WO2013168037A1 - Remote phosphor and led package - Google Patents

Remote phosphor and led package Download PDF

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Publication number
WO2013168037A1
WO2013168037A1 PCT/IB2013/053199 IB2013053199W WO2013168037A1 WO 2013168037 A1 WO2013168037 A1 WO 2013168037A1 IB 2013053199 W IB2013053199 W IB 2013053199W WO 2013168037 A1 WO2013168037 A1 WO 2013168037A1
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WO
WIPO (PCT)
Prior art keywords
led dies
substrate
phosphor
led
reflective material
Prior art date
Application number
PCT/IB2013/053199
Other languages
French (fr)
Inventor
Grigoriy Basin
Original Assignee
Koninklijke Philips N.V.
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Filing date
Publication date
Application filed by Koninklijke Philips N.V. filed Critical Koninklijke Philips N.V.
Publication of WO2013168037A1 publication Critical patent/WO2013168037A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/48—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor body packages
    • H01L33/50—Wavelength conversion elements
    • H01L33/507—Wavelength conversion elements the elements being in intimate contact with parts other than the semiconductor body or integrated with parts other than the semiconductor body
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21K—NON-ELECTRIC LIGHT SOURCES USING LUMINESCENCE; LIGHT SOURCES USING ELECTROCHEMILUMINESCENCE; LIGHT SOURCES USING CHARGES OF COMBUSTIBLE MATERIAL; LIGHT SOURCES USING SEMICONDUCTOR DEVICES AS LIGHT-GENERATING ELEMENTS; LIGHT SOURCES NOT OTHERWISE PROVIDED FOR
    • F21K9/00—Light sources using semiconductor devices as light-generating elements, e.g. using light-emitting diodes [LED] or lasers
    • F21K9/60—Optical arrangements integrated in the light source, e.g. for improving the colour rendering index or the light extraction
    • F21K9/64—Optical arrangements integrated in the light source, e.g. for improving the colour rendering index or the light extraction using wavelength conversion means distinct or spaced from the light-generating element, e.g. a remote phosphor layer
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/48—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor body packages
    • H01L33/52—Encapsulations
    • H01L33/54—Encapsulations having a particular shape
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21Y—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES F21K, F21L, F21S and F21V, RELATING TO THE FORM OR THE KIND OF THE LIGHT SOURCES OR OF THE COLOUR OF THE LIGHT EMITTED
    • F21Y2103/00—Elongate light sources, e.g. fluorescent tubes
    • F21Y2103/30—Elongate light sources, e.g. fluorescent tubes curved
    • F21Y2103/33—Elongate light sources, e.g. fluorescent tubes curved annular
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21Y—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES F21K, F21L, F21S and F21V, RELATING TO THE FORM OR THE KIND OF THE LIGHT SOURCES OR OF THE COLOUR OF THE LIGHT EMITTED
    • F21Y2105/00—Planar light sources
    • F21Y2105/10—Planar light sources comprising a two-dimensional array of point-like light-generating elements
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21Y—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES F21K, F21L, F21S and F21V, RELATING TO THE FORM OR THE KIND OF THE LIGHT SOURCES OR OF THE COLOUR OF THE LIGHT EMITTED
    • F21Y2115/00—Light-generating elements of semiconductor light sources
    • F21Y2115/10—Light-emitting diodes [LED]
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L25/00—Assemblies consisting of a plurality of individual semiconductor or other solid state devices ; Multistep manufacturing processes thereof
    • H01L25/03—Assemblies consisting of a plurality of individual semiconductor or other solid state devices ; Multistep manufacturing processes thereof all the devices being of a type provided for in the same subgroup of groups H01L27/00 - H01L33/00, or in a single subclass of H10K, H10N, e.g. assemblies of rectifier diodes
    • H01L25/04—Assemblies consisting of a plurality of individual semiconductor or other solid state devices ; Multistep manufacturing processes thereof all the devices being of a type provided for in the same subgroup of groups H01L27/00 - H01L33/00, or in a single subclass of H10K, H10N, e.g. assemblies of rectifier diodes the devices not having separate containers
    • H01L25/075—Assemblies consisting of a plurality of individual semiconductor or other solid state devices ; Multistep manufacturing processes thereof all the devices being of a type provided for in the same subgroup of groups H01L27/00 - H01L33/00, or in a single subclass of H10K, H10N, e.g. assemblies of rectifier diodes the devices not having separate containers the devices being of a type provided for in group H01L33/00
    • H01L25/0753—Assemblies consisting of a plurality of individual semiconductor or other solid state devices ; Multistep manufacturing processes thereof all the devices being of a type provided for in the same subgroup of groups H01L27/00 - H01L33/00, or in a single subclass of H10K, H10N, e.g. assemblies of rectifier diodes the devices not having separate containers the devices being of a type provided for in group H01L33/00 the devices being arranged next to each other
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/0001—Technical content checked by a classifier
    • H01L2924/0002—Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2933/00—Details relating to devices covered by the group H01L33/00 but not provided for in its subgroups
    • H01L2933/0008—Processes
    • H01L2933/0033—Processes relating to semiconductor body packages
    • H01L2933/005—Processes relating to semiconductor body packages relating to encapsulations
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2933/00—Details relating to devices covered by the group H01L33/00 but not provided for in its subgroups
    • H01L2933/0091—Scattering means in or on the semiconductor body or semiconductor body package
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/005—Processes
    • H01L33/0095—Post-treatment of devices, e.g. annealing, recrystallisation or short-circuit elimination
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/48—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor body packages
    • H01L33/52—Encapsulations
    • H01L33/56—Materials, e.g. epoxy or silicone resin

Definitions

  • This invention relates to light emitting diodes (LEDs) and, in particular, to a technique of packaging an LED and a remote phosphor.
