Abstract:
In accordance with certain embodiments, thermal stresses are mitigated in illumination systems by mating optical substrates with a plurality of discrete substrates each having one or more light-emitting elements thereon.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of and priority to U.S. Provisional Patent Application No. 61/555,035, filed Nov. 3, 2011, and U.S. Provisional Patent Application No. 61/589,908, filed Jan. 24, 2012, the entire disclosure of each of which is hereby incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     In various embodiments, the present invention generally relates to electronic devices, and more specifically to array-based electronic devices. 
     BACKGROUND 
     Light sources such as light-emitting diodes (LEDs) are an attractive alternative to incandescent and fluorescent light bulbs in illumination devices due to their higher efficiency, smaller form factor, longer lifetime, and enhanced mechanical robustness. However, the high cost of LEDs and associated heat-sinking and thermal-management systems have limited the widespread utilization of LEDs, particularly in broad-area general lighting applications. 
     The high cost of LED-based lighting systems has several contributors. LEDs are typically encased in a package, and multiple packaged LEDs are used in each lighting system to achieve the desired light intensity. In order to reduce costs, LED manufacturers have developed high-power LEDs that emit relatively higher light intensities by operating at higher currents. While reducing the package count, these LEDs require higher-cost packages to accommodate the higher current levels and to manage the significantly higher resulting heat levels. The higher heat loads and currents, in turn, typically require more expensive thermal-management and heat-sinking systems which also add to the cost (as well as to the size) of the system. Higher operating temperatures may also lead to shorter lifetimes and reduced reliability. Finally, LED efficacy typically decreases with increasing drive current, so operation of LEDs at higher currents generally results in a reduction in efficacy when compared to lower-current operation. 
     A further problem associated with using fewer high-power LEDs in broad-area lighting—for example, to replace fluorescent lighting systems—is that the light must be expanded from the relatively small area of the die (on the order of 1 mm 2 ) to emit over a relatively large area (on the order of 1 ft 2  or larger). Such expansion often results in decreased efficiency, reduced performance, and increased cost. For example, a light panel may be edge-lit and incorporate features that redirect or scatter light. However, it is often difficult to achieve uniform light intensity over the entire emitting area of such panels, with the intensity generally being higher at the edge(s) near the light sources. Also, the emission pattern from such devices is typically Lambertian, resulting in poor utilization of light and relatively high glare. 
     An alternate approach to producing broad-area lighting is to use a large array of small LEDs positioned over the desired emitting area. Such LEDs may be unpackaged LEDs (i.e., LED dies) or packaged within, e.g., a leadframe and polymeric encapsulation. A large array tends to reduce the cost and efficiency losses associated with optics required to spread out light from a small number of high-power LEDs. 
     The materials used for the various components of the complete lighting package are often dissimilar and often have different thermal coefficients of expansion (TCEs). This may cause problems during the manufacture of the lighting system, for example, during processing steps involving heating or cooling (e.g., soldering, curing of adhesives and/or encapsulants, etc.), or in the field, either from ambient-induced temperature changes or from self-heating and cooling upon power-cycling of the system. 
       FIG. 1  shows a system  100  featuring a light-emitter substrate  110 , an optical substrate  120 , an LED  130 , and a region  140 . Region  140  may be empty or may include a transparent material or a transparent material in combination with a light-conversion material, such as a phosphor. Light-emitter substrate  110  and optical substrate  120  may be different materials and have different TCEs. When this structure is heated and cooled, stresses will generally develop that may result in cracking of one or both substrates or partial or full delamination of one substrate from the other. Stress-induced changes to the electrical connections to LED  130  can cause intermittent connections or open-circuits or short-circuits. 
     In view of the foregoing, a need exists for systems and procedures enabling the uniform and economical integration of arrays of low-cost light sources (such as LEDs), phosphors, and optical elements, as well as lighting systems based thereon, which minimize TCE-induced problems. 
     SUMMARY 
     In accordance with certain embodiments, illumination devices (which are preferably planar) feature a plurality of light-emitting elements electrically connected in series, parallel, or in series/parallel fashion. The light-emitting elements may have light-conversion materials such as phosphors disposed over and/or around them, and may also be associated with (e.g., aligned to) optical elements (e.g., lenses) disposed on or forming portions of an overlying optical substrate. (An optical substrate comprising a plurality of optical elements is preferably a unitary substrate having the optical elements formed therein or thereon.) Herein, two components such as light-emitting elements, optical elements, and/or other portions of lightsheets or optical substrates (e.g., holes or wells (i.e., depressions or other recessed regions)) being “aligned” may refer to such components being mechanically and/or optically aligned. By “mechanically aligned” is meant coaxial or situated along a parallel axis. By “optically aligned” is meant that at least some light (or other electromagnetic signal) emitted by or passing through one component passes through and/or is emitted by the other. In order to enhance reliability and reduce thermally induced stresses, the light-emitting elements preferably are disposed on substrates having vastly smaller areas than that of an optical substrate to which they are attached. Thus, the different TCEs of the light-emitting elements and the optical substrate result in only minimal amounts of deleterious thermal stress. 
     In preferred embodiments, the integration of the light-conversion material and/or the optical elements with the light-emitting elements is repeatably and uniformly performed in parallel. For example, a substrate having the light-emitting elements disposed thereon (i.e., a “lightsheet”) may be directly bonded to the optical substrate, the light-emitting elements having been positioned for alignment with the optical elements of the optical substrate, and then the lightsheet may be separated into multiple smaller substrates each supporting one or more of the light-emitting elements. Alternatively, the light-emitting elements may initially be provided on small (e.g., having areas at least 100 times, or even 1000 times, smaller than that of the optical substrate) substrates that are attached to the optical substrate. 
     As utilized herein, an “optical substrate” is a material for receiving, manipulating, and/or transmitting light. An optical substrate may include or consist essentially of, e.g., a transparent or translucent sheet or plate, a waveguide and/or one or more (even an array of) optical elements such as lenses. For example, optical elements may include or consist essentially of refractive optics, reflective optics, Fresnel optics, total internal reflection optics, and the like. The optical substrate may include features or additional components or materials to scatter, reflect, or absorb light or a portion of light in the optical substrate, and it may confine light by total internal reflection prior to its emission from the optical substrate. 
     As utilized herein, the term “light-emitting element” (LEE) refers to any device that emits electromagnetic radiation within a wavelength regime of interest, for example, visible, infrared or ultraviolet regime, when activated, by applying a potential difference across the device or passing a current through the device. Examples of light-emitting elements include solid-state, organic, polymer, phosphor-coated or high-flux LEDs (bare-die or packaged), microLEDs, laser diodes or other similar devices as would be readily understood. The emitted radiation of a LEE may be visible, such as red, blue or green, or invisible, such as infrared or ultraviolet, and may have a single wavelength or a spread of wavelengths. A LEE may feature a phosphorescent or fluorescent material for converting a portion of its emissions from one set of wavelengths to another. A LEE may include multiple constituent LEEs, each emitting at essentially the same or different wavelength(s). In some embodiments, a LEE is an LED that may feature a reflector over all or a portion of its surface upon which electrical contacts are positioned. The reflector may also be formed over all or a portion of the contacts themselves. In some embodiments, the contacts are themselves reflective. 
     A LEE may be of any size. In some embodiments, a LEEs has one lateral dimension less than 500 μm. Exemplary sizes of a LEE may include about 250 μm by about 600 μm, about 250 μm by about 400 μm, about 250 μm by about 300 μm, or about 225 μm by about 175 μm. In some embodiments, a LEE includes or consists essentially of a small LED die, also referred to as a “microLED.” A microLED generally has one lateral dimension less than about 300 μm. In some embodiments, the LEE has one lateral dimension less than about 200 μm or even less than about 100 μm. For example, a microLED may have a size of about 225 μm by about 175 μm or about 150 μm by about 100 μm or about 150 μm by about 50 μm. In some embodiments, the surface area of the top surface of a microLED is less than 50,000 μm 2  or less than 10,000 μm 2 . However, the size and/or shape of the LEE is not a limitation of the present invention. 
     As used herein, “phosphor” refers to any material that shifts the wavelengths of light irradiating it and/or that is luminescent, fluorescent, and/or phosphorescent, and is utilized interchangeably with the term “light-conversion material.” As used herein, a “phosphor” may refer to only the photoactive powder or particles or to the powder or particles within a polymeric binder. The specific components and/or formulation of the phosphor and/or binder material are conventional and not limitations of the present invention. The binder may also be referred to as an encapsulant or a matrix material. 
