WO2013104708A1 - Light-emitting module, light source assembly, and methods for manufacturing - Google Patents

Light-emitting module, light source assembly, and methods for manufacturing Download PDF

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Publication number
WO2013104708A1
WO2013104708A1 PCT/EP2013/050387 EP2013050387W WO2013104708A1 WO 2013104708 A1 WO2013104708 A1 WO 2013104708A1 EP 2013050387 W EP2013050387 W EP 2013050387W WO 2013104708 A1 WO2013104708 A1 WO 2013104708A1
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WO
WIPO (PCT)
Prior art keywords
light
emitting
light source
substrate plate
module
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Application number
PCT/EP2013/050387
Other languages
French (fr)
Inventor
Johann Ramchen
Leonid MOISEEV
Karim D. MYNBAEV
Alexey E. Romanov
Vladislav E. Bougrov
Alexey R. Kovsh
Maxim A. Odnoblyudov
Magnus Ahlstedt
Original Assignee
Optogan New Technologies Of Light Llc
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Application filed by Optogan New Technologies Of Light Llc filed Critical Optogan New Technologies Of Light Llc
Publication of WO2013104708A1 publication Critical patent/WO2013104708A1/en

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    • 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
    • H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier 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 with at least one potential-jump barrier or surface barrier 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
    • 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
    • H01L2224/44—Structure, shape, material or disposition of the wire connectors prior to the connecting process
    • H01L2224/45—Structure, shape, material or disposition of the wire connectors prior to the connecting process of an individual wire connector
    • H01L2224/45001—Core members of the connector
    • H01L2224/45099—Material
    • H01L2224/451—Material with a principal constituent of the material being a metal or a metalloid, e.g. boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te) and polonium (Po), and alloys thereof
    • H01L2224/45117—Material with a principal constituent of the material being a metal or a metalloid, e.g. boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te) and polonium (Po), and alloys thereof the principal constituent melting at a temperature of greater than or equal to 400°C and less than 950°C
    • H01L2224/45124—Aluminium (Al) as principal constituent
    • 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
    • H01L2224/44—Structure, shape, material or disposition of the wire connectors prior to the connecting process
    • H01L2224/45—Structure, shape, material or disposition of the wire connectors prior to the connecting process of an individual wire connector
    • H01L2224/45001—Core members of the connector
    • H01L2224/45099—Material
    • H01L2224/451—Material with a principal constituent of the material being a metal or a metalloid, e.g. boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te) and polonium (Po), and alloys thereof
    • H01L2224/45138—Material with a principal constituent of the material being a metal or a metalloid, e.g. boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te) and polonium (Po), and alloys thereof the principal constituent melting at a temperature of greater than or equal to 950°C and less than 1550°C
    • H01L2224/45144—Gold (Au) as principal constituent
    • 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
    • H01L2224/481—Disposition
    • H01L2224/48135—Connecting between different semiconductor or solid-state bodies, i.e. chip-to-chip
    • H01L2224/48137—Connecting between different semiconductor or solid-state bodies, i.e. chip-to-chip the bodies being arranged next to each other, e.g. on a common substrate
    • 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
    • H01L2224/49—Structure, shape, material or disposition of the wire connectors after the connecting process of a plurality of wire connectors
    • H01L2224/491—Disposition
    • H01L2224/4912—Layout
    • H01L2224/49175—Parallel arrangements
    • 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

Definitions

  • the present invention relates generally to light sources based on light-emitting semiconductor elements such as the different variations of light emitting di ⁇ odes LEDs . More particularly, the present invention relates to light-emitting modules and light source el- ements having multiple primary light emitting ele ⁇ ments, e.g. LED chips, arranged on a substrate. Typi ⁇ cally, these kinds of modules are called chip-on-board (COB) light-emitting modules or light source elements. The present invention also relates to manufacturing of such modules and elements.
  • COB chip-on-board
  • any light source such as an indoor lu ⁇ minary or, for example, a headlight of a vehicle
  • a primary light generating/emitting component In the core of any light source, such as an indoor lu ⁇ minary or, for example, a headlight of a vehicle, there is a primary light generating/emitting component.
  • semiconductor light emitting elements like LEDs more and more often replace the convention ⁇ ally used incandescent and gas-discharge lamps as the primary light emitting component.
  • Semiconductor light emitting components provide many superior characteris ⁇ tics, for example, long-term stability, high power ef ⁇ ficiency, and compact size of the single element.
  • An array of LEDs can be generally formed in two alter ⁇ native ways: either through combining a number of individual LEDs, each of them being a finished device, i.e., having its own substrate, electrical connec- tions, 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 lat ⁇ ter solution is commonly known in the LED industry as a "chip-on-board” (COB) module.
  • a LED-based COB module is made of a number of LED components produced as separate chips and then placed on a common substrate with necessary electrical connections. An example is shown in figure 1.
  • US Patent 8,022,626 describes various em- bodiments of "A lighting module comprising a base pan ⁇ el and a plurality of light-emitting diode (LED) chips attached directly to the base panel", where "the LED chips are in electrical communication with conductive traces on the base panel, which deliver a current to the LED chips".
  • US Patent 8,044,570 describes a typical example of the current common approach to the design of LED-based light source modules (COBs) . It discloses a light source module, which "includes a printed wiring board, a plurality of light-emitting elements, a sealing member, and a color conversion unit, and an adhesive lay ⁇ er". The sealing member described in U.S.
  • the color conversion unit includes a cover member with light transmitting properties, and a layer of a fluorescent substance provided on the inner surface of the cover member.
  • the adhesive layer has light-transmitting properties, and ensures adhesion of the sealing member to the fluorescent substance layer of the color conversion unit in an airtight manner.
  • UK Patent GB 2458972 describes a LED (COB) module, which "comprises a plurality of LED die arranged on a substrate in one or more radially concentric rings about a centre point such that each LED die is azi- muthally offset from neighboring LED die".
  • the module includes thermal conduction pads each having lateral dimensions at least as large as the combined lateral dimensions of the LED die attached to it and a total surface area at least five times larger than the total surface area of all the LED die attached to it.
  • the total light emission area of the module is no greater than four times larger than the combined total surface emission area of all individual LED dies disposed on the substrate.
  • a variety of configurations are possible subject to these criteria, which permit good packing density for enhanced brightness whilst ensuring optimal heat transfer.
  • a method for manufac- turing the module is also disclosed in the document.
  • most of the key parameters of the COB module such as the number of the single LEDs and thus the output light power, and the overall module size, are defined at the design stage and can ⁇ not be changed or modified afterwards once the manu ⁇ facturing process has started.
  • the desired pa ⁇ rameters of the COB module such as output power, or just element size
  • the whole COB module has to be re-designed, and the manufacturing process has to be adapted accordingly. This makes the production of COB modules and light source elements inflexible, in ⁇ creasing the time required for changing the module type and raising the production costs of the module.
  • the purpose of the present invention is to provide a chip-on-board type light-emitting module, a light source assembly, as well as methods for manufacturing the same, alleviating the problems of the prior art.
  • the light-emitting module and a light source assembly of the present invention are characterized by what is specified in claims 1 and 3, respectively.
  • the methods for manufacturing those items are characterized by what is presented in claim 7 and 9, respectively.
  • the light-emitting module of the present invention comprises a substrate plate formed of a ceramic mate ⁇ rial and having a patterned metal plating thereon for providing an electrical interface of the light- emitting module and internal electrical connections within the module, and a plurality of light-emitting semiconductor chips placed on the substrate plate and electrically connected to the metal plating, for exam- pie, via wire bonding or via soldered connections, each of the light-emitting semiconductor chips being encapsulated within an encapsulating material.
  • the ceramic substrate plate forms the basic supporting body of the module. Ceramic substrate plates are com ⁇ soirally available, and they can be produced using materials and technologies as such known in the art.
  • any known ceramic material preferably enabling a highly reflective upper surface of the substrate plate for optimizing the light extraction from the module, can be used.
  • the ceramic substrate should also preferably possess high thermal conductivity for dissipating excessive heat during the operation of the light-emitting module. Suitable examples are an AI 2 O 3 wafer with thickness, for example, of 0.2 to 2 mm, or an A1N wafer with similar thickness.
  • the metal plating i.e., a patterned metal layer on the substrate plate, providing an electrical con ⁇ tact interface for the module and also the internal electrical connections within the module can be formed according to the principles known in the art.
