Abstract:
This disclosure discloses an LED assembly. The LED assembly includes a transparent mount with a top surface and a bottom surface opposite to the top surface, an LED chip arranged on the top surface, an electrode plate, a first phosphor layer having a first phosphor, and a second phosphor layer having a second phosphor, wherein the transparent mount and the electrode plate substantially have a same width. The electrode plate is arranged on an edge of the top surface and electrically connected to the LED chip.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation application of U.S. patent application, Ser. No. 14/493,940, filed on Sep. 23, 2014, which claims priority to and the benefit of Taiwan Application Serial Number 102136176 filed on Oct. 7, 2013, which is incorporated by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    The present disclosure relates generally to light emitting diode (LED) assemblies and their applications, more specifically to the LED assemblies suitable for omnidirectional light appliances. 
         [0003]    LED has been used in different kinds of appliances in our life, such as traffic lights, car headlights, street lamps, computer indicators, flash lights, LCD backlight modules, and so on. LED chips, which are used as light sources for appliances, are produced by wafer manufacturing process in the front end, and then undergo LED packaging in the back end to result in LED assemblies or apparatuses. 
         [0004]    LED packaging mainly provides mechanical, electrical, thermal and optical supports to LED chips. LED chips, which are kind of semiconductor products, are prone to degradation, or aging, if being exposed for a long time in an atmosphere full of humidity or chemical. To isolate the LED chips from unfriendly atmosphere, epoxy resins are commonly used to cover and seal them. Heat dissipation and light extraction should be also considered for LED packaging, such that LED products could have long lifespan and high brightness. For example, the heat generated at a p-n junction in an LED chip, if not being well dissipated, could deteriorate the LED chip, shorten its lifespan, and downgrade its reliability. Optical design, such as the way to extract and direct the light into a desired angle or distribution, also plays an important issue for LED packaging. 
         [0005]    Design for packaging white LEDs is more complex and needs to further consider color temperature, color rendering index, phosphor, etc. A white LED could be provided using phosphor to convert a portion of the blue light from a blue LED chip into green/yellow light, such that the mixture of the lights is perceived as white light by human eyes. Because human eyes are vulnerable to high-intensity blue light, the blue light from a blue LED chip in a white LED package should not emit outward directly without its intensity being attenuated. In other words, the blue light should be kind of “sealed” or “capsulated” so as to prevent blue light leakage to human eyes. 
         [0006]    Furthermore, it is a constant trend in the LED industry to pursue LED packaging processes with high stability, low cost, and high product yield. 
       SUMMARY 
       [0007]    This disclosure discloses an LED assembly. The LED assembly includes a transparent mount with a top surface and a bottom surface opposite to the top surface, an LED chip arranged on the top surface, an electrode plate, a first phosphor layer having a first phosphor, and a second phosphor layer with a second phosphor, wherein the transparent mount and the electrode plate substantially have a same width. The electrode plate is arranged on an edge of the top surface and electrically connected to the LED chip. The first phosphor layer covers the LED chip, the top surface and a portion of the electrode plate. The second phosphor layer covers the bottom surface. 
         [0008]    This disclosure also discloses an LED blub. The LED bulb includes an LED assembly, a holding element and a transparent cover. The LED assembly includes a transparent mount with a top surface and a bottom surface opposite the top surface, an LED chip arranged on the top surface, an electrode plate arranged near an edge of the top surface, a first phosphor layer covering the LED chip and the top surface, and a second phosphor layer covering the bottom surface. The transparent mount and the electrode plate substantially have a same width. The holding element is physically connected to the first electrode plate. The transparent cover covers the LED assembly. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Non-limiting and non-exhaustive embodiments of the present disclosure are described with reference to the following drawings. In the drawings, like reference numerals refer to like parts throughout the various figures unless otherwise specified. These drawings are not necessarily drawn to scale. Likewise, the relative sizes of elements illustrated by the drawings may differ from the relative sizes depicted. 
