WO2014128720A2 - Complete led light assembly integrated with heat sink - Google Patents

Complete led light assembly integrated with heat sink Download PDF

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Publication number
WO2014128720A2
WO2014128720A2 PCT/IN2014/000098 IN2014000098W WO2014128720A2 WO 2014128720 A2 WO2014128720 A2 WO 2014128720A2 IN 2014000098 W IN2014000098 W IN 2014000098W WO 2014128720 A2 WO2014128720 A2 WO 2014128720A2
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WO
WIPO (PCT)
Prior art keywords
led
mounting plate
arrangement according
led chip
chip arrangement
Prior art date
Application number
PCT/IN2014/000098
Other languages
French (fr)
Other versions
WO2014128720A3 (en
Inventor
Trivikramanarayanan JAYARAMAN
Original Assignee
Jayaraman Trivikramanarayanan
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 Jayaraman Trivikramanarayanan filed Critical Jayaraman Trivikramanarayanan
Publication of WO2014128720A2 publication Critical patent/WO2014128720A2/en
Publication of WO2014128720A3 publication Critical patent/WO2014128720A3/en

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Classifications

    • 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
    • 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
    • H01L33/64—Heat extraction or cooling elements
    • 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
    • H01L2224/48151—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive
    • H01L2224/48221—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked
    • H01L2224/48245—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked the item being metallic
    • H01L2224/48247—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked the item being metallic connecting the wire to a bond pad of the item
    • 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
    • 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

