Abstract:
A light emitting diode (LED) light engine includes: an LED; an LED driver for driving the LED; a bottom printed circuit board (PCB), the LED and the LED driver being securely mounted to the bottom PCB; and a top PCB secured to the bottom PCB, the top PCB including first and second cavities for receiving the LED and the LED driver therein. The LED light engine further includes a layer potted over the LED and formed of material containing a phosphor, or a plate that is disposed over the LED and secured to the top PCB and includes a layer formed of material containing a phosphor. The phosphor is excited by the light emitted from the LEDs to the intensity distribution over the wavelength of the light emitted by the LED.

Description:
[0001]    CROSS REFERENCES 
         [0002]    This application claims the benefit of U.S. Provisional Applications No. 62/083,467, filed on Nov. 24, 2014, entitled “Method for fabricating an LED module,” which is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    The present invention relates to lighting devices, and more particularly, to light emitting diode (LED) light engines. 
         [0004]    Due to the concept of low energy consumption, LED lamps are prevailing and considered a practice for lighting in the era of energy shortage. Typically, an LED lamp includes an LED module, having LEDs and a driving circuit.  FIG. 1  shows a conventional LED module  100 . As depicted, the LED module  100  includes a bottom substrate  102  and a top substrate  104 . Typically, the top substrate  104  is formed of a PCB so that circuits are formed on the top surface of the top substrate  104 . One or more LEDs  108  are mounted on the top substrate  104 . The bottom substrate  102  is typically formed of metal and secured to the top substrate  104 . Typically, the bottom substrate  102  does not include any circuit and merely provides mechanical strength for the top substrate  104 . 
         [0005]    To protect the LEDs  108  and provide a space for holding phosphor potting, a dam  106  is also mounted on the top substrate  104 . Also, various types of sub-printed-circuit-board (PCB) components  110  are mounted on the top substrate  104 . The dam  106  and sub-PCB components  110  can increase the manufacturing cost and the form factor of the LED module  100 . As such, there is a need for an LED module (or LED light engine) that has a small form factor to thereby reduce the manufacturing cost without compromising the mechanical strength. 
       SUMMARY OF THE INVENTION 
       [0006]    In one embodiment of the present disclosure, a light emitting diode (LED) light engine includes: an LED; an LED driver for driving the LED; a bottom printed circuit board (PCB), the LED and the LED driver being securely mounted to the bottom PCB; and a top PCB secured to the bottom PCB, the top PCB including first and second cavities for receiving the LED and the LED driver therein. The LED light engine further includes a layer potted over the LED and formed of material containing a phosphor or a plate that is disposed over the LED, secured to the top PCB and includes a layer formed of material containing a phosphor. 
         [0007]    These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  shows a schematic diagram of a conventional LED module; 
           [0009]      FIGS. 2A-2C  show cross sectional views of a bottom PCB of an LED light engine, illustrating steps for processing the bottom PCB in accordance with embodiments of the present invention; 
           [0010]      FIG. 2D  shows a top view of the bottom PCB in  FIG. 2C  in accordance with embodiments of the present invention; 
           [0011]      FIGS. 3A and 3B  show two types of substrates that can be used to make the bottom PCB in  FIG. 2D  in accordance with embodiments of the present invention; 
           [0012]      FIG. 3C  shows a cross sectional view of a PCB in accordance with embodiments of the present invention; 
           [0013]      FIG. 4  shows a cross sectional view of a top PCB of an LED light engine in accordance with embodiments of the present invention; 
           [0014]      FIGS. 4B-4C  shows cross sectional views of PCBs in accordance with embodiments of the present invention; 
           [0015]      FIGS. 5A-5D  show the steps for processing an LED light engine in accordance with embodiments of the present invention; 
           [0016]      FIGS. 6A-6B  show cross sectional views of various types of LEDs and integrated circuits (ICs) for driving the LEDs in accordance with embodiments of the present invention; 
           [0017]      FIGS. 7 and 8  show cross sectional views of LED light engines in accordance with embodiments of the present invention; 
           [0018]      FIG. 9  shows a top view of a bottom PCB in accordance with embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    In the following description, for purposes of explanation, specific details are set forth in order to provide an understanding of the invention. It will be apparent, however, to one skilled in the art that the invention can be practiced without these details. Furthermore, one skilled in the art will recognize that embodiments of the present invention, described below, may be implemented in a variety of ways, such as a process, an apparatus, a system, and a device. 
