US20100002437A1 - Low Profile and High Efficiency Light Device for Backlighting Applications - Google Patents
Low Profile and High Efficiency Light Device for Backlighting Applications Download PDFInfo
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- US20100002437A1 US20100002437A1 US12/560,534 US56053409A US2010002437A1 US 20100002437 A1 US20100002437 A1 US 20100002437A1 US 56053409 A US56053409 A US 56053409A US 2010002437 A1 US2010002437 A1 US 2010002437A1
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- light source
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/0001—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems
- G02B6/0011—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems the light guides being planar or of plate-like form
- G02B6/0081—Mechanical or electrical aspects of the light guide and light source in the lighting device peculiar to the adaptation to planar light guides, e.g. concerning packaging
- G02B6/0083—Details of electrical connections of light sources to drivers, circuit boards, or the like
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09F—DISPLAYING; ADVERTISING; SIGNS; LABELS OR NAME-PLATES; SEALS
- G09F13/00—Illuminated signs; Luminous advertising
- G09F13/18—Edge-illuminated signs
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/0001—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems
- G02B6/0011—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems the light guides being planar or of plate-like form
- G02B6/0013—Means for improving the coupling-in of light from the light source into the light guide
- G02B6/0023—Means for improving the coupling-in of light from the light source into the light guide provided by one optical element, or plurality thereof, placed between the light guide and the light source, or around the light source
- G02B6/0031—Reflecting element, sheet or layer
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/0001—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems
- G02B6/0011—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems the light guides being planar or of plate-like form
- G02B6/0066—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems the light guides being planar or of plate-like form characterised by the light source being coupled to the light guide
- G02B6/0068—Arrangements of plural sources, e.g. multi-colour light sources
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/0001—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems
- G02B6/0011—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems the light guides being planar or of plate-like form
- G02B6/0066—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems the light guides being planar or of plate-like form characterised by the light source being coupled to the light guide
- G02B6/0073—Light emitting diode [LED]
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09F—DISPLAYING; ADVERTISING; SIGNS; LABELS OR NAME-PLATES; SEALS
- G09F13/00—Illuminated signs; Luminous advertising
- G09F13/18—Edge-illuminated signs
- G09F2013/1872—Casing
- G09F2013/1877—Stand-like
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09F—DISPLAYING; ADVERTISING; SIGNS; LABELS OR NAME-PLATES; SEALS
- G09F13/00—Illuminated signs; Luminous advertising
- G09F13/20—Illuminated signs; Luminous advertising with luminescent surfaces or parts
- G09F13/22—Illuminated signs; Luminous advertising with luminescent surfaces or parts electroluminescent
- G09F2013/222—Illuminated signs; Luminous advertising with luminescent surfaces or parts electroluminescent with LEDs
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
- H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
- H01L2224/42—Wire connectors; Manufacturing methods related thereto
- H01L2224/47—Structure, shape, material or disposition of the wire connectors after the connecting process
- H01L2224/48—Structure, shape, material or disposition of the wire connectors after the connecting process of an individual wire connector
- H01L2224/4805—Shape
- H01L2224/4809—Loop shape
- H01L2224/48091—Arched
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
- H01L2224/73—Means for bonding being of different types provided for in two or more of groups H01L2224/10, H01L2224/18, H01L2224/26, H01L2224/34, H01L2224/42, H01L2224/50, H01L2224/63, H01L2224/71
- H01L2224/732—Location after the connecting process
- H01L2224/73251—Location after the connecting process on different surfaces
- H01L2224/73265—Layer and wire connectors
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L25/00—Assemblies consisting of a plurality of individual semiconductor or other solid state devices ; Multistep manufacturing processes thereof
- H01L25/03—Assemblies consisting of a plurality of individual semiconductor or other solid state devices ; Multistep manufacturing processes thereof all the devices being of a type provided for in the same subgroup of groups H01L27/00 - H01L33/00, or in a single subclass of H10K, H10N, e.g. assemblies of rectifier diodes
- H01L25/04—Assemblies consisting of a plurality of individual semiconductor or other solid state devices ; Multistep manufacturing processes thereof all the devices being of a type provided for in the same subgroup of groups H01L27/00 - H01L33/00, or in a single subclass of H10K, H10N, e.g. assemblies of rectifier diodes the devices not having separate containers
