WO2013186653A1 - Lead frame light emitting arrangement - Google Patents

Lead frame light emitting arrangement Download PDF

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Publication number
WO2013186653A1
WO2013186653A1 PCT/IB2013/054406 IB2013054406W WO2013186653A1 WO 2013186653 A1 WO2013186653 A1 WO 2013186653A1 IB 2013054406 W IB2013054406 W IB 2013054406W WO 2013186653 A1 WO2013186653 A1 WO 2013186653A1
Authority
WO
WIPO (PCT)
Prior art keywords
light emitting
emitting arrangement
lead frame
electrically conductive
conductive portion
Prior art date
Application number
PCT/IB2013/054406
Other languages
French (fr)
Inventor
Bas Fleskens
Stefan Marcus Verbrugh
Wilhelmus Gerardus Maria Peels
Peter Henri BANCKEN
Original Assignee
Koninklijke Philips N.V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Koninklijke Philips N.V. filed Critical Koninklijke Philips N.V.
Publication of WO2013186653A1 publication Critical patent/WO2013186653A1/en

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/48—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor body packages
    • H01L33/58—Optical field-shaping elements
    • H01L33/60—Reflective elements
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/48—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor body packages
    • H01L33/62—Arrangements for conducting electric current to or from the semiconductor body, e.g. lead-frames, wire-bonds or solder balls
    • 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
    • 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
    • H01L2224/481—Disposition
    • H01L2224/48135—Connecting between different semiconductor or solid-state bodies, i.e. chip-to-chip
    • H01L2224/48137—Connecting between different semiconductor or solid-state bodies, i.e. chip-to-chip the bodies being arranged next to each other, e.g. on a common substrate
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/19—Details of hybrid assemblies other than the semiconductor or other solid state devices to be connected
    • H01L2924/191—Disposition
    • H01L2924/19101—Disposition of discrete passive components
    • H01L2924/19107—Disposition of discrete passive components off-chip wires

Definitions

  • the present invention relates to a light emitting arrangement and especially to a light emitting arrangement comprising LED dies arranged on a lead frame.
  • PCBs printed circuit boards
  • COB chip-on-board
  • LED light arrangements gain market shares and manufacturing costs are of increased importance.
  • a lumen per dollar ratio may be desired to increase at the same time as gaining flexibility in the manufacturing process.
  • the PCB is a relatively large share in the costs. Further, a PCB may be adapted for a fixed number of LED die packages, limiting the flexibility in the manufacturing of LED light arrangements. Other important aspects on the functions of a LED light arrangement are thermal and optical performance.
  • the PCB mounted LED die package arrangement may not be optimally thermally
  • a concern of the present invention is to provide a light-emitting arrangement that is flexible and cost-effective to manufacture and with improved thermal and optical performance in view of known arrangements.
  • a light emitting arrangement comprising a lead frame comprising a reflective portion, a thermally conductive portion, a first electrically conductive portion and a second electrically conductive portion. At least one light source is arranged on said reflective portion of the lead frame. The at least one light source is electrically connected to the first electrically conductive portion and to the second electrically conductive portion, and thermally connected to the thermal portion. The first electrically conductive portion is electrically separated from the second electrically conductive portion.
  • the thermal performance of the light emitting arrangement may be improved by the thermally conductive portion being in thermal contact with the light source. Heat generated by the light source may thereby effectively be transported away from the light source by the thermally conductive portion.
  • the first and second electrically conductive portions may provide electrical connections for the light source that may be easy and cost- effective to manufacture.
  • the electrically conductive portions in the lead frame, the use of a PCB may be avoided.
  • the lead frame may provide necessary mechanical support for the light source.
  • the optical performance of the light emitting arrangement may be improved due to light being reflected by the reflected portion.
  • the light emitting arrangement according to the invention may further be compact in height with few layers forming the arrangement.
  • the light source may be a bare LED die or a packaged LED die directly arranged on the reflective portion of the lead frame.
  • the thickness of the lead frame may be selected depending on desired thermal properties for the thermally conductive portion. Such thickness may be a few or several millimeters.
  • the reflective portion may be a reflective coating arranged on the lead frame.
  • the reflective coating may be provided on the lead frame to improve the optical performance of the light emitting arrangement.
