(12) United States Patent
`Lowery
`
`US006504301B1
`US 6,504,301 B1
`Jan. 7, 2003
`
`(10) Patent N0.:
`(45) Date of Patent:
`
`(54)
`
`(75)
`
`(73)
`
`NON-INCANDESCENT LIGHTBULB
`PACKAGE USING LIGHT EMITTING
`DIODES
`
`Inventor: Christopher H. Lowery, Fremont, CA
`(Us)
`Assignee: LumiLeds Lighting, US, LLC, San
`Jose, CA (US)
`
`(*)
`
`Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21)
`(22)
`(51)
`(52)
`(58)
`
`(56)
`
`Appl. No.: 09/390,006
`Filed:
`Sep. 3, 1999
`
`Int. Cl.7 ............................................... .. H01J 63/04
`
`US. Cl. ...................................... .. 313/512; 362/800
`Field of Search ............................... .. 313/512, 506,
`313/509, 113, 503; 362/800
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`3,760,237
`3,932,881
`4,035,686
`4,168,102
`5,208,462
`5,813,753
`5,962,971
`5,966,393
`
`A * 9/1973
`A
`1/1976
`A * 7/1977
`A
`9/1979
`A
`5/1993
`A
`9/1998
`A * 10/1999
`A 10/1999
`
`Jaffe ........................ .. 313/512
`Mita et a1. .
`357/17
`Fleming ..... ..
`313/503
`Chida et al. .............. .. 313/111
`
`O’Connor et a1. ..... .. 250/493.1
`Vriens et a1. ............. .. 362/293
`
`Chen .............. ..
`
`313/512
`
`Hide et al. .................. .. 372/23
`
`FOREIGN PATENT DOCUMENTS
`
`38 04 293
`298 04 149
`0 855 751
`0 883 195
`0 890 996
`1 024 539
`2 341 274
`10 190065
`11 039917
`WO 97/50132
`
`8/1989
`6/1998
`7/1998
`12/1998
`1/1999
`8/2000
`3/2000
`7/1998
`2/1999
`
`......... .. H01L/33/00
`H01L/33/00
`H01L/51/20
`H01L/33/00
`H01L/33/00
`H01L/33/00
`H01L/33/00
`H01L/33/00
`..... .. F21V/9/08
`
`12/1997
`
`......... .. H01L/33/00
`
`OTHER PUBLICATIONS
`
`Patent Abstracts of Japan, vol. 1998, No. 12, Oct. 31, 1998
`& JP 10 190065 A(Nichia Chem Ind Ltd), abstract (1 page).
`Patent Abstracts of Japan, vol. 1999, No. 05, May 31, 1999,
`& JP 11 039917 A (HeWlett Packard Co), abstract (1 page).
`European
`Search
`Report,
`Application
`No.
`00307565.2—2203, Jan. 17, 2002, (5 pages).
`* cited by examiner
`
`ABSTRACT
`
`Primary Examiner—Vip Patel
`Assistant Examiner—Joseph Williams
`(74) Attorney,
`Agent,
`or Firm—Skjerven Morrill
`MacPherson LLP; Brian D. OgonoWsky; Rachel V.
`Leiterman
`(57)
`An LED package and a method of fabricating the LED
`package utilize a prefabricated ?uorescent member that
`contains a ?uorescent material that can be separately tested
`for optical properties before assembly to ensure the proper
`performance of the LED package With respect to the color of
`the output light. The LED package includes one or more
`LED dies that operate as the light source of the package.
`Preferably, the ?uorescent material included in the prefab
`ricated ?uorescent member and the LED dies of the LED
`package are selectively chosen, so that output light gener
`ated by the LED package duplicates natural White light. In
`a ?rst embodiment of the invention, the prefabricated ?uo
`rescent member is a substantially planar plate having a
`disk-like shape. In a second embodiment, the prefabricated
`?uorescent member is a non-planar disk that conforms to
`and is attached to the inner surface of a concave lens. In this
`embodiment, the optical properties of the ?uorescent mem
`ber are tested by examining an integrated unit formed by the
`concave lens and the attached ?uorescent member. In both
`embodiments, the LED package includes a layer of encap
`sulant material that is deposited betWeen the LED dies and
`the ?uorescent member. In a preferred embodiment, the
`encapsulant material is an optical grade silicone gel, Which
`has a high thermal stability and a desired refractive index for
`an efficient light extraction.
