Patent Publication Number: US-2023142465-A1

Title: Led assembly with omnidirectional light field

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of co-pending application Ser. No. 17/091,938, filed on Nov. 6, 2020, which is a Continuation of application Ser. No. 14/309,828, filed on Jun. 19, 2014, for which priority is claimed under 35 U.S.C. § 120; and this application claims priority of Application No. 102122873 filed in Taiwan on Jun. 27, 2013 and Application No. 103111887 filed in Taiwan on Mar. 27, 2014 under 35 U.S.C. § 119; the entire contents of all of which are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     The present disclosure relates generally to light emitting diode (LED) assemblies, and more specifically, to LED assembly that has an omnidirectional light field. 
     LED has been used in different kinds of appliances in our daily life, such as traffic lights, car headlights, street lamps, computer indicators, flash lights, LCD backlight modules, and so on. Beside the semiconductor manufacturing process in the front end, the LED chips used in these appliances should go through LED packaging in the back end. 
     LED packaging mainly provides mechanical, electrical, thermal, and optical supports to LED chips. LED chips, which are a kind of semiconductor products, are prone to performance degradation, or aging, if exposed for a long time in an atmosphere full of humidity or chemical. Epoxy resin is commonly used in LED packaging to cover or seal LED chips, such that LED chips are effectively isolated from detrimental atmosphere. Furthermore, LED packaging should take heat dissipation and luminance extraction into consideration, in order to make LED assembly more power-saving and reliable. Heat generated in an LED chip must be dissipated efficiently. Otherwise, heat accumulated in the PN junction of an LED chip will damage or degrade its performance, shortening its lifespan. Optical design is also a key factor when designing of LED packaging. Light emitted from an LED chip must be transmitted in a way that results in certain luminance distribution with certain intensity. 
     The design for packaging a white LED further needs to consider color temperature, color rendering index, phosphor, etc. The white LED could be provided by phosphor converting a portion of 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 go outside 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. 
     In order to make products more competitive in the market, LED package manufactures constantly pursue packaging processes which are reliable, low-cost, and high-yield. 
     SUMMARY OF THE DISCLOSURE 
     The present disclosure provides a light emitting diode assembly. 
     The light emitting diode assembly comprises a transparent substrate, comprising first and second surfaces facing to opposite orientations respectively; light emitting diode chips, mounted on the first surface; a circuit electrically connecting the light emitting diode chips; a transparent capsule with a phosphor dispersed therein, formed on the first surface and substantially enclosing the circuit and the light emitting diode chips; and first and second electrode plates, formed on the first or second surface, and electrically connected to the light emitting diode chips. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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. 
       The disclosure can be more fully understood by the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG.  1    illustrates an LED assembly according to embodiments of the disclosure; 
         FIG.  2 A  demonstrates a top view of the LED assembly in  FIG.  1   ; 
         FIG.  2 B  demonstrates a bottom view of the LED assembly in  FIG.  1   ; 
         FIG.  3 A  demonstrates a cross-sectional view of the LED assembly in  FIG.  2 A  along line AA, and  FIG.  3 B  demonstrates that along line BB; 
         FIG.  4    shows a light bulb using several LED assemblies assembled therein as its lighting sources; 
         FIG.  5 A  demonstrates that the LED assembly is fixed on a circuit board by solder joints; 
         FIG.  5 B  demonstrates a clamp with two metal jaws to grasp and hold one LED assembly vertically on a circuit board; 
         FIG.  6    illustrates a manufacturing process for producing the LED assembly of  FIGS.  3 A and  3 B ; 
         FIGS.  7 A and  7 B  demonstrate top and bottom views of an LED assembly respectively, according to embodiments of the disclosure; 
         FIGS.  8 A and  8 B  show two cross-sectional views of the LED assembly in  FIG.  7 A  along line AA and line BB; 
         FIGS.  8 C and  8 D  show two cross-sectional views of an LED assembly 
         FIG.  9    exemplifies a manufacturing method to produce an LED assembly; 
         FIG.  10    is a drawing of LED assembly in one embodiment of the disclosure; 
         FIGS.  11 A and  11 B  are top and bottom views of an LED assembly respectively; 
         FIG.  12 A  demonstrates a cross-sectional view of the LED assembly along line AA in  FIG.  11 A ; 
         FIG.  12 B  demonstrates a cross-sectional view of the LED assembly along line BB in  FIG.  11 A ; 
         FIG.  12 C  shows another LED assembly  400   b;    
         FIG.  13    is a drawing of an LED assembly in one embodiment of the disclosure; 
         FIGS.  14  and  15    are a top view and a cross-sectional view of an LED assembly, respectively; 
         FIGS.  16  and  17    are a top view and a cross-sectional view of an LED assembly, respectively; 
         FIG.  18    is a cross-sectional view of an LED assembly and  FIG.  19    demonstrates a method for manufacturing it; 
         FIG.  20    is a pictorial drawing of an LED assembly; 
         FIGS.  21 A and  21 B  are a top view and a cross-sectional view of an LED assembly, respectively; 
         FIG.  22    demonstrates a cross-sectional view of an LED assembly; 
         FIG.  23    demonstrates a cross-sectional view of LED assembly; 
         FIG.  24    is a drawing of an LED assembly; 
         FIG.  25 A  shows a top view of the LED assembly; 
         FIG.  25 B  shows a top view of the LED assembly; 
         FIG.  26 A  is a pictorial drawing of an LED assembly in one embodiment of the disclosure; 
         FIGS.  26 B and  26 C  are a top view and a cross-sectional view of the LED assembly in  FIG.  26 A , respectively; 
         FIG.  27 A  illustrates an LED lamp using LED assembly as its filament; and 
         FIG.  27 B  illustrates an LED lamp using LED assembly as its filament. 