  • the reflective coating may increase the reflective properties of the reflective portion, thereby improving the optical output provided by the light emitting arrangement.
  • the reflective coating may be of a material with a higher optical reflection coefficient than the material of the rest of the lead frame.
  • the reflective coating may be a reflective plating.
  • the electrically conductive portions may be electrically separated from the reflective portion.
  • the electrically conductive portions may be electrical circuit tracks arranged on the thermally conductive portion of the lead frame.
  • the electrical circuit tracks may connect to a plurality of light sources.
  • the light emitting arrangement may comprise a plurality of light sources in an array arrangement, and the electrical circuit tracks may extend to connect with all light sources, directly or indirectly.
  • the electrical circuit tracks may be electrically insulated from the thermally conductive portion of the lead frame.
  • the electric circuit tracks may provide the electrical connections to the light source, and may be arranged in contact with the thermally conductive portion.
  • the electrical circuit tracks may however be electrically insulated from the thermally conductive portion of the lead frame.
  • the thermally conductive portion may thereby be used for the thermal performance of the light emitting arrangement, and not for the electrical performance. By providing the thermally conductive portion as a portion without the function of providing electrical connection to the light source, it may be optimized for providing heat sink functionality.
  • the thermally conductive portion may be the same as the first electrically conductive portion.
  • the thermally conductive portion may be the same as one of the electrically conductive portions in order to simplify the construction of the light emitting arrangement. By combining two functions in the same portion, the arrangement may be provided in a more compact construction.
  • the reflective portion may be electrically conductive.
  • the reflective portion may be electrically conductive in order to provide an electrical connection from the light source to one of the first electrically conductive portions.
  • the electrical connection from the light source to the second electrically conductive portion may be provided via a wire bond.
  • the reflective portion may be thermally
  • the reflective portion may be thermally conductive in order to provide a heat transportation connection from the light source to the thermally conductive portion acting as a heat sink. If the reflective portion is provided as a reflective coating, the material of the reflective coating may provide heat transfer to the thermally conductive portion of the lead frame.
  • the at least one light source may be connected to at least one of the electrically conductive portions via a wire bond.
  • the light source may be connected to at least one of the electrically conductive portions via a wire bond in order to separate different functions of the lead frame.
  • the electrically conductive portions may be arranged separately from the reflective portion, onto which the light source is arranged.
  • the light source may thereby be connected to one or both of the electrically conductive portions via wire bonds in order to improve the optical performance of the arrangement.
  • the light emitting arrangement may comprise a plurality of light sources connected in series via at least one wire bond. Further, a first light source of the plurality of light sources may be connected to the first electrically conductive portion, and a second light source may be connected to the second electrically conductive portion.
  • the light sources may be connected in series via wire bonds.
  • the same reflective portion and thermally conductive portion may thereby be used for a plurality of light sources.
  • a plurality of light sources may be arranged in a row. The two end light sources in the row may be connected to an electrically conductive portion, respectively.
  • the connections to the electrically conductive portions may be via wire bonds.
  • the reflective portion may comprise a silver coating.
  • the silver plating may provide a high reflectivity of light from the light source, providing an improved optical output from the light emitting arrangement.
  • the reflective portion may be arranged on a top surface of the lead frame.
  • the reflective portion may be a reflective coating, which may be arranged on a top surface of the lead frame.
  • the reflective portion may thereby have direct contact with the underlying portion of the lead frame.
  • a luminaire comprising a light emitting arrangement as presented above may be provided.
  • Fig. la is a perspective view of a light emitting arrangement according to an embodiment of the invention.
  • Fig. lb is a perspective view of a light emitting arrangement according to an embodiment of the invention.
  • Fig. lc is a perspective view of a light emitting arrangement according to an embodiment of the invention.
  • Fig. Id is a perspective view of a light emitting arrangement according to an embodiment of the invention.
  • Fig. 2 is a perspective view of a light bulb comprising a light emitting arrangement according to an embodiment of the invention
  • Fig. 3a is a perspective view of a light emitting arrangement according to an embodiment of the invention.
  • Fig. 3b is a perspective view of a light emitting arrangement according to an embodiment of the invention.
  • Fig. 3c is a perspective view of a light emitting arrangement according to an embodiment of the invention.
  • Fig. 4 is a perspective view of a light bulb comprising a light emitting arrangement according to an embodiment of the invention.