  • the met ⁇ al 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 can be connected to the metal plating, for example, by wire bonding.
  • One suitable material for the metal plating is copper Cu .
  • another single or multi-layered metallization formed of, for example, Ni/Pd/Au, Ag, Al, Ni/Pd, Ni/Au, Ni/Ag, may be formed on the Cu layer for ensur ⁇ ing an optimal electrical contact.
  • the metal plating forming the wiring layout of the substrate plate is preferably formed so that all the light-emitting semiconductor chips of the module can be supplied via one pair of contact pads or contact electrodes only.
  • the light-emitting semiconductor chips can be, for example, those used for light-emitting diodes LEDs of any known type(s) .
  • the present invention is not restricted to any particular type of the light- emitting semiconductor chips.
  • the chips can be at- tached to the substrate plate by any means known in the art .
  • the encapsulating material can be any known material suitable for encapsulating light-emitting semiconduc- tor chips, thereby protecting them against the effects of the possibly harmful substances and moisture pre ⁇ sent in the environment surrounding the light-emitting module.
  • the encapsulating material can also comprise one or more phosphor-based compounds for converting the wavelength of the light initially emitted by the light-emitting semiconductor chips according to the desired output spectrum of the module.
  • the most common group of such encapsulating materials is formed by silicones. Those silicones can be applied in a sub- stantially liquid form and cured thereafter.
  • the encapsulating material forms a single continuous encapsulating layer on the substrate plate, the encapsulating layer being confined in the lateral direction, i.e. in the direc- tion of the plane of the substrate plane, to the free ambient space.
  • the light-emitting module is charac ⁇ terized by that the lateral extent of the encapsulat- ing material is not limited or restricted by any me ⁇ chanical casting barrier or other type of mold struc ⁇ ture defining, in the lateral direction, the volume in which the silicone, when applied in substantially liq ⁇ uid form on the substrate plate, is confined.
  • No such structures are present in the module of the present invention but, instead, also in the lateral direction, the encapsulating material is confined to the free am ⁇ bient space. Forming of such encapsulating layer is discussed later in this document with regard to the method aspect of the present invention.
  • the present invention simpli ⁇ fies the basic construction of the COB type light- emitting module in that no casting mold structures mounted on the substrate plate are needed. Further, perhaps the most important advantages are related to the manufacturing of light source elements based on light-emitting semiconductor chips as the primary light emitting components.
  • Light-emitting modules ac ⁇ cording to the present invention allow easy and straightforward way of manufacturing light source ele ⁇ ments. In this kind of light source element, several light-emitting modules together form a larger light source element. Thus, the light-emitting modules are used as modular building blocks repeated in the light source element.
  • This kind of modular construction of the light source element enables a straightforward and cost-efficient way to implement light source elements of different sizes and with different amounts of sin ⁇ gle light-emitting semiconductor chips therein.
  • the optical power as well as the light distribution pattern of the light source element can be adjusted by just selecting the number of single light-emitting modules in the light source element.
  • the key feature of the light-emitting module enabling such straightforward manufacturing of light source el ⁇ ements is the encapsulating layer being confined in the lateral direction to the free ambient space, i.e. without being limited by any casting mold structure.
  • a light source assembly in the form of a large panel of repeated light-emitting modules can be fabricated on a common substrate plate.
  • the individual light- emitting modules comprise no casting molds or other mechanical casting barriers
  • light source elements with any desired number of light-emitting modules can then be cut or broken off from the panel at any stage after the actual manufacturing process has finished.
  • different needs for different light source ap ⁇ plications can be easily met by using such modular panel as a light source preform.
  • the outer surface of the silicone i.e. the surface facing away from the sub ⁇ strate plate to the free ambient space and thus form- ing the optical interface between the light-emitting module and the surroundings thereof, is structured for enhancing the light extraction from the light-emitting module.
  • structuring is meant here any roughening, patterning, or other structuring of the outer surface so that escaping of light emitted by the light-emitting semiconductor chips from the volume defined by the substrate plate surface and said outer surface is enhanced. Enhancing the light extraction can be based, for example, on reflection, refraction, or diffraction of light.
  • the advantages of the present invention are particularly clear in a light source assembly comprising a plurali ⁇ ty of light-emitting modules as described above, wherein the substrate plates of the light-emitting modules form a single common substrate plate.
  • single common substrate is meant that the substrate plates of the single light-emitting modules form one integrated ceramic substrate plate.
  • This kind of as- sembly can be formed as a large panel serving as a preform from which light source elements with arbi ⁇ trary number of light-emitting modules can be cut or broken off.
  • such an assembly can also be a complete light source element with the de- sired number of light-emitting modules.
  • word “assembly” refers in this document both to a preform- like construction and to a finalized light source ele ⁇ ment .
  • the common substrate plate has preferably weakening scribing for facilitat ⁇ ing separation of the assembly into discrete light source elements each comprising one or more light- emitting modules.
  • the scribing can be implemented, for example, as grooves formed between the adjacent light- emitting modules on the common substrate plates.
  • the individual light-emitting modules of a light source element are preferably electrically connected together so that in a light source element of any size, i.e. comprising any number of single light- emitting modules, all the light-emitting semiconductor chips can be driven via common contact electrodes.
  • the metal plating comprises preferably a contact element electrically connecting together two adjacent light-emitting modules of the light source assembly.
  • at least some, preferably all of the light-emitting modules are con ⁇ nected to each other according to a predetermined con ⁇ tact layout.
  • the contact elements as part of the metal plating means that when forming a light source element by separating a group of light-emitting modules from a larger assembly, also the contact elements extending over the separation line between adjacent light-emitting modules of different light source ele ⁇ ments must be disjointed.
  • the contact element preferably has a thickness in the range of 10 to 40 ym. This has been found as a suitable thickness for many metal plating materials, e.g. Cu .
  • the method of the pre ⁇ sent invention for manufacturing a light-emitting mod- ule comprises the steps of: providing a substrate plate formed of a ceramic material and having a pat ⁇ terned metal plating thereon for providing an electrical interface of the light-emitting module and inter ⁇ nal electrical connections within the module; placing a plurality of light-emitting semiconductor chips on the substrate plate and electrically connecting them to the metal plating; and encapsulating each of the light-emitting semiconductor chips within an encapsulating material.
  • the step of providing a substrate plate can be imple ⁇ mented, for example, by taking a commercially availa- ble ceramic wafer of, for example, AI 2 O 3 or A1N and forming then the metal plating on the wafer so as to form the external and internal electrical connections of the module.
  • a commercially availa- ble ceramic wafer of, for example, AI 2 O 3 or A1N can be used.
  • any suit- able known method such as screen printing or galvanization, can be used.
  • the light-emitting semiconductor chips can be of any type, for example, conventional LED chips.
  • the chips can be located and attached on the substrate plate by using known principles, apparatuses, and processes. 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 electrical connection of a single light-emitting semiconductor chip to the metal plating can be formed directly from the chip to the metallization or via another chip. The most appropriate way depends, for ex- ample, on whether the adjacent chips are to be con ⁇ nected in series or in parallel, and on the location of the chip. Forming the connections can be made, for example, by soldering when placing the chips on the substrate plate, or by wire bonding using any standard bonding wire suitable for this purpose, for example, by a bonding wire with a diameter of 20 to 200 ym (20 to 50ym for Au wire, 30 to 200ym Al wire) .
  • silicones can be used as the encapsu ⁇ lating material. Pure silicone molding or luminophore (phosphor) /silicone molding for white light emitting modules can be used.
  • the step of encap ⁇ sulating each of the light-emitting semiconductor chips within the encapsulating material comprises forming a single continuous encapsulating layer on the substrate plate having the plurality of light emitting semiconductor chips thereon, the encapsulating layer being formed so as to be confined in the lateral di ⁇ rection to the free ambient space.
  • Said forming of a single continuous encapsulating lay ⁇ er can comprise first a step of forming a single con- tinuous encapsulating layer on the substrate plate having the plurality of light emitting semiconductor chips thereon, and then a step of exposing the sub ⁇ strate plate by removing the encapsulating layer in a region surrounding the plurality of light-emitting semiconductor chips so as to make the encapsulating layer confined in the lateral direction to the free ambient space.
  • one single continuous layer of the encapsulating material is formed over the entire module so that the layer encapsulates the all chips.