     
    
    
     DETAILED DESCRIPTION 
     An LED assembly  100  according to an embodiment of the disclosure is described in detail with reference to  FIG.  1   . The LED assembly  100  has a transparent substrate  106 , which is for example an electrically non-conductive glass. The transparent substrate  106  has a top surface  102  and a bottom surface  104  facing to opposite orientations respectively. As shown in  FIG.  1   , the transparent substrate  106  is substantially in the form of a thin and longitudinal strip with two ends  114  and  116 . In this specification, the term, transparent, only means admitting the passage of light and could also be referred to as translucent or semitransparent. Objects situated behind a transparent material in this specification might be distinctly or indistinctly seen. In other embodiments, the transparent substrate  106  is sapphire, ceramic material (ex. Al 2 O 3  or AlN), silicon carbide (SiC), or diamond-like carbon (DLC). It is noted that the transparent substrate  106  can contain a plurality of thermal-conduction particles or other components for reducing process temperature during its manufacturing process. 
       FIG.  2 A  demonstrates a top view of an LED assembly  100   a , which exemplifies the LED assembly  100  in one embodiment. Mounted on the top surface  102  are several blue LED chips  108  electrically connected to each other through a circuit mainly composed of bonding wires  110 , which provide interconnection to the blue LED chips  108 . Each blue LED chip  108  could 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, each blue LED chip  108  might include several LED cells connected in series, and is referred to as a high-voltage LED chip hereinafter, because its forward voltage could be as high as 12V, 24V, or 48V, much higher than that of a low-voltage LED chip. In one embodiment, each LED cell has a light-emitting layer in a diode formed on a substrate, which could be an epitaxial or non-epitaxial substrate. More specifically, the LED cells in a 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 semiconductor processes, such as metallization or lithography that processes all the LED cells at the same time. In  FIG.  1    and  FIG.  2 A , the blue LED chips  108  are arranged in two rows beside a longitudinal line that links two ends  114  and  116  of the transparent substrate  106 . The bonding wires  110  electrically connect the blue LED chips  108  in series, generating an equivalent LED device with a high forward voltage. The blue LED chips  108  are not limited to connect in series and arrange in two rows though. In some other embodiments, the blue LED chips  108  might be arranged to any kind of patterns and could be electrically connected in series, in parallel, in series-parallel, in bridge or in the combination thereof. 
     As shown in  FIG.  2 A , the transparent substrate  106  has a conductive via  107  close to the end  114 . The conductive via  107  has a via hole tunneling through the transparent substrate  106  and the via hole is formed with electrically-conductive material filled therein or coated on its sidewall, so as that the conductive via  107  is capable of coupling or connecting an electric component on the top surface  102  to another on the bottom surface  104 . Nearby the end  114  has a conductive electrode plate  118  on the top surface  102 . The conductive electrode plate  118  locates between the end  114  and the conductive via  107 . The conductive electrode plate  118  does not directly contact with conductive via  107 . One of the blue LED chips  108 , specifically labeled as  108   a  in  FIG.  2 A , is close to the end  114  and has a bonding wire  110  thereon to electrically connect to the electrode plate  118 . Another blue LED chip  108   b , which is close to the end  114 , is electrically connected to the conductive via  107  by another bonding wire  110 . 
     All the blue LED chips  108  and all the bonding wires  110  on the top surface  102  are covered by a transparent body  112  to prevent moisture or chemical in atmosphere from damaging or aging the blue LED chips  108  or the bonding wires  110 . The transparent body  112  is epoxy resin or silicone, for example. Dispersed in the transparent body  112  is at least one kind of phosphor that is capable of converting portion of the blue light from blue LED chips  108  (having a peak wavelength about 430 nm to 480 nm) into yellow light (having a peak wavelength from about 570 nm to 590 nm) or yellowish green light (having a peak wavelength about 540 nm to 570 nm), such that human eyes perceive white light from the mixture. In one embodiment, the transparent body  112  comprises two kinds of phosphors dispersed therein. One of the phosphors is capable of converting portion of the blue light from blue LED chips  108  into yellow light or yellowish green light or green (having a peak wavelength from about 520 nm to 590 nm) and the other of the phosphors is capable of converting portion of the blue light from blue LED chips  108  into red light (having a peak wavelength from about 610 nm to 680 nm).  FIG.  1    is illustrative to show blue LED chips  108  and bonding wires  110  clearly visible under transparent body  112 . In one embodiment, as aforementioned, the term, transparent, only means admitting the passage of light and could also be referred to as translucent or semitransparent. Therefore, the transparent body  112  can be translucent or semitransparent such that the LED chips  108  and the bonding wires  110  could be distinctly or indistinctly seen behind the transparent body  112 . In another embodiment, the LED chips  108  and the bonding wires  110  could be invisible because of the phosphor dispersed inside the transparent body  112  and the transparent body  112  appears the color of the phosphor dispersed therein. 
