Abstract:
An ultrathin LED light engine ( 100 ) comprises a protective cover ( 106 ), a driving circuit board ( 101 ), an aluminum substrate ( 103 ) and at least one LED module ( 104 ). A double-sided high-viscosity heat conducting plate ( 102 ) covers the first surface of the aluminum substrate ( 103 ) to fix the driving circuit board ( 101 ); the at least one LED module ( 104 ) is fixed on the first surface and insulated from the aluminum substrate ( 103 ) by means of an insulating layer ( 200 ) on the first surface; a conductive circuit for electrically connecting the at least one LED module ( 104 ) and the driving circuit board ( 101 ) is arranged on the insulating layer ( 200 ); and the size of the aluminum substrate ( 103 ) at least at the local peripheral outer area is greater than that of the driving circuit board ( 101 ), so that the double-sided high-viscosity heat conducting plate ( 102 ) on the first surface at least locally fixes the protective cover ( 106 ). The LED light engine ( 100 ) realizes ultrathin design and built-in integration of drive and control devices, and realizes heat conduction and fixation of the PCB and the protective cover by using a double-sided high-viscosity film.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates to an integrated LED lighting device in the field of LED lighting, and more particularly, to an ultrathin LED light engine. 
       BACKGROUND 
       [0002]    An LED light Engine is an integrated light source containing an LED packaged element or an LED array (module), an LED driver and other photometric, thermal, mechanical and electrical components. The integrated light source may be directly connected to a branch circuit through a conventional connector which matches with an LED lamp. Accordingly, an LED light Engine is a device interposed between an LED lamp and an LED light source. An LED light Engine differs from an LED light source in that the LED light source cannot be directly connected to a branch circuit unless it is provided with a standard lamp holder. An LED light Engine is similar to an LED lamp in that they both have designed light distribution and heat radiating capabilities. The product of the LED light Engine can effectively enhance stability of an indoor LED lamp and improve performances such as color rendering, lighting system&#39;s efficiency or the like. Therefore, the LED light Engine has become a focus of future development and promotion for LED lighting manufactures. 
         [0003]    Currently, LED light Engines have been used in development and design of lamps. It can simplify development of the lamps and shorten development time of the same, reduce assembling time of lamps and improve reliability of lighting systems. However, a conventional light engine (e.g. see CN200780042271.1) generally has a relatively high height and heavy weight due to thermal and aesthetic requirements, which is not easy for assembling. In addition, CN201010157844.9 discloses a design scheme with separate bodies. Although it is described that the scheme can achieve an ultrathin product, and can solve, to a certain degree, the problem of replacement of the LED module, it is far from achieving an ultrathin product. Since it carries therein with a driving circuit, an LED module, and especially a heat dissipation mechanism, the light Engine has a relatively heavy weight, and a mechanical mounting mechanism such as screws are generally provided for the conventional light engine for securing the components of the LED light engine. However, the screws have certain heights which inevitably increase overall size of the entire mechanism. Accordingly, a side screw mounting mechanism has to be provided to achieve ultrathin objective, such as in the technical solution disclosed by CN201220329399.4. The increased side structure is purely for securing, and compromises the purpose of downsizing. 
       SUMMARY 
       [0004]    In view of the above deficiencies in the prior art, the present disclosure provides an ultrathin LED light engine, comprising a protective cover, a driving circuit board, an aluminum substrate and at least one LED module, characterized in that, a double-sided high-viscosity heat conducting plate covers a first surface of the aluminum substrate to secure the driving circuit board; the at least one LED module is secured on the first surface and insulated from the aluminum substrate by means of an insulating layer on the first surface; a conductive circuit is disposed on the insulating layer for electrically connecting the at least one LED module and the driving circuit board; and at least an outer peripheral area of the aluminum substrate is larger than an outer peripheral area of the driving circuit board, so that the double-sided high-viscosity heat conducting plate on the first surface secures the protective cover at least at a partial area. 
         [0005]    According to a preferred embodiment, an outer peripheral area of the aluminum substrate which is covered by the double-sided high-viscosity heat conducting plate goes beyond an outer perimeter of the driving circuit board, and a lower edge of the protective cover is secured on the double-sided high-viscosity heat conducting plate at the outer peripheral area of the aluminum substrate which goes beyond the outer perimeter of the driving circuit board. 
