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`US 20040126913Al
`
`(19) United States
`(12) Patent Application Publication
`Loh
`
`(10) Pub. No.: US 2004/0126913 Al
`Jul. 1, 2004
`(43) Pub. Date:
`
`(54) COMPOSITE LEADFRAME LED PACKAGE
`AND METHOD OF MAKING THE SAME
`
`(52) U.S. Cl. .............................................. 438/26; 257/680
`
`(76)
`
`Inventor: Ban P. Loh, Durham, NC (US)
`
`(57)
`
`ABSTRACT
`
`Correspondence Address:
`D. James Chung of Silicon Edge Law Group
`LLP
`Suite 245
`6601 Koll Center Parkway
`Pleasanton, CA 94566 (US)
`
`(21) Appl. No.:
`
`10/721,654
`
`(22) Filed:
`
`Nov. 25, 2003
`
`Related U.S. Application Data
`
`(60) Provisional application No. 60/431,523, filed on Dec.
`6, 2002.
`
`Publication Classification
`
`(51)
`
`Int. Cl.7 ........................... HOlL 21/00; H0lL 23/02
`
`Light emitting die package is disclosed. The die package
`includes a leadframe, a bottom heatsink, a top heatsink, a
`reflector and a lens. The top and bottom heatsinks are
`thermally coupled but electrically insulated from the lead(cid:173)
`frame. The leadframe includes a plurality of leads and
`defines a mounting pad for mounting LEDS. The top heat(cid:173)
`sink defines an opening over the mounting pad. The reflector
`is coupled to the top heatsink at the opening. The lens is
`placed over the opening defining an enclosed cavity over the
`mounting pad. At least one light emitting device (LED) is
`mounted on the mounting pad within the cavity. Encapsulant
`optically couples the LED to its surrounding surfaces to
`maximize its optical performance. When energized, the LED
`generates light and heat. The light is reflected by the reflector
`and operated on by the lens. The heat is dissipated by the top
`and the bottom heatsinks.
`
`20-----..._
`
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`Patent Application Publication
`
`Jul. 1, 2004 Sheet 1 of 4
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`US 2004/0126913 Al
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`A
`
`22a
`
`A
`
`FIG. lA
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`VIZIO Ex. 1021 Page 00002
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`

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`Patent Application Publication
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`Jul. 1, 2004 Sheet 2 of 4
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`US 2004/0126913 Al
`
`~10
`
`22a
`
`10~
`
`. 22e 22a
`22a
`
`22d
`
`22a
`
`FIG. lB
`
`40
`
`20
`
`FIG. IC
`
`30
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`VIZIO Ex. 1021 Page 00003
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`

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`Patent Application Publication
`
`Jul. 1, 2004 Sheet 3 of 4
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`US 2004/0126913 Al
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`~70
`
`~60
`
`~40
`
`FIG. 2
`
`~50
`
`•
`
`20 ~
`
`~30
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`VIZIO Ex. 1021 Page 00004
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`

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`Patent Application Publication
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`Jul. 1, 2004 Sheet 4 of 4
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`US 2004/0126913 Al
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`40
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`FIG. 3
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`VIZIO Ex. 1021 Page 00005
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`

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`US 2004/0126913 Al
`
`Jul. 1, 2004
`
`1
`
`COMPOSITE LEADFRAME LED PACKAGE AND
`METHOD OF MAKING THE SAME
`
`PRIORITY
`[0001] This application claims the benefit of the filing date
`of U.S. Provisional Patent Application No. 60/431,523 filed
`Dec. 6, 2002 entitled "Leadframe based LED or semicon(cid:173)
`ductor package with improved heat spreading" under 35
`USC section 119, section 120, or both.
`
`BACKGROUND
`[0002] The present invention relates to the field of pack(cid:173)
`aging semiconductor devices, and more particularly to pack(cid:173)
`aging light emitting diodes.
`[0003] Light emitting devices (LEDS) such as light emit(cid:173)
`ting diodes are often packaged within leadframe packages.
`A leadframe package typically includes an LED connected
`to thin metal leads where the LED and most of the leads are
`completely encapsulated within a plastic body. A part of the
`plastic body defines a lens. A portion of the leads connected
`to the LED extends outside the plastic body. The metal leads
`of the leadframe package serve as the conduit to supply the
`LED with electrical power and, at the same time, may act to
`draw heat away from the LED. Heat is generated by the LED
`when power is applied to the LED to produce light. The
`portion of the leads that extend out from the package body
`connects to circuits external to the leadframe package.
