METHODS OF MAKING LIGHT-EMITTING ASSEMBLIES COMPRISING AN ARRAY OF LIGHT-EMITTING DIODES HAVING AN OPTIMIZED LENS CONFIGURATION

Abstract

Light emitting assemblies comprise a plurality of Light Emitting Diode (LED) dies arranged and attached to common substrate to form an LED array having a desired optimum packing density. The LED dies are wired to one another and are attached to landing pads on the substrate for receiving power from an external electrical source via an interconnect device. The assembly comprises a lens structure, wherein each LED die comprises an optical lens disposed thereover that is configured to promote optimal light transmission. Each optical lens has a diameter that is between about 1.5 to 3 times the size of a respective LED die, and is shaped in the form of a hemisphere. Fillet segments are integral with and interposed between the adjacent optical lenses, and provide sufficient space between adjacent optical lenses so that the diameters of adjacent optical lenses do not intersect with one another.

Claims

1.-20. (canceled)

21. A method for making a light emitting assembly comprising: placing two or more Light Emitting Diode (LED) dies on a surface of a substrate, wherein the LED dies are electrically connected with one another and are electrically connected with two or more landing pads on the substrate; placing a lens structure over the LED dies, wherein the lens structure comprises integral lenses for each of the respective two or more LED dies, wherein the lens structure is in contact with the surface of the substrate between adjacent LED dies.

22. The method of claim 21, wherein during the step of placing the LED dies, the LED dies positioned a distance from one another such that a portion of the substrate surface between adjacent LED dies is exposed.

23. The method of claim 22, wherein the exposed portion of the substrate surface between adjacent LED dies is covered with the lens structure during the step of placing the lens structure over the LED dies.

24. The method of claim 21, wherein the lens structure comprises an integral fillet segment between adjacent lenses that has a reduced thickness as measured from the substrate surface relative to the adjacent lenses.

25. The method of claim 21, wherein the landing pads are positioned along a portion of the substrate surface that is exposed and not covered by the lens structure.

26. The method of claim 21, wherein the step of placing the lens structure comprises forming the lens structure over the LED dies by molding process.

27. The method of claim 21, wherein each of the lenses are substantially hemispherical in shape.

28. The method of claim 21, wherein during the step of placing the LED dies, a first number of the LED dies are positioned on the substrate surface to form a parameter that surrounding a second number of LED dies positioned on the substrate surface.

29. A light emitting assembly comprising: two or more Light Emitting Diode (LED) dies that are electrically connected together on a substrate surface, wherein the LED dies are positioned on the surface such that a portion of the surface between the LED dies is exposed; two or more landing pads on the substrate that are electrically connected with the LED dies; a lens structure disposed over the LED dies, wherein the lens structure comprises integral lenses over each of the respective LED dies, wherein the lens structure contacts the portion of the substrate surface between adjacent LED dies, and wherein the two or more landing pads are free of the lens structure to facilitate electrical contact with an electrical interconnect.

30. The light emitting assembly of claim 29, wherein the lens structure extends over an entirety of a region of the substrate surface on which the LED dies are disposed.

31. The light emitting assembly of claim 29, wherein each of the lenses are substantially hemispherical in configuration and each centered over a respective one of the LED dies.

32. The light emitting assembly of claim 31, wherein the lens structure comprises an integral fillet segment that is interposed between adjacent lenses, wherein the fillet segment has a reduced thickness as measured from the substrate surface relative to the adjacent lenses.

33. The light emitting assembly of claim 29, wherein the LED dies are arranged in a circular pattern on the substrate surface.

34. The light emitting assembly of claim 29 further comprising an interconnection substrate that is configured to electrically connect with the landing pads of the substrate.

35. The light emitting assembly of claim 29, wherein the LED dies are provided in a pattern comprising an outer parameter of LED dies that surround one or more LED dies positioned inside of the outer parameter.