         [0006]    According to a preferred embodiment, the driving circuit board has a shape of a plate with a central opening, the at least one LED module is positioned at the central opening of the driving circuit board, and a power supply interface of the at least one LED module is located within the protective cover. 
         [0007]    According to a preferred embodiment, the protective cover has a shape of a circular ring, an elliptical ring or a rectangular ring in a plan view, and the protective cover has a height adapted for accommodating the driving circuit board. 
         [0008]    According to a preferred embodiment, the protective cover has an internal hole, an outer wall and a light reflecting inclined surface extending from the internal hole to an outer perimeter of the protective cover, wherein a size of the internal hole matches a size of one of the at least one LED module, a lower edge of the internal hole is secured on the double-sided high-viscosity heat conducting plate at a position adjacent to the at least one LED module, and wherein the lower edge of the outer wall is secured on the double-sided high-viscosity heat conducting plate at the outer peripheral area of the aluminum substrate which goes beyond the outer perimeter of the driving circuit board. 
         [0009]    According to a preferred embodiment, the conductive circuit is a printed circuit, the conductive circuit has a power supply port for obtaining power from an external power source, and the conductive circuit has an LED power supply interface for supplying power to the at least one LED module. 
         [0010]    According to a preferred embodiment, the aluminum substrate and the protective cover have circular, elliptical or rectangular shapes corresponding to each other. 
         [0011]    According to a preferred embodiment, the protective cover is provided with a fastener portion for securing an optical element. 
         [0012]    According to a preferred embodiment, a bump-shaped pad is disposed on the conductive circuit on the aluminum substrate, a through-hole-shaped pad corresponding to the bump-shaped pad is disposed on the driving circuit board, and the bump-shaped pad and the through-hole-shaped pad are electrically connected by welding. 
         [0013]    According to a preferred embodiment, at least two mounting holes extending through the protective cover, the driving circuit board and the aluminum substrate are disposed on the LED light engine, so as to secure the LED light engine on a lighting device by means of an external mounting mechanism. 
         [0014]    According to a preferred embodiment, a slope gradient of the light reflecting inclined surface of the protective cover depends on a height of the protective cover which is at least capable of accommodating the driving circuit board. 
         [0015]    According to a preferred embodiment, the fastener portion of the protective cover is a detachable ring-shaped buckle, wherein at least two grooves are evenly distributed on a surface of the fastener portion of the protective cover, and match with at least two corresponding flanges on the optical element to form fasteners. 
         [0016]    According to a preferred embodiment, the at least two mounting holes on the LED light engine are evenly distributed in the outer peripheral area of the LED light engine, wherein the at least two mounting holes are through holes extending through the protective cover, the driving circuit board and the aluminum substrate, and wherein internal surfaces of the through holes are distributed with B-type threads with triangular teeth. 
         [0017]    According to a preferred embodiment, a lower edge of the protective cover overlaps with a side of the aluminum substrate. 
         [0018]    According to a preferred embodiment, the LED light engine is rectangular in a plan view, a first lower edge, a second lower edge and a third lower edge of the protective cover respectively overlap with a first side, a second side and a third side of the aluminum substrate. 
         [0019]    According to a preferred embodiment, a first lower edge and a second lower edge of the protective cover respectively overlap with a first side and a second side of the aluminum substrate. 
         [0020]    According to a preferred embodiment, a first lower edge of the protective cover overlaps with a first side of the aluminum substrate. 
         [0021]    According to a preferred embodiment, a size of the aluminum substrate is 1% larger than an area occupied by the protective cover. 
         [0022]    According to a preferred embodiment, a through hole made of conductive material, a mechanical mounting hole and an electrical connection hole are disposed in the driving circuit board, wherein the mechanical mounting hole and the electrical connection hole are evenly distributed on the driving circuit board. 