           [0010]    The disclosure can be more fully understood by the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
           [0011]      FIG. 1  shows an LED assembly according to an embodiment of the disclosure; 
           [0012]      FIG. 2  shows a top view of the LED assembly in  FIG. 1 ; 
           [0013]      FIGS. 3A and 3B  show two different cross sectional views of the LED assembly in  FIG. 1 ; 
           [0014]      FIGS. 4A, 4B and 4C  illustrate LED bulbs, each using the LED assembly of  FIG. 1  as its filament; 
           [0015]      FIG. 5  demonstrates a method for manufacturing the LED assembly; 
           [0016]      FIG. 6  shows the pattern on a transparent mount; 
           [0017]      FIGS. 7A and 7B  are cross sectional views of a transparent mount; 
           [0018]      FIGS. 8A and 8B  are cross sectional views of a transparent mount after the formation of a phosphor layer; 
           [0019]      FIG. 9  demonstrates a transparent mount is attached on a transparent substrate using a phosphor layer as a glue layer; 
           [0020]      FIGS. 10A and 10B  are cross sectional views after a transparent mount is secured on a transparent substrate; 
           [0021]      FIGS. 11A and 11B  are cross sectional views after the formation of conductive electrode plates; 
           [0022]      FIGS. 12A and 125  are cross sectional views after mounting LED chips; 
           [0023]      FIGS. 13A and 13B  are cross sectional views after forming bonding wires; 
           [0024]      FIGS. 14A and 14B  are cross sectional views after the formation of a phosphor layer; 
           [0025]      FIG. 15  demonstrates another method for manufacturing an LED assembly; 
           [0026]      FIGS. 16A and 16B  show two cross sectional views of the LED assembly fabricated according to the method in  FIG. 15 ; and 
           [0027]      FIGS. 17A and 17B  demonstrate two cross sectional views of another LED assembly. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    A perspective view of an LED assembly  100  according to an embodiment of the disclosure is described in detail with reference to  FIG. 1 , while  FIG. 2  shows a top view of the LED assembly  100 . These drawings are only illustrative, and the dimensions or ratios therein are not intended to limit the invention. 
         [0029]    Shown in  FIGS. 1 and 2 , the LED assembly  100  has a laminate substrate  105  with a rectangular top surface. The manufacturing method and the structure of the laminate substrate  105  will be detailed later. On the top surface of the laminate substrate  105 , there are two conductive electrode plates  102  and  104  at two opposite ends respectively. A phosphor layer  106  is formed on the top surface and positioned on an area substantially between the two conductive electrode plates  102  and  104 . 
         [0030]      FIGS. 3A and 3B  show cross sectional views of the LED assembly  100 , resulted from the cutting planes AA and BE respectively. As shown in  FIGS. 3A and 3B , the laminate substrate  105  is composed of three layers, including a transparent substrate  112 , a phosphor layer  114  and a transparent mount  116 . The phosphor layer  114  is sandwiched between the transparent mount  116  and the transparent substrate  112 . Positioned on the transparent mount  116  are the conductive electrode plates  102  and  104 , and LED chips  108 . The phosphor layer  106  covers and surrounds the LED chips  108 , which are mounted on the transparent mount  116 , and therefore the LED chips  108  are sandwiched between the phosphor layer  106  and the transparent mount  116 . Bonding wires  110  provide electrical interconnection between the LED chips  108  and also electrically connect two of the LED chips  108  to the conductive electrode plates  102  and  104 . 
         [0031]    In this specification, “transparent” means having the property of transmitting rays of visible light, and could refer to as transparent, translucent or semitransparent. In some embodiments, the transparent mount  116  and the transparent substrate  112  are not electrically conductive, and could be made of the same or different material. For example, they could be sapphire, silicon carbide, or diamond-like carbon. 
         [0032]    The LED chips  108  in  FIGS. 1, 2, 3A and 3B  are all blue LED chips in one embodiment and are mounted and arranged as a row on the transparent mount  116 . This invention is not limited to the abovementioned, nevertheless. Based on desired applications, the LED chips  108  might be arranged to form any pattern on the transparent mount  116 , which for instance could have two or three rows. In other embodiments, some of the LED chips  108  emit blue light with a dominant wavelength ranging from 430 nm to 480 nm, some emit red light with a dominant wavelength ranging from 630 nm to 670 nm, and some emit green light with a dominant wavelength ranging from 500 nm to 530 nm. 
         [0033]    An LED chip  108  might have only one single LED cell, whose forward voltage is about 2 to 3 volts, and this kind of LED chip is referred to as a low-voltage LED chip hereinafter. Comparatively, an LED chip  108  in another embodiment might include several LED cells connected in series, and is referred to as a high-voltage LED chip hereinafter, because its forward voltage might be as high as 12V, 24V, or 48V, much higher than that of a low-voltage LED chip. In one high-voltage LED chip, each LED cell has a light-emitting layer, and the LED cell might be formed on an epitaxial or non-epitaxial substrate. More specifically, the LED cells in the high-voltage LED chip are electrically connected to each other on a common substrate; not by wire bonding but by some patterned conductive strips produced by wafer processes, such as metallization or lithography that processes all the LED cells at the same time. The common substrate might be an epitaxial or non-epitaxial substrate. In  FIGS. 1, 2, 3A and 3B , the LED chips  108  are connected in series so the forward voltage is the summation of the forward voltages of the individual LED chips  108 . This disclosure is not limited to the abovementioned, however. In some embodiments, the LED chips  108  could be connected in many different configurations, including series, parallel, bridge or any combination thereof. 
