WO2014104913A1 - Module with light-emitting diodes - Google Patents

Module with light-emitting diodes Download PDF

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Publication number
WO2014104913A1
WO2014104913A1 PCT/RU2012/001127 RU2012001127W WO2014104913A1 WO 2014104913 A1 WO2014104913 A1 WO 2014104913A1 RU 2012001127 W RU2012001127 W RU 2012001127W WO 2014104913 A1 WO2014104913 A1 WO 2014104913A1
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WO
WIPO (PCT)
Prior art keywords
encapsulation
light emitting
semiconductor chips
light
module
Prior art date
Application number
PCT/RU2012/001127
Other languages
French (fr)
Inventor
Vladislav Evgenyevich BOUGROV
Alexey Ruslanovich KOVSH
Karim Dzhafarovich MYNBAEV
Maxim Anatolyevich ODNOBLYUDOV
Johann Ramchen
Alexey Evgenyevich ROMANOV
Valery Vladimirovich KRAMNIK
Svetlana Nikolaevna LIPNITSKAYA
Lidia Andreevna NIKULINA
Original Assignee
Optogan New Technologies Of Light Llc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Optogan New Technologies Of Light Llc filed Critical Optogan New Technologies Of Light Llc
Priority to PCT/RU2012/001127 priority Critical patent/WO2014104913A1/en
Publication of WO2014104913A1 publication Critical patent/WO2014104913A1/en

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B19/00—Condensers, e.g. light collectors or similar non-imaging optics
    • G02B19/0033—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use
    • G02B19/0047—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use for use with a light source
    • G02B19/0061—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use for use with a light source the light source comprising a LED
    • G02B19/0066—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use for use with a light source the light source comprising a LED in the form of an LED array
    • 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
    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L2224/42—Wire connectors; Manufacturing methods related thereto
    • H01L2224/47—Structure, shape, material or disposition of the wire connectors after the connecting process
    • H01L2224/48—Structure, shape, material or disposition of the wire connectors after the connecting process of an individual wire connector
    • H01L2224/4805—Shape
    • H01L2224/4809—Loop shape
    • H01L2224/48091—Arched
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • 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
    • H01L33/508—Wavelength conversion elements having a non-uniform spatial arrangement or non-uniform concentration, e.g. patterned wavelength conversion layer, wavelength conversion layer with a concentration gradient of the wavelength conversion material
    • 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

Definitions

  • the present invention relates generally to light sources based on light emitting semiconductor components, such as light emitting diodes LEDs, as the primary light emitting elements. More particularly, the present invention is related to light emitting modules having a plurality of semiconductorlight emitting chips arranged on a substrate plate. Typically, these kinds of modules are called chip-onboard (COB) light emitting modules. The invention is focused on the extraction of light from such modules.
  • COB chip-onboard
  • any light source such as an indoor luminary or, for example,, a headlight of a vehicle
  • semiconductor light emitting elements like LEDs more and more . often replace the conventionally used incandescent and gas-discharge lamps as the primary light emitting component.
  • Semiconductor light emitting components provide many superior characteristics, such as long-term stability, high power efficiency, and compact size of the single element.
  • 3aMeHHioiuiiH JIHCT reflectors which redistribute light from the point source, thus transforming it into a beam with desired properties, are used.
  • an array of multiple LEDs is used. While the former solution can be used in luminaries whose size and weight is typically not limited very strictly (e.g., in street lamps), whenever a compact (especially, thin and flat, as is the case of the majority of indoor lighting applications) light source module is required, an array of LEDs is the most practical choice.
  • An array- of LEDs can be generally formed in two alternative ways: either through combining a number of individual LEDs, each of them being a complete separate component having its own substrate, electrical connections, optical system, packaging, etc., or by placing LED components, possibly as bare semiconductor chips, on a common substrate and using a common system for electrical connections, and, in many cases, also a common optical system as well as a common packaging arrangement encapsulating the LED chip array.
  • the latter solution is commonly known in the LED . industry as a "chip-on-board” (COB) module.
  • COB chip-on-board
  • a "COB”module, or a “COB-type” module presents a number of advantages over an array of complete individual LED components combined into a common device. These advantages include reduced manufacturing costs (via using common electrical connections and optics) , higher output optical power, and more compact .size .
  • 3aMeHHK)IIHH JIHCT optical power is observed from COB modules as compared to systems based on complete individual LEDs. This is due to the limitations of the optical system used to collect the light from individual LED chips andguide it from the module, i.e. to extract the generated light from the module.
  • anoptical system is designed for a single semiconductor chip, light from the single chip may typically be collected freely in a hemisphere around the chip, resulting in high light extraction efficiency.
  • each chip is surrounded by neighboring chips which partly absorb the emission or redirect it in such a way that it possibly never leaves the module.
  • the chips of a COB module are encapsulated within an encapsulating material often forming a single encapsulating layer, or simply a single “encapsulation", which is common for all the chips.
  • the encapsulation protects the chips from the effects of the ambient conditions.
  • the encapsulation may also comprise so called “phosphors" for converting the primary wavelength emitted by the LED chips to one or more other wavelengths. For example, a typical case is the conversion of blue light emitted by GaN-based LEDs into white light required in lighting applications.
  • the encapsulation often also forms the primary optical systems of the LED chips for redistributing the light emitted by the LED chips.
  • the encapsulation can be shaped to have a lens for each LED chip placed on the substrate plate.
  • COB-type module where the encapsulationcomprises lenses is disclosed in US2012/0119231 Al .
  • a resin encapsulating body including a phosphor layer therein is formed on a circuitboard to cover the LED
  • the encapsulating body includes a bottom portion and a plurality of lens portions integrally formed on the bottomportion, each lens portion being disposedabove a LED chip.
  • a separate lens-shaped encapsulation for each individual LED chip of the module.
  • Another typicalexample of a COB-type light emitting module where an encapsulation also serves as an optical system is disclosed in CN201363572, whereinthe silicone encapsulation molded above the LED chips form one single cambered lens surface. According to CN201363572, an ideal light spot effect and high light-emitting efficiency can be obtained by use of such encapsulation.