       FIG.  2 B  demonstrates a bottom view of the LED assembly  100   a . As shown in  FIG.  2 B , no blue LED chips are mounted on the bottom surface  104 . Formed on the bottom surface  104  nearby the end  114  is another electrode plate  120 , which electrically connects to the conductive via  107 . In one embodiment, the electrode plate  120  geometrically overlaps and physically contacts with the conductive via  107 . In another embodiment, the conductive via  107  and the electrode plate  120  do not overlap, and a conductive device, such as a bonding wire or a metal strip, is located therebetween to electrically connect them to each other.  FIG.  2 B  also shows an optional electrode plate  122  formed on the bottom surface  104  nearby the end  116 . This kind of design could have the electrode plates  122  and  120  coplanar, and therefore the LED assembly  100   a , during handling or transportation, could be steadier to avoid flipping or falling. The electrode plate  122  electrically floats in this embodiment. In other words, the electrode plate  122  does not electrically couple or connect to any electric devices or elements in the LED assembly  100   a . When the LED assembly  100   a  is laid on a planar surface, the electrode plate  122  helps stabilize the LED assembly  100   a.    
     The embodiment shown in  FIGS.  2 A and  2 B  has the electrode plates  120  and  118  located completely within the top surface  102  or the bottom surface  104  as the electrode plates  120  and  118  do not extend across the edges of the top surface  102  and the bottom surface  104 . The electrode plates  120  and  118  are not required to be rectangular or to have the same size. For example, one of the electrode plates  120  and  118  could be about rectangular, indicating a cathode of the LED assembly  100   a , while the other is about spherical, indicating an anode of the LED assembly  100   a.    
     In view of electric connection, the blue LED chips  108  and the conductive via  107  are connected in series between the electrode plates  120  and  118 , which are two power input nodes for powering the LED assembly  100   a . A conventional power supply (not shown) would have two power output terminals respectively contacting the electrode plates  120  and  118  to drive and illuminate the blue LED chips  108 . 
       FIG.  3 A  demonstrates a cross-sectional view of the LED assembly  100   a  in  FIG.  2 A  along line AA, and  FIG.  3 B  demonstrates that along line BB. 
     Shown in  FIG.  3 A , a bonding wire  110  connects the blue LED chip  108   b  to the conductive via  107 , which in turn connects to the electrode plate  120  on the bottom surface  104 . In  FIG.  3 B , another bonding wire  110  connects the blue LED chip  108   a  to the electrode plate  118 .  FIG.  4    shows a light bulb using several LED assemblies  100  as its lighting sources. The light bulb in  FIG.  4    includes a lamp shell  180 , the LED assemblies  100 , a circuit board  192 , a heat dissipation apparatus  182  and an electrical connection structure  183 . The end  114  of each LED assembly  100  fixes on the circuit board  192 , which firmly mounts on the heat dissipation apparatus  182  such that the heat generated by the LED assembly  100  could be dissipated efficiently. The heat dissipation apparatus  182  stays firmly on the electrical connection structure  183 , which is for example an Edison screw base capable of screwing into a matching socket. As both electrode plates  120  and  118  are nearby a common end  114  of the transparent substrate  106  in one LED assembly  100  but locate on opposite surfaces, electrically-conductive blocks, such as solder joints  190 , can electrically connect the electrode plates  120  and  118  to two different terminals on the circuit board  192 , respectively, as shown in  FIG.  5 A . Beside the electrical connection, the solder joints  190  also provide mechanical support to the end  114 , to hold the LED assembly  100  up straight on the circuit board  192 , so the LED assembly  100 , if illuminating, could generate an omnidirectional light field to its surrounding. In  FIG.  5 A , one LED assembly  100  stands, but is not limited to stand, almost vertically, only by way of the mechanical support provided by the solder joints  190 , which also transmit any necessary electric power from the circuit board  192  to the LED assembly  100 .  FIG.  5 B  demonstrates a clamp with two metal jaws  194  to grasp and hold one LED assembly  100  vertically on the circuit board  192 . The metal jaws  194  provide both electrical connection and mechanical support to one LED assembly  100 , simplifying the manufacture processes required to secure the LED assembly  100  on the circuit board  192 . In some embodiments, an LED assembly  100  stands on the circuit board  192  with a sloping position. 