         [0023]    According to a preferred embodiment, the aluminum substrate has an electrical connection through hole corresponding to the electrical connection hole of the driving circuit board, wherein a wire of the driving circuit board passes through the electrical connection through hole to be connected to an external power source to obtain power therefrom. 
         [0024]    According to a preferred embodiment, a double-sided high-viscosity heat conducting plate is covered on a bottom of the aluminum substrate, and the LED light engine is directly secured to another lighting device through the double-sided high-viscosity heat conducting plate. 
         [0025]    According to a preferred embodiment, the light reflecting inclined surface is an inclined surface with an orange-peel effect. 
         [0026]    According to a preferred embodiment, a lower edge of the internal hole has a trapezoidal cross section, wherein convex dots are evenly distributed on a lower surface of the lower edge, so that the lower surface are tightly adhered to the double-sided high-viscosity heat conducting plate. 
         [0027]    According to a preferred embodiment, a downward-opened U-shaped hook element which projects upward is disposed at an outer perimeter of the aluminum substrate; an upward-opened U-shaped hook element matching the downward-opened U-shaped hook element is disposed at a lower end of the outer wall of the protective cover, so that the downward-opened U-shaped hook element and the upward-opened U-shaped hook element are connected to each other in an embedded manner. 
         [0028]    According to a preferred embodiment, the first surface is provided with evenly distributed convex dots, so that the double-sided high-viscosity heat conducting plate tightly covers the aluminum plate. 
         [0029]    According to a preferred embodiment, the double-sided high-viscosity heat conducting plate is made of elastic material having a thickness of 0.1-0.5 mm. 
         [0030]    According to a preferred embodiment, a fracture-reserved slot is disposed at a portion of the aluminum substrate which goes beyond an area of the protective cover; and the fracture-reserved slot is V-shaped. 
         [0031]    The present disclosure achieves at least the following advantages: 
         [0032]    1. it can achieve both of ultrathin design and integration of built-in driving and controlling means; 
         [0033]    2. the double-sided high-viscosity plate can function both for dissipating heat and securing the PCB and the protective cover; 
         [0034]    3. the PCB and the aluminum substrate can be connected both mechanically and electrically by welding corresponding pads; 
         [0035]    4. a side of the LED is designed with an inclined surface, thereby the light emitting angle can be adjusted by selecting a proper protective cover as desired; 
         [0036]    5. the present invention can be implemented in profiles of various shapes; 
         [0037]    6. the protective cover is made of light-weighted material which is excellent for heat dissipation and the light reflecting inclined surface of the protective cover has a larger area than an area of a vertical surface with the same height, thereby the heat dissipation area can be enlarged, and heat dissipation efficiency is further improved; and 
         [0038]    7. the fastener portion is a detachable ring-shaped buckle, thereby it can be disassembled and reassembled repeatedly, which is easy, convenient and fast. 
         [0039]    The LED light engine according to the present disclosure is designed for an ultrathin application with built-in driving and controlling means, and can be applied in widespread fields of spotlights, down-lights and the like. The prevent invention has a reduced size and thickness, is a miniaturized product with a light weight, a small size, and a high cost performance, without requirement for an external driving circuit. In particular, the LED light engine according to the present disclosure can achieve a product having an overall thickness less than 6 mm. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0040]      FIG. 1  is a cross sectional view of an ultrathin LED light engine according to the present disclosure; 
           [0041]      FIG. 2  is a detailed view of an ultrathin LED light engine according to the present disclosure; 
           [0042]      FIG. 3  is a top view of an ultrathin LED light engine according to an embodiment of the present disclosure; 
           [0043]      FIG. 4  is a top view of an ultrathin LED light engine according to an embodiment of the present disclosure; 
           [0044]      FIG. 5  is a top view of an ultrathin LED light engine according to an embodiment of the present disclosure; 
           [0045]      FIG. 6( a )  is a top view of an ultrathin LED light engine according to an embodiment of the present disclosure; 
           [0046]      FIG. 6( b )  is a top view of an ultrathin LED light engine according to an embodiment of the present disclosure; 
           [0047]      FIG. 6( c )  is a top view of an ultrathin LED light engine according to an embodiment of the present disclosure; and 
           [0048]      FIG. 7  is a detailed view of an ultrathin LED light engine according to the present disclosure. 
       
