Patent Application
20150348948
Various embodiments described herein relate to light emitting devices and assemblies and methods of manufacturing the same, and more particularly, to Light Emitting Diodes (LEDs), assemblies thereof and fabrication methods therefore.
LEDs are widely known solid-state lighting elements that are capable of generating light upon application of voltage thereto. LEDs generally include a diode region having first and second opposing faces, and include therein an n-type layer, a p-type layer and a p-n junction. An anode contact ohmically contacts the p-type layer and a cathode contact ohmically contacts the n-type layer. The diode region may be epitaxially formed on a substrate, such as a sapphire, silicon, silicon carbide, gallium arsenide, gallium nitride, etc., growth substrate, but the completed device may not include a substrate. The diode region may be fabricated, for example, from silicon carbide, gallium nitride, gallium phosphide, aluminum nitride and/or gallium arsenide-based materials and/or from organic semiconductor-based materials. Finally, the light radiated by the LED may be in the visible or ultraviolet (UV) regions, and the LED may incorporate wavelength conversion material such as phosphor.
An LED component provides a packaged LED die for mounting on a board, such as a Metal Core Printed Circuit Board (MCPCB), flexible circuit board and/or other printed circuit board, along with other electronic components, for example using surface mount technology. An LED component generally includes an LED die, a submount and other packaging elements.
Submounts are generally used in LED components to interpose an LED die and a printed circuit board. The submount may change the contact configuration of the LED die to be compatible with the pads of the printed circuit board. The submount may also be used to support a phosphor layer and/or an encapsulating dome that surrounds the LED die. The submount may also provide other functionality. Thus, a submount may include a receiving element onto which an LED die is mounted using conventional die-attach techniques, to interface the LED die and a printed circuit board. A submount generally has a thickness of at least 100 μm, and in some embodiments at least 150 μm, and in other embodiments at least 200 μm, and generally includes traces (such as on ceramic panels) and/or leads (such as in Plastic Leaded Chip Carrier (PLCC) package).
LEDs are increasingly being used in lighting/illumination applications, with a goal being to provide a replacement for the ubiquitous incandescent light bulb.
A Light Emitting Diode (LED) component according to various embodiments described herein includes a plurality of discrete LED dies that are spaced apart from one another, a respective one of which comprises first and second opposing faces and an anode contact and a cathode contact on the first face thereof, the plurality of discrete LED dies oriented such that the first faces of adjacent LED dies are adjacent one another and the second faces of adjacent LEDs are adjacent one another. An electrical connection element is provided adjacent the first faces of the LED dies and configured to electrically connect the plurality of discrete LED dies in series and/or in parallel. A unitary optically transparent structure is provided on the second faces of the LED dies remote from the anode and cathode contacts, that spans the plurality of LED dies.
In some embodiments, the LED component is unsupported by a submount adjacent the first faces of the LED dies that spans the first faces of adjacent ones of the LED dies. In some embodiments, the electrical connection element comprises a patterned metal sheet adjacent the first faces of the LED dies that is patterned to electrically connect the plurality of discrete LED dies in series and/or in parallel. In other embodiments, the electrical connection element comprises a plurality of wire bonds adjacent the first faces of the LED dies that are arranged to electrically connect the plurality of discrete LED dies in series and/or in parallel.
In some embodiments, the patterned metal sheet comprises first and second opposing faces, the LED dies being disposed on the first face of the patterned metal sheet such that the anode and cathode contacts are adjacent the first face of the patterned metal sheet and in some embodiments the second face of the patterned metal sheet is free of the submount thereon adjacent the plurality of LED dies. In some embodiments, the LED component may further comprise a plurality of solder structures, a respective one of which electrically connects a respective one of the anode and cathode contacts to the patterned metal sheet. The patterned metal sheet is patterned to selectively electrically connect the anode and cathode contacts of the LED dies in series and/or in parallel through the solder structures and to also provide an external anode contact and an external cathode contact for the LED component.
In other embodiments, the LED dies are disposed on the patterned metal sheet such that the anode contacts of adjacent LED dies are adjacent one another and the cathode contacts of adjacent LED dies are adjacent one another, and the patterned metal sheet is patterned to electrically connect the anode contacts of the plurality of LED dies to one another and to electrically connect the cathode contacts of the plurality of LED dies to one another so that the plurality of LED dies are connected in parallel. In still other embodiments, the LED dies are disposed on the patterned metal sheet such that the anode contacts of adjacent LED dies are opposite one another and the cathode contacts of adjacent LED dies are opposite one another, and the patterned metal sheet is patterned to electrically connect the anode contact and the cathode contact of adjacent LED dies to one another so that the plurality of LED dies are connected in series.
