Abstract:
An LED package is described that acts as a sub-mount between a printed circuit board and a diode. The sub-mount includes a laminate to thermally isolate the diode, for example an LED, from the PCB while providing a thermal heat dissipative sink for the diode.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to U.S. patent application Ser. No. 14/505,557, filed on Oct. 3, 2014, the application of which is incorporated herein by reference in its entirety. 
     FEDERAL SPONSORSHIP 
     Not Applicable 
     JOINT RESEARCH AGREEMENT 
     Not Applicable 
     TECHNICAL FIELD 
     This invention pertains generally to light emitting diodes (LED&#39;s). More particularly, the invention pertains to an LED having a thin laminate sub-mount that dissipates heat and that may be soldered to an MCPCB using conventional reflow processes or alternatively may be adhered, bolted or otherwise attached to the MCPCB. 
     BACKGROUND 
     High output LED&#39;s require an electrical current having flow rates sufficient to generate light from the diode. Current LED&#39;s typically do not convert all electrical current to light. Instead, a significant amount of the electrical current converts to heat and results in an increased temperature of the diode. Depending upon the amount of heat generated, the heat may be destructive to portions of the micro structure of the LED, leading to the failure of the diode. Although the efficiency of LED&#39;s have improved over the years, LED&#39;s continue to generate significant amounts of heat compared to the light generated from the supply of electrical current. Thus, a desire to increase the efficiency of light emission from the diode while improving upon the thermal management continues to motivate new designs for LED packages. Over the years, various heat sinks and thermal adhesives have been utilized in an attempt to dissipate heat from the LED. For example, heat sinks on the printed circuit board itself have been used to draw heat away from the diode. These heat sinks on the pcb, however, may not draw a sufficient amount of heat away from LED itself. As electrical currents required to power the LED continue to increase, there is also a need to further enhance thermal management. 
     SUMMARY 
     Embodiments according to aspects of the invention provide a thinner, heat dissipating sub-mount for an LED with a coefficient of thermal expansion similar to the printed circuit board on which the sub-mount is mounted. The sub-mount may be manufactured in shapes other than rectangular, may be mounted using conventional reflow processes, or may include bolt holes to mount the sub-mount to the PCB. In accordance with aspects of the invention, an embodiment of the invention includes a sub-mount having a metal layer defining a bottom portion of the sub-mount, a middle dielectric layer, and a top metal layer on which the LED is coupled. The top metal layer is segmented to form conductive pads layered above the first dielectric and a metal core on which the LED is mounted. Vias are formed in the dielectric layer to electrically interconnect the conductive pads with electrically isolated portions of the bottom metal layer. The conductive pads form p and n type electrodes for the LED. The bottom metal layer is treated so that it solders to a PCB or MCPCB using conventional reflow processes. The bottom metal layer has a thickness ranging between 17 microns and 70 microns and the top metal layer has a thickness between 17 microns and 1 mm. The first dielectric layer is made from a ceramic filled polymer. 
     In accordance with embodiments of the invention, a second dielectric and third metal layer are sandwiched between the top metal layer and lower dielectric layer. An electrically isolated metal core is layered between the top and bottom to support the diode and acts as a heat sink for the submount, drawing heat from the LED and away from the pcb. The metal core may further comprise a multi-layer metal composite and may include an insulating layer sandwiched between the top portion and bottom portion of the sub-mount to further manage the heat dissipation. A reflective coating may be deposited on the top layer to enhance the illumination of the LED. 
     Also in accordance with aspects of the invention, the ceramic filled polymer includes a polymer selected from the group consisting of epoxies, polyimides, cyanate esters, silicones, phenolics, BT resins, benzocyclobutene, silicone, polyphenylsulfone, polyester, and PEN and a ceramic filler selected from the group consisting of boron nitride, aluminum oxide, aluminum nitride, silicone carbide, silicon nitride, silica, magnesium oxide, zinc oxide, zirconium oxide, and titanium dioxide. 