  • the primary purpose of the shaped encapsulation serving as an optical system is to redistribute the light emitted by the LED chips so that a desired light pattern is formed.
  • the actual efficiency of extraction of light from the module is often ignored, or at least is not optimized.
  • efficient light extraction is of crucial importance for the overall efficiency of a light emitting module.
  • the conventional lensesdesigned for light pattern shaping also sometimes serve for better light extraction from the individual chips, thereby increasing the light extraction efficiency fromthe individual LEDs, and, therefore, of the entire LED array as a whole.
  • the LED chips are packed closely enough, which is often necessary for reaching a sufficiently compact size of the COB, light emitted by an individual chip may still experience interference by the neighboring chips.
  • KR100824716 describes a COB-type flat light source modulehaving a textured encapsulation.
  • the textured encapsulation which can be textured using an additive or subtractive process, is applied to the LED either prior to or during packaging.
  • the textured surface helps to reduce total internal reflection within the encapsulation, thereby improving the extraction efficiency.
  • chips can be mounted beneath a single textured encapsulation.
  • a mold having irregular surfaces can be used to form multiple encapsulations over many LEDs simultaneously.
  • texturing the encapsulation surface in a way that is described in this document is supposed to lead to a very narrow light beam pattern from the array, which is a serious drawback in general lighting applications.
  • 3aMenHiomnfi JIHCT means.
  • the accurate shapes of the texturing and the large-scale surface features are more or less randomly selected in US2011/0316006, and no systematic and general rules for selecting them are defined.
  • turning the general principles into practice in the form of detailed design of the encapsulation still requires burdensome testing and/or simulating.
  • WO2009093498 describes an LED package in which the extraction efficiency of light is enhanced for two contrary directions by reducing leakage of light, and provides also for a method for manufacturing such LED package.
  • a substrate whereup6n an LED bare chip is mounted is sealed with a transparent resin, and a reflector is placed on the surface thereof.
  • Metal reflection films are deposited partially on the reflector, so that the light enters the incident surface of the reflector from the LED bare chip through the sealing resin, and exits the exit surfaces in two contrary directions after being reflected from the reflection surfaces (metal reflection films) .
  • This system is very complicated, and it greatly increases the size of the light emitting device and manufacturing costs.
  • the purpose of the present invention is to provide a novel chip-on-board type light emitting module with efficient light extraction from the module.
  • the light emitting module of the present invention is characterized by what is presented in claim 1.
  • the light emitting module of the present invention comprises a substrate plate having contact means thereon for providing an electrical interface of the light emitting module and internal electrical connections within the light emitting module; a plurality of light emitting semiconductor chipsplaced on the substrate plate in a two-dimensional array and electrically connected via connector . structures to the contact means; and a continuous encapsulation on the substrate plate encapsulating the light emitting semiconductor chips and the connector structures, the encapsulation comprising a convex lens portion above each semiconductor chip.
  • the light emitting module can be a complete "standalone" module to be operated as such or integrated in a larger device. It can also be a part or building block of a larger light source assembly.
  • the module of the present invention can be a separable or non-separable sub-module in a larger module or assembly comprising also other sub-moduleswhich may be different or similar to that of the module according to the present invention.
  • the substrate plate can be fabricated according to the principles known in the art.
  • the substrate plate can be made of a ceramic material.
  • a ceramic substrate plate may provide a highly
  • Ceramics is a good choice also from thermal management point of view because a ceramic substrate plate can possess high thermal conductivity required for dissipating excessive heat during the operation of the light emitting module.
  • One suitable example is an AI2O3 wafer with thickness, for example, of 0.2 to 2 mm, or an A1N wafer with similar thickness.
  • the general principles of the present invention are not limited to any particular substrate plate material.
  • the term "upper” in the contexts of the surfaces of the substrate plate, the encapsulation, and the LED chips refers to the surfacesfacing to the hemisphere into which the module emits light.
  • the "upper” surface is the surface on which the semiconductor chips are located.
  • the “upper” surface is the free surface opposite to the surface facing towards the substrate plate.
  • “up” and “down” are not bound to the. real vertical direction but are linked to the direction of the normal of the substrate plate surface.
  • contact means is meant here any means suitable for providing an electrical interface of the light emitting module and internal electrical connections within the light emitting module.
  • a typical example is a patterned metal plating deposited on the substrate plate.
  • Such metal plating can comprise different kinds of contact pads or electrodes, as well as wirings, via which the individual light emitting semiconductor chips of the module can be electrically connected to an external power source .
  • the individual light emitting semiconductor chips of the module can be electrically connected to an external power source .
  • connection structures can comprise any known structures suitable for electrically connecting the semiconductor chips to the contact means of the substrate plate for supplying electrical current or voltage to the semiconductor chips.
  • the semiconductor chips may be connected to appropriate portions of patterned metal plating by means of wire bonding.
  • soldered connector structures used e.g. in flip-chip technology . may be used.
  • the light emitting semiconductor chips are the primary light emitting elements of the light emitting module. They can be, for example, light emitting diode LED chips of any known type. However, the present invention is not restricted to any particular type of the light emitting semiconductor chips.
  • the chips can be attached to the substrate plate by any means known in the art . For example, possible methods for attaching the LEDs on the substrate plate are gluing with any already known LED die attach glue, and soldering.
  • the encapsulation can be formed of any known encapsulating material suitable for the purpose of encapsulating the plurality of light emitting semiconductor chips, thereby protecting them against the effects of the possibly harmful substances and moisture present in the environment surrounding the light emitting module .
  • examples include siliconesand epoxy, the former being the most common group of encapsulating materials used in the art.
  • the key attributes of silicones that make them attractive materials particularly for high-brightness (HB) LEDs and LED-based light emitting modules include their high transparency in the UV-visible region, controlled refractive index, and stable thermo-opto-mechanical
  • 3aMeHHH)IIHH JIHCT properties These materials are well known to those skilled in the art and are widely used in production of individual LEDs and COB modules.
  • one important property of the encapsulating material is that it should allow formation of an encapsulation with a desired shape of the upper surface thereof. In molding process, such desired shape can be achieved simply by means of a properly shaped mold used during curing the initially substantially liquid encapsulating material.