- H01L25/075—Assemblies consisting of a plurality of individual semiconductor or other solid state devices ; Multistep manufacturing processes thereof all the devices being of a type provided for in the same subgroup of groups H01L27/00 - H01L33/00, or in a single subclass of H10K, H10N, e.g. assemblies of rectifier diodes the devices not having separate containers the devices being of a type provided for in group H01L33/00
- H01L25/0753—Assemblies consisting of a plurality of individual semiconductor or other solid state devices ; Multistep manufacturing processes thereof all the devices being of a type provided for in the same subgroup of groups H01L27/00 - H01L33/00, or in a single subclass of H10K, H10N, e.g. assemblies of rectifier diodes the devices not having separate containers the devices being of a type provided for in group H01L33/00 the devices being arranged next to each other
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K1/00—Printed circuits
- H05K1/02—Details
- H05K1/0274—Optical details, e.g. printed circuits comprising integral optical means
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K1/00—Printed circuits
- H05K1/18—Printed circuits structurally associated with non-printed electric components
- H05K1/189—Printed circuits structurally associated with non-printed electric components characterised by the use of a flexible or folded printed circuit
Abstract
A light source having a flexible substrate and a plurality of dies having LEDs is disclosed. The light source can be conveniently utilized to provide an extended light source by bonding the light source to a suitable light pipe. The substrate is divided into first and second regions. The dies are bonded to the substrate in a first region. A portion of the surface of the substrate in the second region is reflective. The substrate is bent such that the second region forms a reflector that reflects light that would otherwise be emitted in a non-useful direction to a more useful direction. The substrate can be constructed from a three layer flexible circuit carrier in which the dies are mounted on a bottom metal layer to provide an improved thermal path for heat generated in the dies.
Description
- Liquid crystal displays (LCDs) are used in a wide variety of computers and consumer devices such as TVs. A back-lighted LCD is an array of pixels in which each pixel acts as a shutter that either passes or blocks light from a light source that is located behind the pixel. Color displays are implemented by equipping the pixels with color filters such that each pixel transmits or blocks light of a particular color. The intensity of the light from each pixel is set by the time the pixel is in the transmissive state.
- The display is typically illuminated by a white light source that provides a uniform intensity of light across the back surface of the display. Illumination sources based on fluorescent lights are particularly attractive because of their high light output per watt-hour of power consumed. However, such sources require high driving voltages which makes them less attractive for battery operated devices.
- As a result, there has been considerable interest in utilizing light sources based on LEDs in such applications. LEDs have similar electrical efficiency and long lifetimes. In addition, the driving voltages needed are compatible with the battery power available on most portable devices. An LED light source for generating an arbitrary color of light is typically constructed from three LEDs. The relative intensities of the LEDs are adjusted by adjusting the drive current through the LED and/or the duty factor of the LED. In the latter arrangement, the LEDs are turned on and off within a cycle time that is too short to be perceived by a human observer. The intensity of the light seen by the viewer is the average intensity, and hence, the relative intensities of the various colors are determined by the percentage of the time the various LEDs are turned on.
- Back lighted illumination systems for LCD arrays typically utilize some form of light box or light pipe behind the LCD array. The light pipe is a rectilinear transparent solid constructed from a transparent plastic having one surface that has dimensions that are larger than the LCD array. The goal of the illumination system is to have this surface act as an extended light source having a uniform light intensity over the surface. Light is injected into the light pipe at the periphery of the light pipe. The light is trapped in the light pipe by internal reflections until the light is scattered in a manner that allows it to escape through the top surface, which is the surface that is adjacent to the LCD array. The bottom surface of the light box or the material of the light pipe itself has scattering centers that redirect the light hitting each center so that a portion of the light exits through the top surface.
- In many applications, the size of the light source is an important factor. For small handheld devices, size is particularly important both in terms of the thickness of the light source and the amount of space required around the edges of the extended light source that is needed for the light source that illuminates the light box.