`[0004] Some of the heat generated by the LED is dissi(cid:173)
`pated by the plastic package body; however, most of the heat
`is drawn away from the LED via the metal components of
`the package. The metal leads are typically very thin and have
`a small cross section. For this reason, capacity of the metal
`leads to remove heat from the LED is limited. This limits the
`amount of power that can be sent to the LED. This, in turn,
`limits the amount of light that can be generated by the LED.
`[0005] To increase the capacity of an LED package to
`dissipate heat, various designs are used in the industry;
`however, each of these designs results in LED packages with
`limited heat dissipation capacities while increasing the com(cid:173)
`plexity and the costs of manufacturing the LED packages.
`For example, in one approach, LED packages are designed
`to include the LED within a cavity of a heatsink slug. Then,
`the heatsink slug is surrounded by a plastic body except for
`its bottom surface. For example, some LUXEON™ LED
`packages by Lumileds Lighting, LLC embodies such a
`design. Here, the heatsink slug increases the capacity of the
`LED package to dissipate heat; however, LED packages of
`this design are relatively difficult and costly to manufacture.
`Further, the heat dissipation is limited because of its limited
`exposed surface (the bottom surface only).
`[0006]
`In another LED package design, the leads of the
`leadframe are extended (in various shapes and configura(cid:173)
`tions) beyond the immediate edge of the LED package body.
`This increases the surface area of the portions of the leads
`exposed to the surrounding air. The increased exposed
`surface area of the extended leads increases the capacity of
`the LED package to dissipate heat; however, the extended
`leads increase the size of the LED package requiring rela(cid:173)
`tively large area on a circuit board. Circuit board area is a
`scarce and costly factor in many applications.
`[0007] Another undesirable aspect of the current lead(cid:173)
`frame package designs relates to problems associated with
`
`thermal expansion of the package. When heat is generated,
`the LED package experiences thermal expansion. Each of
`the parts of the LED package has a different coefficient of
`thermal expansion (CTE). For example, the CTE of the
`LED, the CTE of the package body, the CTE of the leads,
`and the CTE of lens are different from each other. For this
`reason, when heated, each of these parts experience different
`degrees of thermal expansion resulting in mechanical
`stresses between the parts of the package thereby adversely
`affecting its reliability.
`[0008] Consequently,
`remains a need for an
`there
`improved LED package that overcomes or alleviates one or
`more of the shortcomings of the prior art packages.
`
`SUMMARY
`[0009] The need is met by the present invention. In a first
`embodiment of the present invention, a light emitting die
`package includes a leadframe, a bottom heatsink and a top
`heatsink. The leadframe has a top side and a bottom side and
`includes a plurality of leads. A portion of the leadframe
`defines a mounting pad. The bottom heatsink is coupled to
`the bottom side of the leadframe. The top heatsink is coupled
`to the top side of the leadframe. The top heatsink defines an
`opening which generally surrounds the mounting pad.
`[0010]
`In a second embodiment of the present invention,
`a light emitting die package includes a leadframe, a bottom
`heatsink and a top heatsink. The leadframe has a top side and
`a bottom side and includes a plurality of leads. The bottom
`heatsink is thermally coupled to the bottom side of the
`leadframe under the mounting pad. The bottom heatsink is
`electrically insulated from the leadframe. The top heatsink is
`thermally coupled to the top side of the leadframe and
`defines an opening which generally surrounds the mounting
`pad. The top heatsink is electrically insulated from the
`leadframe and is coupled to a reflector that also surround the
`mounting pad. At least one light emitting device (LED) is
`mounted on the mounting pad, the LED adapted to generate
`light when energized. A lens is coupled to the top heatsink
`over the opening. The lens is adapted to operate on the light
`generated by the LED. The lens covers the opening thereby
`defining an enclosed cavity.
`[0011]
`In a third embodiment of the present invention, a
`method of manufacturing a light emitting die package is
`disclosed. First, a leadframe die is fabricated. The leadframe
`die includes a plurality of leads and die frame, each lead and
`the die frame having a top side and a bottom side. Then, a
`top heatsink is coupled over the leadframe die, the top
`heatsink defining an opening. Next, a bottom heatsink is
`coupled under the leadframe die. Finally, the leadframe die
`is stamped to cut-away the die frame.