  • the encapsulating material is deposited or applied on the substrate plate in liquid form and solidified to have a flat surface. This flat surface can be then structured afterwards mechanically by using, for example, mechanical cutting tools, or optical tools such as a laser beam. These procedures are also well known to those skilled in the art.
  • Continuous means that the encapsulation covers the array of the light emitting semiconductor chips as a continuous layer without any holes in it in the area of the chip array. Thus, the encapsulation covers also the substrate plate between the semiconductor chips.
  • the convex lens portions above each semiconductor chip preferably coincide with the chips so that the middle point of each lens portion lies substantially above the middle point of a semiconductor chip.
  • the surface of the convex lens portion has a curvature of radius Riens meeting the condition W ⁇ Riens ⁇ 2W, wherein is the width of the semiconductor chips, and the convex lens portions of the adjacent semiconductor chips are connected via a concave combining portion, the surface of which has a curvature of radius Rcomb ⁇ Rlens ⁇
  • the width W of the semiconductor chips means the width in the direction of said fictitious plane of observation.
  • a light emitting semiconductor chip emits light substantially from the entire width thereof.
  • the width used in the definition above should be the former.
  • the key element of the present invention is the shape bf the free upper surface of the encapsulation.
  • the large-scale shape of the encapsulation surface comprising e.g. lens-like domes, is typically optimized for the purpose of producing a desired light pattern.
  • the efficiency of extraction of light from the light emitting module in its turn, is usually improved by means of some small-scale structuring of the encapsulation surface.
  • the entire encapsulation is formed and shaped so as to maximize the light extraction.
  • the convex lens portion has a radius of curvature as defined above, and the convex lens portions are connected to each other via a cpncave combining portions as defined above.
  • the surface of the encapsulation is "wavy" with
  • the lowest point of the free upper surface of the encapsulation between the semiconductor chips is above the level of the upper surfaces of the semiconductor chips.
  • the thickness of the encapsulation is preferably adjusted so that, except for the peripheral areas of the encapsulation outside the semiconductor chip array, the free upper surface of the encapsulation lies everywhere above the level of the upper surfaces of the semiconductor chips.
  • the refraction index of the encapsulating material is preferably greater than that of the air, and smaller than that of the material of the chips. With the typical refraction index of the semiconductor chip materials being 1.76 and refraction index of the air being 1.0, the optimum refraction index of the encapsulating material lies in the range of 1.3 to 1.6.
  • Light emitting semiconductor chips such as LED chips are typically is based on multiple quantumwell semiconductor heterostructures, and they emit light with an emission peak around a single wavelength which depends on the semiconductor material used.
  • LEDs made of group III nitrides, such as gallium nitride GaN, typically emit in the blue or near-ultraviolet part of the spectrum.
  • this light must be converted into white light. This is usually performed by means of a "phosphor" material receiving the light emitted by the LEDs at a primary wavelength and emitting the received energy at one or more longer wavelengths.
  • the phosphor material is applied as phosphor particles embedded in a silicone gel or other encapsulating material forming the encapsulation.
  • the encapsulation comprises such phosphor material for wavelength conversion of the light emitted by the semiconductor chips .
  • the width W of the semiconductor chips meets the condition 0.4 mm ⁇ W ⁇ 1.5 mm, and the distance D between the adjacent chips meets the condition 0.5W ⁇ D ⁇ 2W.
  • the width W means the width as defined above, i.e. the width in the direction of said fictitious plane of observation in which the characteristic features of the wavy surface of the encapsulation aredefined.
  • FIGS 2a to 2c illustrate the background of the present invention
  • FIGS 3 and 4a to 4e show examples of embodiments according to the present invention.
  • Figure la shows a schematic cross-section of a LED- based COB-typelight emitting module disclosed in US 2009/0050923.
  • the light emitting module is fabricated on a substrate plate.
  • a metal plating forming the contact pads as well as the internal electrical connections in the form of conductor wirings is arranged on the substrate plate by using screen printing or plating/lithography process.
  • LED chips are placed and attached by gluing on the substrate plate and electrically connected to each other as well as to the metal plating by wire bonding.
  • Each LED chip is encapsulated within a dome-shaped silicone encapsulation. This solution supposedly has a drawbackin that when packing the chips in close proximity it is difficult to avoid interference of the neighboring lenses and chips in the output of a single chip .
  • Figures lb and lc show a side-view and a cross- section, respectively, of a moduledisclosed in KR100824716.
  • the module is fabricated on a substrate plate in which a printed circuit is formed.
  • the module has a reflection layer formed in the substrate plate; LED chips; a transparent glass-ceramic layer; and a multi-function optical member located on the transparent glass-ceramic layer. Improved light extraction is achieved by means of the textured surface of the optical member.Also in this example,
  • Figure Id shows a LED-based light source module disclosed in CN201363572.
  • the module comprises a heat conducting base plate, an array of LEDs on the base plate, and a fluorescent powder and an encapsulation in the form of a molded silicone lens .above the LEDs.
  • the molded silicone lens is shaped as a cambered lens. According to the publication, ideal light spot effect and a high light emitting efficiency can be obtained. Thus, this solution is aimed primarily at obtaining a desired light pattern from the module.
  • Figure le shows a schematic cross-view of a LED array apparatusdisclosed in US2011/0316006, whereinLED chips are covered with a flat layer of encapsulation material, the surface of which is textured in order to improve light extraction from the module.
  • Figure 2a shows a ceramic substrate plate 1 and nine LED chips 2 placed in a two-dimensional (3 x3) array on the substrate plate.
  • the distance D between two adjacent chips in a single row and also between two adjacent rows is 1.4 mm.
  • the width W of the square LED chips is 1.2 mm.
  • Figure 2b shows the same configuration further comprising an encapsulation 3 in the form of a uniform and continuous layer of an encapsulating material.
  • the encapsulation encapsulates the LED chips and the substrate plate in the area of the LED array. The encapsulation protects the chips mechanically and also
  • 3aMeHHiomiiH JIHCT chemically, i.e. from the possibly harmful effects of the ambient conditions.
  • TIR total internal reflections
  • the encapsulation forms a single spherical lens 4 covering all the nine LED chips and having a radius of curvature R.