         [0020]    Components shown in diagrams are illustrative of exemplary embodiments of the invention and are meant to avoid obscuring the invention. It shall also be understood that throughout this discussion that components may be described as separate functional units, which may comprise sub-units, but those skilled in the art will recognize that various components, or portions thereof, may be divided into separate components or may be integrated together, including integrated within a single system or component. 
         [0021]    Furthermore, connections between components within the figures are not intended to be limited to direct connections. Also, additional or fewer connections may be used. It shall also be noted that the terms “coupled” “connected” or “communicatively coupled” shall be understood to include direct connections, indirect connections through one or more intermediary devices. 
         [0022]    Furthermore, one skilled in the art shall recognize: (1) that certain steps may optionally be performed; (2) that steps may not be limited to the specific order set forth herein; and (3) that certain steps may be performed in different orders, including being done contemporaneously. 
         [0023]    Reference in the specification to “one embodiment,” “preferred embodiment,” “an embodiment,” or “embodiments” means that a particular feature, structure, characteristic, or function described in connection with the embodiment is included in at least one embodiment of the invention and may be in more than one embodiment. The appearances of the phrases “in one embodiment,” “in an embodiment,” or “in embodiments” in various places in the specification are not necessarily all referring to the same embodiment or embodiments. 
         [0024]      FIGS. 2A-2C  show cross sectional views of a bottom portion  200  of an LED light engine, illustrating steps for processing the bottom portion in accordance with embodiments of the present invention.  FIG. 2D  shows a top view of the bottom portion  200  in  FIG. 2C  in accordance with embodiments of the present invention. As depicted in  FIG. 2A , the bottom PCB  202  includes one or more circuits are  203  formed on the top surface of the bottom PCB  202 . 
         [0025]    In embodiments, one or more LEDs  204  are mounted on the bottom PCB  202  by bump balls (or solder balls or AuSn)  206 , where the LEDs  204  are flip-chip LEDs. It is noted that other suitable number of LEDs may be mounted on the bottom PCB  202 . 
         [0026]      FIG. 2B  shows an integrated circuit (IC)  208  and electrical wires  209  mounted on the bottom PCB  202 . In embodiments, the IC  208  includes a driver circuit (or, shortly driver) for driving the LEDs  204 . In embodiments, the IC  208  communicates to the LEDs  204  and other electrical components via the wires  209  and circuits  203 . 
         [0027]      FIG. 2C  shows the bottom portion  200  of the LED light engine having one or more glues/adhesive drops  210  and via filling material drops  212  dispensed on the top surface of the bottom PCB  202 . In embodiments, the glue drops  210  are made of dielectric material, such as silicon, and the via-filling material drops  212  are made of electrically conducting material, such as silver epoxy. As discussed in conjunction with  FIG. 5A , a top PCB is mounted over the bottom PCB  202  and the adhesive drops  210  are cured so that the glue drops  210  secure the bottom PCB  202  to the top PCB. Also, the via-filling material drops  212  fill up the vias formed in the top PCB, providing electrical connection between electrical components on the top and bottom PCBs. 
         [0028]      FIG. 2D  shows a top view of the bottom portion  200  of the LED light engine in  FIG. 2C  in accordance with embodiments of the present invention. In  FIG. 2D , only sixteen LEDs  204  and two ICs  208  are shown. However, it should be apparent to those of ordinary skill in the art that other suitable number of LEDs and ICs may be mounted on the bottom PCB  202 . Also, other suitable electrical circuits  203 , such as electrical wires, may be formed on the top surface of the bottom PCB  202 . 
         [0029]      FIGS. 3A and 3B  show two types of PCBs that can be used to make the bottom PCB  202  in  FIG. 2D  in accordance with embodiments of the present invention. The PCB  360  in  FIG. 3A  is a metal-core-PCB (MCPCB) that includes three layers: the metal based layer  366 ; a dielectric layer  364 ; and a top metal layer  362 . The top metal layer  362  may be formed of metal, such as copper, and processed by conventional wafer processing techniques, such as etching, to form electrical circuits. 