     In an aspect, embodiments of the invention feature a method of forming an illumination system. A lightsheet is provided and mated to an optical substrate. The lightsheet includes or consists essentially of a support substrate, a plurality of electrical traces disposed on the substrate, and a plurality of light-emitting elements electrically coupled to the electrical traces. Thereafter, the support substrate is separated into a plurality of discrete substrate portions each (i) having at least one light-emitting element disposed thereon, (ii) having a surface area substantially smaller than a surface area of the optical substrate, and (iii) remaining bonded to the optical substrate. 
     Embodiments of the invention may include one or more of the following in any of a variety of combinations. The optical substrate may include a plurality of optical elements, and at least one light-emitting element may be associated with each optical element. The optical substrate may include a plurality of wells each aligned with an optical element, and mating the lightsheet to the optical substrate may include or consist essentially of disposing at least one light-emitting element within each well. Prior to mating the lightsheet to the optical substrate, each well may include a light-conversion material therewithin. After separating the support substrate into the plurality of discrete substrate portions, each discrete substrate may at least partially seal (i.e., cover and/or enclose) one or more wells. The cross-sectional area of the optical substrate may be at least 100 times, or even at least 1000 times, the cross-sectional area of each of the discrete substrate portions. Separating the support substrate into a plurality of discrete substrate portions may include or consist essentially of removing portions of the support substrate between adjoining discrete substrate portions. At least one of the removed portions of the support substrate may include one or more light-emitting elements disposed thereon. The optical substrate may include a plurality of electrical conductors thereon prior to mating of the lightsheet to the optical substrate. Mating the lightsheet to the optical substrate may include or consist essentially of electrically coupling each electrical trace to an electrical conductor. Prior to mating of the lightsheet to the optical substrate, the lightsheet may be partially separated along lines defining the plurality of discrete substrate portions. Prior to mating of the lightsheet to the optical substrate, the lightsheet may include a light-conversion material disposed over each light-emitting element. 
     In another aspect, embodiments of the invention feature a method of forming an illumination system. A plurality of discrete substrates is provided, and each of the discrete substrates is mated to an optical substrate comprising a plurality of wells defined therein. Each of the discrete substrates includes or consists essentially of (i) a plurality of electrical traces disposed thereon and (ii) one or more light-emitting elements electrically coupled to the electrical traces. After the mating step, (i) each discrete substrate at least partially seals a well and (ii) the one or more light-emitting elements disposed on the discrete substrate are disposed within the well. 
     Embodiments of the invention may include one or more of the following in any of a variety of combinations. The optical substrate may include or consist essentially of a plurality of optical elements each associated with at least one well. Each optical element may be aligned with at least one well. The cross-sectional area of the optical substrate may be at least 100 times, or even at least 1000 times, the cross-sectional area of each of the discrete substrates. Prior to mating the discrete substrates to the optical substrate, each well may include a light-conversion material therewithin. The optical substrate may include a plurality of electrical conductors thereon prior to the mating of the discrete substrates to the optical substrate. Mating the discrete substrates to the optical substrate may include or consist essentially of electrically coupling each electrical trace to an electrical conductor. Prior to the mating of the discrete substrates to the optical substrate, each discrete substrate may include a light-conversion material disposed over each light-emitting element. 
     In yet another aspect, embodiments of the invention feature an illumination system including or consisting essentially of an optical substrate and a plurality of discrete substrates mated to the optical substrate. The optical substrate includes a plurality of wells therein and electrical conductors disposed between the wells. Each of the discrete substrates includes (i) a plurality of electrical traces disposed thereon and (ii) one or more light-emitting elements electrically coupled to the electrical traces. Each discrete substrate at least partially seals a well. The one or more light-emitting elements disposed on the discrete substrate are disposed within the at least partially sealed well. Each electrical conductor is electrically connected to an electrical trace. 
     Embodiments of the invention may include one or more of the following in any of a variety of combinations. A light-conversion material may be disposed in at least one of (e.g., all of) the wells. The cross-sectional area of the optical substrate may be at least 100 times, or even at least 1000 times, the cross-sectional area of each of the discrete substrates. The optical substrate may include a plurality of optical elements each associated with at least one well. Each optical element may be aligned with at least one well. 
     In a further aspect, embodiments of the invention feature an illumination system including or consisting essentially of a plurality of discrete substrates mated to an optical substrate. The optical substrate includes a plurality of holes therethrough and electrical conductors disposed between the holes. Each discrete substrate includes a plurality of electrical traces disposed thereon and one or more light-emitting elements electrically coupled to the electrical traces. Each discrete substrate at least partially covers a hole. The one or more light-emitting elements disposed on the discrete substrate reside within the hole. Each electrical conductor is electrically connected to an electrical trace. A light-conversion material may be disposed in at least one of (e.g., all of) the holes. The cross-sectional area of the optical substrate may be at least 100 times, or even at least 1000 times, the cross-sectional area of each of the discrete substrates. A light-conversion material may be disposed over at least one light-emitting element (e.g., all of the light-emitting elements). 
     In yet a further aspect, embodiments of the invention feature a method of forming an illumination system. A monolithic lightsheet is provided and mated to an optical substrate comprising a plurality of wells therein. The monolithic lightsheet defines a plurality of lighting units each comprising (i) a portion of the support substrate, (ii) a plurality of electrical traces disposed thereon, and (iii) one or more light-emitting elements electrically coupled to the electrical traces. Each of a first plurality of lighting units is aligned with a well such that the one or more light-emitting elements of the lighting unit are disposed within the well, and a second plurality of lighting units are each disposed between wells such that the light-emitting elements thereof are not disposed within a well. Each of the second plurality of lighting units is removed from the optical substrate, the first plurality of lighting units remaining mated to the optical substrate. After removing each of the second plurality of lighting units from the optical substrate, the second plurality of lighting units may be mated to the optical substrate such that (i) each of a third plurality of lighting units is aligned with a well such that the one or more light-emitting elements of the lighting unit are disposed within the well, and (ii) a fourth plurality of lighting units are each disposed between wells such that the light-emitting elements thereof are not disposed within a well. Each of the fourth plurality of lighting units may be removed from the optical substrate, the third plurality of lighting units remaining mated to the optical substrate. 
     These and other objects, along with advantages and features of the invention, will become more apparent through reference to the following description, the accompanying drawings, and the claims. Furthermore, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and can exist in various combinations and permutations. As used herein, the term “substantially” means ±10%, and in some embodiments, ±5%. The term “consists essentially of” means excluding other materials that contribute to function, unless otherwise defined herein. Nonetheless, such other materials may be present, collectively or individually, in trace amounts. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments of the present invention are described with reference to the following drawings, in which: 
         FIG. 1  is a schematic of a light-emitting system; 
         FIG. 2  is a schematic of a lighting apparatus in accordance with an embodiment of the present invention; 
         FIG. 3  is a plan-view schematic of a lighting apparatus in accordance with an embodiment of the present invention; 
         FIG. 4  is a schematic of another lighting apparatus in accordance with an embodiment of the present invention; 
         FIGS. 5A and 5B  are a cross-sectional and plan view, respectively, of a portion of the structure of  FIG. 4  at an early stage of manufacture; 
         FIGS. 6A and 6B  depict the attachment of a light-emitting element to a substrate in accordance with an embodiment of the present invention; 
         FIGS. 7 and 8  show portions of the structure of  FIG. 4  at an early stage of manufacture; 
         FIGS. 9A and 9B  show examples of pads on conductive traces in accordance with an embodiment of the present invention; 
         FIG. 10  is a flow chart of an embodiment of the present invention; 
         FIG. 11  is a schematic of another lighting apparatus in accordance with an embodiment of the present invention; 
         FIGS. 12 and 13  depict lighting apparatuses at an intermediate stage of manufacture in accordance with various embodiments of the present invention; 
         FIGS. 14-16  are schematics of lighting apparatuses in accordance with various embodiments of the present invention; 
         FIGS. 17 and 18  depict portions of the structure of  FIG. 16  at early stages of manufacture; 
         FIG. 19  is a schematic of another lighting apparatus in accordance with an embodiment of the present invention; and 
         FIG. 20  is a flow chart of another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 2  depicts a system  200  that includes one or more LEEs  130 , one or more regions  140 , and an optical substrate  120 . Rather than include a monolithic substrate supporting the LEEs  130 , system  200  features multiple substrates  210 , each of which supports one or more LEEs  130 . In various embodiments, the stress in the system  200  is proportional to the attached or bonded area between the optical substrate  120  and the substrate or substrates on which the LEEs  130  are formed. By using multiple small substrates  210  instead of one large light-emitter substrate (as in  FIG. 1 ), the stress at each LEE  130  is reduced. As an example, a typical light-emitter substrate  110  may have an area of about 1000 cm 2  or more (e.g., about 4000 cm 2  or more). In comparison, a substrate  210  may have an area of about 2 cm 2  or less (e.g., about 0.25 cm 2  or less). The large area reduction, on the order of at least 100×, or even at least 1000×, results in greatly reduced stress in the system. The light-emitter substrates  210  typically include or consist essentially of materials different from that of optical substrate  120 . In some embodiments the TCE of different components, for example light-emitter substrate  210  and optical substrate  120  is different by at least about 25%, or by at least about 50%, or by at least about a factor of two or by at least about a factor of five or even greater. For example, light-emitter substrate  210  may include or consist essentially of GaN (TCE of approximately 4×10 −6 /° C.), optical substrate  120  may include or consist essentially of polyethylene terephthalate (TCE of approximately 10×10 −6 /° C.), and the binder may include or consist essentially of silicone (TCE of approximately 70×10 −6 /° C.). 