  • a remote phosphor it is desirable to separate the phosphor layer from the LED. This is called a remote phosphor.
  • a remote phosphor may be advantageous for various reasons, such as for reducing the heat and light intensity on the phosphor, achieving desired physical characteristics of the phosphor, improving color and brightness uniformity and repeatability, and allowing a pre-formed phosphor layer to be matched with an LED peak wavelength.
  • blue LED dies are singulated from an LED wafer and mounted on a submount wafer (also referred to as a substrate). An optional insulating underfill material is then injected or molded under each LED die.
  • the LED dies may be mounted on the submount wafer to form a plurality of circular arrays of LED dies, where each array will be packaged in a single package for a very high brightness lamp.
  • the submount wafer has bottom metal pads electrically connected to the LED die electrodes by vias which extend through the submount wafer.
  • a phosphor layer is separately formed sandwiched between two transparent plates, such as thin glass plates. The sandwich structure is referred to as a phosphor structure.
  • a plurality of the phosphor structures are formed as discs, with each slightly larger than the circular array of LED dies.
  • the phosphor structures will also be square.
  • each phosphor structure and associated set of LED dies will be packaged to form a single lamp.
  • the sidewalls of the phosphor structures may be encapsulated by a reflective material during a single-step package molding process prior to singulating the submount wafer, described below.
  • the entire submount wafer is then brought against a mold having a cavity filled with a white silicone liquid or white silicone molding compound.
  • the silicon molding compound may be a viscous material.
  • the LED dies and phosphor structures are immersed in the white silicone liquid or white silicone molding compound, and the material is put under compression to fill any voids.
  • the silicone is then cured, such as by heating, and the mold is removed.
  • the hardened white silicone material encapsulates all of the LED dies and at least the sidewalls of the phosphor structures.
  • the white silicone material reflects virtually all side light generated by the LED dies and phosphor, forcing substantially all light to be emitted by the top surface of the phosphor structure. Any silicone molded over the top surface of the phosphor structures is removed by micro-bead blasting or other technique.
  • the submount wafer is then singulated (e.g., sawed through) between the phosphor structures, creating separate, packaged phosphor-converted LED lamps of any size.
  • the exposed bottom metal pads of each package may then be soldered directly to metal pads of a printed circuit board.
  • Figs. 1-4 and 6-15 are all cross-sectional views.
  • Fig. 1 illustrates a phosphor layer that may consist of a single phosphor layer or multiple layers of different phosphors to achieve a desired color.
  • Fig. 2 illustrates the phosphor layer of Fig. 1 laminated over a transparent plate having a size slightly smaller than the outer dimensions of a package. Two identical phosphor structures are shown.
  • Fig. 3 illustrates the phosphor layer of Fig. 2 sandwiched between two thin transparent plates.
  • Fig. 5 is a top down view of a portion of the submount wafer illustrating two arrays of LED dies generally arranged in circles, where each array will be packaged in a single package. Dashed circles illustrate the locations of the remote phosphor structures when affixed over the LED dies.
  • Fig. 6 is a cross-sectional view of Fig. 5 along line 6-6.
  • Fig. 7 illustrates a drop of transparent glue (e.g., silicone or epoxy) deposited on the top surface of each LED die.
  • transparent glue e.g., silicone or epoxy
  • Fig. 8 illustrates the phosphor structures of Fig. 3 positioned over associated sets of LED dies for each package.
  • Fig. 9 illustrates the phosphor structures pressed against the LED dies and the glue cured in preparation for a package molding step. .
  • Figs. 10 and 1 1 illustrate an alternative process for affixing the phosphor structure to the LED dies.
  • Fig. 10 illustrates the phosphor structures being affixed to a thin, silicone sheet that is approximately the size of the submount wafer. This supports the phosphor structures and aligns them with their associated set of LED dies on the submount wafer.
  • Fig. 11 illustrates the silicon sheet laminated over the LED dies in a single step, where the silicone is then cured to affix the phosphor structures to the LED dies, and where the silicone between the sets of LED dies is then removed.
  • Fig. 12 illustrates the submount wafer being brought against a mold for compression molding a white silicone material around each set of LED dies and phosphor structure.
  • Fig. 13 illustrates the submount wafer after the silicone is cured and after the submount wafer is removed from the mold.
  • Fig. 14 illustrates the submount wafer after any excess molded silicone on the top surface of the phosphor structures is removed by micro-bead blasting.
