(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2006/0102914 A1
`(43) Pub. Date:
`May 18, 2006
`Smits et al.
`
`US 200601 02914A1
`
`(54) WIDE EMITTING LENS FOR LED USEFUL
`FOR BACKLIGHTING
`
`(75) Inventors: Willem H. Smits, Veldhoven (NL);
`Robert F. M. Hendriks. Overlangel
`(NL); Grigoriy Basin, San Francisco,
`CA (US); Frans H. Konijn, Huizen
`(NL); Robert Scott West, Morgan Hill,
`CA (US); Paul S. Martin, Pleasanton,
`CA (US); Gerard Harbers, Sunnyvale,
`CA (US)
`
`Correspondence Address:
`PATENT LAW GROUP LLP
`2635 NORTH FIRST STREET
`SUTE 223
`SAN JOSE, CA 95134 (US)
`
`(73) Assignee: Lumileds Lighting U.S., LLC
`
`(21) Appl. No.:
`
`11/093,961
`
`(22) Filed:
`
`Mar. 29, 2005
`
`Related U.S. Application Data
`(63) Continuation-in-part of application No. 11/069,418,
`filed on Feb. 28, 2005, which is a continuation-in-part
`of application No. 10/990,208, filed on Nov. 15, 2004.
`
`Publication Classification
`
`(51)
`
`Int. C.
`(2006.01)
`HOIL 33/00
`(2006.01)
`HOIL 29/22
`(2006.01)
`HOIL 29/227
`U.S. Cl. .............................................. 257/98: 257/E33
`
`(52)
`ABSTRACT
`(57)
`Lenses and certain fabrication techniques are described. A
`wide-emitting lens refracts light emitted by an LED die to
`cause a peak intensity to occur within 50-80 degrees off the
`center axis and an intensity along the center axis to be
`between 5% and 33% of the peak intensity. The lens is
`particularly useful in a LCD backlighting application. In one
`embodiment, the lens is affixed to the backplane on which
`the LED die is mounted and surrounds the LED die. The lens
`has a hollow portion that forms an air gap between the LED
`die and the lens, where the light is bent towards the sides
`both at the air gap interface and the outer lens Surface
`interface. The lens may be a secondary lens Surrounding an
`interior lens molded directly over the LED die.
`
`
`
`O
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`Angular intensity
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`80 degrees
`
`LED source
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`1
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`LGI 1006
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`Patent Application Publication May 18, 2006 Sheet 1 of 15
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`Patent Application Publication May 18, 2006 Sheet 2 of 15
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`Patent Application Publication May 18
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`0 o
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`Patent Application Publication May 18, 2006 Sheet 4 of 15
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`Patent Application Publication May 18, 2006 Sheet 5 of 15
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`10 22
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`1OO
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`98
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`102
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`Fig. 16
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`6
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`Patent Application Publication May 18, 2006 Sheet 6 of 15
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`US 2006/01 02914 A1
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`
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`Overmoided lens
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`2
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`Angular intensity
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`80 degrees
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`LED SOUrce
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`Fig. 2O
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`7
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`Patent Application Publication May 18, 2006 Sheet 7 of 15
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`Fresnel lens
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`8
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`Patent Application Publication May 18, 2006 Sheet 8 of 15
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`9
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`Patent Application Publication May 18, 2006 Sheet 9 of 15
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`10
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`Patent Application Publication May 18, 2006 Sheet 10 of 15
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`11
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`Patent Application Publication May 18, 2006 Sheet 11 of 15
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`/
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`- 22
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`Silicone overmold
`-1
`Sputtered metal
`reflector cup
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`
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`Conformal
`phosphor coat
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`LED die
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`Reflected light scattered and contributing
`to increased surface brightness
`
`Fig. 32
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`12
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`

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`Patent Application Publication May 18, 2006 Sheet 12 of 15
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`US 2006/01 02914 A1
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`Diffuser
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`56
`Backlight
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`52
`58 A
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`54
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`6 O
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`Lens
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`o A
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`
`
`
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`Fig. 33
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`72
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`\ 6 2.