    
    
     MANIFEST 
       [0000]    
       
         
           
               100 —LED light engine 
               106 —protective cover 
               101 —driving circuit board 
               103 —aluminum substrate 
               104 —LED module 
               102 —double-sided high-viscosity heat conducting plate 
               105 —light reflecting inclined surface 
               200 —insulating layer 
               201 —through-hole-shaped pad 
               202 —bump-shaped pad 
           
         
       
     
       DETAILED DESCRIPTION 
       [0059]    Hereinafter, the present disclosure will be described in detail with reference to the accompanying drawings. 
         [0060]      FIG. 1  shows an ultrathin LED light engine  100 , including a protective cover  106 , a driving circuit board  101 , an aluminum substrate  103  and at least one LED module  104 . As shown in the drawing, an upward surface of the ultrathin LED light engine  100  is an out-light surface, and a bottom surface thereof is the aluminum substrate. The protective cover  106  covers the driving circuit board  101  to protect the driving circuit board  101  from being damaged by external forces, and to protect it from influence of moisture. The aluminum substrate  103  and the at least one LED module  104  are adhered to each other by means of a double-sided high-viscosity heat conducting plate  102 . 
         [0061]    A first surface of the aluminum substrate  103  is covered by the double-sided high-viscosity heat conducting plate  102 , and the driving circuit board  101  is secured by means of the double-sided high-viscosity heat conducting plate  102 . The double-sided high-viscosity heat conducting plate is a thermal conductive silicon film, a flame retardant silicone film, or a thermal-conductive insulation film with high performance. The thermal conductive silicon film is high-performance gap-filled thermal conductive material, which is generally used as a transferring interface between an electronic device and a heat radiation sheet or a casing of the product. Such a thermal conductive silicon film is also filled with glass fibers (or carbon fibers) to enhance its mechanical strength. Some thermal conductive silicon films are coated with thermal-resistant and pressure-sensitive adhesive. The flame retardant silicone film has performances of thermal conduction, insulation and anti-vibration, with a soft and self-adhesive material, so it is easy to operate, and may serve as heat conductive filler between surfaces of various irregular parts and radiators, casings, or the like. The thermal-conductive insulation film is high-performance elastic insulation material with a special film as base material. It has an excellent cut resistance and excellent thermal conductive performance, widely used in electrical and electronic industries. The double-sided high-viscosity heat conducting plate  102  has an excellent adhesiveness, flexibility, compression performance and heat conductive rate. In operation, a double-sided high-viscosity heat conducting plate can make an electronic element and a heat dissipation plate in tight contact with each other, and can achieve a desirable heat dissipating effect. Moreover, the double-sided high-viscosity heat conducting plate of a selected thickness can be cut according to a size of heat generating area and a height of a gap. In addition, the double-sided high-viscosity heat conducting plate  102  does not tend to be peeled off, and is easy for operation. It can dissipate heat and can also, in place of screws, secure other members such as the protective cover in the light engine, thereby significantly reduce the size of the product. Physical properties of the double-sided high-viscosity heat conducting plate  102  used in the present disclosure may be referred to the following table: 
         [0000]    
       
         
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Testing 
                   
                   
               
               
                 Testing Items 
                 Methods 
                 Units 
                 HC240 Testing Values 
               
               
                   
               
             
             
               
                 Color 
                 Visual 
                   
                 Grey/Black 
               
               
                 Thickness 
                 ASTM D374 
                 mm 
                 0.5~10.0 
               
               
                 Specific Gravity 
                 ASTM D792 
                 g/cc 
                 1.8 ± 0.1 
               
               
                 Hardness 
                 ASTM D2240 
                 Shore C 
                 18 ± 5~40 ± 5 
               
               
                 Tensile Strength 
                 ASTM D412 
                 Kg/cm 2   
                 8 
               
               
                   
                 ASTM D412 
                 Pa 
                 5.88 * 10 9   
               
               
                 Continuous 
                 EN344 
                 ° C. 
                 −40~+220 
               
               
                 temperature 
               
               
                 resistance 
               
               
                 Volume Resistivity 
                 ASTM D257 
                 Ω · CM 
                 1.0 * 10 11   
               
               
                 Breakdown Voltage 
                 ASTM D149 
                 kv/mm 
                 4 
               
               
                 Flame Rating 
                 UL-94 
                   
                 V-0 
               
               
                 Conductivity 
                 ASTM D5470 
                 w/ (m · k) 
                   2.4 
               
               
                   
               
             
          
         
       
     