- The thickness of the light source, and hence, the device is limited by the thickness of the light box. The thickness of the display is particularly important in displays used for laptop computers and handheld devices such as PDAs and cellular telephones, as the display thickness limits the overall thickness of the device. Some of these portable devices require light boxes that are less than 1 mm in thickness.
- Light sources that are constructed from a light box that is illuminated along one or more edges by discrete packaged LEDs are limited both in terms of the thickness of the light source and the amount of edge space that is needed in addition to the surface that is being illuminated. As the thickness of the display decreases, the efficient injection of light into the light pipe becomes more problematic. Light must enter the edge of the light pipe at a predetermined point within a predetermined cone of angles. Typically, the light source consists of a number of packaged LEDs that are mounted on a small substrate such that the light emission direction of the LEDs is parallel to the surface of the light pipe. This substrate is attached to a circuit board that is under the light pipe such that light is emitted into the edge of the light pipe. If the relative positions of the light source and light pipe are not correct, part of the light can be lost either because the light misses the edge of the light pipe or because the angle at which some of the light enters the light pipe is greater than the critical angle, and hence, that light leaves the light pipe at the first reflection. In either case, the efficiency and/or the uniformity of the illumination system is reduced. In addition, when the thickness of the light pipe becomes less than the diameter of the LED package, providing good coupling of the light into the light pipe becomes even more difficult.
- In addition, there is a minimum distance between the LEDs that is set by the diameter of the LED package. In a color light source, the LEDs are normally arranged as repeating red, green, and blue LEDs along the axis of the light source. The light entering the light source has hot spots immediately adjacent to the packaged LEDs both in terms of intensity and color. Hence, the region adjacent to the edge is reserved as a mixing region, and hence, the surface above this region is not useable as part of the extended light source.
- The present invention includes a light source having a flexible substrate and a plurality of dies having LEDs. In one aspect of the invention, the flexible substrate has a dielectric layer sandwiched between top and bottom metal layers, and the flexible substrate is divided into first and second regions. The dies are bonded to the bottom layer in the first region. The first region is characterized by a normal to the bottom layer in the first region, at least one of the top and bottom metal layers includes a plurality of electrical traces for connecting the dies to circuitry that is external to the light source. The top metal layer of the substrate is reflective in the second region. The substrate is bent such that the first region is at an angle with respect to the second region and a portion of the light, emitted from the dies at an initial angle greater than zero to the normal, striking the second region and is reflected therefrom into a direction having an angle with respect to the normal that is less than the initial angle. In another aspect of the invention, the substrate includes a connector region outside of the first region and having a plurality of electrical contacts connected to the traces, the connector region is configured to mate to a connector that is external to the light source. In another aspect of the invention, a rigid member is bonded to the bottom metal layer. In another aspect of the invention, a light pipe is utilized to form an extended light source. The second region is bonded to a surface of the light pipe such that the dies are positioned to inject light into an edge of the light pipe.