In any of the embodiments described above, the LED component may further include a layer comprising luminophoric material on the second faces of the LED dies. In some embodiments, the layer comprising luminophoric material also extends on sidewalls of the LED dies. In some embodiments, the unitary optically transparent structure is a unitary, rigid, optically transparent sheet on the layer comprising luminophoric material, remote from the LED dies. In some embodiments, the unitary, rigid, optically transparent sheets span the plurality of LED dies, and may comprise a glass sheet.
In yet other embodiments, the LED component further comprises an optically transparent structure on a respective LED die, remote from the anode and cathode contacts, and the patterned metal sheet is configured as a polygonal cylinder having a plurality of polygonal cylinder faces, wherein a respective LED die is on a respective polygonal cylinder face and wherein the patterned metal sheet connects adjacent polygonal cylinder faces to one another. The optically transparent structure may comprise a sheet, in some embodiments a rigid sheet and in some embodiments a glass sheet. In other embodiments, the LED component may further comprise an optical coupling material between the optically transparent structure and the layer comprising luminophoric material.
An LED component according to any of the embodiments described above may be provided on a board along with other electronic components, wherein the LED component is free of a submount between the plurality of LED dies and the board.
An LED component according to other embodiments described herein may comprise a plurality of discrete LED dies that are spaced apart from one another, a respective one of which comprises first and second opposing faces and an anode contact and a cathode contact on the first face thereof, the plurality of discrete LED dies oriented such that the first faces of adjacent LED dies are adjacent one another and the second faces of adjacent LEDs are adjacent one another. The LED component may be unsupported by a submount adjacent the first faces of the LED dies that spans the first faces of adjacent ones of the LED dies, A plurality of wire bonds is provided adjacent the first faces of the LED dies that are configured to electrically connect the plurality of discrete LED dies in series and/or in parallel. A plurality of solder structures are also provided, a respective one of which is on a respective one of the anode and cathode contacts. A unitary optically transparent structure is provided on the second faces of the LED dies remote from the anode and cathode contacts, that spans the plurality of LED dies.
In some embodiments, a layer comprising luminophoric material is provided on the second faces of the LED dies, wherein the layer comprising luminophoric material also extends on sidewalls of the LED dies. An optical coupling material may be provided between the optically transparent structure and the layer comprising luminophoric material. A reflective layer may be provided on the first faces of the LED dies and extending between adjacent ones of the LED dies.
In some embodiments the unitary optically transparent structure comprises a rigid, unitary optically transparent structure, such as a glass sheet. Moreover, in some embodiments, the reflective layer comprises white paint.
In some embodiments, the LED dies are disposed such that the anode contacts of adjacent LED dies are adjacent one another and the cathode contacts of adjacent LED dies are adjacent one another, and the wire bonds are configured to electrically connect the anode contacts of the plurality of LED dies to one another and to electrically connect the cathode contacts of the plurality of LED dies to one another so that the plurality of LED dies are connected in parallel. In other embodiments, the LED dies are disposed such that the anode contacts of adjacent LED dies are opposite one another and the cathode contacts of adjacent LED dies are opposite one another, and the wire bonds are configured to electrically connect the anode contact and the cathode contact of adjacent LED dies to one another so that the plurality of LED dies are connected in series.
In any of the above embodiments, the LED component may be provided on a board along with other electronic components, wherein the LED component is free of a submount between the plurality of LED dies and the board. In some embodiments, the board comprises a contact pad pattern including an external anode contact pad for the LED component, an external cathode contact pad for the LED component and a thermal contact pad for the LED component. A plurality of solder structures also may be provided between the LED component and the board wherein the plurality of solder structures are configured to electrically connect an anode contact to the external anode contact pad, a cathode contact to the external cathode contact pad and an anode contact and/or a cathode contact to the thermal contact pad.