`4
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`Modulator/Optics
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`- \ 7 Co
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`RGB light source
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`1.
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`13
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`Patent Application Publication May 18, 2006 Sheet 13 of 15
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`US 2006/01 02914 A1
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`Brightness profile
`(transfer function)
`
`Screen
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`183
`
`w
`W
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`Lambertian pattem
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`Back plane
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`'
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`WS
`4.
`LED source
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`V
`as "A ta
`18O
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`182
`
`Fig. 35 (Prior Art)
`
`
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`Brightness profile
`(transfer function
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`14
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`

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`Patent Application Publication May 18, 2006 Sheet 14 of 15
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`US 2006/01 02914 A1
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`Angular intensity
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`50 degrees
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`80 degrees
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`LED source
`Fig. 37
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`Center line (normal)
`1.
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`184
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`Screen
`
`
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`ray
`3VS
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`o
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`PCB 190-1
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`194
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`196
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`15
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`Patent Application Publication May 18, 2006 Sheet 15 of 15
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`US 2006/01 02914 A1
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`
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`40
`SO
`60
`Angle from system normat (degrees)
`Fig. 39
`
`TIR Surfaces
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`16
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`

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`US 2006/01 02914 A1
`
`May 18, 2006
`
`WIDE EMITTING LENS FOR LED USEFUL FOR
`BACKLIGHTING
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`0001. This is a continuation-in-part (CIP) of U.S. appli
`cation Ser. No. 11/069,418, filed Feb. 28, 2005, by Grigoriy
`Basin et al., entitled “Overmolded Lens Over LED Die.”
`which is a CIP of U.S. application Ser. No. 10/990,208, filed
`Nov. 15, 2004, by Grigoriy Basin et al., entitled “Molded
`Lens Over LED Die.
`
`FIELD OF THE INVENTION
`0002 This invention relates to light emitting diodes
`(LEDs) and, in particular, to certain lens designs and a
`technique for forming a lens over an LED die.
`
`BACKGROUND
`0003) LED dies typically emit light in a lambertian
`pattern. It is common to use a lens over the LED die to
`narrow the beam or to make a side-emission pattern. A
`common type of lens for a Surface mounted LED is pre
`formed molded plastic, which is bonded to a package in
`which the LED die is mounted. One such lens is shown in
`U.S. Pat. No. 6,274.924, assigned to Lumileds Lighting and
`incorporated herein by reference.
`
`SUMMARY
`0004. A technique for forming a lens for surface mounted
`LEDs is described herein along with various designs of
`lenses. One particularly useful lens creates a wide emission
`pattern so that light from multiple LEDs in a backlight is
`thoroughly mixed to create a homogenous light source in a
`liquid crystal display (LCD) backlight.
`0005. In one method for forming lenses, one LED die or
`multiple LED dice are mounted on a support structure. The
`Support structure may be a ceramic Substrate, a silicon
`substrate, or other type of support structure with the LED
`dice electrically connected to metal pads on the Support
`structure. The Support structure may be a Submount, which
`is mounted on a circuit board or a heat sink in a package.
`0006. A mold has indentations in it corresponding to the
`positions of the LED dice on the support structure. The
`indentations are filled with a liquid, optically transparent
`material. Such as silicone, which when cured forms a hard
`ened lens material. The shape of the indentations will be the
`shape of the lens. The mold and the LED dice/support
`structure are brought together so that each LED die resides
`within the liquid lens material in an associated indentation.
`0007. The mold is then heated to cure (harden) the lens
`material. The mold and the support structure are then
`separated, leaving a complete lens over each LED die. This
`general process will be referred to as overmolding.
`0008. The overmolding process may be repeated with
`different molds to create concentric or overlapping shells of
`lenses. Each lens may have a different property, Such as
`containing a phosphor, being a different material, providing
`a different radiation pattern, having a different hardness
`value, having a different index of refraction, or curable by a
`different technique (e.g., UV vs. heat).
`
`0009. In another embodiment, a secondary lens is secured
`over an overmolded lens. The overmolded lens simplifies the
`design and fabrication of the secondary lens.