Definitions

  • the present invention relates to LED arrangements that are specific to improving the overall heat removal efficiency, light extraction efficiency and a simplified manufacturing process.
  • LEDs Light emitting diodes
  • LEDs are solid-state semiconductor chip devices that convert electric energy to light. They have multiple advantages and are capable of providing light with high brightness, which find applications in illumination, displays, traffic lights, and indicators, amongst others. LEDs are capable of emitting light in the green, blue, or even ultraviolet region of the spectrum, and thus have many promising applications.
  • LED chips normally have an active layer of semiconductor material sandwiched between doped layers (with opposite charges). When a voltage is applied across the layers, holes and electrons are injected into the sandwiched active layer and on combining the energy drop is emitted in the form of heat and light. Light is emitted from the active layer and through the surface of the LED chip.
  • a LED chip that can emit visible light in a useful circuit for illumination or similar configurations, it is first protectively enclosed in what is called a package.
  • the package besides providing environmental protection also is useful to deploy additional materials like phosphor to change the colour of the light and can be shaped suitably to provide secondary optics for changing the exit angle of the light beam.
  • the package also has suitably positioned contacts, leads or traces to allow for use in a mechanism that can apply suitable potential needed to convert the energy to light.
  • Fig 1 shows a conventionally packaged LED chip. It consists of a chip(l2) mounted on a reflective cup(ll) using electrically conductive epoxy bonding(13) with the top ohmic contact of the chip being connected to external lead(17A) using wire bond(16) and the bottom ohmic contact of the chip being connected to the lower lead frame through the electrically conductive epoxy bonding(13).
  • the reflective cup (11) may be filled with encapsulantmaterial(14) mixed with a wavelength converter such as phosphor (in case colour change is desired) which absorbs light emitted at a particular wavelength and in turn emits it at a different (desired) wavelength.
  • a wavelength converter such as phosphor (in case colour change is desired) which absorbs light emitted at a particular wavelength and in turn emits it at a different (desired) wavelength.
  • optically transparent material such as epoxy or silicone which may be additionally shaped like a lens to provide secondary optical characteristics to the assembly.
  • This packaged assembly can then be used for a through-hole soldering connection in the final illumination engine circuit.
  • FIG. 1 Yet other LED packages as shown in Fig 2 used in solid state lighting uses a single high power LED chip(22) per emitter driven at high current in excess of 300 mA. Such chips typically have a larger current spreading area at the ohmic contact and also produce a lot of heat. Such high current emitters need supply circuits that are complex and expensive, large heat sinks and a junction failure results in the failure of the entire device.
  • FIG 3. Yet another assembly of LED chips that is suited to get high brightness visible light is shown in Fig 3.
  • This is called the chip-on-board or COB configuration.
  • the LED chip(33) is mounted directly on the flat surface of a metal clad printed circuit board (MCPCB)(31), and one or more wire bonds(34) connect the ohmic contacts of the chip with the electrical traces(35, 36) on the PCB.
  • MCPCB metal clad printed circuit board
  • Higher brightness is obtained by using an array of such chips electrically interconnected through traces on the MCPCB.
  • the LED chips are then encapsulated en-masse with a phosphor mixed epoxy resin(32)(where needed) or silicone to serve the dual purpose of protection and wavelength change(where needed) to white light.
  • the components typically include:
  • chip chip, lead frame, die bonding resin, bonding wires, phosphor (where needed), epoxy resin or silicone for encapsulation.
  • driver with housing luminaire housing, heat sink compound, heat sink, external reflectors (where needed).
  • the Indian Patent Application 1950/CHE/2009 discloses LED Assembly with integrated heat sink and dispensed with printed circuit board where the LED chip is bonded onto metal directly, which is fixed to the heat sink using a thermally conductive but electrically insulating adhesive in a strip form.
  • LEDs that are available in the prior art to emit light in the visible spectrum generate a significant amount of heat, which can go up to 80-90% of the input energy received by the LED. The rest is converted to light. The heat generated by the LED is substantial and this must be removed quickly from the semiconductor junction to prevent failure or reduced life expectancy due to excessive junction temperature. The heat problem in LEDs is therefore always a concern. As the output power of the HB LED is higher, the heat generated must be controlled such that it does not go beyond the chip's maximum allowable junction temperature. In prior art heat removal is achieved typically by addition of heat sink in the secondary or tertiary manufacturing process step described above.
  • the invention disclosed is a thermally conductive mounting plate on which electrically insulated, electrically conductive, thermally radiative and optically reflective features are included and a plurality of LED chips are directly mounted inside the optically reflective feature and inter connected such that an electrical signal applied along the electrically conductive path spreads along the entire plurality of LED chips, allowing for efficient light extraction both directly and through reflection from the optically reflective path.
  • the arrangement also features efficient heat removal using the thermally conductive path and further through thermal convection and also through the thermally radiative features of the mounting plate.
  • the new design features facilitate simplified mass production, operational efficiency in heat removal through conduction, convection and radiation and operational efficiency in light extraction with integral optical reflector.
  • the present invention is a light emitting diode (LED) chip arrangement comprising of :
  • optically reflective features on the said thin edge of mounting plate that consist of a plurality of reflective cups with suitable contours that directionally reflect light with the individual LED chips of the said LED chip arrangement mounted inside each of the optically reflective cups;
  • the intermediate LEDs in the said plurality of LED chips electrically interconnected such that an electrical signal applied across the said isolated electrically conductive layer on either end of the mounting plate spreads along the conductive path and through the said plurality of LED chips and causes them to emit light and produce heat;
  • Figure 1 prior art shows a sectional view of LED package (Through Hole Device)
  • FIG. 3 prior art -shows a top view of LED package (COB Device)
  • Figure 4 present invention -shows serially connected LED chip array with chip-to-chip wire bonding
  • Figure 4b present invention -shows serially connected LED chip array with chip-to-conductive trace wire bonding