An LED component according to yet other embodiments described herein may comprise a plurality of discrete LED dies that are spaced apart from one another, a respective one of which comprises first and second opposing faces and an anode contact and a cathode contact on the first face thereof, the plurality of discrete LED dies oriented such that the first faces of adjacent LED dies are adjacent one another and the second faces of adjacent LEDs are adjacent one another. The LED component may be unsupported by a submount adjacent the first faces of the LED dies that spans the first faces of adjacent ones of the LED dies. A patterned metal sheet may also be provided that comprises first and second opposing faces, the LED dies being disposed on the first face of the patterned metal sheet such that the anode and cathode contacts are adjacent the first face of the patterned metal sheet and the second face of the patterned metal sheet is free of the submount thereon adjacent the plurality of LED dies. A plurality of solder structures are provided, a respective one of which electrically connects a respective one of the anode and cathode contacts to the patterned metal sheet.
The patterned metal sheet is patterned to selectively electrically connect the anode and cathode contacts of the LED dies in series and/or in parallel through the solder structures and to also provide an external anode contact and an external cathode contact for the LED component. A layer comprising luminophoric material is provided on the second faces of the LED dies, wherein the layer comprising luminophoric material also extends on sidewalls of the LED dies. A unitary optically transparent structure may be provided on the layer comprising luminophoric material, remote from the LED dies. An optical coupling material is provided between the optically transparent structure and the layer comprising luminophoric material. A reflective layer is also provided on the first faces of the LED dies between the first faces of the LED dies and the patterned metal sheet, and extending between adjacent ones of the LED dies.
In some embodiments, the unitary optically transparent structure comprises a rigid, unitary optically transparent structure that spans the plurality of LED dies. The rigid unitary optically transparent structure may comprise a glass sheet. Moreover, in some embodiments, the reflective layer may comprise white paint.
Moreover, in other embodiments, a discrete optically transparent structure may be provided on a respective LED die, and the patterned metal sheet is configured as a polygonal cylinder, having a plurality of polygonal cylinder faces, wherein a respective LED die is on a respective polygonal cylinder face and wherein the patterned metal sheet connects adjacent polygonal cylinder faces to one another.
In some embodiments, the LED dies are disposed such that the anode contacts of adjacent LED dies are adjacent one another and the cathode contacts of adjacent LED dies are adjacent one another, and the patterned metal sheet is configured to electrically connect the anode contacts of the plurality of LED dies to one another and to electrically connect the cathode contacts of the plurality of LED dies to one another so that the plurality of LED dies are connected in parallel. In other embodiments, the LED dies are disposed such that the anode contacts of adjacent LED dies are opposite one another and the cathode contacts of adjacent LED dies are opposite one another, and the patterned metal sheet is configured to electrically connect the anode contact and the cathode contact of adjacent LED dies to one another so that the plurality of LED dies are connected in series.
In any of the above embodiments, the LED component may be provided on a board along with other electronic components, wherein the LED component is free of a submount between the plurality of LED dies and the board.
LED components may be fabricated according to various embodiments described herein by placing a plurality of discrete LED dies on a carrier sheet in spaced apart relation from one another, a respective LED die comprising first and second opposing faces and an anode contact and a cathode contact on the first face thereof, the plurality of discrete LED dies being oriented on the carrier sheet such that the first faces of adjacent LED dies are adjacent the carrier sheet and the second faces of adjacent LEDs are remote from the carrier sheet. A luminophoric layer is coated on the second faces and sidewalls of the LED dies on the carrier sheet. A unitary optically transparent structure is placed on the second faces of the LED dies so that the unitary optically transparent structure spans the LED dies. The carrier sheet is removed such that the unitary optically transparent structure supports the plurality of discrete LED dies thereon. A plurality of LED dies that are on the unitary optically transparent structure are selectively electrically connected in series and/or in parallel. A reflective layer is applied on the first faces of the LED dies and extending between adjacent ones of the LED dies. Groups of the LEDs that are connected in series and/or in parallel are singulated to provide a plurality of the LED components, a respective LED component being unsupported by a submount adjacent the first faces of the LED dies that spans the first faces of adjacent ones of the LED dies.
In some embodiments, the selectively electrically connecting comprises placing a patterned metal sheet on the first faces of the LED dies that is patterned to electrically connect the plurality of discrete LED dies in series and/or in parallel. In these embodiments, the placing of a patterned metal sheet may be preceded by placing a plurality of solder structures between the anode contacts and the patterned metal sheet, and soldering a respective one of the anode and cathode contacts to the patterned metal sheet using the solder structures. In other embodiments, the patterned metal sheet may be bent into a polygonal cylinder having a plurality of polygonal cylinder faces, wherein a respective LED die is on a respective polygonal cylinder face and wherein the patterned metal sheet connects adjacent polygonal cylinder faces to one another. In still other embodiments, the selectively electrically connecting comprises selectively wire bonding the anode and cathode contacts to electrically connect the plurality of discrete LED dies in series and/or in parallel.
