TILE FOR SOLID STATE LIGHTING

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims the benefit of and priority to U. S. Provisional Patent Application No. 60/738,305 entitled "SYSTEM AND METHOD FOR INTERCONNECTION AND INTEGRATION OF LED BACKLIGHTING MODULES" filed November 18, 2005, and U. S. Provisional Patent Application No. 60/749,133 entitled " SOLID STATE BACKLIGHTING UNIT ASSEMBLY AND METHODS" filed December 9, 2005, the disclosures of which are hereby incorporated herein by reference as if set forth in their entirety.

FIELD OF THE INVENTION

[0002] The present invention relates to solid state lighting, and more particularly to components for solid state lighting units.

BACKGROUND

[0003] Solid state lighting panels may be used as solid state backlight units for displays, as lighting panels for general illumination, as backlights for signage, and/or for other purposes. Solid state backlighting units for LCD displays typically include a two dimensional array of discrete light sources arranged behind an LCD screen. The discrete light sources may generate light having a white or near-white color that may be used to illuminate an LCD display, such as a full-color LCD display. In order for the LCD display to display an image on the screen having uniform color and/or intensity, it may be desirable for the backlight unit to provide a light to the LCD screen that is spatially uniform, both in color and intensity. This may be difficult, however, as the discrete light sources may be spaced apart from each other in the backlight unit. In particular, as the brightness of solid state light sources increases, it may be desirable to arrange the light sources with a larger and larger pitch between sources, for example, in order to reduce heat dissipation and/or to increase the efficiency of the display.

[0004] Similar problems relating to color uniformity, efficiency and/or heat dissipation may arise when solid state lighting units including arrays of solid state light emitting devices are used for general illumination.

SUMMARY

[0005] A solid state lighting tile according to some embodiments of the invention includes a substrate having a planar surface. A first plurality of solid state light emitting devices (LEDs) are on the substrate. The first plurality of LEDs are connected in series to form a first string of LEDs of a first color having an anode contact at a first end of the tile and a cathode contact at a second end of the tile. A second plurality of LEDs are on the substrate. The second plurality of LEDs are connected in series to form a second string of LEDs of the first color having a cathode contact at the first end of the tile and an anode contact at the second end of the tile.

[0006] The solid state lighting tile may further include a loopback connector that electrically connects the cathode contact of the first string to the anode contact of the second string so that the first string and the second string form a single string having an anode contact and a cathode contact on the first end of the tile.

[0007] The solid state light emitting devices may include solid state light emitting diodes arranged in a plurality of clusters. Each cluster may include solid state light emitting diodes configured to emit at least two different colors. A respective one of the clusters may include a substrate and a plurality of LED chips mounted on the substrate. In some embodiments, a respective one of the clusters may include a plurality of LED chips mounted on respective traces on the substrate and an encapsulant material on the plurality of LED chips. The substrate may include an FR-4 printed circuit board (PCB) and/or a metal core PCB.

[0008] The solid state lighting tile may further include a plurality of first strings of series-connected LEDs, the first strings having respective anode contacts at a first end of the tile and cathode contacts at a second end of the tile opposite the first end, and a plurality of second strings of series-connected LEDs, the second strings having respective anode contacts at the second end of the tile and cathode contacts at the first end of the tile. At least one of the

first strings and at least one of the second strings may include electrical test pads between a pair of adjacent LEDs.

[0009] Each of the plurality of first strings and the plurality of second strings may include at least a first color string of LEDs configured to emit light having a first wavelength when energized, and a second color string of LEDs configured to emit light having a second wavelength when energized.

[0010] The tile may have a longitudinal center axis, and the first plurality of strings and the second plurality of strings may run generally parallel to the longitudinal center axis. The anode and cathode contacts of the first color string of the first plurality of strings and the anode and cathode contacts of the first color string of the second plurality of strings may be disposed nearer to the longitudinal center axis of the tile than the anode and cathode contacts of the second color string of the first plurality of strings and the anode and cathode contacts of second color string of the second plurality of strings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate certain embodiment(s) of the invention. In the drawings:

[0012] Figure 1 is a plan view illustration of a tile for a solid state lighting unit according to some embodiments of the invention.

[0013] Figure 2 is a plan view illustration of a solid state light source for a solid state lighting unit according to some embodiments of the invention.

[0014] Figure 3 is a circuit diagram illustrating the electrical interconnection of light sources on a tile according to some embodiments of the invention.

[0015] Figure 4 is a plan view illustration of a tile including a loopback connector according to some embodiments of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION [0016] Embodiments of the present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which

embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.

[0017] It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

[0018] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises," "comprising," "includes," and/or "including" when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

[0019] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0020] It will be understood that when an element such as a layer, region or substrate is referred to as being "on" or extending "onto" another element, it can be directly on or extend directly onto the other element or intervening elements may also be present. In contrast, when an element is

referred to as being "directly on" or extending "directly onto" another element, there are no intervening elements present. It will also be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being "directly connected" or "directly coupled" to another element, there are no intervening elements present.