  • Figure 5 present invention -shows parallelly connected LED chip array with chip-to-chip wire bonding
  • Figure 5b present invention -shows parallelly connected LED chip array with chip-to-conductive trace wire bonding
  • Figure 6 present invention -shows serial and parallel combination (hybrid) connected LED chip array with chip-to-chip wire bonding
  • Figure 6b present invention -shows serial and parallel combination (hybrid) connected LED chip array with chip-to-conductive trace wire bonding
  • Figure 7 illustrates the Screenshot from the finite element analysis tool showing the model and one sample result of maximum and minimum temperatures reached
  • Figure 8 illustrates the Screenshot from the finite element analysis tool showing a sample temperature at the probe point where physical measurements were taken.
  • LEDs Light emitting diodes
  • LEDs Light emitting diodes
  • the LED performance is degraded. This can cause decreased light output (flux), a color shift, and a reduction in device lifetime. Consequently, there is a need to develop a LED assembly with new design features that facilitates simplified mass production, operational efficiency in heat removal through conduction, convection and radiation and operational efficiency in light extraction with integral optical reflector.
  • the present invention relates to a LED chip arrangement comprising of : a plurality of LED chips mounted on the thin edge of a thermally conductive mounting plate with isolated electrically insulative and electrically conductive layers on the said mounting plate; optically reflective features on the said thin edge of mounting plate that consist of a plurality of reflective cups with suitable contours that directionally reflect light with the individual LED chips of the said LED chip arrangement mounted inside each of the optically reflective cups;
  • the intermediate LEDs in the said plurality of LED chips electrically interconnected such that an electrical signal applied across the said isolated electrically conductive layer on either end of the mounting plate spreads along the conductive path and through the said plurality of LED chips and causes them to emit light and produce heat;
  • the mounting plate is anodized with black dye to provide radiative properties and weather protection.
  • the mounting plate is without optical reflector feature for applications where such feature is not desirable.
  • the LED chips can be of any suitable type or manufacture or emitting colour.
  • the plurality of LED chips is serially or parallely interconnected directly by suitable wire bonding to complete the electrical path.
  • the plurality of LED chips is serially or parallely interconnected by suitable wire bonding to the conductive layer of the mounting plate.
  • the plurality of LED chips is interconnected both serially and parallely (hybrid) by suitable wire bonding to complete the electrical path.
  • the plurality of LED chips is interconnected both serially and parallely (hybrid) by suitable wire bonding to the conductive layer of the mounting plate.
  • the voltage needed to drive the LED arrangement is dependent on the number of interconnected LEDs, the method of connection (serial, parallel or hybrid) and the junction voltage drop across each of the LEDs.
  • the phosphor compound mix is applied around each LED chip individually or collectively to the LED arrangement to change the colour property of the emitted light.
  • the remote phosphor is applied atop LED to change the colour property of the emitted light.
  • each LED is individually packaged to the mounting plate using one or more layers of encapsulating compound to provide secondary optics and additional environmental and mechanical protection to each LED.
  • entire LED arrangement is integrally packaged with the mounting plate using one or more layers of encapsulating compound to provide secondary optics and additional environmental and mechanical protection to the LED assembly.
  • additional bend is provided in the mounting plate to improve the bending strength of the mounting plate
  • additional groove is provided in the mounting plate to improve the locking strength with encapsulating compound.
  • the electrically conductive layer is printed or electrodeposited on the mounting plate.
  • ananodised(42) thermally conductive mounting plate(41) is prepared with reflective cups(43) at the surface of one of its longer thin edges.
  • the shape of the reflective cup (43) would be such as to ensure that most of the light emitted that bounce onto it would be reflected outward in a narrow angle.
  • Lead frames(48) are bonded to either end using suitable bonding agent such as epoxy resin.
  • the LED chips(45) are directly placed into a reflective cup(43) and bonded using a suitable bonding agent(44) such as epoxy resin.
  • each of the LED chips(45) is serially connected to the opposite ohmic contact of the adjacent chip using a suitable wire bond(47) and the outermost chips are connected to the lead frames(48) so as to form a series circuit.
  • the chip is encapsulated (49) using a wavelength convertor such as phosphor after mixing with a suitable mixing agent.
  • the entire assembly is finally encapsulated (50) using an optically clear compound such as epoxy resin or silicone or other suitable materials to provide needed environmental protection and additionally provide optical characteristics that are desired.
  • the ohmic contacts of the LED chips (45) could also be bonded to adjacent intermediate lead frames (51) instead of bonding directly to the next chip.
  • Fig 5 shows chips connected in parallel configuration with ohmic contacts of LED chips(45) bonded to adjacent intermediate lead frames(51) instead of bonding directly to the next chip.
  • the LED chips could also be connected in a hybrid configuration consisting of serially connected LED strings that are then connected in parallel to similar other strings.
  • Fig 6b shows chips connected in hybrid configuration with ohmic contacts of LED chips(45) bonded to adjacent intermediate lead frames(51 ) instead of bonding directly to the next chip.
  • a wire lead of suitable diameter and suitable insulation is taken out at any point from the conductive elements on the strip as terminals in order to provide the required energy through a power driver suitable for the LED array.
  • the complete LED assembly could additionally be protected by transparent material such as glass, poly carbonate or any such material which would also provide physical protection and also act as lens wherever required.
  • the mounting plate length, width and thickness would be so designed as to be able to conduct maximum heat away from the chip to the atmosphere in consideration of various angular orientations that may be used at the time of final deployment.
  • the final result is a hermetically sealed LED light which can eliminate external heat sink, printed circuit board(PCB) and separate protection from atmosphere.
  • these modules can be used to make lights suitable for external application, internal application and in hazardous areas.
  • thermocouple was connected to the mounting plate very close to the LED chip at the exact middle of the length of the mounting plate.
  • a power supply was connected using a power supply (driver) of suitable supply voltage.
  • thermocouple voltage was recorded in Table 3 (Column 4) using a voltmeter.