35. A light emitting assembly comprising: a substrate having surface; two or more Light Emitting Diode (LED) dies that are disposed on the substrate surface, wherein the LED dies positioned adjacent one another and electrically connected together, and wherein the LED dies are electrically connected with lending pads located on the substrate; a lens structure disposed over the LED dies and comprising a number of integral lenses that each cover a respective LED die, wherein the landing pads are free of the lens structure; and an interconnection substrate that is configured to connect with the substrate to electrically connect with the landing pads to provide electricity to the LED dies.

36. The light emitting assembly of claim 35, wherein a portion of the substrate surface between adjacent LED dies is exposed and covered by the lens structure.

37. The light emitting assembly of claim 36, wherein the lens structure covers an entirety of the LED dies and the exposed portions interposed between the LED dies.

38. The light emitting assembly of claim 35, wherein each of the integral lenses have a hemispherical configuration centered over a respective LED die.

39. The light emitting assembly of claim 38, wherein the lens structure comprises a fillet segment that is interposed between adjacent lenses, wherein the fillet segment is configured so that diameters of the adjacent lenses do not intersect with one another.

40. The light emitting assembly of claim 35, wherein one or more of the LED dies are surrounded by a number of LED dies arranged in a parameter around the one or more LED dies.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] These and other features and advantages of light-emitting assemblies and methods for making the same as disclosed herein will be appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings.

[0014] FIG. 1 is a perspective view of example embodiment light emitting assembly comprising an LED array made up of nine LED dies disposed a MCPCB substrate;

[0015] FIGS. 2a and 2b are perspective views of the example embodiment light emitting assembly of FIG. 1 that includes a lens disposed over each LED die;

[0016] FIG. 3 is a flowchart illustrating the steps used for making the example embodiment light emitting assembly of FIGS. 1 and 2;

[0017] FIGS. 4a to 4c are top plan views of example embodiment light emitting assemblies having different sized lenses per dies;

[0018] FIG. 5 is a perspective view of an example embodiment light emitting assembly comprising an LED array made up of 9 LED dies with a lens over each LED die;

[0019] FIG. 6 is a perspective view of another example embodiment light emitting assembly comprising an LED array made up of 16 LED dies with a lens over each LED die;

[0020] FIG. 7 is a perspective view of another example embodiment light emitting assembly comprising an LED array made up of 18 LED dies with a lens over each LED die;

[0021] FIG. 8 is a cross sectional view of an example light emitting assembly as disclosed herein illustrating its connection to an interconnect substrate;

[0022] FIG. 9 is perspective view of the bottom surface of an example interconnect structure; and

[0023] FIG. 10 is a top perspective view of the interconnect structure of FIG. 9 supporting the light emitting assembly of FIG. 2.

DETAILED DESCRIPTION

[0024] Light-emitting assemblies as disclosed herein comprise an LED array made up of a number of LED dies, wherein the LED dies are specially arranged in a predetermined manner so as to provide an efficient packing that produces an optimized light output, and wherein each LED die comprises a lens or lens per die (LPD) that is specially configured to provide an optimum light transmission. Reference will now be made in detail to some embodiments of such light-emitting assemblies, examples of which are illustrated in the accompanying drawings.

[0025] FIG. 1 is a top view of an example embodiment metal-core printed circuit board (MCPCB) substrate 10 on which an array of LED dies 12 are mounted. The LED dies are made by conventional method and are singulated from a wafer prior to attachment onto the substrate. Because the substrate 10 has a metal core, it would be difficult to supply power to the LED dies 12 through through-hole vias that pass from the LEDs through the printed circuit board to a bottom surface of the board. Thus, the LED dies 12 are electrically connected to landing pads 14 positioned on the top surface of the substrate 10.

[0026] While substrate 10 has been illustrated in FIG. 1 as having a generally square configuration, it is to be understood that substrates as used for forming light-emitting assemblies as disclosed herein may be configured having various different geometric shapes based for example on the particular end-use application. Additionally, while the landing pads 14 are illustrated in FIG. 1 as being at the corners of the substrate, the placement and configuration of the landing pads can also vary. Such variations in substrate shape and landing pad location and configuration are understood to be within the scope of light-emitting assemblies as disclosed herein.