In some embodiments, the unitary optically transparent structure comprises a glass sheet. Moreover, in some embodiments, placing a unitary optically transparent structure on the second faces of the LED dies is preceded by placing an optical coupling material on the layer comprising luminophoric material.
In some embodiments, the plurality of discrete LED dies are placed on the carrier sheet, such that the anode contacts of adjacent LED dies are adjacent one another and the cathode contacts of adjacent LED dies are adjacent one another. In other embodiments, the plurality of LED dies are placed on the carrier sheet such that the anode contacts of adjacent LED dies are opposite one another and the cathode contacts of adjacent LED dies are opposite one another.
Finally, any of the above embodiments may further comprise mounting the LED component on a board along with other electronic components, without providing a submount between the plurality of LED dies and the board.
The present invention now will be described more fully with reference to the accompanying drawings, in which various embodiments 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. 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. 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 and may be abbreviated as “/”.
As used herein, a layer or region is considered to be “transparent” when at least 50% of the radiation that impinges on the transparent layer or region emerges through the transparent layer or region. Moreover, as used herein, a “rigid” structure is a stiff structure that is unable to bend or be forced out of shape; i.e., not flexible or pliant. A rigid structure may be subject to minimal bending without breaking, but bending beyond this minimal bending will break or deform a rigid structure. As also used herein, a “flexible structure” means a structure that is not rigid. In specific examples of materials used herein, glass is considered to be rigid, whereas silicone is considered to be flexible. Finally, as used herein, a “sheet” means a broad, relatively thin piece, plate or slab of material, such as glass.
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.
Embodiments of the invention are described herein with reference to cross-sectional and/or other illustrations that are schematic illustrations of idealized embodiments of the invention. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments of the invention should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, a region illustrated or described as a rectangle will, typically, have rounded or curved features due to normal manufacturing tolerances. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the precise shape of a region of a device and are not intended to limit the scope of the invention, unless otherwise defined herein.
Unless otherwise defined herein, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and this specification and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
Some embodiments now will be described generally with reference to gallium nitride (GaN)-based light emitting diodes on silicon carbide (SiC)-based growth substrates for ease of understanding the description herein. However, it will be understood by those having skill in the art that other embodiments of the present invention may be based on a variety of different combinations of growth substrate and epitaxial layers. For example, combinations can include AlGaInP diodes on GaP growth substrates; InGaAs diodes on GaAs growth substrates; AlGaAs diodes on GaAs growth substrates; SiC diodes on SiC or sapphire (Al2O3) growth substrates and/or a Group III-nitride-based diode on gallium nitride, silicon carbide, aluminum nitride, sapphire, zinc oxide and/or other growth substrates. Moreover, in other embodiments, a growth substrate may not be present in the finished product. For example, the growth substrate may be removed after forming the light emitting diode, and/or a bonded substrate may be provided on the light emitting diode after removing the growth substrate. In some embodiments, the light emitting diodes may be gallium nitride-based LED devices manufactured and sold by Cree, Inc. of Durham, N.C.
Various embodiments described herein can provide submount-free multiple die LED components that may be ready for mounting on a mounting board, such as a printed circuit board. The LED component includes a plurality of discrete LED dies and an electrical connection element is configured to electrically connect the plurality of discrete LED dies in series and/or in parallel. The electrical connection element may include a patterned metal sheet and/or a plurality of wire bonds. The serial and/or parallel connection can provide high current and/or high voltage LED components, such as a 24 volt LED component. Moreover, the LED component is not supported by a submount that spans the LED dies.
Various embodiments described herein may arise from a recognition that, although useful for mounting LED dies, a submount may require additional processing complexity and/or cost, and may also impact the reliability of the LED component. In contrast, various embodiments described herein provide an electrical connection element that electrically connects the plurality of discrete LED dies in series and/or in parallel, without a submount that spans adjacent ones of the LED dies. Moreover, multiple relatively small LED dies may be used in some embodiments, compared to one or more larger LED dies, which can increase luminous flux by providing additional light extraction surfaces (e.g., more sidewalls).