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  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Power Engineering (AREA)
  • Computer Hardware Design (AREA)
  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Manufacturing & Machinery (AREA)
  • Led Device Packages (AREA)

Abstract

A LED arrangement with new design features that facilitates operational efficiency in heat removal through conduction, convection and radiation, simplified mass production and operational efficiency in light extraction with integral optical reflector.

Description

Specification
TITLE OF THE INVENTION
Complete LED light assembly integrated with heat sink
GROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims priority from the Provisional Specification No. 738/CHE/2013 filed on 20.02.2013.
FIELD OF THE INVENTION
[0002] The present invention relates to LED arrangements that are specific to improving the overall heat removal efficiency, light extraction efficiency and a simplified manufacturing process.
BACKGROUND OF THE INVENTION
[0003] Light emitting diodes (LEDs) are solid-state semiconductor chip devices that convert electric energy to light. They have multiple advantages and are capable of providing light with high brightness, which find applications in illumination, displays, traffic lights, and indicators, amongst others. LEDs are capable of emitting light in the green, blue, or even ultraviolet region of the spectrum, and thus have many promising applications. LED chips normally have an active layer of semiconductor material sandwiched between doped layers (with opposite charges). When a voltage is applied across the layers, holes and electrons are injected into the sandwiched active layer and on combining the energy drop is emitted in the form of heat and light. Light is emitted from the active layer and through the surface of the LED chip. [0004] Typically to use a LED chip that can emit visible light in a useful circuit for illumination or similar configurations, it is first protectively enclosed in what is called a package. The package, besides providing environmental protection also is useful to deploy additional materials like phosphor to change the colour of the light and can be shaped suitably to provide secondary optics for changing the exit angle of the light beam. The package also has suitably positioned contacts, leads or traces to allow for use in a mechanism that can apply suitable potential needed to convert the energy to light.
[0005] Fig 1 shows a conventionally packaged LED chip. It consists of a chip(l2) mounted on a reflective cup(ll) using electrically conductive epoxy bonding(13) with the top ohmic contact of the chip being connected to external lead(17A) using wire bond(16) and the bottom ohmic contact of the chip being connected to the lower lead frame through the electrically conductive epoxy bonding(13). The reflective cup (11) may be filled with encapsulantmaterial(14) mixed with a wavelength converter such as phosphor (in case colour change is desired) which absorbs light emitted at a particular wavelength and in turn emits it at a different (desired) wavelength. Finally the entire assembly is encapsulated in an optically transparent material (15) such as epoxy or silicone which may be additionally shaped like a lens to provide secondary optical characteristics to the assembly. This packaged assembly can then be used for a through-hole soldering connection in the final illumination engine circuit.
[0006] Yet other LED packages as shown in Fig 2 used in solid state lighting uses a single high power LED chip(22) per emitter driven at high current in excess of 300 mA. Such chips typically have a larger current spreading area at the ohmic contact and also produce a lot of heat. Such high current emitters need supply circuits that are complex and expensive, large heat sinks and a junction failure results in the failure of the entire device.
[0007] Yet another assembly of LED chips that is suited to get high brightness visible light is shown in Fig 3. This is called the chip-on-board or COB configuration. In this package the LED chip(33) is mounted directly on the flat surface of a metal clad printed circuit board (MCPCB)(31), and one or more wire bonds(34) connect the ohmic contacts of the chip with the electrical traces(35, 36) on the PCB. Higher brightness is obtained by using an array of such chips electrically interconnected through traces on the MCPCB. The LED chips are then encapsulated en-masse with a phosphor mixed epoxy resin(32)(where needed) or silicone to serve the dual purpose of protection and wavelength change(where needed) to white light.
[0008] In nearly all such arrangements of LED chips (except in COB) it is necessary to stage the chip packaging as the primary among three manufacturing process steps. In this step the chip is packaged into a SMD or through hole LED device as shown in Fig 1 and Fig 2. This package is then used as an input to a secondary manufacturing process consisting amongst others, soldering the package onto a printed circuit board or suitable substrate. In most cases, including for the COB type arrangement described earlier (Fig 3) this is further followed by a tertiary mechanical assembly process that assembles the printed circuit board or suitable substrate to a heat sink and luminaire housing. Overall the manufacturing process is quite extensive when considering all steps from the chip to the fully Usable light emitting device, and usually different manufacturing entities in the industry specialize in each step. The number and complexity of the processes substantially increases the total cost of direct labour.
[0009] Also in nearly all such arrangements the number of components that are used in the end to end manufacturing is high thus substantially increasing the cost of direct materials used. The components typically include:
For initial packaging: chip, lead frame, die bonding resin, bonding wires, phosphor (where needed), epoxy resin or silicone for encapsulation.
For primary assembly: packaged chip, printed circuit board or suitable substrate with electrical path, solder to mount package
For secondary assembly: driver with housing, luminaire housing, heat sink compound, heat sink, external reflectors (where needed).