         [0062]    At least one LED module  104  is secured on the first surface, and is insulated from the aluminum substrate  103  by means of an insulating layer  200  on the first surface. A conductive circuit (not shown in the figure) is disposed on the insulating layer  200  for electrically connecting the at least one LED module  104  and the driving circuit board  101 . The conductive circuit has an LED power supply interface for supplying power to the at least one LED module  104 . At least an outer peripheral area of the aluminum substrate  103  is larger than an outer peripheral area of the driving circuit board  101 , so that the double-sided high-viscosity heat conducting plate  102  on the first surface secures the protective cover  106  at least in a partial area. By securing the protective cover  106  through the double-sided high-viscosity heat conducting plate  102 , space is saved due to elimination of screws and bolts. 
         [0063]    According to a preferred embodiment, an outer peripheral area of the aluminum substrate  103  which is covered by the double-sided high-viscosity heat conducting plate  102  goes beyond an outer perimeter of the driving circuit board  101 , and a lower edge of the protective cover  106  is secured on the double-sided high-viscosity heat conducting plate  102  at the outer peripheral area of the aluminum substrate  103  which goes beyond the outer perimeter of the driving circuit board  101 . 
         [0064]    According to a preferred embodiment, the driving circuit board  101  has a shape of a plate with a central opening, the at least one LED module  104  is positioned at the central opening of the driving circuit board  101 , and a power supply interface of the at least one LED module  104  is located within the protective cover  106 . 
         [0065]    According to a preferred embodiment, the protective cover  106  has a shape of a circular ring, an elliptical ring or a rectangular ring in a plan view, and the protective cover  106  has a height adapted for accommodating the driving circuit board,  101 . Since the driving circuit board  101  has a relatively small height, a small overall height of the entire structure can be achieved. The protective cover  106  is made of light-weighted material with excellent heat conductive performance. Accordingly, by means of the double-sided high-viscosity heat conducting plate  102 , the aluminum substrate  103  and the protective cover  106  together form a heat dissipation structure which fully utilizes various casing parts of the light engine to achieve both of an ultrathin size and heat dissipation. 
         [0066]    According to a preferred embodiment, the protective cover  106  has an internal hole, an outer wall and a light reflecting inclined surface  105  extending from the internal hole to an outer perimeter of the protective cover  106 , wherein a size of the internal hole matches a size of at least one LED module  104 , a lower edge of the internal hole is secured on the double-sided high-viscosity heat conducting plate  102  at a position adjacent to the at least one LED module  104 , and wherein the lower edge of the outer wall is secured on the double-sided high-viscosity heat conducting plate  102  at the outer peripheral area of the aluminum substrate  103  which goes beyond the outer perimeter of the driving circuit board  101 . In other words, the protective cover  106  is secured to the aluminum substrate  103  only at the lower edge of the internal hole and the lower edge of the outer wall. The securing is achieved by means of the double-sided high-viscosity heat conducting plate  102 , which fully utilizes the casing parts to dissipate heat. 
         [0067]    According to a preferred embodiment which is not shown in the drawings, the conductive circuit is a printed circuit, the conductive circuit has a power supply port for obtaining power from an external power source, and the conductive circuit has an LED power supply interface for supplying power to the at least one LED module  104 . The advantage of a printed circuit lies in that it can eliminate the requirement to weld on the circuit board repeatedly and many complex manual wiring, and it can achieve a high accuracy and improve the productivity of circuit boards. During manufacture, the conductive patterns are formed on the insulating layer  200  of the aluminum substrate  103  by etching or photosensitive printing. Thereby, the manufacture is made simple and easy, and the produced electronic devices have consistent performances, stable qualities and compact structures. The conductive circuit obtains power from an external power source through the power supply port, and then supplies the power to the at least one LED module through the LED power supply interface of the at least one LED module  104 , so as to achieve an electrical connection. 
         [0068]    According to a preferred embodiment, the aluminum substrate  103  and the protective cover  106  have circular (see  FIG. 3 ), elliptical or rectangular (see  FIG. 4 ) shapes corresponding to each other. As shown in  FIG. 5 , the aluminum substrate  103  and the protective cover  106  also have a square shape. The aluminum substrate  103  and the protective cover  106  have shapes corresponding to each other, to facilitate achieving of an overall structure of the light engine and mounting the light engine  100  to other lighting mechanism later. 
         [0069]    According to a preferred embodiment, the protective cover  106  is provided with a fastener portion for securing an optical element. An optical element can be provided in the light emitting area over the internal hole of the protective cover  106 , to achieve various optical effects. This will not change the overall height of the product. 