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FIG. 1 is a top view of a priorart light source 110. -
FIG. 2 is a cross-sectional view oflight source 110 through line 2-2 shown inFIG. 1 . -
FIG. 3 is a top view of a light source according to one embodiment of the present invention. -
FIG. 4 is a cross-sectional view through line 4-4 shown inFIG. 3 . -
FIG. 5 is a cross-sectional view through line 5-5 shown inFIG. 3 . -
FIG. 6 is a top view of an extended light source according to one embodiment of the present invention. -
FIG. 7 is a cross-sectional view through line 7-7 shown inFIG. 6 . -
FIG. 8 is a cross-sectional view of another embodiment of an extended light source according to the present invention. -
FIG. 9 is a cross-sectional view through line 9-9 shown inFIG. 10 . -
FIG. 10 is a top view of a light source according to one embodiment of the present invention. -
FIG. 11 is a top view of another embodiment of a light source according to the present invention. -
FIG. 12 is a cross-sectional view of another embodiment of an extended light source according to one embodiment of the present invention. -
FIG. 13 is a cross-sectional view of another embodiment of an extended light source according to the present invention. -
FIG. 14 is a cross-sectional view of a linear array of dies on a substrate in which the individual dies are individually encapsulated in a layer of encapsulant. -
FIG. 15 is a cross-sectional view of a linear array of dies according to another embodiment of the present invention. - The manner in which the present invention provides its advantages can be more easily understood with reference to
FIGS. 1 and 2 , which illustrate a prior art light box arrangement for illuminating anLCD display 116.FIG. 1 is a top view oflight source 110, andFIG. 2 is a cross-sectional view oflight source 110 through line 2-2 shown inFIG. 1 .Light source 110 utilizes an array ofLEDs 111 to illuminate alight pipe 112. The LEDs are mounted on acircuit board 113 that is mounted on asecond board 115 that provides power to the LEDs. The LEDs are positioned such that light leaving the top of each LED illuminates the end oflight pipe 112. The light 123 enteringlight pipe 112, at an angle with respect to thesurface 121 that is less than the critical angle, is reflected back and forth withinlight pipe 112 until the light is either absorbed or scattered byparticles 122 onsurface 117. The scattered light that strikessurface 121 at angles greater than the critical angle escapes from the light pipe and illuminates the back surface ofLCD display 116. The bottom surface of the light pipe is covered with a reflective material; hence, any light striking the bottom surface is reflected upward. - In the region of the light pipe near the LEDs, some of the rays will enter the light pipe at angles greater than the critical angle and immediately escape through the top surface of the light pipe as shown at 124. It should be noted that rays striking the bottom surface at angles greater than the critical angle will be reflected upwards at angles greater than the critical angle with respect to
surface 121 and will also be lost. As a result,region 125 of the light pipe is not used to illuminate the LCD display. This region acts as a mixing region for mixing the light from the various LEDs. - It should be noted that the amount of light that is lost through
region 125 will, in general, depend on the vertical positioning of the LEDs. If the LEDs are too low, then more light will leaveregion 125, since a greater fraction of the light leaving the LEDs will strikesurface 121 at angles greater than the critical angle. In addition, the size ofregion 125 is also dependent on the vertical positioning of the LEDs to some extent. While vertical-positioning errors can be accommodated by increasing the size ofregion 125, such increases increase the size of the display and the power needed to provide a given level of illumination to the LCD display. - The size of mixing
region 125 also depends on the separation between the individual LEDs. The LEDs typically include LEDs that emit light in three wavelength bands, namely, red, blue, and green. The relative intensity of the light emitted in the wavelength bands determines the color of the light source as perceived by a human observer. Since each LED is typically limited to emitting light in only one band, the LEDs are normally arranged in an order in which each LED emits light in a different band from that of its neighbors. Mixingregion 125 must be long enough to assure that light from a number of neighboring LEDs is mixed when the light leaves mixingregion 125 to assure that there are no color variations in the regions beyond the mixing region. Accordingly, designs in which three LEDs that emit light in different bands are placed as close to one another as possible are preferred, since such an arrangement provides the better mixing of the colors in any given mixing region. In prior art systems of the type shown inFIGS. 1 and 2 , the minimum spacing for the LEDs is limited by the packaging of the LEDs, and hence, larger mixing regions are needed. - Heat dissipation is also a significant problem for displays of the type discussed above. The heat generated by the LEDs is considerable, and hence, must be dissipated to the surrounding air by a surface that is greater than die area of