         [0030]    The PCB  380  in  FIG. 3B  includes a ceramic layer  384  and a metal layer  382 , where the ceramic layer is a dielectric layer. The metal layer  382  may be formed of metal, such as copper, and processed by conventional techniques, such as etching, to form electrical circuits. 
         [0031]    As discussed in conjunction with  FIGS. 2A-2D , the top PCB  202  includes the electrical circuits  203 , where the circuits may be formed by processing the top metal layers  362  and  382  of the PCBs  360  and  380 , respectively.  FIG. 3C  shows a PCB  300  including electrical circuits  302  formed by processing the top metal layer  382  of the PCB  380  in  FIG. 3B . In embodiments, the PCB  300  and the electrical circuits  302  correspond to the bottom PCB  202  and the electrical circuits  203  in  FIG. 2D , respectively. It is noted that other suitable types of substrate can be used in place of the layers  364 ,  366  and  384  as long as they can provide sufficient mechanical strength and electrical circuits can be formed over the top surfaces thereof. 
         [0032]      FIG. 4A  shows a cross sectional view of a top portion  400  of an LED light engine in accordance with embodiments of the present invention. As depicted, the top portion  400  includes a top PCB  402  that can be made by processing a PCB  420  shown in  FIG. 4B .  FIG. 4B  shows a cross sectional view of the PCB  420  that can be processed to form the bottom PCB  402 . As depicted, the middle layer  421  is formed of suitable dielectric material, such as FR-4, and the top and bottom metal layers  422  and  424  are disposed on the top and bottom surfaces of the middle layer  421 , respectively. It is noted that the PCB  420  may include only one of the two metal layers  422  and  424 . For instance, as depicted in  FIG. 4C , the top metal layer  422  of the PCB  420  is processed to from electrical circuits  444 , where the PCB  440  corresponds to the top PCB  402 . 
         [0033]    The electrical circuits  444  may electrically couple various electrical components  408  mounted on the top PCB  402 . In embodiments, the electrical components  408  may include active and passive elements, such as bridge diode, inductor, resistor, Zener diode, so on. Also, depending on the type of each component, a different method can be used to mount the components to the substrate  402 . For instance, a legged component  410  may be mounted by inserting the legs into the dips formed in the top PCB  402 . 
         [0034]    The top PCB  402  is processed to form cavities (or holes)  404  and  406 , where the cavities  404  and  406  accommodate the LEDs  204  and the IC  208  when the top PCB  402  is combined with the bottom PCB  202 . Also, the bottom PCB  402  is processed to form one or more via holes  412 , where, as will be explained later, the via holes  412  are filled with electrically conducting epoxy  212  when the top PCB  402  is combined with the bottom PCB  202 . 
         [0035]      FIGS. 5A-5D  show the steps for processing an LED light engine  500  in accordance with embodiments of the present invention. As described in conjunction with  FIG. 2C , one or more glue/adhesive drops  210  and via filling material drops  212  are dispensed on the top surface of the bottom PCB  202 . Then, as depicted in  FIG. 5A , the top PCB  402  in  FIG. 4  is mounted on the bottom PCB  202  in  FIG. 2C  and the glue drops  210  are cured to hold the top and bottom PCBs as an integral body of the LED light engine  500 . It should be apparent to those of ordinary skill in the art that the glue drops  201  are squeezed to apply the glue to both the top and bottom PCBs. 
         [0036]    Upon mounting the top PCB  402  on the bottom PCB  202 , the via filling material from the drops  212  fills in the via holes  412  of the top PCB so that the vias  512  electrically couples one or more components of the top PCB  402  to one or more components of the bottom PCB  202 . It is noted that the vias  412  may be filled after the top PCB  402  is secured to the bottom PCB  202  by the glue  210 . 