[0010] The Indian Patent Application 1950/CHE/2009 discloses LED Assembly with integrated heat sink and dispensed with printed circuit board where the LED chip is bonded onto metal directly, which is fixed to the heat sink using a thermally conductive but electrically insulating adhesive in a strip form.
[0011] LEDs that are available in the prior art to emit light in the visible spectrum generate a significant amount of heat, which can go up to 80-90% of the input energy received by the LED. The rest is converted to light. The heat generated by the LED is substantial and this must be removed quickly from the semiconductor junction to prevent failure or reduced life expectancy due to excessive junction temperature. The heat problem in LEDs is therefore always a concern. As the output power of the HB LED is higher, the heat generated must be controlled such that it does not go beyond the chip's maximum allowable junction temperature. In prior art heat removal is achieved typically by addition of heat sink in the secondary or tertiary manufacturing process step described above. Separate heat sinks that are either specially designed for the LED or selected appropriately from standard heat sinks are used in this process depending on the luminaire housing and aesthetic requirements. Due to non-standard packages and secondary manufacturing process and the fact that different manufacturing entities are involved in the three stages, correct heat sink designs are more difficult to achieve, thus resulting in over or under design that increase the cost or reduce the life of the final product. Also inability to correctly assess the end use and deployment configuration results in over or under design of heat sinking, resulting in similar problems.
[0012] Hence there is a need in the art to develop a LED assembly with new design features that facilitates simplified mass production, operational efficiency in heat removal through conduction, convection and radiation and operational efficiency in light extraction with integral optical reflector. The present invention satisfies these needs, as well as others, and generally overcomes the deficiencies found in the background art.
[0013] All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
OBJECTS OF THE INVENTION
[0014] It is a main object of the invention to maximise heat transfer through convection that is predominant at low and medium temperatures by directly mounting LEDs on the thin edge of a thermally conductive mounting plate.
[0015] It is another object of this invention to minimise thermal resistance of the assembly and maximising heat removal by reducing the number of intervening material layers between the chip and the heat sink..
[0016] It is yet another object of the invention to substantially reduce most of the issues described in the section of related art by providing a simplified LED arrangement in such a manner as to simplify mass production by reducing the number of processes and components used in manufacturing of the assembly
[0017] It is another object of the invention to improve the photometric efficiency of the arrangement by keeping the junction temperature of the chips substantially below their optimal specification through an arrangement that promotes efficient heat removal.
[0018] It is another object of the invention to maximise the heat dissipation through radiation to atmosphere by adding a radiation assisting anodizing layer with black dye to the outer surface of the mounting plate.
[0019] It is another object of the invention to eliminate additional weather protection layers by use of the anodizing layer.
[0020] It is a further object of the invention to eliminate need for external lens wherever required by using an integrated lens and optics arrangement on the thin edge surface of the mounting plate.
[0021] It is yet another object of the invention to reduce the need for complex specialised electronics for controlling the supply voltage and current in the circuit by providing a LED arrangement that has a voltage requirement close to the supply voltage.
[0022] Other objects of the inventions will be apparent from the description of the invention herein below.
SUMMARY OF THE INVENTION
[0023] The invention disclosed is a thermally conductive mounting plate on which electrically insulated, electrically conductive, thermally radiative and optically reflective features are included and a plurality of LED chips are directly mounted inside the optically reflective feature and inter connected such that an electrical signal applied along the electrically conductive path spreads along the entire plurality of LED chips, allowing for efficient light extraction both directly and through reflection from the optically reflective path. The arrangement also features efficient heat removal using the thermally conductive path and further through thermal convection and also through the thermally radiative features of the mounting plate. The new design features facilitate simplified mass production, operational efficiency in heat removal through conduction, convection and radiation and operational efficiency in light extraction with integral optical reflector.
[0024] Accordingly the present invention is a light emitting diode (LED) chip arrangement comprising of :
a plurality of LED chips mounted on the thin edge of a thermally conductive mounting plate with isolated electrically insulative and electrically conductive layers on the said mounting plate;
optically reflective features on the said thin edge of mounting plate that consist of a plurality of reflective cups with suitable contours that directionally reflect light with the individual LED chips of the said LED chip arrangement mounted inside each of the optically reflective cups;
isolated electrically conductive layer on either end of the thin edge of mounting plate with the first and last LED chips of said plurality of LED chips electrically connected to the said isolated electrically conductive layer on either end of the mounting plate by suitable wire bonding;
the intermediate LEDs in the said plurality of LED chips electrically interconnected such that an electrical signal applied across the said isolated electrically conductive layer on either end of the mounting plate spreads along the conductive path and through the said plurality of LED chips and causes them to emit light and produce heat;