     Exemplified in  FIG.  3 A  is a vertically-conducting device  130  placed on the top surface  102  above the conductive via  107 . The vertically-conductive device  130  conducts current vertically, and is by way of examples a PN junction diode (such as a vertical-type light-emitting diode, a schottky diode or a zener diode), a resistor, or simply a metal ingot, adhering on the conductive via  107  via a conductive silver paste. In another embodiment, the vertically-conducting device  130  and the conductive silver paste demonstrated in  FIG.  3 A  could be omitted and a bonding wire  110  bonding on both the conductive via  107  and the blue LED chip  108   b  provides necessary electric connection. 
     In both non-limiting  FIGS.  3 A and  3 B , each blue LED chip  108  has a transparent adhesive layer  132  thereunder, each adhering only one corresponding blue LED chip  108  on the top surface  102  of the transparent substrate  106 . In another embodiment, there are several transparent adhesive layers  132  on the top surface  102 , and at least one of the adhesive layers carries several blue LED chips  108 . In another embodiment, there is only one single transparent adhesive layer  132  to adhere all blue LED chips  108  to the top surface  102 . Tradeoff occurs to the area size of one transparent adhesive layer  132 . The larger the area of a transparent adhesive layer  132 , the more effective the heat dissipation that the transparent adhesive layer  132  provides to the blue LED chips  108  thereabove, in expense of the more shear stress due to the difference in thermal expansion coefficients of the transparent adhesive layer  132  and the transparent substrate  106 . Accordingly, the design of both the area size of one transparent adhesive layer  132  and the number of the blue LED chips  132  carried on by one transparent adhesive layer  132  depends on actual applications and might vary. In some embodiments, some particles with excellent thermal conductivity, such as alumina powder, diamond-like carbon, or silicon carbide, whose thermal conductivity is more than 20 W/mK, are dispersed in one transparent adhesive layer  132 . These particles help not only dissipate heat, but also scatter the light from the blue LED chips  108 . 
     The transparent adhesive layers  132  could be epoxy resin or silicone, and mix with phosphor similar with or different from that of the transparent body  112 . The phosphor is, for example, yttrium aluminum garnet (YAG) or terbium aluminum garnet (TAG). As mentioned, the transparent body  112  with phosphor covers above and surrounds each blue LED chip  108  while the transparent adhesive layers  132  locates under each blue LED chips  108 . The transparent body  112  and the transparent adhesive layers  132  sandwich blue LED chips  108 . In other words, the transparent body  112  and the transparent adhesive layers  132  together as a whole become a kind of transparent capsule that encloses all blue LED chips  108 , but leaves a portion of electrode plate  118  exposed for external electric connection. The blue or UV light from any blue LED chip  108  inevitably experiences conversion, so that human eyes could avoid damage or stress caused by over high intensity of the blue or UV light. 
     A manufacturing process for producing the LED assembly  100   a  of  FIGS.  3 A and  3 B  is described in detail with reference to  FIG.  6   . In Step  148 , a transparent substrate  106  is provided with a conductive via  107  formed in advance. For example, a laser beam could be used to melt a small area of the transparent substrate  106  so as to form a via hole on the transparent substrate  106 . An electrically-conductive material could fill in the via hole or be coated on the via hole to form the conductive via  107 . In Step  150 , the transparent substrate  106  is pre-cut, forming some trenches or grooves thereon, which geometrically partition LED assemblies  100  that are formed and separated in the end. In Step  152 , electrode plates  118  and  120  are attached respectively on top and bottom surfaces ( 102 ,  104 ) of the transparent substrate  106 , both nearby the end  114 . In case that an electrode plate  112  is expected, it is formed nearby the end  116  in step  152 . For example, electrode plates would be formed by screen printing and/or lift-off process, to generate specific conductive patterns on the top and bottom surfaces ( 102 ,  104 ) of the transparent substrate  106 . In Step  154 , one or more transparent adhesive layers  132  with phosphor is formed on the top surface  102  by gluing, printing, spraying, dispensing, or coating, for example. 
     In Step  155 , blue LED chips  108  are mounted on the transparent adhesive layers  132 . A vacuum nuzzle, for example, picks up blue LED chips  108  one by one and then put them to adhere on to specific locations of the transparent adhesive layers  132 . In reference to a top view of an LED assembly, preferably each blue LED chip  108  is completely surrounded by the periphery of one transparent adhesive layer  132 , so as to form a phosphor capsule in the end to totally seal a blue LED chip  108  therein. In other words, the transparent adhesive layer  132  has a flat area larger than the total area of all blue LED chips  108 , so as to completely cover the backsides of all blue LED chips  108 . Meanwhile, a silver paste can be used to attach a vertically-conductive device  130  on the top surface  102  and adhere it to the conductive via  107 . Bonding wires  110  are formed in step  156 , to provide an electric connection between every two blue LED chips  108 , between the blue LED chip  108   a  and the electrode plate  118 , and between the blue LED chip  108   b  and the vertically-conductive device  130 . In Step  157 , a transparent body  112  with phosphor is formed on the top surface  102 , to encapsulate the bonding wires  110  and the blue LED chips  108 , by way of dispensing or screen printing. In Step  158 , a singulation process is performed, where the transparent substrate  106  is cut to form a plurality of individual LED assemblies  100 , by way of saw cutting along the previously-formed trenches or grooves for example. 