         [0034]    Trenches  109   a ,  109   h ,  109   c  and  109   d  are formed in the transparent mount  116 . Trenches  109   a  and  109   b  shown in  FIG. 3A  are substantially in parallel to each other, and trenches  109   c  and  109   d  shown in  FIG. 3B  are substantially in parallel to each other. As derivable from  FIGS. 3A and 3B , the trenches  109   a ,  109   b ,  109   c  and  109   d  are positioned to substantially surround the LED chips  108 . In other words, the area where the LED chips  108  is mounted on the transparent mount  116  is between the trenches  109   a  and  109   b , and between trenches  109   c  and  109   d  as well. As shown in  FIGS. 3A and 3B , the phosphor layer  106  entirely fills up the trenches  109   a ,  109   b ,  109   c  and  109   d , and through them contacts the phosphor layer  114 . 
         [0035]    Both the phosphor layers  106  and  114  have at least one kind of phosphor. For example, the phosphor in the phosphor layers  106  and  114  could be excited by the blue light (with a dominant wavelength of 430 nm˜480 nm) emitted from the LED chips  108  to generate yellow light (with a dominant wavelength of 570 nm˜590 nm) or yellowish-green light (with a dominant wavelength of 540 nm˜570 nm), such that the mixture is perceivable as white light by human eyes. The phosphor layers  106  and  114  could be transparent body in which phosphor is dispersed. The transparent body is epoxy resin, or silicone for example. The phosphor in the phosphor layer  106  might be the same as or different from that in the phosphor layer  114 . The phosphor could include, but is not limited to, yttrium aluminum garnet (YAG), or terbium aluminum garnet (TAG). The phosphor layers  106  and  114  might have one or more kinds of phosphor. For instance, in one embodiment the phosphor layers  106  and  114  have two kinds of phosphor, one emitting yellow light and the other emitting red light. Phosphor emitting green light could be also included in some embodiments. 
         [0036]    A phosphor capsule formed by the phosphor layers  106  and  114  substantially encapsulates each LED chip  108 . The light emitted from the LED chips  108 , whether it goes upward or sideward, confronts the phosphor layer  106  and the light emitted from the LED chips  108 , whether it goes downward, confronts the phosphor layer  114 . In case that some of the LED chips  108  are blue LED chips, the blue light therefrom excites the phosphor in the phosphor layer  106  or  114  to generate a yellow light or yellowish-green light such that a mixing light of the blue light and the yellow light or yellowish-green light is sensed by a human eye as a white light, so that the total intensity of the blue light is attenuated to avoid any harmful effect to human eyes. 
         [0037]      FIG. 4A  illustrates an LED bulb  200   a  using the LED assembly  100  as its filament. The LED bulb  200   a  has two clamps  202 , each of which might be in a shape of V or Y. The clamps  202  are made of conductive material, and the two projecting prongs of each clamp  202  clamp one conductive electrode plate (either  102  or  104 ) to hold the LED assembly  100  within a cover  204  of the LED bulb  200   a . In  FIG. 4A , the surface with the phosphor layer  106  faces upward (along the z direction). The clamps  202  also electrically connect both the conductive electrode plates  102  and  104  to the Edison screw base  203  of the LED bulb  200   a , which provides the electric power required for the LED assembly  100  to emit light.  FIG. 4B  is similar with  FIG. 4A , but differs in the direction that the LED assembly  100  faces. In  FIG. 4B , the surface of the LED assembly  100  having the phosphor layer  106  faces sideward (along the y direction), and is substantially perpendicular with the screw axis (along the z direction) of the LED bulb  200   b  in  FIG. 4B .  FIG. 4C  is similar with  FIG. 4B , but differs in that the supports  209  are solid strips with a rectangular shape. Each of the supports  209  has a notch  213  at its end to support the LED assembly  100  within a cover  204  of the LED bulb  200   c . The supports  209  could be made of metal or some kind of conductive material, capable of conducting electric current from the Edison screw base  203  to the conductive electrode plates  102  and  104  at ends of the LED assembly  100 . Because of the transparency of the transparent substrate  112  and the transparent mount  116 , the LED bulb  200   a ,  200   b  and  200   c  all could be omnidirectional lighting apparatuses. 
