Abstract:
Thin, flat solid state light source device and methods for manufacturing is described. LED chips and their circuit boards are mounted on a thermal conductive substrate. The LED chips are surrounded with a flat layer of reflecting material which may embed the circuit boards. The LED chips and the reflecting layer is then topped with a layer of diffusion material and a layer of cover material.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     Priority is claimed from the U.S. Provisional Application 61/270,180 filed on Jul. 6, 2009, entirety of which is hereby incorporated by reference. 
    
    
     BACKGROUND 
     The present application relates to light emitting diode device (LED), and more particularly to thin flat solid state lighting that is cost effective to manufacture, has prolonged life span and better lighting. 
     Note that the points discussed below may reflect the hindsight gained from the disclosed inventions, and are not necessarily admitted to be prior art. 
     Being environment friendly, smaller in sizes, and longer lifetimes, and also having lower power consumption, high efficiency for lighting, less heat radiation, Light emitting diodes (LEDs) lamps have been replacing filament bulbs, halogen or fluorescent lamps for general illumination indoor and outdoors. LED lamps also are especially useful in large screen displays, back light for liquid crystal displays (LCD), the indication lights for electronic apparatus, traffic signal lights, decoration lights or illuminators. 
     To be more robotic and easy to use, LED packages have been developed so that they can be directly plugged into an existing socket intended to receive a conventional filament light bulb. 
     A typical LED package structure is the “spot” type as shown in  FIG. 1 . This package structure includes, from bottom up, a metal substrate-electrical insulator layer or adhesive layer, LED chip layer with reflect cups, electrode layer for wire connection, and a epoxy or silicone gel lens with phosphor layer inside. In  FIG. 1   a , a typical LED package shows to include an LED chip  1 , an adhesive layer  2 , a substrate  3 , an electrode layer  4 , an electrode wire  5 , a base frame  6 , a phosphor layer  7  and transparency lens  8 . 
     Generally, to increase the light output efficiency from LED chip  1 , the back side of substrate  3  may be configured as a heat sink, and the surface of substrate  3  may be configured as a reflective cup, and LED chip  1  is then mounted on substrate  3  by using insulate adhesive gel  2 , which is usually silver paste or transparent insulating paste. LED chip  1  is connected with the electrode layer  4  by Au or Al wire  5 , and the electrode layer  4  and the LED circuit  1  is then set on base frame  6 . 
     A phosphor mixed silicone gel may be used between LED chip  1  and the reflection cup of substrate  3 , forming emission layer  7 . Epoxy or silicone may be injected onto phosphor layer  7  and covers substrate  3 , LED chip  1  and wires  5 , forming optical lens  8 . 
     During the packaging process, insulator material (silver past or transparent insulating paste) as the adhesive layer is dropped onto substrate  3 ; then LED chip  1  is attached on substrate  3  by die bonding. The electrodes  4  in LED PN junction pad and the circuit board are connected by wire bonding. Then transparent epoxy or silicone gel is dropped to the surface of packaged LED unit, forming optical lens  8  on the LED chip surface (encapsulating). Lens  8  conducts light from the chip to the air as well as isolates the chip from the air. In a white LED, a phosphor layer may be coated onto the LED chip surface before the transparency epoxy or silicone lens is formed. 
     This typical LED package structure and packaging process is widely used, and a single LED package can generate 0.05-5 W power depending on the chip size. Many LED units are usually arrayed together on a printed circuit board (PCB) to form a lamp module, and making a lamp, as shown in  FIG. 1   b.    
     The multiple packaged LEDs are mounted to a PCB substrate  9  by a thermal conductive adhesive layer  10 . Due to such “spot” light from each LEDs, the emitted light distribution is not uniform. In practical application, a diffuser transparent plate  12  is normally used by controlling the distance  11  between the plate and LEDs to obtain a uniform illumination. 
     This typical LED package structure sees challenges in increasing illumination efficiency, being cost effective in manufacturing. 
     The thermal conductive efficiency of silver paste or transparent insulating paste is about 1-5 W/m·K, the heat generated from the LED chip therefore cannot be dissipated sufficiently quickly through such material, and causing elevated temperature of the chip, which in turn will decrease the light emission efficiency and shorten the life time of the LED, or even cause LED failure. The several intermediate layers that consist of insulator materials such as epoxy insulator, Ag paste, transparent gel, between the LED chip and the substrate, are thermal resistance materials that also contribute to the poor heat dissipation. 
     The “spot” structure generates high light intensity around the center of the LED chip and lens, weaker light intensity around the edges, thus producing a “glazing” effect which can be harmful to the eyes. For an LED lamp that has many arrayed LED package units, the distribution of light will not be uniform. In order to achieve uniform light distribution, usually a diffuser film or structure of certain thickness is used above the LEDs, however, resulting in decreased light efficiency. 