  • Fig. 15 illustrates two packaged phosphor-converted LED lamps after the submount wafer is singulated.
  • the silicone sidewalls reflect side light and protect the LED dies and phosphor structure.
  • Fig. 1 is a cross-sectional view of a phosphor layer 10 that may consist of a single phosphor or a mixture or phosphors or multiple layers of different phosphors.
  • the phosphor layer 10 consists of a layer of a YAG phosphor 12 (emits yellow light when illuminated by a blue or UV light) and a red emitting phosphor 16, for adding warmth to the resulting white light.
  • the phosphor layer 10 is thin enough to permit a controlled amount of blue light to leak through and combine with red and yellow light to achieve a desired white light.
  • a roll of a support film is provided.
  • the support film may be a commercially available ethyl tetra fluoro ethylene (ETFE) foil (a polymer) about 50 microns thick, 30 cm wide, and 150 meters long. Other dimensions are also suitable, such as providing the support film as small sheets or a ribbon.
  • ETFE ethyl tetra fluoro ethylene
  • a phosphor powder is mixed with silicone, or other suitable binder, to form a slurry, and the slurry is sprayed on or otherwise deposited on the support film to a predetermined thickness in a continuous process (assuming a roll is continuously dispensed).
  • the density of phosphor, the thickness of the layer, and the type of phosphor or combination of phosphors are selected so that the light emitted by the combination of the LED dies and the phosphor(s) has a target white point or other desired color.
  • the phosphor/silicone layer will be about 30-200 microns thick.
  • Other inert inorganic particles, such as light scattering materials e.g., silica, Ti0 2
  • the slurry is then dried or partially dried, such as by infrared lights or other heat sources, as the support film is being unrolled. If the phosphor layer 10 is formed of separate layers of phosphors, the above process may be performed multiple times. The phosphor layer 10 may be tested and then matched with LEDs having a certain peak wavelength to achieve a target color.
  • Fig. 2 illustrates two transparent glass plates 18 and 20, shown in a cross section, formed as circular discs, although they may be any shape, such as square.
  • the phosphor layer 10 of Fig. 1 is laminated on the glass plates 18 and 20, and the support film for the phosphor layer 10 is removed.
  • the phosphor layer 10 may be formed directly on the glass plates 18 and 20 by spraying, screen printing, or other technique.
  • each glass plate 18/20 with the phosphor layer 10 will be simultaneously formed.
  • the size of each glass plate 18/20 is slightly smaller than the intended packaged phosphor-converted LED lamp.
  • each glass plate 18/20 may be on the order of 1 inch in diameter.
  • the glass plate 18/20 is transparent to the blue light of the LED die in one direction but reflects back longer wavelength light from the phosphor layer 10.
  • the glass plate 18/20 may be a dichroic filter. Forming the glass plate 18/20 as a dichroic filter improves the efficiency of the LED lamp since the downward phosphor light does not get absorbed by the underlying structures.
  • the glass plate 18/20 may be substantially transparent to blue light and reflective to the phosphor light, the glass plate 18/20 is referred to herein as transparent due to its passing of the LED light.
  • Fig. 3 illustrates transparent glass plates 22 and 23 being affixed over the phosphor layer 10 under pressure.
  • the phosphor layer 10 (containing a silicone binder) may be only partially cured when sandwiched between the glass plates 18/22 and 20/23 and then fully cured so that the silicone binder acts as an adhesive.
  • the silicone also provides a resilient buffer layer to accommodate different coefficients of thermal expansion (CTE) of the various layers to prevent delamination during use.
  • CTE coefficients of thermal expansion
  • phosphor structures 24 and 25 The completed multi-layer structures of Fig. 3 will be referred to hereinafter as phosphor structures 24 and 25 for simplicity.
  • Glass plates 22 and 23 are transparent to both the light emitted by the phosphor and the blue light emitted from the LEDs.
  • Fig. 4 illustrates a portion of a submount wafer 26 (also referred to as a substrate) populated with blue LED dies 28, where only a single LED die 28 is shown, and where the submount wafer 26 has bottom metal pads 30 for soldering to a printed circuit board (PCB).
  • the submount wafer 26 body may be formed of a ceramic, silicon, or any other suitable material.
  • the submount wafer 26 may be square, rectangular, circular, or any other shape.
  • Metal pads 32 are formed on the top surface of the submount wafer 26 and are electrically connected to the bottom metal pads 30 by vias 34.
  • the LED die electrodes 36 and 38 are bonded to the metal pads 32.
  • Fig. 4 illustrates a portion of a submount wafer 26 (also referred to as a substrate) populated with blue LED dies 28, where only a single LED die 28 is shown, and where the submount wafer 26 has bottom metal pads 30 for soldering to a printed circuit board (PCB).
  • the LED die 28 is a flip chip having an n-type layer 40, an active layer 42, and a p-type layer 44.
  • the electrode 36 contacts the n- type layer 40, and the electrode 38 contacts the p-type layer 44.
  • An insulating layer 48 insulates the electrode 36 from the p-type layer 44.