         [0038]      FIG. 5  demonstrates a process flow for manufacturing the LED assembly  100 . The steps are detailed in reference with the following drawings. 
         [0039]    Regarding to step  302 , a sheet of the transparent mount  116  is provided and has a plurality of the same or similar repeated patterns on its surface as shown in  FIG. 6 . The pattern on the transparent mount  116  in  FIG. 6  has 2 rows in a horizontal direction and 4 columns in a vertical direction to produce eight LED assemblies  100  at one time. The example in  FIG. 6  is not intended to limit the invention. From one single sheet, some embodiments of the invention could produce only one LED assembly  100 , and others might produce more than 8 LED assemblies  100 . 
         [0040]    The pattern in  FIG. 6  is composed of trenches  109   a ,  109   b ,  109   c ,  109   d ,  109   e , and  109   f , where the trenches  109   a  are substantially in parallel to the trenches  109   b , and the trenches  109   c  are substantially in parallel to the trenches  109   d .  FIGS. 7A and 7B  are cross sectional views of the transparent mount  116  resulted from the cutting planes AA and BB in  FIG. 6  respectively. The trenches  109   a ,  109   b ,  109   c  and  109   d  substantially enclose the area where the LED chips  108  are going to be mounted. The trenches  109   e  and  109   f  substantially define the location for a single LED assembly  100 , to ease the singulation in the following step which will be detailed later. The trenches  109   a ,  109   b ,  109   c ,  109   d ,  109   e , and  109   f  might be formed by dry or wet etching, for example. 
         [0041]    Regarding to step  304 , coating or spraying is used to form the phosphor layer  114  on the transparent substrate  112 , as demonstrated in  FIGS. 8A and 8B . Some ditches are formed in the transparent substrate  112  prior to the formation of the phosphor layer  114 . These ditches preferably locate just under the trenches  109   e  and  109   f  after the transparent mount  116  stacks on the transparent substrate  112  for easily singulating. 
         [0042]    Regarding to step  306 , the transparent mount  116  is attached on the transparent substrate  112  using the phosphor layer  114  or an additional transparent material as a glue layer, as demonstrated in  FIG. 9 .  FIGS. 10A and 10B  are cross sectional views corresponding to  FIGS. 7A and 73  after the transparent mount  116  is attached on the transparent substrate  112 . 
         [0043]    Regarding to step  308 , the conductive electrode plates  102  and  104  are formed on the transparent mount  116 , as demonstrated in  FIGS. 11A and 113 . Some metal films or strips could be attached on proper areas of the transparent mount  116  to be the conductive electrode plates  102  and  104 . 
         [0044]    Referring to Step  310 , the LED chips  108  are mounted on the transparent mount  116  by way of silver paste for example, as shown in  FIGS. 12A and 123  which respectively correspond to  FIGS. 11A and 11B . 
         [0045]    Referring to Step  312 , bonding wires  110  are formed to provide electric interconnection between the LED chips  108 , and between the LED chips  108  and the conductive electrode plates  102  and  104 , as demonstrated in  FIGS. 13A and 133 , which respectively correspond to  FIGS. 12A and 123 . 
         [0046]    Regarding to step  314 , the phosphor layer  106  is formed to cover or seal the bonding wires  110 , the LED chips  108 , and the trenches  109   a ,  109   b ,  109   c  and  109   d , as shown in  FIGS. 14A and 143 , which respectively correspond to  FIGS. 13A and 133 . In  FIGS. 14A and 14B , the phosphor layer  106  does not extend over the trenches  109   e  and  109   f . In one embodiment, the phosphor layer  106  is formed on the LED chips  108  by dispensing. 
         [0047]    Referring to Step  316 , the transparent substrate  112  and the transparent mount  116  are singulated, by cleaving, laser cutting, carbon dioxide laser cutting, for example to forma plurality of individual LED assemblies  100 . As aforementioned, the transparent mount  116  is capable of produce eight LED assemblies  100  at one time. These LED assemblies  100  in  FIGS. 14A and 14B  could be separated by cleaving along the trenches  109   e  and  109   f , so as to finalize the LED assemblies  100 , whose cross sectional views have been demonstrated in  FIGS. 3A and 3B , which respectively correspond to  FIGS. 14A and 14B . 
         [0048]    The method exemplified in  FIG. 5  produces no pattern at the backside of the transparent substrate  112 . Therefore, handling, holding or supporting the transparent substrate  112  could be done via the backside of the transparent substrate  112  where scratches are not a concern. Accordingly, the yield rate of the LED assemblies  100  could be improved. 