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LED dies 100 configured as was described above in connection with
Various other configurations of horizontal LEDs that may be used according to any of the embodiments described herein, are described in detail in U.S. Patent Application Publication 2009/0283787 to Donofrio et al., entitled “Semiconductor Light Emitting Diodes Having Reflective Structures and Methods of Fabricating Same”; U.S. Patent Application Publication 2011/0031502 to Bergmann et al., entitled “Light Emitting Diodes Including Integrated Backside Reflector and Die Attach”; U.S. Patent Application Publication 2012/0193660 to Donofrio et al. entitled “Horizontal Light Emitting Diodes Including Phosphor Particles”; and U.S. Patent Application Publication 2012/0193662 to Donofrio et al. entitled “Reflective Mounting Substrates for Flip-Chip Mounted Horizontal LEDs”, assigned to the assignee of the present application, the disclosures of which are hereby incorporated herein by reference in their entirety as if set forth fully herein.
Other configurations of horizontal LEDs may be embodied by the “Direct Attach” LED chips that are marketed by Cree, Inc., the assignee of the present application, and which are described, for example, in Data Sheets entitled “Direct Attach DA2432™ LEDs” (Data Sheet: CPR3FM Rev., 2011); “Direct Attach DA1000™ LEDs” (Data Sheet: CPR3ES Rev. A, 2010); and “Direct Attach DA3547™ LEDs” (Data Sheet: CPR3EL Rev. D, 2010-2012), the disclosures of which are hereby incorporated herein by reference in their entirety as if set forth fully herein.
In order to simplify the drawings which follow, the internal structure of LED dies 100 will not be illustrated. Rather, the following figures will only illustrate the anode contact 160 and cathode contact 170 of the LED die 100. The LED die 100 comprises first and second opposing faces, wherein the first opposing face is the first face 110a of the diode region and the second face is the second face 110b of the diode region when no substrate is present, or the outer face 120b of the substrate 120 when a substrate 120 is present. The anode contact 160 and the cathode contact 170 are on the first face 110a.
Moreover, in various embodiments described herein, all of the LED dies 100 are indicated as being of the same size and generally rectangular. However, the LED dies 100 may be square or of other shapes, and need not all be the same size or type of LED. Moreover, the anode and cathode contacts 160 and 170, respectively, are all illustrated as being the same size as one another. In other embodiments, however, the anode and cathode contact of a given LED need not be of the same size, and the anode and cathode contacts of the various LEDs need not be the same size or shape as one another. The LED dies may emit different colors of light and may include a phosphor layer thereon. For example, in some embodiments, a combination of white and red LED dies may be provided. Moreover, any number of multiple LED dies 100 may be provided based on the requirements of the LED component 300.
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In some embodiments, the unitary optically transparent structure 220 may be embodied as a glass sheet, such as a D 263° thin borosilicate glass marketed by Schott North America, Inc. and/or similar glass sheets from other manufacturers. In some embodiments, the glass sheet is between about 200 μm and about 1 mm thick. In other embodiments, the glass sheet may be about 700 μm thick. The glass sheet may have an index of refraction of about 1.5 and in some embodiments 1.524. In some embodiments, when a 200 μm thick glass sheet is used, a thick layer of index matching gel may be provided to maintain an overall cubic shape. Using glass thicker than about 700 μm may have diminishing returns, and may be harder to singulate. Moreover, using glass thinner than about 700 μm may provide at least some loss of light. In some embodiments, the glass sheet may have a thickness variation of about +/−25 μm and, in a given piece of the glass sheet, the thickness variation may be about +/−5 μm. It will be understood that other rigid transparent sheets may also be employed in other embodiments. It will also be understood that flexible transparent sheets may also be employed in yet other embodiments.
As will be described in more detail below, in some embodiments, the electrical connection element 210 can comprise a patterned metal sheet adjacent the first faces 110a of the LED dies 100 that is patterned to electrically connect the plurality of discrete LED dies in series and/or in parallel. Solder structures may be used to electrically connect the anode and cathode contacts 160, 170, respectively, to the patterned metal sheet. In other embodiments, the electrical connection element comprises a plurality of wire bonds adjacent the first faces 110a of the LED dies 100 that are arranged to electrically connect the plurality of discrete LED dies in series and/or in parallel.
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Moreover, polyhedral LED components may also be provided in other embodiments, depending on the number and orientation of the LED dies and the configuration of the patterned metal sheet. Polygonal or polyhedral wire bonded LED components may also be provided in other embodiments.