substrate 113 on which the LEDs are mounted. Printedcircuit board 115 can be utilized to dissipate the heat, provided there is sufficient contact area betweensubstrate 113 and printedcircuit board 115. To provide adequate heat conduction,substrate 113 is typically soldered to printedcircuit board 115. The solder connections also provide the signal lines for the electrical signals used to drive the LEDs. This rigid coupling causes two problems. First, the accuracy of the alignment of the LEDs relative tolight pipe 112 depends on the precision of this bond. Second, the heat transferred to printedcircuit board 115 causes the printed circuit board to heat up during the operation of the LCD display. This change in temperature can result in the board flexing such that the alignment of the LEDs relative to the printed circuit board is altered. - The present invention utilizes a light source constructed on a flexible circuit carrier. Refer now to
FIGS. 3-5 , which illustrate a light source according to one embodiment of the present invention.FIG. 3 is a top view oflight source 20,FIG. 4 is a cross-sectional view oflight source 20 through line 4-4 shown inFIG. 3 , andFIG. 5 is a cross-sectional view oflight source 20 through line 5-5 shown inFIG. 3 .Light source 20 includes a plurality of dies 21 arranged in a linear array. Each die includes an LED. In the case of a color light source the LEDs typically alternate in the color of light generated. The LEDs are mounted on aflexible circuit carrier 23 that includes a center region on which the dies are mounted and two side regions shown at 29 and 30 that are utilized in the mounting of the light source to a light pipe or other structure and in reflecting light from theLEDs. Circuit carrier 23 also includes tabs shown at 24 and 26 that are also used to secure the light source to a light pipe. -
Circuit carrier 23 includes a number of electrical traces for connecting the LEDs to drive terminals that are accessed on aconnector 25. In the embodiment shown in the Figures, each LED is connected to a common trace by an adhesive applied to the underside of the die and to a second drive trace by awire bond 27. There may be a number of different drive traces, different LEDs being connected to different traces depending on the color of light generated by the particular LED. The details of some of the possible connection schemes will be discussed in more detail below. - The LEDs are encapsulated in a
clear encapsulant 22.Encapsulant 22 can be a flexible encapsulant such us silicone or a rigid encapsulant. In the embodiment shown inFIGS. 3-5 , the encapsulant is a continuous layer that covers all of the LEDs. However, as will be explained in more detail below, other encapsulant arrangements may be utilized. - In one embodiment, the side regions shown at 29 and 30 have
reflective surfaces 43. The reflective surface can be provided by bonding a reflective material to the top surface ofcarrier 23 in the regions in question. In one embodiment of the present invention, the top surface of the carrier is formed from a layer of metal such as copper. In this case, a reflective metal such as nickel, silver, aluminum, tin, gold, solder, or an alloy thereof could be plated or sputtered onto the copper layer. Alternatively, a preformed layer of material having a reflective surface could he bonded to the top layer ofcarrier 23. In one embodiment of a light source according lo the present invention,regions - Refer now to
FIGS. 6 and 7 , which illustrate the manner in which a light source such aslight source 20 described above can be bonded to alight pipe 41 to provide an extendedlight source 40 that is suitable for use in backlit displays.FIG. 6 is a top view of extendedlight source 40, andFIG. 7 is a cross-sectional view of extendedlight source 40 through line 7-7 shown inFIG. 6 .Light pipe 41 is similar to the light pipes discussed above with respect to the light sources shown inFIGS. 1 and 2 , and hence, will not be discussed in detail here. For the purposes of the present discussion, it is sufficient to note thatlight pipe 41 has anedge 47 into which light from the LEDs inlight source 20 is injected. -
Light source 20 is attached tolight pipe 41 alongedge 47 with the aid of the twoside regions regions light pipe 41. Alayer 42 of adhesive is used tobond regions light pipe 41 such that thelayer 22 of encapsulant is butted againstedge 47 with LEDs properly positioned to inject light intolight pipe 41. An index of refraction matching gel can be placed betweenedge 47 andlayer 22. As noted above, a flexible silicone encapsulant is used in one embodiment of the present invention. The encapsulant can thus deform to maximize the area of contact betweenlayer 22 andedge 47. -
Reflective layer 43 forms a cavity that redirects light that would not otherwise enteredge 47 intoedge 47. The reflective surface can be highly polished or a matte finish. A matte finished surface provides additional mixing of the light from adjacent LEDs; however, some of the light that would otherwise enter the light pipe is lost. - As noted above,
circuit carrier 23 also includes aconnector 25 for providing connections to circuitry and power that is located off ofcircuit carrier 23. The bottom surface of theconnector 25 can be patterned to include a number of terminals such asterminals connector 25 is inserted on the external device. - Refer now to
FIG. 8 , which is a cross-sectional view of another embodiment of an extended light source according to the present invention. Extendedlight source 50 is similar to extendedlight source 40 discussed above, and hence, those elements of extendedlight source 50 that serve functions analogous to elements discussed above with respect to extendedlight source 40 have been given the same numeric designations. Extendedlight source 50 includes arigid member 51 that runs along the length of the circuit carrier under the LEDs.Member 51 serves two functions. First,member 51 improves the reproducibility of the spacing of the LEDs with respect to edge 47 when the light source is applied to edge 47. This is particularly useful in embodiments utilizing a flexible encapsulant. in that any pressure applied to the light source during the attachment process is uniformly distributed alongedge 47. - Second,