         [0070]    Referring to  FIG. 2 , a bump-shaped pad  202  is disposed on the conductive circuit on the aluminum substrate  103 , a through-hole-shaped pad  201  corresponding to the bump-shaped pad  202  is disposed on the driving circuit board  101 , and the bump-shaped pad  202  on the aluminum substrate  103  and the corresponding through-hole-shaped pad  201  on the driving circuit board  101  can be connected by a welding wire, so that the aluminum substrate  103  and the driving circuit board  101  can be secured together and also form an electrical connection. 
         [0071]    According to a preferred embodiment, at least two mounting holes extending through the protective cover  106 , the driving circuit board  101  and the aluminum substrate  103  are disposed on the LED light engine  100 , so as to secure the LED light engine  100  on a lighting device by means of an external mounting mechanism. 
         [0072]    According to a preferred embodiment, a slope gradient of the light reflecting inclined surface  105  of the protective cover  106  depends on a height of the protective cover  106  which is at least capable of accommodating the driving circuit board  101 . Since the driving circuit board is provided with electrical elements (such as a capacitor) which occupy a certain three-dimensional space, it requires the protective cover  106  to have a certain three-dimensional structure. In this regard, the present disclosure provides an optimized structural design, in which the protective cover  106  can have both of a protection function and a light reflecting function. 
         [0073]    According to a preferred embodiment, a reflective film made of mirror-surface aluminum, sandblasted aluminum, a plastic surface, a white paint layer or diffusion nanometer coating with a high reflective rate is provided on the light reflecting inclined surfaces of the protective cover  106 . This technical feature further enhances the light emitting effect. With material of various reflective rates and reflective effects, the light engine can have various light emitting effects. In addition, a significant difficulty of a LED light lies in that the light utilization rate is low and it will produce glaring light. Accordingly, in manufacture, a LED lamp will be provided with reflective coating or a reflector which can avoid LED glaring light, so that light will form a secondary surface light source via the reflective surface, solving the problem of LED glaring light as well as improving light utilization. For example, in the ultrathin LED light engine of the present disclosure, the protective cover around the light output surface has a smooth reflective inclined surface coated with reflective paint to produce a star light effect. Such an LED light engine can produce a star light effect in a low-level light circumstance, as a decorative effect. As another example, the protective cover  106  is positioned around a COB encapsulation and the LED light emitting portion, and a mounting base is provided on the light reflecting inclined surface  105 , for the user to mount various optical reflectors depending on specific application. This satisfies various personalization requirements. 
         [0074]    According to a preferred embodiment, the fastener portion of the protective cover  106  is a detachable ring-shaped buckle, wherein at least two hook-shaped grooves are evenly distributed on a surface of the fastener portion of the protective cover  106 , to match at least two corresponding flanges on the optical element to form a buckle. A flange is constituted of a beam and a holding element. The fastener (buckle) is a mechanism for one part imbedded into or wholly locked into another part, typically for connection of plastic members and made of flexible plastic material. The protective cover  106  is made of light-weighted heat conductive composite material with a certain ability of elastic deformation and easy to be mounted and detached even without a tool. In addition to that the fastener portion of the protective cover  106  can connect the LED light engine  100  with another lighting device, the detachable ring-shaped buckle of the present disclosure facilitates replacement of the LED light engine or the lighting device. It is easy to operate and does not cause waste of resources since one damaged member will not render the whole LED lighting device useless. 
         [0075]    According to a preferred embodiment not shown in the drawings, the at least two mounting holes on the LED light engine  100  are evenly distributed in the outer peripheral area of the LED light engine  100 . For example, for a circular or elliptical LED light engine, the mounting holes are distributed at an even interval in the outer peripheral area of the LED light engine  100 . As another example, for an LED light engine  100  of a rectangular shape, the mounting holes on each side are distributed at an even interval, wherein at least two mounting holes are disposed on the diagonal of the LED light engine  100  to enhance the securing. The at least two mounting holes are through holes extending through the protective cover  106 , the driving circuit board  101  and the aluminum substrate  103 , so that the securing screw can pass through the protective cover  106 , the driving circuit board  101  and the aluminum substrate  103 . The length of the screw is larger than the thickness of the LED light engine, and a part of the screw protruding from the LED light engine exactly matches a mounting portion such as a mounting hole on a lamp. Internal surfaces of the through holes are distributed with B-type threads with triangular teeth. The B-type threads are single line with triangle teeth, the teeth art large and the threads have good self-locking performance. Moreover, the teeth have thick roots and high strength and the threads are fast to lock and can be repeatedly used, which is suitable for plastic material and will not cause the plastic material burned, break or damage the locking portion. 