     An embodiment of the invention includes a light emitting diode, a metal core supporting the light emitting diode, and layers of the sub-mount surrounding a portion of the metal core. The sub-mount includes a bottom metal layer, middle dielectric layer, and top metal layer. The bottom metal layer has a thickness ranging between 17 microns and 70 microns and the top metal layer has a thickness ranging between 17 microns and 1 mm. The second metal layer is segmented to form conductive pads layered above the middle dielectric layer, wherein a via is formed in the dielectric layer to electrically interconnect the conductive pads with electrically isolated portions of the bottom metal layer. Another dielectric and metal layers may be sandwiched between the top metal layer and the middle dielectric layer to provide additional heat dissipation. 
     The dielectric layers are made from a ceramic filled polymer that includes a polymer selected from the group consisting of epoxies, polyimides, cyanate esters, silicones, phenolics, BT resins, benzocyclobutene, silicone, polyphenylsulfone, polyester, and PEN and a ceramic filler selected from the group consisting of boron nitride, aluminum oxide, aluminum nitride, silicone carbide, silicon nitride, silica, magnesium oxide, zinc oxide, zirconium oxide, and titanium dioxide. 
     The accompanying drawings, which are incorporated in and constitute a portion of this specification, illustrate embodiments of the invention and, together with the detailed description, serve to further explain the invention. The embodiments illustrated herein are presently preferred; however, it should be understood, that the invention is not limited to the precise arrangements and instrumentalities shown. For a fuller understanding of the nature and advantages of the invention, reference should be made to the detailed description in conjunction with the accompanying drawings. 
     DESCRIPTION OF THE DRAWINGS 
     In the various figures, which are not necessarily drawn to scale, like numerals throughout the figures identify substantially similar components. 
       FIG. 1  is a partial sectional view of an LED package in accordance with an embodiment of the invention; 
       FIG. 2  is a partial sectional view of an LED package in accordance with an embodiment of the invention; 
       FIG. 3  is a partial sectional view of an LED package in accordance with an embodiment of the invention; 
       FIG. 4  is a partial sectional view of an LED package in accordance with an embodiment of the invention; 
       FIG. 5  is a partial sectional view of an LED package in accordance with an embodiment of the invention; 
       FIG. 6  is a partial sectional view of an LED package in accordance with an embodiment of the invention; 
       FIG. 7  is a partial sectional view of an LED package in accordance with an embodiment of the invention; and 
       FIG. 8  is a partial sectional view of an LED package in accordance with an embodiment of the invention. 
    
    
     DETAILED DESCRIPTION 
     The following description provides detail of various embodiments of the invention, one or more examples of which are set forth below. Each of these embodiments are provided by way of explanation of the invention, and not intended to be a limitation of the invention. Further, those skilled in the art will appreciate that various modifications and variations may be made in the present invention without departing from the scope or spirit of the invention. By way of example, those skilled in the art will recognize that features illustrated or described as part of one embodiment, may be used in another embodiment to yield a still further embodiment. Thus, it is intended that the present invention also cover such modifications and variations that come within the scope of the appended claims and their equivalents. 
     The LED packaging  10  of the present invention includes a thin metal substrate that replaces the thicker conventional ceramic substrate sub-mounts. The metal used in the sub-mount may comprise Cu, for example, that includes a coefficient of thermal expansion that more closely matches the coefficient of thermal expansion of the MCPCB or PCB. Matching the coefficient of thermal expansion of the sub-mount and the MCPCB or PCB improves reliability and stability of the solder joints between the sub-mount and MCPCB. Embodiments of the invention include a Cu substrate having a thickness ranging between 17 microns and 70 microns thick. The remaining portion of the sub-mount is layered on top of the substrate and the bottom surface of the substrate is treated so that it can be soldered to a PCB or MCPCB using known reflow processes. 
     A low thermal resistance dielectric layer is deposited on the substrate using known deposition techniques. The dielectric layer may have thickness ranging between 10 microns and 200 microns and a corresponding thermal resistance dependent upon the thickness of the dielectric layer. The dielectric layer preferably comprises a ceramic filled polymer. Without limitation intended, the polymers may be selected from the group consisting of epoxies, polyim ides, cyanate esters, silicones, phenolics, BT resins, benzocyclobutene, silicone, polyphenylsulfone, polyester, and PEN. Additionally, without limitation intended, the ceramic filler may be selected from the group consisting of boron nitride, aluminum oxide, aluminum nitride, silicone carbide, silicon nitride, silica, magnesium oxide, zinc oxide, zirconium oxide, and titanium dioxide. Volume fractions of the ceramic filler can range between 0-80% v/v but preferably will range between 40-65% v/v. An additional top layer of copper is deposited onto the dielectric. This Cu layer may be patterned to isolate contact pads and a core on which the LED built. 