  • Fig. 5 is a perspective view of a light emitting arrangement according to an embodiment of the invention.
  • Fig la illustrates a light emitting arrangement 1 with light sources 20 on a reflective plating 30.
  • the light sources 20 are arranged in a matrix, connected in series in each row. Here illustrated with three light sources 20 in each row.
  • the reflective plating 30 is arranged on a top surface 11 of a lead frame 10.
  • the lead frame 10 may be a standard 70x250 mm lead frame.
  • the rows of light sources 20 extend orthogonally to a longitudinal extension direction of the lead frame 10.
  • the light sources 20 are bare LED dies or packaged LED dies arranged on the reflective plating 30.
  • the lead frame 10 comprises two electrically conductive portions, in this embodiment provided as a cathode electrical circuit track 40 and an anode electrical circuit track 41 arranged on each side of the reflective plating 30 respectively.
  • the electrical circuit tracks 40, 41 extend along the entire length of the lead frame 10.
  • Each electrical circuit track 40, 41 is arranged on an insulating layer 42 to electrically isolate the electrical circuit tracks 40, 41 from the lead frame 10.
  • Each row of light sources 20 is electrically connected to the cathode and anode electric circuit tracks 40, 41. These electrical connections are provided by wire bonds 50.
  • the light sources 20 of each row are further electrically connected in series to each other via wire bonds 52.
  • the cathode and anode electrical connections to the light sources 20 are thereby separated from the reflective plating 30 and the lead frame 10.
  • the reflective plating 30 provides an optical function by reflecting the light from the light sources 20, and thereby enhancing the light output from the light emitting arrangement 1.
  • the reflective plating 30 covers an entire common area of the lead frame 10 onto which all light sources 20 are attached.
  • the reflective plating 30 may further be thermally conductive, providing a heat transfer from the light sources 20 arranged thereon to a thermally conductive portion 60 of the lead frame 10.
  • the light sources 20 may be attached to the reflective plating 30 by means of thermally conductive solder or glue.
  • the lead frame 10 further transports the heat and function as a heat sink.
  • the lead frame 10 of the light emitting arrangement in fig. la may be split up into smaller parts for smaller light emitting arrangements 1, with one or more rows of light sources 20 in each part.
  • an array of light sources 20 may be provided in the same light emitting arrangement 1, each power provided via the electric circuit tracks.
  • a light emitting arrangement 2 comprises a lead frame 10 which may be cut into separate parts, forming thermally conductive portions 60 and electrically conductive portions 43, 44.
  • the electrically conductive portions 43, 44 are connected to the cathode or anode circuit tracks 40, 41 respectively via wire bonds 51.
  • the lead frame 10 may be bent in order to fit a desired application, and to thereby extend the size of the thermally conductive lead frame portion 62 and increase the heat sink functionality of a light emitting arrangement 3. This may further be seen in fig. 2 wherein the light emitting arrangement 3 is arranged in a light bulb 80, providing an arrangement with suitable thermal, electrical, optical and mechanical properties.
  • Fig. 3a illustrates an alternative embodiment for a single light source 20 on a standard lead frame 10.
  • the lead frame 10 is cut to separate row sections. Each row section comprises an anode circuit portion 46.
  • the light source 20 is electrically connected to the anode circuit portion 46 via a wire bond 53.
  • the rest of the row section of the lead frame forms a combined thermally conductive portion and cathode circuit portion 45.
  • the light source 20 is arranged on a reflective plating 30 on the lead framelO.
  • the reflective plating 30 is both thermally and electrically conductive, thereby providing both heat transfer and electrical connection to the combined thermally conductive portion and cathode circuit portion 45.
  • Fig. 3b illustrates a separated single row section constituting a single light emitting arrangement 4.
  • the light source 20 in fig. 3 is of a vertical chip technology, providing that the electrical connections are attached on a bottom and a top surface of the light source 20.
  • the wire bond 53 to the anode circuit portion 46 is attached to the top surface of the light source 20.
  • the connection between the light source 20 and the anode circuit portion 46 may alternatively be provided by the anode circuit portion 46 forming a tong extending to clamp towards the top surface of the light source 20, thereby replacing the wire bond 53.
  • a part of the light emitting arrangement may be enclosed in a translucent mould 70 to protect and to keep the parts together.