`0010. In another embodiment, a wide-emitting lens is
`described that does not require an overmolded lens.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`0011 FIG. 1 is a side view of four LED dice mounted on
`a Support structure, such as a Submount, and a mold for
`forming a lens around each LED die.
`0012 FIG. 2 is a side view of the LED dice being
`inserted into indentations in the mold filled with a liquid lens
`material.
`0013 FIG. 3 is a side view of the LED dice removed
`from the mold after the liquid has been cured, resulting in a
`lens encapsulating each LED die.
`0014 FIG. 4 is a perspective view of an array of LED
`dice on a submount or circuit board with a molded lens
`formed over each LED die.
`0.015 FIG. 5 is a close-up side view of a flip-chip LED
`die mounted on a Submount, which is, in turn, mounted on
`a circuit board, and where a molded lens is formed over the
`LED die.
`0016 FIG. 6 is a close-up side view of a non-flip-chip
`LED die mounted on a Submount, which is, in turn, mounted
`on a circuit board, where wires electrically connect in and p
`metal on the LED die to leads on the circuit board, and
`where a molded lens is formed over the LED die.
`0017 FIGS. 7, 8, 9, 10, and 11 are cross-sectional views
`of an LED die with different lenses formed over it.
`0018 FIG. 12 is a cross-sectional view of a side-emitting
`lens molded onto the LED die using the inventive tech
`niques.
`0019 FIG. 13 is a cross-sectional view of a collimating
`lens molded onto the LED die using the inventive tech
`niques.
`0020 FIG. 14 is a cross-sectional view of a preformed
`side-emitting lens affixed over a lambertian lens that has
`been molded onto the LED die using the inventive tech
`niques.
`FIG. 15 is a cross-sectional view of a backlight for
`0021
`a liquid crystal display or other type of display using the
`LED and side-emitting lens of FIG. 14.
`0022 FIG. 16 is a perspective view of a cell phone with
`a camera that uses as a flash an LED with a molded lens.
`0023 FIGS. 17 and 18 are cross-sectional views of two
`types of molded lenses. All lenses shown are symmetrical
`about the center axis, although the invention may apply to
`non-symmetrical lenses as well.
`0024 FIGS. 19-22 illustrate surface features on an inner
`lens or an outer shell lens for obtaining a desired emission
`pattern.
`0.025 FIG. 23 illustrates the use of a high domed lens for
`a collimated emission pattern.
`0026 FIGS. 24 and 25 illustrate the use of a hard outer
`lens and a soft inner lens to limit the stress on a wire bond.
`
`17
`
`

`

`US 2006/01 02914 A1
`
`May 18, 2006
`
`0027 FIGS. 26-28 illustrate the use of an outer lens
`formed on various types of inner or intermediate lenses for
`a side-emitting pattern.
`0028 FIG. 29 illustrates another side-emitting molded
`lens.
`0029 FIG. 30 illustrates the use of molded shells, each
`containing a different phosphor.
`0030 FIG. 31 illustrates forming a mold portion on the
`Support Substrate for forming a molded lens.
`0031
`FIG. 32 illustrates depositing a metal reflector over
`a portion of the lens for achieving a desired emission pattern.
`0032 FIG. 33 is a side view of a liquid crystal display
`using LEDs with side-emitting lenses in a backlight.
`0033 FIG. 34 is a side view of a rear projection TV using
`LEDs with collimating lenses as a RGB light source.
`0034 FIG. 35 illustrates prior art LED emission patterns
`(Lambertian) and their overlapping brightness profiles on a
`SCC.
`0035 FIG. 36 illustrates the wide angle emission pat
`terns of LEDs using the inventive lens and their overlapping
`brightness profiles on a screen.
`0036 FIG. 37 shows more detail of the emission pattern
`of the LEDs in FIG. 36.
`0037 FIG.38 is a cross-sectional view of an LED and a
`wide emitting lens in accordance with one embodiment of
`the invention.
`0038 FIG. 39 is a graph of light intensity vs. angle for
`the lens of FIG. 38.
`0039 FIG. 40 is a cross-sectional view of an LED and a
`wide emitting lens in accordance with another embodiment
`of the invention.