     Various embodiments of the invention will be described in detail in connection with the corresponding Figures. Referring first to  FIG. 1 , the LED package  10  includes a sub-mount  14 , LED  20  and electrical leads  16 . The sub-mount 14  includes a bottom layer or substrate  32  of copper onto which is layered a first dielectric layer  38 . A middle layer  36  of CU is deposited or layered above the first dielectric  38  and a second dielectric  34  is layered above the middle Cu layer. A top metal layer of Cu is layered above the dielectric  34 . The top metal layer is patterned to isolate conductive pads or electrodes  26  and  28 . Additionally, a reflective layer  40  may be layered or deposited above the top layer of copper. The reflective layer is made of known suitable materials have a reflectance in the visible spectrum of greater than 85% with a reflectance greater than 90% being preferred. Prior to depositing and patterning the top layer of copper, the second dielectric layer may be patterned to form cavities into which the copper deposits. In this manner a via  35  of known suitable construction may be formed to interconnect the conductive pad  26  and middle copper layer  36 , however the conductive pad  28  is electrical conductivity with the middle layer  36 . Further, a thermally conductive core  50  is formed by metal layers  36 ,  54  and  56 . The LED  20  is positioned above the metal core and heat from the LED dissipates through the metal layers. Electrical leads  16  electrically interconnect the LED  20  with the conductive pads  26  and  28 . The substrate may also be patterned to electrically isolate the layer and electrically align portions of the substrate with the conductive pads  26  and  28 . Core layer  52  of the metal substrate aligns with the core  50 . 
       FIG. 2  illustrates the LED package  10  having a sub-mount  14 , LED  20  and electrical leads  16  wherein both conductive pads  26  and  28  require vias  35  of known suitable construction to electrically interconnect the electrical pads with the middle and lower metal layers  36  and  32 . The sub-mount  14  includes a bottom layer or substrate  32  of copper onto which is layered a first dielectric layer  38 . A middle layer  36  of CU is deposited or layered above the first dielectric  38  and a second dielectric  34  is layered above the middle Cu layer. A top metal layer of Cu is layered above the dielectric  34 . The top metal layer is patterned to isolate conductive pads or electrodes  26  and  28 . Additionally, a reflective layer  40  may be layered or deposited above the top layer of copper. A thermally conductive core  50  is formed by metal layers  36 ,  54  and  56 . The LED  20  is positioned above the metal core and heat from the LED dissipates through the metal layers. Electrical leads  16  electrically interconnect the LED  20  with the conductive pads  26  and  28 . Core layer  52  of the metal substrate aligns with the core  50 . 
       FIG. 3  illustrates an embodiment of the LED package  10  including a sub-mount  14 , LED  20  and electrical leads  16  wherein the metal core supporting the LED extends from the bottom surface of the substrate to the top metal surface underlying the LED. Similar to other embodiments, the sub-mount  14  includes a bottom layer or substrate  32  of copper onto which is layered a first dielectric layer  38 . A middle layer  36  of CU is deposited or layered above the first dielectric  38  and a second dielectric  34  is layered above the middle Cu layer. A top metal layer of Cu is layered above the dielectric  34 . The top metal layer is patterned to isolate conductive pads or electrodes  26  and  28 . Additionally, a reflective layer  40  may be layered or deposited above the top layer of copper. A thermally conductive core  50  is formed by metal layers  36 ,  52 ,  54  and  56 . The LED  20  is positioned above this metal core and heat from the LED dissipates through the metal layers to the bottom and outwards through metal layer  36 . Electrical leads  16  electrically interconnect the LED  20  with the conductive pads  26  and  28 . 