  • the translucent mould 70 may be filled with a phosphor compound to achieve a desired color output from the light emitting arrangement.
  • the translucent mould may comprise a translucent silicone compound, optionally mixed with said phosphor compound.
  • the translucent silicone compound 70 may increase the light output from the light emitting arrangement, since silicone has a higher optical refractive index than air.
  • the embodiments illustrated in figs. 1 and 2 may be provided with similar translucent moulds 70. If the translucent mould 70 does not comprise a phosphor compound, a phosphor light conversion may be provided elsewhere in the light emitting arrangement. This may for instance be provided by remote phosphor from the light sources 20, or vicinity phosphor arranged close to the light sources 20, for instance as a film or laminate on top of the translucent mould 70.
  • the present embodiment may be provided as a light emitting arrangement 5 with a bent lead frame as illustrated in figs. 3c and 4, to facilitate the assembly of the arrangement and the thermal properties.
  • the bent lead frame 10 functions in the light bulb 80 as both thermally conductive heat sink and cathode circuit portion 45 for connection to any power providing means.
  • Fig. 5 illustrates another embodiment of a light emitting arrangement 6 wherein the lead frame 10 is cut into three parts, forming a cathode circuit portion 47, an anode circuit portion 48 and a thermally conductive portion 63.
  • a plurality of light sources 20 to be arranged in a row on a reflective plating 30 on the thermally conductive portion 63 of the lead frame 10.
  • the light sources 20 are electrically connected to the cathode and anode circuit portions 47, 48 via wire bonds 54.
  • the plurality of light sources 20 in a row are electrically connected to each other via wire bonds 52.
  • the light sources 20 are further thermally connected to the thermally conductive portion 63 via the reflective plating 30.
  • the light emitting arrangement 6 may further be provided with a translucent mould 71, such as a translucent silicone compound, possibly provided with a phosphor compound.
  • the translucent mould 71 may cover all light sources 20 and at least a part of the portions 47, 48, 63 of the lead frame 10.
  • the lead frame 10 in any of the embodiments is preferably made of copper to provide a desired electrical and thermal conductivity.
  • other metals may be used for the lead frame 10 to lower the cost for the lead frame 10, but which may suffer from reduced conductivity performance.
  • Such metals may be aluminum, NiCr or FeNi.
  • the reflective portion in any of the embodiments may preferably be made of silver to provide for a desired optical reflectivity and thermal and/or electrical conductivity.
  • the light emitting arrangement may comprise a lead frame cut into different forms to form thermally conductive portions and electrically conductive portions.

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  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Manufacturing & Machinery (AREA)
  • Computer Hardware Design (AREA)
  • Power Engineering (AREA)
  • Led Device Packages (AREA)

Abstract

The present invention relates to a light emitting arrangement (1) comprising a lead frame (10). The lead frame comprises a reflective portion (30), a thermally conductive portion (60), a first electrically conductive portion (40; 43) and a second electrically conductive portion (41; 44). At least one light source (20) is arranged on said reflective portion of the lead frame. The at least one light source is electrically connected to the first electrically conductive portion and to the second electrically conductive portion, and thermally connected to the thermal portion. The first electrically conductive portion is electrically separated from the second electrically conductive portion. Preferably a circuit track (41) is connected to the light source or light sources and separated from the thermally conductive portion by an insulating layer (42).

Description

Lead frame light emitting arrangement
FIELD OF THE INVENTION
The present invention relates to a light emitting arrangement and especially to a light emitting arrangement comprising LED dies arranged on a lead frame. BACKGROUND OF THE INVENTION
In the manufacture of LED light arrangements printed circuit boards (PCBs) are used on which LED die packages are arranged. The LED die packages may be directly mounted on the PCB using chip-on-board (COB) technology. The circuit paths are thereby premade in the PCB.
LED light arrangements gain market shares and manufacturing costs are of increased importance. A lumen per dollar ratio may be desired to increase at the same time as gaining flexibility in the manufacturing process.
In an LED light arrangement as described above, the PCB is a relatively large share in the costs. Further, a PCB may be adapted for a fixed number of LED die packages, limiting the flexibility in the manufacturing of LED light arrangements. Other important aspects on the functions of a LED light arrangement are thermal and optical performance.