         [0076]    Referring to  FIGS. 3, 4 and 5 , a lower edge of the protective cover  106  overlaps with a side of the aluminum substrate  103 . Thus, the LED light engine can have a minimum volume. In addition, when the LED light engine is of a rectangular shape, the protective cover  106  and the aluminum substrate  103  can be positioned relative to each other in the following manners: a first lower edge, a second lower edge and a third lower edge of the protective cover  106  respectively overlap with a first side, a second side and a third side of the aluminum substrate  103 , as shown in  FIG. 6( a ) ; a first lower edge and a second lower edge of the protective cover  106  respectively overlap with a first side and a second side of the aluminum substrate  103 , as shown in  FIG. 6( b ) ; and a first lower edge of the protective cover  106  overlaps with a first side of the aluminum substrate  103 , as shown in  FIG. 6( c ) . The manners can be selected depending on specific application of the LED light engine. Referring to  FIGS. 6( a ), 6( b ) and 6( c ) , a size of the aluminum substrate  103  is larger by 1% than an area occupied by the protective cover  106 . 
         [0077]    According to a preferred embodiment not shown in the drawings, the LED module  104  is a LED module with a COB encapsulation, wherein a chip of the LED module is directly encapsulated on the printed circuit. The COB encapsulation directly encapsulates a plurality of LED chips on a metal substrate (such as the aluminum substrate) printed circuit board MCPCB which will directly dissipate heat through the aluminum substrate  103 . This can not only simplify the manufacture process and reduce its cost, but also can reduce heat resistance in heat dissipation. In the LED module with a COB encapsulation, a plurality of LED chips is mounted on the substrate, thereby the brightness can be enhanced by the plurality of LED chips, and the LED chips can be reasonably disposed to reduce input current of each single LED chip and ensure a high efficiency. Moreover, such a surface light source can significantly enlarge the heat dissipating area of the encapsulation, so that heat can be more easily transferred to the protective cover  106 , and discharged outside through the protective cover  106  which is made of light-weighted heat conductive composite material. In addition, through the rational design and molding micro-lenses, the spot lights, glaring lights and other defects existing in the combined device of discrete light sources can be avoided. In addition, if combination of red chips is provided, color performance of the light source can be effectively improved without reducing efficiency and lifespan of the light source. The COB light source module can simplify the manufacture and assembly of the lighting lamps. 
         [0078]    According to a preferred embodiment not shown in the drawings, a through hole of a gold plating (conductive material), a mechanical mounting hole and an electrical connection hole are disposed on the driving circuit board. Wherein, mechanical mounting holes are evenly distributed on the peripheral area of the driving circuit board  101  for securing the driving circuit board. The gold plating through hole is designed for mounting electrical elements on the driving circuit board  101 . In order to distribute the elements neatly, evenly and reasonably on the driving circuit board, gold plating through holes are also arranged accordingly. The electrical connection hole is designed for electrically connecting an element to another element. 
         [0079]    According to a preferred embodiment, the power supply interface of the at least one LED module  104  is exposed to outside as a convex dot. The convex dot of the power supply interface is a tin pad, for electrical connection with the driving circuit board  101  through the conductive circuit. The bump-shaped pad on the conductive circuit is electrically connected to the convex dot of the power supply interface of the at least one LED module  104  and the through-hole-shaped pad of the driving circuit board through welding wires respectively. 
         [0080]    According to a preferred embodiment, the aluminum substrate  103  has an electrical connection through hole corresponding to the electrical connection hole of the driving circuit board  101 , wherein a wire of the driving circuit board  101  passes through the electrical connection through hole to be connected to an external power source to obtain power therefrom. 
         [0081]    According to a preferred embodiment, a double-sided high-viscosity heat conducting plate  102  is covered on a bottom of the aluminum substrate  103 , and the LED light engine  100  is directly secured to another lighting device through the double-sided high-viscosity heat conducting plate  102 . 
         [0082]    According to a preferred embodiment not shown in the drawings, the light reflecting inclined surface of the protective cover  106  is an inclined surface with an orange-peel effect. The inclined surface with an orange-peel effect can reflect light evenly and produce soft spots without glaring lights, which can be widely used in LED lighting devices for daily lives. 
         [0083]    According to a preferred embodiment not shown in the drawings, a lower edge of the internal hole has a trapezoidal cross section, wherein convex dots are evenly distributed on a lower surface of the lower edge, so that the lower surface are tightly adhered to the double-sided high-viscosity heat conducting plate  102 . The lower edge of the trapezoidal cross section increases the contact area of the lower edge of the internal hole and the double-sided high-viscosity heat conducting plate  102 , so that the protective cover  106  can be tightly secured on the aluminum substrate  103 . In addition, the convex dots evenly distributed on the lower surface of the lower edge can further increase the contact area of the lower edge and the double-sided high-viscosity heat conducting plate  102  and make the contact area become coarse. The convex dots, due to small volume, can be embedded into the double-sided high-viscosity heat conducting plate through an external force, so that the lower edge of the internal hole can be adhered to the aluminum substrate more tightly. 