`
`8 Claims, 6 Drawing Sheets
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`
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`Page 1 of 11
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`PHILIPS EXHIBIT 2007
`WAC v. PHILIPS
`IPR2016-01455
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`U.S. Patent
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`Jan. 7 2003
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`Sheet 1 of6
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`FIG. 1
`(PRIOR ART)
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`Sheet 2 0f 6
`Sheet 2 of 6
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`FIG. 2
`FIG. 2
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`Jan. 7, 2003
`Jan. 7, 2003
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`Sheet 3 0f 6
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`FIG. 3
`FIG. 3
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`U.S. Patent
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`Jan. 7, 2003
`Jan. 7, 2003
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`Sheet 4 0f 6
`Sheet 4 of 6
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`FIG. 4
`FIG. 4
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`U.S. Patent
`U.S. Patent
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`Jan. 7, 2003
`Jan. 7, 2003
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`Sheet 5 0f 6
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`FIG. 5
`FIG. 5
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`U.S. Patent
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`Jan. 7, 2003
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`Sheet 6 6f 6
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`US 6,504,301 B1
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`FORM FLUORESCENT MEMBERS
`
`66
`J
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`I
`
`TEST THE FLUORESCENT MEMBERS
`FOR OPTICAL PROPERTIES
`
`J- 68
`
`I
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`MOUNT ONE OR MORE GaN-BASED
`LED DIES ONTO A LEADFRAME
`
`_f— 70
`
`I
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`DEPOSIT A TRANSPARENT ENCAPSULANT f 72
`MATERIAL OVER THE MOUNTED LED DIES
`
`I
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`ATTACH A TESTED FLUORESCENT MEMBER
`ABOVE THE ENCAPSULANT MATERIAL
`
`__j_ 74
`
`I
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`ATTACH A LENS TO THE FLUORESCENT MEMBER _;— 76
`(FIRST EMBODIMENT)
`
`I
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`MOUNT A REFLECTOR OvER THE LENS f 78
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`I
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`ATTACH A DUST COVER TO THE RIM
`OF THE REFLECTOR
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`_f_ 80
`
`FIG. 6
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`US 6,504,301 B1
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`1
`NON-INCANDESCENT LIGHTBULB
`PACKAGE USING LIGHT EMITTING
`DIODES
`
`TECHNICAL FIELD
`
`The invention relates generally to lightbulb packages and
`more particularly to a lightbulb package that utilizes a
`phosphor light emitting diode as the light source.
`
`BACKGROUND ART
`
`Common lightbulb packages utiliZe a light source that
`includes an incandescent ?lament Within a glass enclosure.
`HoWever, these glass enclosures are fragile and, as such, can
`easily break even When subjected to only a moderate impact.
`In addition, the incandescent ?laments themselves are frag
`ile and tend to gradually degrade during use, such that the
`useful light output generated by the ?laments decreases over
`time. The increasing fragility of the ?lament With age
`eventually leads to breakage. Typical incandescent light
`bulbs have a mean life of 500 to 4,000 hours, Which means
`that half of a population of lightbulbs Will fail in that time
`because of ?lament breakage.
`With reference to FIG. 1, a conventional halogen light
`bulb package 10 of MR-16 outline type is shoWn. The
`halogen lightbulb package includes a halogen bulb 12 posi
`tioned in the center of a re?ector 14, Which functions to
`direct the light produced by the halogen bulb in a generally
`uniform direction. The package further includes a pair of
`output terminals 16 and 18 to receive electrical poWer. The
`front open face of the package may be protected With a dust
`cover (not shoWn). A disadvantage of the package of FIG. 1
`is the use of the halogen bulb as the light source. As
`previously described, the fragility of the glass enclosure and
`the incandescent ?lament limits the operating life of the
`halogen bulb.