`
`DETAILED DESCRIPTION
`0040. As a preliminary matter, a conventional LED is
`formed on a growth substrate. In the example used, the LED
`is a GaN-based LED, such as an AlInGaN LED, for pro
`ducing blue or UV light. Typically, a relatively thick n-type
`GaN layer is grown on a Sapphire growth Substrate using
`conventional techniques. The relatively thick GaN layer
`typically includes a low temperature nucleation layer and
`one or more additional layers So as to provide a low-defect
`lattice structure for the n-type cladding layer and active
`layer. One or more n-type cladding layers are then formed
`over the thick n-type layer, followed by an active layer, one
`or more p-type cladding layers, and a p-type contact layer
`(for metallization).
`0041 Various techniques are used to gain electrical
`access to the n-layers. In a flip-chip example, portions of the
`p-layers and active layer are etched away to expose an
`n-layer for metallization. In this way the p contact and in
`contact are on the same side of the chip and can be directly
`electrically attached to the package (or Submount) contact
`pads. Current from the n-metal contact initially flows later
`ally through the n-layer. In contrast, in a vertical injection
`(non-flip-chip) LED, an n-contact is formed on one side of
`the chip, and a p-contact is formed on the other side of the
`chip. Electrical contact to one of the p or n-contacts is
`
`typically made with a wire or a metal bridge, and the other
`contact is directly bonded to a package (or Submount)
`contact pad. A flip-chip LED is used in the examples of
`FIGS. 1-3 for simplicity.
`0042 Examples of forming LEDs are described in U.S.
`Pat. Nos. 6,649,440 and 6,274,399, both assigned to
`Lumileds Lighting and incorporated by reference.
`0043. Optionally, a conductive substrate is bonded to the
`LED layers (typically to the p-layers) and the sapphire
`substrate is removed. One or more LED dice may be bonded
`to a submount, with the conductive substrate directly bonded
`to the submount, to be described in greater detail with
`respect to FIGS. 5 and 6. One or more submounts may be
`bonded to a printed circuit board, which contains metal leads
`for connection to other LEDs or to a power supply. The
`circuit board may interconnect various LEDs in series and/or
`parallel.
`0044) The particular LEDs formed and whether or not
`they are mounted on a Submount is not important for
`purposes of understanding the invention.
`004.5 FIG. 1 is a side view of four LED dice 10 mounted
`on a Support structure 12. The Support structure may be a
`Submount (e.g., ceramic or silicon with metal leads), a metal
`heat sink, a printed circuit board, or any other structure. In
`the present example, the Support structure 12 is a ceramic
`Submount with metal pads/leads.
`0046. A mold 14 has indentations 16 corresponding to the
`desired shape of a lens over each LED die 10. Mold 14 is
`preferably formed of a metal. A very thin non-stick film 18,
`having the general shape of mold 14, is placed over mold 14.
`Film 18 is of a well known conventional material that
`prevents the Sticking of silicone to metal.
`0047 Film 18 is not needed if the lens material does not
`Stick to the mold. This may be accomplished by using a
`non-stick mold coating, using a non-stick mold material, or
`using a mold process that results in a non-stick interface.
`Such processes may involve selecting certain process tem
`peratures to obtain the minimum stick. By not using film 18,
`more complex lenses can be formed.
`0.048. In FIG. 2, the mold indentions 16 have been filled
`with a heat-curable liquid lens material 20. The lens material
`20 may be any Suitable optically transparent material Such as
`silicone, an epoxy, or a hybrid silicone? epoxy. A hybrid may
`be used to achieve a matching coefficient of thermal expan
`sion (CTE). Silicone and epoxy have a sufficiently high
`index of refraction (greater than 1.4) to greatly improve the
`light extraction from an AlInGaN or AlInGaP LED as well
`as act as a lens. One type of silicone has an index of
`refraction of 1.76.
`0049. A vacuum seal is created between the periphery of
`the Support structure 12 and mold 14, and the two pieces are
`pressed against each other so that each LED die 10 is
`inserted into the liquid lens material 20 and the lens material
`20 is under compression.