  • the encapsulating material is removed and thus the substrate plate exposed in a region surround ⁇ ing the plurality of light-emitting semiconductor chips.
  • This region can be a narrow region along a peripheral line on the substrate plate enclosing each of the light-emitting semiconductor chips. Removing of the encapsulating region can be accomplished accurate ⁇ ly and rapidly, for example, by means of a laser beam evaporating the encapsulating material.
  • said forming of a single continuous en ⁇ capsulating layer can comprise forming the layer using a compression molding process where the volume of the encapsulating material, i.e. the encapsulating layer shape and dimensions, is defined by a mold placed against the substrate plate during the molding.
  • the encapsulating layer is formed so that the completed layer is confined in the lateral direction to the free ambient space.
  • Performing the encapsulating step as described above makes it unnecessary to use any mold-like structures mounted on the substrate plate for confining the vol ⁇ ume to be filled by the encapsulating material. This greatly simplifies the manufacturing and lowers the manufacturing costs. Further advantages, as discussed above in the context of the light-emitting module aspect of the present in ⁇ vention, are achieved when the manufacturing method of the present invention is used to produce larger light source assemblies. This will be discussed more below.
  • the method further comprises structuring the outer surface of the encapsulating layer for enhancing the light extraction from the light-emitting module .
  • the advantages of the method of the present invention are particularly clear when the method is used to produce a larger light source assem ⁇ bly comprising a plurality of light-emitting modules.
  • the method for man ⁇ ufacturing a light-emitting module is utilized in a method for manufacturing a light source assembly, the latter method comprising manufacturing, according to the above-described method for manufacturing a light- emitting module, a plurality of light-emitting mod ⁇ ules, wherein the plurality of light-emitting modules are manufactured so that the substrate plates of the light-emitting modules form a single common substrate plate .
  • a light source assembly compris- ing a plurality of light-emitting modules is fabricat ⁇ ed as an integrated structure.
  • the size and thus the light output power of the assembly can be easily ad ⁇ justed by the number of the individual light-emitting modules therein.
  • the assembly can be formed as a large panel on a large ceramic plate serving as the common substrate plate, which panel can then be separated into several discrete light source elements.
  • the exposed regions of the substrate plates of the individual light-emitting modules, above which the encapsulating material has been removed or above which no encapsulating material has been initially de ⁇ posited can, for example, form channels through the encapsulating layer between the modules. These channels free of the encapsulating material enable sepa- rating the assembly into discrete light source ele ⁇ ments without destroying or anyway negatively affect ⁇ ing the encapsulating layer.
  • depositing the encapsulating material as a continuous layer over the entire (common) substrate plate allows for significant reduction of the silicone layer thickness variation, which improves the quality of the light-emitting modules.
  • the silicone layer contains phosphor and thus serves as wavelength conversion layer, a more uniform thickness of such conversion layer results in more uniform emission wavelength over the area of the module and, in the case of a light source element with several such modules, over the overall element.
  • the method for manufacturing a light source assembly preferably further comprises forming weakening scrib ⁇ ing in the common substrate plate for facilitating separation of the assembly into discrete light source elements each comprising one or more light-emitting modules.
  • These scribing may be formed by any known means and in any form suitable for mechanically weak ⁇ ening the common substrate plate between the light- emitting modules, so that the separation into discrete light source modules is facilitated.
  • the substrate plates of two adjacent light- emitting modules are preferably provided so that the metal platings thereof form a contact element electri ⁇ cally connecting together the two adjacent light- emitting modules.
  • the contact element preferably has a thick ⁇ ness in the range of 10 to 40 ym.
  • clutches can be used to hold the COB module and, at the same time, to provide elec ⁇ trical contacts to the light-emitting module.
  • the clutches can be designed in the way that they can be used for all versions and sizes of modules fabricated with described method.
  • FIG. 1 shows a schematic cross-section of a typical prior art LED-based COB light-emitting module
  • Figure 2 represents schematically a part of the cross- section of a COB light-emitting module according to the present invention
  • Figure 3 illustrates the basic stages of the manufac ⁇ turing methods according to the present invention
  • Figure 4 shows examples of COB light source elements fabricated according to the present invention
  • Figure 5 shows one example of a light-emitting module according to the present invention
  • Figure 6 illustrates one manufacturing method accord ⁇ ing to the present invention
  • Figure 7 shows an example of implementation of the ex- ternal electrical connections of a light source ele ⁇ ment according to the present invention.
  • Figure 8 shows yet another possible light source ele ⁇ ment according to the present invention.
  • the prior art light-emitting module 10 of Figure 1 is fabricated on a substrate plate 1.
  • a metal plating 2 forming the contact pads 2a as well as the internal electrical connections in the form of conductor wir ⁇ ings 2b is arranged on the substrate plate by using a screen printing or a plating/lithography process.
  • LED chips 3 are placed and attached by gluing on the sub ⁇ strate plate and electrically connected to each other as well as to the metal plating by wire bonding 4.
  • the LED chips are encapsulated within a silicone layer 5 deposited on the substrate plate. In the lateral di ⁇ rection, i.e. in the direction in which the plane of the substrate extends, the silicone is confined by mold frames 6 mounted on the substrate plate surround ⁇ ing the LED chips .
  • the LED-based light-emitting module 10 shown in Figure 2, comprises a ce ⁇ ramic substrate plate 1, a metal plating 2, 2a, 2b, and LED chips 3 which are similar to those of the mod- ule of Figure 1. It also has a silicone encapsulating layer 5 encapsulating all of the LED chips.
  • the chips 3 have been electrically connected to the conductor wirings 2b of the metal plating 2 directly by solder ⁇ ing. Alternatively, bonding wirings similar to those of Figure 1 could be used.
  • the thickness of the ceram ⁇ ic substrate plate may vary from 0.2 to 2 mm, typical ⁇ ly from 0.5 to 1 mm.
  • the substrate plates 1 of the light- emitting modules are integrated parts of this common substrate plate.
  • the metal plating is made of Cu .
  • the contact interface of the wirings 2a is finalized by depositing, on top of the Cu metallization, another kind of metallization, which ensures best electrical contact.
  • This additional met- allization can be implemented as a layered structure of, for example, Ni/Pd/Au, Ag, Al, Ni/Pd, Ni/Au, or Ni/Ag.
  • the layout of the metal plating 2 is implement ⁇ ed in such a way, that later separation of the assembly 9 into groups of light-emitting modules is possi- ble.
  • Each light-emitting module 10 of the assembly 9 shown in Figure 3 has a rectangular geometry with a size of 10 mm x 10 mm.
  • the assembly could comprise an arbitrary number of light-emitting modules, and its size will be defined only by the size of the ceramic wafer used as substrate.
  • LED semiconductor chips 3 are placed on the common substrate plate 11.
  • an InGaN-based semiconductor chip with linear dimensions 640 ym ⁇ 1135 ym, thickness 100 ym and output power 0.6 watts can be used.
  • Any known technology for placing the LED chips 3 on the ceramic substrate can be used for this purpose, for example, gluing with any already known LED die attach glue or soldering of chips.
  • reflow soldering of chips can be applied in combination with silicone cover of the chips, provided that the assembly or a light source element cut therefrom is not used as an SMT de ⁇ vice and needs no additional reflow process steps to ensure stable chip solder connection.
  • elec ⁇ trical connections between individual chips and to the metal plating formed on the substrate are fabricated. This can be done with any standard technique suitable for this purpose, for example, with bonding wire with the diameter of 20 to 200 ym (20 to 50 ym for Au wire, 30 to 200ym Al wire) .
  • electrical con ⁇ nections can be provided directly to the wirings 2b of the metal plating 2, as shown in Figure 2, using soldering procedure when placing the chips on the sub ⁇ strate .
  • a silicone layer 5 covering the common substrate plate 11 is formed on the LED module by dispensing (drawing 3B) .
  • Silicone film transparent or filled with phosphor for light-conversion
  • an InGaN-based LED chip mentioned above emits light with peak wavelength of 440 to 470nm, and if a clear transparent silicone lay ⁇ er is used, the COB module will emit light with the same peak wavelength. If a wavelength converting phosphor, for example, YAG, nitride, or silicate, is con ⁇ tained in the silicone layer, the COB module will emit white light.
  • the silicone with or without phos ⁇ phor is deposited uniformly over the whole surface of the assembly 9, i.e. so that it covers all light- emitting modules 10 thereof.