  • the LED die 28 and submount wafer 26 construction may be conventional. Non-flip chip LED dies may also be used, such as LED dies with one or more wire bonds connected to the LED electrodes. Many LED dies 28 may be mounted on the submount wafer 26.
  • the LEDs 28 may emit UV light instead of blue light.
  • the LED semiconductor layers will typically be GaN based. If the LED semiconductor layers emit UV light, then glass layers 18, 20, 22 and 23 may be transparent to UV light. In an alternative embodiment, glass layers 18 and 20 are transparent to UV light and glass layers 22 and 23 may reflect UV light. Thus, UV light would be recirculated to more efficiently illuminate the phosphors 16 and 12.
  • Fig. 5 is a top down view of a small portion of the submount wafer 26 illustrating two arrays of LED dies 28 generally arranged in circles, where each array will be packaged in a single package. Dashed circles 50 illustrate the locations of remote phosphor structures 24 and 25 when affixed over the LED dies 28. Any number of LED dies 28, including one, may be in a single package.
  • the LED dies 28 in each substantially circular array may be connected in any combination of series and parallel, using printed circuitry on the top surface of the submount wafer 26, where the bottom electrodes 30 are connected to a power source for the array.
  • Fig. 6 is a cross-sectional view of Fig. 5 along line 6-6 and shows six blue LEDs dies 28.
  • the LED dies 28 are shown having an optional underfill 54, such as silicon, for filling the void under the LED dies 28 and adding mechanical support.
  • the underfill 54 is represented as being clear in order to not obscure the electrodes, but the underfill 54 may be reflective and opaque.
  • Such underfill 54 is optional if the LED dies 28 are supported by the metal electrodes and metal pads, or if the subsequent package molding process can fill the voids, or if its function in providing mechanical support is not needed.
  • Fig. 7 illustrates a portion of a transparent glue 56 (e.g., silicone) deposited over the top surface each LED die 28, such as with a syringe.
  • the portion may be a droplet of transparent glue 56.
  • Fig. 8 illustrates the phosphor structures 24 and 25 of Fig. 3 positioned over an associated set of LED dies.
  • Fig. 9 illustrates the phosphor structures 24 and 25 uniformly pressed against the LED dies 28, such as with a wafer-sized pad, and the glue 56 cured.
  • the glue 56 may be cured by heating.
  • Figs. 10 and 11 illustrate an alternative process for affixing the phosphor structures 24 and 25 to the LED dies 28.
  • Fig. 10 illustrates a thin, silicone film 60 laminated over the phosphor structures 24 and 25 (and over all other phosphor structures for the submount wafer 26).
  • the film 60 is approximately the size of the submount wafer 26, and the various phosphor structures are affixed to the film 60 in the same relative positions as they would be on the submount wafer 26.
  • the film 60 works as a dry glue layer for the phosphor structures 24 and 25.
  • the silicone film 60 is just formed over each phosphor structure 24 and 25, with no film 60 extending between the phosphor structures 24 and 25.
  • the film 60 can be cut around each phosphor structure 24 and 25 if the film 60 is created as a larger sheet.
  • the various phosphor structures (e.g., 24 and 25) are then individually placed over the LED dies 28 using the film 60 as an adhesive.
  • the white silicone material 64 is then cured, such as by heat, to harden it.
  • Fig. 13 illustrates the submount wafer 26 after the silicone material 64 is cured and after the submount wafer 26 is removed from the mold 62.
  • the white silicone material 64 if thick enough, is diffusively reflective so all side light generated by the phosphor and LED dies 28 is reflected back through the top surface of the phosphor structures 24 and 25.
  • the white silicone material 64 also scatters the light so the light will typically exit the package after only one or two reflections.
  • the surface of the submount wafer 26 will also become reflective due to the white silicone material 64 being located between the LED dies 28. Note that there is a thin layer of the silicone material 64 over the top surface of the phosphor structures 24 and 25 that is reflective so should be removed.
  • Fig. 14 illustrates the submount wafer 26 after any excess molded silicone material 64 on the top surface of the phosphor structures 24 and 25 is removed, such as bymicro-bead blasting.
  • the submount wafer 26 is then singulated, such as by sawing, which also saws through the white silicone material 64 between the phosphor structures 24 and 25.
  • the phosphor structures 24 and 25 are not affected by the sawing.
  • a single phosphor structure covers the entire submount wafer 26 and is singulated along with the submount wafer 26.
  • sawing through thin glass without cracking may be problematic, and the reflective material will not cover the sides of the sawed phosphor structure.

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

Abstract

Circular arrays of LED dies are mounted on a substrate. The substrate has bottom electrodes electrically connected to electrodes of the LED dies. A plurality of disc-shaped remote phosphor structures are pre-formed, where each phosphor structure includes a lower transparent plate, an upper transparent plate, and a phosphor layer sandwiched between the two plates. Each phosphor structure is then affixed over an associated circular array of LED dies. A white silicone material is then compression-molded over the substrate, extending from the substrate surface to at least the sides of the upper transparent plates. The substrate is then singulated between all adjacent phosphor structures, so that the reflective material surrounds each phosphor structure and LED array, to form individual packaged lamps. The reflective material reflects side light from the LED dies and phosphor layer to cause reflected light to be emitted from a top surface of the upper transparent plate.