`Confronted With the above disadvantage, the use of light
`emitting diodes as a potential light source in a lightbulb
`package has been examined. Light emitting diodes (LEDs)
`are Well-knoWn solid state devices that can generate light
`having a peak Wavelength in a speci?c region of the light
`spectrum. Traditionally, the most ef?cient LEDs emit light
`having a peak Wavelength in the red region of the light
`spectrum, i.e., red light. HoWever, a type of LED based on
`Gallium Nitride (GaN) has recently been developed that can
`ef?ciently emit light having a peak Wavelength in the blue
`region of the spectrum, i.e., blue light. This neW type of LED
`can provide signi?cantly brighter output light than tradi
`tional LEDs.
`In addition, since blue light has a shorter peak Wavelength
`than red light, the blue light generated by the GaN-based
`LEDs can be more readily converted to produce light having
`a longer peak Wavelength. It is Well knoWn in the art that
`light having a ?rst peak Wavelength (the “primary light”)
`can be converted into light having a longer peak Wavelength
`(the “secondary light”) using a process knoWn as ?uores
`cence. The ?uorescent process involves absorbing the pri
`mary light by a photoluminescent phosphor material, Which
`excites the atoms of the phosphor material, and emitting the
`secondary light. An LED that utiliZes the ?uorescent process
`is de?ned herein as a “phosphor LED.” The peak Wave
`length of the secondary light Will depend on the phosphor
`material. The combined light of unconverted primary light
`and the secondary light produces the output light of the
`phosphor LED. Thus, the particular color of the output light
`Will depend on the spectral distributions of the primary and
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`second lights. Consequently, a lightbulb package can be
`con?gured to generate White output light by selecting an
`appropriate phosphor material for the GaN-based LED.
`U.S. Pat. No. 5,813,753 to Vriens et al. describes a light
`emitting device having an LED as the light source that
`utiliZes phosphor grains dispersed in an epoxy layer to
`transform the color of the light emitted by the LED into a
`desired color. The phosphor grains are described as a single
`type of phosphor material or a mixture of different phosphor
`materials, depending on the desired color of the output light.
`A concern With the use of an epoxy layer that includes
`phosphor grains as described in Vriens et al. is the dif?culty
`in dispensing the phosphor grains in a repeatable and
`uniform manner. Such dif?culty leads to a population of
`?nished devices having variable performances, i.e., the color
`of the output light may vary from one ?nished device to
`another.
`In light of the above concern, What is needed is a lightbulb
`package having a phosphor LED as the light source that can
`generate output light of a prescribed color and a method of
`fabricating such a lightbulb package.
`SUMMARY OF THE INVENTION
`An LED package and a method of fabricating the LED
`package utiliZe a prefabricated ?uorescent member that
`contains a ?uorescent material that can be separately tested
`for optical properties before assembly to ensure the proper
`performance of the LED package With respect to the color of
`the output light. The LED package includes one or more
`LED dies that operate as the light source of the package.
`Preferably, the ?uorescent material included in the prefab
`ricated ?uorescent member and the LED dies of the LED
`package are selectively chosen, so that output light gener
`ated by the LED package duplicates natural White light.
`In a ?rst embodiment of the invention, the LED package
`includes four 3 volt gallium nitride-based LED dies that are
`individually mounted on separate re?ector cups, Which are
`attached to a leadframe. In this embodiment, the LED
`package is con?gured to be interchangeable With an industry
`standard MR-16 halogen outline package. HoWever, the
`LED package may be con?gured to resemble other industry
`standard packages, such as MRC-11, MRC-16, PAR-36,
`PAR-38, PAR-56 and PAR-64. In fact, the LED package
`may be con?gured in a completely different lightbulb outline
`package.