  • such sili ⁇ cone deposition technique allows for significant re- duction of the silicone layer thickness variation, which improves the quality of the light-emitting mod ⁇ ule .
  • Step of the manufacturing process is opening of the silicone layer 5 so that silicone-free channels where the common substrate plate 11 is exposed to the free ambient space are formed. These channels also comprise wider openings through the silicone making the contact pads 2a of the light-emitting modules 10 accessible. This step is illustrated in drawing 3C.
  • Said opening of the silicone can be done, for example by using a CO 2 laser.
  • a CO 2 laser has working wave ⁇ length of about 10 ym (9.4 ym up to 10.6 ym) , which corresponds to the long-wavelength infrared range.
  • Light with such wavelengths is effectively absorbed by silicone, which leads to evaporation of the latter, so that said channels and the openings for the pads are formed.
  • the light emitted by the CO 2 laser is effectively reflected by metals, such as Au or other metals used for forming top metallic layers of electrical contacts, so the laser radiation does not damage the contact pads.
  • the laser used for fabri ⁇ cation of the COB module according to the present in- vention may have output power of 5 to 150 Watts.
  • cleaning procedure may be performed to achieve pure and clean metallic sur ⁇ face for the wire-bonds.
  • cleaning procedure may be performed using standard dry surface cleaning pro- cess, e.g., a CF4 RF-plasma etching process. This kind of treatment also removes a nanometer-thick layer from Au surface, which ensures effective bonding of contact wires and provides the electrical contact with very low resistivity.
  • Irregular roughening or some more regular structuring can be formed on the outer surface 12 of the silicone layer 5 in order to enhance the light extraction from the light-emitting modules 10.
  • the assembly as illustrated in drawing 3C can be used as such a light source element.
  • it can be used as a light source element preform from which light source elements with desired size, i.e. with desired number of light-emitting modules are separated by cutting, cracking, or breaking off in some other way.
  • the contact pads 2a of the adjacent mod- ules can be connected together by wire bonding so that the all modules belonging to a same light source ele ⁇ ment are electrically connected together.
  • Drawings 3D, 3E, and 3F show, for illustrating, a sin- gle light-emitting module 10 of the light source as ⁇ sembly 9 of drawings 3A, 3B, and 3C at different stag ⁇ es of the manufacturing process.
  • the module comprises only a plain substrate with the metal plating.
  • LED chips 3 have been mounted on the substrate plate, each of them having been elec ⁇ trically connected to the wiring 2b by wire bonding.
  • Drawing 3F shows a completed module with the silicone layer 5 patterned to expose the edge region of the substrate plate as well as the contact pads 2a of the module.
  • Figure 4 shows examples of COB light source elements 14 fabricated according to the present invention, i.e. by first producing a large light source assembly comprising a plurality of light-emitting modules, and then separating the light source elements from the assembly.
  • Drawing 4A shows a light source element comprising nine light-emitting modules 10 each having a size of 10 mm ⁇ 10 mm. Each module has nine LED chips 3.
  • Drawing 4B illustrates a triple-sized element with two light-emitting modules, thus having tripled total length and power consumption of the element.
  • Drawings 4C, 4D, and 4E show further examples with 1, 1, and 4 light-emitting modules in the light source element, respectively.
  • Figure 4 il- lustrates the principle of the present invention ac ⁇ cording to which manufacturing of a light source element 14 of any size is straightforward by just select ⁇ ing the number of single light-emitting modules included therein.
  • the encapsulating layer 5 has been opened at the locations of two contact pads of the element only and no channel through the encapsulating layer has been opened be- tween the individual light-emitting modules of a sin ⁇ gle light source element.
  • the contact pads of the ad ⁇ jacent light-emitting modules form contact elements (not visible in the drawings) in the metal plating, thereby electrically connecting together all the light-emitting modules of the light source element.
  • Figure 5 shows one pos ⁇ sible layout of the metal plating 2 and overall geome ⁇ try of a light-emitting module 10 according to the present invention.
  • the ceramic substrate in this case has a thickness of 0.7 mm, and has lateral dimensions of 10 mm x 10 mm.
  • the con- tact pads 2a at the corners of the module extend until to the edge of the module.
  • Drawing 5B shows a light-emitting module 10 with the layout of drawing 5A at the stage of manufacturing af ⁇ ter placing the semiconductor chips 3 on the substrate plate.
  • Drawing 5C shows the same module after deposit ⁇ ing the encapsulating layer 5 and forming openings therein to expose the contact pads 2a.
  • the above-described laser technique is only one option for forming the openings, and any other suitable technique can also be used, such as simple mechanical removal process by knife elements, etc.
  • compression molding can be used to form the encapsulating layer.
  • a mold tool can be used which forms the shape of the encapsulating layer so as to leave the contact pads 2a exposed.
  • the light-emitting module of Figure 5 comprises nine LED chips 3. If the InGaN-based LED chips mentioned above are used, such a nine-chip COB light-emitting module would typically consume about 6 Watts, and would have an efficiency of more than 100 lumens per Watt. However, one skilled in the art would easily adapt this construction to any other LED chip type, so the power consumed and output light power and effi- ciency will be defined by the actual LED chips used. As illustrated in drawing 5c, the LED chips 3 have been connected to the each other and to the metal plating 2 via wire bonding 4.
  • Figure 6 illustrates forming a silicone encapsulating layer 5 of a light-emitting module 10 using compression molding. Molding is performed using a molding machine 16. There is no casting barrier mounted on the substrate plate 1, and the encapsulating layer 5 is formed uniformly over the whole surface of the sub- strate plate.
  • a flat mold tool can be used to form a flat surface of the silicone. Also a mold tool can be used which provides a certain pattern on the outer surface 12 of silicone. It is important that during forming the encapsulating layer 5, the encapsulating material is dispensed over the whole area of the sub ⁇ strate plate, that is, over all light-emitting semiconductor chips (not shown in the drawing) thereon.
  • Figure 7 presents an example of electrical connections to a COB light-emitting module 10 fabricated according to the present invention.
  • the electrical connections are implemented without soldering technique.
  • simple metal clutches 15 with a spring element shown in Figure 7 as an upside down triangle
  • a spring element shown in Figure 7 as an upside down triangle
  • the light source element 14 of Figure 8 illustrates yet an alternative layout for the light-emitting mod ⁇ ules 10 according to the present invention.
  • the light source element has four light-emitting modules in a 2 x 2 array. As one essential feature, the adjacent light-emitting modules are connected together via connecting elements 13 formed by the metal plating 2.

Abstract

A light-emitting module (10) of the present invention comprises a substrate plate (1) formed of a ceramic material and having a patterned metal plating (2, 2a, 2b) thereon for providing an electrical interface of the light-emitting module and internal electrical connections within the light-emitting module, and a plurality of light-emitting semiconductor chips (3) placed on the substrate plate and electrically connected to the metal plating, each of the light- emitting semiconductor chips being encapsulated within an encapsulating material (5). According to the present invention, the encapsulating material forms a single continuous encapsulating layer (5) on the substrate plate (1), the encapsulating layer being confined in the lateral direction to the free ambient space (8).

Description

LIGHT-EMITTING MODULE, LIGHT SOURCE ASSEMBLY, AND METHODS FOR MANUFACTURING
FIELD OF THE INVENTION
The present invention relates generally to light sources based on light-emitting semiconductor elements such as the different variations of light emitting di¬ odes LEDs . More particularly, the present invention relates to light-emitting modules and light source el- ements having multiple primary light emitting ele¬ ments, e.g. LED chips, arranged on a substrate. Typi¬ cally, these kinds of modules are called chip-on-board (COB) light-emitting modules or light source elements. The present invention also relates to manufacturing of such modules and elements.
BACKGROUND OF THE INVENTION
In the core of any light source, such as an indoor lu¬ minary or, for example, a headlight of a vehicle, there is a primary light generating/emitting component. Nowadays, semiconductor light emitting elements like LEDs more and more often replace the convention¬ ally used incandescent and gas-discharge lamps as the primary light emitting component. Semiconductor light emitting components provide many superior characteris¬ tics, for example, long-term stability, high power ef¬ ficiency, and compact size of the single element.