[0027] The LED dies are arranged on the substrate in a manner that provides optimal light output for an optimized spatial packing density, as the spatial packing density reflects a compromise based on the desired emitting area and photometric power. The particular example embodiment illustrated in FIG. 1 comprises an LED array made up of nine LED dies arranged in a special configuration; namely, with one LED die positioned in the middle and surrounded in circular fashion by eight LED dies. This LED die arrangement is desired as it enables the LED dies to be equally spaced apart from one another. The LED dies 12 are electrically connected both to one another and to the landing pads 14 by wire bonds 16. The substrate surface comprises a highly-reflective material 18 that the LED dies are disposed upon.

[0028] In such example embodiment, the LED dies 12 are arranged relative to one another having an optimized packing density that is not too tight (so as to minimize or prevent adjacent LED die light output from interfering or being absorbed with one another), and that is not too loose (so as to increase the flux density and minimize the total space occupied by the LED dies). The LED dies are spaced apart in a predetermined manner calculated to provide optimal LED array light output while occupying a minimum amount of space.

[0029] In an example embodiment, is it desired that the LED dies be arranged relative to one another so that the distance between adjacent LED dies (as measured from the middle of each adjacent die) is about 2.2 times the die size, and in an example embodiment less than about 4 times, and preferably about 3 times or less, the die size. It is to be understood that the exact distance between adjacent LED dies in the array as disclosed herein may vary depending on such factors as the size and/or number of the LED dies. For a particular embodiment where the LED die size is approximately 45 mils (1.143 mm), a desired spatial distance between adjacent LED dies is approximately 3.4 mm.

[0030] FIG. 2a illustrates a light emitting assembly 19 comprising the LED array of FIG. 1, comprising a lens structure 20 disposed over the LED dies. Specifically, the lens structure 20 comprises a lens 22 disposed over each individual LED die 12 or a lens per die (LPD). Accordingly, in such example embodiment, each LED die 12 comprises its own lens 22 that is disposed thereover. In an example embodiment, the lens structure is not provided as a preformed member, but is formed by using a suitable silicone material comprising a wavelength conversion material, such as phosphor particles or the like, dispersed therein. The silicone material is provided in a mold cavity having the desired LPD configuration, and the mold cavity and substrate are brought together under vacuum conditions, and the combined assembly is subjected to compressive force to form the desired lens structure by compression molding technique. Thus, in a preferred embodiment the individual LPDs and lens structure are formed in a single compression molding step.

[0031] FIG. 2b illustrates the light emitting assembly of FIG. 2a, and better shows the LPDs 22 as being configured having a hemispherical dome shape defined by a particular diameter or radius of curvature. Generally, it is desired to use the largest possible LPD diameter for a fixed number and arrangement/position of LED dies as long as the LPDs of adjacent LED dies do not overlap with one another, i.e., do not have hemispheres that overlap with one another, as such overlap may cause unwanted light transmission interference. Accordingly, the LPDs as disclosed herein are sized having a diameter engineered to provide an optimal light transmission for a fixed number and arrangement/position of LED dies.

[0032] In an example embodiment, it is desired that the LPDs each have a diameter that is between about 1.5 to 3 times the size of an LED die (measured as a side length) that it is disposed over. It has been discovered that having a diameter less than about 1.5 times the LED die size is undesired because it will produce a decrease in the desired luminous output. It is theorized that such a result may be due to a reduced phosphor mean free path, causing light emitted from the LED die to be reflected back onto the LED die and not transmitted outwardly therefrom. Additionally, light produced by the LED die may be confined within the LPD when sized too small because the LED die is not centered to the LPD and, thus may be prone to internal reflection also reducing light transmission. Having a LPD diameter greater than about 3 times the LED die size, for a given number and arrangement/position of LED dies, can cause overlapping of adjacent LPDs, which as noted above is not desired for the interference in light transmission that that may occur between adjacent LED dies.