The PCB mounted LED die package arrangement may not be optimally thermally
constructed which may limit its operating condition.
Consequently, there is a need for LED light arrangements which lower the manufacturing costs and increase the flexibility, as well as improves the thermal and optical performance.
SUMMARY OF THE INVENTION
In view of the above discussion, a concern of the present invention is to provide a light-emitting arrangement that is flexible and cost-effective to manufacture and with improved thermal and optical performance in view of known arrangements.
To address at least one of this concern and other concerns, a light-emitting arrangement according to the independent claim is provided.
Preferred embodiments are defined by the dependent claims. According to a first aspect of the invention, a light emitting arrangement is provided comprising a lead frame comprising a reflective portion, a thermally conductive portion, a first electrically conductive portion and a second electrically conductive portion. At least one light source is arranged on said reflective portion of the lead frame. The at least one light source is electrically connected to the first electrically conductive portion and to the second electrically conductive portion, and thermally connected to the thermal portion. The first electrically conductive portion is electrically separated from the second electrically conductive portion.
The thermal performance of the light emitting arrangement may be improved by the thermally conductive portion being in thermal contact with the light source. Heat generated by the light source may thereby effectively be transported away from the light source by the thermally conductive portion. The first and second electrically conductive portions may provide electrical connections for the light source that may be easy and cost- effective to manufacture. By incorporating the electrically conductive portions in the lead frame, the use of a PCB may be avoided. At the same time, the lead frame may provide necessary mechanical support for the light source. Further, by arranging the light source on the reflective portion, the optical performance of the light emitting arrangement may be improved due to light being reflected by the reflected portion. Thereby, all necessary interconnections for the light source may be provided at a lead frame level, and the lead frame does not need to be connected to a PCB. At the same time, thermal, electrical, optical and mechanical performance of the arrangement may be improved. The light emitting arrangement according to the invention may further be compact in height with few layers forming the arrangement. The light source may be a bare LED die or a packaged LED die directly arranged on the reflective portion of the lead frame. The thickness of the lead frame may be selected depending on desired thermal properties for the thermally conductive portion. Such thickness may be a few or several millimeters.
In one embodiment, the reflective portion may be a reflective coating arranged on the lead frame.
The reflective coating may be provided on the lead frame to improve the optical performance of the light emitting arrangement. The reflective coating may increase the reflective properties of the reflective portion, thereby improving the optical output provided by the light emitting arrangement. The reflective coating may be of a material with a higher optical reflection coefficient than the material of the rest of the lead frame. The reflective coating may be a reflective plating. In another embodiment, the electrically conductive portions may be electrically separated from the reflective portion.
By arranging the electrically conductive portions of the lead frame outside of the reflective portion, disturbance of the optical performance of the reflective portion may be avoided.
In a further embodiment, the electrically conductive portions may be electrical circuit tracks arranged on the thermally conductive portion of the lead frame.
The electrical circuit tracks may connect to a plurality of light sources. The light emitting arrangement may comprise a plurality of light sources in an array arrangement, and the electrical circuit tracks may extend to connect with all light sources, directly or indirectly.
In a yet further embodiment, the electrical circuit tracks may be electrically insulated from the thermally conductive portion of the lead frame.
The electric circuit tracks may provide the electrical connections to the light source, and may be arranged in contact with the thermally conductive portion. The electrical circuit tracks may however be electrically insulated from the thermally conductive portion of the lead frame. The thermally conductive portion may thereby be used for the thermal performance of the light emitting arrangement, and not for the electrical performance. By providing the thermally conductive portion as a portion without the function of providing electrical connection to the light source, it may be optimized for providing heat sink functionality.
In one embodiment, the thermally conductive portion may be the same as the first electrically conductive portion.
Alternatively, the thermally conductive portion may be the same as one of the electrically conductive portions in order to simplify the construction of the light emitting arrangement. By combining two functions in the same portion, the arrangement may be provided in a more compact construction.
In another embodiment, the reflective portion may be electrically conductive.
The reflective portion may be electrically conductive in order to provide an electrical connection from the light source to one of the first electrically conductive portions. The electrical connection from the light source to the second electrically conductive portion may be provided via a wire bond.