There is currently a great variety of different LED- based solutions commercially available for different applications. However, using a single LED as a light source in a luminary, e.g., for general lighting, is often practically impossible, as a typical LED repre¬ sents a point light source. To produce evenly distrib- uted light, which is required in many applications, either special reflectors, which redistribute light from the point source, thus transforming it into a beam with desired properties, are used, or an array of multiple LEDs is formed. While the former solution can be used in luminaries, whose size and weight is not limited very strictly (e.g., in street lamps), whenev¬ er 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 (a LED module) is the most practical choice.
An array of LEDs can be generally formed in two alter¬ native ways: either through combining a number of individual LEDs, each of them being a finished device, i.e., having its own substrate, electrical connec- tions, 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 lat¬ ter solution is commonly known in the LED industry as a "chip-on-board" (COB) module.
Commonly, a LED-based COB module is made of a number of LED components produced as separate chips and then placed on a common substrate with necessary electrical connections. An example is shown in figure 1.
For example, US Patent 8,022,626 describes various em- bodiments of "A lighting module comprising a base pan¬ el and a plurality of light-emitting diode (LED) chips attached directly to the base panel", where "the LED chips are in electrical communication with conductive traces on the base panel, which deliver a current to the LED chips". US Patent 8,044,570 describes a typical example of the current common approach to the design of LED-based light source modules (COBs) . It discloses a light source module, which "includes a printed wiring board, a plurality of light-emitting elements, a sealing member, and a color conversion unit, and an adhesive lay¬ er". The sealing member described in U.S. patent 8,044,570, has light transmitting properties and seals the light emitting elements mounted on the printed wiring board. The color conversion unit includes a cover member with light transmitting properties, and a layer of a fluorescent substance provided on the inner surface of the cover member. The adhesive layer has light-transmitting properties, and ensures adhesion of the sealing member to the fluorescent substance layer of the color conversion unit in an airtight manner.
UK Patent GB 2458972 describes a LED (COB) module, which "comprises a plurality of LED die arranged on a substrate in one or more radially concentric rings about a centre point such that each LED die is azi- muthally offset from neighboring LED die". The module includes thermal conduction pads each having lateral dimensions at least as large as the combined lateral dimensions of the LED die attached to it and a total surface area at least five times larger than the total surface area of all the LED die attached to it. At the same time, the total light emission area of the module is no greater than four times larger than the combined total surface emission area of all individual LED dies disposed on the substrate. A variety of configurations are possible subject to these criteria, which permit good packing density for enhanced brightness whilst ensuring optimal heat transfer. A method for manufac- turing the module is also disclosed in the document. In the prior art COB module solutions such as those examples described above, most of the key parameters of the COB module, such as the number of the single LEDs and thus the output light power, and the overall module size, are defined at the design stage and can¬ not be changed or modified afterwards once the manu¬ facturing process has started. Should the desired pa¬ rameters of the COB module (such as output power, or just element size) change, the whole COB module has to be re-designed, and the manufacturing process has to be adapted accordingly. This makes the production of COB modules and light source elements inflexible, in¬ creasing the time required for changing the module type and raising the production costs of the module.
PURPOSE OF THE INVENTION
The purpose of the present invention is to provide a chip-on-board type light-emitting module, a light source assembly, as well as methods for manufacturing the same, alleviating the problems of the prior art.
SUMMARY OF THE INVENTION
The light-emitting module and a light source assembly of the present invention are characterized by what is specified in claims 1 and 3, respectively. The methods for manufacturing those items are characterized by what is presented in claim 7 and 9, respectively.
The light-emitting module of the present invention comprises a substrate plate formed of a ceramic mate¬ rial and having a patterned metal plating thereon for providing an electrical interface of the light- emitting module and internal electrical connections within the module, and a plurality of light-emitting semiconductor chips placed on the substrate plate and electrically connected to the metal plating, for exam- pie, via wire bonding or via soldered connections, each of the light-emitting semiconductor chips being encapsulated within an encapsulating material. The ceramic substrate plate forms the basic supporting body of the module. Ceramic substrate plates are com¬ mercially available, and they can be produced using materials and technologies as such known in the art. Any known ceramic material, preferably enabling a highly reflective upper surface of the substrate plate for optimizing the light extraction from the module, can be used. Moreover, the ceramic substrate should also preferably possess high thermal conductivity for dissipating excessive heat during the operation of the light-emitting module. Suitable examples are an AI2O3 wafer with thickness, for example, of 0.2 to 2 mm, or an A1N wafer with similar thickness.
Also the metal plating, i.e., a patterned metal layer on the substrate plate, providing an electrical con¬ tact interface for the module and also the internal electrical connections within the module can be formed according to the principles known in the art. The met¬ al 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 can be connected to the metal plating, for example, by wire bonding.
One suitable material for the metal plating is copper Cu . To optimize the electrical contact between the metal plating and the light-emitting semiconductor chips, another single or multi-layered metallization formed of, for example, Ni/Pd/Au, Ag, Al, Ni/Pd, Ni/Au, Ni/Ag, may be formed on the Cu layer for ensur¬ ing an optimal electrical contact.
The metal plating forming the wiring layout of the substrate plate is preferably formed so that all the light-emitting semiconductor chips of the module can be supplied via one pair of contact pads or contact electrodes only. The light-emitting semiconductor chips can be, for example, those used for light-emitting diodes LEDs of any known type(s) . However, the present invention is not restricted to any particular type of the light- emitting semiconductor chips. The chips can be at- tached to the substrate plate by any means known in the art .
The encapsulating material can be any known material suitable for encapsulating light-emitting semiconduc- tor chips, thereby protecting them against the effects of the possibly harmful substances and moisture pre¬ sent in the environment surrounding the light-emitting module. The encapsulating material can also comprise one or more phosphor-based compounds for converting the wavelength of the light initially emitted by the light-emitting semiconductor chips according to the desired output spectrum of the module. The most common group of such encapsulating materials is formed by silicones. Those silicones can be applied in a sub- stantially liquid form and cured thereafter. The key attributes of silicones that make them attractive ma¬ terials particularly for high-brightness (HB) LEDs and modules include their high transparency in the UV- visible region, controlled refractive index (RI), and stable thermo-opto-mechanical properties. According to the present invention, the encapsulating material forms a single continuous encapsulating layer on the substrate plate, the encapsulating layer being confined in the lateral direction, i.e. in the direc- tion of the plane of the substrate plane, to the free ambient space.
In other words, the light-emitting module is charac¬ terized by that the lateral extent of the encapsulat- ing material is not limited or restricted by any me¬ chanical casting barrier or other type of mold struc¬ ture defining, in the lateral direction, the volume in which the silicone, when applied in substantially liq¬ uid form on the substrate plate, is confined. No such structures are present in the module of the present invention but, instead, also in the lateral direction, the encapsulating material is confined to the free am¬ bient space. Forming of such encapsulating layer is discussed later in this document with regard to the method aspect of the present invention.
This basic principle of the present invention provides great advantages. First, the present invention simpli¬ fies the basic construction of the COB type light- emitting module in that no casting mold structures mounted on the substrate plate are needed. Further, perhaps the most important advantages are related to the manufacturing of light source elements based on light-emitting semiconductor chips as the primary light emitting components. Light-emitting modules ac¬ cording to the present invention allow easy and straightforward way of manufacturing light source ele¬ ments. In this kind of light source element, several light-emitting modules together form a larger light source element. Thus, the light-emitting modules are used as modular building blocks repeated in the light source element. This kind of modular construction of the light source element enables a straightforward and cost-efficient way to implement light source elements of different sizes and with different amounts of sin¬ gle light-emitting semiconductor chips therein. Thus, the optical power as well as the light distribution pattern of the light source element can be adjusted by just selecting the number of single light-emitting modules in the light source element. The key feature of the light-emitting module enabling such straightforward manufacturing of light source el¬ ements is the encapsulating layer being confined in the lateral direction to the free ambient space, i.e. without being limited by any casting mold structure. A light source assembly in the form of a large panel of repeated light-emitting modules can be fabricated on a common substrate plate. When the individual light- emitting modules comprise no casting molds or other mechanical casting barriers, light source elements with any desired number of light-emitting modules can then be cut or broken off from the panel at any stage after the actual manufacturing process has finished. Thus, different needs for different light source ap¬ plications can be easily met by using such modular panel as a light source preform.