member 51 acts as a heat sink to absorb heat from the LEDs and radiate that heat to the surrounding environment in those cases in which the exposed bottom metal layer ofcarrier 23 does not provide sufficient heat dissipation or thermal mass. In embodiments that make use of this aspect ofmember 51,member 51 is constructed from a material having good heat conduction properties, such as copper. The heat radiating capacity ofmember 51 can be increased by includingfins 52 or other surface area increasing features on the outer surface ofmember 51. If the member does not also need to be rigid, the heat sink material could be formed from a flexible material such as a sheet of graphite or a metal foil. - In one embodiment of the present invention, the circuit carrier is constructed from a three-layer structure. Refer now to
FIGS. 9 and 10 , which illustrate a portion of a light source that has three dies of three different colors attached to a circuit carrier according to one embodiment of the present invention.FIG. 10 is a top view oflight source 60 andFIG. 9 is a cross-sectional view through line 9-9 shown inFIG. 10 . To simplify the figures, the layer of encapsulant has been omitted from the figures. In this example, the dies emit light in the red, blue, and green region of the spectrum.Die 281 is an example of a red emitting die. The dies are mounted on acarrier 272.Carrier 272 is constructed from an insulatingsubstrate 274 that has two layers of metal deposited on opposite sides ofsubstrate 274. Both of these layers are patterned to provide the various traces needed to power the dies and mount the dies.Die 281 is mounted on and connected electrically to pad 263, which is used to provide one of the power connections to die 281. The other power terminal ofdie 281 is on the top ofdie 281 and is connected to atrace 268 onlayer 274 by awire bond 257. Similarly, the green dies are connected to trace 267 onsubstrate 274, and the blue dies are connected to trace 269. In this embodiment, traces 267-269 are connected to traces 275-277, respectively, by conducting vias that pass throughsubstrate 274. The conducting vias are shown at 264-266. - In this embodiment, dies that emit a particular light are driven in parallel and utilize a common ground plane that includes the mounting pads such as mounting
pad 263. The traces 275-277 and a trace connecting the common mounting pads are available on the bottom side ofcircuit carrier 274 and can be connected to the terminals on the bottom surface of the substrate such asterminals - Embodiments in which the LEDs are connected in series can also be constructed. Such embodiments assure that the same current flows through each LED. Refer now to
FIG. 11 , which is a top view of another embodiment of a light source according to the present invention.Light source 90 includes three types of dies that emit light in the red, blue, and green regions of the spectrum. The red-emitting dies are connected to trace 92; the blue-emitting dies are connected to trace 93, and the green-emitting dies are connected to trace 91. Each die is connected across a gap in the corresponding trace by two wire bonds whose other ends are connected to terminals on the die. For example,wire bonds die 97 to trace 93. In this embodiment, the bottom surface of the die is also attached to the bottom metal layer to provide efficient heat conduction. A non-conducting adhesive can be utilized for this bond if the die has a power contact on the bottom surface of the die. Once again, the layer of encapsulant has been omitted from the drawing to simplify the drawing. - The die mounting pads are created by removing a portion of the top metal layer and
substrate 274, thus leaving the bottom layer of metal exposed. The portions of the layers in question can be removed using lithographic techniques that are applied to an entire sheet of carrier material so that the mounting pads for a large number of dies can be fabricated together to reduce the cost per die. The metal layers can be constructed from a high thermal conductivity material such as copper. Hence,pad 263 provides a low thermal resistance path to an underlying heat spreading layer such asrigid member 51 discussed above. - In one embodiment,
carrier 272 is constructed from a flexible printed circuit carrier. Flexible circuit carriers are constructed using polyamide-based insulating layers that are available commercially from Dupont. The insulating layer is provided with a copper layer on the top and bottom surfaces thereof. The top and bottom surfaces can be lithographically patterned to provide the various traces in a manner analogous to that used with conventional printed circuit boards. The dielectric layer is preferably between 10 μm and 100 μm. The metal layers are preferably between 10 μm and 150 μm. As a result,circuit carrier 272 can have a thickness between 30 μm and 400 μm. Hence, a light source according to the present invention does not significantly increase the thickness of a handheld device beyond the thickness restrictions imposed by the thickness of the light pipe. - Other forms of dielectric can also be utilized to construct a flexible circuit carrier of this type. For example, dielectric layers formed from siloxane, polyester, cyanate ester, bismaleimide, and glass fibers can also be utilized. The metal layers can also be formed from nickel, gold, silver, palladium, rhodium, tin, or aluminum.