     Moreover, the epoxy or silicone gel lens which seals the LED chip from moist and dust, generally has poor thermal conductivity, the heat generated from the chip is mainly dissipated through the backside to the substrate. 
     The reflect layer generally uses metals such as Ag, Al thin films, the fabrication process involves sophisticated vacuum or chemical deposition which is highly costly. 
     Further, for “spot” structure LED lamp fabrication, multiple steps are involved. LED chips are first packaged as “spot” tube with the electrodes and lens; then the package LED tubes are arrayed by connecting in parallel or series and mounting on a PCB; a diffuser layer is then placed on top of the LED lenses; finally power supply and driver are connected. 
     This process is relatively complex and time consuming, and needs significant man power in the production line. 
     To overcome some of the above mentioned problems, a highly thermal conductive materials and transparency material with refraction index changing is described in USPTO Patent Application 2009/0026484 and a flat type LED using high thermal conductive substrate is described in USPTO Application No. 2009/0010009. 
     SUMMARY 
     The present application discloses new approaches to LED package structure and fabrication process. 
     It is therefore an aspect to provide a high thermal conductive insulator composite material used between the chip and the substrate for LED package. 
     It is therefore another aspect to provide a thermal conductive transparent material to encapsulate the chip and the substrate for LED package. The material may form a light conductive or a diffuser layer for uniform light distribution from the LED chips, converting the multi-spot light into area light. The refraction index of the material is higher than that of conventional epoxy or silicone gel so that the total internal reflection angle is widened and the light emitting efficiency is thus enhanced. 
     It is therefore another aspect to provide a highly reflective composite material having reflective particles to coat onto the substrate for LED package. By changing the particle size in the composite, the wave-length of the reflected light can be selected, and the reflection efficiency may reach above 95%. 
     In one embodiment, the LED lamp module device includes a high thermal conductive substrate, high thermal conductive insulator layers, patterned electrode circuit layer, a high reflective layer, multiple LED chips, a transparent light conducting and or diffusing layer and a light emission layer. 
     The high thermal conductive substrate material may comprise Al alloy, Cu alloy, carbon based composites such as graphite, carbon fiber or tubes, diamonds, carbon-metals, and ceramic composite materials such as SiC, AlN, BN which also contain metals such as Al, Cu. 
     The high thermal conductive insulator composite materials may include an epoxy resin or a silicone resin that are mixed with diamond, AlN, and/or BN. 
     In one embodiment, a conductive layer including Ag, Au, Cu, Ni, Sn, In and/or their alloys, may be formed onto the insulator layer by screen print, magnetron sputtering, or chemical deposition process. The circuit pattern may be formed by etching process or screen printing process to connect with the multiple LED chips. I 
     In one embodiment, a high reflective composite material layer is formed onto the substrate, except the chip bonding area and wire bonding electrode pad area. A thermal conductive transparent material layer may be formed on top of the whole package array and seal the array. The layer may comprise diamond, TiO2, SiO2, MgO micro-particles mixture with silicone gel that has high quality in light conducting or diffusing for uniform lighting as well as good thermal dissipating quality. 
     Thus the present application, in various embodiments may provide various advantages. The high thermal conductive materials with less intermediate layers for dissipating heat from the LED chips will prevent the LED PN junction overheat, increasing the stability and reliability of the LED lamp. With high reflective composite film, the light flux from chip will be greatly enhanced, and the flat thin packaging structure is cost effective for automatic fabrication. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosed inventions will be described with reference to the accompanying drawings, which show important sample embodiments of the invention and which are incorporated in the specification hereof by reference, wherein: 
         FIG. 1   a  is a schematic structure of a conventional LED package. 
         FIG. 1   b  is a schematic structure of a conventional LED lamp module. 
         FIG. 2  is a schematic structure of a LED lamp module of a first embodiment in accordance with the present disclosure. 
         FIG. 3  is a schematic structure of a LED lamp module of a second embodiment in accordance with the present disclosure. 
         FIG. 4  is a schematic structure of a LED lamp module of a third embodiment in accordance with the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The numerous innovative teachings of the present application will be described with particular reference to presently preferred embodiments (by way of example, and not of limitation). The present application describes several embodiments, and none of the statements below should be taken as limiting the claims generally. 
     For simplicity and clarity of illustration, the drawing figures illustrate the general manner of construction, and description and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the invention. Additionally, elements in the drawing figures are not necessarily drawn to scale, some areas or elements may be expanded to help improve understanding of embodiments of the invention. 
     The terms “first,” “second,” “third,” “fourth,” and the like in the description and the claims, if any, may be used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable. Furthermore, the terms “comprise,” “include,” “have,” and any variations thereof, are intended to cover non-exclusive inclusions, such that a process, method, article, apparatus, or composition that comprises a list of elements, and not necessarily limited to those elements, but may include other elements not expressly listed or inherent to such process, method, article, apparatus, or composition. 