[0033] In a preferred embodiment, where the LED die size is approximately 45 mils, it is desired that LPD have a diameter that is between about 2 to 3 times the size of a respective LED die. In an example embodiment where the LED die size is approximately 45 mils and the LED dies are arranged in the manner disclosed above, a LPD die size of approximately 2.8 mm or 2.45 times the LED die size provides an optimum level of light transmission efficiency for the optimized LED array packaging size.

[0034] Referring still to FIG. 2b, while the LPDs 22 in the lens structure 20 are sized so as to avoid overlapping, i.e., of the adjacent hemispheres, adjacent LPDs are connected to one another via fillets or filler regions 26 (as best illustrated in FIGS. 4d, 5 and 6), which are formed integrally with the LPDs and that are essentially thin sections of the lens material that extend between adjacent LPDs 22. The fillets result from the compression molding process and, in an example embodiment, the fillets have a thickness (as measured from the surface of the substrate) of less than about one times the size of the LED dies, and preferably less than about the size of the LED dies. The fillets may be formed having a concave radiused-shape or having a sharp v-shape between adjacent LPDs.

[0035] FIG. 3 is a flow chart illustrating the steps involved in forming a light-emitting assembly as disclosed herein. In a first step 30 the LED dies are arranged on the MCPCB substrate to form a desired LED array having the disclosed packing density or spacing. In a second step 32, the LED dies are wire bonded to one another and to the substrate landing pads. In a third step 34, a silicone material is disposed within a mold cavity designed having a LPD size as disclosed above, and the substrate is lowered into the mold, and the assembly of the substrate and the mold are subjected to pressure in a vacuum environment. In a fourth step 36, the pressure is removed, and the mold is removed from the substrate to produce the light-emitting assembly comprising the LED array having optimized LED packing and optimized LPD sizing to provide optimal light output efficiency.

[0036] FIGS. 4a to 4c illustrate a top view of different example embodiment light-emitting assemblies 40 that is the same or similar to that shown in FIG. 2, comprising nine LED dies 42 that each have a size of approximately 45 mils (1.143 mm), and that are arranged on the substrate 44 in the manner described above. Each assembly 40 comprises nine LPDs 46 that are disposed on each of the LED dies 42, and that are sized and shaped in the same manner as described above.

[0037] Specifically, FIG. 4a illustrates a light emitting assembly 40 comprising LPDs having a size of approximately 2 mm (or 1.75 times the LED die size), while FIG. 4b illustrates a light emitting assembly 40 comprising LPDs having a size of approximately 2.8 mm (or 2.45 times the LED die size), and while FIG. 4c illustrates a light emitting assembly 40 comprising LPDs having a size of approximately 3.4 mm (or 2.97 times the LED die size).

[0038] FIG. 5 illustrates an example embodiment light-emitting assembly 47 (similar to that illustrated in FIG. 2b) comprising an LED array made up of 9 LED dies (not visible) that are disposed on an MCPCB substrate 48, and where each LED die is covered by a lens 49. The LED dies are arranged as disclosed above with respect to the embodiment illustrated in FIGS. 2a and 2b. The LED dies in this arrangement are positioned at a distance relative to one another as disclosed above to provide the desired packing density, and the LPDs are sized and shaped in the manner disclosed above to provide the combined properties of optimal light transmission efficiency and minimal packaging size.

[0039] FIG. 6 illustrates another example embodiment light-emitting assembly 50 comprising an LED array made up of 16 LED dies (not visible) that are disposed on an MCPCB substrate 52, and where each LED die is covered by a lens 54. The LED dies are arranged with four LED dies disposed within a circular arrangement of twelve LED dies, wherein the four LED dies arranged in two pairs of two. The LED dies in this arrangement are positioned at a distance relative to one another as disclosed above to provide the desired packing density, and the LPDs are sized and shaped in the manner disclosed above to provide the combined properties of optimal light transmission efficiency and minimal packaging size. In an example embodiment, the LED dies have a size of approximately 33 mils (0.84 mm), and a LPD dimension is approximately 2 mm, or 2.4 times the LED die size.