Description

REMOTE PHOSPHOR AND LED PACKAGE
FIELD OF THE INVENTION
This invention relates to light emitting diodes (LEDs) and, in particular, to a technique of packaging an LED and a remote phosphor.
BACKGROUND
Phosphor-converted LEDs are very popular for creating white light and other colors. Typically, a blue LED has a phosphor deposited over it to wavelength-convert the blue light while letting some of the blue light leak through. If the phosphor emits yellow light or red and green light, the resulting light appear white.
In some cases, it is desirable to separate the phosphor layer from the LED. This is called a remote phosphor. Using a remote phosphor may be advantageous for various reasons, such as for reducing the heat and light intensity on the phosphor, achieving desired physical characteristics of the phosphor, improving color and brightness uniformity and repeatability, and allowing a pre-formed phosphor layer to be matched with an LED peak wavelength.
What is needed is an improved packaging technique that reduces the size and cost of the resulting LED lamp, using a remote phosphor, where any number of LED dies may be in a single package for achieving any brightness.
SUMMARY
An improved technique for packaging LED dies, using a remote phosphor, is disclosed.
In one embodiment, blue LED dies are singulated from an LED wafer and mounted on a submount wafer (also referred to as a substrate). An optional insulating underfill material is then injected or molded under each LED die. The LED dies may be mounted on the submount wafer to form a plurality of circular arrays of LED dies, where each array will be packaged in a single package for a very high brightness lamp. The submount wafer has bottom metal pads electrically connected to the LED die electrodes by vias which extend through the submount wafer. A phosphor layer is separately formed sandwiched between two transparent plates, such as thin glass plates. The sandwich structure is referred to as a phosphor structure. If circular arrays of LED dies are mounted on the submount wafer, a plurality of the phosphor structures are formed as discs, with each slightly larger than the circular array of LED dies. Alternatively, if each LED array for a single package is square, the phosphor structures will also be square.
The phosphor structures are then adhesively fixed over their associated set of LED dies, where each phosphor structure and associated set of LED dies will be packaged to form a single lamp. By forming each phosphor structures as pre-formed pieces, and providing space between adjacent phosphor structures, the sidewalls of the phosphor structures may be encapsulated by a reflective material during a single-step package molding process prior to singulating the submount wafer, described below.
The entire submount wafer is then brought against a mold having a cavity filled with a white silicone liquid or white silicone molding compound. The silicon molding compound may be a viscous material. The LED dies and phosphor structures are immersed in the white silicone liquid or white silicone molding compound, and the material is put under compression to fill any voids. The silicone is then cured, such as by heating, and the mold is removed. The hardened white silicone material encapsulates all of the LED dies and at least the sidewalls of the phosphor structures. The white silicone material reflects virtually all side light generated by the LED dies and phosphor, forcing substantially all light to be emitted by the top surface of the phosphor structure. Any silicone molded over the top surface of the phosphor structures is removed by micro-bead blasting or other technique.
The submount wafer is then singulated (e.g., sawed through) between the phosphor structures, creating separate, packaged phosphor-converted LED lamps of any size. The exposed bottom metal pads of each package may then be soldered directly to metal pads of a printed circuit board.
Many variations of the above-described example are envisioned.
BRIEF DESCRIPTION OF THE DRAWINGS
Figs. 1-4 and 6-15 are all cross-sectional views.
Fig. 1 illustrates a phosphor layer that may consist of a single phosphor layer or multiple layers of different phosphors to achieve a desired color.
Fig. 2 illustrates the phosphor layer of Fig. 1 laminated over a transparent plate having a size slightly smaller than the outer dimensions of a package. Two identical phosphor structures are shown.
Fig. 3 illustrates the phosphor layer of Fig. 2 sandwiched between two thin transparent plates.
Fig. 4 illustrates a small portion of a submount wafer populated with blue LED dies, where only a single LED die is shown for simplicity, and where the submount wafer has bottom metal pads for soldering to a printed circuit board. The submount wafer itself and individual LED dies may be conventional.
Fig. 5 is a top down view of a portion of the submount wafer illustrating two arrays of LED dies generally arranged in circles, where each array will be packaged in a single package. Dashed circles illustrate the locations of the remote phosphor structures when affixed over the LED dies.
Fig. 6 is a cross-sectional view of Fig. 5 along line 6-6.
Fig. 7 illustrates a drop of transparent glue (e.g., silicone or epoxy) deposited on the top surface of each LED die.
Fig. 8 illustrates the phosphor structures of Fig. 3 positioned over associated sets of LED dies for each package. Fig. 9 illustrates the phosphor structures pressed against the LED dies and the glue cured in preparation for a package molding step. .
Figs. 10 and 1 1 illustrate an alternative process for affixing the phosphor structure to the LED dies.
Fig. 10 illustrates the phosphor structures being affixed to a thin, silicone sheet that is approximately the size of the submount wafer. This supports the phosphor structures and aligns them with their associated set of LED dies on the submount wafer.