In yet another embodiment, the reflective portion may be thermally
conductive. The reflective portion may be thermally conductive in order to provide a heat transportation connection from the light source to the thermally conductive portion acting as a heat sink. If the reflective portion is provided as a reflective coating, the material of the reflective coating may provide heat transfer to the thermally conductive portion of the lead frame.
In a further embodiment, the at least one light source may be connected to at least one of the electrically conductive portions via a wire bond.
The light source may be connected to at least one of the electrically conductive portions via a wire bond in order to separate different functions of the lead frame. The electrically conductive portions may be arranged separately from the reflective portion, onto which the light source is arranged. The light source may thereby be connected to one or both of the electrically conductive portions via wire bonds in order to improve the optical performance of the arrangement.
In another embodiment, the light emitting arrangement may comprise a plurality of light sources connected in series via at least one wire bond. Further, a first light source of the plurality of light sources may be connected to the first electrically conductive portion, and a second light source may be connected to the second electrically conductive portion.
By arranging the light sources on the reflective portion, and the electrically conductive portions electrically separated from the reflective portion, the light sources may be connected in series via wire bonds. The same reflective portion and thermally conductive portion may thereby be used for a plurality of light sources. A plurality of light sources may be arranged in a row. The two end light sources in the row may be connected to an electrically conductive portion, respectively. The connections to the electrically conductive portions may be via wire bonds.
In an alternative embodiment, the reflective portion may comprise a silver coating.
The silver plating may provide a high reflectivity of light from the light source, providing an improved optical output from the light emitting arrangement.
In one embodiment, the reflective portion may be arranged on a top surface of the lead frame.
The reflective portion may be a reflective coating, which may be arranged on a top surface of the lead frame. The reflective portion may thereby have direct contact with the underlying portion of the lead frame. According to a second aspect of the invention, a lamp comprising a light emitting arrangement as presented above may be provided.
According to a third aspect of the invention, a luminaire comprising a light emitting arrangement as presented above may be provided.
It is noted that the invention relates to all possible combinations of features recited in the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
Various aspects of the invention, including its particular features and advantages, will be readily understood from the following detailed description and the accompanying drawings, in which:
Fig. la is a perspective view of a light emitting arrangement according to an embodiment of the invention;
Fig. lb is a perspective view of a light emitting arrangement according to an embodiment of the invention;
Fig. lc is a perspective view of a light emitting arrangement according to an embodiment of the invention;
Fig. Id is a perspective view of a light emitting arrangement according to an embodiment of the invention;
Fig. 2 is a perspective view of a light bulb comprising a light emitting arrangement according to an embodiment of the invention;
Fig. 3a is a perspective view of a light emitting arrangement according to an embodiment of the invention;
Fig. 3b is a perspective view of a light emitting arrangement according to an embodiment of the invention;
Fig. 3c is a perspective view of a light emitting arrangement according to an embodiment of the invention;
Fig. 4 is a perspective view of a light bulb comprising a light emitting arrangement according to an embodiment of the invention;
Fig. 5 is a perspective view of a light emitting arrangement according to an embodiment of the invention;
DETAILED DESCRIPTION
The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred 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 by way of example so that this disclosure will convey the scope of the invention to those skilled in the art. The steps of any method described herein do not have to be performed in the exact order as described, unless so is specifically stated. Like reference characters refer to like elements throughout.
Fig la illustrates a light emitting arrangement 1 with light sources 20 on a reflective plating 30. The light sources 20 are arranged in a matrix, connected in series in each row. Here illustrated with three light sources 20 in each row. The reflective plating 30 is arranged on a top surface 11 of a lead frame 10. The lead frame 10 may be a standard 70x250 mm lead frame. The rows of light sources 20 extend orthogonally to a longitudinal extension direction of the lead frame 10. The light sources 20 are bare LED dies or packaged LED dies arranged on the reflective plating 30. The lead frame 10 comprises two electrically conductive portions, in this embodiment provided as a cathode electrical circuit track 40 and an anode electrical circuit track 41 arranged on each side of the reflective plating 30 respectively. The electrical circuit tracks 40, 41 extend along the entire length of the lead frame 10. Each electrical circuit track 40, 41 is arranged on an insulating layer 42 to electrically isolate the electrical circuit tracks 40, 41 from the lead frame 10.