     It can be derived from  FIG.  6    that, in step  152 , the electrode plates  120  or  122  are formed on the bottom surface  104 . However, in step  154 - 157 , all the transparent adhesive layer  132 , the LED chips  108 , the bonding wires  110  and the transparent body  112  are formed on the top surface  102 . Therefore, only large patterns like the electrode plates  120  and  122  are formed on the bottom surface  104 , which are immune from casual tiny scratches. In addition, holders, carriers, or robot arms for transporting or holding the transparent substrate  106  could physically contact the bottom surface  104  to avoid any damage to the fine patterned structures on the top surface  102 , such that yield improvement is foreseeable. 
     Embodiments exemplified in  FIGS.  3 A,  3 B, and  6    do not restrain the direction where the light from a blue LED chip  108  goes. The light from a blue LED chip  108  could go downward through the transparent adhesive layer  132  and the transparent substrate  106  to provide light that appears white. The light from a blue LED chip  108  could go upward or vertically through the transparent body  112  to provide white light as well. Therefore, the LED assembly  100   a  is a lighting device that has an omnidirectional white light field. As the lamp in  FIG.  4    uses the LED assemblies  100  as its light resources, it could be an omnidirectional white lighting apparatus, which is possible to replace a traditional incandescent lamp. 
     In  FIGS.  2 A,  2 B,  3 A and  3 B , the blue LED chips  108  mounted directly on the transparent substrate  106  only through the transparent adhesive layers  132 , but this disclosure is not limited to.  FIGS.  7 A and  7 B  demonstrate top and bottom views of an LED assembly  100   b  respectively, according to one embodiment of the disclosure. Two cross-sectional views of the LED assembly  100   b  are shown in  FIGS.  8 A and  8 B , and a manufacturing method to produce the LED assembly  100   b  is exemplified in  FIG.  9   .  FIGS.  7 A,  7 B,  8 A,  8 B and  9    correspond to  FIGS.  2 A,  2 B,  3 A,  3 B , and  6 , where devices, elements or steps with similar or the same symbols represent those with the same or similar functions and could be omitted in the following explanation for brevity. 
     Different from  FIG.  2 A ,  FIG.  7 A  additionally includes a submount  160  positioning inside the periphery of a transparent adhesive layer  132  (from the perspective of a top view) and sandwiched between the transparent adhesive layer  132  and the blue LED chips  108 . Submount  160  could be glass, sapphire, SiC, or diamond-like carbon. Unlike  FIGS.  3 A and  3 B , all or a portion of blue LED chips in  FIGS.  8 A and  8 B  are mounted on the submount  160 , which is adhered onto the transparent substrate  106  through the transparent adhesive layer  132 . 
       FIG.  9    uses steps  154   a  and  155   a  to replace steps  154  and  155  in  FIG.  6   . In Step  154   a , the submount  160  is fixed on the transparent substrate  106  using the transparent adhesive layer  132  with phosphor. In one embodiment, the transparent adhesive layer  132  first adheres to the backside of the submount  160 , followed by attaching the submount  160  on the transparent substrate  106 . In another embodiment, the transparent adhesive layer  132  first adheres to the top surface  102  of the transparent substrate  106  and the submount  160  is then attached over the transparent adhesive layer  132 . In Step  155   a , the blue LED chips  108  are mounted on the submount  160 . 
     The blue LED chips  108  in  FIGS.  7 A,  7 B,  8 A,  8 B, and  9    could be mounted on the submount  160  using the material the same or similar with that of the transparent adhesive layer  132 , but the disclosure is not limited to. Eutectic alloy or transparent glue without phosphor could be used to attach the blue LED chips  108  onto the submount  160 . In one embodiment, the top surface of the submount  160  has patterned conductive strips, over which the blue LED chips  108  are mounted by way of flip chip technique. As known in the art, flip chip technique, which has semiconductor chips facing downward on interconnection metal strips for example, needs no bonding wires shown in step  156  in  FIG.  9    might be skipped. Nevertheless, the bonding wires  100  or the silver paste might be used in some embodiments for electrically connecting the blue LED chip  108   b  to the conductive via  107 , or the blue LED chip  108   a  to the electrode plate  118 . In one embodiment, an anisotropic conductive polymer (ACP) or an anisotropic conductive film (ACF) is used to mount the blue LED chips  108  on the submount  160 . 
     The LED assembly  100   b  in  FIGS.  7 A,  7 B,  8 A,  8 B, and  9    could enjoy the same advantages as the LED assembly  100   a  in  FIGS.  2 A,  2 B,  3 A,  3 B, and  6    does. For instance, the solder joints  190  alone can fix the end  114  of the LED assembly  100   b  onto a printed circuit board and also deliver electric power from the printed circuit board to the LED assembly  100   b . The bottom surface  104  of the LED assembly  100   b  has only large patterns and could be immune from scratch damage, resulting in considerable yield improvement. The blue LED chips  108  in the LED assembly  100   b  are enclosed by a transparent material with phosphor, so as to prevent blue light leakage. An omnidirectional lighting apparatus using the LED assembly  100   b  as its lighting sources could replace a conventional incandescent lamp. 