Fig. 11 illustrates the silicon sheet laminated over the LED dies in a single step, where the silicone is then cured to affix the phosphor structures to the LED dies, and where the silicone between the sets of LED dies is then removed.
Fig. 12 illustrates the submount wafer being brought against a mold for compression molding a white silicone material around each set of LED dies and phosphor structure.
Fig. 13 illustrates the submount wafer after the silicone is cured and after the submount wafer is removed from the mold.
Fig. 14 illustrates the submount wafer after any excess molded silicone on the top surface of the phosphor structures is removed by micro-bead blasting.
Fig. 15 illustrates two packaged phosphor-converted LED lamps after the submount wafer is singulated. The silicone sidewalls reflect side light and protect the LED dies and phosphor structure.
Elements that are the same or equivalent are labeled with the same numeral.
DETAILED DESCRIPTION
Fig. 1 is a cross-sectional view of a phosphor layer 10 that may consist of a single phosphor or a mixture or phosphors or multiple layers of different phosphors. In the example shown, the phosphor layer 10 consists of a layer of a YAG phosphor 12 (emits yellow light when illuminated by a blue or UV light) and a red emitting phosphor 16, for adding warmth to the resulting white light. In some embodiments the phosphor layer 10 is thin enough to permit a controlled amount of blue light to leak through and combine with red and yellow light to achieve a desired white light.
In one embodiment, to form the phosphor layer 10, a roll of a support film is provided. The support film may be a commercially available ethyl tetra fluoro ethylene (ETFE) foil (a polymer) about 50 microns thick, 30 cm wide, and 150 meters long. Other dimensions are also suitable, such as providing the support film as small sheets or a ribbon.
A phosphor powder is mixed with silicone, or other suitable binder, to form a slurry, and the slurry is sprayed on or otherwise deposited on the support film to a predetermined thickness in a continuous process (assuming a roll is continuously dispensed). The density of phosphor, the thickness of the layer, and the type of phosphor or combination of phosphors are selected so that the light emitted by the combination of the LED dies and the phosphor(s) has a target white point or other desired color. In one embodiment, the phosphor/silicone layer will be about 30-200 microns thick. Other inert inorganic particles, such as light scattering materials (e.g., silica, Ti02) may also be included in the slurry.
The slurry is then dried or partially dried, such as by infrared lights or other heat sources, as the support film is being unrolled. If the phosphor layer 10 is formed of separate layers of phosphors, the above process may be performed multiple times. The phosphor layer 10 may be tested and then matched with LEDs having a certain peak wavelength to achieve a target color.
Fig. 2 illustrates two transparent glass plates 18 and 20, shown in a cross section, formed as circular discs, although they may be any shape, such as square. The phosphor layer 10 of Fig. 1 is laminated on the glass plates 18 and 20, and the support film for the phosphor layer 10 is removed. Alternatively, the phosphor layer 10 may be formed directly on the glass plates 18 and 20 by spraying, screen printing, or other technique.
In an actual process, many more glass plates 18/20 with the phosphor layer 10 will be simultaneously formed. The size of each glass plate 18/20 is slightly smaller than the intended packaged phosphor-converted LED lamp. For a high brightness lamp using an array of LED dies, each glass plate 18/20 may be on the order of 1 inch in diameter.
In one embodiment, the glass plate 18/20 is transparent to the blue light of the LED die in one direction but reflects back longer wavelength light from the phosphor layer 10. The glass plate 18/20 may be a dichroic filter. Forming the glass plate 18/20 as a dichroic filter improves the efficiency of the LED lamp since the downward phosphor light does not get absorbed by the underlying structures. Although the glass plate 18/20 may be substantially transparent to blue light and reflective to the phosphor light, the glass plate 18/20 is referred to herein as transparent due to its passing of the LED light.
Fig. 3 illustrates transparent glass plates 22 and 23 being affixed over the phosphor layer 10 under pressure. The phosphor layer 10 (containing a silicone binder) may be only partially cured when sandwiched between the glass plates 18/22 and 20/23 and then fully cured so that the silicone binder acts as an adhesive. The silicone also provides a resilient buffer layer to accommodate different coefficients of thermal expansion (CTE) of the various layers to prevent delamination during use.
The completed multi-layer structures of Fig. 3 will be referred to hereinafter as phosphor structures 24 and 25 for simplicity. Glass plates 22 and 23 are transparent to both the light emitted by the phosphor and the blue light emitted from the LEDs.
Fig. 4 illustrates a portion of a submount wafer 26 (also referred to as a substrate) populated with blue LED dies 28, where only a single LED die 28 is shown, and where the submount wafer 26 has bottom metal pads 30 for soldering to a printed circuit board (PCB). The submount wafer 26 body may be formed of a ceramic, silicon, or any other suitable material. The submount wafer 26 may be square, rectangular, circular, or any other shape. Metal pads 32 are formed on the top surface of the submount wafer 26 and are electrically connected to the bottom metal pads 30 by vias 34. The LED die electrodes 36 and 38 are bonded to the metal pads 32. In the example of Fig. 4, the LED die 28 is a flip chip having an n-type layer 40, an active layer 42, and a p-type layer 44. The electrode 36 contacts the n- type layer 40, and the electrode 38 contacts the p-type layer 44. An insulating layer 48 insulates the electrode 36 from the p-type layer 44. The LED die 28 and submount wafer 26 construction may be conventional. Non-flip chip LED dies may also be used, such as LED dies with one or more wire bonds connected to the LED electrodes. Many LED dies 28 may be mounted on the submount wafer 26.