     Substrate  210  may include or consist essentially of a semicrystalline or amorphous material, e.g., polyethylene naphthalate (PEN), polyethylene terephthalate (PET), acrylic, polycarbonate, polyethersulfone, polyester, polyimide, polyethylene, and/or paper. Substrate  210  may be substantially flexible, substantially rigid, or substantially yielding. Substrate  210  may include multiple layers of the same or different materials, e.g., a deformable layer over a rigid layer, for example, a semicrystalline or amorphous material, e.g., PEN, PET, polycarbonate, polyethersulfone, polyester, polyimide, polyethylene, paint, ink, plastic film, and/or paper formed over a rigid substrate for example including, acrylic, aluminum, steel and the like. 
       FIG. 2  depicts one LEE  130  attached to each light-emitter substrate  210 ; however, this is not a limitation of the present invention and in other embodiments multiple LEEs  130  are attached to each light-emitter substrate  210 .  FIG. 3  shows a plan view of a system  300  in which an underlying substrate has been divided into sections  310 , each of which supports four LEEs  130 . In some embodiments, sections  310  are formed by cutting a light-emitter substrate  110 , shown in  FIG. 1 , into sections  310  after it has been mated to an optical substrate  120 . In other embodiments, sections  310  are formed before mating to optical substrate  120 . In some embodiments, sections  310  have more space between them than the kerf from cutting a light-emitter substrate  110  into sections  310 . 
     While  FIGS. 1 and 2  show region  140  as a well or depression in optical substrate  120 , this is not a limitation of the present invention, and in other embodiments region  140  includes or consists essentially of a structure formed over a portion or all of LEE  130  and/or a portion or all of light-emitter substrate  210 . In some embodiments, the mating side of optical substrate  120  (i.e., the side mated to substrates  210 ) is substantially planar. 
       FIG. 3  depicts the sections  310  as square-shaped; however, this is not a limitation of the present invention and in other embodiments sections  310  are rectangular, hexagonal, circular, or have any arbitrary shape.  FIG. 3  shows sections  310  each supporting four LEEs  130 ; however, this is not a limitation of the present invention and in other embodiments each section  310  supports fewer or more LEEs  130 . In some embodiments, a section  310  includes or consists essentially of a strip of a light-emitter substrate  110 , with a line of LEEs, that is a 1×n array of LEEs, where n is an integer greater than one. 
     In general, the smaller the size of a section  310 , the smaller the stress generated in the system, and the less likely will be stress-induced problems. Embodiments of the present invention do not change the intrinsic TCE of the materials in a light-emitting system, but rather reduce the intensity of the stress generated by the mating of two or more materials with different TCEs. 
       FIGS. 4 through 13  and the accompanying description describe various embodiments of the invention, some of which incorporate elements described in U.S. patent application Ser. No. 13/604,880, filed Sep. 6, 2012, the entire disclosure of which is incorporated by reference herein. 
       FIG. 4  shows a cross-sectional view of a system  400  that features an optical substrate  120  having optical elements  410  formed in or on one side thereof. One or more conductive traces  420  and wells  440  are formed over or within the side of optical substrate  120  opposite the optical elements  410 . The electrical contacts on the LEE  130  (not shown for clarity) are electrically coupled to conductive traces  430  formed over the LEE substrate  210 . The conductive traces  430  are electrically coupled to the conductive traces  420 . The details of the electrical connection of LEE  130  to conductive traces  430  and electrical connection of conductive traces  430  to conductive traces  430  are omitted from  FIG. 4  for clarity. Wells  440  may be unfilled or partially or completely filled with a transparent matrix material and/or a mixture of phosphor and matrix material. In another embodiment, wells  440  are not present in optical substrate  120 , and a transparent matrix material or a mixture of phosphor and matrix material is formed over a portion or all of LEEs  130  and/or a portion or all of LEE substrate  210 . In some embodiments the mating side of optical substrate  120  (i.e., the side facing substrates  210 ) is substantially planar. 
     Optical substrate  120  typically features an array of optical elements  410 ; in some embodiments, one optical element  410  is associated with each LEE  130 , while in other embodiments multiple LEEs  130  are associated with one optical element  410 , or multiple optical elements  410  are associated with a single LEE  130 . Alternatively, one or more LEEs  130  may not be associated with an engineered optical element but may instead be associated with, e.g., a flat or roughened surface. In one embodiment optical substrate  120  includes elements or features to scatter, diffuse, and/or spread out light generated by LEEs  130 . In some embodiments optical substrate  120  may lack optical elements and the side of optical substrate  120  opposite the side with LEEs  130  may be substantially planar. 
     Optical substrate  120  may be substantially optically transparent or translucent. For example, optical substrate  120  may exhibit a transmittance greater than about 70% for optical wavelengths ranging between approximately 400 nm and approximately 700 nm. Optical substrate  120  may include or consist essentially of a material that is transparent to a wavelength of light emitted by LEE  130  and/or phosphor  450 . Optical substrate  120  may be substantially flexible or rigid. Optical substrate  120  may include or consist essentially of, for example, acrylic, polycarbonate, polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polycarbonate, polyethersulfone, polyester, polyimide, polyethylene, polyurethane, glass or the like. In some embodiments, optical substrate  120  includes multiple materials and/or layers. Optical elements  410  may be formed in or on optical substrate  120 . For example, optical elements  410  may be formed by etching, polishing, grinding, machining, molding, embossing, extruding, casting, or the like. The method of formation of optical elements  410  is not a limitation of embodiments of the present invention. In some embodiments optical elements  410  and optical substrate  120  feature multiple components. 
     Optical elements  410  associated with optical substrate  120  may all be the same or may be different from each other. Optical elements  410  may include or consist essentially of, e.g., a refractive optic, a diffractive optic, a total internal reflection (TIR) optic, a Fresnel optic, or the like, or combinations of different types of optical elements. Optical elements  410  may be shaped or engineered to achieve a specific light distribution pattern from the array of light emitters, optical elements, and optional phosphors. 
     Conductive traces  420  and  430  may include or consist essentially of any conductive material, for example metals such as gold, silver, aluminum, copper and the like, conductive oxides, carbon, etc. Conductive traces  420  may be formed on optical substrate  120  by a variety of methods, for example physical deposition, plating, electroplating, printing, lamination, or the like. In one embodiment, conductive traces  420  are formed using printing, for example screen printing, stencil printing, flexo, gravure, ink jet, or the like. In one embodiment conductive traces  420  are formed by laminating a conductive film to substrate  120  or  210  and patterning the film to form conductive traces  420 . Conductive traces  420  may include or consist essentially of a transparent conductor, for example, a transparent conductive oxide such as indium tin oxide (ITO). Conductive traces  420  may include or consist essentially of multiple materials. Conductive traces  420  may optionally feature stud bumps to aid in electrical coupling of conductive trace  420  to conductive trace  430 . Conductive traces  420  and  430  may have a thickness in the range of about 0.05 μm to about 100 μm. While the thickness of one or more of the conductive traces  420  and  430  may vary, the thickness is generally substantially uniform along the length of the conductive trace  420  and  430  to simplify processing. However, this is not a limitation of the present invention and in other embodiments the conductive trace thickness or material varies. 