`[0012] Other aspects and advantages of the present inven(cid:173)
`tion will become apparent from the following detailed
`description, taken in conjunction with the accompanying
`drawings, illustrating by way of example the principles of
`the invention.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`[0013] FIGS. 1A and 1B are perspective views of a light
`emitting die package according to one embodiment of the
`present invention;
`[0014] FIG. lC is a cutaway side view of the light
`emitting die package of FIG. lA cut along line A-A;
`
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`US 2004/0126913 Al
`
`Jul. 1, 2004
`
`2
`
`[0015] FIG. 2 is an exploded perspective view of the
`semiconductor package of FIG. lA;
`
`[0016] FIG. 3 is a perspective view of a light emitting die
`package of FIG. lA during its manufacturing process.
`
`DETAILED DESCRIPTION
`
`[0017] The present invention will now be described with
`reference to the FIGS. 1 through 3, which illustrate various
`embodiments of the present invention. As illustrated in the
`Figures, the sizes of layers or regions are exaggerated for
`illustrative purposes and, thus, are provided to illustrate the
`general structures of the present invention. Furthermore,
`various aspects of the present invention are described with
`reference to a structure or a portion being formed on other
`struc~ur~s, portions, or both. As will be appreciated by those
`of skill m the art, references to a structure being formed "on"
`or "above" another structure or portion contemplates that
`additional structure, portion, or both may intervene. Refer(cid:173)
`ences to a structure or a portion being formed "on" another
`structure or portion without an intervening structure or
`portion are described herein as being formed "directly on"
`the structure or portion. Furthermore, relative terms such as
`"on" or "above" are used herein to describe one structure's
`or portion's relationship to another structure or portion as
`illustrated in the Figures. It will be understood that relative
`terms such as "on" or "above" are intended to encompass
`different orientations of the device in addition to the orien(cid:173)
`tation depicted in the Figures. For example, if the device in
`the Figures is turned over, structure or portion described as
`"above" other structures or portions would now be oriented
`"below" the other structures or portions. Likewise, if the
`device in the Figures is rotated along an axis, structure or
`portion described as "above" other structures or portions
`would now be oriented "next to" or "left of" the other
`structures or portions. Like numbers refer to like elements
`throughout.
`
`[0018] As shown in the figures for the purposes of illus(cid:173)
`tration, embodiments of the present invention are exempli(cid:173)
`fied by a light emitting die package including a leadframe
`with leads, a bottom heatsink, and a top heatsink with an
`op~ni_ng. ~ ligh~ emitting device (LED) such as a light
`emittmg d10de is mounted on the leadframe within the
`op~ni_ng. '? lens covers the opening. In effect, the light
`emittmg die package according to one embodiments of the
`present invention comprises a two part heat sink sandwich(cid:173)
`ing a leadframe. Because both the bottom and the top heat
`sinks draw heat away from the LED, more power can be
`delivered to the LED, and the LED can produce more light.
`Furthermore, for the same reason, the light emitting die
`package of the present invention may not require a separate
`heat sink slugs or leads that extend away from the package.
`Accordingly, the LED die package of the present invention
`may be more compact, more reliable, and less costly to
`manufacture than the die packages of the prior art.
`
`[00_1~] ~IGS. 1A and 1B are perspective views of a light
`emittmg die package 10 according to one embodiment of the
`present invention. FIG. lC is a cutaway side view of the
`light emitting die package 10 of FIG. lA cut along line A-A
`FIG. 2 is an exploded perspective view of the semiconduc(cid:173)
`tor package 10 of FIGS. lA and 1B. Referring to FIGS. 1A
`through 2, the semiconductor package 10 includes a lead(cid:173)
`frame 20, a bottom heatsink 30, and a top heatsink 40.
`
`[0020] The leadframe 20 includes a plurality of leads. In
`the figures, for illustrative purposes only, leads 22a, 22b,
`22c, 22d, and 22e are shown. For convenience, the leads
`22a, 22b, 22c, 22d, and 22e are collectively referred to as
`leads 22 in this document. The leads 22a, 22b, 22c, 22d, and
`22e are electrically isolated from each other. To avoid
`clutter, not all instances of the leads 22 are illustrated with
`a reference numeral in the Figures. The leadframe 20
`includes a top side 24 and a bottom side 26. Further, a
`portion 28 of the leadframe 20 defines a mounting pad 28.