such light emitted being efficiently extracted using the said optically reflective features on the said mounting plate; and the heat so produced being removed efficiently through the said thermally conductive properties of the said mounting plate and further through convective heat transfer and the radiative features of the said mounting plate.
BRIEF DESCRIPTION OF THE DRAWING
[0025] These and other features, aspects and advantages of the invention will become better understood when the following detailed description is read with reference to the accompanying drawings, wherein:
[0026] Figure 1 prior art -shows a sectional view of LED package (Through Hole Device)
[0027] Figure 2 prior art -shows a sectional view of LED package (SM D)
[0028] Figure 3 prior art -shows a top view of LED package (COB Device)
[0029] Figure 4 present invention -shows serially connected LED chip array with chip-to-chip wire bonding
[0030] Figure 4b present invention -shows serially connected LED chip array with chip-to-conductive trace wire bonding
[0031] Figure 5 present invention -shows parallelly connected LED chip array with chip-to-chip wire bonding
[0032] Figure 5b present invention -shows parallelly connected LED chip array with chip-to-conductive trace wire bonding
[0033] Figure 6 present invention -shows serial and parallel combination (hybrid) connected LED chip array with chip-to-chip wire bonding [0034] Figure 6b present invention -shows serial and parallel combination (hybrid) connected LED chip array with chip-to-conductive trace wire bonding [0035] Figure 7 illustrates the Screenshot from the finite element analysis tool showing the model and one sample result of maximum and minimum temperatures reached
[0036] Figure 8 illustrates the Screenshot from the finite element analysis tool showing a sample temperature at the probe point where physical measurements were taken.
DETAILED DESCRIPTION OF THE INVENTION
[0037] Light emitting diodes (LEDs) generate light when a current is applied to the device. However, not all of the power input into the device is converted to light. There is a large portion of energy that is given off as heat. As the semiconductor material heats up, like most electronics devices, the LED performance is degraded. This can cause decreased light output (flux), a color shift, and a reduction in device lifetime. Consequently, there is a need to develop a LED assembly with new design features that facilitates simplified mass production, operational efficiency in heat removal through conduction, convection and radiation and operational efficiency in light extraction with integral optical reflector.
[0038] The present invention relates to a LED chip arrangement comprising of : a plurality of LED chips mounted on the thin edge of a thermally conductive mounting plate with isolated electrically insulative and electrically conductive layers on the said mounting plate; optically reflective features on the said thin edge of mounting plate that consist of a plurality of reflective cups with suitable contours that directionally reflect light with the individual LED chips of the said LED chip arrangement mounted inside each of the optically reflective cups;
isolated electrically conductive layer on either end of the thin edge of mounting plate with the first and last LED chips of said plurality of LED chips electrically connected to the said isolated electrically conductive layer on either end of the mounting plate by suitable wire bonding;
the intermediate LEDs in the said plurality of LED chips electrically interconnected such that an electrical signal applied across the said isolated electrically conductive layer on either end of the mounting plate spreads along the conductive path and through the said plurality of LED chips and causes them to emit light and produce heat;
such light emitted being efficiently extracted using the said optically reflective features on the said mounting plate;
and the heat so produced being removed efficiently through the said thermally conductive properties of the said mounting plate and further through convective heat transfer and the radiative features of the said mounting plate.
[0039] In an embodiment of the present invention, the mounting plate is anodized with black dye to provide radiative properties and weather protection.
[0040] In another embodiment of the present invention, the mounting plate is without optical reflector feature for applications where such feature is not desirable. [0041] In -another embodiment of the present invention, the LED chips can be of any suitable type or manufacture or emitting colour.
[0042] In yet another embodiment of the present invention, the plurality of LED chips is serially or parallely interconnected directly by suitable wire bonding to complete the electrical path.
[0043] In a still another embodiment of the present invention,the plurality of LED chips is serially or parallely interconnected by suitable wire bonding to the conductive layer of the mounting plate.
[0044] In a still another embodiment of the present invention, the plurality of LED chips is interconnected both serially and parallely (hybrid) by suitable wire bonding to complete the electrical path.
[0045] In a still another embodiment of the present invention, the plurality of LED chips is interconnected both serially and parallely (hybrid) by suitable wire bonding to the conductive layer of the mounting plate.
[0046] In another embodiment of the present invention, the voltage needed to drive the LED arrangement is dependent on the number of interconnected LEDs, the method of connection (serial, parallel or hybrid) and the junction voltage drop across each of the LEDs.
[0047] In yet another embodiment of the present invention, the phosphor compound mix is applied around each LED chip individually or collectively to the LED arrangement to change the colour property of the emitted light.
[0048] In a still another embodiment of the present invention, the remote phosphor is applied atop LED to change the colour property of the emitted light. [0049] In- a still another embodiment of the present invention, each LED is individually packaged to the mounting plate using one or more layers of encapsulating compound to provide secondary optics and additional environmental and mechanical protection to each LED.