       FIGS.  8 C and  8 D  are two cross-sectional views of a LED assembly  100   c , alternatives to  FIGS.  8 A and  8 B  respectively. Unlike the LED assembly  100   b  in  FIGS.  8 A and  8 B , where a single transparent adhesive layer  132  mounts the submount  160  on the transparent substrate  106 , the LED assembly  100   c  in  FIGS.  8 C and  8 D  uses two transparent adhesive layers  132  and  133  for mounting the submount  160  on the transparent substrate  106 , and at least one of the transparent adhesive layers  132  and  133  has phosphor. In  FIGS.  8 C and  8 D , the transparent adhesive layer  132  has phosphor, and the transparent adhesive layer  133  does not. The transparent adhesive layer  133  could be epoxy resin or silicone. As the transparent adhesive layer  133  has no phosphor, it could provide better adhesion to stick on the transparent substrate  106 . The transparent adhesive layers  132  and  133  might have the same or different major substance. In one embodiment, another transparent adhesive layer  133  could be formed between the submount  160  and the transparent adhesive layer  132  to improve the adhesion therebetween. 
     The blue LED chips in  FIG.  1    employs bonding wires  110  for electric interconnection, but the disclosure is not limited to.  FIG.  10    is a drawing of a LED assembly  400  in one embodiment of the disclosure, where blue LED chips  108  are mounted on the top surface  102  using a flip chip technique.  FIGS.  11 A and  11 B  are top and bottom views of the LED assembly  400   a  respectively,  FIG.  12 A  demonstrates a cross-sectional view of the LED assembly  400   a  along line AA in  FIG.  11 A , and  FIG.  12 B  demonstrates a cross-sectional view of the LED assembly  400   a  along line BB in  FIG.  11 A .  FIGS.  10 ,  11 A,  11 B,  12 A, and  12 B  correspond to  FIGS.  1 ,  2 A,  2 B,  3 A, and  3 B , respectively, where devices or elements with similar or the same symbols refer to those with the same or similar functions and could be omitted in the following explanation for brevity. 
     Unlike  FIGS.  3 A and  3 B , which use bonding wires  110  for interconnection,  FIGS.  12 A and  12 B  have electrically-conductive strips  402  printed on the top surface  102  of the transparent substrate  106  and these strips  402  connects blue LED chips  108  to each other. As the blue LED chips  108  in  FIGS.  12 A and  12 B  haves omnidirectional light fields, the LED assembly  400   b  could be used as a light source for an omnidirectional lighting apparatus.  FIG.  12 C  shows another LED assembly  400   b , which has an additional phosphor layer  131  coated or attached on the bottom surface  104  of the transparent substrate  106 . Phosphor layer  131  can convert the blue light from blue LED chips  108  into light with a different color, so as to reduce the possibility of blue light leakage from the bottom surface  104 . In one embodiment, all blue LED chips  108  in the LED assembly  400   a  are replaced by white LED chips, each substantially being a blue LED chip coated with a phosphor layer, and accordingly blue light leakage problem might be avoided. 
     Even though each of the LED assemblies  100   a ,  100   b ,  100   c , and  400   a  has a conductive via  107 , which is a part of a circuit and makes it possible that the electrode plates  120  and  118  over the top and bottom surfaces ( 102  and  104 ) act as two power input terminals for driving, but this disclosure is not limited to. 
       FIG.  13    is a drawing of a LED assembly  200  in one embodiment of the disclosure.  FIGS.  14  and  15    are a top view and a cross-sectional view of the LED assembly  200   a , respectively. Different from the LED assemblies  100   a  and  100   b , which have no electrode plate nearby the end  116  on the top surface  102 , the LED assembly  200   a  in  FIGS.  14  and  15    has an electrode plate  119  at the end  116 . The electrode plates  118  and  119  extend across the ends  114  and  116 , respectively. What should be noted is that the LED assembly  200   a  has no conductive via  107 . The way to produce the LED assemblies  200  or  200   a  in  FIGS.  13 ,  14  and  15    can be derived from the aforementioned teaching and therefore is omitted herein for brevity. 
     In the LED assembly  200   a , the blue LED chips  108  are one-on-one mounted on the transparent adhesive layers  132 , but this disclosure is not limited to. In some other embodiments, some blue LED chips  108  could share one of several transparent adhesive layers  132  to mount on the transparent substrate  106 . Alternatively, all blue LED chips  108  might have only one single transparent adhesive layers  132  to mount on the transparent substrate  106  in another embodiment. 
       FIGS.  16  and  17   , similar with  FIGS.  14  and  15   , are a top view and a cross-sectional view of the LED assembly  200   b , respectively.  FIGS.  16  and  17    have nevertheless a submount  160 , which carries the blue LED chips  108  mounted thereabove and fix on to the transparent substrate  106  via the transparent adhesive layer  132 . Detail of the LED assembly  200   b  is omitted herein and could be derived from the teaching in reference to the LED assembly  100   b  in  FIGS.  8 A and  8 B . 