`0050. The mold is then heated to about 150 degrees
`centigrade (or other Suitable temperature) for a time to
`harden the lens material 20.
`0051. The support structure 12 is then separated from
`mold 14. Film 18 causes the resulting hardened lens to be
`easily released from mold 14. Film 18 is then removed.
`
`18
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`

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`
`May 18, 2006
`
`0052. In another embodiment, the LED dice 10 in FIG.
`1 may be first covered with a material, such as silicone or
`phosphor particles in a binder. The mold indentations 16 are
`filled with another material. When the dice are then placed
`in the mold, the mold material is shaped over the covering
`material.
`0053 FIG. 3 illustrates the resulting structure with a
`molded lens 22 over each LED die 10. In one embodiment,
`the molded lens is between 1 mm and 5 mm in diameter. The
`lens 22 may be any size or shape.
`0054 FIG. 4 is a perspective view of a resulting structure
`where the support structure 12 supports an array of LED
`dice, each having a molded lens 22. The mold used would
`have a corresponding array of indentations. If the Support
`structure 12 were a ceramic or silicon submount, each LED
`(with its underlying Submount portion) can be separated by
`sawing or breaking the submount 12 to form individual LED
`dice. Alternatively, the Support structure 12 may be sepa
`rated/diced to support subgroups of LEDs or may be used
`without being separated/diced.
`0.055 The lens 22 not only improves the light extraction
`from the LED die and refracts the light to create a desired
`emission pattern, but the lens also encapsulates the LED die
`to protect the die from contaminants, add mechanical
`strength, and protect any wire bonds.
`0056 FIG. 5 is a simplified close-up view of one
`embodiment of a single flip-chip LED die 10 on a submount
`24 formed of any suitable material, such as a ceramic or
`silicon. In one embodiment, Submount 24 acted as the
`support structure 12 in FIGS. 1-4, and the die? submount of
`FIG. 5 was separated from the structure of FIG. 4 by
`sawing. The LED die 10 of FIG. 5 has a bottom p-contact
`layer 26, a p-metal contact 27, p-type layers 28, a light
`emitting active layer 30, n-type layers 32, and an n-metal
`contact 31 contacting the n-type layers 32. Metal pads on
`submount 24 are directly metal-bonded to contacts 27 and
`31. Vias through submount 24 terminate in metal pads on the
`bottom surface of submount 24, which are bonded to the
`metal leads 40 and 44 on a circuit board 45. The metal leads
`40 and 44 are connected to other LEDs or to a power supply.
`Circuit board 45 may be a metal plate (e.g., aluminum) with
`the metal leads 40 and 44 overlying an insulating layer. The
`molded lens 22, formed using the technique of FIGS. 1-3,
`encapsulates the LED die 10.
`0057 The LED die 10 in FIG.5 may also be a non-flip
`chip die, with a wire connecting the top n-layers 32 to a
`metal pad on the Submount 24. The lens 22 may encapsulate
`the wire.
`0.058. In one embodiment, the circuit board 45 itself may
`be the support structure 12 of FIGS. 1-3. Such an embodi
`ment is shown in FIG. 6. FIG. 6 is a simplified close-up
`view of a non-flip-chip LED die 10 having a top n-metal
`contact 34 connected to a metal lead 40 on circuit board 45
`by a wire 38. The LED die 10 is mounted on a submount 36,
`which in the example of FIG. 6 is a metal slab. A wire 42
`electrically connects the p-layers 26/28 to a metal lead 44 on
`circuit board 45. The lens 22 is shown completely encap
`sulating the wires and submount 36; however, in other
`embodiments the entire submount or the entire wire need not
`be encapsulated.
`0059 A common prior art encapsulation method is to
`spin on a protective coating. However, that encapsulation
`
`process is inappropriate for adding a phosphor coating to the
`LED die since the thickness of the encapsulant over the LED
`die is uneven. Also, such encapsulation methods do not form
`a lens. A common technique for providing a phosphor over
`the LED die is to fill a reflective cup surrounding the LED
`die with a silicone/phosphor composition. However, that
`technique forms a phosphor layer with varying thicknesses
`and does not form a suitable lens. If a lens is desired,
`additional processes still have to create a plastic molded lens
`and affix it over the LED die.