`Also attached to the leadframe are output terminals that
`provide electrical poWer to the LED dies. The LED dies are
`electrically connected to the terminals in a speci?c con?gu
`ration. In one exemplary con?guration, the LED dies are
`connected in series, so that the overall forWard voltage of the
`package is 12 volts. In an alternative exemplary
`con?guration, the LED dies are connected in series and
`parallel to create a 6 volt device. The exact electrical
`con?guration of the LED dies, as Well as the voltage of the
`LED dies, are not critical to the invention. Furthermore, the
`number of LED dies included in the LED package is not
`critical to the invention.
`Deposited over the LED dies is an encapsulant material.
`The encapsulant material may be epoxy or other suitable
`transparent material. Preferably, the encapsulant material is
`an optical grade silicone gel, since silicone gel can Withstand
`exposure to high temperatures Without degradation. In
`addition, silicone gel having a refractive index of 1.5 is
`currently available, Which results in an ef?cient extraction of
`light generated by the LED dies.
`The prefabricated ?uorescent member of the LED pack
`age is af?xed over the encapsulant material. In this
`
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`embodiment, the prefabricated ?uorescent member is a
`substantially planar disk that is optically transparent.
`HoWever, the ?uorescent member may be con?gured in
`another shape, such as a square or a rectangle, depending on
`the speci?cation of the LED package. As previously noted,
`the ?uorescent material contained in the prefabricated ?uo
`rescent member can be chosen to produce White light. As an
`example, the ?uorescent material may include gadolinium
`doped, cerium activated yttrium aluminum garnet phosphor
`grains.
`The LED package further includes a lens that is attached
`to the prefabricated ?uorescent member and a re?ector that
`is positioned over the lens. The lens and the re?ector ensure
`that most of the light energy generated by the LED package
`is output generally along a common direction.
`In a second embodiment of the invention, the lens of the
`LED package is a concave lens and the prefabricated ?uo
`rescent member is formed in the inner surface of the concave
`lens. As such, the prefabricated ?uorescent member con
`forms to the contour of the inner surface of the concave lens.
`In this embodiment, the optical properties of the ?uorescent
`member can be tested by examining the lens and the attached
`?uorescent member as a single component.
`The method of fabricating the LED package in accor
`dance With the invention includes forming a number of
`transparent ?uorescent members. In a ?rst embodiment, the
`?uorescent members may be substantially planar plates,
`such as disks. These plates may be formed by cutting sheets
`of silicone rubber into the desired shapes. In a second
`embodiment, the ?uorescent members may be non-planar
`disks that conform to the inner surface of a concave lens.
`These non-planar disks may be formed by alloWing an
`optically transparent material, such as silicone, polycarbon
`ate or acrylic, to be molded onto the inner surface of a
`concave lens. Next, the ?uorescent members are tested for
`optical properties. As an example, the ?uorescent members
`may be tested using a monochromatic standard source to
`activate the phosphor and then measuring the characteristics
`of the output from the ?uorescent members. The tested
`?uorescent members can then be categoriZed for a set of
`optical properties.
`After the ?uorescent members are tested, one or more
`GaN-based LED dies are mounted onto a leadframe. Next,
`a transparent encapsulant material is deposited over the
`mounted LED dies. Preferably, the encapsulant material is
`an optical grade silicone gel, Which has a high thermal
`stability and has a desired refractive index for an ef?cient
`light extraction. A?uorescent member having a prede?ne set
`of optical properties is then placed over the encapsulant
`material. Next, a lens is attached to the ?uorescent member.
`This step is not applicable for the second embodiment. A
`re?ector is then mounted over the lens. After the re?ector
`has been mounted, a dust cover may be attached to the rim
`of the re?ector to complete the LED package.
`An advantage of the invention is that the ?uorescent
`member can be tested prior to assembly Which ensures that
`the ?nished device Will have speci?c optical properties,
`thereby reducing production costs that are associated to
`fabrication of unWanted devices, i.e., devices that do not
`meet the desired speci?cations.