[0040] FIG. 7 illustrates another example embodiment light-emitting assembly 60 comprising an LED array made up of 18 LED dies (not visible) that are disposed on an MCPCB substrate 62, and where each LED die is covered by a lens 64. The LED dies are arranged with six LED dies disposed within a circular arrangement of twelve LED dies, wherein the six LED dies arranged in three pairs of two. The LED dies in this arrangement are positioned at a distance relative to one another as disclosed above to provide the desired packing density, and the LPDs are sized and shaped in the manner disclosed above to provide the combined properties of optimal light output efficiency and minimal packaging size. In an example embodiment, the LED dies have a size of approximately 33 mils (0.84 mm), and a LPD dimension is approximately 2 mm, or 2.4 times the LED die size.

[0041] FIG. 8 illustrates a sectional view of a connection between the light emitting assembly 70 as disclosed herein with an interconnect substrate 72. In an example embodiment, the interconnect substrate 72 is configured having electrical contact points 74 that are positioned to make contact with the landing pads 76 of the substrate when brought into position and contact with one another to facilitate the passage of electricity to the light emitting assembly. It is to be understood that this is but one example embodiment of how the light emitting assembly may achieve electrical connection with an interconnect substrate, and that the particular manner in which such electrical interconnection is achieved can and will vary depending on the particular end-use application and device configuration.

[0042] FIG. 9 illustrates a bottom surface 80 of an interconnect substrate 82 that can be used in conjunction with the light emitting assemblies as disclosed herein. The interconnect substrate 82 is formed from an electrically insulating material and includes a recessed section or an indentation 84 that is configured to accommodate placement of a light emitting assembly substrate (such as the one illustrated in FIG. 2) therein. The recessed section 84 includes a pair of electrical contact pads 86 positioned to cooperate with and provide an electrical connection with the landing pads on the assembly substrate. The interconnect substrate 82 includes a central opening 88 sized for placement of the LED array on the light emitting assembly substrate therethrough (as best illustrated in FIG. 10). This is but one example interconnect substrate configuration provided for reference, and it is to be understood that many other configurations of the same that provide the same basic function of providing an electrical interface with the light emitting assembly are equally covered herein.

[0043] FIG. 10 illustrates a top surface 90 of the interconnect substrate 82 illustrated in FIG. 8, now including a light emitting assembly 92 (as illustrated in FIG. 2 and as disclosed herein) attached from the bottom surface with its LED array extending through the central opening 88, and with its landing pads (not shown) in electrical connection with the interconnect substrate contact pads. The interconnect substrate 82 includes contact pads 94 on its top surface to facilitate connection with an external construction or fixture (not shown) having a source of electricity thereto. Constructed in this manner, the interconnect substrate functions to facilitate an electrical connection between the external construction or fixture to the light emitting assembly.

[0044] A feature of light-emitting assemblies as disclosed herein is the construction of a LED array that is intentionally engineered to be compact and space efficient to provide optimized light output, and that make use of individual LED die lenses that are specially configured and that are formed in a single mold process to optimize light transmission efficiency, thereby resulting in a highly-compact and efficient light source. Light-emitting assemblies as disclosed herein are formed on a substrate having surface mounted electrical contacts configured for use with a variety of different interconnect substrates to facilitate use in a number of different lighting fixtures to meet the needs of a variety of end-use lighting applications.

[0045] Although certain specific embodiments have been described and illustrated for purposes or reference, it is to be understood that the disclosure and illustrations as provided herein not limited to the specific embodiments. Accordingly, various modifications, adaptations, and combinations of various features of the described embodiments can be practiced without departing from the scope of the invention as set forth in the claims.