`The mounting pad 28 is a portion of the leadframe 20
`(including a portion of the first lead 22a) where an LED
`assembly 50 is mounted. Typically the mounting pad 28 is
`generally located proximal to center of the top side 24 of the
`leadframe 20. In alternative embodiments of the present
`invention, the LED assembly 50 can be replaced by other
`semiconductor circuits or chips. The leadframe 20 is made
`of electrically conductive material and is generally thin. In
`one embodiment the leadframe 20 has thickness in order of
`thousandths or hundredths of inches, and for example,
`ranges from 0.005 inches to 0.010 inches.
`[0021] The bottom heatsink 30 is coupled to the bottom
`side 26 of the leadframe 20 at least under the mounting pad
`28.
`[0022] The bottom heatsink 30 is made of thermally
`conductive material and is thermally coupled to the bottom
`side 26 of the leadframe 20 but is electrically separated from
`the leadframe 20. The bottom heatsink 30 has a top surface
`32 thermally coupled to but is electrically separated from the
`leadframe 20, the electrical separation can be accomplished
`by using a dielectric layer between the leadframe 20 and the
`bottom heatsink 30, for example, adhesive filled with
`ceramic particles. The bottom heatsink 30 has a bottom
`surface 34 defining a bottom plane for the light emitting die
`package 10. The bottom surface 34 of the bottom heatsink 30
`can include a metalized bottom as illustrated in FIG. 1B. As
`illust_rate_d, the le_ads 22 are bent toward the bottom plane,
`termmatmg proximal to the bottom plane.
`[0023] The top heatsink 40 is coupled to the top side 24 of
`the leadf~ame 20. The top heatsink 40 defines an opening 42,
`the opemng 42 generally surrounding the mounting pad 28.
`The top heatsink 40 is made of thermally conductive mate(cid:173)
`rial and is thermally coupled to the top side 24 of the
`leadframe 20 but is electrically separated from the leadframe
`20, the electrical separation can be accomplished by using a
`dielectric layer between the leadframe 20 and the bottom
`heatsink 40. The bottom heatsink 30 and the top heatsink 40
`have generally similar lateral dimensions, or extents, and
`substantially overlap each other sandwiching the leadframe
`20 between them. The top heatsink 40 and the bottom
`heatsink 30 are made with thermally conductive material
`such as, for example only, copper, aluminum, or ceramics
`material.
`
`[0024] The light emitting die package 10 includes the LED
`assembly 50 including at least one light emitting device
`(LED) mounted on the mounting pad. In FIG. 2, the LED
`a~sembly 50 is illustrated as having four light emitting
`d10des. The LEDS are adapted to generate light when
`energized.
`
`[0025] The light emitting die package 10 includes a reflec(cid:173)
`tor 60 coupled to the top heatsink 40, the reflector 60
`surrounding the mounting pad 28. In an alternative embodi-
`
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`US 2004/0126913 Al
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`Jul. 1, 2004
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`3
`
`ment, the reflector 60 is not a separate component but is
`integrated with and is a portion of the top heatsink 40. The
`reflector 60 is adapted to reflect light from the LED assem(cid:173)
`bly 50 toward a lens 70.
`[0026] The light emitting die package 10 includes the lens
`70 coupled to the top heatsink 40, the lens 70 coupled
`generally over the opening 42, the mounting pad 28, and
`over the reflector 60. When the lens 70 is placed over the
`opening 42, an enclosed cavity 44 is defined by the lead(cid:173)
`frame 20, the opening 42 of the top heatsink 40, and the lens
`70. The lens 70 operates on the light generated by the LED
`assembly 50 by, for example, reflecting, directing, focusing,
`and alter wavelength. For example, a bottom surface 72 of
`the lens 70 can be coated with calcium carbonate to diffuse
`the light. Alternately, the bottom surface 72 of the lens 70
`can be coated with phosphors to alter wavelengths of light
`from the LED assembly 50.
`[0027] The enclosed cavity 44 is filled by clear encapsu(cid:173)
`lant such as Silicone. The encapsulant affixes the LED
`assembly 50 to the mounting pad 28. The enclosed cavity 44
`need not be completely filled with the encapsulant. In fact,
`partially filling the cavity 44 with encapsulant while leaving
`gaps within the cavity 44 allows the encapsulant to expand
`(when heat is generated by the LED assembly 50) without
`separating the lens 70 from the top heatsink 40.