     It is contemplated and intended that the design apply to single LED package as well as LED package arrays; for clarity reason, the examples are given based on LED lamp module, but an ordinary person in the art would know the variations to modify the design to make the design to be adapted to other suitable applications. 
     For the conventional LED lamp module as shown in  FIGS. 1   a  and  1   b , there are at least three layers (layers  2 ,  3 ,  10 ) between LED chip and PCB substrate  9 , which creates thermal resistance, and affects reliability and efficiency. Often a diffuser plate  12  either in glass or polycarbonate is used in the front cover of the lamp, further reducing the light efficiency at least 10% by absorption and reflection. The added intermediate layers also increase the thickness of the lamp module. 
     The present disclosure presents a new LED package structure that is both cost effective and with high lighting efficiency.  FIG. 2  illustrates a structure view of a flat panel LED source of an embodiment in accordance with the present disclosure. LED chips  101  are mounted on high thermal conductive substrate  103  via a high thermal conductive adhesive layer  102  and layer  106  by die bonding. LED chip electrodes are connected with circuit electrodes  104  by Au, Cu or Al wires  105  via wire bonding process. 
     A flat, thin, high reflective layer  107  is then placed onto the surface of the PCB, sufficiently to cover the whole PCB but leave the LED chips exposed. The reflection efficiency of this layer may be configured to be above 95% in the visible light range (400-700 nm), the thickness may range from 10 μm to 50 μm. 
     The LED package array is then encapsulated with a flat diffuser layer  108 . A further emission layer  109  may be placed on top of layer  108 . The refraction indexes of layer  108  and  109  may be adjusted to between 2.6 and 1.2, reducing the internal light reflection. For a white LED module, the layer  109  is a phosphor conversion layer which can absorb the light from LED chips and emit white light. 
     For high thermal conductive substrate  103 , Al alloy, Cu alloy, carbon-carbon composite materials including carbon fiber, nanotube, diamond, graphite and graphene, and ceramic (AlN, BN, SiC) composite materials may be used, where their thermal conductivity is not less than 200 W/mK. The thickness of the substrate may ranges between 0.5 to 5 mm. 
     For adhesive layer  102 , an epoxy resin, a silicone resin or poly carbonate glue mixed with carbon and/or ceramic, such as diamond, AlN, BN, SiC, BC4, or metal micro particles including Sn, In, Ag, Au, Cu, or related alloys, may be used. For less than 500 μm LED chips, carbon or ceramic glue may be preferred in bonding the LED chips and insulating substrate  103 . The thermal conductivity of such glue is usually not less than 20 W/mK. The thickness of layer  201  may range from 1 to 10 μm. 
     For above 500 μm LED chips, metal micro particles containing organic gel may be used as layer  102  in bonding the chips to the substrate. The organic content can be evaporated with heat treatment and the LED chip and substrate are then directly soldered together, increasing the efficiency of heat dissipation to the substrate. The thermal conductivity lay  102  may not be less than 50 W/mK. The thickness may be configured in the range of 1 to 10 μm. 
     On top the substrate  103 , may be coated with an electric insulation layer  106 . For layer  106  to be highly thermal conductive, carbon and/or ceramic composites containing diamond, AlN, BN, SiC, of which the electrical resistance is above 10 13  Ωcm and the thermal conductivity is not less than 100 W/mK, may be used. The thickness of layer  106  may be in the range of 20 to 100 μm. 
     Because all layers ( 102 ,  103 ,  106 ) extending from the LED chips are comprised of high thermal conductive materials, the heat dissipation efficiency is greatly improved, the risk of the PN junction of the LED chip being overheated is reduced, therefore reliability of the LED lamp module is improved. 
     The electrical conductive layer  104  comprising Cu, Ag, Au, Ni, Sn, In, and/or related alloy film, may be deposited using magnetron sputtering, e-beam evaporation, electro-chemical deposition, or screen printing. The thickness may range from 1 to 20 μm. 
     After the attachment of the LED chips, a high reflective material (layer  107 ) may be deposited via dropping or screen printing process, to cover and insulate the substrate and the electrical conductive layer  104 . Layer  107  may be inorganic-organic composite contained oxide micro particles, for example, TiO 2 , MgO, ZnO, SnO 2 , SiO 2 , Al 2 O 3 , in the size of 100-400 nm. The organic material may comprise epoxy resin, silicone resin, polycarbonate, polyvinyl acetate, polyurethane, polystyrene, and/or polyacrylate. This composition layer  107 , with a thickness of 10 to 50 μm, usually generates a reflection efficiency of above 95% for the visible light (400-700 nm). 