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A unitary optically transparent structure 220 is provided on the layer 820 comprising luminophoric material, remote from the LED dies 100. The unitary optically transparent structure 220 spans the plurality of LED dies. The unitary optically transparent structure 220 may comprise a sheet, such as a rigid sheet, for example a glass sheet. In some embodiments, the unitary optically transparent structure 220 may be directly on the portion of the layer 820 comprising luminophoric material that is on the second face 120b of the LED dies 100. In other embodiments, the unitary optically transparent structure 220 may be spaced apart therefrom. In some embodiments, the unitary optically transparent structure 220 provides mechanical support for the LED component 800. An optical coupling material 830, such as a gel or resin, for example comprising silicone, may be provided between the optically transparent structure 220 and the layer 820 comprising luminophoric material. The optical coupling material 830 may also include luminophoric material therein. Finally, a reflective layer 840 may be provided on the first faces 110a of the LED dies 100, and extending between adjacent ones of the LED dies 100. The reflective layer 840 may comprise white paint and/or other solder mask material, in some embodiments. In some embodiments, although not illustrated in
It will be understood that the solder structures 810, the layer 820 comprising luminophoric material, the optical coupling material 830, the unitary optically transparent structure 220 and/or the reflective layer 840 may be used in various combinations and subcombinations. For example, the layer 820 comprising luminophoric material may be omitted and, instead, luminophoric material may be provided in the optical coupling material. Alternatively, the optical coupling material may be omitted, and the unitary transparent structure 220 may include luminophoric material therein. In other embodiments, the optical coupling media may contain luminophoric material therein. In yet other embodiments, luminophoric material may be included in each of the layer 820, the coupling media 830 and the optically transparent structure 220, wherein the luminophoric materials may be different in at least two of the layers. The luminophoric material may be uniformly or non-uniformly distributed in a given layer, and multiple luminophoric materials may be provided in a given layer. In still other embodiments, the optically transparent structure 220 may be a flexible unitary optically transparent structure comprising, for example, silicone that may extend on the second faces 120b and at least partially on the sidewalls 120a of the LED dies 100. A separate layer of optical coupling material 830 may or may not be provided. Finally, it will be understood that the LED dies 100 may be disposed, such that the anode contacts 160 of adjacent LED dies are adjacent one another, and the cathode contacts 170 of adjacent LED dies 100 are adjacent one another, and the wire bonds 310 may be configured to electrically connect the anode contacts 160 of the plurality of LED dies to one another, and to electrically connect the cathode contacts 170 of the plurality of LED dies to one another, so that the plurality of LED dies are connected in parallel.
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Methods of fabricating an LED component according to various other embodiments described herein will now be described. These methods may fabricate LED components 1000 of
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Additional discussion of LED components according to various embodiments described herein will now be provided.
Specifically, various embodiments described herein can allow the use of multiple small dies with spacing, which can be advantageous over larger dies in light output due to less self-absorption by the LED dies. Small dies may also be less costly than larger dies, due to higher die-per-wafer yield. The tradeoff may be more placements and interconnects, but these may be almost free with modern manufacturing techniques. Multiple small dies can be used in low voltage applications, or can be structured together to form higher voltage components. Multiple small dies may be used to form one component without a submount. This can provide increased area for better thermal dissipation compared to a single die solution, which can provide less thermal roll-off of luminous flux. Specifically, thermal management may be better as heat sources may be distributed rather than being concentrated or crowded. Moreover, thermal management may be better as connecting substrate pads may be made larger with better heat conduction possible. Finally, an increase in luminous flux may be provided due to less self-absorption compared to a single die.
In other embodiments, a single multi-die component may be used for multiple voltages or staged turn-on within a component. Moreover, since no submount is required, cost and/or reliability may be increased. The increase in die perimeter area compared to a single die can correlate to efficiency gain. It will also be understood that various embodiments described herein may require more accurate placement of a component on a board, because the component may be larger. Moreover, handling this larger component may be mitigated using existing multiple ejector pin arrangements that can eject a large component from a carrier sheet.
Various embodiments described herein can utilize a reflective layer. These reflective layers can include a dielectric mirror, a white paint reflective layer, such as a titania-filled layer, and/or other white/reflective layer. Many different reflectors can be used including a mirror layer comprising silver, diffuse reflectors, materials comprising a reflective white color, and thin film reflectors, such as metal or dielectric layers. The reflective layer may have various thicknesses, including some which do not exceed the thickness of the anode and cathode contacts. The reflective layer shown may also extend between the anode and cathode contacts. In embodiments where the reflective layer exceeds the height of the anode and cathode contacts, it may be desirable to generate a contact with enough material to overcome the height barrier of the reflective layer and also to have a balanced amount of material on both contact pads so that uniform attachment is achieved.