In a preferable embodiment, the outer surface of the silicone, i.e. the surface facing away from the sub¬ strate plate to the free ambient space and thus form- ing the optical interface between the light-emitting module and the surroundings thereof, is structured for enhancing the light extraction from the light-emitting module. By said structuring is meant here any roughening, patterning, or other structuring of the outer surface so that escaping of light emitted by the light-emitting semiconductor chips from the volume defined by the substrate plate surface and said outer surface is enhanced. Enhancing the light extraction can be based, for example, on reflection, refraction, or diffraction of light. According to one aspect of the present invention, the advantages of the present invention are particularly clear in a light source assembly comprising a plurali¬ ty of light-emitting modules as described above, wherein the substrate plates of the light-emitting modules form a single common substrate plate.
By single common substrate is meant that the substrate plates of the single light-emitting modules form one integrated ceramic substrate plate. This kind of as- sembly can be formed as a large panel serving as a preform from which light source elements with arbi¬ trary number of light-emitting modules can be cut or broken off. On the other hand, such an assembly can also be a complete light source element with the de- sired number of light-emitting modules. Thus, word "assembly" refers in this document both to a preform- like construction and to a finalized light source ele¬ ment . To facilitate the cutting or breaking off in another way of the light source assembly, the common substrate plate has preferably weakening scribing for facilitat¬ ing separation of the assembly into discrete light source elements each comprising one or more light- emitting modules. The scribing can be implemented, for example, as grooves formed between the adjacent light- emitting modules on the common substrate plates.
The individual light-emitting modules of a light source element are preferably electrically connected together so that in a light source element of any size, i.e. comprising any number of single light- emitting modules, all the light-emitting semiconductor chips can be driven via common contact electrodes. For this purpose, the metal plating comprises preferably a contact element electrically connecting together two adjacent light-emitting modules of the light source assembly. Thus, in this embodiment, at least some, preferably all of the light-emitting modules are con¬ nected to each other according to a predetermined con¬ tact layout.
The presence of the contact elements as part of the metal plating means that when forming a light source element by separating a group of light-emitting modules from a larger assembly, also the contact elements extending over the separation line between adjacent light-emitting modules of different light source ele¬ ments must be disjointed. To facilitate this, without causing damages to the separated elements, the contact element preferably has a thickness in the range of 10 to 40 ym. This has been found as a suitable thickness for many metal plating materials, e.g. Cu .
According to a method aspect, the method of the pre¬ sent invention for manufacturing a light-emitting mod- ule comprises the steps of: providing a substrate plate formed of a ceramic material and having a pat¬ terned metal plating thereon for providing an electrical interface of the light-emitting module and inter¬ nal electrical connections within the module; placing a plurality of light-emitting semiconductor chips on the substrate plate and electrically connecting them to the metal plating; and encapsulating each of the light-emitting semiconductor chips within an encapsulating material.
The step of providing a substrate plate can be imple¬ mented, for example, by taking a commercially availa- ble ceramic wafer of, for example, AI2O3 or A1N and forming then the metal plating on the wafer so as to form the external and internal electrical connections of the module. In forming the metal plating, any suit- able known method, such as screen printing or galvanization, can be used.
The light-emitting semiconductor chips can be of any type, for example, conventional LED chips. The chips can be located and attached on the substrate plate by using known principles, apparatuses, and processes. 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 electrical connection of a single light-emitting semiconductor chip to the metal plating can be formed directly from the chip to the metallization or via another chip. The most appropriate way depends, for ex- ample, on whether the adjacent chips are to be con¬ nected in series or in parallel, and on the location of the chip. Forming the connections can be made, for example, by soldering when placing the chips on the substrate plate, or by wire bonding using any standard bonding wire suitable for this purpose, for example, by a bonding wire with a diameter of 20 to 200 ym (20 to 50ym for Au wire, 30 to 200ym Al wire) .
In the step of encapsulating each of the light- emitting semiconductor chips within an encapsulating material, known silicones can be used as the encapsu¬ lating material. Pure silicone molding or luminophore (phosphor) /silicone molding for white light emitting modules can be used.
According to the present invention, the step of encap¬ sulating each of the light-emitting semiconductor chips within the encapsulating material comprises forming a single continuous encapsulating layer on the substrate plate having the plurality of light emitting semiconductor chips thereon, the encapsulating layer being formed so as to be confined in the lateral di¬ rection to the free ambient space.
Said forming of a single continuous encapsulating lay¬ er can comprise first a step of forming a single con- tinuous encapsulating layer on the substrate plate having the plurality of light emitting semiconductor chips thereon, and then a step of exposing the sub¬ strate plate by removing the encapsulating layer in a region surrounding the plurality of light-emitting semiconductor chips so as to make the encapsulating layer confined in the lateral direction to the free ambient space. Thus, instead of dispensing or other¬ wise arranging separate encapsulation for each light- emitting semiconductor chip, one single continuous layer of the encapsulating material is formed over the entire module so that the layer encapsulates the all chips. Then, the encapsulating material is removed and thus the substrate plate exposed in a region surround¬ ing the plurality of light-emitting semiconductor chips. This region can be a narrow region along a peripheral line on the substrate plate enclosing each of the light-emitting semiconductor chips. Removing of the encapsulating region can be accomplished accurate¬ ly and rapidly, for example, by means of a laser beam evaporating the encapsulating material.
Alternatively, said forming of a single continuous en¬ capsulating layer can comprise forming the layer using a compression molding process where the volume of the encapsulating material, i.e. the encapsulating layer shape and dimensions, is defined by a mold placed against the substrate plate during the molding. In both cases described above, it is an essential fea¬ ture of the method according to the present invention that the encapsulating layer is formed so that the completed layer is confined in the lateral direction to the free ambient space.
Performing the encapsulating step as described above makes it unnecessary to use any mold-like structures mounted on the substrate plate for confining the vol¬ ume to be filled by the encapsulating material. This greatly simplifies the manufacturing and lowers the manufacturing costs. Further advantages, as discussed above in the context of the light-emitting module aspect of the present in¬ vention, are achieved when the manufacturing method of the present invention is used to produce larger light source assemblies. This will be discussed more below.
Preferably, the method further comprises structuring the outer surface of the encapsulating layer for enhancing the light extraction from the light-emitting module .
As stated above, the advantages of the method of the present invention are particularly clear when the method is used to produce a larger light source assem¬ bly comprising a plurality of light-emitting modules. Thus, according to another aspect, the method for man¬ ufacturing a light-emitting module is utilized in a method for manufacturing a light source assembly, the latter method comprising manufacturing, according to the above-described method for manufacturing a light- emitting module, a plurality of light-emitting mod¬ ules, wherein the plurality of light-emitting modules are manufactured so that the substrate plates of the light-emitting modules form a single common substrate plate .
Thus, in this method, a light source assembly compris- ing a plurality of light-emitting modules is fabricat¬ ed as an integrated structure. The size and thus the light output power of the assembly can be easily ad¬ justed by the number of the individual light-emitting modules therein. On the other hand, the assembly can be formed as a large panel on a large ceramic plate serving as the common substrate plate, which panel can then be separated into several discrete light source elements. The exposed regions of the substrate plates of the individual light-emitting modules, above which the encapsulating material has been removed or above which no encapsulating material has been initially de¬ posited can, for example, form channels through the encapsulating layer between the modules. These channels free of the encapsulating material enable sepa- rating the assembly into discrete light source ele¬ ments without destroying or anyway negatively affect¬ ing the encapsulating layer.
Particularly in the case of a large light source as- sembly but also in the case of a single light-emitting module, depositing the encapsulating material as a continuous layer over the entire (common) substrate plate allows for significant reduction of the silicone layer thickness variation, which improves the quality of the light-emitting modules. For example, if the silicone layer contains phosphor and thus serves as wavelength conversion layer, a more uniform thickness of such conversion layer results in more uniform emission wavelength over the area of the module and, in the case of a light source element with several such modules, over the overall element. The method for manufacturing a light source assembly preferably further comprises forming weakening scrib¬ ing in the common substrate plate for facilitating separation of the assembly into discrete light source elements each comprising one or more light-emitting modules. These scribing may be formed by any known means and in any form suitable for mechanically weak¬ ening the common substrate plate between the light- emitting modules, so that the separation into discrete light source modules is facilitated.
In the method for manufacturing a light source assembly, the substrate plates of two adjacent light- emitting modules are preferably provided so that the metal platings thereof form a contact element electri¬ cally connecting together the two adjacent light- emitting modules. To facilitate the separation of such modules, the contact element preferably has a thick¬ ness in the range of 10 to 40 ym.