`
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`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a perspective vieW of a conventional halogen
`lightbulb package of MR-16 outline type.
`FIG. 2 is a cross-sectional diagram of an LED package in
`accordance With a ?rst embodiment of the present invention.
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`65
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`FIG. 3 is a top vieW of a leadframe of the LED package
`of FIG. 2 in Which mounted LED dies are electrically
`connected in a 12 volt con?guration.
`FIG. 4 is a top vieW of the leadframe of the LED package
`of Fig. in Which mounted LED dies are electrically con
`nected in a 6 volt con?guration.
`FIG. 5 is a cross-sectional diagram of an LED package in
`accordance With a second embodiment of the invention.
`FIG. 6 is a ?oW diagram of a method of fabricating an
`LED package in accordance With the invention.
`
`DETAILED DESCRIPTION
`
`With reference to FIG. 2, an exemplary LED package 20
`in accordance With a ?rst embodiment is shoWn. FIG. 2 is a
`schematic cross-sectional vieW of the LED package. The
`LED package is structurally con?gured to resemble a con
`ventional MR-16 halogen package, such that the LED pack
`age is interchangeable With the MR-16 package. HoWever,
`the LED package utiliZes four LED dies (only dies 22 and
`24 are exposed in the vieW of FIG. 2) as the light source for
`the package, instead of a halogen light bulb, as is the case in
`the conventional MR-16 package. The LED package has an
`operating life of 10,000 hours or more, as compared to a
`halogen package Which has a mean operating life of 500 to
`4,000 hours. Furthermore, unlike halogen packages Which
`fail by ?lament breakage, the LED package degrades by a
`gradual reduction in light output. Typically, at the end of the
`operating life of 10,000 hours, the LED package Would still
`generate 50% of the original light output.
`The LED package 20 includes a leadframe 30 that is
`attached to the bottom of a cylindrical casing 32. As an
`example, the leadframe may be composed of steel or copper.
`Also attached to the casing is a specular re?ector 34 that
`directs the light generated by the LED package. Referring
`noW to FIGS. 2 and 3, four LED dies 22, 24, 26 and 28 of
`the package are affixed to the leadframe via re?ector cups
`36, 38, 40 and 42, respectively. Preferably, the LED dies are
`gallium nitride-based LEDs (indium doped, gallium nitride
`on sapphire) that emit blue light When activated by an
`applied electrical signal. The con?guration of the LED dies
`and the re?ector cups on the leadframe is best illustrated in
`FIG. 3, Which is a top vieW of the leadframe. The LED dies
`are mounted into the cavities of the re?ector cups, as most
`clearly shoWn in FIG. 2. Preferably, the re?ector cups are
`made of a material having a coefficient of thermal expansion
`(CTE) that matches the LED dies. As an example, the
`re?ector cups may be made of silver plated molybdenum.
`The re?ector cups are sWaged into the leadframe, thereby
`af?xing the LED dies to the leadframe. In an alternative
`embodiment, a molybdenum disk (not shoWn) is attached
`underneath each LED die, for example, by solder. The
`molybdenum disk With the attached LED die is then
`mounted on the leadframe. This method also achieves the
`desired CTE matching. The LED dies are electrically con
`nected to an anode terminal 44 and a cathode terminal 46
`that are also attached to the leadframe.
`The LED dies 22, 24, 26 and 28 selected to be included
`in the LED package 20 can be of the type that enables
`activation at a loW forWard voltage of less than 3 volts each,
`at their maximum rated drive current, such that the four LED
`dies Wired in series result in an overall forWard voltage of a
`nominal 12 volts. The series connection is illustrated in FIG.