The LEDs 28 may emit UV light instead of blue light. The LED semiconductor layers will typically be GaN based. If the LED semiconductor layers emit UV light, then glass layers 18, 20, 22 and 23 may be transparent to UV light. In an alternative embodiment, glass layers 18 and 20 are transparent to UV light and glass layers 22 and 23 may reflect UV light. Thus, UV light would be recirculated to more efficiently illuminate the phosphors 16 and 12.
Fig. 5 is a top down view of a small portion of the submount wafer 26 illustrating two arrays of LED dies 28 generally arranged in circles, where each array will be packaged in a single package. Dashed circles 50 illustrate the locations of remote phosphor structures 24 and 25 when affixed over the LED dies 28. Any number of LED dies 28, including one, may be in a single package. The LED dies 28 in each substantially circular array may be connected in any combination of series and parallel, using printed circuitry on the top surface of the submount wafer 26, where the bottom electrodes 30 are connected to a power source for the array.
Fig. 6 is a cross-sectional view of Fig. 5 along line 6-6 and shows six blue LEDs dies 28. The LED dies 28 are shown having an optional underfill 54, such as silicon, for filling the void under the LED dies 28 and adding mechanical support. The underfill 54 is represented as being clear in order to not obscure the electrodes, but the underfill 54 may be reflective and opaque. Such underfill 54 is optional if the LED dies 28 are supported by the metal electrodes and metal pads, or if the subsequent package molding process can fill the voids, or if its function in providing mechanical support is not needed.
Fig. 7 illustrates a portion of a transparent glue 56 (e.g., silicone) deposited over the top surface each LED die 28, such as with a syringe. The portion may be a droplet of transparent glue 56. Fig. 8 illustrates the phosphor structures 24 and 25 of Fig. 3 positioned over an associated set of LED dies.
Fig. 9 illustrates the phosphor structures 24 and 25 uniformly pressed against the LED dies 28, such as with a wafer-sized pad, and the glue 56 cured. The glue 56 may be cured by heating.
Figs. 10 and 11 illustrate an alternative process for affixing the phosphor structures 24 and 25 to the LED dies 28.
Fig. 10 illustrates a thin, silicone film 60 laminated over the phosphor structures 24 and 25 (and over all other phosphor structures for the submount wafer 26). The film 60 is approximately the size of the submount wafer 26, and the various phosphor structures are affixed to the film 60 in the same relative positions as they would be on the submount wafer 26. The film 60 works as a dry glue layer for the phosphor structures 24 and 25.
Fig. 11 illustrates the film 60 laminated over the LED dies 28 in a single positioning step. The film 60 is then heated to affix the phosphor structures to the LED dies 28. The thin film 60 between the phosphor structures 24 and 25 conforms over the surface of the submount wafer 26. This technique avoids the individual placement of glue drops (Fig. 7) on the LED dies 28 and avoids the individual placement of the phosphor structures on the LED dies 28.
In another embodiment, the silicone film 60 is just formed over each phosphor structure 24 and 25, with no film 60 extending between the phosphor structures 24 and 25. For example, the film 60 can be cut around each phosphor structure 24 and 25 if the film 60 is created as a larger sheet. The various phosphor structures (e.g., 24 and 25) are then individually placed over the LED dies 28 using the film 60 as an adhesive.
Fig. 12 illustrates the perimeter of the submount wafer 26 being brought down against the perimeter walls of a mold 62 to make a seal between the submount wafer 26 and the mold 26 for compression molding a softened solid or liquid white silicone material 64 around each set of LED dies 28 and the phosphor structures 24 and 25. Other types of insulating reflective material may be used. The whiteness may be created by titanium oxide particles, aluminum oxide particles, zirconium oxide particles, or other white particles. The mold 62 cavity will typically be slightly smaller than the submount wafer 26 so a vacuum seal may be created around the periphery of the submount wafer 26. All the LED dies 28 and phosphor structures on the wafer 26 are immersed in the white silicone material 64 after the vacuum seal is created. The compression molding fills all the voids. The depth of the cavity is equal to or slightly greater than the height of the phosphor structures 24 and 25 above the submount wafer 26.
The white silicone material 64 is then cured, such as by heat, to harden it.
Fig. 13 illustrates the submount wafer 26 after the silicone material 64 is cured and after the submount wafer 26 is removed from the mold 62. The white silicone material 64, if thick enough, is diffusively reflective so all side light generated by the phosphor and LED dies 28 is reflected back through the top surface of the phosphor structures 24 and 25. The white silicone material 64 also scatters the light so the light will typically exit the package after only one or two reflections. The surface of the submount wafer 26 will also become reflective due to the white silicone material 64 being located between the LED dies 28. Note that there is a thin layer of the silicone material 64 over the top surface of the phosphor structures 24 and 25 that is reflective so should be removed.