  • the lens is superposed on a uniform flat layer 3 of the encapsulation material having a thickness H base .
  • the encapsulation according to Figure 2c formed of an encapsulating material having a refractive index of 1.4, provides an enhancement of light extractionby 9% percent as compared to the flat encapsulation of Figure 2b.
  • the encapsulation according to Figure 2c formed of an encapsulating material having a refractive index of 1.4, provides an enhancement of light extractionby 9% percent as compared to the flat encapsulation of Figure 2b.
  • the module shown in Figure 3 is based on the basic configuration of a . substrate plate and a LED chip array of Figure 2a.
  • An encapsulation 5 forms an optical elementand covers all nine LED chips 2 and the ceramic substrate plate 1, as well as the wirebonding6 connecting the LED chips to contact means on the chip (not shown in the drawings) .
  • the encapsulation has a "wavy" upper surface comprising convex lens portions 7 at the locations of the LED chips, and concave combining portions 8 between the lens portions. This shape of the encapsulation is designed according to
  • 3aMCHHiomnfi JIHCT the principles of the present invention to produce high light extraction.
  • the level of the upper surface of the base portion defines the lowest level of the upper surface of the entire encapsulation.
  • the lowest point of the upper surface of the concave combining portion lies at least at the height defined by the thickness H baS eOf the base portion.
  • the height of theencapsulation over the wirebonding H W i re is 0.65 mm.
  • 3aMeHHH)IIHH JIHCT micrometers converting light emitted by the chip at the wavelength 450 rtm into the light with the wavelength 570 nm, improved light extraction by 12% as compared to the structure shown in Figure 2b.
  • the simulations also confirmed that the light extraction efficiency is not very sensitive to the placement of the spherical-shaped lenses exactly over the geometrical center of the LED chips. Deviation of the apex of the lens from the axis of the chip by 0.1-0.2 mm decreased light extraction improvement only by 1- 2.5 percentage points.
  • Figures4a to 4e show further examples of encapsulations shaped according to the boundary conditions of the present invention.
  • all lens portions of the encapsulations have generally a substantially spherical shape, but the curvature radius of the lens portions and . the combining portions vary.
  • the exact level of the light extraction improvement varies depending on the actual shape of the encapsulation, in all examples the amount of light emitted by each chip and experiencing total internal reflection at the encapsulation/air interface is 50% at highest, as opposed to a typical value of about 60% in COB-type light emitting modules with a flatsurface of the encapsulation.

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

Abstract

A light emitting module (10) comprises a substrate plate (1); a plurality of light emitting semiconductor chips (2) placed on the substrate plate; and a continuous encapsulation (5) on the substrate plate encapsulating the light emitting semiconductor chips, the encapsulation comprising a convex lens portion (7) above each semiconductor chip. According to the present invention, in a cross-section of the encapsulation along a plane passing the middle points of two adjacent semiconductor chips, the surface of the convex lens portion has a curvature of radius Rlens meeting the condition W ≤ Rlens ≤ 2W, wherein W is the width of the semiconductor chips, and the convex lens portions of the adjacent semiconductor chips are connected via a concave combining portion (8), the surface of which has a curvature of radius Rcomb ≤ Rlens.

Description

MODULE WITH LIGHT-EMITTING DIODES
FIELD OF THE INVENTION
The present invention relates generally to light sources based on light emitting semiconductor components, such as light emitting diodes LEDs, as the primary light emitting elements. More particularly, the present invention is related to light emitting modules having a plurality of semiconductorlight emitting chips arranged on a substrate plate. Typically, these kinds of modules are called chip-onboard (COB) light emitting modules. The invention is focused on the extraction of light from such modules.
BACKGROUND OF THE INVENTION
In the core of any light source, such as an indoor luminary or, for example,, a headlight of a vehicle, there are one or more primary light generating/emitting elements or components. Nowadays, semiconductor light emitting elements like LEDs more and more . often replace the conventionally used incandescent and gas-discharge lamps as the primary light emitting component. Semiconductor light emitting components provide many superior characteristics, such as long-term stability, high power efficiency, and compact size of the single element.
There is currently a great variety of different LED- based lighting and illumination devices and modules commercially available for different applications.
Using a single LED as the only light emitting element in a luminary, e.g. for general lighting, is often practically impossible, as a typical LED represents a point light source. To produce evenly distributed light, which is required in many applications, special
3aMeHHioiuiiH JIHCT reflectors which redistribute light from the point source, thus transforming it into a beam with desired properties, are used. Alternatively, an array of multiple LEDs is used. While the former solution can be used in luminaries whose size and weight is typically not limited very strictly (e.g., in street lamps), whenever a compact (especially, thin and flat, as is the case of the majority of indoor lighting applications) light source module is required, an array of LEDs is the most practical choice.
An array- of LEDs can be generally formed in two alternative ways: either through combining a number of individual LEDs, each of them being a complete separate component having its own substrate, electrical connections, optical system, packaging, etc., or by placing LED components, possibly as bare semiconductor chips, on a common substrate and using a common system for electrical connections, and, in many cases, also a common optical system as well as a common packaging arrangement encapsulating the LED chip array. The latter solution is commonly known in the LED. industry as a "chip-on-board" (COB) module. A "COB"module, or a "COB-type" module, presents a number of advantages over an array of complete individual LED components combined into a common device. These advantages include reduced manufacturing costs (via using common electrical connections and optics) , higher output optical power, and more compact .size .
However, placing an array of LED chips on a common substrate usually reduces the light output from the module. As semiconductor chips are positioned within close proximity to each other, typically loweroutput
3aMeHHK)IIHH JIHCT optical power is observed from COB modules as compared to systems based on complete individual LEDs. This is due to the limitations of the optical system used to collect the light from individual LED chips andguide it from the module, i.e. to extract the generated light from the module. When anoptical system is designed for a single semiconductor chip, light from the single chip may typically be collected freely in a hemisphere around the chip, resulting in high light extraction efficiency. In a COB module, instead, each chip is surrounded by neighboring chips which partly absorb the emission or redirect it in such a way that it possibly never leaves the module. Typically, the chips of a COB module are encapsulated within an encapsulating material often forming a single encapsulating layer, or simply a single "encapsulation", which is common for all the chips. The encapsulation protects the chips from the effects of the ambient conditions. The encapsulation may also comprise so called "phosphors" for converting the primary wavelength emitted by the LED chips to one or more other wavelengths. For example, a typical case is the conversion of blue light emitted by GaN-based LEDs into white light required in lighting applications. Moreover, the encapsulation often also forms the primary optical systems of the LED chips for redistributing the light emitted by the LED chips. For example, the encapsulation can be shaped to have a lens for each LED chip placed on the substrate plate.