       FIG.  18    is a cross-sectional view of a LED assembly  200   c  and  FIG.  19    demonstrates a method for manufacturing it. The top view of the LED assembly  200   c  could be similar with  FIG.  16   , while  FIGS.  18  and  19    are similar to  FIGS.  17  and  9   , respectively. Different from  FIG.  17   , where the electrode plates  118  and  119  directly attach on the transparent substrate  106 ,  FIG.  18    has the transparent adhesive layer  132  to provide adhesion between the transparent substrate  106  and each of the electrode plates  118  and  119 . In  FIG.  19   , in step  151 , the transparent adhesive layer  132  forming on the transparent substrate  106  is inserted between steps  150  and  152 . In other words, formation of the transparent adhesive layer  132  could be prior to attaching the electrode plates  118  and  119  on to the transparent substrate  106 . The transparent adhesive layer  132  is epoxy resin or silicone, for example, in which phosphor is dispersed. The phosphor in the transparent adhesive layer  132  could be the same with or similar to that in the transparent body  112 . For example, the phosphor is YAG or TAG. 
     One single transparent adhesive layer  132  is used to mount the submount  160  on the transparent substrate  106  in the LED assemblies  200   b  and  200   c  of  FIGS.  17  and  18   , but this disclosure is not limited to. Alteration could be introduced to the LED assemblies  200   b  and  200   c , to have both the transparent adhesive layers  132  and  133  (of  FIGS.  8 C and  8 D ) between the submount  160  and the transparent substrate  106 . In another embodiment, the transparent adhesive layer  133  without phosphor could be positioned between the submount  160  and transparent adhesive layer  132  to enhance adhesion therebetween. 
     The LED assembly  200   a ,  200   b , or  200   c  has no patterns on the bottom surface  104 , which accordingly does not care any scratches thereon. The LED assemblies  200   a ,  200   b , and  200   c  all are suitable for omnidirectional lighting applications and possibly free from blue light leakage. For instance, a bulb according to an embodiment of the disclosure can use solder joints or electrically-conductive clamps to fix and power the electrode plates  118  and  119  respectively nearby two ends  114  and  116 . 
       FIG.  20    is a drawing of an LED assembly  300 , and  FIGS.  21 A and  21 B  are a top view and a cross-sectional view of the LED assembly  300   a , respectively.  FIG.  22    demonstrates a cross-sectional view of the LED assembly  300   a . Formed on the bottom surface  104  of the transparent substrate  106  of the LED assembly  300   a  are two electrode plates  120  and  122 , at two ends  114  and  116  respectively. In each of  FIGS.  21 A,  21 B, and  22   , the LED assembly  300   a  has two conductive vias  107 A and  107 B, respectively formed somewhere close to two ends  114  and  116 . The electrode plate  120 , as being on the bottom surface  104 , uses conductive via  107 A for electrically connecting to one blue LED chip  108  on the top surface  102 , while the electrode plate  122  uses the conductive via  107 B for electrically connecting to another blue LED chip  108 . The blue LED chips  108  are electrically connected in series between the conductive vias  107 A and  107 B, or, in other words, between the electrode plates  120  and  122 . Details of the LED assembly  300   a  and possible alternatives or variations thereto could be derived in reference to other embodiments disclosed in this specification and are omitted herein. 
       FIG.  23    demonstrates a cross-sectional view of an LED assembly  300   b , where the submount  160  is placed under the blue LED chips and above the transparent adhesive layer  132 . Details of the LED assembly  300   b  and possible alternatives or variations thereto could be derived in reference to other embodiments disclosed in this specification and are omitted herein. 
     The LED assemblies  200  and  300  both have the electrode plates extending across the ends  114  and  116 , but this disclosure is not limited to.  FIG.  24    is a drawing of a LED assembly  600 .  FIG.  25 A  shows the LED assembly  600   a , which could be a top view of the LED assembly  600  and has the electrode plates  118  and  119 , each having an edge aligned with an edge of the transparent substrate  106 .  FIG.  25 B  shows an LED assembly  600   b , which could be another top view of the LED assembly  600  and has the electrode plates  118  and  119  completely inside the edges of the transparent substrate  106 . 