[0021] Relative terms such as "below" or "above" or "upper" or "lower" or "horizontal" or "vertical" may be used herein to describe a relationship of one element, layer or region to another element, layer or region as illustrated in the figures. It will be understood that these terms are intended to encompass different orientations of the device in addition to the orientation depicted in the figures.

[0022] Referring now to Figure 1 , a solid state lighting tile 10 for use in a solid state lighting unit may include thereon a number of solid state lighting element clusters 12 arranged in a regular and/or irregular two dimensional array. The tile 10 may include, for example, a printed circuit board (PCB) on which one or more circuit elements may be mounted. In particular, a tile 10 may include a metal core PCB (MCPCB) including a metal core having thereon a polymer coating on which patterned metal traces 13 may be formed. MCPCB material, and material similar thereto, is commercially available from, for example, The Bergquist Company. The PCB may further include heavy clad (4 oz. copper or more) and/or conventional FR-4 PCB material with thermal vias. MCPCB material may provide improved thermal performance compared to conventional PCB material. However, MCPCB material may also be heavier than conventional PCB material, which may not include a metal core.

[0023] In the embodiments illustrated in Figure 1, the lighting element clusters 12 are multi-chip clusters of three solid state emitting devices per cluster. In the tile 10, four lighting element clusters 12 are serially arranged in a first path 19, while four lighting element clusters 12 are serially arranged in a second path 21. The lighting element clusters 12 of the first path 19 are connected, for example via electrical traces 13, to a set of three anode contacts 22 arranged at a first end 10A of the tile 10, and a set of three

cathode contacts 24 arranged at a second end 10B of the tile 10. The lighting element clusters 12 of the second path 21 are connected to a set of three anode contacts 26 arranged at the second end 10B of the tile 10, and a set of three cathode contacts 28 arranged at the first end 10A of the tile 10. The tile 10 may further include electrical test pads 15 between the lighting element clusters 12. The electrical test pads 15 are configured to permit individual testing of the light emitting devices of the lighting element clusters 12.

[0024] An alignment notch 29 may be provided in the tile 10 to assist connection of an edge connector (not shown) and also to prevent incorrect installation of the edge connector. Furthermore, notches 33 may be provided in the corners of the tiles 10 to avoid contact between the tile 10 and screws of a support member (not shown) on which the tile 10 is mounted. The tile 10 may further include one or more automation indexing holes (not shown) that may be used to move the tile 10 during automated manufacturing steps.

[0025] The solid state lighting element clusters 12 may include, for example, organic and/or inorganic light emitting devices. An example of a solid state lighting element cluster 12 for high power illumination applications is illustrated in Figure 2. A solid state lighting element cluster 12 may include a packaged discrete electronic component including a carrier substrate 13 on which a plurality of LED chips 16 are mounted. In other embodiments, one or more solid state lighting element clusters 12 may include LED chips 16 mounted directly onto electrical traces on the surface of the tile 10, forming a multi-chip module or chip-on-board assembly.

[0026] The LED chips 16 may include at least a red LED 16R, a green LED 16G and a blue LED 16B. The blue and/or green LEDs may include InGaN-based blue and/or green LED chips available from Cree, Inc., the assignee of the present invention. The red LEDs may be, for example, AIInGaP LED chips available from Epistar, Osram and others. The lighting device 12 may include an additional green LED in order to make more green light available.

[0027] In some embodiments, the LEDs 16 may have a square or rectangular periphery with an edge length of about 900 μm or greater (i.e. so- called "power chips." However, in other embodiments, the LED chips 16 may

have an edge length of 500 μm or less (i.e. so-called "small chips"). In particular, small LED chips may operate with better electrical conversion efficiency than power chips. For example, green LED chips with a maximum edge dimension less than 500 microns, and as small as 260 microns, commonly have a higher electrical conversion efficiency than 900 micron chips, and are known to typically produce 55 lumens of luminous flux per Watt of dissipated electrical power and as much as 90 lumens of luminous flux per Watt of dissipated electrical power.

[0028] As further illustrated in Figure 2, the LEDs 16 may be covered by an encapsulant dome 14, which may be clear and/or may include light scattering particles, phosphors, and/or other elements to achieve a desired emission pattern, color and/or intensity. The encapsulant dome 14, which may include a curable epoxy resin, may provide mechanical and/or environmental protection for the LEDs 16. While not illustrated in Figure 2, the lighting element cluster 12 may further include a reflector cup surrounding the LEDs 16, a lens mounted above the LEDs 16, one or more heat sinks for removing heat from the lighting device, an electrostatic discharge protection chip, and/or other elements.

[0029] The LED chips 16 of the lighting element clusters 12 in the tile 10 may be electrically interconnected as shown in the schematic circuit diagram in Figure 3. As shown therein, the LEDs 16 may be interconnected such that the blue LEDs 16B in the first path 19 are connected in series to form a string 3OB. Likewise, the green LEDs 16G in the first path 19 may be arranged in series to form a string 3OG. The red LEDs 16R may be arranged in series to form a string 3OR. Each string 3OR, 3OG, 3OB may be connected to a respective anode contact 22R, 22G, 22B arranged at a first end of the tile 10 and a cathode contact 24 arranged at the second end of the tile 10, respectively.