An example of a COB-type module where the encapsulationcomprises lenses is disclosed in US2012/0119231 Al . In the module of US2012/0119231 , a resin encapsulating body including a phosphor layer therein is formed on a circuitboard to cover the LED
3a eHHK>miifi JIHCT chips. The encapsulating body includes a bottom portion and a plurality of lens portions integrally formed on the bottomportion, each lens portion being disposedabove a LED chip. In another ' example disclosed in US 2009/050923, there is no common encapsulation but, instead, a separate lens-shaped encapsulation for each individual LED chip of the module. Another typicalexample of a COB-type light emitting module where an encapsulation also serves as an optical system is disclosed in CN201363572, whereinthe silicone encapsulation molded above the LED chips form one single cambered lens surface. According to CN201363572, an ideal light spot effect and high light-emitting efficiency can be obtained by use of such encapsulation.
Conventionally, the primary purpose of the shaped encapsulation serving as an optical system is to redistribute the light emitted by the LED chips so that a desired light pattern is formed. At the same time, the actual efficiency of extraction of light from the module is often ignored, or at least is not optimized. However, efficient light extraction is of crucial importance for the overall efficiency of a light emitting module.
The conventional lensesdesigned for light pattern shaping also sometimes serve for better light extraction from the individual chips, thereby increasing the light extraction efficiency fromthe individual LEDs, and, therefore, of the entire LED array as a whole. However, when, the LED chips are packed closely enough, which is often necessary for reaching a sufficiently compact size of the COB, light emitted by an individual chip may still experience interference by the neighboring chips.
aMeHHK)miiH JIHCT When one considers possible ways of improving light extraction from the array of LED chips, the most common method is to structure the surface of the encapsulation covering the LED chips so as to have small-scale structuring thereon. For example, KR100824716 describes a COB-type flat light source modulehaving a textured encapsulation. The textured encapsulation, which can be textured using an additive or subtractive process, is applied to the LED either prior to or during packaging. The textured surface helps to reduce total internal reflection within the encapsulation, thereby improving the extraction efficiency. Several chips can be mounted beneath a single textured encapsulation. A mold having irregular surfaces can be used to form multiple encapsulations over many LEDs simultaneously. However, texturing the encapsulation surface in a way that is described in this document is supposed to lead to a very narrow light beam pattern from the array, which is a serious drawback in general lighting applications.
Other examples of utilizing surface texturing to improve the extraction of light from a light emitting COB-type module are disclosed e.g. in US2011/0316006. In some of the examples in US2011/0316006, in addition to small-scale texturing on the surface of the encapsulation, also the overall . shape of the encapsulation is shaped so as to comprise e.g. dome- like geometry or other large-scale surface features further improving the light extraction. The main principle in those large-scale surface features is that the diameter of at least one such large-scale surface feature is larger than at least two LEDs. The surface features may be formed e.g. by stamping, molding, pattern transferring, or by any other suitable
3aMenHiomnfi JIHCT means. The accurate shapes of the texturing and the large-scale surface features are more or less randomly selected in US2011/0316006, and no systematic and general rules for selecting them are defined. Thus, turning the general principles into practice in the form of detailed design of the encapsulation still requires burdensome testing and/or simulating.
The enhancement of light extraction can be also achieved using complex optical systems with metal reflectors. For example, WO2009093498 describes an LED package in which the extraction efficiency of light is enhanced for two contrary directions by reducing leakage of light, and provides also for a method for manufacturing such LED package. In the disclosed solution, a substrate whereup6n an LED bare chip is mounted is sealed with a transparent resin, and a reflector is placed on the surface thereof. Metal reflection films are deposited partially on the reflector, so that the light enters the incident surface of the reflector from the LED bare chip through the sealing resin, and exits the exit surfaces in two contrary directions after being reflected from the reflection surfaces (metal reflection films) . This system, however, is very complicated, and it greatly increases the size of the light emitting device and manufacturing costs.
To summarize, there is still a strong need in the art for a generic and systematic way to design the encapsulation of a COB-type light emitting module for high light extraction.
PURPOSE OF THE INVENTION
3aMeHflK)ii|HH JIHCT The purpose of the present invention is to provide a novel chip-on-board type light emitting module with efficient light extraction from the module. SUMMARY OF THE INVENTION
The light emitting module of the present invention is characterized by what is presented in claim 1.
The light emitting module of the present invention comprises a substrate plate having contact means thereon for providing an electrical interface of the light emitting module and internal electrical connections within the light emitting module; a plurality of light emitting semiconductor chipsplaced on the substrate plate in a two-dimensional array and electrically connected via connector . structures to the contact means; anda continuous encapsulation on the substrate plate encapsulating the light emitting semiconductor chips and the connector structures, the encapsulation comprising a convex lens portion above each semiconductor chip.
The light emitting module can be a complete "standalone" module to be operated as such or integrated in a larger device. It can also be a part or building block of a larger light source assembly. For example, the module of the present invention can be a separable or non-separable sub-module in a larger module or assembly comprising also other sub-moduleswhich may be different or similar to that of the module according to the present invention.
The substrate plate can be fabricated according to the principles known in the art. For example, the substrate plate can be made of a ceramic material. A ceramic substrate plate may provide a highly
3a enHK)miiH JIHCT reflective upper surface suitable for optimizing the light extraction fromthe module. Ceramics is a good choice also from thermal management point of view because a ceramic substrate plate can possess high thermal conductivity required for dissipating excessive heat during the operation of the light emitting module. One suitable example is an AI2O3 wafer with thickness, for example, of 0.2 to 2 mm, or an A1N wafer with similar thickness. However, the general principles of the present invention are not limited to any particular substrate plate material.