     In some embodiments of the present invention, wells  440  are filled or partially filled with material  450 , which may include or consist essentially of a transparent or optically transmissive material, also called a matrix material or binder. In one embodiment, the transparent matrix or binder includes silicone, epoxy, polyurethane, or other suitable materials. Examples of suitable matrix materials include materials from the ASP series of silicone manufactured by Shin Etsu, or the Sylgard series manufactured by Dow Corning. 
     In other embodiments of the invention, material  450  includes or consists essentially of a mixture of one or more light-conversion materials and a matrix material. The light-conversion material is incorporated to shift one or more wavelengths of at least a portion of the light emitted by LEE  130  to other desired wavelengths (which are then emitted from the larger device alone or color-mixed with another portion of the original light emitted by the die). A light-conversion material may feature phosphor powders, quantum dots, or the like within a transparent matrix. Phosphors are typically available in the form of powders or particles, and in such case may be mixed in binders, e.g., silicone. Phosphors vary in composition, and may include lutetium aluminum garnet (LuAG or GAL), yttrium aluminum garnet (YAG) or other phosphors known in the art. GAL, LuAG, YAG and other materials may be doped with various materials including for example Ce, Eu, etc. Material  450  may include a plurality of individual phosphors. The specific components and/or formulation of the phosphor and/or matrix material are not limitations of the present invention. 
     In some embodiments phosphor  450  includes multiple layers of phosphor-infused matrix and/or matrix. That is, the phosphor may include multiple layers, where each layer includes either a phosphor-infused matrix or solely the matrix material. Where multiple layers of phosphor-infused matrix are used, each layer may include different phosphors and/or different matrix materials. In one embodiment, a phosphor layer includes a first layer (i.e., closer to the LEE  130 ) of a matrix material that is transparent or transmissive to a wavelength of light emitted by LEE  130  and second layer including one or more phosphors within a matrix material. 
     In some embodiments one or more LEEs  130  each includes or consists essentially of an LED. LEEs  130  may emit in a range of wavelengths and may include materials from the group consisting of Si, Ge, InAs, AlAs, GaAs, InP, AlP, GaP, InSb, GaSb, AlSb, GaN, AN, InN, and/or mixtures and alloys (e.g., ternary or quaternary alloys) thereof. In preferred embodiments, a LEE  130  is an inorganic device, rather than a polymeric or organic device. As referred to herein, a LEE  130  may be packaged or unpackaged unless specifically indicated (e.g., a bare-die LEE is an unpackaged semiconductor die). LEE  130  is typically formed on a substrate and in some embodiments all or a portion of the substrate is removed, for example by chemical etching, dry etching, laser lift off, mechanical grinding and/or chemical-mechanical polishing or the like. Optionally a second substrate—e.g., one that is transparent to or reflective of a wavelength of light emitted by LEE  130 —may be attached to LEE  130  prior to or after the attachment of LEE  130  to conductive traces  430 . 
     LEE substrate  210  may include or consist essentially of a semicrystalline or amorphous material, e.g., polyethylene naphthalate (PEN), polyethylene terephthalate (PET), acrylic, polycarbonate, polyethersulfone, polyester, polyimide, polyethylene, polyurethane, and/or paper. LEE substrate  210  may be substantially flexible, substantially rigid or substantially yielding. In some embodiments, the substrate is “flexible” in the sense of being pliant in response to a force and resilient, i.e., tending to elastically resume an original configuration upon removal of the force. A substrate may be “deformable” in the sense of conformally yielding to a force, but the deformation may or may not be permanent; that is, the substrate may not be resilient. Flexible materials used herein may or may not be deformable (i.e., they may elastically respond by, for example, bending without undergoing structural distortion), and deformable substrates may or may not be flexible (i.e., they may undergo permanent structural distortion in response to a force). The term “yielding” is herein used to connote a material that is flexible or deformable or both. 
     LEE substrate  210  may include multiple layers, e.g., a deformable layer over a rigid layer, for example, a semicrystalline or amorphous material, e.g., PEN, PET, polycarbonate, polyethersulfone, polyester, polyimide, polyethylene, paint, polyurethane, plastic film and/or paper formed over a rigid substrate for example including, acrylic, aluminum, steel and the like. Depending upon the desired application for which embodiments of the invention are utilized, LEE substrate  210  may be substantially optically transparent, translucent, or opaque. For example, LEE substrate  210  may exhibit a transmittance or a reflectivity greater than about 70% for optical wavelengths ranging between approximately 400 nm and approximately 700 nm. In some embodiments LEE substrate  210  exhibits a transmittance or a reflectivity of greater than about 70% for one or more wavelengths emitted by LEE  130  and/or light-conversion material  450 . LEE substrate  210  may also be substantially insulating, and may have an electrical resistivity greater than approximately 100 ohm-cm, greater than approximately 1×10 6  ohm-cm, or even greater than approximately 1×10 10  ohm-cm. 
       FIGS. 5A and 5B  (cross-sectional view and plan view respectively) depict the structure of  FIG. 4  at an early stage of manufacture. Shown in  FIGS. 5A and 5B  are an array of LEEs  130  electrically coupled between conductive traces  430  formed over LEE substrate  110 . While  FIG. 5B  depicts the LEEs  130  serially connected in strings  510 , and strings  510  connected or connectable in parallel, other die-interconnection schemes are possible and within the scope of embodiments of the invention. 
     In one embodiment, one or more LEEs  130  are electrically coupled using conductive adhesive, e.g., an isotropically conductive adhesive and/or an anisotropically conductive adhesive (ACA). An ACA is a material that permits electrical conduction only in one direction, e.g., the vertical direction (out of the plane of the page in  FIG. 5B ) but insulates in the orthogonal directions, e.g., insulating conductive traces  430  from each other. As shown, the structure includes two serially-connected strings  510  of LEEs  130 . As used here, ACA includes an anisotropic conductive material in any form, for example paste, gel, liquid, film or otherwise. ACAs may be utilized with or without stud bumps. Embodiments of the present invention may utilize interconnection schemes based on ACA as described in U.S. patent application Ser. No. 13/171,973, filed Jun. 29, 2011, the entire disclosure of which is incorporated by reference herein. 
     Various embodiments utilize one or more other electrically conductive adhesives, e.g., isotropically conductive adhesives, in addition to or instead of one or more ACAs. Various embodiments utilize wire bonding or soldering as the method to connect LEEs  130  to conductive traces  430 . The methods of attachment and/or electrical coupling of LEEs  130  to conductive traces  430  are not a limitation of the present invention. 
       FIG. 6A  shows a more detailed cross-sectional schematic of the connection of an LEE  130  to conductive traces  430  using an adhesive  610 . LEE  130  has contacts  650 , at least a portion of each of which is positioned over a conductive trace  430 . In  FIG. 6A  adhesive  610  is an ACA and electrical contact is only substantially made between the portion of contact  650  that is positioned over conductive trace  430 . This conductive region is identified as region  660 . 
       FIG. 6B  shows a plan-view schematic of the connection of LEEs  130  to conductive traces  430  using adhesive  610 . In one embodiment, one or more of the LEEs  130  includes at least two contacts that are connected to adjacent portions of conductive traces  430 . In one embodiment, adhesive  610  includes or consists essentially of an ACA. One or more LEEs  130  may be an LED having contacts that provide electrical contact to the p- and n-side of the LED respectively. 
     As shown in  FIG. 6B , two or more LEEs  130  may be connected in parallel to the same conductive traces  430  (i.e., within the same gap  630  between conductive traces  430 ), thus providing enhanced functionality and/or redundancy in the event of failure of a single LEE  130 . In a preferred embodiment, each of the LEEs  130  adhered across the same gap  630  is configured not only to operate in parallel with the others (e.g., at substantially the same drive current), but also to operate without overheating or damage at a drive current corresponding to the cumulative drive current operating all of the LEEs  130  disposed within a single gap. Thus, in the event of an open failure of one or more LEEs  130  adhered across the gap  630 , the remaining one or more LEEs  130  will continue to operate at a higher drive current. Of course, as shown in  FIGS. 5A and 5B  only one LEE  130  may be formed between conductive traces  430 . 