As a further preferable feature of the present inven¬ tion, special metallic clutches can be used to hold the COB module and, at the same time, to provide elec¬ trical contacts to the light-emitting module. The clutches can be designed in the way that they can be used for all versions and sizes of modules fabricated with described method.
It is to be noted that in the above description, what is stated about the definitions, preferable embodi¬ ments, and the advantages of the light-emitting module and light source assembly aspects of the present in¬ vention apply, mutatis mutandis, to those of the meth¬ od aspects of the present invention. The same applies vice versa.
BRIEF DESCRIPTION OF THE FIGURES The present invention is described in more detail in the following with reference to the accompanying Figures, wherein Figure 1 shows a schematic cross-section of a typical prior art LED-based COB light-emitting module;
Figure 2 represents schematically a part of the cross- section of a COB light-emitting module according to the present invention;
Figure 3 illustrates the basic stages of the manufac¬ turing methods according to the present invention; Figure 4 shows examples of COB light source elements fabricated according to the present invention;
Figure 5 shows one example of a light-emitting module according to the present invention;
Figure 6 illustrates one manufacturing method accord¬ ing to the present invention;
Figure 7 shows an example of implementation of the ex- ternal electrical connections of a light source ele¬ ment according to the present invention; and
Figure 8 shows yet another possible light source ele¬ ment according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The prior art light-emitting module 10 of Figure 1 is fabricated on a substrate plate 1. A metal plating 2 forming the contact pads 2a as well as the internal electrical connections in the form of conductor wir¬ ings 2b is arranged on the substrate plate by using a screen printing or a plating/lithography process. LED chips 3 are placed and attached by gluing on the sub¬ strate plate and electrically connected to each other as well as to the metal plating by wire bonding 4. The LED chips are encapsulated within a silicone layer 5 deposited on the substrate plate. In the lateral di¬ rection, i.e. in the direction in which the plane of the substrate extends, the silicone is confined by mold frames 6 mounted on the substrate plate surround¬ ing the LED chips .
The LED-based light-emitting module 10 according to present invention, shown in Figure 2, comprises a ce¬ ramic substrate plate 1, a metal plating 2, 2a, 2b, and LED chips 3 which are similar to those of the mod- ule of Figure 1. It also has a silicone encapsulating layer 5 encapsulating all of the LED chips. The chips 3 have been electrically connected to the conductor wirings 2b of the metal plating 2 directly by solder¬ ing. Alternatively, bonding wirings similar to those of Figure 1 could be used. The thickness of the ceram¬ ic substrate plate may vary from 0.2 to 2 mm, typical¬ ly from 0.5 to 1 mm.
There is an essential difference between the modules of Figure 1 and 2 in the construction of the silicone encapsulating layer 5. In Figure 2, no mold frame or any similar structure is mounted on the substrate plate 1. Instead, the side surfaces 7 of this layer are in direct contact with the free ambient space 8 surrounding the module. In other words, in the lateral direction, the silicone encapsulating layer 5 is confined to the free ambient space without any mechanical structures . In the process illustrated in Figure 3 (comprising drawings 3A to 3F) , a light source assembly 9 compris¬ ing nine light-emitting modules 10 is fabricated. First, as shown in drawing 3A, a metal plating 2 forming the contact pads 2a as well as the internal con¬ nection wirings 2b of each of the modules is formed, e.g. by screen printing or galvanization, on a ceramic wafer 11 serving as a common substrate plate of the modules 10. Thus, the substrate plates 1 of the light- emitting modules are integrated parts of this common substrate plate. In the example of Figure 3, the metal plating is made of Cu . To optimize the electrical con- tact to the LED chips 3 (the chips being shown in drawings 3E and 3F only) , the contact interface of the wirings 2a is finalized by depositing, on top of the Cu metallization, another kind of metallization, which ensures best electrical contact. This additional met- allization can be implemented as a layered structure of, for example, Ni/Pd/Au, Ag, Al, Ni/Pd, Ni/Au, or Ni/Ag. The layout of the metal plating 2 is implement¬ ed in such a way, that later separation of the assembly 9 into groups of light-emitting modules is possi- ble.
Each light-emitting module 10 of the assembly 9 shown in Figure 3 has a rectangular geometry with a size of 10 mm x 10 mm. Generally, the assembly could comprise an arbitrary number of light-emitting modules, and its size will be defined only by the size of the ceramic wafer used as substrate.
As the next step of the process, LED semiconductor chips 3 are placed on the common substrate plate 11. Just as one example, an InGaN-based semiconductor chip with linear dimensions 640 ym χ 1135 ym, thickness 100 ym and output power 0.6 watts can be used. Any known technology for placing the LED chips 3 on the ceramic substrate can be used for this purpose, for example, gluing with any already known LED die attach glue or soldering of chips. For example, reflow soldering of chips can be applied in combination with silicone cover of the chips, provided that the assembly or a light source element cut therefrom is not used as an SMT de¬ vice and needs no additional reflow process steps to ensure stable chip solder connection.
After attaching the LED chips on the substrate, elec¬ trical connections between individual chips and to the metal plating formed on the substrate are fabricated. This can be done with any standard technique suitable for this purpose, for example, with bonding wire with the diameter of 20 to 200 ym (20 to 50 ym for Au wire, 30 to 200ym Al wire) . Alternatively, electrical con¬ nections can be provided directly to the wirings 2b of the metal plating 2, as shown in Figure 2, using soldering procedure when placing the chips on the sub¬ strate .
Then, a silicone layer 5 covering the common substrate plate 11 is formed on the LED module by dispensing (drawing 3B) . Silicone film (transparent or filled with phosphor for light-conversion) is placed over the whole LED module. For example, an InGaN-based LED chip mentioned above emits light with peak wavelength of 440 to 470nm, and if a clear transparent silicone lay¬ er is used, the COB module will emit light with the same peak wavelength. If a wavelength converting phosphor, for example, YAG, nitride, or silicate, is con¬ tained in the silicone layer, the COB module will emit white light.
It is important to emphasize that, according to the present invention, the silicone with or without phos¬ phor is deposited uniformly over the whole surface of the assembly 9, i.e. so that it covers all light- emitting modules 10 thereof. This makes it unnecessary to use specially patterned molding forms to form indi- vidual encapsulations over every single light-emitting module or light source element, and thus greatly re¬ duces the cost of the COB production. Also, such sili¬ cone deposition technique allows for significant re- duction of the silicone layer thickness variation, which improves the quality of the light-emitting mod¬ ule .
Next step of the manufacturing process is opening of the silicone layer 5 so that silicone-free channels where the common substrate plate 11 is exposed to the free ambient space are formed. These channels also comprise wider openings through the silicone making the contact pads 2a of the light-emitting modules 10 accessible. This step is illustrated in drawing 3C.
Said opening of the silicone can be done, for example by using a CO2 laser. Such laser has working wave¬ length of about 10 ym (9.4 ym up to 10.6 ym) , which corresponds to the long-wavelength infrared range. Light with such wavelengths is effectively absorbed by silicone, which leads to evaporation of the latter, so that said channels and the openings for the pads are formed. At the same time, the light emitted by the CO2 laser is effectively reflected by metals, such as Au or other metals used for forming top metallic layers of electrical contacts, so the laser radiation does not damage the contact pads. The laser used for fabri¬ cation of the COB module according to the present in- vention, may have output power of 5 to 150 Watts.
For better electrical contact for the wire bonding, clean surface of the contact pads is required, so af¬ ter the laser process, special cleaning procedure may be performed to achieve pure and clean metallic sur¬ face for the wire-bonds. Such cleaning procedure may be performed using standard dry surface cleaning pro- cess, e.g., a CF4 RF-plasma etching process. This kind of treatment also removes a nanometer-thick layer from Au surface, which ensures effective bonding of contact wires and provides the electrical contact with very low resistivity.
Irregular roughening or some more regular structuring can be formed on the outer surface 12 of the silicone layer 5 in order to enhance the light extraction from the light-emitting modules 10.
After the actual manufacturing process, the assembly as illustrated in drawing 3C can be used as such a light source element. Alternatively, it can be used as a light source element preform from which light source elements with desired size, i.e. with desired number of light-emitting modules are separated by cutting, cracking, or breaking off in some other way. In both alternatives, the contact pads 2a of the adjacent mod- ules can be connected together by wire bonding so that the all modules belonging to a same light source ele¬ ment are electrically connected together.