`0060 FIGS. 7-11 illustrate various lenses that may be
`formed using the above-described techniques.
`0061 FIG. 7 illustrates an LED die 10 that has been
`coated with a phosphor 60 using any suitable method. One
`such method is by electrophoresis, described in U.S. Pat. No.
`6.576,488, assigned to Lumileds Lighting and incorporated
`herein by reference. Suitable phosphors are well known. A
`lens 22 is formed using the techniques described above. The
`phosphor 60 is energized by the LED emission (e.g., blue or
`UV light) and emits light of a different wavelength, such as
`green, yellow, or red. The phosphor emission alone or in
`conjunction with the LED emission may produce white
`light.
`0062 Processes for coating an LED with a phosphor are
`time-consuming. To eliminate the process for coating the
`LED die with a phosphor, the phosphor powder may be
`mixed with the liquid silicone so as to become embedded in
`the lens 62, shown in FIG. 8.
`0063 As shown in FIG. 9, to provide a carefully con
`trolled thickness of phosphor material over the LED die, an
`inner lens 64 is formed using the above-described tech
`niques, and a separate molding step (using a mold with
`deeper and wider indentations) is used to form an outer
`phosphor/silicone shell 66 of any thickness directly over the
`inner lens 64.
`0064 FIG. 10 illustrates an outer lens 68 that may be
`formed over the phosphor/silicone shell 66 using another
`mold to further shape the beam.
`0065 FIG. 11 illustrates shells 70, 72, and 74 of red,
`green, and blue-emission phosphors, respectively, overlying
`clear silicone shells 76, 78, and 80. In this case, LED die 10
`emits UV light, and the combination of the red, green, and
`blue emissions produces a white light. All shells are pro
`duced with the above-described methods.
`0066. Many other shapes of lenses can be formed using
`the molding technique described above. FIG. 12 is a cross
`sectional view of LED 10, Submount 24, and a molded
`side-emitting lens 84. In one embodiment, lens 84 is formed
`of a very flexible material, such as silicone, which flexes as
`it is removed from the mold. When the lens is not a simple
`shape, the release film 18 (FIG. 1) will typically not be used.
`0067 FIG. 13 is a cross-sectional view of LED 10,
`submount 24, and a molded collimating lens 86. The lens 86
`can be produced using a deformable mold or by using a soft
`lens material that compresses when being pulled from the
`mold and expands to its molded shape after being released
`from the mold.
`0068 FIG. 14 illustrates how a preformed lens 88 can be
`affixed over a molded lambertian lens 22. In the example of
`FIG. 14, lens 22 is formed in the previously described
`
`19
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`

`US 2006/01 02914 A1
`
`May 18, 2006
`
`manner. Lens 22 serves to encapsulate and protect LED 10
`from contaminants. A preformed side-emitting lens 88 is
`then affixed over lens 22 using a UV curable adhesive or a
`mechanical clamp. This lens-forming technique has advan
`tages over conventional techniques. In a conventional tech
`nique, a preformed lens (e.g., a side emitting lens) is
`adhesively affixed over the LED die, and any gaps are filled
`in by injecting silicone. The conventional process is difficult
`to perform due to, among other reasons, carefully position
`ing the separated die? submount for the lens placement and
`gap-filling steps. Using the inventive technique of FIG. 14.
`a large array of LEDs (FIG. 4) can be encapsulated simul
`taneously by forming a molded lens over each. Then, a
`preformed lens 88 can be affixed over each molded lens 22
`while the LEDs are still in the array (FIG. 4) or after being
`separated.
`0069. Additionally, the molded lens can be made very
`Small (e.g., 1-2 mm diameter), unlike a conventional lens.
`Thus, a very small, fully encapsulated LED can be formed.
`Such LEDs can be made to have a very low profile, which
`is beneficial for certain applications.
`0070 FIG. 14 also shows a circuit board 45 on which
`submount 24 is mounted. This circuit board 45 may have
`mounted on it an array of LEDs/submounts 24.