       FIG. 6B  also illustrates two possible adhesion schemes. One of the LEEs  130  is adhered to the conductive traces  430  via adhesive  610  only at the ends of the LEE  130 , while between the ends within the gap  630 , a second adhesive  620  (which is preferably non-electrically conductive) adheres the middle portion of the LEE  130  to LEE substrate  110 . In some embodiments, the second adhesive  620  is non-conductive and prevents shorting between the two portions of conductive adhesive  610  and/or between conductive trace  430  and/or between the two contacts of LEE  130 . As shown, the other LEE  130  is adhered between the conductive trace  430  with adhesive  610  contacting all or a portion of the bottom surface of LEE  130 . As described above, adhesive  610  is preferably an ACA that permits electrical conduction only in the vertical direction (out of the plane of the page in  FIG. 6B ) but insulates the conductive traces  430  from each other. In other embodiments, one or more LEEs  130  are adhered between conductive trace  430  within the same gap  630 , but there is sufficient “real estate” within the gap  630  (including portions of the conductive trace  430 ) to adhere at least one additional LEE  130  within the gap  630 . In such embodiments, if the one or more LEEs  130  initially adhered within the gap  630  fail, then one or more LEEs  130  (substantially identical to or different from any of the initial LEE  130 ) may be adhered within the gap  630  in a “rework” process. For example, referring to  FIG. 6B , only one of the depicted LEEs  130  may be initially adhered to the conductive trace  430 , and the other LEE  130  may be adhered later, e.g., after failure of the initial die. For example, a first LEE  130  may fail during manufacture and may be removed and replaced by a second operational LEE  130 . Removal of the first LEE  130  may be done, for example, by removing first LEE  130  from conductive trace  430 , e.g., by scraping or pulling first LEE  130  off of conductive trace  430 . If the first LEE  130  fails as an open-circuit, it may not be necessary to remove first LEE  130  from conductive trace  430 . 
       FIG. 7  shows a portion of system  400  of  FIG. 4  at an early stage of manufacture, featuring optical substrate  120  with optical elements  410  on one side and wells  440  and conductive traces  420  on the opposite side. Wells  440  may optionally be filled or partially filled with a matrix material or a phosphor and matrix material. Conductive traces  420  may be similar to conductive traces  430  and may be formed in similar ways as described for conductive traces  430 . In some embodiments the layout of conductive traces  420  matches that or is similar to that of conductive traces  430 . In an embodiment, wells  440  are not present in optical substrate  120 , and a transparent matrix material or a mixture of phosphor and matrix material is formed over a portion or all of LEEs  130  and/or a portion or all of LEE substrate  110  and/or a portion or all of conductive traces  430 . In some embodiments, the mating side of optical substrate  120  is substantially planar. 
     In one embodiment, wells  440  and optical elements  410  are formed simultaneously in the manufacturing process of optical substrate  120 , e.g., using a molding or embossing process. In some embodiments, wells  440  are formed by removal of the material of optical substrate  120 , for example by drilling, abrasive blasting, etching, laser ablation or the like. Wells  440  may be formed before or after formation of optical elements  410 . In some embodiments, wells  440  are aligned relative to optical elements  410 . It should be noted that alignment of wells  440  relative to optical elements  410  may mean that the center of well  440  is aligned to the center of optical element  410 ; however, this is not a limitation of the present invention and in other embodiments alignment refers to a specified relationship between the geometry of wells  440  and the geometry of optical elements  410 . A resulting advantage of this approach is the elimination of the need for alignment between light-conversion material  450  and optical element  410  in subsequent manufacturing steps. 
     In the next step of manufacture, the structure shown in  FIGS. 5A  and B and the structure shown in  FIG. 7  are mated, as shown in  FIG. 8 , where the LEEs  130  are substantially aligned with and fully or partially immersed in light-conversion material  450  in wells  410  in any of a number of different ways. In one embodiment, well  410  is under-filled with light-conversion material  450 , such that after mating substantially all of well  410  is filled with the combination of LEE  130  and light-conversion material  450 . In one embodiment, well  410  is under-filled, filled, or overfilled with light-conversion material  450 , such that after mating substantially all of well  410  is filled with the combination of LEE  130  and light-conversion material  450 , and an excess portion of light-conversion material  450  is forced from well  410  to occupy a portion of the space between LEE substrate  110  and optical substrate  120 . The excess portion of light-conversion material  450  may act to hold LEE substrate  110  and optical substrate  120  together. In one embodiment, well  410  has one or more void spaces that are not filled with either LEEs  130  or light-conversion material  450 . After mating of LEE substrate  110  and optical substrate  120 , the matrix or matrix and phosphor material  450  structure is optionally cured, for example by heating. In some embodiments, this is enough to hold optical substrate  120  and LEE substrate  110  together. In some embodiments, material  450  is partially cured prior to mating of optical substrate  120  and LEE substrate  110 . 
     In order to facilitate electrical conduction and alignment between conductive traces  430  on LEE substrate  110  and conductive traces  420  on optical substrate  120 , the geometry of conductive traces  430  and/or traces  420  may be modified. In one embodiment, pads are formed having at least one dimension larger than that of the conductive traces.  FIG. 9A  shows an example of pads  910  formed at the ends of conductive traces  420  on optical substrate  120 .  FIG. 9B  shows an example of pads  920  formed at the ends of conductive traces  430  on substrate  210 . 
     In some embodiments, electrical conductivity between conductive traces  430  on LEE substrate  110  and conductive traces  420  on optical substrate  120  is enhanced by the use of a conductive material between the two traces. Examples of conductive materials include conductive epoxy, conductive adhesive, ACA, conductive tape, anisotropic conductive tape or film and the like. Such conductive materials may be applied to portions of conductive traces  430  and/or portions of conductive traces  420 . Such material may be applied by, for example, printing, ink jet printing, screen printing, dispensing, deposition, such as evaporation or sputtering, through a mask, lamination and optional patterning or the like. This may also aid in the attachment of LEE substrate  110  to optical substrate  120 . 
     In some embodiments, additional techniques may be used to attach LEE substrate  110  to optical substrate  120 , for example using an adhesive, a UV- or heat-cured adhesive, physical fasteners or the like. For example, an adhesive may be formed by spraying, spinning, spreading, or may be in tape form, or may be deposited using a doctor blade technique, or by printing. The adhesive may cover substantially all of the mating surfaces or only one or more portions of the mating surfaces. In one preferred embodiment, a material used to mate LEE substrate  110  and optical substrate  120  is transparent to a wavelength of light emitted by LEE  130  and/or light-conversion material  450 . More than one material may be used to mate LEE substrate  110  and optical substrate  120 . 
     The size of a LEE  130  may be smaller than well  440  and a modest amount of misalignment of the center of LEE  130  with the center of well  440  may be acceptable. To aid in alignment, alignment features, for example alignment marks or pins or holes or other features on optical substrate  120  that mate or align to corresponding features on LEE substrate  110  may be used. Such alignment features may be formed on optical substrate  120  at the same time or a different time from the formation of wells  440  and/or optical elements  410 . Similarly, such alignment features on LEE substrate  110  may be formed at the same time or a different time as conductive traces  430 . 
     In some embodiments, a reflective surface is formed on the back or front of LEE substrate  110 , so that any light emitted out the back side (i.e., the side adjacent to LEE substrate  110 ) of the LEEs  130  is reflected back toward light-conversion material  450 . Such a reflective coating may include a metal such as gold, silver, aluminum, copper or the like and may be deposited by evaporation, lamination, sputtering, chemical vapor deposition, plating, electroplating or the like, or may include a reflective coating such as paint, ink or the like, for example white ink or white paint. If the reflective coating is on the same side as conductive traces  430 , the reflective coating may be electrically isolated from conductive traces  430  or may be removed in the regions occupied by conductive traces  430 . The reflective coating may even be non-conductive. The reflective coating may be formed either over or under conductive traces  430 . The reflective coating may cover all or portions of LEE  130  and/or conductive traces  430 . The reflective coating may also include other materials, e.g., a Bragg reflector, or one or more layers of a specular or diffuse reflective material. In one embodiment, LEE substrate  110  is backed with a reflective material, for example any one as discussed above, or, e.g., White 97  manufactured by WhiteOptics LLC or MCPET manufactured by Furukawa, or any other reflective material. In one embodiment, LEE substrate  110  includes a material that is reflective to a wavelength of light emitted by LEE  130 , for example white PET, white paper, MCPET, White 97  or the like. In one embodiment, conductive traces  430  include a material reflective to a wavelength of light emitted by LEE  130  and/or light-conversion material  450  and are patterned to provide a region of reflective material surrounding LEE  130 . 