- In the above-described embodiments, the circuit carrier was constructed from a flexible substrate. Utilizing such substrates significantly reduces the cost of the light source. However, embodiments can be utilized in which the substrate is only flexible along the boundaries of the side regions discussed above. In addition, the flexible substrate can be rendered rigid in particular regions by bonding the substrate to a rigid member in those regions in a manner analogous to the use of
rigid member 51 discussed above. Such rigid areas are useful in creating reflectors having particular shapes. - Refer now to
FIG. 12 , which is a cross-sectional view of another embodiment of an extended light source according to the present invention. Extendedlight source 200 is constructed from alight pipe 210 and a light source formed on aflexible carrier 211 in a manner analogous to that discussed above. Three planar rigid sections 212-214 are bonded to the bottom surface ofcarrier 211. The top surface ofcarrier 211 inregions 215 are plated with a reflective material such as nickel to provide planar reflectors for directing light from the sides ofLEDs 216 intolight pipe 210 at angles at which more of this light will strike the surfaces oflight pipe 210 at angles greater than the critical angle. - Since the circuit carrier is flexible, non-planar reflector shapes can also be constructed. Refer now to
FIG. 13 , which is a cross-sectional view of another embodiment of an extended light source according to the present invention. Extendedlight source 220 is constructed from alight pipe 210 and a light source formed on aflexible carrier 221 in a manner analogous to that discussed above. Three rigid sections 222-224 are bonded to the bottom surface ofcarrier 221. The two rigid sections shown at 222 and 223 are cylindrical in shape. - The above-described embodiments utilized a single layer of encapsulant that was formed over all of the dies in the light source. However, other arrangements could be utilized. The choice of any particular arrangement depends on the particular light source being constructed. Refer now to
FIG. 14 , which a cross-sectional view of a linear array of dies on asubstrate 253 in which the individual dies 252 are individually encapsulated in a layer ofencapsulant 251. The encapsulant material could be clear or could include phosphor particles for converting a portion of the light generated by the LED on the die to light of a different spectrum. Such phosphor conversion is common in “white” LEDs. One form of white LED is constructed from a blue-emitting LED and a layer of phosphor that converts a portion of the blue light to light in the yellow region of the optical spectrum. The combination of blue and yellow light is perceived by a human observer to be white light. - The individually encapsulated dies could also be covered by a layer of encapsulant that extends over all of the dies. Refer now to
FIG. 15 , which is a cross-sectional view of a linear array of dies according to another embodiment of the present invention. Each die is encapsulated in an individual layer ofencapsulant 254 that includes phosphor particles to convert a portion of the light generated by the die. Different dies could be encapsulated in layers having different phosphors or all of the dies could utilize the same phosphor. The dies are then covered by a uniform layer ofclear encapsulant 255 that facilitates the injection of light into a light pipe in a manner similar to that discussed above. - It should also be noted that the encapsulant layers can include other materials in addition to the fluorescent or luminescent materials used to convert light from the LEDs. For example, the encapsulant layers could include diffusants to spread the light and provide more uniform light mixing within the encapsulant layer. In addition, the encapsulant layers could include dyes or other agents that filter-out specific bands of light to shape the emission spectrum of the light source.