Each row of light sources 20 is electrically connected to the cathode and anode electric circuit tracks 40, 41. These electrical connections are provided by wire bonds 50. The light sources 20 of each row are further electrically connected in series to each other via wire bonds 52. The cathode and anode electrical connections to the light sources 20 are thereby separated from the reflective plating 30 and the lead frame 10.
The reflective plating 30 provides an optical function by reflecting the light from the light sources 20, and thereby enhancing the light output from the light emitting arrangement 1. The reflective plating 30 covers an entire common area of the lead frame 10 onto which all light sources 20 are attached. The reflective plating 30 may further be thermally conductive, providing a heat transfer from the light sources 20 arranged thereon to a thermally conductive portion 60 of the lead frame 10. The light sources 20 may be attached to the reflective plating 30 by means of thermally conductive solder or glue. The lead frame 10 further transports the heat and function as a heat sink.
As illustrated in fig. lb, the lead frame 10 of the light emitting arrangement in fig. la may be split up into smaller parts for smaller light emitting arrangements 1, with one or more rows of light sources 20 in each part. By using the electric circuit tracks 40, 41, an array of light sources 20 may be provided in the same light emitting arrangement 1, each power provided via the electric circuit tracks.
In an alternative embodiment, as illustrated in fig. lc, a light emitting arrangement 2 comprises a lead frame 10 which may be cut into separate parts, forming thermally conductive portions 60 and electrically conductive portions 43, 44. The electrically conductive portions 43, 44 are connected to the cathode or anode circuit tracks 40, 41 respectively via wire bonds 51.
As illustrated in fig. Id, the lead frame 10 may be bent in order to fit a desired application, and to thereby extend the size of the thermally conductive lead frame portion 62 and increase the heat sink functionality of a light emitting arrangement 3. This may further be seen in fig. 2 wherein the light emitting arrangement 3 is arranged in a light bulb 80, providing an arrangement with suitable thermal, electrical, optical and mechanical properties.
Fig. 3a illustrates an alternative embodiment for a single light source 20 on a standard lead frame 10. The lead frame 10 is cut to separate row sections. Each row section comprises an anode circuit portion 46. The light source 20 is electrically connected to the anode circuit portion 46 via a wire bond 53. The rest of the row section of the lead frame forms a combined thermally conductive portion and cathode circuit portion 45. The light source 20 is arranged on a reflective plating 30 on the lead framelO. The reflective plating 30 is both thermally and electrically conductive, thereby providing both heat transfer and electrical connection to the combined thermally conductive portion and cathode circuit portion 45. Fig. 3b illustrates a separated single row section constituting a single light emitting arrangement 4.
The light source 20 in fig. 3 is of a vertical chip technology, providing that the electrical connections are attached on a bottom and a top surface of the light source 20. The wire bond 53 to the anode circuit portion 46 is attached to the top surface of the light source 20. The connection between the light source 20 and the anode circuit portion 46 may alternatively be provided by the anode circuit portion 46 forming a tong extending to clamp towards the top surface of the light source 20, thereby replacing the wire bond 53.
A part of the light emitting arrangement may be enclosed in a translucent mould 70 to protect and to keep the parts together. The translucent mould 70 may be filled with a phosphor compound to achieve a desired color output from the light emitting arrangement. The translucent mould may comprise a translucent silicone compound, optionally mixed with said phosphor compound. The translucent silicone compound 70 may increase the light output from the light emitting arrangement, since silicone has a higher optical refractive index than air. The embodiments illustrated in figs. 1 and 2 may be provided with similar translucent moulds 70. If the translucent mould 70 does not comprise a phosphor compound, a phosphor light conversion may be provided elsewhere in the light emitting arrangement. This may for instance be provided by remote phosphor from the light sources 20, or vicinity phosphor arranged close to the light sources 20, for instance as a film or laminate on top of the translucent mould 70.
In the same way as illustrated with the previous embodiment in figs. Id and 2, the present embodiment may be provided as a light emitting arrangement 5 with a bent lead frame as illustrated in figs. 3c and 4, to facilitate the assembly of the arrangement and the thermal properties. The bent lead frame 10 functions in the light bulb 80 as both thermally conductive heat sink and cathode circuit portion 45 for connection to any power providing means.