`0071
`FIG. 15 is a cross-sectional view of a backlight for
`a liquid crystal display (LCD) or other display that uses a
`backlight. Common uses are for televisions, monitors, cel
`lular phones, etc. The LEDs may be red, green, and blue to
`create white light. The LEDs form a two-dimensional array.
`In the example shown, each LED structure is that shown in
`FIG. 14, but any suitable lens may be used. The bottom and
`sidewalls 90 of the backlight box are preferably coated with
`a white reflectively-diffusing material. Directly above each
`LED is a white diffuser dot 92 to prevent spots of light from
`being emitted by the backlight directly above each LED. The
`dots 92 are supported by a transparent or diffusing PMMA
`sheet 94. The light emitted by the side-emitting lenses 88 is
`mixed in the lower portion of the backlight, then further
`mixed in the upper portion of the backlight before exiting the
`upper diffuser 96. Linear arrays of LEDs may be mounted on
`narrow circuits boards 45.
`0072 FIG. 16 illustrates an LED 10 with a molded lens
`22 being used as a flash in a camera. The camera in FIG. 16
`is part of a cellular telephone 98. The cellular telephone 98
`includes a color screen 100 (which may have a backlight
`using the LEDs described herein) and a keypad 102.
`0073. As discussed with respect to FIG. 10, an outer lens
`may be formed over the inner shell to further shape the
`beam. Different shell materials may be used, depending on
`the requirements of the various shells. FIGS. 17-30 illustrate
`examples of various lenses and materials that may be used
`in conjunction with the overmolding process.
`0074 FIGS. 17 and 18 illustrate two shapes of molded
`lenses for an inner shell formed using the molding tech
`niques described above. Many LEDs 10 may be mounted on
`the same Support structure 12. The Support structure 12 may
`be a ceramic or silicon Submount with metal traces and
`contact pads, as previously described. Any number of LEDs
`may be mounted on the same Support structure 12, and all
`LEDs on the same support structure 12 would typically be
`processed in an identical manner, although not necessarily.
`
`For example, if the Support structure were large and the light
`pattern for the entire LED array were specified, each LED
`lens may differ to provide the specified overall light pattern.
`0075 An underfill material may be injected to fill any gap
`between the bottom of the LED die 10 and the support
`substrate 12 to prevent any air gaps under the LED and to
`improve heat conduction, among other things.
`0.076 FIG. 17 has been described above with respect to
`FIGS. 3-6, where the inner molded lens 22 is generally
`hemispherical for a lambertian radiation pattern. The inner
`molded lens 106 in FIG. 18 is generally rectangular with
`rounded edges. Depending on the radiation pattern to be
`provided by an outer lens, one of the inner molded lenses 22
`or 106 may be more suitable. Other shapes of inner molded
`lenses may also be suitable. The top down view of each lens
`will generally be circular.
`0.077
`FIG. 19 illustrates the structure of FIG. 18 with the
`lens outer Surface having a pattern that refracts light to
`achieve a desired radiation pattern. The outer Surface pattern
`may be directly formed in the inner molded lens (by the
`mold itself), or the outer surface pattern may be formed in
`an outer lens that is overmolded onto the inner molded lens
`or is affixed to it by an adhesive (e.g., silicone, epoxy, etc.).
`Pattern 108 is a diffraction grating, while pattern 110 uses
`binary steps to refract the light. In the examples, the pattern
`forms a generally side-emitting lens with the radiation
`pattern shown in FIG. 20. In FIG. 20, the peak intensity
`occurs within 50-80 degrees and is significantly greater than
`the intensity at 0 degrees.
`0078. The requirements for the inner lens are generally
`different from the requirements for the outer lens. For
`example, the inner lens should have good adhesion to the
`Support structure, not yellow or become more opaque over
`time, have a high index of refraction (greater than 1.4), not
`break or stress any wires to the LED, withstand the high
`LED temperatures, and have a compatible thermal coeffi
`cient. The inner lens should be non-rigid (e.g., silicone) to
`not provide stress on the LED or any wires. In contrast, the
`outer lens material generally only needs to be able to be
`patterned with the desired pattern and adhere to the inner
`lens. The outer lens may overmolded or may be preformed
`and adhesively affixed to the inner lens. The material for the
`outer lens may be UV curable, while the material for the
`inner lens may be thermally cured. Thermal curing takes
`longer than UV curing.