     In one embodiment, one or more materials are formed over all or portions of LEEs  130  prior to mating with optical substrate  120 . LEEs  130  may be all or partially coated with a transparent material having a refractive index of at least 1.3, preferably at least 1.4, to decrease total internal reflection losses in LEEs  130 . Such an embodiment provides spatial separation between light-conversion material  450  and LEEs  130 , which may result in reduced heating of light-conversion material  450 . Reduced heating of light-conversion material  450  may be desirable because such reduced heating may result in reducing the efficiency loss and wavelength shift associated with higher light-conversion material temperatures. In some embodiments LEE  130  may be covered by a phosphor or a phosphor and a binder prior to mating with optical substrate  120 , as described in U.S. Provisional Patent Application No. 61/589,908, filed Jan. 24, 2012, the entire disclosure of which is incorporated herein by reference. 
     In accordance with various embodiments of the invention, the LEE substrate  110  is then separated into individual substrates  210 , resulting in the structure as shown in  FIG. 4 . Separation of LEE substrate  110  into substrates  210  may be done in various ways. In one embodiment, LEE substrate is separated into sections  310 , as shown in  FIG. 3 . In one embodiment LEE substrate  110  has portions removed between LEE  130 , leaving gaps between substrates  210 , as shown in  FIG. 4 . LEE substrate  110  may be separated or have portions removed using a number of techniques. For example, LEE substrate  110  may be cut using a straight or rotating blade, by die cutting, punching or with a laser. LEE substrate  110  may be partially separated before mating to optical substrate  120 , for example with perforations to facilitate separation after mating to optical substrate  120 . In one embodiment the perforations are sufficient to permit removal of unwanted sections of LEE substrate by pulling or peeling them off of optical substrate  120 . 
     In some embodiments, LEE substrate  110  is separated into substrates  210  before mating to optical substrate  120  and substrates  210  are placed into position individually. One advantage of this approach is that the individual LEEs  130  may be tested and mapped on the original LEE substrate  110 , and then binned after singulation (i.e., formation of substrates  210 ) from LEE substrate  110 . Testing and binning of substrates  210 , with one or more LEEs  130  on each substrate  210 , permits elimination of failed or out-of-specification LEEs  130 . For example LEE substrate  110  may support a plurality of operational LEEs  130  and one or more non-operational or out of specification LEEs  130 . After testing all LEEs  130  on LEE substrate  110  and singulation into substrates  210 , the non-operational or out of specification LEEs  130  may be removed and not attached to optical substrate  120 . 
     Another advantage of this approach is that LEEs  130  may be formed closer together on LEE substrate  110  before singulation than they would be placed on optical substrate  120 , permitting manufacture of a relatively larger number of completed LEE substrate units (LEE substrate  210  and LEE  130 ) per unit area. 
     Such techniques also permit sorting of LEEs  130  to achieve more uniform light characteristics than might be achieved without binning. For example, LEE substrate  110  may feature multiple LEEs  130  in two or more groups, each group including or consisting essentially of one or more LEEs  130  having one or more similar characteristics. For example, all of LEEs  130  may be divided into groups based on emission wavelength. Several wavelength-range groups or bins spanning, for example, about 5 nm or about 2.5 nm may be identified, and all of the LEEs  130  may be assigned to wavelength bins according to their emission wavelength. After singulation into substrates  210 , the different substrates  210  may be sorted into their respective bins and used for different applications that require different wavelength distributions. Other characteristics may be identified for assigning to groups, e.g., forward voltage, light output power, and the like. 
       FIG. 10  is a general flow chart of the process used to make one embodiment of the structure discussed above with reference to  FIG. 4 . The process starts with providing the LEE substrate in step  1010 . Conductive traces  430  are formed over the LEE substrate  110  in step  1015 . LEEs  130  are formed over (and electrically coupled to) conductive traces  430  in step  1020 . Step  1020  may include the use of wire bonding or one or more adhesives, e.g., a conductive adhesive, a non-conductive adhesive or an ACA, soldering, eutectic bonding or other means of electrically coupling LEE  130  to conductive traces  430 . In parallel a second process starts with the provision of optical substrate  120 , as shown in step  1030 . Wells  440  are formed in optical substrate  120  in step  1035 . Optical elements  410  are formed in optical substrate  120  in step  1040 . In some embodiments, steps  1035  and  1040  are performed simultaneously. Conductive traces  420  are formed over optical substrate  120  in step  1045 , and phosphor  450  is formed in wells  440  in step  1050 . The two processes come together in step  1060 , in which the structures are mated together, for example as shown in  FIG. 8 . Step  1060  may include the use of one or more adhesives, for example a conductive tape, a conductive adhesive or epoxy, a non-conductive adhesive or an ACA, or other means of electrically coupling conductive trances  430  to conductive traces  420 . The phosphor  450  is cured in step  1070  and LEE substrate  110  is separated into sections  210  in step  1080 . In some embodiments, the process includes additional steps and/or some steps shown in  FIG. 10  are omitted and/or the order of the steps is different from that shown in  FIG. 10 . 
       FIG. 11  depicts another embodiment of the present invention, system  1100 , which includes substrate  1101  over which conductive traces  1110  have been formed and into which through-holes  1140  have been formed. LEEs  130  are electrically coupled to conductive traces  430  formed over LEE substrate  210 , which are then electrically coupled to conductive traces  1110  on substrate  1101 . 
     Substrate  1101  and substrate  210  may include or consist essentially of a semicrystalline or amorphous material, e.g., polyethylene naphthalate (PEN), polyethylene terephthalate (PET), acrylic, polycarbonate, polyethersulfone, polyester, polyimide, polyethylene, and/or paper. Substrate  1101  and substrate  210  may be substantially flexible, substantially rigid, or substantially yielding. Substrate  1101  and substrate  210  may include multiple layers of the same or different materials, e.g., a deformable layer over a rigid layer, for example, a semicrystalline or amorphous material, e.g., PEN, PET, polycarbonate, polyethersulfone, polyester, polyimide, polyethylene, paint, plastic film, and/or paper formed over a rigid substrate for example including, acrylic, aluminum, steel and the like. Depending upon the desired application for which embodiments of the invention are utilized, substrate  1101  and substrate  210  may be substantially optically transparent, translucent, or opaque. For example, substrate  1101  and substrate  210  may exhibit a transmittance or a reflectivity greater than about 70% for optical wavelengths ranging between approximately 400 nm and approximately 700 nm. In some embodiments substrate  1110  and substrate  210  may exhibit a transmittance or a reflectivity of greater than about 70% for one or more wavelengths emitted by LEEs  130  and/or the light-conversion material (identified as  450  in previous drawings or  1130  in  FIG. 11 ). Substrate  1101  and substrate  210  may also be substantially insulating, and may have an electrical resistivity greater than approximately 100 ohm-cm, greater than approximately 1×10 6  ohm-cm, or even greater than approximately 1×10 10  ohm-cm. As discussed above, in one embodiment a reflective surface is formed on the back or front of substrate  210 , so that any light emitted out the back side (i.e., the side of substrate  210  opposite LEE  130 ) of LEE  130  is reflected back toward light-conversion material  1130 . 
     In one embodiment, substrate  1101  includes one or more optical elements (e.g., as shown in  FIG. 7 ). In some embodiments, one optical element is associated with each LEE  130 , while in other embodiments multiple LEEs  130  are associated with one optical element, or multiple optical elements are associated with a single LEE  130 . One or more LEEs  130  may not be associated with an engineered optical element, but may instead be associated with a flat or roughened surface. In one embodiment, substrate  1101  includes elements or features to scatter, diffuse and/or spread out light generated by LEEs  130 . 
     System  1100  of  FIG. 11  may be manufactured in a substantially similar fashion as that described with respect to system  400 . However, system  1100  includes two materials formed over LEEs  130 , rather than merely a material  450  as in  FIG. 4 . Material  1120  may partially or fully cover a LEE  130  and may be transparent and have a refractive index of at least 1.3, preferably at least 1.4, to decrease total internal reflection losses in the LEE  130 . Such an embodiment provides spatial separation between and LEE  130  and light-conversion material (phosphor)  1130 , which may result in reduced heating of light-conversion material  1130 . Reduced heating of light-conversion material  1130  may be desirable because it may result in reducing the efficiency loss and wavelength shift associated with higher light-conversion material temperatures. 