In this specification, the term "upper" in the contexts of the surfaces of the substrate plate, the encapsulation, and the LED chips refers to the surfacesfacing to the hemisphere into which the module emits light. Thus, in the case of the substrate plate, the "upper" surface is the surface on which the semiconductor chips are located. In the case of the semiconductor chips and the encapsulation, the "upper" surface is the free surface opposite to the surface facing towards the substrate plate. To summarize, "up" and "down" are not bound to the. real vertical direction but are linked to the direction of the normal of the substrate plate surface.
By "contact means" is meant here any means suitable for providing an electrical interface of the light emitting module and internal electrical connections within the light emitting module. A typical example is a patterned metal plating deposited on the substrate plate. Such metal plating can comprise different kinds of contact pads or electrodes, as well as wirings, via which the individual light emitting semiconductor chips of the module can be electrically connected to an external power source . Correspondingly, the
3 MeHttK)ii|HH JIHCT "connector structures" can comprise any known structures suitable for electrically connecting the semiconductor chips to the contact means of the substrate plate for supplying electrical current or voltage to the semiconductor chips. For example, the semiconductor chips may be connected to appropriate portions of patterned metal plating by means of wire bonding. As another example, soldered connector structures used e.g. in flip-chip technology . may be used.
The light emitting semiconductor chips are the primary light emitting elements of the light emitting module. They can be, for example, light emitting diode LED chips of any known type. However, the present invention is not restricted to any particular type of the light emitting semiconductor chips. The chips can be attached to the substrate plate by any means known in the art . For example, possible methods for attaching the LEDs on the substrate plate are gluing with any already known LED die attach glue, and soldering.
The encapsulation can be formed of any known encapsulating material suitable for the purpose of encapsulating the plurality of light emitting semiconductor chips, thereby protecting them against the effects of the possibly harmful substances and moisture present in the environment surrounding the light emitting module . Examples include siliconesand epoxy, the former being the most common group of encapsulating materials used in the art. The key attributes of silicones that make them attractive materials particularly for high-brightness (HB) LEDs and LED-based light emitting modules include their high transparency in the UV-visible region, controlled refractive index, and stable thermo-opto-mechanical
3aMeHHH)IIHH JIHCT properties . These materials are well known to those skilled in the art and are widely used in production of individual LEDs and COB modules. In addition to the necessary optical properties such as sufficient transparency, one important property of the encapsulating material is that it should allow formation of an encapsulation with a desired shape of the upper surface thereof. In molding process, such desired shape can be achieved simply by means of a properly shaped mold used during curing the initially substantially liquid encapsulating material. Another option is that the encapsulating material is deposited or applied on the substrate plate in liquid form and solidified to have a flat surface. This flat surface can be then structured afterwards mechanically by using, for example, mechanical cutting tools, or optical tools such as a laser beam. These procedures are also well known to those skilled in the art.
"Continuous" means that the encapsulation covers the array of the light emitting semiconductor chips as a continuous layer without any holes in it in the area of the chip array. Thus, the encapsulation covers also the substrate plate between the semiconductor chips.
The convex lens portions above each semiconductor chip preferably coincide with the chips so that the middle point of each lens portion lies substantially above the middle point of a semiconductor chip.
According to the present invention, in a cross-section of the encapsulation along a plane passing through the middle points of two adjacent semiconductor chips, the surface of the convex lens portion has a curvature of radius Riens meeting the condition W ≤ Riens ≤ 2W, wherein is the width of the semiconductor chips, and the convex lens portions of the adjacent semiconductor chips are connected via a concave combining portion, the surface of which has a curvature of radius Rcomb ≤ Rlens ·
In the above, by two "adjacent" semiconductor chips means two neighboring chips in a same single row of the two-dimensional array, and thus not two chips in different rows. The width W of the semiconductor chips means the width in the direction of said fictitious plane of observation. Here it is assumed that a light emitting semiconductor chip emits light substantially from the entire width thereof. However, in case the emitting area width is substantially smaller than the physical width of the chip, the width used in the definition above should be the former.
The key element of the present invention is the shape bf the free upper surface of the encapsulation. In prior art, the large-scale shape of the encapsulation surface, comprising e.g. lens-like domes, is typically optimized for the purpose of producing a desired light pattern. The efficiency of extraction of light from the light emitting module, in its turn, is usually improved by means of some small-scale structuring of the encapsulation surface. In the present invention, instead, the entire encapsulation is formed and shaped so as to maximize the light extraction. As an essential feature, when observed in a cross sectional plane combining the middle points of two adjacent semiconductor chips, the convex lens portion has a radius of curvature as defined above, and the convex lens portions are connected to each other via a cpncave combining portions as defined above. Thus, the surface of the encapsulation is "wavy" with
3arvieHHiomnH JIHCT alternating convex and concave sections having the radii of curvature as defined above. This solution was found to ensure a high light extraction for various configurations without any need for further small- scale structuring of the encapsulation surface. This simplifies the manufacturing of the light emitting module, and thus also reduces the costs thereof.
Preferably, the lowest point of the free upper surface of the encapsulation between the semiconductor chips is above the level of the upper surfaces of the semiconductor chips. In other words, the thickness of the encapsulation is preferably adjusted so that, except for the peripheral areas of the encapsulation outside the semiconductor chip array, the free upper surface of the encapsulation lies everywhere above the level of the upper surfaces of the semiconductor chips. This further enhances the light extraction. For maximizing the light extraction, the refraction index of the encapsulating materialis preferably greater than that of the air, and smaller than that of the material of the chips. With the typical refraction index of the semiconductor chip materials being 1.76 and refraction index of the air being 1.0, the optimum refraction index of the encapsulating material lies in the range of 1.3 to 1.6.
Light emitting semiconductor chips such as LED chips are typically is based on multiple quantumwell semiconductor heterostructures, and they emit light with an emission peak around a single wavelength which depends on the semiconductor material used. For example, high brightness LEDs made of group III nitrides, such as gallium nitride GaN, typically emit in the blue or near-ultraviolet part of the spectrum.