Fig. 5 illustrates another embodiment of a light emitting arrangement 6 wherein the lead frame 10 is cut into three parts, forming a cathode circuit portion 47, an anode circuit portion 48 and a thermally conductive portion 63. Such embodiment enables a plurality of light sources 20 to be arranged in a row on a reflective plating 30 on the thermally conductive portion 63 of the lead frame 10. The light sources 20 are electrically connected to the cathode and anode circuit portions 47, 48 via wire bonds 54. The plurality of light sources 20 in a row are electrically connected to each other via wire bonds 52. The light sources 20 are further thermally connected to the thermally conductive portion 63 via the reflective plating 30. The light emitting arrangement 6 may further be provided with a translucent mould 71, such as a translucent silicone compound, possibly provided with a phosphor compound. The translucent mould 71 may cover all light sources 20 and at least a part of the portions 47, 48, 63 of the lead frame 10.
The lead frame 10 in any of the embodiments is preferably made of copper to provide a desired electrical and thermal conductivity. However, other metals may be used for the lead frame 10 to lower the cost for the lead frame 10, but which may suffer from reduced conductivity performance. Such metals may be aluminum, NiCr or FeNi. The reflective portion in any of the embodiments may preferably be made of silver to provide for a desired optical reflectivity and thermal and/or electrical conductivity.
The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. For example, the light emitting arrangement may comprise a lead frame cut into different forms to form thermally conductive portions and electrically conductive portions.
Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.

Claims

CLAIMS:
1. A light emitting arrangement (1; 2; 3; 4; 5; 6) comprising:
a lead frame (10) comprising a reflective portion (30), a thermally conductive portion (60; 62; 63), a first electrically conductive portion (40; 43; 45; 47) and a second electrically conductive portion (41; 44; 46; 48), and
at least one light source (20) arranged on said reflective portion of the lead frame,
wherein the at least one light source is electrically connected to the first electrically conductive portion (40; 43; 45; 47) and to the second electrically conductive portion (41; 44; 46; 48), and thermally connected to the thermal portion (60; 62; 63), and wherein the first electrically conductive portion (40; 43; 45; 47) is electrically separated from the second electrically conductive portion (41; 44; 46; 48).
2. A light emitting arrangement according to claim 1, wherein the reflective portion (30) is a reflective coating arranged on the lead frame (10).
3. A light emitting arrangement according to claim 1 or 2, wherein the electrically conductive portions (40; 41; 43; 44; 46; 47; 48) are electrically separated from the reflective portion (30).
4. A light emitting arrangement according to any of the preceding claims, wherein the electrically conductive portions are electrical circuit tracks (40; 41) arranged on the thermally conductive portion (60; 62) of the lead frame (10).
5. A light emitting arrangement according to claim 4, wherein the electrical circuit tracks (40; 41) are electrically insulated from the thermally conductive portion (60; 62) of the lead frame (10).
6. A light emitting arrangement according to any of the claims 1-3, wherein the thermally conductive portion (45) is the same as the first electrically conductive portion.
7. A light emitting arrangement according to any of the preceding claims, wherein the reflective portion (30) is electrically conductive.
8. A light emitting arrangement according to any of the preceding claims, wherein the reflective portion (30) is thermally conductive.
9. A light emitting arrangement according to any of the preceding claims, wherein the at least one light source (20) is connected to at least one of the electrically conductive portions (40; 41; 43; 44; 46; 47; 48) via a wire bond (50; 51; 53; 54).
10. A light emitting arrangement according to any of the preceding claims, wherein the light emitting arrangement (1) comprises a plurality of light sources (20) connected in series via at least one wire bond (52).
11. A light emitting arrangement according to claim 10, wherein a first light source of the plurality of light sources (20) is connected to the first electrically conductive portion (40; 43; 47), and a second light source is connected to the second electrically conductive portion (41; 44; 48).
12. A light emitting arrangement according to any of the preceding claims, wherein the reflective portion (30) comprises a silver coating.
13. A light emitting arrangement according to any of the preceding claims, wherein the reflective portion (30) is arranged on a top surface (11) of the lead frame (10).
14. A lamp comprising a light emitting arrangement according to any of the claims 1-13.
15. A luminaire comprising a light emitting arrangement according to any of the claims 1-13.
PCT/IB2013/054406 2012-06-12 2013-05-28 Lead frame light emitting arrangement WO2013186653A1 (en)

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US201261658456P 2012-06-12 2012-06-12
US61/658,456 2012-06-12

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