodiments of the present invention, a CCT variation of less than about 500K is provided over a measured 120 or 90 (centered on normal or central axis)-degree range of emission angles. It will be understood that the CCT variation referred to herein is based on a primary emission pattern of a device including primary optics processed with the device without the use of any additional secondary optics added to or used in combination with the packaged semiconductor light emitting device to improve color variation. Primary optics refers to the optics integral to the device, such as a luminescent conversion element in combination with a lens built into the device as described for various embodiments of the present invention herein.
The foregoing is illustrative of the present invention and is not to be construed as limiting thereof. Although a few exemplary embodiments of this invention have been described, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the claims. Therefore, it is to be understood that the foregoing is illustrative of the present invention and is not to be construed as limited to the specific embodiments disclosed, and that modifications to the disclosed embodiments, as well as other embodiments, are intended to be included within the scope of the appended claims. The invention is defined by the following claims, with equivalents of the claims to be included therein.

## Claims

1. A packaged semiconductor light emitting device, comprising:
a body having a sidewall portion defining a cavity;
a light emitting device positioned in the cavity;
a first quantity of cured encapsulant material in the cavity including the light emitting device; and
a luminescent conversion element on an upper surface of the first quantity of encapsulant material, the luminescent conversion element including a wavelength conversion material and having a thickness at a middle region of the cavity greater than at a region proximate a sidewall of the cavity, wherein a variation in the thickness of the luminescent conversion element as the luminescent conversion element extends radially outward from the middle region to the sidewall is selected to provide a desired total correlated color temperature (CCT) variation.

2. The device of claim 1 wherein the thickness of the luminescent conversion element continuously decreases as the luminescent conversion element extends radially outward from the middle region to the sidewall.

3. The device of claim 1 wherein the thickness of the luminescent conversion element varies by more than ten percent of a maximum thickness of the luminescent conversion element.

4. The device of claim 1 wherein the luminescent conversion element has a biconvex, plano-convex or concavo-convex shape.

5. The device of claim 1 wherein the light emitting device comprises a light emitting diode (LED).

6. The device of claim 1 wherein the device has a minimum color temperature no more than 30 percent below a maximum color temperature thereof over a 180 (+/−90 from central axis)-degree range of emission angles.

7. The device of claim 1 wherein the device has a primary emission pattern having a total correlated color temperature (CCT) variation of less than about 1000K over a 180 (+/−90 from central axis)degree range of emission angles.

8. The device of claim 1 wherein the device has a primary emission pattern having a total CCT variation of about 500K over a 180 (+/−90 from central axis)-degree range of emission angles.

9. The device of claim 1 wherein the device has a primary emission pattern having a total correlated color temperature (CCT) variation of less than about 1000K over a 120 (+/−45 from central axis)-degree range of emission angles.

10. The device of claim 1 wherein the device has a primary emission pattern having a total correlated color temperature (CCT) variation of less than about 500K over a 90 (+/−45 from central axis)-degree range of emission angles.

11. The device of claim 1 wherein the body comprises a reflector and wherein the cavity comprises a reflective cavity.

12. A packaged semiconductor light emitting device, comprising:
a body having a sidewall portion defining a cavity;
a light emitting device positioned in the cavity;
a first quantity of cured encapsulant material in the cavity including the light emitting device; and
a luminescent conversion element having a piano-convex shape with a convex surface extending away from the light emitting device or a concavo-convex shape on an upper surface of the first quantity of encapsulant material, the luminescent conversion element including a wavelength conversion material and having a thickness at a middle region of the cavity greater than at a region proximate a sidewall of the cavity, wherein the first quantity of encapsulant material has an index of refraction different from an index of refraction of the luminescent conversion element and wherein the thickness of the luminescent conversion element is selected to compensate for variations in a light path length of light from the light emitting device caused by an interface between the luminescent conversion element and the first quantity of cured encapsulant material.

13. The device of claim 12 wherein the thickness of the luminescent conversion element continuously decreases as the luminescent conversion element extends radially outward from the middle region to the sidewall.

14. The device of claim 12 wherein the thickness of the luminescent conversion element varies by more than ten percent of a maximum thickness of the luminescent conversion element.

15. The device of claim 12 wherein the device has a minimum color temperature no more than 30 percent below a maximum color temperature thereof over a 180 (+/−90 from central axis)-degree range of emission angles.

16. The device of claim 12 wherein the device has a primary emission pattern having a total correlated color temperature (CCT) variation of less than about 1000K over a 180 (+/−90 from central axis)-degree range of emission angles.

17. The device of claim 12 wherein the device has a primary emission pattern having a total CCT variation of about 500K over a 180 (+/−90 from central axis)-degree range of emission angles.

18. The device of claim 12 wherein the device has a primary emission pattern having a total correlated color temperature (CCT) variation of less than about 1000K over a 120 (+/−45 from central axis)-degree range of emission angles.

19. The device of claim 12 wherein the device has a primary emission pattern having a total correlated color temperature (CCT) variation of less than about 500K over a 90 (+/−45 from central axis)-degree range of emission angles.

20. The device of claim 12, further comprising a lens contacting the luminescent conversion element, wherein the luminescent conversion element acts as a mechanical stop for the lens.

21. The device of claim 12, wherein the first quantity of encapsulant material includes a scattering material selected to increase angular uniformity of light emission from the packaged semiconductor light emitting device.

22. A packaged semiconductor light emitting device, comprising:
a substrate;
a light emitting device positioned on the substrate;
a first quantity of cured encapsulant material on the light emitting device; and
a luminescent conversion element on an upper surface of the first quantity of encapsulant material, the luminescent conversion element including a wavelength conversion material and having a thickness over a middle region of the light emitting device greater than over a region displaced from the middle region, wherein a variation in the thickness of the luminescent conversion element as the luminescent conversion element extends radially outward from the middle region to the region displaced therefrom is selected to provide a desired total correlated color temperature (CCT) variation.

23. A packaged semiconductor light emitting device, comprising:
a substrate;
a light emitting device positioned on the substrate;
a first quantity of cured encapsulant material on the light emitting device; and
a luminescent conversion element having a plano-convex shape with a convex surface extending away from the light emitting device or a concavo-convex shape on an upper surface of the first quantity of encapsulant material, the luminescent conversion clement including a wavelength conversion material and having a thickness over a middle region of the light emitting device greater than over a region displaced from the middle region.