- While flexible encapsulant materials such as silicone have a number of advantages, encapsulant layers formed from epoxy could also be utilized. The epoxy has the advantage of providing a rigid member in the region of the dies in addition to encapsulating the dies.
- The embodiment shown in
FIGS. 3-5 utilizes aconnector 25 along one edge of the light source to provide electrical connections to the LEDs on the dies. However, embodiments in which the connector is formed on one or both of the tabs shown at 24 and 26 could also be constructed. - In the above-described embodiments of the present invention, the top surface of the substrate was described as being reflective in certain regions. For the purposes of this discussion a surface is defined to be reflective for the light emitted by the dies or the phosphors, in the case of an encapsulant layer containing phosphors or luminescent materials, if the surface reflects more than 80 percent of that light. The surface can have a mirror finish or a matte finish.
- Various modifications to the present invention will become apparent to those skilled in the art from the foregoing description and accompanying drawings. Accordingly, the present invention is to be limited solely by the scope of the following claims.
Claims (27)
1. A light source comprising:
a flexible substrate having a dielectric layer sandwiched between top and bottom metal layers, said flexible substrate being divided into first and second regions; and
a plurality of dies bonded to said bottom layer in said first region, each die comprising a semiconductor light emitting device that emits light, said first region being characterized by a normal to said bottom layer in said first region, at least one of said top and bottom metal layers comprising a plurality of electrical traces for connecting said dies to circuitry that is external to said light source;
wherein said top metal layer of said substrate is reflective in said second region, said substrate being bent such that said first region is at an angle with respect to said second region and a portion of said light emitted from said dies at an initial angle greater than zero to said normal striking said second region and being reflected therefrom into a direction having an angle with respect to said normal that is less than said initial angle.
2. The light source of claim 1 wherein said flexible substrate has a thickness of less than 600 μm.
3. The light source of claim 1 wherein said second region comprises a reflective layer bonded to said top metal layer.
4. The light source of claim 1 wherein said dies are covered by a layer of encapsulant in said first region.
5. The light source of claim 1 wherein said substrate comprises a connector region outside of said first region and having a plurality of electrical contacts connected to said traces, said connector region being configured to mate to a connector that is external to said light source.
6. The light source of claim 1 further comprising a rigid member bonded to said bottom metal layer.
7-27. (canceled)
8. (canceled)
9. (canceled)
10. (canceled)
11. (canceled)
12. (canceled)
13. (canceled)
14. (canceled)
15. (canceled)
16. (canceled)
17. (canceled)
18. (canceled)
19. (canceled)
20. (canceled)
21. (canceled)
22. (canceled)
23. (canceled)
24. (canceled)
25. (canceled)
26. (canceled)
27. (canceled)
Priority Applications (1)
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US12/560,534 US20100002437A1 (en) | 2006-11-27 | 2009-09-16 | Low Profile and High Efficiency Light Device for Backlighting Applications |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
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US11/605,984 US7607815B2 (en) | 2006-11-27 | 2006-11-27 | Low profile and high efficiency lighting device for backlighting applications |
US12/560,534 US20100002437A1 (en) | 2006-11-27 | 2009-09-16 | Low Profile and High Efficiency Light Device for Backlighting Applications |
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US11/605,984 Division US7607815B2 (en) | 2006-11-27 | 2006-11-27 | Low profile and high efficiency lighting device for backlighting applications |
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US20100002437A1 true US20100002437A1 (en) | 2010-01-07 |
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US11/605,984 Expired - Fee Related US7607815B2 (en) | 2006-11-27 | 2006-11-27 | Low profile and high efficiency lighting device for backlighting applications |
US12/560,534 Abandoned US20100002437A1 (en) | 2006-11-27 | 2009-09-16 | Low Profile and High Efficiency Light Device for Backlighting Applications |
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US11/605,984 Expired - Fee Related US7607815B2 (en) | 2006-11-27 | 2006-11-27 | Low profile and high efficiency lighting device for backlighting applications |
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Also Published As
Publication number | Publication date |
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US20080284308A1 (en) | 2008-11-20 |
JP4709819B2 (en) | 2011-06-29 |
US7607815B2 (en) | 2009-10-27 |
JP2008135387A (en) | 2008-06-12 |
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