         [0037]    As depicted in  FIG. 5B , a phosphor containing material  508  is potted over the LEDs  204  to thereby encapsulate the LEDs  204 , where the phosphor is excited by the light emitted from the LEDs to emit light having an intended wavelength range, i.e., the phosphor changes the intensity distribution over the wavelength of the light emitted by the LED. In embodiments, silicon containing phosphor is applied over the LEDs  204  and cured so that the layer  508  protects the LEDs as well as changes the wavelength range of the light from the LEDs. Also, a cap  504  for protecting the IC  208  may be disposed over the IC  208 . In embodiments, the space  506  between the cap  504  and IC  208  is filled with a sealing material so that the IC  208  is hermetically sealed. 
         [0038]    As depicted in  FIG. 5C , one or more electrical wires  510  are coupled to the LED light engine so that the LED light engine can communicate to other electrical components, such as power source.  FIG. 5D  shows covers  514  and  518  for protecting the electrical components disposed on the substrate  402 . In embodiments, a suitable material may fill in the space  512  (or  516 ) between the cover  514  (or  518 ) and the electrical components. It should be apparent to those of ordinary skill in the art that other suitable number and types of covers/filling materials may be used to protect the electrical components from mechanical and/or thermal damages. For instance, the material filling the space  512  is formed of glue so that the cover  514  is secured to the top PCB  402 . 
         [0039]      FIGS. 6A-6B  show cross sectional view of various types of LEDs and integrated circuits (ICs) for driving the LEDs in accordance with embodiments of the present invention. As depicted in  FIG. 6A , the bottom portion  600  of the LED light engine is similar to the bottom portion in  FIG. 2B , with the difference that the LEDs  608  are lateral LEDs. The LEDs  608  are electrically coupled to each other by electrical wires  610  and to the electrical circuits formed on the top surface of the bottom PCB  602 . The IC  604  are deigned to drive the LEDs  608 . 
         [0040]    As depicted in  FIG. 6B , the bottom portion  620  is similar to the bottom portion in  FIG. 2B , with the difference that the IC  626  is mounted on the bottom PCB  622  by bump balls  628 . The bump balls (or solder balls)  628  not only provide electrical connection between the IC  626  and the electrical circuits formed on the top surface of the substrate  622 , but also mechanically secure the IC  626  to the bottom PCB  622 . The IC  626  is designed to drive the LEDs  624 , where the LEDs  624  are secured to the bottom PCB  622  by bump balls  625 . 
         [0041]      FIGS. 7-8  show cross sectional views of LED light engines in accordance with embodiments of the present invention. As depicted in  FIG. 7 , the LED light engine  700  is similar to the LED light engine in  FIG. 5B , with the difference that a remote phosphor plate  702  is disposed over the LEDs in place of the potted phosphor containing layer  508 . As shown in the inset diagram, the remote phosphor plate  702  includes a phosphor containing layer  706  that is deposited beneath the bottom surface of the substrate  704  and faces the LEDs. In embodiments, the substrate  704  is formed of transparent material and passes through the light emitted by the phosphor in the layer  706 . 
         [0042]    As depicted in  FIG. 8 , the LED light engine  800  is similar to the LED light engine  700  in  FIG. 7 , with the difference that an optical device  804  is disposed over the remote phosphor plate  802  that is similar to the plate  702 . In embodiments, the optical device  804  is a lens for steering the light from the remote phosphor plate  802 . 
         [0043]    It is noted that an optical device similar to the optical device  804  may be disposed over the potted phosphor containing layer  508  so that the light from the phosphor containing layer  508  is steered by the optical device. 
         [0044]    As describe in conjunction with  FIGS. 3A-3B , the top layer  362  (or  382 ) may be patterned by suitable process, such as etching, to form various electrical components.  FIG. 9  shows a top view of a bottom portion of the LED light engine  900  in accordance with embodiments of the present invention. As depicted, the bottom portion  900  is similar to the bottom portion  200  in  FIG. 2D , with the difference that a spiral inductor  904  and meander line resistor  906  are patterned on the top surface of the bottom PCB  902 . It is noted that the other suitable types of electrical components/circuits may be deposited (or, patterned) on the top surface of the bottom PCB  902 . 
         [0045]    It should be understood, of course, that the foregoing relates to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.