Some embodiments of the reflective layer may also comprise a solder mask over portions of the bottom surface, which do not include the anode and cathode contacts. A solder mask may comprise any material that is generally used in microelectronic manufacturing to physically and electrically insulate those portions of the circuit to which no solder or soldering is desired. Solder masks may include thermally cured screen-printed masks, dry film and/or screen-applied or curtain-coated liquid photoimageable solder masks. In some embodiments, the solder mask may comprise a conventional photoresist, or any other material that is non-wettable to solder. A solder mask may be less than about 30 μm thick in some embodiments, less than about 5 μm thick in other embodiments, and may be about 1 μm thick or less in still other embodiments. A wide range of thicknesses and materials may be used, as long as effective solder masking takes place. Moreover, in other embodiments, the solder mask may also include virtually any non-metallic coating, such as silicon dioxide and/or silicon nitride, which may be deposited by physical and/or chemical deposition techniques. In still other embodiments, the solder mask may be reflective, so as to reflect optical radiation that emerges from the diode region, back into the diode region. Examples of such reflective layers include a dielectric mirror, a white reflective layer, such as a titania-filled layer, and/or other white/reflective layer.
Various embodiments described herein may also include a layer comprising luminophoric material, also referred to as a phosphor layer. The phosphor layer may also extend onto the sidewalls of the diode dies, and/or beyond the anode and cathode contacts. In some embodiments, the phosphor layer is a conformal phosphor layer that may be less than about 150 μm thick in some embodiments, less than about 100 μm thick in other embodiments and less than about 50 μm thick in yet other embodiments. It will be understood that the term “phosphor” is used herein to denote any wavelength conversion material, and may be provided according to various configurations. The phosphor layer may also be any type of functional layer or layers, such as any layer disposed to affect the properties of the emitted light, for example, color, intensity and/or direction.
Various techniques may be used to apply the phosphor layer, including dispensing, screen printing, film transfer, spraying, coating and/or other techniques. Phosphor preforms also may be applied. In some embodiments, the phosphor layer may comprise silicone and/or other transparent material having phosphor particles therein. It will also be understood that the phosphor layer may be coplanar with the outer face of the LED dies. However, the outer or edge portions of the phosphor layer need not be co-planar with these outer faces. Specifically, it can be recessed from the outer faces or may protrude beyond the anode and cathode contacts.
The phosphor layer may be a thin conformal layer having uniform phosphor particle density. However, a phosphor layer may be provided that comprises phosphor particles that are nonuniformly dispersed therein, and that, in some embodiments, may include a phosphor-free region at the exterior surfaces of the phosphor layer. Moreover, the phosphor layer may also be configured as a conformal layer.
The phosphor layer, or any wavelength conversion layer, converts a portion of the light emitted from the LED die to a different wavelength, a process that is known in the art. One example of this process, is converting a portion of blue-emitted light from light emitter, such as an LED die, to yellow light. Yttrium aluminum garnet (YAG) is an example of a common phosphor that may be used.
In some embodiments, the phosphor particles comprise many different compositions and phosphor materials alone or in combination. In one embodiment the single crystalline phosphor can comprise yttrium aluminum garnet (YAG, with chemical formula Y3Al5O12). The YAG host can be combined with other compounds to achieve the desired emission wavelength. In one embodiment where the single crystalline phosphor absorbs blue light and reemits yellow, the single crystalline phosphor can comprise YAG:Ce. This embodiment is particularly applicable to light emitters that emit a white light combination of blue and yellow light. A full range of broad yellow spectral emission is possible using conversion particles made of phosphors based on the (Gd,Y)3(Al,Ga)5O12:Ce system, which include Y3Al5O12:Ce (YAG). Other yellow phosphors that can be used for white emitting LED chips include:
In other embodiments, other compounds can be used with a YAG host for absorption and re-emission of different wavelengths of light. For example, a YAG:Nb single crystal phosphor can be provided to absorb blue light and reemit red light. First and second phosphors can also be combined for higher CRI white (i.e., warm white) with the yellow phosphors above combined with red phosphors. Various red phosphors can be used including:
Other phosphors can be used to create saturated color emission by converting substantially all light to a particular color. For example, the following phosphors can be used to generate great saturated light:
The following lists some additional suitable phosphors that can be used as conversion particles, although others can be used. Each exhibits excitation in the blue and/or UV emission spectrum, provides a desirable peak emission, has efficient light conversion:
In some embodiments, the layer comprising luminophoric material, the optical coupling layer and/or the optically transparent structure may also provide a functional layer which comprises a light scattering layer, which comprises a binder material as discussed above and light scattering particles, for example titanium oxide particles. In other embodiments, the layer comprises materials to alter the refractive index of the functional layer. In some embodiments, the functional layer comprises a combination of one or more of the types of functional layers described herein (e.g. a wavelength conversion layer and a scattering or refractive index altering layer).