`3. This Would make the package conform to 12 volt incan
`descent packages. HoWever, if a different series voltage is
`required, other arrangements of LED dies could be imple
`mented. For example, three 4 volt LED dies could be
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`selected and Wired in series to achieve the same overall
`forward voltage of 12 volts. The exact type and number of
`LED dies included in the package and the con?guration by
`Which the LED dies are connected can vary, depending on
`the desired device to be fabricated. As an example, four 3
`volt LED dies can be Wired in series/parallel, as shoWn in
`FIG. 4, to achieve a 6 volt device. The LED dies may be
`electrically connected by Wirebonds, as illustrated in FIGS.
`2, 3 and 4. As shoWn in FIG. 3, more than one Wire may be
`used in order to carry the drive currents betWeen terminals
`and the LED dies. Although the electrical connections
`shoWn in FIGS. 2, 3 and 4 are provided by Wirebonds, other
`electrical connection techniques common in the semicon
`ductor industry may instead be utiliZed, such as ?ip chip
`solder bumping.
`Preferably, the siZe of the LED dies 22, 24, 26 and 28 is
`such that the photometric poWer is of a useful range. This
`may require the siZe of the LED die to be 2.89 square
`millimeter, Which Would result in a current density on the die
`greater than 70 amps per square centimeter. For example, if
`the photometric poWer of these LED dies is 5 lumens (per
`Watt of input poWer) and the input poWer to an assembly of
`four dies is 24 Watts (12 volts at 2 amps), then the total
`optical output poWer is 5><24=120 lumens of blue light.
`When this is modi?ed into White light, a typical output in
`White light is raised by a factor of 1.9, Which results in a ?nal
`White light output of 120><1.9=228 lumens.
`Turning back to FIG. 2, the LED package 20 further
`includes a region 50 of encapsulant material over the LED
`dies. To extract the maximum amount of light from the LED
`dies 22, 24, 26 and 28, an optical grade material of similar
`refractive index must be in contact With the LED dies.
`Sapphire LED substrates commonly have a refractive index
`of 2.5. Such LEDs are commonly encapsulated With a
`material With a refractive index of 1.5. Application of Snell’s
`LaW shoWs that only light emitted from the active region
`With an angle 0 of about 0.644 radians (36.9 degrees) to the
`normal of the interface With the encapsulant Will escape the
`LED. In such case, a fraction of 1-Cos 0 or 20% of the
`internally generated light Will escape. An equal amount of
`light is emitted from the horiZontal edges of the LED die.
`The edge light from the LED die 22, 24, 26 or 28 is re?ected
`and directed forWard by the re?ective cavity of the re?ector
`cup 36, 38, 40 or 42 in Which the LED die is mounted.
`In addition to the refractive index issue, the encapsulant
`material of the region 50 must also be able to Withstand the
`great heat generated by the LED dies 22, 24, 26 and 28
`during their operation. The surface temperature of the LED
`dies may easily reach 200 degrees Centigrade. Under such
`circumstances, epoxy Would rapidly undergo thermal deg
`radation during use, becoming progressively more yelloW
`and absorbing much of the radiation from the LED dies,
`Which Would render the device useless. For the above
`reasons, the encapsulant used for the region is preferably
`made of an optical grade silicone gel material, although
`other less desirable transparent materials may be used, such
`as epoxy. Silicones have excellent thermal stability. In
`addition, a silicone gel material having a refractive index of
`1.5 is available to maximiZe light extraction. HoWever, the
`encapsulating silicone material must be extremely soft, so
`that it does not exert stress on the bond Wires 48 or die and
`break them during operation of the device 20. This Would
`occur due to differential expansion betWeen the silicone and
`the body of the device (or the molybdenum re?ector 36, 38,
`40 or 42). Typically, the CTE of these silicone materials is
`80 parts per million per unit length per degree Centigrade.
`The metal body (for example copper) has a CTE of 10 to 12
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`parts per million per unit length per degree Centigrade, so
`the difference in expansion from the device being on and off
`is a factor of 8 and this difference can create suf?cient
`movement of the encapsulant to damage the bond Wires or
`die.