         [0084]    Referring to the schematic view of  FIG. 7 , a downward-opened U-shaped hook element which projects upward is disposed at an outer perimeter of the aluminum substrate  103 . An upward-opened U-shaped hook element matching with the downward-opened U-shaped hook element is disposed at a lower end of the outer wall of the protective cover  106 , so that the downward-opened U-shaped hook element and the upward-opened U-shaped hook element are connected to each other in an embedded manner. Free ends of the downward-opened U-shaped hook element and the upward-opened U-shaped hook element can be smooth curved surfaces, so that in assembly, the protective cover  106  can be smoothly pushed into the aluminum substrate  103 . Such a connection can make the protective cover  106  and the aluminum substrate  103  connected to each other more tightly, and even if the double-sided high-viscosity heat conducting plate  102  loses viscosity over time, the protective cover  106  will not come off the aluminum plate  103 . 
         [0085]    According to a preferred embodiment not shown in the drawings, the first surface of the aluminum substrate has evenly distributed convex dots, so that the double-sided high-viscosity heat conducting plate  102  can tightly cover the aluminum plate  103 . The convex dots on the aluminum plate  103  not only can increase the contact area between the aluminum plate  103  and the double-sided high-viscosity heat conducting plate  102 , but also can make the contact area become coarse, to increase the friction coefficient, so that the double-sided high-viscosity heat conducting plate  102  can tightly cover the aluminum plate  103 . 
         [0086]    According to a preferred embodiment, the double-sided high-viscosity heat conducting plate  102  is made of elastic material having a thickness of 0.1-0.5 mm. The elastic material not only has viscosity and thermal conductivity, but also has elasticity, so that it can be expanded and contracted depending on the temperature. In other words, the elastic double-sided high-viscosity heat conducting plate  102  can expand and contract correspondingly with a member to which the elastic double-sided high-viscosity heat conducting plate  102  is connected, when the volume of the member (such as the lower ends of the aluminum substrate  103  or the protective cover  106 ) changes with environmental temperature changes or temperature changes caused by LED light emitting. Thereby, the double-sided high-viscosity heat conducting plate will not generate gap between it and the member, and remain adhered to the member tightly. The double-sided high-viscosity heat conducting plate also has a thickness of 0.1-0.5 mm, so that the convex dots on the first surface of the aluminum substrate  103  can be embedded into the double-sided high-viscosity heat conducting plate  102  by external forces without penetrating the double-sided high-viscosity heat conducting plate  102 . Similarly, the convex dots on the lower surface of the lower edge of the internal hole can be embedded into the double-sided high-viscosity heat conducting plate  102  without penetrating the double-sided high-viscosity heat conducting plate  102 . Thus, the double-sided high-viscosity heat conducting plate having a thickness of 0.1-0.5 mm has a depth that can embed the convex dots, and also are not too thin to influence the adhesion effect. Such an elastic double-sided high-viscosity heat conducting plate can be a heat conducting silicon plate. 
         [0087]    According to a preferred embodiment not shown in the drawings, a fracture-reserved slot is disposed at a reserved portion of the aluminum substrate  103  which goes beyond an area of the protective cover  106 . The fracture-reserved slot is V-shaped. Since the LED light engine  100  has an ultrathin structure, it is difficult to hold it during mounting. The reserved portion is disposed on the LED light engine to facilitate the holding and mounting of the LED light engine, and it can be broken off along the fracture-reserved slot after the mounting so that the reserved portion is removed to achieve an aesthetic effect. 
         [0088]    The present disclosure can solve the following technical problems: 
         [0089]    1. since the built-in driving circuit board will generate a lot of heat, the heat dissipating problem of the driving IC requires to be solved with an excellent heat conducting means; and 
         [0090]    2. the driving circuit board and the aluminum substrate are required to be electrically connected through a means which is heat conductive and steady, other than a fly wire, while the LED light engine according to the present disclosure is designed for an ultrathin application with built-in driving and controlling means, and can be applied in widespread fields of spotlights, down-lights and the like. The prevent invention has a reduced size and thickness, is a miniaturized product with a light weight, a small size, and a good cost performance, without requirement of a driving circuit. In particular, the LED light engine according to the present disclosure can achieve a product having an overall thickness less than 6 mm. 
         [0091]    It should be noted that, the above specific embodiments are exemplary. Based on the above embodiments under the above teaching of the present disclosure, one skilled in the art can made various modifications and alterations falling within the protective scope of the present disclosure. It should be appreciated by those skilled in the art that the above specific description is merely for explaining the present disclosure, rather than limiting the present disclosure. The protective scope of the present disclosure is defined by the claims and the equivalent thereof.