     For diffusion layer  108 , silicone or epoxy composites containing oxides, such as TiO 2 , MgO, ZnO, SnO 2 , SiO 2 , or Al 2 O 3 , or diamond micro particles of sizes between 10 to 100 nm may be used. The ratio of the particles to silicone is preferred to be below 5% (wt). The addition of the micro particles enhances the thermal conduction efficiency at least 10% comparing to that of silicone alone. The refraction index of this layer can be configured to range from 1.2 to 2.6 by changing the concentration of the particles in the silicone. 
     This configurable refraction index in layer  108  provides significant advantages, for the refraction index of a LED chip  101  is normally big, for example, the refraction index of GaN chip is about 3.0 and refraction index of conventional packaging gel is usually less than 1.5. The big gap between the chip and packaging layer results in a significant internal reflection. The increases of refraction index in layer  108  widen the total internal reflection angle, thereby enhancing the light emitting efficiency of the LED lamp module. 
     For cover layer  109 , a transparent or phosphor mixed silicone may be used. For white LED module, yellow phosphor or green and red phosphors in the content ratio is 10-80% (wt) may be mixed with silicone. The thickness of the phosphor mixed silicone layer is the range of 0.2 to 500 μm. The phosphor film can also be coated onto the surface of a glass or polycarbonate plate on the opposite side to layer  108 , the film may range from 0.2 to 20 μm thick. When the phosphor layer absorbs the blue light emitted from the LED chip  101 , a broad light spectrum can be exited from the phosphor, which emits as white light. 
       FIG. 3  illustrates an another embodiment in accordance with the present disclosure. In this embodiment, the phosphor layer  109  can be coated onto the surface of LED chip  101 , for which the phosphor emission is more efficiency due to the shorter distance between the phosphor layer and the LED chip. The emitted light can be reflected by layer  107 , and scattered (guided or diffused) by layer  108 , then emitted from the surface uniformly. 
     Further, in  FIG. 4 , the LED chip  101  may be mounted on the substrate through flip chip bonding technology. The electrode pads of LED chip  101  are connected with circuit electrode pads  104  by a bump structure  105 . 
     The flat type structures of the module described above are suitable for automatic large scale production cost effectively. The produced white flat LED module may exhibit high efficiency of above 100 lm/W, and color temperature range of 3000-7000 K, color rendering index of above 75, with a uniform illumination. 
     Modifications and Variations 
     As will be recognized by those skilled in the art, the innovative concepts described in the present application can be modified and varied over a tremendous range of applications, and accordingly the scope of patented subject matter is not limited by any of the specific exemplary teachings given. It is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims. 
     Additional general background, which helps to show variations and implementations, may be found in the following publications, all of which are hereby incorporated by reference herein for all purposes: US Patent Applications 2009/0026484, 2009/0010009; U.S. Pat. Nos. 7,259,403, 7,116,485, they are hereby incorporated by reference. 
     None of the description in the present application should be read as implying that any particular element, step, or function is an essential element which must be included in the claim scope: THE SCOPE OF PATENTED SUBJECT MATTER IS DEFINED ONLY BY THE ALLOWED CLAIMS. Moreover, none of these claims are intended to invoke paragraph six of 35 USC section 112 unless the exact words “means for” are followed by a participle. 
     The claims as filed are intended to be as comprehensive as possible, and NO subject matter is intentionally relinquished, dedicated, or abandoned. According to various embodiments, there is provided: a flat LED package device, comprising: a thermal conductive substrate; at least one LED chip mounted on said substrate; at least one electrical circuit pattern layered on said substrate, wherein said LED chip and said circuit are electrically connected; and a flat reflecting layer, deposited on said substrate, surrounding said LED chip. 
     According to various embodiments, there is provided: a flat LED lamp device, comprising: a thermal conductive substrate; plurality of LED chips mounted on said substrate, and arrayed in parallel; one or more electrical circuits layered on said substrate, and placed in between said LED chips, wherein said LED chip and said circuit are electrically connected; and a flat reflecting layer, deposited on said substrate, surrounding said LED chips. 
     According to various embodiments, there is provided: a method for making flat LED lamp device module, comprising the actions of the steps of: coating a thermal conductive substrate with a layer of thermal conductive and electrical insulating composite; forming circuit boards on the insulated surface of the substrate; mounting a plurality of LED chips via a layer of thermal conductive adhesive composite to the insulated surface of the substrate; electrically connecting said plurality of LED chips with at least one circuit board; depositing a flat layer of reflecting composite on the substrate surrounding the LED chips, but exposing the surfaces of the LED chips, forming a flat LED lamp package; and depositing a light conducting cover layer over the reflecting layer and the surface of the LED chips, encapsulating the surface of lamp package.