`Positioned adjacent to the region 50 of encapsulant mate
`rial is a ?uorescent plate 52 that contains a phosphor
`material. The ?uorescent plate is a prefabricated component
`that can be tested for optical properties, prior to the assembly
`of the LED package. The testing of the ?uorescent plate
`relates to homogeneity of the phosphor contained Within the
`plate and relates to the correct phosphor concentration. As an
`example, the ?uorescent plate can be made of soft, optically
`clear, silicone rubber. HoWever, the plate can be made of
`other optically transparent materials, such as polycarbonate
`or acrylic, that is dispersed With phosphor. The phosphor
`contained in the ?uorescent plate Will depend on the desired
`Wavelength characteristics of the output light generated by
`the LED package 20. As an example, the plate may contain
`gadolinium (Gd) doped, cerium (Ce) activated yttrium alu
`minum garnet (YAG) phosphor grains (“CezYAG phosphor
`grains”) to convert some of the blue radiation (Wavelength
`of 460—480 nm) emitted by the LED dies 22, 24, 26 and 28
`to a longer Wavelength radiation. The use of CezYAG
`phosphor grains Will alloW the ?uorescent plate to absorb the
`emitted blue light and upshift the optical energy to a mean
`Wavelength of approximately 520 nm. This resulting emis
`sion is a broadband light stretching from 480 to 620 nm. The
`combination of this emission With the remaining blue light,
`i.e., the unconverted emitted blue light, creates a ?nal
`emission With color rendering that duplicates natural White
`light.
`In the above example, the ?uorescent plate 52 may be
`modi?ed by the inclusion of several other rare earth metals,
`such as samarium, praseodymium or other similar materials,
`to improve color rendering of the LED package 20. In
`addition, other phosphors may be added to create emissions
`in other Wavelengths to modify the spectral distribution of
`the output light generated by the LED package. The exact
`types of ?uorescent material contained Within the plate are
`not critical to the invention.
`In the illustrated embodiment, the ?uorescent plate 52 is
`a substantially planar disk that resembles the shape of
`leadframe 30, as shoWn in FIGS. 3 and 4. HoWever, in other
`embodiments Where the LED dies 22, 24, 26 and 28 are
`arranged in a different con?guration such that the leadframe
`is non-circular, the ?uorescent plate can be shaped to cor
`respond to the leadframe and the con?guration of the
`mounted LED dies. For example, the ?uorescent plate may
`be a substantially planar rectangular plate, if the LED dies
`of the package are arranged in a rectangular con?guration on
`a rectangular leadframe.
`The LED package 20 further includes a lens 54 that is
`attached to the ?uorescent plate 52 to collimate the light
`emitted from the device and distribute the light uniformly
`into the re?ector 34. The radiation pattern from the lens is
`designed to ?ll the re?ector, Which is situated above the lens.
`As an example, the lens may be made of silicone.
`Alternatively, the lens may be made of a polycarbonate or an
`acrylic material. Situated above the lens and attached to the
`rim of the re?ector is a dust cover 56, Which serves to protect
`the ?nished device.
`Turning noW to FIG. 5, an exemplary LED package 60 in
`accordance With a second embodiment is shoWn. The LED
`package of FIG. 5 includes most of the components of the
`LED package of FIG. 2. The only signi?cant difference is
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`Page 10 of 11
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`US 6,504,301 B1
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`7
`that the lens 54 and the ?uorescent plate 52 included in the
`LED package 20 are replaced With a concave lens 62 and a
`molded ?uorescent non-planar disk 64. The ?uorescent
`non-planar disk is formed on the inside surface of the
`concave lens. Thus, the lens and the molded non-planar disk
`are a single prefabricated component of the LED package.
`That is, the lens and the non-planar disk become an inte
`grated member that can be tested for optical properties as a
`unit, separately from other components of the package.
`Therefore, in this embodiment, the optical properties of the
`?uorescent non-planar disk are tested after the ?uorescent
`non-planar disk has been formed on the inner surface of the
`concave lens.