[0030] A string 3OR, 3OG, 3OB may include all, or less than all, of the corresponding LEDs in the first path 19. For example, the string 3OB may include all of the blue LEDs 16B from all of the lighting element clusters 12 in the first path 19. Alternatively, a string 3OR, 3OG, 3OB may include only a subset of the corresponding LEDs in the first path 19. Accordingly the first

path 19 may include three strings 3OR, 3OG, 3OB arranged in parallel on the tile 10.

[0031] The second path 21 on the tile 10 may include three strings 31 R, 31 G, 31 B arranged in parallel. The strings 31 R, 31 G, 31 B are connected to anode contacts 26R, 26G, 26B, which are arranged at the second end of the tile 10 and to cathode contacts 28R, 28G, 28B, which are arranged at the first end of the tile 10, respectively.

[0032] The first group of strings 3OR, 3OG, 3OB have anode contacts 22R, 22G and 22B generally adjacent a first end 10A of the tile 10 and cathode contacts 24R, 24G, 24B generally adjacent a second end 10B of the tile 10. The second group of strings 31 R, 31 G, 31 B have anode contacts 26R, 26G and 26B generally adjacent the second end 10B of the tile 10 and cathode contacts 28R, 28G, 28B generally adjacent the first end 10A of the tile 10.

[0033] As shown in Figures 1 and 3, The tile 10 may have a longitudinal center axis 17, and the first group of strings 3OR, 3OG, 3OB and the second group of strings 31 R, 31 G, 31 B may run generally parallel to the longitudinal center axis 17.

[0034] The anode and cathode contacts of a first color string of the first group of strings and the anode and cathode contacts of the first color string of the second group of strings may be disposed nearer to the longitudinal center axis 17 of the tile 10 than the anode and cathode contacts of the second and/or third color strings of the first and second groups of strings. For example, the anode and cathode contacts 22B, 24B, 26B, 28B of the blue strings 3OB and 31 B may be disposed closer to the longitudinal center axis 17 than the anode and cathode contacts 22G, 24G, 26G, 28G of the green strings 3OG and 31 G. Likewise, the anode and cathode contacts 22G, 24G, 26G, 28G of the green strings 3OG and 31 G may be disposed closer to the longitudinal center axis 17 than the anode and cathode contacts 22R, 24R, 26R, 28R of the red strings 3OR and 31 R.

[0035] The cathode contact of a first color string of the first group of strings and the anode contact of the first color string of the second group of strings may be offset in a direction parallel to the longitudinal center axis 17 of the tile 10 from the cathode contact of a second color string of the first group

of strings and the anode contact of the second color string of the second group of strings. In particular, the cathode contact of the first color string of the first group of strings and the anode contact of the first color string of the second group of strings may be farther from an end 1OA, 1OB of the tile 10 than the cathode contact of the second color string of the first group of strings and the anode contact of the second color string of the second group of strings.

[0036] For example as shown in Figure 3, the cathode contact 24B of the blue string 3OB and the anode contact 26B of the blue string 31 B may be disposed farther from the end 10B of the tile 10 than the cathode contact 24G of the green string 3OG and the anode contact 26G of the green string 31 G. Staggering the contacts from the end 10B of the tile 10 may facilitate connecting the contacts of the respective strings, for example to form a loopback connector using wire loops.

[0037] It will be appreciated that, while the embodiments illustrated in Figures 1-3 include three LED chips 16 per cluster 12 which are electrically connected to form at least three strings of LEDs 16 per path 19, 21 , more and/or fewer than three LED chips 16 may be provided per lighting device 12, and more and/or fewer than three LED strings may be provided per path 19, 21 on the tile 10. For example, a cluster 12 may include two green LED chips 16G, in which case the LEDs may be connected to form four strings per path 19, 21. Likewise, in some embodiments including two green LED chips per cluster 12, the two green LED chips in a cluster 12 may be connected in series to one another, in which case there may only be a single string of green LED chips per path 19, 21. Further, a tile 10 may include only a single path 19 instead of plural paths 19, 21 and/or more than two paths 19, 21 may be provided on a single tile 10.

[0038] Referring to Figures 1 , 3 and 4, the cathode contacts 24 of the first path 19 of the tile 10 may be electrically connected to the anode contacts 26 of the second path 21 of the tile 10 by a loopback connector 35. For example, the loopback connector 35 may electrically connect the cathode 24R of the string 3OR of red LED chips 16R of the first path 19 of the tile 10 with the anode 26R of the string 31 R of red LED chips of the second path 21 of the tile 10. In this manner, the string 29R of the first path 19 may be connected in

series with the string 31 R of the second path 21 by a conductor 35R of the loopback connector 35 to form a single string of red LED chips 16R. The other strings of the paths 19, 21 of the tile 10 may be connected in a similar manner.

[0039] The loopback connector 35 may include an edge connector, a flexible wiring board, or any other suitable connector. In addition, the loop connector may include printed traces and/or wire loops formed on/in the tile 10.

[0040] In the drawings and specification, there have been disclosed typical embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.