       FIG. 4  illustrates an embodiment of the LED package  10  including a sub-mount  14 , LED  20  and electrical leads  16  wherein the metal core supporting the LED extends from the bottom surface of the substrate to the top metal surface underlying the LED. Similar to other embodiments, the sub-mount  14  includes a bottom layer or substrate  32  of copper onto which is layered a first dielectric layer  34 . The top metal layer is deposited above the dielectric layer  34  and patterned to isolate conductive pads or electrodes  26  and  28 . A thermally conductive core  50  is formed by metal layers  52 ,  54  and  56 . The LED  20  is positioned above this metal core and heat from the LED dissipates through the metal layers to the bottom and outwards through metal layer  36 . Electrical leads  16  electrically interconnect the LED  20  with the conductive pads  26  and  28 . 
       FIG. 5  illustrates an embodiment of the LED package  10  including a sub-mount  14  and LED  20  wherein the LED is supported by and electrically coupled to conductive pads  26  and  28 . Similar to other embodiments, the sub-mount  14  includes a bottom layer or substrate  32  of copper onto which is layered a first dielectric layer  34 . The top metal layer is deposited above the dielectric layer  34  and patterned to isolate conductive pads or electrodes  26  and  28 . Vias  35  of known suitable construction extend through the dielectric layer  34  to electrically connect isolated portions of the top and bottom metal layers. 
       FIG. 6  illustrates an embodiment of the LED package  10  including a sub-mount  14 , LED  20  and one electrical leads  16  wherein a metal core (layers  32  and  30 ) extends from the bottom surface of the substrate to the top metal surface underlying the LED, both supporting the LED and proving a first electrode for the LED. Similar to other embodiments, the sub-mount  14  includes a bottom layer or substrate  32  of copper onto which is layered a first dielectric layer  34 . The dielectric is patterned to define a portion of the core. The top metal layer  30  is deposited into the patterned cavity of the dielectric and above the dielectric layer  34 . The top layer is further patterned to define the electrode  26 . The LED  20  is positioned above the metal core  30  and  32  and heat from the LED dissipates through the metal layers to the bottom of the sub-mount  14 . A via  35  of known suitable construction is formed in dielectric  34  to electrically interconnect and isolate a portion of the substrate  32  and electrical connector pad  26 . 
       FIG. 7  illustrates the LED package  10  having a sub-mount  14 , LED  20  and electrical leads  16  wherein both conductive pads  26  and  28  require vias  35  of known suitable construction to electrically interconnect the electrical pads with the lower metal layer  32 . The sub-mount  14  includes a bottom layer or substrate  32  of copper onto which is layered a first dielectric layer  34 . A top metal layer of Cu is layered above the dielectric  34 . The top metal layer is patterned to isolate conductive pads or electrodes  26  and  28 . The top layer is also patterned to isolate a thermally conductive core  30 . The LED  20  is positioned above the metal core  30  and heat from the LED dissipates through the metal layer  30 . Electrical leads  16  electrically interconnect the LED  20  with the conductive pads  26  and  28 . 
       FIG. 8  illustrates an embodiment of the LED package  10  including a sub-mount  14 , LED  20  and one electrical leads  16  wherein a metal core (layer  30 ) supports the LED and provides a thermal pad for the LED. Similar to other embodiments, the sub-mount  14  includes a bottom layer or substrate  32  of copper onto which is layered a first dielectric layer  34 . The top metal layer is deposited onto the dielectric layer  34 . The top layer is further patterned to define the electrode  26  and thermal pad or core  30 . The LED  20  is positioned above the metal core  30  and heat from the LED dissipates through the metal layer. Vias  35  of known suitable construction are formed in dielectric  34  to electrically interconnect an isolated portion of the substrate  32  and electrical connector pad  26  and an isolated portion of the substrate  32  and the core  30 . 
     These and various other aspects and features of the invention are described with the intent to be illustrative, and not restrictive. This invention has been described herein with detail in order to comply with the patent statutes and to provide those skilled in the art with information needed to apply the novel principles and to construct and use such specialized components as are required. It is to be understood, however, that the invention can be carried out by specifically different constructions, and that various modifications, both as to the construction and operating procedures, can be accomplished without departing from the scope of the invention. Further, in the appended claims, the transitional terms comprising and including are used in the open ended sense in that elements in addition to those enumerated may also be present. Other examples will be apparent to those of skill in the art upon reviewing this document.