         [0049]    In another embodiment, some of the phosphor layer  106  is inside the trenches  109   a ,  109   b ,  109   c , and  109   c , but does not completely fill them up. The phosphor  106 , nevertheless, preferably covers at least one sidewall in each of the trenches  109   a ,  109   b ,  109   c , and  109   c  such that the phosphor  106  form walls inside the trenches to surround the area where the LED chips  108  are disposed. 
         [0050]    The bonding wires  110  are used for electrical interconnection in  FIGS. 3A and 3B , but this invention is not limited to this embodiment. Another embodiment of this disclosure has a printed circuit on the transparent substrate  116 , and the LED chips  108  are flipped over to mount on the printed circuit, which provides the interconnection between the LED chips  108 . As to the electrical connection to the conductive electrode plates  102  and  104 , it could be done using the bonding wires  110  or a printed circuit as well. 
         [0051]      FIG. 15  demonstrates another method for manufacturing an LED assembly, and  FIGS. 16A and 16B  are cross sectional views of the LED assembly  600  produced according to the method illustrated in  FIG. 15 . The similarity between  FIGS. 15 and 5  is comprehensible according to the disclosed teaching and will be omitted herein for brevity. Different from  FIG. 5 , in  FIG. 15 , an additional step  307  is inserted between steps  306  and  308 , and another step  314   a  is in exchange for step  314 . 
         [0052]    In Step  307 , a phosphor layer  107  fills in the trench  109   a ,  109   b ,  109   c  and  109   d , as demonstrated in  FIGS. 16A and 16B . In one embodiment, the top surface of the phosphor layer  107  is even with that of the transparent mount  116 , or in other words the two top surfaces are coplanar. The phosphor layer  107  formed by step  307  could avoid the occurrence of the side leakage of blue light. After the formation of the phosphor layer  107 , in step  314   a , the phosphor layer  106  is formed to cover the LED chips  108  and the bonding wires  110 . The phosphor layer  106  in  FIG. 16A  does not extend over the phosphor layer  107  or the trenches  109   a  and  109   b . Nevertheless, in step  314   a , a phosphor layer  106  can be formed to cover the phosphor layer  107  or the trenches  109   a  and  109   b  in some other embodiments. Demonstrated in  FIG. 16B , the phosphor layer  106  covers or extends over the trenches  109   c  and  109   d . In the embodiment exemplified in  FIGS. 16A and 16B , the LED chips  108  are substantially enclosed by a phosphor capsule composed of the phosphor layers  106 ,  114 , and  107 . The light emitted from the LED chips  108  will encounter the phosphor layer  106  and  107  if going upward and sideward, or the phosphor layer  114  if going downward. Therefore, the LED assembly  600  could avoid blue light leakage. The phosphors in the phosphor layers  106 ,  107 , and  114  could be the same, similar or different. 
         [0053]    In  FIGS. 3A, 3B, 16A, and 16B , the trenches  109   a ,  109   b ,  109   c , and  109   d  penetrate through the transparent mount  116 , so that the phosphor layer  106  or  107  can contact with the phosphor layer  114  via these trenches. This invention is not limited to the abovementioned, however.  FIGS. 17A and 17B  demonstrate two cross sectional views of another LED assembly  700 , and their similarity with  FIGS. 3A and 3B  are omitted herein for brevity. The trenches  109   a ,  109   b ,  109   c  and  109   d  in  FIGS. 17A and 17B  do not penetrate the transparent mount  116 , which means the trenches  109   a ,  109   b ,  109   c  and  109   d  are shallower in comparison with those in  FIGS. 3A and 3B , and each has a bottom larger than 0 μm but not more than 150 μm apart from the top surface of the phosphor layer  114 . The phosphor layer  106  does not contact with the phosphor layer  114 . The light from the LED chips  108  could not leak through the gap between the phosphor layers  106  and  114  if the gap is less than 150 μm. 
         [0054]    In  FIGS. 17A and 17B , the LED chips  108  are mounted on a bottom of a mounting trench  109   g  between the trenches  109   c ,  109   d  and can avoid blue light leakage. 
         [0055]    Some LED assemblies of the disclosure could be used as a filament in an LED bulb to form an omnidirectional lighting apparatus. Some LED assemblies of the disclosure has a blank backside with no pattern, which is immune from scratches and convenient for being contacted, held, or vacuumed during manufacturing processes. 
         [0056]    While the disclosure has been described by way of example and in terms of preferred embodiment, it is to be understood that the disclosure is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.