Fig. 14 illustrates the submount wafer 26 after any excess molded silicone material 64 on the top surface of the phosphor structures 24 and 25 is removed, such as bymicro-bead blasting.
The submount wafer 26 is then singulated, such as by sawing, which also saws through the white silicone material 64 between the phosphor structures 24 and 25. The phosphor structures 24 and 25 are not affected by the sawing.
In another embodiment, a single phosphor structure covers the entire submount wafer 26 and is singulated along with the submount wafer 26. However, sawing through thin glass without cracking may be problematic, and the reflective material will not cover the sides of the sawed phosphor structure.

Claims

Fig. 15 illustrates two packaged phosphor-converted LED lamps 68 and 70 after the submount wafer 26 is singulated. The white silicone material 64 sidewalls reflect side light and protect the delicate LED dies 28 and phosphor structures 24 and 25. Many identical LED lamps are formed from a single submount wafer 26. The exposed bottom metal pads 30 (Fig. 4) of the submount wafer 26 may be bonded to metal pads of a printed circuit board. The above-described process may be applied to any size submount wafer or any other type of substrate, even a substrate including only one LED die. The substrate need not have metal electrodes or other interconnection functions. The phosphor layer may be replaced with a quantum dot layer or with any other material that wavelength-converts light. While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects and, therefore, the appended claims are to encompass within their scope all such changes and modifications as fall within the true spirit and scope of this invention. CLAIMS What is claimed is:
1. A method for fabricating a packaged light emitting diode (LED) device comprising: a. providing a plurality of LED dies on a top surface of a substrate, the substrate having bottom electrodes electrically connected to electrodes of the LED dies; b. providing a plurality of lower plates, each lower plate supporting a phosphor layer and having an upper plate sandwiching the phosphor layer between the lower plate and the upper plate; c. affixing the lower plates to one or more of the LED dies; d. molding a reflective material extending from the top surface of the substrate to at least over sides of each upper plate, the bottom electrodes not being covered by the reflective material; and e. singulating the substrate to create separate packaged LED lamps, each lamp comprising associated one or more LED dies, an associated lower plate, an associated phosphor layer, and an associated upper plate, wherein the reflective material overlies at least sides of the associated one or more LED dies, sides of the associated lower plate, sides of the associated phosphor layer, and sides of the associated upper plate.
2. The method of Claim 1 wherein step a comprises mounting a plurality of flip chip LED dies on a substrate wafer.
3. The method of Claim 1 wherein each lower plate and each upper plate has a disc shape, and wherein the plurality of LED dies are arranged on the substrate to form arrays of LED dies, each array having a diameter smaller than a diameter of the lower plate.
4. The method of Claim 1 wherein step c comprises affixing the lower plates to the associated one or more of the LED dies by a pre-formed layer of silicone.
5. The method of Claim 1 wherein the lower plates comprise dichroic filters.
6. The method of Claim 1 wherein the substrate comprises a body portion having top metal pads connected to the electrodes of the LED dies, and having the bottom electrodes electrically coupled to the top metal pads by conductive vias extending through the body portion.
7. The method of Claim 1 wherein the reflective material comprises a silicone material infused with white particles.
8. The method of Claim 1 wherein step d comprises immersing the LED dies, lower plates, phosphor layer, and upper plates in the reflective material within a cavity of a mold, then curing the reflective material to harden it.
9. The method of Claim 8 further comprising removing any of the reflective material over a surface of the upper plates after step d.
10. The method of Claim 1 wherein the LED dies emit blue light, and the phosphor layer emits a light that, when combined with the blue light, creates white light.
11. A packaged light emitting diode (LED) lamp comprising: one or more LED dies on a substrate, the substrate having bottom electrodes electrically connected to electrodes of the one or more LED dies; a lower plate affixed over the one or more LED dies; a phosphor layer overlying the lower plate; an upper plate sandwiching the phosphor layer between the lower transparent plate and the upper plate; and a reflective material molded over the substrate, extending from the substrate to at least over sides of the upper plate, the bottom electrodes not being covered by the reflective material, the reflective material covering at least sides of the one or more LED dies, sides of the lower plate, sides of the associated phosphor layer, and the sides of the upper plate, wherein the reflective material reflects side light from the one or more LED dies and phosphor layer to cause reflected light to be emitted from a top surface of the upper plate.
12. The lamp of Claim 11 wherein the lower plate and the upper plate have a disc shape.
13. The lamp of Claim 13 wherein the one or more LED dies comprises a plurality of LED dies arranged on the substrate to form a substantially circular array of LED dies.
14. The lamp of Claim 11 wherein the reflective material comprises a silicone material infused with white particles.
15. The lamp of Claim 11 wherein the lamp has been singulated from a substrate wafer, wherein singulating the substrate wafer also cuts through a layer of the reflective material but not through the upper plate and lower plate.
PCT/IB2013/053199 2012-05-08 2013-04-23 Remote phosphor and led package WO2013168037A1 (en)

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