     In some embodiments, material  1120  is applied to cover or partially cover LEEs  130  prior to mating with substrate  1100 . In such embodiments, the LEE  130  with material  1120  formed thereover or partially thereover is immersed or partially immersed into well  1140  of substrate  1100  that is partially or completely filled with material  1130 . This approach may be used in other embodiments of the invention as well. In other embodiments, wells  1140  do not contain materials  1120 ,  1130  prior to mating. 
     In the previously described embodiments LEEs  130  have been formed on LEE substrate  110  with a pattern substantially matching the features of that on the mating piece, for example wells  1140  of substrate  1101  ( FIG. 11 ) or wells  440  of optical substrate  120  ( FIG. 7 ). In another embodiment, LEEs  130  are formed on LEE substrate  110  with a density higher than that of the matching features on the mating piece. In some embodiments the spacing or pitch between LEEs  130  on LEE substrate  110  may be in the range of about 2 mm to about 50 mm. In some embodiments LEEs  130  have a dimension in the range of about 25 μm to about 500 μm. Thus, the density of LEEs  130  on LEE substrate  110  may be in the range of about 5× larger to about 100× larger than the density of matching features on the mating piece. In one embodiment, the LEEs  130  on LEE substrate  110  have a spacing that is an integer divisor of the spacing of the mating features. For example, if the mating features are spaced about 10 mm apart, the LEE  130  may be spaced about 1 mm apart, or may be spaced about 0.5 mm apart. Thus, when LEE substrate  110  is mated with the matching substrate, some of LEEs  130  match up with the matching features and one or more LEEs  130  are positioned on LEE substrate  110  in between adjacent matching features. 
       FIG. 12  shows one embodiment of the invention, similar to that shown and discussed in reference to  FIG. 4 . A difference between system  1200  shown in  FIG. 12  and the structure shown in  FIG. 8  (the structure shown in  FIG. 4  at an early stage of manufacture) is that LEE substrate  110  has one or more LEEs  130  (identified as  1220  and  1230 ) between LEEs  130  that are aligned with wells  440  (identified as  1210  and  1240 ). During the manufacture, LEE substrate  110  is first aligned as shown in  FIG. 12  and LEE units  1210  and  1240  are mated with optical substrate  120  (conductive traces  430  mated with conductive traces  420 ). Then, the portions of LEE substrate  110  associated with LEEs  1210  and  1240  are separated from the main LEE substrate  110  as shown in  FIG. 13 , and the main LEE substrate  110  is removed and repositioned on optical substrate  120  or another optical substrate  120  and the remaining LEEs are matched up with features on optical substrate  120  and mated to optical substrate  120  and again the portions of LEE substrate  110  associated with those LEEs is separated from the main LEE substrate  110 , and the process may be repeated until all or substantially all of the LEEs are placed. After the first set of LEEs are placed and separated, LEE substrate  110  appears as shown in  FIG. 13 , having holes  1310  where LEEs have been separated therefrom. 
       FIG. 14  is a plan view of one embodiment of the present invention that features a 3×3 array of wells  440  on optical substrate  120 . Overlaid on the array is LEE substrate  110  (not identified in  FIG. 14 ) that is delineated into cells  1410 . Each cell  1410  includes one LEE  130  (not shown). Wells  440  have a larger (but preferably with an integer multiplier) pitch than LEEs  130 , resulting in the formation of more LEEs  130  on LEE substrate  110  than wells  440  for the same area. In the example shown in  FIG. 14 , the LEE  130  array (or LEE cell  1410  array) is 9×9 units, while the well  440  array is 3×3. In one cycle of the operation, nine LEE units  130  are mated with wells  440 , identified by the dashed lines. However, in the same area there are an additional  72  (original  81  less the  9  placed) LEE cells  1410  that may be placed in subsequent cycles of the process. One advantage of this approach is that LEEs  130  in LEE cells  1410  may be placed on LEE substrate  110  much closer together than if they had the pitch of the matching units. This increases throughput in the placing tools used to place LEEs  130  on LEE substrate  110 , reduces the amount of LEE substrate required, and in general reduces the overall cost of the system. 
     An additional advantage is that LEEs  130  may be tested and mapped before or after placement on LEE substrate  130 , and this information used to adjust placement and/or separation of the LEE units from LEE substrate  110  in order to increase yield, or to achieve more uniform optical or electrical characteristics within a string or across all or a portion of the array of LEE  130 . For example, referring to  FIG. 14 , if LEE unit  1420  is out of specification or non-functional, it may be left attached to the main portion of LEE substrate  110  while the other  8  LEE units associated with that pitch and placement are separated from the main portion of LEE substrate  110  and mated to optical substrate  120 . This leaves an empty well  440  associated with an LEE unit  1420 . In one embodiment, this is left empty and conductive traces  420  adjacent to LEE unit  1420  may be shorted. In another embodiment the empty well is populated, for example with LEE  130  or another active or passive device, at a later stage of manufacture. While this approach is described with reference to a system having an optical substrate such as optical substrate  120 , this is not a limitation of the present invention and in other embodiments other structures may be employed. 
     The systems described above may be combined with additional electronics to form an electronic device  1500  as shown in  FIG. 15 . In one embodiment, the device includes multiple LEEs  130  that are electrically coupled to traces  420 . As shown, electronic device  1500  includes three serially-connected strings  1510  of LEEs  130 . Electronic device  1500  also includes circuitry  1520  electrically connected to one or more of strings  1510 . Circuitry  1520  may include or consist essentially of portions or substantially all of the drive circuitry, sensors, control circuitry, dimming circuitry, and or power-supply circuitry or the like, and may also be adhered (e.g., via an adhesive) or otherwise attached to a substrate  1530 . In one embodiment, the power supply and driver are distributed, e.g., the device  1500  may have a centralized power supply and all or a portion of the drive circuitry distributed in different locations. Circuitry  1520  may even be disposed on a circuit board (e.g., a printed circuit board) that itself may be mechanically and/or electrically attached to substrate  1530 . In other embodiments, circuitry  1520  is separate from substrate  1530 . In some embodiments circuitry  1520  is formed on substrate  1530 . While  FIG. 15  depicts the LEEs  130  serially connected in strings  1510 , and strings  1510  connected or connectable in parallel, other die-interconnection schemes are possible and within the scope of embodiments of the invention. 
     As shown in  FIG. 15 , the lighting system  1500  may feature multiple strings, each string including or consisting essentially of a combination of one or more LEEs  130  electrically connected in series, in parallel, or in a series-parallel combination with optional fuses, antifuses, current-limiting resistors, zener diodes, transistors, and other electronic components to protect the LEEs  130  from electrical fault conditions and limit or control the current flow through individual LEEs  130  or electrically-connected combinations thereof. In general, such combinations feature an electrical string that has at least two electrical connections for the application of DC or AC power. A string may also include a combination of one or more LEEs  130  electrically connected in series, in parallel, or in a series-parallel combination of LEEs  130  without additional electronic components.  FIG. 15  shows three strings of LEEs  130 , each string having three LEEs  130  in series. 
       FIG. 16  shows another embodiment of the present invention, system  1600 , that includes a base substrate  1610  having holes  1620  formed therein, as well as conductive traces  1110  formed thereover. One or more LEEs  130  are electrically coupled to conductive traces  420  on LEE substrate  210  and conductive traces  430  over LEE substrate  210  are electrically coupled to conductive traces  1110  formed over base substrate  1610 . Base substrate  1610  may include or consist essentially of any of the materials described above with respect to substrate  1101  or other substrate materials. In one embodiment, material  1630  is formed over all or a portion of one or more LEEs  130 . Holes  1620  have sidewalls  1640 . In some embodiments the sidewalls  1640  are perpendicular to the surface of base substrate  1610 ; however, this is not a limitation of the present invention and in other embodiments sidewalls  1640  are sloped, curved or have other shapes. In some embodiments sidewalls  1640  are reflective to a wavelength of light emitted by LEE  130  and/or phosphor material  1630 . In some embodiments sidewalls  1640  are coated with a material that is reflective to a wavelength of light emitted by LEE  130  and/or phosphor material  1630 , for example silver, gold, aluminum, or a white reflective material, for example White 97  manufactured by WhiteOptics LLC or MCPET manufactured by Furukawa, or any other reflective material. In some embodiments the substrate  1610  may include or consist essentially of a reflective material, and thus sidewalls  1640  may be reflective as a result. 