       FIG.  26 A  is a drawing of an LED assembly  700  in one embodiment of the disclosure.  FIG.  26 B  is a top view of the LED assembly  700 .  FIG.  26 C  is a cross-sectional view of the LED assembly  700  along line CC in  FIG.  26 B . The LED assembly  700  in  FIGS.  26 A and  26 B  has both electrode plates  118  and  123  on the top surface  102  at the end  114 , and has nothing on the bottom surface  104  of the transparent substrate  106 . Extending from the electrode plates  118  and  123  toward the end  116  are conductive strips  198  and  196 . Blue LED chips  108  are mounted on the top surface  102  and between the conductive strips  198  and  196 . The cathode and anode of each blue LED chip  108  are electrically connected to the conductive strips  198  and  196  with bonding wires  110 . Accordingly, the blue LED chips  108  in  FIGS.  26 A,  26 B and  26 C  are connected in parallel between the electrode plates  118  and  123 , which therefore acts as two power input nodes for the LED assembly  700 . In one embodiment, the blue LED chips  108  can be electrically connected to the conductive strips  198  and  196  by way of flip chip technique, that is, the blue LED chips  108  are electrically connected to the conductive strips  198  and  196  without using the bonding wires  110 . As shown in  FIG.  26 C , the blue LED chips  108  are substantially encapsulated by the transparent adhesive layer  132  and the transparent body  112 , both having at least one kind of phosphor dispersed therein. In one embodiment, the blue LED chips  108  are totally enclosed by the transparent adhesive layer  132  and the transparent body  112 , however, the bonding wires  110  could be still exposed from the transparent adhesive layer  132  and the transparent body  112 . In one embodiment, the transparent body  112  comprises two kinds of phosphors dispersed therein. One of the phosphors is capable of converting portion of the blue light (having a peak wavelength about 430 nm to 480 nm) from blue LED chips  108  into yellow light or yellowish green light or green light (having a peak wavelength from about 520 nm to 590 nm) and the other of the phosphors is capable of converting portion of the blue light from blue LED chips  108  into red light (having a peak wavelength from about 610 nm to 680 nm). The phosphor emitting yellow light or yellowish green light or green light comprises aluminum oxide (such as YAG or TAG), silicate, vanadate, alkaline-earth metal selenide, or metal nitride. The phosphor emitting red light comprises silicate, vanadate, alkaline-earth metal sulfide, metal nitride oxide, a mixture of tungstate and molybdate. The method to produce the LED assembly  700  in  FIG.  26 A,  26 B , or  26 C can be derived from the aforementioned teaching and therefore is omitted herein for brevity. 
     Alteration could be made to the LED assembly  700  in light of the disclosed embodiments according to the disclosure. For example, the blue LED chips  108  could be mounted on a submount, which adheres to the transparent substrate  106  via at least one transparent adhesive layer with or without a phosphor dispersed therein. 
       FIG.  27 A  illustrates an LED lamp  500   a  using only one LED assembly  300  as its filament. The LED lamp  500   a  has two clamps  502 , and each clamp  502  is in a shape of V or Y. In another embodiment, each clamp  502  could be substantially rectangular in shape, but has a notch in one of its edges for fixing the LED assembly  300  thereon. Two jaws of each clamps  502  vise one electrode plate at one end of the LED assembly  300 , making the top surface  102  of the transparent substrate  106  in the LED assembly  300  face upward (the direction Z shown in  FIG.  27 A ). Preferably, clamps  502  are made of electrically-conductive material, so as to electrically connect the electrode plates in the LED assembly  300  to the Edison screw base of the LED assembly  500   a , which could drain electric power from an Edison socket to power the LED assembly  300 .  FIG.  27 B  is similar with  FIG.  27 A , but the LED lamp  500   b  in  FIG.  27 B  uses one LED assembly  600  as its filament. Different from the LED lamp  500   a  which has the LED assembly  300  facing upward, the LED assembly  600  in the LED lamp  500   b  has its top surface  102  facing the direction Y, which is vertical to the axis (Z axis) of the LED lamp  500   b . Any of the assemblies  300  and  600  in  FIGS.  27 A and  27 B  could be replaced by the LED assembly  200 , details or alternatives of which could be derived in reference to the teaching disclosed in this specification and are omitted herein. 
     The bottom surface  104  of the LED assembly  300   a  or  300   b  has only the electrode plates  120  and  122  occupied in a large area, which is immune to casual scratches, such that yield improvement is expectable. Each of the LED assemblies  600   a  and  600   b  has no pattern on its bottom surface  104 , and therefore scratches on the bottom surface  104  could not impact the yield of LED assemblies  600   a  and  600   b . Each of the LED assemblies  300   a ,  300   b ,  600   a , and  600   b  could be suitable for applications to generate an omnidirectional light field, and could prevent any blue light leakage. 
     The aforementioned embodiments all employ only blue LED chips as their lighting resource, but this disclosure is not limited to. In some embodiments, some or all blue LED chips are replaced with red or green LED chips, for example. 
     Because of the transparency provided by the transparent substrate  106  and the transparent adhesive layer  132 , the LED assemblies in some embodiments could have an omnidirectional light field and be suitable for applications to generate an omnidirectional light field. The blue LED chips  108  in some embodiments are substantially encapsulated by the transparent adhesive layer  132  and transparent body  112  with phosphor, to avoid blue light leakage. One embodiment of the disclosure has a LED assembly with only one end fixed on a circuit board to provide both electric power and mechanic support. Nevertheless, a LED assembly of another embodiment has two ends, both fixed for mechanic support and coupled for receiving electric power from a power source. An LED assembly according to some embodiments has no fine patterns on its bottom surface, immune to scratch damage and convenient for the LED assembly transportation. 
     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.