Drawings 3D, 3E, and 3F show, for illustrating, a sin- gle light-emitting module 10 of the light source as¬ sembly 9 of drawings 3A, 3B, and 3C at different stag¬ es of the manufacturing process. In drawing 3D, the module comprises only a plain substrate with the metal plating. In drawing 3E, LED chips 3 have been mounted on the substrate plate, each of them having been elec¬ trically connected to the wiring 2b by wire bonding. Drawing 3F shows a completed module with the silicone layer 5 patterned to expose the edge region of the substrate plate as well as the contact pads 2a of the module. Figure 4 (comprising drawings 4A to 4E) shows examples of COB light source elements 14 fabricated according to the present invention, i.e. by first producing a large light source assembly comprising a plurality of light-emitting modules, and then separating the light source elements from the assembly. Drawing 4A shows a light source element comprising nine light-emitting modules 10 each having a size of 10 mm χ 10 mm. Each module has nine LED chips 3. Drawing 4B illustrates a triple-sized element with two light-emitting modules, thus having tripled total length and power consumption of the element. Drawings 4C, 4D, and 4E show further examples with 1, 1, and 4 light-emitting modules in the light source element, respectively. Figure 4 il- lustrates the principle of the present invention ac¬ cording to which manufacturing of a light source element 14 of any size is straightforward by just select¬ ing the number of single light-emitting modules included therein.
In the light source elements of drawings 4A to 4E, the encapsulating layer 5 has been opened at the locations of two contact pads of the element only and no channel through the encapsulating layer has been opened be- tween the individual light-emitting modules of a sin¬ gle light source element. The contact pads of the ad¬ jacent light-emitting modules form contact elements (not visible in the drawings) in the metal plating, thereby electrically connecting together all the light-emitting modules of the light source element.
Figure 5 (comprising drawings 5A to 5C) shows one pos¬ sible layout of the metal plating 2 and overall geome¬ try of a light-emitting module 10 according to the present invention. The ceramic substrate in this case has a thickness of 0.7 mm, and has lateral dimensions of 10 mm x 10 mm. In the layout of Figure 5, the con- tact pads 2a at the corners of the module extend until to the edge of the module. Thus, when a light source assembly comprising a plurality of light-emitting mod¬ ules is fabricated, the contact pads of adjacent mod- ules form a continuous metal structure, i.e. a contact element 13 electrically connecting together the two adjacent light-emitting modules.
Drawing 5B shows a light-emitting module 10 with the layout of drawing 5A at the stage of manufacturing af¬ ter placing the semiconductor chips 3 on the substrate plate. Drawing 5C shows the same module after deposit¬ ing the encapsulating layer 5 and forming openings therein to expose the contact pads 2a. It is important to note that the above-described laser technique is only one option for forming the openings, and any other suitable technique can also be used, such as simple mechanical removal process by knife elements, etc. As an alternative to first depositing the layer over the entire substrate plate and then forming the openings afterwards, compression molding can be used to form the encapsulating layer. When using compression molding, a mold tool can be used which forms the shape of the encapsulating layer so as to leave the contact pads 2a exposed.
The light-emitting module of Figure 5 comprises nine LED chips 3. If the InGaN-based LED chips mentioned above are used, such a nine-chip COB light-emitting module would typically consume about 6 Watts, and would have an efficiency of more than 100 lumens per Watt. However, one skilled in the art would easily adapt this construction to any other LED chip type, so the power consumed and output light power and effi- ciency will be defined by the actual LED chips used. As illustrated in drawing 5c, the LED chips 3 have been connected to the each other and to the metal plating 2 via wire bonding 4.
Figure 6 illustrates forming a silicone encapsulating layer 5 of a light-emitting module 10 using compression molding. Molding is performed using a molding machine 16. There is no casting barrier mounted on the substrate plate 1, and the encapsulating layer 5 is formed uniformly over the whole surface of the sub- strate plate. A flat mold tool can be used to form a flat surface of the silicone. Also a mold tool can be used which provides a certain pattern on the outer surface 12 of silicone. It is important that during forming the encapsulating layer 5, the encapsulating material is dispensed over the whole area of the sub¬ strate plate, that is, over all light-emitting semiconductor chips (not shown in the drawing) thereon.
Figure 7 presents an example of electrical connections to a COB light-emitting module 10 fabricated according to the present invention. The electrical connections are implemented without soldering technique. In this case, simple metal clutches 15 with a spring element (shown in Figure 7 as an upside down triangle) are used to hold the COB light-emitting module in place and to connect it to the external electrical circuit.
The light source element 14 of Figure 8 illustrates yet an alternative layout for the light-emitting mod¬ ules 10 according to the present invention. The light source element has four light-emitting modules in a 2 x 2 array. As one essential feature, the adjacent light-emitting modules are connected together via connecting elements 13 formed by the metal plating 2.

Claims

1. A light-emitting module (10) comprising:
- a substrate plate (1) formed of a ceramic material and having a patterned metal plating (2, 2a, 2b) thereon for providing an electrical interface of the light-emitting module and internal electrical connections within the light-emitting module; and
- a plurality of light-emitting semiconductor chips (3) placed on the substrate plate and electrically connected to the metal plating, each of the light-emitting semiconductor chips being encapsulated within an encapsu¬ lating material (5) ;
characteri zed in that the encapsulating material forms a single continuous encapsulating layer (5) on the substrate plate (1), the encapsulating layer being confined in the lateral direction to the free ambient space (8) .
2. A light-emitting module (10) as defined in claim 1, wherein the outer surface (12) of the encapsulating layer is structured for enhancing the light extraction from the light-emitting module.
3. A light source assembly (9) comprising a plurality of light-emitting modules (10) according to claim 1 or 2, wherein the substrate plates (1) of the light- emitting modules form a single common substrate plate (11) .
4. A light source assembly (9) as defined in claim 3, wherein the common substrate plate (11) has weakening scribing for facilitating separation of the light source assembly into discrete light source elements (14) each comprising one or more light-emitting modules (10) .
5. A light-emitting assembly (9) as defined in claim 3 or 4, wherein the metal plating (2) comprises a contact element (13) electrically connecting together two adjacent light-emitting modules (10).
6. A light-emitting assembly (9) as defined in claim 5, wherein the contact element (13) has a thickness in the range of 10 to 40 ym.
7. A method for manufacturing a light-emitting module (10), the method comprising the steps of:
- providing a substrate plate (1) formed of a ceramic material and having a patterned metal plating (2, 2a, 2b) thereon for providing an electrical interface of the light-emitting module and internal electrical connections within the light-emitting module;
- placing a plurality of light-emitting semi- conductor chips (3) on the substrate plate and electrically connecting them to the metal plating; and
encapsulating each of the light-emitting semiconductor chips within an encapsulating material (5) ;
characteri zed in that the step of encapsulating each of the light-emitting semiconductor chips within the encapsulating material comprises forming a single continuous encapsulating layer (5) on the substrate plate (1) having the plurality light emitting semicon¬ ductor chips (3) thereon, the encapsulating layer being formed so as to be confined in the lateral direc¬ tion to the free ambient space (8) .
8. A method as defined in claim 7, wherein the method further comprises structuring the outer surface (12) of the encapsulating layer for enhancing the light extraction from the light-emitting module (10) .
9. A method for manufacturing a light source assembly (9), the method comprising manufacturing, according to claim 7 or 8, a plurality of light-emitting modules (10), wherein the plurality of light-emitting modules are manufactured so that the substrate plates (1) of the light-emitting modules form a single common sub- strate plate (11) .
10. A method as defined in claim 9, wherein the method further comprises forming weakening scribing in the common substrate plate (11) for facilitating separa- tion of the light source assembly (9) into discrete light source elements (14) each comprising one or more light-emitting modules (10).
11. A method as defined in any of claims 9 to 10, wherein the substrate plates (1) of two adjacent light-emitting modules (10) are provided so that the metal platings (2) thereof form a contact element (13) electrically connecting together the two adjacent light-emitting modules.
12. A method as defined in claim 11, wherein the contact element (13) have a thickness in the range of 10 to 40 ym.
PCT/EP2013/050387 2012-01-10 2013-01-10 Light-emitting module, light source assembly, and methods for manufacturing WO2013104708A1 (en)

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