     In one embodiment, the manufacture of system  1600  starts with the structure shown in  FIGS. 5A and 5B .  FIG. 17  shows the structure of  FIG. 16  at a early stage of manufacture.  FIG. 17  shows three different embodiments. The left LEE  130  has material  1630  formed over it and has a substantially hemispherical shape. The center LEE  130  has material  1630  formed over it and has a shape that is substantially conformal to LEE  130 . The right LEE  130  features materials  1120  and  1130 , formed successively over LEE  130 , as described above. 
     Material  1630  may include or consist essentially of a mixture of one or more light-conversion materials and a matrix material. The light-conversion material is incorporated to shift one or more wavelengths of at least a portion of the light emitted by LEE  130  to other desired wavelengths (which are then emitted from the larger device alone or color-mixed with another portion of the original light emitted by the die). In some embodiments material  1630  includes or consists essentially of multiple layers of phosphor-infused matrix and/or matrix. That is, the phosphor may include multiple layers, where each layer includes either a phosphor-infused matrix or solely the matrix material. Where multiple layers of phosphor-infused matrix are used, each layer may include different phosphors and/or different matrix materials. In one embodiment shown for the right LEE  130  in  FIG. 17 , material  1120  includes or consists essentially of a matrix material that is transparent to a wavelength of light emitted by LEE  130  and material  1130  includes or consists essentially of one or more phosphors within a matrix material. 
       FIG. 18  depicts a structure  1800  that includes a base substrate  1610  featuring conductive traces  1110  formed thereover and holes  1620  formed therethrough. Holes  1620  may have any shape, for example square, rectangular, round, elliptical or any other shape. In an embodiment, holes  1620  are replaced by wells (not shown in the Figures), which may have any size or shape. In one embodiment, the wells may be shaped to match the shape of material  1630 , that is, material  1630  fits into a well when system  1700  and system  1800  are mated. In some embodiments, base substrate  1610  features optical elements associated with one or more LEEs  130 . In some embodiments, the space between material  1630  and the walls of the wells are filled with air or other gases or fluids. In one embodiment, the space between material  1630  and the walls of a well is filled with a transparent material, and in one embodiment such transparent material has an index of refraction greater than about 1.4. 
     In the next stage of manufacture structure  1700  ( FIG. 17 ) is mated with structure  1800  ( FIG. 18 ) to form the structure shown in  FIG. 16 . The arrays of holes  1620  are arranged such that at least some holes  1620  match the position of LEEs  130  on base substrate  1610 . In one embodiment, one LEE  130  is associated with one hole  1620 . In one embodiment, multiple LEEs  130  are associated with one hole  1620 . Structure  1700  may be attached to structure  1800  using a variety of techniques, for example via use of a spray adhesive, a liquid adhesive, a tape or film adhesive, or other means. As discussed above, LEE substrate  110  may be separated into substrates  210  before or after mating with base  1610 . 
       FIG. 19  shows another embodiment of the present invention, system  1900 , which is similar to system  1600  shown in  FIG. 16 . However, in system  1900  the LEEs  130  on LEE substrate  210  are replaced by packaged LEDs, i.e., LED dies each in a package, identified as LEDs  1910  and  1920  in  FIG. 19 . Packaged LED  1910  includes contacts  1930  and emission area  1950 , from which the light emanates. Packaged LED  1920  is similar to packaged LED  1910 , with the exception that emission area  1950  is replaced by a domed emission area  1940 . Packaged LEDs  1910  and  1920  are representative of two different styles of LED packages; however, the style of package is not a limitation of the present invention and in other embodiments other styles of packages may be used. Contacts  1930  may be electrically coupled to conductive traces  1110  using a variety of means, for example wire bonding, conductive adhesive, solder, eutectic bonding, conductive epoxy, ACA, ACF, or the like. This approach of using packaged LEDs may also be used in other embodiments of this invention, for example those associated with  FIG. 4  or  11 . 
     In some embodiments, a LEE unit, for example  1410  or  1420  in  FIG. 14 , may be faulty and this fault may be found during or after the manufacturing process thereof. A fault may be, for example, an open circuit, a short circuit or an intermittent connection. When LEEs  130  are formed with one or more LEEs on each of multiple substrates, replacement of the faulty units may be carried out more easily than if all of the LEE were on a single substrate, by removing or bridging the faulty unit. Exemplary such “rework” techniques are detailed below. 
       FIG. 20  is a general flow chart of a process used to make one embodiment of the structure discussed above with reference to  FIG. 16 . The process starts with the provision of the LEE substrate in step  2010 . Conductive traces  430  are formed over LEE substrate  110  in step  2015 . LEEs  130  are formed over (and electrically coupled to) conductive traces  430  in step  2020 . Step  2020  may include or consist essentially of the use of wire bonding, one or more adhesives, for example a conductive adhesive, a conductive epoxy, a non-conductive adhesive or an ACA, or other means of electrically coupling LEE  130  to conductive traces  430 . Phosphor (light-conversion material)  1630  is formed over all or portions of LEE  130  in step  2025  and the phosphor is cured in step  2030 . In parallel, a second process starts with provision of a base substrate  1610  in step  2040 . Holes  1620  are formed in base substrate  1610  in step  2045 . Conductive traces  1110  are formed over base substrate  1610  in step  2050 . The two processes come together in step  2060  where the structures are mated together, for example as shown with reference to  FIG. 16 . Step  1060  may include or consist essentially of the use of one or more adhesives, for example a conductive adhesive, a non-conductive adhesive or an ACA, or other means of electrically coupling conductive trances  430  to conductive traces  1110 . LEE substrate  110  is separated into sections of LEE substrate  210  in step  2070 . In some embodiments the process flow includes additional steps and/or some steps shown in  FIG. 20  are omitted and/or the order of the steps is different from that shown in  FIG. 20 . 
     In some embodiments, the light-emitting element and/or light-conversion materials are different within one lightsheet (i.e., the finished product including one or more LEEs on substrates  210  attached to a substrate  1610 ). For example, a lightsheet may include a plurality of light-emitting elements, each emitting at substantially the same wavelengths, but different composition, concentration or thickness light-conversion materials may be associated with different portions of the light-emitting elements. In one embodiment a yellow-emitting phosphor and a red-emitting phosphor may be formed in different groups of wells to provide improved color temperature and CRI and uniformity of color temperature and CRI. In one embodiment, a lightsheet includes a plurality of light-emitting elements that are divided into groups, and each group emits light of a different wavelength. For example, in one embodiment, a first group of light-emitting elements emits in the red wavelength range and a second group of light-emitting elements emits in the blue wavelength range. In one embodiment, a first group of light-emitting elements is optically coupled with a light-conversion material while a second group of light-emitting elements is not optically coupled with a light-conversion material. 
     In some embodiments all or portions of the process are performed in a roll-to-roll process, in which a sheet of the substrate material travels through different processing stations. Such roll-to-roll processing may, for example, include the formation of conductive traces  420  or  430 , dispensing of the adhesive, and the placement of LEEs  130 . In addition, other passive and/or active electronic devices may be attached to substrate  1530 , including, e.g., sensors, antennas, resistors, inductors, capacitors, thin-film batteries, transistors and/or integrated circuits. Such other passive and/or active electronic devices may be electrically coupled to conductive traces  420  or  430  or LEE  130  with adhesive ( 610  and/or  620 ) or by other approaches. In some embodiments, LEEs  130  include other devices, for example sensors, antennas, resistors, inductors, capacitors, thin-film batteries, transistors and/or integrated circuits. 
     In general in the above discussion the arrays of light emitters, wells, optics and the like have been shown as square or rectangular arrays; however, this is not a limitation of the present invention and in other embodiments these elements are formed in other types of arrays, for example hexagonal, triangular or any arbitrary array. In some embodiments these elements are grouped into different types of arrays on a single substrate. 
     The terms and expressions employed herein are used as terms and expressions of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof. In addition, having described certain embodiments of the invention, it will be apparent to those of ordinary skill in the art that other embodiments incorporating the concepts disclosed herein may be used without departing from the spirit and scope of the invention. Accordingly, the described embodiments are to be considered in all respects as only illustrative and not restrictive.