`[0028] The method of manufacturing the light emitting die
`package 10 of FIGS. lA through 2 can be discussed using
`FIG. 3. FIG. 3 illustrates the light emitting die package 10
`of FIG. lA before it is manufactured. To manufacture the
`light emitting die package 10 of Figure, a leadframe die 80
`is fabricated. For illustratively purposes, in FIG. 2, the
`leadframe die 80 is fabricated for manufacturing of two light
`emitting die packages. In fact, a leadframe die can be
`fabricated to manufacture multiple light emitting die pack(cid:173)
`ages simultaneously. The leadframe die 80 includes a plu(cid:173)
`rality of leads, for example, the leads 22a, 22b, 22c, 22d, and
`22e ( collectively, "leads 22") and a die frame 82 surrounding
`the leads 22. The leadframe die has a top side 24 (that is the
`same side as the top side 24 of leadframe 20 of FIG. 2) and
`a bottom side 26 (that is the same side as the bottom side 26
`of leadframe 20 of FIG. 2). The leadframe die 80 is
`fabricated by stamping a sheet of die material such as metal.
`The thickness of the die material may vary greatly depend(cid:173)
`ing on the desired application, for example, the thickness
`may be in the order of fractions of millimeters (mm), for
`example, ranging from 0.13 mm to 0.25 mm. Alternately, the
`leadframe die 80 can be fabricated using etching processes.
`
`[0029] Referring to FIGS. 2 and 3, the top heatsink 40 is
`coupled to the leadframe die 80. As already described, the
`top heatsink 40 defined the opening 42. The bottom heatsink
`30 is coupled to the bottom side of the leadframe die 80. The
`bottom heatsink 30 has a top surface 32 thermally coupled
`to but is electrically separated from the leadframe die 80. As
`illustrated in FIG. lB, the bottom heatsink 30 has a metal(cid:173)
`ized bottom surface 34 defining a bottom plane for the light
`emitting die package 30. Dielectric but thermally conductive
`adhesive layer 38 of FIG. 3 may be used to separate the
`bottom heatsink 30 from the leadframe 20.
`
`[0030] The top heatsink 40 and the bottom heatsink 30
`have similar lateral extents and substantially overlap each
`other. For example, the later extents 33 and 35 of the bottom
`heatsink 30 may vary widely depending on the implemen-
`
`tation, for example only, the lateral extents 33 and 35 may
`be in the order of mm or centimeters (cm), and may range
`from, for example, seven mm to 20 mm. The bottom
`heatsink 30 and the top heatsink 40 may have thicknesses in
`the order of mm or cm, and may range from, for example,
`1.5 mm to three mm. These measurements may vary greatly
`depending on various desired characteristics and applica(cid:173)
`tions.
`[0031] Referring to FIGS. 2 and 3, the method of manu(cid:173)
`facturing the light emitting die package 10 is further dis(cid:173)
`cussed. The LED assembly 50 including at least one light
`emitting device (LED) such as a light emitting diode is
`mounted on at least one lead, such as the lead 22a, within the
`opening 42. Then, the reflector 60 and the lens 70 are
`attached on the top heatsink 40, the lens 70 covering the
`opening 42. The reflector 60 surrounds the opening 42. The
`reflector 60 may be integrated with the top heatsink 40 in
`which case there is no need for a separate step of coupling
`the reflector 60 with the top heatsink 40.
`[0032] Finally, the leadframe die 80 is stamped to cut
`away the die frame 82. During the stamping, the leads 22 are
`bent towards the bottom plane as illustrated in FIGS. 1A
`through 2.
`[0033] From the foregoing, it will be apparent that the
`present invention is novel and offers advantages over the
`current art. Although specific embodiments of the invention
`are described and illustrated above, the invention is not to be
`limited to the specific forms or arrangements of parts so
`described and illustrated. For example, differing configura(cid:173)
`tions, sizes, or materials may be used to practice the present
`invention. The invention is limited by the claims that follow.