`Although the LED packages 20 and 60 of FIGS. 2 and 5
`have been illustrated and described as being con?gured as an
`MR-16 type outline package, these LED packages may be
`con?gured in other types of industry standard outline
`packages, such as MRC-ll, MRC-16, PAR-36, PAR-38,
`PAR-56, and PAR-64.
`A method of fabricating an LED package, such as the
`LED packages 20 and 60 of FIGS. 2 and 5, Will be described
`With reference to FIG. 6. At step 66, a number of ?uorescent
`members that are optically transparent are formed. The
`?uorescent members contain a phosphor material that is
`distributed Within the ?uorescent members. Preferably, the
`?uorescent members are made of silicone rubber and contain
`Ce:YAG phosphor grains. In a ?rst embodiment, the ?uo
`rescent members are shaped plates that are formed by
`cufting sheets of optically clear material that contains the
`phosphor material into a shape that corresponds to the axial
`con?guration of the LED packages to be fabricated. For
`example, the ?nished plates may be formed in the shape of
`disks. In a second embodiment, the ?uorescent members are
`shaped as non-planar disks that conform to the inner sur
`faces of concave lenses. In this embodiment, the ?uorescent
`members are formed by molding an optically transparent
`material, such as polycarbonate or acrylic, that has been
`dispersed With a ?uorescent material into the non-planar
`disk shape using the contours of the concave lens. During
`step 68, the ?uorescent members are tested for optical
`properties. As an example, the ?uorescent members may be
`tested using a monochromatic standard source to activate the
`phosphor and then measuring the output from the ?uorescent
`members. The tested ?uorescent members can then be
`“binned” or categoriZed for a set of optical properties. Those
`?uorescent members exhibiting similar properties can be
`used to produce ?nished devices of very similar optical
`properties. Thus, devices can be produced to meet speci?c
`customer needs With respect to color temperature and output
`spectrum. Since the optical properties are knoWn prior to the
`production of the devices, unWanted devices With optical
`characteristics that do not meet the desired speci?cations are
`avoided, thereby reducing production costs.
`At step 70, one or more GaN-based LED dies are mounted
`onto a leadframe. During step 72, a transparent encapsulant
`material is deposited over the LED dies. Preferably, a
`silicone gel material is used as the encapsulant, since the
`silicone gel material has excellent thermal characteristics
`and also has a desired refractive index. Next, a tested
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`?uorescent member having speci?c optical properties is
`attached above the encapsulant material, during step 74.
`Clear silicone adhesives may be used to attach the ?uores
`cent member to the encapsulant material. Alternatively, the
`?uorescent member may simply be pressed ?rmly against
`the encapsulant material. Next, during step 76, a lens is
`attached to the ?uorescent member. Similar to the attach
`ment of the ?uorescent member to the encapsulant material,
`the lens may be attached to the ?uorescent member using
`silicone adhesives or by pressing the lens ?rmly against the
`?uorescent member. In the second embodiment, Where the
`lens and the ?uorescent member is a single prefabricated
`component, this step is not applicable. During step 78, a
`re?ector is mounted over the lens. After the re?ector has
`been mounted, a dust cover may be attached to the rim of the
`re?ector, during step 80.
`What is claimed is:
`1. A light source package comprising:
`a light source that generates primary light having a ?rst
`spectral distribution;
`a layer of transparent material over said light source that
`encapsulates said light source; and
`a nonconformal Wavelength converter attached to said
`layer of transparent material, said Wavelength converter
`being optically coupled to said light source to receive
`said primary light, said Wavelength converter compris
`mg:
`a base material selected from the group consisting of
`acrylic, polycarbonate, and soft, optically clear, sili
`cone rubber; and
`a ?uorescent material that emits secondary light in
`response to absorption of said primary light to pro
`duce a composite output light, the ?uorescent mate
`rial being contained in the base material.
`2. The package of claim 1 Wherein said Wavelength
`converter is shaped as a substantially planar plate.
`3. The package of claim 1 further comprising a concave
`lens adjacent to said Wavelength converter, said Wavelength
`converter having a