3aMeiiHiomiiH JIHCT For lighting or illuminating purposes, this light must be converted into white light. This is usually performed by means of a "phosphor" material receiving the light emitted by the LEDs at a primary wavelength and emitting the received energy at one or more longer wavelengths. Usually, the phosphor material is applied as phosphor particles embedded in a silicone gel or other encapsulating material forming the encapsulation. In one embodiment of the present invention, the encapsulation comprises such phosphor material for wavelength conversion of the light emitted by the semiconductor chips .
Preferably, the width W of the semiconductor chips meets the condition 0.4 mm ≤ W ≤ 1.5 mm, and the distance D between the adjacent chips meets the condition 0.5W ≤ D ≤ 2W.Here the width W means the width as defined above, i.e. the width in the direction of said fictitious plane of observation in which the characteristic features of the wavy surface of the encapsulation aredefined.
BRIEF DESCRIPTION OF THE FIGURES
The present invention is described in more detail in the following with reference to the accompanying Figures, wherein
Figures la to Id show examples of prior art light emitting modules,
Figures 2a to 2c illustrate the background of the present invention, and
Figures 3 and 4a to 4e show examples of embodiments according to the present invention.
aMeHHH)iiHif JIHCT Figures la to Id representing prior art solutions are copied from prior art documents, so the reference numbers therein are those of the original prior art documents and they should thus not be confused with the reference numbers of the Figures 3and 4a to 4e representing embodiments of the present inventions.
DETAILED DESCRIPTION OF THE INVENTION
Figure la shows a schematic cross-section of a LED- based COB-typelight emitting module disclosed in US 2009/0050923. The light emitting module is fabricated on a substrate plate. A metal plating forming the contact pads as well as the internal electrical connections in the form of conductor wirings is arranged on the substrate plate by using screen printing or plating/lithography process. LED chips are placed and attached by gluing on the substrate plate and electrically connected to each other as well as to the metal plating by wire bonding. Each LED chip is encapsulated within a dome-shaped silicone encapsulation. This solution supposedly has a drawbackin that when packing the chips in close proximity it is difficult to avoid interference of the neighboring lenses and chips in the output of a single chip .
Figures lb and lc show a side-view and a cross- section, respectively, of a moduledisclosed in KR100824716. The module is fabricated on a substrate plate in which a printed circuit is formed. The module has a reflection layer formed in the substrate plate; LED chips; a transparent glass-ceramic layer; and a multi-function optical member located on the transparent glass-ceramic layer. Improved light extraction is achieved by means of the textured surface of the optical member.Also in this example,
3aivieHHiomiiH JIHCT light emitted by each chip supposedlygets partly absorbed by the neighboring chips and is thereby lost.
Figure Id shows a LED-based light source module disclosed in CN201363572. The module comprises a heat conducting base plate, an array of LEDs on the base plate, and a fluorescent powder and an encapsulation in the form of a molded silicone lens .above the LEDs. The molded silicone lens is shaped as a cambered lens. According to the publication, ideal light spot effect and a high light emitting efficiency can be obtained. Thus, this solution is aimed primarily at obtaining a desired light pattern from the module. Figure le shows a schematic cross-view of a LED array apparatusdisclosed in US2011/0316006, whereinLED chips are covered with a flat layer of encapsulation material, the surface of which is textured in order to improve light extraction from the module.
Figure 2a shows a ceramic substrate plate 1 and nine LED chips 2 placed in a two-dimensional (3 x3) array on the substrate plate. The distance D between two adjacent chips in a single row and also between two adjacent rows is 1.4 mm. The width W of the square LED chips is 1.2 mm. This is the basic COB-type light emitting module configuration serving as a starting point for illustrating below the principles of the embodiments according to the present invention. Figure 2b shows the same configuration further comprising an encapsulation 3 in the form of a uniform and continuous layer of an encapsulating material. The encapsulation encapsulates the LED chips and the substrate plate in the area of the LED array. The encapsulation protects the chips mechanically and also
3aMeHHiomiiH JIHCT chemically,, i.e. from the possibly harmful effects of the ambient conditions.
As known for those skilled in the art, one basic problem in a uniform encapsulation as that of Figure 2b is that the total internal reflections ("TIR") of the light emitted by the LED chips at the encapsulation/air interface decrease the extraction of light from the module. Total internal reflection, i.e. reflection of the light energy back to the encapsulation instead of escaping it, takes place when light meets the upper surface of the encapsulation, i.e. said encapsulation/air interface, in a sufficiently large angle of incidence with respect to the normal of that surface. The critical angle above which TIR takes place depends on the refractive index of the encapsulation.
One obvious solution in order to avoid the TIR is to shape the entire upper surface of the encapsulation as a dome curving above the LED chip array. An example illustrating this is shown in Figure 2c. In the module of Figure 2c, the encapsulation forms a single spherical lens 4 covering all the nine LED chips and having a radius of curvature R. The lens is superposed on a uniform flat layer 3 of the encapsulation material having a thickness Hbase.
According to simulations performed by commercial Zemaxoptics simulation software, the encapsulation according to Figure 2c, formed of an encapsulating material having a refractive index of 1.4, provides an enhancement of light extractionby 9% percent as compared to the flat encapsulation of Figure 2b. However, to achieve this high enhancement, the
3aMeiiHiomHH JIHCT thickness H of the lens had to be set to H=4.17 mm, which is almost half of the width of the ceramic substrate plate on which the LED chips are placed (10x10 mm2) . In the simulations, the thickness of the uniform flat layer of the encapsulating material was set to Hbase=0.6 mm.
Said high thickness required for a single lens covering the LED chips of the module is not usable in practice . Such single lens would require a lot of encapsulating material, thereby increasing the cost of the light emitting module. The problem is further emphasized with increasing the size of the module from the 3 x 3 array of the example above. The advantages of the compact size of the COB-type module would be at least partially lost. Another drawback is that if suchthick lens contains phosphor particles, according both to calculations and experiment, the color temperature of the light emitted by the module would be non-uniform and distorted.