`
`What is claimed is:
`1. A light emitting die package comprising:
`
`a leadframe including a plurality of leads, said leadframe
`having top side and bottom side, and a portion of said
`leadframe defining a mounting pad;
`
`a bottom heatsink coupled to the bottom side of said
`leadframe; and
`
`a top heatsink coupled to the top side of said leadframe,
`said top heatsink defining an opening, the opening
`generally surrounding the mounting pad.
`2. The light emitting die package recited in claim 1
`wherein said top heatsink is electrically separated from said
`leadframe.
`3. The light emitting die package recited in claim 1
`wherein said top heatsink and said bottom heatsink have
`similar lateral extents and substantially overlap each other.
`4. The light emitting die package recited in claim 1
`wherein said bottom heatsink has a top surface thermally
`coupled to but is electrically separated from said leadframe,
`and said bottom heatsink has a metalized bottom surface
`defining a bottom plane for the light emitting die package.
`5. The light emitting die package recited in claim 4
`wherein the leads are bent toward the bottom plane, and the
`leads terminate proximal to the bottom plane.
`6. The light emitting die package recited in claim 1 further
`comprising at least one light emitting device (LED) mounted
`on the mounting pad.
`7. The light emitting die package recited in claim 1 further
`comprising a reflector coupled to said top heatsink, said
`reflector surrounding the mounting pad.
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`Jul. 1, 2004
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`4
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`8. The light emitting die package recited in claim 1 further
`comprising a lens coupled to said top heatsink over the
`mounting pad.
`9. The light emitting die package recited in claim 8
`wherein an enclosed cavity is defined by the opening and
`said lens.
`10. A light emitting die package comprising:
`
`a leadframe including a plurality of leads, said leadframe
`having top side and a bottom side, and a portion of said
`leadframe defining a mounting pad;
`
`a bottom heatsink thermally coupled to the bottom side of
`said leadframe under the mounting pad, said bottom
`heatsink electrically insulated from said leadframe;
`
`a top heatsink thermally coupled to the top side of said
`leadframe, said top heatsink defining an opening, the
`opening generally surrounding the mounting pad, said
`top heatsink electrically insulated from said leadframe,
`and said top heatsink coupled to a reflector also sur(cid:173)
`round the mounting pad;
`
`at least one light emitting device (LED) mounted on the
`mounting pad, the LED adapted to generate light when
`energized; and
`
`a lens coupled to said top heatsink over the opening, said
`lens adapted to operate on the light generated by the
`LED, the lens, covering the opening thereby defining
`an enclosed cavity.
`11. The light emitting die package recited in claim 10
`wherein said bottom heatsink has a metalized bottom surface
`defining a bottom plane for the light emitting die package.
`12. The light emitting die package recited in claim 11
`wherein the leads are bent toward the bottom plane, and the
`leads terminate proximal to the bottom plane.
`13. The light emitting die package recited in claim 10
`wherein the enclosed cavity is at least partially filled with
`encapsulant.
`
`14. A method of manufacturing a light emitting die
`package, the method comprising:
`
`fabricating a leadframe die, the leadframe die including a
`plurality of leads and die frame, each lead and the die
`frame having a top side and a bottom side;
`
`coupling a top heatsink over the leadframe die, the top
`heatsink defining an opening;
`coupling a bottom heatsink under the leadframe die; and
`stamping the leadframe die to cut-away the die frame.
`15. The method recited in claim 14 wherein the leadframe
`die is fabricated by stamping a sheet of die material.
`16. The method recited in claim 14 wherein the leadframe
`die is fabricated by etching process.
`17. The method recited in claim 14 further comprising
`mounting at least one light emitting device (LED) on at least
`one lead, the LED mounted in the opening.
`18. The method recited in claim 14 further comprising
`attaching a lens on the top heatsink, the lens covering the
`opening.
`19. The method recited in claim 14 wherein the top
`heatsink and the bottom heatsink have similar lateral extents
`and substantially overlap each other.
`20. The method recited in claim 14 wherein the bottom
`heatsink has a top surface thermally coupled to but is
`electrically separated from the leadframe die, and the bottom
`heatsink has a metalized bottom surface defining a bottom
`plane for the light emitting die package.
`21. The method recited in claim 20 further comprising
`bending the leads toward the bottom plane.
`22. The method recited in claim 14 further comprising
`coupling a reflector on the top heatsink, said reflector
`surrounding the opening.
`23. The method recited in claim 14 wherein the top
`heatsink includes an integrated reflector.
`
`* * * * *
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