`0079 Generally, the range of hardness for the inner lens
`material is Shore 005-90, while the range of hardness for the
`outer shell(s) is Shore A30 or more.
`0080 FIG. 21 illustrates a Fresnel lens pattern 112
`formed on the outer surface of the lens for creating a
`generally side-emitting light pattern similar to that of FIG.
`20. The outer surface may be the outer surface of the inner
`molded lens or the outer surface of an outer shell, as
`described with respect to FIG. 19. This applies to all
`patterns described herein.
`0081 FIG.22 illustrates pyramid 114 or cone shaped 116
`patterns on the outer lens Surface to create a collimating light
`pattern or another light pattern.
`0082 FIG. 23 illustrates a high dome outer lens 118 for
`creating a collimating pattern.
`
`20
`
`

`

`US 2006/01 02914 A1
`
`May 18, 2006
`
`0083) The surface patterns of FIGS. 19 and 21-23 may
`be configured (e.g., by changing the Surface angles) to create
`any light pattern. Holographic structures, TIR, and other
`patterns may be formed. Collimating light patterns are
`typically used for rear projection TVs, while side-emitting
`light patterns are typically used for backlighting LCD
`SCCS.
`0084 FIG. 24 illustrates the use of a soft (e.g., Shore XX)
`material. Such as a silicone gel, as the inner molded lens 124
`so as to not stress the wire 126 bonded to the LED 10. The
`gel is typically UV cured. The outer lens 128 may be molded
`or preformed and affixed with an adhesive. The outer lens
`128 will typically be much harder for durability, resistance
`to particles, etc. The outer lens 128 may be silicone, epoxy
`silicone, epoxy, silicone elastomers, hard rubber, other poly
`mers, or other material. The outer lens may be UV or
`thermally cured.
`0085 FIG. 25 is similar to FIG. 24 but with a different
`shaped inner molded lens 129 (like FIG. 18) for a different
`emission pattern or a lower profile. Lens 129 may be a soft
`silicone gel. The outer lens 130 will further shape the
`emission pattern and protect the soft inner lens 129.
`0.086 The LEDs in all figures may be flip-chips or wire
`bonded types.
`0087 FIG. 26 illustrates an LED structure with a soft
`inner molded lens 132, having the properties needed for the
`inner lens, a hard intermediate shell 134 to act as an interface
`layer and for structural stability, and an outer lens 136 for
`creating a side-emitting light pattern. The outer lens 136
`may be soft to facilitate the molding process. Alternatively,
`the outer lens 136 may be preformed and adhesively affixed
`to the intermediate shell 134. The use of the intermediate
`shell 134 makes the choice of the outer lens material
`essentially independent of the inner lens material.
`0088 FIG. 27 illustrates how the outer lens 138 may be
`formed on any portion of the intermediate shell 134 or inner
`lens 132.
`0089 FIG. 28 illustrates the formation of the outer lens
`142 directly on the inner lens 144 material.
`0090 FIG. 29 illustrates another shape of side-emitting
`lens 145 molded over an inner lens 132. Lens 145 may be
`directly molded over LED die 10 without any inner lens.
`0091 FIG. 30 illustrates an LED where each shell 146,
`147, and 148 contains a different phosphor material, such as
`a red-emitting phosphor, a green-emitting phosphor, and a
`blue-emitting phosphor. The LED die 10 may emit UV. The
`gaps between phosphor particles allow the UV to pass
`through an inner shell to energize the phosphor in an outer
`shell. Alternatively, only red and green phosphor shells are
`used, and the LED die 10 emits blue light. The combination
`of red, green, and blue light create white light. The thickness
`of the shells, the density of the phosphor particles, and the
`order of the phosphor colors, among other things, can be
`adjusted to obtain the desired light. Any shape of lenses may
`be used.