[0050] In a still another embodiment of the present invention, entire LED arrangement is integrally packaged with the mounting plate using one or more layers of encapsulating compound to provide secondary optics and additional environmental and mechanical protection to the LED assembly.
[0051] In another embodiment of the present invention, additional bend is provided in the mounting plate to improve the bending strength of the mounting plate
[0052] In yet another embodiment of the present invention, additional groove is provided in the mounting plate to improve the locking strength with encapsulating compound.
[0053] In a still another embodiment of the present invention, the electrically conductive layer is printed or electrodeposited on the mounting plate.
[0054] As shown in Fig 4, ananodised(42) thermally conductive mounting plate(41) is prepared with reflective cups(43) at the surface of one of its longer thin edges. The shape of the reflective cup (43) would be such as to ensure that most of the light emitted that bounce onto it would be reflected outward in a narrow angle. [0055] Lead frames(48) are bonded to either end using suitable bonding agent such as epoxy resin. The LED chips(45) are directly placed into a reflective cup(43) and bonded using a suitable bonding agent(44) such as epoxy resin.
[0056] The ohmic contacts(46) of each of the LED chips(45) is serially connected to the opposite ohmic contact of the adjacent chip using a suitable wire bond(47) and the outermost chips are connected to the lead frames(48) so as to form a series circuit.
[0057] Where wavelength change is required, the chip is encapsulated (49) using a wavelength convertor such as phosphor after mixing with a suitable mixing agent. The entire assembly is finally encapsulated (50) using an optically clear compound such as epoxy resin or silicone or other suitable materials to provide needed environmental protection and additionally provide optical characteristics that are desired.
[0058] As shown in Fig 4b the ohmic contacts of the LED chips (45) could also be bonded to adjacent intermediate lead frames (51) instead of bonding directly to the next chip.
[0059] As shown in Fig 5 the LED chips could also be connected in parallel configuration. Fig 5b shows chips connected in parallel configuration with ohmic contacts of LED chips(45) bonded to adjacent intermediate lead frames(51) instead of bonding directly to the next chip.
[0060] As shown in Fig 6 the LED chips could also be connected in a hybrid configuration consisting of serially connected LED strings that are then connected in parallel to similar other strings. Fig 6b shows chips connected in hybrid configuration with ohmic contacts of LED chips(45) bonded to adjacent intermediate lead frames(51 ) instead of bonding directly to the next chip.
[0061] Wherever required, a wire lead of suitable diameter and suitable insulation is taken out at any point from the conductive elements on the strip as terminals in order to provide the required energy through a power driver suitable for the LED array.
[0062] The complete LED assembly could additionally be protected by transparent material such as glass, poly carbonate or any such material which would also provide physical protection and also act as lens wherever required.
[0063] The mounting plate length, width and thickness would be so designed as to be able to conduct maximum heat away from the chip to the atmosphere in consideration of various angular orientations that may be used at the time of final deployment.
[0064] The final result is a hermetically sealed LED light which can eliminate external heat sink, printed circuit board(PCB) and separate protection from atmosphere.
[0065] Thus, just with a use of power driver, these modules can be used to make lights suitable for external application, internal application and in hazardous areas.
[0066] The technology of the instant application is further elaborated with the help of following examples. However, the examples should not be construed to limit the scope of the invention.
EXAMPLES
Example 1 Invention Prototype Testing
[0067] Several prototypes with the configurations given in the detailed description were made to verify the invention. The prototypes were then tested for performance to validate the invention. Table 2 gives the specifications of the sample prototype.
L A thermocouple was connected to the mounting plate very close to the LED chip at the exact middle of the length of the mounting plate.
2. A power supply was connected using a power supply (driver) of suitable supply voltage.
3. The power supply was switched on and the LED array was lighted up and was driven at different drive currents as shown in Table 3 (Column 2). Drive currents were measured using an ammeter.
4. In each of the cases (serial numbers 1 to 4) the prototype was allowed to reach a steady thermal state.
5. At the steady state temperature the thermocouple voltage was recorded in Table 3 (Column 4) using a voltmeter.
6. The same tests were repeated for other prototypes.
Table 1: Specifications of the Sample Prototype
Figure imgf000018_0001
Encapsulation Type Full NA
Distance Between Chips 1.2 mm
Table 2: Sample Prototype Actual Measurements Results
Figure imgf000019_0001
Example 2
Invention Finite Element Simulation
[0068] The prototypes were modelled using an advanced multiphysics finite element simulation software and the results of the simulation were compared to the actual measurements above.
1. Exact geometry of the prototypes were modelled as shown in Fig 7
2. A simulation probe was placed for temperature measurement at exactly same position in the geometry where the physical measurement was taken from as shown in Fig 8 The same parameters listed in the prototype tests were modelled into the simulation software
All the heat transfer methods i.e. conduction, convection and radiation were considered by the model.
Simulation was run
Table 3: Sam pie Prototype Finite Element Modeling Results
Figure imgf000020_0001
[0069] As can be interpreted there is very marginal difference between the simulation and the actual measurements, thus validating the simulation as correct within acceptable levels.
ADVANTAGES OF THE INVENTION
Table 4 : Comparison of the features of the present invention with prior arts
Figure imgf000021_0001