In some embodiments, the LED die is configured to emit blue light, for example light having a dominant wavelength of about 450-460 nm, and the phosphor layer comprises yellow phosphor, such as YAG:Ce phosphor, having a peak wavelength of about 550 nm. In other embodiments, the LED die is configured to emit blue light upon energization thereof, and the phosphor layer may comprise a mixture of yellow phosphor and red phosphor, such CASN-based phosphor. In still other embodiments, the LED die is configured to emit blue light upon energization thereof, and the phosphor layer may comprise a mixture of yellow phosphor, red phosphor and green phosphor, such as LuAG: Ce phosphor particles. Moreover, various combinations and subcombinations of these and/or other colors and/or types of phosphors may be used in mixtures and/or in separate layers. In still other embodiments, a phosphor layer is not used. For example, a blue, green, amber, red, etc., LED need not use phosphor. In embodiments which do use a phosphor, it may be beneficial to provide a uniform coating in order to provide more uniform emissions.
The optical coupling material may comprise silicone without phosphor particles therein, and may provide a primary optic for the light emitting device. The optical coupling material that is free of phosphor may be shaped to provide a lens, dome and/or other optical component, so that the sides and/or tops thereof may be oblique to the diode region. The optical coupling material that is free of phosphor may also encapsulate the phosphor layer and/or light emitting surfaces of the LED die. The optical coupling layer may be at least 1.5 mm thick in some embodiments, at least 0.5 mm thick in other embodiments, and at least 0.01 mm thick in yet other embodiments, and may not be present in still other embodiments. Thus, in other embodiments, an optical coupling material layer may be used without a phosphor layer. For example, the optical coupling material may be directly on the second face of the LED die. In some embodiments, a relatively thick transparent layer may be used. In other embodiments, a conformal transparent layer may be used. In still other embodiments, the transparent layer may be provided on a phosphor layer that comprises phosphor particles that are non-uniformly dispersed therein. The device may further include an additional encapsulant or lens, which may be silicone or glass. Other embodiments may not include this additional lens.
Various embodiments described herein may also include a board, such as a printed circuit board. The printed circuit board may include any conventional circuit board material that is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces. The printed circuit board may comprise laminate, copper-clad laminates, resin-impregnated B-stage cloth, copper foil, metal clad printed circuit boards and/or other conventional printed circuit boards. In some embodiments, the printed circuit board is used for surface mounting of electronic components thereon. The printed circuit board may include multiple LED components and any other device thereon, as well as one or more integrated circuit chip power supplies, integrated circuit chip LED controllers and/or other discrete and/or integrated circuit passive and/or active microelectronic components, such as surface mount components thereon.
Various embodiments of luminophoric layers comprising phosphor, optical coupling material, reflective layers and boards, are described, for example, in U.S. patent application Ser. No. 14/152,829 to Bhat et al. entitled “Wafer Level Contact Pad Solder Bumping for Surface Mount Devices With Non-Planar Recessed Contacting Surfaces”, U.S. patent application Ser. No. 14/201,490 to Bhat et al. entitled “Wafer Level Contact Pad Standoffs With Integrated Reflector”, and U.S. patent application Ser. No. 13/017,845 to Donofrio et al. entitled “Conformally Coated Light Emitting Devices and Methods for Providing the Same”, assigned to the assignee of the present application, the disclosures of which are hereby incorporated herein by reference in their entirety as if set forth fully herein.
Many different embodiments have been disclosed herein, in connection with the above description and the drawings. It will be understood that it would be unduly repetitious and obfuscating to literally describe and illustrate every combination and subcombination of these embodiments. Accordingly, the present specification, including the drawings, shall be construed to constitute a complete written description of all combinations and subcombinations of the embodiments described herein, and of the manner and process of making and using them, and shall support claims to any such combination or subcombination.
In the drawings and specification, there have been disclosed embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.