The module shown in Figure 3 is based on the basic configuration of a . substrate plate and a LED chip array of Figure 2a. An encapsulation 5 forms an optical elementand covers all nine LED chips 2 and the ceramic substrate plate 1, as well as the wirebonding6 connecting the LED chips to contact means on the chip (not shown in the drawings) . The encapsulation has a "wavy" upper surface comprising convex lens portions 7 at the locations of the LED chips, and concave combining portions 8 between the lens portions. This shape of the encapsulation is designed according to
3aMCHHiomnfi JIHCT the principles of the present invention to produce high light extraction. As observed in a cross-section of the encapsulation 5along a fictitious plane passing through the middle points of two adjacent LED chips in a row, the surface of the convex lens portion has a curvature of radius Riens = 1.4 mm (meeting the condition ≤ Riens - 2W, wherein W is the width of the semiconductor chips) , and the concave combining portion, has a curvature of radius RComb= 0.3 mm (thus meeting the condition RComb≤ Riens) · The wavy-shaped upper portion of the encapsulation is superposed on a base portion with a thickness of Hbase = 0.1 mm.
In the module 10 of Figure 3, the level of the upper surface of the base portion defines the lowest level of the upper surface of the entire encapsulation. In other words, e.g. also along a diagonal connection line between two LED chips of different rows, the lowest point of the upper surface of the concave combining portion lies at least at the height defined by the thickness HbaSeOf the base portion. The height of theencapsulation over the wirebonding HWireis 0.65 mm. Based on the simulations, without phosphor particles contained in the encapsulation, this configuration provides light extraction enhancement by 9% as compared to the configuration of Figure 2b with a flat encapsulation. Adding phosphor particles with concentration of 13.4wt% (the phosphor particles thus weighing 13.4 percent of the total mass of the encapsulating material) and mean particle size of 15
3aMeHHH)IIHH JIHCT micrometers, converting light emitted by the chip at the wavelength 450 rtm into the light with the wavelength 570 nm, improved light extraction by 12% as compared to the structure shown in Figure 2b. The simulations also confirmed that the light extraction efficiency is not very sensitive to the placement of the spherical-shaped lenses exactly over the geometrical center of the LED chips. Deviation of the apex of the lens from the axis of the chip by 0.1-0.2 mm decreased light extraction improvement only by 1- 2.5 percentage points.
Figures4a to 4e show further examples of encapsulations shaped according to the boundary conditions of the present invention. As can be seen in the figures, all lens portions of the encapsulations have generally a substantially spherical shape, but the curvature radius of the lens portions and. the combining portions vary. In Figure 4a, the lens portions have a radius of curvature Riens = 2 mm and the radius of curvature' of the combining portion RCOmi) = 1.8 mm, improving light extraction by 7% as compared to configuration presented in Figure 2b if phosphor particles are used (5% without phosphor) . In Figure 4b, the radii of curvature are Rlens=l · 6 mm and Rcomb — 0.5 mm, resulting in an improvement of light extraction by 10% (7% without phosphor) . In Figure 4c, the radii of curvature areRiens=l · 5 mm and RCOmb = 0.4 mm, providing an improvement of light extraction by 11% (8% without phosphor) . In Figure 4d, the radius of curvature of the convex lens portions is Riens=l-4 mm, whereas the radius of curvature of the concave
3a eHHiomnfi JIHCT combining portions is Rfn = 0.3 mm. This results in a 12% (9% without phosphor) higher extraction of light from the module than in the configuration of figure 2b. Finally, in the module of Figure 4e, the radii of curvature of the lens portions and the combining portions are Riens=l-2 mm and RCOmb = 0.1 mm, resulting in light extraction which is 13% higher than that of the configuration of Figure 2b (10% without phosphor) . As can be noted, in all those examples of Figures 3 and 4a to 4e, all the LED chips 2 placed on the substrate plate lare covered by a common encapsulation 5. Though the exact level of the light extraction improvement varies depending on the actual shape of the encapsulation, in all examples the amount of light emitted by each chip and experiencing total internal reflection at the encapsulation/air interface is 50% at highest, as opposed to a typical value of about 60% in COB-type light emitting modules with a flatsurface of the encapsulation.
It is important to be noted that, as is obvious to a person skilled in the art, the basic idea of the invention as defined in the claims may be implemented in various ways. The invention is thus not limited to the examples described above but may vary within the scope of the claims. In particular, though Figures3 and 4a to 4e illustrateembodiments based on a 3 x 3 LED chip array on a ceramic substrate plate, the invention applies to any arbitrary number and type of light emitting semiconductor chips on any substrate plate suitable for a COB-type light emitting module. aMenHH)miiH JIHCT

Claims

1. A light emitting module (10) comprising:
- a substrate plate (1) having contact means thereon for providing an electrical interface of the light emitting module and internal electrical connections within the light emitting module;
a plurality of light emitting semiconductor chips (2) placed on the substrate plate in a two-dimensional array and electrically connectedvia connector structures ( 6) to the contact means; and
a continuous encapsulation (5) on the substrate plate encapsulating the light emitting semiconductor chips and the connector structures, the encapsulation comprising a convex lens portion (7) above each semiconductor chip;
characterized in that in a cross-sectionof the encapsulation along a plane passing through the middle points of two adjacent semiconductor chips (2), the surface of the convex lens portion (7) has a curvature of radiusRieiis meeting the condition W ≤ iens - 2W, wherein W is the width of the semiconductor chips, and the convex lens portions of the adjacent semiconductor chips are connected via a concave combining portion (8), the surface of which has a curvature of radius
Rcomb — ^lens ·
2. A light emitting module (10) as defined in claim 1 or 2, whereinthe lowest point of the surface of the encapsulation (5) between the semiconductor chips (2) is above the level of the upper surfaces of the semiconductor chips.
3arvieHH )iunH JIHCT
3. A light emitting module (10) as defined in claim 1 or 2, wherein the encapsulation (5) is formed of a material having a refractive index in the range of 1.3 to 1.6.
4. A light emittingmodule (10) as defined in any of claims lto3, wherein the encapsulation (5) comprises phosphor for wavelength conversion of the light emitted by the semiconductor chips (2) .
5. A light emitting module (10) as defined in any of claims 1 to 4, wherein the width W of the semiconductor chips meets the condition 0.4 mm W ≤ 2.5 mm, and the distance D between the adjacent chips meets the condition 0.5 ≤ D ≤ 2W.
3aMeHHK)IIHH JIHCT
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