Claims

CLAIMS I claim:
1. A light emitting diode( LED) chip arrangement comprising of
a plurality of LED chips mounted on the thin edge of a thermally conductive mounting plate with isolated electrically insulative and electrically conductive layers on the said mounting plate;
optically reflective features on the said thin edge of mounting plate that consist of a plurality of reflective cups with suitable contours that directionally reflect light with the individual LED chips of the said LED chip arrangement mounted inside each of the optically reflective cups;
isolated electrically conductive layer on either end of the thin edge of mounting plate with the first and last LED chips of said plurality of LED chips electrically connected to the said isolated electrically conductive layer on either end of the mounting plate by suitable wire bonding;
the intermediate LEDs in the said plurality of LED chips electrically interconnected such that an electrical signal applied across the said isolated electrically conductive layer On either end of the mounting plate spreads along the conductive path and through the said plurality of LED chips and causes them to emit light and produce heat;
such light emitted being efficiently extracted using the said optically reflective features on the said mounting plate; and the heat so produced being removed efficiently through the said thermally conductive properties of the said mounting plate and further through convective heat transfer and the radiative features of the said mounting plate.
2. The LED chip arrangement according to claim 1, wherein the mounting plate is anodized with black dye to provide radiative properties and weather protection.
3. The LED chip arrangement according to claim 1, wherein the mounting plate is without optical reflector feature for applications where such feature is not desirable.
4. The LED chip arrangement according to claim 1, wherein the LED chips can be of any suitable type or manufacture or emitting colour.
5. The LED chip arrangement according to claim 1, wherein the plurality of LED chips is serially or parallely interconnected directly by suitable wire bonding to complete the electrical path.
6. The LED chip arrangement according to claim 1, wherein the plurality of LED chips is serially or parallely interconnected by suitable wire bonding to the conductive layer of the mounting plate.
7. The LED chip arrangement according to claim 1, wherein the plurality of LED chips is interconnected both serially and parallely (hybrid) by suitable wire bonding to complete the electrical path.
8. The LED chip arrangement according to claim 1, wherein the plurality of LED chips is interconnected both serially and parallely (hybrid) by suitable wire bonding to the conductive layer of the mounting plate.
9. The LED chip arrangement according to claim 1, wherein the voltage needed to drive the LED arrangement is dependent on the number of interconnected LEDs, the method of connection (serial, parallel or hybrid) and the junction voltage drop across each of the LEDs.
10. The LED chip arrangement according to claim 1, wherein the phosphor compound mix is applied around each LED chip individually or collectively to the LED arrangement to change the colour property of the emitted light.
11. The LED chip arrangement according to claim 1, wherein the remote phosphor is applied atop LED to change the colour property of the emitted light.
12. The LED chip arrangement according to claim 1, wherein each LED is individually packaged to the mounting plate using one or more layers of encapsulating compound to provide secondary optics and additional environmental and mechanical protection to each LED.
13. The LED chip arrangement according to claim 1, wherein entire LED arrangement is integrally packaged with the mounting plate using one or more layers of encapsulating compound to provide secondary optics and additional environmental and mechanical protection to the LED assembly.
14. The LED chip arrangement according to claim 1, wherein additional bend is provided in the mounting plate to improve the bending strength of the mounting plate.
15. The LED chip arrangement according to claim 1, wherein additional groove is provided in the mounting plate to improve the locking strength with encapsulating compound.
16. The LED chip arrangement according to claim 1, wherein the electrically conductive layer is printed or electrodeposited on the mounting plate.
PCT/IN2014/000098 2013-02-20 2014-02-17 Complete led light assembly integrated with heat sink WO2014128720A2 (en)

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20110215345A1 (en) * 2010-03-03 2011-09-08 Cree, Inc. Solid state lamp with thermal spreading elements and light directing optics
US20120268942A1 (en) * 2011-04-19 2012-10-25 Andrew Howard Beregszaszi Reflector Lamp with Improved Heat Dissipation and Reduced Weight

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20110215345A1 (en) * 2010-03-03 2011-09-08 Cree, Inc. Solid state lamp with thermal spreading elements and light directing optics
US20120268942A1 (en) * 2011-04-19 2012-10-25 Andrew Howard Beregszaszi Reflector Lamp with Improved Heat Dissipation and Reduced Weight

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